Retardation plate, and circularly polarizing plate, liquid crystal display device, and organic EL display device equipped with the same

Abstract

This retardation plate comprises a first optically anisotropic layer in which the spiral axis of a stick-shaped liquid crystal compound is aligned with the direction of thickness and which has an in-plane phase difference (Re) of substantially 1 / 2 wavelength, and a second optically anisotropic layer in which the spiral axis of a stick-shaped liquid crystal compound is aligned with the direction of thickness and which has an in-plane phase difference (Re) of 1 / 4 wavelength, the retardation plate being characterized by further comprising a third optically anisotropic layer that is disposed between the first optically anisotropic layer and the second optically anisotropic layer and that satisfies equation (1). Equation (1): nx ≃ ny < nz (In the equation, nx and ny are refractive indices in the plate planar directions crossing each other at a right angle, and nz is the refractive index in the direction perpendicular to the plate planar direction.)

Description

[Technical field]

[0001] The present invention relates to a retardation plate useful for liquid crystal displays and organic EL displays, and to a circular polarizing plate, a liquid crystal display, and an organic EL display provided with the retardation plate. [Background technology]

[0002] Retarders for circular polarizers are used in a wide range of applications in flat panel displays.

[0003] Conventionally, a method has been proposed for reducing reflection of external light by disposing a circular polarizer on the surface of an image display panel or the like. This circular polarizer is composed of a linear polarizer and a quarter-wave retardation plate (hereinafter also referred to as a λ / 4 plate), and external light toward the display surface of the image display panel is converted into linearly polarized light by the linear polarizer, and then converted into circularly polarized light by the subsequent quarter-wave retardation plate. Here, this circularly polarized external light is reflected by the surface of the image display panel, etc., and the rotation direction of the circularly polarized light is reversed during this reflection. As a result, this reflected light is converted into linearly polarized light in a direction that is blocked by the quarter-wave retardation plate and the linear polarizer, in the opposite direction to when it arrived, and is then blocked by the subsequent linear polarizer, suppressing exposure of the reflected light to the outside.

[0004] Conventionally, the retardation plate used in this circular polarizer has a problem that, due to the wavelength dependency (wavelength dispersion) of the retardation value, when used for anti-reflection of an organic EL display device, it does not function as a λ / 4 plate for each wavelength band in the visible light range, and coloring occurs in a dark state (black display). In particular, the above problem is more prominent when the display device is observed at a viewing angle. In order to prevent this, a retardation plate for a circular polarizer that functions as approximately 1 / 4 wavelength in a wide wavelength band and can realize anti-reflection at a wide viewing angle is required. A uniaxially or biaxially stretched retardation plate is used for the above retardation plate. Furthermore, a method of using one or more layers of twisted nematic liquid crystal layers (twisted nematic liquid crystal layers) has also been disclosed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-209220 A [Patent Document 2] JP 2014-224837 A Summary of the Invention [Problem to be solved by the invention]

[0006] For example, a λ / 4 plate obtained by biaxially stretching a modified polycarbonate (PC)-based film is known as a retardation plate for widening the viewing angle. However, a retardation plate obtained by laminating the retardation plate and a λ / 4 plate and a λ / 2 plate described later exhibits inverse wavelength dispersion for retardation values ​​in the visible light wavelength range, but does not sufficiently suppress coloring when viewed from an oblique direction.

[0007] In addition, there is a retardation plate with a wide viewing angle, which is formed by laminating a λ / 4 plate and a λ / 2 plate obtained by uniaxially stretching a cycloolefin (COP) film. However, in this laminated retardation plate, each retardation plate must be cut out so that it has a predetermined optical axis angle with respect to the optical axis of the polarizing plate, and then laminated in sheets using an adhesive layer or the like, which causes a problem in productivity.

[0008] Patent Document 1 also describes that a broadband λ / 4 plate is realized that can convert linearly polarized light of a wider wavelength range into more perfect circularly polarized light than known uniaxially stretched λ / 4 and λ / 2 retardation plates, by using two consecutive layers of twisted nematic liquid crystals with controlled twist angle and Δnd (product of refractive index difference (Δn) and film thickness (d)). However, the circular polarizer using the λ / 4 plate has only been observed from directly above, and the display properties (black reproducibility and coloring) when viewed from an oblique direction have not been fully discussed.

[0009] Regarding the retardation plate, it is generally known that the display performance from an oblique direction can be improved by adding a positive C-plate layer having a retardation value in a predetermined range in the thickness direction. For example, Patent Document 2 attempts to improve the display performance from an oblique direction by adding a positive C-plate layer to the material of a λ / 2 plate and a λ / 4 plate.

[0010] As described above, the conventional configuration using two twisted nematic liquid crystal layers that function as λ / 2 and λ / 4 plates, the broadband λ / 4 wavelength retardation plate that is simply a combination of stretched films, and the circular polarizer that also has a positive C plate layer are not satisfactory in terms of the black reproducibility (low black luminance) and color display performance of the display device when viewed from an oblique direction, and further improvements are required. In addition, the thickness direction retardation value (Rth) of the positive C plate layer and the optimal positional relationship with the retardation plate have not yet been discussed.

[0011] The present application aims to provide a broadband retardation plate for a circular polarizer that reduces the black luminance in black display when viewed from an oblique direction (to display a good black color), a circular polarizer including the same, and a liquid crystal display device and an organic EL display device including the circular polarizer. [Means for solving the problem]

[0012] The inventors of the present invention have conducted extensive research to solve the above problems, and as a result, have succeeded in reducing the black luminance in black display when viewed from an oblique direction by using a positive C-plate layer between two liquid crystal layers having a twisted alignment in the thickness direction.

