Optical film, polarizing plate using same, image display panel and image display device

Abstract

Provided is an optical film capable of suppressing interference color regardless of the value of an in-plane phase difference of a base material. More specifically, an optical film 10 has a first liquid crystal layer 3 on a base material 1, wherein the base material 1 has an in-plane phase difference of 200 nm or more, the first liquid crystal layer 3 has a Schlieren region in a plane, and a resin layer 2 is provided between the base material 1 and the first liquid crystal layer 3.

Description

Optical film, polarizing plate using the optical film, image display panel, and image display device.

[0001] This disclosure relates to an optical film, a polarizing plate using the optical film, an image display panel, and an image display device.

[0002] Optical films are used in image display devices. Optical films for image display devices are preferably those with excellent mechanical strength. Therefore, stretched plastic films are preferred as the substrate for optical films used in image display devices.

[0003] Stretched plastic films have good mechanical strength, but birefringence causes in-plane phase difference. It is known that when a plastic film with an in-plane phase difference exceeding a predetermined value is applied to an image display device equipped with a polarizer, monochromatic or rainbow-like interference colors are produced. These interference colors are easily visible when viewing the image with polarized sunglasses. They can also be seen with the naked eye.

[0004] Techniques have been proposed to suppress interference colors by adjusting the in-plane phase difference of the substrate (Patent Documents 1-2).

[0005] International Publication No. 2013 / 080949, Japanese Patent Publication No. 2012-32819

[0006] The optical film described in Patent Document 1 suppresses interference colors by increasing the in-plane phase difference of the substrate to 3000 nm or more. However, methods for increasing the in-plane phase difference of the substrate, as described in Patent Document 1, require increasing the thickness of the substrate, which prevents the thinning of image display devices. Furthermore, with optical films that increase the in-plane phase difference of the substrate, as described in Patent Document 1, interference colors are more likely to occur when the emission spectrum of the display element becomes sharp.

[0007] The optical film described in Patent Document 2, contrary to Patent Document 1, employs a technique to suppress interference colors by reducing the in-plane phase difference of the substrate. However, while methods to reduce the in-plane phase difference of the substrate, as in Patent Document 2, can make interference colors difficult to see with the naked eye, monochromatic interference colors may still be visible when viewed through polarized sunglasses. As described above, it has been difficult to suppress interference colors in optical films having a substrate with in-plane phase difference.

[0008] The object of this disclosure is to provide an optical film that can suppress interference colors regardless of the in-plane phase difference value of the substrate, and a polarizing plate, an image display panel, and an image display device using the optical film.

[0009] This disclosure provides the following optical films (1) to (4), a polarizing plate using the optical film, an image display panel, and an image display device. <1> An optical film having a first liquid crystal layer on a substrate, wherein the substrate has an in-plane phase difference of 200 nm or more, the first liquid crystal layer has a Schlieren region in its plane, and a resin layer is provided between the substrate and the first liquid crystal layer. <2> A polarizing plate having a polarizer, a first protective film disposed on one side of the polarizer, and a second protective film disposed on the other side of the polarizer, wherein at least one of the first protective film and the second protective film is the optical film described in <1>. <3> An image display panel including a display element and the optical film described in <1>. <4> An image display device including the image display panel described in <3>.

[0010] The optical film, polarizing plate, image display panel, and image display device of this disclosure can suppress interference colors.

[0011] This is a cross-sectional view showing one embodiment of the optical film of the present disclosure. This is a cross-sectional view showing one embodiment of the image display panel of the present disclosure. This is a polarized light microscope image of one embodiment of the Schlieren region. This is a schematic diagram showing the spatial distribution pattern of liquid crystal molecules in the principal axis direction in the Schlieren region. This is a schematic diagram for explaining the singularity of the first liquid crystal layer.

[0012] Embodiments of the present disclosure will be described below. [Optical Film] The optical film of the present disclosure is as follows: An optical film having a first liquid crystal layer on a substrate, wherein the substrate has an in-plane phase difference of 200 nm or more, the first liquid crystal layer has a Schlieren region in its plane, and a resin layer is provided between the substrate and the first liquid crystal layer.

[0013] Figure 1 is a cross-sectional view showing one embodiment of the optical film of the present disclosure. The optical film 10 in Figure 1 has a first liquid crystal layer 3 on a substrate 1, and a resin layer 2 between the substrate 1 and the first liquid crystal layer 3. The optical film 10 in Figure 1 also has a functional layer 4 on the side of the substrate 1 opposite to the side with the first liquid crystal layer 3. Figure 1 is a schematic cross-sectional view. That is, the scale of each layer constituting the optical film 10, and the scale of the recess on the first surface are schematic for ease of illustration and differ from the actual scale. The same applies to the other figures.

[0014] In this specification, the in-plane phase difference is expressed by the following formula, where Nx is defined as the refractive index in the direction of the slow axis with the highest refractive index in the plane, Ny is the refractive index in the direction perpendicular to the slow axis in the plane, Nz is the refractive index in the thickness direction, and d (nm) is the thickness of the layer. In this specification, the phase difference in the thickness direction is expressed by the following formula: In-plane phase difference = (Nx - Ny) × d Phase difference in thickness direction = ((Nx + Ny) / 2 - Nz) × d In this specification, the wavelength of light used as the reference for refractive index and phase difference is 550 nm unless otherwise specified.

[0015] <Layer Structure of Optical Film> Examples of layer structures for optical films include the following (1) and (2). In the following (1) and (2), " / " indicates the interface between layers. (1) Substrate / Resin layer / First liquid crystal layer (2) Functional layer / Substrate / Resin layer / First liquid crystal layer

[0016] <Substrate> The substrate must have an in-plane phase difference of 200 nm or more. A large in-plane phase difference of the substrate means that the substrate is sufficiently stretched and / or that the thickness of the substrate is not too thin. Therefore, by setting the in-plane phase difference of the substrate to 200 nm or more, the mechanical strength of the optical film can be increased. On the other hand, interference colors are more likely to occur when the in-plane phase difference of the substrate is 200 nm or more. However, although the optical film of this disclosure uses a substrate with an in-plane phase difference of 200 nm or more that is prone to interference colors, it has a first liquid crystal layer having a Schlieren region in the plane, so interference colors can be suppressed. Note that the effect of suppressing interference colors and blackout by the first liquid crystal layer can also be obtained when the in-plane phase difference of the substrate is less than 200 nm. The phenomenon of blackout will be described later. The in-plane phase difference of the substrate is preferably 300 nm or more, more preferably 400 nm or more, and even more preferably 520 nm or more.

[0017] The sharper the emission spectrum of a display element, the more likely interference colors are to occur. The optical film of this disclosure can be applied to an image display panel including a display element with a sharp emission spectrum to suppress interference colors. When the optical film of this disclosure is applied to an image display panel including a display element with a sharp emission spectrum, the in-plane phase difference of the substrate is preferably 4000 nm or more, more preferably 6000 nm or more, and even more preferably 8000 nm or more, in order to further suppress interference colors. In this specification, a display element having a sharp emission spectrum means "a display element in which at least one of the full width at half maximum of the R (red) emission spectrum, the G (green) emission spectrum, and the B (blue) emission spectrum is 100 nm or less." Another embodiment of a display element having a sharp emission spectrum is the first display element described below. First display element: A display element in which the full width at half maximum of the emission spectrum of R (red), G (green), and B (blue) are all 100 nm or less.

[0018] If the in-plane phase difference of the substrate is too large, the thickness of the substrate tends to increase. Also, as the in-plane phase difference of the substrate increases, the substrate can be considered uniaxially stretched, and if the in-plane phase difference is too large, the substrate inevitably becomes uniaxially stretched, which tends to reduce the strength of the substrate. Furthermore, if the in-plane phase difference of the substrate is too large, interference colors can be suppressed even without providing a first liquid crystal layer having a Schlieren region in the plane. For this reason, the in-plane phase difference of the substrate is preferably 15,000 nm or less, more preferably 12,000 nm or less, and even more preferably 10,000 nm or less. The in-plane phase difference of the substrate may also be 1,000 nm or less, 900 nm or less, or 800 nm or less.

[0019] In this specification, the in-plane phase difference of the substrate is defined as the average of eight measurements, excluding the upper and lower limits of the ten measured in-plane phase differences. Depending on the area of ​​the substrate, the ten measurements are performed as follows: Substrate area is 2400 cm² ２ In the case of a large sample, divide the substrate into three equal parts. Take a 5cm x 5cm sample from the center of the surface of each of the three divided substrates. Measure the in-plane phase difference at a total of 10 locations using the three 5cm x 5cm samples. To ensure that the 10 measurements are not biased towards one sample, take 3 or 4 measurements from each sample. The substrate area is 150cm². ２ Super 2400cm ２ In the following cases, a 5 cm x 5 cm sample is taken from the center of the substrate's surface, and the in-plane phase difference is measured at 10 locations using the sample. ２ More than 150cm ２ In the following cases, select any 10 locations within the surface of the substrate and take measurements. ２ If the measurement is less than 25 cm², select any 10 locations within the surface of the substrate and take the measurement. ２ If the measurement area is less than the specified area, the measurement areas at the 10 points may slightly overlap. However, regardless of the area of ​​the substrate, the centers of the measurement spots at the 10 points must be offset from each other.

