JP7845264B2 - Film roll - Google Patents

Description

This invention relates to a film roll. More specifically, it relates to a film roll that is less prone to winding failures during transportation and long-term storage, and that maintains its quality.

Resin films primarily composed of cycloolefin resins and (meth)acrylic resins possess excellent transparency and dimensional stability, making them suitable for use as optical films, such as protective films for polarizing plates.

Optical films are typically stored or transported in rolls for ease of handling and manufacturing efficiency. If the film rolls are significantly deformed, or if the optical films stick together or are scratched, the quality of the optical film deteriorates. This leads to increased waste in the polarizing plate manufacturing process and increased labor costs for quality inspections, ultimately resulting in higher product prices.

To suppress quality degradation due to deformation of the film roll, fine irregularities are sometimes formed on both ends of the optical film in the width direction. For example, Patent Document 1 discloses the formation of fine irregularities by embossing, while Patent Documents 2 and 3 disclose the formation of fine irregularities by coating.

By forming microscopic irregularities using the method described above, air pockets are incorporated during the winding of the optical film, suppressing film adhesion. However, during product transportation and over time, the air pockets incorporated into the film roll escape, causing sagging. Furthermore, adhesion can occur at the core of the film roll, rendering the optical film unusable and resulting in wasted waste.

In contrast, as described in Patent Document 4, instead of forming fine irregularities at both ends of the optical film in the width direction, a technique is disclosed that controls the average maximum height difference of the optical film's thickness within a predetermined range. This technique appropriately manages the air layer (air gap) incorporated into the film roll and generates a moderate, minute contact across the entire contact surface where the optical films face each other, to the extent that sticking is not noticeable.

However, when using film rolls manufactured using the above technology, a white powder may adhere to the outer surface of the film roll after transport. This phenomenon can also occur in Patent Documents 1, 2, and 3. Furthermore, this phenomenon can occur even if the film rolls are transported carefully. Although this white powder adheres only to the outer surface, if the film roll is to be used in the next process, it causes process contamination, meaning the problem is not limited to the outer surface.

Based on the above, there was room for improvement in preventing process contamination by suppressing the adhesion of the white powder mentioned above, and eliminating foreign matter that appeared on the film.

Japanese Patent Publication No. 2016-89110 Japanese Patent Publication No. 2012-206312 Japanese Patent Publication No. 2010-58311 International Publication No. 2022/153785

This invention was made in view of the above-mentioned problems and circumstances, and its objective is to provide a film roll that exhibits fewer winding failures during transportation and long-term storage, while maintaining its quality.

The inventors, in an effort to solve the above problems, investigated the causes of the problems and found that the problems could be solved by providing fine irregularities only in the region outside the outer circumference of a circle that is 70% of the maximum radius, extending outward from the center of the side surface in the width direction of the film roll on which the optical film is wound. This led to the present invention. In other words, the above problems according to the present invention are solved by the following means.

1. A film roll on which optical film is wound,
The film roll has fine irregularities only in the region outside the outer circumference of a circle that is 70% of the maximum radius, extending outward from the center of the side surface in the width direction.
The ratio of the length of the outer diameter Rc at the center of the film roll in the width direction to the outer diameter Re at the end, Rc/Re, is within the range of 0.96 to 1.01.
The height of the protrusions in the aforementioned fine uneven area is 0.1 μm to 0.5 μm.
A film roll characterized by the following features.

2. The film roll according to paragraph 1, characterized in that the fine unevenness portion is present only at the end in the width direction, which includes a region outside the outer circumference of a circle that extends outward from the center of the side surface to 90% of the maximum radius.

3. The film roll according to paragraph 1, characterized in that the fine uneven portion is provided in the longitudinal direction of the film roll for a length within the range of 150 to 1500 m.

4. The film roll according to paragraph 1, characterized in that the fine uneven portion is provided in the longitudinal direction of the film roll for a length within the range of 500 to 1000 m.

5. The film roll according to paragraph 1, characterized in that the main component of the optical film is a cycloolefin resin.

6. The film roll according to paragraph 1, characterized in that the optical film is a single layer.

7. The fine irregularities are teardrop-shaped, and the relationship between the maximum width T2 in the long axis direction and the maximum width T1 in the short axis direction of the teardrop shape satisfies the following equation (1): Equation (1): 1.15 ≤ T2/T1 ≤ 1.90
The film roll according to the first claim, characterized in that it is a film roll.

8. The film roll according to paragraph 7 , characterized in that the longitudinal axis direction is the longitudinal direction of the optical film.

9. The film roll according to paragraph 1, characterized in that the optical film has the fine irregularities only at both ends in the width direction.

The above-described means of the present invention makes it possible to provide a film roll that exhibits fewer winding failures during transportation and long-term storage, while maintaining its quality. Although the mechanism of action or mechanism of the present invention's effects is not yet clear, it is inferred as follows.

The film roll of the present invention is a film roll on which an optical film is wound, characterized in that it has fine irregularities only in the region outside the outer circumference of a circle that extends outward from the center of the side surface in the width direction of the film roll, with the outer circumference being 70% of the maximum radius.

Generally, film rolls are transported over several days, and in addition to vibration, they are affected by daily temperature fluctuations. This creates a temperature difference between the outside temperature during transport and the temperature inside and outside the roll, which is thought to cause the outside of the roll to loosen. This loosening can extend for tens to hundreds of meters in severe cases. This repeated friction between the outside of the roll and the packaging paper is thought to be the cause of the white powder formation.

Even if the film roll doesn't loosen during transport, the temperature changes from winter transport conditions to storage in the factory warehouse could cause the roll to loosen. This would likely result in a significant misalignment of the film roll's outer edge when it's set up at the start of production. This could potentially prevent production from even beginning.

In this invention, the above problem can be solved by providing fine irregularities on the outer edge of the film roll, that is, by providing fine irregularities only in the region outside the outer circumference of a circle that is 70% of the maximum radius, extending outward from the center of the side surface in the width direction of the film roll on which the optical film is wound. Compared to the case where fine irregularities are provided over the entire region from the inner to the outer circumference of the film roll, this method appropriately manages the air layer (air gap) incorporated into the film roll, and while creating a moderate, minute contact that prevents sticking across the entire contact surface where the optical films face each other, it is presumed that winding failures during transportation and long-term storage are reduced, and quality is maintained.

Schematic diagram of the side view of the film roll in the width direction, including the winding core. An example of a schematic diagram of the side portion in the width direction of the film roll of the present invention. Relationship diagram between the convex portion and the film thickness profile in the width direction. An example of a schematic diagram illustrating the central and end portions of the longitudinal side surface of a film roll. Enlarged plan view of an example of a teardrop-shaped object according to the present invention formed on a film base. Figure 5 shows a cross-sectional view of a teardrop-shaped object along the line 1B-1B. A schematic plan view showing the distance between teardrop-shaped objects according to the present invention. An example of a plan view of a teardrop-shaped object having multiple protrusions. An example of a plan view of a teardrop-shaped object with a series of dots. (a) An example of a schematic diagram of a heat-pressing embossing method (b) An example of a film base after the formation of a convex portion

The film roll of the present invention is a film roll on which an optical film is wound, and is characterized in that it has fine irregularities only in the region outside the outer circumference of a circle that is 70% of the maximum radius when extending outward from the center of the side surface in the width direction of the film roll.
This feature is a technical feature common to or corresponding to each of the embodiments (appearances) described below.

In embodiments of the present invention, it is preferable that the ratio of the length of the outer diameter Rc at the center of the film roll in the width direction to the outer diameter Re at the end (Rc/Re) is within the range of 0.96 to 1.01, from the viewpoint of suppressing stress concentration due to adhesion caused by contact between optical films and ensuring uniform stress in the width direction.

From the viewpoint of suppressing adhesion between optical films, it is preferable that the average maximum height difference (P-V) _ave1 of the film thickness excluding the fine irregularities within a diameter range of 1000 mm, centered on any point within the optical film, is in the range of 0.15 to 0.40 μm.

From the viewpoint of achieving the effects of the present invention, it is more preferable that the fine irregularities are present only at the ends in the width direction, including the region outside the outer circumference of a circle that extends outward from the center of the side surface to 90% of its maximum radius.

From the viewpoint of thinning and productivity, it is preferable that the aforementioned fine irregularities are provided in a length within the range of 150 to 1500 m in the longitudinal direction of the film roll.

It is more preferable, from the viewpoint of thinning and productivity, that the aforementioned fine irregularities are provided in a length within the range of 500 to 1000 m in the longitudinal direction of the film roll.

It is preferable that the main component of the optical film be a cycloolefin resin from the viewpoint of stretchability, ease of controlling crystallinity, and adhesive penetration.

From the viewpoint of achieving the effects of the present invention, it is preferable that the optical film be a single layer.

From the viewpoint of suppressing deformation of the film roll, it is preferable that the aforementioned fine irregularities are teardrop-shaped, and that the relationship between the maximum width T2 in the long axis direction and the maximum width T1 in the short axis direction of the teardrop shape satisfies formula (1).

It is more preferable, from the viewpoint of suppressing deformation of the film roll, that the aforementioned longitudinal axis direction be the longitudinal direction of the optical film.

It is preferable, from the viewpoint of thinning and productivity, that the fine irregularities are present only at both ends in the width direction of the optical film.

The present invention, its components, and embodiments for carrying out the present invention will be described in detail below. In this application, "~" is used to mean that the numerical values before and after it include the lower and upper limits, respectively.

[Summary of the film roll of the present invention]
The film roll of the present invention is a film roll on which an optical film is wound, and is characterized in that it has fine irregularities only in the region outside the outer circumference of a circle that is 70% of the maximum radius when moving outward from the center of the side surface of the film roll in the width direction. The "center of the side surface of the film roll in the width direction" refers to the center of the circle that has the maximum radius, i.e., the center point of the maximum diameter, when the side surface of the film roll is observed from a direction perpendicular to the width direction of the film roll and appears to be approximately circular.

As mentioned above, conventionally, optical films wound into rolls had fine irregularities formed on both ends in the width direction of the film to prevent quality deterioration during storage or transportation, or the average maximum height difference of the film's thickness was controlled within a predetermined range. This trapped air in the film roll, prevented its escape, and suppressed adhesion between the optical films.

However, since a white powder sometimes adheres to the outer surface of the film roll after transportation, there was room for improvement in suppressing the adhesion of this white powder, thereby preventing process contamination and eliminating foreign matter from appearing on the film.

In this invention, a fine uneven surface is provided on the outer edge of the film roll; that is, the fine uneven surface is provided only in the region outside the outer circumference of a circle that is 70% of the maximum radius, extending outward from the center of the side surface in the width direction of the film roll on which the optical film is wound. This appropriately manages the air layer (air gap) incorporated into the film roll, and while creating a moderate, minute contact across the entire contact surface where the optical films face each other, preventing sticking, it also reduces winding failures during transportation and long-term storage, and maintains quality. The various components and manufacturing methods of the film roll of this invention will be described sequentially below.

1. Film roll (side section in the width direction)
Figure 1 is a schematic diagram of the side view in the width direction of a film roll including the winding core, and Figure 2 is an example of a schematic diagram of the side view in the width direction of a film roll according to the present invention.

In Figure 1, 30c represents the side of the core, _R0 represents the center of the side of the core, _rc represents the radius of the side of the core, _rp represents the radius of the side of the film roll including the core at an arbitrary point, and _rmax represents the maximum radius of the side of the film roll including the core. Note that _Frayer is the optical film layer extending outward from the outer circumference of the side of the core to the maximum radius. The typical size of a core is 150-300 mm in diameter.

In Figure 2, 30c is the side of the core, R ₀ is the center point of the side of the film roll in the width direction, and this point represents 0% of the maximum radius as it extends outward from the center of the side. R ₇₀ represents the outer circumference of a circle that represents 70% of the maximum radius as it extends outward from the center of the side, and R ₁₀₀ represents the outer circumference of a circle with the maximum radius (r _max ), which is the outer circumference of a circle that represents 100% of the maximum radius. Note that F _{rayer 1} is the optical film layer from the center of the side outward to the outer circumference of the circle that represents 70% of the maximum radius.

