WO2018212266A1

WO2018212266A1 - Backlight unit and liquid crystal display device

Info

Publication number: WO2018212266A1
Application number: PCT/JP2018/019052
Authority: WO
Inventors: 隆米本; 信彦一原; 浩史遠山
Original assignee: 富士フイルム株式会社
Priority date: 2017-05-19
Filing date: 2018-05-17
Publication date: 2018-11-22

Abstract

The present invention addresses the problem of providing a direct-type backlight unit, the emission spectrum thereof having been made a narrow band, and a liquid crystal display device that uses this backlight unit and has high color purity. This problem is solved with a backlight unit having: a reflection element; a wavelength-selective reflection sheet with wavelength selectivity; a plurality of light sources; and an absorption element that is positioned between the wavelength-selective reflection sheet and the reflection element, wherein the absorption element has a maximum light absorption in the wavelength range 460-520nm and/or 540-620nm, a cholesteric liquid crystal layer selectively reflects light that the absorption element absorbs, the wavelength-selective reflection sheet has a reflectance distribution within a surface, and the reflectance is in accordance with the positions of the light sources.

Description

Backlight unit and liquid crystal display device

The present invention relates to a backlight unit used in a liquid crystal display device and the like, and a liquid crystal display device using the backlight unit.

LCD (Liquid Crystal Display) has low power consumption, and its use is expanding year by year as a space-saving image display device.
In recent liquid crystal display devices, as a performance improvement, further higher dynamic range, power saving, color reproducibility improvement and the like are required. In particular, from the viewpoint of achieving both a high dynamic range and power saving, a so-called direct-type backlight configuration is preferably used.

As means for improving the color reproducibility of an LCD, Patent Document 1 discloses a display optical device having a function of selectively absorbing light of a specific wavelength, which is arranged in an optical path from the light source of the LCD to the outermost surface of the viewing portion. A filter is disclosed.
By using such an optical filter, unnecessary light emission other than the three primary colors of the backlight, for example, light in the wavelength range of 440 to 510 nm or light in the wavelength range of 570 to 605 nm described in Patent Document 1 is selectively absorbed. By doing so, the emission spectrum of the backlight can be narrowed, the color purity of the display can be improved, and the color reproduction range can be expanded.

However, a dye or the like used as an absorbing material that absorbs light in such an optical filter has a wide absorption band.
Therefore, if the optical filter is placed in the optical path from the light source of the LCD to the outermost surface of the visual recognition part, it not only absorbs light in an unnecessary wavelength range, but also absorbs light of the three primary colors necessary for color display of the LCD at the same time. End up. Therefore, when such an optical filter is used, the color reproduction range can be improved, but at the same time, the efficiency of the display is lowered.

On the other hand, in Patent Document 2, a light absorbing element that absorbs light of a specific wavelength is combined with a cholesteric liquid crystal layer that selectively reflects light of a specific wavelength to be absorbed by the light absorbing element. A method for limiting the bandwidth of light is disclosed.

JP 2002-40233 A International Publication No. 2015-098906

However, as a result of investigations, the inventors of the present invention have a configuration in which the light absorbing element and the cholesteric liquid crystal layer are used in combination. I found out that I was sacrificed.

An object of the present invention is to solve such problems of the prior art, and a backlight unit having a narrow emission spectrum, and a high color purity and color reproduction range using the backlight unit. The object is to provide a wide liquid crystal display (LCD).

As a result of intensive studies, the inventors have used both an absorption element that absorbs light with an extra wavelength and a wavelength selective reflection sheet that selectively reflects light with a specific wavelength, and in the plane of the wavelength selective reflection sheet. In order to narrow the effective reflection band of the wavelength selective reflection sheet, a portion with different reflectance is provided and the reflectance in the plane of the wavelength selective reflection sheet corresponds to the light emission position of the light source. As a result, it has been found that the decrease in display efficiency can be minimized and the color purity can be improved.

That is, this invention solves a subject with the following structures.
[1] A reflection element, a wavelength selection reflection sheet that selectively reflects light of a specific wavelength, a plurality of light sources disposed between the reflection element and the wavelength selection reflection sheet, a reflection element, and a wavelength selection reflection sheet And an absorbent element arranged between
The absorption element has a maximum absorption wavelength in the wavelength range of 460 to 520 nm, a maximum absorption wavelength in the wavelength range of 540 to 620 nm, and one of the wavelength range of 460 to 520 nm and the wavelength range of 540 to 620 nm. One of the maximum absorption wavelength and the second largest absorption wavelength on the other,
The wavelength selective reflection sheet selectively reflects light in the wavelength range that is absorbed by the absorbing element, and further has a portion with a different reflectance in the surface, and the reflectance in the surface is that of the light source. Backlight unit according to the arrangement.
[2] The backlight unit according to [1], wherein the reflectance of the wavelength selective reflection sheet is maximum on the optical axis of the light source.
[3] The backlight unit according to [1] or [2], wherein the wavelength selective reflection sheet has at least one of a transparent region and an opening.
[4] The backlight unit according to any one of [1] to [3], wherein the wavelength selective reflection sheet has portions having different reflectances in the reflection surface.
[5] The reflectance of light having the maximum absorption wavelength λ _max 1 in the wavelength range of 460 to 520 nm of the absorption element of the wavelength selective reflection sheet is R (λ _max 1), and the absorption element of the wavelength selection reflection sheet is 540 to 620 nm. R (λ _max 2) is the reflectance of light having the maximum absorption wavelength λ _max 2 in the wavelength range of Rmax 1, and R _max 1 is the reflectance of light having the maximum reflection wavelength in the wavelength range of 460 to 520 nm of the wavelength selective reflection sheet. When the reflectance of light having the maximum reflection wavelength in the wavelength range of 540 to 620 nm of the wavelength selective reflection sheet is R _max 2, the wavelength selective reflection sheet has the following formula: R _max 1 × 0.8 ≦ R The backlight unit according to any one of [1] to [4], which satisfies at least one of (λ _max 1) and R _max 2 × 0.8 ≦ R (λ _max 2).
[6] The backlight unit according to any one of [1] to [5], wherein the wavelength selective reflection sheet has a reflection layer formed by fixing a cholesteric liquid crystal phase.
[7] A liquid crystal display device comprising the backlight unit according to any one of [1] to [6].

According to the present invention, it is possible to provide a direct type backlight unit having a narrow emission spectrum and a liquid crystal display device having high color purity using the backlight unit.

FIG. 1 is a conceptual diagram showing an example of a backlight unit of the present invention. FIG. 2 is a conceptual diagram showing an example of the wavelength selective reflection sheet of the backlight unit of the present invention. FIG. 3 is a conceptual perspective view for explaining the configuration of the backlight unit shown in FIG. FIG. 4 is a conceptual diagram for explaining the operation of the cholesteric liquid crystal layer. FIG. 5 is a conceptual diagram for explaining the operation of the cholesteric liquid crystal layer. FIG. 6 is a conceptual diagram showing another example of the wavelength selective reflection sheet of the backlight unit of the present invention. FIG. 7 is a plan view conceptually showing another example of the wavelength selective reflection sheet of the backlight unit of the present invention. FIG. 8 is a conceptual diagram showing another example of the wavelength selective reflection sheet of the backlight unit of the present invention. FIG. 9 is a conceptual diagram showing another example of the backlight unit of the present invention. FIG. 10 is a conceptual diagram illustrating an example of a wavelength conversion sheet. FIG. 11 is a conceptual diagram showing another example of the backlight unit of the present invention. FIG. 12 is a conceptual diagram for explaining the embodiment.

Hereinafter, the backlight unit and the liquid crystal display device of the present invention will be described in detail on the basis of preferred embodiments shown in the accompanying drawings.

In addition, although description of the component requirements described below may be made | formed based on the typical embodiment of this invention, this invention is not limited to such an embodiment.
In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
In this specification, “(meth) acrylate” is used to mean “one or both of acrylate and methacrylate”.
In this specification, “same” includes an error range generally allowed in the technical field. In addition, in the present specification, when “all”, “any” or “entire surface” is used, it includes an error range generally allowed in the technical field in addition to the case of 100%, for example, 99% or more, The case of 95% or more, or 90% or more is included.

Although not limited thereto, in this specification, visible light is light having a wavelength range of 400 to 700 nm, and blue light is light having a wavelength range of 400 to 500 nm. The green light is light having a wavelength range of more than 500 nm and not more than 600 nm, and the red light is light having a wavelength range of more than 600 nm and not more than 700 nm.

FIG. 1 conceptually shows an example of the backlight unit of the present invention.
A backlight unit 10 shown in FIG. 1 is used as a backlight of an LCD (Liquid Crystal Display) or the like, and includes a reflection plate 12, a light source 14, an absorption sheet 15, a wavelength selection reflection sheet 16, and a diffusion plate 18. And

prism sheets

20 a and 20 b and a reflective polarizing plate 24.

The backlight unit 10 of the present invention is basically a known direct type backlight except that it has an absorption sheet 15 and a wavelength selective reflection sheet 16.
Accordingly, the diffusing plate 18, the

prism sheets

20a and 20b, the reflective polarizing plate 24, and the like are all known optical members used for the backlight unit of the LCD. In addition, the prism sheet 20a and the prism sheet 20b are arranged so that the prism ridges are orthogonal to each other, as in a known backlight unit.
In the backlight unit 10 of the present invention, optical members such as the diffuser plate 18, the

prism sheets

20a and 20b, and the reflective polarizing plate 24 are provided as necessary and are not essential constituent elements. That is, the backlight unit of the present invention may not have one or more of these optical members.
Further, the backlight unit 10 includes various known members that are provided in a known illumination device such as an LCD backlight, such as one or more of an LED substrate, wiring, and heat dissipation mechanism, in addition to the illustrated members. Also good.

[a reflector]
The reflecting plate 12 is a reflecting element in the present invention. The reflection plate 12 is for reflecting light or the like irradiated by the light source 14 and reflected by the wavelength selective reflection sheet 16 or the like to improve the utilization efficiency of the light emitted by the light source 14.
There is no restriction | limiting in the reflecting plate 12, All the well-known reflecting plates utilized for the backlight of LCD, etc. can be utilized. The main material of the reflecting surface of the reflecting plate 12 may be resin or metal. Since the energy loss at the time of reflection is small, the reflecting plate 12 is preferably formed of a resin. When the reflecting plate 12 is formed of a resin, a fine foam resin is preferably used as an example. In addition, a dielectric multilayer film may be formed on the reflecting plate 12. The reflection characteristic of the reflecting plate 12 may be specular reflection or diffuse reflection.

In the backlight unit 10, the light source 14 is preferably disposed in a housing in which one maximum surface is open and the surface facing the open surface is the reflection plate 12. In this case, it is preferable that the inner surface of the housing in which the light source 14 is disposed is a reflecting plate (light reflecting surface).

[light source]
A light source 14 is disposed on the light reflecting surface of the reflecting plate 12. In the following description, the upper direction in FIG. 1, that is, the light irradiation direction is also referred to as “upper”. Therefore, the upper surface of the reflecting plate 12 is a light reflecting surface, and the light source 14 is disposed on the upper surface of the reflecting plate 12.
The light source 14 is two-dimensionally arranged (arranged) on the upper surface of the reflector 12. An absorption sheet 15 is disposed on the light source 14, and a wavelength selective reflection sheet 16 is disposed on the absorption sheet 15. That is, the light source 14 is disposed between the reflecting plate 12 and the wavelength selective reflection sheet 16. Moreover, the structure which the reflecting plate 12 has covered between the light sources 14 arrange | positioned (arrayed) two-dimensionally is also included in this invention.

In the backlight unit 10 of the present invention, the arrangement of the light sources 14 may be the same as that of a general direct type backlight used in an LCD.
Accordingly, the arrangement of the light sources 14 may be regular or irregular, but is usually regular. Further, the arrangement density of the light sources 14 may be uniform in the surface direction of the reflection plate 12 or may vary in the arrangement density.
In addition, a surface direction is the surface direction of the largest surface, ie, main surface, of a sheet-like thing (a plate-like thing, a film-like thing).

There is no restriction | limiting in the light source 14, Various well-known light sources used for the direct type | mold backlight of LCD can be utilized. An example of the light source 14 is an LED (Light Emitting Diode).
In addition, a configuration in which a plurality of LEDs are two-dimensionally arranged as a direct light source is preferably used as the light source 14 in that local dimming can be suitably performed.

The light source 14 may be a white light source or a light source that emits light having a color such as a blue light source. As an example, the light source 14 of the illustrated backlight unit 10 is a white light source.
A blue light source or the like is usually used in a configuration in which a backlight unit described later has a wavelength conversion element. Moreover, when irradiating white light, as a light source 14, you may make it irradiate white light as a whole by arranging a blue light source, a green light source, and a red light source.

[Absorption sheet]
An absorption sheet 15 is provided on the light source 14. The absorbent sheet 15 is an absorbent element in the present invention.
The absorption sheet 15 is a light absorption sheet that absorbs light in a predetermined wavelength band. In the present invention, the absorption sheet 15 has a maximum absorption wavelength in a wavelength range of 460 to 520 nm, a maximum absorption wavelength in a wavelength range of 540 to 620 nm, and a wavelength range of 460 to 520 nm and a wavelength range of 540 to 620 nm. And having the maximum absorption wavelength in one wavelength range and having the second largest absorption wavelength in the other wavelength range.
The maximum absorption wavelength is a wavelength at which the absorbance is a maximum value, and in other words, an absorption maximum wavelength.

That is, when the absorption sheet 15 has a maximum absorption wavelength in the wavelength range of 460 to 520 nm, assuming that the maximum absorption wavelength of the absorption sheet 15 is λ _max , the absorption sheet 15 satisfies “460 nm <λ _max <520 nm”. Fulfill.
At this time, the maximum absorption wavelength of the absorption sheet 15 preferably satisfies 475 nm <λ _max <510 nm, and more preferably satisfies 480 nm <λ _max <505 nm.

Alternatively, the absorbent sheet 15, if it has a maximum absorption wavelength in the wavelength range of 540 ~ 620nm, and the maximum absorption wavelength of the absorbent sheet 15 and λ _max, the absorbent sheet 15, the "540nm <λ _max <620nm" Fulfill.
In this case, the maximum absorption wavelength of the absorbent sheet 15 preferably satisfies 570 nm <λ _max <605 nm, and more preferably satisfies 580 nm <λ _max <600 nm.

