JP7104803B2 - Reflective sheet and light emitting device - Google Patents

Description

The present invention relates to a reflective sheet that homogenizes light by reflection, and a light emitting device that uses the reflective sheet.

In recent years, as a light source for a direct-type backlight unit in order to improve the contrast of a display device that uses a backlight unit such as a liquid crystal display (LCD (Liquid Crystal Display)), that is, to achieve HDR (High Dynamic Range). It has been proposed to partially control (local dimming) the backlight using an LED (Light Emitting Diode).

In a direct-type backlight unit that uses an LED as a light source, uneven brightness of light emission becomes a problem.
That is, in the direct type backlight unit using the LED as a light source, the place where the LED is arranged in the surface direction becomes high brightness, and the brightness decreases as the distance from the LED increases. Therefore, in a direct-type backlight unit using an LED as a light source, it is not possible to display an image with uniform brightness over the entire surface of an LCD or the like.

Therefore, various proposals have been made for a direct-type backlight unit that uses an LED as a light source in order to make the brightness uniform.
For example, Patent Document 1 proposes a light emitting device that uses a half mirror to make the brightness uniform in a direct-type backlight unit that uses an LED as a light source.
This light emitting device is mounted on a substrate having a light reflecting surface on its surface and a light source such as a plurality of LEDs having a reflecting layer on the upper surface thereof so as to face the substrate with the light source interposed therebetween. It is provided with a half mirror that reflects a part of the incident light and transmits a part of the incident light, and has a configuration in which the reflectance of the half mirror with respect to the emission wavelength of the light source is lower in the oblique incident than in the vertical incident. ..

JP-A-2017-92021

On the other hand, display devices such as LCDs are desired to be thinner. For that purpose, it is necessary to make the backlight unit thin.
For example, in smartphones, tablet terminals, notebook PCs (Personal Computers), etc., a side edge type backlight unit that injects light from a light source such as an LED from the end of the light guide plate and emits light from the main surface of the light guide plate. In, the backlight unit is made thinner by using a light guide plate having a thickness of about 0.3 mm.

In order to reduce the thickness of a backlight unit that uses an LED or the like as a light source, it is necessary to reduce the distance between the light source and the light emitting surface (diffusing plate).
However, in a thin direct-type backlight unit, it is necessary to narrow the distance between the arranged light sources in order to make the brightness of the emitted light uniform.
A conventional backlight unit such as the light emitting device described in Patent Document 1 described above can preferably achieve uniform brightness if it has a certain thickness. However, in the conventional backlight unit, it is necessary to significantly increase the number of light sources in order to make the brightness uniform as the backlight unit becomes thinner. Further, by increasing the number of light sources, the yield in assembling the backlight unit also decreases.

An object of the present invention is to solve such a problem of the prior art, and to reduce the thickness of a light source device such as a backlight unit and to emit light having uniform brightness with a small number of light sources. It is an object of the present invention to provide a reflective sheet capable of the above, and a light emitting device using the reflective sheet.

In order to solve this problem, the present invention has the following configuration.
[1] It has a structure in which a plurality of cholesteric liquid crystal layers having a fixed cholesteric liquid crystal phase are laminated.
In the cholesteric liquid crystal layer, in the cross section of the cholesteric liquid crystal layer observed by the scanning electron microscope, the bright part and the dark part derived from the cholesteric liquid crystal phase are inclined with respect to the main surface of the cholesteric liquid crystal layer, and further.
A reflective sheet comprising at least one set of two cholesteric liquid crystal layers having overlapping wavelength ranges for selective reflection and different turning directions of the reflected circularly polarized light.
[2] The reflective sheet according to [1], wherein the two cholesteric liquid crystal layers constituting the combination of the cholesteric liquid crystal layers have opposite inclination directions with respect to the main surfaces of the bright and dark areas derived from the cholesteric liquid crystal phase. ..
[3] The layer according to [1] or [2], wherein at least one layer of the cholesteric liquid crystal layer has regions in the plane in which the inclination directions of the bright and dark portions derived from the cholesteric liquid crystal phase are different from each other. Reflective sheet.
[4] The reflection according to [3], wherein at least one layer of the cholesteric liquid crystal layer has regions in the plane in which the inclination directions of the bright and dark portions derived from the cholesteric liquid crystal phase are different from each other in a striped manner. Sheet.
[5] It has a cholesteric liquid crystal layer in which the cholesteric liquid crystal phase is fixed.
In the cholesteric liquid crystal layer, in the cross section of the cholesteric liquid crystal layer observed by the scanning electron microscope, the bright part and the dark part derived from the cholesteric liquid crystal phase are inclined with respect to the main surface of the cholesteric liquid crystal layer, and further.
The cholesteric liquid crystal layer is a reflective sheet having regions in the plane in which the inclination directions of the bright and dark portions derived from the cholesteric liquid crystal phase are different from each other.
[6] The reflective sheet according to [5], wherein the bright and dark areas derived from the cholesteric liquid crystal phase have regions in the plane that are inclined in different directions with respect to the main surface in a striped manner.
[7] The reflective sheet according to any one of [1] to [6], wherein at least one of the cholesteric liquid crystal layers has a spiral pitch that changes in the thickness direction.
[8] The method according to any one of [1] to [7], wherein the angle between the bright part and the dark part derived from the cholesteric liquid crystal phase in the cholesteric liquid crystal layer with respect to the main surface of the cholesteric liquid crystal layer is 3 to 40 °. Reflective sheet.
[9] The reflective sheet according to any one of [1] to [8], further having a λ / 4 layer.
[10] The reflective sheet according to any one of [1] to [9], further comprising a diffusion plate.
[11] The reflective sheet according to any one of [1] to [10], further comprising a light distribution film.
[12] Of [1] to [11], the cholesteric liquid crystal layer has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. The reflective sheet described in either.
[13] A light emitting device having a base having a light reflecting surface on the surface, a plurality of light sources provided on the base, and a reflecting sheet according to any one of [1] to [12].
[14] The light emitting device according to [13], wherein the distance between the light sources in the plurality of light sources is five times or more the distance between the base and the reflective sheet.
[15] The light emitting device according to [13] or [14], wherein the light source includes a blue light emitting diode.

According to the present invention, in a light source device used for a backlight such as an LCD, it is possible to irradiate a thin and uniform light with a small number of light sources without uneven brightness.

FIG. 1 is a diagram conceptually showing an example of a light emitting device of the present invention using the reflective sheet of the present invention. FIG. 2 is a conceptual diagram for explaining a left circularly polarized light reflecting layer (cholesteric liquid crystal layer). FIG. 3 is a plan view of the right circularly polarized light reflecting layer (cholesteric liquid crystal layer). FIG. 4 is a conceptual diagram for explaining the action of the right circularly polarized light reflecting layer. FIG. 5 is a conceptual diagram for explaining the reflective sheet of the present invention. FIG. 6 is a conceptual diagram for explaining the operation of the reflective sheet of the present invention. FIG. 7 is a conceptual diagram for explaining another example of the reflective sheet of the present invention. FIG. 8 is a conceptual diagram for explaining another example of the reflective sheet of the present invention. FIG. 9 is a conceptual diagram for explaining another example of the reflective sheet of the present invention. FIG. 10 is a diagram conceptually showing an exposure apparatus for exposing an alignment film used for the reflective sheet of the present invention.

Hereinafter, the reflective sheet and the light emitting device of the present invention will be described in detail based on the preferred embodiments shown in the accompanying drawings.

The numerical range represented by using "-" in the present specification means a range including the numerical values before and after "-" as the lower limit value and the upper limit value.
As used herein, "(meth) acrylate" is used to mean "one or both of acrylate and methacrylate".

In the present specification, visible light is light having a wavelength visible to the human eye among electromagnetic waves, and indicates light in the wavelength range of 380 to 780 nm. Invisible light is light in a wavelength range of less than 380 nm and a wavelength range of more than 780 nm.
Although not limited to this, among the visible light, the light in the wavelength range of 420 to 490 nm is blue light, the light in the wavelength range of 495 to 570 nm is green light, and the light in the wavelength range of 620 to 750 nm is 620 to 750 nm. The light of is red light.

FIG. 1 conceptually shows an example of the light emitting device of the present invention using the reflective sheet of the present invention.
The light emitting device 10 shown in FIG. 1 is used for, for example, a direct type backlight unit in an LCD, and has a housing 12, a light source 13, and a reflector 14.

The housing 12 is a known housing in which a light source or the like is arranged in a backlight unit or the like of an LCD, and is, for example, a rectangular cuboid whose one side is open.
The inner surface of the housing 12 is a light reflecting surface 12a. That is, the bottom plate of the housing 12 serves as a base having a light reflecting surface on the surface in the present invention in which the light source 13 is arranged.
In the present invention, the light reflecting surface 12a is not limited, and is known to be used as a light reflecting surface in an LCD backlight unit or the like, such as a diffuse reflecting surface such as a white plate or a specular reflecting surface such as a metal plate. Various things are available. Further, as the light reflecting surface, a commercially available product such as an ESR (Enhanced Specular Reflector) reflecting film manufactured by 3M Co., Ltd. can also be preferably used.
Further, in the present invention, the inner surface of the housing 12 may be a light reflecting surface 12a by forming the housing 12 with a metal material, a white diffuse reflector, or the like.
The light reflecting surface 12a is preferably a specular reflecting surface, and an ESR reflecting film is preferably used in terms of improving the light diffusion efficiency and improving the uniformity of brightness.

The light source 13 is arranged on the bottom surface of the housing 12, that is, the surface facing the open surface. The light sources 13 are two-dimensionally arranged on the bottom surface of the housing 12.
The light source 13 is also not limited, and various known light sources used in the direct type backlight unit of the LCD and the like can be used.
Examples of the light source 13 include an LED (light emitting diode), a halogen lamp, a fluorescent lamp, and a laser. Among them, LEDs are preferably used.

There is no limitation on the central wavelength (maximum wavelength of light emission) of the light emitted by the light source 13. Therefore, the light source 13 may be a blue light source having a central wavelength in the blue wavelength range, a green light source having the central wavelength in the blue-green wavelength range, a red light source having the central wavelength in the red wavelength range, or a white light source. ..
As a light source, a blue LED having a central wavelength in the blue wavelength region is preferably used. In the illustrated example, the light source 13 is, for example, a blue LED.
The light distribution of the light source 13 is also not limited, and may be, for example, a Lambersian distribution or a bat wing distribution.

The arrangement of the light sources 13 is also not limited, and arrangements used for the direct type backlight unit such as a tetragonal grid and a honeycomb grid can be used.
The distance between the light sources 13, that is, the distance between the light source 13 and the light source closest to the light source 13 is not limited, and may be appropriately set according to the brightness and orientation distribution (emission profile) of the light source 13. good. The distance between the light sources 13 is the distance between the centers of the two light sources 13.
In the light emitting device 10 of the present invention, the distance d1 of the light source 13 is 5 times or more the distance d2 between the bottom surface of the housing 12, that is, the arrangement surface (base) of the light source 13 and the reflective sheet (right circular polarized light reflecting layer 36). Is preferable. This point will be described in detail later.

The open surface of the housing 12, that is, the surface facing the surface on which the light source 13 is arranged is closed by the reflector 14.

The reflector 14 preferably has a diffuser plate (not shown). That is, the reflective sheet of the present invention preferably has a diffuser plate. Even when the reflector 14 has a diffuser, the reflector 14 may be formed by the reflective sheet of the present invention and the alignment film 32, or may be only the reflective sheet of the present invention. Further, the reflector 14 may be formed by using the diffuser plate as the support 30. Further, it is preferable that the diffusion plate and the reflective sheet are attached with an adhesive, an adhesive or the like.
Since the reflector 14 (the reflective sheet of the present invention) has a diffuser, the brightness uniformity of the light emitted from the reflector can be further improved.

The diffusion plate is not limited, and examples thereof include a white diffusion plate and a white diffusion sheet.
Further, a known diffusion plate and a backlight member used in an LCD backlight unit or the like may be arranged on the reflector 14. The backlight member includes a prism sheet, BEF (Brightness Enhancement Film, manufactured by 3M), a lens sheet, a brightness improving film such as DBEF (Dual Brightness Enhancement Film, manufactured by 3M), a quantum dot sheet, a fluorescent sheet, and a sharp cut. A color adjusting film such as an optical filter such as a filter, and a plurality of laminates thereof and the like are included.
When a known diffusion plate, a backlight member, or the like is arranged on the reflector 14, for example, it may be attached to the reflector 14. Alternatively, these members may be arranged on the reflector 14 by fixing with a jig or the like.

The reflector 14 has a support 30, an alignment film 32, a left circularly polarized light reflecting layer 34, and a right circularly polarized light reflecting layer 36. The reflective sheet of the present invention is formed by the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36.
In the light emitting device 10 of the present invention, the reflector 14 does not have to have the support 30 and / or the alignment film 32. That is, in the light emitting device 10 of the present invention, the reflective plate 14 may be formed by the reflective sheet of the present invention and the alignment film 32, or may be formed by the reflective sheet of the present invention and the support 30. Only the reflective sheet of the invention may be used.
In the following description, when it is not necessary to distinguish between the left circularly polarized light reflecting layer and the right circularly polarized light reflecting layer, the left circularly polarized light reflecting layer and the right circularly polarized light reflecting layer are collectively referred to as a "cholesteric liquid crystal layer".

<Support>
In the reflector 14, the support 30 supports the alignment film 32, the left circularly polarized light reflecting layer 34, and the right circularly polarized light reflecting layer 36.
The support 30 is not limited, and various sheet-like objects (films, plate-like objects) can be used as long as they can support the alignment film 32, the left circular polarization reflecting layer 34, and the right circular polarization reflecting layer 36. Is.
The support 30 has a transmittance of 50% or more, more preferably 70% or more, and further preferably 85% or more with respect to the corresponding light.

The thickness of the support 30 is not limited, and the alignment film 32, the left circularly polarized light reflecting layer 34, and the right circularly polarized light reflecting layer 36 can be held depending on the use of the reflector 14 and the material for forming the support 30. The thickness may be set as appropriate.
The thickness of the support 30 is preferably 1 to 1000 μm, more preferably 3 to 250 μm, and even more preferably 5 to 150 μm.

The support 30 may be single-layered or multi-layered.
Examples of the support 30 in the case of a single layer include a support 30 made of glass, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic, polyolefin and the like. Examples of the support 30 in the case of a multi-layer structure include those including any of the above-mentioned single-layer supports as a substrate and providing another layer on the surface of the substrate.

