TWI840616B - Retardation plate, and circularly polarizing plate, liquid crystal display, and organic el display including the same - Google Patents

Abstract

This invention provides a retardation plate, which includes:

a first optically anisotropic layer in which a rod-shaped liquid crystal compound having a spiral axis oriented in the thickness direction and which has an in-plane retardation value (Re) of substantially 1/2 wavelength, and

a second optically anisotropic layer in which a rod-shaped liquid crystal compound having a spiral axis oriented in the thickness direction and which has an in-plane retardation value (Re) of substantially 1/4 wavelength, wherein,

the retardation plate includes a third optically anisotropic layer provided between the first and second optically anisotropic layers, which satisfies the following equation (1):

n_x≒n_y<n_z (1)

(In this equation, n_x and n_y indicate refractive indexes the plate plane directions orthogonal to each other, and n_z indicates a refractive index in the direction perpendicular to the plate plane directions).

Description

Phase difference plate, circular polarizing plate, liquid crystal display device and organic EL display device having the phase difference plate

The present invention relates to a phase difference plate useful for a liquid crystal display device and an organic EL display device, and a circular polarizing plate having the phase difference plate, a liquid crystal display device, and an organic EL display device.

Phase difference plates for circular polarizing plates are used in a wide range of applications in flat panel displays.

In the past, regarding image display panels, a method of reducing the reflection of external light by configuring a circular polarizer on the surface of the image display panel has been proposed. This circular polarizer is composed of a linear polarizer and a 1/4 wavelength phase difference plate (hereinafter also referred to as a λ/4 plate). The linear polarizer converts the external light toward the display surface of the image display panel into linear polarization, and then converts it into circular polarization by the 1/4 wavelength phase difference plate. Here, although the external light from the circular polarization is reflected on the surface of the image display panel, the rotation direction of the circular polarization is reversed at the time of this reflection. As a result, the reflected light is converted into linear polarization in the opposite direction of the direction when it comes and can be shielded by the 1/4 wavelength phase difference plate and the linear polarizer, and then shielded by the linear polarizer, thereby suppressing the reflected light from being exposed to the outside.

The phase difference plate used in this circular polarizing plate has the following problems due to the wavelength dependence of the phase difference value (wavelength dispersion): when used to prevent reflection of an organic EL display device, it does not function as a λ/4 plate for each wavelength band in the visible light region, and produces coloring in a dark state (black screen). The above problem becomes particularly obvious when the display device is viewed at an inclined viewing angle. In order to prevent this problem, a phase difference plate for a circular polarizing plate is required that can function close to 1/4 wavelength in a wide wavelength band and can prevent reflection in a wide range of viewing angles. The above phase difference plate uses a phase difference plate that has been stretched uniaxially or biaxially. Furthermore, a method of using more than one layer of twisted nematic liquid crystal layer (twisted nematic liquid crystal layer) is also disclosed.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Publication No. 2014-209220

[Patent Document 2] Japanese Patent Publication No. 2014-224837

For example, a λ/4 plate formed by biaxially stretching a modified polycarbonate (PC) film is known to be used as a phase difference plate for widening the angle. However, this phase difference plate and the phase difference plate formed by laminating a λ/4 plate with the same λ/2 plate described later show reverse wavelength dispersion in the phase difference value corresponding to the visible light wavelength region, but the effect of suppressing coloring when viewed from an oblique direction is not sufficient.

In addition, there is a wide-angle phase difference plate, which is formed by laminating a λ/4 plate formed by uniaxially stretching a cycloolefin (COP) film and a λ/2 plate of the same type. However, the laminated phase difference plate must be cut in such a way that each phase difference plate has a predetermined optical axis angle relative to the optical axis of the polarizing plate, and then laminated one by one using an adhesive layer, etc., which has problems in productivity.

In addition, Patent Document 1 states that a wideband λ/4 plate is realized by controlling the twist angle and △nd (the product of the refractive index difference (△n) and the film thickness (d)) through two consecutive layers of twist-aligned nematic liquid crystals. Compared with the known uniaxially stretched λ/4 plate and λ/2 plate phase difference plate, it can convert linear polarization with a wider wavelength into more complete circular polarization. However, the circular polarization plate using this λ/4 plate is limited to the results observed from the direction directly above, and the display performance (reproducibility and coloring of black) when viewed from an oblique direction has not been fully discussed.

In addition, regarding the above-mentioned phase difference plate, in order to improve the above-mentioned display when viewed from an oblique direction, generally speaking, a positive C plate layer with a phase difference value in the thickness direction within a predetermined range is added, which is already known. For example, in Patent Document 2, an attempt is made to improve the display when viewed from an oblique direction by adding a positive C plate layer to the materials of the λ/2 plate and the λ/4 plate.

As mentioned above, there has been a circular polarizing plate that has a wideband λ/4 wavelength phase difference plate composed of "a structure using a double-layer twisted nematic liquid crystal layer having the functions of a λ/2 plate and a λ/4 plate" and a "stretched film", and is further equipped with a positive C plate layer. However, this circular polarizing plate cannot satisfy the black reproducibility (the intensity of black brightness) and coloring-related display performance of the display device when viewed from an oblique direction, and further improvement is required. In addition, as for the positive C plate layer, the thickness direction phase difference value (Rth) and its optimal configuration relationship with the phase difference plate have not been discussed.

The purpose of this case is to provide a wideband phase difference plate for a circular polarizing plate that reduces the black brightness of a black screen when viewed from an oblique direction (displays good black), a circular polarizing plate having the phase difference plate, and a liquid crystal display device and an organic EL display device having the aforementioned circular polarizing plate.

The inventor of this case conducted detailed research to solve the above problem. As a result, by using a positive C plate layer between two liquid crystal layers with twisted orientation in the thickness direction, the black brightness of the black screen when viewed from an oblique direction was successfully reduced.

That is, the present invention relates to the following inventions, but is not limited thereto.