The backlight unit of the present invention, the absorbent sheet 15 to meet the maximum absorption wavelength lambda _max is the absorbent sheet 15 satisfying "460nm <λ _max <520nm" maximum absorbance wavelength lambda _max is the "540nm <λ _max <620nm" You may have both.

Alternatively, the absorption sheet 15 is a single absorption sheet 15 having a wavelength of 460 to 520 nm, for example, by a method using a plurality of absorption materials in combination and a method of laminating layers containing absorption materials having different maximum absorption wavelengths. It may have a maximum absorption wavelength in one wavelength region and a second largest absorption wavelength in the other wavelength region of the wavelength region and the wavelength region of 540 to 620 nm. Examples of the absorbing material include pigments, dyes and pigments.
In this case, a preferable wavelength range is the same as described above.

In the backlight unit 10 of the present invention, the absorbing sheet 15 can be disposed at any position as long as it is between the reflecting plate 12 and the wavelength selective reflecting sheet 16.
Therefore, for example, the absorption sheet 15 and the wavelength selective reflection sheet 16 may be provided so as to be laminated with the absorption sheet 15 on the light source 14 side. Alternatively, the absorbing sheet 15 may be provided on the upper surface of the reflecting plate 12, and the light source 14 may be provided on the absorbing sheet 15. That is, the reflection plate 12 may also serve as the absorption sheet 15.
Moreover, the structure provided so that the absorption sheet 15 may cover the whole surface direction of the backlight unit 10 is not limited. For example, the structure which provided the some absorption sheet 15 in the arbitrary positions between the reflecting plate 12 and the wavelength selection reflection sheet 16 mutually spaced apart may be sufficient.

The absorption sheet 15 preferably has an absorption region with an absorbance of 0.1 or more in an at least one wavelength region of 460 to 520 nm and 540 to 620 nm, and more preferably has an absorption region with an absorbance of 1 or more. Preferably, it has an absorption region with an absorbance of 2 or more.
Here, absorbance A = −log ₁₀ (transmittance).

It is preferable that the absorption sheet 15 has a small absorption in the vicinity of emission peaks of blue light, green light, and red light used for displaying the three primary colors of the display. Specifically, it is preferable that the maximum absorbance Ab at 440 to 455 nm, the maximum absorbance Ag at 525 to 540 nm, and the maximum absorbance Ar at 630 to 650 nm are small. The average value of the ratio of Ab, Ag, and Ar to the absorbance A at the absorption maximum wavelength of the absorbent sheet 15 is preferably 0.2 or less, more preferably 0.1 or less, and 0.05 or less. More preferably.

Such an absorption sheet 15 is obtained by introducing an absorbing material (light absorbing material, absorbing compound) that absorbs light into a composition containing a polymerizable compound, molding the sheet into a sheet shape, and curing the polymerizable compound. A method for forming a sheet containing an absorbent material, a method for forming a layer containing an absorbent material on a resin substrate by applying a coating material (coating composition) containing the absorbent material on a transparent resin substrate and drying it, etc. Can be produced by a method.

Examples of the absorbent material used for the absorbent sheet 15 (layer including the absorbent material) include phthalocyanine, cyanine, diimonium, quaterylene, dithiol Ni complex, indoaniline, azomethine complex, aminoanthraquinone, naphthalocyanine, oxonol, squalium, and croconium dye. Etc. are preferably exemplified. As a specific example, “Chemical Reviews” published in 1992, vol. 6 pp. 1971-2226, “JOEM Handbook 2 Absorption Spectra Of Dies for Lasers JOE Handbook 2” (Bunshin Publishing Co., Ltd., published in 1990), and “Infrared Absorbing Dye for Optical Discs” No. 3 ”(Fine Chemical, Vol. 23, No. 3 issued in 1999) and the like, and dyes having a maximum absorption wavelength in the above wavelength range.
As another specific example,
Diimonium dye: JP 2008-0669260 A [0072] to [0115],
Cyanine dyes: JP-A-2009-108267 [0020] to [0051],
Phthalocyanine dyes: JP-A-2013-182028 [0010] to [0019].

Absorbing materials (dyes or pigments) having a maximum absorption wavelength in the wavelength range of 460 to 520 nm and a peak of absorbance with a half width of 50 nm or less include squarylium, azomethine, cyanine, oxonol, anthraquinone Compounds such as azo-type, azo-type, and benzylidene-type are preferably used. As the azo dye, many azo dyes described in GB539970, 575691, US29556879, and “Review Review Synthetic Dye” by Sankyo Publishing by Horiguchi Hiroshi can be used.
Examples of an absorbing material having a maximum absorption wavelength in the wavelength range of 460 to 520 nm and having an absorbance peak with a half width of 50 nm or less are shown below.

Absorbing materials (dyes or pigments) having a maximum absorption wavelength in the wavelength range of 540 to 620 nm and a peak of absorbance with a half-width of 50 nm or less include cyanine-based, squarylium-based, azomethine-based, xanthene-based, oxonol And azo compounds are preferred, and cyanine and oxonol dyes are more preferred.
An example of an absorbing material having a maximum absorption wavelength in the wavelength range of 540 to 620 nm and an absorbance peak having a half-value width of 50 nm or less is shown below.

For the synthesis of cyanine dyes, reference can be made to the descriptions in JP-A-7-230671, European Patent 0778493 and US Pat. No. 5,459,265. Regarding the synthesis of azo dyes, reference can be made to the specifications of British Patent Nos. 539703, 575691 and US Pat. No. 2,956,879, as well as descriptions by Hiroshi Horiguchi, a review / synthetic dye (Sankyo Publishing, published in 1968). For the synthesis of azomethine dyes, the descriptions in JP-A Nos. 62-3250, 4-178646, and 5-323501 can be referred to. The oxonol dye can be synthesized with reference to the descriptions in JP-A-7-230671 and the specifications of European Patent 0778493 and US Pat. No. 5,459,265. For the synthesis of merocyanine dyes, reference can be made to the descriptions in US Pat. No. 2,170,806 and JP-A Nos. 55-155350 and 55-161232. Regarding the synthesis of anthraquinone dyes, the specifications of British Patent 710060 and US Pat. No. 3,575,704, JP-A-48-5425, and Hiroshi Horiguchi, Review / Synthetic dyes (Sankyo Publishing, published in 1968) See description.
As for other dyes, FM Harmer, “Heterocyclic Compounds-Cyanine Dies and Related Compounds”, John Willy, also known as F.M. Harmer, “Heterocyclic Compounds-Cyanine Compounds and Related Compounds”. And John Wiley and Sons, New York, London, 1964;
D.M. Sturmer, “Heterocyclic Compounds in Special Cyclics in Heterocyclic Chemistry, Section 14”, Section 18 of Heterocyclic Compounds-Special Topics in Heterocyclic Chemistry. 482-515, John Wiley and Sons, New York, London, 1977;
“Rodd's Chemistry of Carbon Compounds” 2nd edition, Volume 4, Part B, Chapter 15, pages 369-422, Elsevier Science Publishing, Inc. (Elsevier Science Publishing) Company Inc.), New York, 1977;
It can be synthesized with reference to the descriptions in JP-A-5-88293 and JP-A-6-313939.

As the dye, two or more kinds of pigments as described above can be used in combination. A dye having a maximum absorption wavelength in both the wavelength range of 460 to 520 nm and the wavelength range of 540 to 620 nm can also be used.
For example, when the dye is in an aggregated state as described below, the wavelength generally shifts to the longer wavelength side and the peak becomes sharp. For this reason, some dyes having the maximum absorption wavelength in the range of 460 to 520 nm include those whose aggregates have the maximum absorption wavelength in the range of 540 to 620 nm. When the absorbent material is used in a state in which an aggregate is partially formed, the maximum absorption wavelength can be obtained in both the wavelength range of 460 to 520 nm and the wavelength range of 540 to 620 nm. Examples of such dyes are shown below.

Examples of other absorbing materials include dye compounds described in JP-A No. 2000-32419, JP-A No. 2002-122729, and Japanese Patent No. 45044496. Incorporated into the invention.

The content of the dye in the layer containing the absorbent material is preferably 0.001 to 0.05% by mass, and preferably 0.001 to 0.01% by mass with respect to the total mass of the layer containing the absorbent material. Is more preferable.

-Half width-
In the absorption sheet 15 having the maximum absorption wavelength in the wavelength range of 460 to 520 nm and / or the absorption sheet 15 having the maximum absorption wavelength in the wavelength range of 540 to 620 nm, the absorption spectrum of light has blue light, green light, and In order to selectively cut the light so as not to affect the red light, it is preferably sharp.
Specifically, the half width of the absorption spectrum of the absorption sheet 15 having the maximum absorption wavelength in the wavelength range of 460 to 520 nm (the width of the wavelength range indicating the half of the absorbance at the maximum absorption wavelength) is 50 nm or less. Is preferably 5 to 40 nm, more preferably 10 to 30 nm.
The half width of the absorption spectrum of the absorbent sheet 15 having the maximum absorption wavelength in the wavelength range of 540 to 620 nm is preferably 50 nm or less, more preferably 5 to 40 nm, and even more preferably 10 to 30 nm.

As means for setting the full width at half maximum in such a range, there are means for containing a plurality of dyes and / or pigments having different maximum absorption wavelengths in the layer containing the absorbing material, and a dye aggregate in the layer containing the absorbing material. Examples of the means include.
Specifically, methine dyes (for example, cyanine, merocyanine, oxonol, pyromethene, styryl, arylidene), diphenylmethane dye, triphenylmethane dye, xanthene dye, squarylium dye, croconium dye, azine dye, acridine dye, thiazine dye And oxazine dyes and the like can be selected. These dyes are preferably used in aggregates.

The dye in an associated state forms a so-called J band and shows a sharp absorption spectrum peak. The association of dyes and the J band are described in various literatures (for example, Photographic Science and engineering Vol. 18, No. 323-335 (1974)). The maximum absorption wavelength of the dye in the J-association state moves to the longer wave side than the maximum absorption wavelength of the dye in the solution state. Therefore, whether the dye contained in the layer containing the absorbing material is in an associated state or a non-associated state can be easily determined by measuring the maximum absorption wavelength. The dye in an associated state preferably has a maximum absorption wavelength shift of 30 nm or more, more preferably 40 nm or more, and even more preferably 45 nm or more.

The dye used in the association state is preferably a methine dye, more preferably a cyanine dye or an oxonol dye. Some of these dyes can form aggregates only by dissolving in water, but in general, gelatin or a salt (barium chloride, calcium chloride, sodium chloride, etc.) is added to an aqueous solution of the dye to form an aggregate. Can be formed. As a method for forming the aggregate, a method of adding gelatin to an aqueous dye solution is particularly preferable. A plurality of dyes having different maximum absorption wavelengths can be dispersed in an aqueous solution to which gelatin is added, and then mixed to prepare a sample containing a plurality of aggregates having different maximum absorption wavelengths. Depending on the dye, each aggregate can be formed by simply dispersing a plurality of dyes in an aqueous solution to which gelatin is added.
The dye aggregate can also be formed as a solid fine particle dispersion of the dye. In order to obtain a solid fine particle dispersion, a known disperser can be used. Examples of the disperser include a ball mill, a vibrating ball mill, a planetary ball mill, a sand mill, a colloid mill, a jet mill, and a roller mill. The disperser is described in JP-A-52-92716 and International Publication No. 88/074794. A vertical or horizontal medium disperser is preferred.

-Additive-
In addition, an additive such as an infrared absorber or an ultraviolet absorber may be added to the layer containing the absorbing material, and those described in JP-A-2008-203436, [0031] can be used.

-binder-
The absorbent sheet 15 containing the absorbent material and the layer containing the absorbent material in the absorbent sheet 15 may contain a polymer binder in order to control the stability and reflection characteristics of the absorbent material.
As the polymer binder, a binder known to those skilled in the art can be used, but an aqueous binder is preferably used in order to perform the dispersion operation more easily. Examples of the aqueous binder include gelatin, polyvinyl alcohol, polyacrylamide, and polyethylene glycol.

In the absorbent sheet 15, the thickness of the layer containing the absorbent material may be set as appropriate to obtain a desired light absorption characteristic according to the target absorbance, the type of the absorbent material, and the like.

The absorbing material included in the absorbing sheet 15 may have a light emitting characteristic as long as it absorbs light in a target wavelength range. It is preferable that the emission center wavelength when the absorbing material included in the absorbing sheet 15 has a light emitting characteristic is 520 nm or more and less than 550 nm or 620 nm or more.

[Wavelength selective reflection sheet]
A wavelength selective reflection sheet 16 is provided on the absorption sheet 15.
The wavelength selective reflection sheet 16 is a sheet-like object that selectively reflects light having a specific wavelength. The wavelength selective reflection sheet 16 in the illustrated example has a cholesteric liquid crystal layer 30 as a reflective layer that selectively reflects light having a specific wavelength, and thus selectively reflects light having a specific wavelength.

In the backlight unit 10 of the present invention, the wavelength selective reflection sheet 16 preferably includes a Bragg reflection layer.
The Bragg reflection layer is a layer having a refractive index modulation in the thickness direction of the layer. In the Bragg reflection layer, when light having a component orthogonal to the refractive index modulation is incident, transmitted light and reflected light are generated at each refractive index interface, and they interfere with each other. Part is reflected. The selective reflection in the Bragg reflection layer generally follows Bragg's law, which will be described later. Therefore, the reflection wavelength can be selected by controlling the thickness of each layer in the multilayer structure.
Examples of the Bragg reflection layer include a dielectric multilayer film and a layer formed by fixing a cholesteric liquid crystal phase (cholesteric liquid crystal layer). Among these, a cholesteric liquid crystal layer is preferably used.
In the backlight unit 10 of the present invention, the wavelength selective reflection sheet 16 preferably includes at least a part of a Bragg reflection layer, more preferably a Bragg reflection layer, or a reflection whose entire surface is a Bragg reflection layer. More preferably, it has a layer.

