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

Abstract

To provide an optical biaxially stretched plastic film, a polarizing plate, and an image display device that can suppress blackout when visually recognized with polarized sunglasses or polarized goggles without increasing an in-plane phase difference, and to provide a method for selecting an optical biaxially stretched plastic film.SOLUTION: An optical biaxially stretched plastic film has an area satisfying the following conditions 1 and 2. <Condition 1> The difference (L1.n-L2.n) between brightness obtained in specific measurement 1 and brightness obtained in specific measurement 2 is calculated at 100 measurement points, and a "variation of brightness difference 3σ" calculated from the brightness differences of the 100 measurement points is 100 or more. <Condition 2> The in-plane phase difference (Re) is 2500 nm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an optical biaxially stretched plastic film, a polarizing plate, an image display device, and a method for selecting a biaxially stretched plastic film. [Background technology]

[0002] Liquid crystal display elements and organic electroluminescence (EL) elements are used in various electronic devices to visually transmit information. These display elements are not only used indoors, but in recent years, opportunities for using them outdoors have increased due to the spread of smartphones and digital signage. In the case of a liquid crystal display element, a viewer sees light that has passed through a polarizer on the light output side, and in the case of an organic EL element, a viewer sees light that has passed through a polarizer that is placed on the viewer side of the light emitting layer to prevent reflection of external light. Therefore, in both the liquid crystal display element and the organic EL element, a viewer sees polarized light. When image display devices are used outdoors in this way, a viewer wearing polarized sunglasses or polarized goggles or the like will have the opportunity to come into contact with information in the form of polarized light. In this case, if the vibration plane of the light that has passed through the polarizer on the viewer's side is perpendicular to the absorption axis of the polarizer in the polarized sunglasses or polarized goggles or the like, the light emitted from these image display devices will be blocked by the polarized sunglasses or polarized goggles or the like, and the viewer will see the liquid crystal display element in complete darkness, resulting in a so-called blackout state. Since polarized sunglasses or polarized goggles may be worn not only outdoors but also indoors, it is important to eliminate blackout.

[0003] In order to eliminate blackout, a method has been disclosed in which a polymer film is used and the angle between the absorption axis of the polarizer of the polarizing plate and the slow axis of the polymer film is set at approximately 45 degrees (Patent Document 1).

[0004] Patent Document 1 discloses a liquid crystal display device that can eliminate blackout when viewed through polarized sunglasses or polarized goggles, by using a specific white light source as the light source of the image display device, increasing the in-plane phase difference (Re, retardation) of the stretched plastic film to 3,000 nm or more and 30,000 nm or less, and arranging the absorption axis of the polarizer and the slow axis of the stretched plastic film at approximately 45 degrees. However, the method of Patent Document 1 requires the use of a stretched plastic film with a large in-plane retardation. Since a stretched plastic film with a large in-plane retardation is usually uniaxially stretched, it has problems such as being easily torn in the stretching direction and having a strong bending tendency in the direction perpendicular to the stretching direction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2011-107198 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present disclosure is to provide an optical biaxially stretched plastic film, a polarizing plate, and an image display device that can suppress blackout when viewed through polarized sunglasses or polarized goggles, without increasing the in-plane retardation. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that the above problems can be solved by setting the "brightness difference variation 3σ" (described later) to 100 or more and the in-plane retardation (Re) to 2500 nm or less.

[0008] The present disclosure provides the following optical biaxially stretched plastic film, a functional film, a polarizing plate and an image display device each using the same, and a method for selecting the optical biaxially stretched plastic film.

[0009] [1]<Condition 1> The luminance difference (L1.n-L2.n) between the luminance obtained in Measurement 1 below and the luminance obtained in Measurement 2 below is calculated at 100 measurement points, and the "variation in luminance difference 3σ" calculated from the luminance differences at the 100 measurement points is 100 or more. Measurement 1 A first measurement sample is prepared by arranging a first polarizer, an optical biaxially stretched plastic film, and a second polarizer in this order on a surface light source. In the first measurement sample, the optical biaxially stretched plastic film is arranged so that the slow axis direction is approximately perpendicular to the absorption axis direction of the first polarizer, and the second polarizer is arranged so that the absorption axis direction is approximately perpendicular to the absorption axis direction of the first polarizer. The surface light source of the first measurement sample is displayed as white, and the luminance of the transmitted light emitted from the second polarizer side is measured at 100×100 measurement points set at equal intervals in an arbitrary first region. 100 points are extracted from the measurement results in an arbitrary horizontal row, and are sequentially designated as the 1st measurement point to the 100th measurement point, with the luminance of the 1st measurement point defined as L1.1, the luminance of the 100th measurement point defined as L1.100, and the luminance of the nth measurement point defined as L1.n. Measurement 2 A second measurement sample is prepared by arranging the first polarizer and the second polarizer in this order on the same surface light source as in Measurement 1. In the second measurement sample, the absorption axis of the second polarizer is arranged approximately perpendicular to the direction of the absorption axis of the first polarizer. The surface light source of the second measurement sample is displayed as white, and the luminance of the transmitted light emitted from the second polarizer side is measured at 100×100 measurement points set at equal intervals in an area that approximately coincides with the first measurement area. 100 points are arbitrarily extracted in a horizontal row from the measurement results, and are sequentially designated as the 1st measurement point to the 100th measurement point, with the luminance of the 1st measurement point defined as L2.1, the luminance of the 100th measurement point defined as L2.100, and the luminance of the nth measurement point defined as L2.n. <Condition 2> The in-plane retardation (Re) is 2500 nm or less; An optical biaxially stretched plastic film having a region that satisfies the above <Condition 1> and the above <Condition 2>.

[0010] [2] The optical biaxially stretched plastic film according to [1], wherein the in-plane retardation relative to the retardation in the thickness direction is 0.10 or less. [3] The optical biaxially stretched plastic film according to [1] or [2], having a thickness of 20 μm or more and 200 μm or less. [4] A functional film having a functional layer on one side of the optical biaxially stretched plastic film according to any one of [1] to [3]. [5] A polarizing plate having a polarizer, a first transparent protective plate arranged on one side of the polarizer, and a second transparent protective plate arranged on the other side of the polarizer, wherein at least one of the first transparent protective plate and the second transparent protective plate is an optical biaxially stretched plastic film described in any one of [1] to [3]. [6] An image display device having a display element and a plastic film arranged on the light exit surface side of the display element, wherein the plastic film is an optical biaxially stretched plastic film according to any one of [1] to [3]. [7] The image display device according to [6], further comprising a polarizer between the display element and the plastic film. [8] The image display device according to [6] or [7], further comprising a functional layer on the side of the optical biaxially stretched plastic film opposite to the display element.

[0011] [9]<Condition 1B> The luminance difference (L1.n-L2.n) between the luminance obtained in the following measurement 1B and the luminance obtained in the following measurement 2B is calculated at 100 measurement points, and the "variation in luminance difference 3σ" calculated from the luminance differences at the 100 measurement points is 100 or more. 《Measurement 1B》 A 1B measurement sample is prepared by arranging a first polarizer, an optical biaxially stretched plastic film, and a second polarizer in this order on a display element. In the 1B measurement sample, the slow axis direction of the optical biaxially stretched plastic film is arranged to be approximately perpendicular to the absorption axis direction of the first polarizer, and the absorption axis of the second polarizer is arranged to be approximately perpendicular to the absorption axis direction of the first polarizer. The display element of the 1B measurement sample is made to display white, and the luminance of the transmitted light exiting from the second polarizer side is measured at 100×100 measurement points set at equal intervals in any first region. 100 points are extracted from the measurement results in any horizontal row, and are numbered from the 1st measurement point to the 100th measurement point in order, with the luminance of the 1st measurement point defined as L1.1, the luminance of the 100th measurement point defined as L1.100, and the luminance of the nth measurement point defined as L1.n. 《Measurement 2B》 A measurement sample 2B is prepared by disposing the first polarizer and the second polarizer in this order on the same display element as in measurement 1B. In the measurement sample 2B, the absorption axis of the second polarizer is disposed substantially perpendicular to the absorption axis direction of the first polarizer. The display element of the 2B measurement sample is made to display white, and the luminance of the transmitted light exiting from the second polarizer side is measured at 100×100 measurement points set at equal intervals in an area that substantially coincides with the first measurement area. 100 points are arbitrarily extracted in a horizontal row from the measurement results, and are sequentially designated as the 1st measurement point to the 100th measurement point, with the luminance of the 1st measurement point defined as L2.1, the luminance of the 100th measurement point defined as L2.100, and the luminance of the nth measurement point defined as L2.n. <Condition 2B> The in-plane retardation (Re) is 2500 nm or less; An image display device having the first polarizer and an optical biaxially stretched plastic film on the light exit surface of the display element, wherein the direction of the slow axis of the optical biaxially stretched plastic film and the direction of the absorption axis of the first polarizer are arranged approximately perpendicular to each other, and the optical biaxially stretched plastic film has an area that satisfies <Condition 1B> and <Condition 2B>.

[0012]

[10] A method for selecting a biaxially stretched plastic film for an image display device having an optical biaxially stretched plastic film on the light output surface side of a display element, the method comprising the steps of: determining whether the film has an area that satisfies condition 1 and condition 2; and selecting an optical biaxially stretched plastic film that satisfies the determination condition. Effect of the Invention

[0013] The optical biaxially stretched plastic film of the present disclosure, and the functional film, polarizing plate, and image display device using the same can suppress blackout when viewed through polarized sunglasses or polarized goggles, without increasing the in-plane retardation. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing a measurement form when calculating "brightness difference variation 3σ." [Diagram 2] FIG. 1 is a schematic diagram showing a measurement form when calculating "brightness difference variation 3σ." [Diagram 3] FIG. 13 is a schematic diagram showing an example of a measurement region when calculating the "variation 3σ of brightness difference." [Figure 4] FIG. 2 is a schematic diagram showing an example of a measurement region. [Diagram 5] FIG. 11 is a plan view illustrating five measurement points under conditions 2 to 4. [Figure 6] FIG. 1 is a schematic diagram showing a continuous folding test. [Figure 7] FIG. 1 is a schematic diagram showing the application of the optical biaxially stretched plastic film of the present disclosure to a liquid crystal display element. [Figure 8] FIG. 1 is a schematic diagram showing an organic EL element to which the optical biaxially stretched plastic film of the present disclosure is applied. [Figure 9] A diagram for explaining [+αB-(-αB)], [+αG-(-αG)], and [+αR-(-αR)] under condition A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, embodiments of the present disclosure will be described. [Optical biaxially oriented plastic film] The optical biaxially stretched plastic film of the present disclosure has an area (hereinafter sometimes referred to as "measurement area") that satisfies the following conditions 1 and 2.

[0016] <Measurement conditions> <Condition 1> The "3σ variation in luminance difference" in condition 1 is obtained using L1.n obtained in measurement 1 and L2.n obtained in measurement 2 below. In this specification, 3σ refers to the 3σ used in statistics. In statistics, 3σ means that there is a 99.7% probability that measurement data exists in the ±3σ range for the 100% range of the normal distribution curve obtained from the histogram. In other words, in condition 1, it means that the ±3σ range of the histogram of the luminance difference of 100 measurement points is 100 or more. In addition, in this specification, "luminance" means the light energy detected by the measurement procedure described later, and is a dimensionless value. Measurement 1 A method for measuring the luminance at the n-th measurement point, L1.n, will be described with reference to FIGS. As shown in Fig. 1, the optical biaxially stretched plastic film (10) of the present invention is laminated in the following order: a surface light source (1), a first polarizer (2), an optical biaxially stretched plastic film (10), and a second polarizer (3). This is designated as a first measurement sample (4). The first measurement sample is arranged so that the slow axis direction of the optical biaxially stretched plastic film is approximately perpendicular to the absorption axis direction of the first polarizer, and the absorption axis of the second polarizer is approximately perpendicular to the absorption axis direction of the first polarizer. In this specification, approximately perpendicular means within 90 degrees ± 5 degrees unless otherwise specified, preferably within 90 degrees ± 3 degrees, and more preferably within 90 degrees ± 1 degree. Next, an imaging luminance meter 20 is placed at a position 750 mm away from the surface of the surface light source. The second polarizer may be placed just before the imaging luminance meter 20. In other words, the optical biaxially stretched plastic film and the second polarizer do not need to be in contact with each other. Next, an arbitrary area on the first polarizer is set as the measurement area for measurement 1, and a total of 10,000 measurement points of 100×100 are evenly arranged in the measurement area as shown in FIG. 3. The measurement area for measurement 1 is referred to as the "first measurement area." The arbitrary area is preferably 100 mm×100 mm, but may be smaller in the case of a small display element such as a mobile device. An arbitrary row is selected from the vertical 100, and the leftmost square is set as the first measurement point and the rightmost square is set as the 100th measurement point, defining the first measurement point to the 100th measurement point. The luminance at each of these measurement points is measured by the imaging luminance meter described above. The luminance at the first measurement point is set as L1.1, the luminance at the 100th measurement point is set as L1.100, and the luminance at the nth measurement point in the first measurement sample is set as L1.n. The vertical and horizontal directions of the 100x100 measurement points in Measurement 1 correspond to the vertical and horizontal directions of the first measurement sample, as shown in Figure 3. Similarly, the vertical and horizontal directions of the 100x100 measurement points in Measurement 2 correspond to the vertical and horizontal directions of the second measurement sample. If the planar shapes of the first and second measurement samples are rectangular or square, it is easy to determine the vertical and horizontal directions. It is not necessary to distinguish between the vertical and horizontal directions. If the planar shapes of the first and second measurement samples are other than a rectangle or square (circle, triangle, etc.), draw a rectangle or square that has the largest area that does not extend beyond the outer frame shape of the samples, and determine the vertical or horizontal direction based on the drawn rectangle or square. The luminance is measured in a dark room.

[0017] The first polarizer is preferably arranged so that the absorption axis of the first polarizer is approximately parallel to the horizontal or vertical direction of the surface light source. In this specification, approximately parallel means that the difference between the absorption axis of the polarizer and the horizontal or vertical direction of the surface light source is within ±5 degrees, preferably within ±3 degrees, and more preferably within ±1 degree. The horizontal and vertical directions of the surface light source are determined in the same manner as the horizontal and vertical directions of the first and second measurement samples. The first polarizer is arranged so that the angle between the absorption axis direction and the left-right or up-down direction of the surface light source is approximately parallel, taking into consideration that a polarizer on the light exit surface side of a general-purpose image display device is arranged in such a manner.

[0018] In Measurement 1, any measurement point whose luminance variation with adjacent measurement points exceeds 30% is excluded from the measurement results as it is due to a local defect in the member constituting the first measurement sample. If such an abnormal point is present, the 3σ of Condition 1 is calculated based on points other than the abnormal point. The same applies to Measurement 2 described below. In addition, the adjacent measurement points are, for example, the second measurement point in the case of the first measurement point in FIG. 3, and the fourth and sixth measurement points in the case of the fifth measurement point.

[0019] The number of luminance measurement points used in calculating the "luminance difference variation 3σ" is preferably 10 or more, more preferably 20 or more, more preferably 30 or more, more preferably 40 or more, more preferably 50 or more, more preferably 70 or more, and more preferably 90 or more. If the luminance values ​​used in the calculation are too small, it is not preferable because it does not reflect the properties of the first measurement sample. The aforementioned number of measurement points is preferable especially for small display devices. On the other hand, in the case of a large display device of 20 inches or more (even more preferably 50 inches or more), in order to measure the variations well, the number of measurement points is preferably 80 or more, and more preferably 90 or more. The upper limit of the number of luminance measurement points is 100. It is most preferable that the number of luminance measurement points is 100, but in order to sufficiently reflect the properties of the first measurement sample, it is preferable that the number is 80 or more.

[0020] The optical biaxially stretched plastic film may be in the form of a sheet (see FIG. 4) or a roll. For the measurement according to condition 1, the sheet-like or roll-like optical biaxially stretched plastic film may be used as is, but for ease of handling or when the optical biaxially stretched plastic film is too large to be installed in the measuring device, it may be cut into a size of 100 mm or more in length x 100 mm or more in width (hereinafter referred to as a measurement sample), and a region of 100 mm in length x 100 mm in width, 1 mm or more inward from the outline, may be used as the measurement region. The reason for measuring the inner region of the sample is that when the sample is cut, stress is likely to be applied near the edge of the plastic film, so that the optical axis near the edge of the sample may be distorted. FIG. 4 shows an example of cutting out first to third samples (21, 22, 23) from a sheet-like optical biaxially stretched plastic film 10. When cutting out and using, the sample may be cut out from any location of the optical biaxially stretched plastic film, but if the longitudinal and transverse directions of the sheet and roll can be confirmed, the sample should be cut out along the confirmed longitudinal and transverse directions. 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 transverse direction. Also, if the flow direction and transverse direction of the sheet can be confirmed, the flow direction can be regarded as the longitudinal direction, and the transverse direction can be regarded as the transverse direction. If it is difficult to confirm the flow direction and transverse direction of the sheet, and the sheet is rectangular or square, the longitudinal and transverse directions can be confirmed by the four sides constituting the rectangle or square. If it is difficult to confirm the flow direction and transverse direction of the sheet, and the sheet is a shape other than a rectangle or square (circle, triangle, etc.), the rectangle or square with the largest area that does not protrude from the outer frame shape of the sheet can be drawn, and the longitudinal and transverse directions can be confirmed by the sides of the drawn rectangle or square. In addition, in the case of a sheet-shaped optical biaxially stretched plastic film, it is preferable to cut out a sample near the center, and in the case of a roll-shaped optical biaxially stretched plastic film, it is preferable to cut out a sample near the center in the width direction of the roll. The embodiment of the sampling under condition 1 described above can be applied to the embodiment of the sampling under condition 2 described below (however, under condition 2, the size of the sample is 100 mm×100 mm). In addition, when an optical biaxially stretched plastic film is incorporated in a commercially available image display device, the image display device can be disassembled, and the optical biaxially stretched plastic film can be removed from the laminate arranged on the display element, for example by peeling it off, and the removed optical biaxially stretched plastic film can be evaluated as to whether it satisfies conditions 1 and 2.

