JP2017068111A - Polarizing plate and liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer that can neutralize white display on a front face while saving power in a liquid crystal display, and a liquid crystal display including the polarizer.SOLUTION: There is used, as a backlight-side polarizing plate 20A of a liquid crystal display 50A, one including an absorption polarizer 4 laminated on a reflective polarizer 11, where when the transmissivity of light at a wavelength of 650 nm in the absorption polarizer 4 is T, the transmissivity of light at a wavelength of 550 nm is T, the transmissivity of light at a wavelength of 450 nm is T, and the transmissivity of light at a wavelength of 400 nm is T, the absorption polarizer 4 satisfies 1.11>T/T≥1.00, 1.11>T/T≥0.95, and 1.11>T/T≥0.65.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a polarizing plate and a liquid crystal display device including the polarizing plate.

Flat panel displays such as liquid crystal display devices (hereinafter also referred to as LCD (Liquid Crystal Display)) are often used particularly for small sizes such as tablet PCs and smartphones. In order to realize low power consumption for small and medium-sized devices, LCDs that are thin, highly durable, and capable of improving white front (neutralization) are required in the market.
The LCD has a basic configuration in which a backlight unit, a backlight side polarizing plate, a liquid crystal cell, and a viewing side polarizing plate are provided in this order. In order to save power of the LCD, it has been proposed to provide a reflective polarizer between the backlight unit and the backlight side polarizing plate. The reflective polarizer is an optical element that transmits only light oscillating in a specific polarization direction among light incident while oscillating in all directions, and reflects light oscillating in other polarization directions. This makes it possible to recycle the light that is reflected without being reflected by the reflective polarizer, thereby improving the light utilization efficiency in the LCD.

  As the reflective polarizer, Patent Document 1 discloses a film known as DBEF (registered trademark: Dual Brightness Enhancement Film) between the backlight unit and the backlight-side polarizing plate. In addition, as reflective polarizers, Patent Documents 2 to 4 describe a film having a structure in which a layer formed by fixing a λ / 4 plate and a cholesteric liquid crystal phase is laminated (sometimes referred to as a brightness enhancement film). ing.

  In a liquid crystal display device, a polarizing plate using an industrially popular iodine-based polarizer represented by Patent Document 5 is well known as a display-side and backlight-side polarizing plate.

Japanese Patent No. 3448626 JP-A-1-133003 Japanese Patent No. 3518660 WO2008 / 016056 Japanese Patent No. 3331615

  The technique described in Patent Document 1 has a problem that the manufacturing cost is high due to a complicated design considering the multi-layer structure and the wavelength dispersion of the member in order to improve the light utilization rate in a wide band for white light. In addition, in a liquid crystal display device having a reflective polarizer formed by combining a layer having a fixed cholesteric liquid crystal phase and a λ / 4 plate, there is a limit in color adjustment, and a neutral front white display can be realized. There wasn't. Although it may be realized by adjusting the color of the backlight or color filter, the power consumption may increase.

  Thus, there is a need for a member that can achieve both power saving and neutral white front display.

  The present invention has been made in view of the above circumstances, and includes a polarizing plate capable of realizing power-saving and neutral front white display when incorporated in a liquid crystal display device, and the polarizing plate. An object of the present invention is to provide a liquid crystal display device.

The polarizing plate of the present invention is a polarizing plate disposed between a liquid crystal cell and a light source in a liquid crystal display device,
A reflection polarizer and a dichroic dye-coated absorption polarizer are laminated.
The absorption polarizer has a transmittance of 650 nm light at the absorption polarizer as T ₆₅₀ , a transmittance of 550 nm light as T ₅₅₀ , a transmittance of 450 nm light as T ₄₅₀ , and a transmittance of 400 nm light as T ₄₀₀ . When
1.11> T ₆₅₀ / T ₅₅₀ ≧ 1.00
1.11> T ₄₅₀ / T ₅₅₀ ≧ 0.95
1.11> T ₄₀₀ / T ₄₅₀ ≧ 0.65
It is characterized by satisfying.

The polarizing plate of the present invention has an absorbing polarizer,
1.11> T ₄₀₀ / T ₄₅₀ ≧ 0.96
It is preferable to satisfy.

  In the polarizing plate of the present invention, the reflective polarizer includes a λ / 4 plate and a circularly polarized reflective polarizer in this order from the absorbing polarizer side, and the circularly polarized reflective polarizer includes at least one cholesteric liquid crystal phase. It is preferable to include a fixed light reflecting layer.

  In the polarizing plate of the present invention, the absorbing polarizer is particularly preferably a coating type polarizer using a thermotropic liquid crystalline dichroic dye.

The liquid crystal display device of the present invention includes a display side polarizing plate, a liquid crystal cell, a backlight side polarizing plate and a backlight unit in this order.
As the backlight side polarizing plate, using the polarizing plate of the present invention,
The chromaticity of image light in the normal direction of the screen during white display is a ^* > − 2, and b ^* <9.

  When the polarizing plate of the present invention is applied to a liquid crystal display device, since a reflective polarizer is provided, the luminance is high, and an absorption polarizer that satisfies the above conditions as a transmittance characteristic is provided. White display neutral in the screen normal direction) or white display closer to neutral than before can be realized with power saving.

It is a figure which shows typically the layer structural example 1 of the polarizing plate of this invention. It is a figure which shows typically the layer structural example 2 of the polarizing plate of this invention. It is a figure which shows typically the layer structural example 3 of the polarizing plate of this invention. It is a figure which shows typically the structural example 1 of the liquid crystal display device of this invention. It is a figure which shows typically the structural example 2 of the liquid crystal display device of this invention. It is a figure which shows typically the structural example 3 of the liquid crystal display device of this invention. It is a figure which shows typically the structural example 4 of the liquid crystal display device of this invention. It is a figure which shows typically the structural example 5 of the liquid crystal display device of this invention. It is a figure which shows typically the structural example 6 of the liquid crystal display device of this invention. It is a figure which shows typically the structural example 7 of the liquid crystal display device of this invention. It is a figure which shows the wavelength dependence of the transmittance | permeability of the absorption polarizer in the polarizing plate of an Example and a comparative example. It is a figure which shows the relationship between the chromaticity and the sensory evaluation value of the liquid crystal display device of an Example and a comparative example.

Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments. In the present specification, a numerical range represented by 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, “visible light” means 380 to 780 nm. Moreover, in this specification, when there is no special mention about a measurement wavelength, a measurement wavelength is 550 nm.

In the present specification, the “half width” of a peak means the width of the peak at a peak height of 1/2.
The reflection center wavelength and half width of the light reflection layer can be obtained as follows.
When the transmission spectrum of the light reflection layer is measured using a spectrophotometer UV3150 (Shimadzu Corporation), a peak of decrease in transmittance is observed in the selective reflection region. Of the two wavelengths having a transmittance of 1/2 the maximum peak height, the wavelength value on the short wave side is λ1 (nm), and the wavelength value on the long wave side is λ2 (nm). The reflection center wavelength and the half width can be expressed by the following formula.
Reflection center wavelength = (λ1 + λ2) / 2
Half width = (λ2−λ1)

  In this specification, the “slow axis” means a direction in which the refractive index becomes maximum in the plane.

In the present specification, Re (λ) and Rth (λ) each represent in-plane retardation and retardation in the thickness direction at a wavelength λ. Re (λ) is KOBRA 21AD
In H or WR (trade name, manufactured by Oji Scientific Instruments), light having a wavelength of λ nm is incident in the normal direction of the film.

When the film to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth (λ) is calculated by the following method.
Rth (λ) is Re (λ), with the in-plane slow axis (determined by KOBRA 21ADH or WR) as the tilt axis (rotation axis) (if there is no slow axis, it is arbitrary in the film plane) The light is incident at a wavelength of λ nm from the inclined direction in steps of 10 degrees from the normal direction to 50 degrees on one side with respect to the film normal direction of the rotation axis of It is calculated in KOBRA 21ADH or WR based on the measured retardation value, the assumed value of the average refractive index, and the input film thickness value.

In the above case, in the case of a film having a direction in which the retardation value is zero at a certain tilt angle with the in-plane slow axis from the normal direction as the rotation axis, retardation at a tilt angle larger than the tilt angle. The value is calculated in KOBRA 21ADH or WR after changing its sign to negative.
In addition, the retardation value is measured from the two inclined directions, with the slow axis as the tilt axis (rotation axis) (when there is no slow axis, the arbitrary direction in the film plane is the rotation axis), Based on the value, the assumed value of the average refractive index, and the input film thickness value, Rth can also be calculated by the following formulas (1) and (2).

  In the formula, Re (θ) represents a retardation value in a direction inclined by an angle θ from the normal direction. nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction perpendicular to nx in the plane, and nz represents the refractive index in the direction perpendicular to nx and ny. d represents the film thickness of the film.

In the case where the film to be measured cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a film having no so-called optical axis (OPTIC AXIS), Rth (λ) is calculated by the following method.
Rth (λ) is Re (λ), and the in-plane slow axis (determined by KOBRA 21ADH or WR) is the tilt axis (rotation axis) from −50 degrees to +50 degrees with respect to the film normal direction. The light of wavelength λ nm is incident from each inclined direction in 10 degree steps and measured at 11 points. Based on the measured retardation value, the assumed average refractive index, and the input film thickness value, KOBRA 21ADH or Calculated by WR.

In the above measurement, the assumed average refractive index is the polymer handbook (JOHN WI
LEY & SONS, INC), catalog values of various optical films can be used. Those whose average refractive index is not known can be measured with an Abbe refractometer. The average refractive index values of main optical films are exemplified below: cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), Polystyrene (1.59). By inputting the assumed value of the average refractive index and the film thickness, nx, ny, KO in KOBRA 21ADH or WR
nz is calculated. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

First, the polarizing plate of this invention is demonstrated.
The polarizing plate of the present invention is a polarizing plate disposed between a liquid crystal cell and a light source in a liquid crystal display device, and is formed by laminating a reflective polarizer and an absorbing polarizer, and the absorbing polarizer is absorbing polarized light. When the transmittance of light having a wavelength of 650 nm is T ₆₅₀ , the transmittance of light having a wavelength of 550 nm is T ₅₅₀ , the transmittance of light having a wavelength of 450 nm is T ₄₅₀ , and the transmittance of light having a wavelength of 400 nm is T ₄₀₀ ,
1.11> T ₆₅₀ / T ₅₅₀ ≧ 1.00
1.11> T ₄₅₀ / T ₅₅₀ ≧ 0.95
1.11> T ₄₀₀ / T ₄₅₀ ≧ 0.65
Meet.
In particular, it is preferable that 1.11> T ₄₀₀ / T ₄₅₀ ≧ 0.96.

"Configuration of polarizing plate"
FIG. 1 schematically shows a layer configuration example 1 of the polarizing plate of the present invention. Note that FIG. 1 is a schematic diagram, and the thickness relationship and positional relationship of each layer do not necessarily match the actual ones. The same applies to the following figures.
A polarizing plate 20A in FIG. 1 includes a first protective film 5a, an absorbing polarizer 4, a second protective film 5b, and a reflective polarizer 11 composed of a λ / 4 plate 12 and a circularly polarized reflective polarizer 13. Being done.