Although there is no restriction | limiting in the thickness of a Bragg reflective layer, it is preferable that it is 100 micrometers or less, It is more preferable that it is 30 micrometers or less, It is further more preferable that it is 10 micrometers or less.
By using a Bragg reflection layer for the wavelength selective reflection sheet 16, a sufficient wavelength selective reflection effect can be achieved with a thin layer of 100 μm or less.

Specifically, the wavelength selective reflection sheet 16 selectively reflects light having a wavelength within the wavelength range absorbed by the absorption sheet 15.
More specifically, the wavelength selective reflection sheet 16 (cholesteric liquid crystal layer 30) selects light in the wavelength range of 460 to 520 nm when the absorption sheet 15 satisfies “460 nm <λ _max <520 nm”. Reflectively. As described above, “λ _max ” is the maximum absorption wavelength of the absorption sheet.
The wavelength selective reflection sheet 16 selectively reflects light in the wavelength range of 540 to 600 nm when the absorption sheet 15 satisfies “540 nm <λ _max <600 nm”.
When the backlight unit 10 has both the absorption sheet 15 satisfying “460 nm <λ _max <520 nm” and the absorption sheet 15 satisfying “540 nm <λ _max <620 nm”, the wavelength selective reflection sheet 16 is It selectively reflects both light in the wavelength range of 460 to 520 nm and light in the wavelength range of 540 to 600 nm.
Further, the wavelength selective reflection sheet 16 has the absorption sheet 15 having a maximum absorption wavelength in one of the wavelength range of 460 to 520 nm and the wavelength range of 540 to 600 nm, and second in the other wavelength range. Even when it has a large absorption wavelength, it selectively reflects both light in the wavelength range of 460 to 520 nm and light in the wavelength range of 540 to 600 nm.

In the illustrated backlight unit 10, the wavelength selective reflection sheet 16 is formed by holding a plurality of cholesteric liquid crystal layers 30 on one main surface (maximum surface) of a transparent sheet-like support 28 so as to be separated from each other. It has a configuration.
Therefore, the wavelength selective reflection sheet 16 selectively reflects light in a predetermined wavelength region at the position of the cholesteric liquid crystal layer 30, but hardly reflects light only at the support 28. Preferably, the reflectance of only the support 28 is preferably 10% or less, and more preferably 8% or less.
In the present invention, the reflectance (light reflectance) for light of a certain wavelength λ is calculated in the form of 1-t (λ) by measuring the spectral transmittance t (λ) of the wavelength selective reflection sheet 16. .
The spectral transmittance t (λ) may be measured by a known method. For example, the spectral transmittance t (λ) can be measured with an ultraviolet-visible near-infrared spectrophotometer (for example, UV-3150 manufactured by Shimadzu Corporation). When the wavelength selective reflection sheet 16 has a high haze, for example, when the haze value based on JIS K 7136 is 15 or more, t (λ) uses the total light transmittance measured by using an integrating sphere. As an example, it can be measured using an ultraviolet visible near infrared spectrophotometer (for example, V7200 manufactured by JASCO Corporation).

Further, in the illustrated wavelength selective reflection sheet 16, each cholesteric liquid crystal layer 30 is provided on the optical axis of the light source 14 as conceptually shown in FIGS. 1 and 3. The cholesteric liquid crystal layer 30 has uniform in-plane reflection characteristics. That is, the wavelength selective reflection sheet 16 has the maximum reflectance at the optical axis of the light source 14. In FIG. 3, the absorbent sheet 15 is omitted in order to clearly show the positional relationship between the light source 14 and the cholesteric liquid crystal layer 30.
As an example, as shown in FIG. 3, the cholesteric liquid crystal layer 30 has a circular planar shape and the center coincides with the optical axis of the light source 14. Alternatively, the cholesteric liquid crystal layer 30 may have any one of a triangular shape, a quadrangular shape, and a polygonal shape having a planar shape that coincides with the optical axis of the light source 14. In addition, a planar shape is a shape at the time of seeing from the direction orthogonal to the surface direction of the wavelength selection reflection sheet 16 (shape in a top view).

That is, the wavelength selective reflection sheet 16 has portions with different reflectivities in the surface, and the in-plane reflectivity depends on the arrangement of the light sources 14.
In other words, the wavelength selective reflection sheet 16 has a reflectance distribution according to the arrangement of the light sources 14 in the plane.

The backlight unit 10 of the present invention includes an absorption sheet 15 that absorbs light in a wavelength range unnecessary for light emission, and a wavelength selective reflection sheet 16 having a reflectance distribution according to the arrangement of the light source 14. A backlight unit is realized that narrows the emission spectrum of the backlight and enables image display with high color purity by expanding the color gamut using the LCD.

As is well known, in order to display a wide color gamut with high color purity in LCDs, blue light and green light with a narrow half-value width that do not have light in unnecessary wavelength ranges other than the three primary colors. It is preferable to irradiate white light by red light from the backlight. That is, it is preferable to irradiate the backlight with white light having high color purity such as blue light, green light, and red light.
However, the white light emitted by the current light unit includes light in an unnecessary wavelength range, and the light in the unnecessary wavelength range causes a decrease in color purity of display.

On the other hand, as shown in Patent Document 1, an optical filter that absorbs light in an unnecessary wavelength region is disposed in the backlight unit, thereby absorbing light in an unnecessary wavelength region and By narrowing the emission spectrum, the color purity of the display can be improved.
However, a dye used as an absorbing material in an optical filter has a wide absorption band. Therefore, the configuration using the optical filter not only absorbs light in an unnecessary wavelength range, but also absorbs light of three primary colors necessary for color display of the LCD at the same time, thereby reducing the efficiency of the display. There is.

As described in Patent Document 2, by using an optical filter (light absorbing element) and a wavelength selective reflection layer that selectively reflects light of a specific wavelength, a wavelength necessary for color display by the optical filter can be obtained. It is possible to suppress light absorption, efficiently absorb light having an unnecessary wavelength, and narrow the emission spectrum.
For example, when the wavelength of light to be absorbed by the optical filter (maximum absorption wavelength) is 600 nm, a wavelength selective reflection layer that selectively reflects light in the vicinity of 600 nm is used, and the optical filter is composed of a light source and a wavelength selective reflection layer. Place between.
In the backlight unit having this configuration, when the light irradiated from the light source and transmitted through the optical filter enters the wavelength selective reflection layer, only the light in the vicinity of 600 nm is reflected by the wavelength selective reflection layer, and the other light is To Penetrate. Accordingly, light other than light in the vicinity of 600 nm is used for irradiation, but light in the vicinity of 600 nm is reflected by the wavelength selective reflection layer, and again passes through the optical filter and is absorbed. In addition, light in the vicinity of 600 nm that has not been absorbed by the optical filter is reflected by the reflecting plate under the light source, and is again transmitted through the optical filter and absorbed.
That is, according to this configuration, light in the vicinity of 600 nm that is desired to be removed passes through the optical filter many times due to reflection by the wavelength selective reflection layer. Therefore, unnecessary light in the vicinity of 600 nm is efficiently absorbed by the optical filter, The emission spectrum of the backlight can be narrowed to improve the color purity of the display.

However, as a result of the study, the inventors of the present invention have not sufficiently narrowed the absorption band in the wavelength selective reflection layer in the configuration in which the optical filter, the light absorption element, and the wavelength selective reflection layer are used in combination. It has been found that the efficiency of the display is sacrificed when the emission spectrum is narrowed.

That is, the conventionally known wavelength selective reflection layer uses light interference in a thin film. The selective reflection due to interference is restricted by the following relational expression generally called Bragg's law.
2 ・ d ・ sinθ ＝ n ・ λ
Here, d is the thickness of the thin film, θ is the incident angle of the incident light (angle formed by the plane direction of the layer and the light beam), λ is the wavelength, and n is an integer.

In the backlight unit, the light emitted from the light source is diffused light. Therefore, the light incident on the wavelength selective reflection layer has a wide incident angle, and therefore the effective reflection wavelength range is widened.
Specifically, when light is incident on the reflection selective reflection layer at an angle, the wavelength of the light reflected by the reflection selection reflection layer is shorter on the short wavelength side according to the incident angle of the light with respect to the normal line (perpendicular line) of the reflection selection reflection layer. A so-called short wavelength shift occurs. The short wavelength shift increases as the angle between the normal line of the reflection selective reflection layer and the light incident direction increases. In the following description, “incident at a large angle” means that the angle with respect to the normal (perpendicular) of the incident surface is large.
Therefore, the wavelength selective reflection layer does not reflect the light in the desired wavelength range to be removed when light is incident obliquely at a large angle, and does not reflect the necessary light on the shorter wavelength side than the desired wavelength range. It will be reflected.
As a result, not only light to be absorbed but also necessary light is repeatedly reflected by the wavelength selective reflection layer and incident on the optical filter, and is absorbed by the optical filter. That is, in the configuration in which the conventional wavelength selective reflection layer and the optical filter are used in combination, the absorption band narrowing in the optical filter by the wavelength selective reflection layer is not sufficient, and when narrowing the emission spectrum in the backlight, Efficiency is sacrificed.

As a method of narrowing the effective reflection wavelength range, there is a method of limiting the incident angle of light to the wavelength selective reflection layer by condensing the light in the backlight unit, but the system becomes complicated and practical. Not right.

On the other hand, in the backlight unit 10 of the present invention, the wavelength selective reflection sheet 16 having the cholesteric liquid crystal layer 30 has a reflectance distribution according to the arrangement of the light sources 14. In the illustrated example, as described above, a plurality of cholesteric liquid crystal layers 30 are arranged on the optical axis of the light source 14 while being separated from each other.
Accordingly, light that is irradiated from the light source 14 and obliquely incident on the wavelength selective reflection sheet 16 at a large angle is incident on the region of only the support 28 where the cholesteric liquid crystal layer 30 is not present. Most of the light incident obliquely at an angle passes without being reflected by the wavelength selective reflection sheet 16.
As a result, according to the backlight unit 10 of the present invention, the effective reflection band of the cholesteric liquid crystal layer 30 can be narrowed, and as a result, the decrease in efficiency of the backlight unit (LCD) is minimized, The emission spectrum of the backlight can be narrowed, the color gamut of image display by LCD can be expanded, and the color purity can be improved.

In the wavelength selective reflection sheet 16, the size of the cholesteric liquid crystal layer 30 (a reflective layer that selectively reflects light of a specific wavelength) is not limited. The size referred to here is the size in the surface direction.
As the cholesteric liquid crystal layer 30 is larger, light in an unnecessary wavelength region can be reduced. On the other hand, the larger the cholesteric liquid crystal layer 30 is, the more the reflection of the light in the necessary wavelength region by the cholesteric liquid crystal layer 30 and the absorption in the absorption sheet 15 are caused by the short wavelength shift caused by the light obliquely incident on the cholesteric liquid crystal layer 30. .
Therefore, the size of the cholesteric liquid crystal layer 30 is appropriately set according to the size of the backlight unit 10, the distance between the light source 14 and the cholesteric liquid crystal layer 30, the light emission directivity of the light source 14, and the like. That's fine. In this regard, the same applies to the high reflectance region 34a of the wavelength selective reflection sheet 32 described later.

As described above, the wavelength selective reflection sheet 16 selectively reflects light in the wavelength range of 460 to 520 nm and / or light in the wavelength range of 540 to 620 nm.
Here, it is preferable that the wavelength selective reflection sheet 16 reflects the light having the maximum absorption wavelength in the absorption sheet 15 with a high reflectance. For example, when the maximum absorption wavelength in the absorption sheet 15 is 600 nm, the wavelength selective reflection sheet 16 preferably reflects light of 600 nm with a high reflectance. In particular, the wavelength selective reflection sheet 16 preferably reflects the light having the maximum absorption wavelength in the absorption sheet 15 with a reflectance of 80% or more of the reflectance of the light having the maximum reflection wavelength.

Specifically, as described above, the maximum absorption wavelength of the absorption sheet 15 is λ _max , the reflectance at the maximum reflection wavelength of the wavelength selective reflection sheet 16 is R _max , and the reflectance at the wavelength λ _max of the wavelength selective reflection sheet 16 is Let R (λ _max ).
In this case, when the absorption sheet 15 is an absorption sheet satisfying “460 nm <λ _max <520 nm” or an absorption sheet satisfying “540 nm <λ _max <620 nm”, the wavelength selective reflection sheet 16 is:
R _max × 0.8 ≦ R (λ _max )
It is preferable to have

In addition, as described above, the backlight unit 10 includes both the absorption sheet 15 satisfying “460 nm <λ _max <520 nm” and the absorption sheet 15 satisfying “540 nm <λ _max <620 nm”, and One absorption sheet 15 has a maximum absorption wavelength in one wavelength range of 460 to 520 nm and a wavelength range of 540 to 620 nm, and has the second largest absorption wavelength in the other wavelength range. There are cases.
In this case, the maximum absorption wavelength in the wavelength range of 460 to 520 nm of the absorption sheet 15 is λ _max 1, and the reflectance at the wavelength λ _max 1 of the wavelength selective reflection sheet 16 is R (λ _max 1),
The maximum absorption wavelength in the wavelength range of 540 to 620 nm of the absorption sheet 15 is λ _max 2, and the reflectance at the wavelength λ _max 2 of the wavelength selective reflection sheet 16 is R (λ _max 2),
R _max 1 represents the reflectance of light having the maximum reflection wavelength in the wavelength range of 460 to 520 nm of the wavelength selective reflection sheet 16;
Assuming that the reflectance of light having the maximum reflection wavelength in the wavelength range of 540 to 620 nm of the wavelength selective reflection sheet 16 is R _max 2,
R _max 1 × 0.8 ≦ R (λ _max 1) and R _max 2 × 0.8 ≦ R (λ _max 2)
It is preferable to satisfy at least one of these, and it is more preferable to satisfy both.
That is, when the absorbing sheet 15 is an absorbing sheet satisfying “460 nm <λ _max <520 nm” or an absorbing sheet satisfying “540 nm <λ _max <620 nm” as described above, It is preferable to satisfy the corresponding wavelength range equation.

As described above, the wavelength selective reflection sheet 16 has a configuration in which the cholesteric liquid crystal layer 30 is provided on the support 28 as shown in FIGS.

<Support>
The support 28 of the wavelength selective reflection sheet 16 supports the cholesteric liquid crystal layer 30.