[Invention 1]

A phase difference plate having:

The first optically anisotropic layer is a rod-shaped liquid crystal compound that is oriented with the thickness direction as the helical axis and has an in-plane phase difference (Re) of substantially 1/2 wavelength; and

The second optically anisotropic layer is a rod-shaped liquid crystal compound that is oriented with the thickness direction as the helical axis and substantially has an in-plane phase difference (Re) of 1/4 wavelength;

in,

Between the aforementioned first and second optically anisotropic layers, there is a third optically anisotropic layer satisfying the following formula (1),

n _x ≒n _y <n _z (1)

(where _nx and _ny represent the refractive index in the direction orthogonal to the plate plane, and _nz represents the refractive index in the direction perpendicular to the plate plane).

[Invention 2]

As described in the phase difference plate of Invention 1, the twist angle of the first optical anisotropic layer is substantially 26° or substantially -26°, and the twist angle of the second optical anisotropic layer is substantially 78° or substantially -78° from the twist angle of the first optical anisotropic layer.

[Invention 3]

As described in Invention 2, the phase difference plate, wherein the aforementioned third optical anisotropic layer is a layer having a vertically aligned liquid crystal compound, and the thickness direction phase difference value (Rth) is -150 to -80nm.

[Invention 4]

A circular polarizing plate having a polarizing element and a phase difference plate as described in any one of Inventions 1 to 3.

[Invention 5]

As described in Invention 4, the circular polarizing plate, wherein the polarizing element comprises a dichroic azo dye, the hue of which is an achromatic color.

[Invention 6]

An organic EL display device is provided with a circular polarizing plate as described in Invention 4 or 5.

[Invention 7]

A liquid crystal display device having a circular polarizing plate as described in Invention 4 or 5.

The present invention can provide a wideband phase difference plate for circular polarizers that reduces the black brightness and/or reduces coloring in a black screen when viewed from an oblique direction, a circular polarizer having the phase difference plate, and a liquid crystal display device (LCD) and an organic electroluminescent (EL) display device (organic light-emitting diode (OLED) display device) having the aforementioned circular polarizer. In one form, a display device that displays good black in a black screen when viewed from the front can be provided. In one form, the present invention can provide a thin phase difference plate. In one form, the present invention achieves lower brightness and minimally colored black in the black screen of LCD and OLED display devices not only in the head-on (front) direction, but also in a wide range of directions with varying viewing angles. In one form, the present invention can provide a manufacturing method that does not require complicated steps such as sheet-by-sheet lamination or oblique stretching, and can produce circular polarizing plates by simply laminating them in roll-to-roll manner.

101: The phase difference plate of the present invention

102: 1st optical anisotropic layer

103: Second optical anisotropic layer

104: The third optical anisotropy layer

105: Circular 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: Friction direction (alignment direction) (0°)

203: Torsion angle direction (26°)

204: Friction direction (alignment direction) (26°)

205: Torsion angle direction (104°)

206: Indicates parallel to 201

Figure 1 is a cross-sectional view of a phase difference plate according to one embodiment of the present invention.

Figure 2 is a cross-sectional view of a circular polarizer according to one embodiment of the present invention.

Figure 3 is an explanatory diagram of the "First Form Example" of the present invention.

Figure 4 is a contour map of brightness corresponding to polar angles of 0° to 80° and azimuth angles of 0° to 360° in Example 1.

Figure 5 is a contour map of brightness corresponding to polar angles of 0° to 80° and azimuth angles of 0° to 360° in Example 2.

Figure 6 is a contour map of brightness corresponding to polar angles of 0° to 80° and azimuth angles of 0° to 360° in Example 3.

Figure 7 is a contour map of brightness corresponding to polar angles of 0° to 80° and azimuth angles of 0° to 360° for Example 1.

Figure 8 is a contour map of brightness corresponding to polar angles of 0° to 80° and azimuth angles of 0° to 360° for Example 2.

Figure 9 is a contour map of brightness corresponding to polar angles of 0° to 80° and azimuth angles of 0° to 360° for Example 3.

Figure 10 is a contour map of brightness corresponding to polar angles of 0° to 80° and azimuth angles of 0° to 360° for Example 4.

Figure 11 is a contour map of brightness corresponding to polar angles of 0° to 80° and azimuth angles of 0° to 360° for Example 5.

Figure 12 is a contour map of brightness corresponding to polar angles of 0° to 80° and azimuth angles of 0° to 360° for Example 6.

Figure 13 shows the experimental results of the circular polarizers of Examples 1 to 3 at an extreme angle (tilt angle) of 40° and an azimuth angle of 0 to 360° (in units of 45°).

Figure 14 shows the experimental results of the circular polarizing plates of Examples 1 to 3 at an extreme angle (tilt angle) of 50° and an azimuth angle of 0 to 360° (in units of 45°).

Figure 15 shows the experimental results of the circular polarizers of Examples 1 to 3 at an extreme angle (tilt angle) of 60° and an azimuth angle of 0 to 360° (in units of 45°).

Figure 16 shows the experimental results of the circular polarizers of Example 1 and Comparative Examples 1 to 3 at an extreme angle (tilt angle) of 40° and an azimuth angle of 0 to 360° (in units of 45°).

Figure 17 shows the experimental results of the circular polarizing plates 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 units of 45°).

Figure 18 shows the experimental results of the circular polarizing plates 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 units of 45°).

Figure 19 shows the experimental results of the circular polarizing plates 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 units of 45°).

Figure 20 shows the experimental results of the circular polarizing plates 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 units of 45°).

Figure 21 shows the experimental results of the circular polarizing plates 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 units of 45°).

The following describes the implementation of the present invention.