[0020] In a laminate having a resin layer and a first liquid crystal layer on a substrate, the in-plane phase difference of the substrate is measured by the following procedure: (1) The surface of the laminate on the side with the first liquid crystal layer is scraped with steel wool to remove the first liquid crystal layer. If the resin layer has a phase difference, the resin layer is also scraped off. (2) A sample is prepared by bonding an adhesive glass having an adhesive layer on glass to the surface from which the first liquid crystal layer, etc., was scraped off. The sample cancels out the external haze on the surface from which the first liquid crystal layer, etc., was scraped off. (3) The in-plane phase difference of the sample is measured using a general-purpose measuring device.

[0021] In the constituent elements shown in this specification, if multiple options are given for both the upper and lower limits of a numerical value, the description shall be limited to an embodiment within a range that combines one selected from the upper limit options and one selected from the lower limit options. As a first example, we will consider the statement, "Parameter B may be A1 or greater, A2 or greater, or A3 or greater. Parameter B may be A4 or less, A5 or less, or A6 or less." In the first example, the numerical range of parameter B may be A1 or greater and A4 or less, A1 or greater and A5 or less, A1 or greater and A6 or less, A2 or greater and A4 or less, A2 or greater and A5 or less, A2 or greater and A6 or less, A3 or greater and A4 or less, A3 or greater and A5 or less, or A3 or greater and A6 or less. As a second example, we will consider the statement, "Parameter C may be A1 or greater and A4 or less, A2 or greater and A5 or less, or A3 or greater and A6 or less." In the second example, the numerical range of parameter C may be A1 or greater and A4 or less, A1 or greater and A5 or less, A1 or greater and A6 or less, A2 or greater and A4 or less, A2 or greater and A5 or less, A2 or greater and A6 or less, A3 or greater and A4 or less, A3 or greater and A5 or less, or A3 or greater and A6 or less. Furthermore, in the case of the average range of the in-plane phase difference of the above substrate, "200 nm to 15000 nm, 200 nm to 12000 nm, 200 nm to 10000 nm, 300 nm to 15000 nm, 300 nm to 12000 nm, 300 nm to 10000 nm, 400 nm to 15000 nm, 400 nm to 12000 nm, 400 nm to 10000 nm, 520 nm to 15000 nm, 520 nm to 12000 nm Embodiments of the following wavelength ranges are described: m or less, 520 nm to 10000 nm, 4000 nm to 15000 nm, 4000 nm to 12000 nm, 4000 nm to 10000 nm, 6000 nm to 15000 nm, 6000 nm to 12000 nm, 6000 nm to 10000 nm, 8000 nm to 15000 nm, 8000 nm to 12000 nm, and 8000 nm to 10000 nm.

[0022] Various materials can be used as the base material, but materials with good mechanical properties, optical properties, stability, and processability are preferred. Examples of such materials include resins such as acrylic resin, olefin resin, cellulose resin, polyester, polycarbonate, polyimide, polyamide-imide, polystyrene, acrylonitrile-styrene copolymer, ABS resin, and polyethersulfone; glass; etc., with resin being preferred. In other words, a resin base material is preferred. Furthermore, a stretched resin base material is preferred. The stretching may be uniaxial stretching or biaxial stretching, but biaxial stretching is preferred as it is easier to obtain good mechanical strength. Among resin base materials, a resin base material containing one or more resins selected from acrylic resin, olefin resin, cellulose resin, polyester, polycarbonate, polyimide, and polyamide-imide is preferred.

[0023] The thickness of the substrate is not particularly limited as long as the in-plane phase difference is within the above range. Examples of substrate thickness ranges include 5 μm to 1000 μm. The substrate thickness is measured using a general-purpose film thickness measuring instrument. The substrate thickness is sufficient if the average value of measurements taken at any 10 points is the above value.

[0024] The substrate preferably has a total light transmittance of 70% or more, more preferably 80% or more, and even more preferably 85% or more, according to JIS K7361-1:1997. The substrate preferably has a haze of 10% or less, more preferably 5% or less, and even more preferably 3% or less, according to JIS K7136:2000.

[0025] <Resin Layer> The optical film of this disclosure is required to have a resin layer between the substrate and the first liquid crystal layer. By arranging the resin layer between the substrate and the first liquid crystal layer, it is possible to easily form a Schlieren region within the plane of the first liquid crystal layer. The resin layer is arranged in contact with the first liquid crystal layer in the thickness direction of the optical film. As will be described later, the Schlieren region can be said to be a region formed horizontally in the first liquid crystal layer, starting from the orientation defect of the liquid crystal molecules, when the first liquid crystal layer contains an orientation defect of the liquid crystal molecules. In other words, the resin layer is a layer that makes it easier to cause an orientation defect in the first liquid crystal layer, and is a different layer from the so-called orientation layer. "Horizontal direction" is the direction parallel to the xy plane in Figure 1. Note that if the first liquid crystal layer is formed directly on the substrate without an intervening resin layer, it is difficult to form a Schlieren region within the plane of the first liquid crystal layer because the liquid crystal molecules of the first liquid crystal layer may be oriented along the orientation of the molecules of the substrate, or the orientation of the liquid crystal molecules of the first liquid crystal layer may be completely random.

[0026] The resin layer is preferably composed mainly of resin. The main component refers to 60% by mass or more of the total solid content constituting the resin layer, preferably 80% by mass or more, and more preferably 90% by mass or more. The resin layer may optionally contain additives such as ultraviolet absorbers and light stabilizers.

[0027] The resin layer preferably contains a resin with high wettability to the liquid crystal of the first liquid crystal layer. As will be described later, the Schlieren region is a region formed horizontally in the first liquid crystal layer, starting from the orientation defect of the liquid crystal molecules, when the first liquid crystal layer contains an orientation defect of the liquid crystal molecules. For this reason, it is preferable that the liquid crystal molecules of the first liquid crystal layer are oriented horizontally. By including a resin with high wettability to the liquid crystal of the first liquid crystal layer, the liquid crystal molecules of the first liquid crystal layer are more likely to be oriented horizontally, making it easier to form a Schlieren region within the plane of the first liquid crystal layer. On the other hand, in general-purpose horizontal alignment layers, the orientation of the liquid crystal molecules is aligned in a specific horizontal direction, so a Schlieren region cannot be formed.

[0028] Examples of the resin for the resin layer include acrylic resins, olefin resins, cellulose resins, polyesters, polycarbonates, polyimides, urethane resins, styrene resins, vinyl chloride-vinyl acetate copolymers, and the like. These resins may be used alone or in combination of two or more kinds. The resin of the resin layer may be a resin crosslinked and cured with a curing agent such as an isocyanate-based curing agent or an epoxy-based curing agent. The resin of the resin layer may be a cured product of an ionizing radiation curable compound.

[0029] The resin layer preferably has substantially no action of aligning liquid crystal molecules in a predetermined direction, so as to facilitate formation of a schlieren region in the first liquid crystal layer. A resin layer formed by applying a coating liquid for resin layer containing components constituting the resin layer onto a base material and drying the coating liquid usually has substantially no action of aligning the liquid crystal molecules of the first liquid crystal layer in a predetermined direction.

[0030] The thickness of the resin layer is not particularly limited. An embodiment of the thickness range of the resin layer includes 0.05 μm to 30 μm, preferably 0.07 μm to 10 μm, more preferably 0.08 μm to 1.00 μm, still more preferably 0.10 μm to 0.90 μm, and even more preferably 0.15 μm to 0.80 μm.

[0031] <First Liquid Crystal Layer> The first liquid crystal layer is required to have a schlieren region in its in-plane. A layer in which a schlieren region is observed can be said to be a liquid crystal layer. That is, in the present specification, "a liquid crystal layer having a schlieren region in its in-plane" and "a layer having a schlieren region in its in-plane" are synonymous. The liquid crystal molecules of the first liquid crystal layer are preferably horizontally aligned (homogeneously aligned).

[0032] The schlieren region is formed in the horizontal direction of the first liquid crystal layer starting from an alignment defect when the first liquid crystal layer contains the alignment defect of liquid crystal molecules. The "horizontal direction" refers to a direction parallel to the xy plane in Fig. 1.

[0033] Let's further explain the Schlieren region. In the Schlieren region, the principal axis directions of the liquid crystal molecules are generally random within the plane of the first liquid crystal layer. On the other hand, in local regions of the Schlieren region, the principal axis directions of the liquid crystal molecules are locally approximately constant, and these principal axis directions change continuously in the horizontal direction. The principal axis direction of the liquid crystal molecules refers to the slow axis direction of the liquid crystal molecules.

