Light guide element

Abstract

The present invention provides a light guide element that can achieve a high diffraction efficiency and has a wide incident angle range. The light guide element includes a light guide plate and a diffraction element disposed on a main surface of the light guide plate. The diffraction element has a liquid crystal layer formed using a liquid crystal composition containing a liquid crystal compound, and has a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound continuously rotates and changes along at least one direction in the plane. The refractive index of the light guide plate is 1.70 or more. Let the refractive index of the light guide plate be n d , and let the refractive index of the liquid crystal layer be n k . When k -n d ≥0 is satisfied.

Description

Technical Field

[0001] The present invention relates to a light guide element for propagating light. Background Art

[0002] In recent years, as described in Patent Document 1, AR (Augmented Reality) glasses that superimpose and display virtual images and various information in an actually observed scene have been put into practical use. AR glasses are also called smart glasses, head-mounted displays (HMDs), and AR glasses.

[0003] As shown in Patent Document 1, as an example, an AR glass causes an image displayed by a display (optical engine) to enter one end of a light guide plate and propagate, and then exit from the other end, so as to superimpose and display a virtual image in the scene actually observed by a user.

[0004] In AR glasses, a light guide element having a diffraction element disposed on the surface of a light guide plate is used to guide light (projection light) from a display. Specifically, a diffraction element is used to diffract (refract) the light (projection light) from the display and make it enter one end of the light guide plate. Thereby, light is introduced into the light guide plate at a certain angle, and the light is totally reflected and propagated in the light guide plate. The light propagated in the light guide plate is diffracted by the diffraction element at the other end of the light guide plate and exits from the light guide plate to the position observed by the user.

[0005] In AR glasses using such a light guide element, a wide viewing angle (FOV (Field of View)) of the area for displaying an image is required.

[0006] In contrast, it is possible to consider expanding the FOV by increasing the refractive index of the light guide plate, increasing the refractive index difference from air, and increasing the conditions (angles) for total internal reflection of light in the light guide plate.

[0007] As a diffraction element included in the light guide element, a liquid crystal diffraction element has been proposed, which has a liquid crystal layer formed by aligning a liquid crystal compound with an alignment pattern in which the orientation of the optical axis continuously rotates in one direction in the plane (Patent Document 2).

[0008] This liquid crystal diffraction element has a higher diffraction efficiency than a diffraction element having a surface relief structure.

[0009] Prior Art Documents

[0010] Patent Documents

[0011] Patent Document 1: US2016 / 0231568A1

[0012] Patent Document 2: International Publication No. 2020 / 022504 Summary of the Invention

[0013] Technical Problem to be Solved by the Invention

[0014] According to the research of the present inventors, it is known that in a light guide element having a liquid crystal diffraction element, when the refractive index of the light guide plate is increased, there is an incident angle at which a high diffraction efficiency cannot be obtained.

[0015] Generally, in a liquid crystal diffraction element, the diffraction efficiency at any incident angle can be controlled by one period Λ and film thickness d of an alignment pattern in which the orientation of the optical axis continuously rotates in one direction in the plane, and further, when the liquid crystal layer has a cholesteric orientation, it is controlled by the helical pitch P.

[0016] However, it is known that when the refractive index of the light guide plate is high, there is an incident angle at which the diffraction efficiency cannot be improved only with one period Λ, film thickness d, and helical pitch P.

[0017] An object of the present invention is to solve such problems of the prior art and provide a light guide element having a wide range of incident angles capable of obtaining a high diffraction efficiency.

[0018] Means for Solving the Technical Problem

[0019] To solve this problem, the present invention has the following configuration.

[0020] [1] A light guide element having:

[0021] A light guide plate; and

[0022] A diffraction element disposed on the main surface of the light guide plate,

[0023] The diffraction element has a liquid crystal layer formed using a liquid crystal composition containing a liquid crystal compound, and has a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound continuously rotates in at least one direction in the plane and changes,

[0024] The refractive index of the light guide plate is 1.70 or more,

[0025] Let the refractive index of the light guide plate be n d , and let the refractive index of the liquid crystal layer be n k When,

[0026] Satisfy n k -n d ≥0.

[0027] [2] The light guide element according to [1], wherein

[0028] The liquid crystal layer is a cholesteric liquid crystal layer formed by fixing a cholesteric liquid crystal phase.

[0029] [3] The light guide element according to [1] or [2], wherein

[0030] The cholesteric liquid crystal layer is a pitch gradient layer in which the helical pitch changes in the film thickness direction.

[0031] [4] The light guide element according to [3], wherein

[0032] In the liquid crystal layer, on the main surface where the orientation of the optical axis of the liquid crystal compound continuously rotates and changes in at least one in-plane direction, when the length for rotating the orientation of the optical axis of the liquid crystal compound by 180° is set as one period Λ, the helical pitch on one surface side of the pitch gradient layer is set as P1, and the helical pitch on the other surface side is set as P2, P1 < Λ < P2 is satisfied.

[0033] [5] The light guide element according to any one of [1] to [4], wherein

[0034] The refractive index n of the light guide plate d and the refractive index n of the liquid crystal layer k satisfy 0.1 > n k -n d ≥ 0.

[0035] [6] The light guide element according to any one of [1] to [5], wherein

[0036] The diffraction element is an incident diffraction element for making light enter the light guide plate.

[0037] Advantageous Effects of the Invention

[0038] According to the present invention, it is possible to provide a light guide element having a wide incident angle range with high diffraction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a diagram conceptually showing an example of an image display device using the light guide element of the present invention.

[0040] Figure 2 is a diagram for explaining the relationship between the refractive index of the light guide plate, the incident angle range, and the FOV.

[0041] Figure 3 is a diagram for explaining the relationship between the refractive index of the light guide plate, the incident angle range, and the FOV.

[0042] Figure 4 is a graph showing the relationship between the incident angle and the diffraction efficiency.

[0043] Figure 5It is a graph showing the relationship between the incident angle and the diffraction efficiency.

[0044] Figure 6 It is a diagram conceptually showing another example of an image display device using the light guide element of the present invention.

[0045] Figure 7 It is a plan view conceptually showing a cholesteric liquid crystal layer used as a diffraction element.

[0046] Figure 8 It is Figure 7 A conceptual diagram of the cholesteric liquid crystal layer shown.

[0047] Figure 9 It is conceptually shown Figure 7 A diagram of a cross-sectional SEM image of the cholesteric liquid crystal layer shown.

[0048] Figure 10 It is for explaining Figure 7 A conceptual diagram of the function of the cholesteric liquid crystal layer shown.

[0049] Figure 11 It is a diagram conceptually showing another example of a cholesteric liquid crystal layer used as a diffraction element.

[0050] Figure 12 It is a diagram conceptually showing another example of a cholesteric liquid crystal layer used as a diffraction element.

[0051] Figure 13 It is a conceptual diagram of an example of an exposure device for exposing an alignment film.

[0052] Figure 14 It is a diagram conceptually showing an example of a liquid crystal layer included in a transmissive liquid crystal diffraction element.

[0053] Figure 15 It is Figure 14 A plan view of the liquid crystal layer shown.

[0054] Figure 16 It is for explaining Figure 14 A conceptual diagram of the function of the liquid crystal layer shown.

[0055] Figure 17 It is for explaining Figure 14 A conceptual diagram of the function of the liquid crystal layer shown.

[0056] Figure 18 It is a diagram conceptually showing another example of a liquid crystal layer.

[0057] Figure 19 It is a diagram conceptually showing a method for measuring diffraction efficiency. Detailed Description

[0058] Hereinafter, the light guide element of the present invention will be described in detail based on the preferred embodiments shown in the accompanying drawings.

[0059] In this specification, the numerical range indicated by "~" means the range including the numerical values described before and after "~" as the lower limit value and the upper limit value.

[0060] In this specification, "(meth)acrylate" is used to mean "one or both of acrylate and methacrylate".

[0061] In this specification, the refractive index refers to the refractive index at a wavelength of 550 nm.

[0062] [Light guide element]

[0063] The light guide element of the present invention is a light guide element having:

[0064] A light guide element having:

[0065] A light guide plate; and

[0066] A diffraction element disposed on the main surface of the light guide plate,

[0067] The diffraction element has a liquid crystal layer formed using a liquid crystal composition containing a liquid crystal compound, and has a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound continuously rotates and changes along at least one direction in the plane.

[0068] The refractive index of the light guide plate is 1.70 or more.

[0069] Let the refractive index of the light guide plate be n d , and let the refractive index of the liquid crystal layer be n k When

[0070] It satisfies n k -n d ≥0.

[0071] Figure 1 Conceptually shows an example of an image display device using the light guide element of the present invention.

[0072] As a preferred example, Figure 1 The shown image display device 50 is used as an AR glass. In addition, the light guide element of the present invention can be used in optical elements such as transparent screens, lighting devices (including backlights of liquid crystal displays, etc.) and sensors in addition to AR glasses. And the image display device of the present invention can also be used in image display devices using these optical elements.

[0073] Figure 1The image display device 50 shown has a display element 54 and a light guide element 10a. The light guide element 10a has a light guide plate 16 and diffraction elements 12a and 12b disposed on the main surface of the light guide plate 16.

[0074] In Figure 1 the light guide element 10a shown, the diffraction element 12a and the diffraction element 12b are disposed at different positions in the plane direction of the main surface of the light guide plate 16. In Figure 1 the example shown, the diffraction element 12a is disposed at the left end of the light guide plate 16 in the figure. And, the diffraction element 12b is disposed at the right end of the light guide plate 16 in the figure. In addition, the main surface is the largest surface of the sheet (plate-like object, film, etc.).

[0075] Moreover, in the image display device 50, the display element 54 is disposed so as to face the surface on the side opposite to the side where the diffraction element 12a is disposed with respect to the light guide plate 16 at a position overlapping the diffraction element 12a in the plane direction of the main surface of the light guide plate 16.

[0076] In Figure 1 the example shown, the diffraction element 12a and the diffraction element 12b are reflective diffraction elements that reflect light in a direction different from specular reflection and diffract the reflected light. The diffraction element 12a and the diffraction element 12b have a liquid crystal layer formed using a liquid crystal composition containing a liquid crystal compound, and have a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound continuously rotates and changes along at least one direction in the plane, thereby diffracting light. This will be described in detail later.

[0077] In the image display device 50, the image (light corresponding to the image) displayed by the display element 54 is incident on the light guide plate 16 from a direction perpendicular to the main surface and is incident on the diffraction element 12a. The light incident on the diffraction element 12a is diffracted by the diffraction element 12a and is incident on the light guide plate 16. At this time, the diffraction element 12a diffracts the light at an angle of total reflection within the light guide plate 16, and diffracts the light so that the traveling direction of the diffracted light becomes the direction toward the diffraction element 12b. In Figure 1 the example shown, the diffraction element 12a diffracts the incident light toward Figure 1 the right direction in

[0078] The light diffracted by the diffraction element 12a is totally reflected within the light guide plate 16 and propagates toward the other end side, and is incident on the diffraction element 12b. The diffraction element 12b diffracts the incident light so as to deviate from the angle of total reflection within the light guide plate 16. In Figure 1 the example shown, the diffraction element 12b diffracts the incident light toward Figure 1 the upper side in Figure 1As shown, the diffraction element 12b diffracts the incident light in a direction substantially perpendicular to the main surface of the light guide plate.

[0079] The light diffracted by the diffraction element 12b exits from the light guide plate 16 and exits toward the user U. Thus, the image display device 50 can display an image irradiated by the display element 54.

[0080] Here, in the present invention, the refractive index of the light guide plate 16 is 1.70 or more.

[0081] Using Figure 2 and Figure 3 , the relationship between the refractive index of the light guide plate 16 and the incident angle of the light incident on the light guide plate will be described. Figure 2 The light guide element shown is an example with a low refractive index of the light guide plate 52b, Figure 3 The light guide element shown is an example with a high refractive index of the light guide plate 52.