The support 28 may be a single layer or a multilayer. Examples of the support 28 in the case of a single layer include a support made of glass, triacetyl cellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic, polyolefin, and the like. As an example of the support 28 in the case of a multilayer, a substrate including any one of the above-mentioned single-layer supports as a substrate and another layer provided on the surface of the substrate can be cited.

Further, the thickness of the support 28 is not limited, and a thickness that has sufficient transparency and can support the cholesteric liquid crystal layer 30 may be appropriately set according to the forming material and the like. Specifically, the thickness of the support 28 is preferably 10 to 300 μm, more preferably 12 to 100 μm, and even more preferably 12 to 50 μm.
The support 28 is preferably transparent. Specifically, the support 28 preferably has a total light transmittance of 90% or more as measured in accordance with JIS K 7361.

The support 28 may have an opening (through hole) in a portion where the cholesteric liquid crystal layer 30 is not provided. Regarding this point, the same applies to a portion having a low reflectance in a configuration in which the cholesteric liquid crystal layer 34 has a portion having a different reflectance in the plane, which will be described later.

A base layer may be provided between the support 28 and the cholesteric liquid crystal layer 30. The underlayer is preferably a resin layer, and more preferably a transparent resin layer. Examples of the underlayer include an alignment film for adjusting the alignment of the liquid crystal compound when forming the cholesteric liquid crystal layer 30, and a layer for improving the adhesion characteristics between the support 28 and the cholesteric liquid crystal layer 30. Is mentioned.

<Cholesteric liquid crystal layer>
The cholesteric liquid crystal layer 30 (cholesteric liquid crystal layer 34 described later) is a layer formed by fixing a cholesteric liquid crystal phase. That is, the cholesteric liquid crystal layer 30 is a layer made of a liquid crystal material having a cholesteric structure.
As described above, the cholesteric liquid crystal layer 30 has wavelength selective reflectivity for reflection, and selectively selects at least one of light in the wavelength range of 460 to 520 nm and light in the wavelength range of 540 to 620 nm. reflect.
The following description of the cholesteric liquid crystal layer 30 is the same for the cholesteric liquid crystal layer 34 shown in FIG.

As is well known, the cholesteric liquid crystal phase has wavelength selectivity in reflection, and reflects either left circularly polarized light or right circularly polarized light. That is, as an example, if the cholesteric liquid crystal phase reflects left circularly polarized light having a selective reflection center wavelength in blue light, the cholesteric liquid crystal layer formed by fixing the cholesteric liquid crystal phase has blue left circularly polarized light. Only a part is reflected and the other light is transmitted.

<< Cholesteric liquid crystal phase >>
It is known that the cholesteric liquid crystal phase exhibits selective reflectivity at a specific wavelength. The central wavelength λ of selective reflection depends on the pitch P (= spiral period) of the helical structure in the cholesteric liquid crystal phase, and follows the relationship between the average refractive index n of the cholesteric liquid crystal phase and λ = n × P. Therefore, the selective reflection wavelength (selective reflection center wavelength) of the cholesteric liquid crystal layer can be adjusted by adjusting the pitch of the spiral structure. Since the pitch of the cholesteric liquid crystal phase depends on the kind of chiral agent used together with the polymerizable liquid crystal compound or the concentration of the chiral agent when forming the cholesteric liquid crystal layer, a desired pitch can be obtained by adjusting these.
Regarding the pitch adjustment, Fujifilm Research Report No. 50 (2005) p. There is a detailed description in 60-63. For the measurement of spiral sense and pitch, it is possible to use the method described in “Introduction to Liquid Crystal Chemistry Experiments”, edited by the Japanese Liquid Crystal Society, Sigma Publishing 2007, page 46, and “Liquid Crystal Handbook”, Liquid Crystal Handbook Editorial Committee Maruzen 196 pages. it can.

The cholesteric liquid crystal phase gives a stripe pattern of a bright part and a dark part in a cross-sectional view of the cholesteric liquid crystal layer 30 observed by a scanning electron microscope (SEM (Scanning Electron Microscope)). The two bright parts and the dark part 2 in the repetition of the bright part and the dark part correspond to one pitch of the spiral. From this, the pitch can be measured from the SEM sectional view. In the cholesteric liquid crystal layer 30, the normal line of each line of the striped pattern is the spiral axis direction of the cholesteric liquid crystal phase.

The reflected light of the cholesteric liquid crystal phase is right circularly polarized light or left circularly polarized light. That is, the cholesteric liquid crystal layer 30 reflects either right-handed circularly polarized light or left-handed circularly polarized light. Whether the reflected light is right-handed circularly polarized light or left-handed circularly polarized light depends on the twist direction 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 twist direction of the spiral of the cholesteric liquid crystal phase is right, and reflects left circularly polarized light when the twist direction of the spiral is left.
The direction of rotation of the cholesteric liquid crystal phase can be adjusted by the type of liquid crystal compound forming the cholesteric liquid crystal layer 30 or the type of chiral agent added.

Further, the half width Δλ (nm) of the selective reflection band (circular polarization reflection band) indicating selective reflection depends on Δn of the cholesteric liquid crystal phase and the pitch P of the helix, and follows the relationship of Δλ = Δn × P. Therefore, the width of the selective reflection band can be controlled by adjusting Δn. Δn can be adjusted by the type and mixing ratio of the liquid crystal compound forming the cholesteric liquid crystal layer 30 and the temperature at which the orientation is fixed. The half-value width of the reflection wavelength region is adjusted according to the use of the wavelength selective reflection sheet 16, and may be, for example, 10 to 500 nm.
The half-value width of the reflection wavelength region is preferably narrow. The full width at half maximum of the reflection wavelength region is preferably 10 to 80 nm, more preferably 10 to 50 nm, and still more preferably 10 to 30 nm.
In order to reduce the half-value width of the reflection wavelength region without changing the central wavelength λ of selective reflection, Δn of the cholesteric liquid crystal phase may be reduced and the pitch P of the spiral structure may be increased.
Δn of the cholesteric liquid crystal phase is preferably 0.15 or less, more preferably 0.12 or less, further preferably 0.1 or less, and particularly preferably 0.09 or less.

<< Method for Producing Cholesteric Liquid Crystal Layer >>
The cholesteric liquid crystal layer 30 can be obtained by fixing a cholesteric liquid crystal phase.
The structure in which the cholesteric liquid crystal phase is fixed may be a structure in which the alignment of the liquid crystal compound that is the cholesteric liquid crystal phase is maintained. Typically, the polymerizable liquid crystal compound is in an alignment state of the cholesteric liquid crystal phase. Thus, any structure may be used as long as it is polymerized and cured by ultraviolet irradiation and heating to form a layer having no fluidity, and at the same time, the orientation state 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 may not exhibit liquid crystallinity. For example, the polymerizable liquid crystal compound may have a high molecular weight by a curing reaction and lose liquid crystallinity.

As an example of the material used for forming the cholesteric liquid crystal layer 30 formed by fixing the cholesteric liquid crystal phase, a liquid crystal composition containing a liquid crystal compound can be given. The liquid crystal compound is preferably a polymerizable liquid crystal compound.
The liquid crystal composition containing a liquid crystal compound used for forming the cholesteric liquid crystal layer 30 preferably further contains a surfactant. The liquid crystal composition used for forming the cholesteric liquid crystal layer may further contain a chiral agent and a polymerization initiator.

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

The polymerizable liquid crystal compound can be 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, preferably an unsaturated polymerizable group, and more preferably an ethylenically unsaturated polymerizable group. The polymerizable group can be introduced into the molecule of the liquid crystal compound by various methods.
The number of polymerizable groups possessed by the polymerizable liquid crystal compound is preferably 1 to 6, more preferably 1 to 3.
Examples of polymerizable liquid crystal compounds are described in Makromol. Chem. 190, 2255 (1989), Advanced Materials 5, 107 (1993), US Pat. Nos. 4,683,327, 5,622,648, and 5,770,107, International Publication No. 95/22586. No. 95/24455, No. 97/00600, No. 98/23580, No. 98/52905, JP-A-1-272551, JP-A-6-16616, and JP-A-7-110469. 11-80081 and JP-A 2001-328773, and the like. 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 alignment temperature can be lowered.

Specific examples of the polymerizable liquid crystal compound include compounds represented by the following formulas (1) to (11).

[In the compound (11), X ¹ is 2 to 5 (integer)]

Further, as polymerizable liquid crystal compounds other than the above, cyclic organopolysiloxane compounds having a cholesteric liquid crystal phase as disclosed in JP-A-57-165480 can be used. Further, the above-mentioned polymer liquid crystal compound includes a polymer in which a mesogenic group exhibiting liquid crystal is introduced into the main chain, a side chain, or both positions of the main chain and the side chain, and a polymer cholesteric in which a cholesteryl group is introduced into the side chain. Liquid crystal, a liquid crystalline polymer as disclosed in JP-A-9-133810, a liquid crystalline polymer as disclosed in JP-A-11-293252, and the like can be used.

The addition amount of the polymerizable liquid crystal compound in the liquid crystal composition is preferably 75 to 99.9% by mass, and 80 to 99% by mass with respect to the solid content mass (mass excluding the solvent) of the liquid crystal composition. More preferred is 85 to 90% by mass.

--Surfactant--
The liquid crystal composition used when forming the cholesteric liquid crystal layer 30 may contain a surfactant.
The surfactant is preferably a compound that can function as an alignment control agent that contributes to stably or rapidly producing a planar alignment 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 compounds described in paragraphs [0082] to [0090] of JP-A No. 2014-119605, and compounds described in paragraphs [0031] to [0034] of JP-A No. 2012-203237. , Compounds exemplified in paragraphs [0092] and [0093] of JP-A-2005-99248, paragraphs [0076] to [0078] and paragraphs [0082] to [0085] of JP-A 2002-129162 And the compounds exemplified therein, and fluorine (meth) acrylate polymers described in paragraphs [0018] to [0043] of JP-A-2007-272185, and the like.
In addition, surfactant may be used individually by 1 type and may use 2 or more types together.
As the fluorine-based surfactant, compounds described in paragraphs [0082] to [0090] of JP-A No. 2014-119605 are preferable.

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

--Chiral agent (optically active compound)-
The chiral agent has a function of inducing a helical structure of a cholesteric liquid crystal phase. The chiral agent may be selected according to the purpose because the twist direction or the spiral pitch of the spiral induced by the compound is different.
The chiral agent is not particularly limited, and is a known compound (for example, liquid crystal device handbook, chapter 3-4-3, chiral agent for TN (Twisted Nematic), STN (Super Twisted Nematic), 199 pages, Japan Science Foundation) 142th Committee, edited by 1989), isosorbide, isomannide derivatives, and the like can be used.
A chiral agent generally contains an asymmetric carbon atom, but an axially asymmetric compound and a planar asymmetric compound that do not contain an asymmetric carbon atom can also be used as the chiral agent. Examples of the axial asymmetric compound and the planar asymmetric compound 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, they are derived from the repeating unit derived from the polymerizable liquid crystal compound and the chiral agent by a polymerization reaction between the polymerizable chiral agent and the polymerizable liquid crystal compound. A polymer having repeating units can be formed. In this embodiment, the polymerizable group possessed by the polymerizable chiral agent is preferably the same group as the polymerizable group possessed by the polymerizable liquid crystal compound. Accordingly, the polymerizable group of the chiral agent is also preferably an unsaturated polymerizable group, an epoxy group or an aziridinyl group, more preferably an unsaturated polymerizable group, and an ethylenically unsaturated polymerizable group. Further preferred.
The chiral agent may be a liquid crystal compound.

It is preferable that the chiral agent has a photoisomerizable group because a pattern having a desired reflection wavelength corresponding to the emission wavelength can be formed by photomask irradiation such as actinic rays after coating and orientation. As the photoisomerization group, an isomerization site, an azo group, an azoxy group, and a cinnamoyl group of a compound exhibiting photochromic properties are preferable. Specific examples of the compound include JP2002-80478, JP200280851, JP2002-179668, JP2002-179669, JP2002-179670, and JP2002. Compounds described in JP-A No. 179681, JP-A No. 2002-179682, JP-A No. 2002-338575, JP-A No. 2002-338668, JP-A No. 2003-313189, JP-A No. 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 amount of the polymerizable liquid crystal compound.

--Polymerization 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 advanced by ultraviolet irradiation, the polymerization initiator to be used is preferably a photopolymerization initiator that can start the polymerization reaction by ultraviolet irradiation. Examples of photopolymerization initiators include α-carbonyl compounds (described in US Pat. Nos. 2,367,661 and 2,367,670), acyloin ether (described in US Pat. No. 2,448,828), α-hydrocarbon substituted aromatics. Group acyloin compounds (described in US Pat. No. 2,722,512), polynuclear quinone compounds (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of triarylimidazole dimer and p-aminophenyl ketone (US patent) No. 3549367), acridine and phenazine compounds (JP-A-60-105667, US Pat. No. 4,239,850), oxadiazole compounds (US Pat. No. 4,221,970) and the like Can be mentioned.
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 with respect to the content of the polymerizable liquid crystal compound. .

-Crosslinking agent-
The liquid crystal composition may optionally contain a crosslinking agent in order to improve the film strength after curing and improve the durability. As the cross-linking agent, one that can be cured by ultraviolet rays, heat, moisture, or the like can be suitably used.
There is no restriction | limiting in particular as a crosslinking agent, According to the objective, it can select suitably, For example, polyfunctional acrylate compounds, such as a trimethylol propane tri (meth) acrylate and pentaerythritol tri (meth) acrylate; Glycidyl (meth) acrylate , Epoxy compounds such as ethylene glycol diglycidyl ether; aziridine compounds such as 2,2-bishydroxymethylbutanol-tris [3- (1-aziridinyl) propionate], 4,4-bis (ethyleneiminocarbonylamino) diphenylmethane; hexa Isocyanate compounds such as methylene diisocyanate and biuret type isocyanate; polyoxazoline compounds having an oxazoline group in the side chain; vinyltrimethoxysilane, N- (2-aminoethyl) 3-aminopropylto Alkoxysilane compounds such as methoxy silane. Moreover, a well-known catalyst can be used according to the reactivity of a crosslinking agent, and productivity can be improved in addition to membrane strength and durability improvement. These may be used individually by 1 type and may use 2 or more types together.
The content of the crosslinking agent is preferably 3 to 20% by mass and more preferably 5 to 15% by mass with respect to the solid content mass of the liquid crystal composition. If content of a crosslinking agent is in the said range, the effect of a crosslinking density improvement will be easy to be acquired, and stability of a cholesteric liquid crystal phase will improve more.