(Phase difference plate)

Phase difference plate (wavelength plate) refers to an optical element that gives a predetermined phase difference to incident linear polarization. The phase difference plate of the present invention has two optical anisotropic layers (the first and second optical anisotropic layers) as a λ/2 plate and a λ/4 plate, and further has a third optical anisotropic layer between the first and second optical anisotropic layers to suppress coloring when viewed from an oblique direction. The phase difference plate of the present invention is suitable for circular polarization plates, especially wideband circular polarization plates. The manufacturing method of the phase difference plate of the present invention is not particularly limited, and it can be manufactured by known methods such as roll-to-roll.

Among phase difference plates, broadband ones generally provide a nearly constant phase difference at all wavelengths in the visible light region (380nm to 780nm) when incident linear polarization. Therefore, the phase difference plate used in the production of circular polarization plates provides a phase difference of nearly 1/4 wavelength at all wavelengths in the visible light region.

(1st and 2nd optical anisotropic layers)

The first optical anisotropic layer of the present invention actually has an in-plane phase difference value (Re) of 1/2 wavelength, and functions as a λ/2 plate. As long as the phase difference plate of the present invention is applicable to a circular polarizer, the aforementioned Re may not be completely 1/2 wavelength. For example, it includes a numerical range of ±20%, 15%, 10%, 5%, 2% or 1%.

The second optical anisotropic layer of the present invention has an in-plane phase difference value (Re) of substantially 1/4 wavelength, and functions as a λ/4 plate. The term "substantially" is the same as above.

Liquid crystal compounds forming the first and second optical anisotropic layers are generally classified into rod-shaped (rod-shaped liquid crystal compounds) and disc-shaped (disc-shaped liquid crystal compounds) according to their shapes. The present invention preferably uses rod-shaped liquid crystal compounds to form a twisted nematic (TN) liquid crystal layer. The TN liquid crystal layer is a nematic liquid crystal layer in which rod-shaped elongated molecules are arranged in a roughly fixed direction, and the nematic liquid crystal layer continuously changes into a helical liquid crystal layer in which the direction of the molecules is twisted 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, etc. In this case, it is not necessary to show liquid crystal properties after the layer is formed. The type of polymerizable group contained in the rod-shaped liquid crystal compound is not particularly limited, and it is preferably a functional group that can undergo addition polymerization reaction, and it is preferably a polymerizable ethylene unsaturated group or a cyclic polymerizable group. More specifically, it is preferably (meth)acrylic acid group, vinyl group, styrene group, allyl group, etc., and it is more preferably (meth)acrylic acid group. In the present invention, known TN liquid crystal materials can be used. In addition, when forming a TN liquid crystal layer, the expected chiral reagent can also be used together with the above-mentioned liquid crystal compound according to needs. The chiral reagent is added to make the liquid crystal compound undergo twisted alignment.

Furthermore, by using the polymerizable liquid crystal material as described above in the phase difference plate, generally speaking, the thickness of the film phase difference plate can be thinned to 5μm to 20μm, compared to the film phase difference plate having a film thickness of 50μm to 100μm.

The first and second optically anisotropic layers in the phase difference plate of the present invention are twisted and aligned with the thickness direction as the helical axis. Furthermore, the twist directions of the two liquid crystal layers are the same. Furthermore, the in-plane slow axis on the third optically anisotropic layer side of the first optically anisotropic layer is parallel to the in-plane slow axis on the third optically anisotropic layer side of the second optically anisotropic layer. That is, the twist angle of the second optically anisotropic layer is configured based on the twist angle of the first optically anisotropic layer. The positive and negative (minus: -) of the twist angle are when the absorption axis direction of the polarizing element is set to 0° and the polarizing element of the circular polarizing plate is on the viewing side, with positive indicating the direction rotating counterclockwise from the absorption axis and negative indicating the direction rotating clockwise from the absorption axis.

The twist angle of the first optical anisotropic layer used in the phase difference plate of the present invention is substantially 26° in one form. More specifically, it is preferably 26±10°, more preferably 26±7°, and even more preferably 26±5°. In this case, the twist angle of the second optical anisotropic layer is substantially 78°. More specifically, it is preferably 78±10°, more preferably 78±7°, and even more preferably 78±5°. Or the twist angle of the first optical anisotropic layer is substantially -26° in another form. More specifically, it is preferably -26±10°, more preferably -26±7°, and even more preferably -26±5°. In this case, the twist angle of the second optical anisotropic layer is substantially -78°. More specifically, the best value is -78±10°, the best value is -78±7°, and the best value is -78±5°. The above torsion angle can be measured using a film inspection device (RETS-1100A, manufactured by Otsuka Electronics Co., Ltd.).

In the first optical anisotropic layer used in the phase difference plate of the present invention, the product of the refractive index anisotropy △n1 at a wavelength of 550nm and the thickness d1 of the liquid crystal layer (△n1.d1), that is, the in-plane phase difference value (Re) is substantially 275nm. More specifically, the aforementioned product (△n1.d1) is preferably 275±30nm, more preferably 275±20nm, and even more preferably 275±10nm.

In addition, in the second optical anisotropic layer used in the phase difference plate of the present invention, the product of the refractive index anisotropy △n2 at a wavelength of 550nm and the thickness d2 of the liquid crystal layer (△n2.d2), that is, the in-plane phase difference value (Re) is substantially 137.5nm. More specifically, the aforementioned product (△n2.d2) is preferably 137.5±15nm, more preferably 137.5±10nm, and more preferably 137.5±5nm. The above △n1.d1 and △n2.d2 can be measured using a film inspection device (RETS-1100A, manufactured by Otsuka Electronics Co., Ltd.).

(3rd optical anisotropic layer)

The third optical anisotropic layer of the phase difference plate of the present invention is a type of phase difference plate called a positive C plate, which refers to the following phase difference plate: when the xy orthogonal axes are set on the plate plane and the z axis is set in the direction perpendicular to the plate plane, the refractive index _nx , _ny , and _nz in the directions of each axis become _nx ≒ _ny < _nz . In addition, " _nx ≒ _ny " means that _nx and _ny are substantially equal, and also includes the case where they are completely equal. The aforementioned " _{nx and ny} are substantially equal _" may be different as long as the function as a positive C plate is exerted. For example, from the perspective of one, the other may have a difference of 20%, 15%, 10%, 5%, 2%, or 1%. In addition, the following symbols may also be used instead of "≒".