[0021] In Measurement 1 and Measurement 2, the luminance is measured as follows. As described above, the luminance in Measurement 1 and Measurement 2 means the energy of light detected by the following measurement procedure, and is a dimensionless value. The measurement atmosphere for Measurement 1 and Measurement 2 is set to a temperature of 23°C ± 5°C and a relative humidity of 40% RH to 65% RH. Furthermore, before performing Measurement 1 and Measurement 2, the first measurement sample and the second measurement sample are left to stand in the above atmosphere for 30 minutes or more.

[0022] <Measurement procedure for measurement 1> The surface light source of the first measurement sample is displayed in white. The measurement device used is Cybernet's "Prometric PM1423-1, imaging luminance meter, CCD resolution: 1536 x 1024." The first measurement sample and the imaging luminance meter are set in the positional relationship shown in Figure 1. The distance between the camera and the surface light source is set to 750 mm. Next, the following "Setting before measurement" and "Adjustment of exposure time" are carried out, and then the following "Measurement and analysis" is carried out. The measurement is carried out in a darkroom environment. <Settings before measurement> (1) The imaging luminance meter is connected to a personal computer, and the software provided with the imaging luminance meter (RADIANT IMAGING Prometric 9.1 Version 9.1.32) is launched in the personal computer. (2) When the software is launched, the CCD temperature in the imaging luminance meter is automatically adjusted to a blue display (-10°C). Wait until the CCD temperature stabilizes at -10°C. (3) In the “Measurement Setup” of the software, specify “Color, 1x1 binning.” (4) Set the lens aperture dial to 1.8 and focus on the second polarizer. <Adjusting exposure time> Implement the "Exposure Time Adjustment" in the software. Specifically, press "Adjust" in the order of Y (green), X (red), and Z (blue), and then save. Adjustment of exposure time is implemented every time a sample is measured. <Measurement and analysis> Select "Focus Mode" on the toolbar and check that the area to be measured is displayed in the focus mode image. Click "Execute measurement" to perform the measurement. Save the measurement results. From the toolbar, select "Tools" and "Measurement Data Processing." Next, select "Cutout Range" from the "Select Processing Content" pull-down menu. Next, specify the range that corresponds to 100mm x 100mm of the sample and save it. The above saved data is called "Saved Data 1." (Note that in the case of small display elements such as mobile devices, a range narrower than 100mm x 100mm may be specified. For example, in the case of small display elements, ranges such as 30mm x 100mm, 30mm x 70mm, 30mm x 50mm, 30mm x 30mm, etc. may be specified. Also, in the case of small display elements, a range may be specified with a size and shape that matches the shape of the element.) Open saved data 1. Then, select "Tools" and "Export measurement data" from the toolbar. Next, select "Brightness" as the data type, set the resolution to "X:100, Y:100", and the output format to "XY table", and export the data to Excel. The above procedure obtains luminance data for 100 x 100 measurement points. By extracting 100 points in any horizontal row from the measurement results, the luminance data for 100 points (L1.n, luminance of measurement 1) shown in Figure 3 is obtained.

[0023] <Measurement procedure for measurement 2> In the measurement procedure for measurement 1, if "first measurement sample" and "L1.n. Luminance of measurement 1" are replaced with "second measurement sample" and "L2.n. Luminance of measurement 2", the measurement procedure becomes that for measurement 2.

[0024] Measurement 2 A method for measuring the luminance at the n-th measurement point, L2.n, will be described with reference to FIGS. A second measurement sample obtained by removing the optical biaxially stretched plastic film from the first measurement sample in Measurement 1 is used to measure the luminance in the same manner, except for removing the optical biaxially stretched plastic film. The second measurement area, which is the measurement area in Measurement 2, is approximately matched with the first measurement area, which is the measurement area in Measurement 1. In this specification, approximately matched means that the deviation of the measurement areas is within 0.5 mm, preferably within 0.3 mm, and more preferably within 0.1 mm. 100 measurement points are set in the same manner as described in Measurement 1 using Fig. 3, and the luminance is measured at each point. The first measurement point in the second measurement sample approximately coincides with the first measurement point in the first measurement sample and has a luminance of L2.1, the 100th measurement point in the second measurement sample approximately coincides with the 100th measurement point in the first measurement sample and has a luminance of L2.100, and the luminance of the nth measurement point in the second measurement sample is L2.n. In addition, a horizontal column related to L2.n in measurement 2 shall be matched with an arbitrary horizontal column related to L1.n in measurement 1. For example, if an arbitrary horizontal column related to L1.n in measurement 1 is the horizontal column on the 50th row, the arbitrary horizontal column related to L2.n in measurement 2 shall also be the horizontal column on the 50th row.

[0025] Calculate the difference between the luminance at the first measurement point obtained in Measurement 1 and the luminance at the first measurement point obtained in Measurement 2. Similarly, calculate the luminance difference for each of the 100 points up to the 100th measurement point, and calculate the "luminance difference variation 3σ" from the luminance differences obtained for the 100 points. For confirmation, in measurement 2, the surface light source (1), the first polarizer (2), and the second polarizer (3) were stacked in this order, with the slow axis of the second polarizer being arranged approximately perpendicular to the absorption axis of the first polarizer.

[0026] In the present application, the upper and lower limit values ​​can be appropriately combined to represent a range having the maximum and minimum values.

[0027] Condition 1 specifies that the "brightness difference variation 3σ" is 100 or more. Since L1.n and L2.n are values ​​that include backlight characteristics and environmental factors, condition 1 of the present disclosure calculates the "brightness difference variation 3σ" using the brightness difference (L1.n-L2.n), which is the difference between L1.n and L2.n. When the "brightness difference variation 3σ" is 100 or more, blackout does not occur or its influence is weak, and information on a smartphone using an optical biaxially stretched plastic film can be read while wearing polarized sunglasses or polarized goggles. Therefore, the lower limit of the "brightness difference variation 3σ" must be 100 or more, preferably 105 or more, and more preferably 110 or more. On the other hand, if the "brightness difference variation 3σ" is too large, problems such as a decrease in mechanical strength are likely to occur, and wrinkles of the optical biaxially stretched plastic film due to humidity, iridescent unevenness due to distortion, etc. may occur. For this reason, the upper limit is preferably 800 or less, more preferably 600 or less, more preferably 500 or less, and more preferably 450 or less. By satisfying conditions 3 and 4 described below, condition 1 can be more easily satisfied.

[0028] Suitable ranges for the variation 3σ in luminance difference under condition 1 include, for example, 100 or more and 800 or less, 100 or more and 600 or less, 100 or more and 500 or less, 100 or more and 450 or less, 105 or more and 800 or less, 105 or more and 600 or less, 105 or more and 500 or less, 105 or more and 450 or less, 110 or more and 800 or less, 110 or more and 600 or less, 110 or more and 500 or less, and 110 or more and 450 or less.

[0029] The variation 3σ in brightness difference under condition 1 is calculated from any horizontal row among the 100 rows. In this embodiment, the number of rows that satisfy condition 1 is preferably 50 or more of the 100 rows, more preferably 70 or more, more preferably 90 or more, more preferably 95 or more, and more preferably 100 rows.

[0030] The lower limit of L1.n used in calculating the "brightness difference variation 3σ" is preferably 80 or more, and more preferably 100 or more. The upper limit of L1.n is preferably 1200 or less, more preferably 1000 or less, and even more preferably 500 or less. Preferred ranges for L1.n include 80 or more and 1200 or less, 100 or more and 1000 or less, 80 or more and 500 or less, 100 or more and 1200 or less, 100 or more and 1000 or less, and 100 or more and 500 or less. Furthermore, the lower limit of the average of 100 points of L1.n is preferably 150 or more, more preferably 200 or more, and even more preferably 250 or more, and the upper limit is preferably 800 or less, more preferably 600 or less, and even more preferably 500 or less. By setting the average of 100 points of L1.n within the above range, it becomes easier to satisfy condition 1.

[0031] The lower limit of L2.n used in calculating the "brightness difference variation 3σ" is preferably 20 or more, and more preferably 30 or more. The upper limit of L2.n is preferably 600 or less, more preferably 500 or less, and even more preferably 300 or less. Preferred ranges for L2.n include 20 or more and 600 or less, 30 or more and 600 or less, 20 or more and 500 or less, 30 or more and 500 or less, 20 or more and 300 or less, and 30 or more and 300 or less. Furthermore, the lower limit of the average of 100 points of L2.n is preferably 20 or more, more preferably 30 or more, and the upper limit is preferably 600 or less, more preferably 500 or less, and even more preferably 300 or less. By setting the average of 100 points of L2.n within the above range, condition 1 can be easily satisfied.

[0032] The surface light source is not particularly limited as long as it can display white. The color temperature when the surface light source is displayed in white is preferably 5000K or more, more preferably 6000K or more, and even more preferably 6500K or more, and the upper limit is preferably 13000K or less, more preferably 12000K or less, and even more preferably 11000K or less. By setting the color temperature of the white display in the above range, the measurement results can be easily homogenized. The surface light source may be, for example, a general-purpose image display device such as a liquid crystal display device or an organic EL display device. However, when the image display device has a viewer-side polarizer on the display element, the viewer-side polarizer is excluded from the surface light source. This is because the viewer-side polarizer can be the first polarizer. In addition, when the surface light source is a liquid crystal display device, examples of the backlight of the liquid crystal display device include a backlight using quantum dots and a backlight using white light-emitting diodes. The first polarizer is preferably prepared separately, not a polarizer disposed on a display element of a commercially available image display device. If a polarizer disposed on a display element of a commercially available image display device can be taken out in good condition, the taken out polarizer may be used as the first polarizer.

[0033] A first polarizer is placed on a surface light source, and the luminance of transmitted light emerging from the first polarizer side, as an average of 100 points in a measurement area excluding the second polarizer in Measurement 2, is preferably at least 15,000, more preferably at least 17,000, more preferably at least 18,000, and more preferably at least 20,000, and is preferably at most 60,000, more preferably at most 50,000, more preferably at most 40,000, and more preferably at most 38,000. Within these ranges, the "variation in luminance difference 3σ" can be calculated with high reproducibility. Preferred ranges of the brightness of the transmitted light include 15,000 or more and 60,000 or less, 15,000 or more and 50,000 or less, 15,000 or more and 40,000 or less, 15,000 or more and 38,000 or less, 17,000 or more and 60,000 or less, 17,000 or more and 50,000 or less, 17,000 or more and 40,000 or less, 17,000 or more and 38,000 or less, 18,000 or more and 60,000 or less, 18,000 or more and 50,000 or less, 18,000 or more and 40,000 or less, 18,000 or more and 38,000 or less, 20,000 or more and 60,000 or less, 20,000 or more and 50,000 or less, 20,000 or more and 40,000 or less, and 20,000 or more and 38,000 or less.

[0034] A first polarizer is placed on a surface light source, and the 3σ of the luminance of the transmitted light exiting from the first polarizer side is calculated from 100 points in the measurement area excluding the second polarizer from Measurement 2, and the lower limit is preferably 1000 or more, more preferably 1300 or more, and more preferably 1500 or more, and the upper limit is preferably 10000 or less, more preferably 8000 or less, and more preferably 70000 or less. As described above, the "3σ variation in luminance difference" eliminates the influence of the surface light source, etc. by taking the difference, but by setting the 3σ of the luminance of the transmitted light in the above range, the "3σ variation in luminance difference" can be calculated with high reproducibility. Preferred ranges of 3σ of the luminance of transmitted light include 1,000 or more and 10,000 or less, 1,000 or more and 8,000 or less, 1,000 or more and 70,000 or less, 1,300 or more and 10,000 or less, 1,300 or more and 8,000 or less, 1,300 or more and 70,000 or less, 1,500 or more and 10,000 or less, 15,000 or more and 8,000 or less, and 1,500 or more and 70,000 or less.

[0035] In order to easily suppress rainbow unevenness, the surface light source preferably satisfies the following condition A. Satisfying condition A means that at least one of the full width at half maximum of the intensity peaks present in the blue wavelength region, the green wavelength region, and the red wavelength region is equal to or greater than a predetermined value (10 nm or greater). Figure 9 shows the [+α B -(-α B )], [+α G -(-α G )] and [+α R -(-α R 9 is a diagram for explaining the spectrum of a surface light source of a general-purpose organic EL element.

[0036] <Condition A> A first polarizer is placed on a surface light source, and the intensity of light L1 emitted vertically from the first polarizer side is measured at wavelength intervals of 1 nm. The blue wavelength range is 400 nm or more and less than 500 nm, the green wavelength range is 500 nm or more and less than 570 nm, and the red wavelength range is 570 nm or more and less than 780 nm. The maximum intensity of the blue wavelength range of L1 is B.max , the maximum intensity of the green wavelength region of L1 is G max , the maximum intensity of the red wavelength region of L1 is R max Let us assume that. B max Let L1λ be the wavelength that indicates B , G max Let L1λ be the wavelength that indicates G , R max Let L1λ be the wavelength that indicates R Let us assume that. B max A wavelength that exhibits an intensity of 1 / 2 or less of L1λ B The minimum wavelength located on the negative side of B , B max A wavelength that exhibits an intensity of 1 / 2 or less of L1λ B The minimum wavelength located on the positive side of B , G max A wavelength that exhibits an intensity of 1 / 2 or less of L1λ G The maximum wavelength located on the negative side of G , G max A wavelength that exhibits an intensity of 1 / 2 or less of L1λ G The minimum wavelength located on the positive side of G , R max A wavelength that exhibits an intensity of 1 / 2 or less of L1λ R The maximum wavelength located on the negative side of R , R max A wavelength that exhibits an intensity of 1 / 2 or less of L1λ R The maximum wavelength located on the positive side of R Let us assume that. [+α B -(-α B )], [+α G -(-α G )] and [+α R -(-α R )] is 10 nm or more.

[0037] Condition A is more preferably such that two or more of [+αB-(-αB)], [+αG-(-αG)], and [+αR-(-αR)] are 10 nm or more, and even more preferably such that all three are 10 nm or more.

[0038] [+α B -(-α B )] is more preferably 15 nm or more, and even more preferably 17 nm or more. B -(-α B )] is preferably 70 nm or less, more preferably 50 nm or less, and even more preferably 30 nm or less. [+α G -(-α G )] is more preferably 15 nm or more, and even more preferably 20 nm or more. G -(-α G )] is preferably 70 nm or less, more preferably 50 nm or less, and even more preferably 45 nm or less. [+α R -(-α R )] is more preferably 15 nm or more, even more preferably 20 nm or more, and even more preferably 30 nm or more. R -(-α R )] is preferably 70 nm or less, more preferably 65 nm or less, and even more preferably 60 nm or less.

[0039] <Condition 2> The in-plane retardation (Re) is measured at a total of five locations, including four locations 10 mm from the four corners of a sample measuring 100 mm long by 100 mm wide, and the central portion of the sample (black circles in FIG. 5). When the in-plane retardations at the five locations are defined as Re1, Re2, Re3, Re4, and Re5, the average of Re1 to Re5 is 2500 nm or less. The average value of the in-plane retardation is calculated by the following formula (1) using the refractive index nx in the slow axis direction, which is the direction in which the refractive index is the largest, the refractive index ny in the fast axis direction, which is the direction perpendicular to the slow axis direction, and the thickness T [nm] of the biaxially stretched plastic film. In this specification, the in-plane retardation and the retardation in the thickness direction mean values ​​at a wavelength of 550 nm. Furthermore, when the direction of the slow axis is not uniform within the plane of the biaxially stretched plastic film, the direction of the slow axis of the biaxially stretched plastic film means the average direction of the slow axis within the plane of the biaxially stretched plastic film. In-plane phase difference (Re)=(nx-ny)×T[nm] (1)

[0040] The direction of the slow axis and the in-plane retardation can be measured, for example, by using a product name "RETS-100" manufactured by Otsuka Electronics Co., Ltd. When measuring the in-plane retardation (Re) and the like using the product name "RETS-100" manufactured by Otsuka Electronics Co., Ltd., it is preferable to prepare for the measurement according to the following procedures (A1) to (A4).

[0041] (A1) First, turn on the RETS-100 light source and leave it for 60 minutes or more to stabilize it. After that, select the rotating analyzer method and select θ mode (angle direction phase difference measurement and Rth calculation mode). By selecting this θ mode, the stage becomes a tilt rotation stage. (A2) Next, enter the following measurement conditions into the RETS-100. (Measurement conditions) Retardation measurement range: Rotating analyzer method Measurement spot diameter: φ5mm Tilt angle range: 0° Measurement wavelength range: 400nm to 800nm The average refractive index of biaxially stretched plastic film. For example, in the case of PET film, N=1.617. The average refractive index N of a plastic film can be calculated from nx, ny, and nz using the formula (N=(nx+ny+nz) / 3). Thickness: Thickness measured separately using SEM or optical microscope (A3) Next, background data is obtained without placing a sample in the instrument, in a closed system, and every time the light source is turned on. (A4) After that, the sample is placed on the stage inside the device and measured.