  The polarizing plate of the present invention is not limited to the embodiment of the polarizing plate 20A shown in FIG. 1, and does not include the second protective film 5b and absorbs like the polarizing plate 20B shown as the layer configuration example 2 in FIG. The polarizer 4 and the reflective polarizer 11 may be bonded and laminated via a UV adhesive 18. Further, like the polarizing plate 20C shown as the layer configuration example 3 in FIG. 3, the reflective polarizer 11 is laminated on the surface opposite to the adjacent surface of the first protective film 5a of the absorbing polarizer 4 through the alignment film 19. May be.

  The reflective polarizer in the polarizing plate of the present invention transmits only light that vibrates in a specific polarization direction among incident light that vibrates in all directions, and reflects light that vibrates in other polarization directions. Any combination of a λ / 4 plate and a circularly polarizing reflective polarizer, or a linear polarizing reflective polarizer made of a dielectric multilayer film can be used. When a reflective polarizer comprising a combination of a λ / 4 plate and a circularly polarized reflective polarizer is used, the circularly polarized reflective polarizer includes a light reflective layer formed by fixing at least one cholesteric liquid crystal phase. Is preferred. The circularly polarizing reflective polarizer may include two or more light reflecting layers formed by fixing a cholesteric liquid crystal layer.

In the polarizing plate of the present invention, the transmittance in the blue light region is equal to or higher than the transmittance in the green region, and 1.11> T ₄₅₀ / T ₅₅₀ ≧ 0.95, and the transmittance on the short wavelength side in the blue light region. In other words, 1.11> T ₄₀₀ / T ₄₅₀ ≧ 0.65, and the transmittance in the red light region is slightly higher than the transmittance in other wavelength regions. 11> T ₆₅₀ / T ₅₅₀ ≧ 1.00 Absorbing polarizer is provided. That is, the absorptive polarizer in the polarizing plate of the present invention has a transmittance characteristic in which the variation in transmittance is suppressed in a wide range from blue to red, and more red light is transmitted as compared with other colors. By constructing a liquid crystal display device as this polarizing plate as a backlight-side polarizing plate placed between the backlight unit and the liquid crystal cell, a neutral white front display can be realized compared to the conventional case. Can do. In addition, a power-saving, thin and highly durable liquid crystal display device can be realized.

  In a liquid crystal display device, when a reflective polarizer formed by laminating a layer formed by fixing a λ / 4 plate and a cholesteric liquid crystal phase is used as a reflective polarizer of a backlight side polarizing plate, the color of the resulting image is green. Such a greenish white is a color that an observer is likely to be uncomfortable. In addition, a tint change (also referred to as tint unevenness) is likely to occur when viewed from an oblique direction due to the optical characteristics of the cholesteric liquid crystal phase and the λ / 4 plate. Not only when a reflective polarizer comprising a laminate of a λ / 4 plate provided on a polarizing plate and a cholesteric liquid crystal layer is used, but when a reflective polarizer that produces a green color is used, absorption having the above transmission characteristics Since the polarizer is configured to transmit red, which is a complementary color of green, more effectively, since the color is adjusted as the entire polarizing plate.

By providing the polarizing plate of the present invention, it is possible to measure the power saving because the luminance can be improved, and as the image color in the normal direction of the screen at the time of white display of the liquid crystal display device, a ^* > − 2, b ^* Chromaticity a ^* and b ^* satisfying <9 can be realized. Moreover, it became clear that the change of a tint can also be suppressed with the polarizer of this invention (refer the postscript Example).

<Absorbing polarizer>
The absorbing polarizer is a so-called linear polarizer having a function of converting natural light into specific linearly polarized light. The absorbing polarizer is not particularly limited as long as it satisfies the above transmittance characteristics. For example, an iodine polarizing layer, a dye polarizing layer using a dichroic dye (dichroic dye), and a polyene Any of the polarizing films can be used. The iodine-based polarizing layer and the dye-based polarizing layer are generally produced by adsorbing iodine or a dichroic dye to polyvinyl alcohol and stretching, in order to satisfy the above transmittance characteristics, A dichroic dye-coated polarizing layer is suitable as the absorbing polarizer.

<< Dye-based polarizer >>
It is a particularly preferable embodiment to use a coating type polarizing layer prepared by coating using a thermotropic liquid crystalline dichroic dye as the absorbing polarizer. That is, the absorbing polarizer is preferably a layer formed from a dichroic dye composition containing at least one thermotropic liquid crystalline dichroic dye. By using this absorptive polarizer, a thin film can be realized, and the display performance of the display device can be further prevented from deteriorating even in a humid heat environment. As the dichroic dye for the coating type polarizing layer used in the present invention, a dye described in JP 2011-237513 A can be suitably used.

  Examples of the thermotropic liquid crystalline dichroic dyes are shown below, but are not limited to these compounds.

  In the dichroic dye composition, the proportion of the non-coloring liquid crystal compound is preferably 30% by mass or less, more preferably 20% by mass or less, further preferably 10% by mass or less, It is particularly preferably 5% by mass or less. Here, the non-coloring liquid crystal compound refers to a compound that does not absorb in the visible light spectral region, that is, the spectral region of 400 to 700 nm and exhibits a nematic liquid crystal phase or a smectic liquid crystal phase. Examples thereof include the liquid crystal compounds described in pages 154 to 192 and pages 715 to 722 of “Device Handbook” (edited by the 142th Committee of the Japan Society for the Promotion of Science, Nikkan Kogyo Shimbun, 1989).

  An absorbing polarizer having the above-mentioned transmission characteristics can be obtained by using one or a combination of two or more dichroic dye compositions. For example, a combination of C-21, C-22 and C-15 can be used as the dichroic dye composition. On the other hand, C-20 may be used instead of C-21 in this combination. C-22 can be replaced with C-3. Further, C-16, C-17, or C-13 may be used instead of C-15.

  The thickness of the absorbing polarizer 4 formed using the dichroic dye composition is not particularly limited, but is preferably 250 nm or more, more preferably 350 nm or more, and further preferably 450 nm or more. The upper limit is not particularly limited, but is preferably 2000 nm or less from the viewpoint of thinning.

<Protective film>
As the protective film (sometimes referred to as a polarizer protective film), a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy, and the like is used. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) acrylic resins, cyclic Examples thereof include polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof.

  Cellulose resin is an ester of cellulose and fatty acid. Specific examples of the cellulose ester resin include triacetyl cellulose, diacetyl cellulose, tripropyl cellulose, dipropyl cellulose, and the like. Among these, triacetyl cellulose is particularly preferable. Many products of triacetylcellulose are commercially available, which is advantageous in terms of availability and cost. Examples of commercially available products of triacetyl cellulose include trade names “UV-50”, “UV-80”, “SH-80”, “TD-80U”, “TD-TAC”, “ UZ-TAC "," KC series "manufactured by Konica, and the like.

  Specific examples of the cyclic polyolefin resin are preferably norbornene resins. The cyclic olefin-based resin is a general term for resins that are polymerized using a cyclic olefin as a polymerization unit, and is described in, for example, JP-A-1-240517, JP-A-3-14882, JP-A-3-122137, and the like. Resin. Specific examples include ring-opening (co) polymers of cyclic olefins, addition polymers of cyclic olefins, cyclic olefins and α-olefins such as ethylene and propylene (typically random copolymers), And the graft polymer which modified these with unsaturated carboxylic acid or its derivative (s), and those hydrides, etc. are mentioned. Specific examples of the cyclic olefin include norbornene monomers.

  Various products are commercially available as the cyclic polyolefin resin. Specific examples include the product names “ZEONEX” and “ZEONOR” manufactured by ZEON CORPORATION, the product name “ARTON” manufactured by JSR Corporation, the product name “TOPAS” manufactured by TICONA, and the product rules manufactured by Mitsui Chemicals, Inc. “APEL” may be mentioned.

  Any appropriate (meth) acrylic resin can be adopted as the (meth) acrylic resin. For example, poly (meth) acrylic acid ester such as polymethyl methacrylate, methyl methacrylate- (meth) acrylic acid copolymer, methyl methacrylate- (meth) acrylic acid ester copolymer, methyl methacrylate-acrylic acid ester- (Meth) acrylic acid copolymer, (meth) methyl acrylate-styrene copolymer (MS resin, etc.), a polymer having an alicyclic hydrocarbon group (for example, methyl methacrylate-cyclohexyl methacrylate copolymer, Methyl methacrylate- (meth) acrylate norbornyl copolymer, etc.). Preferably, poly (meth) acrylic acid C1-6 alkyl such as poly (meth) acrylate methyl is used. More preferred is a methyl methacrylate-based resin containing methyl methacrylate as a main component (50 to 100% by mass, preferably 70 to 100% by mass).

  Specific examples of (meth) acrylic resins include (meth) acrylic resins having a ring structure in the molecule described in, for example, Acrypet VH and Acrypet VRL20A manufactured by Mitsubishi Rayon Co., Ltd., and JP-A-2004-70296. And a high Tg (meth) acrylic resin system obtained by intramolecular crosslinking or intramolecular cyclization reaction.

  As the (meth) acrylic resin, a (meth) acrylic resin having a lactone ring structure can also be used. It is because it has high mechanical strength by high heat resistance, high transparency, and biaxial stretching.

  Although the thickness of a protective film can be set suitably, generally it is about 1-80 micrometers from points, such as workability, such as intensity | strength and handling, and thin-layer property. 1-60 micrometers is especially preferable, 5-40 micrometers is more preferable, and 5-25 micrometers is still more preferable.

<Reflective polarizer comprising λ / 4 plate and circularly polarized reflective polarizer>
(Λ / 4 plate)
The λ / 4 plate has an in-plane retardation Re (λ) at a specific wavelength λnm. Re (λ) = λ / 4
An optically anisotropic layer satisfying the above. The above expression only needs to be achieved at any wavelength in the visible light range (for example, 550 nm). In the reflective polarizer, the λ / 4 plate functions as a layer for converting circularly polarized light obtained by passing through the circularly polarized reflective polarizer into linearly polarized light.

  The λ / 4 plate includes a coating / curing layer of a polymerizable liquid crystal composition containing a liquid crystal compound. In the present specification, the coating / curing layer means a layer obtained by curing a polymerizable liquid crystal composition coated on the layer. The λ / 4 plate is a layer showing optical anisotropy expressed by the orientation of molecules of the liquid crystal compound.

  The type of liquid crystal compound used for forming the λ / 4 plate is not particularly limited. For example, an optically anisotropic layer obtained by forming a low-molecular liquid crystal compound in a nematic alignment in a liquid crystal state and then fixing by photocrosslinking or thermal cross-linking, or a polymer liquid crystal compound in a nematic alignment in a liquid crystal state and then cooling. Accordingly, an optically anisotropic layer obtained by fixing the orientation can also be used. In the present invention, even when a liquid crystal compound is used for the optically anisotropic layer, the optically anisotropic layer is a layer formed by fixing the liquid crystal compound by polymerization or the like, and thus becomes a layer. After that, it is no longer necessary to show liquid crystallinity. The polymerizable liquid crystal compound may be a polyfunctional polymerizable liquid crystal or a monofunctional polymerizable liquid crystal compound. The liquid crystal compound may be a discotic liquid crystal compound or a rod-like liquid crystal compound, but a discotic liquid crystal compound is more preferable.

