Optical film, polarizing plate, image display device, and optical film selection method

Abstract

An optical film is provided that eliminates rainbow non-uniformity when viewed with the naked eye and has good color uniformity when viewed at an angle. The optical film comprises a low-refractive-index layer on a plastic film, wherein the plastic film has a ground axis, which is the axis with the highest refractive index within the plane, and a true axis, which is an axis orthogonal to the ground axis within the plane of the plastic film, and the low-refractive-index layer is located on the surface of the optical film. Linear polarized light is incident under predetermined conditions from a surface opposite to the low-refractive-index layer of the optical film, and the a* and b* values ​​of the transmitted light of the linear polarized light are measured at 11 measurement points with different angles. Based on the measurements at the 11 measurement points, the square of the difference of a* and the square of the difference of b* of adjacent measurement points are calculated at 10 adjacent points, respectively. The optical film is such that ΣT, representing the total sum of the above sums, represents a predetermined range.

Description

Technology Field

[0001] The present disclosure relates to an optical film, a polarizer, an image display device, and a method for selecting an optical film. Background Technology

[0002] Various optical plastic films are often used in optical components such as image display devices. For example, in an image display device having a polarizer on a display element, a plastic film is used to protect the polarizer constituting the polarizer. In this specification, "plastic film for protecting the polarizer" may be referred to as "polarizer protection film."

[0003] Plastic films for image display devices, such as polarizer protective films, are preferably made of materials with excellent mechanical strength. For this reason, stretched plastic films are preferably used as plastic films for image display devices.

[0004] When a stretched plastic film is placed on a polarizer, there is a problem in that rainbow pattern unevenness is observed because the stretched plastic film disrupts the polarization state of linearly polarized light passing through the polarizer. To solve the problem of rainbow unevenness, techniques such as those described in Patent Documents 1 to 3 have been proposed. Hereinafter, in this specification, "rainbow pattern unevenness" may be referred to as "rainbow unevenness."

[0005] Patent Document 1 discloses a liquid crystal display device capable of resolving rainbow non-uniformity when viewing an image through polarizing sunglasses by making the light source of the image display device a specific white light source, increasing the in-plane phase difference (retardation) of the stretched plastic film to 3000 nm or more and 30000 nm or less, and aligning the absorption axis of the polarizer and the ground axis of the stretched plastic film at approximately 45 degrees.

[0006] However, the means of Patent Document 1 requires the use of a stretched plastic film with a large in-plane phase difference. And, since a stretched plastic film with a large in-plane phase difference is typically uniaxially stretched, there are problems such as it being prone to tearing in the stretching direction.

[0007] Patent document 2 discloses a polarizer protection film having a reflectance at a specific range at the Brewster angle. Patent document 3 discloses a polarizer protection film having a difference of 20% or less between the reflectance of P-waves and the reflectance of S-waves at an incident angle of 50 degrees.

[0008] The polarizing plate protection films of Patent Documents 2 and 3 aim to eliminate rainbow non-uniformity when viewed with the naked eye without increasing the in-plane phase difference of the film as in Patent Document 1 by reducing the difference in reflectance between the P-wave and S-wave, which are polarization components of light directed from the inside of the image display device toward the viewer.

[0009] The polarizing plate protective films of Patent Documents 2 and 3 can improve rainbow non-uniformity when viewed with the naked eye to some extent. However, the polarizing plate protective films of Patent Documents 2 and 3 had a problem in that the color changed depending on the viewing angle. That is, the polarizing plate protective films of Patent Documents 2 and 3 could not satisfy color uniformity when viewed at an oblique angle. Prior art literature

[0010] Japanese Patent Publication No. 2011-107198 Japanese Patent Publication No. 2009-14886 Japanese Patent Publication No. 2010-204630 The problem to be solved

[0011] The present disclosure aims to provide an optical film that eliminates rainbow non-uniformity when viewed with the naked eye and has good color uniformity when viewed at an angle, and a polarizing plate and an image display device using said optical film. The present disclosure aims to provide a method for selecting an optical film that eliminates rainbow non-uniformity when viewed with the naked eye and has good color uniformity when viewed at an angle. means of solving the problem

[0012] The present disclosure provides the following [1] to

[12] .

[0013] [1] An optical film having a low refractive index layer on a plastic film,

[0014] The above plastic film has a ground axis, which is the axis with the greatest refractive index within the plane, and a true axis, which is an axis orthogonal to the ground axis within the plane of the plastic film.

[0015] The low refractive index layer is located on the surface of the optical film, and

[0016] The above optical film is Σ calculated under the following measurement condition 1. T An optical film having an area that satisfies greater than 0.04 and less than 0.20.

[0017] <Measurement Condition 1>

[0018] Linearly polarized light is incident from the side of the optical film opposite to the low-refractive-index layer. The incident linearly polarized light is defined as light L1. The transmitted light that passes through the optical film after light L1 is defined as light L2.

[0019] After fixing the angle formed by the ground axis and the vibration direction of the light L1 to 45 degrees, the light L1 is incident on the optical film at an angle such that the elevation angle of the vibration direction of the light L1 relative to the plane of the optical film is 50 degrees or more and 70 degrees or less. The elevation angle is varied in increments of 2 degrees within the range of 50 degrees or more and 70 degrees or less, and the light L2 is measured at 11 different elevation angles. Through the aforementioned measurement, the light L2 is measured at 11 measurement points.

[0020] The above light L2 is converted under the conditions of a C light source and a viewing angle of 2 degrees. With respect to the light L2 of the nth measurement point among 11 measurement points, the a* value and b* value of the L*a*b* color system are defined as a*n and b*n. In addition, with respect to the n+1th light L2 among 11 measurement points, the a* value and b* value of the L*a*b* color system are defined as a*n1 and b*n1.

[0021] Based on the measurements of the above 11 measurement points, the sum of the square of the difference a* of adjacent measurement points and the square of the difference b* of adjacent measurement points is calculated. The above sum is calculated for each of the 10 adjacent points, and Σ representing the total sum of the above sums T Calculates. The above Σ T It can be expressed by the following Equation 1.

[0022] Σ T =Σ[{a*na*n1} 2 +{b*nb*n1} 2 ] (Equation 1)

[0023] [2] Based on the measurements of the 11 measurement points above, the maximum value of a* is defined as a*max, the minimum value of a* as a*min, the maximum value of b* as b*max, and the minimum value of b* as b*min, and the optical film described in [1] satisfies the following Equations 2-1 and 2-2.

[0024] a*max - a*min ≤ 0.250 (Equation 2-1)

[0025] b*max - b*min ≤ 0.350 (Equation 2-2)

[0026] [3] Based on the measurements of the 11 measurement points above, the sum of the square of the difference of a* between adjacent measurement points and the square of the difference of b* between adjacent measurement points is calculated. When the sum is defined as S, S can be expressed by Equation 3 below. S is calculated for each of the 10 adjacent points, and the maximum value of S of the 10 points is S MAX When defined as, S MAX An optical film described in [1] or [2] having a value of 0.010 or more and 0.050 or less.

[0027] S={a*na*n1} 2 +{b*nb*n1} 2 (Equation 3)

[0028] [4] When the luminous reflectance Y value of the above optical film is defined as R(%), the above R and the above Σ T An optical film described in any of [1] to [3], wherein the product of is 0.05 or more and 0.25 or less.

[0029] [5] An optical film described in any one of [1] to [4], wherein n2 / n1 is less than 1.23 when the average refractive index of the low-refractive-index layer is defined as n1 and the average refractive index of the layer adjacent to the low-refractive-index layer is defined as n2.

[0030] [6] An optical film described in any one of [1] to [4], wherein n2 / n1 is 1.05 or more and less than 1.23, when the average refractive index of the low-refractive-index layer is defined as n1 and the average refractive index of the layer adjacent to the low-refractive-index layer is defined as n2.

[0031] [7] An optical film described in any one of [1] to [6], wherein the in-plane phase difference of the above plastic film is 2500 nm or less.

[0032] [8] An optical film described in any one of [1] to [7], wherein the above plastic film satisfies condition A below.

[0033] <Condition A>

[0034] A sample measuring 50 mm in height × 50 mm in width is cut from the plastic film. A total of five measurement points are designated, consisting of one point in the center of the sample and four points each located 10 mm from the four corners of the sample toward the center.

[0035] The direction of the ground axis is measured at the five locations of the above sample. The angles formed by any one side of the above sample and the direction of the ground axis at each measurement location are defined as D1, D2, D3, D4, and D5, respectively. The difference between the maximum value of D1 to D5 and the minimum value of D1 to D5 is 1.5 degrees or more.

[0036] [9] An optical film described in any one of [1] to [8] having one or more layers selected from a hard coat layer and a glare-reducing layer between the plastic film and the low refractive index layer.

[0037]

[10] A polarizing plate having a polarizer, a first transparent protective plate located on one side of the polarizer, and a second transparent protective plate located on the other side of the polarizer, wherein at least one of the first transparent protective plate and the second transparent protective plate is an optical film described in any one of [1] to [9], and the side of the optical film on the side of the low refractive index layer is formed facing opposite to the polarizer.

[0038]

[11] An image display device having a display element, a polarizer and an optical film disposed on the light-emitting side of the display element, wherein the optical film is an optical film described in any one of [1] to [7], and the side of the optical film on the low-refractive-index layer side is formed facing the opposite side from the display element.

[0039]

[12] A method for selecting an optical film of an image display device having a polarizer and an optical film on the light-emitting surface of a display element, and selecting an optical film X that satisfies the judgment conditions of (1) to (4) below as the optical film.

[0040] (1) An optical film X having a low refractive index layer on a plastic film;

[0041] (2) The above plastic film has a ground axis, which is the axis with the greatest refractive index within the plane, and a true axis, which is an axis orthogonal to the ground axis within the plane of the plastic film;

[0042] (3) The low refractive index layer is positioned on the surface of the optical film X; and

[0043] (4) The optical film X is Σ calculated in measurement condition 1 T Having an area that satisfies greater than 0.04 and less than 0.20. Effects of the invention

[0044] The optical film of the present disclosure, and the polarizing plate and image display device using the optical film, can eliminate rainbow non-uniformity when viewed with the naked eye and improve color uniformity when viewed at an angle. The method for selecting the optical film of the present disclosure can efficiently select an optical film that eliminates rainbow non-uniformity when viewed with the naked eye and improves color uniformity when viewed at an angle. Brief explanation of the drawing

[0045] FIG. 1 is a cross-sectional view showing one embodiment of an optical film of the present disclosure. Figure 2 is a schematic diagram showing an example of a measurement performed under measurement condition 1. FIG. 3 is a cross-sectional view showing one embodiment of a polarizing plate of the present disclosure. FIG. 4 is a cross-sectional view showing one embodiment of an image display device of the present disclosure. FIG. 5 is a plan view illustrating five measurement locations within a sample when calculating the in-plane phase difference, etc. from the sample. Figure 6 is a schematic diagram showing the mode of a continuous folding test. Figure 7 is a schematic cross-sectional view of a measuring device for the refractory rate. Figure 8 is an image drawing of a plastic film being worn down by a test solution containing pure and spherical silica sprayed from a spraying unit. Specific details for implementing the invention

[0046] Hereinafter, embodiments of the optical film of the present disclosure will be described.

[0047] [Optical Film]

[0048] The optical film of the present disclosure comprises a low-refractive-index layer on a plastic film, wherein the plastic film has a ground axis which is the axis with the greatest refractive index within a plane and a true axis which is an axis orthogonal to the ground axis within the plane of the plastic film, wherein the low-refractive-index layer is located on the surface of the optical film, and the optical film is Σ calculated under the following measurement condition 1 T It has an area that satisfies greater than 0.04 and less than 0.20.

[0049] <Measurement Condition 1>

[0050] Linearly polarized light is incident from the side of the optical film opposite to the low-refractive-index layer. The incident linearly polarized light is defined as light L1. The transmitted light that passes through the optical film after light L1 is defined as light L2.

[0051] After fixing the angle formed by the ground axis and the vibration direction of the light L1 to 45 degrees, the light L1 is incident on the optical film at an angle such that the elevation angle of the vibration direction of the light L1 relative to the plane of the optical film is 50 degrees or more and 70 degrees or less. The elevation angle is varied in increments of 2 degrees within the range of 50 degrees or more and 70 degrees or less, and the light L2 is measured at 11 different elevation angles. Through the aforementioned measurement, the light L2 is measured at 11 measurement points.

[0052] The above light L2 is converted under the conditions of a C light source and a viewing angle of 2 degrees. With respect to the light L2 of the nth measurement point among 11 measurement points, the a* value and b* value of the L*a*b* color system are defined as a*n and b*n. In addition, with respect to the n+1th light L2 among 11 measurement points, the a* value and b* value of the L*a*b* color system are defined as a*n1 and b*n1.

[0053] Based on the measurements of the above 11 measurement points, the sum of the square of the difference a* of adjacent measurement points and the square of the difference b* of adjacent measurement points is calculated. The above sum is calculated for each of the 10 adjacent points, and Σ representing the total sum of the above sums T Calculates. The above Σ T It can be expressed by the following Equation 1.

[0054] Σ T =Σ[{a*na*n1} 2 +{b*nb*n1} 2 ] (Equation 1)

[0055] In this specification, the measurement under measurement condition 1 and the subsequent measurements (measurements of in-plane phase difference, phase difference in the thickness direction, direction of the ground axis, luminous reflectance Y value, etc.) shall be performed in an atmosphere with a temperature of 23℃±5℃ and a relative humidity of 40% or more and 65% or less, unless otherwise specified. In addition, before each measurement, the measurement sample shall be exposed to the above atmosphere for 30 minutes or more and 60 minutes or less.

[0056] In this specification, the a* and b* values ​​are based on the L*a*b* color system standardized by the International Commission on Illumination (CIE) in 1976. The L*a*b* color system is adopted in JIS Z8781-4:2013.

[0057] FIG. 1 is a cross-sectional view showing an embodiment of the optical film (100) of the present disclosure. As shown in FIG. 1, the optical film (100) of the present disclosure has a low refractive index layer (30) on a plastic film (10).

[0058] The optical film (100) of the present disclosure may have layers other than the plastic film (10) and the low refractive index layer (30). Examples of layers other than the plastic film (10) and the low refractive index layer (30) include a hard coat layer, an anti-glare layer, and a high refractive index layer. The optical film (100) of FIG. 1 has a hard coat layer (20) between the plastic film (10) and the low refractive index layer (30).

[0059] In this specification, "inside the plane of the plastic film" means, unless specifically defined otherwise, "inside the plane in a direction orthogonal to the thickness direction of the plastic film." In the case of FIG. 1, the XY plane of the plastic film corresponds to within the plane of the plastic film.

[0060] Regarding Measurement Condition 1

[0061] Figure 2 is a schematic diagram showing an example of a measurement performed under measurement condition 1.

[0062] In condition 1, linearly polarized light L1 is incident from the side opposite to the low-refractive-index layer of the optical film. In FIG. 2(a), an optical film (100) is placed between a light source A1 and a detector A2. In FIG. 2(a), linearly polarized light L1 is emitted from the light source and the light L1 is incident on the side opposite to the low-refractive-index layer (30) of the optical film (100).

[0063] Detector A2 is used to detect the transmitted light of light L1.

[0064] In measurement condition 1, light L1 is incident on the optical film (100) after fixing the angle formed by the ground axis of the plastic film and the vibration direction of light L1 to 45 degrees. FIG. 2(b) is a diagram showing the ground axis of the plastic film “S” and the vibration direction of light L1 “V” when FIG. 2(a) is viewed from the XY plane direction. In FIG. 2(b), θ1 represents the angle formed by the ground axis of the plastic film “S” and the vibration direction of light L1 “V”. In measurement condition 1, θ1 is fixed at 45 degrees. Additionally, the vibration direction of light L1 “V” is actually tilted in the Z-axis direction.

[0065] In measurement condition 1, after fixing θ1 at 45 degrees, light L1 is incident on the optical film at an angle such that the angle of elevation of the vibration direction of light L1 relative to the plane of the optical film is 50 degrees or more and 70 degrees or less. In FIG. 2(a), θ2 represents the angle of elevation of “V,” which is the vibration direction of light L1 relative to the plane of the optical film (the plane of the optical film is set to 0 degrees as the reference). In FIG. 2(a), “F” represents the true axis of the optical film. In FIG. 2(a), the true axis “F” is stretched in the Y-axis direction of FIG. 2(a).

[0066] In measurement condition 1, the angle of elevation is varied in increments of 2 degrees within a range of 50 degrees or more and 70 degrees or less, and light L2 is measured at 11 different angles of elevation. Through the aforementioned measurement, light L2 is measured at 11 measurement points. As a means of varying the angle of elevation in increments of 2 degrees within a range of 50 degrees or more and 70 degrees or less, for example, a means of tilting the optical film (100) with the true axis “F” as the pivot center can be cited.

[0067] In measurement condition 1, the elevation angle is set to between 50 and 70 degrees because the Brewster angle of plastic films, such as polyester films, was taken into account. The unevenness of the rainbow visible to the naked eye in plastic films is easily seen strongly near the Brewster angle.

[0068] In measurement condition 1, light L2 is converted to a condition of C light source and a viewing angle of 2 degrees. By the above conversion, the influence of the light source can be excluded from the a* and b* values ​​obtained.

[0069] With respect to the light L2 of the nth measurement point among 11 measurement points, the a* and b* values ​​of the L*a*b* color system are defined as a*n and b*n. Additionally, with respect to the light L2 of the n+1th measurement point among 11 measurement points, the a* and b* values ​​of the L*a*b* color system are defined as a*n1 and b*n1. a*n, b*n, a*n1, and b*n1 are calculated from the light L2 after the above conversion.

[0070] The above measurements and calculations can be performed, for example, using the spectrophotometer model number "V-7100" of JASCO Corporation.

[0071] In measurement condition 1, based on the measurements of the above 11 measurement points, the sum of the square of the difference a* of adjacent measurement points and the square of the difference b* of adjacent measurement points is calculated. The above sum is calculated for each of the 10 adjacent points, and Σ representing the total sum of the above sums T Calculates. The above Σ T It can be expressed by the following Equation 1.

[0072] Σ T =Σ[{a*na*n1} 2 +{b*nb*n1} 2 ] (Equation 1)

[0073] The optical film of the present disclosure is, the Σ T It is required to have an area that satisfies greater than 0.04 and less than 0.20.

[0074] The above Σ T represents the amount of variation in transmitted color when the optical film is viewed at an angle of 50 degrees or more and 70 degrees or less. The inventors [have] the above Σ T It was discovered that serves as an indicator of the ease of seeing rainbow non-uniformity in an optical film having a low-refractive-index layer on a plastic film. Furthermore, the inventors found that the lower the reflectance of the optical film having a low-refractive-index layer on a plastic film, the more the above Σ T It was discovered that as the size decreases, rainbow anomalies tend to become difficult to see. Rainbow anomalies are based on transmitted light.

[0075] Based on the findings of the inventors described above, the above Σ T It is believed that visibility can be improved by making Σ smaller. However, the inventors, the above Σ T It was discovered that as is made smaller, the color becomes more prone to change when viewed at an angle, leading to a problem of reduced color uniformity. Furthermore, the inventors discovered that the primary cause of the reduced color uniformity lies in reflected light, not transmitted light. Additionally, the inventors found that the above Σ T It was revealed that by setting to a predetermined range, the unevenness of the rainbow when viewed with the naked eye can be resolved, and at the same time, the uniformity of color in the poem when viewed at an angle can be improved. The above Σ T Setting to a value greater than a predetermined value means increasing the reflectance of the optical film having a low refractive index layer. That is, the inventors have discovered that by deliberately increasing the reflectance of the optical film having a low refractive index layer, it is possible to solve the problem of eliminating rainbow non-uniformity when viewed with the naked eye, while simultaneously improving color uniformity when viewed at an angle. The above Σ TIt is believed that by making ≥ a predetermined value, interference of reflected light from an optical film having a low refractive index layer is suppressed, making it easier to improve the uniformity of color tone when viewed at an angle. (Σ T As becomes larger, the refractive index of the low-refractive-index layer tends to increase. Furthermore, as the refractive index of the low-refractive-index layer increases, the difference in refractive index between the low-refractive-index layer and the layer in contact with it tends to decrease, thereby suppressing interference of reflected light in the optical film. As a result, it is believed that it is easier to improve the uniformity of color tone when viewed at an angle.

[0076] Σ T If α is 0.04 or less, interference from reflected light becomes strong, making it impossible to achieve good color uniformity in obliquely viewed poetry. Σ T If α is 0.20 or greater, rainbow non-uniformity when viewed with the naked eye cannot be resolved. As previously mentioned, rainbow non-uniformity is based on transmitted light. Therefore, Σ T By making it greater than 0.04 and less than 0.20, the influence of both transmitted light and reflected light can be suppressed, thereby making visibility extremely good.

[0077] Σ T It is desirable that is 0.05 or higher, and more desirable that it is 0.06 or higher. Σ T It is preferable that it be 0.15 or less, more preferable that it be 0.10 or less, and even more preferable that it be 0.09 or less.

[0078] In the optical film of the present disclosure, the Σ TDesirable ranges include greater than 0.04 and less than or equal to 0.15, greater than 0.04 and less than or equal to 0.10, greater than 0.04 and less than or equal to 0.09, greater than or equal to 0.05 and less than or equal to 0.20, greater than or equal to 0.05 and less than or equal to 0.15, greater than or equal to 0.05 and less than or equal to 0.09, greater than or equal to 0.06 and less than or equal to 0.20, greater than or equal to 0.06 and less than or equal to 0.15, greater than or equal to 0.06 and less than or equal to 0.10, greater than or equal to 0.06 and less than or equal to 0.09, etc.