In the present invention, a known positive C plate can be used. In one form, the third optically anisotropic layer of the phase difference plate of the present invention is, for example, a liquid crystal layer in which a rod-shaped liquid crystal compound is vertically aligned relative to the thickness direction (plane of the plate). The aforementioned vertical includes directions in which the alignment angle of the liquid crystal compound is 90° and almost 90° relative to the plane of the plate (including differences in the extent to which the effect can be ignored, such as differences within ±10°, ±5°, ±3° or ±1°). The third optically anisotropic layer is preferably a layer formed by fixing a rod-shaped liquid crystal compound having a polymerizable group by polymerization, etc. In this case, after forming the layer, it is not necessary to show liquid crystal properties. The type of polymerizable group contained in the rod-shaped liquid crystal compound is not particularly limited, and preferably a functional group capable of undergoing addition polymerization reaction, preferably a polymerizable ethylene unsaturated group or a cyclic polymerizable group. More specifically, preferably: (meth)acryl, vinyl, styryl, allyl, etc., more preferably (meth)acryl.

Furthermore, the thickness direction phase difference (Rth) of the liquid crystal layer can be adjusted by adjusting the film thickness. The film thickness is not particularly limited, but is generally preferably set within the range of 0.1μm to 3μm, and more preferably within the range of 0.5μm to 2μm.

In another embodiment, the cellulose resin material of Japanese Patent Publication No. 2016-108536 can be used. From the perspective of thinning and productivity, it is better to use the aforementioned liquid crystal compound.

The thickness direction phase difference (Rth) of the third optical anisotropic layer of the present invention is determined according to the Poincare sphere theory. In order to minimize the trajectory of the coordinates on the equator representing linear polarization to the coordinates on the North Pole or South Pole representing circular polarization, it is preferred to set the optimal value range, specifically, preferably in the range of -150 to -80nm, more preferably in the range of -132 to -112nm, and even more preferably in the range of -126 to -120nm. Furthermore, the third optical anisotropic layer is preferably disposed between the first optical anisotropic layer and the second optical anisotropic layer. Thus, the circularly polarized light of each wavelength generated by the phase difference plate of the present invention will be concentrated on the coordinates representing the circularly polarized light at the North Pole or the South Pole in the Poincare sphere, thereby forming a nearly ideal circularly polarized light at each wavelength. Therefore, in a display device etc. equipped with the circularly polarizing plate of the present invention, coloring when viewed from an oblique direction can be suppressed.

(Orientation processing)

The first and second optically anisotropic layers of the present invention are processed to align the liquid crystal compound on the substrate, or an alignment film is provided. The liquid crystal alignment is not particularly limited as long as the alignment direction of the optically anisotropic layer is appropriately specified and does not hinder the expected performance of the present invention, and the alignment technology known in the art can be used. A rubbing roll rotated about 0 to 50° relative to the conveying direction of the substrate can be used to physically form anisotropy on the substrate surface, or the method of performing the rubbing treatment on the resin layer provided on the substrate disclosed in Japanese Patent Publication No. 2003-014935 can be used, or a light alignment film can be formed on a polymer film to form an anisotropic alignment film due to linearly polarized ultraviolet light.

(Polarizing element)

The polarizing element (sometimes also referred to as a polarizing filter or a polarizing film) used to obtain the circularly 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) film impregnated with a dichroic dye such as a water-soluble dichroic dye and/or polyiodine ions in a boric acid hot water bath, a polarizing element obtained by uniaxially stretching a polyvinyl alcohol film and then forming a polyene structure by dehydration reaction, a polarizing element obtained by coating a solution containing a dichroic dye on a substrate film and aligning the dichroic dye, a substrate-integrated polarizing element obtained by providing a polyvinyl alcohol layer on a protective film and uniaxially stretching it together with the substrate film and then impregnating the dichroic dye, etc. From the viewpoint of processability and optical characteristics, a polarizing element obtained by uniaxially stretching a PVA film and adsorbing and aligning the dichroic dye is typically used. As a commercially available PVA film, for example, Kuraray's VF-PS (thickness 75μm) can be cited. In this case, the dichroic dye is generally adsorbed and aligned, and then uniaxially stretched to a thickness of 25μm to 35μm to obtain a polarizing element.

系染料等，從色相設計及對於熱之耐久性的觀點來看，較佳係摻合2至3種以上的偶氮系染料以使用。又，使用任一雙色性色素的情況中，偏光元件的光學特性，從在所安裝之顯示裝置中得到抗反射能力與優良之黑屏性的觀點來看，較佳係具有高穿透率及高偏光度(亦稱為高雙色性)者，更詳細而言，視感度修正單體穿透率(Ys)較佳為40%至45%，以及視感度修正偏光度(Py)較佳為99%以上。 The dichroic pigment is preferably iodine ion or dichroic dye, both of which can be used to obtain the polarizing element used in the present invention. Examples of dichroic dyes include azo dyes, anthraquinone dyes and tetrakis

From the perspective of color design and heat durability, it is preferred to use azo dyes mixed with 2 to 3 or more azo dyes. In addition, when any dichroic dye is used, the optical properties of the polarizing element are preferably high transmittance and high polarization (also called high dichroism) from the perspective of obtaining anti-reflection ability and excellent black screen performance in the display device installed. More specifically, the sensitivity correction single transmittance (Ys) is preferably 40% to 45%, and the sensitivity correction polarization (Py) is preferably 99% or more.