[0034] In the schlieren region, the major axis direction of liquid crystal molecules has the aforementioned orientation. Therefore, when the schlieren region is observed with a cross-nicol polarizing microscope, dark-field regions and bright-field regions are observed as a random pattern. Figure 3 is a polarizing micrograph of an embodiment of the schlieren region. The dark-field regions are formed starting from the aforementioned alignment defects. In the present specification, the alignment defect of a liquid crystal layer means a position where the change in the major axis direction becomes discontinuous while the major axis direction of liquid crystal molecules continuously changes in the horizontal direction. Further, in the present specification, the alignment defect of a liquid crystal layer may be referred to as a "singular point". Figure 5 is a schematic diagram for explaining the singular point of the first liquid crystal layer. In Figure 5, a plurality of dark-field regions 31a are radially derived starting from a singular point 32a which is an alignment defect. That a schlieren region is formed starting from a singular point which is an alignment defect of liquid crystal molecules is described in the following Documents 1 and 2. Document 1: Nehring, J. and Saupe, A., "On the schlieren texture in nematic and smectic liquid crystals", Journal of the Chemical Society, Faraday Transactions 2, (GBR), 1972, Vol. 68, pp. 1-15, DOI: 10.1039 / F29726800001. Document 2: T. Ohzono, K. Katoh, C. Wang, A. Fukazawa, S. Yamaguchi and J. Fukuda, "Uncovering different states of topological defects in schlieren textures of a nematic liquid crystal", Scientific Reports, (DEU), 2017, Vol. 7, Article No. 16814, DOI: 10.1038 / s41598-017-16967-1.

[0035] Figures 4(a) to 4(f) are schematic diagrams illustrating the spatial distribution pattern of liquid crystal molecules in the principal axis direction within the Schlieren region. Figures 4(a) to 4(f) do not directly show the location, number, and distribution of orientation defects. Orientation defects are identified as regions that always appear in the dark field when the optical film is rotated using a crossed nicols polarizing microscope.

[0036] As described above, the Schlieren region is formed when the first liquid crystal layer contains orientation defects of liquid crystal molecules. Also, as described above, in the first liquid crystal layer having the Schlieren region, the principal axis directions of the liquid crystal molecules are generally random within the plane of the first liquid crystal layer. On the other hand, the liquid crystal molecules of the first liquid crystal layer are horizontally oriented (homogeneous orientation). Furthermore, in the local region of the Schlieren region, the principal axis directions of the liquid crystal molecules are locally approximately constant, and these principal axis directions change continuously in the horizontal direction. For this reason, the first liquid crystal layer having the Schlieren region can exhibit a local in-plane phase difference. Also, in the first liquid crystal layer having the Schlieren region, the principal axis directions of the liquid crystal molecules within the plane are generally random. For this reason, polarized light incident on the first liquid crystal layer is emitted from the first liquid crystal layer as linearly polarized light with various polarization directions and / or elliptically polarized light with various azimuthal angles. Thus, the light emitted from the first liquid crystal layer having the Schlieren region contains light with various polarization components. Therefore, the optical film of this disclosure can suppress interference colors even when viewed through polarized sunglasses, regardless of the in-plane phase difference value of the substrate. Conventional optical films had difficulty suppressing interference colors when the resolution of the display element was high. However, the optical film of this disclosure can suppress interference colors regardless of the resolution of the display element. Conventional optical films sometimes produced strong interference colors or caused the screen to go completely dark depending on the angle of the optical film relative to the absorption axis of the polarizer. The optical film of this disclosure can suppress interference colors and prevent the screen from going completely dark, regardless of the angle of the polarizer relative to the absorption axis. The phenomenon of the screen going completely dark is sometimes referred to as "blackout". Conventionally, a technology has been proposed to suppress blackout by combining a λ / 2 phase difference plate and a λ / 4 phase difference plate to convert linearly polarized light into circularly polarized light over a wide wavelength range. However, this technology required the angles between the polarizer's absorption axis and the λ / 2 phase difference plate's slow phase axis, and between the polarizer's absorption axis and the λ / 4 phase difference plate's slow phase axis, to be within a predetermined range, which resulted in poor yield. Furthermore, while this technology could suppress blackout, it could not suppress interference colors.Furthermore, light passing through the optical film of this disclosure is emitted from the first liquid crystal layer as linearly polarized light with various polarization directions and / or elliptically polarized light with various azimuthal angles. In other words, the light passing through the optical film of this disclosure is close to natural light. Polarized light stimulates specific parts of the human eye, so prolonged exposure to polarized light can easily cause eye fatigue. The optical film of this disclosure can also suppress eye fatigue.

[0037] The effects of the optical film of this disclosure described above can also be achieved even when other optical films are present on the surface closer to the incident light and / or on the surface closer to the outgoing light than the optical film of this disclosure. Other optical films include, for example, ordinary optical films that are prone to producing interference colors. For example, even in an image display panel or image display device equipped with an ordinary optical film prone to producing interference colors as a surface protective film, interference colors can be suppressed by including the optical film of this disclosure. In other words, while maintaining the basic configuration of the conventional image display panel or conventional image display device, effects such as suppression of interference colors can be achieved simply by adding the optical film of this disclosure or by changing any one optical film to the optical film of this disclosure. From this point of view as well, the optical film of this disclosure is highly convenient and extremely commercially advantageous.

[0038] The optical film of this disclosure preferably has an absolute difference of 10.0% or less between the maximum polarization degree, which is the maximum value of the seven polarization degrees P0, P15, P30, P45, P60, P75, and P90, and the minimum polarization degree, which is the minimum value among the seven polarization degrees. <Measurement of Polarization Degree> The first polarizer and the second polarizer are arranged so that the absorption axis of the polarizer of the first polarizer and the absorption axis of the polarizer of the second polarizer are parallel. A cut sample is prepared by cutting the optical film into a rectangle. A first sample for measuring the transmittance of parallel nicols is prepared by placing the cut sample between the first polarizer and the second polarizer. The total light transmittance of the first sample is denoted as Tp (%). The first polarizer and the second polarizer are arranged so that the absorption axis of the polarizer of the first polarizer and the absorption axis of the polarizer of the second polarizer are orthogonal. A second sample for measuring the transmittance of crossed nicols is prepared by placing the cut sample between the first polarizing plate and the second polarizing plate. The total light transmittance of the second sample is denoted as Tc (%). The degree of polarization is calculated using the following formula 1: Degree of polarization (%) = (Tp - Tc) / (Tp + Tc) × 100 (Formula 1) Let n (degrees) be the angle between any one side of the rectangle of the cut sample and the absorption axis of the polarizer of the first polarizing plate. The degree of polarization when n is 0 degrees is denoted as P0, when n is 15 degrees as P15, when n is 30 degrees as P30, when n is 45 degrees as P45, when n is 60 degrees as P60, when n is 75 degrees as P75, and when n is 90 degrees as P90.

[0039] In the above measurement of polarization degree, the light incident surface is the surface facing the first polarizer. In the above measurement of polarization degree, the optical film is positioned such that the surface having the first liquid crystal layer faces the first polarizer, with respect to the substrate. In the above measurement of polarization degree, the polarizer is preferably polarized at 99.00% or higher and has an average transmittance of 35% or higher, more preferably polarized at 99.90% or higher and has an average transmittance of 37% or higher, and even more preferably polarized at 99.95% or higher and has an average transmittance of 40% or higher. Average transmittance refers to the average of spectral transmittances at wavelengths of 400 nm to 700 nm. The wavelength interval for measuring spectral transmittance is 5 nm.

[0040] A difference of 10.0% or less in absolute value means that the randomness of the liquid crystal molecules in the plane along the principal axis direction is high in the first liquid crystal layer having a Schlieren region. Therefore, by setting the difference of 10.0% or less in absolute value, interference colors and blackout can be more easily suppressed. The difference of 7.5% or less in absolute value is more preferable, and 5.0% or less is even more preferable. When forming the first liquid crystal layer, drying at a low temperature makes it easier to increase the randomness of the liquid crystal molecules in the plane along the principal axis direction.

[0041] The maximum polarization degree, which is the maximum value of the seven polarization degrees P0, P15, P30, P45, P60, P75, and P90, is preferably 15.0% or less, more preferably 11.0% or less, and even more preferably 8.0% or less.

[0042] A first liquid crystal layer having a schlieren region tends to have better heat resistance, moisture resistance, and light resistance than a normal liquid crystal layer aligned in a predetermined pattern. Specifically, even when any durability test selected from heat resistance, moisture resistance, and light resistance, or a combined durability test of these is performed, the first liquid crystal layer having a schlieren region can easily suppress a change in polarization degree as compared with a normal liquid crystal layer. As described above, in the first liquid crystal layer having a schlieren region, although the major axis direction of liquid crystal molecules is locally substantially constant in a local region, the major axis direction of the liquid crystal molecules is random as a whole. On the other hand, in a normal liquid crystal layer, the major axis direction of liquid crystal molecules is regularly aligned in a predetermined pattern. For this reason, it is considered that the first liquid crystal layer having a schlieren region can reduce the degree of mutual instability of liquid crystal molecules more than a normal liquid crystal layer, and can improve durability. Since the optical film of the present disclosure includes the first liquid crystal layer having a schlieren region, the optical film can have better durability than a conventional optical film including a normal liquid crystal layer.