[0079] If the refractive index of the low-refractive-index layer is increased, Σ T tends to increase. If the refractive index of the low-refractive-index layer is lowered, Σ T tends to decrease. If the refractive index of the low-refractive-index layer is lowered, the mechanical strength of the low-refractive-index layer tends to decrease. If the refractive index of the low-refractive-index layer is increased, the reflectance of the optical film is prone to increase. In order to keep the reflectance of the optical film within an appropriate range and also to ensure good mechanical strength of the low-refractive-index layer, the above Σ T It is desirable that it be 0.05 or more and 0.09 or less.

[0080] The above Σ T This can be easily made to fall within the above range by means of "reducing the in-plane phase difference of the plastic film" and "reducing n2 / n1, a parameter related to the refractive index," etc. When a hard coat layer is provided between the plastic film and the low refractive index layer, by using a multifunctional (meth)acrylate oligomer with a molecular weight within a predetermined range as the ionizing radiation-curable compound forming the hard coat layer, the above Σ T It can be made easier to set the above range.

[0081] In an optical film, Σ T The proportion of the area satisfying greater than 0.04 and less than 0.20 is preferably 50% or more, more preferably 70% or more, even more preferably 90% or more, and even more preferably 100%.

[0082] Likewise, Σ T The ratio of the region satisfying various other parameters (Equation 2-1, Equation 2-2, in-plane phase difference, thickness direction phase difference, etc.) within the optical film is preferably 50% or more, more preferably 70% or more, even more preferably 90% or more, and even more preferably 100%.

[0083] The optical film of the present disclosure preferably satisfies the following Equations 2-1 and 2-2 when, based on the measurement of the 11 measurement points, the maximum value of a* is defined as a*max, the minimum value of a* as a*min, the maximum value of b* as b*max, and the minimum value of b* as b*min.

[0084] a*max - a*min ≤ 0.250 (Equation 2-1)

[0085] b*max - b*min ≤ 0.350 (Equation 2-2)

[0086] By satisfying Equations 2-1 and 2-2, it is possible to make it more difficult to perceive changes in transmitted color in the range of 50 degrees or more and 70 degrees or less. For this reason, by satisfying Equations 2-1 and 2-2, it is possible to make it easier to resolve rainbow non-uniformity when viewed with the naked eye.

[0087] Σ T If becomes too small, the left-hand sides of Equations 2-1 and 2-2 tend to increase. The reason for this is, Σ T It is thought that when θ becomes smaller, the color change becomes dominant due to the change in the optical distance of the low-refractive-index layer. More specifically, it is thought that because the optical distance of the low-refractive-index layer changes linearly with angle, the a* and b* values ​​increase or decrease monotonically. For this reason, by satisfying Equations 2-1 and 2-2, it tends to be easier to achieve good uniformity of color when viewed at an angle.

[0088] It is more preferable that a*max-a*min in Equation 2-1 be 0.230 or less, even more preferable that it be 0.210 or less, and even more preferable that it be 0.200 or less. The lower limit of a*max-a*min in Equation 2-1 is not specifically restricted, but is approximately 0.070. By making a*max-a*min 0.070 or more, Σ T It can be made easier to prevent it from growing too large.

[0089] It is more preferable that b*max-b*min in Equation 2-2 be 0.300 or less, more preferable that it be 0.250 or less, more preferable that it be 0.230 or less, more preferable that it be 0.210 or less, and more preferable that it be 0.200 or less. The lower limit of b*max-b*min in Equation 2-2 is not specifically restricted, but is approximately 0.070. By making b*max-b*min 0.070 or more, Σ T It can be made easier to prevent it from growing too large.

[0090] Preferable ranges for a*max-a*min in Equation 2-1 include 0.070 or more and 0.250 or less, 0.070 or more and 0.230 or less, 0.070 or more and 0.210 or less, 0.070 or more and 0.200 or less.

[0091] Preferable ranges for b*max-b*min in Equation 2-2 include 0.070 or more and 0.350 or less, 0.070 or more and 0.300 or less, 0.070 or more and 0.250 or less, 0.070 or more and 0.230 or less, 0.070 or more and 0.210 or less, 0.070 or more and 0.200 or less.

[0092] Formulas 2-1 and 2-2 can be easily satisfied by "reducing the in-plane phase difference of the plastic film" and "reducing n2 / n1, a parameter related to the refractive index." When a hard coat layer is provided between the plastic film and the low refractive index layer, Formulas 2-1 and 2-2 can be easily satisfied by using a multifunctional (meth)acrylate oligomer with a molecular weight in a predetermined range as the ionizing radiation-curable compound forming the hard coat layer.

[0093] a*max is preferably -1.0 or higher and 0 or lower, and more preferably -0.8 or higher and -0.1 or lower.

[0094] b*max is preferably 0 or more and 2.0 or less, and more preferably 0.2 or more and 1.8 or less.

[0095] The optical film of the present disclosure preferably satisfies the following configuration.

[0096] Based on the measurements of the above 11 measurement points, the sum of the square of the difference of a* between adjacent measurement points and the square of the difference of b* between adjacent measurement points is calculated. When the above sum is defined as S, S can be expressed by Equation 3 below. S is calculated for each of the 10 adjacent points, and the maximum value of S of the 10 points is S MAX When defined as, S MAX It is desirable that is 0.010 or more and 0.050 or less.

[0097] S={a*na*n1} 2 +{b*nb*n1} 2 (Equation 3)

[0098] S MAX By making 0.050 or less, it is possible to make it more difficult to perceive changes in transmitted color in the range of 50 degrees to 70 degrees. For this reason, S MAX By making it 0.050 or less, it is easier to resolve rainbow non-uniformity when viewed with the naked eye.

[0099] When the reflectance of an optical film having a low refractive index layer decreases, S MAX There is a tendency for it to become smaller. That is, S MAX If is made too small, it tends to be difficult to suppress interference of reflected light from an optical film having a low-refractive-index layer. For this reason, S MAX By making it 0.010 or higher, it is easier to make the uniformity of the color tone of the oblique poet's poem better.

[0100] S MAX It is more preferable that the lower limit is 0.011 or higher, and even more preferable that it is 0.012 or higher. S MAX It is more desirable that the upper limit is 0.040 or less, even more desirable that it is 0.030 or less, and even more desirable that it is 0.025 or less.

[0101] S MAX Desirable ranges include 0.010 or more and 0.040 or less, 0.010 or more and 0.030 or less, 0.010 or more and 0.025 or less, 0.011 or more and 0.050 or less, 0.011 or more and 0.040 or less, 0.011 or more and 0.030 or less, 0.011 or more and 0.025 or less, 0.012 or more and 0.050 or less, 0.012 or more and 0.040 or less, 0.012 or more and 0.030 or less, 0.012 or more and 0.025 or less.

[0102] S MAX By making it 0.010 or more and 0.040 or less, the increase in b* can be suppressed, thereby preventing damage to the premium feel of the image display device.

[0103] S MAXThis can be easily made to fall within the above range by "reducing the in-plane phase difference of the plastic film", "reducing n2 / n1, a parameter related to the refractive index," etc. When a hard coat layer is provided between the plastic film and the low refractive index layer, by using a polyfunctional (meth)acrylate oligomer with a molecular weight within a predetermined range as the ionizing radiation-curable compound forming the hard coat layer, S MAX It can be made easier to set the above range.

[0104] The optical film of the present disclosure is such that, when the luminous reflectance Y value of the optical film is defined as R(%), the R and the Σ T It is desirable that the product of is between 0.05 and 0.25.

[0105] By making the above product between 0.05 and 0.25, the above Σ T It can make it easier to exert effects based on.

[0106] The above product is more preferably 0.06 or higher, and even more preferably 0.07 or higher. The above product is more preferably 0.19 or lower, even more preferably 0.13 or lower, and even more preferably 0.11 or lower. In particular, if the above product is 0.11 or lower, it is easy to improve the premium feel of the image display device.

[0107] Preferred ranges of the above product include 0.05 or more and 0.19 or less, 0.05 or more and 0.13 or less, 0.05 or more and 0.11 or less, 0.06 or more and 0.25 or less, 0.06 or more and 0.19 or less, 0.06 or more and 0.13 or less, 0.06 or more and 0.11 or less, 0.07 or more and 0.25 or less, 0.07 or more and 0.19 or less, 0.07 or more and 0.13 or less, 0.07 or more and 0.11 or less, etc.

[0108] Plastic film

[0109] Examples of resin components included in plastic films include polyester, polyimide, polyethersulfone, polysulfone, polypropylene, polymethylpentene, polyvinyl chloride, polyvinyl acetal, polyetherketone, polymethyl methacrylate, polycarbonate, polyurethane, triacetylcellulose (TAC), and amorphous olefin (Cyclo-Olefin-Polymer: COP).

[0110] The plastic film preferably has a Brewster angle of 50 degrees or more and 70 degrees or less, and more preferably 55 degrees or more and 65 degrees or less. The optical film of the present disclosure has an elevation angle of measurement condition 1 of 50 degrees or more and 70 degrees or less. Accordingly, by making the Brewster angle of the plastic film 50 degrees or more and 70 degrees or less, it is possible to make it easier to exhibit the effects of the present disclosure.

[0111] Examples of resins with a Brewster angle of 50 degrees or more and 70 degrees or less include acrylics such as polymethyl methacrylate, polyesters, TAC, and COP. Among these, polyesters are preferred because they facilitate good mechanical strength.

[0112] Examples of polyesters include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate (PBT). Among these, PET is preferred because it has low intrinsic birefringence and is easy to reduce in-plane phase difference.

[0113] Plastic films may contain additives such as ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, anti-gelling agents, inorganic particles, organic particles, pigments, dyes, antifouling agents, crosslinking agents, and surfactants.

[0114] To ensure good mechanical strength, the plastic film is preferably a stretched film, and more preferably a biaxially stretched film. A biaxially stretched film is also preferred because it has better tear resistance compared to a uniaxially stretched film. Therefore, the plastic film is preferably a biaxially stretched plastic film.

[0115] In this specification, various embodiments are provided as preferred embodiments of the plastic film, such as "in-plane phase difference," "phase difference in the thickness direction," and "the difference between the maximum value of D1 to D5 and the minimum value of D1 to D5." In the case where the plastic film of the optical film disclosed in this disclosure is a biaxially stretched plastic film, it is more preferable that it satisfies the preferred embodiments such as the in-plane phase difference.

[0116] To facilitate the suppression of rainbow non-uniformity, it is preferable that the in-plane phase difference of the plastic film be 2500 nm or less. Furthermore, if the in-plane phase difference of the plastic film is reduced, the above Σ T It can be made easier to make small.

[0117] The in-plane phase difference of the plastic film is more preferably 2000 nm or less, more preferably 1500 nm or less, more preferably 1400 nm or less, more preferably 1250 nm or less, more preferably 1150 nm or less, more preferably 1100 nm or less, more preferably 1000 nm or less, more preferably 950 nm or less, more preferably 850 nm or less, and more preferably 600 nm or less. By making the in-plane phase difference of the plastic film 2000 nm or less, the above Σ TIt is possible to make it easier to reduce the size. In addition, if the refractive index of the plastic film differs in the ground axis direction and the leading axis direction, the reflectance of the optical film will differ in the ground axis direction and the leading axis direction. To suppress the difference in reflectance depending on the direction, it is desirable to reduce the difference in refractive index between the ground axis direction and the leading axis direction of the plastic film. For this reason, it is desirable that the in-plane phase difference of the plastic film be 1250 nm or less.

[0118] In order to improve mechanical strength, it is preferable for the plastic film to have an in-plane phase difference of 20 nm or more. It is more preferable for the in-plane phase difference of the plastic film to be 100 nm or more, more preferable for 300 nm or more, more preferable for 400 nm or more, and more preferable for 520 nm or more.

[0119] The preferred range of the in-plane phase difference of the plastic film is 20 nm or more and 2000 nm or less, 20 nm or more and 1500 nm or less, 20 nm or more and 1400 nm or less, 20 nm or more and 1250 nm or less, 20 nm or more and 1150 nm or less, 20 nm or more and 1100 nm or less, 20 nm or more and 1000 nm or less, 20 nm or more and 950 nm or less, 20 nm or more and 850 nm or less, 20 nm or more and 600 nm or less, 100 nm or more and 2000 nm or less, 100 nm or more and 1500 nm or less, 100 nm or more and 1400 nm or less, 100 nm or more and 1250 nm or less, 100 nm or more and 1150 nm or less, 20 nm or more and 1100 nm or less, 100 nm or more and 1000 nm or less, and 100 nm or more. 950nm or less, 100nm or more and 850nm or less, 100nm or more and 600nm or less, 300nm or more and 2000nm or less, 300nm or more and 1500nm or less, 300nm or more and 1400nm or less, 300nm or more and 1250nm or less, 300nm or more and 1150nm or less, 300nm or more and 1100nm or less, 300nm or more and 1000nm or less, 300nm or more and 950nm or less, 300nm or more and 850nm or less, 300nm or more and 600nm or less, 400nm or more and 2000nm or less, 400nm or more and 1500nm or less, 400nm or more and 1400nm or less, 400nm or more and 1250nm or less, 400nm or more and 1150nm or less, 400nm or more 1100nm or less, 400nm or more and 1000nm or less, 400nm or more and 950nm or less, 400nm or more and 850nm or less, 400nm or more and 600nm or less, 520nm or more and 2000nm or less, 520nm or more and 1500nm or less, 520nm or more and 1400nm or less, 520nm or more and 1250nm or less, 520nm or more and 1150nm or less, 520nm or more and 1100nm or less, 520nm or more and 1000nm or less, 520nm or more and 950nm or less, 520nm or more and 850nm or less,Examples include 520nm or more and 600nm or less.

[0120] In order to keep the in-plane phase difference of the plastic film within the above range, it is desirable to approximate the stretching ratio in the longitudinal direction (flow direction) and the stretching ratio in the transverse direction (width direction).

[0121] In the range where the in-plane phase difference of the plastic film is 520 nm or more and 1400 nm or less, suppression of rainbow non-uniformity and the above Σ T It is easy to realize a reduction and also easy to improve the mechanical strength of the plastic film. In addition, when the in-plane phase difference of the plastic film is 1250 nm or less, it is easy to suppress the difference in reflectance depending on the direction.

[0122] By making the in-plane phase difference of the plastic film 50 nm or more, it is easier to suppress blackout. This is because plastic films with an average in-plane phase difference of less than 50 nm can barely disrupt linear polarization and transmit it as is, whereas plastic films with an average in-plane phase difference of 50 nm or more can disrupt linear polarization. Blackout refers to the phenomenon where the entire surface becomes dark when light that has passed through a polarizer and a plastic film in this order is viewed through polarizing sunglasses.

[0123] It is preferable that the phase difference (Rth) in the thickness direction of the plastic film be 2,000 nm or more, more preferable that it be 3,000 nm or more, even more preferable that it be 4,000 nm or more, and even more preferable that it be 5,000 nm or more. The upper limit of Rth is approximately 10,000 nm, preferably 8,000 nm or less, and more preferably 7,000 nm or less. By setting Rth within the above range, it is easier to suppress rainbow non-uniformity. In particular, to suppress rainbow non-uniformity, it is preferable that Rth be 5,000 nm or more. Furthermore, to ensure good pencil hardness of the plastic film, it is preferable that Rth be 5,000 nm or more. To facilitate the suppression of breakage of the plastic film, it is preferable that Rth be 10,000 nm or less.

[0124] Preferred ranges of Rth of the plastic film include 2000 nm or more and 10000 nm or less, 2000 nm or more and 8000 nm or less, 2000 nm or more and 7000 nm or less, 3000 nm or more and 10000 nm or less, 3000 nm or more and 8000 nm or less, 3000 nm or more and 7000 nm or less, 4000 nm or more and 10000 nm or less, 4000 nm or more and 8000 nm or less, 4000 nm or more and 7000 nm or less, 5000 nm or more and 10000 nm or less, 5000 nm or more and 8000 nm or less, and 5000 nm or more and 7000 nm or less.

[0125] In order to make the Rth of the plastic film within the above range, it is desirable to increase the stretching ratio in the longitudinal direction (flow direction) and the transverse direction (width direction). By increasing the stretching ratio in the flow direction and the width direction, the refractive index in the thickness direction of the plastic film becomes smaller, making it easier to increase the Rth.

[0126] By setting the in-plane phase difference and the thickness direction phase difference to the above range, the degree of elongation of the plastic film can be approximated to uniform biaxiality, making it easier to improve the mechanical strength of the plastic film.

[0127] The in-plane phase difference (Re) and the phase difference in the thickness direction (Rth) of a plastic film can be expressed by the following Equations i and ii, where the refractive index in the ground axis direction is defined as nx, the refractive index in the leading axis direction as ny, the refractive index in the thickness direction of the plastic film as nz, and the thickness of the plastic film as T [nm]. Additionally, in this specification, the refractive index, the in-plane phase difference, and the phase difference in the thickness direction are defined as values ​​at a wavelength of 590 nm.

[0128] Re=(nx-ny)×T[nm] (Equation i)

[0129] Rth=((nx+ny) / 2-nz)×T[nm] (Equation ii)

[0130] The direction of the ground axis, the in-plane phase difference, and the phase difference in the thickness direction can be measured, for example, by the product name “RETS-100” of Otsuka Electronics Co., Ltd.

[0131] When measuring in-plane phase difference, etc. using the product name “RETS-100” of Otsuka Electronics Co., Ltd., it is preferable to prepare for measurement by following the following steps (A1) to (A4).

[0132] (A1) First, to stabilize the light source of the RETS-100, turn on the light source and leave it for at least 60 minutes. Then, along with selecting the rotary analyzer method, select the θ mode (mode for measuring the phase difference in the angular direction and calculating Rth). By selecting this θ mode, the stage becomes an inclined rotary stage.

[0133] (A2) Next, input the following measurement conditions into the RETS-100.

[0134] (Measurement conditions)

[0135] · Retardation measurement range: Rotating analyzer method

[0136] · Measurement spot diameter: φ5mm

[0137] · Inclination angle range: 0°

[0138] · Measurement wavelength range: 400nm or more, 800nm ​​or less

[0139] · Average refractive index of a plastic film. For example, in the case of a PET film, N=1.617. Also, the average refractive index N of a plastic film can be calculated using the formula (N=(nx+ny+nz) / 3) based on nx, ny, and nz.

[0140] · Thickness: Thickness measured separately using an SEM or optical microscope

[0141] (A3) Next, obtain background data without installing a sample on this device. The device is a closed system, and this is done whenever the light source is turned on.

[0142] (A4) After that, place the sample on the stage inside the device and measure it.

[0143] The in-plane phase difference, the phase difference in the thickness direction, and the direction of the ground axis are preferably determined by cutting a sample measuring 50 mm in length × 50 mm in width from a plastic film and taking the average value of the measurements taken at five locations on the sample. The five measurement locations are one location at the center of the sample and four locations located 10 mm from each of the four corners of the sample toward the center of the sample (the five locations marked by black circles in Fig. 5).

[0144] The in-plane phase difference measured at five locations of the above sample is defined as Re1, Re2, Re3, Re4, and Re5, respectively, and the thickness direction phase difference measured at five locations of the above sample is defined as Rth1, Rth2, Rth3, Rth4, and Rth5, respectively.

[0145] It is preferable that the average of Re1 / Rth1, Re2 / Rth2, Re3 / Rth3, Re4 / Rth4, and Re5 / Rth5 of the plastic film be 0.20 or less.

[0146] A small ratio of the in-plane phase difference to the thickness direction phase difference (Re / Rth) means that the biaxial stretching of the plastic film approximates uniform biaxiality. Therefore, by making Re / Rth 0.20 or less, the mechanical strength of the plastic film can be improved. It is more preferable that Re / Rth be 0.18 or less, and even more preferable that it be 0.16 or less. The lower limit of Re / Rth is about 0.01.

[0147] The Re / Rth of a perfectly uniaxially stretched plastic film is 2.0. A general-purpose uniaxially stretched plastic film is also slightly stretched in the flow direction. Because of this, the Re / Rth of a general-purpose uniaxially stretched plastic film is about 1.0.

[0148] Re1 / Rth1, Re2 / Rth2, Re3 / Rth3, Re4 / Rth4, and Re5 / Rth5 are each preferably 0.20 or less, more preferably 0.18 or less, and even more preferably 0.16 or less. The lower limit of these ratios is about 0.01.

[0149] In the case where a plastic film has a layer and a film that affect the values ​​of the in-plane phase difference and the phase difference in the thickness direction, the in-plane phase difference and the phase difference in the thickness direction of the plastic film can be measured after peeling off these layers and films. In addition, the layer formed by the coating usually does not affect the values ​​of the in-plane phase difference and the phase difference in the thickness direction.

[0150] As means for peeling off layers and films that affect the values ​​of in-plane phase difference and thickness direction phase difference, the following means may be cited.

[0151] Means of exfoliation

[0152] A square sample with sides of 5 cm or more is immersed in hot water at a temperature of 80°C or higher and 90°C or lower for 5 minutes. After that, the sample is removed from the hot water and left at room temperature for 10 minutes or more. After that, it is immersed in hot water again for 5 minutes. The sample is removed from the hot water. A cut mark is made on the sample using a cutter or the like. Then, a means of peeling off the layer and film using the cut mark may be provided.