[0013] That is, the present invention relates to the following inventions, but is not limited thereto. [Invention 1] a first optically anisotropic layer in which rod-like liquid crystal compounds are aligned along a thickness direction with a helical axis and which has an in-plane retardation value (Re) of substantially 1 / 2 wavelength; a second optically anisotropic layer in which rod-like liquid crystal compounds are aligned along a helical axis in the thickness direction and which has an in-plane retardation value (Re) of substantially ¼ wavelength; A retardation plate comprising: Between the first and second optically anisotropic layers, there is formed a layer having the following formula (1): n x ≒n y <n z (1) (n in the formula x and n y is the refractive index in the perpendicular plate plane direction, n z indicates the refractive index perpendicular to the plate plane) and a third optically anisotropic layer satisfying the above. A retardation plate characterized by: [Invention 2] The retardation plate according to invention 1, wherein the twist angle of the first optically anisotropic layer is substantially 26° or substantially −26°, and the twist angle of the second optically anisotropic layer is substantially 78° or substantially −78° from the twist angle of the first optically anisotropic layer. [Invention 3] 3. The retardation plate according to claim 2, wherein the third optically anisotropic layer is a layer having a vertical alignment type liquid crystal compound and has a thickness direction retardation value (Rth) of −150 to −80 nm. [Invention 4] A circular polarizing plate comprising a polarizing element and the retardation plate according to any one of Inventions 1 to 3. [Invention 5] 5. The circularly polarizing plate according to claim 4, wherein the polarizing element contains a dichroic azo dye, the hue of which is achromatic. [Invention 6] An organic EL display device comprising the circular polarizer according to invention 4 or 5. [Invention 7] A liquid crystal display device comprising the circular polarizing plate according to invention 4 or 5. Effect of the Invention

[0014] The present application can provide a broadband retardation plate for a circular polarizer that reduces black luminance and / or reduces coloring in black display when viewed from an oblique direction, a circular polarizer having the same, and a liquid crystal display (LCD) and an organic electroluminescence (EL) display (organic light-emitting diode (OLED) display) having the circular polarizer. In one aspect, a display device that displays a good black color when viewed from the front can be provided. In one aspect, the present application can provide a thin retardation plate. In one aspect, the present application can achieve a black color with lower luminance and significantly reduced coloring in black display of LCD and OLED display devices not only in the head-on (front) orientation but also in a wider orientation with a varying viewing angle. In one aspect, the present application can provide a manufacturing method that enables the production of a circular polarizer by only roll-to-roll lamination without requiring complicated processes such as sheet lamination and oblique stretching. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view of a retardation plate according to one embodiment of the present invention. [Diagram 2] FIG. 1 is a cross-sectional view of a circular polarizing plate according to one embodiment of the present invention. [Diagram 3] FIG. 1 is an explanatory diagram of a "first embodiment" of the present invention. [Figure 4] 1 is a contour map of luminance for polar angles of 0° to 80° and azimuth angles of 0° to 360° in Example 1. [Diagram 5] 13 is a contour map of luminance for polar angles of 0° to 80° and azimuth angles of 0° to 360° in Example 2. [Figure 6] 13 is a contour map of luminance for polar angles of 0° to 80° and azimuth angles of 0° to 360° in Example 3. [Figure 7] 13 is a contour map of luminance for polar angles of 0° to 80° and azimuth angles of 0° to 360° in Comparative Example 1. [Figure 8] 13 is a contour map of luminance for polar angles of 0° to 80° and azimuth angles of 0° to 360° in Comparative Example 2. [Figure 9] 13 is a contour map of luminance for polar angles of 0° to 80° and azimuth angles of 0° to 360° in Comparative Example 3. [Figure 10] 13 is a contour map of luminance for polar angles of 0° to 80° and azimuth angles of 0° to 360° in Comparative Example 4. [Figure 11] 13 is a contour map of luminance for polar angles of 0° to 80° and azimuth angles of 0° to 360° in Comparative Example 5. [Figure 12] 13 is a contour map of luminance for polar angles of 0° to 80° and azimuth angles of 0° to 360° in Comparative Example 6. [Figure 13] 1 shows experimental results for the circular polarizers of Examples 1 to 3 at a polar angle (tilt angle) of 40° and an azimuth angle of 0 to 360° (in 45° increments). [Figure 14] 1 shows experimental results for the circular polarizers of Examples 1 to 3 at a polar angle (tilt angle) of 50° and an azimuth angle of 0 to 360° (in 45° increments). [Figure 15] 1 shows experimental results for the circular polarizers of Examples 1 to 3 at a polar angle (tilt angle) of 60° and azimuth angles of 0 to 360° (in 45° increments). [Figure 16] 1 shows experimental results for the circular polarizers of Example 1 and Comparative Examples 1 to 3 at a polar angle (tilt angle) of 40° and an azimuth angle of 0 to 360° (in increments of 45°). [Figure 17] 1 shows experimental results for the circular polarizers of Example 1 and Comparative Examples 1 to 3 at a polar angle (tilt angle) of 50° and an azimuth angle of 0 to 360° (in 45° increments). [Figure 18] 1 shows experimental results for the circular polarizers of Example 1 and Comparative Examples 1 to 3 at a polar angle (tilt angle) of 60° and an azimuth angle of 0 to 360° (in 45° increments). [Figure 19] 1 shows experimental results for the circular polarizers of Example 1 and Comparative Examples 4 to 6 at a polar angle (tilt angle) of 40° and an azimuth angle of 0 to 360° (in increments of 45°). [Figure 20] 1 shows experimental results for the circular polarizers of Example 1 and Comparative Examples 4 to 6 at a polar angle (tilt angle) of 50° and an azimuth angle of 0 to 360° (in 45° increments). [Figure 21] 1 shows experimental results for the circular polarizers of Example 1 and Comparative Examples 4 to 6 at a polar angle (tilt angle) of 60° and an azimuth angle of 0 to 360° (in 45° increments). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described.