[0043] As described above, when a schlieren region is observed with a crossed Nicols polarizing microscope, dark field regions and bright field regions are observed as a random pattern. In the optical film of the present disclosure, the average size of the dark field regions of the first liquid crystal layer when the optical film is observed with a crossed Nicols polarizing microscope is 5 μm ２ to 550 μm ２ or less, preferably 5 μm ２ to 500 μm ２ or less, more preferably 5 μm ２ to 450 μm ２ or less, more preferably 5 μm ２ to 415 μm ２ or less, more preferably 6 μm ２ to 400 μm ２ or less, more preferably 7 μm ２ to 300 μm ２ or less. The average size of the dark field regions is set to 5 μm ２By doing so, it is easier to suppress excessive haze in the optical film and reduce the contrast of the image display device. The average size of the dark field area is 550 μm. ２ The following measures make it easier to suppress interference colors: The planar shape of each dark-field region in the Schlieren region is random, and there is no regularity in how the outlines of each dark-field region extend. Therefore, even when the individual dark-field regions are large, the Schlieren region is difficult to see with the naked eye.

[0044] Each dark-field region can be described as a region within the Schlieren region where the principal axis direction of the liquid crystal molecules is locally approximately constant, and where this principal axis direction changes continuously in the horizontal direction. Haze is likely to occur at the boundary between the dark-field region and the bright-field region. For this reason, the average size of the dark-field region should be 5 μm. ２ By doing so, it becomes easier to suppress excessive haze in the optical film. Also, if the size of the dark-field area is larger than the size of the pixels of the display element, glare is more likely to occur. For this reason, the average size of the dark-field area is set to 500 μm. ２ By doing the following, glare can be more easily suppressed. Glare is a phenomenon in which the brightness of an image display device becomes locally high, making it visible as bright spots.

[0045] By not exposing the first liquid crystal layer to high temperatures during its formation, the size of the dark-field area can be easily reduced. In other words, by not drying the coating solution for the first liquid crystal layer at low temperatures or heat-treating it at high temperatures after drying, the size of the dark-field area can be easily reduced. Conversely, by exposing the first liquid crystal layer to high temperatures during its formation, the size of the dark-field area can be easily increased. Furthermore, by adding an ionizing radiation-curable compound other than the liquid crystal compound in a predetermined mass ratio or more to the liquid crystal compound as a component of the first liquid crystal layer, the size of the dark-field area can be easily reduced. The lower the wettability of the resin in the resin layer to the liquid crystal of the first liquid crystal layer, the easier it is to reduce the size of the dark-field area. Conversely, the higher the wettability of the resin in the resin layer to the liquid crystal of the liquid crystal layer, the easier it is to increase the size of the dark-field area.

[0046] The size of the dark-field region is affected by the number of singularities and the number of dark-field regions derived from a single singularity. A small number of singularities per unit area tends to result in larger individual dark-field regions. Conversely, a large number of singularities per unit area tends to result in smaller individual dark-field regions. A small number of dark-field regions derived from a single singularity tends to result in larger individual dark-field regions. Conversely, a large number of dark-field regions derived from a single singularity tends to result in smaller individual dark-field regions. If the first liquid crystal layer contains an ionizing radiation-curable compound other than a liquid crystal compound, the number of singularities and the number of dark-field regions derived from a single singularity tend to increase. The lower the wettability of the resin layer to the liquid crystal of the first liquid crystal layer, the more likely it is that the number of singularities and the number of dark-field regions derived from a single singularity will increase. The higher the drying temperature and heat treatment temperature of the coating solution for the liquid crystal layer, the less likely it is that the number of dark-field regions derived from a single singularity will decrease. The lower the drying temperature and heat treatment temperature of the liquid crystal coating solution, the more likely it is that a single singularity will produce a larger number of dark-field regions (the drying temperature and heat treatment temperature of the liquid crystal coating solution are thought to have a greater influence on the number of dark-field regions produced from a single singularity, but less influence on the number of singularities). As described above, the size of the dark-field regions is influenced by the number of singularities and the number of dark-field regions produced from a single singularity. Furthermore, the number of singularities and the number of dark-field regions produced from a single singularity are influenced by multiple factors such as compounds other than liquid crystal compounds, wettability, and temperature. For this reason, even if the number of singularities (number of orientation defects) is the same, the size of the dark-field regions is not necessarily the same.

[0047] In this specification, the average size of the dark-field area of ​​the first liquid crystal layer is measured by the following procedure B1 to B4. B1: A planar photograph of the optical film is taken with a crossed nicol polarizing microscope. The magnification of the photograph is 500x. The optical film for measurement is rectangular in shape. Let θ (degrees) be the angle between any one side of the rectangular optical film and any direction in the xy plane of the sample mounting stage of the polarizing microscope.

[0048] B2: Remove unnecessary parts from the image acquired in B1, such as scale bars, that are not part of the sample-derived image information. Then, using the image analysis freeware "ImageJ" developed by the National Institutes of Health (NIH) and its plugin package "Fiji," the image is binarized to make bright areas white and dark areas black using the following procedure. Furthermore, the average size (area) of the darkfield regions is calculated using the following procedure. The range for image analysis by binarization will include more than 200 independent darkfield regions. <Procedure> 1. Convert to grayscale: Click "Image," "Type," and "8-bit" in that order to convert to grayscale. 2. Binarize: Click "Image," and then "Adjust." Furthermore, set "Threshold" to "0-100." 3. Area Analysis: Click "Analyze," and in "Analyze Particles," set "Size (pixel-^2)" to "0-Infinity" and "Circularity" to "0.00-1.00." This will allow you to calculate the average number of pixels in the darkfield area. 4. Matching Pixels to Actual Length: Click "Straight," measure the length of the scale bar in the image in pixels, and then calculate the length per pixel. (For example, if a 50 μm scale bar has 100 pixels, the length per pixel is 0.5 μm.) 5. Calculating the Actual Area: Multiply the average number of pixels obtained in "3" by the square of the length per pixel obtained in "4" to calculate the average size (area) of the darkfield area.

[0049] B3: Change the angle between any one side of the rectangular optical film and any direction in the xy plane of the polarizing microscope's sample stand to θ+15°, θ+30°, θ+45°, θ+60°, and θ+75°, and perform the operations in B1 and B2 above, measuring the average size of the dark-field area at each angle. B4: The average size of the dark-field area at six angles is measured by B1 to B3. The average of the average sizes of the six dark-field areas is taken as the average size of the dark-field area of ​​the optical film.

[0050] The in-plane phase difference of the first liquid crystal layer is preferably 200 nm to 350 nm, more preferably 225 nm to 325 nm, and even more preferably 250 nm to 300 nm. By setting the in-plane phase difference of the first liquid crystal layer to 200 nm or more, it is easier to suppress the decrease in light transmittance when crossed nicols. By setting the in-plane phase difference of the first liquid crystal layer to 350 nm or less, it is easier to suppress the decrease in light transmittance when parallel nicols. By setting the in-plane phase difference of the first liquid crystal layer to 200 nm to 350 nm, the first liquid crystal layer can be made to act as a λ / 2 phase difference plate with respect to the central wavelength range of visible light (400 nm to 700 nm). Therefore, by setting the in-plane phase difference of the first liquid crystal layer to 200 nm to 350 nm, linearly polarized light in the wavelength range of visible light incident on the first liquid crystal layer can be easily emitted as linearly polarized light in various polarization directions. Furthermore, the aforementioned effects can be obtained regardless of the angle between the vibration direction of the incident linearly polarized light and the slow axis of the optical film substrate.

[0051] The first liquid crystal layer may have positive or negative wavelength dispersion. Negative wavelength dispersion is a characteristic in which the in-plane phase difference given to the transmitted light increases as the wavelength of the transmitted light increases. Positive wavelength dispersion is a characteristic in which the in-plane phase difference given to the transmitted light decreases as the wavelength of the transmitted light increases. In this specification, when the in-plane phase difference at a wavelength of 450 nm is defined as Re450 and the in-plane phase difference at a wavelength of 550 nm is defined as Re550, the characteristic in which Re450 < Re550 is referred to as negative wavelength dispersion. In this specification, the characteristic in which Re450 ≥ Re550 is referred to as positive wavelength dispersion. It is preferable that the first liquid crystal layer exhibits negative wavelength dispersion. By exhibiting negative wavelength dispersion, it is possible to easily reduce the degree of polarization of the optical film over a wide wavelength range.

[0052] The thickness of the first liquid crystal layer is not particularly limited. Examples of the thickness of the first liquid crystal layer include 0.1 μm to 10 μm.