[0153] In the above means, it is preferable to immerse the sample in hot water while the edge of the sample is attached to a metal frame, etc.

[0154] It is desirable for the plastic film to satisfy the following condition A.

[0155] <Condition A>

[0156] The direction of the ground axis is measured at five locations of the above sample. When the angles formed by any one side of the above sample and the direction of the ground axis at each measurement location are defined as D1, D2, D3, D4, and D5, respectively, the difference between the maximum value of D1 to D5 and the minimum value of D1 to D5 is 1.5 degrees or more.

[0157] If the ground axis of the plastic film is cleanly oriented, the above Σ T As it tends to become larger, there is a tendency for rainbow non-uniformity to become more visible. On the other hand, if a variation is introduced to the ground axis of the plastic film, the rainbow non-uniformity becomes fainter and difficult to see. Therefore, by satisfying condition A, it is easier to suppress the visibility of rainbow non-uniformity with the naked eye. In other words, by satisfying condition A, the above Σ T It can make it easier to satisfy the above range.

[0158] General-purpose stretched plastic films are designed so that the direction of the ground axis does not deviate. However, as mentioned above, by deliberately deviating the direction of the plastic film's ground axis, it is possible to suppress rainbow non-uniformity. Furthermore, although the effect of suppressing rainbow non-uniformity is small when the ground axis deviates over a large area, it is possible to suppress rainbow non-uniformity by deviating the ground axis in a relatively small area of ​​50mm in height × 50mm in width.

[0159] In this specification, "the above Σ T The “direction of the ground axis when calculating” means “the average of the directions of the ground axis at 5 locations of the above sample.”

[0160] In condition A, any one side of the sample that serves as the reference for the angle formed with the direction of the ground axis may be any side of the sample's vertical or horizontal axis, provided that it is based on the same side in D1 to D5.

[0161] In addition, a plastic film satisfying condition A is desirable in that it can improve the internal folding bendability of the plastic film.

[0162] On the other hand, a general-purpose orientation film in which the ground axis is aligned without satisfying condition A may break after a bending test, or the bending properties may remain strong. Specifically, a uniaxially stretched film such as that of Patent Document 1 may break when subjected to a bending test along the ground axis, and the bending properties may remain strong when subjected to a bending test in a direction perpendicular to the ground axis. In addition, a general-purpose biaxially stretched film may remain strong when subjected to a bending test in a direction perpendicular to the ground axis.

[0163] A plastic film satisfying condition A is desirable in that it can suppress the retention of bending properties or fracture after a bending test, regardless of the direction of folding and bending.

[0164] In addition, a plastic film satisfying condition A is desirable in that it can easily suppress microcracks in the plastic film after a bending test.

[0165] In addition, a plastic film satisfying condition A is desirable in that it facilitates good internal folding and bending properties of the plastic film even with high pencil hardness.

[0166] The difference between the maximum value of D1 to D5 and the minimum value of D1 to D5 is preferably 2.0 degrees or more, more preferably 3.0 degrees or more, and even more preferably 3.5 degrees or more.

[0167] In addition, if the difference between the maximum value of D1 to D5 and the minimum value of D1 to D5 is too large, the orientation of the plastic film is reduced, and the mechanical strength tends to decrease. For this reason, it is preferable that the difference be 20.0 degrees or less, more preferable that it be 17.0 degrees or less, more preferable that it be 15.0 degrees or less, more preferable that it be 10.0 degrees or less, more preferable that it be 9.0 degrees or less, and more preferable that it be 8.0 degrees or less.

[0168] In Condition A, the preferred range of the difference between the maximum and minimum values ​​of D1 to D5 is, for example, 1.5° or more and 20.0° or less, 2.0° or more and 20.0° or less, 3.0° or more and 20.0° or less, 3.5° or more and 20.0° or less, 1.5° or more and 17.0° or less, 2.0° or more and 17.0° or less, 3.0° or more and 17.0° or less, 3.5° or more and 17.0° or less, 1.5° or more and 15.0° or less, 2.0° or more and 15.0° or less, 3.0° or more and 15.0° or less, 3.5° or more and 15.0° or less, 1.5° or more and 10.0° or less, 2.0° or more and 10.0° or less, 3.0° or more and 10.0° or less, 3.5° or more Examples include 10.0 degrees or less, 1.5 degrees or more and 9.0 degrees or less, 2.0 degrees or more and 9.0 degrees or less, 3.0 degrees or more and 9.0 degrees or less, 3.5 degrees or more and 9.0 degrees or less, 1.5 degrees or more and 8.0 degrees or less, 2.0 degrees or more and 8.0 degrees or less, 3.0 degrees or more and 8.0 degrees or less, and 3.5 degrees or more and 8.0 degrees or less.

[0169] It is preferable that the plastic film D1 to D5 each be 5 degrees or more and 30 degrees or 60 degrees or more and 85 degrees or less, more preferable that they be 7 degrees or more and 25 degrees or 65 degrees or more and 83 degrees or less, and even more preferable that they be 10 degrees or more and 23 degrees or 67 degrees or more and 80 degrees or less.

[0170] By making D1 to D5 each 5 degrees or more or 85 degrees or less, it is easier to suppress blackout when viewed through polarized sunglasses. In addition, by making D1 to D5 each 30 degrees or less or 60 degrees or more, it is easier to suppress the decrease in mechanical strength due to the reduced orientation of the plastic film.

[0171] Plastic films may be in the form of sheets, for example, or in the form of rolls. In either the sheet or roll form, a sample measuring 50 mm in length × 50 mm in width may be cut from any part of the plastic film, provided that it complies with the following criteria.

[0172] However, if the vertical and horizontal orientations of the sheet and roll can be identified, the sample shall be cut along the identified vertical and horizontal directions. For example, in the case of a roll, the roll's flow direction (MD direction) can be considered the vertical direction, and the roll's width direction (TD direction) can be considered the horizontal direction. If the sheet's flow direction and width direction can be identified, the flow direction can be considered the vertical direction, and the width direction the horizontal direction. In cases where it is difficult to identify the sheet's flow direction and width direction, if the sheet is rectangular or square, the vertical and horizontal orientations can be identified from the four sides constituting the rectangle or square. In cases where it is difficult to identify the sheet's flow direction and width direction, if the sheet has a shape other than a rectangle or square (circle, triangle, etc.), a rectangle or square is drawn such that the area not protruding from the outer frame shape of the sheet is maximized, and the vertical and horizontal orientations can be identified from the sides of the drawn rectangle or square.

[0173] The sample shall be cut out excluding 10mm from the corners of the sheet and roll. In the case of a sheet, for a sample of 50mm in height × 50mm in width, the four corners of the sheet shall be cut out first, followed by the center of the sheet. Then, after cutting the sample from the four corners and the center, if an area exceeding 50mm in height × 50mm in width remains, sampling shall be performed by cutting out the maximum amount of 50mm in height × 50mm in width from the remaining area.

[0174] In addition, when multiple samples of a size of 50 mm in length × 50 mm in width can be taken from a plastic film on a sheet, it is preferable that the proportion of samples satisfying condition A among the multiple samples be 50% or more, more preferable that it be 70% or more, even more preferable that it be 90% or more, and even more preferable that it be 100%. The same applies to other parameters such as in-plane phase difference, thickness direction phase difference, and Re / Rth.

[0175] Plastic films on a roll tend to have various physical properties that change in the width direction, but are almost identical in the flow direction. For this reason, if a sample taken from a specific location in the width direction of the roll satisfies a specific physical property such as condition A, then for locations with the same position in the width direction, it can be assumed that the specific physical property is satisfied throughout the entire flow direction of the roll.

[0176] It is desirable that the plastic film does not develop cracks or fractures after performing the folding test shown in the example 100,000 times (more preferably after performing 300,000 times). In addition, it is desirable that the plastic film, after performing the folding test shown in the example 100,000 times (more preferably after performing 300,000 times), has an angle at which the end of the sample rises from the horizontal stand when the measurement sample is placed on a horizontal stand that is 20 degrees or less, and more preferably 15 degrees or less. An angle of rise from the end of the sample that is 15 degrees or less means that properties caused by folding are unlikely to occur. Furthermore, it is desirable that the plastic film exhibits the aforementioned results (no cracks, fractures, or properties caused by folding; and an angle of rise from the end of the sample after the test that is 20 degrees or less) in either direction, the average of the ground axis direction and the average of the true axis direction.

[0177] In addition, when a uniaxially stretched plastic film is subjected to a folding test, fracture occurs in the stretching direction, while strong bending properties remain in the direction perpendicular to the stretching direction. For this reason, among stretched films, a biaxially stretched plastic film is preferred.

[0178] The thickness of the plastic film is preferably 10㎛ or more, more preferably 15㎛ or more, more preferably 21㎛ or more, more preferably 25㎛ or more, more preferably 30㎛ or more, and the upper limit is preferably 200㎛ or less, more preferably 180㎛ or less, more preferably 150㎛ or less, more preferably 100㎛ or less, more preferably 80㎛ or less, more preferably 60㎛ or less, more preferably 50㎛ or less.

[0179] By making the thickness 10㎛ or more, it is easier to ensure good mechanical strength. In addition, to reduce moisture permeability and extend the lifespan of the polarizer, it is preferable for the thickness to be 21㎛ or more, and more preferable for it to be 30㎛ or more. Furthermore, when the panel size becomes large, such as 50 inches or more, deformation due to the self-weight of the plastic film is likely to occur when the panel is set vertically. To suppress the aforementioned deformation, it is preferable for the thickness of the plastic film to be 30㎛ or more.

[0180] By making the thickness 200㎛ or less, it is easier to make the in-plane phase difference of the plastic film 2500nm or less. In addition, for thinning the panel and image display device, it is preferable that the thickness of the plastic film be 60㎛ or less, and more preferable that it be 50㎛ or less.

[0181] The preferred range of the thickness of the plastic film is, for example, 10㎛ or more and 200㎛ or less, 15㎛ or more and 200㎛ or less, 21㎛ or more and 200㎛ or less, 25㎛ or more and 200㎛ or less, 30㎛ or more and 200㎛ or less, 10㎛ or more and 180㎛ or less, 15㎛ or more and 180㎛ or less, 21㎛ or more and 180㎛ or less, 25㎛ or more and 180㎛ or less, 30㎛ or more and 180㎛ or less, 10㎛ or more and 150㎛ or less, 15㎛ or more and 150㎛ or less, 21㎛ or more and 150㎛ or less, 25㎛ or more and 150㎛ or less, 30㎛ or more and 150㎛ or less, 10㎛ or more and 100㎛ or less, 15㎛ or more and 100㎛ or less, 21㎛ or more and 100㎛ or less, 25㎛ or more and 100㎛ or less, 30㎛ or more 100㎛ or less, 10㎛ or more and 80㎛ or less, 15㎛ or more and 80㎛ or less, 21㎛ or more and 80㎛ or less, 25㎛ or more and 80㎛ or less, 30㎛ or more and 80㎛ or less, 10㎛ or more and 60㎛ or less, 15㎛ or more and 60㎛ or less, 21㎛ or more and 60㎛ or less, 25㎛ or more and 60㎛ or less, 30㎛ or more and 60㎛ or less, 10㎛ or more and 50㎛ or less, 15㎛ or more and 50㎛ or less, 21㎛ or more and 50㎛ or less, 25㎛ or more and 50㎛ or less, 30㎛ or more and 50㎛ or less.

[0182] The plastic film preferably has a haze of 3.0% or less according to JIS K7136:2000, more preferably 2.0% or less, even more preferably 1.5% or less, and even more preferably 1.0% or less.

[0183] The plastic film preferably has a total light transmittance of 80% or more according to JIS K7361-1:1997, more preferably 85% or more, and even more preferably 90% or more.

[0184] <Trembling>

[0185] The plastic film is defined as the average of the yaw rate from the surface of the plastic film to a depth of 20㎛, E 0-20 When defined as, E 0-20It is desirable that this be 1.4㎛ / g or more.

[0186] In this specification, E 0-20 It shall be considered as measured under the following measurement conditions.

[0187] <Measurement Conditions>

[0188] A test solution is placed in a container and formed by mixing pure water, a dispersion, and spherical silica having an average particle size of 4.2 μm within ±8% in a mass ratio of 968:2:30. The test solution in the container is sent to a nozzle. Compressed air is sent into the nozzle, and the test solution is accelerated within the nozzle so that a predetermined amount of the test solution is sprayed perpendicularly to the first surface of the plastic film from the spray hole at the tip of the nozzle, causing the spherical silica in the test solution to collide with the plastic film. The cross-sectional shape of the nozzle is a square of 1 mm × 1 mm, and the distance between the spray hole and the plastic film is 4 mm. In addition, the flow rate of the test solution and the compressed air supplied to the nozzle, the pressure of the compressed air, and the pressure of the test solution within the nozzle are set to predetermined values ​​adjusted by calibration described later.

[0189] After spraying a predetermined amount of the above test solution, the spraying of the above test solution is stopped.

[0190] After stopping the spraying of the above test solution, the cross-sectional profile is measured at the location where the spherical silica in the above test solution collided with the plastic film.

[0191] An operation comprising three steps forming one cycle, wherein the step of spraying a predetermined amount of the test liquid from the above-described nozzle, the step of temporarily stopping the spraying of the test liquid after spraying the predetermined amount of the test liquid, and the step of measuring the cross-sectional profile after temporarily stopping the spraying of the test liquid, is performed until the depth of the cross-sectional profile exceeds 20 μm. Then, for each cycle in which the depth of the cross-sectional profile reaches 20 μm, the turnover rate (μm / g) of the plastic film is calculated. The turnover rate of the plastic film for each cycle in which the depth of the cross-sectional profile reaches 20 μm is averaged, and the E 0-20 Produces.

[0192] Proofreading

[0193] The above test solution is placed in the above container. The above test solution in the above container is sent to the above nozzle. Compressed air is sent into the above nozzle, and the above test solution is accelerated within the above nozzle, so that an arbitrary amount of the above test solution is sprayed vertically from the spray hole at the tip of the above nozzle against an acrylic plate with a thickness of 2 mm, causing spherical silica in the above test solution to collide with the above acrylic plate. The cross-sectional shape of the above nozzle is a square of 1 mm × 1 mm, and the distance between the spray hole and the above acrylic plate is 4 mm.

[0194] After spraying an arbitrary amount of the above test solution, the spraying of the test solution is stopped. After stopping the spraying of the test solution, a cross-sectional profile is measured at the location on the acrylic plate where the spherical silica within the test solution collided.

[0195] The evaporation rate (㎛ / g) of the acrylic plate is calculated by dividing the depth (㎛) of the cross-sectional profile by the above arbitrary amount (g).

[0196] The above acrylic plate is calibrated by adjusting the flow rate of the test solution and the compressed air, the pressure of the compressed air, and the pressure of the test solution inside the nozzle, so that the above acrylic plate’s yield rate is within the above range, with a yield rate of ±5% based on 1.88 (㎛ / g) as the acceptance condition.

[0197] Below, the measurement conditions for the cross-transfer rate and the technical significance of the cross-transfer rate calculated by the above measurement conditions will be explained with reference to Fig. 7. Examples of cross-transfer rate measurement devices such as Fig. 7 include the MSE test device part number “MSE-A203” of Palmeso Co., Ltd.

[0198] In the measurement conditions of the yield rate of the present disclosure, first, a test solution is placed in a container (11) by mixing pure water, a dispersant, and spherical silica having an average particle size of 4.2 μm within ±8% in a mass ratio of 968:2:30. It is preferable to stir the test solution within the container (11).

[0199] The dispersant is not particularly limited as long as it can disperse spherical silica. As an example of a dispersant, Wako Junyaku Kogyo Co., Ltd.'s product name "Demol N" can be cited.

[0200] "Within ±8% of the average particle size of 4.2㎛" means, in other words, that the average particle size is 3.864㎛ or more and 4.536㎛ or less.

[0201] In the measurement conditions for the yield rate of the present specification, the “average particle size of spherical silica” is measured as the volume average value d50 in the particle size distribution measurement by laser light diffraction (so-called “median diameter”).

[0202] In the above-described spherical silica, when the frequency of the particle size exhibiting the maximum frequency in the results of the particle size distribution measurement is standardized to 100, it is preferable that the width of the particle size exhibiting a frequency of 50 is within ±10% based on 4.2 μm. The "width of the particle size exhibiting a frequency of 50" is represented as "XY(μm)" when defined as "X is the particle size exhibiting a frequency of 50 and located in the positive direction compared to the particle size exhibiting a frequency of 100" and "Y is the particle size exhibiting a frequency of 50 and located in the negative direction compared to the particle size exhibiting a frequency of 100". Additionally, in this specification, the "width of the particle size exhibiting a frequency of 50" may be referred to as the "half-value full width of the particle size distribution."

[0203] Spherical silica with an average particle size of 4.2 μm within ±8% can be exemplified by model number “MSE-BS-5-3” designated by Palmeso Co., Ltd. As for spherical silica corresponding to model number “MSE-BS-5-3” designated by Palmeso Co., Ltd., for example, part number “BS5-3” from Potters-Ballotini Co., Ltd.

[0204] The test solution in the container flows into the nozzle (51). The test solution can be sent to the nozzle, for example, through a pipe (21) for the test solution. It is preferable that a flow meter (31) for measuring the flow rate of the test solution be placed between the container (11) and the nozzle (51). The flow rate of the test solution is set to a value adjusted by the above calibration.

[0205] In FIG. 7, the nozzle (51) is positioned within the housing (52) that constitutes the injection unit (50).

[0206] Compressed air is sent into the nozzle (51). The compressed air is sent to the nozzle, for example, through a pipe (22) for compressed air. Within the nozzle, it is preferable that the position where the compressed air is introduced be upstream of the position where the test liquid is introduced. The upstream side refers to the side far from the spray hole of the nozzle.

[0207] It is preferable that a flow meter (32) for measuring the flow rate of compressed air and a pressure gauge (42) for measuring the pressure of compressed air be placed until the compressed air reaches the nozzle (51). The compressed air can be supplied by an air compressor, etc., not shown.

[0208] The flow rate and pressure of the compressed air shall be the values ​​adjusted by the above calibration.

[0209] When compressed air is sent into the nozzle (51), the test liquid is mixed and accelerated by the compressed air. Then, the accelerated test liquid is sprayed from the spray hole at the tip of the nozzle (51) and collides perpendicularly with the plastic film (70). The plastic film is mainly worn away by spherical silica particles in the test liquid.

[0210] It is preferable that a pressure gauge (41) for measuring the pressure of the test liquid inside the nozzle (51) be positioned within the nozzle (51). It is preferable that the pressure gauge (41) be positioned downstream of the location where compressed air is introduced and the location where the test liquid is introduced.

[0211] The pressure of the test liquid inside the nozzle (51) is set to the value adjusted by the above calibration.

[0212] The test liquid sprayed from the spray hole at the tip of the nozzle (51) is mixed with air and sprayed in the form of a mist. Because of this, the impact pressure of the spherical silica particles on the plastic film can be lowered. Therefore, the amount of wear on the plastic film caused by a single spherical silica particle can be suppressed to a small amount. FIG. 8 is an image drawing of the state in which the plastic film (70) is worn by the test liquid containing pure water (A1) and spherical silica (A2) sprayed from the spraying unit (50). In FIG. 8, reference numeral A3 represents air, and reference numeral A4 represents the worn plastic film.

[0213] Furthermore, since the test solution contains water with excellent cooling effects, deformation and deterioration of the plastic film caused by heat during impact can be substantially eliminated. In other words, abnormal wear of the plastic film can be substantially eliminated. Additionally, water plays a role in achieving stable wear by cleaning the surface of the worn plastic film. Moreover, water serves to accelerate spherical silica particles or control the fluid of the test solution.

[0214] In addition, since a vast number of spherical silica particles collide with the plastic film, the influence of subtle differences in the physical properties of individual spherical silica particles can be eliminated.

[0215] In addition, the measurement conditions of the present disclosure specify the factors affecting the amount of wear of the plastic film by setting the flow rate of the test liquid supplied to the nozzle, the flow rate of the compressed air supplied to the nozzle, the pressure of the compressed air supplied to the nozzle, and the pressure of the test liquid inside the nozzle to values ​​adjusted by the above calibration, specifying the cross-sectional shape of the nozzle as a 1mm × 1mm square, and specifying the distance between the injection hole and the plastic film as 4mm. The above distance is the distance indicated by “d” in FIG. 7 and refers to the vertical distance between the injection hole, which is the tip of the nozzle, and the plastic film.

[0216] From the above, the measurement conditions of the present disclosure can be said to be measurement conditions capable of forming a statistically stable wear mark on a plastic film.

[0217] The plastic film (70) can be installed on the sample mounting stand (81) of the measuring device (100). It is preferable to install the plastic film (70) on the sample mounting stand (81) through a support (82), such as a stainless steel plate.

[0218] It is preferable that the test liquid sprayed onto the plastic film (70) be recovered from the receiver (12) and returned to the container (11) through the return pipe (23). It is preferable that a return pump (24) be placed between the receiver (12) and the return pipe (23).

[0219] Under the measurement conditions of the present disclosure, it is required to spray a predetermined amount of test solution, stop the spraying of the test solution, and, after stopping the spraying of the test solution, measure the cross-sectional profile of the plastic film at the location where spherical silica in the test solution collided.

[0220] The cross-sectional profile refers to the cross-sectional shape of a plastic film abraded by a test solution. The plastic film is primarily abraded by spherical silica particles in the test solution.