[0082] As is well known, the angle of total internal reflection of light in a light guide plate depends on the difference between the refractive index of the light guide plate and the refractive index of air. When the refractive index of the light guide plate is low, the difference from the refractive index of air becomes small. Therefore, as in the example shown in Figure 2 , the range of the angle of total internal reflection of light in the light guide plate 52b becomes narrow. Here, for example, assuming that the diffraction element 12a on the incident side diffracts the light incident from a direction perpendicular to the main surface of the light guide plate 52b so that it travels to the center of the total internal reflection angle range, and the diffraction element 12a sets the range of the angle of the incident light that can diffract the incident light within the total internal reflection angle range as the incident angle range, when the refractive index of the light guide plate 52b is low, the total internal reflection angle range is narrow, so this incident angle range also becomes narrow. And, as shown in Figure 2 , if the total internal reflection angle range is narrow, the angle range of the light emitted by the diffraction element 12b on the exit side also becomes narrow, and the viewing angle (FOV (Field of View)) of the area for displaying an image becomes narrow.

[0083] In contrast, when the refractive index of the light guide plate is high, the difference from the refractive index of air becomes large. Therefore, as in the example shown in Figure 3 , the range of the angle of total internal reflection of light in the light guide plate 52 becomes wide. Therefore, when the refractive index of the light guide plate 52 is high, the total internal reflection angle range is wide, so the range of the incident angle within which the diffraction element 12a can diffract the incident light within the total internal reflection angle range also becomes wide. And, as shown in Figure 3 , if the total internal reflection angle range is wide, the angle range of the light emitted by the diffraction element 12b on the exit side also becomes wide, and the viewing angle (FOV (Field of View)) of the area for displaying an image becomes wide.

[0084] Here, furthermore, in the present invention, the refractive index of the light guide plate is set to nd When the refractive index of the liquid crystal layer of the diffraction element is set to n k , n satisfies k -n d ≥0. That is, the refractive index of the liquid crystal layer (diffraction element) is equal to or higher than the refractive index of the light guide plate.

[0085] According to the research by the present inventors, it is known that in a light guide element having a diffraction element using a liquid crystal layer (hereinafter, also referred to as a liquid crystal diffraction element), when the refractive index of the light guide plate is increased (set to 1.70 or higher), there is an incident angle at which a high diffraction efficiency cannot be obtained. As a result of various studies by the present inventors on this point, it is known that when the refractive index of the liquid crystal layer of the diffraction element (hereinafter, also referred to as the refractive index of the diffraction element) is lower than the refractive index of the light guide plate, the diffraction efficiency becomes low in a part of the incident angle range.

[0086] As an example, Figure 4 shows a graph representing the relationship between the incident angle range and the diffraction efficiency when the refractive index of the diffraction element is lower than the refractive index of the light guide plate. This graph is an example when the refractive index of the light guide plate is 1.80 and the refractive index of the diffraction element is 1.60.

[0087] In Figure 4 In the example shown, in the total reflection angle range determined by the refractive index of the light guide plate, the incident angle range in which incident light can be refracted is approximately -24° to 24° ( Figure 4 represented by a dashed line in Figure 2 . Regarding the incident angle, a negative value is used to represent an inclination in the direction of light travel in the light guide plate, and a positive value is used to represent an inclination in the direction opposite to the direction of light travel in the light guide plate (refer to Figure 3 ).

[0088] However, it is known that when the refractive index of the diffraction element is lower than the refractive index of the light guide plate, Figure 4 in the angle range (approximately 10° to 24°) represented by a single-dot dash line in

[0089] the diffraction efficiency is almost 0%.

[0090] In contrast, as a result of various studies by the present inventors, it is known that by setting the refractive index of the diffraction element to be equal to or higher than the refractive index of the light guide plate, it is possible to suppress a decrease in the diffraction efficiency in a part of the incident angle range. Figure 5 As an example,

[0091] In Figure 5In the example shown, within the total reflection angle range determined by the refractive index of the light guide plate, the incident angle range that can refract incident light is the same as that of Figure 4 the example, which is approximately -24° to 24° ( Figure 5 represented by the dashed line in

[0092] As Figure 5 shown, it can be seen that when the refractive index of the diffraction element is equal to or higher than that of the light guide plate, within the angle range (approximately 10° to 24°, Figure 5 represented by the dash-dotted line in

[0093] where the diffraction efficiency is almost 0% when the refractive index of the diffraction element is lower than that of the light guide plate), a high diffraction efficiency can also be obtained.

[0094] In contrast, in the light guide element of the present invention, when the refractive index of the light guide plate is set to n d , and the refractive index of the diffraction element is set to n k , satisfying n k - n d ≥0, the incident angle range in which a high diffraction efficiency can be obtained can be expanded.

[0095] Here, from the viewpoint of diffraction efficiency, the refractive index n d of the light guide plate and the refractive index n k of the diffraction element preferably satisfy 0.1 > n k - n d ≥0, and more preferably satisfy 0.05 > n k - n d ≥0.

[0096] Moreover, from the viewpoints of the viewing angle (FOV), diffraction efficiency, etc., the refractive index of the light guide plate is preferably 1.7 to 2.3, and more preferably 1.9 to 2.3.

[0097] Here, in the example Figure 1 shown, the light guide element 10a is configured to include a reflective diffraction element 12a and a diffraction element 12b, but is not limited thereto.

[0098] Figure 6 Another example of an image display device using the light guide element of the present invention is conceptually shown in

[0099] Figure 6The image display device 50b shown has a display element 54 and a light guide element 10b. The light guide element 10b has a light guide plate 16 and diffraction elements 11a and 11b disposed on the main surface of the light guide plate 16.

[0100] In Figure 6 the light guide element 10b shown, the diffraction elements 11a and 11b are disposed at different positions in the plane direction of the main surface of the light guide plate 16. In Figure 6 the example shown, the diffraction element 11a is disposed at the left end of the light guide plate 16 in the figure. Also, the diffraction element 11b is disposed at the right end of the light guide plate 16 in the figure.

[0101] Further, in the image display device 50b, the display element 54 is disposed to face the side of the light guide plate 16 where the diffraction element 11a is disposed at a position overlapping with the diffraction element 11a in the plane direction of the main surface of the light guide plate 16.

[0102] In Figure 6 the example shown, the diffraction elements 11a and 11b are transmissive diffraction elements that diffract light while transmitting it. The diffraction elements 11a and 11b have a liquid crystal layer formed using a liquid crystal composition containing a liquid crystal compound, and have a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound continuously rotates and changes along at least one in-plane direction, thereby diffracting light. This will be described in detail later.

[0103] In the image display device 50b, the image (light corresponding to the image) displayed by the display element 54 is incident on the diffraction element 11a from a direction perpendicular to the main surface on the light guide plate 16. The light incident on the diffraction element 11a is diffracted by the diffraction element 11a and then incident on the light guide plate 16. At this time, the diffraction element 11a diffracts the light at an angle for total internal reflection within the light guide plate 16, and diffracts the light so that the traveling direction of the diffracted light becomes the direction toward the diffraction element 11b. In Figure 6 the example shown, the diffraction element 11a diffracts the incident light toward Figure 6 the right direction in

[0104] The light diffracted by the diffraction element 11a undergoes total internal reflection within the light guide plate 16 and propagates toward the other end side, and is incident on the diffraction element 11b. The diffraction element 11b diffracts the incident light so as to deviate from the angle for total internal reflection within the light guide plate 16. In Figure 6 the example shown, the diffraction element 11b diffracts the incident light toward Figure 6 the upper side in Figure 6 That is, as shown in

[0105] The light diffracted by the diffractive element 11b exits from the light guide plate 16 and is directed toward the user U. Thus, the image display device 50 can display the image irradiated by the display element 54.

[0106] In this way, even in a light guide element having a transmissive diffractive element, by setting the refractive index of the light guide plate 16 to 1.70 or more, the total reflection angle range can be expanded and the viewing angle (FOV) can be expanded, and by setting the refractive index of the diffractive element to be equal to or more than the refractive index of the light guide plate, the incident angle range in which a high diffraction efficiency can be obtained can be expanded.

[0107] In the above description, the relationship between the refractive index difference between the diffractive element and the light guide plate, the incident angle range, and the diffraction efficiency has been described. That is, if the refractive index of the diffractive element on the incident side is equal to or more than the refractive index of the light guide plate, the above effects can be obtained. However, the present invention is not limited thereto, and the refractive index of the diffractive element on the exit side may be equal to or more than the refractive index of the light guide plate. By setting the refractive index of the diffractive element on the exit side to be equal to or more than the refractive index of the light guide plate, in the diffractive element on the exit side, the angle range in which a high diffraction efficiency can be obtained can be expanded, and the viewing angle (FOV) can be expanded.

[0108] Hereinafter, each component will be described.

[0109] [Display element]

[0110] The display element 54 displays an image (video) viewed by the user U and irradiates the image onto the incident diffractive element. Therefore, the display element 54 is arranged such that the irradiated image is incident on the incident diffractive element.

[0111] In the image display device, the display element 54 is not limited, and known display elements (display devices, projectors) used in various AR glasses and the like can be used. As an example of the display element 54, a display element having a display and a projection lens can be exemplified.

[0112] In the image display device, the display is not limited, and for example, known displays used in various AR glasses and the like can be used.

[0113] As an example of the display, a liquid crystal display (including LCOS: Liquid Crystal On Silicon, etc.), an organic electroluminescence display, and a scanning type display using DLP (Digital Light Processing), MEMS (Micro Electro Mechanical Systems) mirrors, etc. can be exemplified.

[0114] In addition, in the case where the image display device has a structure for displaying a multicolor image, a display that can display a multicolor image can be used.

[0115] In the display element 54 used in the image display device, the projection lens is also a well-known projection lens (collimating lens) used in, for example, AR glass.

[0116] Among them, in the image display device, the light irradiated by the display element 54, that is, the display image based on the display element 54, is not limited, but unpolarized light (natural light) or circularly polarized light is preferred.

[0117] When the display element 54 irradiates circularly polarized light, in the case where the display irradiates an image of unpolarized light, the display element 54 preferably has, for example, a circular polarizer formed of a linear polarizer and a λ / 4 plate. And in the case where the display irradiates an image of linearly polarized light, the display element 54 preferably has, for example, a λ / 4 plate.

[0118] In addition, the light irradiated by the display element 54 can be other polarized light (for example, linearly polarized light, etc.).

[0119] [Light guide plate]

[0120] In the light guide element 10a, in addition to the refractive index of the light guide plate 16 being 1.70 or more, the light guide plate 16 is a well-known light guide plate that reflects the light incident on the inside and guides (propagates) it.

[0121] The light guide plate 16 is not limited, and well-known light guide plates used in various AR glasses and backlight units of liquid crystal displays can be used.

[0122] As the material of the light guide plate 16 having a refractive index of 1.70 or more, heavy flint glass, glass containing Ba, La, Nb, etc., and polymer light guide plates can be cited.

[0123] The upper limit of the refractive index of the light guide plate 16 is not particularly limited, and is usually 2.1 or less.

[0124] [Diffraction element]

[0125] A liquid crystal diffraction element is exemplified. Among them, the diffraction element on the incident side and the diffraction element on the exit side have a liquid crystal layer formed using a composition containing a liquid crystal compound, and have a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound continuously rotates and changes along at least one direction in the plane. And as the liquid crystal diffraction element, it is also preferable to have a cholesteric liquid crystal layer in which the cholesteric liquid crystal phase is fixed.

[0126] (Reflective liquid crystal diffraction element)

[0127] Use Figures 7 - 9An example of a liquid crystal diffraction element will be described.

[0128] Figure 7 It is a schematic diagram showing the alignment state of the liquid crystal compound in the plane of the main surface of the liquid crystal layer 34 included in the liquid crystal diffraction element 12. And, Figure 8 It is a cross-sectional schematic diagram showing the state of the liquid crystal phase in a cross-section perpendicular to the main surface. Hereinafter, the main surface of the liquid crystal layer 34 is set as the X-Y plane and the cross-section perpendicular to the X-Y plane is set as the X-Z plane for description. That is, Figure 7 A schematic diagram corresponding to the X-Y plane of the liquid crystal layer 34, Figure 8 A schematic diagram corresponding to the X-Z plane of the liquid crystal layer 34.