[0053] The area ratio of the non-Schlieren region to the total area of ​​the first liquid crystal layer is preferably 20% or less, more preferably 10% or less, more preferably 7% or less, more preferably 5% or less, and more preferably 2% or less. There is no particular lower limit to the area ratio of the non-Schlieren region, but for example, it is 0.05% or more. The region that is always a dark-field region when the optical film is rotated under a crossed-nicols polarizing microscope can be called a non-Schlieren region. The non-Schlieren region corresponds to the singularities described above. The size of each singularity is extremely small, for example, 10 μm. ２ The following applies: The number of singularities (non-Schlieren regions) within a 283 μm × 476 μm region is preferably 50 or more, more preferably 100 or more, more preferably 110 or more, more preferably 130 or more, and more preferably 150 or more. By setting the number of singularities to 50 or more, it is easier to suppress the dark-field region from becoming too large. If the number of singularities is too large, the number of boundaries between the dark-field region and the bright-field region increases, which tends to increase haze. For this reason, the number of singularities within a 283 μm × 476 μm region is preferably 1000 or less, more preferably 500 or less, and more preferably 300 or less. As mentioned above, the size of the dark-field region is affected by the number of dark-field regions derived from singularities, so the size of the dark-field region is not determined solely by the number of singularities. In addition, the interference colors, haze, and glare mentioned above are more easily affected by the size of the dark-field region than by the number of singularities. Therefore, it is more important to adjust the size of the dark-field region than to adjust the number of singularities.

[0054] 《Material of the First Liquid Crystal Layer》 The first liquid crystal layer is preferably a homogeneously oriented liquid crystal layer. For this reason, the liquid crystal compound of the first liquid crystal layer is preferably a rod-shaped liquid crystal compound.

[0055] The liquid crystal compound is preferably a rod-shaped liquid crystal compound. The rod-shaped liquid crystal compound is not particularly limited, but examples include the compounds shown in (1) to (28), (A-1) to (A-24), and (B-1) to (B-26) below. In order to increase the birefringence of the liquid crystal compound, a rod-shaped liquid crystal compound containing a sulfur atom in the molecule is preferred. The liquid crystal compound may be a compound exhibiting positive wavelength dispersibility or a liquid crystal compound exhibiting negative wavelength dispersibility, but a liquid crystal compound exhibiting negative wavelength dispersibility is preferred. In the case of a compound exhibiting positive wavelength dispersibility, the closer the Re450 / Re550 value is to 1.00, the more preferable it is. Examples of liquid crystal compounds exhibiting negative wavelength dispersibility include the liquid crystal compounds shown in (B-1) to (B-26) below, the liquid crystal compound represented by general formula (1) in Japanese Patent Application Publication No. 2019-73712, and the liquid crystal compound represented by general formula (II) in International Publication No. 2017 / 043438.

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075] The liquid crystal compound is preferably a polymerizable rod-shaped liquid crystal material. Polymerizable functional groups of the polymerizable rod-shaped liquid crystal material include those that polymerize by the action of ultraviolet light, ionizing radiation such as electron beams, or heat. Specific examples include radical polymerizable functional groups. Radical polymerizable functional groups include functional groups having at least one addition polymerizable ethylenically unsaturated double bond, and more specifically, vinyl groups, acrylate groups (a general term encompassing acryloyl groups, methacryloyl groups, acryloyloxy groups, and methacryloyloxy groups), with or without substituents.

[0076] The birefringence of the liquid crystal compound is preferably 0.10 to 0.30, and more preferably 0.15 to 0.26. A higher birefringence of the liquid crystal compound is preferable because it allows the same optical performance to be obtained even with a thinner first liquid crystal layer. However, as the birefringence of the liquid crystal compound increases, it becomes necessary to add units sensitive to ultraviolet light, such as aromatic rings like benzene rings, to the liquid crystal molecular structure. For this reason, the birefringence of the liquid crystal compound is preferably 0.30 or less.

[0077] The first liquid crystal layer can be formed, for example, by applying a first liquid crystal layer forming solution containing a liquid crystal compound onto a resin layer, and then drying and irradiating with ultraviolet light as necessary. As described above, lowering the drying temperature when forming the first liquid crystal layer makes it easier to increase the randomness of the liquid crystal molecules in the principal axis direction within the plane.

[0078] <Other Layers> The optical film of this disclosure may further have other layers. Examples of other layers include a primer layer for improving adhesion between the substrate and the resin layer, a functional layer, etc. The primer layer is preferably formed between the substrate and the resin layer. The functional layer is preferably formed on the side of the substrate opposite to the resin layer. Examples of functional layers include an antistatic layer, a hard coat layer, an anti-glare layer, an anti-reflective layer, an adhesive layer, etc.

[0079] The optical film of this disclosure may have a second liquid crystal layer having a Schlieren region in its plane as an additional layer. By having a second liquid crystal layer having a Schlieren region in its plane, the polarization degree of the optical film can be made lower over a wider wavelength range, and interference colors can be more easily suppressed. The size and thickness of the dark-field region of the second liquid crystal layer may be the same as or different from that of the first liquid crystal layer. An optical film having a second liquid crystal layer can be manufactured, for example, by the following methods (1) or (2): (1) A transfer film having a resin layer and a second liquid crystal layer in that order on a peelable substrate is made. The second liquid crystal layer of the transfer film is transferred to a laminate having a resin layer and a first liquid crystal layer on a substrate. (2) After forming a resin layer and a first liquid crystal layer on a substrate, a resin layer and a second liquid crystal layer are formed on the first liquid crystal layer.

[0080] <Optical Properties> The optical film of this disclosure preferably has a haze of 0.5% to 45.0% according to JIS K7136:2000, more preferably 1.0% to 35.0%, and even more preferably 2.0% to 25.0%. The more randomly distributed Schlieren regions are formed in the first liquid crystal layer, the higher the haze tends to be. Therefore, by setting the haze to 0.5% or more, interference colors can be easily suppressed. By setting the haze to 45% or less, the decrease in image resolution can be easily suppressed.

[0081] The haze of an optical film is preferably measured from the center of a 5 cm x 5 cm sample taken from the optical film. If only one sample can be taken from the optical film, it is preferable to measure the haze at the center of the sample and use the obtained value as the haze of the optical film. If two to four samples can be taken from the optical film, it is preferable to measure the haze at the center of each sample and use the average value of each sample as the haze of the optical film. If five or more samples can be taken from the optical film, it is preferable to take five samples. The five samples are preferably taken from the center of the optical film and five locations near the four corners of the optical film. Then, it is preferable to measure the haze at the center of each of the five samples and use the average value of the five samples as the haze of the optical film. The total light transmittance of the optical film is preferably measured according to the haze measurement method described above.

[0082] The optical film of this disclosure preferably has a total light transmittance of 80% or more, more preferably 85% or more, and even more preferably 90% or more, according to JIS K7361-1:1997. The light incident surface when measuring haze and total light transmittance is the substrate side of the optical film.

[0083] [Polarizing plate] The polarizing plate of the present disclosure comprises a polarizer, a first protective film disposed on one side of the polarizer, and a second protective film disposed on the other side of the polarizer, wherein at least one of the first protective film and the second protective film is the optical film of the present disclosure described above.

[0084] <Polarizers> Examples of polarizers include sheet-type polarizers such as polyvinyl alcohol film, polyvinyl formal film, polyvinyl acetal film, and ethylene-vinyl acetate copolymer saponified film dyed with iodine or the like and stretched; wire grid-type polarizers consisting of numerous parallel metal wires; coated polarizers coated with lyotropic liquid crystal or dichroic guest-host material; and multilayer thin-film polarizers. These polarizers may also be reflective polarizers that have the function of reflecting polarization components that do not transmit through them.

[0085] <Protective Film> A first protective film is placed on one side of the polarizer, and a second protective film is placed on the other side of the polarizer. At least one of the first protective film and the second protective film is the optical film of the present disclosure as described above. Both the first protective film and the second protective film may be the optical film of the present disclosure as described above. Examples of protective films other than the optical film of the present disclosure among the first and second protective films include plastic films and glass. Examples of plastic films include polyester films, polycarbonate films, cycloolefin polymer films and acrylic films, and stretched films of these are preferred from the viewpoint of mechanical strength. Examples of glass include alkali glass, nitride glass, soda-lime glass, borosilicate glass and lead glass. The orientation of the optical film of the present disclosure in the thickness direction relative to the polarizer is not particularly limited.

[0086] The polarizer and the protective film may be bonded together using the adhesive properties of the polarizer, or they may be bonded together using an adhesive. A general-purpose adhesive can be used, and a PVA-based adhesive is preferred.

[0087] The polarizing plate of this disclosure can be used as a polarizing plate placed on the light-emitting surface side of a display element. When the optical film of this disclosure is used as a polarizing plate placed on the light-emitting surface side of a display element, it is preferable that the protective film on the light-emitting surface side of the polarizing plate is the optical film of this disclosure.

[0088] Furthermore, the polarizing plate of this disclosure can also be used as a polarizing plate placed on the light incident surface side of a liquid crystal display element. When the optical film of this disclosure is used as a polarizing plate placed on the light incident surface side of a display element, it is preferable that the protective film on the light incident surface side of the polarizing plate is the optical film of this disclosure.

[0089] [Image Display Panel] The image display panel of this disclosure includes a display element and the optical film of this disclosure described above.