[0221] The cross-sectional profile can be measured by a cross-sectional profile acquisition unit (60), such as a stylus-type surface shape measuring device and a laser interference-type surface shape measuring device. Additionally, the cross-sectional profile acquisition unit (60) is typically positioned away from the plastic film (70) when the test liquid is sprayed. For this reason, it is desirable that at least one of the plastic film (70) and the cross-sectional profile acquisition unit (60) be movable.

[0222] The MSE test device part number "MSE-A203" of Palmeso Co., Ltd. has a stylus-type measuring means for cross-sectional profiles.

[0223] In addition, under the measurement conditions of the present disclosure, an operation comprising three steps forming one cycle, the step of spraying a predetermined amount of test liquid from a nozzle, the step of stopping the spraying of the test liquid after spraying a predetermined amount of test liquid, and the step of measuring the cross-sectional profile after stopping the spraying of the test liquid, is performed until the depth of the cross-sectional profile exceeds 20 μm.

[0224] By performing the above operation, the turnover rate of the plastic film in each cycle can be measured, and furthermore, the variation in the turnover rate of the plastic film can be calculated.

[0225] The above cycle may continue even after the depth of the cross-sectional profile exceeds 20 μm, but it is preferable to terminate it when the depth of the cross-sectional profile exceeds 20 μm. The reason for measuring up to a depth of "20 μm from the surface of the plastic film" is that the physical properties of the plastic film tend to fluctuate near the surface, while becoming more stable as they move inward.

[0226] In this specification, the yield rate of each cycle can be calculated by dividing the depth (μm) of the cross-sectional profile progressed in each cycle by the injection amount (g) of the test liquid in each cycle. The depth (μm) of the cross-sectional profile of each cycle is defined as the depth of the highest depth position of the cross-sectional profile of each cycle.

[0227] The amount of test solution injected in each cycle is, in principle, a "definite amount," but slight variations in each cycle are acceptable.

[0228] The amount of test solution sprayed in each cycle is not specifically limited, but the lower limit is preferably 0.5g or more, more preferably 1.0g or more, and the upper limit is preferably 3.0g or less, more preferably 2.0g or less.

[0229] Under the measurement conditions of the present disclosure, the turnover rate (μm / g) is calculated for each cycle in which the depth of the cross-sectional profile is up to 20 μm. Then, the turnover rates of each cycle in which the depth of the cross-sectional profile is up to 20 μm are averaged, and E 0-20 Produces.

[0230] The above cycle is performed until the depth of the cross-sectional profile exceeds 20㎛, but the data of the cycle in which the depth of the cross-sectional profile exceeds 20㎛ is E 0-20 It will be excluded from the data that produces.

[0231] Generally, plastic films are more prone to scratches when flexible and less prone to scratches when rigid. The inventors considered using values ​​obtained from an evaluation including the depth direction using a picotenter (martens hardness, indentation hardness, elastic recovery work amount, etc.) as an indicator of pencil hardness. However, there were cases where the aforementioned parameters, such as martens hardness, indentation hardness, and elastic recovery work amount, could not be used as an indicator of pencil hardness.

[0232] In addition, plastic films tend to increase in strength when stretched. Specifically, uniaxially stretched plastic films tend to have better pencil hardness than unstretched plastic films, and biaxially stretched plastic films tend to have better pencil hardness than uniaxially stretched plastic films. However, there were cases where the pencil hardness was insufficient even with biaxially stretched plastic films.

[0233] The inventors examined the tillage rate as an indicator of the pencil hardness of a plastic film. As described above, since a plastic film is more prone to scratches when flexible and less prone to scratches when rigid, it is believed that a lower tillage rate can improve pencil hardness. However, conversely, the inventors [considered] the tillage rate (E 0-20It was discovered that by increasing the value of ) to 1.4 μm / g or more, the plastic film can have good pencil hardness. In addition, the inventors discovered that the yaw rate of the plastic film is more likely to show a larger value in a biaxially stretched plastic film than in a uniaxially stretched plastic film, and that the quality of the pencil hardness in a biaxially stretched plastic film can be determined by the yaw rate.

[0234] The reason why the yaw rate of a plastic film is related to pencil hardness is thought to be as follows.

[0235] As described above, under the measurement conditions of the present disclosure, a test solution containing water and spherical silica is mixed with air and sprayed in the form of a mist. For this reason, the impact pressure of spherical silica particles on the plastic film is suppressed to a low level. Therefore, it is thought that when the plastic film is flexible, the stress caused by the impact of spherical silica on the plastic film is easily dispersed, making the plastic film less susceptible to wear and thus lowering the erosion rate. On the other hand, when the plastic film is rigid, the stress caused by the impact of spherical silica on the plastic film is difficult to disperse, making the plastic film more susceptible to wear and thus higher the erosion rate.

[0236] In addition, differences in the yield of biaxially stretched plastic films are thought to be caused by differences in the elongation state of molecular chains and differences in the degree of molecular orientation. For example, in principle, molecules in a biaxially stretched plastic film are extended within the plane, but there are cases where molecules are not locally extended within the plane. It is thought that if the proportion of molecules that are not locally extended within the plane increases in this way, the biaxially stretched plastic film becomes locally flexible, and the yield decreases.

[0237] In addition, it is thought that even biaxially stretched plastic films with equivalent in-plane phase difference may exhibit different in-plane phase differences due to differences in local molecular orientation. Conversely, even biaxially stretched plastic films with equivalent in-plane phase difference may exhibit different in-plane phase differences due to differences in the ratio of the stretching ratio in the flow direction to the stretching ratio in the width direction.

[0238] To improve the pencil hardness of the plastic film, E 0-20 It is preferable that the amount be 1.4㎛ / g or more, more preferable that it be 1.6㎛ / g or more, more preferable that it be 1.8㎛ / g or more, more preferable that it be 1.9㎛ / g or more, and more preferable that it be 2.0㎛ / g or more.

[0239] As mentioned above, it is thought that if the proportion of molecules that are not locally sufficiently stretched within the plane increases, the turnover rate decreases. In other words, it is thought that if the turnover rate is high, the proportion of molecules that are not locally sufficiently stretched within the plane decreases. For this reason, E 0-20 By making the amount 1.4㎛ / g or more, it is possible to easily suppress wrinkles from forming on the plastic film under high temperature conditions.

[0240] E 0-20 In order to make it difficult for the plastic film to crack, it is preferable that the amount be 3.0㎛ / g or less, more preferable that it be 2.5㎛ / g or less, and even more preferable that it be 2.2㎛ / g or less.

[0241] E 0-20 Even if the value of is the same, the characteristics of the plastic film may differ if the in-plane phase difference, etc., are different. For example, E 0-20 Even if the value is the same, if the in-plane phase difference exceeds 1450 nm, when the plastic film is folded, the plastic film may retain bending properties or the plastic film may break.

[0242] Also, E0-20 For plastic films with a hardness of less than 1.4㎛ / g, even if a hardened film with high hardness is formed on the plastic film, the pencil hardness of the hardened film may not be good due to the lack of hardness of the plastic film.

[0243] E 0-20 Embodiments of the preferred numerical range include, for example, 1.4 µm / g or more and 3.0 µm / g or less, 1.4 µm / g or more and 2.5 µm / g or less, 1.4 µm / g or more and 2.2 µm / g or less, 1.5 µm / g or more and 3.0 µm / g or less, 1.5 µm / g or more and 2.5 µm / g or less, 1.5 µm / g or more and 2.2 µm / g or less, 1.6 µm / g or more and 3.0 µm / g or less, 1.6 µm / g or more and 2.5 µm / g or less, 1.6 µm / g or more and 2.2 µm / g or less, 1.8 µm / g or more and 3.0 µm / g or less, 1.8 µm / g or less and 2.5 µm / g or less, 1.8 µm / g or more and 2.2 µm / g or less, 1.9 µm / g or more and 3.0 µm / g or less, and 1.9 µm / g or more. Examples include 2.5㎛ / g or less, 1.9㎛ / g or more and 2.2㎛ / g or less, 2.0㎛ / g or more and 3.0㎛ / g or less, 2.0㎛ / g or more and 2.5㎛ / g or less, and 2.0㎛ / g or more and 2.2㎛ / g or less.

[0244] The plastic film has two planes, a front surface and a back surface. The plastic film has E measured on one plane side 0-20 and E measured on the other plane side 0-20 It is desirable that all of them are the values ​​described above. For a typical plastic film, the yield measured on one planar side and the yield measured on the other planar side are approximately the same.

[0245] Before measuring the above-mentioned yield, the above calibration is performed.

[0246] For example, correction can be performed as follows.

[0247] Proofreading

[0248] The above test solution is placed in the above container. The above test solution in the above container is sent to the above nozzle. Compressed air is sent into the above nozzle, and the above test solution is accelerated within the above nozzle, so that an arbitrary amount of the above test solution is sprayed vertically from the spray hole at the tip of the above nozzle against an acrylic plate with a thickness of 2 mm, causing spherical silica in the above test solution to collide with the above acrylic plate. The cross-sectional shape of the above nozzle is a square of 1 mm × 1 mm, and the distance between the spray hole and the above acrylic plate is 4 mm.

[0249] After spraying an arbitrary amount of the above test solution, the spraying of the test solution is stopped. After stopping the spraying of the test solution, a cross-sectional profile is measured at the location on the acrylic plate where the spherical silica within the test solution collided.

[0250] The evaporation rate (㎛ / g) of the acrylic plate is calculated by dividing the depth (㎛) of the cross-sectional profile by the above arbitrary amount (g).

[0251] The above acrylic plate is calibrated by adjusting the flow rate of the test solution and the compressed air, the pressure of the compressed air, and the pressure of the test solution inside the nozzle, so that the above acrylic plate’s yield rate is within the above range, with a yield rate of ±5% based on 1.88 (㎛ / g) as the acceptance condition.

[0252] The test solution used for calibration shall be the same as the test solution used under the measurement conditions to be performed later.

[0253] In addition, the measuring device used for calibration shall be the same as the measuring device used under the measurement conditions to be performed later.

[0254] The difference between the calibration and the measurement conditions that follow is, for example, that in the calibration, a standard sample, a 2mm thick acrylic plate, is used as the sample, whereas in the measurement conditions, a plastic film is used as the sample.

[0255] It is preferable that the standard sample, a 2mm thick acrylic plate, be a polymethyl methacrylate plate (PMMA plate). In addition, it is preferable that the standard sample, a 2mm thick acrylic plate, has an AcE value of 1.786 μm / g or higher and 1.974 μm / g or lower when the average of the dielectric constant of the acrylic plate measured under measurement condition A below is defined as AcE. Furthermore, as the spherical silica under measurement condition A below, the model number "MSE-BS-5-3" designated by Palmeso Co., Ltd. may be used. As for the spherical silica corresponding to the model number "MSE-BS-5-3" designated by Palmeso Co., Ltd., for example, the part number "BS5-3" from Potters-Ballotini Co., Ltd. may be used.

[0256] <Measurement Condition A>

[0257] A test solution is placed in a container and prepared by mixing pure water, a dispersant, and spherical silica with an average particle size of 4.2 μm within ±8% in a mass ratio of 968:2:30. The test solution in the container is sent to a nozzle. Compressed air is sent into the nozzle to accelerate the test solution within the nozzle, and a predetermined amount of the test solution is sprayed perpendicularly toward the acrylic plate from the spray hole at the tip of the nozzle, causing the spherical silica in the test solution to collide with the acrylic plate. The cross-sectional shape of the nozzle is a square of 1 mm × 1 mm, and the distance between the spray hole and the acrylic plate is 4 mm. In addition, the flow rate of the test liquid and the compressed air supplied to the nozzle, the pressure of the compressed air, and the pressure of the test liquid inside the nozzle are such that the flow rate of the test liquid is 100 ml / min or more and 150 ml / min or less, the flow rate of the compressed air is 4.96 L / min or more and 7.44 L / min or less, the pressure of the compressed air is 0.184 MPa or more and 0.277 MPa or less, and the pressure of the test liquid inside the nozzle is 0.169 MPa or more and 0.254 MPa or less.

[0258] After spraying 4g of the above test solution, stop spraying the above test solution for a while.

[0259] After stopping the spraying of the above test solution, the cross-sectional profile is measured at the location where the spherical silica in the above test solution collided with the acrylic plate.

[0260] Then, the AcE (unit is "㎛ / g"), which is the efficiency of the acrylic plate, is calculated by dividing the depth (㎛) of the cross-sectional profile by the amount of test solution sprayed (4g).

[0261] In the calibration, the flow rate of the test solution and the compressed air, the pressure of the compressed air, and the pressure of the test solution inside the nozzle are adjusted so that the flow rate of the acrylic plate is within the above range, with the acceptance condition being a range of ±5% based on 1.88 (㎛ / g).

[0262] "The expression 'transfer rate is ±5% based on 1.88 (㎛ / g)' means, in other words, that the transfer rate is 1.786 (㎛ / g) or higher and 1.974 (㎛ / g) or lower.

[0263] <σ 0-20 / E 0-20 >

[0264] The plastic film comprises a variation in the yield rate calculated from the yield rate from the surface of the plastic film to a depth of 20 μm, σ 0-20 When defined as, σ 0-20 / E 0-20 It is desirable that this be 0.100 or less.

[0265] In this specification, σ 0-20 It can be calculated from the turnover rate of each cycle in which the depth of the cross-sectional profile is up to 20㎛ under the above measurement conditions.

[0266] σ 0-20 / E 0-20 represents the coefficient of variation of the refractory rate, and σ 0-20 / E 0-20 This small value implies that the tillage rate is unlikely to fluctuate in the thickness direction of the plastic film. σ 0-20 / E 0-20 By making it 0.100 or less, the yield in the thickness direction is stabilized, and it is easier to make the pencil hardness better.

[0267] σ 0-20 / E 0-20The upper limit is more preferably 0.080 or less, even more preferably 0.070 or less, even more preferably 0.060 or less, and even more preferably 0.055 or less.

[0268] σ 0-20 / E 0-20 The lower limit of is not specifically restricted, but is typically greater than 0, preferably 0.020 or higher, and more preferably 0.035 or higher. In addition, σ 0-20 / E 0-20 When the value of is low, the elongation of the plastic film may be weak. Plastic films with weak elongation tend to have poor solvent resistance, be prone to breakage, and have low stability against heat and humidity. For this reason, σ 0-20 / E 0-20 It is desirable for it to be 0.020 or higher.

[0269] σ 0-20 / E 0-20 Examples of preferred numerical ranges include greater than 0 and less than or equal to 0.100, greater than 0 and less than or equal to 0.080, greater than 0 and less than or equal to 0.070, greater than 0 and less than or equal to 0.060, greater than 0 and less than or equal to 0.055, greater than or equal to 0.020 and less than or equal to 0.100, greater than or equal to 0.020 and less than or equal to 0.080, greater than or equal to 0.020 and less than or equal to 0.060, greater than or equal to 0.020 and less than or equal to 0.055, greater than or equal to 0.035 and less than or equal to 0.100, greater than or equal to 0.035 and less than or equal to 0.080, greater than or equal to 0.035 and less than or equal to 0.070, greater than or equal to 0.035 and less than or equal to 0.060, and greater than or equal to 0.035 and less than or equal to 0.055.

[0270] The plastic film has two planes, a front surface and a back surface. The plastic film has σ measured on one plane side 0-20 / E 0-20 and σ measured on the other plane side 0-20 / E 0-20 It is desirable that all of them are the values ​​mentioned above.

[0271] The pencil hardness of the plastic film is preferably HB or higher, and more preferably F or higher.

[0272] If the pencil hardness of the plastic film is too high, the in-plane phase difference of the plastic film tends to increase. For this reason, the pencil hardness of the plastic film is preferably 2H or lower.

[0273] In the present specification, pencil hardness is measured and determined in the order of (1) to (6) below.

[0274] (1) Make a sample by cutting a plastic film to a size of 5cm × 10cm.

[0275] (2) Heat the plastic film at 100°C for 10 minutes. After heating, leave the plastic film in an environment at 24°C with a relative humidity of 40% or more and 60% or less for 30 minutes or more and 60 minutes or less.

[0276] (3) For the plastic film, the pencil hardness is measured in accordance with the scratching hardness (pencil method) of JIS K 5600-5-4:1999. Specifically, a pencil having a predetermined hardness is placed against the surface of the plastic film at an angle of 45° and a load is applied to the plastic film by moving it at a speed of 3.0 mm / sec with a load of 100 g.

[0277] (4) After applying a load to the plastic film, heat the sample again at 100°C for 10 minutes.

[0278] (5) Immediately after reheating, the defects in the plastic film are evaluated by visual inspection. The environment for visual inspection is 24°C and relative humidity is 40% or more and 60% or less.

[0279] (6) Perform the operations of (1) to (5) five times. Then, among the pencils that do not have any defects in at least four of the five times, the hardest one is set as the pencil hardness of the plastic film being evaluated.

[0280] In the above method for measuring and determining pencil hardness, if no scratches occur in 4 out of 5 times at hardness B and no scratches occur in 3 out of 5 times at hardness F, it is determined to be hardness B.

[0281] When a plastic film has a ground axis and a leading axis, it is preferable that the pencil hardness be B or higher in either the ground axis direction or the leading axis direction. The ground axis of the plastic film is the direction with the highest refractive index within the plane of the plastic film. The leading axis of the plastic film is the direction within the plane of the plastic film that is orthogonal to the ground axis.

[0282] The laminated structure of the plastic film can include a single-layer structure and a multi-layer structure. Among these, a single-layer structure is preferred.

[0283] To ensure good mechanical strength while suppressing rainbow non-uniformity, it is preferable for the plastic film to be a biaxially stretched plastic film with a small in-plane phase difference. Furthermore, to minimize the in-plane phase difference of the stretched plastic film, it is desirable to achieve uniform elongation in both the flow direction and the width direction. Additionally, to keep the transduction rate of the plastic film within the above range, it is desirable to elongate the molecules uniformly within the plane of the plastic film. Therefore, to achieve the average in-plane phase difference and transduction rate of the plastic film within the aforementioned range, control of stretching is essential. Regarding stretching control, while fine stretching control is difficult in a multilayer structure due to differences in the physical properties of each layer, a single-layer structure is preferable in that it facilitates fine stretching control.

[0284] Examples of plastic film preparation

[0285] Hereinafter, regarding examples of manufacturing plastic films, a biaxially stretched plastic film is described as a representative example.

[0286] A biaxially stretched plastic film can be obtained by stretching a resin layer containing components that constitute the plastic film. Methods of stretching include sequential biaxial stretching and simultaneous biaxial stretching.

[0287] -Sequential 2-axis stretching-

[0288] In sequential biaxial stretching, after stretching the casting film in the flow direction, stretching in the width direction of the film is performed.

[0289] Stretching in the flow direction is typically performed by the difference in peripheral speed of a pair of stretching rolls. Stretching in the flow direction may be performed in a single stage, but it may also be performed in multiple stages using a plurality of pairs of stretching rolls. In order to suppress excessive fluctuations in optical properties such as in-plane phase difference, it is desirable to place a plurality of nip rolls close to the stretching rolls. The stretching ratio in the flow direction is typically 2 times or more and 15 times or less, and in order to suppress excessive fluctuations in optical properties such as in-plane phase difference, it is preferably 2 times or more and 7 times or less, more preferably 3 times or more and 5 times or less, and even more preferably 3 times or more and 4 times or less.

[0290] To suppress excessive fluctuations in optical properties such as in-plane phase difference, the stretching temperature is preferably above the glass transition temperature of the resin and below the glass transition temperature plus 100°C. In the case of PET, it is preferably above 70°C and below 120°C, more preferably above 80°C and below 110°C, and even more preferably above 95°C and below 110°C. The above stretching temperature refers to the set temperature of the device. Furthermore, even if the set temperature of the device is set within the above range, time is required for the temperature to stabilize. For this reason, it is preferable to set the temperature within the above range and manufacture the plastic film after the temperature has stabilized further. In this specification, the set temperature of the device is described at multiple locations. As with the above, it is also preferable to manufacture the plastic film after the temperature has stabilized at the set temperatures at other locations.

[0291] Regarding the stretching temperature, if the film is heated rapidly or the stretching section at low temperature is shortened, the average value of the in-plane phase difference tends to decrease. On the other hand, if the film is heated slowly or the stretching section at low temperature is lengthened, the orientation is improved, and the average value of the in-plane phase difference increases, and the variation of the ground axis tends to decrease.

[0292] When heating during stretching, it is preferable to use a heater that generates turbulence. By heating with air containing turbulence, a temperature difference is created in a minute region within the film surface, and this temperature difference causes a minute misalignment in the orientation axis, making it easier to satisfy Condition A. As the plastic film satisfies Condition A, the Σ of the optical film T It can be made easier to set the above range.

[0293] Furthermore, regarding stretching in the flow direction, shortening the stretching time tends to decrease the yield, while lengthening the stretching time tends to increase the yield. This is thought to be because, when the stretching time is short, it is difficult for molecules to stretch evenly within the surface of the plastic film, whereas when the stretching time is long, it becomes easier for molecules to stretch evenly within the surface of the plastic film. That is, E 0-20 In order to make 1.4㎛ / g or higher, it is desirable to increase the stretching time. In addition, by appropriately increasing the stretching ratio to the extent that the physical properties do not change and increasing the stretching time, more E 0-20 It can be made easier to make it 1.4㎛ / g or higher.