<Alignment film>
In the reflector 14, an alignment film 32 is formed on the surface of the support 30.
The alignment film 32 is, for example, an alignment film 32 for orienting the liquid crystal compound 40 in a predetermined liquid crystal alignment pattern when forming the left circular polarization reflection layer 34 of the reflector 14.
As will be described later, in the reflector 14, as a preferred embodiment, the direction of the optical axis 40A (see FIG. 3 ) derived from the liquid crystal compound 40 is one direction in the plane (in the illustrated example, the arrow X in the drawing). It has a liquid crystal orientation pattern that changes while continuously rotating along the direction). Therefore, the alignment film 32 is formed so that the cholesteric liquid crystal layer can form this liquid crystal alignment pattern.
In the following description, "the direction of the optic axis 40A rotates" is also simply referred to as "the optical axis 40A rotates".

As the alignment film 32, various known ones can be used.
For example, a rubbing-treated film made of an organic compound such as a polymer, an oblique vapor-deposited film of an inorganic compound, a film having a microgroove, Langmuir-Blojet of an organic compound such as ω-tricosanoic acid, dioctadecylmethylammonium chloride and methyl stearylate. Examples thereof include a film obtained by accumulating LB (Langmuir-Blodgett) films according to the method, a film made of a liquid crystal compound, and the like.

The alignment film 32 by the rubbing treatment can be formed by rubbing the surface of the polymer layer with paper or cloth several times in a certain direction.
Materials used for the alignment film 32 include polyimide, polyvinyl alcohol, polymers having a polymerizable group described in JP-A-9-152509, JP-A-2005-97377, JP-A-2005-99228, and JP-A-2005-99228. , JP-A-2005-128503, the material used for forming the alignment film 32 and the like described in JP-A-2005-128503 is preferable.

The material that can be used as the alignment film made of a liquid crystal compound is not particularly limited, and a known compound can be used. As an example, a liquid crystal composition containing a liquid crystal compound can be mentioned.
The liquid crystal compound is preferably a polymerizable liquid crystal compound, and examples of the liquid crystal compound that can be used include materials used for forming a cholesteric liquid crystal layer, which will be described later. Further, the liquid crystal composition used for forming the alignment film made of the liquid crystal compound may further contain a surfactant and a chiral agent.

In the present invention, the alignment film 32 is a so-called photo-alignment film in which a photo-alignable material is irradiated with polarized or non-polarized material to form an alignment film 32, and the above-mentioned photo-alignment film or an alignment film obtained by rubbing treatment. , A so-called liquid crystal film or the like, which is formed by applying and forming a liquid crystal composition to form an alignment film 32, is preferably exemplified. That is, in the reflector 14 of the present invention, as the alignment film 32, a photoalignment film formed by applying a photoalignment material on the support 30, a liquid crystal film having a predetermined orientation fixed, and the like are suitable. It is used for.
Irradiation of polarized light can be performed from a vertical direction or an oblique direction with respect to the photoalignment film, and irradiation of non-polarization can be performed from an oblique direction with respect to the photoalignment film.

Examples of the photoalignment material used for the alignment film that can be used in the present invention include JP-A-2006-285197, JP-A-2007-76839, JP-A-2007-138138, and JP-A-2007-94071. , JP-A-2007-121721, JP-A-2007-140465, JP-A-2007-156439, JP-A-2007-133184, JP-A-2009-109831, Patent No. 3883848 and Patent No. 4151746. The azo compound described in JP-A, the aromatic ester compound described in JP-A-2002-229039, the maleimide having the photo-orientation unit described in JP-A-2002-265541 and JP-A-2002-317013, and / Alternatively, an alkenyl-substituted nadiimide compound, a photocrossbable silane derivative described in Japanese Patent No. 4205195 and Japanese Patent No. 4205198, a photocrossbable property described in Japanese Patent No. 2003-520878, Japanese Patent No. 2004-522220, and Japanese Patent No. 4162850. Polygon, photocrossable polyamide and photocrossable polyester, and Japanese Patent Application Laid-Open No. 9-118717, Japanese Patent Application Laid-Open No. 10-506420, Japanese Patent Application Laid-Open No. 2003-505561, International Publication No. 2010/150748, Japanese Patent Application Laid-Open No. 2013 Photodimerizable compounds described in Japanese Patent Application Laid-Open No. -177561 and Japanese Patent Application Laid-Open No. 2014-12823, particularly synnamate compounds, chalcone compounds, coumarin compounds, and the like are exemplified as preferable examples.
Among them, azo compounds, photocrosslinkable polyimides, photocrosslinkable polyamides, photocrosslinkable polyesters, synnamate compounds, and chalcone compounds are preferably used.

The thickness of the alignment film 32 is not limited, and the thickness at which the required alignment function can be obtained may be appropriately set according to the material for forming the alignment film 32.
The thickness of the alignment film 32 is preferably 0.01 to 5 μm, more preferably 0.05 to 2 μm.

The method for forming the alignment film 32 is not limited, and various known methods depending on the material for forming the alignment film 32 can be used.
As an example, a method of applying a photoalignment film to the surface of the support 30 and drying it, and then using an exposure mask to perform mask exposure with a polarized or non-polarized mercury lamp, a metal halide lamp, or the like, and exposure with laser light. The method of forming the alignment pattern and the like are exemplified as the method of forming the alignment film 32. Further, a liquid crystal layer formed by coating on a rubbing-treated alignment film or a photoalignment film can also be used as the alignment film 32. As an example, a method of forming an alignment pattern on a photoalignment film by the method described above and then further applying a liquid crystal composition to form a liquid crystal film in which a predetermined alignment pattern is immobilized is a method of forming the alignment film 32. Illustrated as a method.
A method of forming an alignment pattern by exposing the alignment film 32 with a laser beam is exemplified.

FIG. 10 conceptually shows an example of an exposure apparatus that exposes the alignment film 32 to form an alignment pattern.
The exposure apparatus 60 shown in FIG. 10 uses a light source 64 provided with a laser 62, a λ / 2 plate 65 that changes the polarization direction of the laser light M emitted by the laser 62, and a laser beam M emitted by the laser 62 as a light beam MA. It includes a polarizing beam splitter 68 that separates the MB into two, mirrors 70A and 70B arranged on the optical paths of the two separated rays MA and MB, respectively, and λ / 4 plates 72A and 72B.
The light source 64 emits linearly polarized light P ₀ . The λ / 4 plates 72A and 72B have optical axes parallel to each other. The λ / 4 plate 72A converts the linearly polarized light P ₀ (ray MA) into the right circularly polarized light PR, and the λ / 4 plate _{72B converts} the linearly polarized light P ₀ (ray MB) into the left circularly polarized light PL.

A support 30 having an alignment film 32 before the alignment pattern is formed is arranged in an exposed portion, and two light rays MA and a light beam MB are crossed and interfered with each other on the alignment film 32, and the interference light is caused to interfere with the alignment film 32. Is exposed to light.
Due to the interference at this time, the polarization state of the light applied to the alignment film 32 periodically changes in the form of interference fringes. As a result, in the alignment film 32, an orientation pattern in which the orientation state changes periodically can be obtained.
In the exposure apparatus 60, the period of the orientation pattern can be adjusted by changing the intersection angle α of the two rays MA and MB. That is, in the exposure apparatus 60, the optical axis 40A, which will be described later, rotates in an orientation pattern in which the optical axis 40A derived from the liquid crystal compound 40 rotates continuously in one direction by adjusting the intersection angle α. The length of one cycle (one cycle Λ) in which the optic axis 40A rotates 180 ° in one direction can be adjusted.
By forming a cholesteric liquid crystal layer on the alignment film 32 having an orientation pattern in which the orientation state changes periodically, the optical axis 40A derived from the liquid crystal compound 40, which will be described later, is continuous in one direction. It is possible to form a cholesteric liquid crystal layer having a liquid crystal orientation pattern that rotates to.
Further, by rotating the optical axes of the λ / 4 plates 72A and 72B by 90 °, respectively, the rotation direction of the optical axis 40A in one direction can be reversed.

As described above, in the present invention, the alignment film 32 is provided as a preferred embodiment and is not an essential constituent requirement.
For example, an orientation pattern may 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, or the like. Due to the orientation pattern of the support 30, the cholesteric liquid crystal layer has 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 along at least one direction in the plane. It is also possible to configure it. That is, in the present invention, the support 30 may act as an alignment film.

<Left circularly polarized light reflecting layer and right circularly polarized light reflecting layer (cholesteric liquid crystal layer)>
In the reflector 14, a left circularly polarized light reflecting layer 34 is formed on the surface of the alignment film 32. Further, in the reflector 14, the right circularly polarized light reflecting layer 36 is formed on the surface of the left circularly polarized light reflecting layer 34. Both the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36 are formed by fixing the cholesteric liquid crystal phase, and as an example, selectively reflect blue light.
The stacking order of the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36 may be the reverse of the illustrated example. That is, as in the embodiment described later, the right circularly polarized light reflecting layer 36 may be formed on the surface of the alignment film 32, and the left circularly polarized light reflecting layer 34 may be formed on the surface of the right circularly polarized light reflecting layer 36. In this regard, the same applies whether the left circularly polarized light reflecting layer and the right circularly polarized light reflecting layer selectively reflect green light or red light.

In FIG. 1, in order to simplify the drawing and clearly show the configuration of the reflector 14, the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36 are the surface of the alignment film 32 and the left circularly polarized light reflecting layer. Only 34 liquid crystal compounds 40 (liquid crystal compound molecules) are conceptually shown.
However, the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36 are formed by fixing a normal cholesteric liquid crystal phase, as conceptually shown by exemplifying the left circularly polarized light reflecting layer 34 in FIG. Similarly, the liquid crystal compound 40 has a spiral structure in which the liquid crystal compound 40 is spirally swirled and stacked, and the configuration in which the liquid crystal compound 40 is spirally rotated once (360 ° rotation) and stacked is spiral 1 pitch (pitch P). ), The liquid crystal compound 40 spirally swirling has a structure in which a plurality of pitches are laminated.

As is well known, the cholesteric liquid crystal layer in which the cholesteric liquid crystal phase is fixed has wavelength selective reflectivity. As will be described in detail later, the selective reflection wavelength range of the cholesteric liquid crystal layer depends on the length of the spiral 1 pitch in the thickness direction described above. The length of the spiral 1 pitch in the thickness direction is the pitch P shown in FIG.
Further, the cholesteric liquid crystal layer selectively reflects only right-handed circularly polarized light or left-handed circularly polarized light in a selective reflection wavelength range. As will be described in detail later, the reflection of selective circular polarization depends on the twisting direction (sense) of the spiral of the liquid crystal compound 40 forming the cholesteric liquid crystal phase. In the illustrated example, the left circularly polarized light reflecting layer 34 selectively reflects the left circularly polarized light in the selective reflection wavelength range, and the right circularly polarized light reflecting layer 36 selectively reflects the left circularly polarized light in the selective reflection wavelength range. Selectively reflect.

The left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36 are formed by fixing the cholesteric liquid crystal phase.
That is, the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36 are both layers made of a liquid crystal compound 40 (liquid crystal material) having a cholesteric structure.

<< Cholesteric liquid crystal phase >>
The cholesteric liquid crystal phase is known to exhibit selective reflectivity at specific wavelengths.
In a general cholesteric liquid crystal phase, the center wavelength of selective reflection (selective reflection center wavelength) λ depends on the pitch P of the spiral in the cholesteric liquid crystal phase, and the relationship between the average refractive index n of the cholesteric liquid crystal phase and λ = n × P. Follow. Therefore, the selective reflection center wavelength can be adjusted by adjusting the spiral pitch.
The longer the pitch P, the longer the selective reflection center wavelength of the cholesteric liquid crystal phase.
The spiral pitch P is one pitch of the spiral structure (spiral period) of the cholesteric liquid crystal phase. In other words, the pitch P of the spiral is the number of turns of the spiral, that is, the length in the spiral axis direction in which the director of the liquid crystal compound constituting the cholesteric liquid crystal phase rotates 360 °. The director of the liquid crystal compound corresponds to the long axis direction in the case of a rod-shaped liquid crystal, for example.

The spiral pitch of the cholesteric liquid crystal phase depends on the type of chiral agent used together with the liquid crystal compound and the concentration of the chiral agent added when forming the cholesteric liquid crystal layer. Therefore, by adjusting these, a desired spiral pitch can be obtained.
For pitch adjustment, see Fujifilm Research Report No. 50 (2005) p. There is a detailed description in 60-63. For the measurement method of spiral sense and pitch, use the method described in "Introduction to Liquid Crystal Chemistry Experiment", ed. be able to.

The cholesteric liquid crystal phase exhibits selective reflectivity to either left or right circular polarization at a particular wavelength. Whether the reflected light is right-handed or left-handed depends on the twisting direction (sense) of the spiral of the cholesteric liquid crystal phase.
The selective reflection of circularly polarized light by the cholesteric liquid crystal phase reflects right circularly polarized light when the twisting direction of the spiral of the cholesteric liquid crystal layer is right, and reflects left circularly polarized light when the twisting direction of the spiral is left. As described above, in the illustrated example, the left circularly polarized light reflecting layer 34 selectively reflects the left circularly polarized light, and the right circularly polarized light reflecting layer 36 selectively reflects the right circularly polarized light.
The direction of rotation of the cholesteric liquid crystal phase can be adjusted by the type of the liquid crystal compound forming the cholesteric liquid crystal layer and / or the type of the chiral agent added.

The full width at half maximum Δλ (nm) of the selective reflection wavelength region (circularly polarized reflection wavelength region) indicating selective reflection depends on Δn of the cholesteric liquid crystal phase and the pitch P of the spiral, and follows the relationship of Δλ = Δn × P. Therefore, the width of the selective reflection wavelength region (selective reflection wavelength region) can be controlled by adjusting Δn. Δn can be adjusted by the type of the liquid crystal compound forming the cholesteric liquid crystal phase, the mixing ratio thereof, and the temperature at the time of fixing the orientation.
Further, by forming a spiral pitch distribution in the film thickness direction of the cholesteric liquid crystal layer, the half width Δλ (nm) of the selective reflection wavelength region (circular polarization reflection wavelength region) can be increased.
The full width at half maximum of the reflection wavelength range is adjusted according to the use of the reflector (reflection sheet), and may be, for example, 10 to 500 nm, preferably 20 to 300 nm, and more preferably 30 to 100 nm.

In the illustrated example, as an example, both the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36 have a selective reflection center wavelength in the wavelength range of blue light, and the left circularly polarized light reflecting layer 34 is blue. The left circular polarization of light is selectively reflected, and the right circular polarization reflection layer 36 selectively reflects the right circular polarization of blue light.