[0090] Figure 2 is a cross-sectional view showing an embodiment of the image display panel 100 of the present disclosure. In the image display panel 100 of Figure 2, an optical film 10 is laminated on the light-emitting surface of the display element 20. The optical film of the present disclosure may be arranged on the light-emitting surface side of the display element, on the light-incident surface side of the display element, or on both the light-emitting and light-incident surfaces of the display element. The optical film 10 may have its substrate-side surface facing the display element side, or its first liquid crystal layer-side surface facing the display element side.

[0091] When the display element is a liquid crystal display element, polarizers are arranged on both the light-emitting and light-incoming sides of the display element. In the case of a display element other than a liquid crystal display element, a polarizer may be provided on the light-emitting side of the display element. The image display panel may have a polarizer between the optical film and the display element. While interference colors are more likely to occur when a polarizer is provided between the optical film and the display element, interference colors can be suppressed by using the optical film of this disclosure as the optical film.

[0092] When a display element has a polarizer and the optical film of this disclosure in this order on the light-emitting surface side, there may be another optical film between the polarizer and the optical film of this disclosure, or on the light-emitting surface side of the optical film of this disclosure. An example of such an optical film is a conventional optical film that is prone to producing interference colors. An example of a conventional optical film that is prone to producing interference colors is an optical film that does not have a liquid crystal layer having a Schlieren region in its plane. Even if the image display panel of this disclosure has such a conventional optical film that is prone to producing interference colors, the presence of the optical film of this disclosure can suppress interference colors. When a display element has a polarizer and the optical film of this disclosure in this order on the light-incident surface side, there may be another optical film between the polarizer and the optical film of this disclosure, or on the light-incident surface side of the optical film of this disclosure. An example of such an optical film is a conventional optical film that is prone to producing interference colors. Even if the image display panel of this disclosure has such a conventional optical film that is prone to producing interference colors, the presence of the optical film of this disclosure can suppress interference colors. Even in image display panels equipped with a conventional optical film that is prone to producing interference colors as a surface protective film, interference colors can be suppressed by including the optical film of this disclosure. In other words, while maintaining the basic configuration of a conventional image display panel, simply by adding the optical film of this disclosure or by replacing any one optical film with the optical film of this disclosure, effects such as suppression of interference colors can be achieved.

[0093] <Display Elements> Examples of display elements include liquid crystal display elements, EL display elements (organic EL display elements, inorganic EL display elements), plasma display elements, and LED display elements such as micro LED display elements. These display elements may have a touch panel function inside the display element. Examples of liquid crystal display methods for liquid crystal display elements include IPS method, VA method, multi-domain method, OCB method, STN method, TSTN method, etc.

[0094] Interference colors may be more likely to occur as the emission spectrum of the display element becomes sharper. Since the image display panel of this disclosure includes the optical film of this disclosure described above, interference colors can be easily suppressed even if the emission spectrum of the display element is sharp.

[0095] The image display panel disclosed herein may be an image display panel with a touch panel, having a touch panel between the display element and the optical film.

[0096] The size of the image display panel is not particularly limited, but the typical maximum diameter is between 2 inches and 500 inches. The maximum diameter refers to the maximum length when connecting any two points within the surface of the image display panel.

[0097] [Image Display Device] The image display device of the present disclosure includes the image display panel of the present disclosure.

[0098] The image display device of the present disclosure is not particularly limited as long as it includes the panel of the present disclosure. Preferably, the image display device of the present disclosure comprises the panel of the present disclosure, a drive control unit electrically connected to the panel, and a housing housing the same. When the display element is a liquid crystal display element, the image display device of the present disclosure requires a backlight. The backlight is positioned on the side opposite to the light-emitting surface of the liquid crystal display element. Either an edge-lit backlight or a direct-lit backlight can be used as the backlight. Examples of backlight sources include LEDs and CCFLs. A backlight using quantum dots can also be used as the backlight.

[0099] The size of an image display device is not particularly limited, but the maximum diameter of the effective display area is generally between 2 inches and 500 inches. The effective display area of ​​an image display device is the area in which an image can be displayed. For example, if an image display device has a housing that surrounds the display element, the area inside the housing is the effective display area. The maximum diameter of the effective display area is defined as the maximum length when connecting any two points within the effective display area. For example, if the effective display area is rectangular, the diagonal of that area is the maximum diameter. If the effective display area is circular, the diameter of that area is the maximum diameter.

[0100] This disclosure includes the following <1> to <8>. <1> An optical film having a first liquid crystal layer on a substrate, wherein the substrate has an in-plane phase difference of 200 nm or more, the first liquid crystal layer has a Schlieren region in its plane, and a resin layer is provided between the substrate and the first liquid crystal layer. <2> The optical film according to <1>, wherein the substrate has an in-plane phase difference of 200 nm or more and 15,000 nm or less. <3> The optical film according to <1> or <2>, wherein the substrate is a resin substrate containing one or more resins selected from acrylic resin, olefin resin, cellulose resin, polyester, polycarbonate, polyimide, and polyamideimide. <4> The optical film according to any one of <1> to <3>, wherein the first liquid crystal layer has an in-plane phase difference of 200 nm or more and 350 nm or less. <5> An optical film according to any of <1> to <4>, wherein the absolute value of the difference between the maximum polarization degree, which is the maximum value of the seven polarization degrees P0, P15, P30, P45, P60, P75, and P90, and the minimum polarization degree, which is the minimum value among the seven polarization degrees, is 10.0% or less. <Measurement of Polarization Degree> The first polarizer and the second polarizer are arranged so that the absorption axis of the polarizer of the first polarizer and the absorption axis of the polarizer of the second polarizer are parallel. A cut sample is made by cutting the optical film into a rectangle. A first sample for measuring the transmittance of parallel nicols is made by placing the cut sample between the first polarizer and the second polarizer. The total light transmittance of the first sample is Tp (%). The first polarizer and the second polarizer are arranged so that the absorption axis of the polarizer of the first polarizer and the absorption axis of the polarizer of the second polarizer are orthogonal. A second sample for measuring the transmittance of crossed nicols is prepared by placing the cut sample between the first polarizing plate and the second polarizing plate. The total light transmittance of the second sample is denoted as Tc (%). The degree of polarization is calculated using the following formula 1: Degree of polarization (%) = (Tp - Tc) / (Tp + Tc) × 100 (Formula 1) Let n (degrees) be the angle between any one side of the rectangle of the cut sample and the absorption axis of the polarizer of the first polarizing plate.Let P0 be the degree of polarization when n is 0 degrees, P15 be the degree of polarization when n is 15 degrees, P30 be the degree of polarization when n is 30 degrees, P45 be the degree of polarization when n is 45 degrees, P60 be the degree of polarization when n is 60 degrees, P75 be the degree of polarization when n is 75 degrees, and P90 be the degree of polarization when n is 90 degrees. <6> A polarizing plate having a polarizer, a first protective film disposed on one side of the polarizer, and a second protective film disposed on the other side of the polarizer, wherein at least one of the first protective film and the second protective film is an optical film according to any of <1> to <5>. <7> An image display panel including a display element and an optical film according to any of <1> to <5>. <8> An image display device including the image display panel according to <7>.

[0101] Next, the present disclosure will be described in more detail by examples, but the present disclosure is not limited in any way by these examples. Unless otherwise specified, "parts" and "%" refer to mass.

[0102] 1. Measurement and Evaluation The following measurements and evaluations were performed on the optical films of the examples and comparative examples. The atmosphere during each measurement and evaluation was a temperature of 23±5°C and a relative humidity of 40% to 65%. Before starting each measurement and evaluation, the target sample was exposed to the above atmosphere for 30 to 60 minutes before measurement and evaluation.

[0103] 1-1. In-plane phase difference of substrate The in-plane phase difference of the substrate was measured using the product name "RETS-100" from Otsuka Electronics Co., Ltd.

[0104] In 1-1 above, the in-plane phase difference was measured using the following procedure (1) to (4). (1) To stabilize the RETS-100 light source, leave it for at least 60 minutes after turning on the light source. Then, select the rotational analyzer method and the one-point mode. (2) Next, input the following measurement conditions into the RETS-100. <Measurement conditions> ・In-plane phase difference measurement range: rotational analyzer method ・Measurement spot diameter: φ5 mm ・Tilt angle range: 0° ・Measurement wavelength range: 400 nm to 800 nm (3) Next, obtain background data without placing a sample in the instrument. The instrument is a closed system, and this is done each time the light source is turned on. (4) After that, place the sample on the stage inside the instrument and perform the measurement. The sample size is 5 cm x 5 cm.

[0105] 1-2. Average size of the dark-field region Following the procedures in B1 to B4 of the main text of the specification, the average size of the dark-field region of the first liquid crystal layer of the optical films of the examples and comparative examples was measured. If the Schlieren region could not be confirmed, it was marked with "-". A polarizing microscope, product name "BX51M" manufactured by Olympus Corporation, was used. The imaging conditions for the polarizing microscope were under orthogonal nicols and a magnification of 500x.