-Other additives-
In the liquid crystal composition, if necessary, a polymerization inhibitor, an antioxidant, an ultraviolet absorber, a light stabilizer, a coloring material, and metal oxide fine particles, etc., do not deteriorate the optical performance or the like. It can be added in a range.

When the cholesteric liquid crystal layer 30 is formed, the liquid crystal composition is preferably used as a liquid.
The liquid crystal composition may contain a solvent. There is no restriction | limiting in particular as a solvent, Although it can select suitably according to the objective, An organic solvent is used preferably.
There is no restriction | limiting in particular as an organic solvent, According to the objective, it can select suitably. Examples of the organic agent include ketones such as methyl ethyl ketone and methyl isobutyl ketone, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. These may be used individually by 1 type and may use 2 or more types together. Among these, ketones are preferable in consideration of environmental load. The above-described components such as the above-described monofunctional polymerizable monomer may function as a solvent.

When the cholesteric liquid crystal layer 30 is formed, a liquid crystal composition is applied to the surface on which the cholesteric liquid crystal layer is formed, the liquid crystal compound is aligned in a cholesteric liquid crystal phase, the liquid crystal compound is cured, and the cholesteric liquid crystal layer 30 is formed. And
That is, when the cholesteric liquid crystal layer 30 is formed on the support 28, the liquid crystal composition is applied to the support 28, the liquid crystal compound is aligned in a cholesteric liquid crystal phase, the liquid crystal compound is cured, and the cholesteric liquid crystal layer 30 is then cured. A cholesteric liquid crystal layer 30 formed by fixing the liquid crystal phase is formed.
For the application of the liquid crystal composition, a printing method such as ink jet and scroll printing, and a known method that can uniformly apply a liquid to a sheet-like material such as spin coating, bar coating, and spray coating can be used.

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

The aligned liquid crystal compound is further polymerized as necessary. The polymerization may be either thermal polymerization or photopolymerization by light irradiation, but photopolymerization is preferred. It is preferable to use ultraviolet rays for light irradiation. The irradiation energy is preferably 20 to 50 J / cm ^{2 and} more preferably 100 to 1500 mJ / cm ² . In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions or in a nitrogen atmosphere. The irradiation ultraviolet wavelength is preferably 250 to 430 nm.

As described above, the cholesteric liquid crystal layer formed by fixing the cholesteric liquid crystal phase has a striped pattern in which bright portions and dark portions are alternately stacked in a cross-sectional view observed with an SEM.
Here, in the present invention, the cholesteric liquid crystal layer 30 preferably has a wavy structure in the bright and dark portions in the cross section. In the following description, the bright part and the dark part of the cholesteric liquid crystal layer 30 are observed by SEM observation of the cross section of the cholesteric liquid crystal layer 30.

FIG. 4 conceptually shows a cross section of a general cholesteric liquid crystal layer 30.
As shown in FIG. 4, in the cross section of the cholesteric liquid crystal layer 30 disposed on the support 28, a stripe pattern of bright portions B and dark portions D is usually observed. That is, in the cross section of the cholesteric liquid crystal layer 30 in which the cholesteric liquid crystal phase is fixed, a layered structure in which bright portions B and dark portions D are alternately stacked is observed.
As described above, the two bright portions and the two dark portions correspond to one pitch of the spiral of the cholesteric liquid crystal phase.
Generally, the stripe pattern (layered structure) of the bright part B and the dark part D is formed to be parallel to the surface of the support 28, that is, the formation surface of the cholesteric liquid crystal layer 30, as shown in FIG. In such an embodiment, the spiral axes of the liquid crystal compound in the cholesteric liquid crystal phase are aligned in a state orthogonal to the surface of the support 28, and thus the cholesteric liquid crystal layer 30 exhibits specular reflectivity. That is, when light is incident from the normal direction of the cholesteric liquid crystal layer 30 formed by fixing the cholesteric liquid crystal phase, the light is reflected in the normal direction, but the light is not easily reflected in the oblique direction, and is diffusely reflective. (See arrow in FIG. 4).

On the other hand, when the bright part B and the dark part D of the cholesteric liquid crystal layer 30 in which the cholesteric liquid crystal phase is fixed have a wavy structure (uneven structure) as conceptually shown in FIG. The liquid crystal compound has a region in which the spiral axis of the liquid crystal compound is inclined. Therefore, when light is incident on the cholesteric liquid crystal layer 30 having a wavy structure from the normal direction of the cholesteric liquid crystal layer 30, there is a region where the spiral axis of the liquid crystal compound is inclined as shown in FIG. A part of the incident light is reflected in an oblique direction (see the arrow in FIG. 7).
That is, the cholesteric liquid crystal layer 30 formed by fixing the cholesteric liquid crystal phase has a waved structure, so that the cholesteric liquid crystal layer 30 has diffuse reflectivity. Therefore, by forming the cholesteric liquid crystal layer 30 having a waved structure, the light incident on the wavelength selective reflection sheet 16 can be appropriately diffusely reflected, and the absorption efficiency of light in an unnecessary wavelength region by the absorption sheet 15 can be improved. Is preferable.

In the cholesteric liquid crystal layer 30 having a wavy structure, a plurality of peaks (tops) and valleys (bottoms) at which the inclination angle of the support 28 with respect to the formation surface of the cholesteric liquid crystal layer 30 is 0 ° in the continuous line formed by the wavy structure, Identified.
Here, the cholesteric liquid crystal layer 30 has a continuous line support 28 formed by a bright portion B or a dark portion D having a wave structure sandwiched between adjacent peaks and valleys in that good diffuse reflectance can be obtained. It is preferable to have a plurality of regions where the angle with respect to the surface, that is, the formation surface of the cholesteric liquid crystal layer 30 is 5 ° or more.

For the same reason, the cholesteric liquid crystal layer 30 preferably has an average peak-to-peak distance (wave period) of 1 to 50 μm in the wavy structure of the bright part B and the dark part D.

The cholesteric liquid crystal layer 30 having such a bright part B and dark part D having a waved structure can be formed as follows, for example.
That is, the cholesteric liquid crystal layer 30 in which a general cholesteric liquid crystal phase is fixed is formed by subjecting the support 28, that is, the surface on which the cholesteric liquid crystal layer 30 is formed, to a rubbing treatment or the like to give an alignment regulating force.
On the other hand, the cholesteric liquid crystal layer 30 in which the bright part B and the dark part D have a waved structure does not impart an alignment regulating force to the formation surface of the cholesteric liquid crystal layer 30, or a state in which a weak alignment regulating force is imparted. By doing so, it can be formed. For example, the above preferred waved structure can be obtained by applying an appropriate alignment regulating force to such an extent that the rubbing treatment is not performed on the formation surface (the support 28 or the base layer) of the cholesteric liquid crystal layer 30 or the weak rubbing treatment is performed. The cholesteric liquid crystal layer 30 can be formed.

As described above, the cholesteric liquid crystal layer 30 has wavelength selective reflectivity for reflection, and selectively selects at least one of light in the wavelength range of 460 to 520 nm and light in the wavelength range of 540 to 620 nm. reflect.

When the cholesteric liquid crystal layer 30 selectively reflects light in the wavelength range of 460 to 520 nm, as an example, the cholesteric liquid crystal layer 30 has a selective reflection center wavelength in the wavelength range of 460 to 520 nm.
When the cholesteric liquid crystal layer 30 selectively reflects light in the wavelength range of 540 to 620 nm, for example, the cholesteric liquid crystal layer 30 has a selective reflection center wavelength in the wavelength range of 540 to 620 nm.
When the cholesteric liquid crystal layer 30 is a reflective layer that selectively reflects both light in the wavelength range of 460 to 520 nm and light in the wavelength range of 540 to 600 nm, the cholesteric liquid crystal layer 30 is, for example, A cholesteric liquid crystal layer having a selective reflection center wavelength in a wavelength range of 460 to 520 nm and a cholesteric liquid crystal layer having a selective reflection center wavelength in a wavelength range of 540 to 600 nm are included.

As described above, the cholesteric liquid crystal layer 30 selectively reflects light in the wavelength range absorbed by the absorption sheet 15.
There is no particular limitation on the relationship between the selective reflection center wavelength of the cholesteric liquid crystal layer 30 and the maximum absorption wavelength (“λ _max ”) of the absorption sheet 15. However, it is preferable that the selective reflection center wavelength of the cholesteric liquid crystal layer 30 and the maximum absorption wavelength of the absorption sheet 15 are close to each other in that the emission spectrum can be narrowed more preferably.
Specifically, the difference between the selective reflection center wavelength of the cholesteric liquid crystal layer 30 and the maximum absorption wavelength of the absorbing sheet 15 is preferably ± 100 nm or less, more preferably ± 50 nm or less, further preferably ± 30 nm or less, and cholesteric liquid crystal It is particularly preferable that the selective reflection center wavelength of the layer 30 matches the maximum absorption wavelength of the absorption sheet 15.

The reflection band of the wavelength selective reflection sheet 16 is preferably narrower than the absorption band of the absorption sheet 15. Specifically, it is preferable that the half width of the reflection band of the wavelength selective reflection sheet 16 is narrower than the wavelength width in which the absorbance takes a value of 10% with respect to the maximum absorption wavelength of the absorption sheet 15.

In the illustrated wavelength selective reflection sheet 16, a cholesteric liquid crystal layer 30 is formed on a single support 28.
Here, when the cholesteric liquid crystal layer 30 has a plurality of cholesteric liquid crystal layers, the wavelength selective reflection sheet 16 may be one in which a plurality of cholesteric liquid crystal layers are formed on one support 28, or A plurality of the cholesteric liquid crystal layers 30 formed on the support 28 may be produced and adhered to form the wavelength selective reflection sheet 16.
Further, the wavelength selective reflection sheet 16 is produced by preparing a plurality of small sheets in which the cholesteric liquid crystal layer 30 is formed on the support 28, and sticking the small sheets to another transparent sheet. Thus, the wavelength selective reflection sheet 16 may be configured.

The cholesteric liquid crystal layer 30 has both a cholesteric liquid crystal layer that reflects right circularly polarized light and a cholesteric liquid crystal layer that reflects right circularly polarized light. But you can.

The film thickness of the cholesteric liquid crystal layer 30 is not particularly limited, and the film thickness that provides the required reflectance may be set as appropriate according to the selective reflection center wavelength and the like. This also applies to the cholesteric liquid crystal layer 34 described later.
For example, as described above, the selective reflection center wavelength of the cholesteric liquid crystal layer 30 is determined by the helical pitch of the cholesteric liquid crystal phase, so that the cholesteric liquid crystal layer 30 having a longer selective reflection center wavelength has a desired reflectance. The required film thickness increases. Further, the reflectance by the cholesteric liquid crystal layer 30 increases as the number of spiral pitches of the cholesteric liquid crystal phase (the number of spiral turns) increases, that is, as the film thickness of the cholesteric liquid crystal layer increases.

Hereinafter, the operation of the backlight unit 10 shown in FIG. 1 will be described to describe the backlight unit of the present invention in more detail.
In this example, as an example, the absorption sheet 15 has a maximum absorption wavelength at 600 nm, and the wavelength selective reflection sheet 16 has a cholesteric layer 30 having a selective reflection center wavelength at 600 nm.

In the backlight unit 10 shown in FIG. 1, the light emitted from the light source 14 first enters the absorption sheet 15, and light in the vicinity of 600 nm is absorbed.
The light transmitted through the absorption sheet 15 then enters the wavelength selective reflection sheet 16.
Of the light incident on the wavelength selective reflection sheet 16, the light incident on the cholesteric liquid crystal layer 30 is selectively reflected only in the vicinity of 600 nm (right circularly polarized light and / or left circularly polarized light), and other wavelength regions. Light passes through the cholesteric liquid crystal layer 30.
Of the light incident on the wavelength selective reflection sheet 16, the light incident on the region of the support 28 only is transmitted through the wavelength selective reflection sheet 16 as it is.

The light near 600 nm reflected by the cholesteric liquid crystal layer 30 enters the absorption sheet 15 again and is absorbed. The light in the vicinity of 600 nm that has passed through the absorption sheet 15 is reflected by the reflection plate 12 and is incident on the absorption sheet 15 again and absorbed. Light in the vicinity of 600 nm that has not been absorbed by the absorption sheet 15 is again reflected by the cholesteric liquid crystal layer 30 and incident on the absorption sheet 15, and is efficiently absorbed by the absorption sheet 15.

As described above, the cholesteric liquid crystal layer 30 is provided on the optical axis of the light source 14. Therefore, the light irradiated from the light source 14 and obliquely incident on the wavelength selective reflection sheet 16 at a large angle hardly enters the cholesteric liquid crystal layer 30. In other words, the cholesteric liquid crystal layer 30 properly reflects only light of a target near 600 nm without causing a short wavelength shift.
On the other hand, most of the light emitted from the light source 14 and obliquely incident on the wavelength selective reflection sheet 16 at a large angle is incident on the region of the support 28 alone, and thus is not reflected and is transmitted as it is.
That is, the backlight unit 10 of the present invention narrows the effective reflection band of the wavelength selective reflection sheet 16 because the wavelength selective reflection sheet 16 has a reflectance distribution according to the arrangement of the light sources 14 in the plane. As a result, the display efficiency can be kept to a minimum, and only the light in the unnecessary wavelength band is removed to suitably narrow the emission spectrum, widen the color gamut, and the LCD has high color purity. Display can be made.

The light transmitted through the wavelength selective reflection sheet 16 is further uniformized by the diffusion plate 18 and the

prism sheets

20a and 20b, and only polarized light in a predetermined direction is transmitted through the reflective polarizing plate 24 and irradiated from the backlight unit 10.
The light reflected by the reflective polarizing plate 24 is reflected by the wavelength selective reflection sheet 16, the reflective plate 12, and the like, and enters the reflective polarizing plate 24 again in the same manner as described above.

