Optical film

Abstract

To provide a method capable of objectively evaluating an interference color by the influence of an optical film.SOLUTION: A method for evaluating an interference color, comprising the following steps 1 to 3, wherein the interference color is evaluated by one type of dispersion or a combination of two or more types of dispersions calculated from the following step 4: Step 1: A surface illuminant including a polarizing element is made to display white color, and linearly polarized white color light L1 is emitted from the surface illuminant. Step 2: The in-plane distribution of tristimulus values is measured at the L1 portion. The tristimulus values of the L1 portion measured in this step is defined as tristimulus values 1. Step 3: The surface light source is displayed in white while the optical film is placed on the surface light source. Then, the in-plane distribution of tristimulus values is measured with respect to light L1 that is the L2 transmitted through the optical film. The tristimulus values of the L2 portion measured in this step is defined as tristimulus values 2. Step 4: The plane in which the tristimulus values 1 and the tristimulus values 2 are measured is divided into a plurality of sections. A color parameter is calculated for each section from the tristimulus values 1 and the tristimulus values 2. Then, the variance of the color parameters of all the sections is calculated. The calculation of the variance is performed for one or more color parameters.

Description

[Technical Field]

[0001] The present disclosure relates to a method for evaluating interference colors, an optical film, a polarizing plate, and an image display device. [Background technology]

[0002] Image display devices such as monitors for televisions, notebook PCs, and desktop PCs often have optical films on their display elements. It is known that when the optical film has a phase difference, interference colors are observed depending on the viewing angle. The interference colors are prominently observed when viewed through polarized sunglasses, but are also observed with the naked eye.

[0003] Various optical films have been proposed to suppress interference colors caused by the retardation of optical films. The method for evaluating interference colors when optical films are applied to image display devices is primarily visual sensory evaluation (Patent Document 1).

[0004] Furthermore, Patent Documents 2 and 3 propose methods for evaluating display unevenness in image display devices. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-124919 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-151527 [Patent Document 3] International Publication No. 2013 / 175973 Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional methods for evaluating interference colors such as those described in Patent Document 1 involve sensory evaluation by human visual inspection, which has led to problems such as variations in evaluation and poor evaluation accuracy due to the inclusion of human subjectivity.

[0007] The methods of Patent Documents 2 and 3 can objectively evaluate the display unevenness of an image display device. However, since the methods of Patent Documents 2 and 3 evaluate the entire image display device, they cannot evaluate the extent to which an optical film affects the display unevenness of an image display device.

[0008] An object of the present disclosure is to provide a method for objectively evaluating interference colors caused by an optical film, and an object of the present disclosure is to provide an optical film, a polarizing plate, and an image display device in which interference colors are suppressed. [Means for solving the problem]

[0009] The present disclosure provides the following interference color evaluation methods [1] to

[14] . [1] A method for evaluating interference colors, comprising the following steps 1 to 3, and evaluating interference colors calculated from one type of dispersion or a combination of two or more types of dispersions in accordance with step 4 below. Step 1: A surface light source including a polarizer is set to display white, and linearly polarized white light L1 is emitted from the surface light source. Step 2: Measure the in-plane distribution of tristimulus values ​​for L1. The tristimulus values ​​of L1 measured in this step are defined as tristimulus values ​​1. Step 3: With an optical film placed on the surface light source, the surface light source is displayed in white. Then, the in-plane distribution of tristimulus values ​​is measured for light L2, which is light L1 transmitted through the optical film. The tristimulus value of L2 measured in this step is called tristimulus value 2. Step 4: Divide the surface where the tristimulus values ​​1 and 2 were measured into a plurality of sections. Calculate color parameters for each section from the tristimulus values ​​1 and 2. Then, calculate the variance of the color parameters for all sections. The calculation of the variance is performed for one or more color parameters. [2] The method for evaluating interference colors according to [1], wherein the dispersion includes any one selected from Group 1 below. <Group 1> Variance of the a* values ​​in the Lab color system, variance of the b* values ​​in the Lab color system, {(a* values ​​in the Lab color system) 2 +(b* value of the Lab color system) 2} 1 / 2 variance of the u* values ​​in the Luv color system, variance of the v* values ​​in the Luv color system, {(u* values ​​in the Luv color system) 2 +(v* value of Luv color system) 2} 1 / 2 Dispersion of [3] The method for evaluating interference colors according to [1], wherein the dispersion includes one selected from the following Group 2-1 and one selected from the following Group 2-2 (however, the dispersion in Group 2-2 is different from the dispersion selected from Group 2-1). <Group 2-1> Variance of the a* values ​​in the Lab color system, variance of the b* values ​​in the Lab color system, {(a* values ​​in the Lab color system) 2 +(b* value of the Lab color system) 2} 1 / 2 Dispersion of <Group 2-2> Variance of L* values ​​in the Lab color system, variance of a* values ​​in the Lab color system, variance of b* values ​​in the Lab color system, {(a* value in the Lab color system) 2 +(b* value of the Lab color system) 2} 1 / 2 Dispersion of [4] The method for evaluating interference colors according to [1], wherein the dispersion includes one selected from the following Group 3-1 and one selected from the following Group 3-2 (however, the dispersion in Group 3-2 is different from the dispersion selected from Group 3-1). <Group 3-1> Variance of u* values ​​in the Luv color system, variance of v* values ​​in the Luv color system, {(u* values ​​in the Luv color system) 2 +(v* value of Luv color system) 2} 1 / 2 Dispersion of <Group 3-2> Variance of L* values ​​in the Luv color system, variance of u* values ​​in the Luv color system, variance of v* values ​​in the Luv color system, {(u* values ​​in the Luv color system) 2 +(v* value of Luv color system) 2} 1 / 2 Dispersion of [5] A method for evaluating interference colors according to any one of [1] to [4], wherein the measurement of tristimulus value 1 in step 2 and the measurement of tristimulus value 2 in step 3 are each carried out at a plurality of measurement angles, and step 4 is carried out for each measurement angle. [6] The method for evaluating interference colors according to [1], wherein the variance includes the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system, and the interference color is evaluated based on the sum of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system. [7] The method for evaluating interference colors according to [6], wherein the interference colors are evaluated as being suppressed when the sum is 5.00 or less.

[0010] [8] The method for evaluating interference colors according to [1], wherein the variance includes the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system, and the interference color is evaluated based on the product of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system. [9] The method for evaluating interference colors according to [8], wherein the interference colors are evaluated as being suppressed when the product is 4,000 or less.

[10] The method for evaluating interference colors according to [1], wherein the variance includes the square root of the variance of the a* value in the Lab color system and the square root of the variance of the b* value in the Lab color system, and the interference color is evaluated by the sum of the square root of the variance of the a* value in the Lab color system and the square root of the variance of the b* value in the Lab color system.

[11] The method for evaluating interference colors according to

[10] , wherein the interference colors are evaluated as being suppressed when the sum is 3.00 or less.

