Optical film, polarizing plate, and image display device

Abstract

To provide an optical film, in which superior scratch resistance and superior abrasion resistance can be realized and superior antifouling property can be realized, as well as a polarizer and an image display device comprising the same.SOLUTION: An optical film 10 comprises: a resin base material 11; and a functional layer 12 that is provided on a first surface 11A side of the resin base material 11, a surface 10A of the optical film 10 being a surface 12A of the functional layer 12, the number of specific depressed areas in an area of being 5 μm square on the surface 10A of the optical film 10 after performing an eraser test in which the surface 10A of the optical film 10 is scraped 4000 times back and forth with weight 500 g using an eraser being more than or equal to one and less than or equal to 50, a dynamic friction coefficient of the surface 10A of the optical film 10 before the eraser test being less than or equal to 0.70, and a change rate of the dynamic friction coefficient of the surface 10 of the optical film 10 after the eraser test relative to the dynamic friction coefficient of the surface 10A of the optical film 10 before the eraser test being 35%. The optical film 10 is provided.SELECTED DRAWING: Figure 1

Description

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority from an earlier Japanese application, Patent Application No. 2018-86886 (filing date: April 27, 2018), the entire disclosure of which is incorporated herein by reference. [Technical Field]

[0002] The present invention relates to an optical film, a polarizing plate, and an image display device. [Background technology]

[0003] In recent years, not only smartphones and tablet terminals but also image display devices such as notebook personal computers have become equipped with touch functions. The surface of an image display device with a touch function is usually made of a cover glass. However, while glass generally has excellent hardness, it is thick and expensive. For this reason, the use of an optical film having a resin substrate instead of the cover glass has been considered (see, for example, Patent Document 1).

[0004] On the other hand, in some image display devices with touch functions, the display surface is sometimes rubbed with a touch pen instead of a finger, and therefore, the optical film used in place of the cover glass is required to have not only scratch resistance but also abrasion resistance so that components present on the surface of the optical film are not easily scraped off by rubbing with a touch pen or the like, and antifouling properties so that dirt does not easily adhere to the optical film even after rubbing with a touch pen or the like. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-125063 Summary of the Invention [Problem to be solved by the invention]

[0006] Although optical films having scratch resistance have been known for some time, scratch resistance and abrasion resistance are completely different properties. On the other hand, even if excellent scratch resistance and excellent abrasion resistance are realized, it has been difficult to realize excellent antifouling properties. Therefore, an optical film that realizes excellent scratch resistance, excellent abrasion resistance, and also excellent antifouling properties has not yet been obtained.

[0007] The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical film that can achieve excellent scratch resistance, excellent abrasion resistance, and excellent stain resistance, as well as a polarizing plate and an image display device that include the same. [Means for solving the problem]

[0008] The present invention includes the following inventions. [1] An optical film comprising a resin substrate and a functional layer provided on a first surface side of the resin substrate, wherein the surface of the optical film is the surface of the functional layer, and when a 5 μm square area of the surface of the optical film is observed using an atomic force microscope after an eraser test in which the surface of the optical film is rubbed back and forth 4,000 times with an eraser at a load of 500 g, there are 1 to 50 depressions within the area, each depression having at least one of the following shapes: annular with an outer diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm, circular with a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm, and irregular with a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm; the coefficient of dynamic friction of the surface of the optical film before the eraser test is 0.70 or less; and the rate of change in the coefficient of dynamic friction of the surface of the optical film after the eraser test relative to the coefficient of dynamic friction of the surface of the optical film before the eraser test is within 35%.

[0009] [2] An optical film comprising a resin substrate and a functional layer provided on a first surface side of the resin substrate, wherein the surface of the optical film is the surface of the functional layer, and when an eraser test is conducted in which the surface of the optical film is rubbed back and forth 5000 times with an eraser at a load of 1000 g, the absolute value of the difference between the average arithmetic height of a 5 μm square area on the surface of the optical film before the eraser test, measured using an atomic force microscope, and the average arithmetic height of a 5 μm square area on the surface of the optical film after the eraser test, measured using the atomic force microscope, is 10 nm or less, the dynamic friction coefficient of the surface of the optical film before the eraser test is 0.70 or less, and the rate of change in the dynamic friction coefficient of the surface of the optical film after the eraser test relative to the dynamic friction coefficient of the surface of the optical film before the eraser test is 35% or less.

[0010] [3] The optical film according to [2] above, wherein, when a 5 μm square area on the surface of the optical film after the eraser test is observed using an atomic force microscope, there are 1 to 50 depressions within the area, each depression having at least one of the following shapes: annular with an outer diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm; circular with a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm; and irregular with a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm.

[0011] [4] The optical film according to any one of [1] to [3] above, wherein when a 5 μm square area on the surface of the optical film before the eraser test is observed using an atomic force microscope, there are 1 to 50 depressions.

[0012] [5] The optical film according to any one of [1] to [3] above, wherein when a 5 μm square area of the surface of the optical film before the eraser test is observed using an atomic force microscope, no depressions are present.

[0013] [6] The optical film according to any one of the above [1] to [5], wherein convex portions with a height of 1 nm or more are present inside the depressions or within the depressions.

[0014] [7] The optical film according to any one of [1] to [6] above, wherein the contact angle retention rate, which is the ratio of the contact angle with water on the surface of the optical film after the eraser test to the contact angle with water on the surface of the optical film before the eraser test, is 80% or more.

[0015] [8] 1kg / cm using steel wool 2 [7] The optical film according to any one of [1] to [7] above, wherein when a steel wool test is performed in which the surface of the optical film before the eraser test is rubbed back and forth 5000 times while applying a load of 1000, no scratches are found on the surface.

[0016] [9] An optical film described in any one of [1] to [8] above, wherein the functional layer comprises a first functional layer containing particles and a second functional layer which is provided on the side of the first functional layer opposite to the side facing the resin substrate and which does not contain particles.

[0017]

[10] The optical film according to any one of [1] to [9] above, wherein the resin substrate comprises a triacetyl cellulose resin and has a thickness of 15 μm or more and 65 μm or less, the resin substrate comprises a polyester-based resin and has a thickness of 5 μm or more and 45 μm or less, the resin substrate comprises a cycloolefin polymer-based resin and has a thickness of 5 μm or more and 35 μm or less, or the resin substrate comprises at least one of a polyimide-based resin and a polyamide-based resin and has a thickness of 5 μm or more and 75 μm or less, wherein the optical film does not crack or break when a test in which the optical film is folded 180° so that the distance between opposing sides of the optical film is 2 mm and the functional layer is on the inside is repeated 100,000 times.

[0018]

[11] An optical film according to any one of [1] to [9] above, wherein the resin substrate comprises at least one of triacetyl cellulose resin, polyester resin, cycloolefin polymer resin, polyimide resin, and polyamide resin, and the thickness of the resin substrate is 35 μm or more and 105 μm or less, and wherein the optical film is folded 180° so that the distance between opposing sides of the optical film is 3 mm and the functional layer is on the outside, and the optical film is folded 180° repeatedly 100,000 times without cracking or breaking.

[0019]

[12] There is provided a polarizing plate comprising the optical film according to any one of [1] to

[11] above, and a polarizer provided on a second surface of the resin substrate of the optical film, the second surface being opposite to the first surface.

[0020]

[13] An image display device comprising: a display element; and the optical film according to any one of [1] to

[11] above or the polarizing plate according to

[12] above, which is arranged closer to the viewer than the display element, wherein the functional layer of the optical film is located closer to the viewer than the resin substrate.

[0021]

[14] The image display device according to

[13] above, further comprising a touch sensor between the display element and the optical film.

[0022]

[15] The image display device according to the above

[13] or

[14] , wherein the display element is an organic light-emitting diode element. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide an optical film that can achieve excellent scratch resistance, excellent abrasion resistance, and excellent stain resistance, and a polarizing plate and an image display device that include this optical film. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic diagram of an optical film according to an embodiment. [Figure 2] FIG. 2 is an enlarged plan view of a portion of the optical film of FIG. [Figure 3] FIG. 3 is an enlarged cross-sectional view of a portion of the functional layer of FIG. [Figure 4] FIG. 4 is a diagram showing a schematic diagram of how the number of dents is counted and how the diameter of the dents is calculated. [Figure 5] FIG. 5 is a diagram of the sample used in the eraser test. [Figure 6] FIG. 6 is an image diagram of the arithmetic mean height (Sa). [Figure 7] 7(A) to 7(C) are diagrams showing the folding test in a schematic manner. [Figure 8] FIG. 8 is a plan view of the sample after the folding test. [Figure 9] FIG. 9 is a schematic diagram of a polarizing plate according to an embodiment. [Figure 10] FIG. 10 is a schematic configuration diagram of an image display device according to an embodiment. [Figure 11] 11(A) and 11(B) are photographs of the surface of the optical film according to Example 1 before the eraser test, observed with an atomic force microscope. [Figure 12] 12(A) and 12(B) are photographs of the surface of the optical film according to Example 1 after the eraser test (500 g×4000 reciprocations) observed with an atomic force microscope. [Figure 13] Figure 13(A) is a photograph of the surface of the optical film of Example 6 observed with an atomic force microscope before the eraser test, and Figure 13(B) is a photograph of the surface of the optical film of Example 6 observed with an atomic force microscope after the eraser test (1000g x 5000 reciprocations). DETAILED DESCRIPTION OF THE INVENTION

[0025] An optical film and an image display device according to an embodiment of the present invention will be described below with reference to the drawings. In this specification, terms such as "film" and "sheet" are not distinguished from each other solely based on differences in name. Therefore, for example, "film" is used to include a member also referred to as a sheet. FIG. 1 is a schematic diagram of an optical film according to this embodiment, FIG. 2 is an enlarged plan view of a portion of the optical film of FIG. 1, FIG. 3 is an enlarged cross-sectional view of a portion of the functional layer of FIG. 1, and FIG. 4 is a schematic diagram illustrating the counting of the number of depressions and the determination of the depression diameter. FIG. 5 is a diagram of a sample used in an eraser test, FIG. 6 is an image diagram of the arithmetic mean height (Sa), FIGS. 7(A) to 7(C) are schematic diagrams illustrating the folding test, and FIG. 8 is a plan view of the sample after the folding test.

[0026] <<<Optical Films>>> The optical film 10 shown in FIG. 1 is optically transparent and includes a resin substrate 11 and a functional layer 12 provided on a first surface 11A, which is one surface of the resin substrate 11. In this specification, a "functional layer" refers to a layer in the optical film that is intended to perform some function. Specific examples of functional layers include layers that perform hard coating, antifouling, and / or slip properties. The functional layer may have a single-layer structure or a multilayer structure of two or more layers. The functional layer 12 shown in FIG. 1 has a multilayer structure consisting of a first functional layer 13 and a second functional layer 14. The surface 10A of the optical film 10 corresponds to the surface 12A of the functional layer 12.

[0027] In optical film 10, an eraser test was conducted using an atomic force microscope (AFM) (for example, product name "WET-9100" manufactured by Shimadzu Corporation) in which the surface of the optical film was rubbed back and forth 4000 times with an eraser at a load of 500 g (hereinafter, this test will be referred to as the eraser test (500 g × 4000 rubs)). After this test, a 5 μm square (5 μm × 5 μm) area on surface 10A of optical film 10 was observed. As shown in Figures 2 and 3, within the area, there were 1 to 50 depressions 10B, each of which had at least one of the following shapes: annular with an outer diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm, circular with a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm, and irregular with a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm. The presence of at least one such annular, circular, or irregularly shaped depression 10B provides satisfactory scratch resistance and abrasion resistance and prevents the antifouling agent from falling off the surface 10A of the optical film 10. Furthermore, having 50 or fewer depressions 10B means that the entire surface 10A does not have the same film quality, but rather has a surface with separate functions for hardness and slippage, resulting in good physical properties. Furthermore, although the outer diameter and diameter of the depressions 10B are specified as 0.1 μm or more and 2.5 μm or less, if the outer diameter is less than 0.1 μm, abrasion resistance may be reduced, and if it exceeds 2.5 μm, scratch resistance may be reduced. For example, although the reason for this is unclear, such depressions 10B can be formed by incorporating both a lubricant and an antifouling agent (described later) into the functional layer 12, or by incorporating a mixture of antifouling agents rather than a single type, or by incorporating an antifouling agent containing multiple elements, even if the functional layer 12 does not contain a lubricant. The observation area is set to 5 μm square because, during macroscopic observation, whether the surface is flat with a mirror finish or uneven with antiglare properties, the flat portion can be observed to observe the true nature of the layer, and the magnification is favorable for confirming whether the surface condition has the functionality to obtain the required physical properties. In areas larger than 5 μm square, it is difficult to observe the presence of the above-mentioned small shapes, and the magnification is insufficient to grasp the true nature of the layer.Furthermore, an area smaller than 5 μm square is not sufficient resolution to observe the shape required for the above-mentioned invention to function. Furthermore, when the eraser test is performed under conditions of 1,000 or 1,500 strokes at a load of 500 g, if the functional layer contains an antifouling agent, scratch resistance and abrasion resistance may be good, but the antifouling properties essential for practical use may not be achieved at the same time. Furthermore, in the more stringent eraser test (500 g x 4,000 strokes) and the even more stringent eraser test (1,000 g x 5,000 strokes) described below, the eraser significantly scrapes off the components of the functional layer, resulting in poor scratch resistance and abrasion resistance. In contrast, the functional layer 12 contains, for example, a lubricant in addition to the antifouling agent, or multiple types of antifouling agents. Therefore, after wear, one to 50 depressions, which are thought to separate the hardness-retaining and sliding functions, are present on the surface in a sea-island pattern. When observing the depressions macroscopically, they appear to be evenly distributed over the surface of the functional layer. Therefore, even after a rigorous eraser test, i.e., wear during practical use, this structure continues to exist, maintaining an appropriate dynamic friction coefficient, and is believed to provide excellent scratch resistance and excellent wear resistance, while also maintaining excellent stain resistance.

[0028] Preferably, three or more or five or more depressions 10B are observed in a 5 μm square (5 μm×5 μm) area on surface 10A of optical film 10 after the eraser test (4000 strokes back and forth).

[0029] When the recess 10B includes a ring-shaped recess 10B1, the lower limit of the outer diameter of the recess 10B1 is preferably 0.2 μm or more, 0.4 μm or more, 0.6 μm or more, 0.8 μm or more, or 1.0 μm or more, and the upper limit of the outer diameter is preferably 2.4 μm or less, 2.2 μm or less, or 2.0 μm or less. The inner diameter and width of the recess 10B1 are not particularly limited. For example, the width of the recess 10B1 is preferably 1.0 nm or more and 5.0 nm or less. A width of the recess 10B1 of 1.0 nm or more can prevent the antifouling agent from falling off, and a width of 5.0 nm or less provides good scratch resistance. The "width of the recess" refers to the distance between the outer and inner edges of the recess.

[0030] When the depression 10B includes a circular depression 10B2, the lower limit of the diameter of the depression 10B2 is preferably 0.2 μm or more, 0.4 μm or more, 0.6 μm or more, 0.8 μm or more, or 1.0 μm or more, and the upper limit of the diameter is preferably 2.4 μm or less, 2.2 μm or less, or 2.0 μm or less.

[0031] When the depression 10B includes an irregularly shaped depression 10B3, the lower limit of the diameter of the depression 10B3 is preferably 0.2 μm or more, 0.4 μm or more, 0.6 μm or more, 0.8 μm or more, or 1.0 μm or more, and the upper limit of the diameter is preferably 2.4 μm or less, 2.2 μm or less, or 2.0 μm or less.

[0032] In the above, the reason why the test was performed using an eraser is that rubbing with an eraser is similar to rubbing with a touch pen, and the eraser test can evaluate the abrasion resistance against a touch pen. Note that the scratch resistance of an optical film has conventionally been evaluated by a steel wool test in which the surface of the optical film is rubbed with steel wool, but since steel wool is a thin metal wire and is significantly different from a touch pen, the abrasion resistance against a touch pen cannot be evaluated by the steel wool test.

[0033] The eraser test (500g x 4000 strokes) is carried out as follows. First, prepare the eraser to be used in the eraser test. The eraser to be used should have a diameter of 6.0mm, a length of 160mm or less, a durometer hardness (Type A durometer, Type A (cylindrical indenter), JIS K6253:1997 / ISO7619 (Rubber)) of 60 to 90, and be made of rubber. Examples of such erasers include the Mitsubishi Pencil Co., Ltd. pencil with eraser (product name "Office Pencil 9852 (with eraser)") and the Minoan Inc. RUBBER STICK. The eraser may be a standalone eraser or a pencil with an eraser attached. The eraser should be long enough to be able to be attached to a jig. The eraser should have a tensile strength of 11kgf / cm. 2 More than 13kgf / cm 2The following may also be used. In this embodiment, the eraser test is performed using a pencil with an eraser attached as the eraser. After preparing a pencil with an eraser attached (product name "Office Pencil 9852 (with eraser)", manufactured by Mitsubishi Pencil Co., Ltd.), the pencil is cut at a position 50 mm from the tip of the eraser. The cut pencil with an eraser attached is then inserted into a jig with a 6 mm diameter hole from the side opposite the eraser so that the tip of the eraser is completely exposed and attached. Care must be taken not to let the tip of the eraser protrude too far from the jig. Specifically, the pencil with an eraser attached is attached to the jig so that the tip of the eraser is exposed approximately 1.5 mm from the jig. The jig with this pencil with an eraser attached is attached to a Gakushin-type abrasion fastness tester (for example, product name "AB-301", manufactured by Tester Sangyo Co., Ltd.). The jig is attached to the tester so that the pencil with an eraser attached is perpendicular to the test surface (the surface of the optical film). Meanwhile, the optical film 10 before the eraser test was cut into a size of 50 mm x 100 mm to obtain sample S1 as shown in Figure 5. Then, a 20 mm x 40 mm frame-shaped mark M1 was drawn with an oil-based pen on the back surface (resin substrate side) of this sample S1 so that the center of the rubbed area could be easily identified. The mark M1 was drawn so that its longitudinal direction was parallel to the longitudinal direction D2 of the sample S1. Then, this sample S1 was fixed to the test piece stage of a Gakushin-type abrasion fastness tester so that it was wrinkle-free and aligned with the surface of the test piece stage. The sample S1 was placed so that the direction of movement of the test piece stage was the longitudinal direction D2 of the sample S1 and the center of the rubbed area was centered within the mark M1. Then, in this state, the surface 10A of the optical film 10 was rubbed back and forth 4,000 times with an eraser at a load of 500 g and a rubbing speed of 30 mm / sec.

[0034] The depression 10B of sample S1 was confirmed by observation with an atomic force microscope. The depression 10B was observed as follows. Specifically, after the eraser test (500 g × 4000 strokes), three locations within the area marked M1 on sample S1 that were at least visually normal (locations without large foreign objects or scratches) were selected and cut into 5 mm squares to obtain three measurement samples. Separately, several flat, circular metal plates with a diameter of 15 mm and a thickness of 1 mm were prepared, and Nissin EM Co., Ltd.'s double-sided carbon tape was attached to each metal plate. One measurement sample was attached to the tape with the surface of the measurement sample (the surface of the optical film) facing up. To ensure proper adhesion between the tape and the measurement sample, the metal plate with the sample attached was left overnight in a desiccator. After leaving the sample overnight, the metal plate with the sample attached was fixed with a magnet to the measurement stage of an atomic force microscope (product name "WET-9400" manufactured by Shimadzu Corporation). The surface profile was observed using the atomic force microscope in tapping mode with a measurement area of 5 μm square. When observing the depressions, the following points should be noted. First, if the observed image is not clear, increase the contrast as much as possible by adjusting the image on the atomic force microscope (AFM). Furthermore, in the AFM image, height is represented by color shading. That is, darker colors represent areas with lower height, and lighter colors represent areas with higher height. Therefore, when observing depressions, the darker colored areas (e.g., if brown is selected as the color to be stained, the dark brown areas) are the areas to be observed. The scale bar in the lower right corner of the observed image also follows this rule, and the histogram, linked to the scale bar area, represents the distribution of each height. This histogram is automatically displayed by reading the surface profile of the optical film with the AFM.

[0035] The number of dimples 10B is calculated by randomly selecting five locations for each measurement sample, counting the number of dimples 10B present in a 5 μm square area for each of the three measurement samples x 5 locations (a total of 15 locations), and calculating the arithmetic mean value of the number of dimples 10B obtained at the 15 locations. Here, if only some but not all of the annular dimples 10B1 are present within the area, the area is observed, and the outer edges of the dimples 10B1 present within the area are extrapolated to form a circle, as shown by the dotted line in Figure 4. If the area inside the outer edges of the dimples 10B1 present within the area is equal to or greater than half the area of the extrapolated circle, the dimples are counted as dimples 10B1 even if they are only part of the area. If the area of the part of the dimples 10B1 present within the area is less than half the area of the extrapolated circle, they are not counted as dimples 10B1. Furthermore, even if only a part of the circular recess 10B2 is present within the above-mentioned region, it is treated in the same manner as the annular recess 10B1.