[0042] Condition 2 specifies that the Re value of an optical biaxially stretched plastic film must be 2500 nm or less. Since the biaxially stretched plastic film for optical use of the present disclosure is subjected to biaxial stretching, the film has good mechanical strength. In addition, the optical biaxially stretched plastic film of the present disclosure has an Re of 2500 nm or less, so that the longitudinal and transverse stretching ratio is in an appropriate range, and the mechanical strength and tear resistance can be improved. In addition, the optical biaxially stretched plastic film of the present disclosure has an Re of 2500 nm or less, so that the optical biaxially stretched plastic film of the present disclosure can contribute to the thinning of plastic films. Furthermore, even in the case of an optical biaxially stretched plastic film, if Re is too small, sufficient mechanical strength may not be obtained. In order to increase Re, it is necessary to highly stretch the plastic film. However, when the plastic film is highly stretched, the orientation of the polymer chains of the plastic film is aligned, and problems occur in mechanical strength such as the plastic film being easily torn in the stretching direction. For this reason, the upper limit of Re of the optical biaxially stretched plastic film of the present disclosure is preferably 2500 nm or less, more preferably 2000 nm or less, more preferably 1800 nm or less, more preferably 1600 nm or less, more preferably 1490 nm or less, more preferably 1400 nm or less, more preferably 1200 nm or less, more preferably 1150 nm or less, more preferably 1000 nm or less, more preferably 800 nm or less, and more preferably 600 nm or less. When the thickness of an optical biaxially stretched plastic film is reduced to 10 μm or more and 50 μm or less, Re is preferably 1400 nm or less.

[0043] If the in-plane retardation of the optical biaxially stretched plastic film is too small, the mechanical strength may not be sufficient even after biaxial stretching. Therefore, the in-plane retardation of the optical biaxially stretched plastic film is preferably 20 nm or more, more preferably 100 nm or more, even more preferably 300 nm or more, and even more preferably 520 nm or more.

[0044] The preferred ranges of Re in condition 2 are 20 nm or more and 2500 nm or less, 20 nm or more and 2000 nm or less, 20 nm or more and 1800 nm or less, 20 nm or more and 1600 nm or less, 20 nm or more and 1490 nm or less, 20 nm or more and 1400 nm or less, 20 nm or more and 1200 nm or less, 20 nm or more and 1150 nm or less, 20 nm or more and 1000 nm or less, 20 nm or more and 800 nm or less, and 20 nm or more and 600 nm or less. Below, 100nm or more and 2500nm or less, 100nm or more and 2000nm or less, 100nm or more and 1800nm ​​or less, 100nm or more and 1600nm or less, 100nm or more and 1490nm or less, 100nm or less Upper 1400nm or less, 100nm or more and 1200nm or less, 100nm or more and 1150nm or less, 100nm or more and 1000nm or less, 100nm or more and 800nm ​​or less, 100nm or more and 600nm or less, 3 00nm to 2500nm, 300nm to 2000nm, 300nm to 1800nm, 300nm to 1600nm, 300nm to 1490nm, 300nm to 14 00nm or less, 300nm or more and 1200nm or less, 300nm or more and 1150nm or less, 300nm or more and 1000nm or less, 300nm or more and 800nm ​​or less, 300nm or more and 600nm or less, 520 nm or more and 2500 nm or less, 520 nm or more and 2000 nm or less, 520 nm or more and 1800 nm or less, 520 nm or more and 1600 nm or less, 520 nm or more and 1490 nm or less, 520 nm or more and 1400 nm or less, 520 nm or more and 1200 nm or less, 520 nm or more and 1150 nm or less, 520 nm or more and 1000 nm or less, 520 nm or more and 800 nm or less, and 520 nm or more and 600 nm or less.

[0045] In a sheet-like optical biaxially stretched plastic film, the proportion of the measurement area satisfying both condition 1 and condition 2 is preferably 50% or more, more preferably 70% or more, even more preferably 90% or more, and even more preferably 100%.

[0046] In addition, when a plurality of samples for measuring conditions 1 and 2 can be taken from a roll-shaped optical biaxially stretched plastic film, it is preferable that the samples taken from a predetermined position in the width direction of the roll satisfy most of the conditions in the flow direction of the roll. By satisfying the above-mentioned configuration, if the optical biaxially stretched plastic film at a predetermined position in the width direction of the roll is picked up, it can be made into an optical biaxially stretched plastic film that exhibits the effects of the present disclosure. That is, the roll-shaped optical biaxially stretched plastic film does not need to satisfy conditions 1 and 2 in the entire width direction, but only needs to satisfy conditions 1 and 2 at least at a predetermined position in the width direction. Note that the physical properties of the roll-shaped plastic film are likely to change in the width direction, but the physical properties are almost the same in the flow direction. For this reason, when the samples taken from a predetermined position in the width direction of the roll satisfy conditions 1 and 2, it can be assumed that the locations at the same positions in the width direction satisfy conditions 1 and 2 in the entire flow direction of the roll. Furthermore, in a biaxially stretched optical plastic film, it is preferable that at least one of the following conditions 3 and 4 is satisfied.

[0047] <Condition 3> The difference between the maximum value of Re1, Re2, Re3, Re4, and Re5 obtained under condition 2 and the minimum value of Re1 to Re5 is preferably 5 nm or more, more preferably 30 nm or more, and even more preferably 50 nm or more. By increasing the difference, condition 4 can be more easily satisfied. In order to suppress variations in optical properties and mechanical strength, the difference is preferably 100 nm or less, and more preferably 70 nm or less.

[0048] <Condition 4> The directions of the slow axes at the five locations under condition 2 are measured, and the angles between any one side of the measurement region under condition 2 and the direction of the slow axis at each measurement location are defined as D1 (the angle at the measurement point of Re1), D2, D3, D4, and D5, respectively. It is preferable that the difference between the maximum and minimum values ​​of D1 to D5 is 5.0 degrees or more. Note that "any one side of the measurement region under condition 2" means any one side of the measurement sample (100 mm x 100 mm) under condition 2. The any one side may be either the vertical or horizontal side of the sample, as long as the same side is used as the reference for all of D1 to D5. Condition 4 specifies that the difference between the maximum value of D1 to D5 and the minimum value of D1 to D5 is 5.0 degrees or more. If the difference is 5.0 degrees or more, blackout is not observed or can be reduced within the sample area when viewed through polarized sunglasses or polarized goggles. Conventional optical plastic films are designed so that the direction of the slow axis does not shift within a narrow region, but the biaxially stretched optical plastic film that satisfies condition 4 is different in configuration from conventional optical films in that the direction of the slow axis is shifted within a narrow region. The narrow region refers to the size of the measurement sample (100 mm x 100 mm). It is also possible to use an optical biaxially stretched plastic film in which the strength of stretching is weakened and the direction of the slow axis is not fully aligned. By satisfying this condition 4, it becomes easier to satisfy conditions 1 and 2. Furthermore, by satisfying condition 4, it becomes easier to improve the bending resistance described later.

[0049] The difference between the maximum value of D1 to D5 and the minimum value of D1 to D5 is preferably 6.0 degrees or more, more preferably 8.0 degrees or more, and further preferably 10.0 degrees or more. If the difference between the maximum value of D1 to D5 and the minimum value of D1 to D5 is too large, the orientation of the optical biaxially stretched plastic film tends to be low, and the mechanical strength tends to decrease. Therefore, the difference is preferably 20.0 degrees or less, more preferably 17.0 degrees or less, and even more preferably 15.0 degrees or less.

[0050] In condition 4, preferred ranges for the difference between the maximum and minimum values ​​of D1 to D5 are, for example, 5.0 degrees or more and 20.0 degrees or less, 6.0 degrees or more and 20.0 degrees or less, 8.0 degrees or more and 20.0 degrees or less, 10.0 degrees or more and 20.0 degrees or less, 5.0 degrees or more and 17.0 degrees or less, 6.0 degrees or more and 17.0 degrees or less, 8.0 degrees or more and 17.0 degrees or less, 10.0 degrees or more and 17.0 degrees or less, 5.0 degrees or more and 15.0 degrees or less, 6.0 degrees or more and 15.0 degrees or less, 8.0 degrees or more and 15.0 degrees or less, and 10.0 degrees or more and 15.0 degrees or less.

[0051] In an optical biaxially stretched plastic film according to one embodiment of the present disclosure, D1 to D5 are 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 even more preferably 10 degrees or more and 23 degrees or less, or 67 degrees or more and 80 degrees or less. By setting D1 to D5 to 5 degrees or more or 85 degrees or less, respectively, it is possible to easily suppress blackout when viewed through polarized sunglasses or polarized goggles, etc. Furthermore, by setting D1 to D5 to 30 degrees or less or 60 degrees or more, respectively, it is possible to easily suppress a decrease in mechanical strength due to a decrease in the orientation of the optical biaxially stretched plastic film.

[0052] In the optical biaxially stretched plastic film according to an embodiment of the present disclosure, the in-plane retardation relative to the retardation in the thickness direction (in-plane retardation / retardation in the thickness direction) is preferably 0.10 or less. In this specification, the in-plane retardation relative to the retardation in the thickness direction may be expressed as "Re / Rth". Re / Rth can be measured, for example, as follows.

[0053] The in-plane retardation values ​​measured at five points on the sample are defined as Re1, Re2, Re3, Re4, and Re5, respectively, and the thickness direction retardation values ​​measured at five points on the sample are defined as Rth1, Rth2, Rth3, Rth4, and Rth5, respectively. In an optical biaxially stretched plastic film, the average of Re1 / Rth1, Re2 / Rth2, Re3 / Rth3, Re4 / Rth4 and Re5 / Rth5 is preferably 0.10 or less. A small ratio (Re / Rth) of the in-plane retardation to the thickness retardation means that the biaxial stretching of the biaxially stretched plastic film approaches uniform biaxiality. Therefore, by making Re / Rth 0.10 or less, the mechanical strength of the biaxially stretched plastic film can be improved. Re / Rth is more preferably 0.07 or less, and even more preferably 0.05 or less. The lower limit of Re / Rth is about 0.01. The Re / Rth of a completely uniaxially stretched plastic film is 2.0. General-purpose uniaxially stretched plastic films are also slightly stretched in the machine direction. For this reason, the Re / Rth of general-purpose uniaxially stretched plastic films is about 1.0.

[0054] Each of Re1 / Rth1, Re2 / Rth2, Re3 / Rth3, Re4 / Rth4 and Re5 / Rth5 is preferably 0.10 or less, more preferably 0.07 or less, and even more preferably 0.05 or less. The lower limit of these ratios is about 0.01.

[0055] The thickness direction retardation (Rth) is expressed by the following formula, where nx is the refractive index in the slow axis direction, which is the direction with the largest refractive index, ny is the refractive index in the fast axis direction, which is the direction perpendicular to the slow axis direction, nz is the refractive index in the thickness direction of the plastic film, and T [nm] is the thickness of the plastic film. Rth = ((nx + ny) / 2-nz) × T [nm]

[0056] The retardation (Rth) in the thickness direction of the optical biaxially stretched plastic film is preferably 2000 nm or more, more preferably 3000 nm or more, and even more preferably 4000 nm or more. The upper limit of Rth is about 10000 nm, preferably 8000 nm or less, more preferably 7000 nm or less. By setting Rth in the above range, it is possible to more easily suppress rainbow unevenness. Preferred ranges of Rth of optical biaxially stretched plastic films include 2000 nm or more and 10000 nm or less, 2000 nm or more and 8000 nm or less, 2000 nm or more and 7000 nm or less, 3000 nm or more and 10000 nm or less, 3000 nm or more and 8000 nm or less, 3000 nm or more and 7000 nm or less, 4000 nm or more and 10000 nm or less, 4000 nm or more and 8000 nm or less, and 4000 nm or more and 7000 nm or less. In order to set the Rth of the optical biaxially stretched plastic film within the above range, it is preferable to increase the stretch ratios in the longitudinal and transverse directions. By increasing the stretch ratios in the longitudinal and transverse directions, the refractive index nz in the thickness direction of the biaxially stretched plastic film decreases, making it easier to increase Rth.

[0057] <Details of folding test> Satisfying conditions 1 and 2 is also preferable in that the mechanical strength of the optical biaxially stretched plastic film, for example, the ease of tearing in the stretching direction can be improved and the bending resistance can be improved. On the other hand, plastic films that do not satisfy conditions 1 and 2 break after bending tests or have a strong bending tendency. Specifically, a uniaxially stretched film such as that in Patent Document 1 breaks when subjected to a bending test along the slow axis, and has a strong bending tendency when subjected to a bending test in a direction perpendicular to the slow axis. Moreover, a general-purpose biaxially stretched film has a strong bending tendency when subjected to a bending test in a direction perpendicular to the slow axis. On the other hand, the optical biaxially stretched plastic film of the present disclosure is preferable in that it can suppress the remaining bending habit or breakage after a bending test regardless of the bending direction. In order to make it easier to improve the bending resistance, it is preferable that the plastic film satisfies condition 4.

[0058] 6(A), in the continuous folding test, first, side portion 10C of optical biaxially stretched plastic film 10 and side portion 10D opposite side portion 10C are fixed by parallel-arranged fixing portions 60. Fixing portions 60 are slidable in the horizontal direction. Next, as shown in Figure 6 (B), the fixing portions 60 are moved closer to each other to deform the optical biaxially stretched plastic film 10 in a folding manner, and further, as shown in Figure 6 (C), the fixing portions 60 are moved to a position where the distance between the two opposing sides of the optical biaxially stretched plastic film 10 fixed by the fixing portions 60 is 2 mm, and then the fixing portions 60 are moved in the opposite direction to eliminate the deformation of the optical biaxially stretched plastic film 10. 6(A) to 6(C), the optical biaxially stretched plastic film 10 can be folded 180 degrees by moving the fixing part 60. In addition, by performing a continuous folding test so that the bent part 10E of the optical biaxially stretched plastic film 10 does not protrude from the lower end of the fixing part 60 and controlling the distance between the fixing parts 60 to 2 mm when they are closest to each other, the distance between the two opposing sides of the optical film 10 can be set to 2 mm.

[0059] It is preferable that the optical biaxially stretched plastic film does not crack or break after 100,000 times (more preferably after 300,000 times) of the folding test shown in the examples. In addition, when the measurement sample is placed on a horizontal table after 100,000 times (more preferably after 300,000 times), the angle at which the end of the sample rises from the table is preferably 20 degrees or less, more preferably 15 degrees or less. The angle at which the end of the sample rises from the table is 15 degrees or less means that the film is unlikely to develop a crease due to folding. In addition, it is preferable that the optical biaxially stretched plastic film shows the above-mentioned results (no cracks, breaks, or creases due to folding are not developed. The angle at which the end of the sample rises from the table after the test is 20 degrees or less) in both the average of the slow axis direction and the average of the fast axis direction of the optical biaxially stretched plastic film. When a uniaxially stretched plastic film is subjected to a folding test, it breaks in the stretching direction, and retains a strong bending tendency in the direction perpendicular to the stretching direction.

[0060] <Optical biaxially oriented plastic film> The laminate structure of the optical biaxially stretched plastic film may be a single-layer structure or a multi-layer structure, of which the single-layer structure is preferred. In order to suppress blackout and rainbow unevenness when viewed through polarized sunglasses or polarized goggles while improving mechanical strength, optical biaxially stretched plastic films are required to have a "brightness difference variation 3σ" of 100 or more and an Re of 2500 nm or less. In order to reduce the in-plane retardation of optical biaxially stretched plastic films, it is important to finely control the stretching, such as making the stretching in the longitudinal and transverse directions nearly uniform. Regarding fine control of stretching, fine control of stretching is difficult in a multilayer structure due to differences in the physical properties of each layer, but a single layer structure is preferable in that it is easy to perform fine control of stretching.

[0061] Examples of resin components constituting the optical biaxially stretched plastic film include polyester, polyamide, polyimide, polyethersulfone, polysulfone, polypropylene, polymethylpentene, polyvinyl chloride, polyvinyl acetal, polyether ketone, polymethyl methacrylate, polycarbonate, polyurethane, and amorphous olefin (Cyclo-Olefin-Polymer: COP). Among these, polyester is preferred because it is easy to improve the mechanical strength. In other words, the optical biaxially stretched plastic film is preferably a polyester film.

[0062] Examples of polyesters constituting the polyester film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), etc. Among these, PET is preferred because it is easy to achieve a "brightness difference variation 3σ" of 100 or more.

[0063] The optical biaxially stretched plastic film may contain additives such as ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, flame retardants, antigelling agents, and surfactants.

[0064] The lower limit of the thickness of the optical biaxially stretched plastic film is preferably 10 μm or more, more preferably 15 μm or more, more preferably 20 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. In order to reduce the thickness, the thickness of the optical biaxially stretched plastic film is preferably 50 μm or less. By setting the thickness to 10 μm or more, it is possible to easily improve the mechanical strength, and by setting the thickness to 200 μm or less, it is possible to easily satisfy condition 2.

