Optical film, film roll, method for manufacturing optical film, and method for manufacturing film roll

Abstract

The invention provides an optical film capable of suppressing winding misalignment. The optical film (1A) has a long shape, and is wound from a starting end (11a) to a terminal end (11b) in the longitudinal direction of the long shape to form a film roll. In the optical film (1A), a plurality of embossments (20) are formed in the longitudinal direction between a starting end (11a) and a terminal end (11b), and the plurality of embossments (20) have the same height in a predetermined range. In the optical film (1A), when a first range (12a) is defined as an intermediate portion (11c) from a start end portion (11a) to a start end portion (11a) and a terminal portion (11b), a second range (12b) is defined as an intermediate portion (11c) from the intermediate portion (11c) to the terminal portion (11b), and the number of embossments (20) per unit length in the longitudinal direction is defined as the embossing density, the embossing density of the embossments (20) formed in the second range (12b) is higher than the embossing density of the embossments (20) formed in the first range (12a).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an optical film formed with embossing, a film roll wound with the optical film, a method for manufacturing the optical film, and a method for manufacturing the film roll. BACKGROUND

[0002] It is known that, when a film used for optical use or the like is wound in a roll shape, an embossed (knurled) region is formed at the end portion in the short side direction. The embossed region functions to prevent the film from being misaligned in winding at the time of winding.

[0003] The embossing is formed by so-called die pressing, which is a method of pressing a convex shape formed on a roller against a film while conveying the film while rotating the roller (Patent Literature 1).

[0004] In the case where the embossing is formed by die pressing, the interval of the embossing along the long side direction of the film is constant. Thus, the density of the embossing per unit length in the long side direction of the film is constant.

[0005] In contrast, a technique of forming embossing by coating with a resin has been proposed (Patent Literature 2). In the method of forming embossing by coating with a resin, it is possible to further increase the height of the embossing. In addition, it is possible to suppress damage to the embossing compared to embossing formed by die pressing.

[0006] PRIOR ART DOCUMENTS

[0007] PATENT LITERATURE

[0008] Patent Literature 1: Japanese Patent Application Laid-Open No. 2007-070514

[0009] Patent Literature 2: Japanese Patent No. 7125995 SUMMARY

[0010] However, if the embossing density is constant, as the winding length of the film roll increases, it is possible that misalignment in winding in the short side direction occurs between the films overlapping in the radial direction of the film roll.

[0011] In addition, in a configuration in which the coating embossing and the die pressing embossing are mixed, the height of the coating embossing is relatively high with respect to the die pressing embossing, and the coating embossing mainly supports the film. However, since the embossing density of the coating embossing is constant, it is possible that misalignment in winding of the film occurs.

[0012] The present disclosure was made in order to solve such a problem, and aims to provide an optical film and a film roll in which misalignment in winding can be suppressed. In addition, the present disclosure aims to provide a method for manufacturing an optical film and a method for manufacturing a film roll.

[0013] To address the aforementioned issues, this disclosure provides an optical film in the form of a strip, formed into a film roll wound from a first end to a second end along the long side direction of the strip. Multiple embossings are formed along the long side direction from the first end to the second end. The multiple embossings are at the same height within a specified range. When the first range is defined as the portion from the first end to the middle between the first and second ends, and the second range is defined as the portion from the middle to the second end, and the number of embossings per unit length along the long side direction is defined as the embossing density, the embossing density of the embossings formed in the second range is higher than that of the embossing density of the embossings formed in the first range.

[0014] In addition, this disclosure provides a film roll in which an optical film is wound from a first end to a second end. The optical film is strip-shaped, and multiple embossings are formed along the long side direction from the first end to the second end. The multiple embossings are at the same height within a specified range. The first range is defined as the portion from the first end to the middle between the first end and the second end, and the second range is defined as the portion from the middle to the second end. When the number of embossings per unit length along the long side direction is defined as the embossing density, the embossing density of the embossings formed in the second range is higher than that of the embossing density of the embossings formed in the first range.

[0015] Furthermore, this disclosure provides a method for manufacturing an optical film, which is a strip-shaped optical film with multiple embossed patterns formed along the long side direction from a first end to a second end. The method involves defining a first range from the first end to the middle portion between the first and second ends, defining a second range from the middle portion to the second end, and defining the number of embossed patterns per unit length along the long side direction as the embossing density. The embossing is formed by coating resin in such a way that the multiple embossed patterns are at the same height within a specified range and the embossing density of the embossed patterns formed in the second range is higher than that of the embossed patterns formed in the first range.

[0016] In addition, this disclosure provides a method for manufacturing a film roll, which involves forming a plurality of embossings along the long side direction from a first end to a second end of an elongated optical film, and winding the optical film from the first end to the second end. The method defines the first range as the portion from the first end to the middle between the first and second ends, the second range as the portion from the middle to the second end, and the number of embossings per unit length along the long side direction as the embossing density. The embossings are formed by coating resin in such a way that the plurality of embossings are at the same height within a specified range and the embossing density of the embossings formed in the second range is higher than that of the embossings formed in the first range. The embossed optical film is then wound onto a core.

[0017] According to this disclosure, even if the winding length of the film roll increases, winding misalignment in the short side direction can be suppressed in the optical films that overlap radially in the film roll. Attached Figure Description

[0018] Figure 1 This is a top view showing an example of an optical film.

[0019] Figure 2 This is a top view of the main part, representing an example of an optical film.

[0020] Figure 3 This is a side view showing an example of a membrane roll.

[0021] Figure 4 This is a side view showing the details of the embossing.

[0022] Figure 5 This is a side view showing the details of the embossing.

[0023] Figure 6 This is an illustrative diagram that schematically shows the relationship between the size of the embossing angle and the angle of the embossing support optical film.

[0024] Figure 7 This is a graph showing the relationship between embossing density and film winding length.

[0025] Figure 8 This is a graph showing the relationship between embossing density and film winding length.

[0026] Figure 9 This is an illustrative diagram illustrating an example of an evaluation method for misalignment.

[0027] Symbol Explanation

[0028] 1A···Optical film, 2···Embossed area, 3···Non-embossed area, 10···Film roll, 11a···Starting end, 11b···Ending end, 11c···Middle section, 12a···First range, 12b···Second range, 20··Embossed Detailed Implementation

[0029] Hereinafter, an example of the optical film and film roll of this embodiment will be described with reference to the accompanying drawings. Additionally, an example of the manufacturing method of the optical film and the manufacturing method of the film roll of this embodiment will be described.

[0030] <Examples of the composition of optical films and film rolls>

[0031] Figure 1 This is a top view showing an example of an optical film. Figure 2 This is a top view of the main part of an example of an optical film. Figure 3This is a side view showing an example of a membrane roll.