[0036] When the depression 10B includes an annular depression 10B1, the outer diameter of the depression 10B1 is determined as follows. First, a 5-μm square region on the surface of the measurement sample S1 is observed with an atomic force microscope. For one depression 10B1, as shown in FIG. 2, a line is drawn from an arbitrary point A on the outer edge of the depression 10B1 to another arbitrary point B on the outer edge of the depression 10B1 so that the line is the longest. The length of the line from point A to point B (outer diameter) is determined. This measurement is then performed at three locations, and the outer diameter of the depression 10B1 is calculated by finding the arithmetic mean of the lengths measured at the three locations. When the depression 10B includes a circular depression 10B2, the diameter is calculated in the same manner as for the annular depression 10B2.

[0037] When the recess 10B includes a recess 10B3 of an irregular shape, the diameter of the recess 10B3 is determined as follows. First, a 5 μm square area on the surface of the measurement sample S1 is observed with an atomic force microscope, and for one recess 10B3, a line L1 is drawn through what is considered to be the center of the recess 10B3, as shown in FIG. 2. Points C1 and D1 where this line L1 intersects with the outer edge of the recess 10B are determined. The distance DS1 between points C1 and D1 is measured, and the midpoint M of the distance DS1 is also determined. A line L2 is then drawn through the midpoint M, at an angle of 60° to the line L1. Points C2 and D2 where this line L2 intersects with the outer edge of the recess 10B are determined, and the distance DS2 between points C2 and D2 is measured. Furthermore, a line L3 is drawn that passes through the midpoint M, forms an angle of 120° with the line L1, and does not overlap with the line L2. Points C3 and D3 where this line L3 intersects with the outer edge of the recess 10B are found, and the distance DS3 between points C3 and D3 is measured. The average value of the distances DS1 to DS3 is then calculated and used as the diameter.

[0038] The "depth of a depression" refers to the distance from a reference position to the deepest position in the depression depth direction D1 (see FIG. 3). The depth of the depression is determined as follows. First, a 5-μm square area on the surface 10A of the optical film 10 is observed with an atomic force microscope. For one depression, the depth from point E to point F is measured along a line extending from point E to point F, as shown in FIG. 2. The deepest depth among the depths extending from point E to point F is then determined. The reference position for the depth is automatically determined by reading the surface shape of the optical film with the atomic force microscope. This measurement is then performed at three locations, and the depth of the depression is calculated by calculating the arithmetic mean value of the three depths measured at the three locations. Note that within the depression 10B, locally deep holes with an aspect ratio of 5 or more may exist. If these holes are taken into account when measuring the depth of the depression 10B, the depth of the depression 10B cannot be accurately determined. Therefore, points E and F are determined so that no locally deep holes exist between points E and F. The lower limit of the depth of the recess 10B may be 3 nm or more, 5 nm or more, or 10 nm or more, and the upper limit is preferably 100 nm or less, since it is preferable that the recess 10B functions but does not become the starting point of microcracks during durability tests and is not visible as a defect when observed macroscopically with the naked eye.

[0039] When observing a 5 μm square (5 μm × 5 μm) area of the surface 10A of the optical film 10 before the eraser test, the optical film 10 may have 1 to 50 depressions 10B within the area, but the depressions 10B do not have to be present. That is, in the optical film 10 before the eraser test, the depressions 10B may or may not appear depending on the components constituting the functional layer 12 and the drying conditions of the functional layer composition used to form the functional layer 12. However, even if the depressions 10B do not exist in the optical film 10 before the eraser test, the depressions 10B potentially exist. Therefore, it is thought that the depressions 10B appear after the eraser test when some component falls off in or on the depressions 10B during the eraser test (500 g × 4000 strokes) or the eraser test (1000 g × 5000 strokes). In the optical film 10 before the eraser test, when a 5 μm square area on the surface 10A of the optical film 10 is observed, three or more or five or more depressions 10B may be present within the area. In this specification, the term "optical film before the eraser test" refers to an optical film in a state that has not been subjected to an eraser test such as the eraser test (500 g × 4000 repetitions) or the eraser test (1000 g × 5000 repetitions) described below. The depressions 10B in the optical film 10 before the eraser test are confirmed by the same method as the depressions 10B in the optical film 10 after the eraser test (500 g × 4000 repetitions).

[0040] Furthermore, in the optical film 10, an eraser test is performed using an atomic force microscope (AFM) (for example, product name "WET-9100" manufactured by Shimadzu Corporation) in which an eraser is rubbed back and forth 5000 times with a load of 1000 g on the surface 10A of the optical film 10 (hereinafter, this test is referred to as the eraser test (1000 g × 5000 rubs)). After this test, when a 5 μm square (5 μm × 5 μm) area on the surface 10A of the optical film 10 is observed, it is preferable that there are 1 to 50 recesses 10B within the area, each having an outer diameter of 0.5 μm to 2.5 μm and a depth of 1 nm to 150 nm, a circular diameter of 0.5 μm to 2.5 μm and a depth of 1 nm to 150 nm, or an irregularly shaped recess 10B having a diameter of 0.5 μm to 2.5 μm and a depth of 1 nm to 150 nm. To evaluate scratch resistance and abrasion resistance, an eraser test (500g x 4000 strokes) is usually sufficient, but nowadays, evaluation under stricter conditions is required, assuming people who press the touch pen hard and rub it frequently. For this reason, an eraser test (1000g x 5000 strokes) is used. The depressions 10B in the optical film 10 after the eraser test (1000g x 5000 strokes) are confirmed using the same method as the depressions 10B in the optical film 10 after the eraser test (500g x 4000 strokes).

[0041] It is preferable that protrusions 10C with a height of 1 nm or more are present inside or within the depressions 10B. The presence of such protrusions 10C inside or within the depressions 10B can further improve the contact angle maintenance rate, which will be described below. The protrusions 10C can be confirmed by observation using an atomic force microscope (AFM) (for example, product name "WET-9100" manufactured by Shimadzu Corporation). The height of the protrusions 10C is calculated by measuring the height of the tallest protrusion 10C among the protrusions 10C confirmed by observation. Specifically, the height of the protrusions 10C is determined as follows. First, a 5 μm square region of the surface 10A of the optical film 10 is observed with an atomic force microscope, and the height from point E to point F of one protrusion 10C is measured along the line drawn from point E to point F as shown in FIG. 4 . Then, the tallest height among the heights from point E to point F is determined. The reference position for the height is automatically determined by reading the surface shape of the optical film with an atomic force microscope.

[0042] Using an atomic force microscope (e.g., product name "AFM-5500" manufactured by Hitachi Technologies, Inc.), the absolute value of the difference between the average arithmetic height (Sa) of a 5 μm square area on the surface 10A of the optical film 10 before the eraser test and the average arithmetic height (Sa) of a 5 μm square area on the surface 10A of the optical film 10 after the eraser test (1000 g × 5000 strokes) is preferably 10 nm or less. If it is 10 nm or less, it is believed that the areas that can provide slip and the areas that can provide hardness remain to a degree that allows them to function in a balanced manner, maintaining good physical properties. The absolute value of the difference in arithmetic mean height (Sa) before and after the eraser test (1000 g × 5000 strokes) was used because the eraser test conducted at a load of 1000 g is a severe test, causing the surface of the optical film to become rough after the eraser test. Unlike the eraser test conducted at a load of 500 g, the depressions themselves often become distorted, making it difficult to determine the characteristics of the depressions themselves. The lower limit of the absolute value of this difference is preferably 0.005 nm or more, and more preferably 0.001 nm or more. Considering abrasion resistance and scratch resistance, it is considered better for Sa to remain unchanged. However, if the film quality remains unchanged, it will be difficult to absorb various external impacts, may be prone to microcracks, and may make it difficult to achieve good foldability. For this reason, the upper limit of Sa is preferably 7 nm or less, 5 nm or less, or 3 nm or less. The definition of Sa follows ISO 25178. Sa is a parameter that expands the two-dimensional arithmetic mean roughness Ra into three dimensions (see Figure 6). It represents the average absolute value of the height Z(x, y) in the measurement area (A). In a three-dimensional display, it corresponds to the arithmetic mean of the measurement area with the valleys converted to peaks by absolute value conversion. Note that the two-dimensional dimension does not refer to a plane. For example, if a plane is represented by x and y and height by z, two dimensions are represented by a line and height, that is, x and z or y and z, and three dimensions are represented by a surface and height, that is, x, y and z. Specifically, Sa can be calculated by the following formula (1) where A is the area of the measurement target region.

number

[0043] The arithmetic mean height (Sa) is calculated using an atomic force microscope (e.g., product name "AFM-5500" manufactured by Hitachi Technologies, Ltd.) as follows. Specifically, first, a 50 mm x 100 mm sample of the optical film before the eraser test is cut to obtain a sample similar to sample S1. Three locations that are at least visually normal (areas without large foreign objects or scratches) are randomly selected from this sample and cut into 5 mm squares to obtain three measurement samples. On the other hand, several flat, circular metal plates with a diameter of 15 mm and a thickness of 1 mm are prepared, and double-sided carbon tape manufactured by Nissin EM Co., Ltd. is attached to each metal plate. One measurement sample is attached to the tape with the surface of the measurement sample (the surface of the optical film) facing up. To ensure proper adhesion between the tape and the measurement sample, the metal plate with the sample attached is left in a desiccator overnight. After leaving the sample overnight, the metal plate with the sample attached was placed on the measurement stage of an atomic force microscope (product name "AFM-5500," manufactured by Hitachi Technologies, Inc.). The surface profile was observed using the atomic force microscope in tapping mode with a measurement area of 5 μm square. The observed data was then used to calculate Sa using the atomic force microscope's built-in surface analysis software. The vertical scale during surface analysis was 20 nm. Observations were performed at room temperature, and an Olympus SI-DF40P2 cantilever was used. Furthermore, for each measurement sample, five locations were randomly selected, and the surface profile was observed for each of the five locations (three measurement samples x 5 locations) (15 points in total). Sa was then calculated for all 15 data points using the atomic force microscope's built-in surface analysis software, and the arithmetic mean value of the 15 points was used as the Sa of the measurement sample. The arithmetic mean height (Sa) of the optical film after the eraser test (1000 g x 5000 strokes) was also measured using the same method as for the optical film before the eraser test.

[0044] The arithmetic mean height (Sa) of a 5 μm square region on the surface 10A of the optical film 10 before the eraser test may be 10 nm or less. The upper limit of Sa may be 7 nm or less, 4 nm or less, 1 nm or less, or 0.8 nm or less. By setting the upper limit of Sa, high transparency and low haze can be obtained even if the above-mentioned depressions are present or if depressions appear after the eraser test. Furthermore, it is believed that this upper limit is responsible for the depressions that result in desirable film quality after the eraser test. If this limit is exceeded, it becomes difficult to control the film quality, and desirable physical properties may not be obtained. Furthermore, the lower limit of Sa may be 0.01 nm or more or 0.05 nm or more, since optical films are likely to be stacked when manufactured in rolls or sheets, and from the viewpoint of preventing films from sticking together during this process.

[0045] The arithmetic mean height (Sa) of a 5 μm square region on the surface 10A of the optical film 10 after the eraser test (1000 g × 5000 reciprocating strokes) may be 7±0.005 nm or less. This is because, as described above, a slight change in the Sa value before and after the eraser test (1000 g × 5000 reciprocating strokes) is better than no change at all. The amount of change may increase or decrease. The upper limit of Sa may be 6 nm or less, 5 nm or less, or 3 nm or less. The lower limit of Sa may be 0.01 nm or more or 0.05 nm or more, from the viewpoint of preventing the films from sticking together when the optical film is produced in rolls or sheets, and from the viewpoint of obtaining a surface 10A having the above-mentioned preferable recessed shape.

[0046] The dynamic friction coefficient (500g load or 1000g load) of the surface 10A of the optical film 10 before the eraser test is 0.70 or less. If the dynamic friction coefficient (500g load or 1000g load) is 0.70 or less, good initial slippage can be obtained, resulting in good scratch resistance and abrasion resistance. When produced using a roll, an extremely low dynamic friction coefficient can cause excessive slippage during winding, which can lead to slippage during winding. Therefore, the lower limit of the dynamic friction coefficient (500g load or 1000g load) is preferably 0.20 or more, and more preferably 0.25 or more. The upper limit of the dynamic friction coefficient (500g load or 1000g load) is preferably 0.65 or less, or 0.60 or less. Such dynamic friction coefficients (500g load or 1000g load) can be obtained, for example, by incorporating a lubricant and an antifouling agent into the functional layer 12, or, even if no lubricant is included, by incorporating multiple types of antifouling agents rather than a single type, or by incorporating an antifouling agent containing multiple elements. On the other hand, if only one type of material is incorporated, such as when the functional layer contains a lubricant without an antifouling agent, when the functional layer contains an antifouling agent without a lubricant, or when only one type of antifouling agent is included, the dynamic friction coefficients (500g load or 1000g load) do not decrease significantly, and such dynamic friction coefficients cannot be obtained. The optical film of the present invention exhibits depressions after an eraser test, and also has areas without depressions. Thus, a surface with a certain degree of unevenness is likely to reduce the dynamic friction coefficient (500g load or 1000g load), which is considered to be effective for scratch resistance and abrasion resistance.

[0047] The dynamic friction coefficient can be measured using a dynamic friction and wear tester (for example, the product name "Handy Tribomaster Type: TL201Ts" manufactured by Trinity Lab Co., Ltd.) as follows. This tester can perform a simulated eraser test and measure the dynamic friction coefficient in real time. Therefore, the eraser test for measuring the dynamic friction coefficient is not performed using a Gakushin-type abrasion fastness tester. The dynamic friction coefficient of the surface 10A of the optical film 10 before the eraser test is the dynamic friction coefficient at the first stroke in the eraser simulation test described below. The dynamic friction coefficient (load 500 g) of the surface 10A of the optical film 10 after the eraser test (500 g × 4000 strokes) is the dynamic friction coefficient at the 4000th stroke in the eraser simulation test. The dynamic friction coefficient (load 1000 g) of the surface 10A of the optical film 10 after the eraser test (1000 g × 5000 strokes) is the dynamic friction coefficient at the 5000th stroke in the eraser simulation test.

[0048] Specifically, first, an eraser is prepared. The eraser used to measure the coefficient of dynamic friction is the same as the eraser used in the eraser test (500 g × 4000 strokes). In this embodiment, the eraser test is performed using a pencil with an eraser attached. After preparing a pencil with an eraser (product name "Office Pencil 9852 (with eraser)" manufactured by Mitsubishi Pencil Co., Ltd.), the pencil is cut 50 mm from the tip of the eraser. Then, as in the eraser test (500 g × 4000 strokes), the cut pencil with an eraser attached is attached to a jig with a 6 mm diameter hole on the side opposite the eraser. Then, the jig with the eraser attached pencil is fixed to the shaft of the measurement unit of the dynamic friction and wear tester with double-sided tape. In this state, dedicated software (triboanalysis software) is launched on the screen of a personal computer (PC) electrically connected to the dynamic friction and wear tester. Meanwhile, the optical film 10 before the eraser test is cut into pieces measuring 50 mm × 100 mm to obtain six samples S1. Of the six samples S1, three samples S1 were used to measure the dynamic friction coefficient (500 g load) before the eraser test and after the eraser test (500 g × 4000 strokes), while the remaining three samples S1 were used to measure the dynamic friction coefficient (1000 g load) before the eraser test and after the eraser test (1000 g × 5000 strokes). Then, as shown in Figure 5, a 20 mm × 40 mm frame-shaped mark M1 was drawn with an oil-based pen on the back surface (resin substrate side) of each sample S1 to easily identify the center of the rubbing area. The mark M1 was drawn so that its longitudinal direction was parallel to the longitudinal direction D2 of the sample S1. Then, the surface to be measured for the dynamic friction coefficient was placed on the drive unit of the dynamic friction and wear tester, with the surface facing up, and the four edges of the sample S1 were fixed with Scotch tape (registered trademark) so that there were no wrinkles and they were aligned with the surface of the drive unit. The sample S1 is placed so that the direction of movement of the drive unit is the longitudinal direction D2 of the sample S1 and the center of the rubbing area is the center of the mark M1. A 500g weight is fixed to the top surface of the jig with double-sided tape, and the eraser of the measurement unit is brought into contact with the surface of the sample S1 perpendicularly.Then, set the rubbing length (one way) to 20 mm, the rubbing speed to 40 strokes / min, the number of strokes to 4000, and the measurement mode to continuous measurement. Press the start switch on the PC screen to begin measuring the kinetic friction coefficient of sample S1 under an environment with a temperature of 23±5°C and a relative humidity of 30% to 70%. This will perform an eraser simulation test (500g x 4000 strokes) that simulates the eraser test (500g x 4000 strokes). During the eraser simulation test, frictional force is continuously measured, and a graph is obtained with time on the horizontal axis and frictional force at that time on the vertical axis. The kinetic friction coefficient at each stroke is calculated by dividing the frictional force at the time reaching that stroke by the normal force. The normal force is the load applied to the eraser. The dynamic friction coefficient (500g load) of the surface 10A of the optical film 10 before and after the eraser test (500g x 4000 strokes) was measured for three samples S1, and the arithmetic mean value of the values obtained for the three samples was used. Similarly, the remaining three samples were used to perform a similar eraser test before and after the eraser test (1000g x 5000 strokes), and the dynamic friction coefficient was measured. In this case, the weight was changed from 500g to 1000g, and the number of strokes was set to 5000. The dynamic friction coefficient (1000g load) of the surface 10A of the optical film 10 after the eraser test (1000g x 5000 strokes) was measured for the remaining three samples S1, and the arithmetic mean value of the values obtained for the three samples was used. After each measurement, adjust the distance of the eraser exposed from the jig to about 1.5 mm (for example, 1 mm to 2 mm).

[0049] The rate of change in the dynamic friction coefficient (500 g load) of the surface 10A of the optical film 10 after the eraser test (500 g x 4000 strokes) relative to the dynamic friction coefficient (500 g load) of the surface 10A of the optical film 10 before the eraser test is within 35%. If this rate of change is within 35%, the surface can maintain its slipperiness even after 4000 strokes with an eraser, thereby achieving excellent scratch resistance and abrasion resistance, and also maintaining the antifouling properties important for use on the surface of an image display device. The dynamic friction coefficient, rather than the static friction coefficient, is measured here because it is believed that this allows for evaluation of the condition of the surface 10A of the optical film 10 during the eraser test. This rate of change is more preferably within 20%, and most preferably within 15%. Furthermore, in an eraser simulation test in which an eraser is used to rub the surface of the optical film 1000, 2000, 3000, 4000, or 5000 times with a load of 500 g, it is preferable that the rate of change in the dynamic friction coefficient (500 g load) of surface 10A of optical film 10 after each eraser simulation test relative to the dynamic friction coefficient (500 g load) of surface 10A of optical film 10 before the eraser test is within 35%.

[0050] The rate of change in the dynamic friction coefficient (1000 g load) of surface 10A of optical film 10 after the eraser test (1000 g x 5000 reciprocations) relative to the dynamic friction coefficient (1000 g load) of surface 10A before the eraser test is within 35%. If this rate of change is within 35%, slipperiness can be maintained even after 5000 reciprocations with an eraser, resulting in excellent scratch resistance and abrasion resistance, and also maintaining antifouling properties, which are important when used on the surface of an image display device. This rate of change is more preferably within 20%, and most preferably within 15%. Furthermore, in an eraser simulation test in which an eraser is used to rub the surface of the optical film 1000, 2000, 3000, 4000, or 5000 times with a load of 1000 g, it is preferable that the rate of change in the dynamic friction coefficient (1000 g load) of surface 10A of optical film 10 after each eraser test relative to the dynamic friction coefficient (1000 g load) of surface 10A of optical film 10 before the eraser test is within 35%.

[0051] The rate of change is calculated by the following formula (2), where A is the rate of change, B is the dynamic friction coefficient of the surface of the optical film before the eraser test, and C is the dynamic friction coefficient of the surface of the optical film after the eraser test. Note that the rate of change A is an absolute value. A = |{(CB) / B} × 100| …(2)

[0052] The dynamic friction coefficient (500 g load) of the surface 10A of the optical film 10 after the eraser test (500 g × 4000 strokes) may be lower than the dynamic friction coefficient (500 g load) of the surface 10A of the optical film 10 before the eraser test. When the dynamic friction coefficient (500 g load) of the surface 10A of the optical film 10 satisfies this relationship, the surface 10A of the optical film 10 is more slippery after the eraser test (500 g × 4000 strokes) than before the eraser test, and therefore the optical film 10 after the eraser test (500 g × 4000 strokes) can achieve better scratch resistance and better wear resistance. Furthermore, when comparing the dynamic friction coefficient (500 g load) before the eraser test and the dynamic friction coefficient (500 g load) after 1000 strokes, the smaller the absolute difference, the better. A smaller difference means excellent wear resistance from the beginning. Such a functional layer 12 is considered to have a film quality in which functions such as smoothness and hardness are well separated even before the eraser test. The dynamic friction coefficient (500 g load) after the eraser test (500 g × 4000 strokes) is preferably 0.70 or less, 0.65 or less, or 0.60 or less. When manufacturing using a roll, if the dynamic friction coefficient is too low, the film may slip during winding due to excessive slippage. Therefore, the lower limit of the dynamic friction coefficient (500 g load) after the eraser test (500 g × 4000 strokes) is preferably 0.2 or more, and more preferably 0.25 or more. Such a dynamic friction coefficient (500 g load) can be achieved, for example, by incorporating a lubricant and an antifouling agent into the functional layer 12. Even if the functional layer 12 does not contain a lubricant, it can be achieved by incorporating multiple types of antifouling agents rather than a single type, or by incorporating an antifouling agent containing multiple elements.