[0011]

[12] An optical film, The optical film has a variance of two or more color parameters calculated by the following steps 1 to 4, which satisfies one or more of the following (1) to (3): Step 1: A surface light source including a polarizer is set to display white, and linearly polarized white light L1 is emitted from the surface light source. Step 2: For L1, the in-plane distribution of tristimulus values ​​is measured. The measurement angle is 60 degrees. The tristimulus values ​​of L1 measured in this step are defined as tristimulus value 1. Step 3: With the optical film placed on the surface light source, the surface light source is displayed in white. Then, the in-plane distribution of tristimulus values ​​is measured for light L2, which is light L1 transmitted through the optical film. The measurement angle is 60 degrees. The tristimulus value of L2 measured in this step is called tristimulus value 2. Step 4: Divide the surface where the tristimulus values ​​1 and 2 were measured into a plurality of sections. Calculate color parameters for each section from the tristimulus values ​​1 and 2. Then, calculate the variance of the color parameters for all sections. The calculation of the variance is performed for two or more types of color parameters. (1) The sum of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system is 5.00 or less. (2) The product of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system is 4,000 or less. (3) The sum of the square root of the variance of the a* value in the Lab color system and the square root of the variance of the b* value in the Lab color system is 3.00 or less.

[0012]

[13] A polarizing plate having a polarizer, a first protective film arranged on one side of the polarizer, and a second protective film arranged 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

[12] .

[14] An image display device having a polarizer and an optical film on a display element, The image display device is an image display device in which the variances of two or more color parameters calculated by the following steps 1 to 4 satisfy one or more of the following (1) to (3): Step 1: A surface light source having the polarizer on the display element is set to display white, and linearly polarized white light L1 is emitted from the surface light source. Step 2: For L1, the in-plane distribution of tristimulus values ​​is measured. The measurement angle is 60 degrees. The tristimulus values ​​of L1 measured in this step are defined as tristimulus value 1. Step 3: With the optical film placed on the surface light source, the surface light source is displayed in white. Then, the in-plane distribution of tristimulus values ​​is measured for light L2, which is light L1 transmitted through the optical film. The measurement angle is 60 degrees. The tristimulus value of L2 measured in this step is called tristimulus value 2. Step 4: Divide the surface where the tristimulus values ​​1 and 2 were measured into a plurality of sections. Calculate color parameters for each section from the tristimulus values ​​1 and 2. Then, calculate the variance of the color parameters for all sections. The calculation of the variance is performed for one or more color parameters. (1) The sum of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system is 5.00 or less. (2) The product of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system is 4,000 or less. (3) The sum of the square root of the variance of the a* value in the Lab color system and the square root of the variance of the b* value in the Lab color system is 3.00 or less. [Effects of the Invention]

[0013] The interference color evaluation method of the present disclosure can objectively evaluate interference colors caused by the influence of an optical film. Furthermore, the optical film, polarizing plate, and image display device of the present disclosure can suppress interference colors. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a flowchart illustrating an embodiment of an interference color evaluation method according to the present disclosure. [Figure 2] 1 is a schematic diagram illustrating an embodiment of the positional relationship between a surface light source and a measurement device when measuring the in-plane distribution of tristimulus values. FIG. [Figure 3] FIG. 2 is a schematic diagram illustrating an embodiment of the positional relationship between a surface light source and an optical film. [Figure 4] FIG. 2 is a schematic diagram illustrating an embodiment of the arrangement of a polarizer and an optical film included in a surface light source. DETAILED DESCRIPTION OF THE INVENTION

[0015] The interference color evaluation method, optical film, polarizing plate, and image display device of the present disclosure will be described below. [Method for evaluating interference colors] The method for evaluating interference colors according to the present disclosure includes the following steps 1 to 3, and is a method for evaluating interference colors using one type of dispersion or a combination of two or more types of dispersions calculated in the following step 4.

[0016] In this specification, the atmosphere during measurements and evaluations is a temperature of 23±5°C and a relative humidity of 40% to 65%, unless otherwise specified. In this specification, the object to be measured is exposed to the above atmosphere for 30 minutes or more before the start of each measurement and evaluation, unless otherwise specified. In this specification, "Lab color system" means "CIE Lab color system", and "Luv color system" means "CIE Luv color system".

[0017] Step 1: A surface light source including a polarizer is set to display white, and linearly polarized white light L1 is emitted from the surface light source. Step 2: Measure the in-plane distribution of tristimulus values ​​for L1. The tristimulus values ​​of L1 measured in this step are defined as tristimulus values ​​1. Step 3: With an optical film placed on the surface light source, the surface light source is displayed in white. Then, the in-plane distribution of tristimulus values ​​is measured for light L2, which is light L1 transmitted through the optical film. The tristimulus value of L2 measured in this step is called tristimulus value 2.

[0018] Step 4: Divide the surface where the tristimulus values ​​1 and 2 were measured into a plurality of sections. Calculate color parameters for each section from the tristimulus values ​​1 and 2. Then, calculate the variance of the color parameters for all sections. The calculation of the variance is performed for one or more color parameters.

[0019] Fig. 1 is a flowchart showing one embodiment of the interference color evaluation method of the present disclosure. In the flowchart of Fig. 1, "Step 1, Step 2, Step 3, Step 4" are written as "S1, S2, S3, S4."

[0020] In steps 2 and 3, the in-plane distribution of the tristimulus values ​​of the white light L1 and the transmitted light L2 can be measured using any measuring device. The measuring device is not particularly limited as long as it can measure in-plane tristimulus values. Measuring device 200, for example, has device main body 21 and lens 22 attached to the device main body (FIG. 2). The device main body preferably has a photodetector. Examples of the photodetector include a CCD image sensor. The number of pixels of the photodetector of the device main body is preferably 1.2 million or more, and more preferably 1.3 million or more. There is no particular upper limit on the number of pixels of the photodetector, but it is preferably 2 million or less. The measuring device preferably has built-in software for calculating predetermined color parameters from tristimulus value 1 and tristimulus value 2, with tristimulus value 1 being the tristimulus value of white as the reference point. By using the above-described measuring device, in steps 2 and 3, tristimulus values ​​for each pixel of the white light L1 and the transmitted light L2 can be obtained. The scale of the members shown in Fig. 2 is a schematic representation for ease of illustration, and differs from the actual scale. The same applies to Figs. 3 and 4.

[0021] An example of a device capable of measuring the in-plane distribution of tristimulus values ​​is the "2D Colorimeter UA-200" manufactured by Topcon Technohouse. By installing the accompanying software (product name "UA Series Application_ver4.1.0"), the measuring device can calculate predetermined color parameters from tristimulus values ​​1 and 2, with tristimulus value 1 being the tristimulus value of white as the reference point. When using the measuring device with the software installed, color parameters selected on the software can be measured. In this specification, tristimulus values ​​refer to the X, Y, and Z values ​​of the CIE XYZ color system, which can be converted to the x and y values ​​of the Yxy color system using the following formula: The Y value of the Yxy color system and the Y value of the XYZ color system are the same parameter. x=X / (X+Y+Z) y=Y / (X+Y+Z) z=Z / (X+Y+Z) x+y+z=1

[0022] <Process 1> In step 1, a surface light source including a polarizer is set to display white, and linearly polarized white light L1 is emitted from the surface light source.