In one form of the present invention, it is preferred to have an achromatic hue, that is, it is preferred that the single transmittance (Ts) of the polarizing element is almost uniform in the entire visible light region (wavelength 400nm to 700nm, preferably 380nm to 780nm). The absolute values of a* and b* values in the L*a*b* color system are both below 1 when measured with a single polarizing element, and when two polarizing elements are overlapped in a manner such that the absorption axes are orthogonal to each other, the hue with an absolute value of a* value below 4 and an absolute value of b* value below 8 is also preferred as a specific form of the achromatic color. Thus, for example, by using a circular polarizer having a wideband phase difference plate of the present invention, not only can the coloring of the reflected light from the display device be suppressed in the entire visible light region, but also the coloring of the reflected light from the surface of the polarizing element can be suppressed in the entire visible light region.

Examples of dichroic azo dyes include C.I.DirectYellow12, C.I.DirectYellow28, C.I.DirectYellow44, C.I.DirectYellow142, C.I.DirectOrange26, C.I.DirectOrange39, C.I.DirectOrange71, C.I.DirectOrange107, C.I.DirectRed2, C.I.DirectRed31, C.I.DirectRed79, C.I.Direct C.I.DirectRed81, C.I.DirectRed117, C.I.DirectRed247, C.I.DirectGreen80, C.I.DirectGreen59, C.I.DirectBlue71, C.I.DirectBlue78, C.I.DirectBlue168, C.I.DirectBlue202, C.I.DirectViolet9, C.I.DirectViolet51, C.I.DirectBrown106, C.I.DirectBrown223, etc. Other dyes that can be produced by known methods can also be used. As known methods, for example, the method described in Japanese Patent Application Laid-Open No. 3-12606 or the method described in Japanese Patent Application Laid-Open No. 59-145255 can be cited. In addition, commercially available dyes include Kayafect Violet P Liquid, Kayafect Yellow Y and Kayafect Orange G, Kayafect Blue KW and Kayafect Blue Liquid 400 (all manufactured by Nippon Kayaku Co., Ltd.). Two to three or more of these azo dyes are blended and used in such a way that the transmittance of each of these azo dyes in the visible light region becomes uniform. Furthermore, in the polarizing element of the present invention, in order to obtain an achromatic polarizing element with high transmittance and high polarization, the azo dye with improved dichroicity for designing an achromatic polarizing element disclosed in International Publication No. WO2017/146212 and International Publication No. WO2019/117131 can be ideally used.

The polarizing element preferably includes a substrate (also called a support or a support film) for protecting the polarizing element. The substrate can be disposed on only one side of the polarizing element, or can be disposed on both sides of the polarizing element by sandwiching the polarizing element with two identical or different substrates. The structure of the polarizing element having a substrate is called a polarizing plate. In the case where the polarizing element has the substrate described later, the substrate disposed between the polarizing element and the display device preferably has a phase difference in the plane (Re) and a phase difference in the thickness direction (Rth) of 0 or almost 0 (as a numerical value, the degree to which its influence can be ignored, for example, in the range of -5nm to 5nm).

(Base material)

The phase difference plate and circular polarizing plate of the present invention (hereinafter also referred to as the article of the present invention) may also have a substrate. As the substrate, as long as it has the expected mechanical strength and thermal stability and does not hinder the expected performance of the present invention, there is no special restriction, and the substrate known in the field can be used. The thickness of the substrate can be appropriately designed, preferably 50 to 200μm, more preferably 10 to 100μm, and even more preferably 20 to 80μm.

Furthermore, when a substrate is disposed between the polarizing element and the display device, the in-plane phase difference value (Re) and the thickness direction phase difference value (Rth) of the substrate are preferably 0 or almost 0. Commercially available substrates having the above-mentioned phase difference values include, for example, triacetylcellulose resin film Z-TAC (manufactured by Fuji Film Co., Ltd.), acrylic resin film OXIS series (manufactured by Okura Industries Co., Ltd.), etc.

(Adhesive and/or Adhesive)

In the article of the present invention, a layer may be formed by placing a layer on a certain layer, or a layer may be formed by bonding multiple layers together with an adhesive (pressure sensitive adhesive) and/or adhesive. As long as the function as an adhesive or adhesive can be exerted and the expected performance of the present invention is not hindered, there is no particular limitation, and an adhesive or adhesive known in the art can be used. As an adhesive, representatively, acrylic resin can be cited. The thickness can be appropriately designed, but is preferably 1 to 50 μm, and is more preferably 5 to 25 μm from the viewpoint of the adhesion between layers and the processability of adhesive coating and lamination. As adhesives, for example, water-based adhesives with PVA-based resins as the main component, adhesives containing thermosetting or light-curing resins, and methods using plasma bonding, etc. can be cited.

The phase difference and twist angle values of the optical anisotropic layer of the present invention are values that can achieve good optical effects. These values are not particularly limited as long as the alignment characteristics of the actual liquid crystal compound and the processability of the product are considered, and may also include tolerances or margins.

(Circular polarizing plate)

The circular polarizer of the present invention is a wideband circular polarizer, and has a polarizing element and a phase difference plate of the present invention. Specifically, it has a polarizing element (or polarizing plate), a first optical anisotropic layer, a third optical anisotropic layer, and a second optical anisotropic layer in sequence. In addition, in one form, the optical axes of the circular polarizer are such that the absorption axis of the polarizing element is in the direction of 0°, and the twist angle of the first optical anisotropic layer is substantially in the direction of 26° relative to the absorption axis of the polarizing element, and the twist angle of the second optical anisotropic layer is substantially in the direction of 78° from the twist angle of the first optical anisotropic layer (i.e., in the direction of 104° relative to the absorption axis of the polarizing element).

The method for manufacturing the circular polarizing plate of the present invention is not particularly limited. For example, the above-mentioned films or sheets can be laminated one by one, or the above-mentioned layers made into a roll can be continuously laminated by roll-to-roll. In particular, the circular polarizing plate of the present invention does not need to cut the phase difference plate according to the predetermined optical axis angle, and the latter can be easily laminated by roll-to-roll. Therefore, compared with the previous method of manufacturing wide-band circular polarizing plates, such as laminating uniaxially stretched films such as COP films, productivity can be improved.