[0065] Preferred ranges of the thickness of the biaxially stretched plastic film are, for example, 10 μm or more and 200 μm or less, 15 μm or more and 200 μm or less, 20 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, 20 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, 20 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, 20 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, 20 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, 20 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, 20 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.

[0066] For optical biaxially stretched plastic films, the haze according to JIS K7136:2000 is preferably 3.0% or less, more preferably 2.0% or less, even more preferably 1.5% or less, and even more preferably 1.0% or less. Furthermore, the total light transmittance of the optical biaxially stretched plastic film according to JIS K7361-1:1997 is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0067] The optical biaxially stretched plastic film is more preferably a biaxially stretched polyester film in order to improve mechanical strength, and more preferably has a single-layer structure of a polyester resin layer.

[0068] Biaxially stretched optical plastic films can be obtained by stretching a resin layer containing components constituting the plastic film. The stretching method includes biaxial stretching such as sequential biaxial stretching and simultaneous biaxial stretching. Among biaxially stretched optical plastic films, biaxially stretched polyester films are preferred, and biaxially stretched polyethylene terephthalate films are more preferred.

[0069] -Sequential biaxial stretching- In sequential biaxial stretching, the casting film is stretched in the machine direction, and then stretched in the width direction of the film. The stretching in the machine direction is usually performed by the difference in peripheral speed between a pair of stretching rolls. The stretching in the machine direction may be performed in one stage, or may be performed in multiple stages using a plurality of pairs of stretching rolls. In order to suppress excessive variation in optical properties such as in-plane retardation, it is preferable to place a plurality of nip rolls close to the stretching roll. The stretching ratio in the machine direction is usually 2 to 15 times, and in order to suppress excessive variation in optical properties such as in-plane retardation, it is preferably 2 to 7 times, more preferably 3 to 5 times, and even more preferably 3 to 4 times. In order to suppress excessive variation in optical properties such as in-plane retardation, the stretching temperature is preferably from the glass transition temperature of the resin to the glass transition temperature + 100° C. In the case of PET, the temperature is preferably from 70° C. to 120° C., more preferably from 80° C. to 110° C., and even more preferably from 95° C. to 110° C. Regarding the stretching temperature, the average in-plane retardation tends to be small by shortening the stretching section at low temperature by heating the film quickly, whereas the average in-plane retardation tends to be large and the variation of the slow axis tends to be small by lengthening the stretching section at low temperature by heating the film slowly. In addition, when heating during stretching, it is preferable to use a heater that generates turbulent airflow. By heating with airflow containing turbulent airflow, temperature differences occur in minute regions within the film plane, and the temperature differences cause minute deviations in the orientation axis, making it easier to satisfy conditions 1 and 4.

[0070] The film stretched in the machine direction may be provided with functions such as easy slippage, easy adhesion, antistatic properties, etc., by in-line coating. Furthermore, before in-line coating, surface treatment such as corona treatment, flame treatment, plasma treatment, etc. may be performed as necessary. The coating film formed in this way by in-line coating is very thin, having a thickness of about 10 nm to 2000 nm (and the coating film is stretched even thinner by stretching treatment). In this specification, such a thin layer is not counted as the number of layers constituting the optical biaxially stretched plastic film.

[0071] The stretching in the width direction is usually performed by conveying the film while holding both ends with clips using a tenter method, and stretching the film in the width direction. The stretching ratio in the width direction is usually 2 to 15 times, and in order to suppress excessive variation in optical properties such as in-plane retardation, it is preferably 2 to 5 times, more preferably 3 to 5 times, and even more preferably 3 to 4.5 times. In addition, it is preferable to make the width stretching ratio higher than the longitudinal stretching ratio. The stretching temperature is preferably from the glass transition temperature of the resin to the glass transition temperature + 120°C, and the temperature preferably increases from the upstream to the downstream. Specifically, when the transverse stretching section is divided into two, the difference between the upstream and downstream temperatures is preferably 20°C or more, more preferably 30°C or more, even more preferably 35°C or more, and even more preferably 40°C or more. In the case of PET, the first-stage stretching temperature is preferably 80°C to 120°C, more preferably 90°C to 110°C, and even more preferably 95°C to 105°C.

[0072] The plastic film sequentially biaxially stretched as described above is preferably heat-treated in a tenter at a temperature equal to or higher than the stretching temperature and lower than the melting point in order to impart flatness and dimensional stability. Specifically, in the case of PET, heat setting is preferably performed in the range of 150°C to 255°C, more preferably 200°C to 250°C. In addition, in order to suppress excessive variation in optical properties such as in-plane retardation, it is preferable to perform additional stretching of 1% to 10% in the first half of the heat treatment. After the plastic film is heat-treated, it is slowly cooled to room temperature and then wound up. If necessary, a relaxation treatment or the like may be used in combination with the heat treatment and the slow cooling. The relaxation rate during the heat treatment is preferably 0.5% to 5%, more preferably 0.5% to 3%, even more preferably 0.8% to 2.5%, and even more preferably 1% to 2% in order to suppress excessive variation in optical properties such as in-plane retardation. The relaxation rate during the slow cooling is preferably 0.5% to 3%, more preferably 0.5% to 2%, even more preferably 0.5% to 1.5%, and even more preferably 0.5% to 1.0% in order to suppress excessive variation in optical properties such as in-plane retardation. In order to obtain good flatness, the temperature during slow cooling is preferably 80° C. or higher and 150° C. or lower, more preferably 90° C. or higher and 130° C. or lower, even more preferably 100° C. or higher and 130° C. or lower, and even more preferably 100° C. or higher and 120° C. or lower.

[0073] -Simultaneous biaxial stretching- In the simultaneous biaxial stretching, the casting film is introduced into a simultaneous biaxial tenter, and the film is conveyed while both ends are held by clips, and stretched simultaneously and / or stepwise in the machine direction and width direction. The simultaneous biaxial stretching machine may be of the pantograph type, screw type, drive motor type, or linear motor type, but the drive motor type or linear motor type is preferred because it can change the stretch ratio at any time and can perform relaxation treatment at any location.

[0074] The area ratio of the simultaneous biaxial stretching is usually 6 to 50 times. In order to suppress excessive variation in optical properties such as in-plane retardation, the area ratio is preferably 8 to 30 times, more preferably 9 to 25 times, even more preferably 9 to 20 times, and still more preferably 10 to 15 times. In the simultaneous biaxial stretching, the stretch ratio in the machine direction and the stretch ratio in the width direction are preferably adjusted to the above area ratio within the range of 2 to 15 times. In the case of simultaneous biaxial stretching, in order to suppress in-plane orientation differences, it is preferable that the stretching ratios in the machine direction and the width direction are approximately the same, and that the stretching speeds in the machine direction and the width direction are also approximately the same.

[0075] In order to suppress excessive variation in optical properties such as in-plane retardation, the stretching temperature in the simultaneous biaxial stretching is preferably from the glass transition temperature of the resin to the glass transition temperature + 120° C. In the case of PET, the stretching temperature is preferably from 80° C. to 160° C., more preferably from 90° C. to 150° C., and even more preferably from 100° C. to 140° C.

[0076] The simultaneously biaxially stretched film is preferably subsequently subjected to a heat treatment at a temperature equal to or higher than the stretching temperature and lower than the melting point in a heat fixing chamber in a tenter in order to impart flatness and dimensional stability. The heat treatment conditions are the same as those after the successive biaxial stretching.

[0077] <Shape, size> The optical biaxially stretched plastic film may be in the form of a sheet cut to a predetermined size, or in the form of a roll obtained by winding a long sheet into a roll. The size of the sheet is not particularly limited, but the maximum diameter is about 2 inches to 500 inches, and in the present disclosure, 30 inches to 80 inches is preferable. The "maximum diameter" refers to the maximum length when any two points on the optical film are connected. For example, when the optical film is rectangular, the diagonal line of the rectangular area is the maximum diameter. When the optical film is circular, the diameter is the maximum diameter. The width and length of the roll are not particularly limited, but generally, the width is about 500 mm to 3000 mm, and the length is about 100 m to 5000 m. The optical film in the form of a roll can be cut into sheets according to the size of an image display device or the like. When cutting, it is preferable to remove the ends of the roll, which have unstable physical properties. The shape of the sheet is not particularly limited, and may be, for example, a polygon (triangle, square, pentagon, etc.), a circle, or a random, indefinite shape. More specifically, when the optical film is a square, the aspect ratio is not particularly limited as long as it does not cause any problems as a display screen. For example, the aspect ratio may be 1:1, 4:3, 16:10, 16:9, 2:1, etc.

[0078] [Functional film] The optical biaxially stretched plastic film of the present disclosure may be further formed with functional layers such as a hard coat layer, a low refractive index layer, a high refractive index layer, an antiglare layer, an antifouling layer, an antistatic layer, a gas barrier layer, an antifogging layer, and a transparent conductive layer to form a functional film. That is, the functional film of the present disclosure has a functional layer on the above-mentioned optical biaxially stretched plastic film of the present disclosure. The functional layer may be provided on at least one side of the optical biaxially stretched plastic film, or may be provided on both sides.

[0079] The total thickness of the functional film is preferably 100 μm or less, more preferably 60 μm or less, in order to maintain mechanical properties, suppress excessive variations in optical properties such as in-plane retardation, and effectively suppress blackout. In the functional film, the balance between the thickness of the biaxially stretched plastic film and the thickness of the functional layer is preferably 10:4 to 10:0.5.

[0080] The functional film may be formed by using an optical biaxially stretched plastic film as a substrate that satisfies conditions 1 and 2, but preferably satisfies the following condition 1A. A preferred embodiment of condition 1A is the same as the preferred embodiment of condition 1 described above. Measurements 1A and 2A are the same as measurements 1 and 2 of the optical biaxially stretched plastic film of the present disclosure described above, except that the biaxially stretched plastic film is replaced with a functional film.

[0081] <Condition 1A> The luminance difference (L1.n-L2.n) between the luminance obtained in Measurement 1A below and the luminance obtained in Measurement 2A below is calculated at 100 measurement points, and the "luminance difference variation 3σ" calculated from the luminance differences of the 100 measurement points is 100 or more. Measurement 1A A first A measurement sample is prepared by arranging a first polarizer, a functional film, and a second polarizer in this order on a surface light source. In the first measurement sample, the functional film is arranged so that the slow axis direction of a biaxially stretched optical plastic film constituting the functional film is approximately perpendicular to the absorption axis direction of the first polarizer, and the absorption axis of the second polarizer is approximately perpendicular to the absorption axis direction of the first polarizer. The surface light source of the 1A measurement sample is displayed as white, and the luminance of the transmitted light exiting from the second polarizer side is measured at 100 x 100 measurement points set at equal intervals in any first region. 100 points are extracted from the measurement results in an arbitrary horizontal row, and are numbered from the 1st measurement point to the 100th measurement point in order, with the luminance of the 1st measurement point defined as L1.1, the luminance of the 100th measurement point defined as L1.100, and the luminance of the nth measurement point defined as L1.n. 《Measurement 2A》 A measurement sample 2A is prepared by arranging the first polarizer and the second polarizer in this order on the same surface light source as in measurement 1A. In the measurement sample 2A, the absorption axis of the second polarizer is arranged approximately perpendicular to the absorption axis direction of the first polarizer. The surface light source of the 2A measurement sample is displayed as white, and the luminance of the transmitted light exiting from the second polarizer side is measured at 100×100 measurement points set at equal intervals in an area that approximately coincides with the first measurement area. 100 points are arbitrarily extracted in a horizontal row from the measurement results, and are sequentially designated as the 1st measurement point to the 100th measurement point, with the luminance of the 1st measurement point defined as L2.1, the luminance of the 100th measurement point defined as L2.100, and the luminance of the nth measurement point defined as L2.n.

[0082] <Functional layer> Examples of the functional layer include a hard coat layer, a low refractive index layer, a high refractive index layer, an antiglare layer, an antifouling layer, an antistatic layer, a gas barrier layer, an antifogging layer, and a transparent conductive layer. The functional layer may be one selected from the above-mentioned layers, or may be a laminate of two or more layers. These functional layers are preferably optically isotropic. Optically isotropic refers to an in-plane retardation of less than 20 nm, preferably 10 nm or less, more preferably 5 nm or less. The functional layer may also be a combination of two or more of the above-mentioned functions. That is, in this specification, the term "hard coat layer", "low refractive index layer", "high refractive index layer", "antiglare layer", "antifouling layer", "antistatic layer", "gas barrier layer", "anti-fogging layer" and "transparent conductive layer" refers not only to a functional layer having a single function, but also to a functional layer having a composite function. For example, the hard coat layer includes an antifouling hard coat layer, an antiglare hard coat layer and a high refractive index hard coat layer. The antifouling layer includes an antiglare antifouling layer and a low refractive index antifouling layer.

[0083] Specific examples of functional layers include the following (1) to (9). In the following (1) to (9), the left side indicates the layer located on the optical biaxially stretched plastic film side. In the following (1) to (9), the anti-stain layer, hard coat layer, high refractive index layer, low refractive index layer and anti-glare layer may be composite functional layers having other functions. For example, the low refractive index layers (1), (2) and (7) to (9) preferably have an anti-stain layer. In addition, the anti-glare layer (3) and the anti-stain layer (5) preferably have hard coat properties. (1) A configuration having a low refractive index layer on a hard coat layer. (2) A configuration having a high refractive index layer and a low refractive index layer on a hard coat layer. (3) The antiglare layer is a single layer. (4) A configuration in which an antiglare layer is provided on a hard coat layer. (5) The antifouling layer is a single layer. (6) A configuration in which an antifouling layer is provided on the hard coat layer. (7) A configuration in which a low refractive index layer is provided on an antiglare layer. (8) A configuration having a low refractive index layer on a high refractive index hard coat layer. (9) A configuration in which an antiglare layer and a low refractive index layer are provided on a hard coat layer.

[0084] Representative examples of the functional layer, namely, a hard coat layer, a low refractive index layer, a high refractive index layer, an antiglare layer, and an antifouling layer, will be specifically described below.

[0085] <Hard coat layer> The hard coat layer, which is an example of a functional layer, preferably contains a cured product of a curable resin composition such as a thermosetting resin composition or an ionizing radiation curable resin composition, and more preferably contains a cured product of an ionizing radiation curable resin composition, in order to improve scratch resistance.

[0086] The thermosetting resin composition is a composition that contains at least a thermosetting resin, and is a resin composition that is cured by heating. Examples of the thermosetting resin include acrylic resin, urethane resin, phenol resin, urea melamine resin, epoxy resin, unsaturated polyester resin, silicone resin, etc. In the thermosetting resin composition, a curing agent is added to the curable resin as necessary.

[0087] 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"). Examples of the ionizing radiation curable functional group include ethylenically unsaturated bond groups such as (meth)acryloyl group, vinyl group, and allyl group, as well as epoxy group and oxetanyl group. As the ionizing radiation curable compound, a compound having an ethylenically unsaturated bond group is preferred, a compound having two or more ethylenically unsaturated bond groups is more preferred, and among them, a (meth)acrylate-based compound having two or more ethylenically unsaturated bond groups is even more preferred. As the (meth)acrylate-based compound having two or more ethylenically unsaturated bond groups, either a monomer or an oligomer can be used. Here, ionizing radiation refers to electromagnetic waves or charged particle beams that have an energy quantum capable of polymerizing or crosslinking molecules. Usually, ultraviolet rays (UV) or electron beams (EB) are used, but other types of radiation, such as electromagnetic waves such as X-rays and gamma rays, and charged particle beams such as alpha rays and ion beams, can also be used. In this specification, (meth)acrylate means acrylate or methacrylate, (meth)acrylic acid means acrylic acid or methacrylic acid, and (meth)acryloyl group means acryloyl group or methacryloyl group.

[0088] The thickness of the hard coat layer is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1.0 μm or more, and even more preferably 2.0 μm or more in order to improve scratch resistance. Also, 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 even more preferably 10 μm or less in order to suppress curling. The thickness of the hard coat layer is preferably 10 μm or less, more preferably 8 μm or less in order to improve bending resistance.

[0089] <Low refractive index layer> The low refractive index layer has the role of enhancing the anti-reflection properties of the optical film and also of making it easier to suppress rainbow unevenness when viewed with the naked eye. Here, the rainbow unevenness is a rainbow-like interference pattern observed due to the disturbance of the polarization state of linearly polarized light when the linearly polarized light passes through a polarizer and then passes through a birefringent body such as a stretched plastic film. Light traveling from inside the image display device toward the viewer is linearly polarized light when it passes through a polarizer, but after passing through an optical biaxially stretched plastic film, the polarization state of the linearly polarized light is disturbed, and the light becomes a mixture of P waves and S waves. Since there is a difference between the reflectance of P waves and the reflectance of S waves, and the reflectance difference is wavelength dependent, it is believed that rainbow unevenness is visible to the naked eye. Here, when a low refractive index layer is provided on the optical biaxially stretched plastic film, the reflectance difference can be reduced, and therefore it is believed that rainbow unevenness can be easily suppressed. The low refractive index layer is preferably formed on the side farthest from the optical biaxially stretched plastic film. By forming a high refractive index layer, which will be described later, adjacent to the low refractive index layer on the optical biaxially stretched plastic film side of the low refractive index layer, the antireflection properties can be further improved and rainbow unevenness can be more easily suppressed.