<< Method of forming a cholesteric liquid crystal layer >>
The cholesteric liquid crystal layer (left circular polarized light reflecting layer 34 and right circular polarized light reflecting layer 36) can be formed by fixing the cholesteric liquid crystal phase in a layered manner.
The structure in which the cholesteric liquid crystal phase is fixed may be a structure in which the orientation of the liquid crystal compound that is the cholesteric liquid crystal phase is maintained, and typically, the polymerizable liquid crystal compound is placed in the orientation state of the cholesteric liquid crystal phase. Therefore, it is preferable that the structure is polymerized and cured by irradiation with ultraviolet rays, heating, etc. to form a non-fluid layer, and at the same time, the structure is changed to a state in which the orientation form is not changed by an external field or an external force.
In the structure in which the cholesteric liquid crystal phase is fixed, it is sufficient that the optical properties of the cholesteric liquid crystal phase are maintained, and the liquid crystal compound 40 does not have to exhibit liquid crystal properties in the cholesteric liquid crystal layer. For example, the polymerizable liquid crystal compound may lose its liquid crystal property by increasing its molecular weight by a curing reaction.

As an example of the material used for forming the cholesteric liquid crystal layer in which the cholesteric liquid crystal phase is fixed, a liquid crystal composition containing a liquid crystal compound can be mentioned. The liquid crystal compound is preferably a polymerizable liquid crystal compound.
Further, the liquid crystal composition used for forming the cholesteric liquid crystal layer may further contain a surfactant and a chiral agent.

--Polymerized liquid crystal compound ---
The polymerizable liquid crystal compound may be a rod-shaped liquid crystal compound or a disk-shaped liquid crystal compound.
Examples of the rod-shaped polymerizable liquid crystal compound forming the cholesteric liquid crystal phase include a rod-shaped nematic liquid crystal compound. Examples of rod-shaped nematic liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, and alkoxy-substituted phenylpyrimidines. , Phenyldioxans, trans, alkenylcyclohexylbenzonitriles and the like are preferably used. Not only low molecular weight liquid crystal compounds but also high molecular weight liquid crystal compounds can be used.

The polymerizable liquid crystal compound is obtained by introducing a polymerizable group into the liquid crystal compound. Examples of the polymerizable group include an unsaturated polymerizable group, an epoxy group, and an aziridinyl group, and an unsaturated polymerizable group is preferable, and an 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 contained in the polymerizable liquid crystal compound is preferably 1 to 6, more preferably 1 to 3.
Examples of polymerizable liquid crystal compounds include Makromol. Chem. , 190, 2255 (1989), Advanced Materials 5, 107 (1993), US Pat. No. 4,683,327, US Pat. No. 5,622,648, US Pat. No. 5,770,107, 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 Application Laid-Open No. 1-272551, Japanese Patent Application Laid-Open No. 6-16616 The compounds described in Japanese Patent Application Laid-Open No. 7-110469, Japanese Patent Application Laid-Open No. 11-8801, Japanese Patent Application Laid-Open No. 2001-328973, and the like are included. Two or more kinds of polymerizable liquid crystal compounds may be used in combination. When two or more kinds of polymerizable liquid crystal compounds are used in combination, the orientation temperature can be lowered.

Further, as the 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. Further, as the above-mentioned polymer liquid crystal compound, a polymer having a mesogen group exhibiting a liquid crystal introduced at the main chain, a side chain, or both the main chain and the side chain, and a polymer cholesteric having a cholesteryl group introduced into the side chain. A liquid crystal, a liquid crystal polymer as disclosed in JP-A-9-133810, a liquid crystal polymer as disclosed in JP-A-11-293252, and the like can be used.

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

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

－－Surfactant －－
The liquid crystal composition used when forming the cholesteric liquid crystal layer may contain a surfactant.
The surfactant is preferably a compound that can function as an orientation control agent that contributes to a stable or rapid planar orientation cholesteric liquid crystal phase. Examples of the surfactant include a silicone-based surfactant and a fluorine-based surfactant, and a fluorine-based surfactant is preferably exemplified.

Specific examples of the surfactant include the compounds described in paragraphs [2002] to [0090] of JP2014-119605A, and the compounds described in paragraphs [0031] to [0034] of JP2012-203237A. , Paragraphs [0092] and [093] of JP-A-2005-999248, paragraphs [0076] to [0078] and paragraphs [0083] to [0085] of JP-A-2002-129162. Examples thereof include the compounds exemplified in the above, and fluorine (meth) acrylate-based polymers described in paragraphs [0018] to [0043] of JP-A-2007-272185.
As the surfactant, one type may be used alone, or two or more types may be used in combination.
As the fluorine-based surfactant, the compounds described in paragraphs [2002] to [0090] of JP-A-2014-119605 are preferable.

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

－－Chiral agent －－
The chiral agent (chiral agent) has a function of inducing a helical structure of a cholesteric liquid crystal phase. Since the twist direction or spiral pitch of the spiral induced by the compound differs depending on the compound, the chiral agent may be selected according to the purpose.
The chiral agent is not particularly limited, and is a known compound (for example, Liquid Crystal Device Handbook, Chapter 3, Section 4-3, TN (twisted nematic), STN (Super Twisted Nematic) chiral agent, page 199, Japan Society for the Promotion of Science. (Described in 1989, edited by the 142nd Committee of the Society), isosorbide, isomannide derivatives and the like can be used.
The chiral agent generally contains an asymmetric carbon atom, but an axial asymmetric compound or a surface asymmetric compound that does not contain an asymmetric carbon atom can also be used as the chiral agent. Examples of axial or asymmetric compounds include binaphthyl, helicene, paracyclophane, and derivatives thereof. The chiral agent may have a polymerizable group. When both the chiral agent and the liquid crystal compound have a polymerizable group, the repeating unit derived from the polymerizable liquid crystal compound and the repeating unit derived from the chiral agent are derived by the polymerization reaction between the polymerizable chiral agent and the polymerizable liquid crystal compound. Polymers with repeating units can be formed. In this aspect, the polymerizable group of the polymerizable chiral agent is preferably a group of the same type as the polymerizable group of the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is preferably an unsaturated polymerizable group, an epoxy group or an aziridinyl group, more preferably an unsaturated polymerizable group, and preferably an ethylenically unsaturated polymerizable group. More preferred.
Moreover, the chiral agent may be a liquid crystal compound.

When the chiral agent has a photoisomerizing group, it is preferable because a pattern of a desired reflection wavelength corresponding to the emission wavelength can be formed by irradiation with a photomask such as an active ray after coating and orientation. As the photoisomerizing group, an isomerization site of a compound exhibiting photochromic properties, an azo group, an azoxy group, or a cinnamoyl group is preferable. Specific compounds include JP-A-2002-80478, JP-A-2002-80851, JP-A-2002-179668, JP-A-2002-179669, JP-A-2002-179670, and JP-A-2002. Compounds described in JP-A-179681, JP-A-2002-179682, JP-A-2002-338575, JP-A-2002-338668, JP-A-2003-313189, JP-A-2003-313292, etc. Can be used.

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

--Polymer initiator ---
When the liquid crystal composition contains a polymerizable compound, it preferably contains a polymerization initiator. In the embodiment in which the polymerization reaction is allowed to proceed by irradiation with ultraviolet rays, the polymerization initiator used is preferably a photopolymerization initiator capable of initiating the polymerization reaction by irradiation with ultraviolet rays.
Examples of photopolymerization initiators include α-carbonyl compounds (described in US Pat. No. 2,376,661 and US Pat. No. 2,376,670), acidoin ethers (described in US Pat. No. 2,448,828), and α-hydrocarbons. Substituted aromatic hydrocarbon compounds (described in US Pat. No. 2,725,512), polynuclear quinone compounds (described in US Pat. Combinations (described in US Pat. No. 3,549,637), hydrocarbon and phenazine compounds (Japanese Patent Laid-Open No. 60-105667, described in US Pat. No. 4,239,850), and oxadiazole compounds (US Pat. No. 4,212,970). Description) and the like.
The content of the photopolymerization initiator in the liquid crystal composition is preferably 0.1 to 20% by mass, more preferably 0.5 to 12% by mass, based on the content of the liquid crystal compound.

－－Crosslinking agent －－
The liquid crystal composition may optionally contain a cross-linking agent in order to improve the film strength and durability after curing. As the cross-linking agent, those that are cured by ultraviolet rays, heat, humidity and the like can be preferably used.
The cross-linking agent is not particularly limited and may be appropriately selected depending on the intended purpose. For example, a polyfunctional acrylate compound such as trimethylolpropane tri (meth) acrylate and pentaerythritol tri (meth) acrylate; glycidyl (meth) acrylate. And epoxy compounds such as ethylene glycol diglycidyl ether; aziridine compounds such as 2,2-bishydroxymethylbutanol-tris [3- (1-aziridinyl) propionate] and 4,4-bis (ethyleneiminocarbonylamino) diphenylmethane; hexa Isocyanate compounds such as methylenediisocyanate 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. Can be mentioned. Further, a known catalyst can be used depending on the reactivity of the cross-linking agent, and the productivity can be improved in addition to the improvement of the film strength and durability. These may be used alone or in combination of two or more.
The content of the cross-linking agent is preferably 3 to 20% by mass, more preferably 5 to 15% by mass, based on the solid content mass of the liquid crystal composition. When the content of the cross-linking agent is within the above range, the effect of improving the cross-linking density can be easily obtained, and the stability of the cholesteric liquid crystal phase is further improved.

--Other additives ---
If necessary, a polymerization inhibitor, an antioxidant, an ultraviolet absorber, a light stabilizer, a coloring material, metal oxide fine particles, etc. are added to the liquid crystal composition within a range that does not deteriorate the optical performance and the like. Can be added with.

The liquid crystal composition is preferably used as a liquid when forming a cholesteric liquid crystal layer (left circular polarized light reflecting layer 34 and right circular polarized light reflecting layer 36).
The liquid crystal composition may contain a solvent. The solvent is not limited and may be appropriately selected depending on the intended purpose, but an organic solvent is preferable.
The organic solvent is not limited and may be appropriately selected depending on the intended purpose. For example, ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. And so on. These may be used alone or in combination of two or more. Among these, ketones are preferable in consideration of the burden on the environment.

When forming the cholesteric liquid crystal layer, the liquid crystal composition is applied to the forming surface of the cholesteric liquid crystal layer, the liquid crystal compound is oriented in the state of the cholesteric liquid crystal phase, and then the liquid crystal compound is cured to form the cholesteric liquid crystal layer. Is preferable.
That is, when forming a cholesteric liquid crystal layer on the alignment film 32, the liquid crystal composition is applied to the alignment film 32, the liquid crystal compound is oriented in the state of the cholesteric liquid crystal phase, and then the liquid crystal compound is cured to form cholesteric. It is preferable to form a cholesteric liquid crystal layer in which the liquid crystal phase is fixed.
For the application of the liquid crystal composition, printing methods such as inkjet and scroll printing, and known methods such as spin coating, bar coating and spray coating that can uniformly apply the liquid to a sheet-like material can be used.

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

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

When the cholesteric liquid crystal layer is formed on the cholesteric liquid crystal layer by such a coating method, the upper cholesteric liquid crystal layer follows (follows) the liquid crystal orientation pattern of the lower layer, that is, the cholesteric liquid crystal layer serving as the forming surface.
Therefore, in the reflecting plate 14 of the illustrated example, the left circularly polarized light reflecting layer 34 is formed on the surface of the alignment film 32 having a predetermined alignment pattern by the coating method, and the left circularly polarized light reflecting layer 34 is coated on the surface of the left circularly polarized light reflecting layer 34. By forming the right circularly polarized light reflecting layer 36, the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36 are optically derived from the liquid crystal compound 40 forming the cholesteric liquid crystal phase as shown in FIG. 3 described later. The orientation of the axis 40A changes in the plane of the cholesteric liquid crystal layer while continuously rotating in one direction, resulting in the same liquid crystal orientation pattern.

There is no limit to the thickness of the cholesteric liquid crystal layer, the selective reflection center wavelength, the width of the selective reflection wavelength range, the light reflectance (transmittance) required for the cholesteric liquid crystal layer, and the reflector 14 (reflection sheet). ), And the thickness at which the required light reflection characteristics can be obtained may be appropriately set according to the material for forming the cholesteric liquid crystal layer and the like.
In the reflective sheet of the present invention, the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36 totally apply a specific circular polarization in a selective reflection wavelength range in order to improve the brightness uniformity of the irradiation light. It is preferable to use a reflective layer such as a half mirror that transmits a part of the light rather than reflecting it.

<< Liquid crystal orientation pattern of cholesteric liquid crystal layer >>
As described above, in the reflector 14 of the present invention, the cholesteric liquid crystal layer (left circularly polarized light reflecting layer 34 and right circularly polarized light reflecting layer 36) is preferably an optical derived from the liquid crystal compound 40 forming the cholesteric liquid crystal phase. The orientation of the shaft 40A has a liquid crystal orientation pattern that changes while continuously rotating in one direction in the plane of the cholesteric liquid crystal layer.
The optical axis 40A derived from the liquid crystal compound 40 is a so-called slow-phase axis having the highest refractive index in the liquid crystal compound 40. For example, when the liquid crystal compound 40 is a rod-shaped liquid crystal compound, the optical axis 40A is along the long axis direction of the rod shape.
In the following description, the optical axis 40A derived from the liquid crystal compound 40 is also referred to as "optical axis 40A of the liquid crystal compound 40" or "optical axis 40A".

FIG. 3 conceptually shows a plan view of the right circularly polarized light reflecting layer 36.
The plan view is a view of the reflector 14 viewed from the light source 13 side in FIG. 1, that is, a view of the reflector 14 viewed from the thickness direction (= the stacking direction of each layer (film)). ..
Further, in FIG. 3, in order to clearly show the configuration of the reflector 14 of the present invention, as in FIG. 1, the liquid crystal compound 40 shows only the liquid crystal compound 40 on the surface of the left circularly polarized light reflecting layer 34.

In FIG. 3 and FIG. 4 described later, the right circularly polarized light reflecting layer 36 will be described as a typical example, but the left circularly polarized light reflecting layer 34 also has the opposite turning direction of the reflected circularly polarized light, that is, the twist of the liquid crystal compound 40. It basically has the same configuration as the right-handed circularly polarized light-reflecting layer 36 except that the directions (senses) are opposite, and exhibits the same effects.