[0294] Functions such as slipperiness, adhesion, and antistatic properties may be imparted to the film stretched in the flow direction by inline coating or offline coating. Prior to inline coating or offline coating, surface treatments such as corona treatment, frame treatment, or plasma treatment may be performed as necessary.

[0295] In this specification, layers formed by inline coating or offline coating are not counted as the number of layers constituting the plastic film.

[0296] Stretching in the width direction is typically performed using a tenter method, by conveying the film while gripping both ends with clips. The stretching ratio in the width direction is typically 2 to 15 times, and to suppress excessive fluctuations in optical properties such as in-plane phase difference, it is preferably 2 to 5 times, more preferably 3 to 5 times, and even more preferably 3 to 4.5 times. It is desirable to make the width stretching ratio higher than the longitudinal stretching ratio.

[0297] The stretching temperature is preferably above the glass transition temperature of the resin and below the glass transition temperature plus 110°C, and it is desirable for the temperature to increase as it moves from upstream to downstream. The above stretching temperature refers to the set temperature of the device. The upstream side is the side closer to the point where stretching in the width direction begins. The downstream side is the side closer to the point where stretching in the width direction ends. Specifically, when the transverse stretching section is divided into two based on length, the difference between the upstream temperature and the downstream temperature is preferably 20°C or more, more preferably 30°C or more, even more preferably 35°C or more, and even more preferably 40°C or more. In the case of PET, the stretching temperature of the first stage is preferably 80°C or more and 120°C or less, more preferably 90°C or more and 110°C or less, and even more preferably 95°C or more and 105°C or less. By dividing the stretching section in the width direction into two and providing a difference in stretching temperature between the first and second stages, the surface temperature of the film during the first stage of stretching and the surface temperature of the film during the second stage of stretching can be controlled to different temperatures. Because of this, orientation and orientation crystallization do not proceed too far in each stretching stage, and the plastic film does not become brittle, so it is possible to easily improve the pencil hardness.

[0298] As described above, to impart flatness and dimensional stability to the plastic film sequentially biaxially stretched, it is desirable to perform heat treatment in a tenter at a temperature above the stretching temperature and below the melting point. The heat treatment temperature refers to the set temperature of the device. Specifically, in the case of PET, it is desirable to perform heat fixation in a range of 140°C to 240°C, and more desirable to perform heat fixation in a range of 200°C to 250°C. To suppress excessive fluctuations in optical properties such as in-plane phase difference, it is desirable to perform stretching of 1% to 10% throughout the heat treatment.

[0299] After heat-treating the plastic film, it is wound after slow cooling to room temperature. If necessary, relaxation treatment, etc., may be used in combination during heat treatment and slow cooling. To suppress excessive fluctuations in optical properties such as in-plane phase difference, the relaxation rate during heat treatment is preferably 0.5% or more and 5% or less, more preferably 0.5% or more and 3% or less, even more preferably 0.8% or more and 2.5% or less, and even more preferably 1% or more and 2% or less. To suppress excessive fluctuations in optical properties such as in-plane phase difference, the relaxation rate during slow cooling is preferably 0.5% or more and 3% or less, more preferably 0.5% or more and 2% or less, even more preferably 0.5% or more and 1.5% or less, and even more preferably 0.5% or more and 1.0% or less. In order to ensure good flatness, the temperature during slow cooling is preferably 80°C or higher and 140°C or lower, more preferably 90°C or higher and 130°C or lower, even more preferably 100°C or higher and 130°C or lower, and even more preferably 100°C or higher and 120°C or lower. The above temperature during slow cooling refers to the set temperature of the device.

[0300] -Simultaneous Biaxial Stretching-

[0301] Simultaneous biaxial stretching involves guiding a casting film to a simultaneous biaxial tenter, gripping both ends of the film with clips, and conveying it to stretch it simultaneously and / or in stages in the flow direction and width direction. As for the simultaneous biaxial stretching machine, there are pantograph type, screw type, drive motor type, and linear motor type, but a drive motor type or linear motor type is preferred as it allows the stretching ratio to be changed arbitrarily and relaxation treatment to be performed at any location.

[0302] The magnification ratio of simultaneous biaxial stretching is typically 6 times or more and 50 times or less as an area magnification ratio. In order to suppress excessive fluctuations in optical properties such as in-plane phase difference, the area magnification ratio is preferably 8 times or more and 30 times or less, more preferably 9 times or more and 25 times or less, even more preferably 9 times or more and 20 times or less, and even more preferably 10 times or more and 15 times or less. In simultaneous biaxial stretching, it is desirable to adjust the area magnification ratio so that the stretching magnification ratio in the flow direction and the stretching magnification ratio in the width direction are within the range of 2 times or more and 15 times or less.

[0303] In the case of simultaneous biaxial stretching, in order to suppress orientation differences within the plane, it is desirable to make the stretching ratio in the flow direction and the width direction nearly the same, and also to make the stretching speed in the flow direction and the width direction nearly the same.

[0304] To suppress excessive fluctuations in optical properties such as in-plane phase difference, the stretching temperature for simultaneous biaxial stretching is preferably above the glass transition temperature of the resin and below the glass transition temperature + 120°C. In the case of PET, it is preferably above 80°C and below 160°C, more preferably above 90°C and below 150°C, and even more preferably above 100°C and below 140°C. The above stretching temperature refers to the set temperature of the device.

[0305] It is desirable to continuously perform heat treatment on the simultaneously biaxially stretched film at a temperature above the stretching temperature and below the melting point in a heat fixing chamber within a tenter to impart flatness and dimensional stability. The temperature of the heat treatment refers to the set temperature of the device. The conditions for the heat treatment are the same as the conditions for heat treatment after sequential biaxial stretching.

[0306] <Low Refractive Index Layer>

[0307] The low refractive index layer serves to enhance the anti-reflective properties of the optical film and facilitate the suppression of rainbow non-uniformity when viewed with the naked eye. It is preferable that the low refractive index layer be located on the surface of the optical film having the low refractive index layer relative to the plastic film. Within a range that does not impair the effects of the optical film of the present disclosure, functional layers such as an antifouling layer and an antistatic layer may be provided on the low refractive index layer.

[0308] Light directed from the interior of an image display device toward the viewer is linearly polarized when it passes through a polarizer, but after passing through a plastic film, the polarization state of the linearly polarized light is disrupted, resulting in light mixed with P-waves and S-waves. Furthermore, since there is a difference between the reflectance of P-waves and S-waves and the difference in reflectance is wavelength-dependent, it is believed that rainbow non-uniformity is visible to the naked eye. Here, it is believed that if a low-refractive-index layer is provided on the plastic film, the aforementioned difference in reflectance can be reduced, making it easier to suppress rainbow non-uniformity.

[0309] However, as described above, when the reflectance of the optical film having a low refractive index layer is lowered, it becomes difficult to achieve good uniformity of color when viewed at an angle. This is thought to be due to interference of reflected light from the optical film having a low refractive index layer.

[0310] For this reason, when the average refractive index of the low-refractive-index layer is defined as n1 and the average refractive index of the layer adjacent to the low-refractive-index layer is defined as n2, it is desirable that n2 / n1 be less than 1.23. By making n2 / n1 less than 1.23, interference of reflected light is suppressed, making it easier to ensure good uniformity of color in oblique viewing.

[0311] It is more preferable that n2 / n1 be 1.20 or less, more preferable that it be 1.15 or less, and even more preferable that it be 1.13 or less. In particular, by making n2 / n1 1.05 or more and 1.15 or less, it is easier to suppress the wavelength dependence of the reflectance. In addition, by making n2 / n1 1.05 or more and 1.15 or less, it is easier to suppress the brittleness of the low refractive index layer.

[0312] If n2 / n1 is made too small, the luminous reflectance Y value of the optical film tends to increase. For this reason, it is preferable that n2 / n1 be 1.05 or higher, and more preferable that it be 1.07 or higher.

[0313] Desirable ranges for n2 / n1 include 1.05 or more and less than 1.23, 1.05 or more and less than 1.20, 1.05 or more and less than 1.15, 1.05 or more and less than 1.13, 1.07 or more and less than 1.23, 1.07 or more and less than 1.20, 1.07 or more and less than 1.15, 1.07 or more and less than 1.13, etc.

[0314] In order to make it easier to keep n2 / n1 within the above range, it is desirable to lower the value of n2. For this reason, the layer adjacent to the low refractive index layer is preferably a plastic film or a hard coat layer, and a hard coat layer is more preferable.

[0315] The average refractive index of each layer can be measured or calculated by the following method after determining, for example, whether the thickness of each layer exceeds 780 nm or is less than or equal to 780 nm from a cross-sectional photograph of the laminate.

[0316] -Average refractive index of layers exceeding 780 nm in thickness-

[0317] The average refractive index of a layer with a thickness exceeding 780 nm is determined by considering the refractive index of the binder component of the layer as the refractive index of the layer. The average refractive index of a layer with a thickness exceeding 780 nm can be calculated, for example, by the Becke method described below. It is preferable to calculate the refractive indices of the plastic film, the hard coat layer, and the anti-glare layer using the Becke method.

[0318] The Beké method

[0319] A method of cutting away the layer to be measured for refractive index with a cutter or the like, preparing a sample in which the binder component is in a powder state, and calculating by the Becke method according to Method B of JIS K7142:2008 (for powder or granular transparent materials).

[0320] -Average refractive index of layers with a thickness of 780 nm or less-

[0321] It is difficult to extract binder components from layers with a thickness of 780 nm or less. For this reason, the average refractive index of layers with a thickness of 780 nm or less can be calculated by, for example, fabricating a laminate 1 having layers with a thickness of 780 nm or less and following the steps (Y1) and (Y2) below. It is preferable to calculate the refractive index n1 of the low refractive index layer in the steps (Y1) and (Y2) below.

[0322] (Y1) Among the layers constituting laminate 1, the average refractive index of the layer with a thickness exceeding 780 nm is calculated using the Becke method described above. Additionally, from a cross-sectional photograph of the laminate, the thickness of the layer with a thickness exceeding 780 nm and the thickness of the layer with a thickness of 780 nm or less are calculated.

[0323] (Y2) Using the information on the average refractive index and thickness of the layer with a thickness exceeding 780 nm and the thickness information of the layer with a thickness of 780 nm or less, calculated in (Y1) above, the average refractive index of the layer with a thickness of 780 nm or less is calculated by the following fitting method. It is preferable that the average refractive index n1 of the low refractive index layer be within the range described below.

[0324] Fitting Method

[0325] A method calculated by fitting the reflection spectrum measured by a reflectometer and the reflection spectrum calculated from an optical model of a multilayer thin film using Fresnel coefficients.

[0326] It is preferable that the average refractive index n2 of a layer adjacent to a low refractive index layer is greater than the average refractive index n1 of the low refractive index layer. It is preferable that n2 be a range in which n1 is within the range described below, and n2 / n1 satisfies the above range. It is preferable that n2 be 1.42 or higher and 1.60 or lower, and more preferable that it be 1.45 or higher and 1.58 or lower.

[0327] The refractive index of the low refractive index layer is preferably 1.45 or less, more preferably 1.43 or less, and more preferably 1.40 or less from the perspective of suppressing rainbow non-uniformity.

[0328] If the refractive index of the low-refractive-index layer is made too low, the Σ of the optical film T The value of tends to be difficult to satisfy the above range. For this reason, the refractive index of the low refractive index layer is preferably 1.30 or higher, more preferably 1.33 or higher, and even more preferably 1.35 or higher.

[0329] The thickness of the low refractive index layer is preferably 60 nm or more and 200 nm or less, more preferably 80 nm or more and 120 nm or less, even more preferably 85 nm or more and 110 nm or less, and even more preferably 90 nm or more and 105 nm or less. The thickness of the low refractive index layer is preferably larger than the average particle size of the low refractive index particles, such as hollow particles.

[0330] Methods for forming a low-refractive-index layer can be broadly classified into wet methods and dry methods. Examples of wet methods include forming by the sol-gel method using metal alkoxides, forming by coating with a low-refractive-index resin such as fluoropolymer, and forming by coating with a coating solution for forming a low-refractive-index layer containing low-refractive-index particles in a resin composition. Examples of dry methods include selecting particles having a desired refractive index from among the low-refractive-index particles described later and forming by physical vapor phase growth or chemical vapor phase growth.

[0331] The wet method is superior to the dry method in terms of production efficiency, suppression of oblique reflection colors, and chemical resistance. Among wet methods, it is preferable to form the layer using a coating solution for forming a low-refractive-index layer containing low-refractive-index particles in a binder resin composition to achieve adhesion, water resistance, scratch resistance, and a low refractive index.

[0332] Examples of low-refractive-index particles include hollow particles and non-hollow particles. As low-refractive-index particles, it is acceptable to include only one of hollow particles or non-hollow particles, but it is preferable to include both. By including both hollow particles and non-hollow particles, it is possible to appropriately lower the refractive index of the low-refractive-index layer while suppressing a decrease in film strength. On the other hand, if only hollow particles are included, the refractive index of the low-refractive-index layer is excessively lowered, and the Σ of the optical film T It becomes difficult to satisfy the above range.

[0333] The material of the hollow and non-hollow particles may be any of inorganic compounds such as silica and magnesium fluoride, or organic compounds, but silica is preferred for low refractive index and strength. The following description focuses on hollow silica particles and non-hollow silica particles.

[0334] Hollow silica particles refer to particles that have an outer layer made of silica, with a cavity inside the particle surrounded by the outer layer containing air. Hollow silica particles are particles in which the refractive index decreases in proportion to the gas content relative to the original silica refractive index due to the inclusion of air. Non-hollow silica particles are particles that do not have a cavity inside, unlike hollow silica particles. Non-hollow silica particles are, for example, solid silica particles.

[0335] The shape of hollow silica particles and non-hollow silica particles is not particularly limited and may be approximately spherical, such as a perfect sphere, a spheroid, or a polyhedral shape that approximates a sphere. Among these, considering scratch resistance, it is preferable to have a perfect sphere, a spheroid, or an approximately spherical shape.

[0336] Hollow silica particles, because they contain air, play a role in lowering the refractive index of the entire low-refractive-index layer. By using large-diameter hollow silica particles with a higher proportion of air, the refractive index of the low-refractive-index layer can be further lowered. On the other hand, hollow silica particles tend to have lower mechanical strength. In particular, when large-diameter hollow silica particles with a higher proportion of air are used, the scratch resistance of the low-refractive-index layer tends to decrease.

[0337] Non-hollow silica particles play a role in improving the scratch resistance of the low refractive index layer by being dispersed in the binder resin.

[0338] In order to contain hollow silica particles and non-hollow silica particles in a high concentration within the binder resin and to uniformly disperse the particles in the film thickness direction within the resin, it is important to bring the hollow silica particles close together and to allow non-hollow particles to be placed between the hollow silica particles by setting the average particle size of the hollow silica particles and the average particle size of the non-hollow silica particles to a predetermined range. The ratio of the average particle size of the non-hollow silica particles to the average particle size of the hollow silica particles (average particle size of non-hollow silica particles / average particle size of hollow silica particles) is preferably 0.29 or less, and more preferably 0.27 or less. The ratio of the average particle sizes is preferably 0.05 or more, and more preferably 0.10 or more.

[0339] The average particle size of the hollow silica particles is preferably smaller than the thickness of the low refractive index layer, for example, 1 nm or more and 150 nm or less. The average particle size of the hollow silica particles is preferably 35 nm or more and 100 nm or less, more preferably 50 nm or more and 100 nm or less, and even more preferably 60 nm or more and 80 nm or less.

[0340] The average particle size of the non-hollow silica particles is preferably smaller than the thickness of the low-refractive-index layer, for example, 0.5 nm or more and 100 nm or less. The average particle size of the non-hollow silica particles is preferably 1 nm or more and 30 nm or less, more preferably 5 nm or more and 20 nm or less, and even more preferably 10 nm or more and 15 nm or less.

[0341] The average particle size of the low-refractive-index particles can be calculated by the following operations (y1) to (y3).

[0342] (y1) A cross-section of the low refractive index layer is imaged using STEM. It is preferable that the acceleration voltage of the STEM be 10 kV or more and 30 kV or less, and the magnification be 50,000 times or more and 300,000 times or less.

[0343] (y2) Ten random particles are extracted from the observed image, and the particle diameter of each particle is calculated. The particle diameter is measured as the distance between two lines in a combination of two lines where the distance between the two lines is maximized when the cross-section of the particle is placed between two randomly parallel lines. If the particles are aggregated, the aggregated particles are considered as one particle for measurement.

[0344] (y3) Perform the same operation 5 times on different screen observation images of the same sample, and the value obtained from the number average of 50 particle sizes is taken as the average particle size of the low refractive index particle.

[0345] It is preferable that the surfaces of hollow silica particles and non-hollow silica particles be coated with a silane coupling agent. General-purpose silane coupling agents may be used, and among them, silane coupling agents having (meth)acryloyl groups or epoxy groups are preferred.

[0346] By surface treating silica particles with a silane coupling agent, the affinity between the silica particles and the binder resin is improved, making it difficult for the silica particles to aggregate. As a result, the dispersion of the silica particles tends to become uniform.

[0347] As the content of hollow silica particles increases, the packing ratio of hollow silica particles in the binder resin increases, and the refractive index of the low refractive index layer decreases. For this reason, it is preferable that the content of hollow silica particles be 100 parts by mass or more per 100 parts by mass of binder resin, and more preferable that it be 120 parts by mass or more.

[0348] On the other hand, if the content of hollow silica particles is too high, the hollow silica particles become prone to damage or detachment, leading to a tendency for mechanical strength, such as scratch resistance, of the low-refractive-index layer to decrease. If the content of hollow silica particles is too high, the refractive index of the low-refractive-index layer decreases excessively, causing the Σ of the optical film T The value of tends to be difficult to satisfy the above range. For this reason, the content of hollow silica particles is preferably 200 parts by mass or less per 100 parts by mass of binder resin, more preferably 180 parts by mass or less, and even more preferably 160 parts by mass or less.

[0349] In order to improve the scratch resistance of the low refractive index layer, the content of non-hollow silica particles is preferably 20 parts by mass or more per 100 parts by mass of binder resin, and more preferably 40 parts by mass or more.

[0350] Meanwhile, if the content of non-hollow silica particles is too high, the non-hollow silica particles tend to aggregate. For this reason, the content of non-hollow silica particles is preferably 100 parts by mass or less per 100 parts by mass of binder resin, and more preferably 80 parts by mass or less.

[0351] The binder resin of the low refractive index layer preferably comprises a cured product of an ionizing radiation-curable resin composition.

[0352] An ionizing radiation-curable resin composition is a composition comprising a compound having an ionizing radiation-curable functional group (hereinafter also referred to as an "ionizing radiation-curable compound"). Examples of ionizing radiation-curable functional groups include ethylenically unsaturated bonding groups such as (meth)acryloyl groups, vinyl groups, and allyl groups, as well as epoxy groups and oxetanyl groups.

[0353] As an ionizing radiation curable compound, a compound having an ethylenically unsaturated bond is preferred, a compound having two or more ethylenically unsaturated bonds is more preferred, and among these, a polyfunctional (meth)acrylate-based compound having two or more ethylenically unsaturated bonds is even more preferred. As a polyfunctional (meth)acrylate-based compound, either a monomer or an oligomer can be used.

[0354] Ionizing radiation refers to electromagnetic waves or charged particle beams that have energy quanta capable of polymerizing or crosslinking molecules. Typically, ultraviolet (UV) rays or electron beams (EB) are used, but other electromagnetic waves such as X-rays and γ-rays, and charged particle beams such as α-rays and ion beams can also be used.

[0355] Among polyfunctional (meth)acrylate compounds, examples of difunctional (meth)acrylate monomers include ethylene glycol di(meth)acrylate, bisphenol A tetraethoxydiaacrylate, bisphenol A tetrapropoxydiaacrylate, 1,6-hexanediol diacrylate, etc.

[0356] Examples of (meth)acrylate monomers with three or more functional groups include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, dipentaerythritol tetra(meth)acrylate, isocyanuric acid modified tri(meth)acrylate, etc.

[0357] The above (meth)acrylate-based monomer may have a part of its molecular backbone modified, and may also be modified with ethylene oxide, propylene oxide, caprolactone, isocyanuric acid, alkyl, cyclic alkyl, aromatic, bisphenol, etc.

[0358] Examples of multifunctional (meth)acrylate-based oligomers include acrylate-based polymers such as urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, and polyether (meth)acrylate.

[0359] Urethane (meth)acrylate is obtained, for example, by the reaction of polyhydric alcohols and organic diisocyanates with hydroxy (meth)acrylates.

[0360] A preferred epoxy (meth)acrylate is a (meth)acrylate obtained by reacting (meth)acrylic acid with a trifunctional or more aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, etc., or with (meth)acrylic acid; a (meth)acrylate obtained by reacting (meth)acrylic acid with a polybasic acid with a difunctional or more aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, etc., or with a difunctional or more aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, etc., or with a difunctional or more aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, etc., or with a phenolic compound and (meth)acrylic acid.

[0361] Ionizing radiation-curable compounds can be used as a single type or in combination of two or more types.

[0362] When the ionizing radiation-curable compound is a UV-curable compound, it is preferable that the ionizing radiation-curable resin composition include additives such as a photopolymerization initiator or a photopolymerization accelerator.

[0363] As photopolymerization initiators, one or more selected from acetophenone, benzophenone, α-hydroxyalkylphenone, methyl ketone, benzoin, benzyldimethylketal, benzoylbenzoate, α-acyloxime ester, α-aminoalkylphenone, anthraquinone, halogenoketone, thioxantone, etc. may be used.