[0017] (phase plate) A retardation plate (wave plate) means an optical element that gives a predetermined phase difference to an incident linearly polarized light. The retardation plate according to the present invention comprises two optically anisotropic layers (first and second optically anisotropic layers) as a λ / 2 plate and a λ / 4 plate, respectively, and further comprises a third optically anisotropic layer between the first and second optically anisotropic layers for suppressing coloring when viewed from an oblique direction. The retardation plate according to the present invention is suitable for a circular polarizing plate, and is particularly suitable for a broadband circular polarizing plate. The method for producing the retardation plate of the present invention is not particularly limited, and it can be produced by a known method such as roll-to-roll. A broadband retarder is generally a retarder that provides a nearly constant phase difference for all wavelengths in the visible light range (380 nm to 780 nm) when linearly polarized light is incident on the retarder. Therefore, a retarder used to manufacture a circular polarizer provides a phase difference of approximately 1 / 4 wavelength for all wavelengths in the visible light range.

[0018] (First and second optically anisotropic layers) The first optically anisotropic layer according to the present invention has an in-plane retardation value (Re) of substantially 1 / 2 wavelength and functions as a λ / 2 plate. As long as the retardation plate according to the present invention is suitable for use as a circular polarizer, the Re does not have to be completely 1 / 2 wavelength. For example, it includes a numerical range of ±20%, 15%, 10%, 5%, 2%, or 1%. The second optically anisotropic layer according to the present invention has an in-plane retardation value (Re) of substantially ¼ wavelength and functions as a λ / 4 plate. The term "substantially" has the same meaning as above.

[0019] The liquid crystal compounds forming the first and second optically anisotropic layers are generally classified into rod-shaped type (rod-shaped liquid crystal compounds) and discotic type (discotic liquid crystal compounds) based on their shape. In the present invention, it is preferable to form a twisted nematic (TN) liquid crystal layer using rod-shaped liquid crystal compounds. The TN liquid crystal layer is a liquid crystal layer in which nematic liquid crystal, in which rod-shaped, elongated molecules are aligned in a roughly fixed direction, is continuously changed in molecular direction into a twisted spiral shape due to chirality. The TN liquid crystal layer is preferably a layer formed by fixing a rod-shaped liquid crystal compound having a polymerizable group by polymerization or the like, and in this case, it is not necessary for the layer to show liquid crystallinity. The type of polymerizable group contained in the rod-shaped liquid crystal compound is not particularly limited, and a functional group capable of an addition polymerization reaction is preferable, and a polymerizable ethylenically unsaturated group or a ring-polymerizable group is preferable. More specifically, a (meth)acryloyl group, a vinyl group, a styryl group, an allyl group, etc. are preferable, and a (meth)acryloyl group is more preferable. In the present invention, a known TN liquid crystal material can be used. In addition, when forming the TN liquid crystal layer, a chiral agent may be used as desired together with the above liquid crystal compound, if necessary. The chiral agent is added to cause the liquid crystal compound to be twisted and aligned.

[0020] Furthermore, by using the above-mentioned polymerizable liquid crystal material for the retardation plate, the thickness can be reduced to 5 μm to 20 μm, compared with a film-type retardation plate that generally has a thickness of 50 μm to 100 μm.

[0021] The first and second optically anisotropic layers in the retardation plate of the present invention are twisted with the thickness direction as the helical axis. The twist directions of both liquid crystal layers are the same. The in-plane slow axis of the first optically anisotropic layer on the third optically anisotropic layer side is parallel to the in-plane slow axis of the second optically anisotropic layer on the third optically anisotropic layer side. That is, the twist angle of the second optically anisotropic layer is arranged based on the twist angle of the first optically anisotropic layer. The positive and negative (minus: -) twist angles are indicated by taking the absorption axis direction of the polarizing element as 0°, and when the polarizing element of the circular polarizing plate is on the viewing side, the counterclockwise direction from the absorption axis is indicated as positive, and the clockwise direction from the absorption axis is indicated as negative.

[0022] The twist angle of the first optically anisotropic layer used in the retardation plate of the present invention is substantially 26° in one embodiment. More specifically, 26±10° is preferable, 26±7° is more preferable, and 26±5° is even more preferable. In this case, the twist angle of the second optically anisotropic layer is substantially 78°. More specifically, 78±10° is preferable, 78±7° is more preferable, and 78±5° is even more preferable. Or, the twist angle of the first optically anisotropic layer is substantially -26° in another embodiment. More specifically, -26±10° is preferable, -26±7° is more preferable, and -26±5° is even more preferable. In this case, the twist angle of the second optically anisotropic layer is substantially -78°. More specifically, -78±10° is preferable, -78±7° is more preferable, and -78±5° is even more preferable. The twist angle is measured using a film inspection device (RETS-1100A, manufactured by Otsuka Electronics Co., Ltd.).

[0023] In the first optically anisotropic layer used in the retardation plate of the present invention, the in-plane retardation value (Re), which is the product (Δn1·d1) of the refractive index anisotropy Δn1 at a wavelength of 550 nm and the thickness d1 of the liquid crystal layer, is substantially 275 nm. More specifically, the product (Δn1·d1) is preferably 275±30 nm, more preferably 275±20 nm, and even more preferably 275±10 nm.

[0024] In the second optically anisotropic layer used in the retardation plate of the present invention, the surface retardation value (Re) which is the product (Δn2·d2) of the refractive index anisotropy Δn2 at a wavelength of 550 nm and the thickness d2 of the liquid crystal layer is substantially 137.5 nm, and more specifically, the product (Δn2·d2) is preferably 137.5±15 nm, more preferably 137.5±10 nm, and further preferably 137.5±5 nm. The above Δn1·d1 and Δn2·d2 are measured using a film inspection device (RETS-1100A, manufactured by Otsuka Electronics Co., Ltd.).