[0032] The optical film 1A is configured as a strip. The optical film 1A is, for example, a polymer film. Arrow LL indicates the long side direction of the strip-shaped optical film 1A. Arrow LS indicates the short side direction of the strip-shaped optical film 1A. The optical film 1A has embossed regions 2 at both ends in the short side direction, and non-embossed regions 3 between the embossed regions 2. The embossed regions 2 and the non-embossed regions 3 extend along the long side direction of the optical film 1A.

[0033] The optical film 1A has embossing 20 in each embossed region 2. The embossing 20 protrudes from the surface of the optical film 1A in a predetermined shape. For example, the cross-sectional shape of the embossing 20 along the long side of the optical film 1A is triangular. The embossing 20 is arranged in a row at predetermined intervals along the long side of the optical film 1A. Alternatively, the embossing 20 may be arranged in a row at predetermined intervals along the long side of the optical film 1A and in multiple rows along the short side of the optical film 1A.

[0034] The optical film 1A is wound in such a way that the embossing 20 faces outward to form a film roll 10.

[0035] The optical film 1A is wound with a film roll 10 starting from the first end. The starting position of the winding of the film roll 10 in the optical film 1A is referred to as the beginning end 11a. Furthermore, the winding of the film roll 10 in the optical film 1A ends at the second end. The ending position of the winding of the film roll 10 in the optical film 1A is referred to as the end portion 11b.

[0036] Furthermore, in optical film 1A, the portion extending from the beginning end 11a to the middle portion 11c between the beginning end 11a and the end portion 11b is referred to as the first range 12a. Additionally, in optical film 1A, the portion extending from the middle portion 11c to the end portion 11b is referred to as the second range 12b.

[0037] The length L of the optical film 1A from the beginning end 11a to the end end 11b is, for example, 3000m or more. Furthermore, the length L1 of the first range 12a of the optical film 1A from the beginning end 11a to the middle portion 11c is, for example, 900m to 1100m. The length L2 of the aforementioned first range 12a of the optical film 1A is preferably 1000m. The first range 12a is also referred to as the core.

[0038] The number of embossed patterns 20 per unit length along the long side of the optical film 1A is called the embossing density. The optical film 1A is configured such that the embossing density outside the first range 12a is higher than the embossing density of the first range 12a. That is, the optical film 1A is configured such that the embossing density of the second range 12b is higher than the embossing density of the first range 12a.

[0039] Figure 4 and Figure 5This is a side view showing the details of the embossing. First, the height of the embossing 20 is explained.

[0040] When the height of the embossing 20 from the surface of the optical film 1A is set to H (mm), the height H of all the embossing 20 is constant. It should be noted that in the embossing 20, the average height H of each 1m of the optical film 1A is limited to the range of -0.05% to +0.05% is referred to as the height H being constant.

[0041] Next, the embossing density will be explained. When the number of embossed flowers 20 in a unit length (1 mm) is set as the embossing density d (flowers / mm) and the interval of embossed flowers 20 is set as L (mm), the embossing density d is calculated by the following formula (1).

[0042] d=1 / L···(1)

[0043] Next, the size of the embossing 20 will be explained. The size of the embossing 20 along the long side of the optical film 1A is represented by the angle θ (°) with the center O of the film roll 10A as the vertex. The angle θ is also called the embossing angle. In this case, if the length of the embossing 20 along the long side of the optical film 1A is set as s (mm) and the radius of the film roll 10 is set as r (mm), then the angle θ is calculated by the following equation (2).

[0044] θ=180s / πr···(2)

[0045] If the length s of embossing 20 is constant, and the radius r of film roll 10 increases, the embossing angle θ decreases compared to the case where the radius r of film roll 10 is small.

[0046] The radius r of membrane roll 10 increases with the increase of the winding length of membrane roll 10. Therefore, as the winding length of membrane roll 10 increases, the embossing angle θ decreases. Figure 5 In this example, the embossing angle θ is set as θ1 when the radius r of the film roll 10 is r1. Additionally, the embossing angle θ is set as θ2 when the radius r of the film roll 10 is r2. When r2 > r1, θ1 > θ2.

[0047] Figure 6 This is an illustrative diagram that schematically shows the relationship between the size of the embossing angle and the angle of the embossing support optical film.

[0048] The force f supporting each embossing 20 of the optical film 1A overlapping radially in the film roll 10 can be defined by an angle with the center O of the film roll 10 as its vertex. This angle corresponds to the embossing angle θ. The force f supported by each embossing 20 varies according to the magnitude of the embossing angle θ. Figure 6 The size of the area represented by the dashed shading is schematically indicated.

[0049] exist Figure 6 In the process, when the embossing angle is θ1, the force supporting the optical film 1A for each embossing 20 is set to f1. Furthermore, when the embossing angle is θ2, the force supporting the optical film 1A for each embossing 20 is set to f2.

[0050] As the radius r of the film roll 10 increases, the embossing angle θ decreases. A decrease in the embossing angle θ means that the angle at which each embossing 20 supports the optical film 1A decreases. This is equivalent to a relative decrease in the force f exerted by each embossing 20 on the optical film 1A. Therefore, if θ1 > θ2, then f1 > f2.

[0051] Thus, if the winding length of the membrane roll 10 increases, the force applied due to the stacking becomes weaker on the outer side of the membrane roll 10 along the radial direction.

[0052] Therefore, if the winding length of the film roll 10 increases, misalignment is likely to occur along the radial outer side of the optical film 1A overlapping in the radial direction of the film roll 10 in the short side direction. Such misalignment is called winding misalignment.

[0053] Therefore, the embossing density d of the optical film 1A increases with the winding length of the film roll 10. This is the same as configuring the second region 12b of the optical film 1A to have a higher embossing density than the first region 12a. In the optical film 1A, the embossing density d is changed by altering the spacing L of the embossing 20 without changing the size of the embossing 20.

[0054] Next, the change Δd of the embossing density d in the first range 12a and the second range 12b is defined.

[0055] First, consider the case where the embossing density d is constant from the starting position (beginning end 11a) to the ending position (end end 11b) of the film roll 10. The product of the embossing density d and the embossing angle θ (d×θ) in this case is used as a reference. The embossing angle θ decreases as the winding length of the film roll 10 increases. Therefore, if the embossing density d is constant, then d×θ decreases as the winding length of the film roll 10 increases.

[0056] In contrast, consider the case where the embossing density d in the second range 12b is increased to the embossing density d′ (d′>d). In this case, the difference Δd×θ between d′×θ and d×θ satisfies the following relationship (3).