As shown in FIG. 3, on the surface of the left circularly polarized light reflecting layer 34, the liquid crystal compound 40 constituting the right circularly polarized light reflecting layer 36 is oriented formed on the lower left circularly polarized light reflecting layer 34 (that is, the alignment film 32). According to the pattern, they are arranged in a two-dimensional manner in a predetermined one direction indicated by an arrow X and in a direction orthogonal to this one direction (arrow X direction). Further, for example, in FIGS. 1, 2 and 4 described later, the liquid crystal compound 40 is shown so as to be parallel to the alignment film, but the liquid crystal compound 40 depends on the alignment pattern formed on the alignment film. When is oriented, the liquid crystal compound 40 may be inclined with respect to the alignment film. In the reflective sheet of the present invention, the liquid crystal compound 40 forming the cholesteric liquid crystal layer may be parallel to the alignment film or may be inclined.
In the following description, the direction orthogonal to the X direction of the arrow will be the Y direction for convenience. That is, in FIGS. 1, 2 and 4, which will be described later, the Y direction is a direction orthogonal to the paper surface.
Further, in the liquid crystal compound 40 forming the right circularly polarized light reflecting layer 36, as a preferred embodiment, the direction of the optical axis 40A continuously rotates along the arrow X direction in the plane of the right circularly polarized light reflecting layer 36. It has a liquid crystal orientation pattern that changes while changing. In the illustrated example, the optical axis 40A of the liquid crystal compound 40 has a liquid crystal orientation pattern that changes while continuously rotating clockwise along the arrow X direction.
As described above, when the cholesteric liquid crystal layer is formed on the cholesteric liquid crystal layer by the coating method, the liquid crystal alignment pattern of the upper cholesteric liquid crystal layer follows the liquid crystal alignment pattern on the surface of the lower cholesteric liquid crystal layer serving as the forming surface. do. Therefore, the left circularly polarized light reflecting layer 34, which is the forming surface of the right circularly polarized light reflecting layer 36, preferably has the same liquid crystal orientation pattern as the right circularly polarized light reflecting layer 36.

The fact that the direction of the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating in the arrow X direction (a predetermined one direction) specifically means that the liquid crystal compounds arranged along the arrow X direction. The angle formed by the optical axis 40A of 40 and the arrow X direction differs depending on the position in the arrow X direction, and the angle formed by the optical axis 40A and the arrow X direction along the arrow X direction is θ to θ + 180 ° or It means that the temperature is gradually changing up to θ-180 °.
The difference in the angles of the optical axes 40A of the liquid crystal compounds 40 adjacent to each other in the X direction of the arrow is preferably 45 ° or less, more preferably 15 ° or less, and less than 15 °. More preferred.

On the other hand, the liquid crystal compound 40 forming the right circularly polarized light reflecting layer 36 has the same optical axis 40A in the Y direction orthogonal to the X direction of the arrow. The Y direction orthogonal to the X direction of the arrow is a direction orthogonal to one direction in which the optic axis 40A rotates continuously.
In other words, the liquid crystal compound 40 forming the right circularly polarized light reflecting layer 36 has the same angle formed by the optical axis 40A of the liquid crystal compound 40 and the arrow X direction in the Y direction.

In the reflector 14 of the present invention, in such a liquid crystal alignment pattern of the liquid crystal compound 40, the optical axis 40A of the liquid crystal compound 40 is 180 in the direction of arrow X in which the optical axis 40A continuously rotates and changes in the plane. Let the length (distance) of ° rotation be the length Λ of one cycle in the liquid crystal alignment pattern.
That is, the distance between the centers of the two liquid crystal compounds 40 having the same angle with respect to the arrow X direction in the arrow X direction is defined as the length Λ of one cycle. Specifically, as shown in FIG. 3 (FIG. 4), the distance between the centers of the two liquid crystal compounds 40 in which the arrow X direction and the direction of the optical axis 40A coincide with each other in the arrow X direction is the length of one cycle. Let's say Λ. In the following description, the length Λ of this one cycle is also referred to as "one cycle Λ".
In the reflector 14 of the present invention, the liquid crystal alignment pattern of the cholesteric liquid crystal layer repeats this one cycle Λ in the direction of arrow X, that is, in one direction in which the direction of the optical axis 40A continuously rotates and changes.

The cholesteric liquid crystal layer in which the cholesteric liquid crystal phase is fixed usually mirror-reflects the incident light (circularly polarized light).
On the other hand, the right circularly polarized light reflecting layer 36 reflects the incident light in a direction having an angle in the arrow X direction with respect to the incident light. The right-handed circularly polarized light-reflecting layer 36 has a liquid crystal alignment pattern in which the optical axis 40A changes while continuously rotating along the arrow X direction (a predetermined one direction) in the plane. Hereinafter, description will be made with reference to FIG.

As described above, the right circularly polarized light reflecting layer 36 is a cholesteric liquid crystal layer that selectively reflects the right circularly polarized light _BR of blue light. Therefore, when light is incident on the right circularly polarized light reflecting layer 36, the right circularly polarized light reflecting layer 36 reflects only the right circularly polarized light _BR of blue light and transmits the other light.

The right circularly polarized _BR of blue light incident on the right circularly polarized light reflecting layer 36 is reflected by the right circularly polarized light reflecting layer 36 (cholesteric liquid crystal layer) according to the orientation of the optical axis 40A of each liquid crystal compound 40. The absolute phase changes.
Here, in the right circularly polarized light reflecting layer 36, the optical axis 40A of the liquid crystal compound 40 changes while rotating along the arrow X direction (one direction). Therefore, the amount of change in the absolute phase of the right circularly polarized light _BR of the incident blue light differs depending on the direction of the optical axis 40A.
Further, the liquid crystal alignment pattern formed on the right circularly polarized light reflecting layer 36 is a periodic pattern in the X direction of the arrow. Therefore, as shown conceptually in FIG. 4, the right-handed circularly polarized light _BR of blue light incident on the right-handed circularly polarized light-reflecting layer 36 has an absolute periodic absolute in the arrow X direction corresponding to the direction of each optical axis 40A. The phase Q is given.
Further, the direction of the optical axis 40A of the liquid crystal compound 40 with respect to the arrow X direction is uniform in the arrangement of the liquid crystal compound 40 in the Y direction orthogonal to the arrow X direction.
As a result, in the right circularly polarized light reflecting layer 36, an _equiphase plane E inclined in the direction of the arrow X with respect to the XY plane is formed with respect to the right circularly polarized light BR of blue light.
Therefore, the right circularly polarized BR of blue light is reflected in the normal direction of the _equiphase plane E, and the reflected right circularly polarized _BR of blue light is in the direction inclined in the arrow X direction with respect to the XY plane. Be reflected. The XY surface is the main surface of the cholesteric liquid crystal layer. The main surface is the maximum surface of a sheet-like material (film, plate-like material, layer).

In the cholesteric liquid crystal layer, the shorter this one cycle Λ is, the larger the inclination angle of the reflected light with respect to the incident light described above. That is, the shorter one cycle Λ is, the more the reflected light can be tilted and reflected.
Therefore, in the cholesteric liquid crystal layer, the reflection angle of the reflected light of the incident light can be adjusted by adjusting the one cycle Λ.

Further, by reversing the rotation direction of the optical axis 40A of the liquid crystal compound 40 in the direction of arrow X, the reflection direction of the right circularly polarized B _B of blue light can be reversed. That is, in FIGS. 1 to 4, the rotation direction of the optical axis 40A in the direction of arrow X is clockwise, and the right circularly polarized _BR of blue light is reflected by tilting in the direction of arrow X, which is counterclockwise. By rotating it, the right circularly polarized _BR of blue light is reflected by tilting it in the direction opposite to the direction of arrow X.

In the reflector 14 (reflection sheet) of the illustrated example, the lower layer (forming surface) of the right circularly polarized light reflecting layer 36 is the left circularly polarized light reflecting layer 34. When viewed from the light source 13 side, the left circularly polarized light reflecting layer 34 is an upper layer of the right circularly polarized light reflecting layer 36.
As described above, the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36 have the same liquid crystal alignment pattern in the plane direction.
Here, the left circularly polarized light reflecting layer 34 selectively reflects the left circularly polarized light of blue light, and the twisting direction of the spiral of the liquid crystal compound 40 is reversed. Therefore, in the left circular polarized light reflecting layer 34, the inclination directions of the equiphase planes E in FIG. 4 are opposite to each other. Therefore, the reflection direction of the left circular polarization by the left circular polarization reflection layer 34 is opposite to the arrow X direction opposite to that of the right circular polarization reflection layer 36.

As is well known, the cholesteric liquid crystal layer in which the cholesteric liquid crystal phase is fixed is derived from the cholesteric liquid crystal phase when a cross section in a direction perpendicular to the main surface is observed with a scanning electron microscope (SEM). A striped pattern of bright areas (bright lines) and dark areas (dark lines) is observed. That is, in the cross section of the cholesteric liquid crystal layer, a layered structure in which bright parts and dark parts are alternately laminated in the thickness direction is observed.
In the cholesteric liquid crystal layer, two repetitions of the bright part and the dark part correspond to the spiral pitch. From this, the spiral pitch of the cholesteric liquid crystal layer, that is, the reflective layer can be measured from the SEM cross-sectional view. The two repetitions of the bright part and the dark part are, that is, three bright parts and two dark parts, or two bright parts and three dark parts.

In a normal cholesteric liquid crystal layer, the bright and dark striped patterns (layered structure) are formed parallel to the main surface (forming surface) of the cholesteric liquid crystal layer.
On the other hand, as described above, the cholesteric liquid crystal layer (left circular polarization reflection) having a liquid crystal orientation pattern in which the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating clockwise along the X direction of the arrow. In the layer 34 and the right circularly polarized light reflecting layer 36), as conceptually shown in FIG. 5, the bright part (bright line) and the dark part (dark line) are inclined in the arrow X direction or the opposite direction with respect to the main surface. ..
The inclinations of the bright and dark areas coincide with the above-mentioned equiphase plane E. Therefore, in the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36, as shown in FIG. 5, the bright and dark portions are inclined in opposite directions, and the corresponding circularly polarized light is also reflected in opposite directions.
By having such a configuration, the reflective sheet and the light emitting device of the present invention make it possible to reduce the thickness of the backlight unit of the LCD and the like, and to emit light having uniform brightness with a small number of light sources. ing.
Hereinafter, a detailed description will be given with reference to the conceptual diagram of FIG.

In FIG. 6, the light source 13 is a blue LED, the right circularly polarized light reflecting layer 36 selectively reflects the right circularly polarized light of blue light, and the left circularly polarized light reflecting layer 34 selectively reflects the left circularly polarized light of blue light. Reflects on.
In FIG. 6, light incident on a position directly above the light source 13 (light on the optical axis of the light source 13) in the reflection sheet including the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36 will be described as an example.
The blue light emitted from the light source 13 first enters the right circularly polarized light reflecting layer 36 in the reflective sheet. As shown in FIG. 6, of the blue light emitted from the light source 13, when the right circularly polarized light component shown by the broken line is incident on the right circularly polarized light reflecting layer 36, a part of the blue light is transmitted through the right circularly polarized light reflecting layer 36. The left circularly polarized light reflecting layer 34 also transmits and emits light, and most of the light is reflected by the right circularly polarized light reflecting layer 36. Here, the reflection of the right circular polarization by the right circular polarization reflection layer 36 is not a specular reflection but a direction inclined in the arrow X direction with respect to the incident direction, as described above.
The right circular polarization of blue light reflected by the right circular polarization reflecting layer 36 in the direction of arrow X is reflected by the light reflecting surface 12a on the bottom surface of the housing 12 in the direction further inclined in the direction of arrow X, and again. It is incident on the right circular polarization reflection layer 36.
Similarly, the light re-entered on the right circularly polarized light reflecting layer 36 is partially transmitted and emitted in the same manner, and most of the light is reflected by the right circularly polarized light reflecting layer 36 in a direction further inclined in the arrow X direction. The right circular polarization of blue light reflected by the right circular polarization reflecting layer 36 in the direction of arrow X is reflected by the light reflecting surface 12a on the bottom surface of the housing 12 in the direction further inclined in the direction of arrow X, and again. The incident on the right circularly polarized light reflecting layer 36 is repeated.

On the other hand, of the blue light emitted from the light source 13 and incident on the position directly above the light source 13 of the reflection sheet, the left circularly polarized component (solid line) passes through the right circularly polarized light reflecting layer 36 and is reflected by the left circularly polarized light. It is incident on the layer 34.
The left circular polarization of blue light incident on the left circular polarization reflection layer 34 is partially transmitted and emitted, and most of it is reflected by the left circular polarization reflection layer 34. Here, as described above, the reflection by the left circularly polarized light reflecting layer 34 is not a specular reflection, but is reflected in a direction inclined in the direction opposite to the arrow X direction.
The left circular polarization of blue light reflected by the left circular polarization reflecting layer 34 in the direction opposite to the arrow X direction is further inclined in the direction opposite to the arrow X direction by the light reflecting surface 12a on the bottom surface of the housing 12. It is reflected in the above direction and is again incident on the left circularly polarized light reflecting layer 34.
Similarly, the light re-entering the left circularly polarized light reflecting layer 34 is partially transmitted, and most of the light is reflected by the left circularly polarized light reflecting layer 34 in a direction inclined in the direction opposite to the arrow X direction. The left circular polarization of blue light reflected on the left circular polarization reflecting layer 34 at an angle opposite to the arrow X direction is further inclined opposite to the arrow X direction due to the light reflecting surface 12a on the bottom surface of the housing 12. It is repeatedly reflected on the left circularly polarized light reflecting layer 34 and incident on the left circularly polarized light reflecting layer 34 again.

As is clear from the above description, according to the reflective sheet and the light emitting device 10 of the present invention having the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36, the light emitted by the light source 13 is directed by the arrow X direction and the arrow. It can be widely diffused by tilting and reflecting in the direction opposite to the X direction and transmitting the number in the direction opposite to the arrow X direction and the arrow X direction. Moreover, as described above, in the present invention, the angle of reflection can be adjusted by adjusting one cycle Λ of the liquid crystal alignment pattern of the cholesteric liquid crystal layer. For example, in the present invention, by shortening one cycle Λ of the liquid crystal alignment pattern, it is possible to greatly tilt and reflect the light and expand the diffusion of the light.
Therefore, according to the present invention, in a light source device such as a backlight unit, it is possible to reduce the thickness and emit light having uniform brightness with a small number of light sources.

As described above, according to the present invention, since the light emitted by the light source 13 can be widely diffused, the light emitting device 10 can be made thinner and the distance between the light sources 13 can be widened to reduce the number of light sources 13. can.
In the light emitting device 10 of the present invention, the distance d1 between the light source 13 and the adjacent light source 13 is 5 of the distance d2 between the bottom surface of the housing 12, that is, the arrangement surface of the light source 13 and the reflective sheet (right circular polarized light reflecting layer 36). It is preferably twice or more, preferably eight times or more, and more preferably 12 times or more.
By setting the distance d1 between the light source 13 and the adjacent light source 13 to be 5 times or more the distance d2 between the arrangement surface of the light source 13 and the reflective sheet, a light emitting device 10 that is sufficiently thin and has a small number of light sources can be obtained. , It is preferable in that the price of the light source itself can be suppressed and the manufacturing yield can be improved.