[0129] Figures 7 - 8 The liquid crystal layer shown is an example of a cholesteric liquid crystal layer in which the liquid crystal compound is cholesterically aligned. And, Figures 7 - 8 The liquid crystal layer shown is an example when the liquid crystal compound is a rod-shaped liquid crystal compound. The cholesteric liquid crystal layer reflects one circularly polarized light of the selective reflection wavelength and transmits light in other wavelength regions and the other circularly polarized light. Therefore, the liquid crystal diffraction element having a cholesteric liquid crystal layer is a reflective liquid crystal diffraction element.

[0130] In Figure 8 the example shown, the liquid crystal diffraction element 12 has a support 30, an alignment film 32, and a liquid crystal layer 34.

[0131] In addition, Figure 8 the liquid crystal diffraction element 12 in the example shown has a support 30, an alignment film 32, and a liquid crystal layer 34, but the present invention is not limited thereto. The liquid crystal diffraction element 12 may be, for example, a liquid crystal diffraction element that is attached to the light guide plate 16 and then the support 30 is peeled off and only has the alignment film 32 and the liquid crystal layer 34. Or, the liquid crystal diffraction element may be, for example, a liquid crystal diffraction element that is attached to the light guide plate 16 and then the support 30 and the alignment film 32 are peeled off and only has the liquid crystal layer 34.

[0132] <Support>

[0133] The support 30 supports the alignment film 32 and the liquid crystal layer 34.

[0134] As long as it can support the alignment film 32 and the liquid crystal layer 34, the support 30 can use various sheet-like materials (films, plate-like materials).

[0135] In addition, the transmittance of the support 30 with respect to the corresponding light is preferably 50% or more, more preferably 70% or more, and further preferably 85% or more.

[0136] The thickness of the support 30 is not limited as long as it is appropriately set according to the use of the liquid crystal diffraction element and the material for forming the support 30 so that the thicknesses of the alignment film 32 and the liquid crystal layer 34 can be maintained.

[0137] The thickness of the support 30 is preferably 1 to 2000 μm, more preferably 3 to 500 μm, and still more preferably 5 to 250 μm.

[0138] The support 30 can be a single layer or a multilayer.

[0139] As the support 30 in the case of a single layer, examples thereof include a support 30 formed of glass, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic acid, polyolefin, etc. As an example of the support 30 in the case of a multilayer, examples thereof include a support including any one of the aforementioned single-layer supports as a substrate and having other layers provided on the surface of the substrate.

[0140] <Alignment Film>

[0141] In the liquid crystal diffraction element 12, an alignment film 32 is formed on the surface of the support 30.

[0142] The alignment film 32 is an alignment film for aligning the liquid crystal compound 40 into a predetermined liquid crystal alignment pattern when forming the liquid crystal layer 34.

[0143] As will be described later, the liquid crystal layer 34 has a liquid crystal alignment pattern in which the orientation of the optical axis 40A (refer to Figure 7 ) derived from the liquid crystal compound 40 continuously rotates in one direction in the plane while changing. Therefore, the alignment film 32 is formed so that the liquid crystal layer 34 can form this liquid crystal alignment pattern.

[0144] In the following description, "rotation of the orientation of the optical axis 40A" will also be simply referred to as "rotation of the optical axis 40A".

[0145] The alignment film 32 can be any of various known alignment films.

[0146] For example, examples thereof include a rubbed film formed of an organic compound such as a polymer, an inclined vapor deposition film of an inorganic compound, a film having microgrooves, and a film formed by accumulating LB (Langmuir - Blodgett) films of organic compounds such as ω - tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearate based on the Langmuir - Blodgett method.

[0147] The alignment film 32 based on rubbing treatment can be formed by rubbing the surface of the polymer layer several times in a predetermined direction with paper or cloth.

[0148] As the material used for the alignment film 32, polyimide, polyvinyl alcohol, a polymer having a polymerizable group described in Japanese Patent Laid-Open No. 9-152509, and materials used in the formation of the alignment film 32 such as those described in Japanese Patent Laid-Open Nos. 2005-097377, 2005-099228, and 2005-128503 are preferred.

[0149] In the liquid crystal diffraction element 12, the alignment film 32 is preferably a so-called photo-alignment film formed by irradiating a raw material having photo-alignment properties with polarized light or non-polarized light. That is, in the liquid crystal diffraction element, as the alignment film, a photo-alignment film 32 formed by coating a photo-alignment material on the support 30 is preferred.

[0150] Regarding the irradiation of polarized light, it can be performed from a vertical direction or an inclined direction with respect to the photo-alignment film, and regarding the irradiation of non-polarized light, it can be performed from an inclined direction with respect to the photo-alignment film.

[0151] Examples of the photoalignment material that can be used in the alignment film of the present invention include azo compounds described in JP-A-2006-285197, JP-A-2007-076839, JP-A-2007-138138, JP-A-2007-094071, JP-A-2007-121721, JP-A-2007-140465, JP-A-2007-156439, JP-A-2007-133184, JP-A-2009-109831, Japanese Patent No. 3883848, and Japanese Patent No. 4151746; aromatic ester compounds described in JP-A-2002-229039; maleimide and / or alkenyl-substituted nadimide compounds having a photoalignment unit described in JP-A-2002-265541 and JP-A-2002-317013; photocrosslinkable silane derivatives described in Japanese Patent No. 4205195 and Japanese Patent No. 4205198; photocrosslinkable polyimide, photocrosslinkable polyamide, and photocrosslinkable polyester described in JP-T-2003-520878, JP-T-2004-529220, and Japanese Patent No. 4162850; and compounds capable of photodimerization described in JP-A-9-118717, JP-T-10-506420, JP-T-2003-505561, WO2010 / 150748, JP-A-2013-177561, and JP-A-2014-012823, particularly cinnamate compounds, chalcone compounds, and coumarin compounds, etc. as preferred examples.

[0152] Among them, azo compounds, photocrosslinkable polyimide, photocrosslinkable polyamide, photocrosslinkable polyester, cinnamate compounds, and chalcone compounds are preferably used.

[0153] The thickness of the alignment film 32 is not limited as long as it is appropriately set according to the formation material of the alignment film 32 to obtain a thickness with the required alignment function.

[0154] The thickness of the alignment film 32 is preferably 0.01 to 5 μm, more preferably 0.05 to 2 μm.

[0155] The method for forming the alignment film 32 is not limited, and various known methods corresponding to the formation material of the alignment film 32 can be used. As an example, a method can be exemplified in which the alignment film 32 is coated on the surface of the support 30 and dried, and then an alignment pattern is formed by exposing the alignment film 32 with a laser beam.

[0156] InFigure 13 Conceptually shows an example of an exposure apparatus for exposing an alignment film 32 to form an alignment pattern.

[0157] Figure 13 The exposure apparatus 60 shown includes: a light source 64 having a laser 62; a λ / 2 plate 65 that changes the polarization direction of the laser beam M emitted from the laser 62; a polarization beam splitter 68 that splits the laser beam M emitted from the laser 62 into two light beams MA and MB; mirrors 70A and 70B respectively disposed on the optical paths of the two split light beams MA and MB; and λ / 4 plates 72A and 72B.

[0158] In addition, the light source 64 emits linearly polarized light P O . The λ / 4 plate 72A converts the linearly polarized light P O (light beam MA) into right-handed circularly polarized light P R , and the λ / 4 plate 72B converts the linearly polarized light P O (light beam MB) into left-handed circularly polarized light P L .

[0159] A support 30 having an alignment film 32 before forming the alignment pattern is disposed in the exposure section, and the two light beams MA and light beam MB are made to cross on the alignment film 32 and interfere with each other, and the interference light is irradiated onto the alignment film 32 for exposure.

[0160] By the interference at this time, the polarization state of the light irradiated onto the alignment film 32 changes periodically in an interference fringe pattern. Thus, an alignment film having an alignment pattern in which the alignment state changes periodically (hereinafter, also referred to as a pattern alignment film) can be obtained.

[0161] In the exposure apparatus 60, by changing the crossing angle α of the two light beams MA and MB, the period of the alignment pattern can be adjusted. That is, in the exposure apparatus 60, by adjusting the crossing angle α, in an alignment pattern in which the optical axis 40A of the liquid crystal compound 40 rotates continuously in one direction, the length of one period in which the optical axis 40A rotates 180° in one direction in which the optical axis 40A rotates can be adjusted.

[0162] By forming a cholesteric liquid crystal layer on the alignment film 32 having such an alignment pattern in which the alignment state changes periodically, as will be described later, a liquid crystal layer 34 having a liquid crystal alignment pattern in which the optical axis 40A of the liquid crystal compound 40 rotates continuously in one direction can be formed.

[0163] Moreover, the rotation direction of the optical axis 40A can be reversed by rotating the optical axes of the λ / 4 plates 72A and 72B by 90° respectively.

[0164] As described above, the pattern alignment film has an alignment pattern that aligns the liquid crystal compound so that the orientation of the optical axis of the liquid crystal compound in the liquid crystal layer formed on the pattern alignment film changes while continuously rotating in at least one in-plane direction. If the axis in the direction of aligning the liquid crystal compound is defined as the alignment axis for the pattern alignment film, it can be said that the pattern alignment film has an alignment pattern in which the orientation of the alignment axis changes while continuously rotating in at least one in-plane direction. The alignment axis of the pattern alignment film can be detected by measuring the absorption anisotropy. For example, when linearly polarized light is rotated and irradiated onto the pattern alignment film and the amount of light transmitted through the pattern alignment film is measured, it is observed that the orientation in which the light amount becomes maximum or minimum gradually changes in one in-plane direction.

[0165] In addition, the alignment film 32 is provided in a preferred manner and is not an essential component.

[0166] For example, an alignment pattern can be formed on the support 30 by a method of rubbing the support 30, a method of processing the support 30 with a laser beam, etc., so that the liquid crystal layer can also have a liquid crystal alignment pattern in which the orientation of the optical axis 40A derived from the liquid crystal compound 40 changes while continuously rotating in at least one in-plane direction. That is, the support 30 can also function as an alignment film.

[0167] <Liquid Crystal Layer>

[0168] In the liquid crystal diffraction element 12, a liquid crystal layer 34 is formed on the surface of the alignment film 32.

[0169] As described above, the liquid crystal layer 34 is a cholesteric liquid crystal layer in which the cholesteric liquid crystal phase is fixed, and is a cholesteric liquid crystal layer having a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating in at least one in-plane direction.

[0170] As Figure 8 conceptually shown in, similar to the cholesteric liquid crystal layer in which a normal cholesteric liquid crystal phase is fixed, the liquid crystal layer 34 has a helical structure in which the liquid crystal compound 40 rotates in a spiral and stacks. The structure in which the liquid crystal compound 40 rotates in a spiral (360° rotation) once and stacks is defined as one helical pitch, and the liquid crystal compound 40 rotating in a spiral has a structure in which a plurality of pitches are stacked.

[0171] It is well known that a cholesteric liquid crystal layer in which a cholesteric liquid crystal phase is fixed has wavelength-selective reflectivity.

[0172] As will be described in detail later, the selective reflection wavelength region of the cholesteric liquid crystal layer depends on the length of the above-mentioned helical pitch ( Figure 9The pitch P shown).

[0173] Therefore, the diffraction element having such a liquid crystal layer has wavelength selectivity and diffracts light of a specified wavelength. Therefore, regarding the wavelength of the light reflected (diffracted) by the diffraction element, it is only necessary to adjust the helical pitch P of the liquid crystal layer to appropriately set the selective reflection wavelength region of the liquid crystal layer.

[0174] As Figure 7 Shown, on the X-Y plane of the liquid crystal layer 34, the liquid crystal compound 40 is arranged along a plurality of arrangement axes D parallel to each other in the X-Y plane, and on each arrangement axis D, the orientation of the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating in one direction in the plane along the arrangement axis D. For the sake of explanation, it is assumed that the arrangement axis D faces the X direction. Also, in the Y direction, the liquid crystal compounds 40 having equal orientations of the optical axis 40A are oriented at equal intervals.