(Method for manufacturing circular polarizing plate)

The manufacturing method of the phase difference plate and circular polarizing plate of the present invention can be illustrated by the following examples 1 and 2, but is not limited thereto. In addition, each optical anisotropic layer is formed on a substrate from which the liquid crystal layer and the substrate can be peeled off after curing, and in the subsequent lamination steps, each substrate can also be removed to form a circular polarizing plate.

(Type 1 example)

As the first step, a coating composition comprising a liquid crystal compound exhibiting a polymerizable nematic liquid crystal phase, a chiral reagent, a photopolymerization initiator, and a diluent solvent is applied to the friction surface of the substrate that has been rubbed in the 0° direction (transportation direction), and then the solvent is removed by a drying step, and the coating is hardened by irradiation, thereby obtaining a first optical anisotropic layer having an alignment axis in the 0° direction, a twist angle of 26°, and a phase difference value (Re@550nm) of 275nm.

As the second step, a coating composition comprising a liquid crystal compound exhibiting a polymerizable nematic liquid crystal phase, a photopolymerization initiator and a diluent solvent is coated on the substrate, followed by a drying step to remove the solvent, and then irradiated with light to harden the coating, thereby obtaining a third optically anisotropic layer oriented in a direction perpendicular to the substrate.

In the third step, a coating composition comprising a TN liquid crystal material, a chiral reagent, a photopolymerization initiator and a diluent solvent is applied on the friction surface of the substrate that has been rubbed at a direction of 26° relative to the transport direction. The solvent is then removed by a drying step, and the coating is hardened by irradiation, thereby obtaining a second optical anisotropic layer having an alignment axis at a direction of 26°, a twist angle of 78° and a phase difference value (Re@550nm) of 137.5nm.

As the fourth step, the polarizing element (or polarizing plate), the first optical anisotropic layer, the third optical anisotropic layer and the second optical anisotropic layer are sequentially laminated in a manner to form the optical axis relationship shown in FIG. 3, thereby obtaining the circularly polarizing plate of the present invention.

(Example 2)

In the aforementioned second step, a coating composition comprising a liquid crystal compound exhibiting a polymerizable nematic liquid crystal phase, a photopolymerization initiator, and a diluent is coated on the liquid crystal surface of the first optically anisotropic layer obtained in the aforementioned first step, and then a drying step is performed to remove the solvent, and the coating is irradiated to harden, thereby obtaining a third optically anisotropic layer oriented in a direction perpendicular to the liquid crystal surface. Thereafter, a polarizing element (or polarizing plate), a first optically anisotropic layer laminated with a third optically anisotropic layer, and a second optically anisotropic layer are sequentially laminated in a manner to form an optical axis relationship as shown in FIG. 3, thereby obtaining the circularly polarizing plate of the present invention, which is the same as the first type example except for this.

(Display device)

The circular polarizer of the present invention is preferably applied to the viewing side of various display devices such as liquid crystal display devices (LCD), organic electroluminescent (EL) display devices (organic light-emitting diode (OLED) display devices). Furthermore, the display device can also be designed to include a touch screen, an anti-glare layer or an anti-reflection layer, a transparent cover plate (also called a front panel), etc. In addition, the aforementioned transparent cover plate can be a flat shape or a curved shape. The manufacturing method of the display device of the present invention is not particularly limited and can be manufactured by a known method.

The liquid crystal display device of the present invention can be a structure of a liquid crystal panel and a backlight unit, which is called a transmissive or semi-transmissive type, or a structure of a liquid crystal panel and a reflective layer, which is called a reflective type.

In general, since an organic EL display device has a metal electrode in the display panel, the OLED (organic EL display device) itself has a higher reflectivity than a liquid crystal panel. This is the reason why the display performance is impaired due to the reflection of external light from the electrode when used in an environment with a lot of external light, such as outdoors during the day. Therefore, in order to suppress the reflection of external light, a circular polarizing plate is generally attached to the viewing side of the organic EL display device. Therefore, the display characteristics of the organic EL display device are also dependent on the optical characteristics of the circular polarizing plate. The circular polarizing plate of the present invention has a wider viewing angle characteristic than the previous circular polarizing plate, so it can be ideally used in organic EL display devices that require a wide range of viewing angles.

The implementation forms of the present invention have been described so far, but the present invention is not limited to the above implementation forms. Various changes and modifications can be made according to the technical ideas of the present invention.

[Implementation example]

The present invention is specifically described below through examples, but the present invention is not limited by these examples.

Assuming that a circular polarizing plate is attached to an ideal reflector, the black brightness (units are standardized values) at the following azimuth angles and tilt angles (polar angles) is calculated using the liquid crystal simulation software LCD master (manufactured by SYMTEC). The composition and calculation conditions of the circular polarizing plate are as follows. Table 1 shows an overview of the relationship between the following calculation conditions and the configuration of the optical anisotropic layer. The in-plane phase difference value (Re) and the thickness direction phase difference value (Rth) are values at a wavelength of 550nm. In addition, the optical anisotropic layers configured in Table 1 are displayed in the columns of the 1st layer, the 2nd layer, and the 3rd layer in order from the incident light side.