[0023] The surface light source including a polarizer may be a laminate having a polarizer on a light source capable of displaying white light. Examples of the light source capable of displaying white light include lighting such as LED lighting and organic EL lighting, and display elements such as organic EL display elements. An image display device including a polarizer may also be used as the surface light source including a polarizer. The Y, x, and y values ​​of the Yxy color system of the white light L1 are preferably in the following ranges: The Y, x, and y values ​​are those of the white light L1 emitted from the center of the surface of the surface light source, and are measured at an angle of 60 degrees. The Y value is preferably 40 or more and 400 or less, and more preferably 50 or more and 350 or less. The value of x is preferably 0.25 or more and 0.45 or less, and more preferably 0.30 or more and 0.40 or less. The y value is preferably 0.25 or more and 0.45 or less, and more preferably 0.30 or more and 0.40 or less.

[0024] The polarizer has a role of converting the white light into linearly polarized white light L1. The polarizer is preferably located on the light exit surface side of a light source capable of displaying white light, such as an illumination or display element.

[0025] Examples of polarizers include sheet-type polarizers (such as polyvinyl alcohol films, polyvinyl formal films, polyvinyl acetal films, and saponified ethylene-vinyl acetate copolymer films) made by stretching a film dyed with iodine or the like, wire-grid polarizers made of a large number of parallelly arranged metal wires, coated polarizers coated with a lyotropic liquid crystal and a dichroic guest-host material, and multilayer thin-film polarizers. These polarizers may also be reflective polarizers that have the function of reflecting polarized light components that are not transmitted.

[0026] The polarizer preferably has a polarization degree of 95.00% or more, more preferably 98.0% or more, and even more preferably 99.0% or more. The polarizer preferably has a total light transmittance of 35% or more, more preferably 37% or more, and even more preferably 40% or more. The total light transmittance of the polarizer is preferably 65% ​​or less, more preferably 55% or less, and even more preferably 45% or less. In this specification, the total light transmittance refers to the total light transmittance defined in JIS K7361-1:1997.

[0027] It is preferable that the polarizer has a protective layer on both sides. Examples of the protective layer include glass and plastic films. The protective layer is preferably optically isotropic. In this specification, optically isotropic refers to an in-plane retardation of less than 20 nm, preferably 10 nm or less, and more preferably 5 nm or less. The polarizer and the protective layer may be in direct contact with each other or may be in contact with each other via an adhesive layer.

[0028] <Process 2> In step 2, the in-plane distribution of tristimulus values ​​for L1 is measured. The tristimulus values ​​of L1 measured in this step are defined as tristimulus values ​​1. The tristimulus value 1 measured in step 2 is the tristimulus value of white, which serves as a reference point for calculating color parameters. The tristimulus values ​​1 for a predetermined number of pixels are obtained in step 2. The "predetermined number of pixels" obtained in step 2 corresponds to the number of pixels of the light receiver of the device main body. Step 2 and step 3 described below are carried out in a darkroom environment.

[0029] The in-plane distribution of the tristimulus values ​​of L1 can be measured, for example, by the above-mentioned measuring device. It is preferable to focus the measuring device on the surface of the surface light source. The measurement conditions when measuring the in-plane distribution of the tristimulus values ​​of L1 using a measurement device are not particularly limited, but it is preferable that the measurement angle, distance, measurement area, etc. be set to the conditions described below.

[0030] The angle between the surface light source and the measuring device is preferably 15 degrees or more, and more preferably 30 degrees or more. This is because interference colors are more easily observed as the angle increases (to be precise, interference colors do not occur in step 2, but do occur in step 3). Furthermore, because the screen is rarely viewed from an extremely large angle, the angle between the surface light source and the measuring device is preferably 75 degrees or less, and more preferably 60 degrees or less. In this specification, the angle between the surface light source and the measurement device means the angle θ formed between the normal N1 of the surface light source and the normal N2 of the lens of the measurement device (FIG. 2). In this specification, the "angle formed between the surface light source and the measuring device" may be referred to as the "measurement angle."

[0031] It is preferable that the angle between the surface light source and the measuring device be the same in steps 2 and 3. When the measurement of tristimulus values ​​1 in step 2 and the measurement of tristimulus values ​​2 in step 3 are each performed at multiple measurement angles, it is preferable that the multiple measurement angles be the same in step 2 and step 3. For example, if step 2 is performed at four measurement angles of 30 degrees, 40 degrees, 50 degrees, and 60 degrees, it is preferable that step 3 is also performed at four measurement angles of 30 degrees, 40 degrees, 50 degrees, and 60 degrees.

[0032] The distance between the surface light source and the measuring device may be adjusted as appropriate depending on the specifications of the measuring device. A preferred distance is 200 mm or more and 440 mm or less, and more preferably 220 mm or more and 350 mm or less. In this specification, the distance between the surface light source and the measuring device means the distance from the surface of the surface light source to the lens of the measuring device.

[0033] The area for measuring the in-plane distribution of the tristimulus values ​​of L1 is preferably 100 mm long x 75 mm wide or more and 290 mm long x 210 mm wide or less, and more preferably 180 mm long x 130 mm wide or more and 200 mm long x 150 mm wide or less.

[0034] <Process 3> With an optical film placed on the surface light source, the surface light source is displayed in white. Then, the in-plane distribution of tristimulus values ​​is measured for light L2, which is light L1 transmitted through the optical film. The tristimulus value of L2 measured in this process is called tristimulus value 2. The tristimulus values ​​2 measured in step 3 are the tristimulus values ​​of light L2 after reference white light has passed through the optical film. Step 3 allows the tristimulus values ​​of the transmitted light L2 for each pixel to be obtained. The tristimulus values ​​2 for a predetermined number of pixels are obtained in step 3. The "predetermined number of pixels" obtained in step 3 corresponds to the number of pixels of the light receiver of the device main body. Between step 2 and step 3, the surface light source may be temporarily turned off or may remain in white display.

[0035] 3 is a schematic diagram illustrating one embodiment of the positional relationship between the surface light source 100 and the optical film 30. In FIG. 3, the solid arrow indicates linearly polarized white light L1 emitted from the surface light source 100, and the dashed-dotted arrow indicates light L2 that is transmitted through the optical film 30 from L1. The surface light source 100 and the optical film 30 may simply be stacked on top of each other, but it is preferable to laminate them via an adhesive layer 40, as shown in Fig. 3. By laminating the surface light source 100 and the optical film 30 via the adhesive layer 40, the optical film 30 conforms to the surface of the surface light source 100, making it easier to more accurately evaluate the influence of the optical film 30 on interference colors.

[0036] The in-plane distribution of the tristimulus values ​​of L2 can be measured, for example, by the above-mentioned measuring device. The focus of the measuring device is preferably adjusted to the surface of the optical film. The measurement conditions for measuring the in-plane distribution of the tristimulus values ​​of L2 using a measurement device are not particularly limited, but it is preferable that the conditions, such as the angle between the surface light source and the measurement device, the distance between the surface light source and the measurement device, and the size of the measurement area for the tristimulus values, be the same as those in step 2. It is preferable that the area for measuring the in-plane distribution of the tristimulus values ​​of L1 and the area for measuring the in-plane distribution of the tristimulus values ​​of L2 coincide with each other in the plane direction.