[0057] 0.0013<Δd×θ<0.3034···(3)

[0058] Figure 7 , Figure 8This is a graph showing the relationship between embossing density and film winding length. The range of possible values ​​for the embossing density, varied within the range specified in equation (3) relative to a baseline embossing density, is as follows: Figure 7 The text is shaded in the middle. Additionally, an example of further changing the embossing density in the second region 12b outside the core is shown below. Figure 8 .

[0059] The change Δd in the embossing density d between the first range 12a and the second range 12b satisfies equation (3), thereby suppressing the winding misalignment of the film roll 10.

[0060] In addition, the spacing L of the embossing 20 and the length s of the embossing 20 are made to satisfy the following relationship (4).

[0061] L>s···(4)

[0062] When the spacing L of the embossing 20 and the length s do not satisfy the relationship of equation (4), the gap between the embossing 20 arranged along the long side of the optical film 1A disappears. At this time, in the film roll 10, the air between the overlapping optical films 1A in the radial direction is difficult to leak out, which can easily cause winding misalignment.

[0063] In contrast, when the spacing L of the embossing 20 and the length s satisfy the relationship of equation (4), a gap is formed between the embossing 20 arranged along the long side direction of the optical film 1A. At this time, air between the radially overlapping optical films 1A in the film roll 10 can easily leak out, which can suppress the generation of winding misalignment.

[0064] Example

[0065] <Making of Membrane Rolls>

[0066] The optical film is fabricated using the conditions shown in Tables I and II below, and then the optical film is wound to form a film roll.

[0067]

[0068]

[0069] The present disclosure is illustrated below with examples, but is not limited thereto. It should be noted that, unless otherwise specified, all operations in the following examples are performed at room temperature (25°C). Furthermore, unless otherwise specified, "%" and "parts" refer to "mass %" and "parts by mass," respectively.

[0070] Optical films can be made of known resins. Specific examples of resins include acrylic resins, cellulose ester resins, and cycloolefin resins. Specific examples of resins will be explained below.

[0071] [Acrylic Resin (A)]

[0072] As acrylic resin (A), acrylic resins A1 to A4 are used. It should be noted that acrylic resin A1 is a commercially available product. Acrylic resins A2 to A4 are prepared by the following method.

[0073] (Acrylic Resin A1)

[0074] Acrylic resin A1 is DIANA BR85 (manufactured by Mitsubishi Chemical Corporation).

[0075] (Preparation of acrylic resin A2)

[0076] The mass ratio of methyl methacrylate (MMA) to methyl acrylate (MA) (MMA:MA) was set to 98:2. The synthesis was carried out according to the method described in paragraphs

[0130] to

[0135] of Japanese Patent Application Publication No. 2006-241263. As a result, acrylic resin A2 with a weight-average molecular weight (Mw) of 80,000 was obtained.

[0077] (Preparation of acrylic resin A3)

[0078] The mass ratio of methyl methacrylate (MMA) to methyl acrylate (MA) (MMA:MA) was set to 97:3. The synthesis was performed according to the method described in paragraphs

[0130] to

[0135] of Japanese Patent Application Publication No. 2006-241263. As a result, acrylic resin A3 with a weight-average molecular weight (Mw) of 930,000 was obtained.

[0079] (Preparation of acrylic resin A4)

[0080] 19 parts by mass of 2-hydroxypropyl methacrylate (HPMA) and 76 parts by mass of methyl methacrylate (MMA) were charged into a reaction apparatus. Additionally, 97 parts by mass of toluene, used as a polymerization solvent, were added to the apparatus. The reaction apparatus was equipped with a stirrer, a temperature sensor, a cooling pipe, and a nitrogen inlet pipe. Nitrogen was introduced and the temperature was raised to 105°C. Then, solution polymerization was carried out at a circulating temperature of 105–110°C for 1 hour to obtain acrylic resin A4. The molecular weight of the obtained acrylic resin A4 was determined, and the weight-average molecular weight (Mw) was 281,000, the number-average molecular weight (Mn) was 133,000, and the molecular weight distribution (Mw / Mn) was 2.1.

[0081] [Cellulose ester resin (CE)]

[0082] The following cellulose ester resins CE1 to CE4 are used as cellulose ester resins (CE).

[0083] (Preparation of cellulose ester resin CE1)

[0084] A mixture of sulfuric acid (7.8 parts by mass relative to 100 parts by mass of cellulose) and carboxylic anhydride, used as a catalyst, was cooled to -20°C. This mixture was then added to cellulose from hardwood pulp, and acylation was performed at 40°C. The type and substitution ratio of acyl groups were adjusted by varying the type and amount of carboxylic anhydride. Furthermore, the total degree of substitution was adjusted by aging at 40°C after acylation. As a result, a cellulose ester resin CE1 with a weight-average molecular weight of 200,000 was obtained. In cellulose ester resin CE1, the total degree of substitution (T) of the acyl groups was 2.75, the degree of substitution of acetyl groups (Ac) was 0.19, and the degree of substitution of propionyl groups (Pr) was 2.56.

[0085] (Preparation of cellulose ester resin CE2)

[0086] In the preparation of cellulose ester resin CE1, the type and substitution ratio of acyl groups were adjusted by appropriately modifying the type and amount of carboxylic anhydride. Furthermore, the total degree of substitution was adjusted by aging at 40°C after acylation. As a result, cellulose ester resin CE2 with a weight-average molecular weight of 200,000 was obtained. In cellulose ester resin CE2, the total degree of substitution (T) of the acyl groups was 2.1, the degree of substitution of the acetyl groups (Ac) was 0.8, and the degree of substitution of the propionyl groups (Pr) was 1.3.

[0087] (Preparation of cellulose ester resin CE3)

[0088] In the preparation of cellulose ester resin CE1, the type and substitution ratio of acyl groups were adjusted by appropriately modifying the type and amount of carboxylic anhydride. Furthermore, the total degree of substitution was adjusted by aging at 40°C after acylation. As a result, cellulose ester resin CE3 with a weight-average molecular weight of 200,000 was obtained. In cellulose ester resin CE3, the total degree of substitution (T) of the acyl groups was 2.8. Additionally, the degree of substitution of acetyl (Ac) was 0.5, propionyl (Pr) was 1.15, and butyryl (Bu) was 1.15.

[0089] (Preparation of cellulose ester resin CE4)

[0090] In the preparation of cellulose ester resin CE1, the type and substitution ratio of acyl groups were adjusted by appropriately modifying the type and amount of carboxylic anhydride. Furthermore, the total degree of substitution was adjusted by aging at 40°C after acylation. As a result, cellulose ester resin CE4 with a weight-average molecular weight of 76,000 was obtained. In cellulose ester resin CE4, the total degree of substitution (T) of the acyl groups was 2.75, the degree of substitution of the acetyl groups (Ac) was 0.19, and the degree of substitution of the propionyl groups (Pr) was 2.56.