F _{rayer 2} is a layer of optical film in the region outside the outer circumference of a circle that is 70% of the maximum radius when moving outward from the center of the side surface, and the film roll of the present invention is characterized in that only the film contained in F _{rayer 2} has fine irregularities. Furthermore, it is more preferable from the viewpoint of achieving the effects of the present invention that the fine irregularities are present only in the region outside the outer circumference of a circle that is 90% of the maximum radius when moving outward from the center of the side surface.

From the viewpoint of thinning and productivity, it is preferable that the aforementioned fine irregularities are provided in a length within the range of 150 to 1500 m in the longitudinal direction of the film roll, and more preferably within the range of 500 to 1000 m.

Furthermore, from the viewpoint of thinning and productivity, it is preferable that the optical film according to the present invention, when wound onto a film roll, has the aforementioned fine irregularities only at both ends in the width direction.

(1.1) Fine unevenness The fine unevenness structure according to the present invention is formed on the film base. In this specification, "film base" means the film in which the fine unevenness structure according to the present invention has not been formed, or the portion of the film that does not contain the fine unevenness structure after the fine unevenness structure has been formed.

In this invention, the "micro-uneven structure" refers to a structure in which recesses and protrusions exist within a minute range. These recesses and protrusions are repeated for at least 1000 mm in the longitudinal direction. The "minute range" is defined as a range of 0.1 to 30 mm square. Multiple recesses and protrusions exist within this range.

In this invention, "recess" refers to a portion of the optical film thickness measured and observed by film thickness measurement that is lower than the average film thickness, i.e., thinner than the peaks and valleys of the uneven shape of the film thickness. The depth of the recess is in the range of 0.05 to 30 μm, preferably in the range of 0.1 to 5 μm.
The recesses of the fine irregularities in this invention include so-called curls. The fine range is in the area of 0.1 to 30 mm square. A curl is a state in which the film is folded. The depth of the curled portion is in the range of 0.2 to 20 μm, preferably in the range of 1 to 5 μm.

In this invention, "protrusions" refer to the parts of the optical film's thickness that are higher than the average film thickness, i.e., the thicker portions, among the peaks and valleys of the uneven surface of the film's thickness as measured and observed by film thickness measurement. Further details are provided below.

The measurement and evaluation of the uneven surface is performed by first measuring the film thickness at an arbitrary position at the edge of the film. Then, for each measurement, the film thickness is measured again at a position 10 mm in the width direction and 30 mm in the length direction from the aforementioned arbitrary position. This process is repeated until the other end of the film is reached. Noise is removed using a Gaussian filter to obtain a film thickness profile in the width direction. Based on this profile, the uneven surface is then measured and evaluated.

Figure 3 is a diagram showing the relationship between the uneven areas and the film thickness profile in the width direction. " _h1 " is the height of the convex areas, and " _h2 " is the depth of the concave areas. The average film thickness is determined by taking the average of the measured film thicknesses in the width direction obtained by the above operation. As shown in Figure 3, areas where the film thickness profile in the width direction is thicker than the average film thickness are defined as convex areas where the thickness is continuous for 50 mm or more in the width direction, and the number of such areas is defined as the number of convex areas. If there are too many convex areas, each peak becomes sharp and deformation occurs in the film, and if there are too few, stress concentrates too much on a small number of convex areas when the film is wound, causing twisting, etc. Therefore, it is preferable to keep the number of convex areas within the range of 1 to 10 per meter in the width direction.

Furthermore, the position where the maximum value is taken at each protrusion determined by the above method is defined as the position of the protrusion, and the height _h1 of each protrusion is defined as the value obtained by subtracting the average film thickness in the width direction from the maximum value of that protrusion. If the height of the protrusion is too high, a chain-like pattern will form at the base of the protrusion after the film roll has been left for a long time, and if the height of the protrusion is too low, the film thickness dispersion effect will be lost. Therefore, it is preferable to set the height of the protrusion within the range of 0.05 to 0.50 μm. In addition, by adjusting the position of the protrusion so that it moves continuously in the longitudinal direction of the film surface, the protrusions do not overlap when the film is wound, thereby further enhancing the effect of the above-mentioned adjustment function for the number and height of the protrusions.

The above film thickness can be measured using the RE-200L2T-Rth+ inline retardation film thickness measuring device (manufactured by Otsuka Electronics Co., Ltd.).

Figure 4 is an example of a schematic diagram illustrating the central and end portions of the longitudinal side surface of a film roll. Re represents the outer diameter of the end portion of the side surface, and Rc represents the outer diameter of the central portion of the side surface. In the present invention, it is preferable that the ratio of the length of the outer diameter Rc of the central portion of the film roll in the width direction to the outer diameter Re of the end portion (Rc/Re) is within the range of 0.96 to 1.01, from the viewpoint of suppressing stress concentration due to adhesion caused by contact between optical films and ensuring uniform stress in the width direction.

"End portion" refers to the area within 0 to 30 mm inward from the end of the optical film (roll) in the width direction. "Center portion" refers to the area of the optical film excluding both ends in the width direction. "Outer diameter" refers to the diameter of the circle formed at the outermost circumference of the roll, when the cross-section perpendicular to the central axis (core) of the film roll is considered a circle. Therefore, "outer diameter of the end portion" refers to the diameter of the circular cross-section observed in the end portion (the average value of diameters measured at at least three randomly selected locations). Furthermore, "outer diameter of the center portion" refers to the diameter of the circular cross-section observed at the center point of the center portion.

One method for measuring the outer diameter of a film roll in the width direction is to measure the outer diameter at arbitrary positions from both ends of the film roll using a measuring tape. Other methods can also be used; for example, a laser displacement meter (Keyence LK-G5000) can be used, with the laser directed at multiple predetermined locations (at least three) within the width direction of the film roll, as well as at the center of the central section, to measure the outer diameter. The average value of the outer diameter at the ends is used, as described above.

(Shape of the finely uneven surface)
[Teardrop shape]
There are no particular restrictions on the shape of the fine uneven portion according to the present invention, but it is preferable that the fine uneven portion is teardrop shaped. Figure 5 is an enlarged plan view of an example of a teardrop-shaped object according to the present invention formed on a film base, and Figure 6 is a cross-sectional view of the teardrop-shaped object in Figure 5 taken along line 1B-1B. In Figure 5, M is the intersection of the major axis LA and the minor axis SA of the teardrop-shaped object. T1 is the maximum width in the minor axis direction, T2 is the maximum width in the major axis direction, t is the height of the teardrop-shaped object, x is the width direction of the film, and y is the longitudinal direction of the film.

A "teardrop shape" refers to a shape having a long axis LA and a short axis SA, where the intersection point M of the long axis LA and short axis SA of the teardrop-shaped object 12 is offset from the center of the long axis LA (i.e., does not coincide with the center of the long axis LA) (see Figure 5).

The long axis LA is preferably aligned with the length direction (y-direction) of the film base, and more preferably parallel to the length direction (y-direction) of the film base. The short axis SA is preferably aligned with the width direction (x-direction) of the film base, and more preferably parallel to the width direction (x-direction) of the film base. The y-direction is also the direction of film transport (direction of travel) during winding.

The long axis LA and the short axis SA are preferably perpendicular to each other. The teardrop shape contour may be straight, curved, or a combination of both, but it is preferably curved.

In this embodiment, it is preferable from the viewpoint of suppressing deformation of the film roll that the multiple teardrop-shaped objects 12 are arranged at both ends in the widthwise direction of the surface of the film base, along the lengthwise direction of the film base, i.e., the longitudinal direction of the optical film (see Figure 5). Furthermore, it is preferable that each of the multiple teardrop-shaped objects 12 is arranged so that its long axis LA direction aligns with the lengthwise direction of the film base (see Figure 5). The teardrop-shaped objects 12 may be integrated with the film base or they may be separate.

From the viewpoint of suppressing deformation of the film roll, it is preferable that the relationship between the maximum width T2 in the long axis direction and the maximum width T1 in the short axis direction of the teardrop shape satisfies the following formula (1). In the following formula, "T1" represents the average value of the maximum widths in the short axis direction of multiple teardrop shapes if there are multiple teardrop shapes 12. Similarly, "T2" represents the average value of the maximum widths in the long axis direction of multiple teardrop shapes if there are multiple teardrop shapes 12.

Formula (1): 1.15≦T2/T1≦1.90

When the (T2/T1) value is 1.15 or higher, even if an oblique force is applied from the front during winding, the teardrop-shaped object 12 can make uniform contact with the film after winding, thereby suppressing deformation of the film roll. When the (T2/T1) value is 1.9 or lower, uniform contact with the film is possible, so the film roll's deformity is less likely to be impaired. From a similar viewpoint, a (T2/T1) value of 1.3 to 1.6 is more preferable.

The (T2/T1) value can be adjusted by factors such as the film transport speed, drying conditions (drying method, drying temperature), the resin concentration of the second resin composition (for forming teardrop-shaped objects), the dropping height, and the film surface condition. Increasing the film transport speed, lowering the drying temperature, and using hot air drying can increase the (T2/T1) value. Furthermore, moderately lowering the resin concentration of the second resin composition and increasing the dropping height can also increase the (T2/T1) value.

The maximum width T1 in the short axis direction is not particularly limited, but can be, for example, within the range of 0.9 to 1.5 mm, preferably within the range of 1.0 to 1.2 mm.

Figure 7 is a schematic plan view showing the distances between teardrop-shaped objects according to the present invention. In Figure 7, T2 represents the maximum width of the teardrop-shaped object in the longitudinal direction, and Th represents the distance between the teardrop-shaped objects in the longitudinal direction (y-direction) of the film base. When T3 is the average distance calculated from the distances Th of multiple teardrop-shaped objects, it is preferable that T3 and T2 satisfy the following equation (2).

Formula (2): T3<T2

By satisfying equation (2) above, the ability to mitigate oblique forces in the front portion of the teardrop-shaped object 12 (the region centered on the intersection M of the long axis LA and the short axis SA) during film transport and winding can be enhanced. Therefore, uneven crushing of the teardrop-shaped object 12 due to oblique forces can be further suppressed.

The difference between T2 and T3 (T2-T3) is not particularly limited, but may be, for example, 0.1 mm or more, preferably 0.6 mm or more. Furthermore, when the length of the film base in the width direction is X, it is more preferable that the following equations (3) and (4) are satisfied.

Formula (3): 0.0003≦T1/X≦0.0063
Formula (4): 2400mm≦X≦2950mm

From the perspective of suppressing deformation of the film roll, a larger value of (T1/X) is preferable. Furthermore, when the film is wider, film flapping during transport is more likely to occur than before. If the value of (T1/X) is within the above range, T1 is not too large, which can suppress transport damage such as wrinkles and roll scratches caused by excessive restraining force on the film. From a similar perspective, a value of (T1/X) within the range of 0.0004 to 0.00051 is more preferable.

Furthermore, when T3 is the average distance between multiple teardrop-shaped objects 12 in the longitudinal direction (y-direction) of the film base, and Y is the length of the film base, it is more preferable that the following equations (5) and (6) are satisfied.

Formula (5): 1.0×10 ⁶ ≦Y/T3≦9.0×10 ⁶
Formula (6): 6000m≦Y≦9000m

From the viewpoint of making it easier to suppress the adhesion between films, a smaller T3 is preferable, and a larger (Y/T3) value is preferable. On the other hand, if T3 is too small, the uniformity of the winding shape is easily impaired. When the (Y/T3) value is within the above range, it is possible to suppress the adhesion (contact) between films to a high degree while maintaining the uniformity of the winding shape. From the same viewpoint, it is more preferable that the (Y/T3) value is within the range of 3.0 × ^10³ to 8.0 × ^10³ .

The length X in the width direction of the film base is preferably within the range of 2000 to 3500 mm, and more preferably within the range of 2400 to 2950 mm, as described above. The length Y of the film base is preferably within the range of 500 to 15000 m, and more preferably within the range of 6000 to 9000 m, as described above.

