Optical film, polarizing plate, image display device, and method for selecting optical film

Abstract

The present disclosure provides an optical film which eliminates rainbow flare when observed with the naked eye and has good uniformity of color tone when observed obliquely. An optical film which is formed by having a low refractive index layer on a plastic film having a slow axis which is an axis of maximum in-plane refractive index and a fast axis which is an axis orthogonal to the slow axis in the plane of the plastic film, the low refractive index layer being on the surface of the optical film. Linearly polarized light is incident from the side of the optical film opposite the low refractive index layer under prescribed conditions, and the a* value and the b* value of the L*a*b* colorimetric system of the transmitted light of the linearly polarized light are measured at 11 measurement points at different angles. Based on the measurements at the 11 measurement points, the sum of the square of the difference in a* of adjacent measurement points and the square of the difference in b* of adjacent measurement points is calculated at 10 adjacent points, respectively. In the optical film, Σ T shows a prescribed range.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an optical film, a polarizing plate, an image display device, and a selection method of an optical film. BACKGROUND

[0002] In optical members such as image display devices, various plastic films for optical use are used. For example, in an image display device having a polarizing plate on a display element, a plastic film for protecting a polarizing member constituting the polarizing plate is used. In the present specification, the "plastic film for protecting a polarizing member" is sometimes referred to as a "polarizing member protective film".

[0003] The plastic film for image display device used as a polarizing member protective film and the like is preferably a plastic film excellent in mechanical strength. Therefore, as the plastic film for image display device, a stretched plastic film is preferably used.

[0004] In the case where a stretched plastic film is arranged on a polarizing member, since the stretched plastic film disturbs the polarization state of linearly polarized light that has passed through the polarizing member, there is a problem that rainbow pattern unevenness is observed. In order to solve the problem of rainbow flare, the technologies of Patent Documents 1 to 3 and the like are proposed. Hereinafter, in the present specification, the "rainbow pattern unevenness" is sometimes referred to as "rainbow unevenness".

[0005] In Patent Document 1, a liquid crystal display device is disclosed, which is capable of eliminating rainbow flare when an image is observed through polarized sunglasses, by setting a light source of an image display device to a specific white light source, increasing an in-plane retardation (delay) of a stretched plastic film to 3000 nm or more and 30000 nm or less, and arranging an absorption axis of a polarizing member and a slow axis of the stretched plastic film to be approximately 45 degrees.

[0006] However, the scheme of Patent Document 1 requires the use of a stretched plastic film having a large in-plane retardation. Furthermore, the stretched plastic film having a large in-plane retardation is usually uniaxially stretched, and thus there are problems that it is easy to crack in the stretching direction and the like.

[0007] In Patent Document 2, a polarizing plate protective film having a reflectance at Brewster's angle in a specific range is disclosed. In Patent Document 3, a polarizing plate protective film having a difference between a reflectance of P wave and a reflectance of S wave at an incident angle of 50 degrees of 20% or less is disclosed.

[0008] The polarizing plate protective films of Patent Literatures 2 and 3 seek to eliminate rainbow flare at naked-eye observation without increasing the in-plane retardation of the film, by reducing the reflectance difference between P wave and S wave, which are polarization components of light from the inside of the image display device toward the observer side.

[0009] The polarizing plate protective films of Patent Literatures 2 and 3 can improve rainbow flare at naked-eye observation to some extent. However, with the polarizing plate protective films of Patent Literatures 2 and 3, there is a problem that the color tone varies depending on the angle of observation. That is, the polarizing plate protective films of Patent Literatures 2 and 3 cannot satisfy the uniformity of the color tone at oblique observation.

[0010] Prior Art Documents

[0011] Patent Literature

[0012] Patent Literature 1: Japanese Patent Application Laid-Open No. 2011-107198

[0013] Patent Literature 2: Japanese Patent Application Laid-Open No. 2009-14886

[0014] Patent Literature 3: Japanese Patent Application Laid-Open No. 2010-204630 SUMMARY

[0015] PROBLEMS TO BE SOLVED BY THE INVENTION

[0016] The present disclosure aims to provide an optical film capable of eliminating rainbow flare at naked-eye observation and having good uniformity of color tone at oblique observation, and a polarizing plate and an image display device using the optical film. The present disclosure aims to provide a selection method of an optical film capable of eliminating rainbow flare at naked-eye observation and having good uniformity of color tone at oblique observation.

[0017] MEANS FOR SOLVING THE PROBLEMS

[0018] The present disclosure provides the following [1] to

[12] .

[0019] [1] An optical film having a low refractive index layer on a plastic film, wherein

[0020] the plastic film has a slow axis which is an axis of the largest in-plane refractive index, and a fast axis which is an axis orthogonal to the slow axis in the in-plane of the plastic film,

[0021] the low refractive index layer is located on a surface of the optical film,

[0022] the optical film has Σ T an area exceeding 0.04 and less than 0.20,

[0023] <Measurement Condition 1>

[0024] Linearly polarized light incident from the side of the optical film opposite to the low refractive index layer is defined as light L1, and the transmitted light after light L1 passes through the optical film is defined as light L2.

[0025] The light L1 is incident on the optical film at an angle in which the angle is fixed at 45 degrees between the slow axis and the vibration direction of the light L1, and 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. The light L2 is measured at 11 elevation angles. Through the aforementioned measurements, the light L2 is measured at 11 measurement points.

[0026] Converting the light L2 into a C light source and a viewing angle of 2 degrees, for the light L2 at the nth measurement point out of 11 measurement points, the a* and b* values ​​of the L*a*b* color system are defined as a*n and b*n. In addition, for the light L2 at the (n+1)th measurement point out of 11 measurement points, the a* and b* values ​​of the L*a*b* color system are defined as a*n1 and b*n1.

[0027] Based on the measurements at the 11 measurement points, the sum of the square of the difference between adjacent measurement points (a*) and the square of the difference between adjacent measurement points (b*) is calculated. This sum is then calculated at each of the 10 adjacent points, and the summation ∑ represents the total sum. T The Σ T It can be represented by the following equation 1,

[0028] ∑ T =∑[{a*na*n1} 2 +{b*nb*n1} 2 (Equation 1).

[0029] [2] According to the optical film described in [1], wherein,

[0030] Based on the measurements at the 11 measurement points, when the maximum value of a* is defined as a*max, the minimum value of a* is defined as a*min, the maximum value of b* is defined as b*max, and the minimum value of b* is defined as b*min, the following equations 2-1 and 2-2 are satisfied.

[0031] a*max - a*min ≤ 0.250 (Equation 2-1)

[0032] b*max-b*min≤0.350(Equation 2-2).

[0033] [3] The optical film according to [1] or [2], wherein,

[0034] Based on the measurement of the 11 measurement points, the sum of the square of the difference in a* of adjacent measurement points and the square of the difference in b* of adjacent measurement points is calculated, and when the sum is defined as S, S can be represented by the following formula 3, S is calculated at 10 adjacent points, respectively, and when the maximum value of S of the 10 points is defined as S MAX S MAX is 0.010 or more and 0.050 or less,

[0035] S = {a*n - a*n1} 2 + {b*n - b*n1} 2 (Formula 3).

[0036] [4] The optical film according to any one of [1] to [3], wherein

[0037] when the visual reflectance Y value of the optical film is defined as R (%), the product of R and the sum T is 0.05 or more and 0.25 or less.

[0038] [5] The optical film according to any one of [1] to [4], wherein

[0039] when the average refractive index of the low refractive layer is defined as n1 and the average refractive index of the layer adjacent to the low refractive layer is defined as n2, n2 / n1 is less than 1.23.

[0040] [6] The optical film according to any one of [1] to [4], wherein

[0041] when the average refractive index of the low refractive layer is defined as n1 and the average refractive index of the layer adjacent to the low refractive layer is defined as n2, n2 / n1 is 1.05 or more and less than 1.23.

[0042] [7] The optical film according to any one of [1] to [6], wherein

[0043] the in-plane retardation of the plastic film is 2500 nm or less.

[0044] [8] The optical film according to any one of [1] to [7], wherein

[0045] the plastic film satisfies the following condition A,

[0046] <Condition A>

[0047] A sample of 50 mm in the longitudinal direction x 50 mm in the lateral direction was cut out from the plastic film, and 5 sites, one site in the central portion of the sample and four sites each advancing 10 mm from the corners of the sample toward the central portion, were defined as measurement sites;

[0048] The direction of the slow axis was measured at the 5 sites of the sample, and the angles formed by any one side of the sample and the direction of the slow axis at each measurement site were 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 was 1.5 degrees or more.

[0049] [9] The optical film according to any one of [1] to [8], wherein

[0050] One or more layers selected from a hard coat layer and an anti-glare layer are provided between the plastic film and the low refractive index layer.

[0051]

[10] A polarizing plate having: a polarizing member; a first transparent protective plate on one side of the polarizing member; and a second transparent protective plate on the other side of the polarizing member, wherein

[0052] At least one of the first transparent protective plate and the second transparent protective plate is the optical film according to any one of [1] to [9], and the surface of the optical film on the low refractive index layer side faces the side opposite to the polarizing member.

[0053]

[11] An image display device having: a display element; and a polarizing member and an optical film provided on the light exit surface side of the display element, wherein

[0054] The optical film is the optical film according to any one of [1] to [7], and the surface of the optical film on the low refractive index layer side faces the side opposite to the display element.

[0055]

[12] A selection method of an optical film for an image display device, the image display device being one having a polarizing member and an optical film on the light exit surface of a display element, wherein

[0056] An optical film X satisfying the following (1) to (4) is selected as the optical film:

[0057] (1) The optical film X has a low refractive index layer on a plastic film;

[0058] (2) The plastic film has a slow axis that is an axis of the maximum in-plane refractive index, and a fast axis that is an axis orthogonal to the slow axis in the plane of the plastic film;

[0059] (3) The low refractive index layer is on the surface of the optical film X; and

[0060] (4) the optical film X has Σ T a region exceeding 0.04 and less than 0.20.

[0061] Effects of the Invention

[0062] The optical film of the present disclosure, and the polarizing plate and the image display device using the same can eliminate rainbow flare at naked-eye observation, and can make the uniformity of color tone at oblique observation good. The selection method of the optical film of the present disclosure can efficiently select an optical film that can eliminate rainbow flare at naked-eye observation, and can make the uniformity of color tone at oblique observation good. BRIEF DESCRIPTION OF DRAWINGS

[0063] Figure 1 is a cross-sectional view showing one embodiment of the optical film of the present disclosure.

[0064] Figure 2 is a schematic view showing one example of measurement performed under measurement condition 1.

[0065] Figure 3 is a cross-sectional view showing one embodiment of the polarizing plate of the present disclosure.

[0066] Figure 4 is a cross-sectional view showing one embodiment of the image display device of the present disclosure.

[0067] Figure 5 is a plan view for explaining five measurement positions in a sample when calculating in-plane retardation and the like from the sample.

[0068] Figure 6 is a view schematically showing a case of a continuous folding test.

[0069] Figure 7 is a schematic cross-sectional view of a measurement device of an erosion rate.

[0070] Figure 8 is a schematic view of a state in which a test liquid containing pure water and spherical silica is abraded by a plastic film being ejected from an ejection portion. DETAILED DESCRIPTION

[0071] Hereinafter, one embodiment of the optical film of the present disclosure will be described.

[0072] The optical film of the present disclosure has a low refractive index layer on a plastic film having an in-plane refractive index maximum axis, that is, a slow axis, and an axis orthogonal to the slow axis in the in-plane of the plastic film, that is, a fast axis, the low refractive index layer being on a surface of the optical film, the optical film having Σ Ta region of more than 0.04 and less than 0.20.

[0073] <Measurement Condition 1>

[0074] A linearly polarized light was incident from a surface of the optical film opposite to the low refractive index layer. The linearly polarized light as the incident light was defined as light Ll. Transmitted light after the light Ll was transmitted through the optical film was defined as light L2.

[0075] The light Ll was made incident to the optical film at an angle where an elevation angle of a vibration direction of the light Ll with respect to the plane of the optical film becomes an angle of 50 degrees or more and 70 degrees or less on the basis of the angle where the slow axis and the vibration direction of the light Ll form an angle of 45 degrees. The elevation angle was varied every 2 degrees in the range of 50 degrees or more and 70 degrees or less, and the light L2 was measured at 11 elevation angles. The light L2 was measured at 11 measurement points through the above measurement.

[0076] The light L2 was converted into a condition where a light source is a C light source and a viewing angle is 2 degrees. With respect to the light L2 at an n-th measurement point of the 11 measurement points, a* value and b* value of L*a*b* colorimetric system were defined as a*n and b*n. In addition, with respect to the light L2 at an (n+l)-th measurement point of the 11 measurement points, a* value and b* value of L*a*b* colorimetric system were defined as a*n1 and b*n1.

[0077] On the basis of the measurement of the 11 measurement points, a sum of a square of a difference in a* between adjacent measurement points and a square of a difference in b* between adjacent measurement points was calculated. The sum was calculated at 10 adjacent points, respectively, and a sum of the sums was calculated as ∑ T . The ∑ T The ∑ can be represented by the following formula 1.

[0078] ∑ T =∑[{a*n-a*n1} 2 +{b*n-b*n1} 2 ] (Formula 1)

[0079] In the present specification, with respect to the measurement under the measurement condition 1 and the measurement (measurement of in-plane retardation, thickness direction retardation, direction of slow axis, visual reflectance Y value, and the like) described later, unless specifically described, it was performed in an atmosphere where a temperature was 23°C ± 5°C and a relative humidity was 40% or more and 65% or less. In addition, before each measurement, a measurement sample was exposed to the atmosphere for 30 minutes or more and 60 minutes or less.

[0080] In the present specification, a* value and b* value are values based on the L*a*b* colorimetric system standardized by the International Commission on Illumination (CIE) in 1976. The L*a*b* colorimetric system is adopted in JIS Z 8781-4:2013.

[0081] Figure 1 is a cross-sectional view showing an embodiment of the optical film 100 of the present disclosure. As shown in Figure 1 , the optical film 100 of the present disclosure has a low refractive index layer 30 on a plastic film 10.

[0082] The optical film 100 of the present disclosure can have a layer other than the plastic film 10 and the low refractive index layer 30. As the layer other than the plastic film 10 and the low refractive index layer 30, a hard coat layer, an anti-glare layer, and a high refractive index layer, and the like can be listed. Figure 1 The optical film 100 of the present disclosure has a hard coat layer 20 between the plastic film 10 and the low refractive index layer 30.

[0083] In the present specification, unless otherwise specified, "in-plane of the plastic film" means "in a plane orthogonal to the thickness direction of the plastic film". In the case of Figure 1 , the XY plane of the plastic film corresponds to the in-plane of the plastic film.

[0084] "Measurement Condition 1"

[0085] Figure 2 is a schematic view showing an example of measurement implemented under Measurement Condition 1.

[0086] In Condition 1, light L1 as linearly polarized light is incident from the side of the optical film opposite to the low refractive index layer. In Figure 2 (a) of FIG. 1, the optical film 100 is disposed between a light source Al and a detector A2. Also, in Figure 2 (a) of FIG. 1, light L1 as linearly polarized light is emitted from the light source, and the above light L1 is incident to the side of the optical film 100 opposite to the low refractive index layer 30.

[0087] For the detector A2, a detector capable of detecting the normally transmitted light L1 is used.

[0088] In Measurement Condition 1, on the basis of fixing the angle formed by the slow axis of the plastic film and the vibration direction of the light L1 to 45 degrees, the light L1 is incident to the optical film 100. Figure 2 (b) of FIG. 1 is a view of the slow axis of the plastic film, that is, "S", and the vibration direction of the light L1, that is, "V", when Figure 2 (a) of FIG. 1 is viewed from the XY plane direction. In Figure 2In (b) of the above, θ1 indicates an angle formed by "S" which is a slow axis of the plastic film and "V" which is a vibration direction of the light L1. In Measurement Condition 1, θ1 is fixed to 45 degrees. Further, "V" which is the vibration direction of the light L1 is actually inclined to the Z-axis direction.

[0089] In Measurement Condition 1, on the basis of θ1 being fixed to 45 degrees, the light L1 is made incident into the optical film so that an elevation angle of the vibration direction of the light L1 with the plane of the optical film as a reference becomes an angle of 50 degrees or more and 70 degrees or less. In Figure 2 In (a) of the above, θ2 indicates an elevation angle of the vibration direction of the light L1, that is, "V" with the plane of the optical film as a reference (0 degrees when the plane of the optical film is set as a reference). In Figure 2 In (a) of the above, "F" indicates a fast axis of the optical film. In Figure 2 In (a) of the above, "F" which is the fast axis extends in the Y-axis direction. Figure 5 In (a) of the above, "F" which is the fast axis extends in the Y-axis direction.

[0090] In Measurement Condition 1, the elevation angle is varied every 2 degrees in a range of 50 degrees or more and 70 degrees or less, and the light L2 is measured at 11 elevation angles. Through the above measurement, the light L2 is measured at 11 measurement points. As a means of varying the elevation angle every 2 degrees in a range of 50 degrees or more and 70 degrees or less, for example, a means of inclining the optical film 100 with "F" which is the fast axis as a center of rotation can be cited.

[0091] In Measurement Condition 1, the elevation angle is set to 50 degrees or more and 70 degrees or less because the Brewster angle of a plastic film such as a polyester film is taken into consideration. A rainbow flare in the naked eye of the plastic film is easily observed strongly in the vicinity of the Brewster angle.

[0092] In Measurement Condition 1, the light L2 is converted into a condition of a C light source and a viewing angle of 2 degrees. Through the conversion, the influence of the light source can be excluded from the obtained a* value and b* value.

[0093] With respect to the light L2 of the nth measurement point among the 11 measurement points, the a* value and the b* value of the L*a*b* colorimetric system are defined as a*n and b*n. In addition, with respect to the light L2 of the (n+1)th measurement point among the 11 measurement points, the a* value and the b* value of the L*a*b* colorimetric system are defined as a*n1 and b*n1. a*n, b*n, a*n1, and b*n1 are calculated from the converted light L2.

[0094] The above measurement and calculation can be performed, for example, by a product with a product number of "V-7100" of a spectrophotometer of JASCO Corporation.

[0095] In Measurement Condition 1, based on the measurement of the 11 measurement points, the sum of the square of the difference in a* of adjacent measurement points and the square of the difference in b* of adjacent measurement points is calculated. The sum is calculated at 10 adjacent points, respectively, and the sum of the sums is calculated as ∑ T . The ∑ T can be represented by the following Formula 1.

[0096] ∑ T =∑[{a*n-a*n1} 2 +{b*n-b*n1} 2 ] (Formula 1)

[0097] The optical film of the present disclosure is characterized in that the optical film has the ∑ T of more than 0.04 and less than 0.20.

[0098] The ∑ T represents the amount of variation in the transmitted color shade when the optical film is observed at an angle of more than 50 degrees and less than 70 degrees. The present inventors have found that the ∑ T becomes an index of the ease of visibility of the rainbow flare in the optical film having a low refractive index layer on a plastic film. In addition, the present inventors have found that there is a tendency that the more the reflectance of the optical film having a low refractive index layer on a plastic film is reduced, the smaller the ∑ T becomes, and the more difficult it is to see the rainbow flare. The rainbow flare is based on transmitted light.

[0099] Based on the above insight of the present inventors, it can be considered that the more the ∑ T is reduced, the better the visibility can be. However, the present inventors have found that the more the ∑ T is reduced, the more the color tone changes when observed obliquely, and thus there is a problem that the uniformity of the color tone is reduced. In addition, the present inventors have found that the main cause of the reduction in the uniformity of the color tone is reflected light rather than transmitted light. Furthermore, the present inventors have found that by making the ∑ T be within a prescribed range, the rainbow flare when observed with the naked eye can be eliminated, and the uniformity of the color tone when observed obliquely can be made good. Making the ∑ T be more than a prescribed value means increasing the reflectance of the optical film having a low refractive index layer. That is, the present inventors have found that by intentionally increasing the reflectance of the optical film having a low refractive index layer, the problem that the rainbow flare when observed with the naked eye is eliminated, and the uniformity of the color tone when observed obliquely is made good can be solved. It can be considered that by making the ∑ T be more than a prescribed value, the interference of the reflected light of the optical film having a low refractive index layer can be suppressed, and the uniformity of the color tone when observed obliquely can be easily made good. (If the ∑ TIf the low-refractive layer has a large thickness, the refractive index of the low-refractive layer tends to increase. If the refractive index of the low-refractive layer increases, the difference in refractive index between the low-refractive layer and the layer in contact with the low-refractive layer tends to decrease, and thus the interference of reflected light is suppressed. As a result, it is considered that the uniformity of the color tone in oblique viewing can be easily made good.

[0100] In Σ T 0.04 or less, the interference of reflected light is strong, and the uniformity of the color tone in oblique viewing cannot be made good. In Σ T 0.20 or more, the rainbow flare in naked-eye viewing cannot be eliminated. As described above, the rainbow flare is based on transmitted light. Therefore, by making Σ T exceed 0.04 and be less than 0.20, the influence of both the transmitted light and the reflected light can be suppressed, and the visibility can be made extremely good.