  In the λ / 4 plate, the molecules of the liquid crystal compound are preferably fixed in one of the alignment states of vertical alignment, horizontal alignment, hybrid alignment, and tilt alignment. In order to produce a retardation plate having a symmetric viewing angle dependency, the disk surface of the disk-like liquid crystal compound is substantially perpendicular to the film surface (optically anisotropic layer surface), or a rod-like liquid crystal It is preferable that the long axis of the compound is substantially horizontal with respect to the film surface (optically anisotropic layer surface). The term “substantially perpendicular to the discotic liquid crystal compound” means that the average value of the angle formed by the film surface (optically anisotropic layer surface) and the disc surface of the discotic liquid crystal compound is in the range of 70 ° to 90 °. To do. 80 ° to 90 ° is more preferable, and 85 ° to 90 ° is still more preferable. That the rod-like liquid crystal compound is substantially horizontal means that the angle formed by the film surface (optically anisotropic layer surface) and the director of the rod-like liquid crystal compound is in the range of 0 ° to 20 °. 0 ° to 10 ° is more preferable, and 0 ° to 5 ° is still more preferable.

The λ / 4 plate is composed of a liquid crystal compound such as a rod-like liquid crystal compound or a disk-like liquid crystal compound, and a polymerizable liquid crystal composition containing a polymerization initiator, an alignment control agent, other additives or a solvent, if desired, on a temporary support. It can form by apply | coating to and hardening the coating film obtained. The polymerizable liquid crystal composition may be applied on the surface of the temporary support, or may be formed on the surface of the alignment layer by forming an alignment layer on the temporary support.
Each component, coating method, and curing method of the polymerizable liquid crystal composition for forming the λ / 4 plate are the same as each component, coating method, and curing method in the polymerizable liquid crystal composition for forming the light reflection layer. However, the polymerizable liquid crystal composition for forming the λ / 4 plate preferably does not contain a chiral agent.

The film thickness of the λ / 4 plate may be 1 to 10 μm, and preferably 1 to 5 μm.
The λ / 4 plate preferably satisfies at least one of the following formulas (A) to (C), and more preferably satisfies all of the following formulas (A) to (C).
Formula (A) 450 nm / 4-35 nm <Re (450) <450 nm / 4 + 35 nm
Formula (B) 550 nm / 4-35 nm <Re (550) <550 nm / 4 + 35 nm
Formula (C) 630 nm / 4-35 nm <Re (630) <630 nm / 4 + 35 nm
Further, Rth (550) of the λ / 4 plate is preferably −120 to 120 nm, more preferably −80 to 80 nm, and particularly preferably −70 to 70 nm.

(Circularly polarized reflective polarizer)
The circularly polarized reflective polarizer includes at least one light reflecting layer formed by fixing a cholesteric liquid crystal layer. The circularly polarized reflective polarizer preferably includes two or more light reflecting layers, more preferably includes two to four layers, and more preferably includes two or three layers. The circularly polarized reflective polarizer preferably includes two or more light reflecting layers having different reflection center wavelengths, and more preferably includes two or three light reflecting layers having different reflection center wavelengths. The wavelength giving the peak of reflectance (that is, the reflection center wavelength) can be adjusted by changing the pitch or refractive index of the helical structure in the cholesteric liquid crystal phase of the light reflection layer formed by fixing the cholesteric liquid crystal phase. The pitch of the helical structure can be easily adjusted by changing the addition amount of the chiral agent. Specifically, Fujifilm research report No. 50 (2005) p. There is a detailed description in 60-63. Moreover, it can also adjust by conditions, such as temperature, illumination intensity, and irradiation time, when fixing a cholesteric liquid crystal phase.
The circularly polarized reflective polarizer preferably has a function of reflecting blue light, green light and red light. The circularly polarized reflective polarizer includes a light reflecting layer that is a coating and curing layer of a polymerizable liquid crystal composition containing a discotic liquid crystal compound and a light reflecting layer that is a coating and curing layer of a polymerizable liquid crystal composition containing a rod-like liquid crystal compound. Are preferably included.
Hereinafter, in a reflective polarizer including two or more light reflecting layers, a preferable combination of optical characteristics of the light reflecting layers will be exemplified.

((Example of reflective polarizer having two light reflecting layers))
Of the two light reflecting layers, any one layer is preferably a layer that also reflects light in a wavelength region exceeding the wavelength region of one color. For example, it is a layer that reflects blue light and green light in one layer, or a layer that reflects green light and red light in one layer.
Here, blue light is light having a wavelength of 380 to 499 nm, green light is light having a wavelength of 500 to 599 nm, and red light is light having a wavelength of 600 to 780 nm. Infrared light is 780-850 nm light.
When a layer having a reflection half-width of 200 nm or less is controlled as a layer that also reflects light in a wavelength region exceeding the wavelength region of one color, the number of pitches is not in a single pitch but in the cholesteric spiral direction (usually the film thickness direction). By gradually changing the pitch gradient method, a pitch gradient method capable of realizing a wide half-value width can be used. Regarding the pitch gradient method, the methods described in 1995 (Nature 378, 467-469 1995), JP-A-6-281814, and Japanese Patent No. 4990426 can be referred to.

-Light reflection layer-
The light reflection layer formed by fixing the cholesteric liquid crystal phase exhibits selective reflection having a reflection center wavelength λ based on the helical period of the cholesteric liquid crystal phase. The light reflection layer formed by fixing the cholesteric liquid crystal phase selectively reflects either the right circularly polarized light or the left circularly polarized light and transmits the other circularly polarized light in the wavelength region exhibiting selective reflection. The reflection center wavelength λ depends on the pitch P (helical 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 layer and λ = n × P. Here, in the light reflecting layer formed by fixing the cholesteric liquid crystal phase, when the normal ordinary refractive index no and the extraordinary refractive index ne of the liquid crystal are used, the in-plane average refractive index n is (nx + ny) / 2 = ( no + ne) / 2.
The half-value width Δλ of selective reflection depends on the relationship of Δλ = Δn × P, where Δλ depends on the birefringence Δn of the liquid crystal compound and the pitch P.

(Polymerizable liquid crystal composition)
The polymerizable liquid crystal composition for forming the light reflecting layer contains a liquid crystal compound. The polymerizable liquid crystal composition for forming the light reflecting layer includes a chiral agent, an alignment controller, a polymerization initiator, an alignment aid, and the like. Other components may be contained.
The light reflection layer can be obtained by applying the polymerizable liquid crystal composition to another layer such as a λ / 4 plate, another light reflection layer, a temporary support, or an alignment layer, and then curing the coating film.

(Liquid crystal compound)
Examples of the liquid crystal compound include a rod-like liquid crystal compound and a disk-like liquid crystal compound.
Examples of the rod-like liquid crystal compound 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. In addition to the above low-molecular liquid crystalline molecules, high-molecular liquid crystalline molecules can also be used.

  It is more preferable to fix the orientation of the rod-like liquid crystal compound by polymerization, and examples of the polymerizable rod-like liquid crystal compound include those 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, WO 95/22586, 95/24455. Publication No. 97/00600, No. 98/23580, No. 98/52905, JP-A-1-272551, No. 6-16616, No. 7-110469, No. 11-80081 The compounds described in the gazette and Japanese Patent Application No. 2001-64627 can be used. Further, as the rod-like liquid crystal compound, for example, those described in JP-T-11-513019 and JP-A-2007-279688 can be preferably used.

As the discotic liquid crystal compound, for example, those described in JP-A-2007-108732 and JP-A-2010-244038 can be preferably used, but are not limited thereto.
Although the preferable example of a disk shaped liquid crystal compound is shown below, this invention is not limited to these.

  When the circularly polarizing reflective polarizer includes two or more light reflecting layers, any one or more of the light reflecting layers is a layer formed from a polymerizable liquid crystal composition containing a rod-like liquid crystal compound, and any other It is preferably a layer formed from a polymerizable liquid crystal composition containing one or more discotic liquid crystal compounds. The rod-like liquid crystal compound substantially acts as a positive Rth for light having a wavelength other than the wavelength range exhibiting selective reflection, and the discotic liquid crystal compound acts as a negative Rth substantially. By reversing the sign of Rth of two light reflecting layers among a plurality of light reflecting layers, it is possible to compensate for the phase difference and improve the oblique color change. Such two light reflection layers are preferably a first light reflection layer and a second light reflection layer. By adopting a configuration using the rod-like liquid crystal compound and the disk-like liquid crystal compound, the phase difference can be compensated and the oblique color change can be improved.

(Chiral agent)
A chiral agent is a compound for adjusting the helical period of a cholesteric liquid crystalline compound, and is also called a chiral agent. In the present invention, various known chiral agents (for example, liquid crystal device handbook, chapter 3-4-3, TN, chiral agent for STN, 199 pages, edited by Japan Society for the Promotion of Science, 42nd Committee, 1989) ) Can be used. A chiral agent generally contains an asymmetric carbon atom, but an axially asymmetric compound or a planar asymmetric compound containing no asymmetric carbon atom can also be used as the chiral agent. Examples of the axial asymmetric compound or the planar asymmetric compound include binaphthyl, helicene, paracyclophane, and derivatives thereof. The chiral agent may have a polymerizable group. When the chiral agent has a polymerizable group and the rod-shaped liquid crystal compound used in combination also has a polymerizable group, it is derived from the rod-shaped liquid crystal compound by a polymerization reaction between the chiral agent having a polymerizable group and the polymerizable rod-shaped liquid crystal compound. And a polymer having a repeating unit derived from a chiral agent. In this embodiment, the polymerizable group possessed by the chiral agent having a polymerizable group is preferably the same group as the polymerizable group possessed by the polymerizable rod-like liquid crystal compound. Therefore, the polymerizable group of the chiral agent is also preferably an unsaturated polymerizable group, an epoxy group or an aziridinyl group, more preferably an unsaturated polymerizable group, and an ethylenically unsaturated polymerizable group. Particularly preferred.

Further, the above chiral agent may be a liquid crystal compound.
Examples of the chiral agent exhibiting a strong twisting force include JP 2010-181852 A, JP 2003-287623 A, JP 2002-80851 A, JP 2002-80478 A, and JP 2002-302487 A. The chiral agent etc. which are described in gazette are mentioned, It can use preferably for this invention. Furthermore, isosorbide compounds having a corresponding structure can be used for the isosorbide compounds described in these publications, and isosorbide compounds having a corresponding structure can be used for the isomannide compounds described in these publications. It can also be used.

(Orientation control agent)
Examples of the alignment control agent include compounds exemplified in [0092] and [0093] of JP-A-2005-99248, and [0076] to [0078] and [0082] of JP-A-2002-129162. To [0085], the compounds exemplified in JP-A-2005-99248, [0094] and [0095], and JP-A-2005-99248, [0096]. Are included.
As the alignment control agent, compounds described in [0082] to [0090] of JP-A No. 2014-119605 can also be used.

(Polymerization initiator)
Examples of the polymerization initiator 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. An acyloin compound (described in US Pat. No. 2,722,512), a polynuclear quinone compound (described in US Pat. Nos. 3,046,127 and 2,951,758), a combination of a triarylimidazole dimer and p-aminophenyl ketone (US Pat. 3549367), acridine and phenazine compounds (JP-A-60-105667, US Pat. No. 4,239,850) and oxadiazole compounds (US Pat. No. 4,221,970), acylphosphine oxides Compound (Japanese Examined Patent Publication Sho 63-407) No. 99, JP-B-5-29234, JP-A-10-95788, JP-A-10-29997) and the like.