[0175] In addition, "the orientation of the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating in one direction in the plane along the arrangement axis D" means that the angle formed by the optical axis 40A of the liquid crystal compound 40 and the arrangement axis D is different according to the position in the direction of the arrangement axis D, and the angle formed by the optical axis 40A and the arrangement axis D gradually changes from θ to θ + 180° or θ - 180° along the arrangement axis D. That is, as Figure 7 Shown, the optical axes 40A of the plurality of liquid crystal compounds 40 arranged along the arrangement axis D change while each rotating a specified angle along the arrangement axis D.

[0176] In addition, the difference in the angles of the optical axes 40A of the liquid crystal compounds 40 adjacent to each other in the direction of the arrangement axis D is preferably 45° or less, more preferably 15° or less, and further preferably an even smaller angle.

[0177] And, in this specification, in the case where the liquid crystal compound 40 is a rod-shaped liquid crystal compound, the optical axis 40A of the liquid crystal compound 40 refers to the molecular long axis of the rod-shaped liquid crystal compound. On the other hand, in the case where the liquid crystal compound 40 is a disc-shaped liquid crystal compound, the optical axis 40A of the liquid crystal compound 40 refers to the axis parallel to the normal direction of the disc surface of the disc-shaped liquid crystal compound.

[0178] In the liquid crystal layer 34, in such a liquid crystal alignment pattern of the liquid crystal compound 40, in the direction of the arrangement axis D where the in-plane optical axis 40A continuously rotates and changes, the length (distance) for rotating the optical axis 40A of the liquid crystal compound 40 by 180° is set as the length Λ of one period in the liquid crystal alignment pattern.

[0179] That is, the distance between the centers in the direction of the arrangement axis D of two liquid crystal compounds 40 having equal angles with respect to the direction of the arrangement axis D is set as the length Λ of one period. Specifically, asFigure 7 As shown, the distance between the centers of the alignment axes D of two liquid crystal compounds 40 with the alignment axis D direction aligned with the optical axis 40A direction is set as the length Λ of one period. In the following description, this length Λ of one period is also referred to as "one period Λ".

[0180] The liquid crystal alignment pattern of the liquid crystal layer 34 repeats this one period Λ in one direction where the liquid crystal alignment continuously rotates in the alignment axis D direction, i.e., the orientation of the optical axis 40A.

[0181] On the other hand, the liquid crystal compound 40 forming the liquid crystal layer 34 is equal in orientation to the optical axis 40A in the direction orthogonal to the alignment axis D direction (the Y direction in Figure 7 ), i.e., the Y direction orthogonal to one direction in which the optical axis 40A continuously rotates.

[0182] In other words, in the Y direction of the liquid crystal compound 40 forming the liquid crystal layer 34, the angles formed by the optical axis 40A of the liquid crystal compound 40 and the alignment axis D direction are equal.

[0183] If the X-Z plane of the liquid crystal layer 34 shown is observed with an SEM (scanning electron microscope), Figure 8 then a stripe pattern is observed in which bright portions 42 and dark portions 44 are alternately arranged, and the arrangement direction is inclined at a specified angle with respect to the main surface (X-Y plane). In such an SEM cross-section, the interval in the normal direction of the line formed by adjacent bright portions 42 to bright portions 42 or dark portions 44 to dark portions 44 is substantially consistent with 1 / 2 pitch. That is, as represented by P in Figure 9 , two bright portions 42 and two dark portions 44 are substantially consistent with the helical 1 pitch amount (the number of turns of the helix once), i.e., the pitch P. As Figure 9 shown, when the inclination of the liquid crystal compound is consistent with the inclination of the bright and dark portions, the helical pitch is substantially consistent with the pitch P of the bright and dark lines shown in Figure 11 . And, as Figure 9 shown, when the inclination of the liquid crystal compound is inconsistent with the inclination of the bright and dark portions, the helical pitch has some deviation from the pitch P of the bright and dark lines shown in Figure 8 , but in the following description, the helical pitch and the pitch of the bright and dark lines are not distinguished and described. Figure 9

[0184] Hereinafter, the action based on the diffraction of the liquid crystal layer will be described.

[0185] ​In a conventional cholesteric liquid crystal layer, the helical axis derived from the cholesteric liquid crystal phase is perpendicular to the main surface (X-Y plane), and the reflection plane is parallel to the main surface (X-Y plane). Also, the optical axis of the liquid crystal compound is not inclined with respect to the main surface (X-Y plane). In other words, the optical axis is parallel to the main surface (X-Y plane). Therefore, when observing the X-Z plane of the conventional cholesteric liquid crystal layer with SEM, the arrangement direction in which bright and dark portions are alternately arranged is perpendicular to the main surface (X-Y plane).

[0186] The cholesteric liquid crystal phase is specularly reflective. Thus, for example, when light is incident on the cholesteric liquid crystal layer from the normal direction, the light is reflected in the normal direction.

[0187] In contrast, the liquid crystal layer 34 reflects the incident light while tilting it with respect to specular reflection in the direction of the alignment axis D. The liquid crystal layer 34 is a layer having a liquid crystal alignment pattern in which the optical axis 40A continuously rotates and changes in the direction of the alignment axis D (a specified one direction) within the plane. Hereinafter, with reference to Figure 10 it will be described.

[0188] As an example, the liquid crystal layer 34 is a cholesteric liquid crystal layer that selectively reflects right-handed circularly polarized light R R of red light. Thus, when light is incident on the liquid crystal layer 34, the liquid crystal layer 34 reflects only the right-handed circularly polarized light R R of red light and transmits the other light.

[0189] Among them, in the liquid crystal layer 34, the optical axis 40A of the liquid crystal compound 40 rotates and changes in the direction of the alignment axis D (one direction). The liquid crystal alignment pattern formed on the liquid crystal layer 34 is a periodic pattern in the direction of the alignment axis D. Therefore, as conceptually shown in Figure 10 the right-handed circularly polarized light R R of red light incident on the liquid crystal layer 34 is reflected (diffracted) in the direction corresponding to the period of the liquid crystal alignment pattern, and the reflected right-handed circularly polarized light R R of red light is reflected (diffracted) in a direction inclined in the direction of the alignment axis D with respect to the XY plane (the main surface of the cholesteric liquid crystal layer).

[0190] As a result, when the liquid crystal layer 34 is applied to a light guide element or the like, it can be used as a diffraction element that can reflect (diffract) light incident from a direction perpendicular to the main surface of the light guide plate at an angle of total internal reflection within the light guide plate and can reflect (diffract) the light that is totally internally reflected and guided within the light guide plate in a direction perpendicular to the main surface of the light guide plate.

[0191] In the liquid crystal layer 34, by appropriately setting the direction of the alignment axis D as the direction in which the optical axis 40A rotates, the reflection direction (diffraction angle) of light can be adjusted.

[0192] Further, in the case of reflecting circularly polarized light with the same wavelength and the same rotational direction, by reversing the rotational direction of the optical axis 40A of the liquid crystal compound 40 toward the alignment axis D, the reflection direction of the circularly polarized light can be reversed.

[0193] For example, in Figure 7 and Figure 8 the rotational direction of the optical axis 40A toward the alignment axis D is clockwise and a certain circularly polarized light is reflected while being inclined toward the alignment axis D, but by setting it to counterclockwise, a certain circularly polarized light is reflected while being inclined in the direction opposite to the alignment axis D.

[0194] Moreover, in a liquid crystal layer having the same liquid crystal alignment pattern, the reflection direction is reversed according to the rotational direction of the helix of the liquid crystal compound 40, i.e., the rotational direction of the reflected circularly polarized light.

[0195] For example, in the case where the rotational direction of the helix is right-handed twist, right-handed circularly polarized light is selectively reflected, and the right-handed circularly polarized light is reflected while being inclined toward the alignment axis D by having a liquid crystal alignment pattern in which the optical axis 40A rotates clockwise along the alignment axis D.

[0196] Further, for example, in the case where the rotational direction of the helix is left-handed twist, left-handed circularly polarized light is selectively reflected, and a liquid crystal layer having a liquid crystal alignment pattern in which the optical axis 40A rotates clockwise along the alignment axis D reflects the left-handed circularly polarized light while being inclined in the direction opposite to the alignment axis D.

[0197] In the liquid crystal layer, in the liquid crystal alignment pattern of the liquid crystal compound, the length at which the optical axis of the liquid crystal compound rotates 180° is one period Λ of the diffraction structure, and one direction (alignment axis D direction) in which the optical axis of the liquid crystal compound changes while rotating is the period direction of the diffraction structure.

[0198] In a liquid crystal layer having a liquid crystal alignment pattern, the shorter the one period Λ is, the larger the angle of the reflected light with respect to the incident light is. That is, the shorter the one period Λ is, the more the reflected light can be reflected while being inclined significantly with respect to the incident light. Therefore, regarding the one period of the liquid crystal alignment pattern in the liquid crystal layer of each diffraction element, it may be appropriately set according to the diffraction angle, arrangement, etc. of each diffraction element.

[0199] The period (one period Λ) of the diffraction structure of these diffraction elements is preferably 0.1 to 10 μm, more preferably 0.1 to 1 μm, still more preferably 0.1 to 0.8 μm, and further preferably not more than the wavelength λ of the incident light from the viewpoint of total reflection propagation in the light guide plate 16.

[0200] Moreover, the rotational directions of the helical twists of the cholesteric liquid crystal phases of the liquid crystal layer of the incident diffractive element that diffracts light of the same wavelength and the liquid crystal layer of the exiting diffractive element are the same.

[0201] Among them, in the example shown in Figure 8 , it is assumed that in the X-Z plane of the liquid crystal layer 34, the liquid crystal compound 40 has its optical axis 40A oriented parallel to the main surface (X-Y plane), but it is not limited thereto. For example, as shown in Figure 11 , it may also be a structure in which in the X-Z plane of the liquid crystal layer 34, the liquid crystal compound 40 has its optical axis 40A inclined with respect to the main surface (X-Y plane).

[0202] Moreover, in the example shown in Figure 11 , in the X-Z plane of the liquid crystal layer 34, the inclination angle (tilt angle) of the liquid crystal compound 40 with respect to the main surface (X-Y plane) is the same in the thickness direction (Z direction), but it is not limited thereto. In the liquid crystal layer 34, there may be regions where the tilt angle of the liquid crystal compound 40 is different in the thickness direction.

[0203] For example, the example shown in Figure 12 has the following structure: at the interface of the liquid crystal layer on the side of the alignment film 32, the optical axis 40A of the liquid crystal compound 40 is parallel to the main surface (the pretilt angle is 0), and the tilt angle of the liquid crystal compound 40 increases as it separates from the interface on the side of the alignment film 32 in the thickness direction, and then the liquid crystal compound is oriented at a specified tilt angle until the other interface (air interface) side.

[0204] In this way, in the liquid crystal layer, it may be a structure in which the optical axis of the liquid crystal compound has a pretilt angle at one of the upper and lower interfaces, or it may be a structure in which both interfaces have a pretilt angle. Moreover, at the two interfaces, the pretilt angles may also be different.

[0205] In this way, by making the liquid crystal compound have a tilt angle (tilt), the birefringence of the liquid crystal compound effective in diffracting light becomes higher, and the diffraction efficiency can be improved.

[0206] The average angle (average tilt angle) formed by the optical axis 40A of the liquid crystal compound 40 and the main surface (X-Y plane) is preferably 5 to 80°, more preferably 10 to 50°. In addition, regarding the average tilt angle, it can be measured by observing the X-Z plane of the liquid crystal layer 34 with a polarized light microscope. Among them, in the X-Z plane of the liquid crystal layer 34, the liquid crystal compound 40 preferably has its optical axis 40A inclined and oriented in the same direction with respect to the main surface (X-Y plane).

[0207] In addition, the tilt angle is as follows: when observing the cross-section of the cholesteric liquid crystal layer with a polarized light microscope, the angle formed by the optical axis 40A of the liquid crystal compound 40 and the main surface is measured at five or more arbitrary positions, and the arithmetic mean value is obtained.

[0208] The light vertically incident on the diffraction element (liquid crystal layer) applies a bending force in the tilt direction within the liquid crystal layer and travels obliquely. When the light travels within the liquid crystal layer, a deviation from the conditions such as the diffraction period originally set to obtain the desired diffraction angle with respect to the vertical incidence occurs, and thus diffraction loss is generated.

