JP7469088B2 - Optical film and flexible display device - Google Patents

Description

The present invention relates to an optical film containing at least one resin selected from the group consisting of polyimide-based resins and polyamide-based resins, and a flexible display device including the optical film.

Traditionally, glass has been used as a material for display components in solar cells, image display devices, and the like. However, glass is not a sufficient material for meeting the recent demands for smaller, thinner, lighter, and more flexible products, and various films are being considered as alternative materials to glass. One such film is polyimide film (for example, Patent Documents 1 and 2).

JP 2009-215412 A JP 2020-3781 A

When a polyimide-based resin film is applied to a transparent member such as the front panel of a flexible display device, images may be displayed on the image display surface in a bent state, and therefore excellent visibility in a wide-angle direction is required compared to a non-flexible image display surface. However, according to the inventor's investigations, there are cases where conventional polyimide-based resin films are unable to fully satisfy visibility in a wide-angle direction. In particular, when a flexible display device is used, the transparent member contained in the display device is repeatedly folded, etc., and such folding operations can cause the visibility in a wide-angle direction to decrease over time.

The inventors' investigations revealed that the optical films described in Patent Documents 1 and 2, for example, may not provide sufficient visibility in wide-angle directions, especially after repeated folding operations.

Therefore, the object of the present invention is to provide an optical film that has excellent visibility in wide-angle directions even after repeated folding operations, and a flexible display device that includes the optical film.

As a result of intensive investigations to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by an optical film comprising at least one resin selected from the group consisting of polyimide-based resins and polyamide-based resins, which has a total light transmittance of 85% or more, a haze of 0.5% or less, a puncture strength according to JIS Z 1707 of 10 to 100 N, and transmission image clarity values (C ₆₀ (MD), C ₆₀ (TD) and C ₀ ) that satisfy a predetermined relationship, and have thus completed the present invention. That is, the present invention includes the following aspects.

[1] An optical film comprising at least one resin selected from the group consisting of polyimide-based resins and polyamide-based resins, the optical film having a total light transmittance of 85% or more, a haze of 0.5% or less, and a puncture strength of 10 to 100 N according to JIS Z 1707;
In the plane of the optical film, a direction parallel to the machine flow direction during production is defined as an MD direction, and a direction perpendicular to the machine flow direction is defined as a TD direction.
a first transmission image clarity value C _{60 (MD) in a direction inclined at 60° from a perpendicular direction to a plane of the optical film toward the MD direction, a second transmission image clarity value C 60} (TD) in a direction inclined at ₆₀ ° from the perpendicular direction toward the TD direction, and a third transmission image clarity value C ₀ in the perpendicular direction, which are obtained in accordance with JIS K 7374 when the width of an optical comb is 0.125 mm,
Formula (1):
87%≦ _C60 (MD)≦100%... (1),
Formula (2):
87%≦C ₆₀ (TD)≦100% (2), and the formula (3):
0.8≦ _C60 (MD) _/C0≦1.0 ... (3)
Optical films that meet these requirements.
[2] The second transmission image clarity value and the third transmission image clarity value are expressed by the formula (4):
0.9≦ _C60 (TD) _/C0≦1.0 ... (4)
The optical film according to [1] above, further satisfying the above.
[3] The fracture displacement L (mm) and the tensile modulus E (GPa) of the optical film in a puncture strength test in accordance with JIS Z 1707 are expressed by the following mathematical formula (5):
0.10≦L/E≦1.00 (5)
The optical film according to [1] or [2] above,
[4] The puncture strength S (N) of the optical film in accordance with JIS Z1707 and the thickness T (μm) are expressed by the formula (6):
0.10≦S/T≦2.00 (6)
The optical film according to any one of [1] to [3] above,
[5] The optical film according to any one of [1] to [4] above, wherein the difference in haze ΔHaze between before and after a bending resistance test in accordance with JIS K 5600-5-1 is less than 0.3%.
[6] The optical film according to any one of [1] to [5], wherein the first transmission image clarity value difference ΔC ₆₀ (MD), the second transmission image clarity value difference ΔC ₆₀ (TD), and the third transmission image clarity value difference ΔC ₀ before and after a bending resistance test in accordance with JIS K 5600-5-1 are each less than 15.
[7] The optical film according to any one of [1] to [6] above, wherein the resin selected from the group consisting of polyimide-based resins and polyamide-based resins has a weight average molecular weight of 350,000 or less.
[8] The optical film according to any one of [1] to [7] above, having a thickness of 10 to 150 μm.
[9] The optical film according to any one of [1] to [8] above, which has a hard coat layer on at least one surface.
[10] The optical film according to [9], wherein the hard coat layer has a thickness of 3 to 30 μm.
[11] A flexible display device comprising the optical film according to any one of [1] to [10] above.
[12] The flexible display device according to [11], further comprising a polarizing plate.
[13] The flexible display device according to [11] or [12], further comprising a touch sensor.

The present invention provides an optical film that has excellent visibility in wide-angle directions even after repeated folding operations, and a flexible display device that includes the optical film.

FIG. 1 is a diagram showing an optical axis in measuring the first transmission image clarity value. FIG. 2 is a diagram showing an optical axis in the measurement of the second transmission image clarity value. FIG. 3 is a diagram showing an optical axis in measuring the third transmission image clarity value. 1A to 1C are cross-sectional views illustrating steps in a preferred embodiment of a method for producing an optical film of the present invention. 1A to 1C are process cross-sectional views that typically illustrate a preferred embodiment of a heating step in the method for producing an optical film of the present invention. 1A to 1C are process cross-sectional views that typically show a preferred embodiment of the inside of a tenter furnace in the optical film producing method of the present invention. FIG. 2 is a schematic diagram for explaining a method for producing an optical film in an example. FIG. 2 is a schematic diagram for explaining a method for producing an optical film in an example.

The following describes in detail the embodiments of the present invention. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention. In addition, when multiple upper and lower limit values are listed for a specific parameter, any of these upper and lower limit values can be combined to create a suitable numerical range.

<Optical film>
The optical film of the present invention is an optical film comprising at least one resin selected from the group consisting of polyimide-based resins and polyamide-based resins, the optical film having a total light transmittance of 85% or more, a haze of 0.5% or less, and a puncture strength according to JIS Z 1707 of 10 to 100 N;
In the plane of the optical film, a direction parallel to the machine flow direction during production is defined as an MD direction, and a direction perpendicular to the machine flow direction is defined as a TD direction.
a first transmission image clarity value C _{60 (MD) in a direction inclined at 60° from a perpendicular direction to a plane of the optical film toward the MD direction, a second transmission image clarity value C 60} (TD) in a direction inclined at ₆₀ ° from the perpendicular direction toward the TD direction, and a third transmission image clarity value C ₀ in the perpendicular direction, which are obtained in accordance with JIS K 7374 when the width of an optical comb is 0.125 mm,
Formula (1):
87%≦ _C60 (MD)≦100%... (1),
Formula (2):
87%≦C ₆₀ (TD)≦100% (2), and the formula (3):
0.8≦ _C60 (MD) _/C0≦1.0 ... (3)
Meet the following.

The MD direction is a direction parallel to the machine flow direction during production in the plane of the optical film, for example, a direction parallel to the direction in which the optical film is transported when produced by a solution casting method. The TD direction is a direction perpendicular to the machine flow direction, for example, a direction perpendicular to the transport direction. When the MD direction and TD direction in the plane of the optical film are unknown, they are determined by the following method. Regarding the MD and TD, cross-sections are taken from at least 20 points of the optical film in different directions. More specifically, a circle is assumed to be centered on any one point of the optical film, and the optical film is cut in a straight line so that the central angles of the sectors after cutting the semicircles are approximately equal, and 20 or more cross-sections are taken. The centers of the thicknesses of the obtained cross-sections are measured by laser Raman spectroscopy, and the one with the largest peak intensity near 1,620 cm ⁻¹ is determined as the MD direction.

に基づいて第１透過写像性値Ｃ_６０（ＭＤ）を算出する。透過写像性値（第１透過写像性値、並びに後述の第２透過写像性値及び第３透過写像性値）は、写像性測定器を用いて測定することができる。 The first transmission image clarity value C ₆₀ (MD) is a transmission image clarity value in a direction inclined 60° in the MD direction from the perpendicular direction to the plane of the optical film, obtained in accordance with Japanese Industrial Standards (JIS) K 7374. The first transmission image clarity value C ₆₀ (MD) will be described in more detail with reference to FIG. 1. FIG. 1 is a diagram showing an optical axis in measuring the first transmission image clarity value. Using an arbitrary point (first incident position 11) on the surface of the optical film 1 as a fulcrum, the optical film 1 is irradiated with a first incident light 10 (white light: indicated by a solid line in FIG. 1) along an axis (first optical axis 14) inclined at an angle of 60° in the MD direction from an axis (vertical axis 3) perpendicular to the optical film 1. Next, the firsta transmitted light 12 (indicated by a dashed line in FIG. 1) transmitted through the optical film 1 is transmitted through a first optical comb 16 extending perpendicular to the first optical axis 14. Next, the 1b transmitted light 18 (indicated by a dashed line in FIG. 1 ) that has been transmitted through the first optical comb 16 is received by a first light receiver 19 extending perpendicular to the first optical axis 14. The first optical comb 16 has an opening that transmits the 1a transmitted light 12, and a light blocking portion that blocks the 1a transmitted light 12. The slit width (width of the opening) of the first optical comb 16 is 0.125 mm.
The first optical comb 16 is moved a predetermined unit width in a direction parallel to the plane of the first optical comb 16 and in a direction in which the slits in the first optical comb 16 are arranged (the direction of the arrow A), and the 1b transmitted light 18 is repeatedly received to obtain a received light waveform. The maximum value M and minimum value m of the relative light amount are obtained from the obtained received light waveform. The obtained M and m are calculated using the formula (7):

The first transmission image clarity value C ₆₀ (MD) is calculated based on the above. The transmission image clarity values (the first transmission image clarity value, and the second transmission image clarity value and the third transmission image clarity value described below) can be measured using an image clarity measurement device.

When the first transmission image clarity value C ₆₀ (MD) satisfies the formula (1), the optical film has excellent visibility in the wide-angle direction in the MD direction. The first transmission image clarity value C ₆₀ (MD) is 87% or more in the formula (1), and from the viewpoint of further improving the visibility in the wide-angle direction in the MD direction of the optical film, it is preferably 88% or more, more preferably 89% or more, even more preferably 90% or more, still more preferably 91% or more, particularly preferably 92% or more, and is usually 100% or less.

The second transmission image clarity value C ₆₀ (TD) is a transmission image clarity value in a direction inclined 60° in the TD direction from the perpendicular direction to the plane of the optical film, obtained in accordance with JIS K 7374. The second transmission image clarity value C ₆₀ (TD) will be described in more detail with reference to FIG. 2. FIG. 2 is a diagram showing an optical axis in measuring the second transmission image clarity value. Using an arbitrary point (second incident position 21) on the surface of the optical film 1 as a fulcrum, the optical film 1 is irradiated with a second incident light 20 (white light: indicated by a solid line in FIG. 2) along an axis (second optical axis 24) inclined at an angle of 60° in the TD direction from an axis (perpendicular axis 3) perpendicular to the optical film 1. Next, the seconda transmitted light 22 (indicated by a dashed line in FIG. 2) transmitted through the optical film 1 is transmitted through a second optical comb 26 extending perpendicular to the second optical axis 24. Next, the 2b transmitted light 28 (indicated by a dashed line in FIG. 2 ) that has been transmitted through the second optical comb 26 is received by a second light receiver 29 extending perpendicular to the second optical axis 24. The second optical comb 26 has an opening that transmits the 2a transmitted light 22 and a light blocking portion that blocks the 2a transmitted light 22. The slit width (width of the opening) of the second optical comb 26 is 0.125 mm.
The second optical comb 26 is moved a predetermined unit width in a direction parallel to the plane of the second optical comb 26 and in the direction in which the slits in the second optical comb 26 are arranged (the direction of arrow B), and the second b transmitted light 28 is repeatedly received to obtain a received light waveform. The maximum value M and minimum value m of the relative light amount are obtained from the obtained received light waveform. The second transmitted image clarity value _C60 (TD) is calculated based on the equation (7) from the obtained M and m.