[0037] The optical film may be an optical film used in an image display device. Examples of optical films used in image display devices include plastic films alone and functional films having a functional layer on a plastic film, such as one or more functional layers selected from a hard coat layer, an antiglare layer, a low refractive index layer, a high refractive index layer, an antistatic layer, and a transparent conductive layer. The number of optical films placed on the surface light source may be one or two or more. When two or more optical films are used, the optical films are preferably laminated together via an adhesive layer. The optical film preferably includes a stretched plastic film, which has optical anisotropy and therefore tends to produce interference colors, making it easier to achieve the effects of the present disclosure.

[0038] The optical film preferably has optical anisotropy. In this specification, optical anisotropy refers to an in-plane retardation of 20 nm or more, preferably 100 nm or more, and more preferably 300 nm or more. The in-plane retardation of the optical film is preferably 5000 nm or less, more preferably 3000 nm or less, and even more preferably 2500 nm or less. When the in-plane retardation is too small or too large, interference colors are difficult to observe. Therefore, by setting the in-plane retardation of the optical film within the above range, the effects of the present disclosure can be easily exhibited. The functional layer is usually optically isotropic, and therefore, it is preferable that the in-plane retardation of the plastic film contained in the optical film is within the above range.

[0039] In this specification, the in-plane retardation (Re) of a plastic film is expressed by the following formula (1), where nx is the refractive index in the slow axis direction, which is the direction in the plane with the largest refractive index, ny is the refractive index in the fast axis direction, which is the direction perpendicular to the slow axis direction, and T [nm] is the thickness of the plastic film. In this specification, the in-plane retardation means the value at a wavelength of 550 nm. Re=(nx-ny)×T[nm] (1)

[0040] The optical film is preferably placed on a surface light source so that the angle between the slow axis of the plastic film and the transmission axis of the polarizer included in the surface light source is in the range of 45 degrees ± 15 degrees. The angle is more preferably in the range of 45 degrees ± 10 degrees, more preferably in the range of 45 degrees ± 5 degrees, more preferably in the range of 45 degrees ± 3 degrees, more preferably in the range of 45 degrees ± 1 degree, and most preferably 45 degrees. In this specification, "in the range of 45 degrees ± α degrees" means "at least 45 degrees - α degrees and at most 45 degrees + α degrees." When the angle formed between the slow axis of the plastic film and the transmission axis of the polarizer is close to 0 degrees or close to 90 degrees, interference colors are unlikely to be observed. Therefore, by setting the angle within the above range, the effects of the present disclosure can be easily exhibited. In Fig. 4, D1 indicates the direction of the transmission axis of the polarizer included in the surface light source, and D2 indicates the direction of the slow axis of the plastic film. In Fig. 4, the angle between D1 and D2 is 45 degrees.

[0041] The adhesive layer that adheres the surface light source and the optical film to each other can be formed from a general-purpose adhesive, and is preferably optically transparent and optically isotropic.

[0042] <Step 4> The method for evaluating interference colors according to the present disclosure includes the above steps 1 to 3, and also includes step 4. Step 4 will be explained below by dividing it into the following steps 4-1 to 4-3. 4-1: The surface on which the tristimulus values ​​1 and 2 were measured is divided into a plurality of sections. 4-2: Calculate color parameters for each section from the tristimulus values ​​1 and 2. 4-3: Calculate the variance of the color parameters of all the sections. The calculation of the variance is performed for one or more color parameters.

[0043] In step 4-1, the surface on which the tristimulus values ​​1 and 2 are measured is divided into a plurality of sections. When dividing the surface, it is preferable that the number of pixels in each section is the same. The number of sections is not particularly limited, but for the sake of reliability of the calculated variance value, a number of 10 vertical x 10 horizontal or more is preferable, and 15 vertical x 15 horizontal or more is more preferable. On the other hand, depending on the size of the measurement area, if the number of sections is increased too much, the resolution limit of the human eye may be exceeded. For this reason, the number of sections is preferably 30 vertical x 30 horizontal or less, and more preferably 20 vertical x 20 horizontal or less. It is preferable that the number of divisions within the plane where tristimulus value 1 is measured is the same as the number of divisions within the plane where tristimulus value 2 is measured. If one section is replaced by the area of ​​a surface light source, the area of ​​one section is 47 mm 2 Over 237mm 2 It is preferable that it is 92 mm or less. 2 Over 118mm 2 It is more preferable to set the following:

[0044] In 4-2, color parameters are calculated for each section from the tristimulus values ​​1 and 2. Because each pixel is extremely small, it is difficult for the human eye to recognize a single pixel. However, by calculating color parameters for each section as in 4-2, the variance calculated in 4-3 can be used as an index that is easily recognized by the human eye. The color parameters can be calculated from the tristimulus value 1, which is the reference point for white, and the tristimulus value 2 using a general-purpose calculation formula.

[0045] The color parameters for each section can be calculated, for example, by the following (1) or (2): In the following (1), the section may be divided after the color parameters are calculated. (1) Calculate color parameters for each pixel from the tristimulus values ​​1 and 2. For each section, calculate the average value of the color parameters of all pixels in the section, and use the average value as the color parameter for each section. (2) For each section, calculate the average value of the tristimulus values ​​1 and the average value of the tristimulus values ​​2. From the average value of the tristimulus values ​​1 and the average value of the tristimulus values ​​2, calculate the color parameters for each section.

[0046] When the above-mentioned measuring device with the above-mentioned software installed is used, the color parameters for each pixel in (1) above can be measured automatically. After that, the surface is divided into desired sections, and the color parameters for each section can be obtained by calculating the average color parameters of all pixels in the section.

[0047] The color parameters are color parameters that can be calculated based on tristimulus values, and examples thereof include the a* value of the Lab color system, the b* value of the Lab color system, and {(a* value of the Lab color system) 2 +(b* value of the Lab color system) 2} 1 / 2 , u* value of the Luv color system, v* value of the Luv color system, {(u* value of the Luv color system) 2 +(v* value of Luv color system) 2} 1 / 2 Furthermore, on the assumption that they will be combined with other color parameters, the L* value of the Lab color system and the L* value of the Luv color system can also be used as color parameters.

[0048] In step 4-3, the variance of the color parameters of all the sections is calculated. The calculation of the variance is performed for one or more color parameters.

[0049] In this specification, "variance" refers to the variance in statistics. In statistics, variance refers to the average of the squares of the differences between the mean value and each individual data point in a group of numerical data. Variance can be expressed by the following formula. In the formula, "V" is the variance, "n" is the number of data points, and "x i " is the data value, "x ave " indicates the average value of the data.

number

[0050] In step 4, the tristimulus value 1 of the reference white light obtained in step 2 is used as a reference, and the dispersion is calculated by comparing this reference with the tristimulus value 2 of the light obtained in step 3 after the reference white light has passed through the optical film. Therefore, the dispersion calculated in step 4 is an element that can objectively evaluate the interference color caused by the influence of the optical film. The methods in Patent Documents 2 and 3 differ from the interference color evaluation method of the present disclosure in that there is no comparison with a reference.

[0051] In the interference color evaluation method of the present disclosure, it is preferable to measure the tristimulus values ​​1 in step 2 and the tristimulus values ​​2 in step 3 at multiple measurement angles, and to perform step 4 for each measurement angle. Since the intensity of interference colors varies depending on the angle, the above-described steps allow the interference colors to be evaluated for each angle, thereby increasing the variety of evaluations and further improving the accuracy of the evaluations.