[0101] Σ T It is preferably 0.05 or more, and more preferably 0.06 or more. Σ T It is preferably 0.15 or less, more preferably 0.10 or less, and further preferably 0.09 or less.

[0102] In the optical film of the present disclosure, for the Σ T preferred range, examples that can be cited include more than 0.04 and 0.15 or less, more than 0.04 and 0.10 or less, more than 0.04 and 0.09 or less, 0.05 or more and less than 0.20, 0.05 or more and 0.15 or less, 0.05 or more and 0.10 or less, 0.05 or more and 0.09 or less, 0.06 or more and less than 0.20, 0.06 or more and 0.15 or less, 0.06 or more and 0.10 or less, 0.06 or more and 0.09 or less, and the like.

[0103] If the refractive index of the low-refractive layer is increased, Σ T tends to increase. If the refractive index of the low-refractive layer is decreased, Σ T tends to decrease. If the refractive index of the low-refractive layer is decreased, the mechanical strength of the low-refractive layer tends to decrease. If the refractive index of the low-refractive layer is increased, the reflectance of the optical film tends to increase. In order to make the reflectance of the optical film be in an appropriate range and the mechanical strength of the low-refractive layer be good, Σ T is preferably 0.05 or more and 0.09 or less.

[0104] By "decreasing the in-plane retardation of the plastic film" and "reducing n2 / n1, which is a parameter related to the refractive index", and the like, the Σ TThe range is described. In the case where a hard coat layer is present between the plastic film and the low refractive index layer, by using a multifunctional (meth)acrylate oligomer having a molecular weight within the prescribed range as the ionizing radiation-curable compound for forming the hard coat layer, it is possible to easily make the Σ T The range is described.

[0105] In the optical film, the Σ T The proportion of the region satisfying more than 0.04 and less than 0.20 is preferably 50% or more, more preferably 70% or more, further preferably 90% or more, and still further preferably 100%.

[0106] Likewise, the proportion of the region satisfying the Σ T The proportion of the region satisfying the various parameters (Equation 2-1, Equation 2-2, in-plane retardation, phase difference in the thickness direction, etc.) other than the Σ

[0107] With respect to the optical film of the present disclosure, it is preferable that, based on the measurement at the 11 measurement points, when the maximum value of a* is defined as a*max, the minimum value of a* is defined as a*min, the maximum value of b* is defined as b*max, and the minimum value of b* is defined as b*min, Equations 2-1 and 2-2 are satisfied.

[0108] a*max-a*min≤0.250 (Equation 2-1)

[0109] b*max-b*min≤0.350 (Equation 2-2)

[0110] By satisfying Equations 2-1 and 2-2, it is possible to make the change in the transmitted color phase in the range of 50 degrees or more and 70 degrees or less more difficult to be felt. Therefore, by satisfying Equations 2-1 and 2-2, it is possible to more easily eliminate the rainbow flare when observed with the naked eye.

[0111] If the Σ T If it is too small, there is a tendency for the left side of Equations 2-1 and 2-2 to become large. It is considered that the reason for this is that if the Σ T becomes small, the change in the optical distance of the low refractive index layer comes to dominate the color change. More specifically, it is considered that this is because the optical distance of the low refractive index layer changes linearly in correspondence with the angle, and thus the a* value and the b* value monotonously increase or monotonously decrease. Therefore, by satisfying Equations 2-1 and 2-2, there is a tendency for the uniformity of the color tone when observed obliquely to also easily become good.

[0112] a*max-a*min of formula 2-1 is more preferably 0.230 or less, further preferably 0.210 or less, and more further preferably 0.200 or less. The lower limit of a*max-a*min of formula 2-1 is not particularly limited and is around 0.070. By setting a*max-a*min to 0.070 or more, Σ T becomes too large.

[0113] b*max-b*min of formula 2-2 is more preferably 0.300 or less, more preferably 0.250 or less, more preferably 0.230 or less, more preferably 0.210 or less, and more preferably 0.200 or less. The lower limit of b*max-b*min of formula 2-2 is not particularly limited and is around 0.070. By setting b*max-b*min to 0.070 or more, Σ T becomes too large.

[0114] For the preferable range of a*max-a*min of formula 2-1, 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, and the like can be exemplified.

[0115] For the preferable range of b*max-b*min of formula 2-2, 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, and the like can be exemplified.

[0116] By "reducing the in-plane retardation of the plastic film" and "reducing n2 / n1 as a parameter related to the refractive index", and the like, formula 2-1 and formula 2-2 can be easily satisfied. In the case where a hard coat layer is present between the plastic film and the low refractive index layer, by using a multifunctional (meth)acrylate oligomer of a prescribed range of molecular weight as the ionizing radiation-curable compound for forming the hard coat layer, formula 2-1 and formula 2-2 can be easily satisfied.

[0117] a*max is preferably -1.0 or more and 0 or less, and more preferably -0.8 or more and -0.1 or less.

[0118] b*max is preferably 0 or more and 2.0 or less, and more preferably 0.2 or more and 1.8 or less.

[0119] The optical film of the present disclosure preferably satisfies the following configuration.

[0120] Based on the measurement at the 11 measurement points, the sum of the square of the difference in a* between adjacent measurement points and the square of the difference in b* between adjacent measurement points is calculated. When the sum is defined as S, S can be represented by the following formula 3. S is calculated at 10 adjacent points, respectively, and when the maximum value of S at the 10 points is defined as S MAX , S MAX is preferably 0.010 or more and 0.050 or less.

[0121] S = {a*n - a*n1} 2 + {b*n - b*n1} 2 (Formula 3)

[0122] By making S MAX 0.050 or less, the change in the transmitted color phase in the range of 50 degrees or more and 70 degrees or less can be made more difficult to be felt. Therefore, by making S MAX 0.050 or less, the rainbow flare at the time of observation with the naked eye can be more easily eliminated.

[0123] If the reflectance of the optical film having the low refractive index layer becomes low, there is a tendency that S MAX becomes small. That is, if S MAX is made too small, there is a tendency that the interference of the reflected light of the optical film having the low refractive index layer is difficult to be suppressed. Therefore, by making S MAX 0.010 or more, the uniformity of the color tone at the time of oblique observation can be easily made more favorable.

[0124] The lower limit of S MAX is more preferably 0.011 or more, and further preferably 0.012 or more. The upper limit of S MAX is more preferably 0.040 or less, further preferably 0.030 or less, and more further preferably 0.025 or less.

[0125] As for the preferable range of S MAX , 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, and the like can be cited.

[0126] By making S MAX 0.010 or more and 0.040 or less, the increase in b* can be suppressed, and the sense of high quality of the image display device can be less impaired.

[0127] By "reducing the in-plane retardation of the plastic film", "reducing n2 / n1 as a parameter related to the refractive index", and the like, S MAX is set to the range. In the case where a hard coat layer is present between the plastic film and the low refractive index layer, by using a multifunctional (meth)acrylate oligomer having a molecular weight in the prescribed range as an ionizing radiation-curable compound for forming the hard coat layer, S MAX is the range.

[0128] The optical film of the present disclosure is preferably: when the visual reflectance Y value of the optical film is defined as R (%), the R and the Σ T product is 0.05 or more and 0.25 or less.

[0129] By setting the product to 0.05 or more and 0.25 or less, the effect based on the Σ T can be more easily exerted.

[0130] The product is more preferably 0.06 or more, and further preferably 0.07 or more. The product is more preferably 0.19 or less, further preferably 0.13 or less, and more further preferably 0.11 or less. In particular, when the product is 0.11 or less, the high-class feeling of the image display device is easily good.

[0131] As the preferable range of the product, 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, and the like can be cited.

[0132] <Plastic film>

[0133] As the resin component contained in the plastic film, polyester, polyimide, polyether sulfone, polysulfone, polypropylene, polymethylpentene, polyvinyl chloride, polyvinyl acetal, polyether ketone, polymethyl methacrylate, polycarbonate, polyurethane, triacetyl cellulose (TAC), and cyclo-olefin polymer (COP), and the like can be cited.

[0134] The plastic film is preferably a plastic film having a Brewster's angle of 50 degrees or more and 70 degrees or less, and more preferably a plastic film having a Brewster's angle of 55 degrees or more and 65 degrees or less. The elevation angle of the measurement condition 1 of the optical film of the present disclosure is 50 degrees or more and 70 degrees or less. Therefore, by setting the Brewster's angle of the plastic film to 50 degrees or more and 70 degrees or less, the effect of the present disclosure can be easily exerted.

[0135] As the resin having a Brewster angle of 50 degrees or more and 70 degrees or less, there are, for example, acrylics such as polymethyl methacrylate, polyesters, TAC, COP, and the like. Among them, from the viewpoint of easily achieving good mechanical strength, a polyester is preferred.

[0136] As the polyester, there are, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), and the like. Among them, from the viewpoint of having a low intrinsic birefringence and easily reducing the in-plane retardation, PET is preferred.

[0137] The plastic film can contain ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, anti-gelation agents, inorganic particles, organic particles, pigments, dyes, antifouling agents, crosslinking agents, surfactants, and the like.

[0138] In order to have 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 in terms of having good tear resistance compared to a uniaxially stretched film. Therefore, the plastic film is preferably a biaxially stretched plastic film.

[0139] In the present specification, as the preferred embodiments of the plastic film, there are various embodiments such as "in-plane retardation", "retardation in the thickness direction", "difference between the maximum value of D1 to D5 and the minimum value of D1 to D5", and the like. With regard to the optical film of the present disclosure, in the case where the plastic film is a biaxially stretched plastic film, it is more preferred to satisfy the preferred embodiments of the in-plane retardation and the like.

[0140] In order to easily suppress rainbow flare, the in-plane retardation of the plastic film is preferably 2500 nm or less. In addition, if the in-plane retardation of the plastic film is reduced, the Σ T .

[0141] The in-plane retardation 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 retardation of the plastic film 2000 nm or less, the Σ T In addition, if the refractive indexes in the slow axis direction and the fast axis direction of the plastic film are different, the reflectance of the optical film differs between the slow axis direction and the fast axis direction. In order to suppress the difference in reflectance due to the direction, it is preferred to reduce the difference in refractive index between the slow axis direction and the fast axis direction of the plastic film. Therefore, the in-plane retardation of the plastic film is preferably 1250 nm or less.

[0142] In order to have good mechanical strength, the in-plane retardation of the plastic film is preferably 20 nm or more. The in-plane retardation of the plastic film is more preferably 100 nm or more, more preferably 300 nm or more, more preferably 400 nm or more, and more preferably 520 nm or more.

[0143] As to the preferable range of the in-plane retardation of the plastic film, 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, 100 nm or more and 950 nm or less, 100 nm or more and 850 nm or less, 100 nm or more and 600 nm or less, 300 nm or more and 2000 nm or less, 300 nm or more and 1500 nm or less, 300 nm or more and 1400 nm or less, 300 nm or more and 1250 nm or less, 300 nm or more and 1150 nm or less, 300 nm or more and 1100 nm or less, 300 nm or more and 1000 nm or less, 300 nm or more and 950 nm or less, 300 nm or more and 850 nm or less, 300 nm or more and 600 nm or less, 400 nm or more and 2000 nm or less, 400 nm or more and 1500 nm or less, 400 nm or more and 1400 nm or less, 400 nm or more and 1250 nm or less, 400 nm or more and 1150 nm or less, 400 nm or more and 1100 nm or less, 400 nm or more and 1000 nm or less, 400 nm or more and 950 nm or less, 400 nm or more and 850 nm or less, 400 nm or more and 600 nm or less, 520 nm or more and 2000 nm or less, 520 nm or more and 1500 nm or less, 520 nm or more and 1400 nm or less, 520 nm or more and 1250 nm or less, 520 nm or more and 1150 nm or less, 520 nm or more and 1100 nm or less, 520 nm or more and 1000 nm or less, 520 nm or more and 950 nm or less, 520 nm or more and 850 nm or less, 520 nm or more and 600 nm or less can be exemplified.

[0144] In order to make the in-plane retardation of the plastic film be in the above range, it is preferable to make the stretching ratio in the longitudinal direction (flow direction) close to the stretching ratio in the transverse direction (width direction).

[0145] When the in-plane retardation of the plastic film is in the range of 520 nm or more and 1400 nm or less, it is easy to achieve suppression of the rainbow flare and reduction of the Σ T When the in-plane retardation of the plastic film is in the range of 520 nm or more and 1400 nm or less, it is easy to achieve suppression of the rainbow flare and reduction of the Σ

[0146] By making the in-plane retardation of the plastic film be 50 nm or more, it is easy to suppress black-out. The reason is that a plastic film having an average value of in-plane retardation of less than 50 nm hardly disturbs linearly polarized light, resulting in direct transmission of the linearly polarized light, whereas a plastic film having an average value of in-plane retardation of 50 nm or more disturbs linearly polarized light. Black-out refers to a phenomenon in which the entire surface becomes dark when observing light that has passed through a polarizing member and a plastic film in that order through a polarizing sunglass.

[0147] The thickness-direction retardation (Rth) of the plastic film is preferably 2000 nm or more, more preferably 3000 nm or more, further preferably 4000 nm or more, and still further preferably 5000 nm or more. The upper limit of Rth is about 10000 nm, and is preferably 8000 nm or less, and more preferably 7000 nm or less. By setting Rth to be in the above range, it is easier to suppress the rainbow flare. In order to suppress the rainbow flare, it is particularly preferable to make Rth be 5000 nm or more. Furthermore, in order to make the pencil hardness of the plastic film be good, Rth is preferably 5000 nm or more. In order to easily suppress breakage of the plastic film, Rth is preferably 10000 nm or less.

[0148] As for the preferable range of Rth of the plastic film, 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, 5000 nm or more and 7000 nm or less, 6000 nm or more and 10000 nm or less, 6000 nm or more and 8000 nm or less, 6000 nm or more and 7000 nm or less, 7000 nm or more and 10000 nm or less, 7000 nm or more and 8000 nm or less, and 8000 nm or more and 10000 nm or less can be cited.

[0149] In order to make the Rth of the plastic film be in the above range, it is preferable 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 small, and thus it is possible to easily increase the Rth.

[0150] By making the in-plane retardation and the thickness direction retardation be in the above ranges, it is possible to make the degree of stretching of the plastic film be close to the biaxiality that is equal, and thus it is possible to easily make the mechanical strength of the plastic film be good.

[0151] In the case where the refractive index in the slow axis direction is defined as nx, the refractive index in the fast axis direction is defined as ny, the refractive index in the thickness direction of the plastic film is defined as nz, and the thickness of the plastic film is defined as T [nm], the in-plane retardation (Re) and the thickness direction retardation (Rth) of the plastic film can be expressed by the following formula i and formula ii. Note that, in the present specification, the refractive index, the in-plane retardation, and the thickness direction retardation refer to the values at a wavelength of 590 nm.

[0152] Re = (nx - ny) x T [nm] (Formula i)

[0153] Rth = ((nx + ny) / 2 - nz) x T [nm] (Formula ii)

[0154] The direction of the slow axis, the in-plane retardation, and the thickness direction retardation can be measured, for example, by the product of Otsuka Electronics Co., Ltd. with the trade name of "RETS-100".

[0155] In the case where the in-plane retardation and the like are measured using the product of Otsuka Electronics Co., Ltd. with the trade name of "RETS-100", it is preferable to perform the preparation for measurement in accordance with the following steps (A1) to (A4).

[0156] (A1) First, in order to stabilize the light source of the RETS-100, it is left for 60 minutes or more after turning on the light source. Thereafter, the rotation compensator method is selected, and the θ mode (a mode for the angle direction retardation measurement and Rth calculation) is selected. By selecting the θ mode, the stage becomes a tilt rotation stage.

[0157] (A2) Next, the following measurement conditions are inputted in the RETS-100.

[0158] (Measurement conditions)

[0159] • Delay measurement range: rotation compensator method

[0160] • Measurement point diameter: φ 5 mm

[0161] • Inclination angle range: 0°

[0162] • Measuring wavelength range: 400 nm or more and 800 nm or less

[0163] • Average refractive index of the plastic film. For example, in the case of a PET film, N = 1.617. Note that the average refractive index N of the plastic film can be calculated based on nx, ny, and nz by the formula (N = (nx + ny + nz) / 3).

[0164] • Thickness: thickness measured separately by SEM or an optical microscope

[0165] (A3) Next, background data is obtained with no sample set in the device. The device is set to a closed system, and this closed system is implemented each time the light source is turned on.

[0166] (A4) Then, a sample is set on the stage in the device and measurement is performed.

[0167] For the in-plane retardation and the thickness direction retardation, and the direction of the slow axis, a sample of 50 mm in the longitudinal direction and 50 mm in the lateral direction is cut out from the plastic film, and the average of the measured values at 5 points of the sample is obtained. The 5 measurement points are 1 point at the central portion of the sample, and 4 points that advance 10 mm from the corners of the sample toward the central portion of the sample, respectively (5 points of the black dots of Figure 7 ).

[0168] The in-plane retardation measured at the 5 points of the above sample is defined as Re1, Re2, Re3, Re4, and Re5, respectively, and the thickness direction retardation measured at the 5 points of the above sample is defined as Rth1, Rth2, Rth3, Rth4, and Rth5, respectively.

[0169] The average of Re1 / Rth1, Re2 / Rth2, Re3 / Rth3, Re4 / Rth4, and Re5 / Rth5 of the plastic film is preferably 0.20 or less.

[0170] A small ratio of the in-plane retardation to the thickness direction retardation (Re / Rth) means that the biaxiality of the stretching of the plastic film is close to equal biaxiality. Therefore, by making Re / Rth 0.20 or less, the mechanical strength of the plastic film can be made good. Re / Rth is more preferably 0.18 or less, and further preferably 0.16 or less. The lower limit of Re / Rth is around 0.01.

[0171] The Re / Rth of a completely uniaxially stretched plastic film is 2.0. A general uniaxially stretched plastic film is also slightly stretched in the flow direction. Therefore, the Re / Rth of a general uniaxially stretched plastic film is around 1.0.

[0172] 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 further preferably 0.16 or less. The lower limit of these ratios is about 0.01.

[0173] In the case of a plastic film having a layer and a film that have an influence on the values of the in-plane retardation and the thickness direction retardation, these layer and film are peeled off, and then the in-plane retardation and the thickness direction retardation of the plastic film are measured. Note that a layer formed by coating generally does not have an influence on the values of the in-plane retardation and the thickness direction retardation.

[0174] As a means of peeling off a layer and a film that have an influence on the values of the in-plane retardation and the thickness direction retardation, the following means can be given.

[0175] <Peeling means>

[0176] A sample of 5 cm square or more is immersed in warm water at 80°C or higher and 90°C or lower for 5 minutes. Then, the sample is taken out of the warm water and left at room temperature for 10 minutes or more. Then, the sample is further immersed in the warm water for 5 minutes. The sample is taken out of the warm water. A notch is cut in the sample with a knife or the like. Furthermore, a means of peeling off a layer and a film from the notch can be given.

[0177] In the above means, it is preferable to immerse the sample in the warm water in a state where the edge of the sample is stuck to a metal frame or the like.

[0178] The plastic film preferably satisfies the following Condition A.

[0179] <Condition A>

[0180] The direction of the slow axis is measured at five sites of the sample. When the angle formed by any one side of the sample and the direction of the slow axis of each measurement site is 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.

[0181] If the slow axis of the plastic film is aligned, there is a tendency that the Σ T The tendency that the rainbow spot is easily large and easily observed. On the other hand, if a deviation is given to the slow axis of the plastic film, the rainbow spot becomes blurred and is difficult to observe. Therefore, by satisfying Condition A, it is possible to easily suppress the case where the rainbow spot is observed with the naked eye. In other words, by satisfying Condition A, it is possible to make the Σ T The range is easily satisfied.

[0182] The general stretched plastic film is designed without deviation in the direction of the slow axis. However, as described above, by intentionally deviating the direction of the slow axis of the plastic film, it is possible to easily suppress rainbow flare. In addition, in a larger area, the suppressing effect of rainbow flare is small even if the slow axis fluctuates, but by making the slow axis fluctuate in a relatively small area of 50 mm in the longitudinal direction x 50 mm in the lateral direction, it is possible to easily suppress rainbow flare.

[0183] In the present specification, "the direction of the slow axis at the time when the Σ T

[0184] In Condition A, with respect to an arbitrary one side of the sample that is a reference for the angle made with the direction of the slow axis, it can be either one of the longitudinal side and the lateral side of the sample as long as the same side is the reference in all of D1 to D5.

[0185] Further, the plastic film satisfying Condition A is preferable in that it is possible to make the plastic film have good resistance to bending.

[0186] On the other hand, with respect to the general oriented film that does not satisfy Condition A and in which the slow axes are uniform, the film breaks after the bending test, or a crease is strongly left. Specifically, with respect to the uniaxially stretched film like that of Patent Literature 1, it breaks in the case where the bending test is performed along the slow axis, and a crease is strongly left in the case where the bending test is performed in a direction orthogonal to the slow axis. In addition, with respect to the general biaxially stretched film, a crease is strongly left in the case where the bending test is performed in a direction orthogonal to the slow axis.

[0187] The plastic film satisfying Condition A is preferable in that it is possible to suppress the case where a crease is left or it breaks after the bending test, regardless of the direction of bending.

[0188] Further, the plastic film satisfying Condition A is preferable in that it is possible to easily suppress microcracks in the plastic film after the bending test.