[0091] (Cyclic Olefin Resin (COP))

[0092] As a cyclic olefin resin, the following commercially available cyclic olefin resin COP is used.

[0093] Cycloolefin resin COP: ARTON (registered trademark) G7810 (manufactured by JSR Corporation)

[0094] [Fabrication of Optical Films]

[0095] The optical films of the examples and comparative examples were prepared using the above-mentioned acrylic resin A1 and cellulose ester resin CE1.

[0096] (Composition of the paint liquid)

[0097] Acrylic resin A1: 160 parts by weight

[0098] Cellulose ester resin CE1: 86 parts by weight

[0099] Rubber granules (Kane Ace M210, manufactured by KANEKA): 2.5 parts by weight

[0100] Dichloromethane: 550 parts by weight

[0101] Ethanol: 100 parts by weight

[0102] The above composition is heated to fully dissolve it, thus preparing a coating liquid.

[0103] (Film fabrication and first-stage stretching of the optical film)

[0104] Using a belt casting apparatus, the above-mentioned coating liquid is uniformly cast onto a stainless steel belt support at a temperature of 22°C and a width of 2m. On the stainless steel belt support, the solvent is evaporated until the residual solvent content is 40% by mass, and then peeled off from the stainless steel belt support with a peel tension of 150 N / m.

[0105] The peeled acrylic resin roll was allowed to evaporate the solvent at 35°C and then cut into 1.6m wide pieces. Next, the rotation speed of the stainless steel strip support and the speed of the stretching device were adjusted, and stretching was performed in the long side direction (MD direction) (first stretch). The first stretch ratio was calculated based on the rotation speed of the stainless steel strip support and the speed of the stretching device, resulting in a ratio of 1.2. Here, the first stretch ratio in the MD direction is defined as (the conveying speed of the stretched film) / (the conveying speed of the film before stretching). Furthermore, the stretching temperature for the first stretch was 50°C.

[0106] Then, the film is stretched to 1.1 times its original width (TD direction) using a stretching device while being heated to 135°C (second stretch). Here, the second stretch ratio in the TD direction is defined as (width of the film after stretching) / (width of the film before stretching). At this point, the residual solvent content at the start of stretching using the stretching device is 10% by mass.

[0107] After being stretched by the stretching device, the film is conveyed through a drying zone at 110°C to complete the drying process. The stretching speed and winding speed are then adjusted, and stretching is performed in the MD direction (third stretch). The third stretch ratio is calculated based on the tenter frame speed and winding speed, and the result is 1.2 times. Here, the aforementioned third stretch ratio in the MD direction is defined as (the conveying speed of the stretched film) / (the conveying speed of the film before stretching).

[0108] The third stretched membrane was wound onto a core with an inner diameter of 15.24 cm under an initial tension of 220 N / m and a final tension of 110 N / m to obtain membrane 1-1.

[0109] The residual solvent content of membrane 1-1 is 0.3% by mass, the membrane thickness is 47 μm, and the roll length is 12000 m.

[0110] (Stage 2 stretching)

[0111] Then, the wound film 1-1 is stretched in the second stage (fourth stretch) at a stretch ratio of 1.35. The fourth stretch is performed by unwinding the film 1-1 from its roll and stretching it in the width direction (TD direction) while heating it to 140°C in the stretching device.

[0112] The stretched membrane was cut at both ends to make it 2260 mm wide, resulting in membrane 1-2 used in Examples 1-3, 6-9, 12-20, and Comparative Example 4. Furthermore, the stretched membrane was cut at both ends to make it 1330 mm wide, resulting in membrane 1-2 used in Examples 4, 11, and Comparative Example 1. The stretched membrane was also cut at both ends to make it 3000 mm wide, resulting in membrane 1-2 used in Examples 5, 10, and Comparative Example 2. Finally, the stretched membrane was cut at both ends to make it 1500 mm wide, resulting in membrane 1-2 used in Comparative Example 3.

[0113] The film thickness of membranes 1-2 used in Examples 1-3, 6-11, 14-17, 18, 19, and Comparative Example 4 was 35 μm. The film thickness of membranes 1-2 used in Examples 5, 13, and Comparative Example 1 was 15 μm. The film thickness of membranes 1-2 used in Examples 6, 12, and Comparative Example 2 was 100 μm. The film thickness of membranes 1-2 used in Example 18 was 30 μm. The film thickness of membranes 1-2 used in Comparative Example 1 was 40 μm.

[0114] (Preparation of solution for coating and embossing)

[0115] Acrylic resins were dissolved in a solvent at a concentration of 5% by mass to obtain a coating and embossing solution. The solvents used were dichloromethane and cyclopentanone.

[0116] (Form of coating embossing)

[0117] The coating and embossing solution was applied to the surfaces of films 1-2 using a SUPER HI JET (manufactured by Musashi Engineering) as a dispensing machine. Then, the films were dried using an IR heater to reach a temperature of 80°C, forming multiple coating embossings. The film temperature was confirmed using a thermal imager.

[0118] In Examples 1-3 and 6, a plurality of coating embossing patterns with a height H of 0.1 μm and a length s of 1 mm are formed at each end of the width direction of the surface of film 1-2. In Examples 4 and 7, a plurality of coating embossing patterns with a height H of 0.1 μm and a length s of 0.883 mm are formed at each end of the width direction of the surface of film 1-2. In Examples 9-14, 19, and 20, a plurality of coating embossing patterns with a height H of 0.1 μm and a length s of 1 mm are formed at each end of the width direction of the surface of film 1-2.

[0119] In Example 5, a series of coating embossings with a height H of 0.4 μm and a length s of 0.3 mm are formed at each end of the width direction of the surface of film 1-2. In Example 8, a series of coating embossings with a height H of 0.4 μm and a length s of 1 mm are formed at each end of the width direction of the surface of film 1-2.

[0120] In Example 15, two rows of coating embossing patterns with a height H of 0.1 μm and a length s of 1 mm are formed at each end of the width direction of the surface of film 1-2. In Example 16, three rows of coating embossing patterns with a height H of 0.1 μm and a length s of 1 mm are formed at each end of the width direction of the surface of film 1-2. In Example 17, four rows of coating embossing patterns with a height H of 0.1 μm and a length s of 1 mm are formed at each end of the width direction of the surface of film 1-2.