(solvent)
The polymerizable liquid crystal composition may contain a solvent. As a solvent of the composition for forming each light reflecting layer, an organic solvent is preferably used. Examples of organic solvents include amides (eg, N, N-dimethylformamide), sulfoxides (eg, dimethyl sulfoxide), heterocyclic compounds (eg, pyridine), hydrocarbons (eg, benzene, hexane), alkyl halides (eg, , Chloroform, dichloromethane), esters (eg, methyl acetate, butyl acetate), ketones (eg, acetone, methyl ethyl ketone, cyclohexanone), ethers (eg, tetrahydrofuran, 1,2-dimethoxyethane). Alkyl halides and ketones are preferred. Two or more organic solvents may be used in combination.

(Application and curing of polymerizable liquid crystal composition)
Application of the polymerizable liquid crystal composition is performed by appropriately applying a liquid crystal composition such as a roll coating method, a gravure printing method, or a spin coating method in which the polymerizable liquid crystal composition is made into a solution state with a solvent or a liquid material such as a melt by heating. It can be performed by a method that develops by various methods. Furthermore, it can be performed by various methods such as a wire bar coating method, an extrusion coating method, a direct gravure coating method, a reverse gravure coating method, and a die coating method. In addition, a coating film can be formed by discharging a liquid crystal composition from a nozzle using an inkjet apparatus.
Thereafter, the polymerizable liquid crystal composition is cured to fix the alignment state of the molecules of the liquid crystal compound. Curing is preferably carried out by a polymerization reaction of a polymerizable group introduced into a liquid crystal molecule.
The coating film may be dried by a known method after the application of the polymerizable liquid crystal composition and before the polymerization reaction for curing. For example, it may be dried by standing or may be dried by heating.
The liquid crystal compound molecules in the polymerizable liquid crystal composition only need to be aligned in the steps of applying and drying the polymerizable liquid crystal composition.

  For example, in an embodiment in which the polymerizable liquid crystal composition is prepared as a coating solution containing a solvent, the coating film may be dried and the solvent may be removed to obtain a cholesteric liquid crystal phase. Further, heating at a transition temperature to the cholesteric liquid crystal phase may be performed. For example, the cholesteric liquid crystal phase can be stably formed by heating to the temperature of the isotropic phase and then cooling to the cholesteric liquid crystal phase transition temperature. The liquid crystal phase transition temperature of the above-described polymerizable liquid crystal composition is preferably in the range of 10 to 250 ° C., more preferably in the range of 10 to 150 ° C. from the viewpoint of production suitability and the like. When the temperature is lower than 10 ° C., a cooling step or the like may be required to lower the temperature to a temperature range exhibiting a liquid crystal phase. When the temperature exceeds 200 ° C., a high temperature is required to make the isotropic liquid state higher than the temperature range once exhibiting the liquid crystal phase, which is disadvantageous from waste of thermal energy, deformation of the substrate, and alteration.

The polymerization reaction includes a thermal polymerization reaction using a thermal polymerization initiator and a photopolymerization reaction using a photopolymerization initiator. A photopolymerization reaction is preferred. It is preferable to use ultraviolet rays for light irradiation for polymerization of liquid crystalline molecules. The irradiation energy is preferably ^{20mJ / cm 2 ~50J / cm 2} , further preferably 100 to 800 mJ / cm ^2. In order to accelerate the photopolymerization reaction, light irradiation may be performed under heating conditions.

In order to accelerate the curing reaction, ultraviolet irradiation may be performed under heating conditions. In particular, when forming the light reflecting layer, it is preferable to maintain the temperature at the time of ultraviolet irradiation within a temperature range exhibiting a cholesteric liquid crystal phase so that the cholesteric liquid crystal phase is not disturbed.
Also, since the oxygen concentration in the atmosphere is related to the degree of polymerization, if the desired degree of polymerization is not reached in the air and the film strength is insufficient, the oxygen concentration in the atmosphere is reduced by a method such as nitrogen substitution. It is preferable. A preferable oxygen concentration is preferably 10% or less, more preferably 7% or less, and most preferably 3% or less. The reaction rate of the curing reaction (for example, polymerization reaction) that proceeds by irradiation with ultraviolet rays is 70% or more from the viewpoint of maintaining the mechanical strength of the layer and suppressing unreacted substances from flowing out of the layer. Preferably, it is 80% or more, more preferably 90% or more. In order to improve the reaction rate, a method of increasing the irradiation amount of ultraviolet rays to be irradiated and polymerization under a nitrogen atmosphere or heating conditions are effective. Moreover, after superposing | polymerizing once, the method of hold | maintaining at a temperature higher than superposition | polymerization temperature, and pushing a reaction further by thermal polymerization reaction, and the method of irradiating an ultraviolet-ray again can also be used. The reaction rate can be measured by comparing the absorption intensity of the infrared vibration spectrum of a reactive group (for example, a polymerizable group) before and after the reaction proceeds.

  It is sufficient that the optical properties based on the orientation of the liquid crystal compound molecules of the polymerizable liquid crystal composition, for example, the optical properties of the cholesteric liquid crystal phase are retained in the layer, and the cured λ / 4 plate or light reflection The liquid crystal composition of the layer no longer needs to exhibit liquid crystallinity. For example, the liquid crystal composition may have a high molecular weight due to a curing reaction and may no longer have liquid crystallinity.

In the formation of the light reflection layer, the cholesteric liquid crystal phase is fixed by the above-described curing, and the light reflection layer is formed. Here, the state in which the liquid crystal phase is “fixed” is the most typical and preferred mode in which the orientation of the liquid crystal compound in the cholesteric liquid crystal phase is maintained. However, it is not limited to this. Specifically, this layer usually has no fluidity in the temperature range of 0 ° C. to 50 ° C., and -30 ° C. to 70 ° C. under more severe conditions. It shall mean a state in which the fixed orientation form can be kept stable without causing a change in form.
Other methods for producing a light reflecting layer having a fixed cholesteric liquid crystal phase include, for example, the methods described in JP-A-1-133003, JP-A-3416302, JP-A-3363565, and JP-A-8-271731. You may refer to it.

<Alignment layer>
The reflective polarizer may include an alignment layer. The alignment layer is used to align the molecules of the liquid crystal compound in the polymerizable composition when the λ / 4 plate or the light reflection layer is formed.
The alignment layer is used in forming the λ / 4 plate or the light reflection layer, and the reflection polarizer may or may not include the alignment layer.

The alignment layer can be provided by means such as a rubbing treatment of an organic compound (preferably a polymer), oblique vapor deposition of an inorganic compound such as SiO, or formation of a layer having microgrooves. Furthermore, an alignment layer in which an alignment function is generated by applying an electric field, applying a magnetic field, or light irradiation is also known.
Depending on the underlying material such as the support, the λ / 4 plate, or the light reflection layer, the support may be functioned as an alignment layer by direct alignment treatment (for example, rubbing treatment) without providing an alignment layer. it can. An example of such a lower layer support is PET.
Further, when the light reflecting layer is laminated directly on the light reflecting layer, the lower light reflecting layer may behave as an alignment layer, and the liquid crystal compound for producing the upper light reflecting layer may be aligned. In such a case, the upper liquid crystal compound can be aligned without providing an alignment layer or without performing a special alignment process (for example, rubbing process).
Hereinafter, a rubbing-treated alignment layer and a photo-alignment layer used by rubbing the surface as preferred examples will be described.

(Rubbing alignment layer)
Examples of the polymer that can be used for the rubbing treatment oriented layer include, for example, a methacrylate copolymer, a styrene copolymer, a polyolefin, polyvinyl alcohol, and the like described in paragraph No. [0022] of JP-A-8-338913. Examples include modified polyvinyl alcohol, poly (N-methylolacrylamide), polyester, polyimide, vinyl acetate copolymer, carboxymethylcellulose, and polycarbonate. Silane coupling agents can be used as the polymer. Water-soluble polymers (eg, poly (N-methylolacrylamide), carboxymethylcellulose, gelatin, polyvinyl alcohol, modified polyvinyl alcohol) are preferred, gelatin, polyvinyl alcohol and modified polyvinyl alcohol are more preferred, and polyvinyl alcohol and modified polyvinyl alcohol are most preferred. .

The aforementioned composition is applied to the rubbing-treated surface of the alignment layer to align the molecules of the liquid crystal compound. After that, if necessary, the alignment layer polymer and the polyfunctional monomer contained in the optically anisotropic layer are reacted, or the alignment layer polymer is crosslinked using a crosslinking agent, thereby the optical anisotropy described above. A layer can be formed.
The thickness of the alignment layer is preferably in the range of 0.1 to 10 μm.

-Rubbing treatment-
The surface of the alignment layer, temporary support, λ / 4 plate, or light reflecting layer to which the polymerizable liquid crystal composition is applied may be rubbed as necessary. The rubbing treatment can be generally performed by rubbing the surface of a film containing a polymer as a main component with paper or cloth in a certain direction. A general method of rubbing is described in, for example, “Liquid Crystal Handbook” (issued by Maruzen, October 30, 2000).

As a method for changing the rubbing density, a method described in “Liquid Crystal Handbook” (published by Maruzen) can be used. The rubbing density (L) is quantified by the following formula (A).
Formula (A) L = Nl (1 + 2πrn / 60v)
In the formula (A), N is the number of rubbing, l is the contact length of the rubbing roller, r is the radius of the roller, n is the number of rotations (rpm) of the roller, and v is the stage moving speed (second speed).

  In order to increase the rubbing density, the rubbing frequency should be increased, the contact length of the rubbing roller should be increased, the radius of the roller should be increased, the rotation speed of the roller should be increased, and the stage moving speed should be decreased, while the rubbing density should be decreased. To do this, you can reverse this. In addition, the description in Japanese Patent No. 4052558 can also be referred to as conditions for the rubbing process.

(Photo-alignment layer)
A large number of documents describe the photo-alignment material used for the photo-alignment layer formed by light irradiation. For example, JP 2006-285197 A, JP 2007-76839 A, JP 2007-138138 A, JP 2007-94071 A, JP 2007-121721 A, JP 2007-140465 A, Azo compounds described in JP 2007-156439 A, JP 2007-133184 A, JP 2009-109831 A, Patent 3888848, Patent 4151746, and Fragrance described in JP 2002-229039 A. Group ester compounds, maleimide and / or alkenyl-substituted nadiimide compounds having a photo-alignment unit described in JP-A No. 2002-265541 and JP-A No. 2002-317013, light described in Japanese Patent No. 4205195 and Japanese Patent No. 4205198 Crosslinkable silane derivative, special 2003-520878, JP-T-2004-529220 and JP-mentioned as photocrosslinkable polyimide, polyamide or ester are preferable examples described in Japanese Patent No. 4162850. Particularly preferred are azo compounds, photocrosslinkable polyimides, polyamides, or esters.

The photo-alignment layer formed from the above material is irradiated with linearly polarized light or non-polarized light to produce a photo-alignment layer.
In this specification, “linearly polarized light irradiation” is an operation for causing a photoreaction in a photo-alignment material. The wavelength of light used varies depending on the photo-alignment material used, and is not particularly limited as long as it is a wavelength necessary for the photoreaction. Preferably, the peak wavelength of light used for light irradiation is 200 nm to 700 nm, more preferably ultraviolet light having a peak wavelength of light of 400 nm or less.

  The light source used for light irradiation is a commonly used light source such as a tungsten lamp, a halogen lamp, a xenon lamp, a xenon flash lamp, a mercury lamp, a mercury xenon lamp, a carbon arc lamp, or various lasers (eg, semiconductor laser, helium). Neon laser, argon ion laser, helium cadmium laser, YAG laser), light emitting diode, cathode ray tube, and the like.