[0189] In addition, the plastic film satisfying Condition A is preferable in that it is possible to easily make the plastic film have good resistance to bending even if the pencil hardness is high.

[0190] 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 further preferably 3.5 degrees or more.

[0191] ​Note that when the difference between the maximum value of D1 to D5 and the minimum value of D1 to D5 is too large, there is a tendency for the orientation of the plastic film to become low and the mechanical strength to decrease. Therefore, the difference is preferably 20.0 degrees or less, more preferably 17.0 degrees or less, more preferably 15.0 degrees or less, more preferably 10.0 degrees or less, more preferably 9.0 degrees or less, and more preferably 8.0 degrees or less.

[0192] In Condition A, as the preferable range of the difference between the maximum value and the minimum value of D1 to D5, for example, 1.5 degrees or more and 20.0 degrees or less, 2.0 degrees or more and 20.0 degrees or less, 3.0 degrees or more and 20.0 degrees or less, 3.5 degrees or more and 20.0 degrees or less, 1.5 degrees or more and 17.0 degrees or less, 2.0 degrees or more and 17.0 degrees or less, 3.0 degrees or more and 17.0 degrees or less, 3.5 degrees or more and 17.0 degrees or less, 1.5 degrees or more and 15.0 degrees or less, 2.0 degrees or more and 15.0 degrees or less, 3.0 degrees or more and 15.0 degrees or less, 3.5 degrees or more and 15.0 degrees or less, 1.5 degrees or more and 10.0 degrees or less, 2.0 degrees or more and 10.0 degrees or less, 3.0 degrees or more and 10.0 degrees or less, 3.5 degrees or more and 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 can be exemplified.

[0193] D1 to D5 of the plastic film are each preferably 5 degrees or more and 30 degrees or less, or 60 degrees or more and 85 degrees or less, more preferably 7 degrees or more and 25 degrees or less, or 65 degrees or more and 83 degrees or less, and further preferably 10 degrees or more and 23 degrees or less, or 67 degrees or more and 80 degrees or less.

[0194] By making D1 to D5 each 5 degrees or more and 85 degrees or less, it is possible to easily suppress the bluish blackness when observed with polarized sunglasses. In addition, by making D1 to D5 each 30 degrees or less and 60 degrees or more, it is possible to easily suppress the decrease in mechanical strength due to the decrease in the orientation of the plastic film.

[0195] As for the plastic film, for example, there are cases where it is in a sheet form and cases where it is in a roll form. In either case of the sheet form and the roll form, as long as the following criteria are met, a sample of 50 mm in the longitudinal direction x 50 mm in the lateral direction can be cut out from any position of the plastic film.

[0196] However, in a case where the directionality of the longitudinal direction and the lateral direction of the sheet and the roll can be confirmed, a sample is cut out along the confirmed longitudinal direction and lateral direction. For example, in the case of a roll, the flow direction (MD direction) of the roll can be regarded as the longitudinal direction, and the width direction (TD direction) of the roll can be regarded as the lateral direction. In a case where the flow direction and the width direction of a sheet can be confirmed, the flow direction can be regarded as the longitudinal direction, and the width direction can be regarded as the lateral direction. In a case where the flow direction and the width direction of a sheet are difficult to confirm, in a case where the sheet is a rectangle or a square, as long as the directionality of the longitudinal direction and the lateral direction is confirmed using the four sides constituting the rectangle or the square. In a case where the flow direction and the width direction of a sheet are difficult to confirm, in a case where the sheet is a shape other than a rectangle and a square (a circle, a triangle, and the like), as long as a rectangle or a square whose area does not exceed the outer frame shape of the sheet is drawn to be the largest, and the directionality of the longitudinal direction and the lateral direction is confirmed using the sides of the drawn rectangle or square.

[0197] A sample is cut out by removing 10 mm from the corner of the sheet and the roll. In the case of a sheet shape, for a sample of 50 mm in the longitudinal direction x 50 mm in the lateral direction, the four corners of the sheet are cut out first in order of priority, and the central portion of the sheet is cut out next in order of priority. Then, after the sample is cut out from the four corners and the central portion, in a case where a region exceeding 50 mm in the longitudinal direction x 50 mm in the lateral direction remains, sampling is performed in such a manner that a sample of 50 mm in the longitudinal direction x 50 mm in the lateral direction is cut out from the remaining region as much as possible.

[0198] Note that, in a case where a plurality of samples of 50 mm in the longitudinal direction x 50 mm in the lateral direction can be collected from a plastic film in a sheet shape, the proportion of samples satisfying Condition A among the plurality of samples is preferably 50% or more, more preferably 70% or more, further preferably 90% or more, and still further preferably 100%. The in-plane retardation, the thickness direction retardation, and other parameters such as Re / Rth are also the same.

[0199] Regarding a plastic film in a roll shape, in the width direction, each property easily varies, but in the flow direction, each property is almost the same. Therefore, in a case where a sample collected from a predetermined position in the width direction of the roll satisfies a predetermined property such as Condition A, for a portion having the same position in the width direction, it can be assumed that the predetermined property is satisfied on the whole in the flow direction of the roll.

[0200] The plastic film is preferably one that does not generate cracks or breakage after 100,000 times of the folding test shown in the examples (more preferably after 300,000 times). In addition, with respect to the plastic film, after 100,000 times of the folding test shown in the examples (more preferably after 300,000 times), the sample is placed on a horizontal table, at which time the angle at which the end of the sample is raised from the table is preferably 20 degrees or less, more preferably 15 degrees or less. An angle of 15 degrees or less at which the end of the sample is raised means that it is difficult to generate a wrinkle due to folding. In addition, for any direction of the average of the direction of the slow axis of the plastic film and the average of the direction of the fast axis, each preferably shows the aforementioned results (generation of no cracks, breakage, and wrinkles due to folding. The angle at which the end of the sample is raised after the test is 20 degrees or less).

[0201] Note that, with respect to the uniaxially stretched plastic film, when the folding test is performed, breakage occurs in the stretching direction, and a wrinkle is strongly left in the direction orthogonal to the stretching direction. Therefore, in the stretched film, a biaxially stretched plastic film is also preferable.

[0202] The lower limit of the thickness of the plastic film is preferably 10 μm or more, more preferably 15 μm or more, more preferably 21 μm or more, more preferably 25 μm or more, more preferably 30 μm or more, and the upper limit is preferably 200 μm or less, more preferably 180 μm or less, more preferably 150 μm or less, more preferably 100 μm or less, more preferably 80 μm or less, more preferably 60 μm or less, more preferably 50 μm or less.

[0203] By making the thickness 10 μm or more, it is easy to make the mechanical strength good. In addition, in order to reduce the moisture permeability and to make the polarizing plate long-lived, the thickness is preferably 21 μm or more, more preferably 30 μm or more. In addition, if it is a large-sized panel of 50 inches or more, when the panel is vertically erected, it is easy to generate deformation due to the weight of the plastic film. In order to suppress the deformation, the thickness of the plastic film is preferably 30 μm or more.

[0204] By making the thickness 200 μm or less, it is easy to make the in-plane retardation of the plastic film 2500 nm or less. In addition, in order to achieve thinning of the panel and the image display device, the thickness of the plastic film is preferably 60 μm or less, more preferably 50 μm or less.

[0205] The thickness of the plastic film is preferably in the range of 10 μm or more and 200 μm or less, 15 μm or more and 200 μm or less, 21 μm or more and 200 μm or less, 25 μm or more and 200 μm or less, 30 μm or more and 200 μm or less, 10 μm or more and 180 μm or less, 15 μm or more and 180 μm or less, 21 μm or more and 180 μm or less, 25 μm or more and 180 μm or less, 30 μm or more and 180 μm or less, 10 μm or more and 150 μm or less, 15 μm or more and 150 μm or less, 21 μm or more and 150 μm or less, 25 μm or more and 150 μm or less, 30 μm or more and 150 μm or less, 10 μm or more and 100 μm or less, 15 μm or more and 100 μm or less, 21 μm or more and 100 μm or less, 25 μm or more and 100 μm or less, 30 μm or more and 100 μm or less, 10 μm or more and 80 μm or less, 15 μm or more and 80 μm or less, 21 μm or more and 80 μm or less, 25 μm or more and 80 μm or less, 30 μm or more and 80 μm or less, 10 μm or more and 60 μm or less, 15 μm or more and 60 μm or less, 21 μm or more and 60 μm or less, 25 μm or more and 60 μm or less, 30 μm or more and 60 μm or less, 10 μm or more and 50 μm or less, 15 μm or more and 50 μm or less, 21 μm or more and 50 μm or less, 25 μm or more and 50 μm or less, 30 μm or more and 50 μm or less.

[0206] The haze of the plastic film according to JIS K7136:2000 is preferably 3.0% or less, more preferably 2.0% or less, further preferably 1.5% or less, and more further preferably 1.0% or less.

[0207] The total light transmittance of the plastic film according to JIS K7361-1:1997 is preferably 80% or more, more preferably 85% or more, and further preferably 90% or more.

[0208] <Corrosion Rate>

[0209] With respect to the plastic film, when the average value of the corrosion rate from the surface of the plastic film to a depth of 20 μm is defined as E 0-20 , E 0-20 is preferably 1.4 μm / g or more.

[0210] In the present specification, E 0-20 is measured under the following measurement conditions.

[0211] <Measurement Conditions>

[0212] A test liquid, which is a mixture of pure water, a dispersion liquid, and spherical silica having an average particle diameter of 4.2 μm within ±8%, is stored in a container in a mass ratio of 968:2:30. The test liquid in the container is supplied to a nozzle. Compressed air is supplied to the nozzle, the test liquid is accelerated in the nozzle, and a prescribed amount of the test liquid is sprayed perpendicularly to a first surface of the plastic film from a spray hole at the tip of the nozzle to cause the spherical silica in the test liquid to collide with the plastic film. The cross-sectional shape of the nozzle is a square of 1 mm x 1 mm, and the distance from the spray hole to the plastic film is 4 mm. In addition, the flow rates 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 in the nozzle are prescribed values adjusted by calibration described later.

[0213] After the prescribed amount of the test liquid is sprayed, the spraying of the test liquid is temporarily stopped.

[0214] After the spraying of the test liquid is temporarily stopped, the cross-sectional profile of the portion of the plastic film that collided with the spherical silica in the test liquid is measured.

[0215] The operation of spraying a prescribed amount of the test liquid from the spray hole, temporarily stopping the spraying of the test liquid after the prescribed amount of the test liquid is sprayed, and measuring the cross-sectional profile after the spraying of the test liquid is temporarily stopped is performed as one cycle in three steps until the depth of the cross-sectional profile exceeds 20 μm. Then, the erosion rate of the plastic film (μm / g) is calculated in each cycle until the depth of the cross-sectional profile reaches 20 μm. The erosion rates of the plastic film in each cycle until the depth of the cross-sectional profile reaches 20 μm are averaged, and the E 0-20 .

[0216] <Calibration>

[0217] The test liquid is stored in the container. The test liquid in the container is supplied to the nozzle. Compressed air is supplied to the nozzle, the test liquid is accelerated in the nozzle, and an arbitrary amount of the test liquid is sprayed perpendicularly to an acrylic plate having a thickness of 2 mm from a spray hole at the tip of the nozzle to cause the spherical silica in the test liquid to collide with the acrylic plate. The cross-sectional shape of the nozzle is a square of 1 mm x 1 mm, and the distance from the spray hole to the acrylic plate is 4 mm.

[0218] After the arbitrary amount of the test liquid is sprayed, the spraying of the test liquid is temporarily stopped. After the spraying of the test liquid is temporarily stopped, the cross-sectional profile of the portion of the acrylic plate that collided with the spherical silica in the test liquid is measured.

[0219] The erosion rate of the acrylic sheet (pm / g) is calculated by dividing the depth of the cross-sectional profile (pm) by the arbitrary amount (g).

[0220] The erosion rate of the acrylic sheet is set to be within ±5% of 1.88 (pm / g) as a pass condition, and the flow rates of the test liquid and the compressed air, the pressure of the compressed air, and the pressure of the test liquid in the nozzle are adjusted and corrected so that the erosion rate of the acrylic sheet becomes within the range.

[0221] Hereinafter, refer to Figure 7 The measurement conditions of the erosion rate and the technical significance of the erosion rate calculated by the measurement conditions will be described. As the measurement conditions of the erosion rate, for example, the following can be cited. Figure 7 Such a measurement device of the erosion rate, for example, can cite the MSE test device of the product number "MSE-A203" of Palmeso Co., Ltd. or the like.

[0222] In the measurement conditions of the erosion rate of the present disclosure, first, a test liquid in which pure water, a dispersant, and spherical silica having an average particle diameter within ±8% of 4.2 pm are mixed at a mass ratio of 968:2:30 is housed in the container (11). In the container (11), it is preferable to stir the test liquid.

[0223] As for the dispersant, there is no particular limitation as long as it can disperse the spherical silica. As the dispersant, for example, the product with the trade name "Demol N" of Wako Pure Chemical Industries, Ltd. can be cited.

[0224] As for "an average particle diameter within ±8% of 4.2 pm", in other words, it means that the average particle diameter is 3.864 pm or more and 4.536 pm or less.

[0225] In the measurement conditions of the erosion rate of the present specification, the "average particle diameter of the spherical silica" is an average particle diameter (so-called "median particle diameter") measured as a volume average value d50 in a particle size distribution measurement based on a laser diffraction method.

[0226] The spherical silica is preferably: in the result of the particle size distribution measurement, the width of the particle diameter at which the frequency is 50, when the frequency at which the particle diameter is the maximum is normalized to 100, is within ± 10% of 4.2 μm. As for the "width of the particle diameter at which the frequency is 50", when "the particle diameter at which the frequency is 50, and which is in the positive direction from the particle diameter at which the frequency is 100" is defined as X, and "the particle diameter at which the frequency is 50, and which is in the negative direction from the particle diameter at which the frequency is 100" is defined as Y, the "width of the particle diameter at which the frequency is 50" is represented by "X-Y (μm)". Note that in this specification, the "width of the particle diameter at which the frequency is 50" is sometimes referred to as "full width at half maximum of the particle size distribution".

[0227] As the spherical silica of which the average particle diameter is within ± 8% of 4.2 μm, for example, there can be mentioned the product of Palmeso Co., Ltd. designated as "MSE-BS-5-3". As the spherical silica which conforms to the product of Palmeso Co., Ltd. designated as "MSE-BS-5-3", for example, there can be mentioned the product of Potters-Ballotini Co., Ltd. with product number "BS5-3".

[0228] The test liquid in the container is fed to the nozzle (51). The test liquid can be, for example, delivered to the nozzle by a test liquid pipe (21). Preferably, a flow meter (31) for measuring the flow rate of the test liquid is arranged between the container (11) and the nozzle (51). The flow rate of the test liquid is set to the value adjusted by the correction.

[0229] In the Figure 8 , the nozzle (51) is arranged in a housing (52) constituting the jetting section (50).

[0230] Compressed air is delivered to the nozzle (51). The compressed air is fed to the nozzle, for example, by a compressed air pipe (22). In the nozzle, the position at which the compressed air is fed is preferably more upstream than the position at which the test liquid is fed. The upstream side refers to the side of the nozzle away from the jetting hole.

[0231] Preferably, a flow meter (32) for measuring the flow rate of the compressed air before the compressed air reaches the nozzle (51), and a pressure gauge (42) for measuring the pressure of the compressed air are arranged. The compressed air can be supplied from an air compressor or the like not shown.

[0232] The flow rate and the pressure of the compressed air are set to the values adjusted by the correction.

[0233] If compressed air is supplied to the nozzle (51), the test liquid is accelerated while being mixed with the compressed air. Moreover, the accelerated test liquid is ejected from the ejection hole at the tip of the nozzle (51) and collides perpendicularly with the plastic film (70). The plastic film is mainly abraded by the spherical silica particles in the test liquid.

[0234] A pressure gauge (41) that measures the pressure of the test liquid in the nozzle (51) is preferably provided. The pressure gauge (41) is preferably located at a position that is more downstream than the position at which the compressed air is supplied and the position at which the test liquid is supplied.

[0235] The pressure of the test liquid in the nozzle (51) is a value adjusted by the correction.

[0236] The test liquid ejected from the ejection hole at the tip of the nozzle (51) is mixed with air and ejected in a mist state. Therefore, the impact pressure of the spherical silica particles on the plastic film can be reduced. Thus, the amount of abrasion of the plastic film caused by one spherical silica particle can be suppressed to a small amount. Figure 8 is a schematic view of a state in which the plastic film (70) is abraded by the test liquid containing pure water (A1) and spherical silica (A2) that is ejected from the ejection section (50). In Figure 7 , reference numeral A3 denotes air, and reference numeral A4 denotes the plastic film after abrasion.

[0237] In addition, since the test liquid contains water that has an excellent cooling effect, deformation and deterioration of the plastic film caused by heat at the time of collision can be substantially excluded. That is, abnormal abrasion of the plastic film can be substantially excluded. In addition, water also has the effect of cleaning the surface of the plastic film after abrasion, thereby achieving stable abrasion. In addition, water has the effect of accelerating the spherical silica particles or controlling the flow of the test liquid.

[0238] In addition, since a large number of spherical silica particles collide with the plastic film, the effects of subtle differences in the physical properties of the individual spherical silica particles can be excluded.

[0239] Further, the measurement conditions of the present disclosure are values adjusted by the correction for 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 in the nozzle, and the cross-sectional shape of the nozzle is determined to be a square shape of 1 mm x 1 mm, and the distance of the ejection hole from the plastic film is determined to be 4 mm, thereby determining the elements that affect the amount of abrasion of the plastic film. The distance is the distance indicated by "d" of Figure 3 , and refers to the perpendicular distance of the ejection hole at the tip of the nozzle from the plastic film.

[0240] As described above, the measurement condition of the present disclosure can be said to be a measurement condition capable of forming a statistically stable abrasion mark on a plastic film.

[0241] The plastic film (70) is mounted on the sample mounting table (81) of the measurement device (100). The plastic film (70) is preferably mounted on the sample mounting table (81) via a support body (82) such as a stainless steel plate.

[0242] The test liquid sprayed to the plastic film (70) is preferably recovered by the receiver (12) and returned to the container (11) through the return pipe (23). A return pump (24) is preferably provided between the receiver (12) and the return pipe (23).

[0243] In the measurement condition of the present disclosure, as essential elements, there are: a step of temporarily stopping the spraying of the test liquid after spraying a prescribed amount of the test liquid; and a step of measuring the cross-sectional profile of the portion of the plastic film that collides with the spherical silica in the test liquid after temporarily stopping the spraying of the test liquid.

[0244] The cross-sectional profile refers to the cross-sectional shape of the plastic film that is abraded by the test liquid. The plastic film is mainly abraded by the spherical silica particles in the test liquid.

[0245] The cross-sectional profile is measured by, for example, a cross-sectional profile acquisition unit (60) such as a stylus-type surface shape measurement device and a laser interference-type surface shape measurement device. Note that the cross-sectional profile acquisition unit (60) is usually disposed at a position that is separated from the plastic film (70) when the test liquid is sprayed. Therefore, it is preferable that at least either the plastic film (70) or the cross-sectional profile acquisition unit (60) is movable.

[0246] The cross-sectional profile measurement means of the MSE test device of Palmeso Co., Ltd. with product number "MSE-A203" is a stylus type.

[0247] Further, in the measurement condition of the present disclosure, an operation of three steps as one cycle is performed until the depth of the cross-sectional profile exceeds 20 μm: a step of spraying a prescribed amount of the test liquid from the spray port; a step of temporarily stopping the spraying of the test liquid after spraying a prescribed amount of the test liquid; and a step of measuring the cross-sectional profile after temporarily stopping the spraying of the test liquid.

[0248] By performing the above operation, the erosion rate of the plastic film in each cycle can be measured, and further, the deviation of the erosion rate of the plastic film can be calculated.

[0249] The above cycle can also continue after the depth of the cross-sectional profile exceeds 20 μm, but it is preferable to end when the depth of the cross-sectional profile exceeds 20 μm. The reason for performing the measurement "from the surface of the plastic film to a depth of 20 μm" is that the physical properties of the plastic film tend to change easily near the surface, while becoming more stable towards the interior.

[0250] In this specification, the erosion rate of each cycle can be calculated by dividing the depth (μm) of the cross-sectional profile advanced in each cycle by the amount (g) of test liquid injected in each cycle. The depth (μm) of the cross-sectional profile in each cycle is the depth of the deepest point of the cross-sectional profile in each cycle.

[0251] The amount of test solution sprayed in each cycle is in principle "fixed quantity", but there may be some variation in each cycle.

[0252] There is no particular limitation on the amount of test solution sprayed in each cycle, 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.

[0253] Under the measurement conditions of this disclosure, the erosion rate (μm / g) is calculated for each cycle up to a depth of 20 μm in the cross-sectional profile. Then, the erosion rate for each cycle up to a depth of 20 μm in the cross-sectional profile is averaged to calculate E. 0-20 .

[0254] The loop is performed until the depth of the cross-sectional profile exceeds 20 μm, but the data for loops where the depth of the cross-sectional profile exceeds 20 μm is taken from the data used to calculate E. 0-20 The data deviates.