[0053] The dynamic friction coefficient (1000 g load) of the surface 10A of the optical film 10 after the eraser test (1000 g × 5000 strokes) may be lower than the dynamic friction coefficient (1000 g load) of the surface 10A of the optical film 10 before the eraser test. When the dynamic friction coefficient of the surface 10A of the optical film 10 satisfies this relationship, the surface 10A of the optical film 10 is more slippery after the eraser test (1000 g × 5000 strokes) than before the eraser test, thereby achieving better scratch resistance and better wear resistance in the optical film 10 after the eraser test (1000 g × 5000 strokes). Furthermore, when comparing the dynamic friction coefficient (1000 g load) before the eraser test and the dynamic friction coefficient (1000 g load) after 1000 strokes, the smaller the absolute difference, the better. A smaller difference means excellent wear resistance from the beginning. Such a functional layer 12 is considered to have a film quality in which functions such as smoothness and hardness are well separated even before the eraser test. The dynamic friction coefficient (1000 g load) after the eraser test (1000 g × 5000 strokes) is preferably 0.65 or less, 0.60 or less, or 0.55 or less. When manufacturing using a roll, an extremely low dynamic friction coefficient can cause excessive slippage during winding, so the lower limit of the dynamic friction coefficient (1000 g load) after the eraser test (1000 g × 5000 strokes) is preferably 0.20 or more, and more preferably 0.25 or more. Such a dynamic friction coefficient (1000 g load) can be achieved by incorporating a lubricant and an antifouling agent into the functional layer 12, or, even if no lubricant is included, by incorporating a mixture of multiple types of antifouling agents rather than a single type, or by incorporating an antifouling agent containing multiple elements.

[0054] When an eraser test (500 g × 4000 reciprocating strokes) is performed on the optical film 10, the contact angle retention rate, which is the ratio of the contact angle with water on the surface 10A of the optical film 10 after the eraser test (500 g × 4000 reciprocating strokes) to the contact angle with water on the surface 10A of the optical film 10 before the eraser test, is preferably 80% or more. If the contact angle retention rate is 80% or more, most of the antifouling agent remains on the surface 10A of the optical film 10 without being scraped off by the eraser test, that is, depressions appear in a balanced manner relative to areas without depressions after the eraser test (500 g × 4000 reciprocating strokes), and therefore the optical film 10 can be determined to have excellent abrasion resistance and can also obtain excellent antifouling properties.

[0055] Furthermore, when an eraser test (1000g x 5000 reciprocations) is performed, the contact angle maintenance rate, which is the ratio of the contact angle of water on surface 10A of optical film 10 after the eraser test (1000g x 5000 reciprocations) to the contact angle of water on surface 10A of optical film 10 before the eraser test, is more preferably 80% or more. If the contact angle maintenance rate is 80% or more, optical film 10 can be determined to have better abrasion resistance and can also obtain better antifouling properties.

[0056] The contact angles with water are measured using a microscope contact angle meter (for example, product name "DropMaster300" manufactured by Kyowa Interface Science Co., Ltd.) according to the sessile drop method described in JIS R3257:1999. Specifically, a measurement sample is first obtained by cutting a piece of 30 mm x 50 mm from the sample S1 before the eraser test. The measurement sample is cut so as to include a 20 mm x 40 mm frame-shaped mark M1. The measurement sample is then attached flat to a 25 mm x 75 mm glass slide with double-sided tape. The measurement sample is attached so that the frame fits within the glass slide. To attach the measurement sample flat, it is recommended to use double-sided tape that is larger than the frame. The frame is also attached so that it fits within the glass slide. In other words, the cross section of the measurement sample is in the form of glass slide / double-sided tape / measurement sample. To prevent static electricity from affecting the measurement results, the sample is then de-ionized for 30 seconds by irradiating it with ions using an ionizer (e.g., product name "KD-730B" manufactured by Kasuga Electric Co., Ltd.). After de-ionization, 1 μL of water is dropped onto the surface of the functional layer using a syringe and held there for 5 seconds. The contact angle with water is then measured by pressing the switch on the microscope contact angle meter. The contact angle is measured in an environment with a temperature of 23±5°C and a relative humidity of 30% to 70%. The contact angle is measured at 10 points, and the arithmetic average of these measurements is used as the contact angle of the optical film surface before the eraser test. The contact angle of water on the surface of the optical film after the eraser test (500 g × 4000 reciprocating strokes) is measured by a method similar to that for measuring the contact angle of water on the surface of the optical film before the eraser test, except that sample S1 after the eraser test (500 g × 4000 reciprocating strokes) is used, and the contact angle of water on the surface of the optical film after the eraser test (1000 g × 5000 reciprocating strokes) is measured by a method similar to that for measuring the contact angle of water on the surface of the optical film before the eraser test, except that sample S1 after the eraser test (1000 g × 5000 reciprocating strokes) is used.

[0057] The contact angle maintenance rate is calculated by the following formula (3), where D (%) is the contact angle maintenance rate, E is the contact angle of water on the surface of the optical film before the eraser test, and F is the contact angle of water on the surface of the optical film after the eraser test. D=F / E×100 …(3)

[0058] The contact angle of water on the surface 10A of the optical film 10 before the eraser test is preferably 100° or more. If this contact angle is 100° or more, the optical film 10 has sufficient anti-fouling properties, can suppress the adhesion of fingerprints and dirt, and even if fingerprints or dirt do adhere, they can be easily wiped off. The lower limit of the contact angle of water on the surface 10A of the optical film 10 is more preferably 95° or more, and the upper limit is preferably 120° or less.

[0059] For the optical film 10, steel wool was used at 1 kg / cm 2 It is preferable that no scratches are found on the surface 10A of the optical film 10 when a steel wool test is performed in which the surface 10A (surface 12A of the functional layer 12) of the optical film 10 before the eraser test is rubbed back and forth 5,000 times while applying a load of 1 kg / cm. The steel wool test is performed as follows. First, the optical film 10 before the eraser test is cut into a size of 50 mm x 100 mm to obtain a sample. Then, the sample is fixed flat on the test piece stage of a Gakushin-type abrasion fastness tester (for example, product name "AB-301" manufactured by Tester Sangyo Co., Ltd.) so that the surface of the sample (the surface of the optical film) faces up, without wrinkles or curls. Then, steel wool #0000 (manufactured by Nippon Steel Wool Co., Ltd., product name "Bonstar B-204") is set in the tester and brought into contact with the surface of the sample, and a load of 1 kg / cm is applied at a movement speed of 100 mm / sec, a movement distance of 200 mm per reciprocation (one-way movement distance 100 mm). 2 The steel wool is rubbed back and forth 5000 times while applying a pressure of 1000 kJ / cm. The contact area between the steel wool and the sample surface is 1 cm. 2Unless otherwise specified, the test environment is a temperature of 23±5°C and a relative humidity of 30% to 70%. The Bonstar B-204 mentioned above is a commercial size with a width of approximately 390mm, length of approximately 75mm, and thickness of approximately 110mm. An appropriate amount is torn off from this and rolled up evenly (do not cut with a blade as cutting will expose the cross section of the steel wool fibers) until there are no unusual protruding parts of the steel wool. Then, when a load of 1kg is applied, the contact area is 1cm2. 2 The thickness of the steel wool is set to 20 mm at this time. The sample is then observed with the naked eye under fluorescent lighting (illuminance on the sample: 800-1200 Lx, observation distance: 30 cm) and under LED lighting (illuminance on the sample: 4000-6000 Lx, observation distance: 30 cm) to see if any scratches are visible.

[0060] The surface 10A of the optical film 10 before the eraser test preferably has a hardness (pencil hardness) of 3H or more, more preferably 6H, and even more preferably 7H or more, as measured by the pencil hardness test specified in JIS K5600-5-4:1999. The pencil hardness test is performed as follows. First, the optical film before the eraser test is cut into a size of 50 mm x 100 mm to obtain a sample. Then, this sample is fixed with the functional layer facing up on a glass plate using Cellotape (registered trademark) manufactured by Nichiban Co., Ltd., so as not to be bent or wrinkled. Next, a load of 500 g is applied to the pencil, and the pencil is moved at a scratching speed of 1 mm / sec. The pencil hardness is defined as the highest hardness that does not scratch the surface of the sample in the pencil hardness test. When measuring pencil hardness, multiple pencils with different hardnesses are used, and the pencil hardness test is performed five times for each pencil. If the sample surface is not scratched four or more times out of the five, it is determined that the pencil of that hardness did not scratch the sample surface. The above scratches refer to those visible when the surface of the sample that has undergone the pencil hardness test is observed through transmission under fluorescent light.

[0061] It is preferable that the optical film 10 does not crack or break even when a folding test (folding test) is repeatedly performed 100,000 times, 200,000 times, 500,000 times, or 1,000,000 times in an environment with a temperature of 23±5°C and a relative humidity of 30% to 70%, in which the optical film 10 is folded 180° so that the distance φ between opposing sides of the optical film 10 is 2 mm and the functional layer 12 is on the inside. If the optical film 10 cracks or breaks when the folding test is repeated 100,000 times, the foldability of the optical film 10 is insufficient. Note that the greater the number of folding times, the more likely the optical film is to crack or break. Therefore, there is a significant technical difference between an optical film that does not crack or break after the folding test with 200,000, 300,000, 500,000, or 1,000,000 times and an optical film that does not crack or break after the folding test with 100,000 times. The folding test is evaluated at a minimum of 100,000 folding times for the following reason. For example, if the optical film is incorporated into a foldable smartphone, the frequency of folding (opening and closing) will be extremely high. Therefore, an evaluation of the folding test with a folding number of, for example, 10,000 or 50,000 times may not be practical. Specifically, for example, assuming a person who regularly uses a smartphone, it is expected that the smartphone will be opened and closed 5 to 10 times just during the morning commute on a train or bus, and therefore the smartphone will be opened and closed at least 30 times per day. Therefore, assuming that a smartphone is opened and closed 30 times per day, a folding test with 10,000 folding times would be 30 times × 365 days = 10,950 folding times, which is a test assuming one year of use. In other words, even if the results of a folding test with 10,000 folding times are good, the optical film may crack or break after one year has passed. Therefore, an evaluation of 10,000 folds in a folding test only confirms a level at which the product cannot be used as a product, and products that are usable but not sufficient are also classified as good and cannot be evaluated.Therefore, to evaluate whether or not the optical film 10 is at a practical level, the folding test must be performed with at least 100,000 folding cycles. It is more preferable that the optical film 10 does not crack or break even when the optical film 10 is folded 100,000 times so that the distance φ between the opposing sides of the optical film 10 is 3 mm and the functional layer 12 is on the outside.

[0062] The folding test is conducted with the distance φ between the opposing sides of optical film 10 set to 2 mm, but from the viewpoint of reducing the thickness of image display devices, it is more preferable that the distance φ between the opposing sides of optical film 10 be set to a narrower range, specifically 1 mm, so that no cracks or breaks occur even when the folding test is conducted by folding the film 10 by 180° 100,000 times. Note that even when the number of foldings is the same, the narrower the distance φ, the more difficult it becomes to prevent cracks or breaks. Therefore, no cracks or breaks occur in an optical film after a folding test with the distance φ set to 1 mm, and no cracks or breaks occur in an optical film after a folding test with the distance φ set to 2 mm.

[0063] When conducting the folding test, first, a sample S2 of a predetermined size (for example, a rectangular shape of 125 mm x 50 mm) is cut out from any location of the optical film 10 before the folding test (see FIG. 8). If it is not possible to cut out a sample of 125 mm x 50 mm, any size that allows for the various evaluations to be performed after the folding test, as described below, may be used; for example, a rectangular sample of 80 mm x 25 mm may be cut out. After cutting out the sample S2 from the optical film 10 before the folding test, the folding test is performed on the sample S2.

[0064] The folding test is performed as follows. As shown in FIG. 7A, in the folding test, first, side S2a of sample S2 and side S2b opposite side S2a are fixed by fixing parts 15 of a parallel-arranged folding endurance tester (for example, a "U-shaped extension / contraction tester DLDMLH-FS" manufactured by Yuasa System Co., Ltd., conforming to IEC 62715-6-1). Fixation by fixing parts 15 is performed by holding a portion of sample S2 of approximately 10 mm on one side in the longitudinal direction of sample S2. However, if sample S2 is smaller than the above size, measurement is possible by attaching it to fixing part 15 with tape as long as the portion of sample S2 required for this fixation is up to approximately 20 mm (i.e., the minimum sample is 60 mm × 25 mm). Furthermore, as shown in FIG. 7A, fixing part 15 is slidable horizontally. The above-described device is preferable because it allows evaluation of durability against bending load without generating tension or friction in the sample, unlike conventional methods such as winding a sample around a rod.

[0065] Next, as shown in Figure 7(B), the fixing portions 15 are moved closer to each other, thereby deforming the central portion S2c of the sample S2 in a folding manner, and then, as shown in Figure 7(C), the fixing portions 15 are moved to a position where the distance φ between the two opposing side portions S2a, S2b of the sample S2 fixed by the fixing portions 15 is 2 mm, and then the fixing portions 15 are moved in the opposite direction to eliminate the deformation of the sample S2.

[0066] As shown in Figures 7(A) to 7(C), sample S2 can be folded 180° at the center portion S2c by moving the fixing portion 15. Furthermore, by ensuring that the bent portion S2d of sample S2 does not protrude from the lower end of the fixing portion 15, conducting the folding test under the following conditions, and controlling the distance between the fixing portions 25 to 2 mm when they are closest, the distance φ between the two opposing sides S2a and S2b of sample S2 can be set to 2 mm. In this case, the outer diameter of the bent portion S2d is considered to be 2 mm. Note that because the thickness of sample S2 is sufficiently small compared to the distance between the fixing portions 25 (2 mm), the results of the folding test of sample S2 can be considered unaffected by differences in the thickness of sample S2. (Folding conditions) Reciprocating speed: 80 rpm (revolutions per minute) Test stroke: 60mm Flexion angle: 180°

[0067] When the folding test is performed on sample S2, even if no cracks or breaks occur in sample S2 after the folding test, creases and microcracks may form at the bent portions, potentially resulting in poor appearance, specifically, cloudiness or delamination (poor adhesion) originating from the microcracks. One possible cause of cloudiness is a change in the crystalline state of the organic compound that constitutes one of the layers of the optical film. If localized poor adhesion occurs, changes in temperature and humidity can cause moisture to accumulate at the delamination or air to enter the delamination, potentially increasing the cloudiness. In recent years, displays have become more diverse, incorporating foldable, curved, and three-dimensional designs, rather than simply flat displays. Therefore, preventing creases and microcracks at the bent portions is extremely important for use as image display devices. For these reasons, it is preferable that the optical film 10 be flexible. In this specification, "flexibility" refers not only to the absence of cracks or breaks after the folding test, but also to the absence of creases and microcracks. Therefore, the "flexibility" in this specification is different from the flexibility that simply requires that no cracks or breaks occur after the folding test.

[0068] The observation of fold creases is to be carried out visually, but when observing fold creases, the bend should be observed thoroughly using transmitted and reflected light in a bright room with white lighting (800 lux to 2000 lux), and both the inside and outside of the bend should be observed. The observation of fold creases should be carried out in an environment with a temperature of 23±5°C and a relative humidity of 30% to 70%.

[0069] The microcracks are observed using a digital microscope. An example of a digital microscope is the VHX-5000 manufactured by Keyence Corporation. Microcracks are observed using a ring light as the digital microscope's illumination, and in dark field and reflected light. Specifically, the sample after the folding test is first slowly unfolded and fixed to the microscope stage with tape. If the fold is severe, the area to be observed is made as flat as possible. However, the area to be observed near the center of the sample (the bent portion) is not touched with the hands, and no force is applied. Both the inside and outside portions of the sample that will be folded are then observed. The microcrack observation is performed in an environment with a temperature of 23±5°C and a relative humidity of 30% to 70%.

[0070] In observing the fold creases and microcracks, to easily identify the positions to be observed, the sample before the folding test is placed on a fixed portion of a durability tester, and when folded once, marks M2 indicating the bent portion can be made with an oil-based pen or the like on both ends S2d1 of the bent portion S2d that are located in a direction perpendicular to the folding direction D3, as shown in Figure 8. Furthermore, in the case of a sample in which no fold creases or the like are observed after the folding test, a line M3 (dotted line in Figure 8) connecting the marks M2 on both ends S2d1 of the bent portion S2d can be drawn with an oil-based pen or the like after the sample is removed from the durability tester after the folding test to prevent the observation position from becoming unclear. Then, in observing the fold creases, the entire bent portion S2d, which is the area formed by the marks M2 on both ends S2d1 of the bent portion S2d and the line M3 connecting these marks M2, is visually observed. When observing microcracks, the microscope is positioned so that the center of the microscope field of view (the area surrounded by the two-dot chain line in Figure 8) is at the center of the bend S2d. Note that care should be taken not to mark the sample area required for actual measurement with an oil-based pen or the like.

[0071] Furthermore, when the folding test is performed on sample S2, there is a risk that the adhesion between the resin substrate and the functional layer may be reduced. Therefore, when the vicinity of the interface between the resin substrate 11 and the functional layer 12 at the bent portion of the optical film after the folding test is observed with a digital microscope, it is preferable that no peeling or the like is observed near the interface between the resin substrate 11 and the functional layer 12. An example of a digital microscope is the VHX-5000 manufactured by Keyence Corporation.

[0072] Before the eraser test, the optical film 10 is preferably wrapped around a cylinder with the functional layer 12 facing outward in a mandrel test (a test in which a sample is wrapped around a metal cylinder of 2 mm to 32 mm) described in JIS K5600-5-1:1999. The minimum diameter of the cylinder where no cracks occur is preferably 20 mm or less. This measurement is performed three times, and the smallest diameter of the three minimum diameters is defined as the minimum diameter.

[0073] If another film, such as a polarizing plate, is provided on one side of the optical film 10 via a pressure-sensitive adhesive layer or adhesive layer, the pressure-sensitive adhesive layer and the other film are peeled off together using the same method as above, and then the folding test and mandrel test are performed. Peeling of the other film can be performed, for example, as follows: First, a laminate in which the other film is attached to the optical film via a pressure-sensitive adhesive layer or adhesive layer is heated with a dryer, and the blade of a cutter is inserted into the area believed to be the interface between the optical film and the other film, and the films are slowly peeled off. By repeating this heating and peeling process, the pressure-sensitive adhesive layer, adhesive layer, and other film can be peeled off. Note that even if such a peeling process is performed, it does not significantly affect the mandrel test.

[0074] The total light transmittance of the optical film 10 before the eraser test is preferably 90% or more. If the total light transmittance of the optical film 10 is less than 90%, the optical performance may be insufficient. The total light transmittance can be measured using a haze meter (e.g., product name "HM-150" manufactured by Murakami Color Research Laboratory) in accordance with JIS K7361-1:1997. The total light transmittance is measured by cutting the optical film 10 before the eraser test into a sample measuring 50 mm x 100 mm. The total light transmittance is then measured three times for this sample, and the arithmetic mean value of the values obtained is used. The total light transmittance of the optical film 10 is more preferably 91% or more, and even more preferably 92% or more.

[0075] The total light transmittance can be measured using a haze meter (e.g., product name "HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd.) according to a method conforming to JIS K7361-1:1997. The optical film is cut into 50 mm x 100 mm pieces, and the pieces are placed in a state free of curls, wrinkles, fingerprints, dust, etc., and each sample is measured three times. The total light transmittance is then calculated as the arithmetic mean of the three measurements. In this specification, "measured three times" does not mean measuring the same location three times, but rather measuring three different locations. In the optical film 10, the visually observed surface 10A is flat, and the layers to be laminated, such as the functional layer 12, are also flat, with film thickness variations within a range of ±10%. Therefore, measuring the total light transmittance at three different locations on the cut sample is believed to provide an approximate average value for the total light transmittance throughout the entire in-plane area of the optical film. The variation in total light transmittance is within ±10%, even when the measurement object is as long as 1m x 3000m, or the size of a 5-inch smartphone. If the optical film cannot be cut to the above size, it can be cut to an appropriate size of 22mm x 22mm or larger. If the optical film is small, three measurement points are used by shifting the light source spot slightly or by changing the angle, as long as the light source spot does not shift.

[0076] Furthermore, when another film such as a polarizing plate is provided on the optical film 10 via a pressure-sensitive adhesive layer or an adhesive layer, the pressure-sensitive adhesive layer or the adhesive layer and the other film are peeled off together using the same method as above, and then the total light transmittance is measured. Note that even if such a peeling step is performed, it does not have a significant effect on the measurement of the total light transmittance.

[0077] The haze value (total haze value) of the optical film 10 before the eraser test is preferably 1% or less when the surface 10A of the optical film 10 is flat and mirror-like. If the haze value of the optical film 10 exceeds 1%, the optical performance may be insufficient.

[0078] When surface 10A of optical film 10 has antiglare properties, the haze value may exceed 1%. For example, when image clarity is important, the haze value is preferably 5% or less, and more preferably 3% or less. On the other hand, when the pattern of a display element is visible, i.e., when preventing bones from appearing, the total haze value is preferably 25% or less, more preferably 20% or less, and even more preferably 15% or less.