[0025] (Third optically anisotropic layer) The third optically anisotropic layer of the retardation plate of the present invention is a type of retardation plate called a positive C plate. When orthogonal x and y axes are set on the plate plane and the z axis is set perpendicular to the plate plane, the refractive index in each axis direction is n x , n y , n z But, n x ≒n y <n z In addition, "n x ≒n y " is n x and y The above "n" means that the number of the elements is substantially equal to the number of the elements, including the case where the number of the elements is completely equal to the number of the elements. x and y "Substantially equal" means that n x and y may differ, for example, from one side to the other by 20%, 15%, 10%, 5%, 2%, or 1%.

number

[0026] The thickness direction retardation (Rth) of the third optically anisotropic layer of the present invention is determined based on the Poincaré sphere theory. It is preferable to set an optimal value range to minimize the trajectory of movement from the coordinate on the equator showing linearly polarized light to the coordinate showing circularly polarized light on the north pole or south pole on the Poincaré sphere, specifically, a range of -150 to -80 nm is preferable, a range of -132 to -112 nm is more preferable, and a range of -126 to -120 nm is even more preferable. Furthermore, it is preferable to dispose the third optically anisotropic layer between the above-mentioned first optically anisotropic layer and the second optically anisotropic layer. Thereby, the circularly polarized light of each wavelength generated by the retardation plate of the present invention is concentrated at the coordinate showing circularly polarized light on the north pole or south pole on the Poincaré sphere, and the circularly polarized light of each wavelength is formed close to ideal. Therefore, in a display device or the like in which the circularly polarizing plate of the present invention is mounted, coloring when viewed from an oblique direction can be suppressed.

[0027] (Alignment treatment) The first and second optically anisotropic layers of the present invention are provided with a treatment for aligning liquid crystal compounds on a substrate, or with an alignment film. The liquid crystal alignment is not particularly limited, and any alignment technique known in the art can be used, as long as it properly defines the alignment direction of the optically anisotropic layer and does not prevent the present invention from exhibiting the desired performance. The substrate surface may be physically anisotropic using a rubbing roll rotating in a direction of about 0 to 50° relative to the substrate conveying direction, or a method of subjecting a resin layer provided on a substrate as disclosed in JP-A-2003-014935 to the rubbing treatment may be used, or a photo-alignment film may be used in which an alignment film is formed by providing anisotropy to a polymer film using linearly polarized ultraviolet light.

[0028] (Polarizing element) The polarizing element (sometimes called a polarizer or a polarizing film) used to obtain the circular polarizing plate, liquid crystal display device, and organic EL display device of the present invention is not particularly limited, and a known polarizing element can be appropriately selected and used depending on the application. For example, a polarizing element obtained by uniaxially stretching a polyvinyl alcohol (PVA)-based film impregnated with a dichroic dye such as a water-soluble dichroic dye and / or polyiodine ion in a boric acid warm water bath, a polarizing element obtained by uniaxially stretching a polyvinyl alcohol film and then forming a polyene structure by a dehydration reaction, a polarizing element obtained by applying a solution containing a dichroic dye onto a substrate film to orient the dichroic dye, and a substrate-integrated polarizing element obtained by providing a polyvinyl alcohol layer on a protective film, uniaxially stretching the film together with the substrate film, and then impregnating the dichroic dye, etc. can be mentioned. From the viewpoint of processability and optical properties, a polarizing element obtained by uniaxially stretching a PVA-based film and adsorbing and orienting a dichroic dye can be typically used. An example of a commercially available PVA film is VF-PS (thickness 75 μm) manufactured by Kuraray. In this case, a dichroic dye is generally adsorbed and aligned, and then the film is uniaxially stretched to a thickness of 25 μm to 35 μm to obtain a polarizing element.

[0029] The dichroic dye is preferably an iodine ion or a dichroic dye, and any of them can be used to obtain the polarizing element of the present invention. Examples of the dichroic dye include azo dyes, anthraquinone dyes, and tetrazine dyes, and from the viewpoint of hue design and durability against heat, it is preferable to use a mixture of two to three or more azo dyes. In addition, when any dichroic dye is used, the optical characteristics of the polarizing element preferably have high transmittance and high polarization degree (also called high dichroism) from the viewpoint of obtaining anti-reflection ability and excellent black display performance in the display device to which it is mounted, and more specifically, it is preferable that the luminous efficiency-corrected single transmittance (Ys) is 40% to 45%, and the luminous efficiency-corrected polarization degree (Py) is 99% or more.

[0030] In one embodiment of the present invention, it is preferable that the polarizing element has an achromatic hue, that is, the single transmittance (Ts) of the polarizing element is preferably almost uniform over the visible light range (wavelength 400 nm to 700 nm, more preferably 380 nm to 780 nm). A specific embodiment of the achromatic hue is also preferable in which the absolute values ​​of a* and b* in the L*a*b* color system are 1 or less when measured on a polarizing element alone, and the absolute value of a* is 4 or less and the absolute value of b* is 8 or less when two polarizing elements are overlapped so that the absorption axis directions are perpendicular to each other and measured. Thereby, for example, the circular polarizing plate having the broadband retardation plate of the present invention can suppress coloring of reflected light from a display device over the visible light range, as well as suppress coloring of reflected light from the surface of the polarizing element over the visible light range.