In the right circularly polarized light reflecting layer 36 and the left circularly polarized light reflecting layer 34, the angle θ formed by the main surface and the dark part and the bright part is not limited, and the required diffuse reflectance, the light source 13 and the adjacent light source It may be appropriately set according to the interval d1 and the distance d2 between the arrangement surface of the light source 13 and the reflective sheet.
Here, the angle θ formed by the main surface and the dark portion and the bright portion is preferably 3 to 40 °, more preferably 8 to 35 °, still more preferably 10 to 30 °.
By setting the angle θ formed by the main surface, the dark portion, and the bright portion to 3 ° or more, the reflection angle of the reflected light with respect to the incident light can be increased, and the spread of the light can be secured by multiple reflections, which is preferable.
By setting the angle θ between the main surface, the dark part and the bright part to 40 ° or less, the reflectance can be kept moderate, and the light of the backlight can be made uniform even if the light source interval is wide. It is preferable in that high brightness can be obtained by reducing the reflection component.
Further, the dark part and the bright part may form a wavy structure in which at least a part thereof forms periodic wavy irregularities. That is, the dark part and the bright part may be formed only in a straight line, may be a mixture of a straight line and a wavy part, or may be formed only in a wavy shape. In particular, when the bright and dark areas near the interface of each layer form a wavy shape, it may be easier to spread the light. When the dark part and the bright part have a wavy region, the angle θ formed by the main surface and the dark part and the bright part can be considered as an average value of each region.

In addition to the right circularly polarized light reflecting layer 36 and the left circularly polarized light reflecting layer 34, the reflecting plate 14 (the reflecting sheet of the present invention) has a λ / 4 layer on the light source 13 side of the reflecting sheet as shown by a broken line in FIG. It is preferable to have 38. In the illustrated example, it is preferable to have the λ / 4 layer 38 on the light source 13 side of the right circularly polarized light reflecting layer 36.

Taking right-handed circular polarization as an example, when the right-handed circularly polarized light reflected by the right-handed circularly polarized light-reflecting layer 36 is reflected by the light-reflecting surface 12a on the inner surface of the housing 12, the turning direction is reversed and the left-handed circularly polarized light is polarized. become. This left circular polarization passes through the right circularly polarized light reflecting layer 36 and is incident on the left circularly polarized light reflecting layer 34, but the left circularly polarized light reflecting layer 34 has an inclination of a bright part and a dark part with respect to the right circularly polarized light reflecting layer 36. Due to the different angles, the reflectance can be significantly reduced.
When the light reflecting surface 12a is a diffuse reflecting plate such as a white reflecting plate, the polarization is eliminated by the diffuse reflection by the light reflecting surface 12a, so that this problem is small. That is, when the light reflecting surface 12a is a diffuse reflecting plate, there are few cases where a problem occurs even if the λ / 4 layer 38 is not provided.
On the other hand, when the light reflecting surface 12a is a metal reflecting surface and a specular reflecting surface like the ESR reflecting sheet described above, the light reflecting surface 12a reflects the light reflecting surface, so that the sense of circular polarization is reversed. .. For example, the right circular polarization reflected by the right circular polarization reflecting layer 36 becomes left circular polarization when reflected by the light reflecting surface 12a. Therefore, even if the light is incident on the right circularly polarized light reflecting layer 36 again, it is transmitted without being reflected, so that the uneven brightness of the light source 13 cannot be eliminated.

Further, by having the λ / 4 layer 38 on the light source 13 side of the right circularly polarized light reflecting layer 36, the light incident on the right circularly polarized light reflecting layer 36 is converted into the right circularly polarized light again by the λ / 4 layer 38. Therefore, rereflection by the right circularly polarized light reflecting layer 36 becomes possible. Therefore, it is possible to eliminate the uneven brightness of the light source 13.

The λ / 4 layer 38 is not limited, and various known λ / 4 layers can be used.
As an example, a liquid crystal compound (disk-shaped liquid crystal, rod-shaped liquid crystal compound) formed by polymerizing a retardation film (optically substantially uniaxial or substantially biaxial), a nematic liquid crystal layer or a liquid crystal monomer forming a smectic liquid crystal layer by stretching. Etc.), examples thereof include one or more layers of retardation films containing at least one of these, a λ / 4 film formed by using a polymerizable liquid crystal compound, and the like.
Examples of the retardation film by stretching include a retardation film stretched in the transport direction at the time of film production, stretched in the direction perpendicular to the transport direction, and stretched by 45 ° ± 10 ° with respect to the transport direction. A retardation film in which a cyclic polyolefin resin (norbornene resin) is stretched by 45 ° ± 10 ° or a transparent film is orientated, and a liquid crystal compound is applied to the treated surface at 45 ° ± with respect to the transport direction during film production. A film having a layer oriented in a 10 ° orientation is preferred.

In the light emitting device 10 of the illustrated example, as a preferred embodiment, the right circularly polarized light reflecting layer 36 and the left circularly polarized light reflecting layer 34 constituting the reflective sheet have an inclination direction of a bright portion and a dark portion due to the cholesteric liquid crystal layer. On the contrary, the present invention is not limited to this.
That is, in the present invention, the right circularly polarized light reflecting layer 36 and the left circularly polarized light reflecting layer 34 constituting the reflective sheet may have the same inclination directions of the bright portion and the dark portion due to the cholesteric liquid crystal layer. However, in this configuration, the right circularly polarized light reflecting layer 36 and the left circularly polarized light reflecting layer 34 have the same direction in which the incident light is tilted and reflected. It is disadvantageous.
As described above, the reflective sheet in which the right circularly polarized light reflecting layer 36 and the left circularly polarized light reflecting layer 34 have the same inclination directions of the bright part and the dark part due to the cholesteric liquid crystal layer is the left circularly polarized light reflecting layer 34. Instead of directly forming the right circularly polarized light reflecting layer 36 on the left circularly polarized light reflecting layer 36 by the coating method, an alignment film in which the rotation direction of the optical axis 40A in the direction of arrow X is reversed is formed on the left circularly polarized light reflecting layer 34. It can be produced by forming and forming a right-handed circular polarization reflecting layer 36 on the alignment film by a coating method.

Here, the light diffusion direction (light propagation direction) by the right circularly polarized light reflecting layer 36 and the left circularly polarized light reflecting layer 34 is only the direction in which the optical axis 40A of the liquid crystal compound 40 continuously rotates and changes. That is, the light diffusion direction by the right circularly polarized light reflecting layer 36 and the left circularly polarized light reflecting layer 34 is only in the direction opposite to the arrow X direction or the arrow X direction. For example, the light is diffused in the arrow Y direction. I can't.
Therefore, light may not be sufficiently diffused depending on the use of the light emitting device 10, the type and orientation distribution of the light source 13, the arrangement of the light sources 13, the spacing of the light sources 13, and the like.

Correspondingly, the reflective sheet of the present invention preferably has one, or preferably both, the right circularly polarized light reflecting layer and the left polarized light reflecting layer, in the plane of the optical axis 40A of the liquid crystal compound 40 in the liquid crystal alignment pattern. It is preferable that the in-plane directions that change while the orientation is continuously rotating have regions different from each other. With such a configuration, as a preferred embodiment, it is possible to form a cholesteric liquid crystal layer having regions in which the inclination directions of the bright and dark portions derived from the cholesteric liquid crystal phase are different from each other.
In the following description, "the in-plane direction in which the direction of the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating in the liquid crystal alignment pattern" is also simply referred to as "the direction in which the direction of the optical axis 40A changes". ..

FIG. 7 shows an example thereof.
The reflective sheet of the present invention shown in FIG. 7 has a left circularly polarized light reflecting layer 50 and a right circularly polarized light reflecting layer 52. The reflective sheet of the present invention shown in FIG. 7 basically has the above-mentioned right except that each circularly polarized light reflecting layer has a region in the plane in which the direction in which the direction of the optical axis 40A changes is different from each other. It has the same configuration as the circularly polarized light reflecting layer 36 and the left circularly polarized light reflecting layer 34.
Therefore, the left circularly polarized light reflecting layer 50 and the right circularly polarized light reflecting layer 52 have the same liquid crystal alignment pattern.

Explaining the left circularly polarized light reflecting layer 50 as a typical example, the left circularly polarized light reflecting layer 50 is divided into stripes in the horizontal direction in the drawing, and the direction in which the direction of the optical axis 40A changes is the arrow Xa direction. The 50a and the region 50b in which the direction in which the direction of the optical shaft 40A changes is the direction of the arrow Xb are alternately provided.
The arrow Xa direction and the arrow Xb direction are orthogonal to each other. That is, the arrow Xa direction is inclined by 45 ° with respect to the horizontal direction in the figure, and the arrow Xb direction is inclined by −45 ° with respect to the horizontal direction in the figure. Therefore, in this example, the region 50a and the region 50b form a striped region in which the inclination directions of the bright and dark regions derived from the cholesteric liquid crystal phase are orthogonal to each other.

The cholesteric liquid crystal layer having a liquid crystal orientation pattern in which the optical axis 40A of the liquid crystal compound 40 continuously rotates and changes is directed in a direction in which the direction of the optical axis 40A changes or in a direction opposite to the incident direction of light. , The incident circular polarization is tilted and reflected.
Therefore, the left-handed circularly polarized light incident on the region 50a of the left-handed circularly polarized light-reflecting layer 50, which is indicated by the broken line in the figure, is reflected at an angle in the direction of the arrow Xa with respect to the incident direction. On the other hand, the left circular polarization incident on the region 50b of the left circular polarization reflecting layer 50 shown by the solid line in the figure is reflected at an angle in the arrow Xb direction orthogonal to the arrow Xa direction with respect to the incident direction.
That is, the left circularly polarized light incident on the left circularly polarized light reflecting layer 50 has a reflection direction inclined by 90 ° with respect to the incident direction depending on the incident region.
The left circularly polarized light reflecting layer 50 and the right circularly polarized light reflecting layer 52 have the same liquid crystal alignment pattern. Therefore, the right circularly polarized light reflecting layer 52 also has a similar striped region. That is, in the right circularly polarized light reflecting layer 52, the region 52a has the same liquid crystal alignment pattern as the region 50a of the left circularly polarized light reflecting layer 50, and the region 52b has the same liquid crystal alignment pattern as the region 50b of the left circularly polarized light reflecting layer 50. Has. Therefore, the right-handed circularly polarized light incident on the right-handed circularly polarized light-reflecting layer 52 also has a reflection direction inclined by 90 ° with respect to the incident direction depending on the incident region.

Therefore, the reflective sheet of the present invention has a cholesteric liquid crystal layer (right-handed circularly polarized light-reflecting layer and left-handed polarized light-reflecting layer) having regions in which the directions of the optical axes 40A change are different from each other in the plane. Circular polarization can be reflected by tilting in different directions depending on the region where the polarization is incident. Therefore, according to this configuration, the diffusion direction (propagation direction) of the light can be made two-dimensional, the light can be diffused more preferably, and the brightness of the irradiated light can be made uniform.

As shown in FIG. 7, the right circularly polarized light reflecting layer and the left polarized light reflecting layer (cholesteric liquid crystal layer) having regions in which the directions of the optical axes 40A change are different from each other are oriented in the directions orthogonal to each other. There are no restrictions on the configuration in which the optics rotate.
In general, the more types of regions the optical axis 40A changes in different directions, the more preferably circular polarization can be diffused.

As a suitable example, the configuration shown in FIG. 8 is illustrated.
The cholesteric liquid crystal layer (right circular polarized light reflecting layer or left polarized light reflecting layer) shown in FIG. 8 also has a striped region.
In the example shown in FIG. 8, the direction in which the direction of the optical axis 40A on the left side of the figure changes is the horizontal direction (X1 direction) in the figure as a reference (0 °), and is adjacent to the stripe arrangement direction. In the figure, the direction in which the direction of the optical axis 40A changes is the arrow X2 direction inclined by 45 ° with respect to the X1 direction, and the direction in which the direction of the optical axis 40A changes is the X1 direction. A region c in the direction of the arrow X3 tilted by 90 ° and a region d in which the direction in which the direction of the optical axis 40A changes is the direction of the arrow X4 tilted by 135 ° with respect to the X1 direction are repeatedly formed. That is, in this example, the region in which the inclination direction of the bright portion and the dark portion derived from the cholesteric liquid crystal phase with respect to the main surface is the X1 direction to the X4 direction is formed in a striped shape.
According to such a configuration, the diffusion direction (propagation direction) of the light can be set to various directions, the light can be more preferably two-dimensionally diffused, and the brightness of the irradiated light can be made uniform.

The cholesteric liquid crystal layer having regions in which the directions of the optical axes 40A change in different directions is masked in the exposure of the alignment film 32 using the exposure apparatus 60 shown in FIG. 10 to perform masking on the alignment film 32 (support 30). ) Can be produced by performing exposure with different angles (directions).
For example, in the case of the cholesteric liquid crystal layer shown in FIG. 8, first, the position other than the position corresponding to the region a is masked so that the direction in which the direction of the optical axis 40A changes is the arrow X1 direction (0 °). The alignment film 32 is exposed by the exposure apparatus 60.
Next, masking a position other than the position corresponding to the region b, the alignment film 32 (or the exposure apparatus 60) is rotated by 45 ° in the plane direction, and the direction in which the direction of the optical axis 40A changes is the arrow X2 direction (45 °). The alignment film 32 is exposed by the exposure apparatus 60 so as to be.
Next, masking a position other than the position corresponding to the region c, the alignment film 32 is rotated by 45 ° in the plane direction so that the direction in which the direction of the optical axis 40A changes is the arrow X3 direction (90 °). The alignment film 32 is exposed by the exposure apparatus 60.
Finally, masking other than the position corresponding to the region d, the alignment film 32 is rotated by 45 ° in the plane direction so that the direction in which the direction of the optical axis 40A changes is the arrow X4 direction (135 °). The exposure device 60 exposes the alignment film 32.
Thereby, the cholesteric liquid crystal layer having the regions a to d in which the direction in which the direction of the optical axis 40A changes is the direction of the arrow X1 to the direction of the arrow X4 can be produced.