[0079] The haze value can be measured using a haze meter (for example, product name "HM-150" manufactured by Murakami Color Research Laboratory Co., Ltd.) according to a method in accordance with JIS K7136:2000. Specifically, the haze value is measured in the same manner as the method for measuring the total light transmittance.

[0080] In addition, when another film such as a polarizing plate is provided on the optical film via a pressure-sensitive adhesive layer or an adhesive layer, the pressure-sensitive adhesive layer or the adhesive layer and the other film are peeled off together in the same manner as above, and then the haze value is measured. Note that even if such a peeling step is performed, it does not have a significant effect on the measurement of the haze value.

[0081] The optical film 10 preferably has a yellow index (YI) of 15 or less. If the YI of the optical film 10 is 15 or less, the yellowness of the optical film 10 can be suppressed, making it suitable for applications requiring transparency. The upper limit of YI is more preferably 10 or less, 7 or less, or 6 or less. The yellow index (YI) is determined as follows: First, a sample measuring 50 mm x 50 mm is obtained from the optical film 10. Then, this sample is placed in a spectrophotometer (product name "UV-2450" manufactured by Shimadzu Corporation, light source: tungsten lamp and deuterium lamp) under an environment of a temperature of 23±5°C and a relative humidity of 30% to 70%, with the resin substrate side facing the light source, and the transmittance of the sample at wavelengths of 300 nm to 780 nm is measured. The chromaticity tristimulus values X, Y, and Z are calculated from the measured sample transmittance according to the formula specified in JIS Z8722:2009, and YI is calculated from the tristimulus values X, Y, and Z according to the formula specified in ASTM D1925:1962. YI is calculated by measuring the transmittance of each sample three times from wavelengths of 300 nm to 780 nm, and then calculating the arithmetic mean of the three values. With the UV-2450, the yellow index is calculated by loading the transmittance measurement data into a personal computer (PC) connected to the UV-2450 and checking the "YI" box in the calculation items. The transmittance from wavelengths of 300 nm to 780 nm is measured at a minimum of five points within 1 nm of each wavelength from 300 nm to 780 nm under the following conditions, and the average value is calculated. If the spectral transmittance spectrum exhibits undulations, smoothing with a delta of 5.0 nm may be performed. (Measurement conditions) ·Wavelength range: 300nm~780nm Scan speed: Fast Slit width: 2.0 Sampling interval: Auto (0.5 nm interval) ·Lighting:C Light source: D2 and WI ·Field of view: 2° Light source switching wavelength: 360nm S / R switching: Standard Detector: PM Autozero: Performed at 550 nm after baseline scan

[0082] The use of the optical film 10 is not particularly limited, but examples of uses of the optical film 10 include image display devices such as smartphones, tablet terminals, personal computers (PCs), wearable terminals, digital signage, televisions, and car navigation systems. The optical film 10 is also suitable for in-vehicle use. The form of each of the above image display devices is also preferred for uses requiring flexibility, such as foldable or rollable configurations.

[0083] The optical film 10 may be cut to a desired size or may be in a roll form. When the optical film 10 is cut to a desired size, the size of the optical film is not particularly limited and is appropriately determined depending on the size of the display surface of the image display device. Specifically, the size of the optical film 10 may be, for example, 2.8 inches to 500 inches. In this specification, "inches" refers to the length of the diagonal when the optical film is rectangular, the diameter when the optical film is circular, and the average value of the sum of the minor axis and the major axis when the optical film is elliptical. Here, when the optical film is rectangular, the aspect ratio of the optical film used to calculate the above-mentioned inches is not particularly limited as long as it does not cause any problems as a display screen for the image display device. Examples include length:width = 1:1, 4:3, 16:10, 16:9, and 2:1. However, these aspect ratios are not limited, particularly for in-vehicle applications and digital signage, which require sophisticated design. Furthermore, when the optical film 10 is large, for example, it is cut into an A5 size (148 mm × 210 mm) from an arbitrary position, and then cut into the size of each measurement item. Note that, for example, when the optical film 10 is in a roll form, a predetermined length of the optical film 10 is unwound from the roll, and the desired size is cut from the effective region near the center where quality is stable, rather than from the non-effective region including both ends extending along the longitudinal direction of the roll.

[0084] <<Resin substrate>> The resin substrate 11 is a substrate made of a light-transmitting resin. In this specification, "light-transmitting" refers to the property of transmitting light, and includes, for example, a total light transmittance of 50% or more, preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more. Light-transmitting does not necessarily mean transparency, and may also be translucent.

[0085] The resin constituting the resin substrate 11 is not particularly limited, but is preferably a resin having optical transparency. Examples of such optically transparent resins include acetyl cellulose resins, polyolefin resins, polycarbonate resins, acrylic resins, polyester resins, aromatic polyether ketone resins, polyether sulfone resins, polyimide resins, polyamideimide resins, polyamide resins, and mixtures of two or more of these resins. Among these, acetyl cellulose resins are preferred from the viewpoints of adhesion of the resin to the resin substrate and pencil hardness. Furthermore, resin substrates are easily scratched when they come into contact with a coating device during coating of functional layers, etc. However, resin substrates made of polyester resins are less susceptible to scratches even when they come into contact with the coating device, thereby suppressing an increase in haze value. Furthermore, polyester resins are also preferred from the viewpoints of heat resistance, barrier properties, and water resistance, which are superior to substrates made of resins other than polyester resins.

[0086] When obtaining a foldable optical film as an optical film, it is preferable to use a polyimide-based resin, a polyamideimide-based resin, a polyamide-based resin, a polyester-based resin, a cycloolefin polymer-based resin, or a mixture thereof as the resin constituting the resin substrate, because of its excellent foldability. However, depending on the application, an acetylcellulose-based resin (e.g., triacetylcellulose) can also be preferably used. Among these, polyimide-based resins, polyamide-based resins, or mixtures thereof are preferable from the viewpoints that they not only have excellent foldability but also excellent hardness and transparency, and also have excellent heat resistance, and can be imparted with even greater hardness and transparency by baking. Furthermore, when outdoors, etc., people sometimes wear sunglasses to view images displayed on image display devices. However, if the sunglasses are polarized sunglasses, there is a risk of reduced visibility when viewing the displayed image through the polarized sunglasses. Therefore, there is currently a demand for a method that can suppress the reduction in visibility even when viewing a displayed image through polarized sunglasses. In contrast, cycloolefin polymer resins can impart a phase difference to image light and suppress the decrease in visibility, so from the viewpoint of suppressing the decrease in visibility, cyclopolyolefin polymer resins are preferred.

[0087] The present inventors have speculated that when flexibility is important in an optical film, a substrate containing a polyimide-based resin is preferable as the resin substrate. When a polyimide-based resin is used, microcracks and breakage are indeed less likely to occur compared to conventional, commonly used transparent substrates (e.g., substrates containing polymethyl methacrylate-based resins, triacetyl cellulose-based resins, or polyethylene terephthalate-based resins). However, even when a polyimide-based resin is used, observation reveals that, like other resin substrates, wrinkles and creases may occur in the functional layer, etc. In particular, when an optical film is used for smartphones, the screen is small, so visible creases may make characters unreadable. In contrast, the inventors have found that when a substrate containing, for example, an extremely thin cycloolefin polymer-based resin is used as the resin substrate, foldability is superior to that of a substrate containing a polyimide-based resin with a thickness of 60 μm to 100 μm. Furthermore, for example, when the thickness of a resin substrate containing a cycloolefin polymer resin is extremely thin, such as 5 μm to 35 μm (even 5 μm to 18 μm), the in-plane and thickness direction retardation values are very small, resulting in excellent optical performance. For example, in the case of a resin substrate containing a polyimide resin, a polyamideimide resin, or a polyamide resin, due to the structure of the film, even if the in-plane retardation is less than 100 nm, the thickness direction retardation may be 1000 or more, which may affect visibility when used in an image display device. On the other hand, in the case of a resin substrate containing a cycloolefin polymer resin, both the in-plane and thickness direction retardation can be easily controlled to less than 100 nm or less than 50 nm, and the three-dimensional optical isotropy is excellent, making it compatible with polarized sunglasses and highly desirable for optical applications. For this reason, resin substrates containing extremely thin cycloolefin polymer resins are preferred for flexible and optical applications. Resin substrates containing triacetyl cellulose-based resins and polycarbonate-based resins also have optical isotropy, but when folded at the thickness of 5 μm or more and 35 μm or less, defects such as wrinkles and cracks are likely to occur. Therefore, resin substrates containing cycloolefin polymer-based resins, which have the same optical isotropy, are thought to be more foldable due to their molecular structure.

[0088] Examples of acetyl cellulose resins include triacetyl cellulose (TAC) resins and diacetyl cellulose resins. Triacetyl cellulose resins are resins that can achieve an average light transmittance of 50% or more in the visible light range of 380 to 780 nm. The average light transmittance of triacetyl cellulose resins is preferably 70% or more, and more preferably 85% or more.

[0089] The triacetyl cellulose resin may be pure triacetyl cellulose or may contain a component other than acetic acid as a fatty acid that forms an ester with cellulose, such as cellulose acetate propionate or cellulose acetate butyrate. If necessary, these triacetyl celluloses may contain other cellulose lower fatty acid esters such as diacetyl cellulose, or various additives such as plasticizers and ultraviolet absorbers.

[0090] Examples of polyolefin resins include resins containing at least one of polyethylene, polypropylene, cycloolefin polymer (COP) resins, cycloolefin copolymer (COC) resins, and the like as a constituent component.

[0091] Examples of cycloolefin polymer-based resins include norbornene-based resins, monocyclic olefin-based resins, cyclic conjugated diene-based resins, vinyl alicyclic hydrocarbon-based resins, and hydrogenated versions thereof. Among these, norbornene-based resins are preferred because of their excellent transparency and moldability.

[0092] Examples of norbornene-based resins include ring-opening polymers of monomers having a norbornene structure, ring-opening copolymers of monomers having a norbornene structure and other monomers, and hydrogenated products thereof; addition polymers of monomers having a norbornene structure, addition copolymers of monomers having a norbornene structure and other monomers, and hydrogenated products thereof.

[0093] Examples of commercially available cycloolefin polymer resins include "ZEONEX (registered trademark)" and "ZEONOR (registered trademark)" (norbornene-based resins) manufactured by Zeon Corporation, "SUMILITE (registered trademark) FS-1700" manufactured by Sumitomo Bakelite Co., Ltd., "ARTON (registered trademark)" (modified norbornene-based resin) manufactured by JSR Corporation, "APEL (registered trademark)" (cyclic olefin copolymer) manufactured by Mitsui Chemicals, Inc., "TOPAS (registered trademark)" (cyclic olefin copolymer) manufactured by Ticona, and "OPTREZ OZ-1000 Series" (alicyclic acrylic resin) manufactured by Hitachi Chemical Co., Ltd. A light-transmitting substrate can be obtained by forming a film from such cycloolefin resins. The film formation method is not particularly limited, and known film formation methods such as solvent casting and melt extrusion can be used. Furthermore, formed cycloolefin polymer films are also commercially available, and these can also be used as resin substrates. Examples of cycloolefin polymer films include those manufactured by Sekisui Chemical Co., Ltd. under the trade names "S-Cina (registered trademark)" and "SCA40," those manufactured by Zeon Corporation under the trade name "ZEONORFILM (registered trademark)," and those manufactured by JSR Corporation under the trade name "ARTON (registered trademark) FILM."

[0094] Examples of cycloolefin copolymer resins include copolymers of ethylene and norbornene monomers, and copolymers of ethylene and tetracyclododecene.

[0095] Examples of polycarbonate resins include aromatic polycarbonates based on bisphenols (such as bisphenol A), and aliphatic polycarbonates such as diethylene glycol bisallyl carbonate.

[0096] Examples of acrylic resins include polymethyl(meth)acrylate resins, polyethyl(meth)acrylate resins, and methyl(meth)acrylate-butyl(meth)acrylate copolymer resins.

[0097] Examples of polyester resins include resins containing at least one of polyethylene terephthalate (PET), polypropylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate as a constituent component.

[0098] Examples of aromatic polyether ketone resins include polyether ether ketone (PEEK).

[0099] The polyimide resin may be an aliphatic polyimide resin, but is preferably an aromatic polyimide resin containing an aromatic ring, which is a polyimide resin containing an aromatic ring in at least one of a tetracarboxylic acid component and a diamine component.

[0100] The polyimide resin may partially contain a polyamide structure. Examples of the polyamide structure include a polyamideimide structure containing a tricarboxylic acid residue such as trimellitic anhydride, and a polyamide structure containing a dicarboxylic acid residue such as terephthalic acid. The polyamide resin is a concept that includes not only aliphatic polyamides but also aromatic polyamides (aramids). Specifically, examples of the polyimide resin include compounds having structures represented by the following chemical formulas (1) and (2). In the following chemical formulas, n is a repeating unit and represents an integer of 2 or more. Among the compounds represented by the following chemical formulas (1) and (2), the compound represented by chemical formula (1) is preferred because it has low retardation and high transparency. [ka] [ka]

[0101] The thickness of the resin substrate 11 is preferably 25 μm or more and 100 μm or less. When the thickness of the resin substrate is 25 μm or more, the optical film is less likely to curl and has sufficient hardness. Furthermore, when the optical film is produced by a roll-to-roll process, wrinkles are less likely to occur, which prevents deterioration of the appearance. On the other hand, when the thickness of the resin substrate is 100 μm or less, the bendability is sufficient, and both hardness and bendability can be achieved. The lower limit of the resin substrate 11 is more preferably 30 μm or more, 35 μm or more, or 40 μm or more, and the upper limit of the resin substrate 11 is more preferably 90 μm or less, 85 μm or less, or 80 μm or less. The thickness of the resin substrate can be determined by photographing a cross section of the resin substrate using a scanning transmission electron microscope (STEM) or a scanning electron microscope (SEM), measuring the thickness of the resin substrate at 20 points on the image of the cross section, and calculating the arithmetic average of the thicknesses at the 20 points. Note that the scanning electron microscope photographs are taken at a magnification appropriate for the thickness of the resin substrate, after clearly identifying the interface line between the resin substrate and the functional layer. Specifically, the magnification is adjusted appropriately depending on the thickness of the resin substrate, for example, 1000x if the resin substrate is 50 μm thick, or 500x if the resin substrate is 100 μm thick. The thickness variation of the resin substrate 11 is preferably 15% or less, 10% or less, or 7% or less. When measuring the thickness of the resin substrate using a scanning transmission electron microscope (STEM), it can be measured using a method similar to that for measuring the film thickness of the functional layer. However, the magnification when photographing the cross section of the resin substrate is 100 to 20,000x.

[0102] When flexibility (e.g., foldability) is required for an optical film, if the resin substrate or functional layer is thick, cracks may occur in the resin substrate or functional layer at the bends when the film is folded, and creases or microcracks may also occur in the resin substrate or functional layer at the bends. The occurrence of cracks, creases, or microcracks can result in poor appearance, specifically, cloudiness or poor adhesion due to cracks. For this reason, when using an optical film for flexible applications, controlling the thickness of the resin substrate and functional layer and the adhesion between each layer (adhesion due to chemical bonds influenced by the materials, or physical adhesion that prevents cracks) are important. In particular, when the resin substrate 11 contains a cycloolefin polymer resin, a polyester resin, or a polyimide resin, controlling the thickness of the resin substrate is important because the resistance to cracking varies depending on the thickness. However, the preferred thickness of the resin substrate 11 differs depending on whether the optical film 10 is folded so that the functional layer 12 faces inward (inward bending) or so that the optical film 10 faces outward (outward bending). Specifically, the resin substrate 11 may be thicker when the optical film 10 is used in outward bending than when it is used in inward bending. Increasing the thickness can impart a function to absorb external impacts.

[0103] <When optical film is used in inward bending> When the resin substrate 11 contains, for example, triacetyl cellulose resin, the thickness of the resin substrate 11 is preferably 15 μm or more and 65 μm or less. If the resin substrate is too thin, there is a risk that the resin substrate will bend when folded. However, if the thickness of the resin substrate 11 is 15 μm or more, the resin substrate 11 will not bend when folded. Furthermore, if the thickness of the resin substrate 11 is 65 μm or less, cracking of the resin substrate 11 at the bent portion when folded can be suppressed, and clouding at the bent portion can also be suppressed. In this case, the upper limit of the thickness of the resin substrate 11 is preferably 50 μm or less, or 30 μm or less.

[0104] When resin substrate 11 contains, for example, a cycloolefin polymer resin, the thickness of resin substrate 11 is preferably 5 μm or more and 45 μm or less. If the thickness of resin substrate 11 is 5 μm or more, the handleability is good, and if the thickness is 45 μm or less, cracking of resin substrate 11 at bent portions when folded can be suppressed, and clouding at bent portions can be suppressed. In this case, the upper limit of the thickness of resin substrate 11 is preferably 35 μm or less, or 18 μm or less.

[0105] When resin substrate 11 contains, for example, a polyester resin, the thickness of resin substrate 11 is preferably 5 μm or more and 45 μm or less. If the thickness of resin substrate 11 is 5 μm or more, the handleability is good, and if the thickness is 45 μm or less, cracking of resin substrate 11 at bent portions when folded can be suppressed, and clouding at bent portions can be suppressed. In this case, the upper limit of the thickness of resin substrate 11 is preferably 35 μm or less, or 18 μm or less.

[0106] When the resin substrate 11 contains, for example, a polyimide resin, a polyamide resin, a polyamideimide resin, or a mixture thereof, the thickness of the resin substrate 11 is preferably 5 μm or more and 75 μm or less. If the thickness of the resin substrate 11 is 5 μm or more, the resin substrate 11 is easy to handle, and if the thickness is 75 μm or less, the resin substrate 11 can be prevented from cracking when folded, and the optical and mechanical properties are good. In this case, the upper limit of the thickness of the resin substrate 11 is preferably 70 μm or less, 60 μm or less, 50 μm or less, 35 μm or less, or 18 μm or less. In addition, in terms of handleability, the lower limit of the thickness of the resin substrate 11 is preferably 5 μm or more.

[0107] When the thickness of each of the above resin substrates is 35 μm or less, it is preferable to apply a protective film to the resin substrate 11 during production, as this improves processability.

[0108] <When optical film is used in outward bending> When resin substrate 11 contains, for example, triacetyl cellulose resin, cycloolefin polymer resin, polyester resin, polyimide resin, polyamide resin, polyamideimide resin, or a mixture thereof, the thickness of resin substrate 11 is preferably 35 μm or more and 105 μm or less. If resin substrate 11 is 35 μm or more, it can absorb various external impacts when used on the exterior, and if it is 105 μm or less, it can prevent cracking of resin substrate 11 at bent portions when folded and can also prevent clouding at bent portions. In this case, the upper limit of the thickness of resin substrate 11 is preferably 85 μm or less, or 80 μm or less.

[0109] <<Functional Layer>> The functional layer 12 will be described as a layer that exhibits a hard coat function, i.e., a hard coat layer. In this specification, the term "hard coat layer" refers to a layer having an indentation hardness greater than that of the resin substrate, as described below. To obtain flexibility, the functional layer may be a layer other than a hard coat layer. In this case, the functional layer may have a pencil hardness less than that shown below. Even in such a case, the mechanical strength is higher than that of the resin substrate alone, so the functional layer functions as a hard coat layer.

[0110] The functional layer 12 preferably has a hardness (pencil hardness) of "H" or higher when measured by the pencil hardness test specified in JIS K5600-5-4:1999. By achieving a pencil hardness of "H" or higher, the optical film 10 becomes harder and its durability can be improved. The pencil hardness test is performed by applying a load of 500 g to a pencil and setting the scratching speed to 1 mm / sec. The pencil hardness is defined as the highest hardness that does not scratch the surface of the optical film in the pencil hardness test. When measuring the pencil hardness, multiple pencils of different hardness are used. The pencil hardness test is performed five times for each pencil. If the optical film surface is not scratched four or more times out of the five times, it is determined that the pencil of that hardness did not scratch the optical film surface. The scratches are visually observed when the surface of the optical film that has been subjected to the pencil hardness test is observed under fluorescent light. The functional layer may have a single-layer structure or, as in this embodiment, a multilayer structure of two or more layers.

[0111] The indentation hardness (H IT ) is preferably 100 MPa or more. When flexibility is the most important factor, it is preferably 20 MPa or more but less than 100 MPa. The lower limit of the indentation hardness of the functional layer 12 may be 200 MPa or more or 300 MPa or more, and the upper limit may be 800 MPa or less from the viewpoint of preventing microcracks and maintaining adhesion at the interface between the functional layer and the resin substrate. By setting such lower and upper limits, the flexibility of the functional layer itself can be maintained. Furthermore, for practical use of optical films, it is necessary that the physical and optical properties after a folding test remain substantially the same as before the test. Furthermore, the functional layer is effective as a layer that prevents scratches during processing. For these reasons, in order to maintain flexibility while obtaining the above-mentioned practical physical properties, it is preferable that the value be within the above-mentioned numerical range. Depending on the application, the functional layer may be provided on only one side of the resin substrate, or on both sides of the resin substrate.