[0255] Generally speaking, soft plastic films are easily damaged, while hard plastic films are difficult to damage. The inventors investigated the following situation: [The invention will be based on...] PICODENTOR Values ​​obtained from evaluations including the depth direction (marvelous hardness, indentation hardness, elastic recovery work, etc.) are used as indicators of pencil hardness. However, these parameters, such as marvelous hardness, indentation hardness, and elastic recovery work, are sometimes unsuitable as indicators of pencil hardness.

[0256] In addition, plastic films tend to increase in strength when stretched. Specifically, compared to unstretched plastic films, uniaxially stretched plastic films tend to have better pencil hardness, and compared to uniaxially stretched plastic films, biaxially stretched plastic films tend to have better pencil hardness. However, even biaxially stretched plastic films can sometimes have insufficient pencil hardness.

[0257] As an index of the pencil hardness of the plastic film, the present inventors studied the erosion rate. As described above, the plastic film is easily damaged when it is soft, and the plastic film is difficult to damage when it is hard, and thus it is considered that the erosion rate is small, and the pencil hardness is good. However, the present inventors found, on the contrary, that the plastic film can have good pencil hardness by increasing the erosion rate (E 0-20 ) to 1.4 μm / g or more. In addition, the present inventors found that, regarding the erosion rate of the plastic film, the biaxially-stretched plastic film has a tendency to show a larger value than the uniaxially-stretched plastic film, and the erosion rate can be used to determine the pencil hardness of the biaxially-stretched plastic film.

[0258] The reason why the erosion rate of the plastic film is related to the pencil hardness is considered as follows.

[0259] As described above, under the measurement conditions of the present disclosure, the test liquid containing water and spherical silica is sprayed in a mist state after being mixed with air. Thus, it is considered that the collision pressure of the spherical silica particles against the plastic film is suppressed to be low. Therefore, in the case where the plastic film is soft, the stress at the time when the spherical silica collides with the plastic film is easily dispersed, and thus the plastic film is not easily damaged, and the erosion rate is low. On the other hand, it is considered that, in the case where the plastic film is hard, the stress at the time when the spherical silica collides with the plastic film is difficult to disperse, and thus the plastic film is easily damaged, and the erosion rate is high.

[0260] In addition, it is considered that the difference in the erosion rate in the biaxially-stretched plastic film is caused by the difference in the degree of elongation of the molecular chain, and the difference in the degree of orientation of the molecules, and the like. For example, for the biaxially-stretched plastic film, in principle, the molecules are stretched in the plane, but there are sometimes molecules that are not sufficiently stretched locally in the plane. In this way, it is considered that, if the proportion of the molecules that are not sufficiently stretched locally in the plane increases, the biaxially-stretched plastic film becomes soft locally, and thus the erosion rate decreases.

[0261] In addition, it is considered that even the biaxially-stretched plastic films that have the same in-plane retardation show different erosion rates due to the difference in the local molecular orientation. On the contrary, there are cases where even the biaxially-stretched plastic films that have the same erosion rate show different in-plane retardations due to the difference in the ratio of the stretching ratio in the flow direction to the stretching ratio in the width direction, and the like.

[0262] In order to make the pencil hardness of the plastic film good, E 0-20 It is preferably 1.4 μm / g or more, more preferably 1.6 μm / g or more, more preferably 1.8 μm / g or more, more preferably 1.9 μm / g or more, and more preferably 2.0 μm / g or more.

[0263] As described above, it can be considered that if the proportion of molecules that are not sufficiently stretched locally in-plane increases, the erosion rate decreases. In other words, it can be considered that if the erosion rate is high, the proportion of molecules that are not sufficiently stretched locally in-plane decreases. Therefore, by setting E 0-20 to 1.4 μm / g or more, it is possible to easily suppress the occurrence of wrinkles on the plastic film in a high-temperature environment.

[0264] In order to make the plastic film less likely to break, E 0-20 is preferably 3.0 μm / g or less, more preferably 2.5 μm / g or less, and further preferably 2.2 μm / g or less.

[0265] Even if the value of E 0-20 is the same, the characteristics of the plastic film can differ depending on the in-plane retardation and the like. For example, even if the value of E 0-20 is the same, in the case where the in-plane retardation exceeds 1450 nm, a crease can remain on the plastic film when the plastic film is folded, or the plastic film can break.

[0266] In addition, in the case of a plastic film in which E 0-20 is less than 1.4 μm / g, even if a cured film having a high hardness is formed on the plastic film, the hardness of the plastic film is not sufficient, and thus the pencil hardness of the cured film can not be good.

[0267] In the case of a plastic film in which E 0-20 is within the preferable numerical range, 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 more 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, 1.9 μm / g or more and 2.5 μm / g or less, 1.9 μm / g or more and 2.2 μm / g or less, 2.0 μm / g or more and 3.0 μm / g or less, 2.0 μm / g or more and 2.5 μm / g or less, and 2.0 μm / g or more and 2.2 μm / g or less, the plastic film is preferably used.

[0268] The plastic film has two planes, a front surface and a back surface. The plastic film is preferably one in which E 0-20 measured from one plane side is 1.4 μm / g or more, and E 0-20are the same values as described above. For a general plastic film, the erosion rate measured from one planar side is approximately the same as the erosion rate measured from the other planar side.

[0269] The correction is performed before the measurement of the erosion rate described above.

[0270] For example, the correction can be performed as follows.

[0271] <Correction>

[0272] The test liquid is housed in the container. The test liquid in the container is delivered to the nozzle. Compressed air is delivered to the nozzle, the test liquid is accelerated in the nozzle, and an arbitrary amount of the test liquid is sprayed perpendicularly from a spray hole at the end of the nozzle toward an acrylic plate having a thickness of 2 mm, and the spherical silica in the test liquid collides with the acrylic plate. The cross-sectional shape of the nozzle is a square of 1 mm x 1 mm, and the distance from the spray hole to the acrylic plate is 4 mm.

[0273] After the arbitrary amount of the test liquid is sprayed, the spraying of the test liquid is temporarily stopped. After the spraying of the test liquid is temporarily stopped, the cross-sectional profile of the portion of the acrylic plate that collided with the spherical silica in the test liquid is measured.

[0274] The erosion rate of the acrylic plate (μm / g) is calculated by dividing the depth of the cross-sectional profile (μm) by the arbitrary amount (g).

[0275] The erosion rate of the acrylic plate is taken as a pass condition in a range of ± 5% from 1.88 (μm / g), and the flow rate of the test liquid and the compressed air, the pressure of the compressed air, and the pressure of the test liquid in the nozzle are adjusted and corrected in such a manner that the erosion rate of the acrylic plate becomes in the range.

[0276] The test liquid used in the correction is the same as the test liquid used under the measurement conditions implemented thereafter.

[0277] In addition, the measurement device used in the correction is the same as the measurement device used under the measurement conditions implemented thereafter.

[0278] The difference between the correction and the measurement conditions implemented thereafter is that, for example, an acrylic plate having a thickness of 2 mm is used as a standard sample in the correction, and a plastic film is used as a sample in the measurement conditions.

[0279] The thickness of the acrylic plate used as the standard test piece is preferably 2 mm, and is preferably a polymethyl methacrylate plate (PMMA plate). In addition, for the acrylic plate having a thickness of 2 mm used as the standard test piece, the average value of the erosion rate of the acrylic plate measured under the following Measurement Condition A is defined as AcE, and AcE is preferably 1.786 μm / g or more and 1.974 μm / g or less. In addition, as the spherical silica under the following Measurement Condition A, a spherical silica of a type "MSE-BS-5-3" designated by Palmeso Co., Ltd. can be cited. As the spherical silica of the type "MSE-BS-5-3" designated by Palmeso Co., Ltd., for example, a product of Product No. "BS5-3" of Potters-Ballotini Co., Ltd. can be cited.

[0280] Measurement Condition A

[0281] The test liquid, which is a mixture of pure water, a dispersant, and spherical silica having an average particle diameter of 4.2 μm ± 8% at a mass ratio of 968:2:30, was stored in a container. The test liquid in the container was supplied to a nozzle. Compressed air was supplied to the nozzle, and the test liquid was accelerated in the nozzle, and a prescribed amount of the test liquid was sprayed vertically from a spray hole at the tip of the nozzle to the acrylic plate, and the spherical silica in the test liquid collided with the acrylic plate. The cross-sectional shape of the nozzle was a square of 1 mm x 1 mm, and the distance from the spray hole to the acrylic plate was 4 mm. In addition, the flow rates 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 in the nozzle were as follows: the flow rate of the test liquid was 100 ml / min or more and 150 ml / min or less, the flow rate of the compressed air was 4.96 L / min or more and 7.44 L / min or less, the pressure of the compressed air was 0.184 MPa or more and 0.277 MPa or less, and the pressure of the test liquid in the nozzle was 0.169 MPa or more and 0.254 MPa or less.

[0282] After 4 g of the test liquid was sprayed, the spraying of the test liquid was temporarily stopped.

[0283] After the spraying of the test liquid was temporarily stopped, the cross-sectional profile of the portion of the acrylic plate that collided with the spherical silica in the test liquid was measured.

[0284] Then, the erosion rate AcE (unit: "μm / g") of the acrylic plate was calculated by dividing the depth of the cross-sectional profile (μm) by the amount of the test liquid sprayed (4 g).

[0285] In the correction, the erosion rate of the acrylic plate was set to be within ±5% of 1.88 (μm / g) as a pass condition, and adjustment was performed on the flow rates of the test liquid and the compressed air, the pressure of the compressed air, and the pressure of the test liquid in the nozzle so that the erosion rate of the acrylic plate would be within the range.

[0286] Regarding "the erosion rate is within ±5% of 1.88 (μm / g)", in other words, the erosion rate is 1.786 (μm / g) or more and 1.974 (μm / g) or less.

[0287] <σ 0-20 / E 0-20 >

[0288] The plastic film is preferably such that, when the deviation of the erosion rate calculated from the erosion rate from the surface of the plastic film to a depth of 20 μm is defined as σ 0-20 / E 0-20 , σ 0-20 / E

[0289] In the present specification, σ 0-20 / E

[0290] σ 0-20 / E 0-20 represents the coefficient of variation of the erosion rate, and σ 0-20 / E 0-20 / E 0-20 / E 0-20 of 0.100 or less, the erosion rate in the thickness direction of the plastic film is stabilized, and it is possible to easily make the pencil hardness better.

[0291] The upper limit of σ 0-20 / E 0-20 is more preferably 0.080 or less, further preferably 0.070 or less, further preferably 0.060 or less, and further preferably 0.055 or less.

[0292] The lower limit of σ 0-20 / E 0-20 is not particularly limited, but is generally more than 0, and is preferably 0.020 or more, and more preferably 0.035 or more. In addition, in the case where the value of σ 0-20 / E 0-20 is low, the stretch of the plastic film is sometimes weak. The plastic film having a weak stretch has a tendency to have poor solvent resistance, to be easily broken, and to have low stability against heat and humidity. Therefore, σ 0-20 / E0-20 Preferably, it is 0.020 or more.

[0293] Regarding σ 0-20 / E 0-20 For example, the following can be mentioned as embodiments of the preferable numerical range of σ

[0294] The plastic film has two planes, a front plane and a back plane. The plastic film is preferably one in which σ 0-20 / E 0-20 and σ 0-20 / E 0-20 measured from the other plane side are each the above value.

[0295] The plastic film preferably has a pencil hardness of HB or more, more preferably F or more.

[0296] When the pencil hardness of the plastic film is too high, there is a tendency that the in-plane retardation of the plastic film becomes large. Therefore, the pencil hardness of the plastic film is preferably 2H or less.

[0297] In the present specification, the pencil hardness is measured and determined according to the following (1) to (6).

[0298] (1) A sample is prepared by cutting the plastic film to 5 cm x 10 cm.

[0299] (2) The plastic film is heated at 100°C for 10 minutes. After the heating, the plastic film is left to stand in an environment of 24°C and a relative humidity of 40% or more and 60% or less for 30 minutes or more and 60 minutes or less.

[0300] (3) The pencil hardness is measured according to the scratch hardness (pencil method) of JIS K 5600-5-4: 1999 for the plastic film. Specifically, a pencil having a prescribed hardness is brought into contact with the surface of the plastic film at an angle of 45°, and moved at a speed of 3.0 mm / sec under a load of 100 g, thereby applying a load to the plastic film.

[0301] (4) After the load is applied to the plastic film, the sample is again heated at 100°C for 10 minutes.

[0302] (5) Immediately after the re-warming, the damage to the plastic film is visually evaluated. The environment for the visual evaluation is set to a temperature of 24°C and a relative humidity of 40% or more and 60% or less.

[0303] (6) The operations of (1) to (5) above are performed 5 times. Then, the hardest pencil among the pencils that have not been damaged in 4 or more of the 5 times is taken as the pencil hardness of the plastic film that is the evaluation object.

[0304] In the measurement and determination method of the pencil hardness described above, in the case where the hardness B is not damaged in 4 of the 5 times and the hardness F is not damaged in 3 of the 5 times, the determination is made for the hardness B.

[0305] In the case where the plastic film has a slow axis and a fast axis, it is preferable that the pencil hardness be B or more in either of the slow axis direction and the fast axis direction. The slow axis of the plastic film refers to the direction in which the in-plane refractive index of the plastic film is the highest. The fast axis of the plastic film refers to the direction in which the in-plane refractive index of the plastic film is orthogonal to the slow axis.

[0306] As for the layered structure of the plastic film, a single-layer structure and a multi-layer structure can be cited. Of these, the single-layer structure is preferable.

[0307] In order to have a good mechanical strength while suppressing rainbow flare, the plastic film is preferably a biaxially-stretched plastic film having a small in-plane retardation. Also, in order to reduce the in-plane retardation of the stretched plastic film, it is preferable to make the stretching in the flow direction and the width direction approximately equal. In addition, in order to make the etching rate of the plastic film be in the range described above, it is preferable to uniformly elongate the molecules in the plane of the plastic film. Therefore, in order to make the average of the in-plane retardation and the etching rate of the plastic film be in the range described above, it is important to control the stretching. As for the stretching control, in a multi-layer structure, it is difficult to perform fine stretching control due to the difference in the properties of the layers and the like, but the single-layer structure is preferable in that it is easy to perform fine stretching control.

[0308] Example of the Production of a Plastic Film

[0309] Hereinafter, an example of the production of a plastic film will be described taking a biaxially-stretched plastic film as a representative example.

[0310] A biaxially-stretched plastic film can be obtained by stretching a resin layer containing the components that constitute the plastic film. As for the method of stretching, sequential biaxial stretching and simultaneous biaxial stretching can be cited.

[0311] Sequential Biaxial Stretching

[0312] In sequential biaxial stretching, after the cast film is stretched in the flow direction, stretching in the width direction of the film is performed.

[0313] The stretching in the flow direction is usually performed using a difference in peripheral speed of a pair of stretching rollers. The stretching in the flow direction can be performed in one stage, or can be performed in multiple stages using multiple pairs of stretching rollers. In order to suppress excessive deviation of optical characteristics such as in-plane retardation, it is preferable to bring multiple nip rollers close to the stretching rollers. The stretching ratio in the flow direction is usually 2 or more and 15 or less, and in order to suppress excessive deviation of optical characteristics such as in-plane retardation, it is preferable to be 2 or more and 7 or less, more preferably 3 or more and 5 or less, and further preferably 3 or more and 4 or less.

[0314] In order to suppress excessive deviation of optical characteristics such as in-plane retardation, the stretching temperature is preferably the glass transition temperature of the resin or more and the glass transition temperature + 100°C or less. In the case of PET, it is preferable to be 70°C or more and 120°C or less, more preferably 80°C or more and 110°C or less, and further preferably 95°C or more and 110°C or less. The stretching temperature refers to the set temperature of the device. In addition, even if the set temperature of the device is set within the range, time is required until the temperature stabilizes. Therefore, it is preferable to set the temperature within the range, and further, to manufacture the plastic film after the temperature stabilizes. In the present specification, the set temperature of the device is described at multiple sites. The set temperature of the other sites is also the same as the foregoing, and it is preferable to manufacture the plastic film after the temperature stabilizes.

[0315] Regarding the stretching temperature, by shortening the stretching interval at low temperature by rapidly increasing the temperature of the film or the like, there is a tendency that the average value of the in-plane retardation becomes small. On the other hand, by lengthening the stretching interval at low temperature by slowly increasing the temperature of the film or the like, there is a tendency that the orientation increases, the average value of the in-plane retardation becomes large, and the deviation of the slow axis becomes small.

[0316] When heating is performed at the time of stretching, it is preferable to use a heater that generates turbulence. By heating with air containing turbulence, a temperature difference is generated in a fine region in the film plane, a fine shift is generated in the orientation axis due to the temperature difference, and thus it is possible to easily satisfy Condition A. By causing the plastic film to satisfy Condition A, it is possible to easily cause the optical film to satisfy Condition B. T to be within the range.

[0317] In addition, in the stretching in the flow direction, if the stretching time is shortened, there is a tendency that the etching rate decreases, and if the stretching time is lengthened, there is a tendency that the etching rate increases. The reason is considered to be that if the stretching time is short, the molecules in the plane of the plastic film are difficult to stretch equally, and on the other hand, if the stretching time is long, the molecules in the plane of the plastic film are easy to stretch equally. That is, in order to make E 0-20 It is preferable to lengthen the stretching time. Further, by moderately increasing the stretching ratio to the extent that the physical properties do not deviate, while lengthening the stretching time, it is possible to more easily make E 0-201.4 μm / g or more.

[0318] The film stretched in the flow direction can also be given a function such as slipperiness, easy adhesion, antistatic property, etc. by online coating or offline coating. Surface treatment such as corona treatment, flame treatment, plasma treatment, etc. can be performed as needed before online coating or offline coating.

[0319] In the present specification, the layer formed by online coating or offline coating is not counted as the number of layers constituting the plastic film.

[0320] As for the stretching in the width direction, a tenter method is generally used, and the film is transported while being held by grips at both ends, and stretched in the width direction. The stretching ratio in the width direction is usually 2 times or more and 15 times or less, and in order to suppress excessive deviation in optical characteristics such as in-plane retardation, it is preferably 2 times or more and 5 times or less, more preferably 3 times or more and 5 times or less, and further preferably 3 times or more and 4.5 times or less. It is preferable to make the width stretching ratio higher than the longitudinal stretching ratio.

[0321] The stretching temperature is preferably the glass transition temperature of the resin or more and the glass transition temperature + 110°C or less, and it is preferable to increase the temperature as it goes from the upstream to the downstream. The stretching temperature refers to the set temperature of the device. The upstream side refers to the side close to the point at which the stretching in the width direction is started. The downstream side refers to the side close to the point at which the stretching in the width direction is ended. Specifically, in the case where the transverse stretching section is divided into 2 by a length reference, the difference between the temperature of the upstream and the temperature of the downstream is preferably 20°C or more, more preferably 30°C or more, further preferably 35°C or more, and still further 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 further preferably 95°C or more and 105°C or less. By dividing the stretching section in the width direction into 2 and setting the difference between the stretching temperature of the first stage and the stretching temperature of the second stage, it is possible to control the surface temperature of the film at the time of stretching in the first stage and the surface temperature of the film at the time of stretching in the second stage to be different temperatures. Therefore, in each stretching stage, the orientation and the orientation crystallization do not proceed excessively, and it is possible to prevent the plastic film from becoming brittle, and thus it is possible to easily increase the pencil hardness.

[0322] In order to impart planarity and dimensional stability, the plastic film that has been sequentially biaxially stretched as described above is preferably subjected to heat treatment at a temperature above the stretching temperature and below the melting point in a tenter. The heat treatment temperature refers to the set temperature of the apparatus. Specifically, in the case of PET, heat setting is preferably performed in a range of 140°C or higher and 240°C or lower, more preferably 200°C or higher and 250°C or lower. In order to suppress excessive deviation of optical properties such as in-plane retardation, additional stretching of 1% or more and 10% or less is preferably performed in the first half of the heat treatment.

[0323] After the heat treatment of the plastic film, slow cooling to room temperature is performed, followed by winding. If necessary, relaxation treatment or the like can also be performed in conjunction with the heat treatment and slow cooling. In order to suppress excessive deviation of optical properties such as in-plane retardation, the relaxation rate during the heat treatment is preferably 0.5% or more and 5% or less, more preferably 0.5% or more and 3% or less, further preferably 0.8% or more and 2.5% or less, and more further preferably 1% or more and 2% or less. In order to suppress excessive deviation of optical properties such as in-plane retardation, the relaxation rate during the slow cooling is preferably 0.5% or more and 3% or less, more preferably 0.5% or more and 2% or less, further preferably 0.5% or more and 1.5% or less, and more further preferably 0.5% or more and 1.0% or less. In order to achieve good planarity, the temperature during the slow cooling is preferably 80°C or higher and 140°C or lower, more preferably 90°C or higher and 130°C or lower, further preferably 100°C or higher and 130°C or lower, and more further preferably 100°C or higher and 120°C or lower. The temperature during the slow cooling refers to the set temperature of the apparatus.