The wavelength selective reflection sheet 16 shown in FIGS. 1 and 2 is formed on the transparent support 28 by forming cholesteric liquid crystal layers 30 that coincide with the optical axis of the light source 14 and are separated from each other. The surface has a portion with different reflectivity, and the in-plane reflectivity has a configuration corresponding to the arrangement of the light source 14.
The present invention is not limited to this, and the wavelength selective reflection sheet has a portion with different reflectance in the plane of the wavelength selective reflection sheet by having a portion with different reflectance in the plane of the cholesteric liquid crystal layer. In addition, the in-plane reflectance may be configured according to the arrangement of the light source 14. That is, in the backlight unit of the present invention, the wavelength selective reflection sheet may have a cholesteric liquid crystal layer having a reflectance distribution according to the arrangement of the light sources 14.

That is, in the backlight unit of the present invention, the wavelength selective reflection sheet is provided with a light source in an in-plane by discretely providing a reflective layer that selectively reflects a specific wavelength, like the wavelength selective reflection sheet 16 described above. The reflectance distribution according to the arrangement of the light source may be provided, or the reflection layer having the reflectance distribution in the reflection surface may be provided so that the wavelength selection reflection sheet can be provided in accordance with the arrangement of the light sources. A reflection distribution may be provided.

An example is shown in FIGS.
The wavelength selective reflection sheet 32 shown in FIGS. 6 and 7 is obtained by forming a cholesteric liquid crystal layer 34 on the same support 28 as described above. FIG. 7 is a plan view of the cholesteric liquid crystal layer 34 as seen from a direction orthogonal to the plane direction.

The cholesteric liquid crystal layer 34 selectively reflects light in the wavelength range of 460 to 520 nm and / or light in the wavelength range of 540 to 620 nm, like the cholesteric liquid crystal layer 30 described above.
Here, the cholesteric liquid crystal layer 34 includes a high reflectance region 34a and a low reflectance region 34b having a lower reflectance than the high reflectance region 34a in other regions. The high reflectance region 34a and the low reflectance region 34b have the same selective reflection wavelength.
The high reflectivity region 34 a has a circular planar shape, and its center coincides with the optical axis of the light source 14 as in the case of the cholesteric liquid crystal layer 30 described above. Therefore, the reflectance of the wavelength selective reflection sheet 32 is also maximized on the optical axis of the light source 14.
Note that the planar shape of the high reflectance region 34 a conforms to the cholesteric liquid crystal layer 30 described above.

The wavelength selective reflection sheet 32 includes the cholesteric liquid crystal layer 34 having such a high reflectance region 34a and the low reflectance region 34b, thereby having portions having different reflectances in the plane, and the arrangement of the light source 14. It has in-plane reflectivity according to.
That is, the wavelength selective reflection sheet 32 has a cholesteric liquid crystal layer 34 composed of such a high reflectance region 34a and a low reflectance region 34b, and thus has a reflectance distribution corresponding to the arrangement of the light source 14 in the plane. .

As described above, the high reflectance region 34 a is provided with its center aligned with the optical axis of the light source 14. Therefore, the light irradiated from the light source 14 and obliquely incident on the wavelength selective reflection sheet 32 at a large angle hardly enters the high reflectance region 34a. Accordingly, the cholesteric liquid crystal layer 30 appropriately reflects only light in the target wavelength range without causing a short wavelength shift.
On the other hand, most of the light irradiated from the light source 14 and obliquely incident on the wavelength selective reflection sheet 32 at a large angle is incident on the low reflectance region 34b. Since the low reflectance region 34b has a low reflectance, a short wavelength shift occurs, and even if light in a necessary wavelength region is reflected, the amount of reflected light is small.
Accordingly, even in this configuration, the effective reflection band of the wavelength selective reflection sheet 32 can be substantially narrowed. As a result, the efficiency of the display is minimized, and only light in an unnecessary wavelength band is obtained. And the emission spectrum is preferably narrowed to broaden the color gamut and display with high color purity can be performed by the LCD.

There is no particular limitation on the difference in reflectance between the high reflectance region 34a and the low reflectance region 34b.
The high reflectivity region 34a needs a certain reflectivity in order to remove light in an unnecessary wavelength region. On the other hand, since the low reflectance region 34b is likely to cause a short wavelength shift, it is preferable that the reflectance is low.
Considering this point, the difference in reflectance between the high reflectance region 34a and the low reflectance region 34b is preferably 40% or more, more preferably 70% or more, and 90% or more. Is more preferable.

The cholesteric liquid crystal layer 34 having an in-plane reflectance distribution is not limited to a configuration having a high reflectance region 34a and a low reflectance region 34b as shown in FIGS. That is, as long as the wavelength selective reflection sheet has a reflectance distribution according to the position of the light source 14 in the plane, cholesteric liquid crystal layers having various configurations can be used.
For example, a cholesteric liquid crystal layer having a reflectance distribution in which the reflectance is maximized on the optical axis of the light source 14 in the plane direction and gradually changes as the distance from the optical axis increases in the plane direction. Is also available. At this time, the decrease in reflectance in the direction away from the optical axis may be continuous or stepwise.

The wavelength ratio distribution of the cholesteric liquid crystal layer 34 may be measured by measuring the reflectance of the cholesteric liquid crystal layer 34 two-dimensionally in the plane direction using the above-described reflectance measurement method.

<Formation of reflectance distribution in reflective layer>
When the wavelength selective reflection sheet has a reflective layer having a reflectance distribution, the reflectance distribution in the reflective layer may be formed by a known method according to the material for forming the reflective layer. As an example, a method of partially changing the number of layers of the reflective layer, a method of partially changing the thickness of the reflective layer, a method of partially changing the forming material of the reflective layer, and the like are exemplified.

As described above, when the cholesteric liquid crystal layer 34 is formed as the reflective layer, the thickness of the cholesteric liquid crystal layer 34 is set to the target reflectance as a method for forming the reflectance distribution in the plane of the cholesteric liquid crystal layer 34. A method of partially changing according to the distribution is exemplified.
As described above, the reflectivity of the cholesteric liquid crystal layer increases as the film thickness increases, that is, as the number of spiral pitches of the cholesteric liquid crystal phase increases. Therefore, the reflectance distribution can be formed in the plane of the cholesteric liquid crystal layer 34 by changing the film thickness of the cholesteric liquid crystal layer 34 in accordance with the target reflectance distribution.
When the thickness of the cholesteric liquid crystal layer 34 is partially changed, for example, a cholesteric liquid crystal layer that reflects right circularly polarized light is formed with a uniform thickness, and a cholesteric liquid crystal that reflects left circularly polarized light is formed thereon. The layer may be configured to be partially or entirely formed by changing the thickness partially as necessary.

As a method of changing the thickness of the cholesteric liquid crystal layer 34, as an example, a method of adjusting the coating thickness by applying the above-described liquid crystal composition by a printing method such as scroll printing and inkjet, and a liquid crystal composition An example is a method in which coating is performed by spray coating and the coating thickness is adjusted by the coating amount.

Further, as a method of partially changing the thickness of the cholesteric liquid crystal layer 34 in accordance with the target reflectance distribution, as shown conceptually in FIG. 8, the support 28 (formation surface of the cholesteric liquid crystal layer is formed). A method of forming a cholesteric liquid crystal layer 4 so as to cover the protrusion 28a by providing a transparent protrusion 28a on the surface 28) can also be used.
In this case, for example, a cholesteric liquid crystal layer that reflects right circularly polarized light is formed to a thickness that embeds the protrusion 28a indicated by a broken line, and a cholesteric liquid crystal layer that reflects left circularly polarized light is formed thereon. But you can.

As another method for forming the reflectance distribution in the plane of the cholesteric liquid crystal layer 34, a method for partially changing the degree of orientation of the cholesteric liquid crystal phase forming the cholesteric liquid crystal layer 34 is exemplified.
The reflectance in the cholesteric liquid crystal phase is higher as the degree of orientation of the cholesteric liquid crystal phase is higher. Therefore, a reflectance distribution can be formed in the reflecting surface of the cholesteric liquid crystal layer 34 by partially changing the degree of orientation of the cholesteric liquid crystal phase.
As a method for partially changing the degree of orientation of the cholesteric liquid crystal phase, a method for partially changing the heating temperature at the time of forming the cholesteric liquid crystal layer, a method for curing the liquid crystal compound at the time of forming the cholesteric liquid crystal layer by masking, etc. Examples thereof include a method of partially changing the irradiation amount (that is, the exposure amount) of ultraviolet rays.

Further, as another method for forming the reflectance distribution in the plane of the cholesteric liquid crystal layer 34, a single cholesteric liquid crystal layer 30 is formed by patterning cholesteric liquid crystal layers made of liquid crystal compounds having different compositions. A method is illustrated.
For example, the reflectivity of the cholesteric liquid crystal layer increases as the Δn (birefringence) of the liquid crystal compound increases. Accordingly, a plurality of types of liquid crystal compositions containing liquid crystal compounds having different Δn from each other are prepared, and each liquid crystal composition is patterned and applied to form a cholesteric liquid crystal layer. Can be formed.
Further, when the content of the chiral agent is different, the selective reflection center wavelength is changed, so that the reflectance of light having a target wavelength is changed. Accordingly, a plurality of types of liquid crystal compositions having different chiral agent contents are prepared, and each liquid crystal composition is patterned and applied to form a cholesteric liquid crystal layer. A reflectance distribution can be formed inside.

Examples of the method of patterning a plurality of liquid crystal compositions and applying them to the support 28 include methods using a printing method such as scroll printing and ink jet.

Although the above example is an example in which the wavelength selective reflection sheet 16 has a cholesteric liquid crystal layer as a reflective layer that selectively reflects a specific wavelength, the present invention is not limited to this.
For example, even in a configuration in which a dielectric multilayer film is formed on the support 28 instead of the cholesteric liquid crystal layer, in the same manner as the cholesteric liquid crystal layer, a part of light is reflected and a part of light is transmitted within a continuous reflecting surface. A luminance uniforming sheet having a reflectance distribution can be formed.

FIG. 9 conceptually shows an example of another aspect of the backlight unit of the present invention.
The backlight unit 35 shown in FIG. 9 further has a wavelength conversion sheet 36.
That is, the backlight unit of the present invention uses, for example, a light source that emits light in a predetermined wavelength region such as blue light (light including the first wavelength) as a light source, and a part of the light emitted by the light source is used. White light may be irradiated by irradiating light of a wavelength region different from light irradiated by a light source such as green light and red light after being absorbed by the wavelength conversion element.

The backlight unit 35 shown in FIG. 9 has the wavelength conversion sheet 36 and uses many of the same members as the above-described backlight unit 10 except that the light source 14B is different from the above-described light source 14. The same reference numerals are given, and the following description mainly focuses on different parts.

[light source]
The light source 14B is a light source that emits monochromatic light, and emits blue light as an example. As the light source 14B, various types similar to the light source 14 described above can be used.

[Wavelength conversion sheet]
The backlight unit 35 includes a wavelength conversion sheet 36 between the light source 14 and the wavelength selective reflection sheet 16.
The wavelength conversion sheet 36 is a known wavelength conversion sheet that receives the blue light irradiated by the light source 14B, absorbs a part thereof, converts the wavelength, and irradiates one or more kinds of light having different wavelengths.
FIG. 10 conceptually shows the configuration of the wavelength conversion sheet 36. The wavelength conversion sheet 36 includes a wavelength conversion layer 40 and a support 42 that supports the wavelength conversion layer 40 while sandwiching it.

<Wavelength conversion layer>
For example, the wavelength conversion layer 40 is a fluorescent layer in which a large number of phosphors are dispersed in a matrix such as a curable resin, and converts the wavelength of light incident on the wavelength conversion layer 40 as described above. And has a function of emitting light.
As an example, when the blue light irradiated from the light source 14B enters the wavelength conversion layer 40, the wavelength conversion layer 40 converts at least a part of the blue light into red light and green light due to the effect of the phosphor contained therein. The wavelength is converted and emitted.
The wavelength conversion function expressed by the wavelength conversion layer 40 is not limited to a configuration that converts the wavelength of blue light into red light and green light, but converts at least part of incident light into light of different wavelengths. I just need it.

<< phosphor >>
The phosphor is excited at least by incident excitation light and emits fluorescence.
The kind of the phosphor contained in the phosphor layer is not particularly limited, and various known phosphors may be appropriately selected according to the required wavelength conversion performance.
Examples of such phosphors include, for example, phosphors, aluminates and metal oxides doped with rare earth ions in addition to organic fluorescent dyes and organic fluorescent pigments, metal sulfides and metal nitrides, etc. Illustrative are phosphors doped with activating ions in a semiconducting substance, and phosphors utilizing the quantum confinement effect known as quantum dots. Among them, a quantum dot having a narrow emission spectrum width, capable of realizing a light source excellent in color reproducibility when used in a display, and excellent in light emission quantum efficiency is preferably used in the present invention.
That is, in the present invention, as the wavelength conversion layer 40, a quantum dot layer formed by dispersing quantum dots in a matrix such as a resin is preferably used. In the wavelength conversion sheet 36, as a preferred embodiment, the wavelength conversion layer 40 is a quantum dot layer.

Regarding the quantum dots, for example, paragraphs [0060] to [0066] of JP 2012-169271 A can be referred to, but are not limited to those described here. As the quantum dots, commercially available products can be used without any limitation. The emission wavelength of the quantum dots can usually be adjusted by the composition and size of the particles.

The quantum dots are preferably dispersed uniformly in the matrix, but may be dispersed with a bias in the matrix. Moreover, only 1 type may be used for a quantum dot and it may use 2 or more types together.
When using 2 or more types of quantum dots together, you may use 2 or more types of quantum dots from which the wavelength of emitted light differs.

Specifically, the known quantum dots include a quantum dot (A) having an emission center wavelength in a wavelength range of more than 600 nm and in a range of 680 nm, and a quantum dot having an emission center wavelength in a wavelength range of more than 500 nm and 600 nm. (B) There is a quantum dot (C) having an emission center wavelength in a wavelength region of 400 nm to 500 nm. The quantum dots (A) are excited by excitation light to emit red light, the quantum dots (B) emit green light, and the quantum dots (C) emit blue light.
For example, when blue light is incident as excitation light on a quantum dot layer including quantum dots (A) and (B), red light emitted from the quantum dots (A) and light emitted from the quantum dots (B) are emitted. White light can be realized by green light and blue light transmitted through the quantum dot layer. Alternatively, by making ultraviolet light enter the quantum dot layer including the quantum dots (A), (B), and (C) as excitation light, the red light emitted from the quantum dots (A) and the quantum dots (B) White light can be realized by the emitted green light and the blue light emitted by the quantum dots (C).