Structure of circular polarizing plate:

Example 1: (from the incident light side in order) polarizing element, first optical anisotropic layer, third optical anisotropic layer 1, second optical anisotropic layer, reflector

Example 2: (from the incident light side in order) polarizing element, first optical anisotropic layer, third optical anisotropic layer 2, second optical anisotropic layer, reflector

Example 3: (from the incident light side in order) polarizing element, first optical anisotropic layer, third optical anisotropic layer 3, second optical anisotropic layer, reflector

Example 4: (from the incident light side in order) polarizing element, first optical anisotropic layer, third optical anisotropic layer 4, second optical anisotropic layer, reflector

Example 5: (from the incident light side in order) polarizing element, first optical anisotropic layer, third optical anisotropic layer 5, second optical anisotropic layer, reflector

Comparative Example 1: (from the incident light side) polarizing element, first optical anisotropic layer, second optical anisotropic layer, third optical anisotropic layer 1, reflector

Comparative Example 2: (from the incident light side) polarizing element, third optical anisotropic layer 1, first optical anisotropic layer, second optical anisotropic layer, reflector

Comparative Example 3: (from the incident light side) polarizing element, first optical anisotropic layer, second optical anisotropic layer, reflector

Comparative Example 4: (from the incident light side in order) polarizing element, general 1/2 wavelength plate 1, third optical anisotropic layer 6, general 1/4 wavelength plate 1, reflector

Comparative Example 5: (from the incident light side) polarizing element, general 1/2 wavelength plate 2, third optical anisotropic layer 7, general 1/4 wavelength plate 2, reflector

Comparative Example 6: (from the incident light side in order) polarizing element, general 1/2 wavelength plate 1, general 1/4 wavelength plate 1, third optical anisotropic layer 8, reflector

1st optical anisotropic layer:

Liquid crystal layer: ZLI-4792 (Merck)

The resulting phase difference = 1/2λ

△n1. d1=275nm

Pre-twist angle = 0°

Twist angle = -26°

Thickness of liquid crystal layer = 2.136μm

Second optical anisotropic layer:

Liquid crystal layer: ZLI-4792 (Merck)

The resulting phase difference = λ/4

△n2. d2=137.5nm

Pre-twist angle = -26°

Twist angle = -78°

Thickness of liquid crystal layer = 1.068μm

3rd optical anisotropic layer:

Liquid crystal layer: polymerizable vertical alignment liquid crystal compound (manufactured by Merck)

n _x =1.5283

n _y =1.5283

n _z =1.6725

Thickness of liquid crystal layer = 0.60μm to 1.45μm

Rth: recorded in 1 to 8 below

3rd optical anisotropic layer 1:

Rth=-120nm

3rd optical anisotropic layer 2:

Rth=-115nm

Optical anisotropy layer 3:

Rth=-130nm

3rd optical anisotropic layer 4:

Rth=-80nm

3rd optical anisotropic layer 5:

Rth=-150nm

3rd optical anisotropic layer 6:

Rth=-174nm

3rd optical anisotropic layer 7:

Rth=-209nm

The third optical anisotropic layer 8:

Rth=-133nm

Polarizing element: JET-12 (made by Polatechno, using spectral data with sensitivity-corrected single-body transmittance Ys=41.5% and sensitivity-corrected polarization Py=99.99%, without a supporting layer)

Reflective plate:

Material: Ideal reflector

General 1/2 wavelength board (HWP) 1:

Material: Cyclic olefin polymer (COP)

Nz coefficient = 1.0

General 1/4 wavelength plate (QWP)1:

Material: Cyclic olefin polymer (COP)

Nz coefficient = 1.0

General 1/2 wavelength board (HWP)2:

Material: Cyclic olefin polymer (COP)

Nz coefficient = 1.5

General 1/4 wavelength plate (QWP)2:

Material: Cyclic olefin polymer (COP)

Nz coefficient = 1.5

Incident light: natural light (wavelength range: 380nm to 780nm)

Tilt angle (polar angle) θ = 40°, 50° and 60°)

Azimuth Φ = 0° to 360° (each in 5° units)

In the above test conditions, the nz coefficient is one of the indices showing the magnitude relationship between the refractive index components _nx , _ny and _nz , and is a value represented by the following formula (2).

In the above calculation conditions, ZLI-4792 (Merck) and cycloolefin polymer (COP) are standard data attached to LCDmaster. In addition, _nx , _ny and _nz of the third optical anisotropic layer using a polymerizable vertical alignment type liquid crystal compound (Merck) are measured by using an Abbe's refractometer (DR-M2ATAGO) on a test piece obtained by film-forming the liquid crystal compound.

[Table 1]

Table 2 shows the evaluation results of the black brightness values of Examples 1 to 5 and Comparative Examples 1 to 6.

In the calculations of Examples 1 to 5 and Comparative Examples 1 to 6, the black brightness value at the polar angle θ=0° (head-on) was shown to be below 0.1, confirming that the light incident from the polarizing element is sufficiently suppressed by the circular polarizing plate from reflecting the reflector. The black brightness value at this polar angle θ=0° was used as the basis for evaluation. In addition, this black brightness value is 0 or almost 0, indicating that the circular polarizing plate suppresses the reflection of the incident light and performs its function ideally.

Using the above calculation results, the center is taken as the polar angle θ=0° (head-on), and the distribution of black brightness at azimuth angle Φ=0° to 360° corresponding to the range of polar angle θ=0° to 80° is represented by a contour diagram. At this time, the black brightness is fixed in the range of the minimum value of 0 to the maximum value of 10. Figures 4 to 6 respectively show the contour diagrams of Examples 1 to 3, and Figures 7 to 12 respectively show the contour diagrams of Comparative Examples 1 to 6. In the contour diagrams of Examples 1 to 3, the contour lines showing the maximum brightness value when the polar angle θ is shifted from 0° to 80° (from the center of the circle of the figure to the outer circle end) are 1.6 to 1.8, which is smaller than the value of each comparative example, so it is known that it presents a wider viewing angle. In addition, in the case of Comparative Example 5, the maximum brightness value exceeds 10.

Furthermore, in order to quantitatively compare the improvement effect of black brightness when viewed from an oblique angle, the black brightness value is selected from the above calculation results under the conditions of the polar angle θ and the azimuth angle Φ described below. The results of plotting the black brightness value at this time against the azimuth angle Φ are shown in Figures 13 to 21.