The average spacing T3 of the multiple teardrop-shaped objects 12 in the longitudinal direction (y-direction) of the film base is not particularly limited as long as it satisfies the above ratio, but is preferably in the range of 0.5 to 4 mm, and more preferably in the range of 1 to 3 mm.

When the average spacing T3 between multiple teardrop-shaped objects 12 is above the lower limit, it is easier to appropriately adjust the amount of air contained between the films when winding them into a roll. When it is below the upper limit, it is easier to suppress the films from sticking together due to the average spacing T3 between the multiple teardrop-shaped objects 12 being too wide.

The average spacing T3 between multiple teardrop-shaped objects 12 refers to the minimum distance between the ends of adjacent teardrop-shaped objects 12 in the longitudinal direction (y-direction) of the film base. The ends of the teardrop-shaped objects 12 refer to the ends along the long axis LA.

In a cross-section passing through the apex (highest point) of the teardrop-shaped object 12 along the width direction (x direction) of the film base, the height t of the teardrop-shaped object is in the range of 0.5 to 3 μm (see Figure 6). If the height t of the teardrop-shaped object is 0.1 μm or more, adhesion between the film bases can be sufficiently suppressed when the film 10 is wound into a roll. If the height t of the teardrop-shaped object is 3 μm or less, the absolute amount of crushing of the teardrop-shaped object 12 when the film 10 is wound into a roll is small, making the film roll less prone to deformation. From a similar viewpoint, the height t of the teardrop-shaped object 12 is preferably in the range of 0.1 to 0.8 μm. Note that the height t of the teardrop-shaped object 12 is the height from the surface of the film base to the apex of the teardrop-shaped object 12. The height t of the teardrop-shaped object 12 is preferably in the range of 0.2 to 10% of the thickness of the film base, and more preferably in the range of 0.3 to 5%.

In a cross-section passing through the apex of the teardrop-shaped object 12 along the width direction (x direction) of the film base, the width w of the teardrop-shaped object 12 is not particularly limited, but is preferably in the range of 500 to 2000 μm. If the width w of the teardrop-shaped object 12 is 500 μm or more, the support area can be increased, making the teardrop-shaped object 12 less likely to collapse. If it is 2000 μm or less, drying proceeds easily when forming the teardrop-shaped object 12 by solution coating, and cooling proceeds easily when forming by melt, thus facilitating efficient production of the film of the present invention. From a similar viewpoint, it is more preferable that the width w of the teardrop-shaped object 12 is in the range of 700 to 1500 μm. The width w of the teardrop-shaped object 12 is the maximum width of the teardrop-shaped object 12 in the above cross-section.

The height t and width w of the teardrop-shaped object 12 can be measured using a laser microscope. For example, a Keyence VK-X1000 laser microscope can be used. The measurement is performed by measuring the height t and width w of the teardrop-shaped objects within a 100 mm range in the longitudinal direction (y-direction) of the film base in a region where multiple teardrop-shaped objects 12 are arranged, and defining the average value of these measurements as the "height t and width w of the teardrop-shaped object."

In a cross-section passing through the apex of the teardrop-shaped object 12 along the width direction (x direction) of the film base, the shape of the teardrop-shaped object 12 is not particularly limited, but is usually circular. A circular shape is a shape formed by connecting the ends of a circular or elliptical arc with a straight line; examples include semicircular and semi-elliptical shapes.

It is preferable that the multiple teardrop-shaped objects 12 are arranged such that the intersection point M of the long axis LA and the short axis SA is located upstream in the winding direction from the center of the long axis LA. This prevents the multiple teardrop-shaped objects 12 from being unevenly crushed even when an oblique force is applied to them, thereby suppressing deformation of the film roll and adhesion between the films.

The teardrop-shaped object 12 contains a second resin composition comprising a thermoplastic resin. The thermoplastic resin contained in the teardrop-shaped object 12 may be the same type as the thermoplastic resin contained in the film base, or it may be a different type. However, from the viewpoint of improving adhesion with the film base, it is preferable that it be the same type. For example, if the thermoplastic resin contained in the film base is a cycloolefin resin, it is preferable that the resin contained in the teardrop-shaped object 12 is also a cycloolefin resin.

If the thermoplastic resin contained in the film base and the thermoplastic resin contained in the teardrop-shaped object 12 are of the same type, the adhesion between the teardrop-shaped object 12 and the film base can be improved. A thermoplastic resin of the same type refers to a thermoplastic resin having the same main component monomer (the most abundant component). The type and content of copolymer component monomers, as well as physical properties such as the weight-average molecular weight (Mw) and glass transition temperature (Tg) of the resin, may differ. The resin content is not particularly limited, but it is preferably 60% by mass or more, and more preferably 70-100% by mass, relative to the second resin composition constituting the teardrop-shaped object 12.

The teardrop-shaped object 12 may further contain components similar to those in the film base (e.g., fine particles) as needed. However, from the viewpoint of preventing slippage between the teardrop-shaped object 12 and the back surface of the film base when the film is wound, and facilitating appropriate adhesion, it is preferable that the fine particle content in the teardrop-shaped object 12 is less than the fine particle content in the film base, and more preferably that it contains no fine particles at all.

[Variation]
The teardrop-shaped object 12 is not limited to the shape shown in Figure 5. Figure 8 is an example of a plan view of a teardrop-shaped object having multiple protrusions, and Figure 9 is an example of a plan view of a teardrop-shaped object with a series of dots. In Figures 8 and 9, T1 is the maximum width of the teardrop-shaped object in the short axis direction, T2 is the maximum width of the teardrop-shaped object in the long axis direction, and M is the intersection of the long axis LA and the short axis SA of the teardrop-shaped object.

The teardrop-shaped object 12 may be placed on both sides of the film base, rather than just one side. Furthermore, the second resin composition for forming the teardrop-shaped object 12 does not necessarily have to be a solution containing resin and solvent; it may be a molten material. That is, when producing the film roll of the present invention by the molten casting method described later, the roll body can be formed by casting the molten first resin composition, then cooling and solidifying it to obtain a strip-shaped film base. Multiple teardrop-shaped objects can then be formed by applying droplets of the molten second resin composition to this strip-shaped film base, and then cooling and solidifying it.

(1.2) Film Thickness The wound optical film is preferably a single layer from the viewpoint of achieving the effects of the present invention. The effects of the present invention are most valuable in the thin film range. The film thickness of the optical film according to the present invention is preferably in the range of 5 to 80 μm, more preferably in the range of 10 to 65 μm, and even more preferably in the range of 10 to 45 μm. If the film thickness is 5 μm or more, the rigidity of the film roll is high, and it is easy to maintain the roll shape. If the film thickness is 80 μm or less, the mass does not increase too much, and it becomes easier to manufacture long film rolls.

From the viewpoint of suppressing adhesion between optical films, it is preferable that the average maximum height difference (P-V) _ave1 of the film thickness excluding the fine irregularities within a diameter range of 1000 mm, centered on any point within the optical film, is in the range of 0.15 to 0.40 μm.

The average maximum height difference (P-V) _ave1 of the film thickness, which is between 0.15 and 0.40, indicates that the optical film has minute stress-relaxed and non-stress-relaxed regions in adjacent areas. Based on these optical film characteristics, it can be inferred that during local adhesion, the non-stress-relaxed regions perform local relaxation, thereby suppressing local adhesion.

"Average maximum height difference (P-V) _ave1 of the optical film thickness" refers to the average value of the maximum height difference between the peaks and valleys of the uneven shape of the optical film thickness, as measured and observed by the thickness measurement described later. By measuring the thickness, the height difference between the highest part of the convex structure and the lowest part of the concave structure of the optical film is calculated, and the average value is taken as (P-V) _ave1 . There are no particular restrictions on the method of measuring the thickness, but for example, it can be measured using the inline retardation thickness measuring device RE-200L2T-Rth + thickness (manufactured by Otsuka Electronics Co., Ltd.).

(1.3) Resins constituting the film (1.3.1) Thermoplastic resins The thermoplastic resin used in the film according to the present invention is not limited as long as it can be handled as a film roll after film formation. For example, thermoplastic resins used for polarizing plate applications include cellulose ester resins such as triacetylcellulose (TAC), cellulose acetate propionate (CAP), and diacetylcellulose (DAC), cyclic olefin resins such as cycloolefin polymers (cycloolefin resins (COP)) (hereinafter also referred to as cycloolefin resins), polypropylene resins such as polypropylene (PP), acrylic resins such as polymethyl methacrylate (PMMA), and polyester resins such as polyethylene tereftate (PET).

In particular, with low-modulus films, such as resins with an elastic modulus of less than 3.0 GPa, it is difficult to relieve stress at multiple points on the film when forming a film roll. This makes it difficult to stretch and contract in the width and length directions, and when the film is in a roll state, the stress cannot be fully absorbed across the surface, leading to a tendency for winding misalignment. Furthermore, from another perspective, if there is a difference in height between the longitudinal and longitudinal directions of the film, the difference in stretching and contraction between the higher and lower parts of the film becomes significant.

Therefore, in embodiments of the present invention, it is preferable to control the maximum height difference (P-V) of the longitudinal average film thickness within the range of 0.02 to 0.40 μm, and it is effective to apply this to film rolls using cycloolefin polymers (cycloolefin resins (COP)) or polymethyl methacrylate (acrylic resins (PMMA)), which are resins with low elastic modulus, as thermoplastic resins.

However, it is preferable to use cycloolefin resin (COP) because it allows for easier control of stretchability and crystallinity, and because it facilitates adhesive penetration, ensuring better adhesion to the polarizer layer. Furthermore, the above film may be subjected to surface modification treatment after manufacturing.

(Cycloolefin resin)
The cycloolefin resin contained in the film roll according to the present invention is preferably a polymer of cycloolefin monomers, or a copolymer of a cycloolefin monomer and another copolymerizable monomer.

The cycloolefin monomer is preferably a cycloolefin monomer having a norbornene skeleton, and more preferably a cycloolefin monomer having a structure represented by the following general formula (A-1) or (A-2).

In general formula (A-1), ^R1 to ^R4 each independently represent a hydrogen atom, a hydrocarbon group having 1 to 30 carbon atoms, or a polar group. p represents an integer from 0 to 2. However, it is not the case that all of ^R1 to ^R4 simultaneously represent a hydrogen atom, nor that ^R1 and ^R2 simultaneously represent a hydrogen atom, nor that that ^R3 and ^R4 simultaneously represent a hydrogen atom.

In general formula (A-1), the hydrocarbon groups having 1 to 30 carbon atoms represented by ^R1 to ^R4 are preferably hydrocarbon groups having 1 to 10 carbon atoms, and more preferably hydrocarbon groups having 1 to 5 carbon atoms. The hydrocarbon groups having 1 to 30 carbon atoms may further have linking groups containing, for example, halogen atoms, oxygen atoms, nitrogen atoms, sulfur atoms, or silicon atoms. Examples of such linking groups include divalent polar groups such as carbonyl groups, imino groups, ether bonds, silyl ether bonds, and thioether bonds. Examples of hydrocarbon groups having 1 to 30 carbon atoms include methyl groups, ethyl groups, propyl groups, and butyl groups.

Examples of polar groups represented by ^R1 to ^R4 in general formula (A-1) include carboxyl groups, hydroxyl groups, alkoxy groups, alkoxycarbonyl groups, aryloxycarbonyl groups, amino groups, amide groups, and cyano groups. Among these, carboxyl groups, hydroxyl groups, alkoxycarbonyl groups, and aryloxycarbonyl groups are preferred, and alkoxycarbonyl groups and aryloxycarbonyl groups are preferred from the viewpoint of ensuring solubility during solution film formation.

In general formula (A-1), p is preferably 1 or 2 from the viewpoint of improving the heat resistance of the film. This is because when p is 1 or 2, the resulting polymer becomes bulkier, and the glass transition temperature tends to improve.