When the second transmission image clarity value C ₆₀ (TD) satisfies the mathematical formula (2), the optical film has excellent visibility in the wide-angle direction in the TD direction. The second transmission image clarity value C ₆₀ (TD) is 87% or more in the mathematical formula (2), and from the viewpoint of further improving the visibility in the wide-angle direction in the TD direction of the optical film, is preferably 88% or more, more preferably 89% or more, even more preferably 90% or more, still more preferably 91% or more, particularly preferably 92% or more, and is usually 100% or less.

The third transmission image clarity value C ₀ is a transmission image clarity value in a direction perpendicular to the plane of the optical film, obtained in accordance with JIS K 7374. The third transmission image clarity value C ₀ will be described in detail with reference to FIG. 3. FIG. 3 is a diagram showing an optical axis in measuring the third image clarity value. A third incident light 30 (white light: indicated by a solid line in FIG. 3) is irradiated to an arbitrary point (third incident position 31) on the surface of the optical film 1 along an axis (third optical axis 34) parallel to an axis (vertical axis 3) perpendicular to the optical film 1. Next, the third a transmitted light 32 (indicated by a dashed line in FIG. 3) transmitted through the optical film 1 is transmitted through a third optical comb 36 extending perpendicular to the third optical axis 34. Next, the third b transmitted light 38 (indicated by a dashed line in FIG. 3) transmitted through the third optical comb 36 is received by a light receiver 39 extending perpendicular to the third optical axis 34. The third optical comb 36 has an opening portion that transmits the thirda transmitted light 32 and a light blocking portion that blocks the thirda transmitted light 32. The slit width (width of the opening portion) of the third optical comb 36 is 0.125 mm.
The third optical comb 36 is moved a predetermined unit width in a direction parallel to the plane of the third optical comb 36 and in a direction in which the slits in the third optical comb 36 are arranged (the direction of arrow C), and the third b transmitted light 38 is repeatedly received to obtain a received light waveform. The maximum value M and minimum value m of the relative light amount are obtained from the obtained received light waveform. The third transmitted image clarity value _C0 is calculated based on the obtained M and m according to the formula (7).

When the first transmission image clarity value _C60 (MD) and the third transmission image clarity value _C0 satisfy the mathematical formula (3), the optical film has excellent visibility in the MD direction relative to the perpendicular direction of the optical film. The ratio of the first image clarity value _C60 (MD) to the third transmission image clarity value _C0 ( _C60 (MD)/ _C0 ) in the mathematical formula (3) is 0.8 or more, and from the viewpoint of further improving the visibility in the MD direction, is preferably 0.89 or more, more preferably 0.90 or more, even more preferably 0.93 or more, still more preferably 0.94 or more, and is usually 1.0 or less.

The third transmission image clarity value C ₀ is preferably 97% or more, more preferably 98% or more. The first transmission image clarity value C ₆₀ (MD) is preferably 89% or more, more preferably 90% or more, and even more preferably 92% or more.

The transmission image clarity value (more specifically, the first transmission image clarity value C ₆₀ (MD), the second transmission image clarity value C ₆₀ (TD), and the third transmission image clarity value C ₀ ) can be adjusted by improving the smoothness of the optical film surface to suppress scattering of transmitted light on the optical film surface. Furthermore, the smoothness of the optical film surface can be adjusted, for example, by the composition of the optical film (more specifically, the type, particle size, and content of the filler, etc.) and the manufacturing conditions of the optical film (more specifically, the drying temperature, drying time, air flow in the drying system, the thickness of the coating film, the conveying speed in the drying process, and the amount of solvent in the varnish, etc.). When the optical film further includes a hard coat layer, the smoothness of the hard coat layer surface can be improved to suppress scattering on the hard coat layer surface, and the like, and the smoothness of the hard coat layer can be adjusted. In addition to the above-mentioned method of adjusting the smoothness of the optical film, the smoothness of the hard coat layer can be adjusted, for example, by adjusting the type of solvent, component ratio, and solid content concentration, and adding a leveling agent.

In terms of improving visibility in a TD direction with respect to a perpendicular direction of the optical film of the present invention, the second transmission image clarity value and the third transmission image clarity value are represented by Formula (4):
0.9≦ _C60 (TD) _/C0≦1.0 (4)
From the viewpoint of further enhancing visibility in the TD direction of the present invention, the ratio of the first transmission image clarity value to the third transmission image clarity value (C ₆₀ (TD)/C ₀ ) is preferably 0.9 or more, more preferably 0.91 or more, even more preferably 0.92 or more, still more preferably 0.93 or more, particularly preferably 0.94 or more, and is usually 1.0 or less.

The second transmission image clarity value _C60 (TD) is preferably 89% or more, more preferably 90% or more, and even more preferably 92% or more. The third transmission image clarity value _C0 is preferably 97% or more, more preferably 98% or more, and even more preferably 99% or more.

The optical film of the present invention only needs to satisfy formulas (1) to (3) (and optionally formula (4)) when light is transmitted through at least one of the surfaces of the optical film, but more preferably satisfies formulas (1) to (3) (and optionally formula (4)) when light is transmitted through either surface of the optical film. If the formulas are satisfied when light is transmitted through either surface, the optical film will have excellent visibility in wide-angle directions, for example, when either surface of the optical film is used as the image display surface of an electronic device.

In particular, when the optical film of the present invention is applied to the front panel of a flexible device, from the viewpoint of further improving visibility in the wide-angle direction, the absolute value of the difference in the first transmission image clarity value ΔC ₆₀ (MD), the absolute value of the difference in the second transmission image clarity value ΔC ₆₀ (TD), and the absolute value of the difference in the third transmission image clarity value ΔC ₀ before and after the bending resistance test in accordance with JIS K 5600-5-1 are each preferably less than 15. When the difference in the transmission image clarity value before and after the bending resistance test is less than 15, the flexible device has excellent visibility in the wide-angle direction, especially even when the image display surface of the flexible device is used in a bent state and/or after it is used in a bent state. ΔC ₆₀ (MD) is more preferably less than 1.5, even more preferably less than 1.0, and even more preferably less than 0.5. _{ΔC 60} (TD) is more preferably less than 2.8, even more preferably less than 2.3, even more preferably less than 2.1, and particularly preferably less than 1.5. ΔC ₀ is more preferably less than 2, even more preferably less than 1, even more preferably less than 0.7, and especially preferably less than 0.5.

Furthermore, in the optical film of the present invention, the total light transmittance is 85% or more, the haze is 0.5% or less, and the puncture strength according to JIS Z 1707 is 10 to 100 N. When the optical film satisfies the above characteristics, high visibility in the wide-angle direction can be maintained even when the optical film is subjected to repeated folding operations. When the total light transmittance is less than 85% or the haze is more than 0.5%, the initial optical properties of the optical film are low, and therefore sufficient visibility of the optical film cannot be achieved. Furthermore, when the puncture strength according to JIS Z 1707 is less than 10 N, it becomes difficult to maintain good visibility, especially in the wide-angle direction, by repeated folding operations.

The total light transmittance of the optical film of the present invention is 85% or more, and from the viewpoint of further improving the visibility in the wide angle direction, it is preferably 87% or more, more preferably 88% or more, and even more preferably 89% or more, and is usually 100% or less. The total light transmittance of the optical film can be measured using a haze computer in accordance with JIS K 7361-1:1997, and can be measured, for example, by the method described in the Examples. Since the optical film of the present invention exhibits a high total light transmittance, it is possible to suppress the luminous intensity of a display element or the like required to obtain a certain brightness, compared to, for example, a film with a low transmittance. This makes it possible to reduce power consumption. For example, when the optical film of the present invention is incorporated into an image display device, a bright display tends to be obtained even if the amount of light from the backlight is reduced, which contributes to energy savings. The upper limit of the total light transmittance is usually 100% or less. The total light transmittance may be the total light transmittance within the thickness range of the optical film described later.

The haze of the optical film of the present invention is 0.5% or less, and from the viewpoint of further improving visibility in the wide angle direction, it is preferably 0.4% or less, more preferably 0.3% or less. The haze of the optical film can be measured in accordance with JIS K 7136:2000. The haze can be measured using a haze computer in accordance with JIS K 7136:2000, for example, by the method described in the Examples. Furthermore, the optical film of the present invention has an absolute value ΔHaze of the difference in the haze before and after the bending resistance test in accordance with JIS K 5600-5-1 of preferably 0.3% or less, more preferably 0.2% or less.

The tensile modulus of the optical film of the present invention at 25°C is preferably 5.1 GPa or more, more preferably 5.2 GPa or more, and even more preferably 5.3 GPa or more, from the viewpoint of easily improving the visibility in the wide angle direction after the bending resistance test and preventing defects such as dents from occurring in the optical film. In addition, the tensile modulus is preferably 10 GPa or less, more preferably 9 GPa or less, and even more preferably 8 GPa or less, from the viewpoint of easily improving the flexibility of the optical film. The modulus can be measured using a tensile tester (chuck distance 50 mm, tensile speed 10 mm/min), for example, by the method described in the Examples. When the tensile modulus is within the above range, dent defects are unlikely to occur in the optical film. In addition, it is easy to suppress the decrease in visibility in the wide angle direction due to repeated bending operations. The tensile modulus of the optical film can be measured using a tensile tester in accordance with JIS K 7127, for example, by the method described in the Examples. The tensile modulus can be adjusted to the above range, for example, by increasing the stretch ratio when producing the optical film or by using a resin having a preferred structure described below.

The tensile modulus of the optical film of the present invention at 80°C is preferably 4 to 9 GPa, more preferably 4.5 to 8.5 GPa. When the tensile modulus is within the above range, the optical film is less likely to develop dent defects. The modulus can be measured in accordance with JIS K 7127, for example, by the method described in the Examples.

The optical film of the present invention has a puncture strength according to JIS Z 1707 of 10 to 100 N. If the puncture strength is less than 10 N, it becomes difficult to maintain good visibility, particularly in the wide-angle direction, by repeated folding operations. If the puncture strength exceeds 100 N, the film becomes difficult to deform during folding operations and when an object comes into contact with the film surface, and the film surface may be destroyed. The puncture strength is preferably 20 N or more, more preferably 22 N or more, and even more preferably 24 N or more from the viewpoint of easily improving visibility in the wide-angle direction after folding operations, and is preferably 90 N or less, more preferably 70 N or less, and even more preferably 60 N or less from the viewpoint of the film surface being difficult to destroy. The puncture strength can be adjusted to the above range, for example, by increasing the stretch ratio when producing the optical film or by using a resin having a preferred structure described later.

The fracture displacement L (mm) and the tensile modulus E (GPa) of the optical film of the present invention in a puncture strength test in accordance with JIS Z 1707 are expressed by the following mathematical formula (5):
0.10≦L/E≦1.00 (5)
It is preferable to satisfy the above. In the mathematical formula (5), L/E is preferably 0.25 or more, more preferably 0.35 or more, even more preferably 0.45 or more, more preferably 0.50 or more, and is preferably 0.95 or less, more preferably 0.90 or less. When L/E is equal to or more than the above lower limit, the brittleness of the film is sufficiently low, so that it is easy to prevent cracks when the optical film is deformed. On the other hand, when L/E is equal to or less than the above upper limit, the film is easy to deform, so that it is easy to prevent cracks when the film is bent.

The break point displacement L of the optical film of the present invention in a puncture strength test conforming to JIS Z 1707 is not particularly limited, but from the viewpoint of fragility, it is preferably 1.0 to 10.0 mm, more preferably 1.5 to 9.0 mm.