[0209] When the liquid crystal compound is tilted, compared with the non-tilted case, there is an azimuth with a higher birefringence with respect to the azimuth diffracted by the light. The extraordinary refractive index effective in this direction becomes larger, and thus the birefringence, which is the difference between the extraordinary refractive index and the ordinary refractive index, becomes higher.

[0210] By setting the azimuth of the tilt angle according to the target diffraction azimuth, it is possible to suppress the deviation from the original diffraction conditions in this azimuth. As a result, it is considered that when using a liquid crystal compound having a tilt angle, a higher diffraction efficiency can be obtained.

[0211] Moreover, the tilt angle is preferably controlled according to the treatment of the interface of the liquid crystal layer. On the interface on the support side, by performing a pre-tilt treatment on the alignment film, the tilt angle of the liquid crystal compound can be controlled. For example, when forming the alignment film, after exposing the alignment film to ultraviolet light from the front, it is exposed from the oblique side, so that a pre-tilt angle can be generated in the liquid crystal compound in the liquid crystal layer formed on the alignment film. In this case, the pre-tilt is performed in the direction where the uniaxial side of the liquid crystal compound can be observed with respect to the second irradiation direction. However, the liquid crystal compound in the azimuth perpendicular to the second irradiation direction is not pre-tilted, so there are regions where pre-tilting is performed and regions where pre-tilting is not performed in the plane. This is because when diffracting light in the target azimuth, it is most helpful for improving birefringence in this direction, and thus it is suitable for improving the diffraction efficiency.

[0212] Furthermore, an additive that promotes the pre-tilt angle can also be added to the liquid crystal layer or the alignment film. In this case, as a factor for further improving the diffraction efficiency, the additive can be utilized.

[0213] This additive can also be used to control the pre-tilt angle of the interface on the air side.

[0214] Here, the liquid crystal layer 34 is preferably a pitch gradient layer in which the helical pitch P changes in the film thickness direction. Specifically, in the liquid crystal layer 34, it is preferred that the helical pitch changes in a gradually increasing (or decreasing) manner from one major surface of the liquid crystal layer 34 toward the other major surface side. The liquid crystal layer 34 can broaden the selection reflection wavelength band by changing the helical pitch P in the film thickness direction.

[0215] Moreover, when the liquid crystal layer 34 is a pitch gradient layer, in the liquid crystal layer 34, one period Λ, the helical pitch P1 on one surface side of the pitch gradient layer, and the helical pitch P2 on the other surface side preferably satisfy P1 < Λ < P2.

[0216] Thereby, the diffraction efficiency with respect to light incident from an oblique direction can be improved.

[0217] Among them, in the cross-section of the liquid crystal layer observed by SEM, the bright and dark portions derived from the cholesteric liquid crystal phase are inclined with respect to the major surface. In the liquid crystal layer, when measuring the in-plane retardation Re in the normal direction and the direction inclined with respect to the normal direction, it is preferred that in either the slow axis plane or the fast axis plane, the direction in which the in-plane retardation Re is the smallest is inclined from the normal direction. Specifically, it is preferred that the absolute value of the measurement angle formed by the direction in which the in-plane retardation Re is the smallest and the normal is 5° or more. In other words, it is preferred that the liquid crystal compound of the liquid crystal layer is inclined with respect to the major surface, and the inclination direction is substantially the same as the bright and dark portions of the liquid crystal layer. In addition, the normal direction is the direction orthogonal to the major surface.

[0218] By making the liquid crystal layer have such a structure, compared with a liquid crystal layer in which the liquid crystal compound is parallel to the major surface, circularly polarized light can be diffracted with high diffraction efficiency.

[0219] In the structure in which the liquid crystal compound of the liquid crystal layer is inclined with respect to the major surface and the inclination direction is substantially the same as the bright and dark portions, the bright and dark portions corresponding to the reflection surface coincide with the optical axis of the liquid crystal compound. Therefore, the action of the liquid crystal compound with respect to the reflection (diffraction) of light becomes larger, and the diffraction efficiency can be improved. As a result, the amount of reflected light with respect to the incident light can be further increased.

[0220] On the fast axis plane or the slow axis plane of the liquid crystal layer, the absolute value of the inclination angle of the optical axis of the liquid crystal layer is preferably 5° or more, more preferably 15° or more, and still more preferably 20° or more.

[0221] By setting the absolute value of the inclination angle of the optical axis to 15° or more, and more preferably making the direction of the liquid crystal compound coincide with the bright and dark portions, it is preferable from the viewpoint of improving the diffraction efficiency.

[0222] Here, in the present invention, the refractive index of the liquid crystal layer constituting the diffraction element is equal to or higher than the refractive index of the light guide plate.

[0223] The method for adjusting the refractive index of the liquid crystal layer is not particularly limited. For example, a method of using a liquid crystal compound with a high refractive index and a method of adding nanoparticles with a high refractive index to the liquid crystal layer can be cited.

[0224] For increasing the refractive index of the liquid crystal compound, for example, it is effective to increase the long wavelength of absorption and / or the molar extinction coefficient of the liquid crystal compound, and to make the structure of the liquid crystal compound a rigid chain, etc. More specifically, for example, there is a method of introducing at least one selected from the group including an aromatic ring, a halogen atom other than a fluorine atom, a sulfur atom, an alicyclic group, a double bond group, and a triple bond group into the liquid crystal compound.

[0225] And, as the nanoparticles with a high refractive index, for example, zirconia, titanium oxide, etc. can be cited.

[0226] As a method for measuring the refractive index of the liquid crystal layer, for example, it can be measured by the following method: The liquid crystal composition forming the liquid crystal layer is coated on a separately prepared support with an alignment film, and the in-plane average refractive index is obtained by measuring the liquid crystal immobilized layer (cured layer) obtained by irradiating ultraviolet rays and immobilizing it after the director of the liquid crystal compound is horizontally oriented on the substrate using a reflection spectroscopic thickness meter FE-3000 (manufactured by Otsuka Electronics Co., Ltd.), etc. Or, a cholesteric liquid crystal layer can be directly measured using an Abbe refractometer or an ellipsometer.

[0227] In addition, when the diffraction element includes a support, etc., it is preferable to dispose the liquid crystal layer with a high refractive index in contact with the light guide plate. Or, it is preferable to use a support made of a material with a high refractive index.

[0228] <<Method for forming liquid crystal layer>>

[0229] The liquid crystal layer can be formed by fixing the liquid crystal phase in which the liquid crystal compound is oriented in a predetermined orientation state into a layer. For example, in the case of a cholesteric liquid crystal layer, the cholesteric liquid crystal phase can be fixed into a layer.

[0230] The structure formed by fixing the liquid crystal phase only needs to be a structure that maintains the orientation of the liquid crystal compound that becomes the liquid crystal phase. Typically, the following structure is preferable: On the basis of setting the polymerizable liquid crystal compound in a predetermined liquid crystal phase orientation state, it is polymerized and cured by ultraviolet irradiation, heating, etc. to form a layer without fluidity, and at the same time, it is changed to a state where the orientation morphology will not change due to an external field or external force.

[0231] In addition, in the structure formed by fixing the liquid crystal phase, as long as the optical properties of the liquid crystal phase are maintained, in the liquid crystal layer, the liquid crystal compound 40 may not exhibit liquid crystallinity. For example, the polymerizable liquid crystal compound can be polymerized to a high molecular weight through a curing reaction and lose liquid crystallinity.

[0232] As a material used in the formation of the liquid crystal layer, as an example, a liquid crystal composition containing a liquid crystal compound can be cited. The liquid crystal compound is preferably a polymerizable liquid crystal compound.

[0233] In addition, the liquid crystal composition used in the formation of the liquid crystal layer may further contain a surfactant and a chiral agent.

[0234] --Polymerizable liquid crystal compound--

[0235] The polymerizable liquid crystal compound may be a rod-shaped liquid crystal compound or a disc-shaped liquid crystal compound.

[0236] As an example of the rod-shaped polymerizable liquid crystal compound, a rod-shaped nematic liquid crystal compound can be cited. As the rod-shaped nematic liquid crystal compound, it is preferable to use azomethines, azoxy compounds, cyanobiphenyls, cyanobenzoates, benzoates, phenyl cyclohexanecarboxylates, cyanophenyl cyclohexanes, cyanide-substituted phenyl pyrimidines, alkoxy-substituted phenyl pyrimidines, phenyl dioxanes, diphenylacetylenes, and alkenyl cyclohexyl benzonitriles, etc. Not only low molecular liquid crystal compounds but also high molecular liquid crystal compounds can be used.

[0237] Regarding the polymerizable liquid crystal compound, it is obtained by introducing a polymerizable group into the liquid crystal compound. Among the examples of the polymerizable group, an unsaturated polymerizable group, an epoxy group, and an aziridinyl group are included. The unsaturated polymerizable group is preferable, and the ethylenically unsaturated polymerizable group is more preferable. The polymerizable group can be introduced into the molecule of the liquid crystal compound 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.

[0238] Examples of the polymerizable liquid crystal compound include compounds described in Makromol.Chem., Vol. 190, p. 2255 (1989), Advanced Materials, Vol. 5, p. 107 (1993), U.S. Patent No. 4683327, U.S. Patent No. 5622648, U.S. Patent No. 5770107, International Publication No. 95 / 22586, International Publication No. 95 / 24455, International Publication No. 97 / 00600, International Publication No. 98 / 23580, International Publication No. 98 / 52905, Japanese Patent Laid-Open No. 1-272551, Japanese Patent Laid-Open No. 6-16616, Japanese Patent Laid-Open No. 7-110469, Japanese Patent Laid-Open No. 11-80081, and Japanese Patent Laid-Open No. 2001-328973, etc. Two or more kinds of polymerizable liquid crystal compounds can be used simultaneously. If two or more kinds of polymerizable liquid crystal compounds are used simultaneously, the alignment temperature can be reduced.

[0239] In addition, as a polymerizable liquid crystal compound other than the above, a cyclic organopolysiloxane compound having a cholesteric phase as disclosed in Japanese Patent Application Laid-Open No. 57-165480 can be used. Moreover, as the above-mentioned polymer liquid crystal compound, a polymer in which a mesogenic group exhibiting liquid crystal is introduced into the main chain, side chain or both the main chain and side chain, a polymer cholesteric liquid crystal in which a cholesteryl group is introduced into the side chain, a liquid crystalline polymer as disclosed in Japanese Patent Application Laid-Open No. 9-133810, a liquid crystalline polymer as disclosed in Japanese Patent Application Laid-Open No. 11-293252, etc. can be used.

[0240] As the liquid crystal compound, a compound represented by the general formula (1) is preferably used.

[0241] [Chemical formula 1]

[0242]

[0243] In the general formula (1),

[0244] P 1 and P 2 each independently represents a polymerizable group.

[0245] The type of the polymerizable group is not particularly limited, and known polymerizable groups can be cited. From the viewpoint of reactivity, a functional group capable of undergoing addition polymerization reaction is preferred, and a polymerizable ethylenically unsaturated group or a ring polymerizable group is more preferred. As the polymerizable group, for example, (meth)acryloyloxy, vinyl, maleimide, acetyl, styryl, allyl, epoxy, oxetanyl, and groups containing these groups can be cited. In addition, a hydrogen atom in each of the above groups may be substituted with another substituent such as a halogen atom.

[0246] L 1 and L 2 each independently represents a single bond or a divalent linking group.

[0247] As the above-mentioned divalent linking group, for example, an ether group (-O-), a carbonyl group (-CO-), an ester group (-COO-), a thioether group (-S-), -SO 2 -, -NR- (R represents a hydrogen atom or an alkyl group), a divalent hydrocarbon group (for example, a saturated hydrocarbon group such as an alkylene group, an alkenylene group (e.g., -CH=CH-), an alkynylene group (e.g., -C≡C-), and an arylene group), and a group formed by combining them can be cited.