  As means for obtaining linearly polarized light, a method using a polarizing plate (eg, iodine polarizing plate, dichroic dye polarizing plate, wire grid polarizing plate), reflection using a prism-based element (eg, Glan-Thompson prism) or Brewster angle A method using a type polarizer or a method using light emitted from a laser light source having polarization can be employed. Moreover, you may selectively irradiate only the light of the required wavelength using a filter, a wavelength conversion element, etc.

In the case of linearly polarized light, a method of irradiating light from the top surface or the back surface to the alignment layer surface perpendicularly or obliquely with respect to the alignment layer is employed. Although the incident angle of light changes with photo-alignment materials, it is 0-90 degrees (vertical), for example, Preferably it is 40-90.
When non-polarized light is used, the non-polarized light is irradiated obliquely. The incident angle is 10 to 80 °, preferably 20 to 60, and particularly preferably 30 to 50 °.
The irradiation time is preferably 1 minute to 60 minutes, more preferably 1 minute to 10 minutes.

<Preparation of broadband light reflection layer>
Examples of a method for broadening the light reflection layer formed by fixing the cholesteric liquid crystal phase include use of a high Δn liquid crystal compound and a pitch gradient method.
Δn is the birefringence of the liquid crystal compound as described above. For example, in the case of a rod-like liquid crystal compound, it is the difference in refractive index between the minor axis and the major axis of the compound.
The liquid crystal compound used in the light reflecting layer formed by fixing the cholesteric liquid crystal phase is practically about 0.06 ≦ Δn ≦ 0.5 (the high Δn liquid crystal material described in JP 2011-510915 A can be used). Yes, corresponding to 15 to 150 nm in half width. Further, examples of the high Δn liquid crystal compound include compounds described in Japanese Patent No. 3999400, Japanese Patent No. 4053782, Japanese Patent No. 4947676, and the like, but are not limited thereto. The method of paragraph [0112] of Japanese Patent No. 40537882 and paragraph [0142] of Japanese Patent No. 4947676 can be referred to for the method of measuring Δn.
When manufacturing by controlling the half-value width of 200 nm or less, a pitch gradient method that can realize a wide half-value width can be used by gradually changing the number of pitches in the cholesteric spiral direction instead of a single pitch. The pitch is the pitch length P of the helical structure in the cholesteric liquid crystal phase, and means the thickness of the molecular layer when the orientation direction of the molecular layer of the liquid crystal compound is rotated 360 degrees.

From the viewpoints of half-width expansion and film thickness reduction (thinning) with a pitch gradient, Δn is preferably 0.16 or more, more preferably 0.2 or more, still more preferably 0.3 or more, and particularly preferably the present situation. It is about 0.5 which is the upper limit of Δn of the liquid crystal that has been industrialized. However, if further high Δn liquid crystal is developed in the future, it can be applied to the present invention in principle and can be made thinner.
In the case of using a liquid crystal compound having a Δn of 0.156 from the viewpoint of luminance performance, and having at least a pitch gradient band of 400 to 600 nm, the film thickness of the wideband pitch gradient layer is preferably 6 μm or more, and 8 μm or more. More preferably, 10 μm or more is even more preferable. In the case of using a liquid crystal compound having Δn of 0.3 and having at least a pitch gradient band of 400 to 600 nm, the film thickness is preferably 2 μm or more, more preferably 3 μm or more, further preferably 4 μm or more, and 5 μm or more. Is particularly preferred.

  It is known that it is preferable that the Δn dispersion of the liquid crystal has a small dispersion at each wavelength. Preferably Δn (450/550 ratio) ≦ 1.6, more preferably Δn (450/550 ratio) ≦ 1.4, more preferably Δn (450/550 ratio) ≦ 1.2, particularly preferably Δn. (450/550 ratio) ≦ 1.1.

In the pitch gradient method, a wide half-value width can be realized by gradually changing the pitch in the spiral direction (normal film thickness direction) of the cholesteric liquid crystal phase. In the light reflection layer to which the pitch gradient method is applied, it is preferable that the pitch continuously changes in the film thickness direction. Moreover, in the light reflection layer to which the pitch gradient method is applied, it is preferable that the pitch continuously increases or decreases continuously from one surface of the layer to the other surface. In the pitch gradient method, the concentration of a compound that does not form a spiral in the thickness direction of the liquid crystal layer is continuously changed in the thickness direction of the liquid crystal layer, or the concentration of the chiral agent is continuously changed in the thickness direction of the liquid crystal layer. Alternatively, use a chiral agent with a photoisomerization moiety, and change the HTP (helical twisting power) of the chiral agent by isomerizing the photoisomerization part of the chiral agent with UV irradiation etc. when forming the light reflection layer. To achieve this. As this photoisomerization moiety, a vinylene group, an azo group, or the like is preferable.
As the pitch gradient method, those described in (Nature 378, 467-469 1995), Japanese Patent No. 4990426, Japanese Patent Application Laid-Open No. 2005-265896, and the like can be applied. Moreover, the compound which does not form a helix and has a fluorinated alkyl group as described in Japanese Patent No. 4570377 can also be used.

<Phase difference element>
The reflective polarizer may have a phase difference element, for example, to compensate for the phase difference of light incident obliquely on the ¼ plate from the backlight unit side. The retardation element has Rth in the range of −20 nm to −1000 nm, preferably −50 nm to −500 nm. Regarding the retardation element, the description in paragraphs 0045 to 0051 of Japanese Patent No. 4570377 can be referred to.

<< Reflective polarizer made of dielectric multilayer film >>
As the reflective polarizer, a linearly polarized reflective polarizer made of a dielectric multilayer film may be used. The method for producing the dielectric multilayer film is not particularly limited. For example, the method described in Japanese Patent No. 387821, Japanese Patent No. 3704364, Japanese Patent No. 4037835, Japanese Patent No. 4091978, Japanese Patent No. 3709402, Japanese Patent No. 4860729, Japanese Patent No. 3448626, etc. The contents of these publications are incorporated into the present invention. The dielectric multilayer film may be referred to as a dielectric multilayer reflective polarizing plate or a birefringence interference polarizer having an alternating multilayer film.

"Polarizer"
The optical sheet member has a brightness enhancement film and a polarizing plate. An example of the layer structure of the optical sheet member is shown in FIG. The angle formed by the slow axis of the λ / 4 plate and the absorption axis of the polarizer is 30 to 60 °, and the polarizing plate, the λ / 4 plate and the reflective polarizer are in direct contact with each other in this order, or an adhesive. It is preferable to laminate via (adhesive layer).
The optical sheet member may have a polarizing plate protective film. When a protective film is not provided between the polarizer and the reflective polarizer, the reflective polarizer may be provided directly on the polarizer or via an adhesive. The λ / 4 plate may also serve as a polarizing plate protective film, or the polarizing plate protective film may serve as a part of the λ / 4 plate realized by lamination.
Among these protective films, as the protective film disposed on the side opposite to the liquid crystal cell, a thermoplastic resin excellent in transparency, mechanical strength, thermal stability, moisture barrier property, isotropy and the like is used. Specific examples of such thermoplastic resins include cellulose resins such as triacetyl cellulose, polyester resins, polyethersulfone resins, polysulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, (meth) acrylic resins, cyclic Examples thereof include polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof.

(Adhesive (adhesive layer))
Between the λ / 4 plate included in the reflective polarizer and the circularly polarized reflective polarizer, or between the light reflective layers when the reflective polarizer includes two or more light reflective layers, a polarizing plate or a polarizer An adhesive layer may be included between the λ / 4 plate and the like.
As the adhesive, for example, a substance having a ratio (tan δ = G ″ / G ′) of storage elastic modulus G ′ and loss elastic modulus G ″ measured by a dynamic viscoelasticity measuring device is 0.001 to 1.5. This includes so-called pressure-sensitive adhesives and substances that easily creep. Examples of the pressure-sensitive adhesive include, but are not limited to, an acrylic pressure-sensitive adhesive and a polyvinyl alcohol-based adhesive.

Examples of the adhesive include a boron compound aqueous solution, an epoxy compound curable adhesive that does not contain an aromatic ring in the molecule, as disclosed in JP-A-2004-245925, and 360 described in JP-A-2008-174667. An active energy ray-curable adhesive comprising a photopolymerization initiator having a molar extinction coefficient of 400 or more at a wavelength of ˜450 nm and an ultraviolet curable compound as essential components, (meth) acrylic as described in JP-A-2008-174667 (A) (meth) acrylic compound having 2 or more (meth) acryloyl groups in the molecule in 100 parts by mass of the total amount of the compound, and (b) having a hydroxyl group in the molecule, and only having a polymerizable double bond (Meth) acrylic compound having one and (c) phenol ethylene oxide modified acrylate or nonylphenol ethylene oxide The active energy ray-curable adhesive containing a sex acrylate, and the like.

  Examples of the pressure-sensitive adhesive include resins such as polyester resins, epoxy resins, polyurethane resins, silicone resins, and acrylic resins. You may use these individually or in mixture of 2 or more types. In particular, an acrylic resin is preferable because it is excellent in reliability such as water resistance, heat resistance, and light resistance, has good adhesion and transparency, and can easily adjust the refractive index to be compatible with a liquid crystal display. As the acrylic pressure-sensitive adhesive, acrylic acid and its esters, methacrylic acid and its esters, acrylamide, homopolymers of acrylic monomers such as acrylonitrile, or copolymers thereof, and at least one of the aforementioned acrylic monomers, Mention may be made of copolymers with aromatic vinyl monomers such as vinyl acetate, maleic anhydride and styrene. In particular, main monomers such as ethylene acrylate, butyl acrylate, 2-ethylhexyl acrylate, etc. that exhibit tackiness, monomers such as vinyl acetate, acrylonitrile, acrylamide, styrene, methacrylate, methyl acrylate as cohesive components, Functional group containing methacrylic acid, acrylic acid, itaconic acid, hydroxyethyl methacrylate, hydroxypropyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, acrylamide, methylol acrylamide, glycidyl methacrylate, maleic anhydride, etc. A copolymer composed of monomers, having a Tg (glass transition point) in the range of −60 ° C. to −15 ° C. and a weight average molecular weight in the range of 200,000 to 1,000,000. Shall is preferable.

As the adhesive, a sheet-like photo-curing adhesive (Toagosei Group Research Annual Report 11 TREND 2011 No. 14) can be used for the adhesive layer. Like an adhesive, it is easy to bond between optical films, and is preferably crosslinked and cured with ultraviolet rays (UV) to improve storage elastic modulus, adhesive strength and heat resistance.
These pressure-sensitive adhesives and adhesives can also be applied when the liquid crystal display device is assembled, between the liquid crystal cell and the display side polarizing plate, and between the liquid crystal cell and the backlight side polarizing plate.

"Liquid Crystal Display"
The liquid crystal display device includes a display side polarizing plate, a liquid crystal cell, a backlight side polarizing plate, and a backlight unit in this order. The liquid crystal display device of the present invention includes a polarizing plate formed by laminating the absorbing polarizer and the reflective polarizer of the present invention as a backlight side polarizing plate.
One embodiment of a liquid crystal display device has a liquid crystal cell in which a liquid crystal layer is sandwiched between substrates on which electrodes are provided on at least one opposite side, and the liquid crystal cell is arranged between two polarizing plates. It is. The liquid crystal display device includes a liquid crystal cell in which liquid crystal is sealed between upper and lower substrates, and can display an image by changing the alignment state of the liquid crystal by applying a voltage. Furthermore, you may have a polarizing plate protective film and the retardation film for viewing angle compensation as needed. The retardation film for viewing angle compensation may be included between each of the polarizers and the liquid crystal cell. The liquid crystal display device of the present invention includes, for example, a color filter substrate, a thin layer transistor substrate, a lens film, a diffusion sheet, a hard coat layer, an antireflection layer, a low reflection layer, an antiglare layer, and the like (or instead of) Other members such as a forward scattering layer, a primer layer, an antistatic layer, and an undercoat layer may be included.