The puncture strength S (N) of the optical film of the present invention in accordance with JIS Z 1707 and the thickness T (μm) are expressed by the following mathematical formula (6):
0.10≦S/T≦2.00 (6)
It is preferable to satisfy the above. S/T in the formula (6) is preferably 0.20 or more, more preferably 0.30 or more, even more preferably 0.40 or more, and is preferably 1.90 or less, more preferably 1.80 or less, and even more preferably 1.50 or less. When S/T is equal to or more than the above lower limit, the film is easily cracked, and is easily cracked when deformed. When S/T is equal to or less than the above upper limit, the film is difficult to deform, and is difficult to deform. The method for measuring the puncture strength S is as described above, and the method for measuring the thickness T is as described below.

The YI value, which represents a scale of yellowness of the optical film of the present invention, is preferably 4.0 or less, more preferably 3.0 or less, even more preferably 2.5 or less, even more preferably 2.0 or less, particularly preferably 1.9 or less, and particularly preferably 1.8 or less, from the viewpoint of facilitating further improvement of visibility. The YI value is preferably -5 or more, more preferably -2 or more. The YI value can be calculated by measuring the transmittance for light of 300 to 800 nm using an ultraviolet-visible-near infrared spectrophotometer, determining the tristimulus values (X, Y, Z), and then based on the formula YI = 100 x (1.2769X - 1.0592Z) / Y.

From the viewpoint of improving the folding resistance, the number of folding times of the optical film of the present invention is preferably 20,000 times or more, more preferably 100,000 times or more, even more preferably 200,000 times or more, even more preferably 350,000 times or more, particularly preferably 400,000 times or more, particularly preferably 500,000 times or more, particularly more preferably 600,000 times or more, and especially preferably 700,000 times or more. If the number of folding times is equal to or more than the above lower limit, cracks or breaks are unlikely to occur even when the optical film is folded. In addition, the upper limit of the number of folding times is usually 50,000,000 times or less. The number of folding times of the optical film can be measured by the MIT folding fatigue test in accordance with ASTM standard D2176-16. The MIT folding fatigue test is, for example, a test described in the examples. In addition, the optical film of the present invention preferably has high wide-angle visibility even after the MIT folding fatigue test under the above conditions, and it is more preferable that, for example, the difference in image clarity and/or the difference in haze before and after the MIT folding fatigue test under the above conditions is within the range of the difference in image clarity and/or the difference in haze before and after the above bending fatigue test.

The thickness of the optical film of the present invention may be adjusted appropriately depending on the application, but is preferably 10 μm or more, more preferably 20 μm or more, even more preferably 25 μm or more, even more preferably 30 μm or more, and is preferably 200 μm or less, more preferably 150 μm or less, even more preferably 100 μm or less, and even more preferably 85 μm or less. When the thickness of the optical film is within the above range, it is easier to increase the tensile modulus and puncture strength of the optical film. The thickness of the optical film can be measured using a micrometer, for example, by the method described in the Examples.

<Polyimide-based resin and polyamide-based resin>
The optical film of the present invention contains at least one resin selected from the group consisting of polyimide resins and polyamide resins. In this specification, the polyimide resin refers to at least one resin selected from the group consisting of polyimide resins, polyamideimide resins, polyimide precursor resins, and polyamideimide precursor resins. The polyimide resin is a resin containing a repeating structural unit containing an imide group, and the polyamideimide resin is a resin containing a repeating structural unit containing both an imide group and an amide group. The polyimide precursor resin and the polyamideimide precursor resin are precursors before imidization that give polyimide resins and polyamideimide resins by imidization, respectively, and are also called polyamic acids. In this specification, the polyamide resin is a resin containing a repeating structural unit containing an amide group. The optical film of the present invention may contain one type of polyimide resin or polyamide resin, or may contain a combination of two or more types of polyimide resins and/or polyamide resins. The optical film of the present invention preferably contains a polyimide-based resin from the viewpoints of easily increasing the tensile modulus and puncture strength of the optical film and easily increasing the visibility in a wide-angle direction after a bending resistance test, and the polyimide-based resin is preferably a polyimide resin or a polyamideimide resin, and more preferably a polyamideimide resin.

In a preferred embodiment of the present invention, the polyimide-based resin and polyamide-based resin are preferably aromatic resins, from the viewpoint of easily increasing the tensile modulus and puncture strength of the optical film and easily increasing the visibility in the wide-angle direction after the bending resistance test. In this specification, aromatic resin refers to a resin in which the structural units contained in the polyimide-based resin and polyamide-based resin are mainly aromatic structural units.

In the above preferred embodiment, from the viewpoint of easily increasing the tensile modulus and puncture strength of the optical film and easily increasing the visibility in the wide-angle direction after the bending resistance test, the ratio of the structural units derived from aromatic monomers to the total structural units contained in the polyimide resin and the polyamide resin is preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and even more preferably 85 mol% or more. Here, the structural units derived from aromatic monomers are structural units derived from monomers that at least partially contain an aromatic structure (e.g., an aromatic ring) and that at least partially contain an aromatic structure (e.g., an aromatic ring). Examples of aromatic monomers include aromatic tetracarboxylic acid compounds, aromatic diamines, and aromatic dicarboxylic acids.

［式（１）中、Ｙは４価の有機基を表し、Ｘは２価の有機基を表し、＊は結合手を表す］
で表される構成単位を有するポリイミド樹脂であるか、又は、式（１）で表される構成単位及び式（２）：

［式（２）中、Ｚ及びＸは、互いに独立に、２価の有機基を表し、＊は結合手を表す］
で表される構成単位を有するポリアミドイミド樹脂であることが好ましい。また、ポリアミド系樹脂は、式（２）で表される構成単位を有するポリアミド樹脂であることが好ましい。以下において式（１）及び式（２）について説明するが、式（１）についての説明は、ポリイミド樹脂及びポリアミドイミド樹脂の両方に関し、式（２）についての説明は、ポリアミド樹脂及びポリアミドイミド樹脂の両方に関する。 In a preferred embodiment of the present invention, the polyimide resin has the formula (1):

[In formula (1), Y represents a tetravalent organic group, X represents a divalent organic group, and * represents a bond.]
or a polyimide resin having a structural unit represented by formula (1) and a structural unit represented by formula (2):

[In formula (2), Z and X each independently represent a divalent organic group, and * represents a bond.]
The polyamide-based resin is preferably a polyamide resin having a structural unit represented by formula (2). Formulas (1) and (2) are described below, but the description of formula (1) relates to both polyimide resins and polyamideimide resins, and the description of formula (2) relates to both polyamide resins and polyamideimide resins.

The structural unit represented by formula (1) is a structural unit formed by the reaction of a tetracarboxylic acid compound with a diamine compound, and the structural unit represented by formula (2) is a structural unit formed by the reaction of a dicarboxylic acid compound with a diamine compound.

In formula (1), Y represents a tetravalent organic group, preferably a tetravalent organic group having 4 to 40 carbon atoms, more preferably a tetravalent organic group having 4 to 40 carbon atoms and having a cyclic structure. Examples of the cyclic structure include alicyclic, aromatic, and heterocyclic structures, and from the viewpoint of easily increasing the tensile modulus, puncture strength, and bending resistance of the optical film and easily increasing the visibility in the wide-angle direction after the bending resistance test, preferably an aromatic ring is used. The organic group is an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, and in that case, the number of carbon atoms in the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably 1 to 8. In one embodiment of the present invention, the polyimide resin may contain multiple types of Y, and the multiple types of Y may be the same or different from each other. Examples of Y include groups represented by the following formulas (20), (21), (22), (23), (24), (25), (26), (27), (28), and (29); groups in which hydrogen atoms in the groups represented by formulas (20) to (29) are substituted with methyl groups, fluoro groups, chloro groups, or trifluoromethyl groups; and tetravalent chain hydrocarbon groups having 6 or less carbon atoms.

In formulas (20) to (29), * represents a bond, and W ¹ represents a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -Ar-, -SO ₂ -, -CO-, -O-Ar-O-, -Ar-O-Ar-, -Ar-CH ₂ -Ar-, -Ar-C(CH ₃ ) ₂ -Ar-, or -Ar-SO ₂ -Ar-. Ar represents an arylene group having 6 to 20 carbon atoms in which a hydrogen atom may be substituted with a fluorine atom, and a specific example is a phenylene group. When a plurality of Ars are present, the Ars may be the same or different from each other. In formulas (20) to (29), the hydrogen atoms on the rings may be substituted with an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified in formula (3) described below.

Among the groups represented by formulae (20) to (29), from the viewpoint of easily increasing the tensile elastic modulus, puncture strength, and bending resistance of the optical film, the groups represented by formula (26), formula (28), or formula (29) are preferred, and the group represented by formula (26) is more preferred. From the viewpoint of easily increasing the tensile modulus, puncture strength and bending resistance of the optical film and easily reducing the YI value of the optical film, ^W1 is preferably, independently of one another, a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -, more preferably a single bond, -O-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -, still more preferably a single bond, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -, and most preferably a single bond or -C(CF ₃ ) ₂ -.

In a preferred embodiment of the present invention, preferably 50 mol % or more, more preferably 60 mol % or more, and even more preferably 70 mol % or more of Y in the polyimide resin is represented by formula (26). When Y in the polyimide resin within the above range is represented by formula (26), preferably formula (26) in which W ¹ is a single bond, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -, more preferably formula (26) in which W ¹ is a single bond or -C(CF ₃ ) ₂ -, the tensile modulus, puncture strength and bending resistance of the optical film are easily increased, and the YI value of the optical film is easily reduced. The proportion of the constitutional unit in which Y in the polyimide resin is represented by formula (26) can be measured using, for example, ¹ H-NMR, or can be calculated from the charging ratio of the raw materials.

［式（４）中、Ｒ^２～Ｒ^７は、互いに独立に、水素原子、炭素数１～６のアルキル基、炭素数１～６のアルコキシ基又は炭素数６～１２のアリール基を表し、Ｒ^２～Ｒ^７に含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、Ｖは、単結合、－Ｏ－、－ＣＨ_２－、－ＣＨ_２－ＣＨ_２－、－ＣＨ（ＣＨ_３）－、－Ｃ（ＣＨ_３）_２－、－Ｃ（ＣＦ_３）_２－、－ＳＯ_２－、－Ｓ－、－ＣＯ－又は－Ｎ（Ｒ^８）－を表し、Ｒ^８は、水素原子、又はハロゲン原子で置換されていてもよい炭素数１～１２の１価の炭化水素基を表し、＊は結合手を表す］
で表される基を含む。すなわち、複数の式（１）で表される構成単位中のＹのうち、少なくとも一部のＹが式（４）で表される基であることが好ましい。このような態様であると、光学フィルムの引張弾性率、突刺し強度及び耐屈曲性を高めやすく、光学フィルムのＹＩ値を低減しやすい。なお、式（１）で表される構成単位は、Ｙとして式（４）で表される基を１種又は複数種含んでいてもよい。 In a preferred embodiment of the present invention, the constitutional unit represented by formula (1) is represented by formula (4):

[In formula (4), R ² to R ⁷ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms; the hydrogen atoms contained in R ² to R ⁷ may each independently be substituted with a halogen atom; V represents a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, -S-, -CO-, or -N(R ⁸ )-; R ⁸ represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom; and * represents a bond]
It contains a group represented by the formula (4). That is, it is preferable that at least some of the Y's in the structural units represented by the formula (1) are groups represented by the formula (4). In such an embodiment, it is easy to increase the tensile modulus, puncture strength and bending resistance of the optical film, and it is easy to reduce the YI value of the optical film. The structural unit represented by the formula (1) may contain one or more groups represented by the formula (4) as Y.

In formula (4), R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, or the aryl group having 6 to 12 carbon atoms include those exemplified above for the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, or the aryl group having 6 to 12 carbon atoms in R ^3a in formula (3). Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, or the aryl group having 6 to 12 carbon atoms in R ^{3a in formula (3) include those exemplified above for R 3a} in formula (3). R ² to R ⁷ each independently represent preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and the hydrogen atoms contained in R ² to R ⁷ may each independently be substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. V represents a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, -S-, -CO-, or -N(R ⁸ )-, and R ⁸ represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom include those exemplified above for R ⁹ in W in formula (3) described below. Among these, from the viewpoint of easily increasing the tensile modulus, puncture strength, optical properties, surface hardness and bending resistance of the optical film, V is preferably a single bond, -O-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -, more preferably a single bond, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -, and even more preferably a single bond or -C(CF ₃ ) ₂ -.