[0248] An atom directly bonded to the phenyl ring group in the general formula (1) in the above-mentioned divalent linking group is preferably a carbon atom, and the carbon atom is preferably an sp3 carbon atom (a carbon atom having only a single bond).

[0249] As the divalent linking group described above, a divalent hydrocarbon group having 1 to 20 carbon atoms which may have substituents is preferred. One or more methylenes in the divalent hydrocarbon group may each independently be substituted with -O- or -C(=O)-. One methylene may be substituted with -O-, and the adjacent methylene may be substituted with -C(=O)- to form an ester group.

[0250] Examples of the substituents that the divalent hydrocarbon group may have include, preferably, a fluorine atom.

[0251] The divalent hydrocarbon group has 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, and more preferably 1 to 5 carbon atoms.

[0252] The divalent hydrocarbon group may be linear or branched and may have a cyclic structure.

[0253] Among them, preferably, L 1 represents a group represented by formula (A), and L 2 represents a group represented by formula (B).

[0254] Formula (A) *-Z 1 -Sp 1 -**

[0255] Formula (B) *-Z 2 -Sp 2 -**

[0256] Z 1 and Z 2 each independently represent -C(R za )(R zb )-.

[0257] R za and R zb each independently represent a hydrogen atom or a substituent, and preferably a hydrogen atom.

[0258] Sp 1 and Sp 2 each independently represent a divalent hydrocarbon group having 1 to 19 carbon atoms which may have a fluorine atom or a single bond. One or more methylenes in the divalent hydrocarbon group may each independently be substituted with -O- or -C(=O)-. One methylene may be substituted with -O-, and the adjacent methylene may be substituted with -C(=O)- to form an ester group.

[0259] The divalent hydrocarbon group may be linear or branched and may have a cyclic structure.

[0260] * represents the bonding position of the benzene ring group directly bonded to L 1 or L 2 respectively, and ** represents the bonding with P1 or P 2 bonding position of

[0261] X represents -C(R xa )(R xb ). R xa and R xb each independently represents a hydrogen atom or a substituent.

[0262] R xa and R xb are preferably hydrogen atoms.

[0263] Y represents -C(R ya )(R yb )-, -O-, -NR yn -, or -S-. R ya and R yb each independently represents a hydrogen atom or a substituent. R yn represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms (which may be linear or branched and may have a cyclic structure. Further, it may have a substituent).

[0264] Among them, Y is preferably -C(R ya )(R yb ), or -O-. From the viewpoint of further suppressing the coloring of the compound, it is more preferably -C(R ya )(R yb ).

[0265] R 1 to R 4 each independently represents a substituent.

[0266] As the above-mentioned substituent, it is preferably independently an alkyl group having 1 to 20 carbon atoms (preferably 1 to 10 carbon atoms, more preferably 2 to 5 carbon atoms), an alkoxy group having 1 to 20 carbon atoms, an alkanoyl group having 1 to 20 carbon atoms, an alkanoyloxy group having 1 to 20 carbon atoms, an alkoxycarbonyl group having 1 to 20 carbon atoms (preferably 2 to 6 carbon atoms), an alkylamino group having 1 to 20 carbon atoms, an alkylaminocarbonyl group having 1 to 20 carbon atoms, an alkanoylamino group having 1 to 20 carbon atoms, a cyano group, a nitro group, a halogen atom, or a group having a polymerizable group.

[0267] When the above-mentioned substituent may be linear or branched, the above-mentioned substituent may be linear or branched. Further, when possible, it may have a cyclic structure.

[0268] One or more methylenes in the above-mentioned alkyl group and the alkyl part of the above-mentioned substituent (for example, the part other than -O- in the above-mentioned alkoxy group) may be independently replaced by -O- or -C(=O)-.

[0269] Also, when possible, the above substituents may further have substituents (preferably a fluorine atom). For example, the above alkyl group preferably becomes a fluoroalkyl group (e.g., a perfluoroalkyl group having 1 to 10 carbon atoms such as trifluoromethyl). Also, for example, the alkyl moiety of the above substituent preferably has a fluorine atom.

[0270] Among them, from the viewpoint of excellent liquid crystallinity and solubility of the compound, as the substituent, the above alkyl group, the above alkoxycarbonyl group or the above alkylaminocarbonyl group is preferred, more preferably an alkyl group having 2 or more carbon atoms, fluoromethyl (preferably trifluoromethyl), the above alkoxycarbonyl group or the above alkylaminocarbonyl group, still more preferably the above alkoxycarbonyl group or the above alkylaminocarbonyl group, and particularly preferably the above alkoxycarbonyl group.

[0271] m 1 ~m 4 each independently represents an integer of 0 to 4. When there are multiple corresponding Rs 1 ~m 4 because m 1 ~R 4 is 2 or more, the multiple Rs 1 ~R 4 may be the same or different from each other.

[0272] From the viewpoint of excellent liquid crystallinity and solubility of the compound, at least one of m 1 ~m 4 preferably represents an integer of 1 or more. Among them, it is preferred that m 3 represents an integer of 1 or more.

[0273] Among them, at least one of m 1 ~m 4 represents an integer of 1 or more, and at least one of the Rs 1 ~m 4 corresponding to at least one of m 1 ~R 4 that represents an integer of 1 or more is preferably the above alkyl group, the above alkoxycarbonyl group or the above alkylaminocarbonyl group, more preferably an alkyl group having 2 or more carbon atoms, fluoromethyl (preferably trifluoromethyl), the above alkoxycarbonyl group or the above alkylaminocarbonyl group, still more preferably the above alkoxycarbonyl group or the above alkylaminocarbonyl group, and particularly preferably the above alkoxycarbonyl group. In particular, when m 3 represents an integer of 1 or more, at least one of Rs 3 is preferably the above alkyl group, the above alkoxycarbonyl group or the above alkylaminocarbonyl group.

[0274] "At least one of the Rs 1 ~m 4 corresponding to at least one of m1 ~R 4 At least one of the following “alkyl groups, etc.” can be exemplified in the following manner: m 1 represents an integer of 1 or more. When m 2 ~m 4 is 0, the R 1 corresponding to m 1 is the above group. Further, as another example, the following manner can be exemplified: When m 1 ~m 2 represents an integer of 1 or more and m 3 ~m 4 is 0, the R 1 corresponding to m 1 and the R 2 corresponding to m 2 at least one of which is the above group.

[0275] --Discotic liquid crystal compound--

[0276] As the discotic liquid crystal compound, for example, the discotic liquid crystal compounds described in JP-A-2007-108732 or JP-A-2010-244038 can be preferably used.

[0277] Moreover, the addition amount of the polymerizable liquid crystal compound in the liquid crystal composition is preferably 75 to 99.9% by mass, more preferably 80 to 99% by mass, and still more preferably 85 to 90% by mass with respect to the solid content mass (mass excluding the solvent) of the liquid crystal composition.

[0278] --Surfactant--

[0279] The liquid crystal composition used for forming the liquid crystal layer may contain a surfactant.

[0280] The surfactant is preferably a compound that can function as an alignment control agent, and the alignment control agent helps to stably or rapidly align the cholesteric liquid crystal phase. As the surfactant, for example, silicone-based surfactants and fluorine-based surfactants can be exemplified, and fluorine-based surfactants can be preferably exemplified.

[0281] As specific examples of the surfactant, compounds described in paragraphs

[0082] to

[0090] of Japanese Patent Application Laid-Open No. 2014-119605, compounds described in paragraphs

[0031] to

[0034] of Japanese Patent Application Laid-Open No. 2012-203237, compounds exemplified in paragraphs

[0092] and

[0093] of Japanese Patent Application Laid-Open No. 2005-099248, compounds exemplified in paragraphs

[0076] to

[0078] and

[0082] to

[0085] of Japanese Patent Application Laid-Open No. 2002-129162, and fluoro(meth)acrylate polymers described in paragraphs

[0018] to

[0043] of Japanese Patent Application Laid-Open No. 2007-272185, etc. can be cited.

[0282] In addition, the surfactant may be used alone in one kind or two or more kinds may be used simultaneously.

[0283] As the fluorine-based surfactant, the compound described in paragraphs

[0082] to

[0090] of Japanese Patent Application Laid-Open No. 2014-119605 is preferably used.

[0284] The addition amount of the surfactant in the liquid crystal composition is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass, and still more preferably 0.02 to 1% by mass with respect to the total mass of the liquid crystal compound.

[0285] --Chiral reagent (optically active compound)--

[0286] The chiral reagent has the function of inducing the helical structure of the cholesteric liquid crystal phase. Since the twisting direction or the helical pitch of the helix induced by the compound is different, the chiral reagent can be selected according to the purpose.

[0287] As the chiral reagent, there is no particular limitation, and known compounds (for example, described in the Liquid Crystal Device Handbook, Chapter 3, Section 4-3, chiral reagents for TN (twisted nematic) and STN (Super Twisted Nematic), page 199, edited by the 142nd Committee of the Japan Society for the Promotion of Science, 1989), isosorbide, isomannitol derivatives, etc. can be used.

[0288] Chiral reagents usually contain asymmetric carbon atoms, but axially asymmetric compounds or surface asymmetric compounds that do not contain asymmetric carbon atoms can also be used as chiral reagents. In the examples of axially asymmetric compounds or surface asymmetric compounds, there are included binaphthyl, helicene, p-xylene dimer and their derivatives. The chiral reagent may also have a polymerizable group. When both the chiral reagent and the liquid crystal compound have polymerizable groups, a polymer having a repeating unit derived from the polymerizable liquid crystal compound and a repeating unit derived from the chiral reagent can be formed by the polymerization reaction of the polymerizable chiral reagent and the polymerizable liquid crystal compound. In this way, the polymerizable group possessed by the polymerizable chiral reagent is preferably the same group as the polymerizable group possessed by the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral reagent is also preferably an unsaturated polymerizable group, an epoxy group or an aziridinyl group, more preferably an unsaturated polymerizable group, and still more preferably an ethylenically unsaturated polymerizable group.

[0289] Moreover, the chiral reagent may also be a liquid crystal compound.

[0290] When the chiral reagent has a photo-isomerizable group, it is preferably possible to form a pattern of a desired reflection wavelength corresponding to the emission wavelength by irradiation with actinic light through a photomask after coating and alignment. As the photo-isomerizable group, the isomerization site of a compound showing photochromism, an azo group, an azoxy group or a cinnamoyl group is preferred. As specific compounds, those described in JP-A-2002-080478, JP-A-2002-080851, JP-A-2002-179668, JP-A-2002-179669, JP-A-2002-179670, JP-A-2002-179681, JP-A-2002-179682, JP-A-2002-338575, JP-A-2002-338668, JP-A-2003-313189 and JP-A-2003-313292 can be used.

[0291] The content of the chiral reagent in the liquid crystal composition is preferably 0.01 to 200 mol% and more preferably 1 to 30 mol% relative to the molar amount of the liquid crystal compound contained.

[0292] --Polymerization initiator--

[0293] When the liquid crystal composition contains a polymerizable compound, a polymerization initiator is preferably contained. In the method of carrying out the polymerization reaction by ultraviolet irradiation, the polymerization initiator used is preferably a photo-polymerization initiator that can initiate the polymerization reaction by ultraviolet irradiation.

[0294] Examples of the photoinitiator include α-carbonyl compounds (described in the specifications of U.S. Patent No. 2367661 and U.S. Patent No. 2367670), acyloin ethers (described in the specification of U.S. Patent No. 2448828), α-hydrocarbon-substituted aromatic acyloin compounds (described in the specification of U.S. Patent No. 2722512), polynuclear quinone compounds (described in the specifications of U.S. Patent No. 3046127 and U.S. Patent No. 2951758), a combination of triarylimidazole dimer and p-aminophenyl ketone (described in the specification of U.S. Patent No. 3549367), acridine and phenazine compounds (described in Japanese Patent Application Laid-Open No. 60-105667 and the specification of U.S. Patent No. 4239850), and oxadiazole compounds (described in the specification of U.S. Patent No. 4212970), etc.

[0295] The content of the photoinitiator in the liquid crystal composition is preferably 0.1 to 20% by mass, more preferably 0.5 to 12% by mass, relative to the content of the liquid crystal compound.