[0052] The measurement angle means the angle between the surface light source and the measurement device. The measurement angles are preferably selected from the range of 15 degrees to 75 degrees, and more preferably from the range of 30 degrees to 60 degrees.

[0053] <Evaluation> The method for evaluating interference colors according to the present disclosure evaluates interference colors based on one type of dispersion or a combination of two or more types of dispersion calculated in step 4 above.

[0054] When evaluating interference colors using one type of dispersion, it is possible to objectively evaluate that the larger the dispersion value, the stronger the interference color, and the smaller the dispersion value, the weaker the interference color. Although the absolute value of dispersion varies depending on the surface light source, the strength of the interference color can be objectively evaluated depending on the size of the dispersion value. By setting a predetermined value as the pass / fail threshold for one type of dispersion, the pass / fail of the interference color can be objectively evaluated. Because the absolute value of dispersion varies depending on the surface light source, it is preferable to set a threshold for each surface light source.

[0055] Methods for evaluating interference colors using a combination of two or more types of dispersion include "the sum of one dispersion and another," "the sum of the square root of one dispersion and the square root of another dispersion," and "the product of one dispersion and another dispersion."Since color is usually embodied by two or more color parameters, evaluating interference colors using a combination of two or more types of dispersion makes it easier to evaluate the strength of the interference color more objectively. In the "sum of one variance and another variance," "sum of the square root of one variance and the square root of another variance," and "product of one variance and another variance," it is possible to objectively evaluate that the larger the sum and product, the stronger the interference color, and the smaller the sum and product, the weaker the interference color. Although the absolute values ​​of the sum and product vary depending on the surface light source, the strength of the interference color can be objectively evaluated based on the magnitude of the sum and product. In this specification, "square root of variance" means the value of the positive square root of the variance. The value of the square root of variance can be calculated by raising the right side of the above variance equation to the 1 / 2 power. By setting predetermined values ​​of the sum and product as pass / fail thresholds, it is possible to objectively evaluate the pass / fail of interference colors. Because the absolute values ​​of the sum and product vary depending on the surface light source, it is preferable to set a threshold for each surface light source.

[0056] The interference color evaluation method of the present disclosure may be embodied in such a way that the dispersion is any one selected from Group 1 below. <Group 1> Variance of the a* values ​​in the Lab color system, variance of the b* values ​​in the Lab color system, {(a* values ​​in the Lab color system) 2 +(b* value of the Lab color system) 2} 1 / 2 variance of the u* values ​​in the Luv color system, variance of the v* values ​​in the Luv color system, {(u* values ​​in the Luv color system) 2 +(v* value of Luv color system) 2} 1 / 2 Dispersion of

[0057] {(a* value of the Lab color system) 2 +(b* value of the Lab color system) 2} 1 / 2 The variance of (u* value of Luv color system) 2+(v* value of Luv color system) 2} 1 / 2 The variance of saturation can be said to be the variance of saturation. Since saturation can embody a color tone by itself, if you select only one from Group 1 above, {(a* value of the Lab color system) 2 +(b* value of the Lab color system) 2} 1 / 2 Variance of, or {(u* value of Luv color system) 2 +(v* value of Luv color system) 2} 1 / 2 It is preferable to select the variance of

[0058] The interference color evaluation method of the present disclosure may include an embodiment in which the dispersion includes one selected from the following Group 2-1 and one selected from the following Group 2-2 (however, the dispersion in Group 2-2 is different from the dispersion selected from Group 2-1). <Group 2-1> Variance of the a* values ​​in the Lab color system, variance of the b* values ​​in the Lab color system, {(a* values ​​in the Lab color system) 2 +(b* value of the Lab color system) 2} 1 / 2 Dispersion of <Group 2-2> Variance of L* values ​​in the Lab color system, variance of a* values ​​in the Lab color system, variance of b* values ​​in the Lab color system, {(a* value in the Lab color system) 2 +(b* value of the Lab color system) 2} 1 / 2 Dispersion of

[0059] The difference between Group 2-1 and Group 2-2 is that Group 2-2 includes the variance of the L* value of the Lab color system. Because the L* value is an index of brightness, it is difficult to evaluate interference colors using only the variance of the L* value of the Lab color system. However, by combining it with any of the variances in Group 2-1, it is possible to evaluate interference colors. The method of combining one type of dispersion selected from Group 2-1 and one type of dispersion selected from Group 2-2 includes a sum and a product, with a sum being preferred.

[0060] The interference color evaluation method of the present disclosure may be embodied in such a way that the dispersion includes one selected from the following group 3-1 and one selected from the following group 3-2 (however, the dispersion in group 3-2 is different from the dispersion selected from group 3-1). <Group 3-1> Variance of u* values ​​in the Luv color system, variance of v* values ​​in the Luv color system, {(u* values ​​in the Luv color system) 2 +(v* value of Luv color system) 2} 1 / 2 Dispersion of <Group 3-2> Variance of L* values ​​in the Luv color system, variance of u* values ​​in the Luv color system, variance of v* values ​​in the Luv color system, {(u* values ​​in the Luv color system) 2 +(v* value of Luv color system) 2} 1 / 2 Dispersion of

[0061] The difference between Group 3-1 and Group 3-2 is that Group 3-2 includes the dispersion of the L* value of the Luv color system. Because the L* value is an index of brightness, it is difficult to evaluate interference colors using only the dispersion of the L* value of the Luv color system. However, by combining it with any dispersion in Group 3-1, it is possible to evaluate interference colors. The method of combining one type of dispersion selected from Group 3-1 and one type of dispersion selected from Group 3-2 includes a sum and a product, with a sum being preferred.

[0062] The interference color evaluation method of the present disclosure may be embodied in such a way that the dispersion includes any one selected from Group 4 below. <Group 4> The square root of the variance of the a* value in the Lab color system, the square root of the variance of the b* value in the Lab color system, {(the a* value in the Lab color system) 2 +(b* value of the Lab color system) 2} 1 / 2 The square root of the variance of the u* values ​​in the Luv color system, the square root of the variance of the v* values ​​in the Luv color system, {(u* values ​​in the Luv color system) 2 +(v* value of Luv color system) 2} 1 / 2 square root of the variance of

[0063] The interference color evaluation method of the present disclosure may be embodied in such a way that the dispersion includes one selected from the following group 5-1 and one selected from the following group 5-2 (however, the dispersion in group 5-2 is different from the dispersion selected from group 5-1). <Group 5-1> The square root of the variance of the a* value in the Lab color system, the square root of the variance of the b* value in the Lab color system, {(the a* value in the Lab color system) 2 +(b* value of the Lab color system) 2} 1 / 2 square root of the variance of <Group 2-2> The square root of the variance of the L* values ​​in the Lab color system, the square root of the variance of the a* values ​​in the Lab color system, the square root of the variance of the b* values ​​in the Lab color system, {(the a* value in the Lab color system) 2 +(b* value of the Lab color system) 2} 1 / 2 square root of the variance of

[0064] The difference between Group 5-1 and Group 5-2 is that Group 5-2 includes the square root of the variance of the L* value in the Lab color system. Because the L* value is an index of brightness, it is difficult to evaluate interference colors using only the square root of the variance of the L* value in the Lab color system. However, by combining it with the square root of the variance of one of Group 5-1, it is possible to evaluate interference colors. The method of combining the square root of one type of variance selected from Group 5-1 and the square root of one type of variance selected from Group 5-2 includes a sum and a product, with a sum being preferred.