[0106] 1-3. Polarization Degree For the optical films of the examples and comparative examples, the absolute value of the difference between the maximum polarization degree, which is the maximum value of seven polarization degrees P0, P15, P30, P45, P60, P75, and P90, and the minimum polarization degree, which is the minimum value among the seven polarization degrees, was measured. The first and second polarizers used had a polarization degree of 99% or higher and an average transmittance of 40% or higher. A haze meter (HM-150, manufactured by Murakami Color Technology Laboratory) was used as the device for measuring the total light transmittance of the first and second samples. The results are shown in Table 1. In Table 1, "PL1", "PL2", "X1", "X2", "Y1", and "Y2" mean the following values. PL1: Maximum polarization degree (%) PL2: Minimum polarization degree (%) X1: Transmittance at crossed nicols at maximum polarization degree (%) X2: Transmittance at parallel nicols at maximum polarization degree (%) Y1: Transmittance at crossed nicols at minimum polarization degree (%) Y2: Transmittance at parallel nicols at minimum polarization degree (%) <Measurement of polarization degree> The first polarizer and the second polarizer are arranged so that the absorption axis of the polarizer of the first polarizer and the absorption axis of the polarizer of the second polarizer are parallel. A cut sample is made by cutting the optical film into a rectangle. A first sample for measuring the transmittance at parallel nicols is made by placing the cut sample between the first polarizer and the second polarizer. The total light transmittance of the first sample is denoted as Tp (%). The first polarizer and the second polarizer are arranged so that the absorption axis of the polarizer of the first polarizer and the absorption axis of the polarizer of the second polarizer are orthogonal. A second sample for measuring the transmittance of crossed nicols is prepared by placing the cut sample between the first polarizing plate and the second polarizing plate. The total light transmittance of the second sample is denoted as Tc (%). The degree of polarization is calculated using the following formula 1: Degree of polarization (%) = (Tp - Tc) / (Tp + Tc) × 100 (Formula 1) Let n (degrees) be the angle between any one side of the rectangle of the cut sample and the absorption axis of the polarizer of the first polarizing plate. The degree of polarization when n is 0 degrees is denoted as P0, when n is 15 degrees as P15, when n is 30 degrees as P30, when n is 45 degrees as P45, when n is 60 degrees as P60, when n is 75 degrees as P75, and when n is 90 degrees as P90.In the above measurement of polarization degree, the light incident surface was the surface on the first polarizer side. In the above measurement of polarization degree, the optical film was positioned such that the surface having the first liquid crystal layer faced the first polarizer side, relative to the substrate.

[0107] 1-4. Total Light Transmittance and Haze Five 5cm x 5cm samples were cut from the optical film. The total light transmittance (JIS K7361:1997) and haze (JIS K7136:2000) of the center of each sample were measured using a haze meter (HM-150, manufactured by Murakami Color Technology Laboratory). To stabilize the light source, measurements were taken after the light source had been lit for at least 15 minutes. The average values ​​of the five samples were taken as the total light transmittance and haze of the optical film for each example and comparative example.

[0108] 1-5. As an interference color surface light source, we prepared the "Treviewer A2-450-W" product from Tritech Co., Ltd. An evaluation sample was prepared by arranging a lower polarizer, an optical film, and an upper polarizer in that order on the surface light source. The lower and upper polarizers were arranged in crossed nicols. In the sample, the optical film was positioned so that the surface of the first liquid crystal layer facing the upper polarizer. With the surface light source displayed in white, the presence or absence of interference colors was visually evaluated while rotating the optical film. In the sample, the lower polarizer acts as a polarizer on the display element of an image display device, and the upper polarizer acts as polarized sunglasses. A: No interference colors are visible at all, regardless of the orientation of the optical film. A-: There are directions in which interference colors are slightly visible depending on the orientation of the optical film, but in many directions, no interference colors are visible at all. B: There are directions in which interference colors are hardly visible depending on the orientation of the optical film, but in many directions, weak interference colors are visible. C: While interference colors are weaker in certain directions depending on the orientation of the optical film, they are strongly visible in most directions.

[0109] 2. Preparation of Optical Film [Example 1] A resin layer with a thickness of 0.2 μm was formed by applying the resin layer coating solution 1 according to the following formulation to a substrate (biaxially oriented polyethylene terephthalate film with a thickness of 100 μm (Toyobo "A4160"), in-plane phase difference: 3200 nm) and drying it at 80°C for 1 minute. Next, the first liquid crystal layer coating solution 1 described below was applied to the resin layer and dried at 70°C for 1 minute. Then, ultraviolet light was irradiated (cumulative light intensity: 150 mJ / cm²). ２ A first liquid crystal layer with a thickness of 1.7 μm was formed. The optical film of Example 1 was obtained through the above steps.

[0110] <Coating solution for resin layer 1> A solution (solid content 4.5% by mass) obtained by diluting a resin composition containing a polycinnamate compound with propylene glycol monomethyl ether.

[0111] <First liquid crystal layer coating solution 1> - Rod-shaped liquid crystal molecules: 10 parts by mass (Rod-shaped liquid crystal compound of (A-1) in the main text of the specification) - Photopolymerization initiator: 0.4 parts by mass (Manufactured by IGM, trade name: Omnirad 184) - Methyl ethyl ketone: 89.6 parts by mass

[0112] [Example 2] An optical film of Example 2 was obtained in the same manner as in Example 1, except that the substrate was changed to a uniaxially oriented polyethylene terephthalate film with a thickness of 80 μm (TA044, manufactured by Toyobo, in-plane phase difference: 8400 nm).

[0113] [Examples 3-7, 11, 12, 16] Optical films of Examples 3-7, 11, 12, and 16 were obtained in the same manner as in Example 1, except that the drying temperature of the first liquid crystal layer was changed to the temperature shown in Table 1.

[0114] [Examples 8-10, 13-15] Optical films of Examples 8-10 and 13-15 were obtained in the same manner as in Example 1, except that the substrate was changed to the substrate described below and the drying temperature of the first liquid crystal layer was set to the temperature shown in Table 1. Substrate of Example 8: Biaxially oriented polyethylene terephthalate film with a thickness of 12 μm (Toray Industries "Lumirror #12-S-10", in-plane phase difference: 500 nm) Substrate of Example 9: Biaxially oriented polyethylene terephthalate film with a thickness of 5 μm (Nitto Denko "No. 5600", in-plane phase difference: 200 nm) Substrate of Example 10: Biaxially oriented polyethylene terephthalate film with a thickness of 38 μm (Toyobo "A4360", in-plane phase difference: 1500 nm) Substrate of Example 13: Biaxially oriented polyethylene terephthalate film with an in-plane phase difference of 2000 nm Substrate of Example 14: Substrate made by laminating two biaxially oriented polyethylene terephthalate films with an in-plane phase difference of 2000 nm via a pressure-sensitive adhesive layer (total in-plane phase difference: 4000 nm) Substrate of Example 15: A substrate formed by laminating two biaxially oriented polyethylene terephthalate films with an in-plane phase difference of 3200 nm via a pressure-sensitive adhesive layer (total in-plane phase difference: 6400 nm).

[0115] [Example 17] The first liquid crystal layer coating solution 1 was replaced with the first liquid crystal layer coating solution 2 described below. Furthermore, the drying temperature of the first liquid crystal layer was changed to the temperature shown in Table 1. Except for these changes, the optical film of Example 17 was obtained in the same manner as in Example 1. <First liquid crystal layer coating solution 2> ・Rod-shaped liquid crystal molecules: 10 parts by mass (Rod-shaped liquid crystal compound as described in (13) of the main text of the specification) ・Photopolymerization initiator: 0.4 parts by mass (Manufactured by IGM, trade name: Omnirad 184) ・Methyl ethyl ketone: 89.6 parts by mass

[0116] [Comparative Example 1] An optical film of Comparative Example 1 was obtained in the same manner as in Example 1, except that the first liquid crystal layer was formed directly on the substrate without an intervening resin layer.

[0117] [Comparative Example 2] An optical film of Comparative Example 2 was obtained in the same manner as in Example 2, except that the first liquid crystal layer was formed directly on the substrate without an intervening resin layer.

[0118]

[0119] In Table 1, "Re" indicates the in-plane phase difference of the substrate, "Temp" indicates the drying temperature of the first liquid crystal layer, "Size" indicates the average size of the dark-field region, "PL1" indicates the maximum polarization degree, "PL2" indicates the minimum polarization degree, "Absolute difference" indicates the absolute difference between PL1 and PL2, "Tt" indicates the total light transmittance, and "Hz" indicates the haze.

[0120] As is clear from Table 1, it can be confirmed that the optical film of the example can suppress interference colors regardless of the in-plane phase difference value of the substrate. The optical films of Comparative Examples 1 and 2 have the first liquid crystal layer formed directly on the substrate without a resin layer. For this reason, in the optical films of Comparative Examples 1 and 2, the liquid crystal molecules of the first liquid crystal layer are oriented along the orientation of the molecules of the substrate, or the orientation of the liquid crystal molecules of the first liquid crystal layer is completely random, so no Schlieren region is formed in the plane of the first liquid crystal layer. The polarization degree values ​​of Comparative Examples 1 and 2 are due to the effect of birefringence of the substrate. Even when the orientation of the thickness direction of the optical film was reversed within the evaluation sample, the evaluation of the interference colors of the optical films of the example and comparative examples was the same as the evaluation in Table 1.