[0090] The refractive index of the low refractive index layer is preferably from 1.10 to 1.48, more preferably from 1.20 to 1.45, more preferably from 1.26 to 1.40, more preferably from 1.28 to 1.38, and more preferably from 1.30 to 1.32. The thickness of the low refractive index layer is preferably 80 nm to 120 nm, more preferably 85 nm to 110 nm, and even more preferably 90 nm to 105 nm. The thickness of the low refractive index layer is preferably larger than the average particle size of the low refractive index particles such as hollow particles.

[0091] The method of forming a low refractive index layer can be roughly divided into a wet method and a dry method. The wet method includes a method of forming by a sol-gel method using metal alkoxide or the like, a method of forming by coating a resin with a low refractive index such as a fluororesin, and a method of forming by coating a coating liquid for forming a low refractive index layer in which low refractive index particles are contained in a resin composition. The dry method includes a method of selecting particles having a desired refractive index from the low refractive index particles described later and forming by a physical vapor deposition method or a chemical vapor deposition method. The wet method is superior to the dry method in terms of production efficiency, suppression of oblique reflection hue, and chemical resistance. Among the wet methods, it is preferable to form the low refractive index layer using a coating liquid for forming the low refractive index layer in which low refractive index particles are contained in a binder resin composition in order to improve adhesion, water resistance, scratch resistance, and reduce the refractive index.

[0092] The low refractive index layer is often located on the outermost surface of the optical film, and therefore is required to have good scratch resistance, and general-purpose low refractive index layers are also designed to have a certain level of scratch resistance. In recent years, hollow particles with large particle diameters have been used as low-refractive index particles to reduce the refractive index of the low-refractive index layer. The present inventors have found a problem that even if the surface of a low-refractive index layer containing hollow particles with large particle diameters is rubbed with an object with only fine solid matter (e.g., sand) or only oil, and no scratches are visible, the surface is scratched when rubbed with an object with both solid matter and oil (hereinafter, this problem may be referred to as "oil dust resistance"). The action of rubbing with an object with solid matter and oil corresponds to, for example, the action of a user operating a touch panel type image display device with a finger with oil contained in cosmetics and food, etc., and sand contained in the air. Improving the oil dust resistance of the low refractive index layer is preferable because it leads to maintaining the effect of suppressing iridescent unevenness for a long period of time.

[0093] As a result of the study by the present inventors, it was found that the above-mentioned scratches are mainly caused by a part of the hollow particles contained in the low refractive index layer being chipped or the hollow particles falling off. It was thought that the cause of this was the large unevenness caused by the hollow particles formed on the surface of the low refractive index layer. That is, when the surface of the low refractive index layer is rubbed with a finger having solid matter and oil on it, the oil becomes a binder and the finger moves on the surface of the low refractive index layer with the solid matter still attached to the finger. At this time, the phenomenon that a part of the solid matter (for example, a sharp point of sand) enters the recessed part of the low refractive index layer surface, and the phenomenon that the solid matter that entered the recessed part passes through the recessed part together with the finger and overcomes the protruding part (hollow particle) is likely to occur, and at that time, a large force is applied to the protruding part (hollow particle), so it was thought that the hollow particle is damaged or falls off. In addition, it was thought that the resin itself located in the recessed part is also scratched by friction caused by the solid matter, and the hollow particle becomes more likely to fall off due to the damage of the resin.

[0094] In order to obtain good oil dust resistance, the low refractive index particles preferably include hollow particles and non-hollow particles. In order to improve the oil dust resistance, it is preferable to use a combination of hollow particles and non-hollow particles as the low refractive index particles, and to uniformly disperse the hollow particles and non-hollow particles. The material of the hollow particles and non-hollow particles may be either an inorganic compound such as silica or magnesium fluoride, or an organic compound, but silica is preferred for its low refractive index and strength. The following description will be centered on hollow silica particles and non-hollow silica particles.

[0095] Hollow silica particles refer to particles that have an outer shell layer made of silica, the inside of the particle surrounded by the outer shell layer is hollow, and the inside of the cavity contains air. Hollow silica particles are particles that contain air, and the refractive index is reduced in proportion to the occupancy rate of gas compared to the refractive index of silica itself. Non-hollow silica particles are particles that are not hollow like hollow silica particles. Non-hollow silica particles are, for example, solid silica particles. The shape of the hollow silica particles and non-hollow silica particles is not particularly limited, and may be a perfect sphere, a spheroid, or a nearly spherical shape such as a polyhedron that can approximate a sphere, etc. Among these, in consideration of scratch resistance, a perfect sphere, a spheroid, or a nearly spherical shape is preferable.

[0096] Since hollow silica particles contain air inside, they play a role in lowering the refractive index of the entire low refractive index layer. By using hollow silica particles with a large particle size and a high ratio of air, the refractive index of the low refractive index layer can be further lowered. On the other hand, hollow silica particles tend to have poor mechanical strength. In particular, when hollow silica particles with a large particle size and a high ratio of air are used, the scratch resistance of the low refractive index layer tends to be easily reduced. The non-hollow silica particles, when dispersed in the binder resin, play a role in improving the scratch resistance of the low refractive index layer.

[0097] In order to make hollow silica particles and non-hollow silica particles contained in binder resin at high concentration and to disperse the particles uniformly in the thickness direction in the resin, it is preferable to set the average particle size of hollow silica particles and the average particle size of non-hollow silica particles so that the hollow silica particles are close to each other and the non-hollow particles can be inserted between the hollow silica particles.Specifically, the ratio of the average particle size of non-hollow silica particles to the average particle size of hollow silica particles (average particle size of non-hollow silica particles / average particle size of hollow silica particles) is preferably 0.29 or less, more preferably 0.20 or less.In addition, it is preferable that the ratio of the average particle sizes is 0.05 or more. Considering optical properties and mechanical strength, the average particle size of the hollow silica particles is preferably 20 nm or more and 100 nm or less. Since it is easy to lower the refractive index of the entire low refractive index layer, the average particle size of the hollow silica particles is more preferably 50 nm or more and 100 nm or less, and further preferably 60 nm or more and 80 nm or less. In addition, in consideration of dispersibility while preventing aggregation of the non-hollow silica particles, the average particle size of the non-hollow silica particles is preferably 5 nm or more and 20 nm or less, and more preferably 10 nm or more and 15 nm or less.

[0098] The surfaces of the hollow silica particles and non-hollow silica particles are preferably coated with a silane coupling agent, and it is more preferable to use a silane coupling agent having a (meth)acryloyl group or an epoxy group. By subjecting the silica particles to a surface treatment with a silane coupling agent, the affinity between the silica particles and the binder resin is improved, and the silica particles are less likely to aggregate, which makes it easier for the silica particles to be dispersed uniformly.

[0099] Examples of silane coupling agents include 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-di methyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, tris-(trimethoxysilylpropyl)isocyanurate, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, 1,6-bis(trimethoxysilyl)hexane, trifluoropropyltrimethoxysilane, vinyltrimethoxysilane and vinyltriethoxysilane. In particular, it is preferable to use one or more selected from 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, and 3-methacryloxypropyltriethoxysilane.

[0100] The higher the content of hollow silica particles, the higher the filling rate of hollow silica particles in the binder resin, and the lower the refractive index of the low refractive index layer. Therefore, the content of hollow silica particles is preferably 100 parts by mass or more, more preferably 150 parts by mass or more, per 100 parts by mass of the binder resin. On the other hand, if the content of hollow silica particles relative to the binder resin is too high, the hollow silica particles exposed from the binder resin will increase, and the binder resin that bonds between the particles will decrease. Therefore, the hollow silica particles tend to be easily damaged or fall off, and the mechanical strength of the low refractive index layer, such as scratch resistance, tends to decrease. In addition, if the content of hollow silica particles is too high, the transferability tends to be impaired. Therefore, the content of hollow silica particles is preferably 400 parts by mass or less, more preferably 300 parts by mass or less, relative to 100 parts by mass of the binder resin.

[0101] When the content of non-hollow silica particles is small, even if non-hollow silica particles are present on the surface of the low refractive index layer, it may not affect the hardness increase.In addition, when non-hollow silica particles are contained in a large amount, the effect of shrinkage unevenness caused by polymerization of binder resin can be reduced, and the unevenness generated on the surface of the low refractive index layer after resin hardening can be reduced.For this reason, the content of non-hollow silica particles is preferably 90 parts by mass or more, more preferably 100 parts by mass or more, relative to 100 parts by mass of binder resin. On the other hand, if the content of non-hollow silica particles is too high, non-hollow silica is easily aggregated, causing uneven shrinkage of binder resin, and the surface unevenness becomes large.In addition, if the content of non-hollow silica particles is too high, transferability tends to be impaired.Therefore, the content of non-hollow silica particles is preferably 200 parts by mass or less, more preferably 150 parts by mass or less, relative to 100 parts by mass of binder resin.

[0102] By incorporating hollow silica particles and non-hollow silica particles in the binder resin in the above ratio, the barrier properties of the low refractive index layer can be improved, which is presumably because the silica particles are uniformly dispersed at a high filling rate, thereby inhibiting the permeation of gases and the like. In addition, various cosmetics such as sunscreens and hand creams may contain low-volatility low-molecular-weight polymers. By improving the barrier properties of the low-refractive index layer, it is possible to prevent the low-molecular-weight polymer from penetrating into the coating film of the low-refractive index layer, and to prevent problems (e.g., abnormal appearance) caused by the low-molecular-weight polymer remaining in the coating film for a long period of time.

[0103] The binder resin of the low refractive index layer preferably contains a cured product of an ionizing radiation curable resin composition. The ionizing radiation curable compound contained in the ionizing radiation curable resin composition is preferably a compound having an ethylenically unsaturated bond group. Among them, a (meth)acrylate-based compound having a (meth)acryloyl group is more preferable. Hereinafter, a (meth)acrylate compound having four or more ethylenically unsaturated bond groups will be referred to as a "polyfunctional (meth)acrylate compound." Also, a (meth)acrylate compound having two or more and three or less ethylenically unsaturated bond groups will be referred to as a "low-functional (meth)acrylate compound."

[0104] As the (meth)acrylate-based compound, either a monomer or an oligomer can be used. In particular, in order to suppress uneven shrinkage during curing and to easily smooth the uneven shape of the low refractive index layer surface, it is more preferable that the ionizing radiation curable compound contains a low-functional (meth)acrylate-based compound. The proportion of the low-functional (meth)acrylate compound in the ionizing radiation curable compound is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and most preferably 100% by mass. In addition, in order to suppress the uneven shrinkage during curing described above and to facilitate smoothing of the uneven shape of the surface of the low refractive index layer, the low-functional (meth)acrylate compound is preferably a (meth)acrylate compound having two ethylenically unsaturated bond groups.

[0105] Among the (meth)acrylate compounds, examples of bifunctional (meth)acrylate compounds include isocyanuric acid di(meth)acrylate, polyalkylene glycol di(meth)acrylates such as ethylene glycol di(meth)acrylate, polyethylene glycol diacrylate, and polybutylene glycol di(meth)acrylate, bisphenol A tetraethoxydiacrylate, bisphenol A tetrapropoxydiacrylate, and 1,6-hexanediol diacrylate. Examples of trifunctional (meth)acrylate compounds include trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and isocyanuric acid modified tri(meth)acrylate. Examples of polyfunctional (meth)acrylate compounds having 4 or more functional groups include pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and dipentaerythritol tetra(meth)acrylate. These (meth)acrylate compounds may be modified as described below.

[0106] Examples of the (meth)acrylate oligomer include acrylate polymers such as urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, and polyether (meth)acrylate. The urethane (meth)acrylate can be obtained, for example, by reacting a polyhydric alcohol and an organic diisocyanate with a hydroxy (meth)acrylate. In addition, preferred epoxy (meth)acrylates are (meth)acrylates obtained by reacting a tri- or higher functional aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, or the like with (meth)acrylic acid, (meth)acrylates obtained by reacting a di- or higher functional aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, or the like with a polybasic acid and (meth)acrylic acid, and (meth)acrylates obtained by reacting a di- or higher functional aromatic epoxy resin, alicyclic epoxy resin, aliphatic epoxy resin, or the like with a phenol and (meth)acrylic acid.

[0107] In addition, the (meth)acrylate-based compound may have a part of its molecular skeleton modified in order to suppress uneven shrinkage caused by crosslinking and improve surface smoothness. For example, the (meth)acrylate-based compound may be modified with ethylene oxide, propylene oxide, caprolactone, isocyanuric acid, alkyl, cyclic alkyl, aromatic, bisphenol, or the like. In particular, in order to increase affinity with low refractive index particles (silica particles therein) and suppress aggregation of low refractive index particles, the (meth)acrylate-based compound is preferably modified with alkylene oxide such as ethylene oxide or propylene oxide. The proportion of the alkylene oxide-modified (meth)acrylate compound in the ionizing radiation curable compound is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and most preferably 100% by mass. The alkylene oxide-modified (meth)acrylate compound is preferably a low-functional (meth)acrylate compound, and more preferably a (meth)acrylate compound having two ethylenically unsaturated bond groups.

[0108] Examples of the (meth)acrylate-based compound having two ethylenically unsaturated bond groups modified with alkylene oxide include bisphenol F alkylene oxide modified di(meth)acrylate, bisphenol A alkylene oxide modified di(meth)acrylate, isocyanuric acid alkylene oxide modified di(meth)acrylate, and polyalkylene glycol di(meth)acrylate, among which polyalkylene glycol di(meth)acrylate is preferred. The average repeat unit of the alkylene glycol contained in the polyalkylene glycol di(meth)acrylate is preferably 3 or more and 5 or less. In addition, the alkylene glycol contained in the polyalkylene glycol di(meth)acrylate is preferably ethylene glycol and / or polyethylene glycol. Examples of the (meth)acrylate compound having three ethylenically unsaturated bond groups modified with an alkylene oxide include trimethylolpropane alkylene oxide modified tri(meth)acrylate and isocyanuric acid alkylene oxide modified tri(meth)acrylate. The above ionizing radiation curable resins may be used alone or in combination of two or more.

[0109] The low refractive index layer preferably contains a leveling agent for antifouling properties and surface smoothness. The leveling agent may be fluorine-based or silicone-based, but silicone-based is preferred. By including a silicone-based leveling agent, the surface of the low reflectance layer can be made smoother. Furthermore, the slipperiness and antifouling properties (fingerprint wiping ability, large contact angle with pure water and hexadecane) of the surface of the low reflectance layer can be improved.

[0110] The content of the leveling agent is preferably 1 part by mass or more and 25 parts by mass or less, more preferably 2 parts by mass or more and 20 parts by mass or less, and even more preferably 5 parts by mass or more and 18 parts by mass or less, relative to 100 parts by mass of the binder resin. By making the content of the leveling agent 1 part by mass or more, it is possible to easily impart various properties such as antifouling properties. In addition, by making the content of the leveling agent 25 parts by mass or less, it is possible to suppress the deterioration of scratch resistance.

[0111] The low refractive index layer has a maximum height roughness Rz of preferably 110 nm or less, more preferably 90 nm or less, even more preferably 70 nm or less, and even more preferably 60 nm or less. In addition, Rz / Ra (Ra is arithmetic mean roughness) is preferably 12.0 or less, more preferably 10.0 or less. Setting Rz / Ra in the above range is particularly effective when Rz is large, about 90 nm or more and 110 nm or less. In this specification, Ra and Rz are the three-dimensional extension of the two-dimensional roughness parameters described in the Shimadzu Corporation Scanning Probe Microscope SPM-9600 Upgrade Kit Instruction Manual (SPM-9600 February 2016, pp. 194-195). Ra and Rz are defined as follows:

[0112] (Arithmetic mean roughness Ra) When only a reference length (L) is cut out from the roughness curve in the direction of the average line, the X-axis is taken in the direction of the average line of this cut-out portion and the Y-axis is taken in the direction of the longitudinal magnification, and the roughness curve is expressed as y = f(x), the following formula can be used.

[0113]

number

[0114] (Maximum height roughness Rz) A reference length is cut out from the roughness curve in the direction of the average line, and the distance between the peak line and the valley line of this cut out portion is measured in the longitudinal direction of the roughness curve.

[0115] When using a scanning probe microscope SPM-9600 manufactured by SHIMADZU CORPORATION, it is preferable to measure and analyze Ra and Rz under the following conditions, for example. <Measurement conditions> Measurement mode: Phase Scanning range: 5μm×5μm Scanning speed: 0.8Hz to 1Hz Number of pixels: 512 x 512 Cantilever used: NanoWorld Holding AG, product number "NCHR", resonance frequency: 320 kHz, spring constant: 42 N / m <Analysis conditions> Deskew: Line Fit

[0116] Small Rz means that the convex part caused by hollow silica particles in the micro domain is small. Small Rz / Ra means that the irregularities caused by silica particles in the micro domain are uniform, and do not have protruding irregularities with respect to the average elevation difference of the irregularities. In this disclosure, the value of Ra is not particularly limited, but Ra is preferably 15 nm or less, more preferably 12 nm or less, even more preferably 10 nm or less, and even more preferably 6.5 nm or less. By uniformly dispersing the low refractive index particles in the low refractive index layer and by suppressing uneven shrinkage of the low refractive index layer, it becomes easier to satisfy the above ranges of Rz and Rz / Ra.