[0065] The interference color evaluation method of the present disclosure may include an embodiment in which the dispersion includes one selected from the following group 6-1 and one selected from the following group 6-2 (however, the dispersion in group 6-2 is different from the dispersion selected from group 6-1). <Group 6-1> The square root of the variance of the u* values ​​in the Luv color system, the square root of the variance of the v* values ​​in the Luv color system, {(u* values ​​in the Luv color system) 2 +(v* value of Luv color system) 2} 1 / 2 square root of the variance of <Group 6-2> The square root of the variance of the L* value in the Luv color system, the square root of the variance of the u* value in the Luv color system, the square root of the variance of the v* value in the Luv color system, {(u* value in the Luv color system) 2 +(v* value of Luv color system) 2} 1 / 2 square root of the variance of

[0066] The difference between Group 6-1 and Group 6-2 is that Group 6-2 includes the square root of the variance of the L* value in the Luv color system. Because the L* value is an index of brightness, it is difficult to evaluate interference colors using only the square root of the variance of the L* value in the Luv color system. However, by combining it with any of the variances in Group 6-1, it is possible to evaluate interference colors. The method of combining one type of dispersion selected from group 6-1 and one type of dispersion selected from group 6-2 includes a sum and a product, with a sum being preferred.

[0067] In the method for evaluating interference colors disclosed herein, the variances preferably include the variance of the a* values ​​in the Lab color system and the variance of the b* values ​​in the Lab color system, and the interference color is evaluated by the sum of the variance of the a* values ​​in the Lab color system and the variance of the b* values ​​in the Lab color system.

[0068] It can be objectively evaluated that the larger the sum of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system, the stronger the interference color, and the smaller the sum, the weaker the interference color. Although the absolute value of the sum varies depending on the surface light source, the strength of the interference color can be objectively evaluated depending on the size of the sum. By setting a predetermined value of the sum as a threshold for pass / fail, the pass / fail of the interference color can be objectively evaluated. The threshold for the sum can be, for example, preferably 5.00 or less, more preferably 3.00 or less, more preferably 2.00 or less, and more preferably 1.30 or less. In other words, when the sum is 5.00 or less, it can be evaluated that the interference color is suppressed. However, since the absolute value of the sum varies depending on the surface light source, it is preferable to set a threshold for each surface light source. The sum value also varies depending on the measurement angle. Therefore, it is preferable to set the threshold value taking the measurement angle into consideration. For example, it is preferable to set the threshold value of the sum to 5.00 or less, assuming that the measurement angle is 60 degrees or less. The value of the sum varies depending on the surface light source. For this reason, it is preferable to set the threshold value taking into consideration the characteristics of the white light L1. For example, it is preferable to set the threshold value of the sum to 5.00 or less, assuming that the Y value, x value, and y value of the Yxy color system of the white light L1 are within the following ranges. Furthermore, the following Y value, x value, and y value are values ​​of the white light L1 emitted from the center of the surface of the surface light source, and the measurement angle is 60 degrees. The Y value is preferably 40 or more and 400 or less, and more preferably 50 or more and 350 or less. The value of x is preferably 0.25 or more and 0.45 or less, and more preferably 0.30 or more and 0.40 or less. The y value is preferably 0.25 or more and 0.45 or less, and more preferably 0.30 or more and 0.40 or less.

[0069] In the method for evaluating interference colors disclosed herein, the variances preferably include the variance of the a* values ​​in the Lab color system and the variance of the b* values ​​in the Lab color system, and the interference color is evaluated by the product of the variance of the a* values ​​in the Lab color system and the variance of the b* values ​​in the Lab color system.

[0070] It can be objectively evaluated that the larger the product of the variance of the a* values ​​in the Lab color system and the variance of the b* values ​​in the Lab color system, the stronger the interference color, and the smaller the product, the weaker the interference color. Although the absolute value of the product varies depending on the surface light source, the strength of the interference color can be objectively evaluated depending on the size of the product. By setting a predetermined value of the product as a threshold for pass / fail, the pass / fail of the interference color can be objectively evaluated. The threshold for the product can be, for example, preferably 4.000 or less, more preferably 1.000 or less, more preferably 0.3000 or less, and more preferably 0.058 or less. In other words, when the product is 4.000 or less, it can be evaluated that the interference color is suppressed. However, since the absolute value of the product varies depending on the surface light source, it is preferable to set a threshold for each surface light source. The value of the product also varies depending on the measurement angle. Therefore, it is preferable to set the threshold value taking the measurement angle into consideration. For example, it is preferable to set the threshold value of the product to 4,000 or less, assuming that the measurement angle is 60 degrees or less. The value of the product varies depending on the surface light source. For this reason, it is preferable to set the threshold value taking into consideration the characteristics of the white light L1. For example, it is preferable to set the threshold value of the product to 4.000 or less, assuming that the Y value, x value, and y value of the Yxy color system of the white light L1 are within the following ranges. Furthermore, the following Y value, x value, and y value are values ​​of the white light L1 emitted from the center of the surface of the surface light source, and the measurement angle is 60 degrees. The Y value is preferably 40 or more and 400 or less, and more preferably 50 or more and 350 or less. The value of x is preferably 0.25 or more and 0.45 or less, and more preferably 0.30 or more and 0.40 or less. The y value is preferably 0.25 or more and 0.45 or less, and more preferably 0.30 or more and 0.40 or less.

[0071] In the method for evaluating interference colors according to the present disclosure, it is preferable that the variance includes the square root of the variance of the a* values ​​in the Lab color system and the square root of the variance of the b* values ​​in the Lab color system, and that the interference color is evaluated by the sum of the square root of the variance of the a* values ​​in the Lab color system and the square root of the variance of the b* values ​​in the Lab color system.

[0072] It can be objectively evaluated that the larger the sum of the square root of the variance of the a* value in the Lab color system and the square root of the variance of the b* value in the Lab color system, the stronger the interference color, and the smaller the sum, the weaker the interference color. Although the absolute value of the sum varies depending on the surface light source, the strength of the interference color can be objectively evaluated depending on the size of the sum. By setting a predetermined value of the sum as a threshold for pass / fail, the pass / fail of the interference color can be objectively evaluated. The threshold for the sum can be, for example, preferably 3.00 or less, more preferably 1.50 or less, and more preferably 1.00 or less. In other words, when the sum is 3.00 or less, it can be evaluated that the interference color is suppressed. However, since the absolute value of the sum varies depending on the surface light source, it is preferable to set a threshold for each surface light source. The sum value also varies depending on the measurement angle. Therefore, it is preferable to set the threshold value taking the measurement angle into consideration. For example, it is preferable to set the threshold value of the sum to 3.00 or less, assuming that the measurement angle is 60 degrees or less. The value of the sum varies depending on the surface light source. For this reason, it is preferable to set the threshold value taking into consideration the characteristics of the white light L1. For example, it is preferable to set the threshold value of the sum to 3.00 or less, assuming that the Y value, x value, and y value of the Yxy color system of the white light L1 are within the following ranges. Furthermore, the following Y value, x value, and y value are values ​​of the white light L1 emitted from the center of the surface of the surface light source, and the measurement angle is 60 degrees. The Y value is preferably 40 or more and 400 or less, and more preferably 50 or more and 350 or less. The value of x is preferably 0.25 or more and 0.45 or less, and more preferably 0.30 or more and 0.40 or less. The y value is preferably 0.25 or more and 0.45 or less, and more preferably 0.30 or more and 0.40 or less.