[0324] - simultaneous biaxial stretching -

[0325] The simultaneous biaxial stretching is performed by introducing the cast film into a simultaneous biaxial tenter, conveying the film while holding both ends of the film with clamps, and simultaneously and / or in stages stretching in the flow direction and the width direction. As the simultaneous biaxial stretching machine, there are a pantograph type, a screw type, a drive motor type, and a linear motor type, but the drive motor type or the linear motor type, which can arbitrarily change the stretching ratio and can perform relaxation treatment at an arbitrary site, is preferred.

[0326] The stretching ratio of the simultaneous biaxial stretching is usually 6 times or more and 50 times or less in terms of the area ratio. In order to suppress excessive deviation of optical properties such as in-plane retardation, the area ratio is preferably 8 times or more and 30 times or less, more preferably 9 times or more and 25 times or less, further preferably 9 times or more and 20 times or less, and more further preferably 10 times or more and 15 times or less. In the simultaneous biaxial stretching, it is preferred that the stretching ratio in the flow direction and the stretching ratio in the width direction be adjusted in a manner such that the area ratio becomes the above-mentioned range of 2 times or more and 15 times or less.

[0327] In the case of simultaneous biaxial stretching, in order to suppress the in-plane orientation difference, it is preferable to make the stretching ratio in the flow direction and the width direction substantially the same, and also to make the stretching speed in the flow direction and the width direction substantially the same.

[0328] In order to suppress excessive deviation of optical characteristics such as in-plane phase difference, the stretching temperature of 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 further preferably above 100°C and below 140°C. The stretching temperature refers to the set temperature of the device.

[0329] In order to impart planarity and dimensional stability, the film subjected to simultaneous biaxial stretching is preferably further subjected to heat treatment at a temperature above the stretching temperature and below the melting point in the heat fixation chamber of the tenter. The temperature of the heat treatment refers to the set temperature of the device. The conditions of the heat treatment are the same as those after sequential biaxial stretching.

[0330] <Low-refractive layer>

[0331] The low-refractive layer has the effect of improving the antireflection property of the optical film and easily suppressing the rainbow flare when observed with the naked eye. The low-refractive layer is preferably located on the surface of the optical film on the side having the low-refractive layer with respect to the plastic film. In a range not impeding the effects of the optical film of the present disclosure, a functional layer such as a stain-proof layer and an antistatic layer can also be provided on the low-refractive layer.

[0332] The light from the inside of the image display device toward the observer side is linearly polarized light at the stage of passing through the polarizing member, but after passing through the plastic film, the polarization state of the linearly polarized light is disturbed to become light in which P wave and S wave exist mixed. Also, since there is a difference in reflectance between P wave and S wave, and the reflectance difference has wavelength dependence, it is considered that the rainbow flare will be seen with the naked eye. Here, in the case where the low-refractive layer is provided on the plastic film, the aforementioned reflectance difference can be reduced, and thus it is considered that the rainbow flare can be easily suppressed.

[0333] However, as described above, in the case where the reflectance of the optical film having the low-refractive layer is reduced, it is difficult to make the uniformity of the color tone in the oblique observation good. It is considered that the reason is caused by the interference of the reflected light of the optical film having the low-refractive layer.

[0334] Therefore, in the case where the average refractive index of the low-refractive layer is defined as n1 and the average refractive index of the layer adjacent to the low-refractive layer is defined as n2, n2 / n1 is preferably less than 1.23. By making n2 / n1 less than 1.23, the interference of the reflected light can be suppressed, and thus the uniformity of the color tone in the oblique observation can be easily made good.

[0335] n2 / n1 is more preferably 1.20 or less, further preferably 1.15 or less, and still further preferably 1.13 or less. In particular, by making n2 / n1 1.05 or more and 1.15 or less, the wavelength dependence of the reflectance can be easily suppressed. In addition, by making n2 / n1 1.05 or more and 1.15 or less, the low refractive layer can be easily made less brittle.

[0336] If n2 / n1 is made too small, the visual reflectance Y value of the optical film easily becomes high. Therefore, n2 / n1 is preferably 1.05 or more, and more preferably 1.07 or more.

[0337] As for the preferable range of n2 / n1, 1.05 or more and less than 1.23, 1.05 or more and 1.20 or less, 1.05 or more and 1.15 or less, 1.05 or more and 1.13 or less, 1.07 or more and less than 1.23, 1.07 or more and 1.20 or less, 1.07 or more and 1.15 or less, 1.07 or more and 1.13 or less, and the like can be exemplified.

[0338] In order to easily make n2 / n1 in the above range, it is preferable to lower the value of n2. Therefore, the layer adjacent to the low refractive layer is preferably a plastic film or a hard coat layer, and more preferably a hard coat layer.

[0339] As for the average refractive index of each layer, for example, it can be measured or calculated using the following method on the basis of whether the thickness of each layer is more than 780 nm or 780 nm or less, which is determined from a cross-sectional photograph of the laminate.

[0340] - Average refractive index of a layer having a thickness more than 780 nm -

[0341] As for the average refractive index of a layer having a thickness more than 780 nm, the refractive index of the adhesive component of the layer is regarded as the refractive index of the layer. The average refractive index of a layer having a thickness more than 780 nm can be calculated, for example, by the Becke method described below. The refractive index of a plastic film, a hard coat layer, and an antiglare layer is preferably calculated by the Becke method.

[0342] Becke method

[0343] It is a method in which a layer that is the measurement target of the refractive index is shaved with a knife or the like, a sample in which the adhesive component is in a powder state is prepared, and calculation is performed by the Becke method according to the B method (for transparent materials in powder or granular form) of JIS K7142:2008.

[0344] - Average refractive index of a layer having a thickness 780 nm or less -

[0345] For a layer having a thickness of 780 nm or less, it is difficult to collect the adhesive component. Therefore, for the average refractive index of a layer having a thickness of 780 nm or less, for example, the laminate 1 having a layer having a thickness of 780 nm or less can be prepared, and the average refractive index can be calculated according to the following steps (Y1), (Y2). The refractive index n1 of the low-refractive layer is preferably calculated according to the following steps (Y1), (Y2).

[0346] (Y1) The average refractive index of a layer having a thickness exceeding 780 nm among the layers constituting the laminate 1 is calculated by the Becke method described above. Further, the thickness of the layer having a thickness exceeding 780 nm and the thickness of the layer having a thickness of 780 nm or less are calculated from the cross-sectional photograph of the laminate.

[0347] (Y2) Using the information of the average refractive index and the thickness of the layer having a thickness exceeding 780 nm calculated in the above (Y1) and the information of the thickness of the layer having a thickness of 780 nm or less, the average refractive index of the layer having a thickness of 780 nm or less is calculated by the fitting method described below. The average refractive index n1 of the low-refractive layer is preferably in the range described later.

[0348] "Fitting method"

[0349] It is a method of calculating by fitting of the reflection spectrum measured by the reflection spectrometer with the reflection spectrum calculated by the optical model of the multilayer film using the Fresnel coefficient.

[0350] The average refractive index n2 of the layer adjacent to the low-refractive layer is preferably greater than the average refractive index n1 of the low-refractive layer. n2 is preferably in the range where n1 is in the range described later and n2 / n1 satisfies the range. n2 is preferably 1.42 or more and 1.60 or less, more preferably 1.45 or more and 1.58 or less.

[0351] From the viewpoint of suppressing rainbow flare, the refractive index of the low-refractive layer is preferably 1.45 or less, more preferably 1.43 or less, and more preferably 1.40 or less.

[0352] If the refractive index of the low-refractive layer is too low, there is a tendency that the value of the optical film Σ T Therefore, the refractive index of the low-refractive layer is preferably 1.30 or more, more preferably 1.33 or more, and further preferably 1.35 or more.

[0353] The thickness of the low-refractive layer is preferably 60 nm or more and 200 nm or less, more preferably 80 nm or more and 120 nm or less, further preferably 85 nm or more and 110 nm or less, and more further preferably 90 nm or more and 105 nm or less. The thickness of the low-refractive layer is preferably greater than the average particle diameter of the low-refractive particles such as hollow particles.

[0354] As a method of forming a low refractive index layer, wet and dry methods can be roughly classified. As the wet method, a method of forming by sol-gel method using a metal alkoxide or the like, a method of forming by coating a low refractive index resin such as a fluorine resin, and a method of forming by coating a low refractive index layer forming coating liquid containing low refractive index particles in a resin composition can be listed. As the dry method, a method of selecting particles having a desired refractive index from low refractive index particles described later and forming by physical vapor deposition method or chemical vapor deposition method can be listed.

[0355] The wet method is superior to the dry method in terms of production efficiency, suppression of oblique reflection color, and chemical resistance. In the wet method, it is preferable to form using a low refractive index layer forming coating liquid containing low refractive index particles in an adhesive resin composition for adhesion, water resistance, scratch resistance, and low refractive index.

[0356] As the low refractive index particles, hollow particles and non-hollow particles can be listed. As the low refractive index particles, either of the hollow particles and the non-hollow particles can be included alone, but both of the hollow particles and the non-hollow particles are preferably included. By including both of the hollow particles and the non-hollow particles, it is possible to suppress the reduction of the coating film strength while easily moderately reducing the refractive index of the low refractive index layer. On the other hand, in the case of including only the hollow particles, the refractive index of the low refractive index layer is excessively reduced, and the optical film Σ T It is difficult to satisfy the range.

[0357] The material of the hollow particles and the non-hollow particles can be any of inorganic compounds such as silica and magnesium fluoride, and organic compounds, but in order to achieve low refractive index and improve strength, silica is preferable. Hereinafter, a hollow silica particle and a non-hollow silica particle will be described as the center.

[0358] The hollow silica particle is a particle having a shell layer composed of silica, a particle interior surrounded by the shell layer being a void, and air contained in the interior of the void. The hollow silica particle is a particle in which the refractive index is reduced in proportion to the occupancy rate of the gas compared to the refractive index of silica as it is by containing the air. The non-hollow silica particle is a particle that is not hollow in the interior as in the hollow silica particle. The non-hollow silica particle is, for example, a solid silica particle.

[0359] The shape of the hollow silica particle and the non-hollow silica particle is not particularly limited, and can be a substantially spherical shape such as a regular spherical shape, a rotational ellipsoid shape, and a polyhedral shape that can approximate a sphere, or the like. Among them, if the scratch resistance is considered, a regular spherical shape, a rotational ellipsoid shape, or a substantially spherical shape is preferable.

[0360] The hollow silica particles, because they contain air inside, function to lower the refractive index of the low-refractive layer as a whole. By using hollow silica particles having a large particle diameter with an increased air ratio, the refractive index of the low-refractive layer can be further lowered. On the other hand, hollow silica particles tend to have poor mechanical strength. In particular, in the case of using hollow silica particles having a large particle diameter with an increased air ratio, there is a tendency to easily lower the scratch resistance of the low-refractive layer.

[0361] The non-hollow silica particles function to improve the scratch resistance of the low-refractive layer by being dispersed in the adhesive resin.

[0362] In order to contain the hollow silica particles and the non-hollow silica particles in the adhesive resin at a high concentration while dispersing the particles uniformly in the resin in the film thickness direction, it is important to bring the hollow silica particles close to each other and to cause the non-hollow particles to enter between the hollow silica particles by setting the average particle diameter of the hollow silica particles and the average particle diameter of the non-hollow silica particles to a prescribed range. The ratio of the average particle diameter of the non-hollow silica particles to the average particle diameter of the hollow silica particles (average particle diameter of non-hollow silica particles / average particle diameter of hollow silica particles) is preferably 0.29 or less, more preferably 0.27 or less. The ratio of the average particle diameters is preferably 0.05 or more, more preferably 0.10 or more.

[0363] The average particle diameter of the hollow silica particles is preferably less than the thickness of the low-refractive layer, and for example, can be 1 nm or more and 150 nm or less. The average particle diameter 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 further preferably 60 nm or more and 80 nm or less.

[0364] The average particle diameter of the non-hollow silica particles is preferably less than the thickness of the low-refractive layer, and for example, can be 0.5 nm or more and 100 nm or less. The average particle diameter 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 further preferably 10 nm or more and 15 nm or less.

[0365] The average particle diameter of the low-refractive particles can be calculated by the following operations (y1) to (y3).

[0366] (y1) A cross section of the low-refractive layer is photographed with a STEM. The acceleration voltage of the STEM is preferably set to 10 kV or more and 30 kV or less, and the magnification is preferably set to 50,000x or more and 300,000x or less.

[0367] (y2) From the observation image, 10 particles are extracted at random, and the particle diameters of the respective particles are calculated. The particle diameter is measured as the distance between the straight lines in the combination of two straight lines that sandwich the particle in a cross section, in which the distance between the two straight lines becomes the largest. In the case where the particles are agglomerated, the agglomerated particles are regarded as one particle and measured.

[0368] (y3) The same operation is performed 5 times in the observation images of other frames of the same sample, and the value obtained from the number average of the total of 50 particle diameters is taken as the average particle diameter of the low-refractive particles.

[0369] As for the hollow silica particles and the non-hollow silica particles, it is preferable that the surfaces are coated with a silane coupling agent. As for the silane coupling agent, a general silane coupling agent can be cited, and among them, a silane coupling agent having a (meth)acryl group or an epoxy group is preferable.

[0370] By subjecting the silica particles to surface treatment based on a silane coupling agent, the affinity of the silica particles to the adhesive resin is improved, and the agglomeration of the silica particles is less likely to occur. Therefore, the dispersion of the silica particles easily becomes uniform.

[0371] The more the content of the hollow silica particles, the higher the filling rate of the hollow silica particles in the adhesive resin, and the lower the refractive index of the low-refractive layer. Therefore, the content of the hollow silica particles is preferably 100 parts by mass or more, more preferably 120 parts by mass or more, with respect to 100 parts by mass of the adhesive resin.

[0372] On the other hand, when the content of the hollow silica particles is too much, the hollow silica particles are easily damaged or peeled off, and there is a tendency that the mechanical strength such as the scratch resistance of the low-refractive layer is reduced. When the content of the hollow silica particles is too much, there is a tendency that the refractive index of the low-refractive layer is excessively reduced, and the value of the optical film Σ T is difficult to satisfy the range. Therefore, the content of the hollow silica particles is preferably 200 parts by mass or less, more preferably 180 parts by mass or less, and further preferably 160 parts by mass or less, with respect to 100 parts by mass of the adhesive resin.

[0373] In order to make the scratch resistance of the low-refractive layer good, the content of the non-hollow silica particles is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, with respect to 100 parts by mass of the adhesive resin.

[0374] On the other hand, if the content of the non-hollow silica particles is too much, the non-hollow silica particles are easily agglomerated. Therefore, the content of the non-hollow silica particles is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, with respect to 100 parts by mass of the adhesive resin.

[0375] The adhesive resin of the low refractive index layer preferably contains a cured product of an ionizing radiation-curable resin composition.

[0376] The ionizing radiation-curable resin composition is a composition containing a compound having an ionizing radiation-curable functional group (hereinafter, also referred to as "ionizing radiation-curable compound"). As the ionizing radiation-curable functional group, an ethylenic unsaturated bond group such as (meth)acryloyl group, vinyl group, allyl group, and the like, and an epoxy group, oxetane group, and the like can be exemplified.

[0377] As the ionizing radiation-curable compound, a compound having an ethylenic unsaturated bond group is preferable, a compound having two or more ethylenic unsaturated bond groups is more preferable, and a multifunctional (meth)acrylate compound having two or more ethylenic unsaturated bond groups is further preferable. As the multifunctional (meth)acrylate compound, either of a monomer and an oligomer can be used.

[0378] The ionizing radiation refers to an electromagnetic wave or a charged particle beam having an energy quantum capable of polymerizing or crosslinking molecules among electromagnetic waves or charged particle beams, and ultraviolet rays (UV) or electron beams (EB) are generally used, but electromagnetic waves such as X-rays, γ-rays, and charged particle beams such as α-rays, ion rays can also be used.

[0379] As the 2-functional (meth)acrylate monomer in the multifunctional (meth)acrylate compound, ethylene glycol di(meth)acrylate, bisphenol A tetraethoxy diacrylate, bisphenol A tetrapropoxy diacrylate, 1,6-hexanediol diacrylate, and the like can be exemplified.

[0380] As the (meth)acrylate monomer of 3 or more functions, for example, 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, and the like can be exemplified.

[0381] The above (meth)acrylate monomer can be a monomer in which a part of the molecular skeleton is modified, and a monomer modified with ethylene oxide, propylene oxide, caprolactone, isocyanuric acid, alkyl group, cyclic alkyl group, aromatic group, bisphenol, and the like can also be used.

[0382] As the multifunctional (meth)acrylate oligomer, urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, polyether (meth)acrylate, and the like can be exemplified.

[0383] As the urethane (meth) acrylate, for example, a (meth) acrylate obtained by reacting a polyol and an organic diisocyanate with a hydroxy (meth) acrylate.

[0384] The preferred epoxy (meth) acrylate is a (meth) acrylate obtained by reacting a 3 or more functional aromatic epoxy resin, an alicyclic epoxy resin, an aliphatic epoxy resin, or the like with (meth) acrylic acid; a (meth) acrylate obtained by reacting a 2 or more functional aromatic epoxy resin, an alicyclic epoxy resin, an aliphatic epoxy resin, or the like with a polybasic acid and (meth) acrylic acid; and a (meth) acrylate obtained by reacting a 2 or more functional aromatic epoxy resin, an alicyclic epoxy resin, an aliphatic epoxy resin, or the like with a phenol and (meth) acrylic acid.

[0385] As the ionizing radiation-curable compound, one kind can be used alone or two or more kinds can be used in combination.

[0386] In the case where the ionizing radiation-curable compound is an ultraviolet-curable compound, the ionizing radiation-curable resin composition preferably contains an additive such as a photopolymerization initiator or a photopolymerization accelerator.

[0387] As the photopolymerization initiator, one or more kinds selected from the group consisting of phenones, benzophenones, α-hydroxyalkylphenones, Michler's ketone, benzoin, benzyl dimethyl ketal, benzoylbenzoic acid esters, α-acyloxime esters, α-aminoalkylphenones, anthraquinones, haloketones, thioxanthone-based compounds, and the like can be exemplified.

[0388] The photopolymerization accelerator can reduce the polymerization inhibition by air at the time of curing, thereby accelerating the curing speed, and for example, one or more kinds selected from the group consisting of isopentyl-p-dimethylaminobenzoate, ethyl-p-dimethylaminobenzoate, and the like can be exemplified.

[0389] In the low-refractive layer, a leveling agent can be contained for the purpose of stain resistance and surface smoothness. As the leveling agent, fluorine-based and silicone-based ones can be exemplified, but the silicone-based one is preferred. By containing the silicone-based leveling agent, the sliding property and the stain resistance of the surface of the low-refractive layer can be made good. As specific examples of "the stain resistance is good", examples in which the fingerprint wiping property is good and the contact angle with respect to pure water and hexadecane is large can be exemplified.

[0390] The content of the leveling agent is preferably 0.01 parts by mass or more and 10 parts by mass or less, more preferably 0.05 parts by mass or more and 1 part by mass or less, with respect to 100 parts by mass of the adhesive resin.

[0391] The low-refractive layer can be formed, for example, by coating a low-refractive layer forming coating liquid in which the components constituting the low-refractive layer are dissolved or dispersed, and drying. In the low-refractive layer forming coating liquid, a solvent can be contained in order to adjust the viscosity or to enable the components to be dissolved or dispersed.

[0392] <Reflectance>

[0393] The visual reflectance Y value measured from the low-refractive layer side of the optical film according to the present disclosure is preferably 4.0% or less, more preferably 2.0% or less, further preferably 1.7% or less, and more further preferably 1.5% or less.

[0394] If the visual reflectance of the optical film is too low, there is a tendency that the value of Σ T is difficult to satisfy the range. Therefore, the visual reflectance Y value is preferably 0.5% or more, more preferably 0.7% or more, and further preferably 1.0% or more.

[0395] In the present specification, the visual reflectance Y value means the visual reflectance Y value of the CIE 1931 standard colorimetric system. For the reflectance, it is preferable to measure any 10 sites of one sample, and to calculate the average of the values of 8 sites excluding the maximum and minimum values.

[0396] In the present specification, the reflectance of the optical film is measured by preparing a sample in which a black plate is attached to the side opposite to the reflectance measurement surface of the optical film via a transparent adhesive layer, and measuring the reflectance by making light enter from the low-refractive layer side of the sample at an incident angle of 5°. The light source at the time of measuring the reflectance is preferably a C light source.

[0397] The difference in the refractive index between the member (e.g., plastic film) of the sample that is in contact with the transparent adhesive layer, and the transparent adhesive layer is preferably set to be 0.15 or less, more preferably 0.10 or less, more preferably 0.05 or less, and more preferably 0.01 or less. The black plate is preferably a black plate having a total light transmittance of 1% or less according to JIS K7361-1:1997, and more preferably 0%. The difference in the refractive index between the resin constituting the black plate and the refractive index of the transparent adhesive layer is preferably set to be 0.15 or less, more preferably 0.10 or less, more preferably 0.05 or less, and more preferably 0.01 or less.

[0398] <Haze, Total Light Transmittance>

[0399] The haze of the optical film according to JIS K7136:2000 is preferably 5% or less, more preferably 4% or less, and further preferably 3% or less. In the case where anti-glare properties are required, the upper limit of the haze of the optical film can be 90% or less, 65% or less, or 40% or less. The haze of the optical film according to JIS K7136:2000 is preferably 0.5% or more, more preferably 1.0% or more, and further preferably 1.5% or more. The haze refers to the haze of the entire optical film.