[0296] --Crosslinking agent--

[0297] In order to improve the film strength after curing and improve the durability, the liquid crystal composition may optionally contain a crosslinking agent. As the crosslinking agent, a crosslinking agent curable by ultraviolet rays, heat, moisture, etc. can be preferably used.

[0298] There is no particular limitation on the crosslinking agent, and it can be appropriately selected according to the purpose. For example, polyfunctional acrylate compounds such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate can be cited; epoxy compounds such as glycidyl (meth)acrylate and ethylene glycol diglycidyl ether; aziridine compounds such as 2,2-bis(hydroxymethyl)butanol-tris[3-(1-aziridinyl)propionate] and 4,4-bis(ethyleneimino carbonylamino)diphenylmethane; isocyanate compounds such as hexamethylene diisocyanate and biuret-type isocyanate; polyoxazoline compounds having an oxazoline group in the side chain; and alkoxysilane compounds such as vinyltrimethoxysilane and N-(2-aminoethyl)-3-aminopropyltrimethoxysilane. In addition, a known catalyst can be used according to the reactivity of the crosslinking agent, and in addition to improving the film strength and durability, the productivity can also be improved. These can be used alone or two or more of them can be used simultaneously.

[0299] The content of the crosslinking agent is preferably 3 to 20% by mass, more preferably 5 to 15% by mass, relative to the solid content mass of the liquid crystal composition. As long as the content of the crosslinking agent is within the above range, it is easy to obtain the effect of increasing the crosslinking density, thereby further improving the stability of the liquid crystal phase.

[0300] --Other additives--

[0301] In a liquid crystal composition, a polymerization inhibitor, an antioxidant, an ultraviolet absorber, a light stabilizer, a colorant, metal oxide fine particles, etc. can be further added as needed within a range that does not deteriorate optical properties, etc.

[0302] When forming a liquid crystal layer, the liquid crystal composition is preferably used as a liquid.

[0303] The liquid crystal composition may contain a solvent. The solvent is not limited and can be appropriately selected according to the purpose, but an organic solvent is preferred.

[0304] The organic solvent is not limited and can be appropriately selected according to the purpose. For example, ketones, halogenated alkanes, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, ethers, etc. can be cited. These can be used alone or two or more of them can be used simultaneously. Among these, in consideration of the environmental burden, ketones are preferred.

[0305] When forming a liquid crystal layer, it is preferred to coat the liquid crystal composition on the formation surface of the liquid crystal layer, orient the liquid crystal compound into a desired liquid crystal phase state, and then cure the liquid crystal compound to form a liquid crystal layer.

[0306] That is, when forming a cholesteric liquid crystal layer on the alignment film 32, it is preferred to coat the liquid crystal composition on the alignment film 32, orient the liquid crystal compound into a cholesteric liquid crystal phase state, and then cure the liquid crystal compound to form a liquid crystal layer in which the cholesteric liquid crystal phase is fixed.

[0307] Regarding the coating of the liquid crystal composition, all printing methods such as inkjet and roll printing, and known methods such as spin coating, bar coating, and spray coating that can uniformly coat a liquid on a sheet can be used.

[0308] The coated liquid crystal composition is dried and / or heated as needed, and then cured to form a liquid crystal layer. In this drying and / or heating process, as long as the liquid crystal compound in the liquid crystal composition is oriented into a cholesteric liquid crystal phase. When heating, the heating temperature is preferably 200 °C or lower, more preferably 130 °C or lower.

[0309] The oriented liquid crystal compound is further polymerized as needed. The polymerization can be either thermal polymerization or photopolymerization based on light irradiation, but photopolymerization is preferred. Light irradiation preferably uses ultraviolet light. The irradiation energy is preferably 20 mJ / cm 2 ~50 J / cm 2 ,more preferably 50~1500 mJ / cm 2 。To promote the photopolymerization reaction, light irradiation can also be carried out under heating conditions or in a nitrogen atmosphere. The wavelength of the irradiated ultraviolet light is preferably 250~430 nm.

[0310] The thickness of the liquid crystal layer is not limited, and as long as it is appropriately set according to the use of the diffraction element, the required light reflectance in the liquid crystal layer, the material for forming the liquid crystal layer, etc., a thickness capable of obtaining the required light reflectance can be obtained.

[0311] (Transmissive liquid crystal diffraction element)

[0312] In the above example, a liquid crystal layer in which a liquid crystal compound is cholesterically oriented is used as the liquid crystal diffraction element. However, as long as the liquid crystal diffraction element used in the present invention has a liquid crystal alignment pattern in which the optical axis 40A derived from the liquid crystal compound 40 continuously rotates in at least one direction in the plane, various liquid crystal diffraction elements can be utilized.

[0313] In the present invention, a liquid crystal diffraction element having a liquid crystal alignment pattern in which the liquid crystal compound continuously rotates in at least one direction in the plane and the liquid crystal compound does not form a cholesteric liquid crystal phase in the thickness direction can also be utilized. In addition, the liquid crystal diffraction element may have a structure that twists and rotates in the thickness direction to such an extent that the liquid crystal compound does not become a cholesteric liquid crystal phase.

[0314] In Figure 14 and Figure 15 a transmissive liquid crystal diffraction element is illustrated, and one example thereof will be described.

[0315] Figure 14 and Figure 15 The liquid crystal diffraction element shown has a support 30, an alignment film 32, and a liquid crystal layer 36.

[0316] Similar to the liquid crystal layer 34, Figure 15 the liquid crystal layer 36 of the liquid crystal diffraction element shown also has a liquid crystal alignment pattern in which the optical axis 40A of the liquid crystal compound 40 continuously rotates in the direction of the alignment axis D. In addition, similar to the above Figure 7 the same, Figure 15 only the liquid crystal compound on the surface of the alignment film 32 is shown.

[0317] In Figure 14 the liquid crystal diffraction element shown, the liquid crystal compound 40 forming the liquid crystal layer 36 does not twist and rotate in a spiral shape in the thickness direction, and the optical axis 40A is located at the same position in the plane direction. Regarding such a liquid crystal layer, when forming the above liquid crystal layer, it can be formed without adding a chiral reagent to the liquid crystal composition.

[0318] As described above, the liquid crystal layer 36 has a liquid crystal alignment pattern in which the orientation of the optical axis 40A derived from the liquid crystal compound 40 continuously rotates and changes in one direction in the plane along the alignment axis D, i.e., the direction indicated by the arrow D.

[0319] On the other hand, in the liquid crystal compound 40 that forms the liquid crystal layer 36, the liquid crystal compounds 40 with the same orientation of the optical axis 40A are arranged at equal intervals in the Y direction orthogonal to the alignment axis D direction, that is, in the Y direction orthogonal to one direction in which the optical axis 40A continuously rotates.

[0320] In other words, in the liquid crystal compound 40 that forms the liquid crystal layer 36, between the liquid crystal compounds 40 arranged in the Y direction, the angles formed by the orientation of the optical axis 40A and the alignment axis D direction are equal.

[0321] In the liquid crystal layer 36, among the liquid crystal compounds arranged in the Y direction, the angles formed by the optical axis 40A and the alignment axis D direction (one direction in which the orientation of the optical axis of the liquid crystal compound 40 rotates) are equal. The region where the liquid crystal compounds 40 with the equal angles formed by the optical axis 40A and the alignment axis D direction are arranged in the Y direction is set as region R.

[0322] In this case, it is preferable that the value of the in-plane retardation (Re) in each region R is half a wavelength, that is, λ / 2. Regarding these in-plane retardations, they are calculated by the product of the refractive index difference Δn associated with the refractive index anisotropy of region R and the thickness of the optically anisotropic layer. Among them, the refractive index difference associated with the refractive index anisotropy of region R in the optically anisotropic layer is the refractive index difference defined as the difference between the refractive index in the direction of the slow axis in the plane of region R and the refractive index in the direction orthogonal to the direction of the slow axis. That is, the refractive index difference Δn associated with the refractive index anisotropy of region R is equal to 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 in the plane of region R. That is, the refractive index difference Δn is equal to the refractive index difference of the liquid crystal compound 40.

[0323] When circularly polarized light is incident on such a liquid crystal layer 36, the light is refracted and the direction of the circularly polarized light is converted.

[0324] In Figure 16 and Figure 17 this effect is conceptually shown. In addition, the liquid crystal layer 36 is set such that the product of the refractive index difference of the liquid crystal compound and the thickness of the optically anisotropic layer has a value of λ / 2.

[0325] As Figure 16 shown, when the product of the refractive index difference of the liquid crystal compound in the liquid crystal layer 36 and the thickness of the optically anisotropic layer has a value of λ / 2, if the incident light L 1 which is left-handed circularly polarized light is incident on the liquid crystal layer 36, then the incident light L 1 passes through the liquid crystal layer 36 to impart a phase difference of 180°, and the transmitted light L 2 is converted into right-handed circularly polarized light.

[0326] Moreover, the liquid crystal alignment pattern formed on the liquid crystal layer 36 is a periodic pattern along the alignment axis D. Therefore, the transmitted light L 2 travels in a direction different from the traveling direction of the incident light L 1 . Thus, the incident light L of left-handed circular polarization 1 is converted into the transmitted light L of right-handed circular polarization that is inclined by a predetermined angle only in the direction of the alignment axis D with respect to the incident direction 2 .

[0327] On the other hand, as Figure 17 shown, when the product of the refractive index difference of the liquid crystal compound in the liquid crystal layer 36 and the thickness of the optically anisotropic layer is λ / 2, if the incident light L of right-handed circular polarization 4 is incident on the liquid crystal layer 36, the incident light L 4 is given a phase difference of 180° by passing through the liquid crystal layer 36, and thus is converted into the transmitted light L of left-handed circular polarization 5 .

[0328] Moreover, the liquid crystal alignment pattern formed on the liquid crystal layer 36 is a periodic pattern along the alignment axis D. Therefore, the transmitted light L 5 travels in a direction different from the traveling direction of the incident light L 4 . At this time, the transmitted light L 5 travels in a direction different from the direction of the transmitted light L 2 , that is, in a direction opposite to the arrow X direction with respect to the incident direction. Thus, the incident light L 4 is converted into the transmitted light L of left-handed circular polarization that is inclined by a predetermined angle only in the direction opposite to the alignment axis D with respect to the incident direction 5 .

[0329] Similar to the liquid crystal layer 34, the liquid crystal layer 36 can also adjust the refraction angles of the transmitted lights L 2 and L 5 by changing one period Λ of the formed liquid crystal alignment pattern. Specifically, the shorter one period Λ of the liquid crystal alignment pattern of the liquid crystal layer 36 is, the stronger the interference between the lights passing through the adjacent liquid crystal compounds 40 is. Therefore, the transmitted lights L 2 and L 5 can be refracted more greatly.

[0330] Moreover, by setting the rotation direction of the optical axis 40A of the liquid crystal compound 40 rotating along the alignment axis D1 to the opposite direction, the refraction direction of the transmitted light can be set to the opposite direction. That is, in the example Figures 14 - 17 shown, the rotation direction of the optical axis 40A toward the alignment axis D is the clockwise direction. However, by setting this rotation direction to the counterclockwise direction, the refraction direction of the transmitted light can be set to the opposite direction.

[0331] In addition, from the viewpoint of diffraction efficiency, even when using such a liquid crystal diffraction element that transmits diffracted incident light, it is also preferable to use a liquid crystal diffraction element having a region where the liquid crystal compound is twisted and rotated (the twist angle is less than 360°). In particular, when diffracting light at an angle of total reflection within the light guide plate, from the viewpoint of diffraction efficiency, it is possible to preferably use a liquid crystal diffraction element having a region where the liquid crystal compound is twisted and rotated. Also, regarding laminating liquid crystal diffraction elements having different twist angles of the liquid crystal compound twisted and rotated or laminating liquid crystal diffraction elements having different twisting directions of the liquid crystal compound twisted and rotated, it is more preferable from the viewpoint of diffraction efficiency.