  FIG. 4 shows a configuration example 1 of the liquid crystal display device of the present invention. A liquid crystal display device 50A shown in FIG. 4 includes a backlight unit 30A, the polarizing plate 20A, the liquid crystal cell 40, and the display-side polarizing plate 10 shown in FIG. That is, the polarizing plate of the present invention is used as a backlight-side polarizing plate disposed between the backlight unit 30A and the liquid crystal cell 40.

  The display-side polarizing plate 10 includes the display-side absorbing polarizer 3 sandwiched between polarizer protective films 5c and 5d. The display side polarizing plate 10 and the liquid crystal cell 40, and the liquid crystal cell 40 and the backlight side polarizing plate 20 </ b> A are laminated with the adhesive 17 interposed therebetween.

  The backlight unit 30A includes a backlight light source 31A and a backlight sheet 16A. The backlight light source 31 </ b> A is an edge light type light source including a light guide plate 33 and a light source 32 that receives light from the side of the light guide plate 33. The backlight sheet 16A is formed by laminating a lower diffusion sheet 36, two prism sheets 37, and an upper diffusion sheet 38. It is preferable that the directions of the prisms of the two prism sheets 37 are substantially parallel. The direction in which the prisms of the two prism sheets 37 are substantially parallel means that the angle formed by the prisms of the two prism sheets is within ± 5 °. Note that the prism sheet has a plurality of protrusions (in the present specification, these protrusions are also referred to as prisms) extending in one direction within the surface of the prism sheet. The directions in which the plurality of prisms arranged in are extended are parallel. The direction of the prism refers to the extending direction of a plurality of prisms arranged in a row.

  The liquid crystal display device of the present invention is not limited to the embodiment shown in FIG. 4, but includes a polarizing plate 20B shown in FIG. 2 instead of the polarizing plate 20A as in the liquid crystal display device 50B shown as the configuration example 2 in FIG. Also good. Further, like the liquid crystal display device 50C shown as the configuration example 3 in FIG. 6, the polarizing plate 20C in FIG. 3 may be provided instead of the polarizing plate 20A.

  Further, the liquid crystal display device of the present invention includes a lower diffusion sheet 36, a prism sheet 37, and a diffusion prism sheet 39 in place of the backlight unit 30A of FIG. 4 as in the liquid crystal display device 50D shown as the configuration example 4 in FIG. The configuration may include a backlight unit 30D including a laminated backlight sheet 16D and a backlight light source 31A.

  Alternatively, as in the liquid crystal display device 50E shown as the configuration example 5 in FIG. 8, instead of the backlight unit 30A, a backlight sheet 16E in which a lower diffusion sheet 36 and two prism sheets 37 are laminated, and quantum dots And a backlight unit 30E having a light source 34 for exciting quantum dots to embody white light and a backlight source 31E having a light guide plate 33. Also good.

Further, like the liquid crystal display device 50F shown as the configuration example 6 in FIG. 9, a backlight unit 30F including a direct type backlight light source 31F composed of a surface light source 35 is provided instead of the edge light type light source. May be.
Further, as in the liquid crystal display device 50G shown as the configuration example 7 in FIG. 10, the reflected polarized light composed of the dielectric multilayer film 14 that is a linear reflective polarizer instead of the reflective polarizer 11 including the circularly polarized reflective polarizer 13. The reflective polarizer 11G may be provided with a polarizer 20G having a configuration in which the reflective polarizer 11G is bonded to the protective film 5b via the adhesive 17.

<Chromaticity a ^* , b ^* of image light of liquid crystal display device>
In the liquid crystal display device of the present invention, the chromaticity of image light in the image normal direction during white display (hereinafter, front chromaticity) is a ^* > − 2 and b ^* <9.
In this specification, the image light means light emitted from the image display surface of the liquid crystal display device, and emits light in the backlight unit. At least the backlight side polarizing plate, the brightness enhancement film, the liquid crystal cell, and the display side polarized light. It means light emitted from the image display surface of the liquid crystal display device via the plate.

The chromaticities a ^* and b ^* are chromaticities represented by coordinates in the international standard CIE1976 (L ^* a ^* b ^* ) color space. The CIE1976 (L ^* a ^* b ^* ) color space is also adopted in Japanese Industrial Standard JIS 8781-4 created based on ISO 11664-4. The chromaticities a ^* and b ^* can be obtained with a measuring machine such as SR3 manufactured by Topcon, which is also used in the following examples. Redness increases as the value of the chromaticity a ^* is larger than 0, can be considered as the value of the chromaticity a ^* is increasing greenness as less than 0.

In the process of improving the luminance of a liquid crystal display device using a polarizing plate having a reflective polarizer including a light reflecting layer in which a cholesteric liquid crystal phase is fixed as described later, It has been found that the result of sensory evaluation becomes poor when the image of the liquid crystal display device is observed from an oblique direction depending on the configuration of the child. And as a result of earnest research, it adjusted to the structure which front chromaticity satisfy | fills -2 <a ^* , b ^* <9, and obtained the liquid crystal display device with the favorable result of sensory evaluation. The color produced by the use of the reflective polarizer is green, and the color is likely to be unpleasant for the observer (human). Therefore, it is considered that the result of sensory evaluation was improved by bringing the color to red.

The front chromaticity is preferably −2 <a ^* <5, −6 <b ^* <9, more preferably −1.5 <a ^* <3, −5 <b ^* <7, More preferably, 0 <a ^* <2 and −2 <b ^* <3.

In the present invention, as a method for adjusting the chromaticity of the liquid crystal display device, the polarizing plate of the present invention is also used as a backlight polarizing plate disposed between the liquid crystal cell and the backlight. That is, as a backlight-side polarizing plate, a reflective polarizer and an absorbing polarizer are laminated, and the absorbing polarizer has a transmittance of 650 nm light at the absorption polarizer T ₆₅₀ , and a transmittance of 550 nm light at the wavelength T ₅₅₀ , when the transmittance of 450 nm wavelength light is T ₄₅₀ and the transmittance of 400 nm wavelength light is T ₄₀₀ ,
1.11> T ₆₅₀ / T ₅₅₀ ≧ 1.00
1.11> T ₄₅₀ / T ₅₅₀ ≧ 0.95
1.11> T ₄₀₀ / T ₄₅₀ ≧ 0.65
A polarizing plate is used. It is particularly preferable that 1.11> T ₄₀₀ / T ₄₅₀ ≧ 0.96.

<Display-side polarizing plate>
Although the display side polarizing plate may consist only of a polarizer, it is preferably composed of a polarizer and a polarizing plate protective film that protects at least one surface thereof. It is also preferable to consist of a polarizer and two polarizing plate protective films disposed on both sides thereof. The polarizing plate protective film is equivalent to the protective film described above.
As the polarizer of the display-side polarizing plate, it is preferable to use the polymer film described above as an example of the absorbing polarizer used in the polarizing plate of the present invention in which iodine is adsorbed and oriented on the polymer film.

<Liquid crystal cell>
There is no restriction | limiting in particular about the structure of a liquid crystal cell, The liquid crystal cell of a general structure is employable. The liquid crystal cell includes, for example, a pair of substrates arranged opposite to each other and a liquid crystal layer sandwiched between the pair of substrates, and may include a color filter layer, if necessary. The driving mode of the liquid crystal cell is not particularly limited, and is twisted nematic (TN), super twisted nematic (STN), vertical alignment (VA), in-plane switching (IPS), optically compensated bend cell (OCB). Various modes such as can be used.

<Backlight unit>
As described above, the configuration of the backlight light source of the backlight unit may be an edge light method using a light guide plate, a reflection plate, or the like as a constituent member, or a direct type.
An example of the light source provided in the backlight light source is a white light source such as a white LED (Light Emitting Diode). As another example, a light source having a blue light-emitting diode that emits blue light and a fluorescent material that emits green light and red light when blue light from the blue light-emitting diode is incident, emits light in a wavelength band of 300 nm to less than 430 nm. A light source having a UV light emitting diode that emits UV light having a central wavelength, and a fluorescent material that emits blue light, green light, and red light when the UV light of the UV light emitting diode is incident, and blue light that emits the blue light described above Emits blue light such as a light source (pseudo white LED) having a light emitting diode and a fluorescent material (yellow phosphor, etc.) that emits a broad peak light from the green light to the red light when the blue light is incident. Examples include a blue light emitting diode, a green light emitting diode that emits green light, and a red light emitting diode that emits red light. Specifically, as shown in FIG. 8, it can be realized by a light conversion sheet 15 containing a fluorescent material such as a quantum dot and a light source 34 for exciting the fluorescent material.

  Among these, white LEDs and blue light emitting diodes emitting blue light from the viewpoint of energy conversion (power-light conversion efficiency) and the aforementioned green light and red light described above when blue light from the blue light emitting diode is incident. A light source having a fluorescent material that emits light, or a blue light emitting diode that emits blue light, and a fluorescent material that emits a broad peak of light from the green light to the red light when the blue light is incident (yellow fluorescent light) It is more preferable that the light source of the backlight unit is a white LED or a blue light emitting diode that emits blue light and a blue light emitting diode. It is more preferable to have a fluorescent material that emits the aforementioned green light and the aforementioned red light when blue light is incident. In a more preferred embodiment, the backlight unit has blue light having an emission center wavelength in a wavelength band of 430 to 480 nm, green light having an emission center wavelength in a wavelength band of 500 to 600 nm, and a wavelength band of 600 to 700 nm. It is preferable to emit red light having at least part of the peak of emission intensity.

Examples of fluorescent materials include yttrium / aluminum / garnet yellow phosphors and terbium / aluminum / garnet yellow phosphors. The fluorescence wavelength of the fluorescent material can be controlled by changing the particle diameter of the phosphor.
In the liquid crystal display device, the blue light-emitting diode that emits the blue light and the fluorescent material that emits the green light and the red light when the blue light of the blue light-emitting diode is incident are quantum dots. It is a member (for example, a quantum dot sheet or a bar-shaped quantum dot bar), and the quantum dot member is preferably disposed between the optical sheet member and the blue light source. There is no restriction | limiting in particular as such a quantum dot member, Although a well-known thing can be used, For example, Unexamined-Japanese-Patent No. 2012-169271, SID'12 DIGEST p. 895, etc., and the contents of these documents are incorporated in the present invention. As such a quantum dot sheet, QDEF (Quantum Dot Enhancement Film, manufactured by Nanosys) can be used.

The features of the present invention will be described more specifically with reference to examples and comparative examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate 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.
Detailed configurations of Examples and Comparative Examples are shown in Tables 2 to 4 below.

<Production of iodine polarizer I>
An iodine polarizer was produced in the same manner as [0219] of Japanese Patent Application Laid-Open No. 2006-293275.

<Production of iodine polarizer II>
In the production method of the iodine polarizer I, the iodine polarizer II was obtained by setting the draw ratio to 8 times and the immersion time to 300 seconds.