［式（５）中、Ｒ^１８～Ｒ^２５は、互いに独立に、水素原子、炭素数１～６のアルキル基、炭素数１～６のアルコキシ基又は炭素数６～１２のアリール基を表し、Ｒ^１８～Ｒ^２５に含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、＊は結合手を表す］
及び／又は式（９）：

［式（９）中、Ｒ^３５～Ｒ^４０は、互いに独立に、水素原子、炭素数１～６のアルキル基又は炭素数６～１２のアリール基を表し、Ｒ^３５～Ｒ^４０に含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、＊は結合手を表す］
で表される。複数の式（１）中のＹの少なくとも一部が式（５）で表される、及び／又は、式（９）で表されると、光学フィルムの引張弾性率、突刺し強度及び光学特性を向上させやすい。 In a preferred embodiment of the present invention, at least a portion of Y in the plurality of formulas (1) is represented by formula (5):

[In formula (5), R ¹⁸ to R ²⁵ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and the hydrogen atoms contained in R ¹⁸ to R ²⁵ each independently may be substituted with a halogen atom, and * represents a bond.]
And/or formula (9):

[In formula (9), R ³⁵ to R ⁴⁰ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, the hydrogen atoms contained in R ³⁵ to R ⁴⁰ each independently may be substituted with a halogen atom, and * represents a bond.]
When at least a part of Y in the plurality of formulas (1) is represented by formula (5) and/or formula (9), the tensile modulus, puncture strength, and optical properties of the optical film are easily improved.

In formula (5), R ¹⁸ , R ¹⁹ , R ²⁰ , R ²¹ , R ²² , R ²³ , R ²⁴ and R ²⁵ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, or the aryl group having 6 to 12 carbon atoms include those exemplified above as the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, or the aryl group having 6 to 12 carbon atoms in R ^3a in formula (3). R ¹⁸ to R ²⁵ each independently represent preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and the hydrogen atoms contained in R ¹⁸ to R ²⁵ may each independently be substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, ^a bromine atom, and an iodine atom. From the viewpoint of easily increasing the tensile modulus, puncture strength, and bending resistance of the optical film, and from the viewpoint of easily increasing the transparency and easily maintaining the transparency, R 18 to R ²⁵ are more preferably a hydrogen atom, a methyl group, a fluoro group, a chloro group, or a trifluoromethyl group, still more preferably R ¹⁸ , R ¹⁹ , R ²⁰ , R ²³ , R ²⁴ , and R ²⁵ are hydrogen atoms, R ²¹ and R ²² are hydrogen atoms, a methyl group, a fluoro group, a chloro group, or a trifluoromethyl group, and particularly preferably R ²¹ and R ²² are a methyl group or a trifluoromethyl group.

In formula (9), from the viewpoint of easily increasing the tensile modulus, puncture strength, and bending resistance of the optical film, and from the viewpoint of easily increasing the transparency and easily maintaining the transparency, R ³⁵ to R ⁴⁰ are preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and even more preferably a hydrogen atom. Here, the hydrogen atoms contained in R ³⁵ to R ⁴⁰ may be substituted, independently of one another, with a halogen atom, and examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Examples of the alkyl group having 1 to 6 carbon atoms and the aryl group having 6 to 12 carbon atoms in R ³⁵ to R ⁴⁰ include those exemplified above.

で表される。すなわち、複数のＹの少なくとも一部は、式（５’）及び／又は式（９’）で表される。この場合、光学フィルムの引張弾性率、突刺し強度及び耐屈曲性を高めやすい。さらに、式（５）が式（５’）で表される場合、フッ素元素を含有する骨格によりポリイミド系樹脂の溶媒への溶解性を高め、該樹脂を含有するワニスの保管安定性を向上しやすいと共に、該ワニスの粘度を低減しやすく、光学フィルムの加工性を向上しやすい。その結果、数式（１）～数式（３）を満たす本発明の光学フィルムを製造しやすい。また、フッ素元素を含有する骨格により、光学フィルムの光学特性を向上しやすい。 In a preferred embodiment of the present invention, formula (5) is represented by formula (5') and formula (9) is represented by formula (9'):

That is, at least a part of the multiple Y's is represented by formula (5') and/or formula (9'). In this case, the tensile modulus, puncture strength and bending resistance of the optical film are easily increased. Furthermore, when formula (5) is represented by formula (5'), the fluorine-containing skeleton increases the solubility of the polyimide resin in a solvent, and the storage stability of a varnish containing the resin is easily improved, and the viscosity of the varnish is easily reduced, which makes it easy to improve the processability of the optical film. As a result, it is easy to manufacture the optical film of the present invention that satisfies formulas (1) to (3). Furthermore, the fluorine-containing skeleton makes it easy to improve the optical properties of the optical film.

In a preferred embodiment of the present invention, preferably 50 mol % or more, more preferably 60 mol % or more, and even more preferably 70 mol % or more of Y in the polyimide resin is represented by formula (5), particularly formula (5'). When Y in the polyimide resin is represented by formula (5), particularly formula (5') within the above range, the solubility of the polyimide resin in a solvent is increased by the skeleton containing a fluorine element, the viscosity of a varnish containing the resin is easily reduced, and the processability of the optical film is easily improved. As a result, the optical film of the present invention that satisfies formulas (1) to (3) is easily produced. In addition, the skeleton containing a fluorine element makes it easy to improve the optical properties of the optical film. It is preferable that 100 mol % or less of Y in the polyimide resin is represented by formula (5), particularly formula (5'). Y in the polyimide resin may be formula (5), particularly formula (5'). The ratio of the structural unit represented by formula (5) of Y in the polyimide resin can be measured, for example, using ¹ H-NMR, or can be calculated from the charging ratio of the raw materials.

［式（２０）～式（２９）中、Ｗ^１は、単結合、－Ｏ－、－ＣＨ_２－、－ＣＨ_２－ＣＨ_２－、－ＣＨ（ＣＨ_３）－、－Ｃ（ＣＨ_３）_２－、－Ｃ（ＣＦ_３）_２－、－Ａｒ－、－ＳＯ_２－、－ＣＯ－、－Ｏ－Ａｒ－Ｏ－、－Ａｒ－Ｏ－Ａｒ－、－Ａｒ－ＣＨ_２－Ａｒ－、－Ａｒ－Ｃ（ＣＨ_３）_２－Ａｒ－又は－Ａｒ－ＳＯ_２－Ａｒ－を表し、ここで、Ａｒは、互いに独立に、水素原子がフッ素原子で置換されていてもよい炭素数６～２０のアリーレン基（例えばフェニレン基）を表し、＊は結合手を表す］
で表される基の結合手のうち、隣接しない２つが水素原子に置き換わった基及び炭素数６以下の２価の鎖式炭化水素基が例示され、Ｚのヘテロ環構造としてはチオフェン環骨格を有する基が例示される。光学フィルムのＹＩ値を低減しやすい観点、全光線透過率を高めやすい観点及びヘーズを低減しやすい観点から、Ｚにおける環状構造としては、式（２０）～式（２９）で表される基、及び、チオフェン環骨格を有する基が好ましく、式（２６）、式（２８）及び式（２９）で表される基がより好ましい。 In formula (2), Z is a divalent organic group, preferably an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms (hydrogen atoms in these groups may be substituted with halogen atoms (preferably fluorine atoms)), a divalent organic group having 4 to 40 carbon atoms, more preferably an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms (hydrogen atoms in these groups may be substituted with halogen atoms (preferably fluorine atoms)), a divalent organic group having 4 to 40 carbon atoms having a cyclic structure. In addition, as examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, or the aryl group having 6 to 12 carbon atoms, the examples of R ^3a and R ^3b in formula (3) described later apply similarly. Examples of the cyclic structure include an alicyclic ring, an aromatic ring, and a heterocyclic structure. The organic group of Z is represented by the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25), the formula (26), the formula (27), the formula (28), and the formula (29):

[In formulae (20) to (29), W ¹ represents a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -Ar-, -SO ₂ -, -CO-, -O-Ar-O-, -Ar-O-Ar-, -Ar-CH ₂ -Ar-, -Ar-C(CH ₃ ) ₂ -Ar- or -Ar-SO ₂ -Ar-, where each Ar is independently an arylene group having 6 to 20 carbon atoms (e.g., a phenylene group) in which a hydrogen atom may be substituted with a fluorine atom, and * represents a bond]
Examples of the heterocyclic structure of Z include a group having a thiophene ring skeleton. From the viewpoints of easily reducing the YI value of the optical film, easily increasing the total light transmittance, and easily reducing haze, the cyclic structure in Z is preferably a group represented by any of formulas (20) to (29) or a group having a thiophene ring skeleton, and more preferably a group represented by formula (26), formula (28), or formula (29).

［式（２０’）～式（２９’）中、Ｗ^１及び＊は、式（２０）～式（２９）において定義した通りである］
で表される２価の有機基がより好ましい。なお、式（２０）～式（２９）及び式（２０’）～式（２９’）における環上の水素原子は、炭素数１～６のアルキル基、炭素数１～６のアルコキシ基、又は炭素数６～１２のアリール基（これらの基における水素原子はハロゲン原子（好ましくはフッ素原子）で置換されていてもよい）で置換されていてもよい。 The organic group of Z includes those represented by the formula (20'), (21'), (22'), (23'), (24'), (25'), (26'), (27'), (28') and (29'):

[In formulae (20') to (29'), ^W1 and * are as defined in formulae (20) to (29)]
In addition, the hydrogen atoms on the rings in the formulae (20) to (29) and (20') to (29') may be substituted with an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms (the hydrogen atoms in these groups may be substituted with a halogen atom (preferably a fluorine atom)).

［式（ｄ１）中、Ｒ^４１は、互いに独立に、後述する式（３）中のＲ^３ａについて定義する基又は水素原子であり、Ｒ^４２は、Ｒ^４１又は－Ｃ（＝Ｏ）－＊を表し、＊は結合手を表す］
で表されるカルボン酸由来の構成単位をさらに有することが、ワニスの成膜性を高めやすく、光学フィルムの均一性を高めやすい観点から好ましい。構成単位（ｄ１）としては、具体的には、Ｒ^４１及びＲ^４２がいずれも水素原子である構成単位（ジカルボン酸化合物に由来する構成単位）、Ｒ^４１がいずれも水素原子であり、Ｒ^４２が－Ｃ（＝Ｏ）－＊を表す構成単位（トリカルボン酸化合物に由来する構成単位）等が挙げられる。 When the polyamide-based resin or polyamideimide resin has a constitutional unit represented by any one of the above formulas (20') to (29') in which Z in formula (2) has a constitutional unit represented by the formula (3') described later, the polyamide-based resin or polyamideimide resin has, in addition to the constitutional unit, the following formula (d1):

[In formula (d1), R ⁴¹ each independently represents a group defined for R ^3a in formula (3) described later or a hydrogen atom, and R ⁴² represents R ⁴¹ or -C(=O)-*, where * represents a bond.]
From the viewpoint of easily improving the film-forming properties of the varnish and easily improving the uniformity of the optical film, it is preferable that the structural unit (d1) further has a structural unit derived from a carboxylic acid represented by the following formula: Specific examples of the structural unit (d1) include a structural unit in which R ⁴¹ and R ⁴² are both hydrogen atoms (structural unit derived from a dicarboxylic acid compound), a structural unit in which R ⁴¹ are both hydrogen atoms and R ⁴² represents -C(=O)-* (structural unit derived from a tricarboxylic acid compound), and the like.