In general formula (A-2), ^R5 represents a hydrogen atom, a hydrocarbon group having 1 to 5 carbon atoms, or an alkylsilyl group having an alkyl group having 1 to 5 carbon atoms. ^R6 represents a carboxyl group, a hydroxyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an amino group, an amide group, a cyano group, or a halogen atom (fluorine atom, chlorine atom, bromine atom, or iodine atom). p represents an integer from 0 to 2.

In general formula (A-2), R ⁵ preferably represents a hydrocarbon group having 1 to 5 carbon atoms, and more preferably represents a hydrocarbon group having 1 to 3 carbon atoms.

In general formula (A-2), R ⁶ preferably represents a carboxyl group, a hydroxyl group, an alkoxycarbonyl group, or an aryloxycarbonyl group, and from the viewpoint of ensuring solubility during solution film formation, an alkoxycarbonyl group and an aryloxycarbonyl group are more preferred.

In general formula (A-2), p is preferably represented as 1 or 2 from the viewpoint of improving the heat resistance of the film. This is because when p is 1 or 2, the resulting polymer becomes bulkier, and the glass transition temperature tends to improve.

Cycloolefin monomers having the structure represented by general formula (A-2) are preferred because they improve solubility in organic solvents. Generally, disrupting the symmetry of organic compounds reduces their crystallinity, thus improving their solubility in organic solvents.

In general formula (A-2), ^R5 and ^R6 are substituted only on one side of the ring-forming carbon atoms relative to the molecular axis of symmetry. Therefore, the molecular symmetry is low, and cycloolefin monomers having the structure represented by general formula (A-2) have high solubility, making them suitable for manufacturing films by solution casting.

The content of cycloolefin monomers having the structure represented by general formula (A-2) in a polymer of cycloolefin monomers can be, for example, 70 mol% or more, preferably 80 mol% or more, and more preferably 100 mol% of the total amount of cycloolefin monomers constituting the cycloolefin resin. When a certain amount of cycloolefin monomers having the structure represented by general formula (A-2) is included, the orientation of the resin increases, and therefore the phase difference (retardation) value tends to rise.

Below, specific examples of cycloolefin monomers having the structure represented by general formula (A-1) are shown in example compounds 1 to 14, and specific examples of cycloolefin monomers having the structure represented by general formula (A-2) are shown in example compounds 15 to 34.

Examples of copolymerizable monomers that can copolymerize with cycloolefin monomers include copolymerizable monomers that can undergo ring-opening copolymerization with cycloolefin monomers, and copolymerizable monomers that can undergo addition copolymerization with cycloolefin monomers.

Examples of ring-opening copolymerizable monomers include cycloolefins such as cyclobutene, cyclopentene, cycloheptene, cyclooctene, and dicyclopentadiene.

Examples of copolymerizable monomers that can be added copolymerized include unsaturated double-bond-containing compounds, vinyl cyclic hydrocarbon monomers, and (meth)acrylates.

Examples of unsaturated double bond-containing compounds include olefin compounds with 2 to 12 (preferably 2 to 8) carbon atoms, such as ethylene, propylene, and butene.

Examples of vinyl cyclic hydrocarbon monomers include vinylcyclopentene monomers such as 4-vinylcyclopentene and 2-methyl-4-isopropenylcyclopentene.

Examples of (meth)acrylates include alkyl (meth)acrylates with 1 to 20 carbon atoms, such as methyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate.

The content of the cycloolefin monomer in a copolymer of a cycloolefin monomer and a copolymerizable monomer can be, for example, in the range of 20 to 80 mol%, preferably in the range of 30 to 70 mol%, relative to the total amount of monomers constituting the copolymer.

As described above, cycloolefin resins are polymers obtained by polymerizing or copolymerizing cycloolefin monomers having a norbornene skeleton, preferably cycloolefin monomers having a structure represented by general formula (A-1) or (A-2). Examples include the polymers (1) to (7) below.

(1) Ring-opening polymers of cycloolefin monomers (2) Ring-opening copolymers of cycloolefin monomers and copolymerizable monomers capable of ring-opening copolymerization with them (3) Hydrogenated ring-opening (co)polymers of (1) or (2) above (4) (co)polymers obtained by cyclizing the ring-opening (co)polymers of (1) or (2) above by a Friedel-Crafts reaction and then adding hydrogen (5) Saturated copolymers of cycloolefin monomers and unsaturated double-bond-containing compounds (6) Addition copolymers of cycloolefin monomers and vinyl cyclic hydrocarbon monomers and their hydrogenated products (7) Alternating copolymers of cycloolefin monomers and (meth)acrylates

The polymers described in (1) to (7) above can all be obtained by known methods, for example, the methods described in Japanese Patent Publication No. 2008-107534 and Japanese Patent Publication No. 2005-227606.

For example, the catalyst and solvent used in the ring-opening copolymerization described in (2) above can be those described in paragraphs 0019 to 0024 of Japanese Patent Publication No. 2008-107534. The catalyst used in the hydrogenated products described in (3) and (6) above can be those described in paragraphs 0025 to 0028 of Japanese Patent Publication No. 2008-107534. The acidic compound used in the Friedel-Crafts reaction described in (4) above can be those described in paragraph 0029 of Japanese Patent Publication No. 2008-107534. The catalyst used in the addition polymerization described in (5) to (7) above can be those described in paragraphs 0058 to 0063 of Japanese Patent Publication No. 2005-227606. The alternating copolymerization reaction described in (7) above can be carried out by the method described in paragraphs 0071 and 0072 of Japanese Patent Publication No. 2005-227606. Among these, polymers (1) to (3) and (5) are preferred, and polymers (3) and (5) are more preferred.

In other words, the cycloolefin resin preferably contains at least one of the structural units represented by the following general formula (B-1) and the following general formula (B-2), in order to increase the glass transition temperature and light transmittance of the resulting cycloolefin resin. It is more preferable to contain only the structural units represented by general formula (B-2), or both the structural units represented by general formula (B-1) and general formula (B-2).

The structural unit represented by general formula (B-1) is a structural unit derived from the cycloolefin monomer represented by general formula (A-1) mentioned above, and the structural unit represented by general formula (B-2) is a structural unit derived from the cycloolefin monomer represented by general formula (A-2) mentioned above.

In general formula (B-1), X represents -CH=CH- or _-CH2CH2- . ^R1 to ^R4 and p are equivalent to ^R1 to ^R4 and p in general formula (A-1) _, respectively.

In general formula (B-2), X represents -CH=CH- or -CH ₂ CH _2- . ^R5 to ^R6 and p are equivalent to ^R5 to ^R6 and p in general formula (A-2), respectively.

The cycloolefin resin according to the present invention may be a commercially available product. Examples of commercially available cycloolefin resins include Arton G (e.g., G7810), Arton F, Arton R (e.g., R4500, R4900, and R5000), and Arton RX, all manufactured by JSR Corporation.

The intrinsic viscosity [η]inh of the cycloolefin resin is preferably in the range of 0.2 to 5 ^cm³ /g, more preferably in the range of 0.3 to 3 ^cm³ /g, and even more preferably in the range of 0.4 to 1.5 ^cm³ /g when measured at 30°C.

The number-average molecular weight (Mn) of the cycloolefin resin is preferably in the range of 8,000 to 100,000, more preferably in the range of 10,000 to 80,000, and even more preferably in the range of 12,000 to 50,000.

The weight-average molecular weight (Mw) of the cycloolefin resin is preferably in the range of 20,000 to 300,000, more preferably in the range of 30,000 to 250,000, and even more preferably in the range of 40,000 to 200,000.

The number-average molecular weight and weight-average molecular weight of cycloolefin resins can be measured in polystyrene equivalents using gel permeation chromatography (GPC).

(Gel permeation chromatography)
Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Three columns manufactured by Showa Denko K.K. were connected together)
Column temperature: 25°C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml/min
Calibration curve: A calibration curve was used for 13 samples of standard polystyrene STK (manufactured by Tosoh Corporation) with Mw values ranging from 500 to 2,800,000. It is preferable to use the 13 samples at approximately equal intervals.

When the intrinsic viscosity [η]inh, number-average molecular weight, and weight-average molecular weight are within the above range, the cycloolefin resin exhibits good heat resistance, water resistance, chemical resistance, mechanical properties, and moldability as a film.

The glass transition temperature (Tg) of cycloolefin resins is typically 110°C or higher, preferably within the range of 110 to 350°C, more preferably within the range of 120 to 250°C, and even more preferably within the range of 120 to 220°C. A glass transition temperature (Tg) of 110°C or higher makes it easier to suppress deformation under high-temperature conditions. On the other hand, a glass transition temperature (Tg) of 350°C or lower facilitates molding and reduces resin degradation due to heat during molding.

The cycloolefin resin content is preferably 70% by mass or more, and more preferably 80% by mass or more, relative to the film.

(Acrylic resin)
The acrylic resin according to the present invention is a polymer of acrylic acid ester or methacrylic acid ester, and also includes copolymers with other monomers. Therefore, the acrylic resin according to the present invention also includes methacrylic resin.

While there are no particular restrictions on the resin, it is preferable that it contains methyl methacrylate units in the range of 50 to 99% by mass, and other monomer units copolymerizable thereto in the range of 1 to 50% by mass.

Other units constituting the acrylic resin formed by copolymerization include alkyl methacrylates with 2 to 18 C12 alkyl groups, alkyl acrylates with 1 to 18 C12 alkyl groups, hydroxyalkyl acrylates such as isobornyl methacrylate and 2-hydroxyethyl acrylate, α,β-unsaturated acids such as acrylic acid and methacrylic acid, acrylamides such as acryloylmorpholine and N-hydroxyphenylmethacrylamide, unsaturated group-containing dicarboxylic acids such as N-vinylpyrrolidone, maleic acid, fumaric acid, and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α,β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, N-substituted maleimide, glutarimide, and glutaric anhydride. Copolymerizable monomers that form units excluding glutarimide and glutaric anhydride from these units include monomers corresponding to the above units.

Specifically, examples include monomers such as alkyl methacrylates with 2 to 18 C12 alkyl groups, alkyl acrylates with 1 to 18 C12 alkyl groups, hydroxyalkyl acrylates such as isobornyl methacrylate and 2-hydroxyethyl acrylate, α,β-unsaturated acids such as acrylic acid and methacrylic acid, acrylamides such as acryloylmorpholine and N-hydroxyphenylmethacrylamide, unsaturated group-containing dicarboxylic acids such as N-vinylpyrrolidone, maleic acid, fumaric acid, and itaconic acid, aromatic vinyl compounds such as styrene and α-methylstyrene, α,β-unsaturated nitriles such as acrylonitrile and methacrylonitrile, maleic anhydride, maleimide, and N-substituted maleimide.

Furthermore, glutarimide units can be formed, for example, by reacting an intermediate polymer having (meth)acrylic acid ester units with a primary amine (imidizing agent) to imidize it (see Japanese Patent Publication No. 2011-26563). Glutaric anhydride units can be formed, for example, by heating an intermediate polymer having (meth)acrylic acid ester units (see Japanese Patent Publication No. 4961164).

Among the above-mentioned constituent units, the acrylic resin according to the present invention is particularly preferably composed of isobornyl methacrylate, acryloylmorpholine, N-hydroxyphenylmethacrylamide, N-vinylpyrrolidone, styrene, hydroxyethyl methacrylate, maleic anhydride, maleimide, N-substituted maleimide, glutaric acid anhydride, or glutarimide, from the viewpoint of mechanical strength.

The acrylic resin according to the present invention preferably has a weight-average molecular weight (Mw) in the range of 50,000 to 1,000,000, more preferably in the range of 100,000 to 1,000,000, and particularly preferably in the range of 200,000 to 800,000, from the viewpoint of controlling dimensional changes in response to changes in ambient temperature and humidity, and improving peelability from metal supports during film production, drying properties with organic solvents, heat resistance, and mechanical strength. A Mw of 50,000 or higher provides excellent heat resistance and mechanical strength, while a Mw of 1,000,000 or lower provides excellent peelability from metal supports and drying properties with organic solvents.

The method for producing the acrylic resin according to the present invention is not particularly limited, and any known method such as suspension polymerization, emulsion polymerization, bulk polymerization, or solution polymerization may be used.