[0121] In Comparative Example 1, a plurality of coating embossings with a height H of 0.1 μm and a length s of 0.815 mm were formed at each end of the width direction of the surface of film 1-2. In Comparative Example 2, a plurality of coating embossings with a height H of 0.4 μm and a length s of 0.3 mm were formed at each end of the width direction of the surface of film 1-2.

[0122] (The formation of intervals in the coating embossing)

[0123] In Examples 1-3 and 7-17, embossing is formed at intervals of 5.3 mm from the beginning of film 1-2 to 1000 mm. In Examples 1-3 and 7-17, the position 1000 mm from the beginning is called the middle part.

[0124] In Examples 1, 8-17, coating embossing is formed at intervals of 3.533 mm between 1000 μm and 12000 μm from film 1-2. In Examples 1, 8-17, the position 12000 μm from the beginning end is designated as the end portion. Furthermore, in Examples 1, 8-17, the intervals for coating embossing are also 3.533 mm at positions 2000 μm, 5000 μm, 8000 μm, and 10000 μm from the beginning end.

[0125] In Example 2, coating embossing is formed at intervals of 1.767 mm between 1000 μm and 12000 μm from film 1-2. In Example 2, the position 12000 μm from the beginning end is designated as the end end. Furthermore, in Example 2, the intervals of the coating embossing are also 1.767 mm at positions 2000 μm, 5000 μm, 8000 μm, and 10000 μm from the beginning end.

[0126] In Example 3, coating embossing is formed at intervals of 1.060 mm between 1000 μm and 12000 μm from film 1-2. In Example 3, the position 12000 μm from the beginning end is designated as the end end. Furthermore, in Example 3, the intervals of the coating embossing are also 1.060 mm at positions 2000 μm, 5000 μm, 8000 μm, and 10000 μm from the beginning end.

[0127] In Examples 4 and 7, coating embossing is formed at intervals of 0.883 mm between 1000 μm and 12000 μm from film 1-2. In Examples 4 and 7, the position 12000 μm from the beginning end is designated as the end portion. Furthermore, in Examples 4 and 7, the intervals of the coating embossing are also 0.883 mm at positions 2000 μm, 5000 μm, 8000 μm, and 10000 μm from the beginning end.

[0128] In Examples 5 and 6, coating embossing is formed at intervals of 7.067 mm between 1000 μm and 12000 μm from film 1-2. In Examples 5 and 6, the position 12000 μm from the beginning end is designated as the end portion. Furthermore, in Examples 5 and 6, the intervals for coating embossing are also 7.067 mm at positions 2000 μm, 5000 μm, 8000 μm, and 10000 μm from the beginning end.

[0129] In Examples 19 and 20, embossed coatings are formed at intervals of 5.3 mm from the beginning of film 1-2 to 1000 mm. In Examples 19 and 20, the position 1000 mm from the beginning is designated as the first intermediate section.

[0130] In Examples 19 and 20, coating embossing is formed at intervals of 3.533 mm between 1000 μm and 5000 μm from film 1-2. In Examples 19 and 20, the position 5000 μm from the beginning end is designated as the second intermediate portion. Furthermore, in Examples 19 and 20, the interval of the coating embossing is also 3.533 mm at a position 2000 μm from the beginning end.

[0131] In Example 19, coating embossing is formed at intervals of 2.650 mm between 5000 μm and 12000 μm from film 1-2. In Example 19, the position 12000 μm from the beginning end is designated as the end end. Furthermore, in Example 19, the intervals of the coating embossing are also 2.650 mm at positions 5000 μm, 8000 μm, and 10000 μm from the beginning end.

[0132] In Example 20, coating embossing is formed at intervals of 4.240 mm between 5000 μm and 12000 μm from film 1-2. In Example 20, the position 12000 μm from the beginning end is designated as the end end. Furthermore, in Example 19, the intervals for coating embossing are also 4.240 mm at positions 5000 μm, 8000 μm, and 10000 μm from the beginning end.

[0133] In Comparative Examples 1 and 2, embossing was formed at intervals of 10.6 mm from the beginning of film 1-2 to 1000 μm. In Comparative Examples 1 and 2, the position 1000 μm from the beginning was designated as the middle section.

[0134] In Comparative Example 1, coating embossing was formed at intervals of 0.815 mm between 1000 μm and 12000 μm from film 1-2. In Comparative Example 1, the position 12000 μm from the beginning end was designated as the end portion. Furthermore, in Comparative Example 1, the intervals of the coating embossing were also 0.815 mm at positions 2000 μm, 5000 μm, 8000 μm, and 10000 μm from the beginning end.

[0135] In Comparative Example 2, coating embossing was formed at intervals of 8.833 mm between 1000 μm and 12000 μm from film 1-2. In Comparative Example 2, the position 12000 μm from the beginning end was designated as the end portion. Furthermore, in Comparative Example 2, the intervals of the coating embossing were also 8.833 mm at positions 2000 μm, 5000 μm, 8000 μm, and 10000 μm from the beginning end.

[0136] (Formed using laser embossing)

[0137] In Example 18, a laser is used to form multiple embossed patterns with a height H of 3 μm and a length s of 1.2 mm at each end of the width direction on the surface of film 1-2.

[0138] A carbon dioxide laser is used as the laser device. Furthermore, the output of the laser device is set to 20W, the center wavelength of the emission wavelength is set to 9.4μm, and the emission wavelength range is set to within ±0.01μm of the center wavelength.

[0139] Laser irradiation of the membrane is achieved by focusing a parallelized beam emitted from a carbon dioxide laser device onto the surface of the conveyed membrane through an fθ lens. The fθ lens has a focal length of 200 mm. The parallelized beam emitted from the carbon dioxide laser device is reflected by two galvanometer mirrors. By controlling the angle of the galvanometer mirrors, the focusing position is moved in the direction of the membrane plane, thereby controlling the trajectory of the laser irradiation on the membrane surface.

[0140] (Using lasers to create the embossed patterns)

[0141] In Example 18, embossing is formed using a laser at 4.2 mm intervals from the beginning of film 1-2 to 1000m. In Example 18, the position 1000m from the beginning is designated as the middle section.

[0142] In Example 18, embossing is formed using a laser at 3mm intervals between 1000m and 12000m from membrane 1-2. In Example 18, the position 12000m from the beginning end is designated as the end portion. Furthermore, in Example 18, the embossing patterns formed using the laser are also spaced at 3mm intervals at positions 2000m, 5000m, 8000m, and 10000m from the beginning end.

[0143] (Embossing is achieved through coating and molding)

[0144] In Comparative Example 3, a plurality of coating embossings were formed at both ends of the surface of film 1-2 in the width direction with a height H of 10 μm and a spacing of 2 mm. In Comparative Example 3, embossings were formed at both ends of the surface of film 1-2 in the width direction by knurling. The knurling process used the method described in paragraphs

[0583] to

[0629] of Japanese Patent Application Publication No. 2020-75482. In this case, the height H was adjusted to 5 μm and the spacing to 1.4 mm.