［式（３）中、Ｒ^３ａ及びＲ^３ｂは、互いに独立に、炭素数１～６のアルキル基、炭素数１～６のアルコキシ基、又は炭素数６～１２のアリール基を表し、Ｒ^３ａ及びＲ^３ｂに含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、Ｗは、互いに独立に、単結合、－Ｏ－、－ＣＨ_２－、－ＣＨ_２－ＣＨ_２－、－ＣＨ（ＣＨ_３）－、－Ｃ（ＣＨ_３）_２－、－Ｃ（ＣＦ_３）_２－、－ＳＯ_２－、－Ｓ－、－ＣＯ－又は－Ｎ（Ｒ^９）－を表し、Ｒ^９は水素原子、ハロゲン原子で置換されていてもよい炭素数１～１２の１価の炭化水素基を表し、ｓは０～４の整数であり、ｔは０～４の整数であり、ｕは０～４の整数であり、＊は結合手を表す］
、より好ましくは式（３’）：

［式（３’）中、Ｒ^３ａ、Ｒ^３ｂ、ｓ、ｔ、ｕ、Ｗ及び＊は、式（３）において定義した通りである］
で表される構成単位を少なくとも有することが好ましい。なお、本明細書において、ポリアミド系樹脂又はポリアミドイミド樹脂が式（２）中のＺが式（３）で表される構成単位を有することと、ポリアミド系樹脂又はポリアミドイミド系樹脂が式（２）中のＺとして式（３）で表される構造を有することとは、同様の意味を有し、ポリアミド系樹脂又はポリアミドイミド樹脂に含まれ得る複数の式（２）で表される構成単位のうち、少なくとも一部の構成単位におけるＺが式（３）で表されることを意味する。当該記載は、他の同様の記載にもあてはまる。 The polyamide-based resin or polyamideimide resin may contain a plurality of types of Z as Z in formula (2), and the plurality of types of Z may be the same or different from each other. In particular, from the viewpoint of easily increasing the tensile modulus and puncture strength of the optical film of the present invention and easily improving the optical properties, Z in formula (2) is preferably represented by formula (3):

[In formula (3), R ^3a and R ^3b each independently represent an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms; hydrogen atoms contained in R ^3a and R ^3b each independently may be substituted with a halogen atom; W each independently represent a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, -S-, -CO-, or -N(R ⁹ )-; R ⁹ represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom; s represents an integer of 0 to 4, t represents an integer of 0 to 4, u represents an integer of 0 to 4, and * represents a bond]
, more preferably formula (3'):

[In formula (3'), R ^3a , R ^3b , s, t, u, W and * are as defined in formula (3)]
In this specification, the term "polyamide-based resin or polyamideimide resin having a structural unit represented by formula (3) as Z in formula (2)" and the term "polyamide-based resin or polyamideimide resin having a structure represented by formula (3) as Z in formula (2)" have the same meaning, and mean that Z in at least some structural units of a plurality of structural units represented by formula (2) that can be contained in the polyamide-based resin or polyamideimide resin is represented by formula (3). This description also applies to other similar descriptions.

In formula (3) and formula (3'), W each independently represents a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, -S-, -CO- or -N(R ⁹ )-, and from the viewpoint of the bending resistance of the optical film, preferably represents -O- or -S-, more preferably -O-.
R ^3a and R ^3b each independently represent an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 2-methyl-butyl group, a 3-methylbutyl group, a 2-ethyl-propyl group, and an n-hexyl group. Examples of the alkoxy group having 1 to 6 carbon atoms include a methoxy group, an ethoxy group, a propyloxy group, an isopropyloxy group, a butoxy group, an isobutoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group, and a cyclohexyloxy group. Examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a biphenyl group. From the viewpoint of the tensile modulus, puncture strength, surface hardness and flexibility of the optical film, R ^3a and R ^3b each independently preferably represent an alkyl group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms or an alkoxy group having 1 to 3 carbon atoms. Here, the hydrogen atoms contained in R ^3a and R ^3b each independently may be substituted with a halogen atom.
R ⁹ represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 2-methyl-butyl group, a 3-methyl-butyl group, a 2-ethyl-propyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, a tert-octyl group, an n-nonyl group, and an n-decyl group, which may be substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

In formula (3) and formula (3'), t and u are each independently an integer of 0 to 4, preferably an integer of 0 to 2, and more preferably 1 or 2.

In formula (3) and formula (3'), s is an integer in the range of 0 to 4. When s is within this range, the tensile modulus, puncture strength, and bending resistance of the optical film are easily improved. From the viewpoint of more easily improving the tensile modulus, puncture strength, and bending resistance of the optical film, the s is preferably an integer in the range of 0 to 3, more preferably an integer in the range of 0 to 2, even more preferably 0 or 1, and even more preferably 0. The polyamideimide resin or polyamide-based resin may contain one or more types of structural units represented by formula (3) or formula (3') in Z.

In a preferred embodiment of the present invention, from the viewpoint of improving the tensile modulus, puncture strength, modulus and flex resistance of the optical film and reducing the YI value, Z is preferably represented by formula (3) or formula (3') in which s is 0 and u is preferably 1 to 3, more preferably 1 or 2. Furthermore, in addition to the structural unit represented by formula (2) having Z represented by formula (3) or formula (3') in which s is 0, it is also preferable to further have a structural unit represented by the above formula (d1).

When the polyamideimide resin or polyamide-based resin has a structural unit represented by formula (3) or formula (3'), the ratio is preferably 20 mol% or more, more preferably 30 mol% or more, even more preferably 40 mol% or more, even more preferably 50 mol% or more, particularly preferably 60 mol% or more, and preferably 90 mol% or less, more preferably 85 mol% or less, and even more preferably 80 mol% or less, when the total of the structural unit represented by formula (1) and the structural unit represented by formula (2) of the polyamideimide resin or polyamide-based resin is taken as 100 mol%. When the ratio of the structural unit represented by formula (3) or formula (3') is equal to or more than the above lower limit, the tensile modulus, puncture strength and bending resistance of the optical film are easily increased. When the ratio of the structural unit represented by formula (3) or formula (3') is equal to or less than the above upper limit, the viscosity increase of the resin-containing varnish due to hydrogen bonding between amide bonds derived from formula (3) is suppressed, and the processability of the film is easily improved. The ratio of the constitutional units represented by formula (1), formula (2), formula (3) or formula (3') can be measured, for example, by ¹ H-NMR, or can be calculated from the charge ratio of the raw materials.

In a preferred embodiment of the present invention, preferably 30 mol% or more, more preferably 40 mol% or more, even more preferably 45 mol% or more, and even more preferably 50 mol% or more of Z in the polyamideimide resin or polyamide-based resin is a structural unit represented by formula (3) or formula (3') in which s is 0 to 4. When Z is a structural unit represented by formula (3) or formula (3') in which s is 0 to 4 or more, the tensile modulus, puncture strength, and bending resistance of the optical film are easily improved. In addition, 100 mol% or less of Z in the polyamideimide resin or polyamide-based resin may be a structural unit represented by formula (3) or formula (3') in which s is 0 to 4. The proportion of the structural unit represented by formula (3) or formula (3') in which s is 0 to 4 in the resin can be measured using, for example, ¹ H-NMR, or can be calculated from the charging ratio of the raw materials.

In formula (1) and formula (2), X each independently represents a divalent organic group, preferably a divalent organic group having 4 to 40 carbon atoms, more preferably a divalent organic group having 4 to 40 carbon atoms and a cyclic structure. Examples of the cyclic structure include an alicyclic ring, an aromatic ring, and a heterocyclic structure. The organic group may have a hydrogen atom in the organic group substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, in which case the number of carbon atoms in the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably 1 to 8. In one embodiment of the present invention, the polyamide-based resin and polyimide resin of the present invention may contain multiple types of X, and the multiple types of X may be the same or different from each other. Examples of X include groups represented by formula (10), formula (11), formula (12), formula (13), formula (14), formula (15), formula (16), formula (17) and formula (18); groups in which the hydrogen atoms in the groups represented by formulas (10) to (18) are substituted with methyl groups, fluoro groups, chloro groups or trifluoromethyl groups; and chain hydrocarbon groups having 6 or less carbon atoms.

In formulas (10) to (18), * represents a bond.
V ¹ , V ² and V ³ each independently represent a single bond, -O-, -S-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, -CO- or -N(Q)-, where Q represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms include the groups described above for R ⁹ .
In one example, ^V1 and ^V3 are single bonds, -O- or -S-, and ^V2 is _-CH2- , -C( _CH3 ) _2- , -C( _CF3 ) _2- or _-SO2- . The bonding positions of ^V1 and ^V2 to each ring, and the bonding positions of ^V2 and ^V3 to each ring, are each independently preferably meta or para positions, more preferably para positions, to each ring.

Among the groups represented by formulae (10) to (18), from the viewpoint of easily increasing the tensile modulus, puncture strength and flexibility of the optical film, the groups represented by formulae (13), (14), (15), (16) and (17) are preferred, and the groups represented by formulae (14), (15) and (16) are more preferred. Furthermore, from the viewpoint of easily increasing the tensile modulus, puncture strength and flexibility of the optical film, V ¹ , V ² and V ³ are each independently preferably a single bond, -O- or -S-, more preferably a single bond or -O-.

［式（５）中、Ａｒ^２は互いに独立に置換基を有していてもよい２価の芳香族基を表し、Ｖは、単結合、－Ｏ－、ジフェニルメチレン基、フルオレニル基、炭素数１～１２の２価の炭化水素基、－ＳＯ_２－、－Ｓ－、－ＣＯ－、－ＰＯ－、－ＰＯ_２－、－Ｎ（Ｒ^ａ）－又は－Ｓｉ（Ｒ^ｂ）_２－を表し、ここで、該炭化水素基は脂環式構造を含んでいてもよく、該炭化水素基に含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、Ｒ^ａ及びＲ^ｂは、互いに独立に、水素原子、又はハロゲン原子で置換されていてもよい炭素数１～１２の１価の炭化水素基を表し、ｍは０～３の整数を表し、＊は結合手を表す］
で表される２価の有機基を含む。構成単位（１）及び構成単位（２）が、Ｘとして式（５）で表される２価の有機基を含む場合、構成単位（１）及び構成単位（２）は、Ｘとして、式（５）で表される１種類又は２種類以上の２価の有機基を含んでよい。構成単位（１）及び構成単位（２）は、Ｘとして、式（５）で表される２価の有機基の他に、式（５）で表される２価の有機基に該当しない他の２価の有機基を含んでいてもよい。 In a preferred embodiment of the present invention, the polyamide-based resin and/or polyimide-based resin is represented by the formula (5):

[In formula (5), Ar ² each independently represents a divalent aromatic group which may have a substituent; V represents a single bond, -O-, a diphenylmethylene group, a fluorenyl group, a divalent hydrocarbon group having 1 to 12 carbon atoms, -SO ₂ -, -S-, -CO-, -PO-, -PO ₂ -, -N(R ^a )- or -Si(R ^b ) ₂ -, where the hydrocarbon group may contain an alicyclic structure and hydrogen atoms contained in the hydrocarbon group may each independently be substituted with a halogen atom; R ^a and R ^b each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom; m represents an integer of 0 to 3; and * represents a bond]
When the structural unit (1) and the structural unit (2) contain a divalent organic group represented by formula (5) as X, the structural unit (1) and the structural unit (2) may contain one or more types of divalent organic groups represented by formula (5) as X. The structural unit (1) and the structural unit (2) may contain, in addition to the divalent organic group represented by formula (5) as X, other divalent organic groups that do not fall under the divalent organic group represented by formula (5).

Ar ² in formula (5) represents a divalent aromatic group which may have a substituent. The divalent aromatic group is a group in which two hydrogen atoms of a monocyclic aromatic ring, a condensed polycyclic aromatic ring, or a ring assembly aromatic ring are replaced by bonds. The divalent aromatic group may contain an aromatic ring in which a ring (monocyclic, condensed polycyclic, or ring assembly) is formed only by carbon atoms, or may contain a heteroaromatic ring in which a ring is formed by including atoms other than carbon atoms. Examples of atoms other than carbon atoms include nitrogen atoms, sulfur atoms, and oxygen atoms. The total number of carbon atoms and atoms other than carbon atoms forming an aromatic ring is not particularly limited, but is preferably 5 to 18, more preferably 5 to 14, and even more preferably 5 to 12. When m in formula (5) is 1 or more, the multiple Ar ^2s present may be the same or different from each other.