Here, conventional peroxide and azo-based polymerization initiators can be used, and redox-based initiators can also be used. The polymerization temperature can be within the range of 30 to 100°C for suspension or emulsion polymerization, and within the range of 80 to 160°C for bulk or solution polymerization. To control the reduced viscosity of the resulting copolymer, alkyl mercaptans or the like can be used as chain transfer agents during polymerization.

From the viewpoint of maintaining the mechanical strength of the film, it is preferable that the glass transition temperature (Tg) of the acrylic resin be within the range of 80 to 120°C.

The acrylic resin used in this invention can also be a commercially available product. Examples include Delpet 60N, 80N, 980N, SR8200 (all manufactured by Asahi Kasei Chemicals Corporation), Dianaal BR52, BR80, BR83, BR85, BR88, EMB-143, EMB-159, EMB-160, EMB-161, EMB-218, EMB-229, EMB-270, EMB-273 (all manufactured by Mitsubishi Rayon Co., Ltd.), KT75, TX400S, and IPX012 (all manufactured by Denki Kagaku Kogyo Co., Ltd.). Two or more acrylic resins can also be used in combination.

The acrylic resin according to the present invention preferably contains additives. As an example of additives, it is preferable to include acrylic particles (rubber elastic particles) described in International Publication No. 2010/001668, for the purpose of improving the mechanical strength of the film and adjusting the dimensional change rate.

Examples of commercially available multilayer acrylic granular composites include, for example, "Metablen W-341" from Mitsubishi Rayon, "Kaneace" from Kaneka Corporation, "Paraloid" from Kureha Corporation, "Acryloid" from Rohm & Haas Corporation, "Stafloid" from Aica Corporation, Chemisnow MR-2G, MS-300X (all manufactured by Soken Chemical Co., Ltd.), and "Parapet SA" from Kuraray Corporation. These can be used individually or in combination of two or more types.

The volume-average particle diameter of the acrylic particles is 0.35 μm or less, preferably in the range of 0.01 to 0.35 μm, and more preferably in the range of 0.05 to 0.30 μm. If the particle diameter is above a certain level, the film can be easily stretched under heat; if the particle diameter is below a certain level, the transparency of the resulting film is less likely to be impaired.

From the viewpoint of flexibility, the film according to the present invention preferably has a flexural modulus (JIS K7171) of 10.5 GPa or less. More preferably, this flexural modulus is 1.3 GPa or less, and even more preferably 1.2 GPa or less. This flexural modulus varies depending on the type and amount of acrylic resin and rubber elastic particles in the film; for example, the higher the content of rubber elastic particles, the lower the flexural modulus generally becomes. Furthermore, using a copolymer of alkyl methacrylate and alkyl acrylate, etc., as the acrylic resin generally results in a lower flexural modulus than using a homopolymer of alkyl methacrylate.

(Cellulose ester resin)
In the film roll according to the present invention, it is also preferable to use a cellulose ester resin. The cellulose ester used in the present invention refers to a cellulose acylate resin in which some or all of the hydrogen atoms of the hydroxyl groups (-OH) at positions 2, 3, and 6 in the glucose units that are linked by β-1,4 bonds and constitute cellulose are replaced with acyl groups.

The cellulose ester used is not particularly limited, but it is preferably an ester of a linear or branched carboxylic acid with approximately 2 to 22 carbon atoms. The carboxylic acid constituting the ester may be an aliphatic carboxylic acid, a ring-forming carboxylic acid, or an aromatic carboxylic acid.

For example, cellulose esters are formed in which the hydrogen atoms of the hydroxyl group portion of cellulose are replaced with acyl groups having 2 to 22 carbon atoms, such as acetyl groups, propionyl groups, butyryl groups, isobutyryl groups, valeryl groups, pivaloyl groups, hexanoyl groups, octanoyl groups, lauroyl groups, and stearoyl groups.

The carboxylic acid (acyl group) constituting the ester may have substituents. The carboxylic acid constituting the ester is preferably a lower fatty acid with six or fewer carbon atoms, and more preferably a lower fatty acid with three or fewer carbon atoms. The acyl group in the cellulose ester may be a single type or a combination of multiple acyl groups.

Preferred cellulose esters include cellulose acetates such as diacetylcellulose (DAC) and triacetylcellulose (TAC), as well as mixed fatty acid esters of cellulose in which propionate or butyrate groups are bonded in addition to acetyl groups, such as cellulose acetate propionate (CAP), cellulose acetate butyrate, and cellulose acetate propionate butyrate. These cellulose esters may be used individually or in combination of multiple types.

(Type of acyl group and degree of substitution)
By adjusting the type and degree of substitution of the acyl groups in the cellulose ester, the humidity fluctuations in the phase difference can be controlled within a desired range, thereby improving the uniformity of the film thickness. A smaller degree of substitution of the acyl groups in the cellulose ester improves the phase difference expression, making thin film formation possible. On the other hand, if the degree of substitution of the acyl groups is too small, durability may deteriorate, which is undesirable.

On the other hand, the greater the degree of substitution of the acyl groups in cellulose esters, the less phase difference occurs. Therefore, it is necessary to increase the stretching ratio during film formation. However, uniform stretching at high stretching ratios is difficult, leading to increased (worsening) variations in film thickness. Furthermore, the Rt humidity fluctuation, which is the retardation (phase difference) in the thickness direction, is caused by the coordination of water molecules to the carbonyl groups of cellulose. Therefore, the higher the degree of substitution of the acyl groups, i.e., the more carbonyl groups in the cellulose, the worse the Rt humidity fluctuation tends to be.

The cellulose ester preferably has a total substitution degree within the range of 2.1 to 2.5. This range helps suppress environmental fluctuations (especially Rt fluctuations due to humidity) and improves the uniformity of the film thickness. More preferably, from the viewpoint of improving the castability and stretchability during film formation and further improving the uniformity of the film thickness, the degree of substitution is within the range of 2.2 to 2.45.

More specifically, cellulose esters satisfy both formulas (a) and (b) below. In formulas (a) and (b), X is the degree of substitution of an acetyl group, and Y is the degree of substitution of a propionyl group or a butyryl group, or a mixture thereof.

Formula (a): 2.1≦X+Y≦2.5
Formula (b): 0≦Y≦1.5

The cellulose ester is more preferably cellulose acetate (Y=0) and cellulose acetate propionate (CAP) (Y; propionyl group, Y>0), and even more preferably cellulose acetate with Y=0, as this reduces variations in film thickness.

The cellulose acetate particularly preferred is cellulose diacetate (DAC) with a x-value of 2.1 ≤ X ≤ 2.5 (more preferably 2.15 ≤ X ≤ 2.45), which allows for desired phase difference expression, Rt humidity fluctuation, and film thickness variation.

Furthermore, when Y > 0, the cellulose acetate propionate (CAP) that is particularly preferred is one that satisfies the following conditions: 0.95 ≤ X ≤ 2.25, 0.1 ≤ Y ≤ 1.2, and 2.15 ≤ X + Y ≤ 2.45.

By using the aforementioned cellulose acetate or cellulose acetate propionate, a film roll with excellent retardation, mechanical strength, and resistance to environmental changes can be obtained.

The degree of substitution of acyl groups indicates the average number of acyl groups per glucose unit, and how many hydrogen atoms of the hydroxyl groups at positions 2, 3, and 6 of a glucose unit are substituted by acyl groups. Therefore, the maximum degree of substitution is 3.0, which means that all hydrogen atoms of the hydroxyl groups at positions 2, 3, and 6 are substituted by acyl groups. These acyl groups may be evenly substituted at positions 2, 3, and 6 of the glucose unit, or they may be substituted in a distributed manner. The degree of substitution is determined by the method specified in ASTM-D817-96.

To obtain the desired optical properties, cellulose acetates with different degrees of substitution may be mixed and used. In the above case, the mixing ratio of the different cellulose acetates is not particularly limited.

From the viewpoint of increasing the mechanical strength of the resulting film roll, it is preferable that the number-average molecular weight (Mn) of the cellulose ester is within the range of 2 × ^10⁴ to 3 × ^10⁵ , more preferably within the range of 2 × ^10⁴ to 1.2 × ^10⁵ , and even more preferably within the range of 4 × ^10⁴ to 8 × ^10⁴ . The number-average molecular weight (Mn) of the cellulose ester is calculated by measurement using gel permeation chromatography (GPC) under the measurement conditions described above.

From the viewpoint of increasing the mechanical strength of the resulting film roll, it is preferable that the weight-average molecular weight (Mw) of the cellulose ester is in the range of 2 × ^10⁴ to 1 × ^10⁶ , more preferably in the range of 2 × ^10⁴ to 1.2 × ^10⁵ , and even more preferably in the range of 4 × ^10⁴ to 8 × ^10⁴ .

The raw material cellulose for cellulose esters is not particularly limited, but examples include cotton linters, wood pulp, and kenaf. Furthermore, the cellulose esters obtained from these can be mixed and used in any desired proportion.

Cellulose esters such as cellulose acetate and cellulose acetate propionate can be produced by known methods.

Generally, the cellulose raw material is mixed with a specified organic acid (acetic acid, propionic acid, etc.), an acid anhydride (acetic anhydride, propionic anhydride, etc.), and a catalyst (sulfuric acid, etc.) to esterify the cellulose, and the reaction proceeds until a cellulose triester is produced.

In triesters, the three hydroxyl groups of the glucose unit are replaced by acylic acid, an organic acid. By using two different organic acids simultaneously, mixed ester-type cellulose esters, such as cellulose acetate propionate and cellulose acetate butyrate, can be produced.

Next, a cellulose ester resin having the desired degree of acyl substitution is synthesized by hydrolyzing the cellulose triester. Subsequently, the cellulose ester resin is obtained through processes such as filtration, precipitation, washing, dehydration, and drying. Specifically, it can be synthesized by referring to the method described in Japanese Patent Publication No. 10-45804.

(1.3.2) Other additives The material used in the film according to the present invention may contain the following additives in addition to the thermoplastic resin described above.

(Plasticizer)
The optical film according to the present invention preferably contains at least one plasticizer for the purpose of imparting processability to, for example, polarizing plate protective films. The plasticizer is preferably used alone or in a mixture of two or more. Among the plasticizers, it is preferable to include at least one plasticizer selected from the group consisting of sugar esters, polyesters, and styrene compounds, from the viewpoint of achieving both effective control of moisture permeability and high compatibility with base resins such as cellulose esters.

The plasticizer is preferably 15,000 or less in molecular weight, and more preferably 10,000 or less, from the viewpoint of achieving both improved heat and humidity resistance and compatibility with base resins such as cellulose esters. If the compound with a molecular weight of 10,000 or less is a polymer, it is preferable that its weight-average molecular weight (Mw) is 10,000 or less. The preferred range for the weight-average molecular weight (Mw) is 100 to 10,000, and more preferably 400 to 8,000.

In particular, to obtain the effects of the present invention, it is preferable to include the compound with a molecular weight of 1500 or less in an amount of 6 to 40 parts by mass per 100 parts by mass of the base resin, and more preferably in an amount of 10 to 20 parts by mass. Including it within this range allows for effective control of moisture permeability and compatibility with the base resin, which is preferable.

[Sugar esters]
To prevent hydrolysis, a sugar ester compound may be included as a plasticizer. Specifically, as the sugar ester compound, a sugar ester can be used that has at least one pyranose structure or furanose structure with 1 to 12 such structures, and in which all or part of the OH groups of the structure are esterified.

〔polyester〕
Polyester can also be included as a plasticizer. The polyester is not particularly limited, but for example, a polymer with terminal hydroxyl groups (polyester polyol) obtained by a condensation reaction of dicarboxylic acid or its ester-forming derivative with glycol, or a polymer in which the terminal hydroxyl groups of the polyester polyol are encapsulated with monocarboxylic acid (end-capped polyester) can be used. The ester-forming derivative referred to here is an esterified product of dicarboxylic acid, a dicarboxylic acid chloride, or an anhydride of dicarboxylic acid.