In the examples shown in FIGS. 7 and 8, as a preferred embodiment, a region in which the direction in which the direction of the optical axis 40A changes is different from each other, that is, a region in which the inclination directions of the bright portion and the dark portion derived from the cholesteric liquid crystal phase are different from each other with respect to the main surface. However, the present invention is not limited to this.
For example, the circularly polarized light reflecting layer (cholesteric liquid crystal layer) is divided in half in the plane direction to have regions in which the directions of the optical axes 40A change in different directions, and the circularly polarized light reflecting layer is formed in the plane direction by orthogonal straight lines. It may be divided into four parts and have regions in which the directions in which the directions of the optical shaft 40A change are different.

In the present invention, the circularly polarized light reflecting layer (cholesteric liquid crystal display) having in-plane directions in which the direction of the optical axis 40A of the liquid crystal compound 40 in the liquid crystal alignment pattern changes while continuously rotating has regions different from each other. When having a layer), the reflective sheet of the present invention is not necessarily limited to a configuration having both a right circularly polarized light reflecting layer and a left circularly polarized light reflecting layer.
That is, the second aspect of the reflective sheet of the present invention has only one cholesteric liquid crystal layer, for example, even if it has only the left circularly polarized light reflecting layer 50, it has only the right circularly polarized light reflecting layer 52. It may have.

The light emitting device 10 described above uses a blue LED that emits blue light as a light source 13, and emits light that irradiates blue light in which the right circularly polarized light reflecting layer 36 and the left circularly polarized light reflecting layer 34 selectively reflect blue light. Although it is an apparatus, the present invention is not limited to this.
For example, it may be a light emitting device that irradiates red light by using a red LED that emits red light as a light source and the right circular polarization reflecting layer and the left circular polarization reflecting layer selectively reflect red light. A light emitting device that irradiates green light may be used, in which a green LED that emits light is used as a light source, and the right circularly polarized light reflecting layer and the left circularly polarized light reflecting layer selectively reflect green light.
Further, the light emitting device of the present invention uses a blue LED, a green LED and a red LED as light sources, and selects green light in combination with a right circularly polarized light reflecting layer and a left circularly polarized light reflecting layer that selectively reflect blue light. Three sets of circularly polarized light, a combination of a right-handed circularly polarized light-reflecting layer and a left-handed circularly polarized light-reflecting layer, and a combination of a right-handed circularly polarized light-reflecting layer and a left-handed circularly polarized light-reflecting layer that selectively reflect red light. It may be a light emitting device that irradiates white light by laminating a combination of reflective layers (cholesteric liquid crystal layers).
Further, the light emitting device of the present invention may be a light emitting device that irradiates light corresponding to two colors appropriately selected from blue, green and red.

Further, in the reflective sheet of the present invention, at least one layer, preferably both of the left circularly polarized light reflecting layer 34 and the right circularly polarized light reflecting layer 36 (cholesteric liquid crystal layer), changes the spiral pitch of the cholesteric liquid crystal phase in the thickness direction. It may be a thing. In the following description, the structure in which the spiral pitch of the cholesteric liquid crystal phase changes in the thickness direction is also referred to as a "pitch gradient structure" for convenience.

As described above, the selective reflection center wavelength (selective reflection wavelength range) of the cholesteric liquid crystal phase depends on the pitch P of the spiral of the cholesteric liquid crystal phase. That is, the longer the pitch P, the longer the selective reflection center wavelength of the cholesteric liquid crystal phase.
Therefore, since the cholesteric liquid crystal layer has a pitch gradient structure, the selective center reflection wavelength can be changed according to the position in the thickness direction, and right-handed circular polarization or left-handed circular polarization can be selected corresponding to a wide wavelength range. Can be reflected.

The pitch gradient structure in the cholesteric liquid crystal layer is not limited, and various configurations can be used as long as the pitch P changes in the thickness direction.
As an example, a configuration in which the pitch P gradually decreases from the light source 13 side toward the support 30 side and a configuration in which the pitch P gradually increases from the light source 13 side toward the support 30 side are exemplified. .. In this case, the pitch P may partially have a constant region.
For example, in a cholesteric liquid crystal layer in which the pitch P gradually shortens from the light source 13 side toward the support 30 side, the selective reflection center wavelength, that is, the light selectively reflected from the light source 13 side toward the support 30 side. The wavelength band gradually becomes shorter.

The cholesteric liquid crystal layer having a pitch gradient structure is a chiral agent whose spiral inducing force (HTP: Helical Twisting Power) changes due to return isomerization, dimerization, isomerization, dimerization, etc. by irradiation with light. It can be formed by irradiating light having a wavelength that changes the HTP of the chiral agent before curing the liquid crystal composition for forming the cholesteric liquid crystal layer or during curing of the liquid crystal composition.
Examples of the chiral agent whose HTP is changed by irradiation with light include a chiral agent having a cinnamoyl group.

For example, by using a chiral agent whose HTP is reduced by irradiation with light, the HTP of the chiral agent is reduced by irradiation with light.
Here, the HTP distribution in the film thickness direction of the cholesteric liquid crystal layer can be adjusted by adjusting the absorbance of light having a wavelength that changes the HTP of the chiral auxiliary with the material for forming the cholesteric liquid crystal layer. Therefore, for example, when light is irradiated from the surface (opposite side to the support 30), the amount of light irradiation gradually decreases from the surface toward the support 30. That is, the amount of decrease in HTP of the chiral agent gradually decreases from the surface toward the support 30. Therefore, on the surface side where HTP is greatly reduced, the spiral induction is small and the spiral pitch becomes long. On the other hand, on the support 30 side where the decrease in HTP is small, the spiral is induced by the HTP that the chiral auxiliary originally has, so that the spiral pitch becomes short.
That is, in this case, the cholesteric liquid crystal layer (right circularly polarized light reflecting layer 36 and left circularly polarized light reflecting layer 34) selectively reflects long-wavelength light on the light source 13 side, and the light source 13 on the support 30 side. It selectively reflects light with a shorter wavelength than the side. Therefore, by using a cholesteric liquid crystal layer having a pitch gradient structure in which the spiral pitch changes in the thickness direction, light in a wide wavelength band can be selectively reflected.

As described above, in the cholesteric liquid crystal layer having a liquid crystal orientation pattern in which the optical axis 40A of the liquid crystal compound 40 changes while continuously rotating along one direction in the plane, SEM is conceptually shown in FIG. In the cross section observed in 1 above, the bright and dark areas are inclined with respect to the main surface.
In the cholesteric liquid crystal layer having a pitch gradient structure, the angle θ between the bright part and the dark part with respect to the main surface becomes large in the region where the pitch P of the spiral becomes long. Therefore, for example, in the case of a cholesteric liquid crystal layer in which the pitch P gradually decreases from the light source 13 side toward the support 30 side, the bright and dark areas gradually decrease from the light source 13 side toward the support 30 side. , The angle θ of the tangent line becomes smaller.

In the above example, the cholesteric liquid crystal layer (right circular polarization reflecting layer 36 and left circular polarization reflecting layer 34) continuously rotates along at least one direction in the plane of the optical axis 40A derived from the liquid crystal compound 40. By having a liquid crystal orientation pattern that changes while being changed, the cholesteric liquid crystal layer realizes a configuration in which the bright part and the dark part derived from the cholesteric liquid crystal phase are inclined with respect to the main surface in the cross section observed by SEM. ing.
However, the present invention is not limited to this, as long as the cholesteric liquid crystal layer has a structure in which the bright and dark parts derived from the cholesteric liquid crystal phase are inclined with respect to the main surface in the cross section observed by SEM. Various aspects are available.
As an example, in the formation of the cholesteric liquid crystal layer, by using the chiral agent X whose spiral inducing force (HTP) is changed by irradiation with light, the bright and dark parts derived from the cholesteric liquid crystal phase are formed in the cross section observed by SEM. , A method of forming a cholesteric liquid crystal layer inclined with respect to the main surface is exemplified.

(Formation of cholesteric liquid crystal layer by liquid crystal composition containing chiral agent X)
Hereinafter, by using a liquid crystal composition containing a chiral agent X, a method for forming a cholesteric liquid crystal layer in which bright and dark parts derived from the cholesteric liquid crystal phase are inclined with respect to the main surface in a cross section observed by SEM. Will be explained.
First, steps 1-1 and 1-2 shown below are performed.
Step 1-1: A step of forming a composition layer on a substrate on which a rubbing alignment film having a pretilt angle is arranged on the surface using a composition containing a disk-shaped liquid crystal compound (composition for forming a liquid crystal layer). 2: Step of orienting the disk-shaped compound in the composition layer

When a cholesteric liquid crystal layer is formed using a liquid crystal composition containing a chiral agent X, a composition layer satisfying condition 1 or condition 2 is formed in step 2-1 below, and then the composition is formed in step 2-2. By subjecting the layer to light irradiation treatment, the liquid crystal compound in the composition layer is cholesterically oriented. That is, in step 2-2, the liquid crystal compound in the composition layer is cholesterically oriented by changing the spiral inducing force of the chiral agent X in the composition layer by the light irradiation treatment.
Step 2-1:
Step of forming a composition layer satisfying the following condition 1 or the following condition 2 on the liquid crystal layer formed in steps 1-1 and 1-2 Condition 1: At least a part of the liquid crystal compound in the composition layer is composed. Inclined orientation with respect to the surface of the material layer Condition 2: The liquid crystal compound is oriented so that the tilt angle of the liquid crystal compound in the composition layer continuously changes along the thickness direction Step 2-2. :
A step of forming a cholesteric liquid crystal layer by performing a treatment for cholesteric alignment of a liquid crystal compound in the composition layer.
The steps 2-1 and 2-2 will be described below.

<Mechanism of action in step 2-1>
First, FIG. 9 shows a schematic cross-sectional view of a composition layer satisfying condition 1 obtained in step 2-1. The liquid crystal compound 40 shown in FIG. 9 is a rod-shaped liquid crystal compound.

As shown in FIG. 9, the composition layer 100 is formed on the liquid crystal layer 102 formed by using the disk-shaped liquid crystal compound. The liquid crystal layer 102 has an inclined orientation surface 102a on the surface of the liquid crystal layer 102 on the side in contact with the composition layer 100, in which the molecular axis of the disk-shaped liquid crystal compound is inclined with respect to the surface of the liquid crystal layer 102.
As shown in FIG. 9, in the composition layer 100 arranged on the inclined alignment surface 102a of the liquid crystal layer 102, the liquid crystal compound 40 is loosely oriented by the inclined alignment surface 102a, so that the liquid crystal compound 40 is loosely oriented with respect to the inclined alignment surface 102a. Oriented so as to incline. In other words, in the composition layer 100, the liquid crystal compound 40 is in a certain direction (uniaxial direction) so that the molecular axis L ₁ of the liquid crystal compound 40 has a predetermined angle θ ₁₀ with respect to the surface of the composition layer 100. Oriented.

In FIG. 9, the liquid crystal compound 40 is oriented so that the molecular axis L ₁ is at a predetermined angle θ ₁₀ with respect to the inclined alignment surface 102 a over the entire area of the composition layer 100 in the thickness direction R ₁ . The embodiment is shown. However, as the composition layer that satisfies the condition 1 obtained in step 2-1 it is sufficient that a part of the liquid crystal compound 40 is inclined-oriented, and the surface of the composition layer 100 on the inclined-oriented surface 102a side (in FIG. 9). The liquid crystal compound 40 is on the surface of the composition layer 100 on at least one of the surface (corresponding to the region A) and the surface of the composition layer 100 opposite to the inclined orientation surface 102a side (corresponding to the region B in FIG. 9). On the other hand, it is preferable that the molecular axis L ₁ is oriented so as to have a predetermined angle θ ₁₀ , and on the surface on the inclined alignment surface 102a side, the liquid crystal compound 40 has the molecular axis L ₁ with respect to the surface of the composition layer 100. Is more preferably tilted so that is at a predetermined angle θ ₁₀ .
If the liquid crystal compound 40 is oriented so that the molecular axis L ₁ has a predetermined angle θ ₁₀ with respect to the surface of the composition layer 100 in at least one of the region A and the region B, the following step 2 When the liquid crystal compound 40 is in the state of the cholesteric liquid crystal phase in -2, the cholesteric orientation of the liquid crystal compound 40 in the other region is caused by the orientation restricting force based on the oriented liquid crystal compound 40 in the region A and / or the region B. It can be induced.

Although not shown, the composition layer satisfying the condition 2 corresponds to a liquid crystal compound 40 hybrid-oriented with respect to the surface of the composition layer 100. That is, it corresponds to a mode in which the angle θ ₁₀ changes continuously in the thickness direction.
As the composition layer satisfying the condition 2 obtained in step 2-1 it is sufficient that a part of the liquid crystal compound 40 is hybrid-oriented, and the surface of the composition layer 100 on the inclined orientation surface 102a side (in FIG. 9). The liquid crystal compound 40 relates to the inclined alignment surface 102a on at least one of the surface (corresponding to the region A) and the surface of the composition layer 100 opposite to the inclined alignment surface 102a side (corresponding to the region B in FIG. 9). The hybrid orientation is preferable, and the liquid crystal compound 40 is more preferably hybrid-oriented with respect to the surface of the composition layer 100 on the surface on the inclined alignment surface 102a side.

The angle θ ₁₀ is not particularly limited unless it is 0 ° in the entire composition layer. When the angle θ ₁₀ is 0 ° in the entire composition layer, the molecular axis L ₁ of the liquid crystal compound 40 is parallel to the inclined alignment plane 102 a when the liquid crystal compound 40 is a rod-shaped liquid crystal compound. In other words, it does not prevent the angle θ ₁₀ from being 0 ° in some regions of the composition layer.
The angle θ ₁₀ is, for example, 0 to 90 °. Among them, the angle θ ₁₀ is preferably 0 to 50 °, more preferably 0 to 30 °.

The composition layer obtained in step 2-1 is preferably a composition layer satisfying condition 2 in that the reflection anisotropy of the cholesteric liquid crystal layer is more excellent.

<Mechanism of action in step 2-2>
After obtaining a composition layer satisfying Condition 1 or Condition 2 in Step 2-1 the liquid crystal compound in the composition layer is cholesterically oriented in Step 2-2 to form a cholesteric liquid crystal layer. In other words, cholesteric orientation of a liquid crystal compound means that the liquid crystal compound is a cholesteric liquid crystal phase.
As a result, in the cross section observed by the SEM, the bright and dark areas derived from the cholesteric liquid crystal phase can form a cholesteric liquid crystal layer inclined with respect to the main surface.