[0332] Moreover, it is also possible to use such a liquid crystal diffraction element having a region where the liquid crystal compound is not cholesterically oriented and twisted and rotated (the twist angle is less than 360°) as a reflective diffraction element. In such a liquid crystal diffraction element, the diffracted light is reflected by the interface of the liquid crystal diffraction element and exits from the light incident side to reflect the light while diffracting it, so it can also function as a reflective diffraction element.

[0333] Here, Figure 14 The liquid crystal layer 36 shown has a structure in which the optical axis of the liquid crystal compound is parallel to the main surface of the liquid crystal layer, but it is not limited thereto.

[0334] For example, as Figure 18 the liquid crystal layer 36b shown, in the aforementioned liquid crystal layer, the optical axis of the liquid crystal compound can be inclined with respect to the main surface of the liquid crystal layer. Such a liquid crystal layer is the same as the aforementioned liquid crystal layer 36 in that it has a liquid crystal alignment pattern in which the orientation of the optical axis of the liquid crystal compound continuously rotates in one direction within the plane and changes. That is, the plan view of the liquid crystal layer 36b is the same as Figure 15 the same.

[0335] In the light guide element of the present invention, as each diffraction element, different types of diffraction elements can be used in combination. For example, a transmissive liquid crystal diffraction element can be used as the diffraction element on the incident side, and a reflective liquid crystal diffraction element can be used as the diffraction element on the exit side.

[0336] In order to improve visual recognition, the light guide element of the present invention can also use a diffractive optical method for expanding the exit pupil.

[0337] Specifically, it is possible to use an optical method using a plurality of diffractive elements (diffraction elements), that is, a diffractive optical method having inner coupling, intermediate, and outer coupling diffractive elements. This method is described in detail in Japanese Patent Application Laid-Open No. 2008-546020.

[0338] As described above, the light guide element of the present invention has been described in detail. However, the present invention is not limited to the above examples, and various improvements or changes can be made without departing from the spirit of the present invention.

[0339] Example

[0340] Examples are given below to more specifically illustrate the features of the present invention. The materials, reagents, usage amounts, amounts of substances, ratios, treatment contents, treatment steps, etc. shown in the following examples can be appropriately changed as long as they do not depart from the gist of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0341] [Example 1]

[0342] <Fabrication of Diffraction Element>

[0343] (Formation of Alignment Film)

[0344] As a support, a glass substrate was prepared. Using a spin coater, the following alignment film-forming coating solution was coated on the support at 2500 rpm for 30 seconds. The support having the coating film of the alignment film-forming coating solution was dried on a hot plate at 60°C for 60 seconds to form an alignment film.

[0345] Alignment Film-Forming Coating Solution

[0346]

[0347] -Raw Materials for Photoalignment-

[0348] [Chemical Formula 1]

[0349]

[0350] (Exposure of Alignment Film)

[0351] Using Figure 13 the exposure apparatus shown, the alignment film was exposed to form an alignment film P-1 having an alignment pattern.

[0352] In the exposure apparatus, a device using a laser beam with an emission wavelength (325 nm) was used as the laser. The exposure amount based on the interference light was set to 320 mJ / cm 2 . The crossing angle (crossing angle α) of the two lights was adjusted to 51.3° such that one cycle of the alignment pattern formed by the interference of the two laser beams (the length of the optical axis rotation of 180°) became 0.410 μm.

[0353] (Formation of Cholesteric Liquid Crystal Layer)

[0354] As the liquid crystal composition for forming the cholesteric liquid crystal layer, the following liquid crystal composition LC-1 was prepared.

[0355] Liquid crystal composition LC-1

[0356]

[0357] Liquid crystal compound L-1

[0358] [Chemical formula 2]

[0359]

[0360] Liquid crystal compound L-2

[0361] [Chemical formula 3]

[0362]

[0363] The Δn of the liquid crystal compound obtained by mixing liquid crystal compound L-1 and liquid crystal compound L-2 in a ratio of 40:60 is measured by the following method: The mixed liquid crystal compound is injected into a wedge cell, and a laser beam with a wavelength of 552 nm is irradiated thereon, and the refraction angle of the transmitted light is measured. The Δn of liquid crystal compound L-1 is 0.23.

[0364] Chiral reagent Ch-1

[0365] [Chemical formula 4]

[0366]

[0367] This chiral reagent Ch-1 is a chiral reagent that causes the liquid crystal compound to rotate in a right-handed helical shape. Therefore, the cholesteric liquid crystal layer selectively reflects right-circularly polarized light.

[0368] The above liquid crystal composition LC-1 was coated on the alignment film P-1 at 800 rpm for 10 seconds using a spin coating method. The coating film of the liquid crystal composition LC-1 was heated on a hot plate at 80 °C for 3 minutes (180 sec). Thereafter, ultraviolet light with a wavelength of 365 nm was irradiated onto the coating film at an irradiation dose of 300 mJ / cm 2 under a nitrogen ambient gas at 80 °C, thereby curing the liquid crystal composition LC-1 to fix the orientation of the liquid crystal compound and forming a cholesteric liquid crystal layer. Thus, a liquid crystal diffraction element having a support, an alignment film, and a cholesteric liquid crystal layer as shown in Figure 12 was fabricated.

[0369] It was confirmed by a polarized light microscope that the cholesteric liquid crystal layer became a periodic alignment surface as shown in Figure 7 .

[0370] The liquid crystal diffraction element was cut in the direction of rotation along the optical axis, and the cross-section was observed by SEM. By analyzing the SEM image, one period Λ in the liquid crystal alignment pattern of the cholesteric liquid crystal layer and the pitch lengths P1 and P2 of one turn of the helix were measured. P1 is the measured value on the glass substrate side with respect to the film thickness direction in the cholesteric liquid crystal layer, and P2 is the measured value on the air interface side with respect to the film thickness direction in the cholesteric liquid crystal layer. The measurement results are shown in Table 1 below.

[0371] [Measurement of in-plane average refractive index of diffraction element]

[0372] The liquid crystal composition LC-1 was coated on a separately prepared support with an alignment film, and the in-plane average refractive index was determined by measuring the liquid crystal immobilized layer (cured layer) obtained by irradiating ultraviolet rays and immobilizing it after aligning the director of the liquid crystal compound horizontally on the substrate using a reflection spectroscopic thickness meter FE-3000 (manufactured by Otsuka Electronics Co., Ltd.).

[0373] [Example 2]

[0374] The composition of the liquid crystal composition, the coating process, and the conditions in the exposure process were changed as shown in Table 1, and a liquid crystal diffraction element was produced in the same manner as in Example 1.

[0375] In Example 2, before the second exposure process for curing the liquid crystal composition, as the first exposure process, a high-pressure mercury lamp was used, and the liquid crystal composition was exposed at 100 °C through a 300 nm long-pass filter and a 350 nm short-pass filter. The first exposure process was carried out in such a way that the irradiation amount of light measured at a wavelength of 315 nm reached 4 mJ / cm 2 of.

[0376] The liquid crystal diffraction element produced in Example 2 has a pitch gradient layer.

[0377] [Examples 3-4, Comparative Example 1]

[0378] The composition of the liquid crystal composition, the coating process, and the conditions in the exposure process were changed as shown in Table 1, and otherwise, a liquid crystal diffraction element was produced in the same manner as in Example 2, and the same measurements were carried out.

[0379] Chiral reagent Ch-2

[0380] [Chemical formula 5]

[0381]

[0382] [Evaluation]

[0383] (Measurement of diffraction efficiency)

[0384] The diffraction efficiency within a specified incident angle range was measured when the liquid crystal diffraction element to be fabricated was disposed on a light guide plate having a high refractive index by the following method.

[0385] As Figure 19 shown, the fabricated liquid crystal diffraction element D was disposed on a Dove prism 80. The Dove prism 80 used a prism having a bevel angle of 45°. Further, the refractive index of the Dove prism was set to 1.70.

[0386] In the Dove prism 80, laser light having a wavelength of 552 nm was transmitted through a linear polarizer 82 and a λ / 4 plate 84 to become right circularly polarized light, and was incident on the surface of the liquid crystal diffraction element D while changing the angle within the light guiding angle range shown in Table 1.

[0387] The intensities of the diffracted light Ld and the 0th transmitted light L 0 were measured using a measuring instrument 86 (manufactured by NewPort Co., Ltd., power meter 1918-C), and the diffraction efficiency was obtained from the formula of Ld / (Ld + L 0 ) × 100 (%). The obtained diffraction efficiency was evaluated according to the following criteria. The results are shown in Table 1.

[0388] · AA: When the value of the lowest diffraction efficiency within the light guiding incident angle range is greater than 80% and 100% or less

[0389] · A: When the value of the lowest diffraction efficiency within the light guiding incident angle range is greater than 50% and 80% or less

[0390] · B: When the value of the lowest diffraction efficiency within the light guiding incident angle range is greater than 10% and 50% or less

[0391] · C: When the value of the lowest diffraction efficiency within the light guiding incident angle range is greater than 0% and 10% or less

[0392] [Table 1]

[0393]

[0394] As can be seen from Table 1, compared with the comparative example, the example of the present invention has a high diffraction efficiency within the light guiding incident angle range. That is, it can be seen that the incident angle range in which a high diffraction efficiency can be obtained is wide.

[0395] Further, from the comparison between Example 2 and Example 4, it is preferable that the refractive index n d of the light guide plate and the refractive index n k of the liquid crystal layer satisfy 0.1 > n k - n d ≥ 0.

[0396] Moreover, from the comparison between Example 3 and Example 4, it can be seen that when the liquid crystal layer is a pitch gradient layer, it is preferable that one period Λ, helical pitch P1, and helical pitch P2 satisfy P1 < Λ < P2.

[0397] Based on the above results, the effects of the present invention can be clarified.

[0398] Industrial Applicability

[0399] It can be preferably used in various optical devices using guiding, such as AR glass.

[0400] Symbol Explanation

[0401] 10a, 10b - light guiding elements, 11, 12 - diffraction elements, 16, 116 - light guide plates, 30 - support, 32 - alignment film, 34, 36 - liquid crystal layers, 40 - liquid crystal compound, 40A - optical axis, 42 - bright part, 44 - dark part, 50 - image display device, 54 - display, 60 - exposure device, 62 - laser, 64 - light source, 65 - λ / 2 plate, 68 - polarization beam splitter, 70A, 70B - mirrors, 72A, 72B - λ / 4 plates, 80 - Dove prism, 82 - linear polarizer, 84 - λ / 4 plate, 86 - detector, R R - Right-handed circularly polarized light of red light, M - laser beam, MA, MB - light rays, P O - Linearly polarized light, P R - Right-handed circularly polarized light, P L - Left-handed circularly polarized light, α - crossing angle, U - user, D - arrangement axis, Λ - one period, P - pitch, L 1 , L 4 - Incident light, L 2 , L 5 - Exit light, L - laser, Lr - exit light.

Claims

1. A light guide element having: a light guide plate; and a diffraction element disposed on a main surface of the light guide plate, the diffraction element having a liquid crystal layer formed using a liquid crystal composition containing a liquid crystal compound and having a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound continuously rotates and changes in at least one in-plane direction, the refractive index of the light guide plate being 1.70 or more, Set the refractive index of the light guide plate as n d and set the refractive index of the liquid crystal layer as n k when Satisfy 0.1 > n k -n d ≥ 0, the liquid crystal layer being a cholesteric liquid crystal layer in which a cholesteric liquid crystal phase is fixed, the cholesteric liquid crystal layer being a pitch gradient layer in which the helical pitch changes in the film thickness direction, in the liquid crystal layer, on a main surface where the orientation of the optical axis of the liquid crystal compound continuously rotates and changes in at least one in-plane direction, when the length for rotating the orientation of the optical axis of the liquid crystal compound by 180° is defined as one period Λ and the helical pitch on one surface side of the pitch gradient layer is P1 and the helical pitch on the other surface side is P2, P1 < Λ < P2 is satisfied, the liquid crystal layer contains the liquid crystal compound whose optical axis is inclined with respect to the main surface of the liquid crystal layer and has a region where the inclination angle of the optical axis with respect to the main surface of the liquid crystal layer is different in the thickness direction.

2. The light guide element according to claim 1, wherein the diffraction element is an incident diffraction element for making light enter the light guide plate.

Images