[0073] [Optical film] The optical film of the present disclosure comprises: An optical film, The optical film has variances of two or more color parameters calculated in the following steps 1 to 4 that satisfy one or more of the following conditions (1) to (3): Step 1: A surface light source including a polarizer is set to display white, and linearly polarized white light L1 is emitted from the surface light source. Step 2: For L1, the in-plane distribution of tristimulus values ​​is measured. The measurement angle is 60 degrees. The tristimulus values ​​of L1 measured in this step are defined as tristimulus value 1. Step 3: With the optical film placed on the surface light source, the surface light source is displayed in white. Then, the in-plane distribution of tristimulus values ​​is measured for light L2, which is light L1 transmitted through the optical film. The measurement angle is 60 degrees. The tristimulus value of L2 measured in this step is called tristimulus value 2. Step 4: Divide the surface where the tristimulus values ​​1 and 2 were measured into a plurality of sections. Calculate color parameters for each section from the tristimulus values ​​1 and 2. Then, calculate the variance of the color parameters for all sections. The calculation of the variance is performed for two or more types of color parameters. (1) The sum of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system is 5.00 or less. (2) The product of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system is 4,000 or less. (3) The sum of the square root of the variance of the a* value in the Lab color system and the square root of the variance of the b* value in the Lab color system is 3.00 or less.

[0074] In the optical film of the present disclosure, the dispersion of two or more color parameters calculated in steps 1 to 4 preferably satisfies two or more, and more preferably three, of the above (1) to (3).

[0075] Examples of optical films include plastic films alone and functional films having a functional layer on a plastic film, such as one or more functional layers selected from a hard coat layer, an antiglare layer, a low refractive index layer, a high refractive index layer, an antistatic layer, and a transparent conductive layer.

[0076] Steps 1 to 4 of the optical film of the present disclosure are the same as steps 1 to 4 of the interference color evaluation method of the present disclosure, except that the measurement angle is specified to 60 degrees.

[0077] [Polarizing plate] The polarizing plate of the present disclosure has a polarizer, a first protective film arranged on one side of the polarizer, and a second protective film arranged on the other side of the polarizer, and at least one of the first protective film and the second protective film is the optical film of the present disclosure described above.

[0078] Examples of polarizers include sheet-type polarizers (such as polyvinyl alcohol films, polyvinyl formal films, polyvinyl acetal films, and saponified ethylene-vinyl acetate copolymer films) made by stretching a film dyed with iodine or the like, wire-grid polarizers made of a large number of parallelly arranged metal wires, coated polarizers coated with a lyotropic liquid crystal and a dichroic guest-host material, and multilayer thin-film polarizers. These polarizers may also be reflective polarizers that have the function of reflecting polarized light components that are not transmitted.

[0079] The polarizer preferably has a polarization degree of 95.00% or more, more preferably 98.0% or more, and even more preferably 99.0% or more. The polarizer preferably has a total light transmittance of 35% or more, more preferably 37% or more, and even more preferably 40% or more, and preferably has a total light transmittance of 65% or less, more preferably 55% or less, and even more preferably 45% or less.

[0080] Only one of the first protective film and the second protective film may be the optical film of the present disclosure, or both may be the optical film of the present disclosure.

[0081] [Image display device] The image display device of the present disclosure includes: An image display device having a polarizer and an optical film on a display element, In the image display device, the variances of two or more color parameters calculated in the following steps 1 to 4 satisfy one or more of the following conditions (1) to (3): Step 1: A surface light source having the polarizer on the display element is set to display white, and linearly polarized white light L1 is emitted from the surface light source. Step 2: For L1, the in-plane distribution of tristimulus values ​​is measured. The measurement angle is 60 degrees. The tristimulus values ​​of L1 measured in this step are defined as tristimulus value 1. Step 3: With the optical film placed on the surface light source, the surface light source is displayed in white. Then, the in-plane distribution of tristimulus values ​​is measured for light L2, which is light L1 transmitted through the optical film. The measurement angle is 60 degrees. The tristimulus value of L2 measured in this step is called tristimulus value 2. Step 4: Divide the surface where the tristimulus values ​​1 and 2 were measured into a plurality of sections. Calculate color parameters for each section from the tristimulus values ​​1 and 2. Then, calculate the variance of the color parameters for all sections. The calculation of the variance is performed for one or more color parameters. (1) The sum of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system is 5.00 or less. (2) The product of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system is 4,000 or less. (3) The sum of the square root of the variance of the a* value in the Lab color system and the square root of the variance of the b* value in the Lab color system is 3.00 or less.

[0082] In the image display device of the present disclosure, the variances of the two or more color parameters calculated in steps 1 to 4 preferably satisfy two or more, and more preferably three, of the above (1) to (3).

[0083] Examples of the display element include a liquid crystal display element, an EL display element such as an organic EL display element and an inorganic EL display element, an LED display element such as a mini LED display element and a micro LED display element, a plasma display element, etc. When the display element is a liquid crystal display element, a backlight is required as the surface light source on the light incident surface side of the liquid crystal display element.

[0084] Examples of optical films include plastic films alone and functional films having a functional layer on a plastic film, such as one or more functional layers selected from a hard coat layer, an antiglare layer, a low refractive index layer, a high refractive index layer, an antistatic layer, and a transparent conductive layer.

[0085] Steps 1 to 4 of the image display device of the present disclosure are the same as steps 1 to 4 of the interference color evaluation method of the present disclosure, except that the measurement angle is specified to 60 degrees. [Example]

[0086] Next, the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to these examples in any way. The atmosphere during the measurements and evaluations in the examples was a temperature of 23±5°C and a relative humidity of 40% to 65%. Before the start of the measurements and evaluations, the test object was exposed to the atmosphere for 30 to 60 minutes.

[0087] 1.Material The following materials and equipment were prepared or fabricated: 1-1. Surface light source including polarizer Surface light source 1 including polarizer: a commercially available image display device (Apple product name "iPad (registered trademark) MGLW2J / A"). The Y value, x value, and y value of the Yxy color system of white light L1 are as follows (values ​​when the measurement angle is 60 degrees): Y value: 60 x value: 0.31 y-value: 0.32 Surface light source 2 including polarizer: A surface light source formed by laminating a commercially available polarizing plate (polarization degree: 99.0%) on a commercially available LED light (Mutoh Industries' product name "Light Board Slim SLT-A4C") via an adhesive layer (a 25 μm thick transparent adhesive layer, Panac's product name "Panaclean PD-S1"). The Y, x, and y values ​​of the Yxy color system of white light L1 are as follows (values ​​when the measurement angle is 60 degrees): Y value: 330 x value: 0.34 y-value: 0.36

[0088] 1-2.Optical film Optical film 1: Biaxially stretched polyester film with an in-plane retardation of 500 nm Optical film 2: Biaxially stretched polyester film with an in-plane retardation of 800 nm Optical film 3: Biaxially stretched polyester film with an in-plane retardation of 1000 nm Optical film 4: Biaxially stretched polyester film with an in-plane retardation of 2300 nm

[0089] 1-3.Measuring equipment The measurement device used was a Topcon Technohouse 2D Colorimeter UA-200. The photodetector of the measurement device had 1.3 million pixels. The standard objective lens (UA-200A standard: f=8 mm) that came with the measurement device was used.