In the method for producing a cholesteric liquid crystal layer of the present embodiment, for example, a chiral agent X whose spiral-inducing force is changed by light irradiation in the composition layer, and a chiral agent X in which the spiral-inducing force is not changed by light irradiation. When the chiral agent Y having a spiral-inducing force in the opposite direction is included, the chiral agent X in the composition layer cancels the spiral-inducing force to almost zero in step 2-1 to the composition layer. The liquid crystal compound inside can be oriented to be inclined or hybrid oriented.
Next, triggered by the light irradiation treatment in step 2-2, the spiral-inducing force of the chiral agent X is changed to increase the spiral-inducing force of the chiral agent in the composition layer in the right direction (+) and the left direction (-). By increasing in either direction, it is possible to form a cholesteric liquid crystal layer in which the bright and dark parts derived from the cholesteric liquid crystal phase are inclined with respect to the main surface in the cross section observed by SEM.

In the formation of the cholesteric liquid crystal layer using the chiral agent X, when forming the cholesteric liquid crystal layer having regions having different inclination directions of the bright part and the dark part derived from the cholesteric liquid crystal phase as shown in FIGS. 7 and 8. In this method, as shown in Examples described later, the orientation direction of the alignment film may be adjusted according to the inclination direction of the bright portion and the dark portion for each region.
Further, when the pitch gradient structure is formed in the cholesteric liquid crystal layer using the chiral agent X, the amount of reached light in the film thickness direction is formed by adjusting the amount of isomerized light to be irradiated in order to obtain the pitch gradient structure. , A pitch gradient structure is obtained.

Although the reflective sheet and the light emitting device of the present invention have been described in detail above, the present invention is not limited to the above-mentioned examples, and various improvements and changes may be made without departing from the gist of the present invention. Of course.

The features of the present invention will be described in more detail with reference to Examples below. The materials, reagents, amounts of substances used, amounts of substances, proportions, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed as long as they do not deviate from the gist of the present invention. Therefore, the scope of the present invention should not be construed in a limited manner by the specific examples shown below.

(Preparation of reflective sheet 1)
The half mirror (dielectric multilayer film) described in Example 1 of JP-A-2017-92021 was formed on a polycarbonate film having a film thickness of 50 μm to form a reflective sheet 1.

(Preparation of reflective sheet 2)
<Preparation of alignment film 2>
A TAC film having a thickness of 80 μm (TD80UL manufactured by FUJIFILM Corporation) was prepared as a support.
The following coating liquid for forming an alignment film was continuously applied onto the support with a # 2 wire bar. The support on which the coating film of the coating film for forming the alignment film was formed was dried on a hot plate at 60 ° C. for 60 seconds to form a coating film.

Coating liquid for forming an alignment film ――――――――――――――――――――――――――――――――――
Material for photo-alignment A 1.00 parts by mass Water 16.00 parts by mass Butoxyethanol 42.00 parts by mass Propylene glycol monomethyl ether 42.00 parts by mass ―――――――――――――――――― ―――――――――――――――

-Material for photo-alignment A-

A 160 W / cm ² air-cooled metal halide lamp (manufactured by Eye Graphics Co., Ltd.) is used as a UV (ultraviolet) lamp on the formed coating film via a mask (exposure mask) and a wire grid polarizer. Then, the alignment film 2 was prepared by performing the following four times of ultraviolet irradiation. In order to match the number of the reflective sheet with the number of the alignment film, the alignment film 1 is a missing number in this embodiment.
As the mask, a stripe mask was used in which transmission portions having a stripe width of 50 μm and shielding portions having a stripe width of 170 μm were alternately arranged. The stripe width is the length of the stripe in the lateral direction.
The first exposure is performed in a state where the periodic direction of the mask (hereinafter referred to as the direction A below the arrangement direction of the stripes) and the transmission axis of the wire grid polarizer are aligned, and the UV lamp is tilted to the direction from the film normal direction. UV light was irradiated from a direction slightly inclined to A.
The second exposure was carried out with the mask shifted 55 μm in the direction A from the first exposure and the transmission axis of the wire grid polarizer shifted clockwise by 45 °, and from the direction of the first exposure, the film. UV light was irradiated from a direction rotated 45 ° clockwise with respect to the normal direction.
The third exposure was carried out with the mask shifted 110 μm in the direction A from the first exposure and the transmission axis of the wire grid polarizer shifted 90 ° clockwise, from the direction of the first exposure to the film. UV light was irradiated from a direction rotated 90 ° clockwise with respect to the normal direction.
The fourth exposure was carried out with the exposure mask shifted in the direction A by 165 μm from the time of the first exposure and the transmission axis of the wire grid polarizer shifted clockwise by 135 °. UV light was irradiated from a direction rotated by 135 ° clockwise with respect to the film normal direction.
The illuminance of ultraviolet rays was 100 mW / cm ² in the UV-A region (integration of wavelengths of 380 nm to 320 nm), and the irradiation amount was 50 mJ / cm ² in the UV-A region.

<Chiral agent>
The following chiral agent A and chiral agent B were prepared. Bu represents a butyl group.

Chiral agent A

Chiral agent B

The chiral agent A is a chiral agent that forms a right-handed spiral. The chiral agent B is a chiral agent that forms a left-handed spiral.

<Formation of right circular polarization reflection layer>

The composition shown below was stirred and dissolved in a container kept at 25 ° C. to prepare a coating liquid Ch-A for a reflective layer.

Coating liquid for reflective layer Ch-A
―――――――――――――――――――――――――――――――――
Methyl ethyl ketone 144.9 parts by mass Mix of rod-shaped liquid crystal compounds below 100.0 parts by mass Photopolymerization initiator A 1.5 parts by mass Photopolymerization initiator B 0.5 parts by mass Chiral agent A 6.5 parts by mass The following surface activity Agent F1 0.027 parts by mass The following surfactant F2 0.067 parts by mass ―――――――――――――――――――――――――――――――― ―

上記混合物において、数値は質量％である。また、Ｒは酸素原子で結合する基である。上記の棒状液晶化合物の波長３００～４００ｎｍにおける平均モル吸光係数は、１４０／ｍｏｌ・ｃｍであった。Mixture of rod-shaped liquid crystal compounds

In the above mixture, the numerical value is% by mass. Further, R is a group bonded with an oxygen atom. The average molar extinction coefficient of the rod-shaped liquid crystal compound at a wavelength of 300 to 400 nm was 140 / mol · cm.

Photopolymerization Initiator A; IRGACURE 907 (manufactured by Ciba Geigy)
Photopolymerization Initiator B; KayaCure DETX (manufactured by Nippon Kayaku Co., Ltd.)

Surfactant F1

Surfactant F2

The prepared coating liquid for the reflective layer Ch-A was applied to the surface of the support having the prepared alignment film 2 with a wire bar coater of # 10.5, and dried at 105 ° C. for 60 seconds.
Then, in a low oxygen atmosphere (100 ppm or less), the light of a metal halide lamp having an irradiation amount of 60 mJ is irradiated through an optical filter SH0350 (manufactured by Asahi Spectroscopy Co., Ltd.) at 40 ° C., and further, the irradiation amount is 500 mJ at 100 ° C. By irradiating with the light of a metal halide lamp, a right circularly polarized light reflecting layer having a thickness of 6.4 μm, which is a cholesteric liquid crystal layer, was produced.

<Formation of left circular polarization reflection layer>
The composition shown below was stirred and dissolved in a container kept at 25 ° C. to prepare a coating liquid Ch-B for a reflective layer.

Coating liquid for reflective layer Ch-B
―――――――――――――――――――――――――――――――――
Methyl ethyl ketone 150.6 parts by mass Mix of rod-shaped liquid crystal compounds 100.0 parts by mass Photopolymerization initiator B 1.5 parts by mass Chiral agent B 10.3 parts by mass Surfactant F1 0.027 parts by mass Above interface Activator F2 0.067 parts by mass ――――――――――――――――――――――――――――――――――

The prepared coating liquid for the reflective layer Ch-B was applied to the surface of the prepared right circular polarized light reflecting layer with a wire bar coater of # 10.5, and dried at 105 ° C. for 60 seconds.
Then, in a low oxygen atmosphere (100 ppm or less), the light of a metal halide lamp having an irradiation amount of 60 mJ is irradiated at 75 ° C. through an optical filter SH0350 (manufactured by Asahi Spectroscopy Co., Ltd.), and further, the irradiation amount is 500 mJ at 100 ° C. By irradiating with the light of a metal halide lamp, a left circularly polarized light reflecting layer having a thickness of 6.4 μm, which is a cholesteric liquid crystal layer, was formed. In this procedure, a left circularly polarized light reflecting layer was formed on the right circularly polarized light reflecting layer to prepare a reflective sheet 2.

(Preparation of reflective sheets 3 to 6)
An exposure apparatus for emitting a laser beam having a wavelength (325 nm) shown in FIG. 10 was prepared.
In the preparation of the alignment film 2 described above, instead of irradiating ultraviolet rays through a mask (striped mask) and a wire grid polarizer, the exposure apparatus shown in FIG. 10 was used, and four lasers through the same mask shown below were used. Alignment films 3 to 6 were produced by light exposure.
Assuming that the periodic direction of the orientation pattern formed by the interference of the two laser beams is the direction B, the first exposure was performed in a state where the direction A and the direction B of the mask coincide with each other. The mask direction A is the periodic direction of the mask (the direction in which the stripes are arranged) as described above.
The second exposure was carried out in a state where the mask was shifted in the direction A by 55 μm from the time of the first exposure, and the direction B was the direction 45 ° clockwise from the direction A of the mask.
The third exposure was carried out in a state where the mask was shifted in the direction A by 110 μm from the time of the first exposure, and the direction B was 90 ° clockwise from the direction A of the mask.
The fourth exposure was carried out in a state where the mask was shifted in the direction A by 165 μm from the time of the first exposure, and the direction of 135 ° clockwise from the direction A of the mask was the direction B.
The exposure amount was set to 300 mJ / cm ² .
One cycle of the orientation pattern formed by the two laser beams and their interference (the length of the optical axis derived from the liquid crystal compound rotating 180 °) changes the intersection angle (intersection angle α) of the two lights. Controlled by. As a result, the alignment films 3 to 6 of the reflective sheets 3 to 6 were produced.

Further, in the formation of the right circularly polarized light reflecting layer and the left circularly polarized light reflecting layer of the reflective sheet 2, the film thickness is formed by the same method except that the amount of the photopolymerization initiator and the type and amount of the chiral agent are appropriately changed. A 6.4 μm right circularly polarized light reflecting layer and a left circularly polarized light reflecting layer were formed to prepare reflective sheets 3 to 6.
Specifically, the right circularly polarized light reflecting layer and the left circularly polarized light reflecting layer of the reflective sheet 3 have the same formulation as the right circularly polarized light reflecting layer and the left circularly polarized light reflecting layer of the reflective sheet 2, but because the alignment films are different. It differs from the reflective sheet 2 in that the bright and dark portions of the cross section of the reflective layer (cholesteric liquid crystal layer) are inclined.
The reflective sheet 4 is exposed at an incident angle different from that of the alignment film 3 to form the alignment film 4, and photopolymerization in the coating liquid forming the right circularly polarized light reflecting layer and the left circularly polarized light reflecting layer in the reflective sheet 3. It differs from the reflective sheet 3 in that the amount of the initiator is reduced and the amount of the chiral agent is increased. Since the amount of light reaching in the film thickness direction is different due to the increase in the amount of the chiral agent, a pitch gradient structure is formed.
The reflective sheet 5 is exposed at an incident angle different from that of the alignment film 3 to form the alignment film 5, and photopolymerization in the coating liquid forming the right circularly polarized light reflecting layer and the left circularly polarized light reflecting layer in the reflective sheet 3. It differs from the reflective sheet 3 in that the amount of the initiator is reduced and the amount of the chiral agent is increased.
The reflective sheet 6 is different in that the alignment film 6 is formed by exposing the reflective sheet 6 at an incident angle different from that of the alignment film 4 and shortening one cycle of the alignment pattern. By shortening one cycle of the orientation pattern, the inclination of reflection with respect to the incident direction when reflecting circularly polarized light becomes large. In this example, the right circularly polarized light reflecting layer and the left circularly polarized light reflecting layer are the same as the reflective sheet 4.
If the cholesteric liquid crystal layer (right circularly polarized light reflecting layer and left circularly polarized light reflecting layer) is misaligned, the prepared coating liquid is applied in multiple layers to form a right circularly polarized light reflecting layer with a thickness of 6.4 μm. And left circular polarization reflection layer was formed. In multi-layer coating, a liquid crystal coating liquid is applied, dried and then UV-cured to prepare a liquid crystal-immobilized layer, and then the second and subsequent layers are repeatedly coated and dried, and then UV-cured. Refers to repeating the steps to perform. By forming by multi-layer coating, the orientation direction of the alignment film is reflected from the lower surface to the upper surface of the liquid crystal layer even when the total thickness of the cholesteric liquid crystal layer is increased, and poor orientation can be suppressed. When a pitch gradient structure was formed by multi-layer coating, multi-layer coating was performed using a coating liquid in which the amount of chiral agent contained in the coating liquid was reduced as the number of layers increased.

The cross section of the reflective sheet was confirmed by SEM, and the periodic structure derived from the orientation state of the liquid crystal in the cholesteric liquid crystal layer of the reflective layer was confirmed.
The cholesteric liquid crystal layers of the reflective sheets 3 to 6 are uniformly inclined or oriented in one in-plane domain of the alignment film, and the right circularly polarized light reflecting layer and the left circularly polarized light reflecting layer are oriented with respect to the boundary portion of the reflecting layer. It was confirmed that the tilt angle was opposite. It was confirmed that the cholesteric liquid crystal layers of the reflective sheets 4 to 6 have a pitch gradient structure in which the spiral pitch changes in the film thickness direction in each reflective layer.

(Preparation of reflective sheet 7)
The composition shown below was stirred and dissolved in a container kept warm at 25 ° C. to prepare a composition for coating a disk-shaped liquid crystal display.
The prepared disc-shaped liquid crystal coating liquid was filtered through a polypropylene filter having a pore size of 0.2 μm and used as the coating liquid. The coating liquid was applied to the surface of the support having the alignment film 2 prepared as described above with a wire bar coater of # 2.4, and dried at 120 ° C. for 60 seconds. Subsequently, the coating film was cured by irradiating UV (ultraviolet rays) at an irradiation amount of 500 mJ / cm ² at 30 ° C. in a nitrogen atmosphere to prepare an alignment film 7.
The produced alignment film 7 had an in-plane liquid crystal alignment pattern based on the alignment pattern of the alignment film 2.

Disc-shaped liquid crystal coating composition ――――――――――――――――――――――――――――――――――
The following disc-shaped liquid crystal compound D-1 100 parts by mass Initiator Irg-907 (manufactured by BASF) 3.0 parts by mass Solvent (methyl ethyl ketone / cyclohexanone = 90/10 (mass ratio))
Amount of solute concentration of 30% by mass ――――――――――――――――――――――――――――――――――

The composition shown below was stirred and dissolved in a container kept at 25 ° C. to prepare a coating liquid Ch-C for a reflective layer.