[0031] Examples of azo dyes having dichroism include CIDirect Yellow 12, CIDirect Yellow 28, CIDirect Yellow 44, CIDirect Yellow 142, CIDirect Orange 26, CIDirect Orange 39, CIDirect Orange 71, CIDirect Orange 107, CIDirect Red 2, CIDirect Red 31, CIDirect Red 79, CIDirect Red 81, CIDirect Red 117, CIDirect Red 247, CIDirect Green 80, CIDirect Green 59, CIDirect Blue 71, CIDirect Blue 78, CIDirect Blue 168, CIDirect Blue 202, CIDirect Violet 9, CIDirect Violet 51, CIDirect Brown 106, and CIDirect Brown 223. In addition, dyes that can be produced by known methods may be used, and examples of known methods include the method described in JP-A-3-12606 or the method described in JP-A-59-145255. In addition, commercially available dyes include Kayafect Violet P Liquid, Kayafect Yellow Y, Kayafect Orange G, Kayafect Blue KW, and Kayafect Blue Liquid 400 (all manufactured by Nippon Kayaku Co., Ltd.). These azo dyes are used in combination of 2 to 3 types so that the transmittance in the visible light range is uniform. Furthermore, in the polarizing element according to the present invention, in order to obtain an achromatic polarizing element with high transmittance and high polarization degree, azo dyes with improved dichroism for designing an achromatic polarizing element disclosed in International Publication WO2017 / 146212, International Publication WO2019 / 117131, etc. can be suitably used.

[0032] The polarizing element preferably includes a substrate (also referred to as a support or a support film) for protecting the polarizing element. The substrate may be disposed on only one side of the polarizing element, or may be disposed on both sides of the polarizing element so that two identical or different substrates sandwich the polarizing element. A configuration in which a polarizing element has a substrate is called a polarizing plate. When the polarizing element includes a substrate described later, the substrate disposed between the polarizing element and the display device preferably has an in-plane retardation value (Re) and thickness direction retardation value (Rth) of 0 or nearly 0 (to the extent that the effect can be ignored as a numerical value, for example, in the range of −5 nm to 5 nm).

[0033] (base material) The retardation plate and circular polarizing plate of the present invention (hereinafter also referred to as the article of the present invention) may have a substrate. As the substrate, there is no particular limitation, and any substrate known in the art can be used as long as it has the desired mechanical strength, thermal stability, etc., and does not prevent the present invention from exhibiting the desired performance. The thickness of the substrate can be appropriately designed, but is preferably 50 to 200 μm, more preferably 10 to 100 μm, and even more preferably 20 to 80 μm.

[0034] In addition, when a substrate is disposed between the polarizing element and the display device, the in-plane retardation value (Re) and thickness direction retardation value (Rth) of the substrate are preferably 0 or approximately 0. Examples of commercially available substrates having the above retardation values ​​include triacetyl cellulose-based resin film Z-TAC (manufactured by Fujifilm Corporation) and acrylic resin film OXIS series (manufactured by Okura Kogyo Co., Ltd.).

[0035] (Adhesive and / or adhesive) In the article of the present invention, a laminate may be formed by providing a next layer on a layer, or a laminate may be formed by bonding a plurality of layers with a pressure-sensitive adhesive and / or adhesive. There is no particular limitation, and any pressure-sensitive adhesive or adhesive known in the art may be used as long as it functions as a pressure-sensitive adhesive or adhesive and does not prevent the present invention from achieving the desired performance. Representative examples of pressure-sensitive adhesives include acrylic resins. The thickness can be appropriately designed, but is preferably 1 to 50 μm, and more preferably 5 to 25 μm from the viewpoints of adhesion between layers and processability of pressure-sensitive adhesive application and lamination. Examples of adhesives include water-based adhesives mainly composed of PVA resins, adhesives containing thermosetting or photocurable resins, and methods using plasma bonding.

[0036] The retardation value and twist angle value of the optically anisotropic layer of the present invention are values ​​that provide good optical effects. These values ​​are not limited and may include tolerances and margins, taking into consideration the alignment characteristics of the actual liquid crystal compound and product processability.

[0037] (Circular polarizing plate) The circular polarizer of the present invention is a broadband circular polarizer, and includes a polarizing element and the retardation plate of the present invention, and more specifically, includes a polarizing element (or polarizing plate), a first optically anisotropic layer, a third optically anisotropic layer, and a second optically anisotropic layer in this order. In one embodiment, the optical axes of the circular polarizer are such that the absorption axis of the polarizing element is in the direction of 0°, the twist angle of the first optically anisotropic layer is substantially in the direction of 26° with respect to the absorption axis of the polarizing element, and the twist angle of the second optically anisotropic layer is substantially in the direction of 78° from the twist angle of the first optically anisotropic layer (i.e., in the direction of 104° with respect to the absorption axis of the polarizing element).

[0038] The method for producing the circular polarizing plate of the present invention is not particularly limited, and for example, the films or sheets of the above-mentioned layers may be laminated one by one, or the above-mentioned layers produced in roll form may be continuously laminated by roll-to-roll. In particular, the circular polarizing plate of the present invention does not need to cut out the retardation plate according to a predetermined optical axis angle, so that the latter lamination by roll-to-roll can be easily performed. Therefore, the productivity can be improved compared to the conventional manufacturing method of a wideband circular polarizing plate in which a uniaxially stretched film such as a COP film is laminated.

[0039] (Manufacturing method of circularly polarizing plate) The method for producing the retardation plate and the circular polarizer according to the present invention will be described below with reference to the first and second embodiments, but is not limited thereto. Each optically anisotropic layer may be formed on a substrate that is peelable from the liquid crystal layer and the substrate after curing, and each substrate may be removed in the step of successive lamination described later to form a circular polarizer.