[0145] (Embossing is achieved through molding)

[0146] In Comparative Example 4, knurling was used to form embossing at both ends of the surface of films 1-2 in the width direction. The knurling was performed using the method described above. The height H was adjusted to 3 μm and the spacing to 1.4 mm.

[0147] (Membrane winding)

[0148] The films with embossed patterns in Examples 1-4, 6-13, 15-17, 19, and 20 were wound onto a core with a diameter of 153.5 mm at an initial tension of 60 N / m and a final tension of 25 N / m. This yielded rolled films. Additionally, the films with embossed patterns in Examples 5, 14, 18, and Comparative Example 2 were wound onto a core with a diameter of 83.5 mm at an initial tension of 60 N / m and a final tension of 25 N / m. This yielded rolled films. Furthermore, the films with embossed patterns in Comparative Examples 1 and 4 were wound onto a core with a diameter of 153.5 mm at an initial tension of 60 N / m and a final tension of 25 N / m. The film with embossed patterns in Comparative Example 3 was wound onto a core with a diameter of 250 mm at an initial tension of 60 N / m and a final tension of 25 N / m.

[0149] [Examples of other optical film fabrication]

[0150] The optical films of the examples and comparative examples can be prepared using any one of the above-described acrylic resins A1 to A4 and any one of the cellulose ester resins CE1 to CE4, employing the above-described method.

[0151] (Fabrication of optical films using cyclic olefin resins (COP))

[0152] The optical films of the examples and comparative examples can also be made using cyclic olefin resins (COP).

[0153] (film formation)

[0154] Granules of cyclic olefin resin G7810 (manufactured by JSR Corporation) were fed into an extruder under a nitrogen atmosphere for melt casting. The melt-cast film was then cooled with cooling rollers and peeled off to obtain a film. The cyclic olefin resin is a cyclic olefin resin containing structural units derived from norbornene monomers as shown in the following formula, with a Tg of 165°C.

[0155] [Chemical Formula 1]

[0156]

[0157] The resulting membrane was stretched to twice its original length in the width direction at 175°C, then heated to 100°C until completely dry and conveyed. The ends were then cut to obtain a membrane with a thickness of 40 μm, a width of 2260 mm, and a length of 12000 m. The membrane was conveyed at a speed of 20 m / min.

[0158] (Preparation of solution for coating and embossing)

[0159] A cycloolefin resin G7810 (manufactured by JSR Corporation) was dissolved in a solvent at a concentration of 5% by mass to obtain a coating and embossing solution. The solvents used were dichloromethane and cyclopentanone.

[0160] (Form of coating embossing)

[0161] The surface of the above-mentioned film was subjected to corona treatment and plasma treatment. Then, a coating embossing solution was applied to both ends of the treated surface of the film in the width direction, and then dried to form multiple coating embossings. The coating embossing solution was applied using a SUPER HI JET dispensing machine manufactured by Musashi Engineering Co., Ltd. Furthermore, the applied coating embossing solution was dried using an IR heater to bring the film temperature to 80°C. The film temperature was confirmed using a thermal imager. The size and spacing of the embossings are as described above.

[0162] As a film-forming method using cyclic olefin resins (COP), the following examples can also be applied.

[0163] (Preparation of coatings)

[0164] First, dichloromethane was added to the pressurized dissolving tank at a flow rate of 400 kg / min and ethanol at a flow rate of 20 kg / min. Three minutes after the solvent addition began, the cyclic polyolefin resin was added to the tank while stirring. Next, five minutes after the solvent addition began, the particulate additive solution was added and heated to 60°C, dissolving completely while stirring. The heating rate was increased from room temperature by 5°C / min, and after 30 minutes of dissolution, the temperature was decreased by 3°C / min. The solution was then filtered at a flow rate of 300 L / m³. 2 •h, filtration pressure 1.0×10 6 The coating with the following composition was prepared by filtration using Pa. Anji Filter Paper No. 244 (filtration accuracy 0.005 mm) manufactured by Anji Filter Paper Co., Ltd. was used for filtration.

[0165] Cycloolefin resin G7810 (manufactured by JSR Corporation): 100% by mass

[0166] Dichloromethane: 380% by mass

[0167] Ethanol: 20% by mass

[0168] (film formation)

[0169] Next, using a ring-shaped tape casting device, the obtained coating is uniformly cast onto a stainless steel tape support at a temperature of 31°C and a width of 2300 mm. The temperature of the stainless steel tape is adjusted to 28°C, and the conveying speed of the stainless steel tape is 30 m / min. On the stainless steel tape support, the solvent is evaporated until the residual solvent content in the cast (cast) coating is 30% by mass. Then, it is peeled off from the stainless steel tape support with a peel tension of 110 N / m to obtain a film.

[0170] The resulting film is stretched 1.3 times while being heated to 120°C in the conveying direction (MD direction) using a roller method that utilizes the difference in circumferential speed of the conveying rollers. Then, it is stretched 1.65 times while being heated to 130°C in the TD direction using a tenter frame. The resulting film is then conveyed while being heated to complete dryness at 70°C, and the ends are cut to obtain the final film. The film conveying speed is 20 m / min.

[0171] (Stage 2 stretching)

[0172] Then, the wound film 1-1 is stretched in the second stage (fourth stretch) at a stretch ratio of 1.35. The fourth stretch is performed by unwinding the film 1-1 from its roll and stretching it in the width direction (TD direction) while heating it to 140°C in the stretching device.

[0173] Then, the wound film is stretched in the second stage (fourth stretch) with an elongation ratio of 1.35. The fourth stretch is performed by unwinding the film from the roll and stretching it in the width direction (TD direction) while heating it to 180°C in the stretching device.

[0174] In addition to the film-forming method, the optical film 1A can be fabricated by forming multiple coating embossings at both ends of the film in the width direction using the above method.

[0175] <Evaluation of Membrane Roll Winding Misalignment>

[0176] The winding misalignment of the membrane rolls produced above was verified.

[0177] (1) Evaluation criteria

[0178] In the optical film 1A of Examples 1 to 20, as described above, the length from the beginning end 11a to the end end 11b is set to 12000 (m). In Comparative Examples 1 to 4, the length from the beginning end to the end end of the optical film is also set to 12000 (m).

[0179] In the optical film 1A of Examples 1 to 18, the length of the first range 12a from the beginning end 11a to the middle portion 11c is set to 1000 (m). In addition, in the optical film 1A of Examples 19 and 20, the length of the first range 12a from the beginning end 11a to the first middle portion 11c1 is set to 1000 (m).