[0364] The photopolymerization accelerator is capable of reducing polymerization inhibition by air during curing and increasing the curing speed, and one or more selected from, for example, p-dimethylaminobenzoate isoamyl ester, p-dimethylaminobenzoate ethyl ester, etc.

[0365] The low refractive index layer may include a leveling agent for antifouling properties and surface smoothness. Examples of leveling agents include fluorine-based and silicone-based agents, but silicone-based agents are preferred. By including a silicone-based leveling agent, the slipperiness and antifouling properties of the surface of the low reflectance layer can be improved. Specific examples of having "good antifouling properties" include good fingerprint wiping properties and a large contact angle with pure water and hexadecane.

[0366] The content of the leveling agent is preferably 0.01 parts by mass or more and 10 parts by mass or less per 100 parts by mass of binder resin, and more preferably 0.05 parts by mass or more and 1 part by mass or less.

[0367] A low refractive index layer can be formed, for example, by applying and drying a low refractive index layer forming coating solution formed by dissolving or dispersing each component constituting the low refractive index layer. The low refractive index layer forming coating solution may contain a solvent to control viscosity or to enable the dissolution or dispersion of each component.

[0368] Reflectance

[0369] The optical film of the present disclosure preferably has a luminous reflectance Y value measured at the low refractive index layer side of 4.0% or less, more preferably 2.0% or less, even more preferably 1.7% or less, and even more preferably 1.5% or less.

[0370] If the luminous reflectance of the optical film is made too low, Σ TThe value of tends to be difficult to satisfy the above range. For this reason, it is desirable for the luminous reflectance Y value to be 0.5% or higher, more desirable to be 0.7% or higher, and even more desirable to be 1.0% or higher.

[0371] In this specification, the luminous reflectance Y value refers to the luminous reflectance Y value of the CIE1931 standard color system. It is preferable to calculate the reflectance as the average value of eight values ​​excluding the maximum and minimum values, by measuring at any 10 points of a single sample.

[0372] In the present specification, the reflectance of an optical film is measured by preparing a sample in which a black plate is bonded with a transparent adhesive layer interposed on the side opposite to the reflectance measurement surface of the optical film, and by irradiating light at an angle of incidence of 5° from the low refractive index layer side of the sample. It is preferable that the light source used to measure the reflectance be a C light source.

[0373] It is preferable that the difference in refractive index between the member (e.g., plastic film) in contact with the transparent adhesive layer of the sample and the transparent adhesive layer be within 0.15, more preferable that it be within 0.10, more preferable that it be within 0.05, and more preferable that it be within 0.01. It is preferable that the total light transmittance of the black plate according to JIS K7361-1:1997 be 1% or less, and more preferable that it be 0%. It is preferable that the difference in refractive index between the resin constituting the black plate and the transparent adhesive layer be within 0.15, more preferable that it be within 0.10, more preferable that it be within 0.05, and more preferable that it be within 0.01.

[0374] <Haze, Total Light Transmittance>

[0375] It is preferable for the optical film that the haze of JIS K7136:2000 is 5% or less, more preferable that it is 4% or less, and even more preferable that it is 3% or less. In cases where anti-gloss properties are required, the upper limit of the haze of the optical film may be 90% or less, 65% or less, or 40% or less. It is preferable for the optical film that the haze of JIS K7136:2000 is 0.5% or more, more preferable that it is 1.0% or more, and even more preferable that it is 1.5% or more. The aforementioned haze refers to the haze of the entire optical film.

[0376] The optical film preferably has an optical light transmittance of 80% or more according to JIS K7361-1:1997, more preferably 90% or more, even more preferably 91% or more, and even more preferably 92% or more.

[0377] Other Floors

[0378] The optical film of the present disclosure may have a plastic film and other layers other than a low refractive index layer. It is preferable that the low refractive index layer and other layers other than the low refractive index layer are optically isotropic. An optically isotropic layer refers to one having an in-plane phase difference of less than 20 nm, preferably 10 nm or less, more preferably 5 nm or less.

[0379] Other layers other than the plastic film and the low refractive index layer may include an antifouling layer, a hard coat layer, an antiglare layer, and a high refractive index layer, and a hard coat layer and an antiglare layer are preferred. That is, the optical film of the present disclosure preferably has one or more layers selected from a hard coat layer and an antiglare layer between the plastic film and the low refractive index layer. Among these, a hard coat layer is preferred. Within a range that does not impair the effect of the optical film of the present disclosure, an antifouling layer may be provided on the opposite side of the plastic film of the low refractive index layer. For example, within a range that does not impair the effect of the optical film of the present disclosure, a plastic film, a low refractive index layer, and an antifouling layer may be provided in this order.

[0380] Hard Coat Layer

[0381] A hard coat layer is formed as needed to improve the scratch resistance of the optical film. It is preferable to form the hard coat layer between the plastic film and the low refractive index layer. If the optical film also has a high refractive index layer, it is preferable to arrange the hard coat layer, the high refractive index layer, and the low refractive index layer on the plastic film in this order.

[0382] To ensure good scratch resistance, the hard coat layer preferably comprises a cured product of a curable resin composition, such as a thermosetting resin composition or an ionizing radiation-curable resin composition, and more preferably comprises a cured product of an ionizing radiation-curable resin composition.

[0383] A thermosetting resin composition is a composition comprising at least a thermosetting resin and is a resin composition that hardens upon heating. Examples of thermosetting resins include acrylic resin, urethane resin, phenolic resin, urea melamine resin, epoxy resin, unsaturated polyester resin, silicone resin, etc. In the thermosetting resin composition, a curing agent is added to these curable resins as needed.

[0384] The ionizing radiation-curable resin composition of the hard coat layer may be the same as the ionizing radiation-curable resin composition exemplified in the low refractive index layer.

[0385] The ionizing radiation-curable resin composition of the hard coat layer preferably includes a multifunctional (meth)acrylate oligomer as an ionizing radiation-curable compound. The number average molecular weight of the multifunctional (meth)acrylate oligomer is preferably 2000 or higher, more preferably 2500 or higher, and preferably 6000 or lower, more preferably 5000 or lower.

[0386] In a hard coat layer formed from a composition containing a polyfunctional (meth)acrylate oligomer with a number average molecular weight of 2000 or more, solvents of the coating solution for forming a low-refractive-index layer or ionizing radiation-curable compounds can easily penetrate, thereby suppressing reflection at the interface between the hard coat layer and the low-refractive-index layer. For this reason, it is possible to easily suppress interference of reflected light from the optical film, and Σ T It can be made easier to set the above range.

[0387] A hard coat layer formed from a composition containing a polyfunctional (meth)acrylate oligomer with a number average molecular weight of 6000 or less can easily suppress the decrease in hardness of the hard coat layer.

[0388] With respect to the total amount of ionizing radiation-curable compounds in the hard coat layer's ionizing radiation-curable resin composition, the content of a polyfunctional (meth)acrylate oligomer having a number average molecular weight of 2000 or more and 6000 or less is preferably 5 mass% or more, more preferably 10 mass% or more, and even more preferably 12 mass% or more.

[0389] To ensure good scratch resistance, the thickness of the hard coat layer is preferably 0.1 μm or more, more preferably 0.5 μm or more, more preferably 1.0 μm or more, and more preferably 2.0 μm or more. To suppress curl, the thickness of the hard coat layer is preferably 100 μm or less, more preferably 50 μm or less, more preferably 30 μm or less, more preferably 20 μm or less, more preferably 15 μm or less, and more preferably 10 μm or less.

[0390] Banghyeoncheung

[0391] The anti-glare layer can be formed, for example, by a coating solution for forming an anti-glare layer comprising a binder resin composition and particles. As the binder resin composition, for example, a curable resin composition exemplified in the hard coat layer can be used.

[0392] The particles may be either organic or inorganic particles. Examples of organic particles include particles composed of polymethyl methacrylate, polyacryl-styrene copolymer, melamine resin, polycarbonate, polystyrene, polyvinyl chloride, benzoguanamine-melamine-formaldehyde condensate, silicone, fluorinated resin, and polyester resin. Examples of inorganic particles include particles composed of silica, alumina, antimony, zirconia, and titania.

[0393] The average particle size of organic particles in the anti-glare layer cannot be stated uniformly as it varies depending on the thickness of the anti-glare layer, but it is preferably 0.5㎛ or more and 10.0㎛ or less, more preferably 1.0㎛ or more and 8.0㎛ or less, and even more preferably 1.5㎛ or more and 6.0㎛ or less.

[0394] Inorganic particles are prone to aggregation. For this reason, it is preferable that the average particle size of the inorganic particles be 1 nm or more and 10 µm or less, rather than the above range.

[0395] The average particle size of the particles in the antifouling layer can be calculated by the following operations (z1) to (z3).

[0396] (z1) An image of the fluorescence layer is captured using an optical microscope or a STEM. When the average particle size of the particles is on the order of micrometers, it is preferable to capture an image of the planar surface of the fluorescence layer using an optical microscope. In this case, the magnification is preferably 500x or more and 2000x or less. When the average particle size of the particles is on the order of nanometers, it is preferable to capture an image of the cross-section of the fluorescence layer using a STEM. In this case, the magnification is preferably 20,000x or more and 100,000x or less. The acceleration voltage of the STEM is preferably 10kV or more and 30kV or less.

[0397] (z2) 10 random particles are extracted from the observed image, and the particle diameter of each particle is calculated. The particle diameter is measured as the distance between two lines in a combination of two lines where the distance between the two lines is maximized when the cross-section of the particle is placed between two randomly parallel lines.

[0398] (z3) The same operation is performed 5 times on different screen observation images of the same sample, and the value obtained from the number average of 50 particle sizes is taken as the average particle size of the particles in the fluorescence layer.

[0399] The content of particles in the anti-fouling layer cannot be stated uniformly as it varies depending on the degree of anti-fouling properties desired, but it is preferable that it be 1 part by mass or more and 100 parts by mass or less per 100 parts by mass of resin components, more preferable that it be 5 parts by mass or more and 50 parts by mass or less, and even more preferable that it be 10 parts by mass or more and 30 parts by mass or less.

[0400] The anti-static layer may contain fine particles with an average particle size of less than 500 nm in order to impart antistatic properties, control the refractive index, or adjust the shrinkage of the anti-static layer caused by the curing of the curable resin composition.

[0401] The thickness of the anti-glare layer is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 2.0 μm or more. The thickness of the anti-glare layer is preferably 50 μm or less, more preferably 30 μm or more, more preferably 20 μm or less, more preferably 15 μm or less, and more preferably 10 μm or less. In order to ensure good hardness of the anti-glare layer, it is preferable to make the thickness of the anti-glare layer thicker than the average particle size of the particles.

[0402] <Example of Layered Structure>

[0403] The following (1) to (5) are examples of layer configurations of the optical film of the present disclosure. Among the configurations below, (2) and (4) are preferred.

[0404] (1) A configuration having a low refractive index layer on a plastic film.

[0405] (2) A configuration having a hard coat layer and a low refractive index layer in this order on a plastic film.

[0406] (3) A configuration having a high refractive index layer and a low refractive index layer in that order on a plastic film.

[0407] (4) A configuration having a light-repellent layer and a low-refractive-index layer in that order on a plastic film.

[0408] (5) A composition having a hard coat layer, a high refractive index layer, and a low refractive index layer in that order on a plastic film.

[0409] <Shape, Size>

[0410] The optical film may be in the form of a single-sheet cut to a predetermined size, or in the form of a roll wound from a long sheet. The size of the single-sheet is not particularly limited, but the maximum diameter is approximately 2 inches or more and 500 inches or less. In the present disclosure, the size of the single-sheet is preferably 30 inches or more and 100 inches or less, and more preferably 40 inches or more and 100 inches or less. "Maximum diameter" refers to the maximum length when any two points of the optical film are connected. For example, if the optical film is rectangular, the diagonal of the rectangular area becomes the maximum diameter. If the optical film is circular, the diameter becomes the maximum diameter.

[0411] The width and length of the roll are not specifically limited, but generally, the width is 500 mm or more and 5000 mm or less, and the length is 100 m or more and 5000 m or less. The optical film in roll form can be cut into sheets to fit the size of an image display device, etc. When cutting, it is preferable to exclude the ends of the roll where the physical properties are unstable.

[0412] The shape of the sheet is not particularly limited and, for example, may be polygonal (triangle, rectangle, pentagon, etc.), circular, or random irregular. When the optical film is rectangular, the aspect ratio of the rectangle is not particularly limited as long as there is no problem with the display screen. For example, width:height ratios of 1:1, 4:3, 16:10, 16:9, 2:1, 5:4, etc. can be given.

[0413] <Uses>

[0414] The optical film of the present disclosure can be suitably used as an optical film for an image display device.

[0415] In addition, the optical film of the present disclosure can be suitably used as an optical film disposed on the light-emitting surface side of a display element of an image display device. In this case, it is preferable to have a polarizer between the display element and the optical film of the present disclosure.

[0416] If the plastic film satisfies condition A, it is possible to suppress the retention of bending properties or breakage after the bending test, regardless of the direction of folding and bending. For this reason, if the plastic film satisfies condition A, it can be more suitablely used as a plastic film for curved image display devices or foldable image display devices.

[0417] In addition, the optical film of the present disclosure can also be used as a material when manufacturing a functional film. For example, in a transfer sheet having a transfer layer on a substrate, the optical film of the present disclosure can be used as the substrate. In this case, the transfer layer should be formed on the side opposite to the side having the low refractive index layer of the plastic film. In addition, as the material, a substrate used to protect or reinforce the functional film during the manufacturing process of the functional film may be cited.

[0418] [Polarizing plate]

[0419] The polarizing plate of the present disclosure is a polarizing plate having a polarizer, a first transparent protective plate located on one side of the polarizer, and a second transparent protective plate located on the other side of the polarizer, wherein at least one of the first transparent protective plate and the second transparent protective plate is the optical film of the present disclosure described above, and the surface of the optical film on the side of the low refractive index layer is formed to face the opposite side to the polarizer.

[0420] FIG. 3 is a cross-sectional view showing an embodiment of the polarizing plate (700) of the present disclosure. The polarizing plate (700) of FIG. 3 has a polarizer (300), a first transparent protective plate (500) disposed on one side of the polarizer, and a second transparent protective plate (600) disposed on the other side of the polarizer. The polarizing plate (700) of FIG. 3 uses an optical film (100) as the first transparent protective plate (500). In FIG. 3, the side of the optical film (100) with the low refractive index layer (30) faces the opposite side to the polarizer (300). The polarizing plate (700) of FIG. 3 has the polarizer (300), the first transparent protective plate (500), and the second transparent protective plate (600) laminated with an adhesive layer (400) interposed therebetween.

[0421] A polarizer is used to impart anti-reflective properties, for example, in combination with a λ / 4 phase difference plate. In this case, a λ / 4 phase difference plate is placed on the display element of an image display device, and a polarizer is placed on the viewer side rather than the λ / 4 phase difference plate.

[0422] For liquid crystal display devices, a polarizing plate is used to provide the function of a liquid crystal shutter. In this case, the liquid crystal display device is arranged in the order of a lower polarizing plate, a liquid crystal display element, and an upper polarizing plate from the backlight side, and the absorption axis of the polarizer of the lower polarizing plate and the absorption axis of the polarizer of the upper polarizing plate are arranged to be orthogonal. In the configuration of the liquid crystal display device, the polarizing plates of the present disclosure may be used as the upper polarizing plate and the lower polarizing plate, and it is preferable to use the polarizing plate of the present disclosure as the upper polarizing plate. For the upper polarizing plate, it is preferable to use the optical film of the present disclosure as a transparent protective plate on the light-emitting surface side of the polarizer. For the lower polarizing plate, it is preferable to use the optical film of the present disclosure as a transparent protective plate on the light-incident surface side of the polarizer.

[0423] Transparent protective plate

[0424] The polarizing plate of the present disclosure uses the optical film of the present disclosure described above as at least one of the first transparent protective plate and the second transparent protective plate. It is preferable that both the first transparent protective plate and the second transparent protective plate are the optical film of the present disclosure described above.

[0425] When one of the first transparent protective plate and the second transparent protective plate is the optical film of the present disclosure described above, the other transparent protective plate is not particularly limited, but is preferably an optically isotropic transparent protective plate. In this specification, an optically isotropic transparent protective plate refers to one having an in-plane phase difference of less than 20 nm, preferably 10 nm or less, more preferably 5 nm or less. Examples of transparent protective plates having optical isotropy include acrylic films, triacetylcellulose films, polycarbonate films, amorphous olefin films, etc.

[0426] Polarizer

[0427] Examples of polarizers include sheet-type polarizers formed by stretching a film dyed with iodine, etc. (polyvinyl alcohol film, polyvinyl formal film, polyvinyl acetal film, ethylene-vinyl acetate copolymer saponification film, etc.), wire grid-type polarizers formed by a plurality of metal wires arranged in parallel, coating-type polarizers coated with lyotropic liquid crystals and dichromatic guest-host materials, and multilayer thin-film polarizers. These polarizers may also be reflective polarizers equipped with the function of reflecting polarization components that are not transmitted.

[0428] It is preferable to arrange the polarizer so that the angle formed between its absorption axis and the ground axis of the plastic film is within 90 degrees ± 5 degrees. More preferably, the angle is within 90 degrees ± 3 degrees, and even more preferably within 90 degrees ± 1 degree.

[0429] [Image display device]

[0430] The image display device of the present disclosure is an image display device having a display element, a polarizer and an optical film disposed on the light emission surface side of the display element, wherein the optical film is the optical film of the present disclosure described above, and furthermore, the surface of the optical film on the low refractive index layer side is formed to face the opposite side to the display element.

[0431] FIG. 4 is a cross-sectional view showing an embodiment of the image display device of the present disclosure.

[0432] The image display device (1000) of FIG. 4 has an optical film (100) on the light emission side (upper side of FIG. 4) of the display element (800). In FIG. 4, the side of the optical film (100) with the low refractive index layer faces the opposite side to the display element (800). The image display device (100) of FIG. 4 has a polarizer (300) between the display element (800) and the optical film (100).

[0433] The image display device (1000) is not limited to the form of FIG. 4. For example, in FIG. 4, each component constituting the image display device (1000) is arranged at a predetermined interval, but it is preferable that each component be integrated and laminated by interposing an adhesive layer. The image display device may have other components not shown, such as optical films. For example, the image display device may have a surface plate such as a glass plate or a plastic plate. If the image display device has a surface plate, the optical film of the present disclosure may be bonded to the surface plate.

[0434] In the image display device of the present disclosure, it is preferable that the angle formed by the absorption axis of the polarizer and the ground axis of the plastic film of the optical film is within 90 degrees ± 5 degrees. More preferably, the angle is within 90 degrees ± 3 degrees, and even more preferably within 90 degrees ± 1 degree.

[0435] <Display element>

[0436] Examples of display devices include liquid crystal display devices, EL display devices (organic EL display devices, inorganic EL display devices), plasma display devices, and display devices using QD (Quantum dot), and furthermore, LED display devices such as mini LED and micro LED display devices.

[0437] If the display element of the display device is a liquid crystal display element, a backlight is required on the side opposite to the resin sheet of the liquid crystal display element.

[0438] The image display device may be an image display device equipped with a touch panel function.

[0439] Examples of touch panels include resistive, capacitive, electromagnetic induction, infrared, and ultrasonic types.

[0440] The touch panel function may be one in which the function is added within the display element, such as an in-cell touch panel liquid crystal display element, or one in which the touch panel is mounted on the display element.

[0441] If the plastic film satisfies condition A, the optical film can prevent residual bending properties or fracture after the bending test. For this reason, if the plastic film satisfies condition A, it is preferable that the image display device be a curved image display device or a foldable image display device.

[0442] In the case where the image display device is a curved image display device or a foldable image display device, it is preferable that the display element be an organic EL display element. In the case where the image display device is a curved image display device or a foldable image display device, it is preferable that the glass included in the image display device be thin glass. It is preferable that the thin glass have a thickness of 5㎛ or more and 80㎛ or less.

[0443] Other plastic films

[0444] The image display device of the present disclosure may have other plastic films to the extent that it does not impede the effects of the present disclosure.

[0445] Other plastic films are preferably optically isotropic.

[0446] [Method for Selecting Optical Film for Image Display Devices]

[0447] The method for selecting an optical film of an image display device of the present disclosure is a method for selecting an optical film of an image display device comprising a polarizer and an optical film on a light-emitting surface of a display element, and selecting an optical film X that satisfies the judgment conditions of (1) to (4) below as the optical film.

[0448] (1) An optical film X having a low refractive index layer on a plastic film;

[0449] (2) The above plastic film has a ground axis, which is the axis with the greatest refractive index within the plane, and a true axis, which is an axis orthogonal to the ground axis within the plane of the plastic film;

[0450] (3) The low refractive index layer is positioned on the surface of the optical film X; and

[0451] (4) The optical film X above, Σ calculated under the following measurement condition 1 T Having an area that satisfies greater than 0.04 and less than 0.20.

[0452] <Measurement Condition 1>

[0453] Linearly polarized light is incident from the side of the optical film opposite to the low-refractive-index layer. The incident linearly polarized light is defined as light L1. The transmitted light that passes through the optical film after light L1 is defined as light L2.