[0121] 3. Durability of the Liquid Crystal Layer An optical film was prepared as shown in Reference Example 1 below. [Reference Example 1] A composition containing a polycinnamate compound (4% solids, solvent: propylene glycol monomethyl ether) was applied to a substrate (uniaxially oriented polyethylene terephthalate film with a thickness of 80 μm (Toyobo "TA044"), in-plane phase difference: 8400 nm) to form a coating film. The obtained coating film was then dried at 120°C for 1 minute and exposed to polarized light at 20 mJ / cm². ２ An orientation layer with a thickness of 300 nm was formed by irradiation with (310 nm) light. Next, a λ / 4 phase difference layer coating solution with the following formulation was applied to the orientation layer and dried at 70°C for 1 minute. Then, ultraviolet light was irradiated (cumulative light intensity: 150 mJ / cm²). ２A λ / 4 phase difference layer with a thickness of 1.0 μm was formed. In the λ / 4 phase difference layer, the principal axis directions of the liquid crystal molecules were regularly oriented along the pattern of the orientation layer. The angle between the slow axis of the substrate and the slow axis of the λ / 4 phase difference layer was set to 45 degrees. The principal axis direction of the liquid crystal molecules in the λ / 4 phase difference layer was equal to the slow axis direction of the λ / 4 phase difference layer. By the above steps, the optical film of Reference Example 1 was obtained.

[0122] <Coating solution for λ / 4 phase difference layer> ・Rod-shaped liquid crystal molecules: 10 parts by mass (Rod-shaped liquid crystal compound of (A-1) in the main text of the specification) ・Photopolymerization initiator: 0.4 parts by mass (Manufactured by IGM, trade name: Omnirad184) ・Methyl ethyl ketone: 89.6 parts by mass

[0123] The spectral polarization of the optical films of Example 2 and Reference Example 1 was measured. <Method for measuring the spectral polarization of an optical film> The first polarizer and the second polarizer are arranged so that the absorption axis of the polarizer of the first polarizer and the absorption axis of the polarizer of the second polarizer are parallel. A first sample for parallel nicol transmittance measurement is prepared by placing the optical film to be measured between the first polarizer and the second polarizer. The first polarizer, the second polarizer and the optical film are all rectangular and are arranged in the first sample so that the four sides of the rectangle are parallel to each other. The spectral transmittance of the first sample is measured. The spectral transmittance of the first sample at a predetermined wavelength is denoted as sTp (%). The first polarizer and the second polarizer are arranged so that the absorption axis of the polarizer of the first polarizer and the absorption axis of the polarizer of the second polarizer are orthogonal. A second sample for measuring the transmittance of crossed nicols is prepared by placing the optical film to be measured between the first polarizer and the second polarizer. The first polarizer, the second polarizer, and the optical film are all rectangular and arranged in the second sample so that the four sides of the rectangle are parallel to each other. The spectral transmittance of the second sample is measured. The spectral transmittance of the second sample at a predetermined wavelength is denoted as sTc (%). The degree of polarization at a predetermined wavelength is expressed by the following formula 2: Degree of polarization at a predetermined wavelength (%) = |(sTp - sTc) / (sTp + sTc)| × 100 (Formula 2)

[0124] In the above measurement of spectral polarization, spectral transmittance was measured in a range including wavelengths from 400 nm to 700 nm. The wavelength interval for spectral transmittance measurement was set to 1 nm. In the above measurement of spectral polarization, the first and second polarizers used had a polarization degree of 99% or higher and an average transmittance of 40% or higher. The spectral transmittance measuring device for the first and second samples was the "V-670" manufactured by JASCO Corporation. The rectangular optical film used for the above measurement of spectral polarization was manufactured so that the direction of one pair of opposite sides of the rectangle was parallel to the direction of the slow axis of the substrate.

[0125] Next, the optical films of Example 2 and Reference Example 1 were subjected to the following first to third durability tests. <First durability test (heat resistance test)> The optical film was exposed to an atmosphere of 85°C and relative humidity of 40% to 65% for 250 hours. <Second durability test (humidity and heat resistance test)> The optical film was exposed to an atmosphere of 60°C and relative humidity of 95% for 250 hours. <Third durability test (light resistance test)> Using an ultraviolet fade meter (Suga Test Instruments Co., Ltd., product name: U48AU), the liquid crystal layer side of the optical film was irradiated with an irradiation dose of 500 W / m². ２ The sample was exposed to ultraviolet light for 100 hours.

[0126] Next, the spectral polarization degree of each optical film after the durability test was measured in the same manner as described above. For the optical films of Example 2 and Reference Example 1, the absolute value of the difference between the spectral polarization degree before the durability test and the spectral polarization degree after the durability test was calculated for each wavelength. That is, for wavelengths between 400 nm and 700 nm, the absolute value of the difference between the spectral polarization degree before the durability test and the spectral polarization degree after the durability test was calculated for every 1 nm. Then, the average value of the "absolute value of the difference" for each wavelength was calculated. The results are shown in Table 2. The lower the average value mentioned above, the better the durability of the optical film.

[0127]

[0128] Table 2 shows that the liquid crystal layer having a Schlieren region in Example 2 exhibits a smaller change in polarization degree after the durability test compared to the liquid crystal layer of Reference Example 1, which does not have a Schlieren region, confirming its superior durability. The third durability test involves irradiating the liquid crystal layer with ultraviolet light. Since liquid crystal compounds are susceptible to degradation from ultraviolet light, it is common practice to place a UV-absorbing layer on top of the liquid crystal layer. In Reference Example 1, the liquid crystal compound degrades due to UV irradiation, resulting in a significant change in polarization degree after the third durability test. On the other hand, the optical film in Example 2 shows a smaller change in polarization degree after the third durability test compared to Reference Example 1, indicating good durability against ultraviolet light. Therefore, by comparing the third durability tests of Example 2 and Reference Example 1, it can be confirmed that the liquid crystal layer having a Schlieren region in Example 2 is more likely to exhibit UV resistance even without the placement of a UV-absorbing layer.

[0129] 1: Substrate 2: Resin layer 3: First liquid crystal layer 3a: Dark-field region 3b: Singularity 4: Functional layer 10: Optical film 20: Display element 100: Image display panel

Claims

1. An optical film having a first liquid crystal layer on a substrate, wherein the substrate has an in-plane phase difference of 200 nm or more, the first liquid crystal layer has a Schlieren region in its plane, and a resin layer is provided between the substrate and the first liquid crystal layer.

2. The optical film according to claim 1, wherein the substrate has an in-plane phase difference of 200 nm or more and 15,000 nm or less.

3. The optical film according to claim 1, wherein the substrate is a resin substrate containing one or more resins selected from acrylic resin, olefin resin, cellulose resin, polyester, polycarbonate, polyimide, and polyamideimide.

4. The optical film according to claim 1, wherein the first liquid crystal layer has an in-plane phase difference of 200 nm or more and 350 nm or less.

5. The optical film according to claim 1, wherein the absolute value of the difference between the maximum polarization degree, which is the maximum value of the seven polarization degrees P0, P15, P30, P45, P60, P75 and P90, and the minimum polarization degree, which is the minimum value among the seven polarization degrees, is 10.0% or less. <Measurement of Polarization Degree> A first polarizing plate and a second polarizing plate are arranged such that the absorption axis of the polarizer of the first polarizing plate is parallel to the absorption axis of the polarizer of the second polarizing plate. A cut sample is prepared by cutting the optical film into a rectangle. A first sample for measuring the transmittance of parallel nicols is prepared by placing the cut sample between the first polarizing plate and the second polarizing plate. The total light transmittance of the first sample is denoted as Tp (%). The first polarizer and the second polarizer are arranged so that the absorption axis of the polarizer of the first polarizer and the absorption axis of the polarizer of the second polarizer are perpendicular to each other. A second sample for measuring the transmittance of crossed nicols is prepared by placing the cut sample between the first polarizing plate and the second polarizing plate. The total light transmittance of the second sample is denoted as Tc (%). The degree of polarization is calculated using the following formula 1. Degree of polarization (%) = (Tp - Tc) / (Tp + Tc) × 100 (Formula 1) Let n (degrees) be the angle between any one side of the rectangle of the cut sample and the absorption axis of the polarizer of the first polarizing plate. Let P0 be the degree of polarization when n is 0 degrees, P15 be the degree of polarization when n is 15 degrees, P30 be the degree of polarization when n is 30 degrees, P45 be the degree of polarization when n is 45 degrees, P60 be the degree of polarization when n is 60 degrees, P75 be the degree of polarization when n is 75 degrees, and P90 be the degree of polarization when n is 90 degrees.

6. A polarizing plate comprising a polarizer, a first protective film disposed on one side of the polarizer, and a second protective film disposed on the other side of the polarizer, wherein at least one of the first protective film and the second protective film is an optical film according to any one of claims 1 to 5.

7. An image display panel comprising a display element and an optical film according to any one of claims 1 to 5.

8. An image display device including the image display panel described in claim 7.

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