[0180] In Examples 1 to 20, the embossing density d′1 of the second range 12b is higher than the embossing density d of the first range 12a. In addition, in Examples 1 to 20, the product of the difference Δd1 between the modified embossing density d′1 and the reference embossing density d and the embossing angle θ satisfies Equation (3) specified in this disclosure.

[0181] Example 2 is an example of Example 1 with an added embossing density d′1 within the range satisfying equation (3). Example 3 is an example of Example 2 with an added embossing density d′1 within the range satisfying equation (3). In Examples 1-3, the length s of the embossing 20 is kept the same, the interval L of the embossing 20 is different, and the embossing density d is changed.

[0182] Example 4 is an example in which the product of the difference between the reference and the changed embossing density Δd1 and the embossing angle θ is the upper limit of equation (3) specified in this disclosure. Example 5 is an example in which the product of the difference between the reference and the changed embossing density Δd1 and the embossing angle θ is the lower limit of equation (3) specified in this disclosure.

[0183] Examples 6 and 7 are examples in which the spacing L of the embossing 20 is changed. Example 6 is an example in which the spacing L of the embossing 20 is an upper limit value. Example 7 is an example in which the spacing L of the embossing 20 is a lower limit value.

[0184] Examples 8 and 9 are examples in which the height H of the embossing 20 is changed. Example 8 is an example in which the height H of the embossing 20 is the upper limit value. Example 9 is an example in which the height H of the embossing 20 is the lower limit value.

[0185] Examples 10 and 11 are embodiments in which the width of the optical film 1A is changed. Example 10 is an embodiment in which the width of the optical film 1A is the upper limit value. Example 11 is an embodiment in which the width of the optical film 1A is the lower limit value.

[0186] Examples 12 and 13 are examples in which the thickness of the optical film 1A is changed. Example 12 is an example in which the thickness of the optical film 1A is set to the upper limit. Example 13 is an example in which the thickness of the optical film 1A is set to the lower limit.

[0187] Example 14 is an example in which the diameter of the core of the film roll 10 is changed. Examples 15-17 are examples in which the number of rows of embossing 20 is changed. Example 18 is an example in which the method of forming embossing 20 is changed.

[0188] Examples 19 and 20 are examples in which the embossing density d′ is further changed within the second range 12b. Example 19 is an example in which the embossing density d′2 is further increased within the second range 12b. Example 20 is an example in which the embossing density d′2 is decreased within the second range 12b. The decreased embossing density d′2 within the second range 12b is higher than the embossing density d of the first range 12a. In Examples 19 and 20, the product of the difference Δd2 between the changed embossing density d′2 and the reference embossing density d and the embossing angle θ also satisfies Equation (3) specified in this disclosure.

[0189] (2) Evaluation Methods

[0190] Figure 9 This is an explanatory diagram illustrating an example of a method for evaluating misalignment. The difference between the length 'a' from one end of the membrane roll 10 to one end of the core 100 and the length 'b' from the other end of the membrane roll 10 to the other end of the core 100 is measured. This difference is taken as the misalignment.

[0191] (3) Evaluation Criteria

[0192] Case A is defined as the misalignment amount of 0mm, case B is defined as the misalignment amount exceeding 0mm but less than 2mm, and case C is defined as the misalignment amount exceeding 2mm. The preferred evaluation is A or B, the more preferred evaluation is A, and the least preferred evaluation is C.

[0193] (4) Evaluation Results

[0194] The evaluation results are shown in Table III below.

[0195]

[0196] In Examples 1 to 20, the embossing density d′(d′1) in the second range 12b is higher than the embossing density d in the first range 12a of the optical film 1A. In Examples 1 to 20, the product of the difference Δd(Δd1) between the modified embossing density d′1 and the reference embossing density d and the embossing angle θ is 0.0013 to 0.3034. This satisfies the above equation (3).

[0197] Furthermore, in Examples 19 and 20, in the second range 12b, the embossing density d′ is further changed from d′1 to d′2. In Examples 19 and 20, the product of the difference Δd (Δd2) between the changed embossing density d′2 and the reference embossing density d and the embossing angle θ is also 0.0013 to 0.3034. This also satisfies the above equation (3).

[0198] Furthermore, in Examples 1 to 20, the height H of the embossing 20 is constant within the range of -0.05% to +0.05% relative to the average.

[0199] In Comparative Examples 1 and 2, the embossing density d′(d′1) in the second range is higher than the embossing density d in the first range of the optical film. Furthermore, in Comparative Examples 1 and 2, the embossing height H is constant within the range of -0.05% to +0.05% relative to the average.

[0200] In Comparative Example 1, the product of the difference Δd(Δd1) between the modified embossing density d′1 and the reference embossing density d and the embossing angle θ exceeds 0.3034 in the core portion. In Comparative Example 2, the product of the difference Δd(Δd1) between the modified embossing density d′1 and the reference embossing density d and the embossing angle θ is less than 0.0013 outside the core portion. Neither satisfies the above equation (3).

[0201] In Comparative Example 3, coated embossing with a height H of 10 μm and molded embossing with a height H of 5 μm coexisted, and the height H of embossing 20 was not constant.

[0202] Furthermore, in Comparative Example 3, the embossing density d3 of the coated embossing is less than the embossing density d4 of the molded embossing. Therefore, the embossing density of the relatively high-height embossing is relatively small compared to the embossing density of the relatively low-height embossing. In addition, the ranges of relatively low and relatively high embossing densities are mixed.

[0203] Furthermore, in Comparative Example 3, the embossing density d3 of the coating embossing is constant from the beginning to the end of the film roll. Additionally, in Comparative Example 3, the embossing density d4 of the molding embossing is constant from the beginning to the end of the film roll.

[0204] It should be noted that in Comparative Example 3, for example, the embossing density d4 of molded embossing is used as a reference, and the embossing density d3 of coated embossing is regarded as the modified embossing density. In this case, the product of the difference Δd3 between the modified embossing density d3 and the reference embossing density d4 and the embossing angle θ does not satisfy the above equation (3).

[0205] In Comparative Example 4, the embossing density d of the molding embossing is constant from the beginning to the end of the film roll. In addition, the embossing height H is constant.

[0206] In Comparative Example 1, the evaluation result for the core section is C. This indicates that if the product of the difference Δd1 between the modified embossing density d′1 and the baseline embossing density d and the embossing angle θ exceeds 0.3034, winding misalignment will occur.