[0112] In this specification, the "indentation hardness" is a value determined from the load-displacement curve from loading to unloading of the indenter. ITThe measurement of the σ is performed on the measurement sample using a Bruker TI950 TriboIndenter under an environment with a temperature of 23±5°C and a relative humidity of 30% to 70%. The measurement sample may be prepared using the same method as the sample prepared for the SEM cross-sectional photograph described above. When the functional layer 12 is thin, it is preferable to use an oblique cutting device such as a Surface and Interfacial Cutting Analysis System (SAICAS) to obtain a sufficiently large measurement area. Cross-sectional analysis is typically performed by analyzing a surface (vertical cross-section) cut perpendicular to the surface of the sample. However, when a multilayered sample has thin layers, selective analysis of a specific layer is difficult when a large analysis area is required. However, when a cross-section is prepared by oblique cutting, a wider sample surface can be exposed than when a vertical cross-section is used. For example, when a 10° inclined plane is prepared relative to the horizontal plane, the sample surface is slightly less than six times larger than when a vertical cross-section is used. Therefore, by preparing a cross-section by oblique cutting using SAICAS, it is possible to analyze samples that are difficult to analyze using a vertical cross-section. Next, a flat spot was found on the cross section of the obtained measurement sample. At this flat spot, a Berkovich indenter (triangular pyramid, Bruker TI-0039) was pressed vertically into the functional layer 12 at a speed of 10 nm / s, from 0 to 100 nm over 10 seconds, so that the maximum indentation displacement in the displacement-based measurement was 100 nm. Here, the Berkovich indenter was pressed into a portion of the functional layer 12 500 nm away from the interface between the resin substrate and the functional layer toward the center of the functional layer, and at least 500 nm away from each of the two ends of the functional layer toward the center of the functional layer, to avoid the influence of the light-transmitting substrate and the side edges of the functional layer. The indenter was then held at a displacement of 100 nm for 5 seconds, and then unloaded from 100 to 0 nm over 10 seconds. The indentation depth h (nm) corresponding to the indentation load F (N) was continuously measured, and a load-displacement curve was created. The indentation hardness was calculated from the load-displacement curve using the maximum indentation load F as shown in the following formula (4). max (N) is the contact projection area A where the indenter and the functional layer 12 are in contact. p(mm 2 The indentation hardness is calculated by dividing the value by the maximum and minimum values of the 10 measured values. The indentation hardness is the arithmetic mean value of the 8 measured values. p is the projected contact area corrected for the indenter tip curvature by the Oliver-Pharr method using a standard sample of fused silica. H IT =F max / A p …(4)

[0113] The thickness of the functional layer 12 is preferably 11 μm or more and 50 μm or less. If the thickness of the functional layer 12 is 11 μm or more, the functional layer 12 can obtain sufficient hardness, and if it is 50 μm or less, deterioration of processability can be suppressed. From the viewpoint of obtaining the desired hardness, the lower limit of the thickness of the functional layer 12 is more preferably 14 μm or more, 17 μm or more, or 20 μm or more. From the viewpoint of improving bendability, the upper limit of the thickness of the functional layer 12 is more preferably 45 μm or less, 42 μm or less, or 39 μm or less. When the functional layer has a multilayer structure, the thickness of the functional layer means the sum of the thicknesses of the individual functional layers. The variation in thickness of the functional layer 12 is preferably 15% or less, 10% or less, or 7% or less.

[0114] The functional layer thickness was determined by photographing a cross section of the functional layer using a scanning electron microscope (SEM). The functional layer thickness was measured at 20 locations on the cross section image, and the arithmetic mean of the 20 measurements was calculated. The specific method for photographing the cross section is described below. First, a 1 mm x 10 mm block of optical film was embedded in an embedding resin to create a block. From this block, uniform, hole-free sections with a thickness of 70 nm to 100 nm were cut using a standard sectioning method. The reason for cutting out sections with a thickness of 70 nm to 100 nm is that the remaining block after the sectioning was used for measurement. Cutting sections of this thickness ensures good cross-sectional flatness of the remaining block. Note that poor flatness of the remaining block may result in poor measurement accuracy. Sections can be prepared using an Ultramicrotome EM UC7 (Leica Microsystems Inc.) or similar. The remaining block after the cut, uniform, hole-free section was used as the measurement sample. Next, a cross-sectional photograph of the measurement sample is taken using a scanning electron microscope (SEM) (product name "S-4800" manufactured by Hitachi High-Technologies Corporation). When taking cross-sectional photographs using the S-4800, the detector is set to "SE," the acceleration voltage is set to "5 kV," and the emission current is set to "10 μA." The magnification is adjusted appropriately between 100 and 100,000 times, preferably between 1,000 and 10,000 times depending on the thickness of the functional layer, while adjusting the focus and observing whether the contrast and brightness of each layer can be distinguished. To reduce measurement blur, it is recommended to measure the thickness of the functional layer at as low a magnification as possible. For example, a magnification of 2,000 times is preferable for a functional layer thickness of approximately 30 μm, and a magnification of 2,000 to 5,000 times is preferable for a functional layer thickness of approximately 15 μm. When taking cross-sectional photographs using the S-4800, the aperture may be set to "beam monitor aperture 3," the objective lens aperture to "3," and the working distance to "8 mm." When measuring the film thickness of the first layer, it is important that the interfacial contrast between the first functional layer and other layers (e.g., resin substrate) can be observed as clearly as possible when observing the cross section.If the interface is difficult to see due to insufficient contrast, dyeing with osmium tetroxide, ruthenium tetroxide, phosphotungstic acid, or the like can be used to make the interface between the organic layers more visible. Furthermore, the contrast of the interface may be more difficult to see at higher magnifications. In such cases, observations should also be made at lower magnifications. For example, observations should be made at two magnifications, high and low, such as 25,000x and 50,000x, or 50,000x and 100,000x, and the arithmetic mean value described above should be calculated at both magnifications. This mean value is then used as the film thickness of the first functional layer.

[0115] The functional layer 12 includes a first functional layer 13 and a second functional layer 14 provided on the surface of the first functional layer 13 opposite to the surface on the resin substrate 11 side.

[0116] <First functional layer> The first functional layer 13 is a layer for increasing hardness. The first functional layer 13 contains a binder resin and particles dispersed in the binder resin. By incorporating particles into the first functional layer 13, a higher pencil hardness can be achieved. In addition to the binder resin, the first functional layer 13 may contain various additives other than those described above, as needed, as long as they do not impair the effects of the present invention. Examples of such additives include ultraviolet absorbers, antistatic agents, adhesion improvers, leveling agents, thixotropy-imparting agents, coupling agents, plasticizers, antifoaming agents, fillers, colorants, and fillers.

[0117] The thickness of the first functional layer 13 is preferably 10 μm or more and 40 μm or less. If the thickness of the first functional layer is 10 μm or more, the hardness of the first functional layer is not insufficient, and if the thickness is 40 μm or less, deterioration of processability can be suppressed. The lower limit of the thickness of the first functional layer 13 is more preferably 12 μm or more, 14 μm or more, or 16 μm or more from the viewpoint of suppressing interference fringes. The upper limit of the thickness of the first functional layer 13 is more preferably 38 μm or less, 34 μm or less, or 30 μm or less from the viewpoint of adhesion to the resin substrate 11. The thickness of the first functional layer 13 is measured using the same method as for the thickness of the functional layer 12. The variation in the thickness of the first functional layer 13 is preferably 15% or less, 10% or less, or 7% or less.

[0118] (binder resin) The resin contains a polymer (cured product) of a polymerizable compound (curable compound). The polymerizable compound has at least one polymerizable functional group in the molecule. Examples of the polymerizable functional group include ethylenically unsaturated groups such as a (meth)acryloyl group, a vinyl group, and an allyl group. The term "(meth)acryloyl group" includes both an "acryloyl group" and a "methacryloyl group."

[0119] The polymerizable compound is preferably a polyfunctional (meth)acrylate. Examples of the polyfunctional (meth)acrylate include trimethylolpropane tri(meth)acrylate, tripropylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and dipentaerythritol penta(meth)acrylate. acrylate, tripentaerythritol octa(meth)acrylate, tetrapentaerythritol deca(meth)acrylate, isocyanuric acid tri(meth)acrylate, isocyanuric acid di(meth)acrylate, polyester tri(meth)acrylate, polyester di(meth)acrylate, bisphenol di(meth)acrylate, diglycerin tetra(meth)acrylate, adamantyl di(meth)acrylate, isoboronyl di(meth)acrylate, dicyclopentane di(meth)acrylate, tricyclodecane di(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, and those modified with PO, EO, caprolactone, etc.

[0120] Among these, tri- to hexa-functional compounds are preferred because they can suitably satisfy the above-mentioned pencil hardness requirements, and examples thereof include pentaerythritol triacrylate (PETA), dipentaerythritol hexaacrylate (DPHA), pentaerythritol tetraacrylate (PETTA), dipentaerythritol pentaacrylate (DPPA), trimethylolpropane tri(meth)acrylate, tripentaerythritol octa(meth)acrylate, tetrapentaerythritol deca(meth)acrylate, etc. In this specification, (meth)acrylate means acrylate and methacrylate.

[0121] The composition may further contain a monofunctional (meth)acrylate monomer in order to adjust the hardness or viscosity of the composition, improve adhesion, etc. Examples of the monofunctional (meth)acrylate monomer include hydroxyethyl acrylate (HEA), glycidyl methacrylate, methoxypolyethylene glycol (meth)acrylate, isostearyl (meth)acrylate, 2-acryloyloxyethyl succinate, acryloylmorpholine, N-acryloyloxyethyl hexahydrophthalimide, cyclohexyl acrylate, tetrahydrofuryl acrylate, isobornyl acrylate, phenoxyethyl acrylate, and adamantyl acrylate.

[0122] From the viewpoint of improving the hardness of the resin layer, the weight-average molecular weight of the monomer is preferably less than 1,000, and more preferably from 200 to 800. The weight-average molecular weight of the polymerizable oligomer is preferably from 1,000 to 20,000, more preferably from 1,000 to 10,000, and even more preferably from 2,000 to 7,000.

[0123] (particle) The particles are components that increase the hardness of the functional layer and may be inorganic particles, organic particles, or a mixture thereof. Examples of inorganic particles include inorganic oxide particles such as silica (SiO2) particles, alumina particles, titania particles, tin oxide particles, antimony-doped tin oxide (ATO) particles, and zinc oxide particles. Among these, silica particles are preferred for their enhanced hardness. Examples of silica particles include spherical silica particles and irregularly shaped silica particles, with irregularly shaped silica particles being preferred. In this specification, "spherical particles" refers to particles with, for example, a spherical or ellipsoidal shape, and "irregularly shaped particles" refers to particles with a potato-like shape (an aspect ratio of 1.2 to 40 when observed cross-sectionally) that have random irregularities on the surface. Because the irregularly shaped particles have a larger surface area than spherical particles, the inclusion of such irregularly shaped particles increases the contact area with the binder resin, thereby improving the pencil hardness of the first functional layer 13. Whether the silica particles contained in the first functional layer 13 are irregular silica particles can be confirmed by observing the cross section of the first functional layer 13 with a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM). When spherical silica particles are used, the smaller the particle diameter of the spherical silica particles, the higher the hardness of the functional layer. In contrast, irregular silica particles can achieve a hardness equivalent to that of spherical silica even if they are not as small as the smallest spherical silica particles commercially available.

[0124] The average particle diameter of the silica particles is preferably 5 nm or more and 200 nm or less. If the particle diameter is less than 5 nm, it may be difficult to manufacture the particles themselves, the particles may aggregate, and it may be extremely difficult to form irregular shapes. Furthermore, the irregular silica particles may have poor dispersibility and aggregate in the ink stage before coating. On the other hand, if the average particle diameter of the irregular silica particles exceeds 200 nm, problems such as the formation of large irregularities in the first functional layer or increased haze may occur. When the silica particles are spherical silica particles, the average particle diameter of the silica particles is determined by measuring the particle diameters of 20 particles from images of the cross sections of the particles taken using a transmission electron microscope (TEM) or scanning transmission electron microscope (STEM), and then calculating the arithmetic mean value of the particle diameters of the 20 particles. In addition, when the silica particles are irregularly shaped silica particles, the average particle diameter of the silica particles is determined by measuring the maximum (long diameter) and minimum (short diameter) distances between two points on the outer periphery of the particles from an image of the cross section of the functional layer taken using a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM), averaging them, and calculating the particle diameter, which is the arithmetic mean value of the particle diameters of 20 particles.

[0125] The particle content in the first functional layer 13 is preferably 20% by mass or more and 70% by mass or less. If the particle content is 20% by mass or more, sufficient hardness can be ensured, and if the particle content is 70% by mass or less, the filling rate does not increase too much, which can prevent deterioration of adhesion between the particles and the binder resin and prevent a decrease in hardness of the first functional layer.

[0126] As the inorganic particles, it is preferable to use inorganic particles having a polymerizable functional group on the surface (reactive inorganic particles). Such inorganic particles having a polymerizable functional group on the surface can be prepared by surface-treating the inorganic particles with a silane coupling agent or the like. Methods for treating the surfaces of inorganic particles with a silane coupling agent include a dry method in which the silane coupling agent is sprayed onto the inorganic particles, and a wet method in which the inorganic particles are dispersed in a solvent and then a silane coupling agent is added to cause a reaction.

[0127] Examples of organic particles include plastic beads, such as polystyrene beads, melamine resin beads, acrylic beads, acrylic-styrene beads, silicone beads, benzoguanamine beads, benzoguanamine-formaldehyde condensation beads, polycarbonate beads, and polyethylene beads.

[0128] <Second functional layer> The second functional layer 14 is a layer for enhancing scratch resistance and slip resistance. The second functional layer 14 is a hard coat layer, but may be, for example, a vapor deposition layer or a spray-coated layer instead of a hard coat layer. The second functional layer 14 includes a binder resin, a lubricant, and an antifouling agent. In addition to the binder resin, the second functional layer 14 may contain various additives other than those described above, as needed, as long as they do not impair the effects of the present invention. Examples of such additives include particles (e.g., micron-order particles for achieving antiglare properties or nano-order particles for expressing functionality), ultraviolet absorbers, antistatic agents, adhesion improvers, leveling agents, thixotropy-imparting agents, coupling agents, plasticizers, defoamers, bulking agents, colorants, and fillers.

[0129] The thickness of the second functional layer 14 is preferably 1 μm or more and 10 μm or less. A thickness of 1 μm or more of the second functional layer provides sufficient scratch resistance, while a thickness of 10 μm or less can suppress curling and maintain flexibility. The lower limit of the thickness of the second functional layer 14 is preferably 2 μm or more, 3 μm or more, or 4 μm or more from the viewpoint of achieving the desired hardness. The upper limit of the thickness of the second functional layer 14 is preferably 7 μm or less, 8 μm or less, or 9 μm or less from the viewpoint of transparency. The thickness of the second functional layer 14 is measured in the same manner as the thickness of the functional layer 12. The variation in the thickness of the second functional layer 14 is preferably 15% or less, 10% or less, or 7% or less.

[0130] The arithmetic mean height (Sa) of a 5 μm square region on the surface 14A of the second functional layer 14 of the optical film 10 before the eraser test is preferably 10 nm or less. The upper limit of Sa may be 7 nm or less, 4 nm or less, 1 nm or less, or even 0.8 nm or less. This upper limit ensures high transparency and low haze even when the depressions 10B are present or appear after the eraser test. Furthermore, this upper limit is believed to be responsible for the formation of depressions sufficient to obtain desirable film quality after the eraser test. If this upper limit is exceeded, film quality control becomes difficult, and desirable physical properties may not be obtained. Furthermore, the lower limit of Sa may be 0.01 nm or more, or 0.05 nm or more, from the viewpoint of preventing films from sticking together when the optical films are likely to be stacked during roll or sheet production.

[0131] (binder resin) The binder resin contained in the second functional layer 14 is the same as the binder resin contained in the first functional layer 13, and therefore a description thereof will be omitted here.

[0132] (lubricant) The lubricant is used to impart slipperiness to the surface 10A of the optical film 10. The lubricant preferably has a polymerizable functional group. When a lubricant having a polymerizable functional group is used as the lubricant, the lubricant exists in the second functional layer 14 in a state of being bound to the binder resin.

[0133] As the lubricant, a silicone-based lubricant is preferred from the viewpoint of easily improving the lubricity of the surface of the optical film. The silicone-based lubricant is not particularly limited, but examples thereof include straight silicones and modified silicones such as dimethylpolysiloxane, methylphenylpolysiloxane, and methylhydrogenpolysiloxane.

[0134] Examples of modified silicones include ethylenically unsaturated group-modified silicones such as (meth)acrylic-modified silicones, amino-modified silicones, amide-modified silicones, epoxy-modified silicones, carboxy-modified silicones, alcohol-modified silicones, carbinol-modified silicones, and mercapto-modified silicones.

[0135] Commercially available lubricants include, for example, BYK-313, BYK-322, BYK-331, BYK-333, BYK-345, BYK-377, BYK-378, BYK-UV3500, and BYK-UV3510 (all manufactured by BYK Japan Co., Ltd.).

[0136] The weight-average molecular weight of the lubricant is preferably 3000 or more and 20000 or less. When the weight-average molecular weight of the lubricant is 3000 or more, the occurrence of problems with surface quality can be suppressed, and when the weight-average molecular weight of the lubricant is 20000 or less, the deterioration of compatibility with the resin can be suppressed.

[0137] The content of the lubricant is preferably 0.01 to 0.5 parts by mass relative to 100 parts by mass of the polymerizable compound constituting the binder resin. When the content of the lubricant is 0.01 part by mass or more, the coefficient of dynamic friction of the surface of the second functional layer is low, and excellent slip properties can be obtained. When the content of the lubricant is 0.5 part by mass or less, a decrease in scratch resistance can be suppressed.

[0138] When both a lubricant and an antifouling agent are contained, the content ratio is preferably 1:9 to 5:5. When the content ratio is within this range, an optical film having better scratch resistance and better wear resistance can be obtained.

[0139] (Anti-fouling agent) The antifouling agent is used to prevent stains such as fingerprints from adhering to the surface 10A of the optical film 10. The antifouling agent preferably has a polymerizable functional group. When an antifouling agent having a polymerizable functional group is used as the antifouling agent, the antifouling agent is present in the second functional layer in a state of being bound to the binder resin.

[0140] As the antifouling agent, fluorine-containing antifouling agents such as fluorine-based antifouling agents and fluorine silicone-based antifouling agents are preferred. When a fluorine-containing antifouling agent is used, fingerprints are less likely to stick (are less noticeable) and wiping is also easy. In addition, the surface tension during application of the composition for the second functional layer can be reduced, resulting in good leveling properties and a good appearance for the second functional layer formed. Among fluorine-containing antifouling agents, fluorine silicone-based antifouling agents, which are compounds containing both an Si-containing structure such as a siloxane skeleton and an F-containing structure such as a perfluoroether, are preferred from the viewpoint of reducing friction with an eraser. In the case of an antifouling agent containing both Si and F, good physical properties can be obtained even by using only this. Note that the slipperiness and antifouling properties can also be improved by incorporating multiple fluorine-based antifouling agents and silicone-based antifouling agents together.

[0141] Commercially available fluorine-based antifouling agents include, for example, Optool DAC and Optool DSX (both manufactured by Daikin Industries, Ltd.), Megafac RS-56, Megafac RS-71, Megafac RS-74 and Megafac RS-75 (all manufactured by DIC Corporation), LINC152EPA, LINC151EPA and LINC182UA (all manufactured by Kyoeisha Chemical Co., Ltd.), Ftergent 650A, Ftergent 601AD and Ftergent 602.

[0142] Commercially available fluorine silicone antifouling agents include, for example, Megafac RS-851, Megafac RS-852, Megafac RS-853, Megafac RS-854 (all manufactured by DIC Corporation), Opstar TU2225, Opstar TU2224 (all manufactured by JSR Corporation), and the like.

[0143] The weight-average molecular weight of the antifouling agent is preferably 3000 or more and 20000 or less. When the weight-average molecular weight of the antifouling agent is 3000 or more, the occurrence of problems with surface quality can be suppressed, and when the weight-average molecular weight of the antifouling agent is 20000 or less, deterioration of compatibility with resin can be suppressed.

[0144] The content of the antifouling agent is preferably 0.01 to 0.5 parts by mass relative to 100 parts by mass of the polymerizable compound constituting the binder resin. When the content of the antifouling agent is 0.01 part by mass or more, excellent antifouling properties can be obtained, and when the content is 0.5 part by mass or less, deterioration of scratch resistance can be suppressed.

[0145] (particle) Adding particularly large particles to the second functional layer creates large irregularities on the surface of the optical film. Therefore, when the surface of the optical film is subjected to an eraser test (500 g × 4000 reciprocating strokes) or an eraser test (1000 g × 5000 reciprocating strokes), the particles may fall off, potentially causing scratches on the surface of the optical film. In contrast, the dynamic friction coefficient of the surface 10A of the optical film 10 is 0.70 or less, making it easy for an eraser to slide. Therefore, even if particles are added to the second functional layer 14, the particles are less likely to fall off when the eraser test (500 g × 4000 reciprocating strokes) or the eraser test (1000 g × 5000 reciprocating strokes) is performed, thereby preventing scratches. The particles are similar to those described in the section on the first functional layer 13, and therefore will not be described here.

[0146] <<Optical film manufacturing method>> The optical film 10 can be produced, for example, as follows: First, a first functional layer composition is applied to the first surface 11A of the resin substrate 11 using a coating device such as a bar coater to form a coating film of the first functional layer composition.