[0400] The total light transmittance of the optical film according to JIS K7361-1:1997 is preferably 80% or more, more preferably 90% or more, further preferably 91% or more, and still further preferably 92% or more.

[0401] <Other Layer>

[0402] The optical film of the present disclosure can also have other layers in addition to the plastic film and the low refractive index layer. The low refractive index layer, and the other layers in addition to the low refractive index layer are preferably optically isotropic. A layer having optical isotropy refers to a layer having an in-plane retardation of 20 nm or less, preferably 10 nm or less, and more preferably 5 nm or less.

[0403] As the other layers in addition to the plastic film and the low refractive index layer, an anti-fouling layer, a hard coat layer, an anti-glare layer, and a high refractive index layer, etc. can be listed, and the hard coat layer and the anti-glare layer are preferred. That is, the optical film of the present disclosure preferably has one or more layers selected from the group consisting of a hard coat layer and an anti-glare layer between the plastic film and the low refractive index layer. Among them, the hard coat layer is preferred. In a range not impairing the effects of the optical film of the present disclosure, an anti-fouling layer can be provided on the side of the low refractive index layer opposite to the plastic film. For example, in a range not impairing the effects of the optical film of the present disclosure, a plastic film, a low refractive index layer, and an anti-fouling layer can be sequentially provided.

[0404] <Hard Coat Layer>

[0405] A hard coat layer is formed as needed in order to improve the scratch resistance of the optical film. The hard coat layer is preferably formed between the plastic film and the low refractive index layer. In the case where the optical film further has a high refractive index layer, the hard coat layer, the high refractive index layer, and the low refractive index layer are preferably sequentially provided on the plastic film.

[0406] In order to have good scratch resistance, the hard coat layer preferably contains a cured product of a curable resin composition such as a thermally curable resin composition or an ionizing radiation curable resin composition, and more preferably contains a cured product of an ionizing radiation curable resin composition.

[0407] The thermosetting resin composition is a composition containing at least a thermosetting resin, and is a resin composition that is cured by heating. As the thermosetting resin, an acrylic resin, a urethane resin, a phenol resin, a urea melamine resin, an epoxy resin, an unsaturated polyester resin, a silicone resin, or the like can be exemplified. In the thermosetting resin composition, a curing agent is added to these curable resins as needed.

[0408] As the ionizing radiation-curable resin composition of the hard coat layer, the same composition as the ionizing radiation-curable resin composition exemplified in the low-refractive layer can be exemplified.

[0409] In the ionizing radiation-curable resin composition of the hard coat layer, a multifunctional (meth)acrylate oligomer is preferably contained as the ionizing radiation-curable compound. The lower limit of the number average molecular weight of the multifunctional (meth)acrylate oligomer is preferably 2000 or more, more preferably 2500 or more, and the upper limit is preferably 6000 or less, more preferably 5000 or less.

[0410] In the hard coat layer formed of a composition containing a multifunctional (meth)acrylate oligomer having a number average molecular weight of 2000 or more, the solvent of the coating solution for the low-refractive layer formation or the ionizing radiation-curable compound easily penetrates, and thus the reflection at the interface between the hard coat layer and the low-refractive layer can be suppressed. Thus, the interference of the reflected light of the optical film can be easily suppressed, and the Σ T is set to the range.

[0411] The hard coat layer formed of a composition containing a multifunctional (meth)acrylate oligomer having a number average molecular weight of 6000 or less can easily suppress the decrease in the hardness of the hard coat layer.

[0412] The content of the multifunctional (meth)acrylate oligomer having a number average molecular weight of 2000 or more and 6000 or less is preferably 5% by mass or more, more preferably 10% by mass or more, and further preferably 12% by mass or more, relative to the total amount of the ionizing radiation-curable compound in the ionizing radiation-curable resin composition of the hard coat layer.

[0413] In order to have good scratch resistance, the thickness of the hard coat layer is preferably 0.1 μm or more, more preferably 0.5 μm or more, further preferably 1.0 μm or more, and more further preferably 2.0 μm or more. In order to suppress curling, 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.

[0414] Antiglare layer

[0415] The antiglare layer can be formed, for example, from an antiglare layer-forming coating liquid containing an adhesive resin composition and particles. As the adhesive resin composition, for example, the curable resin composition exemplified in the hard coat layer can be used.

[0416] The particles can use any of organic particles and inorganic particles. As the organic particles, particles formed of polymethyl methacrylate, polyacrylic-styrene copolymer, melamine resin, polycarbonate, polystyrene, polyvinyl chloride, benzoguanamine-melamine-formaldehyde condensate, silicone, fluorine-based resin, and polyester-based resin, etc. can be listed. As the inorganic particles, particles composed of silica, alumina, antimony, zirconia, and titanium dioxide, etc. can be listed.

[0417] The average particle diameter of the organic particles in the antiglare layer differs depending on the thickness of the antiglare layer, and thus cannot be generalized, but is preferably 0.5 μm or more and 10.0 μm or less, more preferably 1.0 μm or more and 8.0 μm or less, and further preferably 1.5 μm or more and 6.0 μm or less.

[0418] The inorganic particles are apt to aggregate. Therefore, the average particle diameter of the inorganic particles is not limited to the above, and is preferably 1 nm or more and 10 μm or less.

[0419] The average particle diameter of the particles of the antiglare layer can be calculated by the following operations (z1) to (z3).

[0420] (z1) An image of the antiglare layer is captured with an optical microscope or STEM. In the case where the average particle diameter of the particles is in the micron order, it is preferable to capture an image of the plane of the antiglare layer using an optical microscope. At this time, the magnification is preferably 500x or more and 2000x or less. In the case where the average particle diameter of the particles is in the nanometer order, it is preferable to capture an image of the cross section of the antiglare layer using STEM. At this time, the magnification is preferably 20000x or more and 100000x or less. The acceleration voltage of STEM is preferably 10 kV or more and 30 kV or less.

[0421] (z2) From the observed image, 10 arbitrary particles are extracted, and the particle diameter of each particle is calculated. The particle diameter is measured as the distance between the two straight lines in the combination of the two straight lines that sandwich the cross section of the particle, when the two straight lines are arbitrarily set to be parallel.

[0422] (z3) The same operation is performed 5 times in the observed image of another plane of the same sample, and the value obtained from the number average of the total of 50 particle diameters is taken as the average particle diameter of the particles in the antiglare layer.

[0423] The content of the particles in the antiglare layer varies depending on the degree of antiglare properties as the object, and thus cannot be generalized, and is preferably 1 part by mass or more and 100 parts by mass or less, more preferably 5 parts by mass or more and 50 parts by mass or less, and further preferably 10 parts by mass or more and 30 parts by mass or less, with respect to 100 parts by mass of the resin component.

[0424] In order to impart antistatic properties, control the refractive index, or adjust the shrinkage of the antiglare layer caused by curing of the curable resin composition, the antiglare layer can contain microparticles having an average particle diameter of less than 500 nm.

[0425] The thickness of the antiglare layer is preferably 0.5 μm or more, more preferably 1.0 μm or more, and further preferably 2.0 μm or more. The thickness of the antiglare 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 have good hardness of the antiglare layer, the thickness of the antiglare layer is preferably thicker than the average particle diameter of the particles.

[0426] <Examples of layer structure>

[0427] The following (1) to (5) are examples of the layer structure of the optical film of the present disclosure. Of the following structures, (2) and (4) are preferred.

[0428] (1) A structure having a low-refractive-index layer on a plastic film.

[0429] (2) A structure having a hard coat layer and a low-refractive-index layer in this order on a plastic film.

[0430] (3) A structure having a high-refractive-index layer and a low-refractive-index layer in this order on a plastic film.

[0431] (4) A structure having an antiglare layer and a low-refractive-index layer in this order on a plastic film.

[0432] (5) A structure having a hard coat layer, a high-refractive-index layer, and a low-refractive-index layer in this order on a plastic film.

[0433] <Shape, size>

[0434] The optical film can be in a single-piece shape cut to a prescribed size, or can be in a roll shape in which a long strip is wound into a roll. The size of the single piece is not particularly limited, but the maximum diameter is about 2 inches or more and 500 inches or less. In the present disclosure, the size of the single piece is preferably 30 inches or more and 100 inches or less, and more preferably 40 inches or more and 100 inches or less. The "maximum diameter" refers to the maximum length when connecting any two points of the optical film. For example, in the case where the optical film is rectangular, the diagonal of the rectangular region is the maximum diameter. In the case where the optical film is circular, the diameter is the maximum diameter.

[0435] The width and length of the roll shape are not particularly limited, and in general, 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 of the roll shape can be cut into a single sheet and used according to the size of an image display device or the like. At the time of cutting, the end portion of the roll, which is unstable in physical properties, is preferably removed.

[0436] The shape of the single sheet is also not particularly limited, and can be, for example, a polygonal shape (triangle, rectangle, pentagon, etc.), a circular shape, or a random irregular shape. In the case where the optical film is a rectangular shape, the aspect ratio of the rectangle is not particularly limited as long as it is not problematic as a display screen. For example, the following can be cited: 1:1, 4:3, 16:10, 16:9, 2:1, 5:4, and the like.

[0437] <Usage>

[0438] The optical film of the present disclosure can be suitably used as an optical film for an image display device.

[0439] 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. At this time, it is preferable to have a polarizing member between the display element and the optical film of the present disclosure.

[0440] In the case where the plastic film satisfies Condition A, the case where a crease remains after the bending test or the case where a breakage occurs can be suppressed regardless of the direction of the bending. Therefore, in the case where the plastic film satisfies Condition A, the plastic film can be more suitably used as a plastic film for a curved image display device and a foldable image display device.

[0441] In addition, the optical film of the present disclosure can also be used as a member at the time of 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, it is only necessary to form a transfer layer on the side of the plastic film opposite to the side having the low-refractive-layer. In addition, as the member, a substrate for protecting or reinforcing a functional film during the manufacturing process of the functional film can be cited.

[0442] [Polarizing plate]

[0443] The polarizing plate of the present disclosure has a polarizing member, a first transparent protective plate on one side of the polarizing member, and a second transparent protective plate on the other side of the polarizing member, at least one of the first transparent protective plate and the second transparent protective plate being the optical film of the present disclosure described above, the side of the low-refractive-layer of the optical film facing the side opposite to the polarizing member.

[0444] Figure 3 is a cross-sectional view showing an embodiment of the polarizing plate 700 of the present disclosure. Figure 3The polarizing plate 700 of the present embodiment has a polarizing member 300, a first transparent protective sheet 500 disposed on one side of the polarizing member, and a second transparent protective sheet 600 disposed on the other side of the polarizing member. Figure 3 The polarizing plate 700 of the present embodiment uses the optical film 100 as the first transparent protective sheet 500. In the present embodiment, the low-refractive layer 30 side of the optical film 100 faces the side opposite to the polarizing member 300. Figure 3 In the present embodiment, the low-refractive layer 30 side of the optical film 100 faces the side opposite to the polarizing member 300. Figure 4 In the polarizing plate 700 of the present embodiment, the polarizing member 300 is laminated with the first transparent protective sheet 500 and the second transparent protective sheet 600 via the adhesive layer 400.

[0445] The polarizing plate is used, for example, for the purpose of imparting antireflection property by combination with a λ / 4 phase difference plate. In this case, the λ / 4 phase difference plate is disposed on a display element of an image display device, and the polarizing plate is disposed on the observer side of the λ / 4 phase difference plate.

[0446] In the case of use for a liquid crystal display device, the polarizing plate is used for the purpose of imparting the function of a liquid crystal shutter. In this case, in a liquid crystal display device, the polarizing member of a lower polarizing plate and the polarizing member of an upper polarizing plate are disposed in this order from the backlight side, and the absorption axis of the polarizing member of the lower polarizing plate is disposed orthogonally to the absorption axis of the polarizing member of the upper polarizing plate. In the structure of the liquid crystal display device, the polarizing plate of the present disclosure can be used as the upper polarizing plate and the lower polarizing plate, and preferably as the upper polarizing plate. In the upper polarizing plate, as the transparent protective sheet on the light exit side of the polarizing member, the optical film of the present disclosure is preferably used. In the lower polarizing plate, as the transparent protective sheet on the light incident side of the polarizing member, the optical film of the present disclosure is preferably used.

[0447] <Transparent protective sheet>

[0448] The polarizing plate of the present disclosure uses the above-described optical film of the present disclosure as at least one of the first transparent protective sheet and the second transparent protective sheet. Both the first transparent protective sheet and the second transparent protective sheet are preferably the above-described optical film of the present disclosure.

[0449] In the case where one of the first transparent protective sheet and the second transparent protective sheet is the above-described optical film of the present disclosure, the transparent protective sheet on the other side is not particularly limited, but is preferably an optically isotropic transparent protective sheet. In the present specification, the optically isotropic transparent protective sheet refers to a transparent protective sheet having an in-plane retardation of less than 20 nm, preferably 10 nm or less, and more preferably 5 nm or less. The optically isotropic transparent protective sheet can include an acrylic film, a triacetyl cellulose film, a polycarbonate film, an amorphous olefin film, and the like.

[0450] <Polarizing member>

[0451] As the polarizing member, for example, a sheet-type polarizing member (polyvinyl alcohol film, polyvinyl formal film, polyvinyl acetal film, ethylene-vinyl acetate copolymer saponified film, etc.) stretched from a film dyed with iodine or the like, a wire grid-type polarizing member composed of a plurality of metal wires arranged in parallel, a coated-type polarizing member coated with a lyotropic liquid crystal and a dichroic guest-host material, and a multilayer thin film-type polarizing member, etc. can be listed. These polarizing members can be reflective-type polarizing members having a function of reflecting a non-transmitted polarizing component.

[0452] The polarizing member is preferably disposed so that the angle formed by the absorption axis thereof and the slow axis of the plastic film is within 90 degrees ± 5 degrees. The angle is more preferably within 90 degrees ± 3 degrees, and further preferably within 90 degrees ± 1 degree.

[0453] The image display device of the present disclosure has a display element and a polarizing member and an optical film disposed on the light exit surface side of the display element, wherein the optical film is the optical film of the present disclosure described above, and the side of the low refractive index layer of the optical film faces the side opposite to the display element.

[0454] Figure 4 is a cross-sectional view showing an embodiment of the image display device of the present disclosure.

[0455] Figure 4 The image display device 1000 of Figure 4 has the optical film 100 on the light exit surface side of the display element 800 (the upper side of Figure 4 In the Figure 4 image display devices 1000, the polarizing member 300 is disposed between the display element 800 and the optical film 100.

[0456] The image display device 1000 is not limited to Figure 4 the manner shown in Figure 6 For example, in each component constituting the image display device 1000 is disposed apart by a prescribed interval, but it is preferable that the components be integrated and stacked via an adhesive layer or the like. The image display device can also have other components such as an optical film not shown. For example, the image display device can also have a surface plate such as a glass plate or a plastic plate. In the case where the image display device has a surface plate, the optical film of the present disclosure can be attached to the surface plate.

[0457] In the image display device of the present disclosure, the angle formed by the absorption axis of the polarizing member and the slow axis of the plastic film of the optical film is preferably within 90 degrees ± 5 degrees. The angle is more preferably within 90 degrees ± 3 degrees, and further preferably within 90 degrees ± 1 degree.

[0458] <Display Element>

[0459] As the display element, a liquid crystal display element, an EL display element (organic EL display element, inorganic EL display element), a plasma display element, a display element using a QD (Quantum dot), and the like can be given, and further, a mini LED, a micro LED display element, and the like can be given as the LED display element.

[0460] In a case where the display element of the display device is a liquid crystal display element, a backlight is required on a surface on the opposite side of the resin sheet of the liquid crystal display element.

[0461] The image display device can also be an image display device provided with a touch panel function.

[0462] As the touch panel, a resistive film type, an electrostatic capacity type, an electromagnetic induction type, an infrared type, an ultrasonic wave type, and the like can be given.

[0463] The touch panel function can be a case where a function is added in the display element as in an in-cell touch panel liquid crystal display element, or a case where a touch panel is placed on the display element.

[0464] If the plastic film satisfies the condition A, the case where the optical film has a crease or is broken after the bending test can be suppressed. Therefore, if the plastic film satisfies the condition A, the image display device is preferably a curved image display device, a foldable image display device.

[0465] In a case where the image display device is a curved image display device, a foldable image display device, the display element is preferably an organic EL display element. In a case where the image display device is a curved image display device, a foldable image display device, the glass contained in the image display device is preferably a thin glass. The thickness of the thin glass is preferably 5 μm or more and 80 μm or less.

[0466] <Other Plastic Film>

[0467] The image display device of the present disclosure can have other plastic films within a range not impairing the effects of the present disclosure.

[0468] As the other plastic film, a plastic film having optical isotropy is preferable.

[0469] [Method for Selecting Optical Film of Image Display Device]

[0470] The method for selecting the optical film of the image display device of the present disclosure is a method for selecting an optical film of an image display device having a polarizing member and an optical film on a light emission surface of a display element, in which an optical film X satisfying the following (1) to (4) of the determination conditions is selected as the optical film.

[0471] (1) an optical film X having a low refractive index layer on a plastic film;

[0472] (2) the plastic film has an in-plane refractive index maximum axis, i.e., a slow axis, and an in-plane axis of the plastic film orthogonal to the slow axis, i.e., a fast axis;

[0473] (3) the low refractive index layer is on a surface of the optical film X; and

[0474] (4) the optical film X has Σ T in a range exceeding 0.04 and less than 0.20.

[0475] <Measurement Condition 1>

[0476] A linearly polarized light is incident from a surface of the optical film opposite to the low refractive index layer. The linearly polarized light as the incident light is defined as light L1. Transmitted light after the light L1 is transmitted through the optical film is defined as light L2.

[0477] On the basis of fixing an angle formed by the slow axis and a vibration direction of the light L1 to 45 degrees, the light L1 is incident to the optical film at an elevation angle of the vibration direction of the light L1 in the plane of the optical film becoming an angle of 50 degrees or more and 70 degrees or less. The elevation angle is varied every 2 degrees in a range of 50 degrees or more and 70 degrees or less, and the light L2 is measured at 11 kinds of elevation angles. The light L2 is measured at 11 measurement points by the above measurement.

[0478] The light L2 is converted into a condition of a C light source and a viewing angle of 2 degrees. With respect to the light L2 of the n-th measurement point of the 11 measurement points, a* value and b* value of L*a*b* colorimetric system are defined as a*n and b*n. In addition, with respect to the light L2 of the n+1-th measurement point of the 11 measurement points, a* value and b* value of L*a*b* colorimetric system are defined as a*n1 and b*n1.

[0479] On the basis of the measurement of the 11 measurement points, a sum of a square of a difference in a* of adjacent measurement points and a square of a difference in b* of adjacent measurement points is calculated. The sum is calculated at 10 adjacent points, respectively, and ∑ T representing a total sum of the sums is calculated. The ∑ T can be represented by the following formula 1.

[0480] ∑ T =∑[{a*n-a*n1} 2 +{b*n-b*n1} 2 ] (Formula 1)

[0481] In the method for selecting the optical film of the image display device disclosed herein, the angle between the absorption axis of the polarizer and the slow axis of the plastic film of the optical film is preferably within 90 degrees ± 5 degrees. More preferably, the angle is within 90 degrees ± 3 degrees, and even more preferably within 90 degrees ± 1 degree.

[0482] The embodiment of measurement condition 1 in the method for selecting the optical film of the image display device disclosed herein is the same as the embodiment of measurement condition 1 of the optical film of the present disclosure described above.

[0483] In the method for selecting the optical film of the image display device disclosed herein, as a determination condition, it is preferable to also include an additional determination condition. As an additional determination condition, preferred embodiments of the optical film of the present disclosure can be listed (for example, Formula 2-1, Formula 2-2, n2 / n1, in-plane phase difference of the plastic film, etc.).

[0484] The method for selecting the optical film of the image display device disclosed herein is useful as a method for selecting the optical film of an image display device having a polarizing element on the light emitting surface side of the display element.

[0485] Example

[0486] The present disclosure will now be described in more detail by way of examples, but the present disclosure is not limited to these examples.

[0487] 1. Measurement and evaluation

[0488] The following measurements and evaluations were conducted at an atmosphere of 23°C ± 5°C and a relative humidity of 40% to 65%. Furthermore, the samples to be measured were exposed to this atmosphere for at least 30 minutes and no more than 60 minutes before measurement and evaluation. The samples were collected from clean, undamaged areas. Measurements and evaluations were performed while the samples were in a planar condition.

[0489] 1-1. Measurement under Measurement Condition 1

[0490] A 5cm × 5cm sample was cut from the optical film of the experimental example. Measurements were performed on the sample under measurement conditions 1. The measuring apparatus used was a spectrophotometer from JASCO Corporation, product number "V-7100". Based on the measurement results, Σ of Equation 1 was calculated. T “Equation 2-1 (a*max-a*min)”, “Equation 2-2 (b*max-b*min)”, “Maximum value of the sum (S)” MAX Under measurement condition 1, calculate the sum of the squared difference of a* between adjacent measurement points and the squared difference of b* between adjacent measurement points at 10 adjacent points. The maximum value of the sum (S) MAX) is the maximum value of the sum of 10. In addition, the visual reflectance Y value of the optical film of the experimental example is defined as "R (%)", and "R x Σ T " (the visual reflectance Y value is measured by the method of 1-6 described later) is calculated. The results are shown in Table 1.