[0117] By having the Rz and Rz / Ra of the low refractive index layer surface within the above range, the resistance when a solid object overcomes the convex portion (caused by hollow silica particles present near the surface) of the low refractive index layer surface can be reduced. Therefore, even if the solid object is rubbed with oily sand under a load, it is considered that the solid object moves smoothly on the low refractive index layer surface. It is also considered that the hardness of the concave portion itself is increased. As a result, it can be presumed that the breakage or falling off of the hollow silica particles is prevented, and the damage to the binder resin itself is also prevented.

[0118] Surface roughness such as Rz and Ra means the average value of measurements taken at 14 points excluding the minimum and maximum values ​​of the measurements taken at 16 points, unless otherwise specified. In this specification, the 16 measurement points are preferably centered on 16 intersections of lines drawn to divide the area inside the 0.5 cm margin from the outer edge of the measurement sample into 5 equal parts vertically and horizontally. It is preferable to use the same measurement sample as the sample in Condition 1. The surface roughness shall be measured at a temperature of 23°C ± 5°C and a relative humidity of 40% RH to 65% RH. Before each measurement, the sample shall be exposed to the above atmosphere for 30 minutes or more before measurement and evaluation.

[0119] The low refractive index layer can be formed by applying and drying a coating liquid for forming a low refractive index layer, in which each component constituting the low refractive index layer is dissolved or dispersed. Usually, a solvent is used in the coating liquid for forming a low refractive index layer to adjust the viscosity or to make each component soluble or dispersible. Examples of the solvent include ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.), ethers (dioxane, tetrahydrofuran, etc.), aliphatic hydrocarbons (hexane, etc.), alicyclic hydrocarbons (cyclohexane, etc.), aromatic hydrocarbons (toluene, xylene, etc.), halogenated carbons (dichloromethane, dichloroethane, etc.), esters (methyl acetate, ethyl acetate, butyl acetate, etc.), alcohols (butanol, cyclohexanol, etc.), cellosolves (methyl cellosolve, ethyl cellosolve, etc.), cellosolve acetates, sulfoxides (dimethyl sulfoxide, etc.), glycol ethers (1-methoxy-2-propyl acetate, etc.), amides (dimethylformamide, dimethylacetamide, etc.), and mixtures of these may also be used.

[0120] If the solvent evaporates too quickly, the solvent will convect violently when the coating liquid for forming a low refractive index layer is dried. Therefore, even if the silica particles in the coating liquid are in a uniformly dispersed state, the state of uniform dispersion is likely to be destroyed by the violent convection of the solvent during drying. For this reason, it is preferable that the solvent contains one with a slow evaporation rate. Specifically, it is preferable to contain a solvent with a relative evaporation rate (relative evaporation rate when the evaporation rate of n-butyl acetate is set to 100) of 70 or less, and more preferably a solvent with a relative evaporation rate of 30 to 60. In addition, the solvent with a relative evaporation rate of 70 or less is preferably 10% by mass to 50% by mass, and more preferably 20% by mass to 40% by mass of the total solvent. Examples of relative evaporation rates for slow evaporating solvents are isobutyl alcohol 64, 1-butanol 47, 1-methoxy-2-propyl acetate 44, ethyl cellosolve 38, and cyclohexanone 32. The remaining solvent (solvent other than the solvent having a slow evaporation rate) is preferably one having excellent resin solubility. The remaining solvent is preferably one having a relative evaporation rate of 100 or more.

[0121] In order to suppress the convection of the solvent during drying and to improve the dispersibility of the silica particles, it is preferable that the drying temperature during the formation of the low refractive index layer is as low as possible. The drying temperature can be appropriately set in consideration of the type of solvent, the dispersibility of the silica particles, the production speed, etc.

[0122] <High refractive index layer> The high refractive index layer, which is an example of a functional layer, preferably has a refractive index of 1.53 to 1.85, more preferably 1.54 to 1.80, more preferably 1.55 to 1.75, and even more preferably 1.56 to 1.70. The thickness of the high refractive index layer is preferably 200 nm or less, more preferably 50 nm or more and 180 nm or less, and even more preferably 70 nm or more and 150 nm or less. When a high refractive index hard coat layer is used, the thickness is preferably similar to that of the hard coat layer.

[0123] The high refractive index layer can be formed from a coating liquid for forming a high refractive index layer, which contains, for example, a binder resin composition and high refractive index particles. As the binder resin composition, for example, the curable resin composition exemplified in the hard coat layer can be used.

[0124] Examples of high refractive index particles include antimony pentoxide, zinc oxide, titanium oxide, cerium oxide, tin-doped indium oxide, antimony-doped tin oxide, yttrium oxide, and zirconium oxide. The refractive index of antimony pentoxide is about 1.79, that of zinc oxide is about 1.90, that of titanium oxide is about 2.3 to 2.7, that of cerium oxide is about 1.95, that of tin-doped indium oxide is about 1.95 to 2.00, that of antimony-doped tin oxide is about 1.75 to 1.85, that of yttrium oxide is about 1.87, and that of zirconium oxide is 2.10.

[0125] The average particle size of the high refractive index particles is preferably 2 nm or more, more preferably 5 nm or more, and even more preferably 10 nm or more. In order to suppress whitening and ensure transparency, the average particle size of the high refractive index particles is preferably 200 nm or less, more preferably 100 nm or less, more preferably 80 nm or less, more preferably 60 nm or less, and more preferably 30 nm or less. The smaller the average particle size of the high refractive index particles, the better the transparency, and by making it 60 nm or less, the transparency can be made extremely good.

[0126] In this specification, the average particle size of the high refractive index particles or the low refractive index particles can be calculated by the following steps (y1) to (y3). (y1) A cross section of the high refractive index layer or the low refractive index layer is imaged by a TEM or STEM. The acceleration voltage of the TEM or STEM is preferably 10 kV to 30 kV, and the magnification is preferably 50,000 to 300,000. (y2) Randomly extract 10 particles from the observed image, and calculate the particle diameter of each particle. The particle diameter is measured as the distance between two parallel lines that is the maximum distance between the two lines when the cross section of the particle is sandwiched between the two lines. If the particles are aggregated, the aggregated particles are considered to be a single particle and are measured. (y3) The same procedure is carried out five times on a separate observation image of the same sample, and the value obtained from the number average of the particle diameters of a total of 50 particles is regarded as the average particle diameter of the high refractive index particles or low refractive index particles.

[0127] <Anti-glare layer> An antiglare layer, which is an example of a functional layer, has the role of enhancing the antiglare properties of an adherend. The antiglare layer can be formed from, for example, a coating liquid for forming an antiglare layer, which contains a binder resin composition and particles. As the binder resin composition, for example, the curable resin composition exemplified in the hard coat layer can be used.

[0128] The particles may be either organic or inorganic. Examples of the organic particles include particles made of polymethyl methacrylate, polyacrylic-styrene copolymer, melamine resin, polycarbonate, polystyrene, polyvinyl chloride, benzoguanamine-melamine-formaldehyde condensate, silicone, fluorine-based resin, polyester resin, etc. Examples of the inorganic particles include particles made of silica, alumina, antimony, zirconia, titania, etc.

[0129] The average particle size of the particles in the antiglare layer cannot be generally determined because it varies depending on the thickness of the antiglare layer, but is preferably from 1.0 μm to 10.0 μm, more preferably from 2.0 μm to 8.0 μm, and even more preferably from 3.0 μm to 6.0 μm.

[0130] The average particle size of the particles in the antiglare layer can be calculated by the following steps (z1) to (z3). (z1) A transmission observation image of the cross section of the antiglare layer is taken using an optical microscope. The magnification is preferably 500 times or more and 2000 times or less. (z2) Randomly extract 10 particles from the observed image, and calculate the particle diameter of each particle. The particle diameter is measured as the distance between two parallel lines that is the maximum distance between the two lines when the cross section of the particle is sandwiched between the two lines. (z3) The same procedure is repeated five times on a separate observation image of the same sample, and the value obtained from the number average of the particle diameters of a total of 50 particles is regarded as the average particle diameter of the particles in the antiglare layer.

[0131] The particle content in the antiglare layer cannot be generalized as it varies depending on the desired level of antiglare properties, but it 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 even more preferably 10 parts by mass or more and 30 parts by mass or less, per 100 parts by mass of the resin component. The antiglare layer may contain fine particles having an average particle size of less than 500 nm in order to impart antistatic properties, control the refractive index, and adjust the shrinkage of the antiglare layer due to curing of the curable resin composition.

[0132] The thickness of the antiglare layer is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 2.0 μm or more. The thickness of the 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 even more preferably 10 μm or less. In order to improve the bending resistance, the thickness of the antiglare layer is preferably 10 μm or less, and more preferably 8 μm or less.

[0133] <Anti-stain layer> The antifouling layer is preferably formed on the side farthest from the optical biaxially stretched plastic film. The antifouling layer can be formed from, for example, a coating liquid for forming an antifouling layer, which contains a binder resin composition and an antifouling agent. As the binder resin composition, for example, the curable resin composition exemplified in the hard coat layer can be used.

[0134] Examples of the antifouling agent include fluorine-based resins, silicone-based resins, and fluorine-silicone copolymer resins. The antifouling agent preferably has a reactive group capable of reacting with the binder resin composition in order to suppress bleeding out from the antifouling layer, in other words, the antifouling agent is preferably fixed to the binder resin composition in the antifouling layer. In order to suppress bleeding out from the stain-resistant layer, a stain-resistant agent capable of self-crosslinking is also preferred. In other words, the stain-resistant agent is preferably self-crosslinked in the stain-resistant layer.

[0135] The content of the antifouling agent in the antifouling layer is preferably from 5 to 30% by mass, and more preferably from 7 to 20% by mass, of the total solid content of the antifouling layer.

[0136] The thickness of the antifouling layer is not particularly limited. For example, when it is an antifouling hard coat layer, it is preferably based on the thickness of the hard coat layer. Also, when it is an antifouling low refractive index layer, it is preferably based on the thickness of the low refractive index layer.

[0137] The functional film preferably has a haze of 5% or less, more preferably 4% or less, and even more preferably 3% or less according to JIS K7136:2000.The functional film preferably has a haze of 0.5% or more, more preferably 1.0% or more, and even more preferably 1.5% or more according to JIS K7136:2000. Furthermore, the functional film preferably has a total light transmittance according to JIS K7361-1:1997 of 90% or more, more preferably 91% or more, and even more preferably 92% or more.

[0138] <Application> The optical biaxially stretched plastic film of the present disclosure can be suitably used as a plastic film for an image display device. As described above, the biaxially stretched plastic film of the present disclosure suppresses blackout when viewed through polarized sunglasses or polarized goggles, and can be suitably used for an image display device used outdoors. In addition, when the optical biaxially stretched plastic film satisfies conditions 3 and 4, it can suppress the remaining bending tendency or breakage after a bending test regardless of the bending direction, so it can be more suitably used as a plastic film for a curved image display device or a foldable image display device. In addition, the optical plastic film of the present disclosure can be suitably used as a plastic film arranged on the light exit surface side of an image display device. In this case, it is preferable to have a polarizer between the light source of the image display device and the optical biaxially stretched plastic film of the present disclosure. Examples of the plastic film for the image display device include plastic films used as substrates for various functional films such as polarizer protective films, surface protective films, anti-reflection films, and conductive films constituting touch panels.

[0139] [Polarizing plate] The polarizing plate of the present disclosure has a polarizer, a first transparent protective plate arranged on one side of the polarizer, and a second transparent protective plate arranged on the other side of the polarizer, and at least one of the first transparent protective plate and the second transparent protective plate is the optical biaxially stretched plastic film of the present disclosure described above.

[0140] The polarizing plate is used, for example, in combination with a λ / 4 retardation plate to provide anti-reflection properties. In this case, the λ / 4 retardation plate is disposed on the image display device, and the polarizing plate is disposed closer to the viewer than the λ / 4 retardation plate. When the polarizing plate is used for a liquid crystal display device, it is used to provide a liquid crystal shutter function. In this case, the liquid crystal display device is arranged in the order of a lower polarizing plate, a liquid crystal layer, and an upper polarizing plate, and the absorption axis of the polarizer of the lower polarizing plate is arranged perpendicular to the absorption axis of the polarizer of the upper polarizing plate. The polarizer included in the upper polarizing plate corresponds to the first polarizer. The polarizing plate includes a polarizer, which will be described later.

[0141] The polarizing plate of the present disclosure uses the above-mentioned optical biaxially stretched plastic film of the present disclosure as at least one of the first transparent protective plate and the second transparent protective plate. In a preferred embodiment, both the first transparent protective plate and the second transparent protective plate are the above-mentioned optical biaxially stretched plastic film of the present disclosure. The first and / or second transparent protective plates in the polarizing plate of the present disclosure may have a functional layer on the optical biaxially stretched plastic film of the present disclosure. In other words, the first and / or second transparent protective plates in the polarizing plate of the present disclosure may be a functional film having a functional layer on the above-mentioned optical biaxially stretched plastic film of the present disclosure.

[0142] When one of the first transparent protective plate and the second transparent protective plate is the optical biaxially stretched plastic film of the present disclosure, the other transparent protective plate is not particularly limited, but is preferably an optically isotropic transparent protective plate. Optically isotropic refers to an in-plane retardation of less than 20 nm, preferably 10 nm or less, more preferably 5 nm or less. Examples of transparent substrates having optical isotropy include acrylic films, cyclic olefin films, and triacetyl cellulose (TAC) films. In addition, acrylic films and cyclic olefin films are preferred because the closer moisture permeability to the biaxially stretched plastic film can prevent deformation of the polarizing plate due to water absorption and can also prevent deterioration of the polarizer. Furthermore, when one of the first transparent protective plate and the second transparent protective plate is the optical biaxially stretched plastic film of the present disclosure described above, it is preferable to use the optical biaxially stretched plastic film of the present disclosure described above as the transparent protective plate on the light exit side.

[0143] <Polarizer> Examples of polarizers include sheet-type polarizers (polyvinyl alcohol film, polyvinyl formal film, polyvinyl acetal film, ethylene-vinyl acetate copolymer saponified film, etc.) made by stretching a film dyed with iodine or the like, wire grid-type polarizers made of a large number of metal wires arranged in parallel, coating-type polarizers coated with lyotropic liquid crystal and a dichroic guest-host material, multilayer thin film-type polarizers, etc. These polarizers may be reflective polarizers that have the function of reflecting polarized components that are not transmitted.

[0144] The polarizer preferably has a polarization degree of 99.00% or more and an average transmittance of 35% or more, more preferably a polarization degree of 99.90% or more and an average transmittance of 37% or more, and even more preferably a polarization degree of 99.95% or more and an average transmittance of 40% or more. In this specification, the average transmittance means the average of the spectral transmittance at a wavelength of 400 nm or more and 700 nm or less. The wavelength interval for measuring the average transmittance is 5 nm.

[0145] The polarizer is preferably disposed so that its absorption axis is approximately parallel or approximately perpendicular to any one side of the sample of the optical biaxially stretched plastic film cut out according to the above-mentioned technique.

[0146] [Image display device (1)] The image display device (1) of the present disclosure is an image display device having a display element and a plastic film arranged on the light emission surface side of the display element, and the plastic film is the optical biaxially stretched plastic film of the present disclosure described above.

[0147] The optical biaxially stretched plastic film of the present disclosure used in the image display device of the present disclosure may have a functional layer on the optical biaxially stretched plastic film. In other words, the optical biaxially stretched plastic film in the image display device of the present disclosure may be a functional film having a functional layer on the optical biaxially stretched plastic film of the present disclosure described above. The functional layer is preferably disposed on the opposite side of the optical biaxially stretched plastic film from the display element.

[0148] <Display element> Examples of display elements include liquid crystal display elements, EL display elements (organic EL elements, inorganic EL elements), plasma display elements, and further include LED display elements such as mini LED and micro LED display elements, and liquid crystal display elements and LED display elements using quantum dots. When the display element is a liquid crystal display element, a backlight is required on the side of the liquid crystal display element opposite to the plastic film.

[0149] The image display device may be an image display device equipped with a touch panel function. Examples of touch panels include resistive, capacitive, electromagnetic induction, infrared, and ultrasonic touch panels. The touch panel function may be added to a display element, such as an in-cell touch panel liquid crystal display element, or may be a display element having a touch panel placed on it. Fig. 7 shows an example of the configuration of an image display device (1) having the optical biaxially stretched plastic film and polarizer of the present disclosure, and an image display device (2) described below. In Fig. 7, 1A represents a display element, such as a liquid crystal display element or an organic EL element. In contrast to this 1A, 2A is a first polarizer, which is the polarizer in the image display device attached closest to the viewer 30. 3A is a second polarizer, such as polarized sunglasses. FIG. 8 is a schematic diagram of an image display device in which a low refractive index layer 40 is further added to the structure of FIG. Examples of the liquid crystal display element include an active matrix driving type such as a thin film transistor type, and a simple matrix driving type such as a twisted nematic type and a super twisted nematic type.

[0150] The optical biaxially stretched plastic film of the present disclosure can also be suitably used in an organic EL device. Figure 8 shows a schematic diagram of an organic EL device. In general, an organic EL element forms a light emitter (organic electroluminescence light emitter) by sequentially laminating a transparent electrode, an organic light emitting layer, and a metal electrode on a transparent substrate. Here, the organic light emitting layer is a laminate of various organic thin films, and various combinations are known, such as a laminate of a hole injection layer made of a triphenylamine derivative or the like and a light emitting layer made of a fluorescent organic solid such as anthracene, a laminate of such a light emitting layer and an electron injection layer made of a perylene derivative or the like, and a laminate of these hole injection layer, light emitting layer, and electron injection layer.