[0207] Furthermore, in Comparative Example 2, the evaluation result outside the core section was C. This indicates that if the product of the difference Δd1 between the modified embossing density d′1 and the baseline embossing density d and the embossing angle θ is less than 0.0013, winding misalignment will occur.

[0208] Furthermore, the evaluation result for Comparative Example 3 was C. In Comparative Example 3, the embossing density d3 of the coating embossing and the embossing density d4 of the die-cutting embossing were constant from the beginning to the end of the film roll. Compared to die-cutting embossing, the height of the coating embossing was relatively high, and in the film roll, the coating embossing mainly supported the film. However, the embossing density of the coating embossing was constant, and no optimization was performed in the core portion and outside the core portion. Therefore, it can be seen that even if a range of relatively low and relatively high embossing densities exists mixed together, winding misalignment will still occur due to the mixture of embossing densities with different heights.

[0209] Furthermore, in Comparative Example 4, the evaluation result was C. This indicates that if the embossing density d is constant, then even if the embossing height H is constant, winding misalignment will still occur.

[0210] In contrast, in Examples 1-20, the evaluation result was A or B in the core portion and the entire area outside the core portion. Therefore, it can be seen that if the product of the difference Δd1 between the changed embossing density d′1 and the reference embossing density d and the embossing angle θ satisfies the above equation (3), then winding misalignment will not occur. Alternatively, it can be seen that winding misalignment can be sufficiently suppressed. Furthermore, it can be seen that if multiple embossing heights H are constant, then winding misalignment will not occur.

[0211] Furthermore, as demonstrated in Examples 8 and 9, it is evident that even if the height H of the embossing 20 is changed, as long as the above conditions are met, no winding misalignment will occur.

[0212] Furthermore, as demonstrated in Examples 10 and 11, it is evident that even if the width of the optical film 1A is altered, no winding misalignment will occur as long as the aforementioned conditions are met.

[0213] Furthermore, as demonstrated in Examples 12 and 13, it is evident that even if the thickness of the optical film 1A is altered, no winding misalignment will occur as long as the aforementioned conditions are met.

[0214] Furthermore, in Example 14, it is known that even if the diameter of the core of the film roll 10 is changed, as long as the above conditions are met, no winding misalignment will occur.

[0215] Furthermore, as demonstrated in Examples 15-17, it is known that even if the number of columns of embossing 20 is changed, as long as the above conditions are met, no winding misalignment will occur.

[0216] Furthermore, as shown in Example 18, even if laser is used to form the embossing 20, as long as the above conditions are met, no winding misalignment will occur.

[0217] Furthermore, in Examples 19 and 20, it can be seen that even if the embossing density is further changed within the second range 12b, as long as the above conditions are met, no winding misalignment will occur.

[0218] It should be noted that regardless of which of the above examples the composition and manufacturing method of the optical film is used, the same effect can be obtained as long as the above conditions are met.

Claims

1. An optical film which is in a long strip shape, and which is formed into a film roll wound from a first end portion to a second end portion in a long side direction of the long strip shape, a plurality of embossments are formed in the long side direction between the first end portion and the second end portion, and the plurality of embossments are of the same height in a prescribed range, when a first range is set from the first end portion to an intermediate portion between the first end portion and the second end portion, a second range is set from the intermediate portion to the second end portion, and an embossment density is set as the number of embossments per unit length in the long side direction, the embossment density of the embossments formed in the second range is higher than the embossment density of the embossments formed in the first range.

2. The optical film according to claim 1, wherein the length from the first end portion to the second end portion is 3000 m or more, the length of the first range from the first end portion to the intermediate portion is 900 m to 1100 m.

3. The optical film according to claim 1, wherein the embossment density is set as d, and the interval of the embossments in the long side direction of the optical film is set as L, the embossment density d is obtained by the following formula (1), the length of the embossments in the long side direction of the optical film is set as s, the radius of the film roll is set as r, the size of the embossments in the long side direction of the optical film is expressed by an angle with the center of the film roll as a vertex, and the embossment angle representing the size of the embossments is set as θ, the embossment angle θ is obtained by the following formula (2), at this time, if the product of the embossment density d and the embossment angle θ in the first range is set as d x θ, and the product of the embossment density d' and the embossment angle θ in the second range is set as d' x θ, the difference Δd x θ between d x θ and d' x θ satisfies the following formula (3), where d' > d, d = 1 / L...(1), θ = 180s / πr...(2), 0.0013 < Δd x θ < 0.3034...(3).

4. The optical film of claim 1, wherein, The height of the embossments is in the range of -0.05% to +0.05% with respect to the average of the heights of the embossments contained in the unit length in the long side direction.

5. The optical film of claim 1, wherein, The embossments are formed by coating of a resin.

6. The optical film of claim 1, wherein, The height of the embossments is determined by the amount of coating of the resin.

7. The optical film of claim 1, wherein, The embossment density varies with the length from the first end portion.

8. A film roll which is formed by winding an optical film which is in a long strip shape and in which a plurality of embossments of the same height in a prescribed range are formed in the long side direction between a first end portion and a second end portion in the long side direction of the long strip shape, from the first end portion to the second end portion, when a first range is set from the first end portion to an intermediate portion between the first end portion and the second end portion, a second range is set from the intermediate portion to the second end portion, and an embossment density is set as the number of embossments per unit length in the long side direction, the embossment density of the embossments formed in the second range is higher than the embossment density of the embossments formed in the first range.

9. A method for manufacturing an optical film, the method being a method for manufacturing an optical film that is long and has a plurality of embossments formed in a longitudinal direction between a first end portion and a second end portion in the longitudinal direction, when a range from the first end portion to an intermediate portion between the first end portion and the second end portion is set as a first range, a range from the intermediate portion to the second end portion is set as a second range, and a number of embossments per unit length in the longitudinal direction is set as an embossment density, the embossments are formed by coating of resin in such a manner that the plurality of embossments are of the same height in a prescribed range and the embossment density of the embossments formed in the second range is higher than the embossment density of the embossments formed in the first range.

10. A method for manufacturing a film roll, the method being a method for manufacturing a film roll in which an optical film that is long is wound from a first end portion to a second end portion in a longitudinal direction of the optical film, the optical film having a plurality of embossments formed in the longitudinal direction between the first end portion and the second end portion, when a range from the first end portion to an intermediate portion between the first end portion and the second end portion is set as a first range, a range from the intermediate portion to the second end portion is set as a second range, and a number of embossments per unit length in the longitudinal direction is set as an embossment density, the embossments are formed by coating of resin in such a manner that the plurality of embossments are of the same height in a prescribed range and the embossment density of the embossments formed in the second range is higher than the embossment density of the embossments formed in the first range, the optical film having the embossments is wound around a core.

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