Examples of monocyclic aromatic rings include benzene, furan, pyrrole, thiophene, pyridine, imidazole, pyrazole, oxazole, thiazole, and imidazoline.

Fused polycyclic aromatic rings include, for example, naphthalene, anthracene, phenanthrene, indole, benzothiazole, benzimidazole, and benzoxazole.

Examples of ring assembly aromatic rings include structures in which two or more monocyclic aromatic rings and/or fused polycyclic aromatic rings are linked by a single bond, and examples thereof include groups in which two or more of the rings described above as examples of monocyclic aromatic rings or fused polycyclic aromatic rings are linked by a single bond, such as biphenyl, terphenyl, quaterphenyl, binaphthyl, 1-phenylnaphthalene, 2-phenylnaphthalene, and bipyridine.

From the viewpoint of easily increasing the tensile modulus and puncture strength of the optical film, the divalent aromatic group which may have a substituent is preferably a group in which two hydrogen atoms of an aromatic hydrocarbon ring which may have a substituent are replaced by bonds, more preferably a group in which two hydrogen atoms of an aromatic hydrocarbon ring which may have a substituent are replaced by bonds, and even more preferably a group in which two hydrogen atoms of an aromatic hydrocarbon ring which may have a substituent are replaced by bonds, and even more preferably a group in which two hydrogen atoms of an aromatic hydrocarbon ring which may have a substituent are replaced by bonds.

Examples of the substituent for ^Ar2 include a halogen group, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, and groups in which a hydrogen atom contained in these groups is substituted with a halogen atom.

The alkyl group having 1 to 12 carbon atoms may be a linear or branched alkyl group having 1 to 12 carbon atoms, and is preferably a linear or branched alkyl group having 1 to 6 carbon atoms. Examples of such groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, 2-methylbutyl, 3-methylbutyl, 2-ethylpropyl, n-hexyl, n-heptyl, n-octyl, tert-octyl, n-nonyl, and n-decyl groups.

Examples of alkoxy groups having 1 to 6 carbon atoms include methoxy, ethoxy, propyloxy, isopropyloxy, butoxy, isobutoxy, tert-butoxy, pentyloxy, hexyloxy, and cyclohexyloxy groups.

Examples of aryl groups having 6 to 12 carbon atoms include phenyl groups, tolyl groups, xylyl groups, naphthyl groups, and biphenyl groups.

Halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, iodine atoms, etc.

The substituent in ^Ar2 is preferably a halogen group or an alkyl group having 1 to 12 carbon atoms in which a hydrogen atom may be substituted with a halogen atom, and more preferably a methyl group, a fluoro group, a chloro group or a trifluoromethyl group.

In formula (5), V represents a single bond, -O-, a diphenylmethylene group, a fluorenyl group, a divalent hydrocarbon group having 1 to 12 carbon atoms, -SO ₂ -, -S-, -CO-, -PO-, -PO ₂ -, -N(R ^a )- or -Si(R ^b ) ₂ -, where the hydrocarbon group may contain an alicyclic structure, hydrogen atoms contained in the hydrocarbon group may be each independently substituted with a halogen atom, and R ^a and R ^b each independently represent a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, 2-methylbutyl, 3-methylbutyl, 2-ethylpropyl, n-hexyl, n-heptyl, n-octyl, tert-octyl, n-nonyl, n-decyl, cyclopentyl, and cyclohexyl groups, which may be substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. From the viewpoint of easily improving the tensile modulus, puncture strength and bending resistance of the optical film, V in formula (5) is preferably a single bond, a divalent hydrocarbon group having 1 to 12 carbon atoms or a group in which at least a portion of the hydrogen atoms contained in such a hydrocarbon group have been substituted with a halogen atom, more preferably a single bond, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ ) -, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -, even more preferably a single bond, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -, and even more preferably a single bond or -C(CF ₃ ) ₂ -.

In formula (5), m represents an integer of 0 to 3, and from the viewpoint of easily increasing the tensile modulus and puncture strength of the optical film, it is preferably 0 to 2, more preferably 0 or 1, and even more preferably 1.

In a preferred embodiment of the present invention, in which the structural unit (1) and/or structural unit (2) that may be contained in the polyamide-based resin and/or polyimide-based resin contained in the optical film of the present invention contains a divalent organic group represented by formula (5) as X, from the viewpoint of easily increasing the tensile modulus and puncture strength of the optical film, when the total of the structural units (1) and (2) is taken as 100 mol%, the total proportion of the structural units in which X in formula (1) is a divalent organic group represented by formula (5) and the structural units in which X in formula (2) is a divalent organic group represented by formula (5) is preferably 70 to 100 mol%, more preferably 80 to 100 mol%, and even more preferably 90 to 100 mol%, and X may be a divalent organic group represented by formula (5) in all structural units of the structural units (1) and (2).

［式（５ａ）中、Ｒ^２は、炭素数１～１２のフルオロアルキル基を表し、ｐ及びｑは、互いに独立に、１～４の整数を表し、ただし、ｐ及び／又はｑが２～４の整数を表す場合に複数存在するＲ^２は、互いに同一であっても異なっていてもよく、＊は結合手を表す］
で表される２価の有機基を含む。なお、式（５ａ）で表される２価の有機基は、式（５）で表される２価の有機基に包含される基であり、具体的には、式（５）中のＶが単結合を表し、Ａｒ^２が炭素数１～１２のフルオロアルキル基（Ｒ^２）で置換されたベンゼン環を表し、ｍが０～３の整数を表す２価の有機基に相当する基である。構成単位（１）及び構成単位（２）が、Ｘとして式（５ａ）で表される２価の有機基を含む場合、構成単位（１）及び構成単位（２）は、Ｘとして、式（５ａ）で表される１種類又は２種類以上の２価の有機基を含んでよい。構成単位（１）及び／又は構成単位（２）は、Ｘとして、式（５ａ）で表される２価の有機基の他に、式（５ａ）で表される２価の有機基に該当しない他の２価の有機基を含んでいてもよい。 In a preferred embodiment of the present invention, from the viewpoint of easily increasing the tensile modulus and puncture strength of the optical film, the structural unit represented by formula (1) and/or the structural unit represented by formula (2) is represented by the formula (5a):

[In formula (5a), R ² represents a fluoroalkyl group having 1 to 12 carbon atoms, p and q each independently represent an integer of 1 to 4, provided that when p and/or q each represents an integer of 2 to 4, a plurality of R ² 's may be the same or different, and * represents a bond.]
The divalent organic group represented by formula (5a) is a group included in the divalent organic group represented by formula (5), specifically, V in formula (5) represents a single bond, Ar ² represents a benzene ring substituted with a fluoroalkyl group (R ² ) having 1 to 12 carbon atoms, and m is a group corresponding to a divalent organic group representing an integer of 0 to 3. When the structural unit (1) and the structural unit (2) contain a divalent organic group represented by formula (5a) as X, the structural unit (1) and the structural unit (2) may contain one or more types of divalent organic groups represented by formula (5a) as X. The structural unit (1) and/or the structural unit (2) may contain, in addition to the divalent organic group represented by formula (5a) as X, other divalent organic groups not corresponding to the divalent organic group represented by formula (5a).

R ² in formula (5a) represents a fluoroalkyl group having 1 to 12 carbon atoms. The fluoroalkyl group having 1 to 12 carbon atoms is a group in which at least one hydrogen atom of a linear or branched alkyl group having 1 to 12 carbon atoms is substituted with a fluorine atom. Examples of the linear or branched fluoroalkyl group having 1 to 12 carbon atoms include groups in which at least one hydrogen atom of a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 2-methyl-butyl group, a 3-methylbutyl group, a 2-ethyl-propyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, a tert-octyl group, an n-nonyl group, and an n-decyl group is substituted with a fluorine atom. Specific examples of the fluoroalkyl group having 1 to 12 carbon atoms include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a fluoroethyl group, a difluoroethyl group, a trifluoroethyl group, a pentafluoroethyl group, a heptafluoropropyl group, a nonafluorobutyl group, etc. The number of carbon atoms in the fluoroalkyl group is preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 or 2.

p and q each independently represent an integer of 1 to 4. From the viewpoint of easily increasing the tensile modulus of elasticity and the puncture strength of the optical film, p is preferably an integer of 1 or 2, more preferably 2. From the viewpoint of easily increasing the tensile modulus of elasticity and the puncture strength of the optical film, q is preferably an integer of 1 or 2, more preferably 1. Here, when p and/or q represent an integer of 2 to 4, multiple R ^2s may be the same or different, but it is preferable that multiple R ^2s are the same.

The positions of the two bonds in formula (5a) are not particularly limited and may be ortho, meta, or para, but from the viewpoint of easily increasing the tensile modulus and puncture strength of the optical film, the bonds are preferably located in the para position.

Preferred examples of the divalent aromatic group represented by formula (5a) include aromatic groups in which R ² in formula (5a) represents a perfluoroalkyl group having 1 to 12 carbon atoms, p is 2, q is 1 or 2, and/or the two bonds are located in the para position relative to each other.

In a preferred embodiment of the present invention, in which the structural unit (1) and/or structural unit (2) that may be contained in the resin contained in the optical film of the present invention contains a divalent organic group represented by formula (5a) as X, from the viewpoint of easily increasing the tensile modulus and puncture strength of the optical film, when the total of the structural units (1) and (2) contained in the polyamideimide resin is taken as 100 mol%, the total proportion of the structural units in which X in formula (1) is a divalent organic group represented by formula (5a) and the structural units in which X in formula (2) is a divalent organic group represented by formula (5a) is preferably 70 to 100 mol%, more preferably 80 to 100 mol%, and even more preferably 90 to 100 mol%, and X may be a divalent organic group represented by formula (5a) in all structural units of the structural units (1) and (2).

［式（４）中、Ｒ^１０～Ｒ^１７は、互いに独立に、水素原子、炭素数１～６のアルキル基、炭素数１～６のアルコキシ基又は炭素数６～１２のアリール基を表し、Ｒ^１０～Ｒ^１７に含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、＊は結合手を表す］
で表される構造を含む。式（１）及び式（２）で表される複数の構成単位中のＸの少なくとも一部が式（４）で表される構造であると、光学フィルムの引張弾性率、突刺し強度及び透明性を高めやすい。 In a preferred embodiment of the present invention, the polyamide-based resin and the polyimide-based resin are represented by the formula (4):

[In formula (4), R ¹⁰ to R ¹⁷ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, the hydrogen atoms contained in R ¹⁰ to R ¹⁷ each independently may be substituted with a halogen atom, and * represents a bond.]
When at least a part of X in the multiple structural units represented by formula (1) and formula (2) has a structure represented by formula (4), the tensile modulus, puncture strength, and transparency of the optical film are easily increased.

In formula (4), R ¹⁰ , R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ and R ¹⁷ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, or the aryl group having 6 to 12 carbon atoms in formula (3) include the groups exemplified as the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, or the aryl group having 6 to 12 carbon atoms. R ¹⁰ to R ¹⁷ each independently represent preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and the hydrogen atoms contained in R ¹⁰ to R ¹⁷ may each independently be substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. From the viewpoints of the tensile modulus and puncture strength, transparency and bending resistance of the optical film, R ¹⁰ to R ¹⁷ are more preferably a hydrogen atom, a methyl group, a fluoro group, a chloro group or a trifluoromethyl group, even more preferably R ¹⁰ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ and R ¹⁶ are a hydrogen atom, R ¹¹ and R ¹⁷ are a hydrogen atom, a methyl group, a fluoro group, a chloro group or a trifluoromethyl group, and particularly preferably R ¹¹ and R ¹⁷ are a methyl group or a trifluoromethyl group.