[0147] <First functional layer composition> The first functional layer composition contains a polymerizable compound and particles that become a binder resin after curing. The first functional layer composition may also contain an ultraviolet absorber, a leveling agent, a solvent, and a polymerization initiator, as needed.

[0148] (solvent) Examples of the solvent include alcohols (e.g., methanol, ethanol, propanol, isopropanol, n-butanol, s-butanol, t-butanol, benzyl alcohol, PGME, ethylene glycol, and diacetone alcohol), ketones (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, heptanone, diisobutyl ketone, diethyl ketone, and diacetone alcohol), esters (methyl acetate, ethyl acetate, butyl acetate, n-propyl acetate, isopropyl acetate, and methyl formate), and Examples of suitable solvents include methyl isobutyl ketone and methyl ethyl ketone (PGMEA), aliphatic hydrocarbons (e.g., hexane and cyclohexane), halogenated hydrocarbons (e.g., methylene chloride, chloroform and carbon tetrachloride), aromatic hydrocarbons (e.g., benzene, toluene and xylene), amides (e.g., dimethylformamide, dimethylacetamide and n-methylpyrrolidone), ethers (e.g., diethyl ether, dioxane and tetrahydrofuran), ether alcohols (e.g., 1-methoxy-2-propanol), and carbonates (dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate). These solvents may be used alone or in combination of two or more. Among these, methyl isobutyl ketone and methyl ethyl ketone are preferred as the solvents, as they can dissolve or disperse components such as urethane (meth)acrylate and other additives, and allow the first functional layer composition to be suitably applied.

[0149] (Polymerization initiator) The polymerization initiator is a component that is decomposed by irradiation with ionizing radiation to generate radicals and initiate or advance the polymerization (crosslinking) of the polymerizable compound.

[0150] The polymerization initiator is not particularly limited as long as it is capable of releasing a substance that initiates radical polymerization upon exposure to ionizing radiation. The polymerization initiator is not particularly limited, and known initiators can be used, specific examples of which include acetophenones, benzophenones, Michler's benzoyl benzoate, α-amyloxime ester, thioxanthones, propiophenones, benzils, benzoins, and acylphosphine oxides. It is also preferable to use a photosensitizer in combination, specific examples of which include n-butylamine, triethylamine, and poly-n-butylphosphine.

[0151] After forming a coating film of the composition for the first functional layer, the coating film is dried by various known methods, for example, by heating at a temperature of 30°C or higher and 120°C or lower for 10 to 120 seconds, thereby evaporating the solvent.

[0152] After drying, the coating film is irradiated with ionizing radiation such as ultraviolet light to semi-cure the coating film. As used herein, "semi-cure" means that further irradiation with ionizing radiation will substantially advance the curing. However, the coating film may be fully cured at this stage. As used herein, "fully cured" means that further irradiation with ionizing radiation will not substantially advance the curing. As used herein, ionizing radiation includes visible light, as well as ultraviolet light, X-rays, electron beams, α-rays, β-rays, and γ-rays.

[0153] After the coating film is semi-cured, a second functional layer composition for forming a second functional layer is applied onto the coating film using an application device such as a bar coater to form a coating film of the second functional layer composition.

[0154] <Composition for second functional layer> The second functional layer composition contains a polymerizable compound that becomes a binder resin after curing, a lubricant, and an antifouling agent. The second functional layer composition may also contain an ultraviolet absorber, a solvent, and a polymerization initiator as needed. The solvent and polymerization initiator of the second functional layer composition are the same as those described for the first functional layer composition, so their description will be omitted here.

[0155] After forming a coating film of the composition for the second functional layer, the coating film is dried by various known methods, for example, by heating at a temperature of 30°C or higher and 120°C or lower for 10 to 120 seconds, and the solvent is evaporated.

[0156] After drying the coating, the coating of the second functional layer composition is irradiated with ionizing radiation such as ultraviolet light to fully cure the coating of the first functional layer composition and the coating of the second functional layer composition, thereby forming the first functional layer 13 and the second functional layer 14, thereby obtaining the functional layer 12. This results in the optical film 10 shown in FIG.

[0157] According to this embodiment, when a 5 μm square region on the surface 10A of the optical film 10 after the eraser test (500 g × 4000 reciprocations) is observed using an atomic force microscope, the region contains 1 to 50 depressions, each depression having at least one of the following shapes: annular with an outer diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm, circular with a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm, or irregular with a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm. Furthermore, the coefficient of dynamic friction (500 g load) of the surface 10A of the optical film 10 before the eraser test is 0.70 or less, and the rate of change of the coefficient of dynamic friction (500 g load) of the surface 10A of the optical film 10 after the eraser test (500 g × 4000 reciprocations) relative to the coefficient of dynamic friction (500 g load) of the surface 10A of the optical film 10 before the eraser test is within 35%, so that an optical film 10 can be obtained that can achieve excellent scratch resistance and excellent abrasion resistance, as well as excellent antifouling properties. This is believed to be due to the following reason. When the functional layer contains a lubricant and an antifouling agent, or even if the functional layer does not contain a lubricant, when a mixture of multiple types of antifouling agents rather than a single type is present or when an antifouling agent containing multiple types of elements is contained, the coefficient of dynamic friction of the surface of the optical film before the eraser test can be made 0.70 or less, so the dynamic friction force acting between the steel wool or eraser and the surface of the functional layer is low, making the steel wool or eraser more easily slippery. In particular, when a lubricant and an antifouling agent are contained in the functional layer, the lubricant (e.g., a silicone-based lubricant) or antifouling agent is present in a locally high concentration, making steel wool or an eraser more slippery. Furthermore, if the dynamic friction force acting between the eraser and the surface of the functional layer is low, significant detachment of the antifouling agent from the surface of the optical film due to friction with the eraser can be suppressed, thereby suppressing a decrease in the contact angle in the eraser test and achieving excellent antifouling properties. When such an optical film is subjected to an eraser test (500 g x 4,000 strokes), the surface of the optical film is rubbed, causing a small amount of the lubricant or antifouling agent present locally to detach, forming the above-mentioned depressions.Here, most of the lubricant or antifouling agent remains in the depressions, which reduces the dynamic friction force between the steel wool or eraser and the surface of the functional layer not only before the eraser test but also after the eraser test (500g x 4000 strokes). Therefore, the change rate of the dynamic friction coefficient (500g load) of the surface 10A of the optical film 10 after the eraser test (500g x 4000 strokes) to the dynamic friction coefficient (500g load) of the surface 10A of the optical film 10 before the eraser test can be kept within 35%. Therefore, even after the eraser test (500g x 4000 strokes), the steel wool or eraser becomes easily slippery. This allows for excellent scratch resistance and excellent abrasion resistance, as well as excellent stain resistance, to be achieved not only before the eraser test but also after the eraser test (500g x 4000 strokes).

[0158] In addition, according to this embodiment, when carrying out eraser test (1000g x 5000 reciprocating motions), the absolute value of the difference between the average arithmetic height of the 5 μm square area of the surface of the optical film measured by atomic force microscope before eraser test and the average arithmetic height of the 5 μm square area of the surface of the optical film measured by atomic force microscope after eraser test (1000g x 5000 reciprocating motions) is 0.1nm or more and 5nm or less, and the dynamic friction coefficient (load 1000g) of the surface of the optical film before eraser test is 0.70 or less, and the dynamic friction coefficient (load 1000g) of the surface 10A of the optical film 10 after eraser test (1000g x 5000 reciprocating motions) is within 35% relative to the dynamic friction coefficient (load 1000g) of the surface 10A of the optical film 10 before eraser test, so that the optical film can be obtained with excellent scratch resistance and excellent wear resistance.This is believed to be due to the following reasons. Usually, when carrying out eraser test (1000g x 5000 times back and forth), the components on the surface of optical film are easy to fall off, so the arithmetic mean height of the surface of optical film after eraser test (1000g x 5000 times back and forth) tends to be significantly large.On the other hand, when functional layer contains lubricant and antifouling agent as in the functional layer of the present embodiment, or even if functional layer does not contain lubricant, when not a single type but a mixture of multiple types of antifouling agent or when the antifouling agent that contains multiple types of elements is contained, the dynamic friction coefficient (load 1000g) on the surface of optical film before eraser test can be made to be 0.70 or less, so that the dynamic friction force that works between steel wool or eraser and the surface of functional layer is low, and steel wool or eraser is easy to slide.When such an optical film is subjected to an eraser test (1000g x 5000 strokes), although some of the locally present lubricant or antifouling agent falls off as described above, the lubricant or antifouling agent makes the film slippery, so few components are scraped off by the eraser. Therefore, the absolute value of the difference in the average arithmetic height of the optical film's surface before and after the eraser test (1000g x 5000 strokes) can be 0.1nm or more and 5nm or less. Furthermore, the rate of change in the dynamic friction coefficient (1000g load) of the surface 10A of the optical film 10 after the eraser test (1000g x 5000 strokes) relative to the dynamic friction coefficient (1000g load) of the surface 10A of the optical film 10 before the eraser test can be kept within 35%. This allows for excellent scratch resistance and excellent abrasion resistance, as well as excellent antifouling properties, not only before the eraser test but also after the eraser test (1000g x 5000 strokes).

[0159] <<<<Polarizing plate>>>> The optical film 10 can be incorporated into a polarizing plate for use. FIG. 9 is a schematic diagram of a polarizing plate according to this embodiment. As shown in FIG. 9, a polarizing plate 20 includes the optical film 10, a polarizer 21, and a protective film 22, in this order. In this specification, the term "polarizing plate" refers to a laminate containing at least a polarizer, and includes, in addition to the configuration of the polarizing plate 20, a laminate in which, for example, a polarizer and the optical film of the present invention are integrated via a pressure-sensitive adhesive or adhesive. In this case, a functional layer having some function may be present between the polarizer and the optical film of the present invention.

[0160] The optical film 10 and the polarizer 21, and the polarizer 21 and the protective film 22 are bonded together with, for example, a water-based adhesive or an ultraviolet-curable adhesive.

[0161] <<<Polarizer>>> The polarizer 21 is provided on the second surface 11B of the resin substrate 11, opposite the first surface 11A. The polarizer 21 may be a polyvinyl alcohol resin film dyed with iodine or a dichroic dye and uniaxially stretched. Examples of the polyvinyl alcohol resin include a saponified polyvinyl acetate resin. Examples of the polyvinyl acetate resin include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate with other monomers copolymerizable therewith. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and acrylamides having an ammonium group. The polyvinyl alcohol resin may be modified; for example, polyvinyl formal or polyvinyl acetal modified with aldehydes may also be used.

[0162] <<<Protective film>>> Examples of the protective film 22 include a triacetyl cellulose film (TAC film) and a (meth)acrylic resin film.

[0163] <<<<Image display devices>>>> The optical film 10 can be incorporated into a foldable image display device. FIG. 10 is a schematic diagram of an image display device according to this embodiment. As shown in FIG. 10, the image display device 30 includes a housing 31 accommodating a battery and other components, a protective film 32, a display element 33, a circular polarizer 34, a touch sensor 35, and an optical film 10 stacked in this order facing the viewer. Light-transmitting adhesive layers 36, such as OCA (Optical Clear Adhesive), are disposed between the display element 33 and the circular polarizer 34, between the circular polarizer 34 and the touch sensor 35, and between the touch sensor 35 and the optical film 10, and these components are fixed to each other by the light-transmitting adhesive layers 36. Note that the above image display device is merely an example, and this does not necessarily apply to foldable or rollable devices.

[0164] The optical film 10 is disposed so that the functional layer 12 is closer to the viewer than the resin substrate 11. In the image display device 30, the surface 12A of the functional layer 12 of the optical film 10 forms the surface 30A of the image display device 30.

[0165] The display element 33 is an organic light emitting diode (OLED) element, but the display element may also be a liquid crystal display element, an inorganic light emitting diode element, or a quantum dot light emitting diode (QLED).

[0166] The touch sensor 35 is disposed closer to the display element 33 than the circular polarizer 34, but may be disposed between the circular polarizer 34 and the optical film 10. The touch sensor 35 may be of an on-cell type or an in-cell type.

[0167] The use of the optical film 10 is not particularly limited, but it can be particularly suitably used in image display devices such as smartphones, tablet terminals, and personal computers with touch functions. [Example]

[0168] In order to explain the present invention in detail, the following examples are given, but the present invention is not limited to these examples. Note that the "value calculated based on 100% solids content" below refers to a value when the solids content in the solvent-diluted product is taken as 100%.

[0169] <Preparation of hard coat layer composition> First, the components were mixed so as to obtain the composition shown below, thereby obtaining a composition for a hard coat layer.

[0170] (Hard Coat Layer Composition 1) Dipentaerythritol polyacrylate (product name "A-9550", manufactured by Shin-Nakamura Chemical Co., Ltd.): 70 parts by mass Silica particles (product name "PGM-AC-2140Y", manufactured by Nissan Chemical Industries, Ltd.): 30 parts by mass Fluorine-based leveling agent (product name "Megafac F-444", manufactured by DIC Corporation): 0.1 parts by mass

[0171] (Hard Coat Layer Composition 2) Pentaerythritol triacrylate (product name "A-TMM-3", manufactured by Shin-Nakamura Chemical Co., Ltd.): 100 parts by mass Silicone lubricant (product name "BYK-333", manufactured by BYK Japan Co., Ltd.): 0.1 parts by weight Fluorine-containing antifouling agent (product name "Megafac RS-56", manufactured by DIC Corporation): 0.1 parts by mass

[0172] (Hard Coat Layer Composition 3) Pentaerythritol triacrylate (product name "A-TMM-3", manufactured by Shin-Nakamura Chemical Co., Ltd.): 100 parts by mass Silicone lubricant (product name "BYK-377", manufactured by BYK Japan Co., Ltd.): 0.1 parts by mass Fluorine-containing antifouling agent (product name "Megafac RS-56", manufactured by DIC Corporation): 0.1 parts by mass

[0173] (Hard Coat Layer Composition 4) Pentaerythritol triacrylate (product name "A-TMM-3", manufactured by Shin-Nakamura Chemical Co., Ltd.): 100 parts by mass Silicone lubricant (product name "BYK-378", manufactured by BYK Japan Co., Ltd.): 100 parts by weight Fluorine-containing antifouling agent (product name "Megafac RS-56", manufactured by DIC Corporation): 0.1 parts by mass

[0174] (Hard Coat Layer Composition 5) Pentaerythritol triacrylate (product name "A-TMM-3", manufactured by Shin-Nakamura Chemical Co., Ltd.): 100 parts by mass Silicone lubricant (product name "BYK-UV3510", manufactured by BYK Japan Co., Ltd.): 100 parts by weight Fluorine-containing antifouling agent (product name "Megafac RS-56", manufactured by DIC Corporation): 0.1 parts by mass

[0175] (Hard Coat Layer Composition 6) Pentaerythritol triacrylate (product name "A-TMM-3", manufactured by Shin-Nakamura Chemical Co., Ltd.): 100 parts by mass Silicone lubricant (product name "BYK-UV3500", manufactured by BYK Japan Co., Ltd.): 0.1 parts by mass Fluorine-containing antifouling agent (product name "Megafac RS-56", manufactured by DIC Corporation): 0.1 parts by mass

[0176] (Hard Coat Layer Composition 7) Mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate (product name "M403", manufactured by Toagosei Co., Ltd.): 25 parts by mass Dipentaerythritol EO-modified hexaacrylate (product name "A-DPH-6E", manufactured by Shin-Nakamura Chemical Co., Ltd.): 25 parts by mass Irregular shaped silica particles (average particle size 25 nm, manufactured by JGC Catalysts and Chemicals Co., Ltd.): 50 parts by mass (based on 100% solids) Photopolymerization initiator (1-hydroxycyclohexyl phenyl ketone, product name "Omnirad184", manufactured by IGM Resins BV): 4 parts by mass Fluorine silicone leveling agent (product name: Fluorine silicone coating agent KP911, manufactured by Shin-Etsu Chemical Co., Ltd.): 0.2 parts by mass (based on 100% solids) Methyl isobutyl ketone (MIBK): 150 parts by weight

[0177] (Hard Coat Layer Composition 8) Pentaerythritol triacrylate (product name "A-TMM-3", manufactured by Shin-Nakamura Chemical Co., Ltd.): 100 parts by mass Silicone lubricant (product name "BYK-345", manufactured by BYK Japan Co., Ltd.): 0.1 parts by mass Fluorine-containing antifouling agent (product name "Megafac RS-75", manufactured by DIC Corporation): 0.1 parts by mass Lubricant (product name "H65", manufactured by CIK Nanotech Co., Ltd.): 1.5 parts by weight

[0178] (Hard Coat Layer Composition 9) Pentaerythritol triacrylate (product name "A-TMM-3", manufactured by Shin-Nakamura Chemical Co., Ltd.): 100 parts by mass Fluorine-containing antifouling agent (product name "Megafac RS-75", manufactured by DIC Corporation): 0.1 parts by mass

[0179] (Hard Coat Layer Composition 10) Pentaerythritol triacrylate (product name "A-TMM-3", manufactured by Shin-Nakamura Chemical Co., Ltd.): 100 parts by mass Silicone lubricant (product name "BYK-313", manufactured by BYK Japan Co., Ltd.): 0.1 parts by mass Fluorine-containing antifouling agent (product name "Megafac RS-75", manufactured by DIC Corporation): 0.1 parts by mass

[0180] (Hard Coat Layer Composition 11) Pentaerythritol triacrylate (product name "A-TMM-3", manufactured by Shin-Nakamura Chemical Co., Ltd.): 100 parts by mass Silicone lubricant (product name "BYK-322", manufactured by BYK Japan Co., Ltd.): 0.1 parts by mass Fluorine-containing antifouling agent (product name "Megafac RS-75", manufactured by DIC Corporation): 0.1 parts by mass

[0181] (Hard Coat Layer Composition 12) Pentaerythritol triacrylate (product name "A-TMM-3", manufactured by Shin-Nakamura Chemical Co., Ltd.): 100 parts by mass Silicone lubricant (product name "BYK-331", manufactured by BYK Japan Co., Ltd.): 0.1 parts by mass Fluorine-containing antifouling agent (product name "Megafac RS-75", manufactured by DIC Corporation): 0.1 parts by mass

[0182] Example 1 A triacetyl cellulose substrate (product name "KC8UAW", manufactured by Konica Minolta, Inc.) measuring 210 mm x 297 mm (A4 size) and 80 μm thick was prepared as the resin substrate. Composition 1 for hard coat layer was applied to the first surface (one surface) of the triacetyl cellulose substrate using a bar coater to form a coating film. The formed coating film was then heated at 90°C for 40 seconds to evaporate the solvent in the coating film, and ultraviolet light was irradiated in air using an ultraviolet irradiation device (light source H bulb, manufactured by Fusion UV Systems Japan Co., Ltd.) at an integrated light intensity of 100 mJ / cm. 2 The coating film was semi-cured (half-cured) by irradiating it so that the hard coat layer composition 2 was applied to the surface of the semi-cured coating film of the hard coat layer composition 1 using a bar coater, to form a coating film. The formed coating film was heated at 90°C for 1 minute to evaporate the solvent in the coating film, and then ultraviolet light was irradiated using an ultraviolet irradiation device (manufactured by Fusion UV Systems Japan, light source H bulb) at an accumulated light dose of 400 mJ / cm under conditions of an oxygen concentration of 200 ppm or less. 2 The coating film was fully cured by irradiating the film so that the film was completely cured (fully cured). This resulted in an optical film having a hard coat layer on the triacetyl cellulose substrate, the hard coat layer being composed of a first hard coat layer having a thickness of 15 μm and a second hard coat layer having a thickness of 5 μm laminated on the first hard coat layer.

[0183] The film thickness of the first hard coat layer and the second hard coat layer was measured using a scanning electron microscope (SEM) by photographing a cross section of the hard coat layer. The film thickness of the hard coat layer was measured at 20 locations on the cross section image, and the arithmetic mean value of the film thicknesses at those 20 locations was used. The specific method for photographing the cross section is described below. First, a 1 mm × 10 mm optical film was cut out and embedded in an embedding resin to prepare a block. From this block, uniform, hole-free slices with a thickness of 70 nm to 100 nm were cut using a standard sectioning method. An "Ultramicrotome EM UC7" (Leica Microsystems) or similar was used to prepare the slices. The remaining block from which the uniform, hole-free slices were cut was used as the measurement sample. Then, a scanning electron microscope (SEM) (product name "S-4800" manufactured by Hitachi High-Technologies Corporation) was used to photograph the cross section of the measurement sample. When taking cross-sectional photographs using the S-4800, cross-sectional observation was performed with the detector set to "SE," the acceleration voltage set to "5 kV," and the emission current set to "10 μA." The magnification was appropriately adjusted within the range of 10,000 to 50,000 times by adjusting the focus and observing whether the contrast and brightness of each layer could be distinguished. When taking cross-sectional photographs using the S-4800, the beam monitor aperture was set to "3," the objective lens aperture was set to "3," and the WD was set to "8 mm." In Examples 2 to 13 and Comparative Examples 1 to 5, the thickness of the substrate and the film thickness of the hard coat layer were measured using the same method as in Example 1.

[0184] <Example 2> In Example 2, an optical film was obtained in the same manner as in Example 1, except that composition 3 for a hard coat layer was used instead of composition 2 for a hard coat layer.