[0454] After fixing the angle formed by the ground axis and the vibration direction of the light L1 to 45 degrees, the light L1 is incident on the optical film at an angle such that the elevation angle of the vibration direction of the light L1 relative to the plane of the optical film is 50 degrees or more and 70 degrees or less. The elevation angle is varied in increments of 2 degrees within the range of 50 degrees or more and 70 degrees or less, and the light L2 is measured at 11 different elevation angles. Through the aforementioned measurement, the light L2 is measured at 11 measurement points.

[0455] The above light L2 is converted under the conditions of a C light source and a viewing angle of 2 degrees. With respect to the light L2 of the nth measurement point among 11 measurement points, the a* value and b* value of the L*a*b* color system are defined as a*n and b*n. In addition, with respect to the n+1th light L2 among 11 measurement points, the a* value and b* value of the L*a*b* color system are defined as a*n1 and b*n1.

[0456] Based on the measurements of the above 11 measurement points, the sum of the square of the difference a* of adjacent measurement points and the square of the difference b* of adjacent measurement points is calculated. The above sum is calculated for each of the 10 adjacent points, and Σ representing the total sum of the above sums T Calculates. The above Σ T It can be expressed by the following Equation 1.

[0457] Σ T =Σ[{a*na*n1} 2 +{b*nb*n1} 2 ] (Equation 1)

[0458] In the method for selecting an optical film of an image display device of the present disclosure, it is preferable that the angle formed by the absorption axis of a polarizer and the ground axis of a plastic film of the optical film be within 90 degrees ± 5 degrees. More preferably, the angle is within 90 degrees ± 3 degrees, and even more preferably within 90 degrees ± 1 degree.

[0459] An embodiment of measurement condition 1 in the method for selecting an optical film of an image display device of the present disclosure is the same as the embodiment of measurement condition 1 of the optical film of the present disclosure described above.

[0460] The method for selecting an optical film of an image display device of the present disclosure preferably has additional judgment conditions as judgment conditions. Suitable embodiments of the optical film of the present disclosure (e.g., Equation 2-1, Equation 2-2, n2 / n1, in-plane phase difference of a plastic film, etc.) may be cited as additional judgment conditions.

[0461] The method for selecting an optical film of an image display device of the present disclosure is useful as a method for selecting an optical film of an image display device having a polarizer on the light-emitting surface side of a display element.

[0462] Examples

[0463] Next, the present disclosure will be explained in more detail by way of examples, but the present disclosure is not limited in any way by these examples.

[0464] 1. Measurement, Evaluation

[0465] The atmosphere for the following measurements and evaluations shall be a temperature of 23℃±5℃ and a relative humidity of 40% or more and 65% or less. In addition, prior to the measurements and evaluations, the sample for measurement shall be exposed to the above atmosphere for 30 minutes or more and 60 minutes or less. The sample for measurement shall be taken from a clean and undamaged location. The measurements and evaluations shall be performed under conditions where the flatness of the sample is good.

[0466] 1-1. Measurement of Measurement Condition 1

[0467] A 5cm × 5cm sample was cut from the optical film of the experimental example. Measurement under measurement condition 1 was performed on the sample. The measuring device used was the spectrophotometer model number "V-7100" manufactured by JASCO Corporation. Based on the measurement results, "Σ of Equation 1 T ”, 「(a*max-a*min) of Equation 2-1」, 「(b*max-b*min) of Equation 2-2」, 「Maximum sum (S MAX )」 was calculated. In measurement condition 1, the sum of the square of the difference of a* between adjacent measurement points and the square of the difference of b* between adjacent measurement points is calculated at each of the 10 adjacent points. 「Maximum sum (S MAX )」 refers to the maximum value of the sum of 10 locations. In addition, the luminous reflectance Y value of the optical film in the experimental example is defined as “R(%)”, and “R×Σ T 」 was calculated (the visual reflectance Y value was measured using the method described in 1-6 below). The results are shown in Table 1.

[0468] 1-2. n1 and n2

[0469] Regarding the optical film of the experimental example, the average refractive index n1 of the low refractive index layer was measured by the combined use of the Becke method and the Fitting method described in the text of the specification.

[0470] In addition, regarding the optical film of the experimental example, the average refractive index n2 of the layer adjacent to the low refractive index layer was measured. Whether the layer adjacent to the low refractive index layer was a plastic film or a hard coat layer, n2 was measured by the Becke method described in the text of the specification. The results are shown in Table 1.

[0471] 1-3. Rainbow Inequality

[0472] A liquid crystal display device having a polarizer on a liquid crystal display element (EIZO’s product name “EV2450”, width: 527.0 mm, height: 596.4 mm, the absorption axis of the polarizer is parallel to the vertical direction of the screen, backlight: backlight using a white light-emitting diode) was prepared.

[0473] A laminate was fabricated by laminating the optical film of the experimental example onto the above-mentioned liquid crystal display device with an adhesive layer interposed therebetween. At this time, the polarizer was positioned so that its absorption axis and the ground axis of the plastic film of the optical film were at a 90-degree angle. Then, the laminate was displayed in white in a dark room environment, and visibility was assessed from all directions at all locations at a distance of 30 cm to 100 cm from the laminate. The evaluators were healthy individuals in their 20s to 40s with visual acuity of 0.7 or higher who evaluated the presence or absence of rainbow non-uniformity with the naked eye according to the following criteria. The above visual acuity includes corrected visual acuity. The results are shown in Table 1.

[0474] AA: Rainbow inhomogeneity cannot be observed even when observed from all positions and all directions.

[0475] A: There are slight locations where rainbow inhomogeneity is visible in extremely limited areas, or slight directions where rainbow inhomogeneity is visible in extremely limited areas.

[0476] B: There are many locations where rainbow inhomogeneity is visible in only a very small area, or many directions where rainbow inhomogeneity is visible in only a very small area.

[0477] B - There are many locations where rainbow inhomogeneity is visible in some areas, or many directions where rainbow inhomogeneity is visible in some areas.

[0478] C: There are many locations where rainbow inhomogeneity is visible over most of the area, or many directions where rainbow inhomogeneity is visible over most of the area.

[0479] 1-4. Color Uniformity

[0480] The laminates fabricated in 1-3 were observed visually in a bright environment with the power off. The bright conditions were set such that the surface brightness of the laminate was between 1,000 lux and 1,500 lux. Observations were made from three directions: the front of the laminate, a direction at approximately 50 degrees relative to the laminate, and a direction at approximately 70 degrees relative to the laminate. The distance between the laminate and the evaluator's eyes was set to between 30 cm and 100 cm. The evaluators were 20 healthy individuals in their 20s to 40s with visual acuity of 0.7 or higher, who evaluated the uniformity of color in oblique viewing according to the following criteria. The results are shown in Table 1.

[0481] A: More than 18 people answered that they did not perceive a change in color when comparing the colors in three directions.

[0482] B: 15 to 17 people answered that they did not perceive a change in color when comparing the colors in three directions.

[0483] C: When comparing the colors in three directions, 10 or more and 14 or fewer people answered that they did not perceive a change in color.

[0484] D: 5 to 9 people answered that they did not perceive a change in color when comparing the colors in 3 directions.

[0485] E: Four or fewer people answered that they did not perceive a change in color when comparing the colors in three directions.

[0486] 1-5. Saturation based on reflected light

[0487] A sample (5cm × 5cm) was prepared by interposing a transparent adhesive layer (PANAC CO., LTD., trade name "Panaclean PD-S1", refractive index 1.49) with a thickness of 25㎛ on the plastic film side of the optical film of the experimental example and bonding a black plate (KURARAY CO., LTD., trade name "COMOGLAS DFA2CG 502K (Black) type", total light transmittance 0%, thickness 2mm, refractive index 1.49).

[0488] When the direction perpendicular to the surface of the low-refractive-index layer side of the above sample was set to 0 degrees, light was incident on the sample from directions of 5 degrees, 50 degrees, and 70 degrees, and saturation was measured based on the specular reflection of the incident light. Saturation was measured at 10 locations for each sample, and the average value was taken as the saturation of each sample at each angle. Saturation (C*) can be calculated using the following formula based on the a* and b* values ​​of the L*a*b* color system.

[0489] C*={(a*) 2 +(b*) 2} 1 / 2

[0490] The measuring device used was the spectrophotometer model number "V-7100" from JASCO Corporation. The measuring device measured in the wavelength range from 380 nm to 780 nm and then performed a conversion using software that converts the results into brightness perceived by the human eye [software embedded in the measuring device <JASCO Corporation model number "JASCO Spectrum Manager">. Conditions for calculating reflectance: C light source and viewing angle 2 degrees]. The results are shown in Table 1.

[0491] Optical films that do not have a low refractive index layer did not undergo chroma measurement.

[0492] 1-6. Luminous Reflectance Y Value (Reflectance)

[0493] When the direction perpendicular to the surface of the low-refractive-index layer side of the sample prepared in 1-5 was set to 0 degrees, light was incident on the sample from a direction of 5 degrees, and the reflectance (visual reflectance Y value) was measured based on the specular reflection of the incident light.

[0494] The measuring device used was the spectrophotometer model number "V-7100" from JASCO Corporation. The above measuring device measured in the wavelength range from 380 nm to 780 nm and then performed a conversion using software that converts the values ​​into brightness perceived by the human eye [software embedded in the above measuring device <JASCO Corporation model number "JASCO Spectrum Manager">. Conditions for calculating reflectance: C light source and viewing angle of 2 degrees]. Reflectance was measured at 10 locations for each sample, and the average value was taken as the luminous reflectance Y value for each sample. The results are shown in Table 1.

[0495] Optical films that do not have a low refractive index layer did not have their luminous reflectance Y value measured.

[0496] 1-7. In-plane phase difference (Re), thickness direction phase difference (Rth), and ground axis direction

[0497] A sample measuring 50 mm in length × 50 mm in width was cut from the plastic film used in the experimental and reference examples prepared or manufactured in "2" described below. At that time, the flow direction (MD direction) of the plastic film was considered as the vertical direction, and the width direction (TD direction) of the plastic film was considered as the horizontal direction. For four locations located 10 mm from the four corners of the sample toward the center and a total of five locations at the center of the sample, the in-plane phase difference, the phase difference in the thickness direction, and the direction of the ground axis were measured. The average of Re1 to Re5, etc., was calculated from the measurement results. The results are shown in Table 2.

[0498] The measuring device used was the "RETS-100" (measuring spot: diameter 5 mm) manufactured by Otsuka Electronics Co., Ltd. The direction of the ground axis was measured in the range of 0 degrees or more and 90 degrees or less, with the flow direction (MD direction) of the plastic film as the reference at 0 degrees.

[0499] 1-8. Flexural Resistance

[0500]

[0501] A rectangular sample measuring 30 mm in the width direction (TD direction) × 100 mm in the flow direction (MD direction) was cut from the plastic film used in the experimental and reference examples produced or prepared in "2" described below. After fixing both ends of the short side (30 mm side) of the sample to a durability tester (product name "DLDMLH-FS", YUASA SYSTEM CO., LTD.), a continuous folding test of 180 degrees was performed 100,000 times. The ends of the short side of the sample were fixed in an area 10 mm from the leading edge of the sample. The folding speed was set to 120 times per minute. A more detailed method of the folding test is shown below.

[0502] After the folding test, the rectangular sample was placed on a horizontal stand, and the angle at which the end of the sample lifted off the stand was measured. An angle of 15 degrees or less was considered acceptable. If the sample broke midway, it was classified as "broken." The results are shown in Table 2. Through this evaluation, the bending resistance in the TD direction (≈ground axis direction) can be evaluated.

[0503] <MD 방향>

[0504] From the biaxially stretched plastic film used in the example and comparative example prepared or manufactured in “2” described below, a rectangular sample of 30 mm in the flow direction (MD direction) × 100 mm in the width direction (TD direction) was cut out, and an evaluation similar to that above was performed. Through this evaluation, the flexural strength in the MD direction (≈ true axis direction) can be evaluated.

[0505] <Details of the Fold Test>

[0506] As shown in (A) of FIG. 6, in a continuous folding test, first, the edge (10C) of the plastic film (10) and the edge (10D) opposite to the edge (10C) are each fixed by a fixing part (60) arranged in parallel. The fixing part (60) is movable horizontally.

[0507] Next, as shown in (B) of FIG. 6, the plastic film (10) is deformed to be folded by moving the fixing part (60) so that it is close to each other. Additionally, as shown in (C) of FIG. 6, the fixing part (60) is moved to a position where the distance between two opposing edges fixed by the fixing part (60) of the plastic film (10) is 10 mm, and then the fixing part (60) is moved in the reverse direction to relieve the deformation of the plastic film (10).

[0508] As shown in (A) to (C) of FIG. 6, the plastic film (10) can be folded 180 degrees by moving the fixed part (60). Additionally, a continuous folding test is performed so that the curved part (10E) of the plastic film (10) does not protrude from the bottom of the fixed part (60), and by controlling the gap when the fixed part (60) is closest to 10 mm, the gap between the two opposing edges of the optical film (10) can be set to 10 mm.

[0509] 1-9. Pencil Hardness

[0510] Pencil hardness was measured for polyester films 1 to 5 of “2” below. The method for measuring pencil hardness followed the steps of (1) to (6) in the text of the specification. For commercially available polyester films with an adhesive-friendly layer formed on one side, the pencil hardness was measured on the side where the adhesive-friendly layer was not formed. Pencil hardness was measured on both the ground axis and the true axis. The results are shown in Table 2.

[0511] 1-10. Irojeonryul

[0512] Using a tillage rate measuring device (Palmeso Co., Ltd. MSE test device, part number “MSE-A203”, nozzle cross-sectional shape is a 1mm × 1mm square, cross-sectional profile measuring means: stylus type), the tillage rate of polyester films 1 to 5 of “2” below was measured, and E 0-20 It was calculated. The measurement area of ​​the yaw rate is 1 mm × 1 mm.

[0513] The measurement of the yield of each sample was performed after the following calibration using a standard acrylic plate. In addition, the test solution was prepared prior to calibration, and a preliminary dispersion operation was performed prior to calibration. Furthermore, the standard acrylic plate was within the range where the AcE (average yield of the acrylic plate measured under measurement condition A) specified in the main text of the specification was 1.786 μm / g or higher and 1.974 μm / g or lower.

[0514] (0-1) Preparation of test solution

[0515] In a beaker, a test solution was prepared by mixing pure water, a dispersant (product name "Demol N" of Wako Junyaku Kogyo Co., Ltd.), and spherical silica with an average particle size (median diameter) of 3.94 μm (model number "MSE-BS-5-3" designated by Palmeso Co., Ltd., half-width of particle size distribution: 4.2 μm) in a mass ratio of 968:2:30, and mixed with a glass rod. After placing the prepared test solution and a stirrer into a container (pot), a lid was placed over the pot and a clamp was installed. Subsequently, the pot was placed in a measuring device. In this example, model number "MSE-BS-5-3" designated by Palmeso Co., Ltd. and part number "BS5-3" of Potters-Ballotini Co., Ltd. were used.

[0516] (0-2) Distributed operation

[0517] After inserting the port containing the test solution into the measuring device, a dummy sample was set on the sample holder. Next, the buttons "Erosion Force Setting" and "Execute" on the control panel of the measuring device body were pressed sequentially. Then, predetermined values ​​were entered for the flow rates of the test solution and compressed air, the pressure of the compressed air, and the pressure of the test solution inside the nozzle, and the test solution was projected onto the dummy sample. After stopping the projection, the buttons "Return," "Complete," and "Confirm" on the same control panel were pressed sequentially.

[0518] (1) Correction

[0519] A 4mm thick acrylic plate, which is a calibration sample, was fixed to the sample holder of the measuring device by interposing it with double-sided tape (Kapton double-stick tape from Nitto Denko America, part number: P-2231-6299-01). The acrylic plate is a PMMA plate.

[0520] Next, a sample holder with an acrylic plate fixed thereto was set in the measuring device.

[0521] Next, the lock on the micro gauge was released, and the height of the sample stand was adjusted using the height gauge. The distance between the spray hole of the measuring device and the acrylic plate was adjusted to 4 mm.

[0522] Next, the "To Processing Condition Input Screen" button on the control panel of the measuring device body was pressed, and the setting was set to "Number of Steps: 1, Specified Projection Amount g × 1 time." The injection amount was set to 4g.

[0523] Next, the buttons “Setting Complete,” “Start Operation,” and “Yes” on the same control panel were pressed in sequence. The flow rates of the test liquid and compressed air, the pressure of the compressed air, and the pressure of the test liquid inside the nozzle were maintained at the values ​​entered in “(0-2) Dispersion Operation.”

[0524] Next, click "Online" on the operation screen of the data processing PC to disable online and change it to offline.

[0525] Next, click "Down" on the same operation screen to lower the stylus of the stylus-type step meter of the cross-sectional profile acquisition unit.

[0526] Next, check that the micro gauge is unlocked and turn the micro gauge upward. At this time, adjust it so that the red arrow on the monitor is centered. Through the above adjustment, the stylus of the stylus-type step gauge comes into contact with the surface of the calibration sample, allowing the zero point of the z-axis in the height direction to be adjusted.

[0527] Next, the lock of the micro gauge was switched from off to on.

[0528] Next, clicked "Up" to raise the stylus of the stylus-type step gauge of the cross-sectional profile acquisition unit.

[0529] Next, click "Offline" on the operation screen of the data processing PC to disable offline and change it to online.

[0530] Next, the cover of the measuring device body was closed, and the "Confirm" button on the control panel of the measuring device body was pressed to spray 4g of the test solution.

[0531] After stopping the spraying of the test solution, click "Run" to calculate the evaporation rate. If the evaporation rate was within the range of ±5% based on 1.88 (㎛ / g), the calibration was terminated. If the evaporation rate deviated from the above range, the flow rate of the test solution, the flow rate of the compressed air, the pressure of the compressed air, and the pressure of the test solution inside the nozzle were adjusted, and the calibration was repeated until the evaporation rate was within the above range.

[0532] (2) Measurement of the yield of each sample

[0533] (2-1) Installation of Sample

[0534] A laminate was prepared by bonding samples (polyester films 1 to 5 of “2” below) to a stainless steel plate, and the laminate was fixed to a sample stand by interposing double-sided tape (Kapton double-stick tape of Nitto Denko America, part number: P-2231-6299-01). The samples were made to be 1 cm × 1 cm in size.

[0535] Next, the sample holder was set in the measuring device. Next, the lock on the micro gauge was released, and the height of the sample holder was adjusted using the height gauge. The distance between the injection hole of the measuring device and the plastic film was adjusted to 4 mm.

[0536] Next, the button “To processing condition input screen” on the control panel of the measuring device body was pressed, the number of steps was entered, and the amount of test liquid sprayed (g / time) for each step was entered. The amount of sprayed for each step was set to a range of 0.5g or more and 3.0g or less. The flow rates of the test liquid and compressed air, the pressure of the compressed air, and the pressure of the test liquid inside the nozzle were maintained under the conditions that passed in “(1) calibration”.

[0537] Next, the buttons “Setting Complete,” “Start Operation,” and “Yes” on the same control panel were pressed in sequence.

[0538] Next, click "Online" on the operation screen of the data processing PC to disable online and change it to offline.

[0539] Next, click "Down" on the same operation screen to lower the stylus of the stylus-type step meter of the cross-sectional profile acquisition unit.

[0540] Next, check that the micro gauge is unlocked and turn the micro gauge upward. At this time, adjust it so that the red arrow on the monitor is centered. Through the above adjustment, the stylus of the stylus-type step gauge comes into contact with the surface of the calibration sample, allowing the zero point of the z-axis in the height direction to be adjusted.

[0541] Next, the lock of the micro gauge was switched from off to on.

[0542] Next, clicked "Up" to raise the stylus of the stylus-type step gauge of the cross-sectional profile acquisition unit.

[0543] Next, click "Offline" on the operation screen of the data processing PC to disable offline and change it to online.

[0544] (2-2) Start of measurement

[0545] The cover of the measuring device body was closed, and the "Confirm" button on the control panel of the measuring device body was pressed. A measurement in which the injection of the test liquid and the measurement of the cross-sectional profile constitute one cycle was performed until the depth of the cross-sectional profile exceeded 20 μm. Specifically, the measurement was performed until the depth of the cross-sectional profile was 25 μm or more and 30 μm or less.

[0546] After the measurement, the attached software "MseCalc" was launched and "Analysis Method" was clicked. Next, "Average Value Analysis" was clicked. Then, "Add" on the Average Value Analysis screen was clicked twice to display "A-1" and "A-2" in the analysis name column. The "Reference" column of "A-1" was double-clicked to display "0" in the reference column.

[0547] Next, click "A-1" on the average value analysis screen to activate it, and adjust the position of the X-axis position bar. The position of the position bar is determined as a location within the cross-sectional profile screen where the plastic film is not worn.

[0548] Next, click A-2 on the average value analysis screen to activate it, and adjust the position of the X-axis position bar. The position of the position bar is determined as the deepest part where the plastic film is worn within the cross-sectional profile screen.

[0549] Next, output the cross-sectional profile and yield rate data for each step in CSV, and yield rate E 0-20...was calculated. Specifically, among the CSV output data, the "turnover rate (corrected)" with a depth of 0㎛ or more and 20㎛ or less was averaged, and the turnover rate E 0-20 ...was calculated. The results are shown in Table 2.