[0040] (First embodiment) In the first step, a coating composition containing a liquid crystal compound exhibiting a polymerizable nematic liquid crystal phase, a chiral agent, a photopolymerization initiator, and a dilution solvent is applied to the rubbed surface of a substrate that has been rubbed in the 0° direction (transport direction), and then the solvent is removed through a drying step. The coating film is then cured by irradiating with light to obtain a first optically anisotropic layer having an alignment axis in the 0° direction, a twist angle of 26°, and a phase difference value (Re@550nm) of 275nm. In the second step, a coating composition containing a liquid crystal compound exhibiting a polymerizable nematic liquid crystal phase, a photopolymerization initiator, and a dilution solvent is applied to a substrate, followed by a drying step to remove the solvent, and then the coating is cured by irradiation with light to obtain a third optically anisotropic layer oriented perpendicular to the substrate. In the third step, a coating composition containing a TN liquid crystal material, a chiral agent, a photopolymerization initiator, and a dilution solvent is applied to the rubbed surface of the substrate that has been rubbed in a direction at 26° to the transport direction, and then a drying step is performed to remove the solvent. The coating film is then cured by irradiating light to obtain a second optically anisotropic layer having an alignment axis in the 26° direction, a twist angle of 78°, and a phase difference value (Re@550nm) of 137.5nm. In the fourth step, a polarizing element (or polarizing plate), a first optically anisotropic layer, a third optically anisotropic layer and a second optically anisotropic layer are sequentially laminated so as to have the optical axis relationship shown in Figure 3, thereby obtaining the circular polarizing plate of the present invention.

[0041] (Second embodiment) In the second step, a coating composition containing a liquid crystal compound exhibiting a polymerizable nematic liquid crystal phase, a photopolymerization initiator, and a dilution solvent is applied to the liquid crystal surface of the first optically anisotropic layer obtained in the first step, and then the solvent is removed through a drying step, and the coating is cured by irradiating light to obtain a third optically anisotropic layer oriented in a direction perpendicular to the liquid crystal surface. The process is the same as the first embodiment, except that a polarizing element (or polarizing plate), the first optically anisotropic layer on which the third optically anisotropic layer is laminated, and the second optically anisotropic layer are sequentially laminated so as to have the optical axis relationship shown in Figure 3, thereby obtaining a circular polarizing plate of the present invention.

[0042] (display device) The circularly polarizing plate of the present invention can be preferably applied to the viewing side of various display devices such as liquid crystal display devices (LCDs) and organic electroluminescence (EL) display devices (organic light-emitting diode (OLED) display devices). Furthermore, the display device may be configured to include a touch panel, an anti-glare layer, an anti-reflection layer, a light-transmitting cover (also called a front panel), etc., depending on the design. The light-transmitting cover may have a flat shape or a curved shape. The method for producing the display device of the present invention is not particularly limited, and the display device may be produced by a known method.

[0043] The liquid crystal display device of the present invention may be configured to include a liquid crystal panel called a transmissive or semi-transmissive type and a backlight unit, or may be configured to include a liquid crystal panel called a reflective type and a reflective layer.

[0044] In addition, since an organic EL display device generally has a metal electrode in the display panel portion, the OLED (organic EL display device) itself has a higher reflectance than a liquid crystal panel. For example, when used in an environment with a lot of external light, such as outdoors during the day, the external light reflection from the electrode causes the display quality to be impaired. Therefore, a circular polarizing plate is generally attached to the viewing side of the organic EL display device to suppress the external light reflection. Therefore, the display characteristics of the organic EL display device also depend on the optical characteristics of the circular polarizing plate. The circular polarizing plate of the present invention has a wider viewing angle characteristic than conventional circular polarizing plates, and can be suitably used for organic EL display devices that require a wide viewing angle.

[0045] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications and changes are possible based on the technical concept of the present invention. EXAMPLES