[0185] Example 3 In Example 3, an optical film was obtained in the same manner as in Example 1, except that composition 4 for a hard coat layer was used instead of composition 2 for a hard coat layer.

[0186] Example 4 In Example 4, an optical film was obtained in the same manner as in Example 1, except that composition 5 for a hard coat layer was used instead of composition 2 for a hard coat layer.

[0187] <Example 5> In Example 5, an optical film was obtained in the same manner as in Example 1, except that composition 6 for a hard coat layer was used instead of composition 2 for a hard coat layer.

[0188] Example 6 In Example 6, an optical film was obtained in the same manner as in Example 1, except that a 60 μm thick triacetyl cellulose substrate (product name "KC6UAW", manufactured by Konica Minolta, Inc.) was used instead of an 80 μm thick triacetyl cellulose substrate (product name "KC8UAW", manufactured by Konica Minolta, Inc.), and that composition 7 for hard coat layer was used instead of composition 2 for hard coat layer.

[0189] Example 7 In Example 7, an optical film was obtained in the same manner as in Example 1, except that a 25 μm thick triacetyl cellulose substrate (product name "Z-TAC", manufactured by Fujifilm Corporation) was used instead of an 80 μm thick triacetyl cellulose substrate (product name "KC8UAW", manufactured by Konica Minolta, Inc.), and that composition 7 for hard coat layer was used instead of composition 2 for hard coat layer.

[0190] Example 8 In Example 8, an optical film was obtained in the same manner as in Example 1, except that a 48 μm thick polyethylene terephthalate substrate (product name "Cosmoshine (registered trademark) A4100", manufactured by Toyobo Co., Ltd.) was used instead of the triacetyl cellulose substrate, and that composition 7 for hard coat layer was used instead of composition 2 for hard coat layer.

[0191] Example 9 In Example 9, an optical film was obtained in the same manner as in Example 1, except that a 38 μm thick polyethylene terephthalate substrate (product name "Cosmoshine (registered trademark) A4100", manufactured by Toyobo Co., Ltd.) was used instead of the triacetyl cellulose substrate, and that composition 7 for hard coat layer was used instead of composition 2 for hard coat layer.

[0192] Example 10 In Example 10, an optical film was obtained in the same manner as in Example 1, except that a 50 μm thick cycloolefin polymer substrate (product name "ZEONORFILM (registered trademark) ZF16", manufactured by Zeon Corporation) was used instead of the triacetyl cellulose substrate.

[0193] Example 11 In Example 11, an optical film was obtained in the same manner as in Example 1, except that a 25 μm thick cycloolefin polymer substrate (product name "ZEONORFILM (registered trademark) ZF16", manufactured by Zeon Corporation) was used instead of the triacetyl cellulose substrate.

[0194] Example 12 In Example 12, an optical film was obtained in the same manner as in Example 1, except that a 60 μm thick polyimide substrate (trade name "Neoprim (registered trademark), manufactured by Mitsubishi Gas Chemical Company, Inc.) was used instead of the triacetyl cellulose substrate. Note that the Neoprim (registered trademark) was a commercially available polyimide substrate.

[0195] Example 13 In Example 13, an optical film was obtained in the same manner as in Example 1, except that a 20 μm thick polyimide substrate (trade name "Neoprim (registered trademark), manufactured by Mitsubishi Gas Chemical Company, Inc.) was used instead of the triacetyl cellulose substrate. Note that the Neoprim (registered trademark) is a commercially available polyimide substrate.

[0196] <Comparative Example 1> In Comparative Example 1, an optical film was obtained in the same manner as in Example 1, except that Composition 8 for a hard coat layer was used instead of Composition 2 for a hard coat layer.

[0197] <Comparative Example 2> In Comparative Example 2, an optical film was obtained in the same manner as in Example 1, except that Composition 9 for a hard coat layer was used instead of Composition 2 for a hard coat layer.

[0198] <Comparative Example 3> In Comparative Example 3, an optical film was obtained in the same manner as in Example 1, except that the composition 10 for a hard coat layer was used instead of the composition 2 for a hard coat layer.

[0199] <Comparative Example 4> In Comparative Example 4, an optical film was obtained in the same manner as in Example 1, except that Composition 11 for a hard coat layer was used instead of Composition 2 for a hard coat layer.

[0200] <Comparative Example 5> In Comparative Example 5, an optical film was obtained in the same manner as in Example 1, except that Composition 12 for a hard coat layer was used instead of Composition 2 for a hard coat layer.

[0201] <Checking the indentation before and after the eraser test> For the optical films according to Examples 1 to 6, 8, 10, and 12 and Comparative Examples 1 to 5, an atomic force microscope (AFM) (product name "WET-9100" manufactured by Shimadzu Corporation) was used to observe a 5-μm square region on the surface of the optical film before and after the eraser test. The presence of at least one of the following recesses within the region was confirmed: annular with an outer diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm; circular with a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm; and irregular with a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm. The number of such recesses was counted. The presence of 1 to 50 such recesses was recorded as "present," and the presence of 1 to 50 such recesses was recorded as "absent." The presence of protrusions with a height of 1 nm or more inside the recesses was also confirmed. The absence of such protrusions was recorded as "absent," and the presence of such protrusions was recorded as "present." In the optical film according to Example 7, observation of depressions was not performed because the hard coat layer was formed using the same composition 7 for hard coat layer as in Example 6. In the optical film according to Example 9, observation of depressions was not performed because the hard coat layer was formed using the same composition 7 for hard coat layer as in Example 8. In the optical film according to Example 11, observation of depressions was not performed because the hard coat layer was formed using the same composition 7 for hard coat layer as in Example 10. In the optical film according to Example 13, observation of depressions was not performed because the hard coat layer was formed using the same composition 7 for hard coat layer as in Example 12.

[0202] To check for dents, the optical film was first cut into three pieces measuring 50 mm x 100 mm to obtain three samples. A rectangular frame measuring 20 mm x 40 mm was then drawn on the back of each of the three samples using an oil-based pen. The rectangular frame was drawn so that its longitudinal direction was parallel to the longitudinal direction of the sample. An eraser test was then performed on two of the three samples.

[0203] The eraser test was performed as follows. First, a pencil with an eraser attached (product name "Office Pencil 9852 (with eraser)", manufactured by Mitsubishi Pencil Co., Ltd.) was prepared. This pencil with an eraser attached had a diameter of 6 mm and a durometer hardness (Type A durometer, Type A (cylindrical indenter), JIS K6253:1997 / ISO7619 (Rubber)) of 65 to 90. After preparing the pencil with an eraser attached, the pencil was cut at a position 50 mm from the tip of the eraser. The cut pencil with an eraser attached was then inserted into a jig with a 6 mm diameter hole from the side opposite the eraser so that the eraser was completely exposed. The pencil with an eraser attached was attached to the jig so that the tip of the eraser was exposed approximately 1.5 mm from the jig. The jig with this pencil with an eraser attached was then attached to a Gakushin-type abrasion fastness tester (product name "AB-301", manufactured by Tester Sangyo Co., Ltd.). The fixture was attached to the tester so that the pencil with the eraser was perpendicular to the sample surface.

[0204] One of the samples obtained above was fixed to the test piece stage of the Gakushin-type abrasion fastness tester, ensuring no wrinkles and conforming to the surface of the test piece stage. The sample was placed so that the direction of movement of the test piece stage was the longitudinal direction of the sample and the center of the rub was the center of the frame. Then, in this state, an eraser test (500g x 4000 rubs) was performed in which the surface of the sample was rubbed 4000 times with an eraser at a load of 500g and a rub speed of 30mm / s. Similarly, a rubber test (1000g x 5000 rubs) was performed using another sample obtained above, in which the surface of the sample was rubbed 5000 times with an eraser at a load of 1000g and a rub speed of 30mm / s. That is, one of the three samples had not been subjected to the eraser test (before the eraser test), another sample had been subjected to the eraser test (500g x 4000 strokes), and the remaining sample had been subjected to the eraser test (1000g x 4000 strokes).

[0205] The presence of annular, circular, or irregularly shaped depressions on the surface of each sample was confirmed by observation using an atomic force microscope (AFM) (product name "WET-9100" manufactured by Shimadzu Corporation). The observations were performed as follows. Specifically, three locations within the sample frame that were at least visually normal (locations without large foreign objects or scratches) were randomly selected and cut into 5 mm squares to obtain three measurement samples. On the other hand, several flat, circular metal plates with a diameter of 15 mm and a thickness of 1 mm were prepared, and double-sided carbon tape manufactured by Nissin EM Co., Ltd. was attached to each metal plate. One measurement sample was attached to the tape with the surface of the measurement sample (the surface of the optical film) facing up. The metal plates with the sample attached were then left overnight in a desiccator to ensure proper adhesion between the tape and the measurement sample. After leaving it overnight, the metal plate with the sample was fixed with a magnet onto the measurement stage of an atomic force microscope (product name "WET-9400", manufactured by Shimadzu Corporation), and the surface shape was observed with the atomic force microscope in tapping mode over a measurement area of 5 μm square.

[0206] The number of dimples was calculated by randomly selecting five locations for each measurement sample, counting the number of dimples present in a 5-μm square area for each of three measurement samples x 5 locations (15 locations in total), and calculating the arithmetic average of the numbers of dimples at the 15 locations. When the dimples were annular and only some, but not all, of the dimples were present within the area, a 5-μm square area on the surface of the optical film was observed with an atomic force microscope, and the outer edges of the dimples present within the area were extrapolated to form a circle, as shown by the dotted line in Figure 2. If the area inside the outer edge of a dimple present within the area was equal to or greater than half the area of the extrapolated circle, even a portion of the dimple was counted as a dimple; if the area of a portion of the dimple present within the area was less than half the area of the extrapolated circle, the dimple was not counted as a dimple.

[0207] When the depressions were annular, the outer diameter and depth of the depressions were determined as follows to determine whether they were depressions. First, a 5-μm square area on the surface of the sample was observed with an atomic force microscope. For one depression, a line was drawn from an arbitrary point A on the outer edge of the depression to another arbitrary point B on the outer edge of the depression, as shown in FIG. 2, so that the longest line was measured. The length of the line from point A to point B (outer diameter) was then determined. The depth along this line was then measured from point A to point B, and the deepest depth from point A to point B from a reference position was determined. The reference position for the depth was automatically determined by reading the surface shape of the optical film with the atomic force microscope. This measurement was then performed at three locations, and the outer diameter of the depression was calculated by calculating the arithmetic mean of the lengths measured at the three locations. The depth of the depression was also calculated by calculating the arithmetic mean of the three depths measured at the three locations. Note that within a depression, there may be locally deep holes with an aspect ratio of 5 or more, and if these holes are taken into account when measuring the depth of the depression, the value of the depression depth cannot be determined accurately. Therefore, points A and B were determined so that such locally deep holes would not exist between points A and B. When the depression was circular, the diameter and depth were determined in the same way as when the depression was annular.

[0208] When the depressions had an irregular shape, the diameter of the depressions was determined as follows. First, as shown in FIG. 2, a 5 μm square area on the surface of the sample was observed with an atomic force microscope, and a line L1 passing through what was considered to be the center of one depression was drawn. Points C1 and D1 where this line L1 intersected with the outer edge of the depression were determined. The distance DS1 between points C1 and D1 was then measured, and the midpoint M of the distance DS1 was determined. An imaginary line L2 was also drawn that passed through midpoint M and was at an angle of 60° to line L1. Points C2 and D2 where this line L2 intersected with the outer edge of depression 10B were determined, and the distance DS2 between points C2 and D2 was measured. Furthermore, an imaginary line L3 was drawn that passed through the midpoint M, was at an angle of 120° to the line L1, and did not overlap with the line L2. Points C3 and D3 were determined where this line L3 intersected with the outer edge of the recess 10B, and the distance DS3 between points C3 and D3 was measured. The average value of the distances DS1 to DS3 was then calculated and used as the diameter. Furthermore, when the recess had an irregular shape, the depth was calculated in the same manner as when the recess was annular.

[0209] <Measurement of arithmetic mean height (Sa) before and after the eraser test> For the optical films according to Examples 1 to 6, 8, 10, and 12 and Comparative Examples 1 to 5, the arithmetic mean height (Sa) before and after the eraser test (5000 strokes) was calculated using an atomic force microscope (for example, product name "AFM-5500" manufactured by Hitachi Technologies, Ltd.) as follows, and the absolute value of the difference between the arithmetic mean height (Sa) before the eraser test and the arithmetic mean height (Sa) after the eraser test (1000g x 5000 strokes) was determined. Specifically, first, the optical film before the eraser test was cut into two pieces measuring 50mm x 100mm to obtain two samples. Then, a rectangular frame measuring 20mm x 40mm was drawn on the back of each of the two samples using an oil-based pen. The rectangular frame was drawn so that the longitudinal direction was parallel to the longitudinal direction of the sample. Then, an eraser test (1000g x 5000 strokes) was performed on one of the two samples. The eraser test (1000g x 5000 strokes) was carried out under the same conditions as the eraser test (1000g x 5000 strokes) in the above section <Checking the indentations before and after the eraser test>.

[0210] Three randomly selected areas within the frame of each sample that were at least visually normal (areas free of large foreign objects or scratches) were cut into 5 mm squares to obtain three measurement samples. Several flat, circular metal plates with a diameter of 15 mm and a thickness of 1 mm were prepared, and Nissin EM double-sided carbon tape was attached to each metal plate. One measurement sample was attached to the tape with the surface of the measurement sample (the surface of the optical film) facing up. The metal plates with the sample attached were then left overnight in a desiccator to ensure proper adhesion between the tape and the measurement sample.

[0211] After leaving the sample overnight, the metal plate with the sample attached was placed on the measurement stage of an atomic force microscope (product name "AFM-5500," manufactured by Hitachi Technologies, Ltd.). The surface profile was observed using the atomic force microscope in tapping mode with a measurement area of 5 μm square. The arithmetic mean height (Sa) was calculated from the observed data using the surface analysis software built into the atomic force microscope. The vertical scale during surface analysis was 20 nm. The observations were performed at room temperature, and an Olympus SI-DF40P2 cantilever was used. Five locations were randomly selected for each sample, and the surface profile was observed for each of the five locations (3 samples x 5 locations, a total of 15 locations). The surface profile (Sa) was calculated for all 15 data points using the surface analysis software built into the atomic force microscope. The arithmetic mean value of the 15 locations was used as the Sa of the sample. The arithmetic mean height (Sa) of the sample after the eraser test (1000g x 5000 strokes) was measured in the same manner as for the optical film before the eraser test.The absolute value of the difference between the arithmetic mean height (Sa) of a 5 μm square area on the surface of the measured sample before the eraser test and the arithmetic mean height (Sa) of a 5 μm square area on the surface of the measured sample after the eraser test (1000g x 5000 strokes) was calculated.

[0212] <Measurement of dynamic friction coefficient before and after eraser test> For the optical films of Examples 1 to 6, 8, 10, and 12 and Comparative Examples 1 to 5, the dynamic friction coefficient of the surface of the optical film was measured before and after the eraser test, and the rate of change in the dynamic friction coefficient of the surface of the optical film after the eraser test relative to the dynamic friction coefficient of the surface of the optical film before the eraser test was determined. The dynamic friction coefficient (load 500 g) of the surface of the optical film before the eraser test was taken as the dynamic friction coefficient of the sample when rubbed back and forth once in the eraser simulation test (500 g × 4000 reciprocating strokes) described below. The dynamic friction coefficient (load 1000 g) of the surface of the optical film before the eraser test was taken as the dynamic friction coefficient of the sample when rubbed back and forth once in the eraser simulation test (1000 g × 5000 reciprocating strokes) described below. The dynamic friction coefficient (load 500 g) of the surface of the optical film after the eraser test (500 g × 4000 reciprocating strokes) was taken as the dynamic friction coefficient of the sample when rubbed back and forth 4000 times in the eraser simulation test (500 g × 4000 reciprocating strokes). The dynamic friction coefficient (load 1000 g) of the surface of the optical film after the eraser test (1000 g × 5000 reciprocating strokes) was taken as the dynamic friction coefficient of the sample when rubbed back and forth 5000 times in the eraser simulation test (1000 g × 5000 reciprocating strokes). The eraser simulation test conducted when measuring the coefficient of dynamic friction is a replica of the eraser test described in the section "Checking for depressions and protrusions before and after the eraser test."

[0213] Specifically, a pencil with an eraser (product name "Office Pencil 9852 (with eraser)", manufactured by Mitsubishi Pencil Co., Ltd.) was prepared and cut at a position 50 mm from the tip of the eraser. The cut pencil with an eraser was then inserted into a jig with a 6 mm diameter hole from the side opposite the eraser so that the tip of the eraser was completely exposed, and attached to the jig. The pencil with an eraser was attached to the jig so that the tip of the eraser was exposed approximately 1.5 mm from the jig. The jig with the eraser pencil was then fixed with double-sided tape to the axis of the measurement unit of a dynamic friction and wear tester (product name "Handy Tribomaster Type: TL201Ts", manufactured by Trinity Lab Co., Ltd.). In this state, dedicated software (triboanalysis software) was launched on the screen of a personal computer (PC) electrically connected to the dynamic friction and wear tester.

[0214] Separately, the optical film before the eraser test was cut into 50 mm x 100 mm pieces to obtain six samples. Of the six samples, three were used to measure the dynamic friction coefficient before the eraser test and after the eraser test (500 g x 4000 reciprocations), and the remaining three were used to measure the dynamic friction coefficient after the eraser test (1000 g x 5000 reciprocations). A 20 mm x 40 mm frame-shaped mark was drawn on the back of each sample with an oil-based pen to easily identify the center of the rubbing area. The mark was drawn so that its longitudinal direction was parallel to the longitudinal direction of the sample. The sample was then placed on the drive unit of the static / dynamic friction and wear tester with the surface to be measured for the dynamic friction coefficient facing up, and the four edges of the sample were fixed with Cellotape (registered trademark) so that there were no wrinkles and it was aligned with the surface of the drive unit. The sample was placed so that the direction of movement of the drive unit was the longitudinal direction of the sample and the center of the rubbing area was centered within the mark. A 500g weight was fixed to the top of the jig with double-sided tape, and the eraser portion of the measurement unit was placed perpendicularly against the sample surface. Then, the rubbing length (one way) was set to 20mm, the rubbing speed to 40 strokes / min, the number of strokes to 4000, and the measurement mode to continuous measurement. The start switch on the PC screen was pressed to perform an eraser simulation test (500g x 4000 strokes) at a temperature of 23°C and a relative humidity of 50%, and the measurement of the sample's kinetic friction coefficient (500g load) was initiated. During this eraser simulation test, the kinetic friction coefficient (500g load) was continuously measured, and a graph was obtained with time on the horizontal axis and kinetic friction force on the vertical axis. The kinetic friction coefficient (500g load) at each stroke was calculated by dividing the kinetic friction force at the time reaching that stroke by the normal force. Each kinetic friction coefficient (500g load) was measured for three samples, and the arithmetic mean of the three measurements was used. The exposed tip of the eraser was adjusted to 1.5 mm for each measurement. Furthermore, based on the above formula (2), the rate of change in the dynamic friction coefficient (1000 g load) of the sample surface after the pseudo-eraser test (500 g x 4000 strokes) relative to the dynamic friction coefficient (500 g load) of the sample surface before the pseudo-eraser test was calculated.

[0215] The remaining three samples were subjected to a similar eraser simulation test (1000g x 5000 strokes) and the dynamic friction coefficient (1000g load) was measured. In this case, the weight was changed from 500g to 1000g, and the number of strokes was set to 5000. The dynamic friction coefficient (1000g load) was measured for the three samples, and the arithmetic mean value of the three measurements was used. Furthermore, based on the above formula (2), the rate of change in the dynamic friction coefficient (1000g load) of the sample surface after the eraser simulation test (1000g x 5000 strokes) relative to the dynamic friction coefficient (1000g load) of the sample surface before the eraser simulation test was calculated.

[0216] <Contact angle maintenance rate before and after eraser test> For the optical films according to Examples 1 to 6, 8, 10, and 12 and Comparative Examples 1 to 5, the contact angle of the surface of the optical film with water was measured before and after the eraser test, and the maintenance rate of the contact angle after the eraser test relative to the contact angle before the eraser test was calculated. The eraser test was carried out in two ways: a 500g eraser test (4000 strokes) and a 1000g eraser test (500g x 5000 strokes).

[0217] First, three samples similar to the sample described in the above section <Confirming dents before and after the eraser test> were obtained. Then, one of the three samples was subjected to the eraser test (500g x 4000 strokes) described in the above section <Confirming dents and protrusions before and after the eraser test>, and the other sample was subjected to the eraser test (1000g x 5000 strokes) described in the above section <Confirming dents before and after the eraser test>.