[0491] 1-2. n1 and n2

[0492] Regarding the optical film of the experimental example, the average refractive index n1 of the low refractive index layer was measured by using the Becke method and the fitting method described in the main text of the specification in combination.

[0493] 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. In the case where the layer adjacent to the low refractive index layer is any of the plastic film and the hard coat layer, n2 was also measured using the Becke method described in the main text of the specification. The results are shown in Table 1.

[0494] 1-3. Rainbow flare

[0495] A liquid crystal display device having a polarizing member on a liquid crystal display element (trade name "EV2450" of EIZO Corporation; horizontal: 527.0 mm, vertical: 596.4 mm; the absorption axis of the polarizing member is parallel to the vertical direction of the screen; backlight: a backlight using a white light emitting diode) was prepared.

[0496] A laminate in which the optical film of the experimental example was stacked on the liquid crystal display device via an adhesive layer was produced. At this time, it was disposed so that the absorption axis of the polarizing member and the slow axis of the plastic film of the optical film were at 90 degrees. Then, white display was performed on the laminate in a dark room, and observation was performed from all positions and all directions at a distance of 30 cm or more and 100 cm or less from the laminate. The evaluator was a healthy person of 20 to 40 years old with a visual acuity of 0.7 or more, and the presence or absence of rainbow flare was evaluated with the naked eye according to the following criteria. The visual acuity also includes corrected visual acuity. The results are shown in Table 1.

[0497] AA: Rainbow flare was not observed from all positions and from all directions.

[0498] A: Rainbow flare was observed in a slightly small number of positions, or rainbow flare was observed in a slightly small number of directions.

[0499] B: Rainbow flare was observed in a large number of positions, or rainbow flare was observed in a large number of directions.

[0500] B -: Rainbow light spots are observed in a large number of positions in a part of the area, or in a large number of directions in a part of the area.

[0501] C: Rainbow light spots are observed in a large number of positions in a large part of the area, or in a large number of directions in a large part of the area.

[0502] 1-4. Uniformity of color tone

[0503] The laminate produced in 1-3 was visually observed in a bright room environment in a state where the power was turned off. The conditions of the bright room were such that the brightness of the surface of the laminate was in the range of 1000 lux or more and 1500 lux or less. The observation was performed from three directions, i.e., the front direction of the laminate, a direction of about 50 degrees with respect to the laminate, and a direction of about 70 degrees with respect to the laminate. The distance between the laminate and the evaluator's eyes was 30 cm or more and 100 cm or less. The evaluators were 20 healthy persons of 20 to 40 years old with a visual acuity of 0.7 or more, and the uniformity of color tone upon oblique observation was evaluated in accordance with the following criteria. The results are shown in Table 1.

[0504] A: When the color tones of the three directions were compared, the number of persons who answered that they did not feel a change in color tone was 18 or more.

[0505] B: When the color tones of the three directions were compared, the number of persons who answered that they did not feel a change in color tone was 15 or more and 17 or less.

[0506] C: When the color tones of the three directions were compared, the number of persons who answered that they did not feel a change in color tone was 10 or more and 14 or less.

[0507] D: When the color tones of the three directions were compared, the number of persons who answered that they did not feel a change in color tone was 5 or more and 9 or less.

[0508] E: When the color tones of the three directions were compared, the number of persons who answered that they did not feel a change in color tone was 4 or less.

[0509] 1-5. Chroma based on reflected light

[0510] A sample (5 cm x 5 cm) of the optical film of Experimental Example was prepared by bonding a black plate (KURARAY CO., LTD.; trade name: "COMOGLAS DFA2CG 502K (Black) type"; total light transmittance: 0%; thickness: 2 mm; refractive index: 1.49) to the plastic film side of the optical film via a transparent adhesive layer (PANAC CO., LTD.; trade name: "Panaclean PD-S1"; thickness: 25 μm; refractive index: 1.49).

[0511] The chroma was measured based on the regular reflection light of the incident light when the light was incident on the sample from a direction of 5 degrees, 50 degrees, and 70 degrees, with the direction perpendicular to the surface of the low-refractive layer side of the sample being set to 0 degrees. The chroma was measured at 10 places for each sample, and the average value was used as the chroma at each angle for each sample. The chroma (C*) can be calculated based on the a* value and the b* value of the L*a*b* color system by the following equation.

[0512] C* = {(a*) 2 + (b*) 2} 1 / 2

[0513] The measuring device used was a product number "V-7100" of a spectrophotometer of JASCO Corporation. The measuring device was used to measure in a wavelength range of 380 nm or more and 780 nm or less, and then the conversion was performed by software for converting to the brightness perceived by the human eye [software built into the measuring device <product number "JASCO Spectral Manager" of JASCO Corporation>. The conditions for calculating the reflectance: C light source and a viewing angle of 2 degrees]. The results are shown in Table 1.

[0514] The chroma was not measured for the optical film having no low-refractive layer.

[0515] 1-6. Visual reflectance Y value (reflectance)

[0516] The reflectance (visual reflectance Y value) was measured based on the regular reflection light of the incident light when the light was incident on the sample from a direction of 5 degrees, with the direction perpendicular to the surface of the low-refractive layer side of the sample prepared in 1-5 being set to 0 degrees.

[0517] The measuring device used was a product number "V-7100" of a spectrophotometer manufactured by JASCO Corporation. The measuring device measured in a wavelength range of 380 nm or more and 780 nm or less, and then, by software for converting to luminance perceived by a human eye [software built in the measuring device <product number "JASCO Spectral Manager" of JASCO Corporation>. Conditions for calculating reflectance: C light source and a viewing angle of 2 degrees], conversion was performed. The reflectance was measured at 10 places for each sample, and the average value was taken as the visual reflectance Y value of each sample. The results are shown in Table 1.

[0518] For the optical film not having a low refractive index layer, measurement of the visual reflectance Y value was not performed.

[0519] 1-7. In-plane retardation (Re), thickness direction retardation (Rth), and direction of slow axis

[0520] A sample of 50 mm in the longitudinal direction x 50 mm in the lateral direction was cut out from a plastic film used in the experimental examples and reference examples, which was produced or prepared by "2" described later. At this time, the flow direction (MD direction) of the plastic film was regarded as the longitudinal direction, and the width direction (TD direction) of the plastic film was regarded as the lateral direction. For four sites of 10 mm advancing from the corners of the sample toward the central portion, and the central portion of the sample, in-plane retardation, thickness direction retardation, and the direction of the slow axis were measured. From the measurement results, the average value of Re1 to Re5, and the like were calculated. The results are shown in Table 2.

[0521] The measuring device used was a product name "RETS-100 (measurement point: diameter 5 mm)" manufactured by Otsuka Electronics Co., Ltd. For the direction of the slow axis, 0 degrees were measured in a range of 0 degrees or more and 90 degrees or less, with the flow direction (MD direction) of the plastic film as a reference.

[0522] 1-8. Bending resistance

[0523]

[0524] Cut a strip of sample with a width (TD direction) of 30 mm and a flow direction (MD direction) of 100 mm from the plastic film used in the experimental and reference examples, prepared or made as described in "2" below. Fix both ends of the sample along its short side (30 mm side) to a durability testing machine (product name "DLDMLH-FS", YUASA SYSTEMCO., LTD.), and then perform a continuous folding test of 100,000 folds at 180 degrees. At both ends of the short side of the sample, a region 10 mm from the end of the sample is fixed. The folding speed is 120 times per minute. A more detailed method for the folding test is shown below.

[0525] After the folding test, the long strip sample was placed on a horizontal platform, and the angle at which the end of the sample tilted up from the platform was measured. If the angle was less than 15 degrees, it was considered acceptable. A sample that broke midway was defined as "fracture." The results are shown in Table 2. This evaluation allows assessment of the bending resistance in the TD direction (≈slow axis direction).

[0526] <MD Direction>

[0527] Strip samples measuring 30 mm in the flow direction (MD direction) and 100 mm in the width direction (TD direction) were cut from the biaxially stretched plastic film used in the examples and comparative examples, which were prepared or fabricated using the method described in "2" below, and the same evaluation as described above was performed. This evaluation allows for assessment of the bending resistance in the MD direction (≈ fast axis direction).

[0528] <Details of the folding test>

[0529] like Figure 6 As shown in (A), in the continuous folding test, firstly, the edge 10C of the plastic film 10 and the edge 10D opposite to the edge 10C are fixed with parallelly arranged fixing parts 60. The fixing parts 60 can slide in the horizontal direction.

[0530] Next, as Figure 6 As shown in (B), by moving the fixing parts 60 closer together, the plastic film 10 is deformed in a folding manner. Furthermore, as... Figure 6 As shown in (C), after the fixing part 60 is moved to a position where the distance between the two opposing sides of the plastic film 10 fixed by the fixing part 60 is 10mm, the fixing part 60 is moved in the opposite direction, thereby eliminating the deformation of the plastic film 10.

[0531] like ​As shown in (A) to (C) of the same drawing, by moving the fixing portion 60, the plastic film 10 can be folded by 180 degrees. In addition, the continuous folding test is performed in a manner that the bent portion 10E of the plastic film 10 does not protrude from the lower end of the fixing portion 60, and the interval at the closest position of the fixing portion 60 is controlled to 10 mm, whereby the interval of the two opposing edge portions of the optical film 10 can be 10 mm.

[0532] 1-9. Pencil hardness

[0533] For the polyester films 1-5 of "2" described below, the pencil hardness was measured. The measurement method of the pencil hardness was in accordance with the steps of (1) to (6) of the specification. For the commercially available polyester film in which an easy-adhesion layer was formed on one side in advance, the pencil hardness was measured on the side on which the easy-adhesion layer was not formed. The measurement of the pencil hardness was performed on both the slow axis and the fast axis. The results are shown in Table 2.

[0534] 1-10. Erosion rate

[0535] The erosion rate of the polyester films 1 to 5 of "2" described below was measured using an erosion rate measuring device (MSE tester of Palmeso Co., Ltd., product number "MSE-A203", the cross-sectional shape of the nozzle was a square of 1 mm x 1 mm, and the measurement means of the cross-sectional profile was a stylus type), and E 0-20 The measurement area of the erosion rate was 1 mm x 1 mm.

[0536] The measurement of the erosion rate of each sample was performed after the following correction using a standard acrylic plate. In addition, as for the test liquid, it was prepared before the correction, and was preliminarily dispersed and operated before the correction. In addition, as for the standard acrylic plate, AcE (the average value of the erosion rate of the acrylic plate measured under Measurement Condition A) in the specification was in the range of 1.786 μm / g or more and 1.974 μm / g or less.

[0537] (0-1) Preparation of test liquid

[0538] In a beaker, an experimental liquid was prepared by mixing pure water, a dispersant (a product with a trade name of "Demol N" by Wako Pure Chemical Industries, Ltd.), and spherical silica (a type "MSE-BS-5-3" by Palmeso Co., Ltd., a full width at half maximum of a particle size distribution: 4.2 μm) with an average particle diameter (median particle diameter) of 3.94 μm in a mass ratio of 968:2:30, and mixed with a glass rod. After the adjusted experimental liquid and a stirring member were put in a container (tank), a lid was put on the tank and a jig was attached. Then, the tank was housed in the measuring device. In this example, as the type "MSE-BS-5-3" by Palmeso Co., Ltd., a product with a product number "BS5-3" by Potters-Ballotini Co., Ltd. was used.

[0539] (0-2) Dispersion operation

[0540] After the tank containing the experimental liquid was housed in the measuring device, a dummy sample was set on the sample mounting table. Then, buttons "Erosion force setting" and "Proceed" on the operation panel of the measuring device main body were sequentially pressed. Then, a prescribed value was input as the flow rate of the experimental liquid and compressed air, the pressure of the compressed air, and the pressure of the experimental liquid in the nozzle, and the experimental liquid was projected onto the dummy sample. After the projection was stopped, buttons "Return", "Complete", and "Confirm" on the operation panel were sequentially pressed.

[0541] (1) Calibration

[0542] An acrylic plate with a thickness of 4 mm as a calibration sample was fixed to the sample mounting table of the measuring device by double-sided tape ("Kapton double-stick tape" by Nitto Electric Industrial Co., Ltd., product number: P-223 1-6299-01). The acrylic plate was a PMMA plate.

[0543] Then, the sample mounting table with the acrylic plate fixed thereto was set in the measuring device.

[0544] Then, the lock of the micrometer was released, and the height adjustment of the sample mounting table was performed with the height gauge. The distance between the ejection hole of the measuring device and the acrylic plate was adjusted to 4 mm.

[0545] Then, after a button "Treatment condition input screen" on the operation panel of the measuring device main body was pressed, it was set to "Step number: 1; specified projection amount g x 1 time". The projection amount was 4 g.

[0546] Next, the buttons "setting completion", "start operation", and "yes" on the operation panel are sequentially pressed. The flow rate of the test liquid and the compressed air, the pressure of the compressed air, and the pressure of the test liquid in the nozzle are maintained at the values input in "(0-2) dispersion operation".

[0547] Next, "online" of the operation screen of the data processing PC is clicked to release the online and change to offline.

[0548] Next, "lower" of the operation screen is clicked to lower the stylus of the stylus step difference meter of the cross-sectional profile acquisition unit.

[0549] Next, it is confirmed that the lock of the micrometer is released, and the micrometer is turned to be raised. At this time, the adjustment is performed so that the red arrow of the monitor comes to the center. By the adjustment, the stylus of the stylus step difference meter contacts the surface of the calibration sample, and the 0 point of the z axis as the height direction can be adjusted.

[0550] Next, the lock of the micrometer is switched from release (off) to on.

[0551] Next, "raise" is clicked to raise the stylus of the stylus step difference meter of the cross-sectional profile acquisition unit.

[0552] Next, "offline" of the operation screen of the data processing PC is clicked to release the offline and change to online.

[0553] Next, the cover of the measurement device main body is closed, and the button "confirm" on the operation panel of the measurement device main body is pressed to inject 4 g of the test liquid.

[0554] After the injection of the test liquid is stopped, "proceed" is clicked to calculate the erosion rate. If the erosion rate is within the range of ±5% based on 1.88 (μm / g), the calibration is finished. In the case where the erosion rate deviates from the range, the flow rate of the test liquid, the flow rate of the compressed air, the pressure of the compressed air, and the pressure of the test liquid in the nozzle are adjusted, and the calibration is repeatedly performed until the erosion rate becomes the range.

[0555] (2) Measurement of the Erosion Rate of Each Sample

[0556] (2-1) Installation of the Sample

[0557] A laminate in which the sample (polyester films 1 to 5 of "2" described below) is attached to a stainless steel plate is prepared, and the laminate is fixed to the sample mounting table by a double-sided tape ("Kapton double-stick tape" of Daito Kogyo America, Inc.; product number: P-223 1-6299-01). The sample has a size of 1 cm x 1 cm.

[0558] Next, the sample mounting table was set to the measuring device. Then, the lock of the micrometer was released, and the height of the sample mounting table was adjusted with the height gauge. The distance between the spray hole of the measuring device and the plastic film was adjusted to 4 mm.

[0559] Next, after pressing the button "treatment condition input screen" on the operation panel of the measuring device main body, the number of steps was input, and the spray amount (g / time) of the test liquid was input for each step. The spray amount for each step was set to a range of 0.5 g or more and 3.0 g or less. The flow rate of the test liquid and the compressed air, the pressure of the compressed air, and the pressure of the test liquid in the nozzle were maintained at the conditions that passed in "(1) calibration".

[0560] Next, the buttons "setting completion", "start operation", and "yes" on the operation panel were pressed in this order.

[0561] Next, "online" of the operation screen of the data processing PC was clicked, and the online was released, and changed to offline.

[0562] Next, "lower" of the operation screen was clicked, and the stylus of the stylus-type step difference gauge of the cross-sectional profile acquisition section was lowered.

[0563] Next, it was confirmed that the lock of the micrometer was released, and the micrometer was turned to the upward direction. At this time, the adjustment was performed so that the red arrow of the monitor came to the center. By the adjustment, the stylus of the stylus-type step difference gauge contacted the surface of the calibration sample, and the 0 point of the z axis as the height direction could be adjusted.

[0564] Next, the lock of the micrometer was switched from the release (off) to the on.

[0565] Next, "raise" was clicked, and the stylus of the stylus-type step difference gauge of the cross-sectional profile acquisition section was raised.

[0566] Next, "offline" of the operation screen of the data processing PC was clicked, and the offline was released, and changed to online.

[0567] (2-2) Measurement Start

[0568] The cover of the measuring device main body was closed, and the button "confirm" on the operation panel of the measuring device main body was pressed, and the measurement of one cycle of the spray of the test liquid and the measurement of the cross-sectional profile 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.

[0569] After the measurement, start the attached software "MseCalc", click "Analysis Method". Next, click "Average Value Analysis". Next, click "Add" twice in the Average Value Analysis screen, and "A-1" and "A-2" are displayed in the Analysis Name column. Double-click the "Reference" column of "A-1", and "0" is displayed in the Reference column.

[0570] Next, click "A-1" of the Average Value Analysis screen to activate it, and operate the position of the X-axis position bar. The position of the position bar is determined as a position where the plastic film is not worn in the cross-sectional profile screen.

[0571] Next, click "A-2" of the Average Value Analysis screen to activate it, and operate the position of the X-axis position bar. The position of the position bar is determined as a position where the plastic film is worn the most in the cross-sectional profile screen.

[0572] Next, output the data of the cross-sectional profile and the erosion rate of each step in csv, and calculate the erosion rate E 0-20 . Specifically, average the "Erosion Rate (Corrected)" of the data output in csv, which is the depth of 0 μm or more and 20 μm or less, and calculate the erosion rate E 0-20 . The results are shown in Table 2.

[0573] 2. Production and Preparation of Plastic Film

[0574] [Polyester Film 1]

[0575] 1 kg of PET (melting point: 258°C, absorption center wavelength: 320 nm) and 0.1 kg of ultraviolet absorber (2,2'-(1,4-phenylene) bis(4H-3,1-benzoxazinone-4-ketone) were melt-mixed at 280°C in a kneader, thereby producing a pellet containing an ultraviolet absorber. The pellet and PET having a melting point of 258°C were fed into a single-screw extruder, melt-kneaded at 280°C, and then extruded from a T die, thereby casting a cast film on a casting drum whose surface temperature was controlled to 25°C. The amount of the ultraviolet absorber in the cast film was 1 part by mass with respect to 100 parts by mass of the PET.

[0576] The obtained cast film was heated with a roll set set to 95°C, and then stretched 3.3 times in the flow direction while heating both sides of the film with a radiation heater, with the film temperature at a point 250 mm in a 400 mm stretching interval being 103°C, and then temporarily cooled, to obtain a uniaxially stretched film. The starting point of the stretching interval was a stretching roll A, and the end point was a stretching roll B, and the stretching rolls A and B each had two pressure rolls. When heating with the radiation heater, turbulence was generated on both sides of the film by blowing air at 92°C and 4 m / s from the side of the radiation heater opposite the film, to thereby disturb the uniformity of the temperature of the film.

[0577] Next, the wetting tension of the substrate film was made 55 mN / m by subjecting both sides of the uniaxially stretched film to corona discharge treatment in air. Next, an easy slip layer coating liquid containing a polyester resin having a glass transition temperature of 18°C, a polyester resin having a glass transition temperature of 82°C, and silica particles having an average particle diameter of 100 nm was applied on the corona discharge treated surfaces of both sides of the film on-line, to thereby form an easy slip layer.

[0578] Next, the uniaxially stretched film was introduced into a tenter, preheated with hot air at 95°C, and then stretched 4.5 times in the film width direction at 105°C in the first stage and 140°C in the second stage. Here, in the case where the width direction stretching interval was divided into two, the film was stretched in two stages in such a manner that the stretching amount of the film at the middle point in the width direction stretching interval became 80% of the stretching amount at the end of the width direction stretching interval. The aforementioned "stretching amount" refers to the difference between the film width at the measurement point and the film width before stretching. The film after stretching in the width direction was directly heat treated with hot air in the tenter. The temperature of the hot air was increased from 180°C to 245°C in stages. Next, 1% relaxation treatment was performed in the width direction under the same temperature conditions, and further, the film was rapidly cooled to 100°C, and then 1% relaxation treatment was performed in the width direction. Then, the film was wound up, to obtain a biaxially stretched polyester film 1 having a thickness of 40 μm.

[0579] The polyester film 1 was used as the plastic film of Experimental Example 3.

[0580] [Polyester Film 2]

[0581] A biaxially stretched polyester film 2 having a thickness of 40 μm was obtained by the same operation as the biaxially stretched polyester film 1, except that the width direction stretching ratio was changed from 4.5 times to 5.1 times. The polyester film 2 was used as the plastic film of Experimental Example 2.