[Styrene compounds]
As a plasticizer, in addition to or instead of the above-mentioned sugar esters and polyesters, styrene compounds may also be used for the purpose of improving the water resistance of the film. The styrene compound may be a homopolymer of styrene monomers, or a copolymer of styrene monomers and other copolymer monomers. The content of constituent units derived from styrene monomers in the styrene compound is preferably in the range of 30 to 100 mol%, more preferably in the range of 50 to 100 mol%, in order for the molecular structure to have a certain level of bulkiness.

Examples of styrene monomers include styrene; alkyl-substituted styrenes such as α-methylstyrene, β-methylstyrene, and p-methylstyrene; halogen-substituted styrenes such as 4-chlorostyrene and 4-bromostyrene; hydroxystyrenes such as p-hydroxystyrene, α-methyl-p-hydroxystyrene, 2-methyl-4-hydroxystyrene, and 3,4-dihydroxystyrene; vinylbenzyl alcohols; alkoxy-substituted styrenes such as p-methoxystyrene, p-tert-butoxystyrene, and m-tert-butoxystyrene; 3-vinylbenzoic acid, 4-vinylbenzoic acid This includes vinylbenzoic acids such as benzoic acid; 4-vinylbenzyl acetate; 4-acetoxystyrene; amidestyrenes such as 2-butylamidostyrene, 4-methylamidostyrene, and p-sulfonamidostyrene; aminostyrenes such as 3-aminostyrene, 4-aminostyrene, 2-isopropenylaniline, and vinylbenzyldimethylamine; nitrostyrenes such as 3-nitrostyrene and 4-nitrostyrene; cyanostyrenes such as 3-cyanostyrene and 4-cyanostyrene; vinylphenylacetonitrile; arylstyrenes such as phenylstyrene, and indenes.
The styrene monomer may be a single type or a combination of two or more types.

(optional ingredient)
The optical film according to the present invention may contain other optional components such as antioxidants, colorants, ultraviolet absorbers, matting agents, acrylic particles, hydrogen-bonding solvents, and ionic surfactants. These components can be added in an amount of 0.01 to 20 parts by mass per 100 parts by mass of the base resin.

[Antioxidant]
The film roll according to the present invention can use commonly known antioxidants. In particular, lactone-based, sulfur-based, phenol-based, double-bond-based, hindered amine-based, and phosphorus-based compounds can be preferably used.

These antioxidants are added in an amount of 0.05 to 20% by mass, preferably 0.1 to 1% by mass, relative to the resin, which is the main raw material of the film. A synergistic effect can be obtained by using several different types of compounds in combination rather than using only one type of antioxidant. For example, the combination of lactone-based, phosphorus-based, phenol-based, and double-bond-based compounds is preferred.

[Coloring agents]
The film roll according to the present invention preferably contains a coloring agent for color adjustment, to the extent that it does not impair the effects of the present invention. A coloring agent refers to a dye or pigment, and in the present invention, it refers to one that has the effect of making the color tone of the liquid crystal screen bluer, or adjusting the yellow index, or reducing haze. Various dyes and pigments can be used as coloring agents, but anthraquinone dyes, azo dyes, phthalocyanine pigments, etc. are effective.

[UV absorber]
Since the film roll according to the present invention can be used on the viewing side or backlight side of a polarizing plate, it may contain an ultraviolet absorber for the purpose of imparting ultraviolet absorption functionality. The ultraviolet absorber is not particularly limited, but examples include benzotriazole-based, 2-hydroxybenzophenone-based, or phenyl salicylate-based ultraviolet absorbers.

Examples include triazoles such as 2-(5-methyl-2-hydroxyphenyl)benzotriazole, 2-[2-hydroxy-3,5-bis(α,α-dimethylbenzyl)phenyl]-2H-benzotriazole, and 2-(3,5-di-t-butyl-2-hydroxyphenyl)benzotriazole, and benzophenones such as 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-octoxybenzophenone, and 2,2'-dihydroxy-4-methoxybenzophenone. The UV absorbers can be used individually or in combination of two or more.

The amount of UV absorber used varies depending on the type of UV absorber and the usage conditions, but generally, it is added in the range of 0.05 to 10% by mass, preferably 0.1 to 5% by mass, relative to the base resin.

[Fine particles]
In the film roll according to the present invention, it is preferable to add fine particles that impart slipperiness to the film roll. In particular, adding fine particles is effective from the viewpoint of improving the slipperiness of the film surface according to the present invention, improving slipperiness during winding, and preventing the occurrence of scratches and blocking.

The fine particles can be either inorganic or organic, as long as they do not impair the transparency of the resulting film roll and have heat resistance during melting; however, inorganic particles are more preferred. These fine particles can be used individually or in combination of two or more types. By using particles with different particle sizes and shapes (e.g., needle-shaped and spherical), it is possible to achieve both high transparency and slipperiness.

Among the compounds constituting the above-mentioned fine particles, silicon dioxide is particularly preferred because its refractive index is close to that of the cycloolefin resin, acrylic resin, and cellulose ester resin, resulting in excellent transparency (haze).

Specific examples of silicon dioxide include commercially available products with product names such as Aerosil® 200V, Aerosil® R972V, Aerosil® R972, R974, R812, 200, 300, R202, OX50, TT600, NAX50 (all manufactured by Nippon Aerosil Co., Ltd.), Seahostar® KEP-10, Seahostar® KEP-30, Seahostar® KEP-50 (all manufactured by Nippon Shokubai Co., Ltd.), Silohobic® 100 (manufactured by Fuji Silicia Co., Ltd.), Nipseal® E220A (manufactured by Nippon Silica Industry Co., Ltd.), and Admafine® SO (manufactured by Admatex Co., Ltd.), which can be preferably used.

The particle shape can be irregular, needle-shaped, flattened, spherical, etc., without any particular restrictions, but spherical particles are preferred because they result in a film roll with good transparency.

The particle size should preferably be smaller than the wavelength of visible light, and even more preferably less than or equal to half the wavelength of visible light, because light scattering occurs and transparency deteriorates if the particle size is close to the wavelength of visible light. If the particle size is too small, the slipperiness may not improve, so a range of 80 to 180 nm is particularly preferred. Note that particle size refers to the size of the aggregate if the particles are aggregates of primary particles. If the particles are not spherical, it refers to the diameter of the circle corresponding to their projected area.

The fine particles are preferably added to the base resin in an amount of 0.05 to 10% by mass, more preferably 0.1 to 5% by mass.

(1.4) Applications of the film The optical film unwound from the film roll according to the present invention is suitably used as a protective film for polarizing plates and the like, and can be used in various optical measuring devices and display devices such as liquid crystal display devices and organic electroluminescent display devices.

2. Method for Manufacturing Film Rolls The film rolls of the present invention can be manufactured by solution casting or melt casting, for example, by the methods described in International Publication No. 2022/259668, International Publication No. 2022/153785, and International Publication No. 2022/224635. In particular, the teardrop shape of the aforementioned fine uneven surface can be formed by the method described in International Publication No. 2022/224635, etc.

The film roll of the present invention can be manufactured through a film formation process, a fine surface formation process, and a winding process.

(2.1) Film Forming Process In the film forming process, the first resin composition is prepared, cast, dried, and peeled, then dried and stretched to produce a strip-shaped film base. The casting of the first resin composition may be carried out by a molten casting method or by a solution casting method. In particular, from the viewpoint of being able to use high molecular weight resins, it is preferable to cast the first resin composition by a solution casting method. That is, the film base can be produced through a dope preparation process, a casting, drying, and peeling process, and a drying and stretching process.

(2.1.1) Dope preparation process: First resin composition preparation process In the film-forming process, first, a first resin composition for producing the film base is prepared.

(First resin composition)
Examples of resins that can be used to prepare the first resin composition include the aforementioned cellulose ester resins, cycloolefin resins (COP), polypropylene resins, acrylic resins, and polyester resins.

The solvent includes at least an organic solvent (a good solvent) capable of dissolving the resin. Examples of good solvents include chlorinated organic solvents such as dichloromethane, as well as non-chlorinated organic solvents such as methyl acetate, ethyl acetate, acetone, and tetrahydrofuran. Among these, methylene chloride is preferred.

The solvent may further contain a poor solvent. Examples of poor solvents include linear or branched aliphatic alcohols having 1 to 4 carbon atoms. A higher proportion of alcohol in the dope makes the film-like material more likely to gel, and easier to peel from the metal support. Examples of linear or branched aliphatic alcohols having 1 to 4 carbon atoms include methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Among these, methanol and ethanol are preferred from the viewpoint of stability and drying properties.

(2.1.2) Casting, Drying, and Peeling Process Next, the first resin composition prepared in the dope preparation process is cast onto the support. The first resin composition can be cast by extrusion from a casting die. The temperature of the first resin composition during casting is usually in the range of 15 to 30°C, preferably room temperature (23°C).

Next, the solvent in the first resin composition cast onto the support is appropriately evaporated (dried), and then the first resin composition after solvent evaporation is peeled off the support to obtain a film-like material of the first resin composition. The residual solvent content of the film-like material of the first resin composition is preferably, for example, 25% by mass or more, more preferably in the range of 30 to 37% by mass, and even more preferably in the range of 30 to 35% by mass. If the residual solvent content of the film-like material of the first resin composition at the time of peeling is 25% by mass or more, the solvent is easily volatilized rapidly from the film-like material after peeling. Furthermore, if the residual solvent content of the film-like material of the first resin composition at the time of peeling is 37% by mass or less, excessive stretching of the film-like material due to peeling can be suppressed.

The amount of residual solvent in the film-like substance of the first resin composition upon peeling is defined by the following formula. The same applies hereafter. Note that "heat treatment when measuring the amount of residual solvent" in the following formula refers to a heat treatment at 140°C for 15 minutes.

Residual solvent amount (mass%) = (Mass of the first resin composition before heat treatment - Mass of the first resin composition after heat treatment) / Mass of the first resin composition after heat treatment × 100

(2.1.3) Drying and stretching process The obtained film-like material of the first resin composition is then dried. Drying may be carried out in one step or in multiple steps. Drying may also be carried out while stretching as needed. Stretching may be carried out according to the desired optical properties, and it is preferable to stretch in at least one direction, and stretching may be carried out in two mutually orthogonal directions (for example, biaxial stretching in the width direction of the film-like material (x direction) and the transport direction (y direction) perpendicular to it).

The stretching ratio can be within the range of 1.01 to 2.00 times, for example, when used as a phase difference film. The stretching ratio is defined as (stretched size of the film after stretching) / (stretched size of the film before stretching). When biaxial stretching is performed, it is preferable to use the above stretching ratio for both the x and y directions. The in-plane slow phase axis direction of the film (the direction in which the refractive index is maximum) is usually the direction in which the stretching ratio is maximum.

The drying temperature during stretching (stretching temperature) is preferably within the range of (Tg - 65)°C to (Tg + 60)°C, and more preferably within the range of (Tg - 50)°C to (Tg + 50)°C, where Tg is the glass transition temperature of the resin. If the stretching temperature is above a certain level, the solvent is easily evaporated to an appropriate degree, making it easier to adjust the stretching tension within an appropriate range. If the stretching temperature is below a certain level, the solvent does not evaporate excessively, thus preventing damage to the stretchability.

The amount of residual solvent in the film-like substance of the first resin composition at the start of stretching is preferably about the same as the amount of residual solvent in the film-like substance of the first resin composition at the time of peeling, preferably in the range of 20 to 30% by mass, and more preferably in the range of 25 to 30% by mass.

The film-like material of the first resin composition can be stretched in the x-direction (TD direction) by, for example, fixing both ends of the film-like material with clips or pins and widening the distance between the clips or pins in the direction of travel (tenter method). The film-like material of the first resin composition can be stretched in the y-direction (MD direction) by, for example, creating a difference in peripheral speed between multiple rolls and utilizing that difference in peripheral speed (roll method).

From the viewpoint of further reducing the amount of residual solvent in the film-like material of the first resin composition, it is preferable to further dry (post-dry) the film-like material of the first resin composition obtained after stretching. For example, it is preferable to further dry the film-like material of the first resin composition obtained after stretching while conveying it (under constant tension) using rolls or the like.