[Display-side polarizing plate]
A cellulose acylate (TAC) film was bonded to one surface of the iodine polarizer I, and a low retardation film having a thickness of 25 μm was bonded to the other surface to obtain a display-side polarizing plate. The display-side polarizing plate has the same configuration for all examples and comparative examples.

[Backlight-side polarizing plate (Examples and comparative examples of the polarizing plate of the present invention)]
<Absorbing polarizer>
In Comparative Examples 1 and 2, the above-described iodine polarizer I was used as the absorbing polarizer of the backlight side polarizing plate, and in Comparative Example 3, the iodine polarizer II was used.
As an absorption polarizer of the coating-type absorption polarizing layer (hereinafter, coating-type polarizing layer) 1 to 11 used as the absorption polarizer of the backlight side polarizing plate of Examples 1 to 19 and the backlight side polarizing plate of Comparative Example 4 Table 1 shows the formulation of the absorbing polarizing layer coating solution for forming the coating type absorbing polarizing layer 12 used. In Table 1, the unit of prescription is parts by mass. The film thickness was measured with an optical microscope (NIKON ECLIPSE LV100POL) after cutting the absorbing polarizer after fabrication with a microtome.

Hereinafter, the production of the coating type polarizing layer 3 will be described as an example.
A coating liquid for the coating type polarizing layer 3 was prepared according to the following formulation. The following dichroic dyes correspond to the exemplary compounds (C-15, C-21, C-22) exemplified in the above-described thermotropic liquid crystalline dichroic dyes.
As a protective film, a long cellulose acylate film (25 μm TAC, manufactured by Fuji Film Co., Ltd.) having a thickness of 25 μm is used. On this TAC film, an alignment film A coating solution having the following composition is continuously applied with a # 14 wire bar. Applied. Next, the coating film was dried with warm air of 60 ° C. for 60 seconds and further with warm air of 100 ° C. for 120 seconds to obtain alignment film A.

The alignment film A was rubbed. At this time, the angle formed by the film longitudinal direction and the rubbing rotation axis was 90 °. The coating type polarizing layer coating solution was coated on the rubbing surface using a bar coater. Next, the film was aged at a film surface temperature of 160 ° C. for 15 seconds and cooled to room temperature. Thereafter, an ultraviolet ray of 500 mJ was irradiated in a nitrogen atmosphere (oxygen concentration of 100 ppm or less) to form a coating type polarizing layer (corresponding to an absorbing polarizer). The thickness of the formed coating type polarizing layer was 0.3 μm. The laminated body I provided with the absorption polarizing layer on the protective film by the above process was produced. The absorption axis of the absorption polarizing layer of this example was parallel to the film longitudinal direction (perpendicular to the rubbing rotation axis), and the degree of polarization was 98% when the degree of polarization was calculated by absorption measurement with a spectrophotometer.
In examples other than Examples 12-15, a TAC film having a predetermined thickness (see Tables 2 to 4) is prepared as the second protective film, and this second protective film is used as the first protective film of the absorbing polarizing layer. It was bonded to the opposite surface using a polyvinyl alcohol-based adhesive. The absorptive polarizers of Examples 12 to 16 are configured not to include the second protective film.

The result of having measured the wavelength dependence of the transmittance | permeability about the iodine polarizer I, the iodine polarizer II, and the coating type polarizing layers 1-12 is shown in FIG. The wavelength dependence of the transmittance was measured using a spectrophotometer: UV3150 (manufactured by Shimadzu Corporation) in an atmosphere of 25 ° C. environment. T ₆₅₀ / T _550, T ₄₅₀ / T _550, and T ₄₀₀ / T ₄₅₀ calculated based on this measurement result are shown in Tables 2 to 4 below.
As shown in FIG. 11, the wavelength dependence of the transmittance in the region of wavelength 500 nm or less is greatly different for each polarizing layer. The coating type polarizing layers 1 to 12 satisfy the transmittance characteristic condition of the absorbing polarizer of the polarizing plate of the present invention. In particular, the coating type polarizing layers 3 to 8 satisfy the more preferable condition 1.11> T ₄₀₀ / T ₄₅₀ ≧ 0.96 of the transmittance characteristic.

<Reflective polarizer>
In Examples 1 to 19 and Comparative Examples 1, 3 and 4, a combination of a λ / 4 plate and a circularly polarized reflective polarizer including at least one light reflective layer containing cholesteric liquid crystal was used as a reflective polarizer. .

  In Tables 2 to 4, Examples 1 to 11, 16 to 19 and Comparative Examples 1, 3, and 4 in which “None (direct application)” is described in the column of the intermediate layer are the second adjacent to the absorbing polarizer. A λ / 4 plate and a light reflection layer were sequentially applied to the other surface of the protective film to form a laminate. On the other hand, when the absorbing polarizer does not include the second protective film as in Examples 12 to 15, the lamination method with the absorbing polarizer is different. In Example 12, the absorbing polarizer and the reflecting polarizer were laminated by transfer via a 3 μm UV adhesive layer. In Examples 13 to 16, a 1 μm photo-alignment film was applied and formed on one surface of the absorbing polarizer, and a λ / 4 plate and a light reflection layer were sequentially applied and laminated on the photo-alignment film.

  In Comparative Example 2, a reflective polarizer made of a dielectric multilayer film was used, and a 10 μm thick adhesive was applied to the other surface of the second protective film adjacent to the absorbing polarizer without providing a λ / 4 plate. Glued through.

<Λ / 4 plate>
(Production of liquid crystal layer of λ / 4 plate)
The composition of the coating solution for the liquid crystal layer of the λ / 4 plate produced in Example 1 is shown below. A solute having the following composition was dissolved in MEK (methyl ethyl ketone) to prepare a coating solution for preparing a liquid crystal layer for a λ / 4 plate. This coating solution was applied onto the second protective film of the laminate I by adjusting the concentration and the coating amount so that the dry film thickness was 1 μm. Before applying the coating solution, the surface of the protective film was rubbed. On the other hand, an alignment film was formed on the surface of the absorption polarizing layer of the laminate I of the example that was not provided with the second protective film, and then a coating solution for preparing a liquid crystal layer for a λ / 4 plate was applied.
The alignment film was formed as follows. First, a solution prepared by dissolving Kuraray's Poval PVA-103 in pure water was applied to a bar by adjusting the concentration and coating amount of the solution so that the dry film thickness was 1 μm. Thereafter, the coating film was heated at 100 ° C. for 5 minutes. Further, after rubbing the surface to obtain an alignment layer, a coating solution for preparing a liquid crystal layer for a λ / 4 plate was applied in the same manner on the alignment layer.
After applying the coating liquid for preparing a liquid crystal layer for λ / 4 plate, the solvent was kept at 85 ° C. for 2 minutes to evaporate the solvent, and then heat-aged at 100 ° C. for 4 minutes to obtain a uniform alignment state. The discotic compound was aligned perpendicular to the support plane.
Thereafter, this coating film was kept at 80 ° C. and irradiated with ultraviolet rays using a high-pressure mercury lamp in a nitrogen atmosphere to produce a λ / 4 plate. The λ / 4 plate thus produced had a retardation Re = 130 nm. For the λ / 4 plate, the same formulation was used in all Examples and Comparative Examples except Comparative Example 2.

<Formation of the light reflection layer B>
The composition of the coating solution for forming the light reflection layer B ("first layer: B" in Table 2) produced in Comparative Example 1 is shown below, and the formation method will be described. In addition, about the other comparative example and Example provided with the light reflection layer B, it produced with the same method.
A solute having the following composition was dissolved in MEK to prepare a coating solution for forming the light reflection layer B containing a discotic liquid crystal compound. This coating solution was adjusted to have a concentration and coating amount of 3.0 μm when dried, and applied to a bar on a λ / 4 plate, and the solvent was vaporized by holding the solvent at 70 ° C. for 2 minutes. Then, the mixture was aged at 100 ° C. for 4 minutes to obtain a uniform alignment state.
Thereafter, this coating film was kept at 45 ° C., and irradiated with ultraviolet rays using a high-pressure mercury lamp in a nitrogen atmosphere, thereby producing a light reflection layer B. The film thickness of the light reflection layer B was 3.0 μm. As a result of measuring the pitch of cholesteric using AXOSCAN manufactured by AXOMETRIX, the center wavelength of the reflection wavelength was 480 nm. The B layer of each example and comparative example uses solute composition components of the same formulation, except that the amount of each component added, coating thickness, aging temperature, and / or ultraviolet irradiation conditions are changed, respectively. A reflective layer having the described thickness and reflection center wavelength was produced.

<Formation of light reflection layer GR>
As the light reflection layer GR (“second layer: GR” in Table 2), a pitch gradient layer in which the pitch number gradually changed in the cholesteric spiral direction (normal film thickness direction) was formed. The composition of the coating solution for forming the light reflection layer GR produced in Comparative Example 1 is shown below, and the formation method will be described. In addition, about the other comparative example and Example provided with the light reflection layer GR layer, it produced with the same method.

First, a terminal fluorinated alkyl group-containing polymer (compound A) having an optically active site was obtained by the procedure described in Japanese Patent No. 4570377 [0065]. Specifically, Compound A was obtained as follows.
To a four-necked flask equipped with a condenser, a thermometer, a stirrer, and a dropping funnel, a fluorinated solvent AK-225 (Asahi Glass Co., Ltd., 1,1,1,2,2-pentafluoro-3,3-dichloropropane: 1 , 1,2,2,3-pentafluoro-1,3-dichloropropane = 1: 1.35 (molar ratio) mixed solvent)) 50 parts by mass, a reactive chiral agent (compound) having optical activity of the following structure 7. In the formula, * indicates an optically active site) 5.22 parts by mass are charged, the reaction vessel is heated to 45 ° C., and then 10 mass of diperfluoro-2-methyl-3-oxahexanoyl peroxide / AK225 6.58 parts by mass of a% solution was added dropwise over 5 minutes. After completion of dropping, the reaction is carried out in a nitrogen stream at 45 ° C. for 5 hours, and then the product is concentrated to 5 ml, reprecipitated with hexane, and dried to contain a terminal fluorinated alkyl group-containing polymer. (Compound A) 3.5 parts by mass (yield 60%) was obtained.
When the molecular weight of the obtained polymer was measured using GPC and THF (tetrahydrofuran) as a developing solvent, Mn = 4,000 (Mw / Mn = 1.77) and the fluorine content was measured to determine the fluorine content. Was 5.89% by mass.

  On the light reflection layer B, a composition for forming the light reflection layer GR having the following composition was applied using a bar coater, dried at room temperature for 10 seconds, and then heated in an oven at 100 ° C. for 2 minutes (alignment aging). Further, ultraviolet irradiation was performed for 30 seconds to form a light reflection layer GR having a thickness of 6 μm.

  The light reflecting layer GR of each of the other Examples and Comparative Examples uses a polymer compound (Compound A) having the same formulation as Comparative Example 1, except that the addition amount, coating thickness, aging temperature, and ultraviolet irradiation conditions are changed. As a result, a reflective layer having a thickness and a reflection wavelength region described in the table was obtained.