[0151] In organic EL devices, at least one of the electrodes must be transparent in order to extract light emitted from the organic light-emitting layer, and a transparent electrode made of a transparent conductor such as indium tin oxide (ITO) is usually used as the anode. On the other hand, to facilitate electron injection and increase luminous efficiency, it is important to use a material with a small work function for the cathode, and metal electrodes such as Mg-Ag and Al-Li are usually used.

[0152] In an organic EL element with this configuration, the organic light-emitting layer is an extremely thin film with a thickness of about 10 nm. Therefore, like the transparent electrode, the organic light-emitting layer also transmits light almost completely. As a result, when no light is emitted, light enters from the surface of the transparent substrate, passes through the transparent electrode and the organic light-emitting layer, and is reflected by the metal electrode and exits again from the surface of the transparent substrate, making the display surface of the organic EL display device look like a mirror when viewed from the outside. However, by combining a birefringent layer such as a λ / 4 phase difference plate (not shown) with a polarizer (first polarizer) and adjusting the angle between the polarization directions of the polarizer and the birefringent layer to π / 4, the mirror surface of the metal electrode can be completely shielded. That is, only the linearly polarized component of external light incident on this organic EL display device is transmitted by the polarizer. This linearly polarized light is generally converted to elliptically polarized light by the birefringent layer, but when the birefringent layer is a λ / 4 retardation plate and the angle between the polarization direction and the polarizer is π / 4, it becomes circularly polarized light. This circularly polarized light passes through the transparent substrate, transparent electrode, and organic thin film, is reflected by the metal electrode, passes through the organic thin film, transparent electrode, and transparent substrate again, and becomes linearly polarized again by the λ / 4 retardation plate. And since this linearly polarized light is perpendicular to the polarization direction of the polarizer, it cannot pass through the polarizer. As a result, the mirror surface of the metal electrode can be completely shielded. This 2A is a polarizer (first polarizer) and is the polarizer in the image display device attached closest to the viewer. The optical biaxially stretched plastic film of the present disclosure is disposed in an image display device between a first polarizer and polarized sunglasses 3A (second polarizer). The optical biaxially stretched plastic film and the first polarizer may be laminated via a pressure-sensitive adhesive layer (not shown; the same applies below).

[0153] The adhesive used in the adhesive layer of the present disclosure is not particularly limited, and can be appropriately selected and used, for example, those based on acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyethers, fluorine-based and rubber-based polymers. The adhesive is required to have excellent adhesive properties such as optical transparency, moderate wettability, cohesiveness, adhesion, weather resistance, heat resistance, etc. Furthermore, an adhesive layer with low moisture absorption and excellent heat resistance is required from the viewpoints of preventing foaming and peeling caused by moisture absorption, preventing deterioration of optical properties and warping of liquid crystal cells caused by thermal expansion differences, etc., and thus forming an image display device with high quality and excellent durability. In order to meet these requirements, an acrylic adhesive is preferred.

[0154] The adhesive may contain additives such as natural resins, synthetic resins, tackifying resins, glass fibers, glass beads, metal powder, pigments, colorants, antioxidants, etc. The adhesive layer may also contain fine particles and exhibit light diffusing properties.

[0155] The above-mentioned adhesive can be applied to the polarizing plate of the present disclosure by any suitable method without any particular limitation. For example, a method of preparing an adhesive solution of about 10% by mass or more and 40% by mass or less by dissolving or dispersing a base polymer or its composition in a solvent consisting of a single or mixture of suitable solvents such as toluene and ethyl acetate, and directly applying it to the polarizing plate of the present disclosure by a suitable spreading method such as a casting method or a coating method, or a method of forming an adhesive layer on a release base film according to this method and transferring it to the polarizing plate of the present disclosure, etc. can be mentioned. Various coating methods are possible, such as gravure coating, bar coating, roll coating, reverse roll coating, and comma coating, with gravure coating being the most common.

[0156] The pressure-sensitive adhesive layer can be provided on one or both sides of the polarizing plate of the present disclosure as a superimposed layer of layers having different compositions or types. When provided on both sides, the pressure-sensitive adhesives on the front and back of the polarizing plate of the present disclosure do not need to have the same composition or thickness. Pressure-sensitive adhesive layers of different compositions and thicknesses can also be used. The thickness of the adhesive layer can be appropriately determined depending on the purpose of use, adhesive strength, etc., and is generally from 1 μm to 500 μm, preferably from 5 μm to 200 μm, and particularly preferably from 10 μm to 100 μm.

[0157] <Other plastic films> The image display device of the present disclosure may include other plastic films as long as the effects of the present disclosure are not impaired. As the other plastic films, those having optical isotropy are preferred. Examples of the plastic film arranged on the light exit surface side of the display element include plastic films used as substrates for various functional films such as polarizer protective films, surface protective films, anti-reflection films, and conductive films that constitute touch panels.

[0158] [Image display device (2)] <Condition 1B> The luminance difference (L1.n-L2.n) between the luminance obtained in the following measurement 1B and the luminance obtained in the following measurement 2B is calculated at 100 measurement points, and the "variation in luminance difference 3σ" calculated from the luminance differences at the 100 measurement points is 100 or more. 《Measurement 1B》 A 1B measurement sample is prepared by arranging a first polarizer, an optical biaxially stretched plastic film, and a second polarizer in this order on a display element. In the 1B measurement sample, the slow axis direction of the optical biaxially stretched plastic film is arranged to be approximately perpendicular to the absorption axis direction of the first polarizer, and the absorption axis of the second polarizer is arranged to be approximately perpendicular to the absorption axis direction of the first polarizer. The display element of the 1B measurement sample is made to display white, and the luminance of the transmitted light exiting from the second polarizer side is measured at 100×100 measurement points set at equal intervals in any first region. 100 points are extracted from the measurement results in any horizontal row, and are numbered from the 1st measurement point to the 100th measurement point in order, with the luminance of the 1st measurement point defined as L1.1, the luminance of the 100th measurement point defined as L1.100, and the luminance of the nth measurement point defined as L1.n. 《Measurement 2B》 A measurement sample 2B is prepared by disposing the first polarizer and the second polarizer in this order on the same display element as in measurement 1B. In the measurement sample 2B, the absorption axis of the second polarizer is disposed substantially perpendicular to the absorption axis direction of the first polarizer. The display element of the 2B measurement sample is made to display white, and the luminance of the transmitted light exiting from the second polarizer side is measured at 100×100 measurement points set at equal intervals in an area that substantially coincides with the first measurement area. 100 points are arbitrarily extracted in a horizontal row from the measurement results, and are sequentially designated as the 1st measurement point to the 100th measurement point, with the luminance of the 1st measurement point defined as L2.1, the luminance of the 100th measurement point defined as L2.100, and the luminance of the nth measurement point defined as L2.n. <Condition 2B> The in-plane retardation (Re) is 2500 nm or less;

[0159] The image display device (2) of the present disclosure is an image display device having the first polarizer and an optical biaxially stretched plastic film on the light exit surface of the display element, in which the direction of the slow axis of the optical biaxially stretched plastic film and the direction of the absorption axis of the first polarizer are arranged approximately perpendicular to each other, and the optical biaxially stretched plastic film has an area that satisfies the <Condition 1B> and the <Condition 2B>.

[0160] The "1B measurement sample" in the measurement 1B of the image display device (2) refers to an image display device (2) in which a second polarizer is disposed on the light exit surface thereof. Moreover, the "2B measurement sample" in the measurement 2B of the image display device (2) refers to an image display device (2) in which the optical biaxially stretched plastic film of the present disclosure described above is removed and a second polarizer is disposed on the light exit surface side of the first polarizer.

[0161] Measurement 1B and Measurement 2B in the image display device (2) of the present disclosure are the same as Measurement 1 and Measurement 2 in the optical biaxially stretched plastic film of the present disclosure described above, except that the surface light source and the display element are different. In addition, the preferred embodiments of Measurement 1B and Measurement 2B are similar to the preferred embodiments of Measurement 1 and Measurement 2 (for example, a first polarizer is placed on a display element, and the preferred range of the luminance of the transmitted light exiting from the first polarizer side is similar to the preferred range of the luminance of the transmitted light exiting from the first polarizer side when a first polarizer is placed on a surface light source). In addition, the preferred embodiments of Condition 1B and Condition 2B are similar to the preferred embodiments of Condition 1 and Condition 2 described above.

[0162] <Applications of image display devices> The image display device of the present disclosure is an image display device having a display element and an optical biaxially stretched plastic film arranged on the light exit surface side of the display element. The image display device of the present disclosure may be an image display device for use indoors, but is preferably an image display device for use outdoors in an environment where a viewer uses polarized sunglasses or polarized goggles, etc. Specifically, it is preferable that the image display device is used in a tablet, a smartphone, a watch such as a smart watch, a car navigation system, a PID (public information display), a fish finder, or a drone operation screen. In the case of a portable image display device such as a tablet or a smartphone, the conditions of the external light and the position between the viewer and the light emitting surface change, so that blackout is less likely to occur by using the optical biaxially stretched plastic film of the present invention. In addition, in the case of a stationary image display element device such as a PID, although the image display device does not move, the viewer watches the image display device while moving, so it is required that blackout does not occur at a wide viewing angle, and it is preferable to use the optical biaxially stretched plastic film of the present disclosure and a functional film using the same.

[0163] As described above, the optical biaxially stretched plastic film of the present disclosure can suppress the remaining bending tendency or breakage after a bending test, and therefore the image display device of the present disclosure is preferable in that it can exert a more remarkable effect when it is a curved image display device or a foldable image display device. When the image display device is a curved image display device or a foldable image display device, the image display device is preferably an organic EL element.

[0164] <Relationship between the absorption axis of a polarizing plate and the slow axis of optical plastics> The second polarizer corresponds to a lens such as polarized sunglasses or polarized goggles, but in the case of polarized sunglasses, for example, the absorption axis is horizontal to absorb reflected light from a horizontal surface such as a water surface. The slow axis of the optical biaxially stretched plastic film of the present disclosure is preferably parallel to the absorption axis of the second polarizer, that is, horizontal or approximately horizontal to the ground. Furthermore, the absorption axis of the first polarizer is preferably perpendicular or approximately perpendicular to the absorption axis of the second polarizer, since the effect of the present disclosure is maximized. Since a portrait-oriented image display device for PID is a landscape-oriented image display device for television rotated 90 degrees, the absorption axis of the first polarizer differs by 90 degrees between the image display device for PID and the image display device for television in most cases. For this reason, it is particularly preferable that the absorption axis of the second polarizer is perpendicular or approximately perpendicular to the first polarizer, since the effect of the present disclosure is maximized. In addition, when the direction of the slow axis is not uniform within the plane of the optical biaxially stretched plastic film, the direction of the slow axis of the optical biaxially stretched plastic film means the average direction of the slow axis of the optical biaxially stretched plastic film.

[0165] [How to select biaxially oriented plastic films for optical applications] The method for selecting an optical biaxially stretched plastic film for an image display device disclosed herein is a method for selecting an optical biaxially stretched plastic film for an image display device having a polarizing plate and an optical biaxially stretched plastic film on the light output surface side of the image display device, in which the judgment criterion is that the film has an area that satisfies conditions 1 and 2, and one that satisfies the judgment condition is selected as the optical biaxially stretched plastic film.

[0166] Conditions 1 and 2 are the above conditions. The method for selecting the optical biaxially stretched plastic film of the image display device of the present disclosure preferably further includes an additional judgment condition as a judgment condition. The additional judgment condition includes a preferred embodiment of the optical biaxially stretched plastic film of the present disclosure (for example, an embodiment that satisfies condition 3 and / or condition 4).

[0167] According to the method of selecting an optical film for a display device of the present disclosure, an optical film capable of suppressing blackout when observed through polarized sunglasses can be efficiently selected, thereby improving workability. EXAMPLES

[0168] Next, the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to these examples in any way.

[0169] 1. Measurement and Evaluation The atmosphere for the following measurements and evaluations shall be a temperature of 23°C ± 5°C, and a relative humidity of 40% RH to 65% RH. Furthermore, before the measurements and evaluations, the samples shall be exposed to the above atmosphere for 30 minutes or more.

[0170] 1-1.Brightness A measurement sample measuring 120 mm in length and 120 mm in width was cut out from an optical biaxially stretched plastic film. A surface light source (described below), a first polarizer (hereinafter, the polarizer used was a MeCan Imaging Inc. product number: MUHD40S, polarization degree: 99.97%, average transmittance: 40.0%), the cut-out biaxially stretched plastic film, and a second polarizer were stacked in this order to prepare a first measurement sample. The optical biaxially stretched plastic film was arranged so that the direction of the slow axis was perpendicular to the direction of the absorption axis of the first polarizer, and the second polarizer was arranged so that the absorption axis was perpendicular to the direction of the absorption axis of the first polarizer. The surface light source of the first measurement sample was displayed as white. The measurement device used was Cybernet's "Prometric PM1423-1, imaging luminance meter, CCD resolution: 1536 x 1024." The first measurement sample and the imaging luminance meter were set in the positional relationship shown in Figure 1. The distance between the camera and the surface light source was set to 750 mm. The measurement area was a 100 mm x 100 mm region within the first measurement sample, 10 mm inside the outline of the cut biaxially stretched plastic film on the top, bottom, left and right. Next, the following "Settings before measurement" and "Adjustment of exposure time" were performed, and then the following "Measurement and analysis" was performed. The measurement was performed in a darkroom environment. <Settings before measurement> (1) The imaging luminance meter was connected to a personal computer, and the software provided with the imaging luminance meter (RADIANT IMAGING Prometric 9.1 Version 9.1.32) was launched in the personal computer. (2) When the software was launched, the CCD temperature in the imaging luminance meter was automatically adjusted to a blue display (-10°C). I waited until the CCD temperature stabilized at -10°C. (3) In the “Measurement Setup” of the software, “Color, 1x1 binning” was specified. (4) Set the lens aperture dial to 1.8 and focus on the second polarizer. <Adjusting exposure time> The "exposure time adjustment" of the software was performed. Specifically, "adjust" was pressed in the order of Y (green), X (red), and Z (blue), and then saved. The exposure time adjustment was performed every time a sample was measured. <Measurement and analysis> I selected "Focus Mode" on the toolbar and confirmed that the area to be measured was visible in the focus mode image. Click "Execute measurement" to perform the measurement. The measurement results were saved. From the tool bar, select "Tools" and "Measurement data processing." Next, select "Cut area" from the "Select processing content" pull-down menu. Next, specify the area of ​​the sample that corresponds to 100 mm x 100 mm, and save it. The above saved data is referred to as "Saved data 1." Saved data 1 was opened. Then, from the toolbar, "Tools" and "Export measurement data" were selected. Next, the data type was selected as "Brightness", the resolution was set to "X:100, Y:100", and the output format was set to "XY table", and the data was exported to Excel. By the above procedure, luminance data of measurement points of 100×100 in both vertical and horizontal directions were obtained. By extracting any 100 points in a horizontal row from the measurement results, luminance data of 100 points (L1.n, luminance of measurement 1) shown in FIG. 3 were obtained. In addition, in measurement 1, measurement points where the luminance variation from adjacent measurement points exceeded 30% were excluded from the measurement results as being due to local defects in the members constituting the first measurement sample. The same applies to measurement 2 described later.

[0171] As the surface light source, the following three types were used. Note that the luminance shown below means the average value of the luminance obtained at 100 measurement points under the condition that the second polarizer was further removed from the measurement of measurement 2, and 3σ of the luminance was calculated from the luminance of the 100 points obtained. The color temperature of the surface light source was measured using the product number of Cybernet "Prometric PM1423-1, imaging luminance meter, CCD resolution: 1536×1024". The data of the color temperature of the surface light source can be obtained in the same manner as the above luminance measurement except that the type of data to be exported is changed from "luminance" to "correlated color temperature". Then, the average value of the color temperatures at five locations, namely, four locations 10 mm advanced from the four corners of the 100 mm×100 mm measurement region toward the center and the center of the sample, was taken as the color temperature of each surface light source. <LED light source (LED)> An LED light source (product name "Dbmier A4S" of GraphicsPower, thin type 4.5 mm USB powered (278×372×4.5 mm)) was used as the surface light source. Luminance: 23021, 3σ of luminance: 6917, color temperature of white display: 10526K <OLED with RGB display (OLED)> What was obtained by removing the polarizer from the product name "galaxy Note4" of Samsung was white-displayed and used as the surface light source. Luminance: 32995, 3σ of luminance: 2433, color temperature of white display: 6962K <LCD display (LCD)> An EIZO product "EV2450Z" was used as a surface light source by removing the polarizer on the outermost surface of the display element to display white light. Brightness: 36907, Brightness 3σ: 1564, White display color temperature: 7772K

[0172] Measurement 2 was carried out in the same manner as Measurement 1, except that the optical biaxially stretched plastic film was removed, and the luminance (L2.n. Luminance of Measurement 2) was measured. Note that the second measurement area, which was the measurement area of ​​Measurement 2, was approximately the same as the first measurement area, which was the measurement area of ​​Measurement 1.