で表される構成単位であり、すなわち、式（１）及び式（２）で表される複数の構成単位中のＸの少なくとも一部は、式（４’）で表される構成単位である。この場合、フッ素元素を含有する骨格によりポリイミド系樹脂又はポリアミド系樹脂の溶媒への溶解性を高め、該樹脂を含有するワニスの保管安定性を向上しやすいと共に、該ワニスの粘度を低減しやすく、光学フィルムの加工性を向上しやすい。その結果、数式（１）～数式（３）を満たす本発明の光学フィルムを製造しやすい。また、フッ素元素を含有する骨格により、光学フィルムの光学特性を向上しやすい。 In a preferred embodiment of the present invention, the constitutional unit represented by formula (4) is represented by formula (4'):

That is, at least a part of X in the plurality of structural units represented by formula (1) and formula (2) is a structural unit represented by formula (4'). In this case, the skeleton containing the fluorine element increases the solubility of the polyimide resin or polyamide resin in a solvent, and the storage stability of the varnish containing the resin is easily improved, and the viscosity of the varnish is easily reduced, and the processability of the optical film is easily improved. As a result, the optical film of the present invention that satisfies formulas (1) to (3) is easily produced. In addition, the skeleton containing the fluorine element makes it easy to improve the optical properties of the optical film.

In a preferred embodiment of the present invention, preferably 30 mol % or more, more preferably 50 mol % or more, and even more preferably 70 mol % or more of X that can be contained in the polyimide-based resin or polyamide-based resin is represented by formula (4), particularly formula (4'). When X within the above range in the polyimide-based resin or polyamide-based resin is represented by formula (4), particularly formula (4'), the resulting optical film has a fluorine-containing skeleton that increases the solubility of the resin in a solvent, and the storage stability of a varnish containing the resin is easily improved, and the viscosity of the varnish is easily reduced, making it easy to produce the optical film of the present invention that satisfies formulas (1) to (3). In addition, the fluorine-containing skeleton also easily improves the optical properties of the optical film. Preferably, 100 mol % or less of X in the polyimide-based resin or polyamide-based resin is represented by formula (4), particularly formula (4'). X in the resin may be formula (4), particularly formula (4'). The ratio of the structural unit represented by formula (4) of X in the resin can be measured, for example, using ¹ H-NMR, or can be calculated from the charge ratio of the raw materials.

The polyimide resin may contain a constitutional unit represented by formula (30) and/or a constitutional unit represented by formula (31), or may contain a constitutional unit represented by formula (30) and/or a constitutional unit represented by formula (31) in addition to the constitutional unit represented by formula (1) and optionally formula (2).

In formula (30), Y ¹ is a tetravalent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Examples of Y ¹ include groups represented by formulas (20), (21), (22), (23), (24), (25), (26), (27), (28) and (29), groups in which a hydrogen atom in the groups represented by formulas (20) to (29) is substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group, and a tetravalent chain hydrocarbon group having 6 or less carbon atoms. In one embodiment of the present invention, the polyimide resin may contain multiple types of Y ¹ , and the multiple types of Y ¹ may be the same or different from each other.

In formula (31), ^Y2 is a trivalent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Examples of ^Y2 include a group in which one of the bonds of the groups represented by the above formulas (20), (21), (22), (23), (24), (25), (26), (27), (28) and (29) is replaced with a hydrogen atom, and a trivalent chain hydrocarbon group having 6 or less carbon atoms. In one embodiment of the present invention, the polyimide resin may contain multiple types of ^Y2 , and the multiple types of ^Y2 may be the same or different from each other.

In formula (30) and formula (31), ^X1 and ^X2 are each independently a divalent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Examples of ^X1 and ^X2 include groups represented by the above formulas (10), (11), (12), (13), (14), (15), (16), (17) and (18); groups in which a hydrogen atom in the groups represented by the formulas (10) to (18) is substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group; and chain hydrocarbon groups having 6 or less carbon atoms.

In one embodiment of the present invention, the polyimide resin comprises constitutional units represented by formula (1) and/or formula (2), and optionally constitutional units represented by formula (30) and/or formula (31). From the viewpoint of easily increasing the tensile modulus, puncture strength, optical properties, and bending resistance of the optical film, the proportion of constitutional units represented by formula (1) and formula (2) in the polyimide resin is preferably 80 mol% or more, more preferably 90 mol% or more, and even more preferably 95 mol% or more based on all constitutional units represented by formula (1) and formula (2), and optionally formula (30) and formula (31). In the polyimide resin, the proportion of constitutional units represented by formula (1) and formula (2) is usually 100% or less based on the total of all constitutional units represented by formula (1) and formula (2), and optionally formula (30) and/or formula (31). The above proportion can be measured, for example, using ¹ H-NMR, or can be calculated from the charge ratio of the raw materials.

In one embodiment of the present invention, the content of the polyimide-based resin and/or polyamide-based resin in the optical film is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and even more preferably 50 parts by mass or more, and is preferably 99.5 parts by mass or less, and more preferably 95 parts by mass or less, relative to 100 parts by mass of the optical film. When the content of the polyimide-based resin and/or polyamide-based resin is within the above range, it is easy to improve the tensile modulus, puncture strength, optical properties, and bending resistance of the optical film.

From the viewpoint of easily increasing the tensile modulus, puncture strength and bending resistance of the optical film, the weight average molecular weight (Mw) of the polyimide resin and polyamide resin, in terms of standard polystyrene, is preferably 100,000 or more, more preferably 130,000 or more, even more preferably 150,000 or more, still more preferably 170,000 or more, particularly preferably 200,000 or more, particularly preferably 230,000 or more, particularly still more preferably 250,000 or more, and especially preferably 260,000 or more. In addition, the weight average molecular weight of the polyimide resin and the polyamide resin is preferably 1,000,000 or less, more preferably 800,000 or less, even more preferably 700,000 or less, even more preferably 500,000 or less, particularly preferably 400,000 or less, particularly preferably 350,000 or less, and particularly preferably 300,000 or less, from the viewpoint of easily improving the solubility of the resin in a solvent and easily improving the stretchability and processability of the optical film. The weight average molecular weight can be determined, for example, by performing GPC measurement and converting it into standard polystyrene, and may be calculated, for example, by the method described in the Examples. When the weight average molecular weight (Mw) of the polyimide resin and the polyamide resin is equal to or less than the above upper limit, it is easy to increase the solid content of the varnish containing the resin and to reduce the viscosity of the varnish, and as a result, it is easy to manufacture the optical film of the present invention that satisfies the formulas (1) to (3). In addition, it is easy to maintain the visibility in the wide angle direction after the bending resistance test.

In the polyamide-imide resin, the content of the structural unit represented by formula (2) is preferably 0.1 mol or more, more preferably 0.5 mol or more, even more preferably 1.0 mol or more, even more preferably 1.5 mol or more, and preferably 6.0 mol or less, more preferably 5.0 mol or less, and even more preferably 4.5 mol or less, per mol of the structural unit represented by formula (1). When the content of the structural unit represented by formula (2) is equal to or more than the above lower limit, the tensile modulus and puncture strength of the optical film are easily increased. When the content of the structural unit represented by formula (2) is equal to or less than the above upper limit, thickening due to hydrogen bonds between amide bonds in formula (2) is suppressed, and the viscosity of the varnish when manufacturing the optical film is easily reduced, making it easy to manufacture the optical film of the present invention that satisfies formulas (1) to (3).

In a preferred embodiment of the present invention, the polyimide resin and/or polyamide resin contained in the optical film may contain halogen atoms such as fluorine atoms, which can be introduced, for example, by the above-mentioned fluorine-containing substituents. When the polyimide resin and/or polyamide resin contains halogen atoms, the tensile modulus of the optical film is easily improved and the YI value is easily reduced. When the tensile modulus of the optical film is high, it is easy to suppress the occurrence of scratches and wrinkles, and it is easy to improve the visibility in the wide-angle direction after the bending resistance test. In addition, when the YI value is low, it is easy to improve the transparency and visibility of the film. The halogen atom is preferably a fluorine atom. Examples of fluorine-containing substituents that are preferable for containing fluorine atoms in the polyimide resin include a fluoro group and a trifluoromethyl group.

The content of halogen atoms in the polyimide resin and the polyamide resin is preferably 1 to 40 mass%, more preferably 5 to 40 mass%, and even more preferably 5 to 30 mass%, based on the mass of the polyimide resin and the polyamide resin, respectively. When the content of halogen atoms is equal to or greater than the above lower limit, it is easier to improve the tensile modulus of the optical film and to reduce the YI value. As a result, it is easier to improve the visibility in the wide-angle direction after the bending resistance test. When the content of halogen atoms is equal to or less than the above upper limit, synthesis is easier.

The imidization rate of the polyimide resin and the polyamide-imide resin is preferably 90% or more, more preferably 93% or more, and even more preferably 96% or more. From the viewpoint of easily improving the optical properties of the optical film, it is preferable that the imidization rate is equal to or higher than the above lower limit. The upper limit of the imidization rate is 100% or less. The imidization rate indicates the ratio of the molar amount of imide bonds in the polyimide resin to twice the molar amount of the constituent units derived from the tetracarboxylic acid compound in the polyimide resin. In addition, when the polyimide resin contains a tricarboxylic acid compound, it indicates the ratio of the molar amount of imide bonds in the polyimide resin to the sum of twice the molar amount of the constituent units derived from the tetracarboxylic acid compound in the polyimide resin and the molar amount of the constituent units derived from the tricarboxylic acid compound. In addition, the imidization rate can be determined by IR method, NMR method, etc.

In the present invention, the optical film may contain a polyamide-based resin. The polyamide-based resin according to this embodiment is a polymer mainly composed of a repeating structural unit represented by formula (2). Preferred examples and specific examples of Z in formula (2) in the polyamide-based resin are the same as the preferred examples and specific examples of Z in the polyimide-based resin. The polyamide-based resin may contain two or more types of repeating structural units represented by formula (2) with different Z.

(Method of producing resin)
The method for producing the polyimide resin and polyamide resin contained in the optical film of the present invention is not particularly limited. The polyimide resin and polyimide precursor resin can be produced, for example, from a tetracarboxylic acid compound and a diamine compound as main raw materials, the polyamideimide resin and polyamideimide precursor resin can be produced, for example, from a tetracarboxylic acid compound, a dicarboxylic acid compound and a diamine compound as main raw materials, and the polyamide resin can be produced, for example, from a diamine compound and a dicarboxylic acid compound as main raw materials.

The structural units represented by formula (1) and formula (30) are usually derived from a diamine compound and a tetracarboxylic acid compound. The structural unit represented by formula (2) is usually derived from a diamine compound and a dicarboxylic acid compound. The structural unit represented by formula (31) is usually derived from a diamine compound and a tricarboxylic acid compound.

Examples of diamine compounds used in the production of resins include aliphatic diamines, aromatic diamines, and mixtures thereof. In this embodiment, "aromatic diamine" refers to a diamine in which an amino group is directly bonded to an aromatic ring, and may contain an aliphatic group or other substituents as part of its structure. The aromatic ring may be a single ring or a condensed ring, and examples include a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring, but are not limited to these. Of these, a benzene ring is preferable. In addition, "aliphatic diamine" refers to a diamine in which an amino group is directly bonded to an aliphatic group, and may contain an aromatic ring or other substituents as part of its structure.

Examples of aliphatic diamines include acyclic aliphatic diamines such as hexamethylenediamine, and cyclic aliphatic diamines such as 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, norbornanediamine, and 4,4'-diaminodicyclohexylmethane. These can be used alone or in combination of two or more.

Examples of aromatic diamines include aromatic diamines having one aromatic ring, such as p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, and 2,6-diaminonaphthalene, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene, and bis[4-(4-aminophenyl)phenyl]phenyl. Examples of aromatic diamines having two or more aromatic rings include aromatic diamines having two or more aromatic rings, such as bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl (sometimes referred to as TFMB), 4,4'-bis(4-aminophenoxy)biphenyl, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene, 9,9-bis(4-amino-3-chlorophenyl)fluorene, and 9,9-bis(4-amino-3-fluorophenyl)fluorene. These can be used alone or in combination of two or more.