[0046] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0047] Assuming that the circular polarizer is attached to an ideal reflector, the black luminance (units are normalized values) at the following azimuth and tilt angles (polar angles) was calculated using liquid crystal simulation software LCDmaster (manufactured by Shintech Co., Ltd.). The configuration of the circular polarizer and the calculation conditions are as follows. Table 1 shows a list of the calculation conditions and the arrangement of the optically anisotropic layers. The in-plane retardation value (Re) and thickness direction retardation value (Rth) are shown at a wavelength of 550 nm. In addition, in Table 1, the arranged optically anisotropic layers are shown in the columns for the first layer, second layer, and third layer, in order from the incident light side. Structure of a circular polarizer: Example 1: (in order from the incident light side) a polarizing element, a first optically anisotropic layer, a third optically anisotropic layer 1, a second optically anisotropic layer, and a reflector Example 2: (in order from the incident light side) a polarizing element, a first optically anisotropic layer, a third optically anisotropic layer 2, a second optically anisotropic layer, and a reflector Example 3: (in order from the incident light side) a polarizing element, a first optically anisotropic layer, a third optically anisotropic layer 3, a second optically anisotropic layer, and a reflector Example 4: (in order from the incident light side) a polarizing element, a first optically anisotropic layer, a third optically anisotropic layer 4, a second optically anisotropic layer, and a reflector Example 5: (in order from the incident light side) a polarizing element, a first optically anisotropic layer, a third optically anisotropic layer 5, a second optically anisotropic layer, and a reflector Comparative Example 1: (in order from the incident light side) a polarizing element, a first optically anisotropic layer, a second optically anisotropic layer, a third optically anisotropic layer 1, and a reflector Comparative Example 2: (in order from the incident light side) a polarizing element, a third optically anisotropic layer 1, a first optically anisotropic layer, a second optically anisotropic layer, and a reflector Comparative Example 3: (in order from the incident light side) a polarizing element, a first optically anisotropic layer, a second optically anisotropic layer, and a reflector Comparative Example 4: (in order from the incident light side) a polarizing element, a general half-wave plate 1, a third optically anisotropic layer 6, a general quarter-wave plate 1, and a reflector Comparative Example 5: (in order from the incident light side) a polarizing element, a general half-wave plate 2, a third optically anisotropic layer 7, a general quarter-wave plate 2, and a reflector Comparative Example 6: (in order from the incident light side) a polarizing element, a general half-wave plate 1, a general quarter-wave plate 1, a third optically anisotropic layer 8, and a reflector First optically anisotropic layer: Liquid crystal layer: ZLI-4792 (Merck) Phase difference caused = 1 / 2λ Δn1·d1=275nm Pre-twist angle = 0° Twist angle = -26° Liquid crystal layer thickness = 2.136 μm Second optically anisotropic layer: Liquid crystal layer: ZLI-4792 (Merck) Phase difference caused = λ / 4 Δn2 d2 = 137.5 nm Pre-twist angle = -26° Twist angle = -78° Liquid crystal layer thickness = 1.068 μm Third optically anisotropic layer: Liquid crystal layer: Polymerizable vertical alignment type liquid crystal compound (Merck) n x =1.5283 n y =1.5283 n z =1.6725 Liquid crystal layer thickness = 0.60μm~1.45μm Rth: See 1 to 8 below Third optically anisotropic layer 1: Rth=-120nm Third optically anisotropic layer 2: Rth=-115nm Third optically anisotropic layer 3: Rth=-130nm Third optically anisotropic layer 4: Rth=-80nm Third optically anisotropic layer 5: Rth=-150nm Third optically anisotropic layer 6: Rth=-174nm Third optically anisotropic layer 7: Rth=-209nm Third optically anisotropic layer 8: Rth=-133nm Polarizing element: JET-12 (manufactured by Polatechno Co., Ltd., using spectral data of luminous efficiency-corrected single transmittance Ys = 41.5% and luminous efficiency-corrected polarization degree Py = 99.99%, no support layer) Reflector: Material: Ideal reflector Common Half Wave Plates (HWP)1: Material: Cycloolefin Polymer (COP) Nz coefficient = 1.0 Common Quarter Wave Plates (QWP)1: Material: Cycloolefin Polymer (COP) Nz coefficient = 1.0 Common Half Wave Plates (HWP)2: Material: Cycloolefin Polymer (COP) Nz factor = 1.5 Common Quarter Wave Plates (QWP)2: Material: Cycloolefin Polymer (COP) Nz factor = 1.5 Incident light: Natural light (wavelength range: 380nm~780nm) Tilt angle (polar angle) θ = 40°, 50°, and 60° Azimuth angle Φ=0°~360° (each in 5° increments)

[0048] Under the above test conditions, the Nz coefficient is the refractive index component n x , n y and n z This is a value expressed by the following formula (2) as one of the indices showing the magnitude relationship between

number

[0049] In the above calculation conditions, ZLI-4792 (manufactured by Merck) and cycloolefin polymer (COP) were used according to the standard data attached to LCDmaster. In addition, the n of the third optically anisotropic layer using a polymerizable vertical alignment type liquid crystal compound (manufactured by Merck) was x , n y , and n z The liquid crystal compound was used to form a film of a test piece, and the measurement was performed using an Abbe refractometer (DR-M2 manufactured by ATAGO). [Table 1]

[0050] Table 2 shows the evaluation results of the black luminance values ​​of Examples 1-5 and Comparative Examples 1-6. In the calculations of Examples 1 to 5 and Comparative Examples 1 to 6, the black luminance value at a polar angle θ=0° (head-on) was 0.1 or less, and it was confirmed that the light incident from the polarizing element was sufficiently prevented from being reflected by the reflector by the circular polarizer. Evaluation was performed based on the black luminance value at a polar angle θ=0°. Note that the black luminance value being 0 or nearly 0 indicates that the circular polarizer is suppressing the reflection of the incident light and is functioning ideally.

[0051] Using the above calculation results, the distribution of black luminance at azimuth angles Φ=0°-360° for the range of polar angles θ=0°-80° with the center at polar angle θ=0° (head-on) is shown in an isopleth diagram (contour diagram). At this time, the black luminance is shown fixed in the range from a minimum value of 0 to a maximum value of 10. FIGS. 4-6 show the contour diagrams of Examples 1-3, and FIGS. 7-12 show the contour diagrams of Comparative Examples 1-6, respectively. In the contour diagrams of Examples 1-3, the isopleths indicating the maximum luminance value when the polar angle θ is shifted from 0° to 80° (from the center of the circle to the edge of the outer circle) are 1.6-1.8, which is a smaller value than each of the comparative examples, and therefore it was found to show a wider viewing angle. In the case of Comparative Example 5, the maximum luminance value exceeded 10.

[0052] Furthermore, in order to quantitatively compare the improvement effect of the black luminance when viewed from an oblique direction, the black luminance values ​​were extracted from the above calculation results under the conditions of the polar angle θ and azimuth angle Φ described below. The results of plotting the black luminance values ​​at this time against the azimuth angle Φ are shown in Figures 13 to 21. Polar angle θ=θ=40°, 50°, 60° Azimuth angle Φ=0°~360° (in 45° increments)

[0053] The results of plotting the above conditions for Examples 1 to 3 are shown in Figures 13 to 15. In detail, in Examples 1 to 3 in which the Rth range of the third optically anisotropic layer is -130 nm to -115 nm, there is almost no difference in the black luminance values ​​at polar angles θ=40°, 50°, and 60°, respectively, and the average value (B) of the black luminance at the azimuth angle Φ=0° to 360° (in 45° increments) at each of the polar angles was 0.26 to 0.68. This means that the black luminance when viewed from an oblique direction at polar angles θ=40°, 50°, and 60° increases by 2.7 to 7.6 times compared to the polar angle θ=0° (A). In addition, when the calculation was performed in the same manner as above for Examples 4 and 5 in which the Rth range of the third optically anisotropic layer is -80 nm and -150 nm, the increase in black luminance was 3.2 to 10.0 times. From this, it was found that the black luminance when viewed from an oblique direction can be further reduced by setting the Rth range of the third optically anisotropic layer preferably to -130 nm to -115 nm.