[0550] 2. Production and Preparation of Plastic Film

[0551] [Polyester Film 1]

[0552] A pellet containing an ultraviolet absorber was prepared by melt-mixing 1 kg of PET (melting point 258°C, absorption center wavelength: 320 nm) and 0.1 kg of an ultraviolet absorber (2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazinone-4-one) in a mixer at 280°C. The pellet and the PET with a melting point of 258°C were fed into a single-screw extruder and melt-mixed at 280°C, then extruded from a T-die and cast onto a cast drum with a surface temperature controlled to 25°C to obtain a cast film. The amount of ultraviolet absorber in the cast film was 1 part by mass per 100 parts by mass of PET.

[0553] After heating the obtained casting film with a roll group set to 95°C, the film was stretched 3.3 times in the flow direction while heating both the front and back sides of the film with a radiation heater so that the film temperature at the 250mm point of the 400mm stretching section became 103°C, and then cooled to obtain a uniaxially stretched film. The stretching section has stretching roll A at the starting point and stretching roll B at the end point, and stretching rolls A and B each have two nip rolls. When heating with the radiation heater, a wind of 92°C and 4 m / s was blown toward the film from the side of the radiation heater opposite to the film, thereby generating turbulence on the front and back sides of the film and disrupting the temperature uniformity of the film.

[0554] Next, corona discharge treatment in air was performed on both sides of this uniaxially stretched film, thereby making the wetting tension of the base film 55 mN / m. Subsequently, an "easy-slipping layer coating solution comprising a polyester resin with a glass transition temperature of 18°C, a polyester resin with a glass transition temperature of 82°C, and silica particles with an average particle size of 100 nm" was inline coated on the corona discharge treated surfaces of both sides of the film to form an easy-slipping layer.

[0555] Next, the uniaxially stretched film was guided into a tenter and, after preheating with hot air at 95°C, stretched 4.5 times in the film width direction at temperatures of 105°C in the first stage and 140°C in the second stage. Here, when the stretching section in the width direction was divided into two parts, the film was stretched in two stages such that the amount of film stretched at the midpoint of the stretching section in the width direction was 80% of the amount of film stretched at the end of the stretching section in the width direction. The aforementioned "amount of stretch" refers to the difference between the film width at the measurement point and the film width before stretching. The film stretched in the width direction was then subjected to heat treatment with hot air inside the tenter. The temperature of the hot air was gradually increased from 180°C to 245°C. Subsequently, a 1% relaxation treatment in the width direction was performed under the same temperature conditions, and after rapidly cooling to 100°C, a 1% relaxation treatment in the width direction was performed. After that, it was wound to obtain a biaxially stretched polyester film 1 with a thickness of 40 μm.

[0556] Polyester film 1 was used as the plastic film of Experimental Example 3.

[0557] [Polyester Film 2]

[0558] A biaxially stretched polyester film 2 with a thickness of 40 μm was obtained by making the same process as biaxially stretched polyester film 1, except that the stretching ratio in the width direction was changed from 4.5 times to 5.1 times. Polyester film 2 was used as the plastic film of Experimental Example 2.

[0559] [Polyester Film 3]

[0560] As polyester film 3, a commercially available biaxially stretched polyester film (TOYOBO CO., LTD., product name: Cosmoshine A4300, thickness: 38 μm) was prepared. Polyester film 3 was used as the plastic film of Experimental Example 1.

[0561] [Polyester Film 4]

[0562] As polyester film 4, a commercially available biaxially stretched polyester film (TOYOBO CO., LTD., product name: Cosmoshine A4100, thickness: 50 μm) was prepared. Polyester film 4 was used as the plastic film of Reference Example 1.

[0563] [Polyester Film 5]

[0564] As polyester film 5, a commercially available uniaxially stretched polyester film (TOYOBO CO., LTD., product name "Cosmoshine TA044", thickness: 80 μm) was prepared. Polyester film 5 was used as the plastic film of Reference Example 2.

[0565] 3. Synthesis of Compounds

[0566] Compound α used in “4. Preparation of Coating Solution” was synthesized by the following method.

[0567] Air gas was introduced into a reaction vessel equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen gas inlet tube. The pressure in the reaction vessel during the introduction of air gas was controlled to 1.0 atm ± 0.1 atm. Subsequently, 57 parts by mass of pentaerythritol triacrylate, 43 parts by mass of pentaerythritol tetraacrylate, 0.02 parts by mass of dibutyltin dilaurate, 0.02 parts by mass of p-methoxyphenol, and 30 parts by mass of butyl acetate were added into the reaction vessel, and the temperature was raised to 60°C while stirring under a nitrogen flow. The pressure in the reaction vessel under the nitrogen flow was controlled to 1.2 atm ± 0.1 atm. (By raising the pressure under nitrogen flow to be higher than atmospheric pressure, the oxygen concentration inside the reaction vessel can be reduced more efficiently.) Subsequently, 30 parts by mass of hexamethylene diisocyanate were added to a dropping vessel and uniformly dropped into the reaction vessel over a period of 1 hour. After dropping, the temperature of the reaction vessel was raised to 75°C and held at 75°C ± 3°C for 6 hours. Then, 150 parts by mass of methyl ethyl ketone were added to obtain a transparent resin solution. Finally, the solvent was removed using an evaporator to obtain compound α. Compound α is an ionizing radiation curable compound. The number average molecular weight of compound α was approximately 4500.

[0568] 4. Preparation of the coating solution

[0569] A coating solution used in "5. Fabrication of Optical Film" was prepared.

[0570] <Coating Solution A for Forming a Hard Coat Layer>

[0571] · Ionizing radiation-hardenable compound 1: 0.6 parts by mass

[0572] (Compound α synthesized in "3")

[0573] · Ionizing radiation-hardenable compound 2: 0.2 parts by mass

[0574] (Daicel Co., Ltd., Product name "EBECRYL230", Solid content 100%)

[0575] · Ionizing radiation-hardenable compound 3: 0.2 parts by mass

[0576] (Kyoeisha Kagaku Kabushiki Kaisha, Product name "Light Acrylate IAA", Solid content 100%)

[0577] · Leveling agent: 0.01 parts by mass

[0578] (Dainichi Seika Kogyo Co., Ltd., Product Name "10-28(TL)", Solid Content (10 mass%))

[0579] · Photopolymerization initiator: 0.1 parts by mass

[0580] (IGM Resins BV, Product Name "Omnirad 184")

[0581] · Solvents

[0582] (A 5:5 mixed solvent of methyl isobutyl ketone and cyclohexanone. The solvent is used in an amount such that the solid content of the coating solution is 35 mass%.)

[0583] <Coating Solution B for Forming Hard Coat Layer>

[0584] · Ionizing radiation-hardenable compound 1: 1 part by mass

[0585] (Compound α synthesized in "3")

[0586] · Acrylic resin particles: 0.1 parts by mass

[0587] (Average particle size: 2㎛, Refractive index: 1.535)

[0588] · Leveling agent: 0.01 parts by mass

[0589] (Dainichi Seika Kogyo Co., Ltd., Product Name "10-28(TL)", Solid Content (10 mass%))

[0590] · Photopolymerization initiator: 0.1 parts by mass

[0591] (IGM Resins BV, Product Name "Omnirad 184")

[0592] · Solvents

[0593] (A 5:5 mixed solvent of methyl isobutyl ketone and cyclohexanone. The solvent is used in an amount such that the solid content of the coating solution is 35 mass%.)

[0594] <Coating solution C for forming a hard coat layer>

[0595] · Ionizing radiation-hardenable compound 1: 0.625 parts by mass

[0596] (Compound α synthesized in "3")

[0597] · Ionizing radiation-curable compound 4: 0.375 parts by mass

[0598] (Arakawa Kagaku Kogyo Co., Ltd., Product Name "Opster Z7415", Solid Content 100%)

[0599] · Leveling agent: 0.01 parts by mass

[0600] (Dainichi Seika Kogyo Co., Ltd., Product Name "10-28(TL)", Solid Content (10 mass%))

[0601] · Photopolymerization initiator: 0.1 parts by mass

[0602] (IGM Resins BV, Product Name "Omnirad 184")

[0603] · Solvents

[0604] (A 5:5 mixed solvent of methyl isobutyl ketone and cyclohexanone. The solvent is used in an amount such that the solid content of the coating solution is 35 mass%.)

[0605] <Coating solution for forming a low-refractive-index layer i>

[0606] · UV-curing acrylate-containing composition: 1 part by mass

[0607] (Nippon Kayaku Co., Ltd., Product name "KAYARAD PET-30", Solid content 100%)

[0608] · Photopolymerization initiator: 0.1 parts by mass

[0609] (IGM Resins BV, Product Name "Omnirad 127")

[0610] · Hollow silica particles: 1.3 parts by mass

[0611] (Average primary particle size 60 nm)

[0612] · Solid silica particles: 0.7 parts by mass

[0613] (Average primary particle size 15 nm)

[0614] · Leveling agent: 0.1 parts by mass

[0615] (Shin-Etsu Kagaku Kogyo Co., Product Name "X-22-164E")

[0616] · Solvents

[0617] (A 5:5 mixed solvent of methyl isobutyl ketone and cyclohexanone. The solvent is used in an amount such that the solid content of the coating solution is 2 mass%.)

[0618] <Coating solution for forming a low-refractive-index layer ii>

[0619] · UV-curing acrylate-containing composition: 1 part by mass

[0620] (Nippon Kayaku Co., Ltd., Product name "KAYARAD PET-30", Solid content 100%)

[0621] · Photopolymerization initiator: 0.1 parts by mass

[0622] (IGM Resins BV, Product Name "Omnirad 127")

[0623] · Hollow silica particles: 1.55 parts by mass

[0624] (Average primary particle size 60 nm)

[0625] · Solid silica particles: 0.45 parts by mass

[0626] (Average primary particle size 15 nm)

[0627] · Leveling agent: 0.1 parts by mass

[0628] (Shin-Etsu Kagaku Kogyo Co., Product Name "X-22-164E")

[0629] · Solvents

[0630] (A 5:5 mixed solvent of methyl isobutyl ketone and cyclohexanone. The solvent is used in an amount such that the solid content of the coating solution is 2 mass%.)

[0631] <Coating solution for forming a low-refractive-index layer iii>

[0632] · UV-curing acrylate-containing composition: 1 part by mass

[0633] (Nippon Kayaku Co., Ltd., Product name "KAYARAD PET-30", Solid content 100%)

[0634] · Photopolymerization initiator: 0.1 parts by mass

[0635] (IGM Resins BV, Product Name "Omnirad 127")

[0636] · Hollow silica particles: 2 parts by mass

[0637] (Average primary particle size 60 nm)

[0638] · Leveling agent: 0.1 parts by mass

[0639] (Shin-Etsu Kagaku Kogyo Co., Product Name "X-22-164E")

[0640] · Solvents

[0641] (A 5:5 mixed solvent of methyl isobutyl ketone and cyclohexanone. The solvent is used in an amount such that the solid content of the coating solution is 2 mass%.)

[0642] 5. Production of Optical Films

[0643] [Experimental Example 1-1]

[0644] As the optical film of Experimental Example 1-1, the polyester film 3 prepared in “2” was prepared. The optical film of Experimental Example 1-1 does not have a hard coat layer and a low refractive index layer on the polyester film 3.

[0645] [Experimental Example 1-2]

[0646] Coating solution A for forming a hard coat layer was applied onto polyester film 3 prepared in [2], and then dried at 70°C for 1 minute to volatilize the solvent. Subsequently, ultraviolet irradiation (100 mJ / cm²) was applied. 2 By doing so, a hard coat layer (dry thickness 10㎛) was formed.

[0647] Coating solution i for forming a low-refractive-index layer was applied onto the hard coat layer, and then dried at 60°C for 1 minute to volatilize the solvent. Subsequently, ultraviolet irradiation (200 mJ / cm²) 2 By doing so, a low refractive index layer (dry thickness 100 nm) was formed to obtain the optical film of Experimental Example 1-2.

[0648] [Experimental Examples 1-3, 1-4]

[0649] Optical films of Experimental Examples 1-3 and 1-4 were obtained in the same manner as Experimental Example 1-2, except that the coating solution for forming a hard coat layer and the coating solution for forming a low refractive index layer listed in Table 1 were used.

[0650] [Experimental Example 1-5]

[0651] The optical film of Experimental Example 1-5 was obtained in the same manner as Experimental Example 1-2, except that a low refractive index layer was formed directly on the polyester film without forming a hard coat layer, and the coating solution for forming the low refractive index layer was used as described in Table 1.

[0652] [Experimental Example 2-1]

[0653] As the optical film of Experimental Example 2-1, polyester film 2 produced in “2” was prepared. The optical film of Experimental Example 2-1 does not have a hard coat layer and a low refractive index layer on polyester film 2.

[0654] [Experimental Example 2-2]

[0655] The optical film of Experimental Example 2-2 was obtained in the same manner as Experimental Example 1-2, except that polyester film 3 was changed to polyester film 2.

[0656] [Experimental Examples 2-3, 2-4]

[0657] Optical films of Experimental Examples 2-3 and 2-4 were obtained in the same manner as Experimental Example 2-2, except that the coating solution for forming a hard coat layer and the coating solution for forming a low refractive index layer listed in Table 1 were used.

[0658] [Experimental Examples 2-5, 2-6]

[0659] Optical films of Experimental Examples 2-5 and 2-6 were obtained in the same manner as Experimental Example 2-2, except that a low refractive index layer was formed directly on a polyester film without forming a hard coat layer, and the coating solution for forming the low refractive index layer was used as described in Table 1.

[0660] [Experimental Examples 3-1, 3-2]

[0661] Optical films of Experimental Examples 3-1 and 3-2 were obtained in the same manner as Experimental Examples 1-2, except that polyester film 3 was changed to polyester film 1, and the coating solution for forming a hard coat layer and the coating solution for forming a low refractive index layer were used as those listed in Table 1.

[0662] [Experimental Example 3-3]

[0663] Except for changing polyester film 3 to polyester film 1, changing the method so that a low refractive index layer is formed directly on the polyester film without forming a hard coat layer, and using the coating solution listed in Table 1 for forming the low refractive index layer, the optical film of Experimental Example 3-3 was obtained in the same manner as Experimental Example 1-2.

[0664] [Table 1]

[0665]

[0666] [Table 2]

[0667]

[0668] From the results in Table 1, Σ TIt can be confirmed that an optical film with a value greater than 0.04 and less than 0.20 can resolve rainbow non-uniformity when viewed with the naked eye, and also improve color uniformity when viewed at an angle. Among the experimental examples in Table 1, those corresponding to the examples are experimental examples 1-2, 1-3, 1-4, 2-2, 2-3, 2-4, 2-6, 3-1, and 3-2.

[0669] In addition, from the results of Tables 1 and 2, "small in-plane phase difference of the plastic film" and "large difference between the maximum and minimum values ​​in the direction of the ground axis of the plastic film" are Σ T It can be confirmed that it is easy to set the value of to an appropriate value.

[0670] In addition, from the results in Table 2, it can be confirmed that polyester films 1 and 2 can suppress the retention of bending properties or breakage after the bending test regardless of the direction of folding and bending. Polyester films 1 and 2 are "those with a large difference between the maximum and minimum values ​​in the direction of the ground axis of the plastic film."

[0671] In addition, no microcracks were found in polyester films 1 and 2 after the bending test. Microcracks can be observed as follows.

[0672] Microcracks can be observed with a digital microscope. An example of a digital microscope is the "VHX-5000" manufactured by Keyence Co., Ltd.

[0673] Microcracks are observed using a dark field and reflected light, along with selecting ring lighting as the illumination for the digital microscope. Specifically, first, the sample after the bending test is slowly unfolded, and then the sample is secured to the microscope stage with tape. At this time, if the bending properties are strong, the area being observed should be made as flat as possible. During the aforementioned operation, care must be taken not to touch the bent portion of the sample that is the area to be evaluated with one's hands, and also not to apply force to the bent portion. Furthermore, both the inner and outer portions of the bending test are evaluated.

[0674] Observation of microcracks is carried out in a white light room (illumination of 1,000 lux to 2,000 lux). Explanation of the symbols

[0675] 10: Plastic film 20: Hard coat layer 30: Low refractive index layer 100: Optical film 200: Planar light source 300: Polarizer 400: Adhesive layer 500: 1st transparent protective plate 600: Second transparent protective plate 700: Polarizer 800: Display element 1000: Image display device A1: Light source A2: Detector S: Ground axis F: True axis V: Vibration direction of light L1 11: Courage 12: Receptor 21: Piping for test solution 22: Piping for compressed air 23: Return Piping 24: Return Pump 31, 32: Flow meter 41, 42: Pressure gauges 50: Spray part 51: Nozzle 52: Housing 60: Sectional profile acquisition unit 70: Plastic film 81: Sample stand 82: Support body 90: Iro conversion rate measuring device A1: Water A2: Spherical silica A3: Air A4: Worn-out plastic film

Claims

Claim 1 An optical film having a low refractive index layer on a polyester film, wherein the polyester film has a ground axis, which is the axis with the greatest refractive index within the plane, and a true axis, which is an axis orthogonal to the ground axis within the plane of the polyester film, wherein the in-plane phase difference of the polyester film is 20 nm or more and 2500 nm or less, and the phase difference in the thickness direction of the polyester film is 3000 nm or more and 10000 nm or less, wherein the low refractive index layer is located on the surface of the optical film, and the optical film is Σ calculated in the following measurement condition 1 T go An optical film having a region satisfying 0.05 or more and 0.15 or less. <Measurement Condition 1> Linear polarized light is incident from a surface opposite to the low refractive index layer of the optical film. The incident linear polarized light is defined as light L1. The transmitted light that passes through the optical film from light L1 is defined as light L2. After fixing the angle formed by the ground axis and the vibration direction of light L1 to 45 degrees, light L1 is incident on the optical film at an angle such that the elevation angle of the vibration direction of light L1 relative to the plane of the optical film is 50 degrees or more and 70 degrees or less. The elevation angle is varied in increments of 2 degrees within the range of 50 degrees or more and 70 degrees or less, and the spectral transmittance of light L2 is measured at 11 different elevation angles. By the aforementioned measurement, the spectral transmittance of the light L2 is measured at 11 measurement points. The light L2 is converted under the conditions of a C light source and a viewing angle of 2 degrees. With respect to the light L2 at the n-th measurement point among the 11 measurement points, the a* and b* values ​​of the L*a*b* color system are defined as a*n and b*n. Furthermore, with respect to the (n+1)-th light L2 among the 11 measurement points, the a* and b* values ​​of the L*a*b* color system are defined as a*n1 and b*n1. Based on the measurements at the 11 measurement points, the sum of the square of the difference of a* between adjacent measurement points and the square of the difference of b* between adjacent measurement points is calculated. The sum is calculated for each of the 10 adjacent points, and Σ representing the total sum of the sums T Calculates. The above Σ T can be expressed by the following Equation 1. Σ T =Σ[{a*na*n1} 2 +{b*nb*n1} 2 ](Equation 1) Claim 2 In claim 1, within the optical film, Σ T An optical film having a ratio of 50% or more of the area satisfying 0.05 or more and 0.15 or less. Claim 3 In claim 1, within the optical film, Σ T An optical film in which the ratio of the area satisfying 0.05 or more and 0.15 or less is 100%. Claim 4 In claim 1, the optical film is Σ calculated in measurement condition 1 T An optical film having an area satisfying 0.05 or more and 0.09 or less. Claim 5 An optical film according to claim 1 or 2, wherein the in-plane phase difference of the polyester film is 20 nm or more and 1400 nm or less. Claim 6 An optical film according to claim 1 or 2, wherein the in-plane phase difference of the polyester film is 520 nm or more and 1400 nm or less. Claim 7 An optical film according to claim 1 or 2, wherein the in-plane phase difference of the polyester film is 455 nm or more and 1429 nm or less. Claim 8 An optical film according to claim 1 or 2, wherein the phase difference in the thickness direction of the polyester film is 5,000 nm or more and 10,000 nm or less. Claim 9 An optical film according to claim 1 or 2, wherein the polyester film satisfies the following condition A. <Condition A> A sample measuring 50 mm in length × 50 mm in width is cut from the polyester film. A total of five measurement points are designated: one point in the center of the sample and four points each located 10 mm from the four corners of the sample toward the center. The direction of the ground axis is measured at the five points of the sample. The angles formed by any one side of the sample and the direction of the ground axis at each measurement point are defined as D1, D2, D3, D4, and D5, respectively. The difference between the maximum value of D1 to D5 and the minimum value of D1 to D5 is 1.5 degrees or more and 20.0 degrees or less. Claim 10 In claim 9, the above condition A is an optical film in which the difference between the maximum value of D1 to D5 and the minimum value of D1 to D5 is 2.0 degrees or more and 10.0 degrees or less. Claim 11 In claim 9, the above condition A is an optical film in which the difference between the maximum value of D1 to D5 and the minimum value of D1 to D5 is 3.5 degrees or more and 8.0 degrees or less. Claim 12 An optical film according to claim 1 or 2, having one or more layers selected from a hard coat layer and an anti-glare layer between the polyester film and the low refractive index layer. Claim 13 A polarizing plate having a polarizer, a first transparent protective plate located on one side of the polarizer, and a second transparent protective plate located on the other side of the polarizer, wherein at least one of the first transparent protective plate and the second transparent protective plate is an optical film as described in claim 1 or 2, and the surface of the optical film on the side of the low refractive index layer faces the opposite side to the polarizer. Claim 14 An image display device having a display element, a polarizer and an optical film disposed on the light emission side of the display element, wherein the optical film is the optical film described in claim 1 or 2, and further wherein the side of the low refractive index layer of the optical film faces the opposite side to the display element.

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