[0090] 2. Evaluation of interference colors [Example 1] The surface light source 1 was set to display white, and linearly polarized white light L1 was emitted from the surface light source 1. Next, the measurement device was used to measure the in-plane distribution of the tristimulus values ​​of L1, and tristimulus value 1 was obtained. The measurement was carried out in a darkroom environment. During the measurement, the focus was set on the surface of surface light source 1. The distance between the surface light source and the measurement device during the measurement was 255 mm. The tristimulus values ​​were also measured at four angles between the surface light source and the measurement device: 30 degrees, 40 degrees, 50 degrees, and 60 degrees. Although the measurement angle varied, an area of ​​approximately 176 mm long x 132 mm wide was measured. After tristimulus value 1 was obtained, the surface light source was temporarily turned off. Next, an optical film 1 was bonded to the surface light source 1 via an adhesive layer (a 25 μm-thick transparent adhesive layer, PANAC Corporation's product name "Panaclean PD-S1"). The angle between the slow axis of the optical film 1 (biaxially stretched polyester film) and the transmission axis of the polarizer included in the surface light source 1 was 45 degrees. The surface light source 1 was set to white, and linearly polarized white light L1 was emitted from the surface light source 1. The in-plane distribution of tristimulus values ​​of light L2 transmitted through the optical film 1 from L1 was measured using the measuring device to obtain tristimulus values ​​2. The measurement was performed in a darkroom environment. The focus was set on the surface of the optical film 1 during the measurement. The distance between the surface light source and the measuring device during the measurement was 255 mm. The tristimulus values ​​were also measured at four angles between the surface light source and the measuring device: 30 degrees, 40 degrees, 50 degrees, and 60 degrees. Although the measurement angle varied, the measurement was performed over an area of ​​approximately 176 mm long x 132 mm wide. The area for measuring the in-plane distribution of the tristimulus values ​​of L1 and the area for measuring the in-plane distribution of the tristimulus values ​​of L2 were aligned in the plane direction. While measuring the tristimulus values, interference colors were visually evaluated at four angles of 30 degrees, 40 degrees, 50 degrees, and 60 degrees according to the following evaluation criteria. Ten subjects (healthy people in their 20s to 40s) evaluated the samples, giving a score of 4 for no visible interference color, 3 for slight visible interference color, 2 for visible but not bothersome interference color, and 1 for visible but bothersome interference color. The average scores of the 10 subjects were calculated and ranked. The results are shown in Table 1. Next, the surface on which tristimulus values ​​1 and 2 were measured was divided into 16 vertical and 16 horizontal sections. From tristimulus values ​​1 and 2, color parameters in the Lab color system were calculated for each pixel. For each section, the average value of the color parameters of all pixels within the section was calculated, and this average value was used as the color parameter for that section. The average value of the color parameters for each section was calculated, and this average value was used as the color parameter for that section. The variance of the color parameters for all sections was then calculated. Two color parameters were used as the color parameters: the a* value of the Lab color system and the b* value of the Lab color system. The sum of the variance of the a* value and the variance of the b* value is shown in Table 1. Furthermore, the product of the variance of the a* value and the variance of the b* value is shown in Table 2, and the sum of the square root of the variance of the a* value and the square root of the variance of the b* value is shown in Table 3.

[0091] <Evaluation criteria for visual evaluation of interference colors> A: Average score of 3.5 or above B: Average score is 3.0 or more and less than 3.5 C: Average score is 2.0 or more but less than 3.0 D: Average score is less than 2.0

[0092] [Examples 2 to 8] The evaluation method for interference colors of Examples 2 to 8 was carried out in the same manner as in Example 1, except that the surface light source having a polarizer and the optical film shown in Tables 1 to 3 were used.

[0093] [Examples 9 to 10] The interference colors of Examples 9 and 10 were evaluated in the same manner as in Example 3, except that the angle between the slow axis of optical film 3 and the transmission axis of the polarizer included in surface light source 1 was changed to the angle shown in Table 4 and the measurement angle and observation angle were fixed at 40 degrees. Table 4 shows the sum of the variance of the a* value and the variance of the b* value.

[0094] [Table 1]

[0095] [Table 2]

[0096] [Table 3]

[0097] [Table 4]

[0098] The results in Tables 1 to 4 confirm that the interference color evaluation method of the examples can objectively evaluate interference colors based on the dispersion value. Furthermore, the results in Table 4 confirm that the closer the angle between the slow axis of the optical film and the transmission axis of the polarizer is to 45 degrees, the stronger the interference color becomes. Therefore, it can be said that the usefulness of the interference color evaluation method of the examples increases as the angle between the slow axis of the optical film and the transmission axis of the polarizer approaches 45 degrees. Furthermore, the results in Tables 1 to 3 show that the optical film and image display device of the present disclosure that satisfy one or more of the following conditions (1) to (3) can suppress interference colors. Similarly, the polarizing plate of the present disclosure that uses the optical film as a polarizer protective film can suppress interference colors. (1) The sum of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system is 5.00 or less. (2) The product of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system is 4,000 or less. (3) The sum of the square root of the variance of the a* value in the Lab color system and the square root of the variance of the b* value in the Lab color system is 3.00 or less. [Explanation of symbols]

[0099] 10: Polarizer 100: Surface light source 21: Device body 22: Lens 200: Measuring equipment 30: Optical film 31: Plastic film

Claims

[Claim 1] An optical film, The optical film has a variance of two or more color parameters calculated by the following steps 1 to 4, which satisfies one or more of the following (1) to (3): Step 1: A surface light source including a polarizer is set to display white, and linearly polarized white light L1 is emitted from the surface light source. Step 2: Measure the in-plane distribution of tristimulus values ​​for L1. The measurement angle is 60 degrees. The tristimulus values ​​of L1 measured in this step are defined as tristimulus value 1. Step 3: With the optical film placed on the surface light source, the surface light source is displayed in white. Then, the in-plane distribution of tristimulus values ​​is measured for light L2, which is light L1 transmitted through the optical film. The measurement angle is 60 degrees. The tristimulus value of L2 measured in this step is defined as tristimulus value 2. Step 4: The surface on which the tristimulus values ​​1 and 2 have been measured is divided into a plurality of sections. Color parameters are calculated for each section from the tristimulus values ​​1 and 2. Then, the variance of the color parameters for all sections is calculated. The variance is calculated for two or more color parameters. (1) The sum of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system is 5.00 or less. (2) The product of the variance of the a* value in the Lab color system and the variance of the b* value in the Lab color system is 4,000 or less. (3) The sum of the square root of the variance of the a* value in the Lab color system and the square root of the variance of the b* value in the Lab color system is 3.00 or less.

Images