Coating liquid for reflective layer Ch-C
―――――――――――――――――――――――――――――――――
Mixture of the above rod-shaped liquid crystal compound 5 100.0 parts by mass Photopolymerization initiator B 0.2 parts by mass Chiral agent CD-1 6.7 parts by mass Chiral agent CD-2 6.7 parts by mass The above surfactant F1 0.01 parts by mass Solvent (methyl ethyl ketone / cyclohexanone = 90/10 (mass ratio))
Amount of solute concentration of 30% by mass ――――――――――――――――――――――――――――――――――

なお、ＣＤ－１は左巻きの螺旋を形成するキラル剤、ＣＤ－２は光により異性化し、右巻きの螺旋を形成するキラル剤である。

CD-1 is a chiral agent that forms a left-handed helix, and CD-2 is a chiral agent that is isomerized by light to form a right-handed helix.

The prepared coating liquid for the reflective layer Ch-C was applied to the surface of the prepared alignment film 7 with a # 15 wire bar coater, and dried at 105 ° C. for 60 seconds.
Subsequently, at 30 ° C., light having a wavelength of 365 nm was irradiated from a light source (UVP, 2UV, transilluminator) at an irradiation intensity of 2 mW / cm ² for 70 seconds. Then, in a low oxygen atmosphere (100 ppm or less), the light of a metal halide lamp having an irradiation amount of 120 mJ is irradiated through an optical filter SH0350 (manufactured by Asahi Spectroscopy Co., Ltd.) at 50 ° C., and further, the irradiation amount is 500 mJ at 100 ° C. By irradiating with the light of a metal halide lamp, a left circularly polarized light reflecting layer having a thickness of 6.4 μm, which is a cholesteric liquid crystal layer, was formed.
By such a procedure, a left circular polarization reflection layer was formed on the alignment film 7.

A container in which the same composition as the coating liquid for the reflective layer Ch-A was kept at 25 ° C. except that the photopolymerization initiator A was changed to 0.01 parts by mass and the photopolymerization initiator B was changed to 0.3 parts by mass. Inside, the mixture was stirred and dissolved to prepare a coating solution Ch-D for a reflective layer.

The prepared coating liquid for the reflective layer Ch-D was applied to the surface of the prepared left circular polarized light reflecting layer with a wire bar coater of # 10.5, and dried at 105 ° C. for 60 seconds.
Then, in a low oxygen atmosphere (100 ppm or less), the light of a metal halide lamp having an irradiation amount of 100 mJ is irradiated at 40 ° C. through an optical filter SH0350 (manufactured by Asahi Spectroscopy Co., Ltd.), and further, the irradiation amount is 500 mJ at 100 ° C. By irradiating with the light of a metal halide lamp, a right circularly polarized light reflecting layer having a thickness of 6.4 μm, which is a cholesteric liquid crystal layer, was formed. In this procedure, a right circularly polarized light reflecting layer was formed on the left circularly polarized light reflecting layer to prepare a reflective sheet 7.

(Preparation of reflective sheet 8)
<Formation of alignment film 8>
A TAC film with a thickness of 80 μm (TD80UL manufactured by FUJIFILM Corporation) was prepared.
On this TAC film, the alignment layer coating liquid Y1 having the following composition was applied with a # 16 wire bar coater. Then, it was dried at 60 ° C. for 60 seconds and further at 90 ° C. for 150 seconds.
Next, the oriented layer 8 was produced by rotating the coated surface side with a rubbing roll in a direction parallel to the transport direction at a clearance of 1.0 mm and 1000 rotations / minute to perform a rubbing treatment.

Orientation layer coating liquid Y1
―――――――――――――――――――――――――――――――――
The following modified polyvinyl alcohol 10 parts by mass Water 370 parts by mass Methanol 120 parts by mass Glutaraldehyde (bridging agent) 0.5 parts by mass ――――――――――――――――――――――― ――――――――――

Polyvinyl alcohol

<Preparation of λ / 4 layer>
The following composition for an optically anisotropic layer was prepared.
The prepared composition for an optically anisotropic layer was filtered through a polypropylene filter having a pore size of 0.2 μm and used as a coating liquid.
A coating liquid is applied onto the formed alignment layer 8 and dried at a film surface temperature of 105 ° C. for 2 minutes to obtain a liquid crystal phase state, then cooled to 75 ° C. and air-cooled metal halide at 160 W / cm ² under air. A film A having an optically anisotropic layer (λ / 4 layer) on the alignment layer 8 was produced by irradiating ultraviolet rays with a lamp (manufactured by Eye Graphics Co., Ltd.) to fix the orientation state.
The film thickness of the optically anisotropic layer was 1.33 μm, and Re at a wavelength of 550 nm was 135 nm.

Composition for optically anisotropic layer ―――――――――――――――――――――――――――――――――
The following rod-shaped liquid crystal (LC242, manufactured by BASF) 100 parts by mass The following horizontal alignment agent A 0.3 parts by mass Photopolymerization initiator A 3.3 parts by mass Photopolymerization initiator B 1.1 parts by mass Methyl ethyl ketone 300 parts by mass- ――――――――――――――――――――――――――――――――

<Preparation of reflective sheet 8>
After peeling off the TAC film of the reflective sheet 5, the reflective sheet 8 was produced by laminating the λ / 4 layer of the film A on the peeled surface with an adhesive.

<Evaluation>
The prepared reflective sheet was confirmed and evaluated as follows.

[Confirmation of pitch gradient structure of reflective layer and inclination angle of bright and dark areas]
The cross section of the produced reflective sheet is observed by SEM, and from the SEM image, whether or not the right circularly polarized light reflecting layer and the left circularly polarized light reflecting layer have a pitch gradient structure (PG structure), and the bright part and the bright part and The inclination angle of the dark part was confirmed.
The tilt angle is expressed according to the following criteria.
W: The tilt angle is larger than 40 °.
X: The tilt angle is greater than 30 ° and less than 40 °.
Y: The tilt angle is 3 ° or more and 30 ° or less.
Z: Not tilted or tilted at less than 3 °.

[Measurement of integrated reflectance]
A spectrophotometer (V-550 manufactured by Nippon Spectroscopy Co., Ltd.) equipped with a large integrating sphere device (ILV-471 manufactured by Japan Spectroscopy Co., Ltd.) is used to reflect positively reflected light without using an optical trap. The integrated reflection spectrum of the sheet at a wavelength of 450 nm was measured.
Here, in the reflective sheet 1, the measurement was made so that the light was incident from the dielectric multilayer film side. In the reflective sheets 2 to 8, as a measurement sample, the circularly polarized light reflective layer side of each reflective sheet is attached to glass with an adhesive, and then a TAC film is peeled off, and light is emitted from the peeled surface measurement. It was measured so as to be incident.

[Evaluation of light uniformity of backlight (BL)]
A backlight unit of LCD (RS65-B2 manufactured by VISIO) was prepared.
A blue LED (blue LED) having a center wavelength of light emission at a wavelength of 445 to 455 nm is used as a light source in the backlight unit. The base on which the blue LED is arranged is a white sheet. Further, on the liquid crystal cell side, a diffuser plate, a brightness improving film (BEF manufactured by 3M), a DBEF manufactured by 3M, and a quantum dot sheet are used.
With respect to this backlight unit, the light uniformity was evaluated by adjusting the interval of the blue LEDs.
The blue LED of this backlight unit has a lens mounted on the upper part. The light distribution of the blue LED (light source) was adjusted depending on the presence or absence of the lens. The light distribution of the light source when the lens mounted on the blue LED is removed is the Lambersian distribution, and the light distribution of the light source when the lens is mounted on the blue LED is the bat wing distribution. Here, in a broad sense, the bat wing distribution means that the amount of light is large at an angle (oblique direction) in which the absolute value of the light distribution angle is larger than 0 °, where 0 ° is directly above the LED (normal direction of the backlight surface). It is defined by the emission intensity distribution. In a narrow sense, it is defined by the emission intensity distribution in which the emission intensity is strongest in the vicinity of 45 ° to 90 °. That is, in the bat wing distribution, the central portion is darker than the outer peripheral portion.
In Example 6 using the reflective sheet 8, an ESR reflective film (manufactured by 3M) was used instead of the white sheet (white plate).
The composition shown in Table 1 was evaluated using a diffuser plate prepared separately, BEF and DBEF used for LCD (RS65-B2 manufactured by VISIO), and a quantum dot sheet. Although omitted in Table 1, the evaluation was performed in a state where the quantum dot sheet, BEF, BEF, and DBEF were arranged in this order from the diffuser plate toward the liquid crystal cell. The two BEFs were used for evaluation with the ridges orthogonal to each other.
The reflective sheet 1 was used for evaluation by sticking the support side of the reflective sheet 1 to the diffusion plate with an adhesive. For the reflective sheets 2 to 8, the circularly polarized light reflective layer side of each reflective sheet was attached to the diffuser plate with an adhesive, and subsequently, the TAC film peeled off was used for evaluation.
The aspect ratio (aspect ratio = d1 / d2) was obtained from the ratio of the distance d1 of the blue LED to the distance d2 between the blue LED and the reflective sheet, and the optical uniformity of BL was evaluated from the following viewpoints.
A: Brightness unevenness is not visible in BL.
B: Luminance unevenness is visually recognized in BL.
The results are shown in the table below.

As shown in Comparative Example 1, when a dielectric multilayer film is used for the reflective sheet, the light diffusivity is low and the uniformity of the backlight (BL) is poor. Further, in Comparative Example 2 having a right circularly polarized light reflecting layer and a left circularly polarized light reflecting layer composed of a cholesteric liquid crystal layer, the light diffusivity is low because the bright and dark parts of the cross section derived from the cholesteric liquid crystal phase are not inclined. , The uniformity of the backlight is poor.
On the other hand, as compared with Comparative Example 2 and Example 1, good diffuse reflectance was obtained and a good backlight was obtained because the bright and dark parts of the cross section derived from the cholesteric liquid crystal phase were inclined. Light uniformity is obtained.
As shown in Example 2 and other examples, according to the present invention, good backlight light uniformity can be obtained regardless of whether the light distribution of the light source is Lambersian light distribution or Batwing light distribution. ..
As shown in Example 3, according to the present invention, good backlight uniformity can be obtained even if the aspect ratio is increased, that is, the number of light sources is reduced. This result also shows that if the number of light sources is the same, good backlight uniformity can be obtained even if the backlight is thin.
In Example 4 in which the reflective sheet 6 is used, since the inclination angles of the bright and dark parts of the cholesteric liquid crystal phase exceed 40 °, the luminance unevenness does not pose a problem in terms of product quality when the aspect ratio exceeds 5. Was scattered.
Further, as shown in Example 6, the reflectance can be increased by using a specular reflecting surface having a high reflectance such as an ESR reflecting sheet for the light reflecting surface on the light source side. Further, by providing the λ / 4 layer, it is possible to reduce the decrease in reflectance due to the specular reflection by the light reflecting surface and the reversal of the turning direction (sense) of the circular polarization.
From the above results, the effect of the present invention is clear.

It can be suitably used for an LCD backlight unit or the like.

10 Light emitting device 12 Housing 12a Light reflecting surface 13 Light source 14 Reflecting plate 30 Support 32 Alignment film 34 Left circular polarized light reflecting layer 36 Right circular polarized light reflecting layer 38 λ / 4 layer 40 Liquid crystal compound 40A Optical axis 60 Exposure device 62 Laser 64 Light source 65 λ / 2 plate 68 Polarized beam splitter 70A, 70B Mirror 72A, 72B λ / 4 plate BR Blue light right circular polarization _M Laser light MA, MB light P _O Linear polarization Q Absolute phase E Equal phase plane

Claims (12)

It has a structure in which a plurality of cholesteric liquid crystal layers having a fixed cholesteric liquid crystal phase are laminated.
In the cholesteric liquid crystal layer, in the cross section of the cholesteric liquid crystal layer observed by a scanning electron microscope, bright and dark parts derived from the cholesteric liquid crystal phase are inclined with respect to the main surface of the cholesteric liquid crystal layer. moreover,
It has at least one set of two layers of the cholesteric liquid crystal layers in which the wavelength regions that are selectively reflected overlap and the turning directions of the reflected circularly polarized light are different from each other.
At least one layer of the cholesteric liquid crystal layer has two or more regions in the plane in which the inclination directions of the bright portion and the dark portion derived from the cholesteric liquid crystal phase are different from each other in a striped shape . A reflective sheet , wherein the two or more regions of the above are repeatedly formed in the arrangement direction of the stripes . The reflective sheet according to claim 1, wherein the two cholesteric liquid crystal layers constituting the combination of the cholesteric liquid crystal layers have the bright and dark portions derived from the cholesteric liquid crystal phase in opposite directions with respect to the main surface. .. It has a cholesteric liquid crystal layer in which the cholesteric liquid crystal phase is fixed.
In the cholesteric liquid crystal layer, in the cross section of the cholesteric liquid crystal layer observed by a scanning electron microscope, bright and dark parts derived from the cholesteric liquid crystal phase are inclined with respect to the main surface of the cholesteric liquid crystal layer. moreover,
The cholesteric liquid crystal layer has two or more regions in the plane in which the bright and dark portions derived from the cholesteric liquid crystal phase have different inclination directions with respect to the main surface , and has the striped shape. A reflective sheet characterized in that the above regions are repeatedly formed in the stripe arrangement direction . The reflective sheet according to any one of claims 1 to 3 , wherein at least one of the cholesteric liquid crystal layers has a spiral pitch that changes in the thickness direction. The method according to any one of claims 1 to 4 , wherein the angle between the bright part and the dark part derived from the cholesteric liquid crystal phase in the cholesteric liquid crystal layer with respect to the main surface of the cholesteric liquid crystal layer is 3 to 40 °. Reflective sheet. The reflective sheet according to any one of claims 1 to 5 , further comprising a λ / 4 layer. The reflective sheet according to any one of claims 1 to 6 , further comprising a diffusion plate. The reflective sheet according to any one of claims 1 to 7 , further comprising a light distribution film. Any one of claims 1 to 8 , wherein the cholesteric liquid crystal layer has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane. The reflective sheet described in. A light emitting device having a base having a light reflecting surface on the surface, a plurality of light sources provided on the base, and a reflecting sheet according to any one of claims 1 to 9 . The light emitting device according to claim 10 , wherein the distance between the light sources in the plurality of light sources is five times or more the distance between the base and the reflective sheet. The light emitting device according to claim 10 or 11 , wherein the light source includes a blue light emitting diode.

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