[0582] [Polyester Film 3]

[0583] As the polyester film 3, a commercially available biaxially-stretched polyester film (TOYOBO CO., LTD.; trade name: Cosmoshine A4300; thickness: 38 μm) was prepared. The polyester film 3 was used as the plastic film of Experimental Example 1.

[0584] [Polyester film 4]

[0585] As the polyester film 4, a commercially available biaxially-stretched polyester film (TOYOBO CO., LTD.; trade name: Cosmoshine A4100; thickness: 50 μm) was prepared. The polyester film 4 was used as the plastic film of Reference Example 1.

[0586] [Polyester film 5]

[0587] As the polyester film 5, a commercially available uniaxially-stretched polyester film (TOYOBO CO., LTD.; trade name: Cosmoshine TA044; thickness: 80 μm) was prepared. The polyester film 5 was used as the plastic film of Reference Example 2.

[0588] 3. Synthesis of compound

[0589] The compound α used in "4. Preparation of coating solution" was synthesized by the following method.

[0590] An air gas was introduced into a reaction vessel equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen gas introduction tube. The pressure of the reaction vessel at the time of introduction of the air gas was controlled to 1.0 atm ± 0.1 atm. Next, 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 put into the reaction vessel, and the temperature was raised to 60°C while stirring under a nitrogen stream. The pressure of the reaction vessel at the time of the nitrogen stream was controlled to 1.2 atm ± 0.1 atm. (By making the pressure at the time of the nitrogen stream higher than the normal pressure, the oxygen concentration in the reaction vessel can be more effectively reduced.) Next, 30 parts by mass of hexamethylene diisocyanate was added to a dropping vessel, and was uniformly dropped into the reaction vessel over 1 hour. After the dropping, the temperature of the reaction vessel was raised to 75°C, and was kept at 75 ± 3°C for 6 hours. Then, 150 parts by mass of methyl ethyl ketone was added, and a transparent resin solution was obtained. Finally, the solvent was removed using an evaporator, and the compound α was obtained. The compound α is an ionizing radiation-curable compound. The number average molecular weight of the compound α was about 4500.

[0591] 4. Preparation of coating solution

[0592] A coating solution used in "5. Production of optical film" was prepared.

[0593] <Hard coat layer forming coating solution A>

[0594] • Ionizing radiation-curable compound 1: 0.6 parts by mass

[0595] (Compound α synthesized in "3")

[0596] • Ionizing radiation-curable compound 2: 0.2 parts by mass

[0597] (Showa Denko K.K., trade name "EBECRYL 230", solid content 100%)

[0598] • Ionizing radiation-curable compound 3: 0.2 parts by mass

[0599] (Kosé Corporation, trade name "Light Acrylate IAA", solid content 100%)

[0600] • Leveling agent: 0.01 parts by mass

[0601] (Daiei Seiyaku Kogyo Co., Ltd., trade name "10-28 (TL)", solid content 10% by mass)

[0602] • Photopolymerization initiator: 0.1 parts by mass

[0603] (IGM Resins B.V., trade name "Omnirad 184"

[0604] • Solvent

[0605] (Methyl isobutyl ketone and cyclohexanone mixed at 5:5. The solvent was used in an amount such that the solid content of the coating solution was 35% by mass.)

[0606] <Hard coat layer forming coating solution B>

[0607] • Ionizing radiation-curable compound 1: 1 part by mass

[0608] (Compound α synthesized in "3")

[0609] • Acrylic resin particles: 0.1 parts by mass

[0610] (Average particle diameter: 2 μm, refractive index: 1.535)

[0611] • Leveling agent: 0.01 parts by mass

[0612] (Daiei Seiyaku Kogyo Co., Ltd., trade name "10-28 (TL)", solid content 10% by mass)

[0613] • Photopolymerization initiator: 0.1 part by mass

[0614] (IGM Resins B.V., trade name "Omnirad 184"

[0615] • Solvent

[0616] (A mixed solvent of methyl isobutyl ketone and cyclohexanone at 5:5. The solvent was used in an amount such that the solid content of the coating liquid became 35 mass%.)

[0617] Coating liquid C for forming a hard coat layer

[0618] • Ionizing radiation-curable compound 1: 0.625 parts by mass

[0619] (Compound α synthesized in "3")

[0620] • Ionizing radiation-curable compound 4: 0.375 parts by mass

[0621] (Arakawa Chemical Industries, Ltd., trade name "OPSTAR Z7415", solid content 100%)

[0622] • Leveling agent: 0.01 parts by mass

[0623] (Daiei Seiyaku Kogyo Co., Ltd., trade name "10-28(TL)", solid content 10 mass%)

[0624] • Photopolymerization initiator: 0.1 part by mass

[0625] (IGM Resins B.V., trade name "Omnirad 184"

[0626] • Solvent

[0627] (A mixed solvent of methyl isobutyl ketone and cyclohexanone at 5:5. The solvent was used in an amount such that the solid content of the coating liquid became 35 mass%.)

[0628] Coating liquid i for forming a low-refractive layer

[0629] • Composition containing an ultraviolet-curable acrylate: 1 part by mass

[0630] (Nippon Kayaku Co., Ltd., trade name "KAYARAD PET-30", solid content 100%)

[0631] • Photopolymerization initiator: 0.1 part by mass

[0632] (Omnirad 127" (IGM Resins B.V., trade name)

[0633] • Hollow silica particles: 1.3 parts by mass

[0634] (average primary particle diameter: 60 nm)

[0635] • Solid silica particles: 0.7 parts by mass

[0636] (average primary particle diameter: 15 nm)

[0637] • Leveling agent: 0.1 parts by mass

[0638] (X-22-164E" (Shin-Etsu Chemical Co., Ltd., trade name)

[0639] • Solvent

[0640] (a mixed solvent of methyl isobutyl ketone and cyclohexanone at 5:5. The solvent was used in an amount such that the solid content of the coating liquid became 2% by mass.)

[0641] <Low-refractive-index layer-forming coating liquid ii>

[0642] • Composition containing ultraviolet-curable acrylate: 1 part by mass

[0643] (KAYARAD PET-30" (Nippon Kayaku Co., Ltd., trade name, solid content: 100%)

[0644] • Photopolymerization initiator: 0.1 parts by mass

[0645] (Omnirad 127" (IGM Resins B.V., trade name)

[0646] • Hollow silica particles: 1.55 parts by mass

[0647] (average primary particle diameter: 60 nm)

[0648] • Solid silica particles: 0.45 parts by mass

[0649] (average primary particle diameter: 15 nm)

[0650] • Leveling agent: 0.1 parts by mass

[0651] (X-22-164E" (Shin-Etsu Chemical Co., Ltd., trade name)

[0652] • Solvent

[0653] (Methyl isobutyl ketone and cyclohexanone at a mixing ratio of 5:5. The solvent was used in an amount of 2 mass% relative to the solid content of the coating liquid.)

[0654] < Low-refractive layer forming coating liquid iii >

[0655] • Ultraviolet ray-curable acrylate-containing composition: 1 mass part

[0656] (Methyl isobutyl ketone and cyclohexanone at a mixing ratio of 5:5. The solvent was used in an amount of 2 mass% relative to the solid content of the coating liquid.)

[0657] • Photopolymerization initiator: 0.1 mass part

[0658] (Methyl isobutyl ketone and cyclohexanone at a mixing ratio of 5:5. The solvent was used in an amount of 2 mass% relative to the solid content of the coating liquid.)

[0659] • Hollow silica particles: 2 mass parts

[0660] (Average primary particle diameter: 60 nm)

[0661] • Leveling agent: 0.1 mass part

[0662] (Shin-Etsu Chemical Co., Ltd., trade name "X-22-164E")

[0663] • Solvent

[0664] (Methyl isobutyl ketone and cyclohexanone at a mixing ratio of 5:5. The solvent was used in an amount of 2 mass% relative to the solid content of the coating liquid.)

[0665] 5. Production of optical film

[0666] [Experimental Example 1-1]

[0667] 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 did not have a hard coat layer and a low-refractive layer on the polyester film 3.

[0668] [Experimental Example 1-2]

[0669] The hard coat layer forming coating liquid A prepared in "2" was applied to the polyester film 3 prepared in "2", and then dried at 70°C x 1 minute to volatilize the solvent. Subsequently, ultraviolet irradiation (100 mJ / cm 2 ) was performed to form a hard coat layer (dried thickness: 10 μm).

[0670] The low-refractive layer forming coating liquid i was applied to the hard coat layer, and then dried at 60°C x 1 minute to volatilize the solvent. Subsequently, ultraviolet irradiation (200 mJ / cm2 ), to form a low refractive index layer (dried thickness: 100 nm), to obtain the optical film of Experimental Example 1-2.

[0671] [Experimental Examples 1-3, 1-4]

[0672] As the coating liquid for forming the hard coat layer and the coating liquid for forming the low refractive index layer, the coating liquids described in Table 1 were used, and otherwise, the same operations as in Experimental Example 1-2 were performed, to obtain the optical films of Experimental Examples 1-3, 1-4.

[0673] [Experimental Example 1-5]

[0674] The low refractive index layer was formed directly on the polyester film without forming the hard coat layer, and further, the coating liquid described in Table 1 was used as the coating liquid for forming the low refractive index layer, and otherwise, the same operations as in Experimental Example 1-2 were performed, to obtain the optical film of Experimental Example 1-5.

[0675] [Experimental Example 2-1]

[0676] As the optical film of Experimental Example 2-1, the polyester film 2 produced in "2" was prepared. The optical film of Experimental Example 2-1 did not have the hard coat layer and the low refractive index layer on the polyester film 2.

[0677] [Experimental Example 2-2]

[0678] The polyester film 3 was changed to the polyester film 2, and otherwise, the same operations as in Experimental Example 1-2 were performed, to obtain the optical film of Experimental Example 2-2.

[0679] [Experimental Examples 2-3, 2-4]

[0680] As the coating liquid for forming the hard coat layer and the coating liquid for forming the low refractive index layer, the coating liquids described in Table 1 were used, and otherwise, the same operations as in Experimental Example 2-2 were performed, to obtain the optical films of Experimental Examples 2-3, 2-4.

[0681] [Experimental Examples 2-5, 2-6]

[0682] The low refractive index layer was formed directly on the polyester film without forming the hard coat layer, and further, the coating liquid described in Table 1 was used as the coating liquid for forming the low refractive index layer, and otherwise, the same operations as in Experimental Example 2-2 were performed, to obtain the optical films of Experimental Examples 2-5, 2-6.

[0683] [Experimental Examples 3-1, 3-2]

[0684] The polyester film 3 was changed to the polyester film 1, and further, the coating liquid described in Table 1 was used as the coating liquid for forming the hard coat layer and the coating liquid for forming the low refractive index layer, and otherwise, the same operations as in Experimental Example 1-2 were performed, to obtain the optical films of Experimental Examples 3-1, 3-2.

[0685] [Experimental Example 3-3]

[0686] The polyester film 3 was changed to the polyester film 1, and instead of forming the hard coat layer, a low refractive index layer was formed directly on the polyester film, and further, the coating liquid described in Table 1 was used as the low refractive index layer forming coating liquid, and other than that, the same operation as Experimental Example 1-2 was performed, and an optical film of Experimental Example 3-3 was obtained.

[0687] [Table 1]

[0688]

[0689] [Table 2]

[0690] Table 2

[0691]

[0692] From the results of Table 1, it was confirmed that the optical film having a value of ∑ T The optical film having a value of more than 0.04 and less than 0.20 was able to eliminate rainbow flare when observed with the naked eye, and was able to make the uniformity of the color tone in oblique observation good. In the experimental examples of Table 1, examples corresponding to the embodiments were Experimental Examples 1-2, 1-3, 1-4, 2-2, 2-3, 2-4, 2-6, 3-1, and 3-2.

[0693] In addition, from the results of Table 1 and Table 2, it was confirmed that the "film in which the in-plane retardation of the plastic film is small" and the "film in which the difference between the maximum value and the minimum value of the direction of the slow axis of the plastic film is large" easily made the value of ∑ T an appropriate value.

[0694] In addition, from the results of Table 2, it was confirmed that both the polyester film 1 and the polyester film 2 were able to suppress the case where a crease remained or a breakage occurred after the bending test, regardless of the direction of the bending. The polyester film 1 and the polyester film 2 were "films in which the difference between the maximum value and the minimum value of the direction of the slow axis of the plastic film was large".

[0695] In addition, the polyester film 1 and the polyester film 2 were not able to confirm microcracks after the bending test. The microcracks can be observed as follows.

[0696] The microcracks can be observed with a digital microscope. As the digital microscope, for example, a digital microscope manufactured by KEYENCE Corporation, trade name "VHX-5000" can be cited.

[0697] As for the microcracks, annular illumination was selected as the illumination of the digital microscope, and observation was performed by dark field and reflected light. Specifically, first, after slowly unrolling the sample after the bend test, the sample was fixed on the stage of the microscope with a tape. At this time, in the case where the fold is strong, the region to be observed is made as flat as possible. When performing the described work, care was taken not to touch the bent portion of the sample in the region to be evaluated with the hand, and not to apply force to the bent portion. Then, both the portion that became the inner side at the time of the bend test and the portion that became the outer side were evaluated.

[0698] The observation of the microcracks was performed in a bright room under white illumination (illuminance: 1000 lux to 2000 lux).

[0699] Explanation of Reference Numerals

[0700] 10: plastic film;

[0701] 20: hard coat layer;

[0702] 30: low refractive index layer;

[0703] 100: optical film;

[0704] 200: surface light source;

[0705] 300: polarizing member;

[0706] 400: adhesive layer;

[0707] 500: first transparent protective plate;

[0708] 600: second transparent protective plate;

[0709] 700: polarizing plate;

[0710] 800: display element;

[0711] 1000: image display device;

[0712] A1: light source;

[0713] A2: detector;

[0714] S: slow axis;

[0715] F: fast axis;

[0716] V: vibration direction of light L1;

[0717] 11: container;

[0718] 12: receiver;

[0719] 21: piping for test solution;

[0720] 22: compressed air pipe;

[0721] 23: return pipe;

[0722] 24: return pump;

[0723] 31, 32: flow meter;

[0724] 41, 42: pressure gauge;

[0725] 50: injection section;

[0726] 51: nozzle;

[0727] 52: housing;

[0728] 60: cross-sectional profile acquisition section;

[0729] 70: plastic film;

[0730] 81: sample mounting table;

[0731] 82: support;

[0732] 90: erosion rate measuring device;

[0733] A1: water;

[0734] A2: spherical silica;

[0735] A3: air;

[0736] A4: worn plastic film.

Claims

1. An optical film having a low refractive index layer on a plastic film, wherein the plastic film has a slow axis which is an axis of maximum in-plane refractive index, and a fast axis which is an axis in the in-plane of the plastic film orthogonal to the slow axis, the plastic film satisfies the following Condition A, the plastic film is a polyester film, the low refractive index layer is on a surface of the optical film, The optical film has Σ T a region of more than 0.04 and less than 0.20, < Measurement Condition 1> a linearly polarized light is made to enter from a surface of the optical film opposite to the low refractive index layer, the linearly polarized light is defined as light LI as incident light, and transmitted light after the light LI is transmitted through the optical film is defined as light L2; the light LI is made to enter the optical film at an angle where, on the basis of the angle between the slow axis and the vibration direction of the light LI being fixed at 45 degrees, the elevation angle of the vibration direction of the light LI with respect to the plane of the optical film becomes an angle of 50 degrees or more and 70 degrees or less, the elevation angle is varied every 2 degrees in the range of 50 degrees or more and 70 degrees or less, and the light L2 is measured at 11 kinds of elevation angles, the light L2 is measured at 11 measurement points by the aforementioned measurement; the light L2 is converted into a condition of a C light source and a viewing angle of 2 degrees, with respect to the light L2 of the nth measurement point among the 11 measurement points, the a* value and the b* value of the L*a*b* colorimetric system are defined as a*n and b*n, and with respect to the light L2 of the n+1th measurement point among the 11 measurement points, the a* value and the b* value of the L*a*b* colorimetric system are defined as a*n1 and b*n1; Based on the measurements of the 11 measurement points, the sum of the square of the difference between a* of adjacent measurement points and the square of the difference between b* of adjacent measurement points is calculated, the sum is calculated at 10 adjacent points respectively, and ∑ representing the sum of the sums is calculated T , the Σ T is represented by the following formula 1, ∑ T = ∑[{a*n - a*n1} 2 + {b*n - b*n1} 2 (Equation 1), < Condition A> a sample of 50 mm in the longitudinal direction x 50 mm in the lateral direction is cut out from the plastic film, and 1 site in the central portion of the sample and 4 sites each advancing 10 mm from the corners of the sample toward the central portion, for a total of 5 sites, are defined as measurement sites; the directions of the slow axis are measured at the 5 sites of the sample, and the angles formed by any one side of the sample and the directions of the slow axis of each measurement site are defined as D1, D2, D3, D4, and D5, respectively, and the difference between the maximum value of D1 to D5 and the minimum value of D1 to D5 is 1.5 degrees or more.

2. The optical film according to claim 1, wherein on the basis of the measurement of the 11 measurement points, when the maximum value of a* is defined as a*max, the minimum value of a* is defined as a*min, the maximum value of b* is defined as b*max, and the minimum value of b* is defined as b*min, the following formulas 2-1 and 2-2 are satisfied, a*max - a*min ≤ 0.250 (Formula 2-1) b*max - b*min ≤ 0.350 (Formula 2-2).

3. The optical film according to claim 1 or 2, wherein Based on the measurement of the 11 measurement points, the sum of the square of the difference in a* of adjacent measurement points and the square of the difference in b* of adjacent measurement points is calculated, and when the sum is defined as S, S is represented by the following formula 3, S is calculated at 10 adjacent points, respectively, and when the maximum value of S of the 10 points is defined as S MAX MAX S is 0.010 or more and 0.050 or less,​ S = {a*n - a*n1} 2 + {b*n - b*n1} 2 (Formula 3).

4. The optical film according to claim 1 or 2, wherein In the case where the visual reflectance Y value of the optical film is defined as R, the product of R and the Σ T is 0.05 or more and 0.25 or less.

5. The optical film according to claim 1 or 2, wherein 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, n2 / n1 is less than 1.

23.

6. The optical film according to claim 1 or 2, wherein When the average refractive index of the low refractive layer is defined as n1 and the average refractive index of the layer adjacent to the low refractive layer is defined as n2, n2 / n1 is 1.05 or more and less than 1.

23.

7. The optical film according to claim 1 or 2, wherein, The in-plane retardation of the plastic film at a wavelength of 590 nm is 2500 nm or less.

8. The optical film according to claim 1 or 2, wherein, One or more layers selected from a hard coat layer and an anti-glare layer are provided between the plastic film and the low refractive layer.

9. A polarizing plate having: a polarizing member; a first transparent protective plate on one side of the polarizing member; and a second transparent protective plate on the other side of the polarizing member, wherein At least one of the first transparent protective plate and the second transparent protective plate is the optical film according to any one of claims 1 to 8, and the side of the low refractive layer of the optical film faces the side opposite to the polarizing member.

10. An image display device having: a display element; and a polarizing member and an optical film disposed on the light exit surface side of the display element, wherein The optical film is the optical film according to any one of claims 1 to 8, and the side of the low refractive layer of the optical film faces the side opposite to the display element.

11. A selection method of an optical film for an image display device having a polarizing member and an optical film on the light exit surface of a display element, wherein An optical film X satisfying the following (1) to (5) is selected as the optical film: (1) The optical film X has a low refractive layer on a plastic film; (2) The plastic film has a slow axis which is an axis of the largest in-plane refractive index, and a fast axis which is an axis orthogonal to the slow axis in the in-plane of the plastic film; (3) The low refractive layer is on the surface of the optical film X; (4) The optical film X has Σ T an area of more than 0.04 and less than 0.20; and (5) The plastic film is a polyester film, <Measurement Condition 1> A linearly polarized light is incident from the side of the optical film opposite to the low refractive layer, the linearly polarized light as the incident light is defined as light L1, and the transmitted light after the light L1 is transmitted through the optical film is defined as light L2; The light L1 is made incident to the optical film at an angle where the elevation angle of the vibration direction of the light L1 with the plane of the optical film becomes an angle of 50 degrees or more and 70 degrees or less on the basis of the slow axis and the angle formed by the slow axis and the vibration direction of the light L1 is fixed at 45 degrees, the elevation angle is varied every 2 degrees in the range of 50 degrees or more and 70 degrees or less, the light L2 is measured at 11 kinds of elevation angles, the light L2 is measured at 11 measurement points by the aforementioned measurement; The light L2 is converted into the condition of a C light source and a viewing angle of 2 degrees, the a* value and the b* value of the L*a*b* colorimetric system for the light L2 of the n-th measurement point among the 11 measurement points are defined as a*n and b*n, and the a* value and the b* value of the L*a*b* colorimetric system for the light L2 of the n+1-th measurement point among the 11 measurement points are defined as a*n1 and b*n1; Based on the measurement of the 11 measurement points, the sum of the square of the difference of a* of adjacent measurement points and the square of the difference of b* of adjacent measurement points is calculated, the sum is calculated at 10 adjacent points respectively, and ∑ representing the sum of the sums is calculated T , the Σ T is represented by the following formula 1, ∑ T = ∑[{a*n - a*n1} 2 + {b*n - b*n1} 2 (Equation 1).

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