[0054] 16 to 18 show the results of plotting the above conditions for Comparative Examples 1 to 3. In Comparative Examples 1 to 3, in which the Rth of the third optically anisotropic layer was fixed at -120 nm and the third optically anisotropic layer was disposed after the second optically anisotropic layer or before the first optically anisotropic layer, or in which the third optically anisotropic layer was not present, the black luminance values ​​at polar angles θ=40°, 50°, and 60° were all greater than those in Examples 1 to 5. In addition, the average black luminance (B) at the azimuth angle at each polar angle calculated in the same manner as above was 0.59 to 1.72 in Comparative Examples 1 and 2, and 1.27 to 3.88 in Comparative Example 3. This indicates that the black luminance when viewed from oblique directions at polar angles θ=40°, 50°, and 60° compared to the polar angle θ=0° (A) is increased by 6.3 to 18.2 times in Comparative Examples 1 and 2, and by 13.4 to 41.1 times in Comparative Example 3. This result indicates that the configurations of Examples 1 to 5 have improved viewing angle characteristics compared to conventional Comparative Examples 1 to 3.

[0055] In Comparative Examples 4 to 6, a third optically anisotropic layer having an Rth value (Comparative Example 4: -174 nm, Comparative Example 5: -209 nm, and Comparative Example 6: -133 nm) was used when the display having the circular polarizer with the retardation plate under the conditions had the widest viewing angle. As in Examples 1 to 5, the black luminance values ​​were calculated for polar angles θ=40°, 50°, and 60°, respectively, and the results are shown in Figs. 19 to 21. Under all conditions, the black luminance values ​​were larger than those of Examples 1 to 5 as well as Comparative Examples 1 to 3, and the configurations of Comparative Examples 4 to 6 using conventional COP-based films were unable to achieve a wide viewing angle even when the third optically anisotropic layer was disposed.

[0056] [Table 2]

[0057] From the above results, in the configuration of the circular polarizer of the present invention, the bandwidth of the circular polarizer can be broadened more than that of a conventional circular polarizer by selecting the arrangement of the third optical anisotropic layer relative to the first and second optical anisotropic layers, as well as by optimizing the presence or absence of the third optical anisotropic layer and its Rth value. Therefore, according to the present invention, for example, a black display with little light leakage when viewed from an oblique direction can be obtained in a black display of an organic EL display device or the like.

[0058] In addition, the retardation plate of the present invention may include first and second optically anisotropic layers having optimal wavelength dispersion characteristics (meaning wavelength dependency of retardation) in order to further reduce the black luminance at a polar angle of 0°. Similarly, in the third optically anisotropic layer, the wavelength dispersion characteristics are set to negative dispersion (reverse wavelength dispersion), so that the black luminance in black display when viewed from an oblique direction can be further reduced. [Industrial Applicability]

[0059] The present application provides a retardation plate that reduces coloring or reflectance in black display when viewed from an oblique direction, a circular polarizing plate having the retardation plate, and a liquid crystal display device and an organic EL display device having the circular polarizing plate. For example, an organic EL display device can provide a wider viewing angle, and therefore can be suitably used in a vehicle where the display device is installed and the viewing location is fixed. In addition, a manufacturing method can be provided that enables a circular polarizing plate to be produced by simply laminating the plates in a roll-to-roll process, and therefore the method can also be used to produce circular polarizing plates for large display devices. [Explanation of symbols]

[0060] 101 Retardation plate of the present invention 102 First optically anisotropic layer 103 Second optically anisotropic layer 104 Third optically anisotropic layer 105 Circularly polarizing plate of the present invention 106 Polarizing element (polarizing plate) 107 Twisted Nematic Liquid Crystal 108 Substrate 1 (alignment film) 109 Substrate 2 (alignment film) 201 Absorption axis direction (0°) 202 Rubbing direction (orientation direction) (0°) 203 Twist angle direction (26°) 204 Rubbing direction (orientation direction) (26°) 205 Twist angle direction (104°) 206 Parallel to 201

Claims

1. a first optically anisotropic layer in which rod-like liquid crystal compounds are aligned along a thickness direction with a helical axis and which has an in-plane retardation value (Re) of ½ wavelength; a second optically anisotropic layer in which a rod-like liquid crystal compound is aligned with a helical axis in the thickness direction and has an in-plane retardation value (Re) of ¼ wavelength; A retardation plate comprising: Between the first and second optically anisotropic layers, there is formed a layer having the following formula (1): n ｘ =n ｙ <n ｚ (1) (In the formula n ｘ and n ｙ is the refractive index in the perpendicular plate plane direction, n ｚ indicates the refractive index perpendicular to the plate plane) A third optically anisotropic layer is provided, A retardation plate characterized in that the third optically anisotropic layer is a layer having a vertical alignment type liquid crystal compound, and has a thickness direction retardation value (Rth) of −150 to −80 nm; Retardation plate.

2. 2. The retardation plate according to claim 1, wherein the twist angle of the first optically anisotropic layer is 26° or −26°, and the twist angle of the second optically anisotropic layer is 78° or −78° from the twist angle of the first optically anisotropic layer.

3. A circular polarizing plate comprising a polarizing element and the retardation plate according to claim 1 or 2.

4. 4. The circularly polarizing plate according to claim 3, wherein the polarizing element contains a dichroic azo dye, the hue of which is achromatic.

5. An organic electroluminescence display device comprising the circular polarizer according to claim 3 .

6. A liquid crystal display comprising the circular polarizer according to claim 3 or 4.

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