[0218] Then, at 23°C, a microscopic contact angle meter (product name "DropMaster300", manufactured by Kyowa Interface Science Co., Ltd.) was used to measure the contact angle of water on the sample surface according to the sessile drop method described in JIS R3257:1999. Specifically, a measurement sample was first obtained by cutting a piece of 30mm x 50mm from the sample before the eraser test. The measurement sample was cut out so as to include a 20mm x 40mm frame-shaped mark. The measurement sample was then attached flat on a 25mm x 75mm glass slide with double-sided tape. The measurement sample was attached so that the frame fit within the glass slide. Thereafter, to prevent static electricity carried by the measurement sample from affecting the measurement results, the measurement sample was de-electrified for 30 seconds by irradiating it with ions using an ionizer (for example, product name "KD-730B", manufactured by Kasuga Electric Co., Ltd.). After de-electrification, 1μL of water was dropped onto the surface of the second hard coat layer using a syringe and held for 5 seconds. The switch on the microscope contact angle meter was then pressed to measure the contact angle with water. The contact angle measurement was performed under an environment of 23°C temperature and 50% relative humidity. The contact angle was measured at 10 points, and the arithmetic average of the measured values was used as the contact angle of the optical film surface before the eraser test. The contact angle with water on the surface of the optical film after the eraser test (500g x 4000 reciprocations) was measured using the same method as that for measuring the contact angle with water on the surface of the optical film before the eraser test, except that the sample after the eraser test (500g x 4000 reciprocations) was used. The contact angle retention rate was then calculated according to the above formula (3).

[0219] <Steel wool (SW) test> The surfaces of the optical films (surfaces of the hard coat layers) before the eraser test in Examples 1 to 6, 8, 10, and 12 and Comparative Examples 1 to 5 were subjected to a steel wool test and evaluated. Specifically, a 50 mm × 100 mm sample was cut out from the optical film before the eraser test to obtain a sample before the eraser test. The sample was then fixed flat on the test piece stage of a Gakushin-type abrasion fastness tester (product name "AB-301", manufactured by Tester Sangyo Co., Ltd.) so that the surface of the sample (the surface of the optical film) was facing up, without wrinkles or curls. Steel wool #0000 (manufactured by Nippon Steel Wool Co., Ltd., product name "Bonstar B-204") was then set in the tester and brought into contact with the surface of the sample. The test was carried out at a temperature of 23°C and a relative humidity of 50%, with a moving speed of 100 mm / sec, a moving distance of 200 mm in one round trip (one-way moving distance 100 mm), and a load of 1 kg / cm. 2 The steel wool was rubbed back and forth 5,000 times while applying a pressure of 1000 kJ / cm. The contact area between the steel wool and the surface of the optical film was 1 cm. 2 The Bonstar B-204 mentioned above was a commercial size, measuring approximately 390mm wide, 75mm long, and 110mm thick. An appropriate amount was torn off from this and rolled up evenly (do not cut with a blade, as cutting would expose the cross section of the steel wool fibers) until there were no unusual protruding steel wool parts. When a load of 1kg was applied, the contact area was 1cm2. 2 The thickness of the steel wool was set to 20 mm at this time. The sample was then observed with the naked eye under fluorescent light (illuminance on the sample: 800-1200 Lx, observation distance: 30 cm) and under LED light (illuminance on the sample: 4000-6000 Lx, observation distance: 30 cm), and the presence or absence of scratches on the sample surface was visually confirmed. The evaluation criteria were as follows: ○: No scratches were found. ×: Scratches were observed.

[0220] <Pencil hardness test> The pencil hardness of the surface (the surface of the hard coat layer) of the optical film before the eraser test in Examples 1 to 6, 8, 10, and 12 and Comparative Examples 1 to 5 was measured according to JIS K5600-5-4:1999. For pencil hardness measurement, a 50 mm x 100 m sample was cut from the optical film to obtain a sample before the eraser test. This sample was fixed to a glass plate with Cellotape (registered trademark) manufactured by Nichiban Co., Ltd. to prevent folds or wrinkles, and a load of 1 kg was applied to the pencil while the pencil was moved at a speed of 1 mm / sec. The pencil hardness was defined as the highest hardness at which the surface of the optical film was not scratched in the pencil hardness test. Pencil hardness measurement was performed using multiple pencils of different hardness. Pencil hardness tests were performed five times for each pencil. If scratches were not visually observed on the surface of the sample (optical film) when the surface was observed through a fluorescent lamp four or more times out of the five times, it was determined that the pencil of that hardness did not scratch the surface of the sample.

[0221] <Total light transmittance measurement> The total light transmittance of the optical films according to Examples 1 to 6, 8, 10, and 12 and Comparative Examples 1 to 5 before the eraser test was measured using a haze meter (product name "HM-150", manufactured by Murakami Color Research Laboratory) in accordance with JIS K7361-1:1997. The total light transmittance was measured by cutting a sample of 50 mm x 100 mm from the optical film before the eraser test. The sample was then placed with the hard coat layer facing away from the light source, without curling or wrinkles and without fingerprints or dust, and each sample was measured three times, and the arithmetic mean value of the values obtained from the three measurements was used.

[0222] <Haze value measurement> The haze values (total haze values) of the optical films before the eraser test in Examples 1 to 6, 8, 10, and 12 and Comparative Examples 1 to 5 were measured in accordance with JIS K7136:2000 using a haze meter (product name "HM-150", manufactured by Murakami Color Research Laboratory). The haze values were measured by cutting a sample of 50 mm x 100 mm from the optical film before the eraser test. The sample was then placed with the hard coat layer facing away from the light source, without curling or wrinkles and without fingerprints or dust, and each optical film was measured three times, and the arithmetic mean value of the values obtained from the three measurements was used.

[0223] <Flexibility evaluation> (1) Evaluation of cracks and breakage after folding test The optical films according to Examples 6 to 13 were subjected to a folding test to evaluate cracking and breakage. Specifically, a rectangular sample measuring 125 mm x 50 mm was cut out from the optical film before the eraser test. After cutting out the sample, the short sides (50 mm) of the sample were fixed to a U-shaped stretch tester (product name "DLDMLH-FS", manufactured by Yuasa System Equipment Co., Ltd.) as a folding durability tester, and the sample was attached so that the minimum distance between the two opposing sides was 2 mm (the outer diameter of the bent part was 2 mm) as shown in FIG. 5(C). Under the following conditions, a test was performed in which the surface of the hard coat layer of the sample was folded 180° (a test in which the hard coat layer was folded inside and the substrate was folded outside) 100,000 times. (Folding conditions) Reciprocating speed: 80 rpm (revolutions per minute) Test stroke: 60mm Flexion angle: 180°

[0224] The bent portion was then examined for cracks or breaks. The evaluation criteria were as follows. When the region that would become the bent portion of each optical film was observed before the folding test, no cracks or breaks were observed. The evaluation criteria were as follows. (foldability) ⊚: No cracks or breaks were observed at the bent portion even after the folding test. ◯: After the folding test, some cracks were observed at the bent portion, but the level was not problematic in practical use. △: After the folding test, cracks or breaks occurred at the bent portion.

[0225] Similarly, samples similar to those described above were prepared from the optical films according to Examples 6 to 13. The short sides of the samples were fixed with fixing parts, the two opposing sides were attached so that the minimum distance φ was 2 mm (the outer diameter of the bent part was 2 mm), and the samples were folded 180° 200,000 times with the hard coat layer side facing inward. Similarly, the samples were observed for cracks and breaks after the folding test, and were evaluated according to the above criteria. Furthermore, samples similar to those described above were prepared from the optical films according to Examples 6 to 13. The short sides of the samples were fixed with fixing parts, the two opposing sides were attached so that the minimum distance φ was 2 mm (the outer diameter of the bent part was 2 mm), and the samples were folded 180° 300,000 times with the hard coat layer side facing inward. Similarly, the samples were observed for cracks and breaks after the folding test, and were evaluated according to the above criteria.

[0226] (2) Evaluation of fold creases after folding test The appearance of the optical films according to Examples 6 to 13 after a folding test was observed to evaluate whether creases had occurred at the bent portions of the optical films. The folding test was performed using the method described in the section on surface resistance evaluation before and after the folding test. The creases were observed visually in an environment with a temperature of 23°C and a relative humidity of 50%. The creases were observed in a bright room with white lighting (800 lux to 2000 lux), with transmitted and reflected light, and both the inside and outside portions of the bent portion when folded were observed. To easily identify the positions to be observed, the sample before the folding test was placed on the fixing section of a durability tester. When folded once, marks indicating the bent portions were made with an oil-based pen on both ends of the bent portion located perpendicular to the folding direction, as shown in FIG. 7 . After the folding test, the optical film was removed from the durability tester and a line connecting the marks at both ends of the bent portion was drawn with an oil-based pen. The fold crease observation was performed by visually observing the entire bent portion, which was the area formed by the marks at both ends of the bent portion and the line connecting these marks. When the area that would become the bent portion of each optical film before the folding test was observed, no fold crease was observed. The evaluation criteria were as follows: ⊚: No creases were observed in the optical film even after the folding test. ◯: After the folding test, some creases were observed in the optical film, but they were at a level that would not cause any problems in practical use. △: After the folding test, creases were observed in the optical film.

[0227] (3) Microcrack evaluation after folding test The appearance of the optical films according to Examples 6 to 13 after a folding test was observed to evaluate whether microcracks had occurred at the bent portions of the optical film. The folding test was performed using the method described in the section on surface resistance evaluation before and after the folding test. Microcrack observation was performed using a digital microscope (product name "VHX-5000," manufactured by Keyence Corporation) in an environment of 23°C temperature and 50% relative humidity. Specifically, the sample after the folding test was first slowly unfolded and fixed to the microscope stage with tape. If the fold was strong, the observation area was made as flat as possible. However, the area to be observed near the center of the sample (the bent portion) was not touched with the hand, and only to the extent that no force was applied. Next, both the inner and outer portions of the folded sample were observed. Microcrack observation was performed using a ring light as the illumination for the digital microscope at 200x magnification, using dark field and reflected light. To observe microcracks, the sample before the folding test was placed on the fixed part of the durability tester so that the observation position could be easily identified. When folded once, marks indicating the bent portion were made with an oil-based pen on both ends of the bent portion located in a direction perpendicular to the folding direction, as shown in Figure 8. After the folding test, the sample was removed from the durability tester and a line connecting the marks on both ends of the bent portion was drawn with an oil-based pen. The microscope was positioned so that the center of the microscope's field of view was the center of the bent portion. When the bent portion of each optical film was observed before the folding test, no microcracks were observed. The evaluation criteria were as follows: (microcracks) ⊚: No microcracks were observed in the optical film even after the folding test. ◯: After the folding test, some microcracks were observed in the optical film, but the level was not problematic in practical use. △: Microcracks were observed in the optical film after the folding test.

[0228] The results are shown in Tables 1 to 3 below. [Table 1]

[0229] [Table 2]

[0230] [Table 3]

[0231] The results are described below. In the optical films according to Comparative Examples 1 to 5, no 1 to 50 dents were found after the eraser test (500 g × 4000 reciprocating strokes), or the rate of change in the dynamic friction coefficient before and after the eraser test (500 g × 4000 reciprocating strokes) exceeded 35%. Therefore, although the optical films according to Comparative Examples 1 and 2 had good results in the steel wool test, they had low contact angle maintenance rates and poor abrasion resistance. Furthermore, in the optical films according to Comparative Examples 3 to 5, although the contact angle maintenance rates were good, they had poor results in the steel wool test and poor scratch resistance. In contrast, in the optical films of Examples 1 to 6, 8, 10, and 12, one to 50 of the above-mentioned depressions were confirmed after the eraser test (500g x 4000 reciprocations), the dynamic friction coefficient before the eraser test (500g x 4000 reciprocations) was within the range of 0.70 or less, and the rate of change in the dynamic friction coefficient before and after the eraser test (500g x 4000 reciprocations) was within 35%, so the results of the steel wool test and the contact angle retention rate were also good. The hard coat layer of the optical film according to Example 7 is the same as that of the optical film according to Example 6, the hard coat layer of the optical film according to Example 9 is the same as that of the optical film according to Example 8, the hard coat layer of the optical film according to Example 11 is the same as that of the optical film according to Example 10, and the hard coat layer of the optical film according to Example 13 is the same as that of the optical film according to Example 12. Therefore, it is considered that the results obtained for Example 7 are similar to those for Example 6, Example 9 is similar to that for Example 8, Example 11 is similar to that for Example 10, and Example 13 is similar to that for Example 12. From these results, it was confirmed that the optical films according to Examples 1 to 13 were excellent in both scratch resistance and abrasion resistance.

[0232] In the optical films according to Comparative Examples 1 to 5, the absolute value of the difference in arithmetic mean height (Sa) before and after the eraser test (1000 g × 5000 reciprocations) was outside the range of 0.1 nm or more and 5 nm or less, and the rate of change in the dynamic friction coefficient before and after the eraser test (1000 g × 5000 reciprocations) exceeded 35%. Therefore, although the optical films according to Comparative Examples 1 and 2 had good results in the steel wool test, they had low contact angle maintenance rates and poor abrasion resistance. Furthermore, in the optical films according to Comparative Examples 3 to 5, although the results in the contact angle maintenance rates were good, they had poor results in the steel wool test and poor scratch resistance. In contrast, for the optical films of Examples 1 to 6, 8, 10, and 12, the absolute value of the difference in arithmetic mean height (Sa) before and after the eraser test (1000g x 5000 reciprocating strokes) was within the range of 0.1nm or more and 5nm or less, the dynamic friction coefficient before the eraser test (1000g x 5000 reciprocating strokes) was within the range of 0.70 or less, and the rate of change in the dynamic friction coefficient before and after the eraser test (1000g x 5000 reciprocating strokes) was within 35%, so the results of the steel wool test and the contact angle retention rate were also good. The hard coat layer of the optical film according to Example 7 is the same as that of the optical film according to Example 6, the hard coat layer of the optical film according to Example 9 is the same as that of the optical film according to Example 8, the hard coat layer of the optical film according to Example 11 is the same as that of the optical film according to Example 10, and the hard coat layer of the optical film according to Example 13 is the same as that of the optical film according to Example 12. Therefore, it is considered that the results obtained for Example 7 are similar to those for Example 6, Example 9 is similar to that for Example 8, Example 11 is similar to that for Example 10, and Example 13 is similar to that for Example 12. From these results, it was confirmed that the optical films according to Examples 1 to 13 were excellent in both scratch resistance and abrasion resistance.

[0233] For reference, Figure 11(A) shows a photograph of a 5 μm square area on the surface of the optical film of Example 1 before the eraser test, observed with an atomic force microscope; Figure 11(B) shows a photograph of the surface of the optical film before the eraser test, observed with an atomic force microscope; Figure 12(A) shows a photograph of the surface of the optical film of Example 1 after the eraser test (500 g x 4000 reciprocations), observed with an atomic force microscope; and Figure 12(B) shows a photograph of the surface of the optical film of Example 1 after the eraser test (500 g x 4000 reciprocations), observed with an atomic force microscope. In the optical film of Example 1, as shown in Figures 11(A) and 11(B), before the eraser test, there were no annular, circular, or irregularly shaped depressions. However, after the eraser test (500g x 4000 strokes), as shown in Figures 12(A) and 12(B), depressions of approximately 0.8 nm in width were formed along the edges of the circular portions that appeared circular, indicating the presence of annular depressions. Figures 11(A), 11(B), 12(A), and 12(B) were photographed using an atomic force microscope, AFM-5500 (manufactured by Hitachi Technologies, Ltd.). Note that the height scale in Figure 11(B) is 7.00 nm, while the height scale in Figure 12(B) is 20.04 nm due to the presence of protrusions. For this reason, at first glance, the sample surface in Figure 11(B) appears to be rougher than that in Figure 12(B), but because the scale in the height direction is different, it cannot be said that the sample surface in Figure 11(B) is rougher than that in Figure 12(B). The scale in the height direction was automatically determined by reading the surface shape of the sample with an atomic force microscope.

[0234] 13(A) shows a photograph of a 5 μm square area on the surface of the optical film according to Example 6 before the eraser test using an atomic force microscope (product name "AFM-5500", manufactured by Hitachi Technologies, Ltd.), and FIG. 13(B) shows a photograph of the surface of the optical film according to Example 6 after the eraser test (1000 g × 5000 reciprocations) using an atomic force microscope (product name "AFM-5500", manufactured by Hitachi Technologies, Ltd.). In Example 6, the above-mentioned depressions were present in both the sample before the eraser test and the sample after the eraser test (1000 g × 5000 reciprocations).

[0235] In the above folding test, the folding test was performed with the hard coat layer facing inward, but the samples were attached so that the minimum distance φ between the two opposing sides was 3 mm (outer diameter of the bent part: 3 mm), and the folding test was performed by folding the samples 180° repeatedly 100,000 times with the hard coat layer side facing outward.As a result, the optical films according to Examples 6 to 13 were evaluated for cracking / breakage, creases, and microcracks after the folding test, all of which were evaluated as good ("Good" or better). [Explanation of symbols]

[0236] 10...Optical film 10A…Surface 10B...depression 11...Resin substrate 11A...First side 11B...Second side 12...Functional layer 12A…Surface 13...First functional layer 14...Second functional layer 20...Polarizing plate 21...Polarizer 30...Image display device 33...Display element 35...Touch sensor

Claims

1. An optical film comprising a resin substrate and a functional layer provided on a first surface side of the resin substrate, the functional layer comprises a first functional layer containing particles, and a second functional layer which is provided on a surface of the first functional layer opposite to the surface on the resin substrate side and does not contain particles; the surface of the optical film is the surface of the second functional layer, The thickness of the second functional layer is 1 μm or more and 10 μm or less, an eraser test is conducted in which the surface of the optical film is rubbed back and forth 4,000 times with an eraser under a load of 500 g, and then a 5 μm square region on the surface of the optical film is observed with an atomic force microscope, and the region contains 1 to 50 depressions having at least one of annular shapes having an outer diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm, circular shapes having a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm, and irregular shapes having a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm, a dynamic friction coefficient measured on the surface of the optical film using the eraser under a load of 500 g before the eraser test is 0.60 or less; a rate of change in the dynamic friction coefficient of the surface of the optical film after the eraser test, measured using the eraser under a load of 500 g, relative to the dynamic friction coefficient of the surface of the optical film before the eraser test, is within 35%; the second functional layer contains a fluorine-based antifouling agent and a silicone-based lubricant, or contains a fluorine-based silicone-based antifouling agent; An optical film in which the resin substrate contains at least one of a polyimide-based resin and a polyamide-based resin, the thickness of the resin substrate is 5 μm or more and 75 μm or less, the distance between opposing sides of the optical film is 2 mm, and the optical film does not crack or break when a test in which the optical film is folded 180° with the functional layer on the inside is repeated 100,000 times.

2. An optical film comprising a resin substrate and a functional layer provided on a first surface side of the resin substrate, the functional layer comprises a first functional layer containing particles, and a second functional layer which is provided on a surface of the first functional layer opposite to the surface on the resin substrate side and does not contain particles; the surface of the optical film is the surface of the second functional layer, The thickness of the second functional layer is 1 μm or more and 10 μm or less, when an eraser test is performed in which the surface of the optical film is rubbed back and forth 5000 times with an eraser under a load of 1000 g, the absolute value of the difference between the average arithmetic height of a 5 μm square area on the surface of the optical film before the eraser test, as measured using an atomic force microscope, and the average arithmetic height of a 5 μm square area on the surface of the optical film after the eraser test, as measured using the atomic force microscope, is 10 nm or less; When a 5 μm square region on the surface of the optical film after the eraser test is observed using an atomic force microscope, there are 1 to 50 depressions in the region, each depression having at least one of annular shape having an outer diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm, circular shape having a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm, and irregular shape having a diameter of 0.1 μm to 2.5 μm and a depth of 1 nm to 150 nm, a dynamic friction coefficient measured on the surface of the optical film before the eraser test using the eraser under a load of 1000 g is 0.70 or less; a rate of change in the dynamic friction coefficient of the surface of the optical film after the eraser test, measured using the eraser under a load of 1000 g, relative to the dynamic friction coefficient of the surface of the optical film before the eraser test, is within 35%; the second functional layer contains a fluorine-based antifouling agent and a silicone-based lubricant, or contains a fluorine-based silicone-based antifouling agent; An optical film in which the resin substrate contains at least one of a polyimide-based resin and a polyamide-based resin, the thickness of the resin substrate is 5 μm or more and 75 μm or less, the distance between opposing sides of the optical film is 2 mm, and the optical film does not crack or break when a test in which the optical film is folded 180° with the functional layer on the inside is repeated 100,000 times.

3. 3. The optical film according to claim 1, wherein, when a 5 μm square area on the surface of the optical film before the eraser test is observed using an atomic force microscope, the number of depressions is 1 to 50.

4. 3. The optical film according to claim 1, wherein no depressions are present when a 5 μm square area on the surface of the optical film before the eraser test is observed using an atomic force microscope.

5. The optical film according to claim 1 , wherein protrusions having a height of 1 nm or more are present inside the depressions or within the depressions.

6. 6. The optical film according to claim 1, wherein the contact angle retention rate, which is the ratio of the contact angle with water on the surface of the optical film after the eraser test to the contact angle with water on the surface of the optical film before the eraser test, is 80% or more.

7. The optical film according to any one of claims 1 to 6; a polarizer provided on a second surface side of the resin substrate of the optical film opposite to the first surface; A polarizing plate comprising:

8. A display element; the optical film according to any one of claims 1 to 6 or the polarizing plate according to claim 7, which is disposed closer to a viewer than the display element; The image display device, wherein the functional layer of the optical film is located closer to a viewer than the resin substrate.

9. The image display device according to claim 8 , further comprising a touch sensor between the display element and the optical film.

10. 10. The image display device according to claim 8, wherein the display element is an organic light-emitting diode element.

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