[0173] 1-2. Calculation of "3σ variation in brightness difference" The luminance difference (L1.n-L2.n) was calculated using the luminance L1.n and L2.n of the 100 measured points. Negative values ​​were removed from the luminance differences of the 100 points obtained, and the "variation in luminance difference 3σ" was calculated. Since the first polarizer and second polarizer are arranged in a crossed Nicol, the luminance of L2.n is usually low. Measurement points with negative luminance differences are considered to be anomalous points where light leaks locally from the crossed Nicol and L2.n shows a high value, so they were excluded from the calculation of 3σ. In the examples and comparative examples, the number of luminance measurement points used in calculating the luminance difference variation 3σ was 80 or more.

[0174] 1-2. Variation in in-plane retardation (Re), retardation in thickness direction (Rth) and slow axis A measurement sample measuring 100 mm in length and 100 mm in width was cut out from a biaxially stretched plastic film for optical use. The flow direction (MD direction) of the measurement sample was regarded as the longitudinal direction, and the width direction (TD direction) of the plastic film was regarded as the lateral direction. In total, five locations were measured for the in-plane retardation, retardation in the thickness direction, and direction of the slow axis, including four locations 10 mm from the four corners of the sample toward the center, and the center of the sample. Table 1 shows the average values of Re1 to Re5 calculated from the measurement results. As the measuring device, the product named “RETS-100 (measurement spot: diameter 5 mm)” manufactured by Otsuka Electronics Co., Ltd. was used. Note that the direction of the slow axis was measured in the range of 0 degrees or more and 90 degrees or less, with the flow direction (MD direction) of the plastic film as the reference 0 degrees.

[0175] 1-3. Blackout Evaluation The blackout was evaluated by evaluating the readability of 18-point characters. The evaluation was carried out in a light room environment where the brightness of the surface of the image display device was 300 lux or more and 750 lux or less with the power of the image display device turned off. The power of the image display device was turned on, 18-point characters were displayed in black on a white background, and 20 evaluators (five from each of the 20s, 30s, 40s, and 50s age groups) observed from a distance of approximately 750 mm from the image display device to evaluate whether the characters were legible. The line of sight of the evaluators was adjusted to the height of the image display device. Also, the position of the evaluators was in the front direction of the image display device. Those that could be read by 15 or more and 20 or fewer people were rated “A,” those that could be read by 10 or more and 14 or fewer people were rated “B,” and those that could be read by 9 or fewer people were rated “C.”

[0176] 1-4. Flexural Resistance A strip-shaped sample with a short side (TD direction) of 30 mm × a long side (MD direction) of 100 mm was cut out from an optically biaxially stretched plastic film. Both ends of the short side (30 mm) of the sample were fixed to a durability tester (product name "DLDMLH-FS", manufactured by YUASA SYSTEM CO., LTD.) (fixing the area 10 mm from the tip), and a continuous folding test of folding 180 degrees was performed 100,000 times. The folding speed was 120 times per minute. A more detailed method of the folding test is shown below. The TD direction generally coincides with the average direction of the direction of the slow axis. After the folding test, the strip-shaped sample was placed on a horizontal table, and the angle at which the end of the sample lifted from the table was measured. The results are shown in Table 1. Samples that broke during the test were regarded as "broken". <MD direction> A strip-shaped sample with a short side (MD direction) of 30 mm × a long side (TD direction) of 100 mm was cut out from an optically biaxially stretched plastic film, and the same evaluation as above was performed.

[0177] <Details of the folding test> As shown in Fig. 6(A), in the continuous folding test, first, the side portion 10C of the plastic film 10 and the side portion 10D opposite to the side portion 10C are respectively fixed by the fixing portions 60 arranged in parallel. The fixing portion 60 is slidable in the horizontal direction. Next, as shown in Fig. 6(B), by moving the fixing portions 60 closer to each other, the plastic film 10 is deformed to be folded. Further, as shown in Fig. 6(C), after moving the fixing portions 60 to a position where the distance between the two opposite side portions fixed by the fixing portions 60 of the plastic film 10 becomes 2 mm, the fixing portions 60 are moved in the reverse direction to eliminate the deformation of the plastic film 10. 6(A) to 6(C), the plastic film 10 can be folded 180 degrees by moving the fixing part 60. Moreover, by performing a continuous folding test so that the bent part 10E of the plastic film 10 does not protrude from the lower end of the fixing part 60 and controlling the distance between the fixing parts 60 at their closest point to 2 mm, the distance between the two opposing sides of the optical film 10 can be set to 2 mm.

[0178] [Examples 1 to 3] 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-benzoxazinon-4-one) were melt-mixed at 280°C in a kneader to produce pellets containing the ultraviolet absorber. The pellets and PET with a melting point of 258°C were fed into a single-screw extruder and melt-kneaded at 280°C, extruded from a T-die, and cast onto a cast drum with a surface temperature controlled at 25°C to obtain a casting film. The amount of ultraviolet absorber in the casting film was 1 part by mass per 100 parts by mass of PET. The obtained casting film was heated with a group of rolls set at 95°C, and then stretched 3.3 times in the machine direction while heating both sides of the film with a radiation heater so that the film temperature at a point 250 mm into the 400 mm stretching section (starting point is stretching roll A and ending point is stretching roll B; stretching rolls A and B each have two nip rolls) would be 103°C, and then cooled once. During heating with the radiation heater, air at 92°C and 4 m / s was blown toward the film from the opposite side of the film from the radiation heater, generating turbulence on the front and back of the film and disrupting the temperature uniformity of the film. Next, both sides of this uniaxially stretched film were subjected to a corona discharge treatment in air to set the wetting tension of the base film to 55 mN / m, and the corona discharge-treated surfaces of both sides of the film were in-line coated with "a lubricity layer coating solution containing a polyester resin with a glass transition temperature of 18°C, a polyester resin with a glass transition temperature of 82°C, and silica particles with an average particle size of 100 nm" to form a lubricity layer. 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 a temperature of 105°C in the first stage and 140°C in the second stage. Here, when the transverse stretching section was divided into two, the film was stretched in two stages so that the stretch amount of the film at the midpoint of the transverse stretching section (film width at the measurement point - film width before stretching) was 80% of the stretch amount at the end of the transverse stretching section. The transversely stretched film was heat-treated in the tenter stepwise from 180°C to 245°C with hot air, followed by 1% relaxation treatment in the width direction under the same temperature conditions, and further quenched to 100°C, followed by 1% relaxation treatment in the width direction, and then wound up to obtain a biaxially stretched polyester film 1 (biaxially stretched polyester film used in Examples 1 to 3) having a thickness of 40 μm.

[0179] Table 1 shows the physical properties of the obtained biaxially stretched polyester film 1, as well as the evaluations of "brightness difference variation" and "blackout evaluation (readability)" when the above-mentioned three types of surface light source were used.

[0180] [Table 1]

[0181] The biaxially stretched polyester films of the examples showed good results in terms of readability regardless of the surface light source, and the biaxially stretched polyester film 1 showed good bending resistance.

[0182] [Comparative Examples 1 to 8] Blackout (readability) was evaluated in the same manner as in Example 1, except that the following Comparative Films 1 to 3 were used as the polyester films. The surface light sources used were those shown in Tables 2 to 4. The results are shown in Tables 2 to 4. <Comparative film 1> "Cosmoshine A4300, biaxially oriented polyester film" (film thickness: 188 μm, average Re 8259 nm) by Toyobo Co., Ltd. <Comparative film 2> Toyobo Co., Ltd.'s product name "Cosmoshine TA048, uniaxially stretched film" (film thickness: 80 μm, average Re 10302 nm) <Comparative film 3> "Cosmoshine A4300" biaxially oriented polyester film (film thickness: 100 μm, average Re 4207 nm) by Toyobo Co., Ltd.

[0183] [Table 2]

[0184] [Table 3]

[0185] [Table 4]

[0186] In all of Comparative Examples 1 to 8, readability was low and blackouts occurred.

[0187] [Example 4] A functional film of Example 4 was produced by further laminating a low refractive index layer having a reflectance of 0.15% as a functional layer on the optical biaxially stretched plastic film of Example 1. The "brightness difference variation 3σ" and blackout evaluation were carried out in the same manner as in Example 1, except that the functional film of Example 4 was used instead of the optical biaxially stretched plastic film of Example 1. The surface light source used was one shown in Table 5. The results are shown in Table 5.

[0188] [Table 5]

[0189] As shown in Table 5, the functional film of Example 4 exhibited good readability. Furthermore, even when the reflectance of the low refractive index layer in Example 4 was changed to 0.65%, 1.00%, or 1.65%, the readability was good, similar to that in Example 4.

[0190] [Examples 5 to 7] Biaxially oriented polyester film 2 used in Examples 5 to 7 was obtained in the same manner as in the biaxially oriented polyester film 1, except that the stretching ratio in the transverse direction was changed from 4.5 times to 4.9 times.

[0191] Table 6 shows the physical properties of the obtained biaxially stretched polyester film 2, as well as the evaluation of "brightness difference variation" and "blackout evaluation (readability)" when the above three types of surface light source were used.

[0192] [Table 6]

[0193] As shown in Table 6, the readability was good regardless of the surface light source in Examples 5 to 7. Moreover, the biaxially oriented polyester film 2 had good bending resistance.

[0194] [Reference examples 1~2] As the optical plastic film of Reference Example 1, a commercially available biaxially stretched polyester film (TOYOBO CO., LTD., product name "Cosmoshine A4100", thickness: 50 μm, average Re: 2202 nm) was prepared. As an optical plastic film for Reference Example 2, a commercially available uniaxially stretched polyester film (TOYOBO CO., LTD., product name "Cosmoshine TA048", thickness: 80 μm) was prepared.

[0195] The polyester films of Reference Examples 1 and 2 were used to evaluate bending resistance in the same manner as in Examples 1 and 2. The results are shown in Table 7.

[0196] [Table 7]

[0197] From the results in Table 7, it can be confirmed that the biaxially stretched polyester films of the examples have better bending resistance than the uniaxially stretched polyester films and general biaxially stretched films. [Explanation of symbols]

[0198] 1. Surface light source 1A. Display element 2. First polarizer 2A. Polarizer closest to the viewer (first polarizer) 3. Second polarizer 3A. Polarized sunglasses (second polarizer) 4. First measurement sample 5. Second measurement sample 10. Biaxially oriented plastic films for optical applications 10C. Side of optical biaxially stretched plastic film 10 Sides corresponding to 10D and 10C 10E. Bend of optical biaxially stretched plastic film 10 20. Imaging Photometer 21. First measurement sample 22. Second first measurement sample 23. 3rd 1st measurement sample 24. Diagonal 30. Viewer 40.Low refractive index layer 60. Fixtures arranged parallel to each other Re1~5. Measurement points for condition 2

Claims

1. <Condition 1> The luminance difference (L1.n-L2.n) between the luminance obtained in Measurement 1 below and the luminance obtained in Measurement 2 below is calculated at 100 measurement points, and the "variation in luminance difference 3σ" calculated from the luminance differences at the 100 measurement points is 100 or more. <<Measurement 1>> A first measurement sample is prepared by arranging a first polarizer, an optical biaxially stretched polyester film, and a second polarizer in this order on a surface light source. In the first measurement sample, the optical biaxially stretched polyester film is arranged so that the slow axis direction is approximately perpendicular to the absorption axis direction of the first polarizer, and the second polarizer is arranged so that the absorption axis direction is approximately perpendicular to the absorption axis direction of the first polarizer. The surface light source of the first measurement sample is displayed as white, and the luminance of the transmitted light emitted from the second polarizer side is measured at 100×100 measurement points set at equal intervals in an arbitrary first region. 100 points are arbitrarily extracted in a horizontal row from the measurement results, and are sequentially defined as the 1st measurement point to the 100th measurement point, with the luminance of the 1st measurement point being defined as L1.1, the luminance of the 100th measurement point being defined as L1.100, and the luminance of the nth measurement point being defined as L1.n. Measurement 2 A second measurement sample is prepared by arranging the first polarizer and the second polarizer in this order on the same surface light source as in Measurement 1. In the second measurement sample, the absorption axis of the second polarizer is arranged approximately perpendicular to the direction of the absorption axis of the first polarizer. The surface light source of the second measurement sample is displayed as white, and the luminance of the transmitted light emitted from the second polarizer side is measured at 100×100 measurement points set at equal intervals in an area that substantially coincides with the first area. 100 points are arbitrarily extracted in a horizontal row from the measurement results, and are sequentially defined as the first measurement point to the 100th measurement point, with the luminance of the first measurement point being defined as L2.1, the luminance of the 100th measurement point being defined as L2.100, and the luminance of the nth measurement point being defined as L2.n. <Condition 2> The in-plane retardation is measured at a total of five locations, including four locations 10 mm from the four corners toward the center of a sample of an optical biaxially stretched polyester film having a size of 100 mm length×100 mm width, and one location at the center of the sample. When the in-plane retardation at the five points is defined as Re1, Re2, Re3, Re4, and Re5, the average of Re1 to Re5 is 2500 nm or less; A biaxially oriented polyester film for optical use having a region that satisfies the above <Condition 1> and the above <Condition 2>.

2. 2. The optical biaxially oriented polyester film according to claim 1, wherein an in-plane retardation relative to a retardation in a thickness direction is 0.01 or more and 0.10 or less.

3. 2. The optical biaxially oriented polyester film according to claim 1, having a thickness of 20 μm or more and 200 μm or less.

4. 2. The optical biaxially oriented polyester film according to claim 1, wherein the average of Re1 to Re5 in condition 2 is 520 nm or more and 2500 nm or less.

5. 2. The optical biaxially stretched polyester film according to claim 1, wherein the directions of the slow axes at the five points under the condition 2 are measured, and the angles formed between any one side of the sample and the directions of the slow axes at the respective measurement points are defined as D1, D2, D3, D4, and D5, respectively, and the difference between the maximum value and the minimum value of D1 to D5 is 5.0 degrees or more.

6. 6. The optical biaxially oriented polyester film according to claim 5, wherein the difference between the maximum and minimum values ​​of D1 to D5 is 5.0 degrees or more and 20.0 degrees or less.

7. A functional film comprising the optical biaxially oriented polyester film according to any one of claims 1 to 6, and a functional layer on one side of the film.

8. A polarizing plate having a polarizer, a first transparent protective plate arranged on one side of the polarizer, and a second transparent protective plate arranged on the other side of the polarizer, wherein at least one of the first transparent protective plate and the second transparent protective plate is the optical biaxially stretched polyester film described in any one of claims 1 to 6.

9. 7. An image display device having a display element and a plastic film arranged on a light exit surface side of the display element, the plastic film being the optical biaxially stretched polyester film according to any one of claims 1 to 6.

10. 10. The image display device according to claim 9, further comprising a polarizer between the display element and the plastic film.

11. 11. The image display device according to claim 9, further comprising a functional layer on the side of said optical biaxially stretched polyester film opposite to said display element.

12. <Condition 1B> The luminance difference (L1.n-L2.n) between the luminance obtained in Measurement 1B below and the luminance obtained in Measurement 2B below is calculated at 100 measurement points, and the "variation in luminance difference 3σ" calculated from the luminance differences at the 100 measurement points is 100 or more. 《Measurement 1B》 A first B measurement sample is prepared by arranging a first polarizer, an optical biaxially stretched polyester film, and a second polarizer in this order on a display element. In the first B measurement sample, the optical biaxially stretched polyester film is arranged so that the slow axis direction is approximately perpendicular to the absorption axis direction of the first polarizer, and the absorption axis of the second polarizer is arranged so that the absorption axis direction is approximately perpendicular to the absorption axis direction of the first polarizer. The display element of the 1B measurement sample is made to display white, and the luminance of the transmitted light emitted from the second polarizer side is measured at 100×100 measurement points set at equal intervals in an arbitrary first region. 100 points are arbitrarily extracted in a horizontal row from the measurement results, and are sequentially defined as the 1st measurement point to the 100th measurement point, with the luminance of the 1st measurement point being defined as L1.1, the luminance of the 100th measurement point being defined as L1.100, and the luminance of the nth measurement point being defined as L1.n. 《Measurement 2B》 A measurement sample 2B is prepared by arranging the first polarizer and the second polarizer in this order on the same display element as in measurement 1B. In the measurement sample 2B, the absorption axis of the second polarizer is arranged substantially perpendicular to the absorption axis direction of the first polarizer. The display element of the 2B measurement sample is made to display white, and the luminance of the transmitted light emitted from the second polarizer side is measured at 100×100 measurement points set at equal intervals in an area that substantially coincides with the first area. 100 points are arbitrarily extracted in a horizontal row from the measurement results, and are sequentially defined as the 1st measurement point to the 100th measurement point, with the luminance of the 1st measurement point being defined as L2.1, the luminance of the 100th measurement point being defined as L2.100, and the luminance of the nth measurement point being defined as L2.n. <Condition 2B> The in-plane retardation is measured at a total of five locations, including four locations 10 mm from the four corners toward the center of a sample of an optical biaxially stretched polyester film having a size of 100 mm length×100 mm width, and one location at the center of the sample. When the in-plane retardation at the five points is defined as Re1, Re2, Re3, Re4, and Re5, the average of Re1 to Re5 is 2500 nm or less; An image display device having the first polarizer and an optical biaxially stretched polyester film on a light exit surface of the display element, wherein a direction of a slow axis of the optical biaxially stretched polyester film and a direction of an absorption axis of the first polarizer are arranged approximately perpendicular to each other, and the optical biaxially stretched polyester film has an area that satisfies <Condition 1B> and <Condition 2B>.

Images