The drying temperature after stretching is preferably within the range of (Tg-30) to (Tg+30)°C, and more preferably within the range of (Tg-20) to Tg°C, where Tg is the glass transition temperature of the resin. If the drying temperature after stretching is above a certain level, the rate of solvent evaporation from the film-like substance of the first resin composition after stretching is increased, thus improving drying efficiency. If the drying temperature is below a certain level, deformation due to stretching of the film-like substance of the first resin composition is suppressed.

Based on the above, a film base formed by the first resin composition is manufactured.

(2.2) Process for forming fine irregularities The method for forming fine irregularities according to the present invention is not particularly limited as a method for forming after preparing the second resin composition. Examples include a method of forming by coating the second resin composition onto the film base and then drying it, a method of forming by pressing the second resin composition onto the film base, and a method of forming by laser processing the film base and the second resin composition. Among these, the method of forming by coating onto the film base and then drying it is particularly preferred. As an example of a method for forming fine irregularities by pressing or laser, the method described in Japanese Patent Application Publication No. 2021-056302 can be cited. Hereinafter, a method for forming fine irregularities by coating the second resin composition onto the film base and then drying it will be described, that is, a method for forming fine irregularities via a second resin composition preparation step, a second resin composition coating step, and a second resin composition drying step.

(2.2.1) Second resin composition preparation step In the second resin composition preparation step, the resin is dissolved in a solvent to prepare the second resin composition.

(Second resin composition)
The resin that can be used to prepare the second resin composition is of the same type as that used in the first resin composition. The solvent contained in the second resin composition contains at least an organic solvent (good solvent) capable of dissolving the resin. Examples of good solvents include chlorinated organic solvents such as methylene chloride and non-chlorinated organic solvents such as methyl acetate, ethyl acetate, acetone, tetrahydrofuran, cyclopentanone, and toluene. Among these, methylene chloride, cyclopentanone, and toluene are preferred from the viewpoint of easily dissolving cycloolefin resins. The solvent contained in the second resin composition may further contain a poor solvent. As the poor solvent, the same poor solvent as that contained in the dope can be used.

The resin concentration of the second resin composition is preferably lower than that of the first resin composition, and preferably 50% by mass or less of the resin concentration of the first resin composition. Specifically, the resin concentration of the second resin composition is preferably more than 2% by mass and 10% by mass or less, and more preferably in the range of 3 to 7% by mass. By adjusting the resin concentration and amount of the second resin composition, the height of the teardrop-shaped object can be adjusted. For example, by increasing the resin concentration and amount of the second resin composition, the height of the teardrop-shaped object can be increased.

(2.2.2) Second resin composition coating step In the second resin composition coating step, droplets of the second resin composition are applied (dropped) to both ends in the width direction of the surface of the formed film base to form a plurality of fine irregularities. At this time, it is preferable from the viewpoint of suppressing deformation of the film roll that the fine irregularities are teardrop shaped and that the relationship between the maximum width T2 in the long axis direction and the maximum width T1 in the short axis direction of the teardrop shape satisfies the following formula (1).

Formula (1): 1.15≦T2/T1≦1.90

The second resin composition may be a molten material or a solution, but a solution is preferred from the viewpoint of ease of adjusting the shape and dimensions. That is, teardrop-shaped objects can be formed by applying droplets of the second resin composition (knurling solution), which contains resin and solvent, to both ends of the film base in the width direction, and then drying them.

The second resin composition can be applied by any method, such as a dispenser method or an inkjet method. The inkjet method is more preferable from the viewpoint of easier adjustment of the teardrop shape. The temperature of the second resin composition at this time is, for example, in the range of 10 to 30°C, preferably room temperature (23°C).

(2.2.3) Second resin composition drying step The second resin composition drying step can be carried out by any drying method, for example, by blow-air drying (including hot air drying) or by heating with electromagnetic waves (for example, by heating with an infrared (IR) heater). In particular, when the fine uneven portion is a teardrop-shaped object, it is preferable to use hot air drying in order to adjust the relationship between the maximum width T2 in the long axis direction and the maximum width T1 in the short axis direction of the teardrop-shaped object to satisfy formula (1). Furthermore, in the case of blow-air drying (hot air drying), it is preferable to blow air in a direction parallel to the surface of the film, and more preferably in the opposite direction to the film transport direction.

The drying temperature is preferably within the range that satisfies the above formula (1). From the viewpoint of maximizing the (T2/T1) value, a higher drying temperature is preferable. Specifically, when Tg is the glass transition temperature of the resin contained in the second resin composition, the drying is preferably carried out within the range of 40 to (Tg-20)°C, and more preferably within the range of 80 to (Tg-10)°C. Specifically, it is preferably within the range of 40 to 115°C, and more preferably within the range of 80 to 100°C.

The value of (T2/T1) can be adjusted by factors such as the film transport speed, drying conditions (drying method, drying temperature), the resin concentration of the second resin composition (for forming teardrop-shaped objects), the dropping height, and the surface condition of the film.

The (T2/T1) value can be increased by increasing the film transport speed, lowering the drying temperature, and using hot air drying. Furthermore, the (T2/T1) value can also be increased by moderately lowering the resin concentration of the second resin composition and increasing the dropping height.

When the aforementioned fine irregularities are teardrop-shaped, the average distance T3 between multiple teardrop-shaped objects can be adjusted by means of the dispensing frequency of the droplets of the second resin composition. The height of the teardrop-shaped objects can be adjusted, for example, by the droplet concentration and dispensing volume of the second resin composition.

(2.3) Winding Process The film, which has been prepared by forming fine irregularities on the film base, is wound in the length direction of the film using a winding machine. This makes it possible to produce a film roll in which the strip-shaped film is wound into a roll shape around a winding core. The winding method is not particularly limited and may be a constant torque method, a constant tension method, a tapered tension method, etc. The winding tension when winding the film is not particularly limited but may be around 50 to 170 N.

(2.4) Other (Effects of teardrop-shaped objects on the film roll)
As described above, when the optical film wound onto the film roll of the present invention has multiple teardrop-shaped objects formed as fine irregularities during its manufacturing process, it is preferable that the optical film has multiple teardrop-shaped objects 12 at both ends in the width direction of the optical film, such that the intersection M of the long axis LA and the short axis SA is located on the upstream side in the winding direction. This allows the teardrop-shaped objects 12 to be less likely to be unevenly crushed while mitigating the diagonal force applied from the front in the direction of travel during winding, thus enabling winding in a state of uniform contact with the film (in an ideal convex shape). Therefore, deformation of the film roll can be suppressed while uniformly taking in air.

(Application)
The optical film wound onto a film roll produced by the above manufacturing method is used as an optical film for display devices such as liquid crystal displays and organic EL displays, after the teardrop-shaped portion is removed during use. Examples include polarizing plate protective films (including phase difference films and brightness-enhancing films), transparent substrate films, and light-diffusing films. Among these, film 10 is preferably used as a polarizing plate protective film.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. In the examples, the units "parts" or "%" are used, and unless otherwise specified, they represent "parts by mass" or "mass percent".

A. Preparation of film rolls (A.1) Preparation of film roll 1 (A.1.1) Film formation First, dichloromethane was added to a pressurized dissolution tank at a flow rate of 400 kg/min and ethanol at a flow rate of 20 kg/min. Three minutes after the start of solvent addition, cyclic polyolefin resin was added to the pressurized dissolution tank while stirring. Next, five minutes after the start of solvent addition, the fine particle additive solution was added and heated to 60°C, and completely dissolved while stirring. The heating temperature was increased from room temperature at a rate of 5°C/min, dissolved in 30 minutes, and then cooled at a rate of 3°C/min.

This was filtered using Asaka Filter Paper No. 244 (filtration accuracy 0.005 mm) manufactured by Asaka Filter Paper Co., Ltd., at a filtration flow rate of 300 L/ ^m² ·h and a filtration pressure of 1.0 × ^10⁶ Pa, to prepare a dope with the following composition.

<Composition>
Cycloolefin resin "G7810" (manufactured by JSR Corporation) 100% by mass
Dichloromethane 380% by mass
Ethanol 20% by mass

Next, the obtained dope was uniformly cast onto a stainless steel belt support at a temperature of 31°C and a width of 2300 mm using an endless belt casting apparatus. The temperature of the stainless steel belt was adjusted to 28°C, and the conveying speed of the stainless steel belt was set to 30 m/min. After evaporating the solvent in the cast dope on the stainless steel belt support until the residual solvent content was 30% by mass, the dope was peeled off the stainless steel belt support with a peeling tension of 110 N/m to obtain a film-like material.

The obtained film was stretched 1.3 times in the transport direction (MD direction) while heating to 120°C using a roll method that utilizes the difference in peripheral speed of the transport rolls, and then stretched 1.65 times in the TD direction while heating to 130°C using a tenter method. The obtained film was transported while being heated to 70°C until completely dry, and the ends were slit to form a film base with an average film thickness of 30 μm, a width of 2260 mm, and a length of 6000 m. The transport speed was 20 m/min.

(Measurement and calculation of film thickness and the average maximum height difference (P-V) of film thickness _ave1 )
The film thickness was measured at 1612 locations using an inline retardation film thickness measuring device RE-200L2T-Rth + film thickness (manufactured by Otsuka Electronics Co., Ltd.). The traverse speed was 100 mm/sec. From the film thickness measurements, the height difference between the highest and lowest points of the uneven structure formed on the surface of the film base was calculated, and the average value was defined as (P-V) _ave1 .

(Measurement of thermal expansion coefficient)
A measuring plate measuring 3 mm square x 15 mm long was prepared using the same material as the film base described above. Next, a thermomechanical testing apparatus (TMA apparatus) TM-9500 manufactured by ULVAC, Inc. was used as the measuring device, and measurements were taken with a tensile load of 2 g. The temperature range was set to 25 to 100°C (heating rate 5°C/min, measurement environment: 25°C, 50% RH). The thermal expansion coefficient was determined by measuring 10 measuring plates and performing an approximation using the TMA apparatus to find a linear relationship between temperature and expansion within the above temperature range, and then calculating the average value.

Specifically, a measuring plate was set in the apparatus, the temperature was raised at a constant rate, and the change in length from _A0 to _A1 during the temperature rise from _T0 to _T1 was measured. The thermal expansion coefficient [/°C] was then determined according to the following formula. The thermal expansion coefficient of the film base was 80 × ^10⁻⁶ /°C (80 ppm/°C).

Thermal expansion coefficient [/°C] = (A ₁ - _{A 0} )/(T ₁ - _{T 0} )/L _o

(A.1.2) Formation of uneven surfaces (teardrop-shaped objects) A solution for teardrop-shaped objects was obtained by dissolving cycloolefin resin G7810 (manufactured by JSR Corporation) in a solvent to a concentration of 2% by mass. Dichloromethane was used as the solvent.

After corona and plasma treatment of the surface of the film base, a teardrop-shaped object solution was applied to both ends in the width direction of the treated surface of the film base. A dispenser, "SUPER HI JET" (manufactured by Musashi Engineering Co., Ltd.), was used for application. The film was then dried using an IR heater to a temperature of 80°C, forming multiple teardrop-shaped objects on the film base. The film temperature was confirmed using a thermal camera. This resulted in the formation of multiple roughly mound-shaped teardrop objects, each approximately 0.4 μm high, in a single row on both ends in the width direction of the film base surface, thereby creating optical film 1. The teardrop-shaped objects were formed until the optical film 1 reached a length of 1500 m, with the longest end of the optical film 1 being 0 m, so that when the optical film 1 is wound, the uneven surface area on the width direction is limited to 90-100%.