Further, as the quantum dots, so-called quantum rods having a rod shape and directivity and emitting polarized light, tetrapod quantum dots, or the like may be used.

<< Matrix >>
As described above, in the wavelength conversion sheet 36, the wavelength conversion layer 40 is formed by dispersing quantum dots or the like using a resin or the like as a matrix.
Here, various known matrices used for the quantum dot layer can be used as the matrix, but those obtained by curing a polymerizable composition (coating composition) containing at least two or more polymerizable compounds are preferable. . The polymerizable group of the polymerizable compound used in combination of at least two may be the same or different. Preferably, the at least two compounds have at least one common polymerizable group. It is preferable.
The kind of the polymerizable group is not particularly limited, but preferably, a (meth) acrylate group, a vinyl group, an epoxy group, an oxetanyl group, etc. are exemplified, more preferably a (meth) acrylate group, and still more preferably. Is an acrylate group.

The matrix that forms the wavelength conversion layer 40, in other words, the polymerizable composition that becomes the wavelength conversion layer 40 may contain necessary components such as a viscosity modifier and a solvent, if necessary. The polymerizable composition that becomes the wavelength conversion layer 40 is, in other words, a polymerizable composition for forming the wavelength conversion layer 40.

--Viscosity modifier--
The polymerizable composition may contain a viscosity modifier as necessary. The viscosity modifier is preferably a filler having a particle size of 5 to 300 nm. The viscosity modifier is preferably a thixotropic agent for imparting thixotropic properties. Examples of thixotropic agents include fumed silica and alumina.

--solvent--
The polymerizable composition to be the wavelength conversion layer 40 may contain a solvent as necessary. In this case, the type and amount of the solvent used are not particularly limited. For example, one or a mixture of two or more organic solvents can be used as the solvent.

-Other ingredients-
In addition, the polymerizable composition to be the wavelength conversion layer 40 may be a compound having a fluorine atom such as trifluoroethyl (meth) acrylate and pentafluoroethyl (meth) acrylate, 2, 2, 6, 6- Contains hindered amine compounds such as tetramethyl-4-piperidylbenzoate and N- (2,2,6,6-tetramethyl-4-piperidyl) dodecylsuccinimide, surfactants, silane coupling agents, etc. Also good.

In the wavelength conversion layer 40, the amount of the resin serving as a matrix may be appropriately determined according to the type of functional material included in the wavelength conversion layer 40 and the like.
In the illustrated example, since the wavelength conversion layer 40 is a quantum dot layer, the resin serving as a matrix is preferably 90 to 99.9 parts by mass, and 92 to 99 parts by mass with respect to 100 parts by mass of the total amount of the quantum dot layer. Is more preferable.

The thickness of the wavelength conversion layer 40 may be appropriately determined according to the type of the wavelength conversion layer 40 and the application of the wavelength conversion sheet 36.
In the illustrated example, since the wavelength conversion layer 40 is a quantum dot layer, the thickness of the wavelength conversion layer 40 is preferably 5 to 200 μm, and more preferably 10 to 150 μm, from the viewpoint of handleability and light emission characteristics.

<Support>
As the support 42, various film-like materials (sheet-like materials) that can support the wavelength conversion layer 40 and the polymerizable composition that becomes the wavelength conversion layer 40 can be used.
The support 42 is preferably a so-called gas barrier film in which a gas barrier layer that does not allow oxygen or the like to pass through is formed on the surface of the support substrate. That is, the support 42 covers the main surface of the wavelength conversion layer 40 and is a member for suppressing the intrusion of a substance that degrades the wavelength conversion layer 40 such as moisture and oxygen from the main surface of the wavelength conversion layer 40. It is also preferable to act.

As described above, in the backlight unit 35 shown in FIG. 9, the light source 14B emits blue light.
The blue light irradiated by the light source 14B enters the wavelength conversion sheet 36. When blue light enters the wavelength conversion sheet 36, the wavelength conversion sheet 36 absorbs part of the blue light and irradiates green light and red light. Thereby, the wavelength conversion sheet 36 emits white light in which blue light, green light, and red light are mixed.

The subsequent steps are the same as those of the backlight unit 10 described above, and the white light irradiated from the wavelength conversion sheet 36 is then absorbed by the absorption sheet 15 in the vicinity of 600 nm, for example, as described above.
The light transmitted through the absorption sheet 15 then enters the wavelength selective reflection sheet 16. As for the light incident on the cholesteric liquid crystal layer 30 of the wavelength selective reflection sheet 16, only light in the vicinity of 600 nm is selectively reflected, and light in other wavelength regions is transmitted through the cholesteric liquid crystal layer 30.
The light in the vicinity of 600 nm reflected by the wavelength selective reflection sheet 16 repeats absorption by the absorption sheet 15, reflection by the reflection plate 12, and reflection by the cholesteric liquid crystal layer 30 as before, and efficiently absorbs the light in the absorption sheet 15. Is done. Further, light that is incident on the wavelength selective reflection sheet 16 obliquely at a large angle does not enter the cholesteric liquid crystal layer 30 but enters only the support 28 of the wavelength selective reflection sheet 16, and the wavelength selective reflection sheet. 16 is transmitted.
As a result, the effective reflection band of the wavelength selective reflection sheet 16 can be narrowed, and as a result, the display efficiency can be minimized, and only the light in the unnecessary wavelength region can be removed to suitably emit light. The spectrum can be narrowed to widen the color gamut and display with high color purity can be performed by the LCD.

The light transmitted through the wavelength selective reflection sheet 16 is made uniform in luminance in the surface direction by the diffusion plate 18 and further made uniform by the

prism sheets

20 a and 20 b, and only polarized light in a predetermined direction is transmitted through the reflective polarizing plate 24. Then, the light is emitted from the backlight unit 35.
The light reflected by the reflective polarizing plate 24 is reflected by the wavelength selective reflection sheet 16, the reflective plate 12, and the like, and enters the reflective polarizing plate 24 again in the same manner as described above.

In the backlight unit of the present invention, the wavelength selective reflection sheet 16 needs to be disposed at a position where white light is incident.
Therefore, when the backlight unit of the present invention includes the wavelength conversion sheet 36, the wavelength conversion sheet 36 is disposed between the reflection plate 12 and the wavelength selection reflection sheet 16.
When the backlight unit of the present invention includes the wavelength conversion sheet 36, the absorption sheet 15 and the wavelength conversion sheet 36 are disposed between the reflection plate 12 and the wavelength selective reflection sheet 16 if the absorption sheet 15 and the wavelength conversion sheet 36 are disposed. There is no limitation on the positional relationship between the wavelength conversion sheet 15 and the wavelength conversion sheet 36. Therefore, contrary to the example shown in FIG. 9, the wavelength conversion sheet 36 may be disposed on the absorption sheet 15.

Here, the blue light emitted from the light source 14B is incident on the wavelength conversion sheet before being uniformed in the plane. That is, the intensity of the blue light incident on the wavelength conversion sheet varies depending on the position in the plane.
Therefore, in the backlight unit of the present invention in which the wavelength conversion sheet 36 is disposed on the light source 14B side with respect to the wavelength selective reflection sheet 16, the wavelength conversion sheets are separated from each other in the plane direction only in a portion where the intensity of blue light is high. Can be arranged. By partially arranging only the portion where the intensity of the blue light is high, the amount of quantum dots used can be reduced while the backlight unit emits white light. In such a configuration, it is preferable that the wavelength conversion sheet is disposed in the same cycle as the light source 14B in correspondence with the light source 14B. As an example of such a configuration, a small wavelength conversion sheet 36s can be provided corresponding to each light source 14B as in the backlight unit 54 shown in FIG.

The LCD (liquid crystal display device) of the present invention is an LCD using such a backlight unit of the present invention as a backlight.
The LCD of the present invention is the same as the known LCD having a polarizer, a thin film transistor (TFT), a liquid crystal cell, a transparent electrode, a color filter, etc., except that the backlight unit of the present invention is used. It has a configuration.
As described above, the backlight unit of the present invention can irradiate a backlight whose emission spectrum is narrowed. Therefore, the LCD of the present invention using this backlight unit is an LCD having high color purity and a wide color reproduction range.

As described above, the backlight unit and the liquid crystal display device of the present invention have been described in detail. However, the present invention is not limited to the above-described examples, and various improvements and modifications may be made without departing from the gist of the present invention. Of course it is good.

Hereinafter, the features of the present invention will be described more specifically with reference to examples. The materials, reagents, used amounts, substance amounts, ratios, processing details, processing procedures, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

<Preparation of transparent support 1>
The following components were put into a mixing tank and stirred while heating to dissolve each component to prepare a cellulose acetate solution.

(Cellulose acetate solution composition)
Cellulose acetate having an acetylation degree of 60.7 to 61.1% 100 parts by weight Triphenyl phosphate 7.8 parts by weight Biphenyl diphenyl phosphate 3.9 parts by weight Methylene chloride 336 parts by weight Methanol 29 parts by weight 1-butanol 11 parts by weight

In another mixing tank, 16 parts by mass of the following retardation increasing agent (A), 92 parts by mass of methylene chloride and 8 parts by mass of methanol were added and stirred while heating to prepare a retardation increasing agent solution. A dope was prepared by mixing 474 parts by mass of the cellulose acetate solution with 25 parts by mass of the retardation increasing agent solution and stirring sufficiently. The addition amount of the retardation increasing agent was 6 parts by mass with respect to 100 parts by mass of cellulose acetate.

Retardation increasing agent (A)

The obtained dope was cast using a band stretching machine. After the film surface temperature on the band reaches 40 ° C., the film is dried with warm air of 70 ° C. for 1 minute, and the film from the band is dried with 140 ° C. drying air for 10 minutes, and the residual solvent amount is 0.3% by mass. A triacetyl cellulose film having a thickness of 40 μm was prepared.
This film is referred to as a transparent support 1.

<Preparation of transparent support 1 with undercoat layer>
An undercoat layer coating solution having the following composition was applied to the surface of the transparent support 1 with a # 16 wire bar coater. Then, it dried at 60 degreeC for 60 second, and also at 90 degreeC for 150 second, the undercoat layer was formed, and the transparent support body 1 with an undercoat layer was produced.
(Undercoat layer coating solution)
The following modified polyvinyl alcohol 10 parts by mass Water 370 parts by mass Methanol 120 parts by mass Glutaraldehyde 0.5 parts by mass

<Preparation of coating solution 600R1 for cholesteric liquid crystal layer>
The components shown below were stirred and dissolved in a container kept at 25 ° C. to prepare a cholesteric liquid crystal layer coating solution 600R1.
Methyl ethyl ketone 145 parts by weight Mixture of the following rod-like liquid crystal compounds 100 parts by weight IRGACURE OXE01 (manufactured by BASF) 1.5 parts by weight Chiral agent A having the following structure 4.87 parts by weight Surfactant having the following structure F1 0.067 parts by weight Below Surfactant with structure F2 0.027 parts by mass

Mixture of rod-like liquid crystal compounds

Chiral agent A

Surfactant F1

Surfactant F2

The cholesteric liquid crystal layer coating liquid 600R1 is a material that forms a cholesteric liquid crystal layer that reflects right-handed circularly polarized light with a selective reflection center wavelength of 600 nm.

<Preparation of coating solution 600L1 for cholesteric liquid crystal layer>
The components shown below were stirred and dissolved in a container kept at 25 ° C. to prepare a cholesteric liquid crystal layer coating solution 600L1.
Methyl ethyl ketone 45 parts by weight Mixture of the above rod-shaped liquid crystal compounds 100 parts by weight IRGACURE OXE01 (BASF) 1.5 parts by weight Chiral agent B having the following structure 7.21 parts by weight Surfactant F1 0.067 parts by weight Surfactant F2 0 .027 parts by mass

Chiral agent B

The cholesteric liquid crystal layer coating liquid 600L1 is a material for forming a cholesteric liquid crystal layer that reflects left circularly polarized light having a selective reflection center wavelength of 600 nm.

<Preparation of Sheet 600R1>
The surface of the transparent support 1 with an undercoat layer was rubbed by rotating it with a rubbing roll in a direction parallel to the conveying direction at a clearance of 2 mm and 1000 rpm.
Next, the prepared coating liquid 600R1 for cholesteric liquid crystal layer was applied with a # 11 wire bar coater. After drying at 95 ° C. for 60 seconds, exposure was performed at 500 mJ / cm ² while heating at 130 ° C. to prepare a sheet 600R1 having a cholesteric liquid crystal layer that reflects right circularly polarized light with a selective reflection center wavelength of 600 nm.
<Production of Sheet 600L1>
The surface of the transparent support 1 with an undercoat layer was rubbed by rotating it with a rubbing roll in a direction parallel to the conveying direction at a clearance of 2 mm and 1000 rpm.
Subsequently, the prepared coating liquid 600L1 for cholesteric liquid crystal layer was applied with a wire bar coater of # 3.2. After drying at 95 ° C. for 60 seconds, exposure was performed at 500 mJ / cm ² while heating at 130 ° C. to prepare a sheet 600L1 having a cholesteric liquid crystal layer that reflects left circularly polarized light with a selective reflection center wavelength of 600 nm.

<Preparation of wavelength selective reflection sheet 1>
The produced sheets 600R1 and 600L1 were bonded with an adhesive (SK2057, manufactured by Soken Chemical Co., Ltd.) with the cholesteric layers facing each other to obtain a cholesteric liquid crystal cured layer A.
A plurality of obtained cholesteric liquid crystal cured layers A were cut into a circle having a diameter of 25 mm.
The cut-off cholesteric liquid crystal cured layer A was adhered to a transparent substrate with an adhesive (manufactured by Soken Chemical Co., Ltd., SK2057), thereby producing a wavelength selective reflection sheet 1 in which a cholesteric liquid crystal layer was provided on a support. The cholesteric liquid crystal cured layer A cut out in a circular shape was arranged in a lattice pattern at regular intervals so that the center is positioned on the optical axis of the direct type LED of the liquid crystal television used in the example (see FIG. 7).
When measured with an ultraviolet-visible near-infrared spectrophotometer (manufactured by Shimadzu Corporation, UV-3150), the reflectance of the produced wavelength selective reflection sheet 1 with respect to light having a wavelength of 600 nm is 75% at the maximum value in the plane, and the minimum value. 4%, and had a reflectance distribution in the plane of the wavelength selective reflection sheet 1. Moreover, the location where the reflectance in the surface of the wavelength selection reflection sheet 1 was the maximum was circular and distributed in a lattice shape (see FIG. 7).