When the cross section of the light reflection layer GR formed of the cholesteric liquid crystal layer was observed with a scanning electron microscope, it had a structure having a helical axis in the normal direction of the layer and continuously changing the cholesteric pitch. Here, regarding the cholesteric pitch, when the cross section of the cholesteric liquid crystal layer is observed with a scanning electron microscope, the width in the layer normal direction of the light portion and the dark portion repeated twice (brightness, darkness, and darkness) is counted as one pitch.
The reflection wavelength range of the GR layer in the table is the result of calculation from the measured cholesteric pitch, where the surface side with a small cholesteric pitch is defined as the x plane and the surface with the large surface is defined as the y plane. Is the shortest wavelength, and the cholesteric reflection wavelength near the y-plane is the longest wavelength.

<Formation of light reflection layer RGB>
In Example 15, instead of forming a reflective polarizer having a two-layer structure of a light reflecting layer B and a light reflecting layer GR, a single light reflecting layer RGB (“first layer: RGB” in Table 4) is used. A reflective polarizer.

An alignment film coating solution consisting of 10 parts by weight of polyvinyl alcohol and 371 parts by weight of water was applied to a λ / 4 plate and dried on one side of the λ / 4 plate to form an alignment film having a thickness of 1 μm. Next, rubbing treatment was performed on the alignment film continuously in a direction parallel to the longitudinal direction.
On the alignment film, a composition for forming the light reflection layer RGB having the following composition was applied using a bar coater, dried at room temperature for 10 seconds, and then heated in an oven at 100 ° C. for 2 minutes (alignment aging). Irradiation with ultraviolet rays for 30 seconds produced a light reflection layer having a thickness of 5.0 μm.

As a result of calculation from the cholesteric pitch measured for the composition for forming the light reflecting layer RGB, the cholesteric reflection wavelength near the x-plane side was 455 nm, and the cholesteric reflection wavelength near the y-plane side was 730 nm.

<Formation of light reflecting layers R, G, B>
In Example 19, the light reflecting layer R (“first layer: R” in Table 4), the light reflecting layer B (“second layer: B” in Table 4), and the light reflecting layer G (“No. A reflective polarizer having a three-layer structure consisting of three layers: G ") was provided.
On the λ / 4 plate produced by the above method, a light reflecting layer R was formed as a light reflecting layer formed by fixing a cholesteric liquid crystal phase using a discotic liquid crystal compound as a cholesteric liquid crystal material by the following method.
First, as an alignment layer, Sunever SE-130 (manufactured by Nissan Chemical Co., Ltd.) was dissolved in N-methylpyrrolidone, adjusted to a dry film thickness of 0.5 μm, and coated on a glass plate at 100 ° C. Heated for 5 minutes and heated at 250 ° C. for 1 hour. Further, this surface was rubbed to form an alignment layer.
Subsequently, a solute having the following composition is dissolved in MEK by adjusting the concentration so as to have a dry film thickness of the light reflecting layer R shown in Table 4 below, and applied for forming the light reflecting layer R containing a discotic liquid crystal compound. A liquid was prepared. This coating solution was applied onto the alignment layer with a bar, and the solvent was kept at 70 ° C. for 2 minutes to evaporate the solvent, followed by heat aging at 100 ° C. for 4 minutes to obtain a uniform alignment state.
Thereafter, this coating film was kept at 45 ° C. and irradiated with ultraviolet rays using a high-pressure mercury lamp in a nitrogen atmosphere to form a light reflection layer.
The light reflecting layer was bonded to the λ / 4 plate using the acrylic adhesive described above, and the glass plate was peeled off to form a light reflecting layer R in which the cholesteric liquid crystal phase was fixed.

  Further, cholesteric liquid crystalline mixtures using the following rod-like liquid crystal compounds are disclosed in JP2013-203827 (described in [0016]-[0148]) and Fuji Film Research Report No. 50 (2005) pp. The second light-reflecting layer and the second light-reflecting layer, which are light-reflecting layers formed by fixing a cholesteric liquid crystal phase using a rod-like liquid crystal compound as a cholesteric liquid crystal material by changing the addition amount of the chiral agent using 60-63 as a reference Three light reflecting layers were respectively produced on a PET film manufactured by FUJIFILM Corporation. After the second light reflecting layer was bonded to the first light reflecting layer using an acrylic adhesive, the PET film was attached. The PET film was peeled and formed after peeling and further bonding a third light reflecting layer thereon using an acrylic adhesive.

<Preparation of cholesteric liquid crystalline mixture using rod-shaped liquid crystal compound>
The following compounds 11 and 12, a fluorine-based horizontal alignment agent, a chiral agent, a polymerization initiator, and a solvent methyl ethyl ketone were mixed to prepare a coating solution having the following composition. The obtained coating liquid was made into the coating liquid which is a cholesteric liquid crystalline mixture.

<Reflective polarizer composed of dielectric multilayer>
The linearly polarized light reflective polarizing plate was peeled off from the backlight side polarizing plate used in iPad Air (trademark) manufactured by Apple.

<Quantum dot film>
With reference to Japanese Patent Application Laid-Open No. 2012-169271, a quantum that emits fluorescence of green light having a center wavelength of 535 nm and a half-value width of 40 nm and red light having a center wavelength of 630 nm and a half-value width of 40 nm when blue light from a blue light-emitting diode is incident. A dot film (wavelength conversion sheet) was formed.

<Manufacture of liquid crystal display devices>
Disassemble a commercially available liquid crystal display device (trade name TH-L42D2 manufactured by Panasonic Corporation), change the display side polarizing plate to the display type polarizing plate, change the backlight side polarizing plate to the polarizing plate, and change the backlight unit The liquid crystal display device of each Example and Comparative Example was manufactured by changing the backlight unit described in the table to a backlight unit composed of a backlight light source. That is, the liquid crystal cell uses the above-mentioned commercially available liquid crystal display device in FFS (Fringe Field Switching) mode.

For Examples 1 to 15 and Comparative Examples 1 to 4, a commercially available tablet (iPad (trademark) manufactured by Apple) was disassembled, and the white LED and the reflector / light guide plate / diffusion sheet / prism sheet / A backlight unit including a backlight sheet having a prism sheet / diffusion sheet configuration was used.
In Examples 18 and 19, a quantum dot film is further provided as a wavelength conversion sheet between the light guide plate and the diffusion sheet of the backlight unit, and a blue light emitting diode (Nichia) is used as a backlight light source instead of a white LED. A backlight unit having a B-LED, a main wavelength of 465 nm, and a half width of 20 nm was used.

  On the other hand, Example 16 and Example 17 differ in the structure of a backlight sheet from other structures. Regarding Example 16, a backlight obtained by disassembling a commercially available tablet, KindlFireHD (trademark), of the diffusion sheet and the prism sheet arranged on the liquid crystal unit side of the iPad (trademark) backlight sheet. The diffusing prism sheet in the uppermost layer (most liquid crystal unit side) of the sheet was used instead. For Example 17, a prism sheet taken out from the iPad (trademark) was used to form a resin-forming mold, and a UV curable resin was coated thereon and then cured with UV to prepare an acrylic resin low Re prism sheet. The diffusion sheet and the two prism sheets that were prepared and arranged on the liquid crystal unit side in the above-mentioned iPad (trademark) backlight sheet were replaced with acrylic resin-based low Re prism sheets.

Tables 2 to 4 summarize the details of the configurations of the examples and comparative examples and the evaluation results.

<Evaluation of liquid crystal display device>
The front and oblique colors of the liquid crystal display device during white display were measured using a colorimetric luminance meter (Spectroradiometer SR3 manufactured by Topcon), and the hues (a ^* , b ^* ) were measured.
(Sensory evaluation 1)
The front luminance at the time of white display was visually observed at a polar angle of 0 degrees, and sensory evaluation was performed according to the following criteria.
5: Brighter than the display device of Comparative Example 1.
4: Brighter than the display device of Comparative Example 1.
3: Equivalent to the display device of Comparative Example 1.
2: The brightness is slightly lower than that of the display device of Comparative Example 1.
1: Brightness is clearly lower than that of the display device of Comparative Example 1.
Note that the luminance of the display device of Comparative Example 1 is at a level that is not particularly problematic in use.

(Sensory evaluation 2)
The polar angle of 0 to 60 degrees and the omnidirectional angle of the liquid crystal display device were visually observed, and sensory evaluation was performed according to the following criteria.
5: Hue change is small and there is no problem in display performance.
4: Although there is some hue change, there is no problem in display performance.
3: There is a problem of hue change and display performance is a concern.
2: The hue change is large, which is a problem in display performance.
1: The hue change is very large, which is very problematic in display performance.

  FIG. 12 is a graph plotting the chromaticity at the time of white display of each Example and Comparative Example obtained by measurement.

In FIG. 12, a ^* = 0 and b ^* = 0 are neutral white. The range of the alternate long and short dash line (-2 <a, b ^* <9) is the range of the liquid crystal display device of the present invention, −2 <a ^* <5, −6 <b ^* <9 is preferable, and the range of the two-dot chain line (−1.5 <a ^* <3, −5 <b ^* <7) is more preferable, and broken line regions (0 <a ^* <2, −2 <b ^* <3) are particularly preferable ranges. In human vision, neutral white to slightly red are preferred. In FIG. 12, the diagonally upward-slashed area is a yellowish area, and the mesh area is a greenish area. While Comparative Examples 1 to 4 are all yellow or greenish white display, all the examples are within the range of the alternate long and short dash line. As described above, by using the absorbing polarizer of the present invention, it was possible to approximate neutral white.

5a, 5b, 5c, 5d Protective film 10 Display-side polarizing plate 11, 11G Reflective polarizer 12 λ / 4 plate 13 Circularly polarized reflective polarizer 14 Dielectric multilayer (linearly polarized reflective polarizer)
15 Light conversion sheet 16A, 16D, 16E Backlight sheet 17 Adhesive 18 UV adhesive 19 Orientation film 20A-20C, 20G Polarizing plate (backlight side polarizing plate)
30A, 30D-30F Backlight unit 40 Liquid crystal cell 50A-50G Liquid crystal display device

Claims (5)

In a liquid crystal display device, a polarizing plate disposed between a liquid crystal cell and a light source,
A reflection polarizer and a dichroic dye-coated absorption polarizer are laminated.
The absorbing polarizer has a transmittance of 650 nm light at the absorption polarizer T ₆₅₀ , a transmittance of 550 nm light at T ₅₅₀ , a transmittance of 450 nm light at T ₄₅₀ , and a transmittance of 400 nm light at T _400. When
1.11> T ₆₅₀ / T ₅₅₀ ≧ 1.00
1.11> T ₄₅₀ / T ₅₅₀ ≧ 0.95
1.11> T ₄₀₀ / T ₄₅₀ ≧ 0.65
A polarizing plate characterized by satisfying 1.11> T ₄₀₀ / T ₄₅₀ ≧ 0.96
The polarizing plate of Claim 1 which satisfy | fills. The reflective polarizer includes a λ / 4 plate and a circularly polarized reflective polarizer in this order from the absorbing polarizer side,
The polarizing plate according to claim 1, wherein the circularly polarizing reflective polarizer includes a light reflecting layer formed by fixing at least one cholesteric liquid crystal phase.   The polarizing plate according to claim 1, wherein the absorbing polarizer is a coating type polarizer using a thermotropic liquid crystalline dichroic dye. In a liquid crystal display device including a display side polarizing plate, a liquid crystal cell, a backlight side polarizing plate and a backlight unit in this order,
As the backlight side polarizing plate, using the polarizing plate according to any one of claims 1 to 4,
A liquid crystal display device in which chromaticity a *> − 2 and b * <9 of image light in a screen normal direction during white display.