Polar angle θ=θ=40°, 50°, 60°

Azimuth Φ = 0° to 360° (in units of 45°)

For Examples 1 to 3, the results of plotting under the above conditions are shown in Figures 13 to 15. In detail, in Examples 1 to 3 where the Rth of the third optical anisotropic layer ranges from -130nm to -115nm, there is almost no difference in the black brightness values at polar angles θ = 40°, 50° and 60°, respectively, and the average value (B) of the black brightness at the azimuth angle Φ = 0° to 360° (in units of 45°) in the above polar angles is 0.26 to 0.68. It can be estimated that the black brightness will increase by 2.7 times to 7.6 times when viewed from the oblique direction of the polar angles θ = 40°, 50° and 60° relative to the polar angle θ = 0° (A). In addition, for the cases of Examples 4 and 5 in which the Rth of the third optical anisotropic layer is in the range of -80nm and -150nm, when the calculation is performed in the same manner as above, the increase in black brightness is 3.2 to 10.0 times. It can be seen that the Rth of the third optical anisotropic layer is preferably in the range of -130nm to -115nm, thereby further reducing the black brightness when viewed from an oblique direction.

For Comparative Examples 1 to 3, the above conditions were used to plot the results, and the results are shown in Figures 16 to 18. In Comparative Examples 1 to 3, where the Rth of the third optical anisotropic layer was fixed at -120 nm and the third optical anisotropic layer was arranged after the second optical anisotropic layer or before the first optical anisotropic layer, or there was no third optical anisotropic layer, the black brightness values at the respective polar angles θ = 40°, 50°, and 60° all showed larger values than those of Examples 1 to 5. In addition, the average value (B) of the black brightness at the azimuth angle in each polar angle was obtained in the same manner as above, and was 0.59 to 1.72 in Comparative Examples 1 to 2, and 1.27 to 3.88 in Comparative Example 3. It can be estimated that the black brightness relative to the polar angle θ=0° (A) increases to 6.3 to 18.2 times in Comparative Examples 1 to 2 and 13.4 to 41.1 times in Comparative Example 3 when viewed obliquely at polar angles θ=40°, 50°, and 60°. The results show that the configurations of Examples 1 to 5 have improved viewing angle characteristics compared to the previous Comparative Examples 1 to 3.

In Comparative Examples 4 to 6, a third optical anisotropic layer having the following Rth values was used: the Rth values of the display body having a circular polarizing plate with a phase difference plate having the conditions at the widest angle (Comparative Example 4: -174nm, Comparative Example 5: -209nm, and Comparative Example 6: -133nm). As in Examples 1 to 5, the black brightness values at polar angles θ = 40°, 50°, and 60° were obtained and plotted, and the results are shown in Figures 19 to 21. In any condition, the black brightness value not only shows a larger value compared to Examples 1 to 5, but also shows a larger value compared to Comparative Examples 1 to 3. In the configuration of Comparative Examples 4 to 6 using the conventional COP film, even if the third optical anisotropic layer is configured, a wide angle cannot be achieved.

[Table 2]

From the above results, the broadband of the circular polarizing plate of the present invention can be achieved not only by optimizing the presence or absence of the third optical anisotropic layer and its Rth value, but also by selecting the configuration of the third optical anisotropic layer relative to the first optical anisotropic layer and the second optical anisotropic layer, and the broadband is further improved compared to the circular polarizing plate of the previous structure. Therefore, according to the present invention, for example, a black screen with less light leakage when viewed from an oblique direction can be obtained in the black screen of an organic EL display device.

In addition, in order to further reduce the black brightness at the polar angle of 0°, the phase difference plate of the present invention can also have the first and second optical anisotropic layers with optimal wavelength dispersion characteristics (meaning the wavelength dependence of the phase difference). Similarly, in the third optical anisotropic layer, by making the wavelength dispersion characteristics negatively dispersed (reverse wavelength dispersion), the black brightness in the black screen when viewed from an oblique direction can be further reduced.

[Industrial availability]

This case can provide a phase difference plate that reduces the coloring or reflectivity in a black screen when viewed from an oblique direction, a circular polarizing plate having the phase difference plate, and a liquid crystal display device and an organic EL display device having the aforementioned circular polarizing plate. For example, an organic EL display device can provide a wider range of viewing angles, so it can be ideally used for display device settings and vehicles with fixed viewing positions. In addition, a manufacturing method for circular polarizing plates that can be manufactured by roll-to-roll bonding can be provided, so it can also correspond to the manufacture of circular polarizing plates for large display devices.

101: The phase difference plate of the present invention

102: 1st optical anisotropic layer

103: Second optical anisotropic layer

104: The third optical anisotropy layer

107: Twisted nematic liquid crystal

Claims (6)

A phase difference plate comprises: a first optical anisotropic layer, in which a rod-like liquid crystal compound is aligned with the thickness direction as a helical axis and has an in-plane phase difference (Re) of substantially 1/2 wavelength; a second optical anisotropic layer, in which a rod-like liquid crystal compound is aligned with the thickness direction as a helical axis and has an in-plane phase difference (Re) of substantially 1/4 wavelength; wherein a third optical anisotropic layer satisfying the following formula (1) is provided between the first and second optical anisotropic layers, wherein the third optical anisotropic layer is a layer having a vertically aligned liquid crystal compound, and the thickness direction phase difference (Rth) is -150 to -80 nm, and _nx ≒ _ny < _nz (1) wherein _nx and nz are _y represents the refractive index in the direction orthogonal to the plate plane, and _nz represents the refractive index in the direction perpendicular to the plate plane. The phase difference plate as described in claim 1, wherein the twist angle of the first optical anisotropic layer is substantially 26° or substantially -26°, and the twist angle of the second optical anisotropic layer is substantially 78° or substantially -78° from the twist angle of the first optical anisotropic layer. A circular polarizing plate having a polarizing element and a phase difference plate as described in claim 1 or 2. The circular polarizing plate as described in claim 3, wherein the polarizing element comprises a dichroic azo dye, the hue of which is achromatic. An organic EL display device having a circular polarizing plate as described in claim 3 or 4. A liquid crystal display device having a circular polarizing plate as described in claim 3 or 4.

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