Specifically, the teardrop-shaped objects were formed such that point M in Figure 5 was located 3 mm from the edge of the optical film in the width direction (x direction in Figures 5 and 7). The plan view shape of the teardrop-shaped object was as shown in Figure 5, with a maximum width T1 of 1.00 mm along its short axis SA, a maximum width T2 of 1.89 mm along its long axis LA, and a T2/T1 ratio of 1.89. The average distance T3 between multiple teardrop-shaped objects was 1.5 mm. The height of the teardrop-shaped objects was adjusted to 0.4 μm by the amount of film dispensed by the dispenser. The optical film with multiple teardrop-shaped objects formed on it was then wound onto a core (a winding core with a diameter of 280 mm) to produce a film roll 1. During winding, the initial tension was 150 N, the taper was 70%, and the corners were 25%.

(A.2) Preparation of film rolls 2, 3 and 6-19 (A.2.1) Film formation The film base was formed in the same manner as when film roll 1 was prepared, and the film thickness, the average maximum height difference (P-V) of the film thickness _ave1 , and the coefficient of thermal expansion were calculated.

(A.2.2) Formation of uneven surfaces (teardrop-shaped objects) Multiple teardrop-shaped objects were formed in a row at both ends in the width direction of the film base surface. The height of these objects and the value of "T2/T1" were changed to match the values shown in Table I. The length from the outermost end in the longitudinal direction of each optical film was also changed to match the range shown in Table II so that the uneven surface area on the side in the width direction would be within the range shown in Table II when each optical film was wound up. Multiple teardrop-shaped objects were formed in the same manner as in film roll 1 to produce each optical film. Film rolls 2, 3, and 6-19 were produced by winding each optical film under the same conditions as in film roll 1. The average distance (T3) and the value of T2/T1 between the multiple teardrop-shaped objects were adjusted according to the drying conditions (method, temperature).

Specifically, film rolls 2, 3, 6-9, and 11-19 were dried by heating them to 90°C (Tg - 70°C) using an infrared heater. Film roll 10, however, was dried at a drying temperature of 30°C by applying 40°C hot air in the direction of film transport.

For film roll No. 8, an acrylic resin was used. The acrylic resin used in film roll No. 8 is a methacrylic resin, with a methyl methacrylate:N-phenylmaleimide composition ratio of 95:5, a weight-average molecular weight (Mw) of 500,000, and a glass transition temperature (Tg) of 110°C. The weight-average molecular weight (Mw) and glass transition temperature (Tg) were measured using the following method.

(Measurement of weight-average molecular weight)
The weight-average molecular weight (Mw) of methacrylic resins was measured using gel permeation chromatography (Tosoh HLC8220GPC) and a column (Tosoh TSK-GEL G6000HXL-G5000HXL-G5000HXL-G4000HXL-G3000HXL in series). 20 mg ± 0.5 mg of the sample was dissolved in 10 ml of tetrahydrofuran and filtered through a 0.45 mm filter. 100 ml of this solution was injected into the column (at 40°C), and the value was measured at a detector RI temperature of 40°C. The value converted to styrene equivalent was used.

(Measurement of glass transition temperature)
The glass transition temperature of methacrylic resins was measured using DSC (Differential Scanning Colorimetry) in accordance with JIS K 7121-2012.

(A.3) Production of film roll 4 (production of film roll by embossing)
(A.3.1) Film Formation The film base was formed in the same manner as when film roll 1 was made, and the film thickness, the average maximum height difference (P-V) of the film thickness _ave1 , and the coefficient of thermal expansion were calculated.

(A.3.2) Formation of uneven surfaces After corona treatment and plasma treatment of the surface of the film base, multiple uneven surfaces were formed by embossing at both ends in the width direction of the treated surface of the film (3 mm from the edge of the film in the width direction of the film) with a spacing of 1.5 mm between them. Furthermore, the length from the outermost end in the longitudinal direction of the optical film was formed to be within the range shown in Table II so that when the optical film is wound up, the uneven surface area on the side surface in the width direction is within the range shown in Table II. As a result, multiple roughly mound-shaped uneven surfaces with a height of 2.5 μm were formed in a row at both ends in the width direction of the film surface. Multiple uneven surfaces were formed as shown in Figures 10(a) and (b). Figures 10(a) and (b) are schematic diagrams showing a heated pressing method for forming the protrusions 8 on the film base 1 by embossing.

Figure 10(a) is a schematic diagram of a heated pressing method embossing process. It illustrates a "heated pressing method" in which an embossing ring 4, having a convex shape formed on a metal roll (not shown), is pressed against the film base 1 while the metal roll is heated. The back roll is a metal roll 5. Because the back roll is metal, the stress generated when the embossing ring 4 is pressed against the film base 1 is directed towards the interior of the film base 1 and the periphery of the embossing ring 4, forming a convex portion 8 in the shape shown in Figure 10(b). The processing conditions for the convex portion 8 were as follows:

<Conditions for machining protruding parts>
Processing temperature: 250℃
Processing pressure: 0.5 MPa
Metal back roll

Then, the optical film with multiple protrusions 8 formed on it was wound onto a core under the same conditions as film roll 1 to produce film roll 4.

(A.4) Production of film roll 5 (production of film roll by laser)
(A.4.1) Film Formation The film base was formed in the same manner as when film roll 1 was made, and the film thickness, the average maximum height difference (P-V) _ave1 of the film thickness, and the coefficient of thermal expansion were calculated.

(A.4.2) Formation of uneven surfaces After corona treatment and plasma treatment of the surface of the film base described above, multiple uneven surfaces were formed by laser at both ends in the width direction of the treated surface of the film (at a position 3 mm from the edge of the film in the width direction of the film) with a spacing of 1.5 mm between them. Furthermore, the length from the outermost end in the longitudinal direction of the optical film was formed to be within the range shown in Table II so that when the optical film is wound up, the uneven surface area on the side surface in the width direction is within the range shown in Table II. As a result, multiple roughly mound-shaped uneven surfaces with a height of 1.5 μm were formed in a row at both ends in the width direction of the film surface.

A carbon dioxide laser was used as the laser device, with an output of 20 W, a central emission wavelength of 9.4 μm, and an emission wavelength range of ±0.01 μm or less from the central wavelength.

The laser beam onto the film was illuminated by reflecting a parallelized beam emitted from a carbon dioxide laser device using two galvanometer mirrors and focusing it onto the surface of the transported film via an fθ lens (focal length 200 mm). By controlling the angle of the galvanometer mirrors, the focusing position was shifted in the direction of the film's plane, thereby controlling the trajectory of the laser beam onto the film surface.

Then, the optical film with multiple uneven surfaces was wound onto a core under the same conditions as film roll 1 to produce film roll 5.

B. Measurement of the outer diameter of the center and end of the film roll and calculation of Rc/Re After storing each prepared film roll at 40°C and 80% RH for one week, the outer diameter at a point 30 mm from both ends in the width direction of each film roll and the outer diameter at the center of the center were measured using a tape measure and recorded as the outer diameter of the end and the outer diameter of the center, respectively. The outer diameter of the end was the average of the outer diameters of both ends. The results are shown in Table II.

C. Evaluation (C.1) Adhesion of film fragments (Evaluation method)
A vibration test ("Sine wave sweep vibration test," JIS Z 0232) was performed on each of the fabricated film rolls, ensuring that an 8G impact was immediately applied to each roll. Afterward, the optical film was unwound from each film roll, the end of the optical film was cut, and the cross-section of the optical film was observed visually and under an optical microscope (50x magnification) to check for the presence of white powder. The white powder was identified as small fragments of the transparent film.

(Evaluation criteria)
A: No white powder was detected through visual inspection or detailed analysis.
B: No white powder is visible to the naked eye, but it is detected in detailed analysis.
C: A small amount of white powder is visible to the naked eye.
D: A white powder is clearly visible to the naked eye.

(C.2) Winding misalignment on the outer side of the winding (Evaluation method)
After conducting a vibration test similar to the one used to evaluate film fragment adhesion, the movement in the width direction was measured using a tape measure, with the lengthwise end face of the optical film wound on the film roll in contact with the winding core set as 0. Since the winding core is fixed by the film and tape and does not shift, this part was used as the reference, and the film position in contact with the winding core was set as 0.

(Evaluation criteria)
A: The width in the lateral direction is 0 mm, meaning it is not moving.
B: It is moving in the width direction, but the distance moved is less than 2 mm.
C: It is moving in the width direction, but the distance moved is between 2 mm and 5 mm.
D: It is moving in the width direction, but the distance moved is 5 mm or more.

(C.3) Dispensing ability (evaluation method)
The feeding performance was evaluated by conducting vibration tests similar to those used for evaluating film fragment adhesion. After feeding the optical film from the roll and transporting it, reflected light was shone onto the optical film. If any abnormalities were detected, the line was stopped and the presence or absence of adhesion failure was visually checked. The state of adhesion between overlapping optical films (hereinafter referred to as blocking) was visually observed and evaluated based on the following criteria.

(Evaluation criteria)
A: No blocking.
B: There is occasional, albeit weak, blocking, but it does not pose a practical problem.
C: The blocking is weak, but it's not a practical problem.
D: Blocking is at a level other than those mentioned above, and is at a level that may lead to complaints from users.

D. Overall Assessment Based on the above, it can be seen that the example does not have a "D" listed as an evaluation item and is practically without problems, and is overall superior to the comparative example. This indicates that the film roll of the example is less prone to winding failures during transportation and long-term storage, and can maintain its quality.

1 Film base 4 Embossing ring 5 Metal roll 8 Protrusion 30c Side of the winding core R ₀ Center of the side of the winding core, center point of the side of the film roll in the width direction R ₇₀ Outer circumference of a circle that is 70% of the maximum radius extending outward from the center of the side R ₁₀₀ Outer circumference of a circle that is the maximum radius (r _max ) r _c Radius of the side of the winding core r _p Radius of the side of the film roll including the winding core at an arbitrary point r _max Maximum radius of the side of the film roll including the winding core F _rayer Layers of optical film extending outward from the outer circumference of the side of the winding core to the maximum radius F _{rayer 1} Layers of optical film extending outward from the center of the side of the side to the outer circumference of a circle that is 70% of the maximum radius F _{rayer 2} Layers of optical film in the region outside the outer circumference of a circle that is 70% of the maximum radius extending outward from the center of the side h ₁ Height of the protrusion h ₂ Depth of the recess Re Outer diameter of the end on the side Rc LA: Outer diameter of the central part on the side surface; SA: Long axis of the teardrop shape; M: Intersection of the long and short axes of the teardrop shape; T1: Maximum width in the short axis direction; T2: Maximum width in the long axis direction; Th: Spacing between teardrop shapes; t: Height of the teardrop shape; x: Width of the film in the lateral direction; y: Long axis direction of the film; w: Width of the teardrop shape; t: Height of the teardrop shape

Claims (9)

A film roll on which optical film is wound,
The film roll has fine irregularities only in the region outside the outer circumference of a circle that is 70% of the maximum radius, extending outward from the center of the side surface in the width direction.
The ratio of the length of the outer diameter Rc at the center of the film roll in the width direction to the outer diameter Re at the end, Rc/Re, is within the range of 0.96 to 1.01.
The height of the protrusions in the aforementioned fine uneven area is 0.1 μm to 0.5 μm.
A film roll characterized by the following features. The film roll according to claim 1, characterized in that the fine unevenness portion is present only at the end in the width direction, including the region outside the outer circumference of a circle that extends outward from the center of the side portion to 90% of the maximum radius. The film roll according to claim 1, characterized in that the fine uneven portion is provided in the longitudinal direction of the film roll for a length within the range of 150 to 1500 m. The film roll according to claim 1, characterized in that the fine uneven portion is provided in the longitudinal direction of the film roll for a length within the range of 500 to 1000 m. The film roll according to claim 1, characterized in that the main component of the optical film is a cycloolefin resin. The film roll according to claim 1, characterized in that the optical film is a single layer. The aforementioned fine irregularities are teardrop-shaped, and the relationship between the maximum width T2 in the long axis direction and the maximum width T1 in the short axis direction of the teardrop shape satisfies the following equation (1): Equation (1): 1.15 ≤ T2/T1 ≤ 1.90
The film roll according to feature 1. The film roll according to claim 7, characterized in that the longitudinal axis direction is the longitudinal direction of the optical film. The film roll according to claim 1, characterized in that the fine irregularities are present only at both ends in the width direction of the optical film.