<Preparation of Sheet 600R2>
The surface of the transparent support 1 with an undercoat layer was rubbed by rotating it with a rubbing roll in a direction parallel to the conveying direction at a clearance of 2 mm and 1000 rpm.
Next, the prepared coating liquid 600R1 for cholesteric liquid crystal layer was applied with a # 11 wire bar coater. Dry at 95 ° C. for 60 seconds.
Thereafter, the OHP sheet black ink is printed in a predetermined pattern as a mask, minimum 30 mJ / cm ^2, most 500 mJ / cm ^2, so as to irradiate, at a temperature of 25 ° C., using an ultraviolet irradiation device The cholesteric liquid crystal layer coating solution 600R1 was irradiated with ultraviolet rays.
Thereafter, the mask is removed, and while heating to 130 ° C., the UV irradiator is used to irradiate the coating liquid 600R1 for cholesteric liquid crystal layer with 500 mJ / cm ^{2 of} UV light, and the right-handed polarized light is reflected at the selective reflection center wavelength of 600 nm. A sheet 600R2 having a cholesteric liquid crystal layer was prepared.

<Preparation of Sheet 600L2>
The surface of the transparent support 1 with an undercoat layer was rubbed by rotating it with a rubbing roll in a direction parallel to the conveying direction at a clearance of 2 mm and 1000 rpm.
Subsequently, the prepared coating liquid 600L1 for cholesteric liquid crystal layer was applied with a wire bar coater of # 3.2. Dry at 95 ° C. for 60 seconds.
Thereafter, the OHP sheet black ink is printed in a predetermined pattern as a mask, minimum 30 mJ / cm ^2, most 500 mJ / cm ^2, so as to irradiate, at a temperature of 25 ° C., using an ultraviolet irradiation device The cholesteric liquid crystal layer coating solution 600R1 was irradiated with ultraviolet rays.
Thereafter, the mask is removed, and while heating to 130 ° C., the UV irradiator is used to irradiate the coating liquid 600R1 for cholesteric liquid crystal layer with 500 mJ / cm ^{2 of} UV light, and the right-handed polarized light is reflected at the selective reflection center wavelength of 600 nm. A sheet 600R2 having a cholesteric liquid crystal layer was prepared.

The pattern of black ink printed on the mask, minimum 30 mJ / cm ^2, as UV 500 mJ / cm ² at maximum is irradiated, from the most transmittance higher position, continuously transmitting concentrically The distribution of ultraviolet transmittance is provided in the plane so that the rate is low.
A region having a high transmittance, in other words, a region where the amount of ultraviolet irradiation is maximized, is provided in a grid pattern at regular intervals so that the center coincides with the optical axis of the direct type LED of the liquid crystal television used in the embodiment (FIG. 7). reference).

<Preparation of wavelength selective reflection sheet 2>
The prepared sheets 600R2 and 600L2 were bonded to each other with an adhesive (SK2057, manufactured by Soken Chemical Co., Ltd.) with the cholesteric layers facing each other to obtain the wavelength selective reflection sheet 2. Both sheets were stuck so that the circular light transmission regions of the mask overlapped.
When measured in the same manner as the wavelength selective reflection sheet 1, the reflectance of the produced wavelength selective reflection sheet 2 with respect to light having a wavelength of 600 nm is 75% at the maximum value in the plane and 4% at the minimum value, and the surface of the cholesteric liquid crystal layer. It had a reflectance distribution inside. Further, as conceptually shown in FIG. 12, the wavelength selective reflection sheet 2 is a two-dimensional distribution in which the maximum in-plane reflectivity is two-dimensionally distributed in a lattice shape, and the concentric circles from the maximum reflectivity. It had a reflectance distribution in which the reflectance continuously decreased. The portion having the highest reflectance had a distribution that coincided with the optical axis of the direct type LED of the liquid crystal television used in the examples. In FIG. 12, concentric circles are described step by step in order to show that the reflectance decreases concentrically, but in reality, the reflectance distribution is continuous as described above.

<Preparation of wavelength selective reflection sheet 3>
A cholesteric liquid crystal layer that reflects right circularly polarized light with a selective reflection center wavelength of 500 nm in the same manner as the sheet 600R01, except that the amount of the chiral agent A is 5.88 parts by mass and the wire bar coater is # 9 at the time of coating. A sheet 500R1 having the following was obtained.
Further, except that the amount of the chiral agent B is 8.86 parts by mass and the wire bar coater at the time of coating is # 2.8, the selective reflection center wavelength is 500 nm and the left circularly polarized light is reflected in the same manner as the sheet 600L1. A sheet 500L1 having a cholesteric liquid crystal layer was obtained.
Thus, the wavelength selection reflection sheet 3 was produced by sticking the sheet | seat 500R1 and 500L1 which were obtained in the same way as the wavelength selection reflection sheet 1, cutting out, and sticking to a transparent base material.
When measured in the same manner as the produced wavelength selective reflection sheet 1, the reflectance of the produced wavelength selective reflection sheet 3 with respect to light having a wavelength of 500 nm is 90% at the maximum value in the plane and 4% at the minimum value. The sheet 3 had a reflectance distribution in the plane. Moreover, the location where the reflectance in the surface of the wavelength selection reflection sheet 3 was the maximum was circular and distributed in a lattice shape (see FIG. 7).

<Production of Absorbent Sheet 1>
The dye filter was taken out from the backlight unit of a commercially available liquid crystal television (JS7000FXZA, manufactured by Samsung), and used as an absorbent sheet 1.
When measured with an ultraviolet-visible near-infrared spectrophotometer (manufactured by Shimadzu Corporation, UV-3150), the maximum absorption wavelength of the absorption sheet 1 was 583 nm.

<Production of Absorbent Sheet 2>
The following components were put into a mixing tank and stirred to dissolve each component to prepare cycloolefin resin solution 101 (dope).
(Cycloolefin resin solution 101)
Arton RX4500 100 parts by mass manufactured by JSR Co., Ltd. Dye (manufactured by Yamada Chemical Co., Ltd., FDB-007) 0.017 parts by mass Methylene chloride 430.1 parts by mass Ethanol 17.8 parts by mass

<< Casting >>
Using the band casting apparatus, the prepared cycloolefin-based resin solution 101 was cast on a stainless steel casting support (support temperature 22 ° C.). Stripped in a state where the amount of residual solvent in the cycloolefin-based resin solution 101 is approximately 20% by mass, gripped at both ends in the width direction of the film with a tenter, and in a state where the amount of residual solvent was 5-10% by mass, It dried, extending | stretching 1.10 time (10%) in the width direction under temperature.
Then, it further dried at 130 degreeC, conveying between the rolls of a heat processing apparatus, and produced the absorption sheet 2. FIG. The obtained absorbent sheet 2 had a thickness of 60 μm and a width of 1480 mm.
When measured in the same manner as the absorbent sheet 1, the maximum absorption wavelength of the produced absorbent sheet 2 was 493 nm.

<Production of Absorbent Sheet 3>
An absorbent sheet 3 was prepared in the same manner as the absorbent sheet 2 except that the dye was changed to FDG-002 (manufactured by Yamada Chemical Co., Ltd.) in the preparation of the cycloolefin-based resin solution 101.
When measured in the same manner as the absorbent sheet 1, the maximum absorption wavelength of the produced absorbent sheet was 550 nm.

[Example 1]
A commercially available liquid crystal television (Samsung, JS7000FXZA) was disassembled, and the backlight unit was taken out.
To the extracted backlight unit, a wavelength selective reflection sheet 1 (selective reflection center wavelength 600 nm) and an absorption sheet 1 (maximum absorption wavelength 583 nm), a reflector, a direct type LED, an absorption sheet 1, a wavelength selective reflection sheet 1, and The backlight unit 101 of Example 1 was obtained by additionally arranging the diffusing plates in order.
The wavelength selective reflection sheet 1 was arranged so that the position where the reflectance at 583 nm was the maximum coincided with the optical axis of all the direct LEDs.

[Example 2]
In the backlight unit 101 of Example 1, the backlight unit 102 of Example 2 was obtained by using the wavelength selective reflection sheet 2 instead of the wavelength selective reflection sheet 1.

[Example 3]
In the backlight unit 101 of Example 1, the wavelength selective reflection sheet 3 is used instead of the wavelength selective reflection sheet 1, and the absorption sheet 2 (maximum absorption wavelength 493 nm) is used instead of the absorption sheet 1. 3 backlight units 103 were obtained.

[Comparative Example 1]
By removing the wavelength selective reflection sheet 1 from the backlight unit 101 of Example 1, the backlight unit 201 of Comparative Example 1 was obtained.

[Comparative Example 2]
The backlight unit 202 of the comparative example 2 was obtained by extracting the wavelength selection reflection sheet 1 and the absorption sheet 1 from the backlight unit 101 of the example 1.

[Comparative Example 3]
In the backlight unit 101, the backlight unit 203 of the comparative example 3 was obtained by replacing the absorption sheet 1 with the absorption sheet 3 (maximum absorption wavelength 525 nm).

[Comparative Example 4]
In the backlight unit 101 of Example 1, the wavelength selective reflection sheet 1 is moved in the plane direction, and the region having the maximum reflectance is shifted from the optical axis of all the direct LEDs, thereby the backlight unit of Comparative Example 4 204 was obtained.

[Evaluation of color gamut and brightness]
An LCD was manufactured by incorporating the manufactured backlight unit into a commercially available liquid crystal television from which the backlight unit was taken out.
Red, green, and blue were displayed on the full screen of the produced LCD, and the chromaticity and luminance of each were measured using a spectroradiometer (SR-UL1R manufactured by Topcon Technohouse).
Area of the portion where the triangle formed by connecting the measured red, green and blue chromaticity points on the CIE color system u'v 'chromaticity diagram overlaps the triangle formed by connecting the three primary color points of the BT2020 standard The coverage ratio for the BT2020 standard was calculated by dividing the three primary color points of the BT2020 standard by the area of the triangle formed. The results are shown in the table below.
The headings in the table are the reflectance R (λ _max 1) of light having the maximum absorption wavelength λ _max 1 in the wavelength range of 460 to 520 nm of the absorption sheet of the wavelength selection reflection sheet, and 540 of the absorption sheet of the wavelength selection reflection sheet. The reflectance R (λ _max 2) of light having the maximum absorption wavelength λ _max 2 within the wavelength range of ˜620 nm is collectively represented as R (λ _max ),
The reflectance R _max 1 of the light with the maximum reflection wavelength in the wavelength range of 460 to 520 nm of the wavelength selective reflection sheet, and the reflectance R _max 2 of the light with the maximum reflection wavelength in the wavelength range of 540 to 620 nm of the wavelength selective reflection sheet. And _Rmax .
The three primary color points of the BT2020 standard are as follows.
Red: u ′ = 0.557, v ′ = 0.517,
Green: u ′ = 0.056, v ′ = 0.487,
Blue: u ′ = 0.159, v ′ = 0.126

From the above results, the effects of the present invention are clear.

It can be used suitably for LCD.

10, 35, 54 Backlight unit 12 Reflector 14,

14B Light source

16, 32 Wavelength selective reflection sheet 18

Diffuser plate

20a, 20b Prism sheet 24 Reflective

polarizing plate

28, 42

Support 28a Protrusion

30, 34 Cholesteric liquid crystal layer 34a High reflection Rate region 34b

Low reflectivity region

36, 36s Wavelength conversion sheet 40 Wavelength conversion layer B Dark part D Bright part

Claims

A reflection element; a wavelength selective reflection sheet that selectively reflects light of a specific wavelength; a plurality of light sources disposed between the reflection element and the wavelength selective reflection sheet; the reflection element and the wavelength selective reflection; An absorbent element arranged between the sheet and
The absorbing element has a maximum absorption wavelength in a wavelength range of 460 to 520 nm, a maximum absorption wavelength in a wavelength range of 540 to 620 nm, and one of a wavelength range of 460 to 520 nm and a wavelength range of 540 to 620 nm. Satisfying one of the following, having the maximum absorption wavelength in the
The wavelength selective reflection sheet selectively reflects light in a wavelength range absorbed by the absorbing element, and further has a portion having a different reflectance in the surface, and the reflectance in the surface is A backlight unit according to the arrangement of the light sources.
The backlight unit according to claim 1, wherein the reflectance of the wavelength selective reflection sheet is maximum on the optical axis of the light source.
The backlight unit according to claim 1 or 2, wherein the wavelength selective reflection sheet has at least one of a transparent region and an opening.
The backlight unit according to any one of claims 1 to 3, wherein the wavelength selective reflection sheet has a portion having a different reflectance in a reflection surface.
The reflectance of light having the maximum absorption wavelength λ max 1 in the wavelength range of 460 to 520 nm of the absorption element of the wavelength selective reflection sheet is R (λ max 1),
R (λ max 2) is a reflectance of light having a maximum absorption wavelength λ max 2 in the wavelength range of 540 to 620 nm of the absorption element of the wavelength selective reflection sheet,
The reflectance of light having the maximum reflection wavelength in the wavelength range of 460 to 520 nm of the wavelength selective reflection sheet is R max 1, and
When the reflectance of light having the maximum reflection wavelength in the wavelength range of 540 to 620 nm of the wavelength selective reflection sheet is R max 2, the wavelength selective reflection sheet has the following formula: R max 1 × 0.8 ≦ R (λ max 1), and, R max 2 × 0.8 ≦ R (λ max 2)
The backlight unit according to any one of claims 1 to 4, which satisfies at least one of the following.
The backlight unit according to any one of claims 1 to 5, wherein the wavelength selective reflection sheet has a reflection layer formed by fixing a cholesteric liquid crystal phase.
A liquid crystal display device comprising the backlight unit according to any one of claims 1 to 6.