The aromatic diamine is preferably 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 1,4-bis(4-aminophenoxy)benzene, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl 1,4-bis(4-aminophenoxy)benzene, bis[4-(4-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl (TFMB), 4,4'-bis(4-aminophenoxy)biphenyl. These can be used alone or in combination of two or more.

Among the above diamine compounds, from the viewpoint of easily increasing the tensile modulus, puncture strength, transparency, flexibility, and bending resistance of the optical film and easily reducing the YI value, it is preferable to use one or more selected from the group consisting of aromatic diamines having a biphenyl structure. It is more preferable to use one or more selected from the group consisting of 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)benzidine, 4,4'-bis(4-aminophenoxy)biphenyl, and 4,4'-diaminodiphenyl ether, and it is even more preferable to use 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl (TFMB).

Tetracarboxylic acid compounds used in the production of resins include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic acid dianhydrides; and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic acid dianhydrides. The tetracarboxylic acid compounds may be used alone or in combination of two or more. The tetracarboxylic acid compounds may be dianhydrides or tetracarboxylic acid compound analogs such as acid chloride compounds.

Specific examples of aromatic tetracarboxylic acid dianhydrides include non-condensed polycyclic aromatic tetracarboxylic acid dianhydrides, monocyclic aromatic tetracarboxylic acid dianhydrides, and condensed polycyclic aromatic tetracarboxylic acid dianhydrides. Examples of non-condensed polycyclic aromatic tetracarboxylic acid dianhydrides include 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride, 2,2',3,3'-benzophenone tetracarboxylic acid dianhydride, 3,3',4,4'-biphenyl tetracarboxylic acid dianhydride (sometimes referred to as BPDA), 2,2',3,3'-biphenyl tetracarboxylic acid dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic acid dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenoxy ... phenyl)propane dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (sometimes referred to as 6FDA), 1,2-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,2-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, 4,4'-(p-phenylenedioxy)diphthalic dianhydride, and 4,4'-(m-phenylenedioxy)diphthalic dianhydride. In addition, an example of a monocyclic aromatic tetracarboxylic dianhydride is 1,2,4,5-benzenetetracarboxylic dianhydride, and an example of a condensed polycyclic aromatic tetracarboxylic dianhydride is 2,3,6,7-naphthalenetetracarboxylic dianhydride.

Among these, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 2,2',3,3'-biphenyl tetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenoxyphenyl)propane dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA), 1,2-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, Examples of the dianhydride include 1,2-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, 4,4'-(p-phenylenedioxy)diphthalic dianhydride, and 4,4'-(m-phenylenedioxy)diphthalic dianhydride, and more preferably 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA), bis(3,4-dicarboxyphenyl)methane dianhydride, and 4,4'-(p-phenylenedioxy)diphthalic dianhydride. These can be used alone or in combination of two or more types.

Examples of aliphatic tetracarboxylic acid dianhydrides include cyclic or non-cyclic aliphatic tetracarboxylic acid dianhydrides. Cyclic aliphatic tetracarboxylic acid dianhydrides are tetracarboxylic acid dianhydrides having an alicyclic hydrocarbon structure, and specific examples thereof include cycloalkane tetracarboxylic acid dianhydrides such as 1,2,4,5-cyclohexane tetracarboxylic acid dianhydride, 1,2,3,4-cyclobutane tetracarboxylic acid dianhydride, and 1,2,3,4-cyclopentane tetracarboxylic acid dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, dicyclohexyl-3,3',4,4'-tetracarboxylic acid dianhydride, and positional isomers thereof. These can be used alone or in combination of two or more. Specific examples of non-cyclic aliphatic tetracarboxylic acid dianhydrides include 1,2,3,4-butane tetracarboxylic acid dianhydride and 1,2,3,4-pentane tetracarboxylic acid dianhydride, and the like, and these can be used alone or in combination of two or more. Additionally, a combination of a cyclic aliphatic tetracarboxylic acid dianhydride and an acyclic aliphatic tetracarboxylic acid dianhydride may be used.

Among the above tetracarboxylic dianhydrides, from the viewpoint of easily increasing the tensile modulus, puncture strength, surface hardness, transparency, flexibility, and bending resistance of the optical film and easily reducing the YI value, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 2,2',3,3'-biphenyl tetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 2,2-bis(3,4-diphenylsulfone tetracarboxylic dianhydride, Preferred are 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride, and mixtures thereof, more preferred are 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride, and mixtures thereof, and even more preferred are 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA).

Examples of dicarboxylic acid compounds used in the synthesis of the resin include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and acid chloride compounds and acid anhydrides related thereto, and two or more of them may be used in combination. Specific examples include terephthalic acid, isophthalic acid, 2-methoxyterephthalic acid, 2-methylterephthalic acid, 2,5-bis(trifluoromethyl)terephthalic acid, isophthalic acid, 2,5-dimethylterephthalic acid, 2,5-dimethoxyterephthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 3,3'-biphenyldicarboxylic acid, 2,2'-bis(trifluoromethyl)-4,4'-biphenyldicarboxylic acid, dicarboxylic acid compounds of chain hydrocarbons having 8 or less carbon atoms, compounds in which two benzoic acids are linked by a single bond, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, or a phenylene group, and acid chloride compounds thereof. Among these dicarboxylic acid compounds, from the viewpoint of easily increasing the tensile modulus, puncture strength and bending resistance of the optical film, 4,4'-oxybisbenzoic acid, terephthalic acid, isophthalic acid, 2-methoxyterephthalic acid, 2-methylterephthalic acid, 2,5-dimethylterephthalic acid, 2,5-dimethoxyterephthalic acid, 2,5-bis(trifluoromethyl)terephthalic acid, 2,2'-bis(trifluoromethyl)-4,4'-biphenyldicarboxylic acid and acid chlorides thereof are preferred, and 2-methoxyterephthalic acid, 2-methylterephthalic acid, 2,5-dimethylterephthalic acid chloride (DMTPC), 2,5-dimethoxyterephthalic acid chloride (DMTPC) and 2,5-dimethoxyterephthalic acid chloride (DMTPC) are preferred. Of these, terephthaloyl chloride (MOTPC), 2,5-bis(trifluoromethyl)terephthalic acid chloride (6FTPC), terephthaloyl chloride (TPC), and isophthaloyl chloride are more preferred, and terephthaloyl chloride (TPC), 2-methoxyterephthalic acid, 2-methylterephthalic acid, 2,5-dimethylterephthalic acid chloride (DMTPC), and 2,5-dimethoxyterephthalic acid chloride (MOTPC) are even more preferred, and 2-methoxyterephthalic acid, 2-methylterephthalic acid, 2,5-dimethylterephthalic acid chloride (DMTPC), and 2,5-dimethoxyterephthalic acid chloride (MOTPC) are even more preferred.

The polyimide resin may be a product obtained by further reacting other tetracarboxylic acids and tricarboxylic acids, as well as their anhydrides and derivatives, in addition to the tetracarboxylic acid compounds used in the synthesis of the resin, as long as the various physical properties of the optical film are not impaired.

Other tetracarboxylic acids include water adducts of the anhydrides of the above tetracarboxylic acid compounds.

Examples of the tricarboxylic acid compound include aromatic tricarboxylic acids, aliphatic tricarboxylic acids, and acid chloride compounds and acid anhydrides related thereto, and two or more of these may be used in combination. Specific examples include anhydrides of 1,2,4-benzenetricarboxylic acid, acid chloride compounds of 1,3,5-benzenetricarboxylic acid, 2,3,6-naphthalenetricarboxylic-2,3-anhydride, and compounds in which phthalic anhydride and benzoic acid are linked via a single bond, -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, or a phenylene group.

In producing the resin, the amount of the diamine compound, tetracarboxylic acid compound and/or dicarboxylic acid compound used can be appropriately selected according to the ratio of each structural unit of the desired resin.

In the production of the resin, the reaction temperature of the diamine compound, tetracarboxylic acid compound, and dicarboxylic acid compound is not particularly limited, but is, for example, 5 to 350°C, preferably 20 to 200°C, and more preferably 25 to 100°C. The reaction time is also not particularly limited, but is, for example, about 30 minutes to 10 hours. If necessary, the reaction may be carried out under an inert atmosphere or reduced pressure. In a preferred embodiment, the reaction is carried out under normal pressure and/or an inert gas atmosphere with stirring. In addition, the reaction is preferably carried out in a solvent that is inert to the reaction. The solvent is not particularly limited as long as it does not affect the reaction, and examples of the solvent include alcohol solvents such as water, methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, 1-methoxy-2-propanol, 2-butoxyethanol, and propylene glycol monomethyl ether; ester solvents such as ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, γ-butyrolactone, γ-valerolactone, propylene glycol methyl ether acetate, and ethyl lactate; acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, and the like. Examples of suitable solvents include ketone-based solvents such as methylisobutyl ketone, 2-heptanone, and methylisobutyl ketone; aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; alicyclic hydrocarbon solvents such as ethylcyclohexane; aromatic hydrocarbon solvents such as toluene and xylene; nitrile-based solvents such as acetonitrile; ether-based solvents such as tetrahydrofuran and dimethoxyethane; chlorine-containing solvents such as chloroform and chlorobenzene; amide-based solvents such as N,N-dimethylacetamide and N,N-dimethylformamide; sulfur-containing solvents such as dimethylsulfone, dimethylsulfoxide, and sulfolane; carbonate-based solvents such as ethylene carbonate and propylene carbonate; and combinations thereof. Among these, amide-based solvents can be preferably used from the viewpoint of solubility.

In the imidization step in the production of polyimide resins, imidization can be carried out in the presence of an imidization catalyst. Examples of the imidization catalyst include aliphatic amines such as tripropylamine, dibutylpropylamine, and ethyldibutylamine; alicyclic amines (monocyclic) such as N-ethylpiperidine, N-propylpiperidine, N-butylpyrrolidine, N-butylpiperidine, and N-propylhexahydroazepine; azabicyclo[2.2.1]heptane, azabicyclo[3.2.1]octane, azabicyclo[2.2.2]octane, and azabicyclo[3.2. 2] Alicyclic amines (polycyclic) such as nonane; and aromatic amines such as pyridine, 2-methylpyridine (2-picoline), 3-methylpyridine (3-picoline), 4-methylpyridine (4-picoline), 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2,4-dimethylpyridine, 2,4,6-trimethylpyridine, 3,4-cyclopentenopyridine, 5,6,7,8-tetrahydroisoquinoline, and isoquinoline. In addition, from the viewpoint of facilitating the imidization reaction, it is preferable to use an acid anhydride together with the imidization catalyst. Examples of the acid anhydride include conventional acid anhydrides used in imidization reactions, and specific examples thereof include aliphatic acid anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride, and aromatic acid anhydrides such as phthalic acid.

Polyimide-based resins and polyamide-based resins may be separated, purified, and isolated by conventional methods, such as filtration, concentration, extraction, crystallization, recrystallization, column chromatography, or a combination of these separation methods. In a preferred embodiment, a large amount of alcohol such as methanol is added to a reaction solution containing a transparent polyamideimide resin to precipitate the resin, which can then be isolated by concentration, filtration, drying, etc.

<Additives>
The optical film of the present invention may further contain additives, such as fillers, UV absorbers, brighteners, antioxidants, pH adjusters, and leveling agents.

(Filler)
The optical film of the present invention may contain at least one filler. Examples of the filler include organic particles and inorganic particles, and preferably inorganic particles. Examples of the inorganic particles include metal oxide particles such as silica, zirconia, alumina, titania, zinc oxide, germanium oxide, indium oxide, tin oxide, indium tin oxide, antimony oxide, and cerium oxide, and metal fluoride particles such as magnesium fluoride and sodium fluoride. Among these, from the viewpoint of increasing the elastic modulus and/or tear strength of the optical film and easily improving the impact resistance, silica particles, zirconia particles, and alumina particles are preferably used, and silica particles are more preferably used. These fillers can be used alone or in combination of two or more kinds.

The average primary particle diameter of the filler, preferably silica particles, is 1 nm or more, more preferably 5 nm or more, even more preferably 10 nm or more, even more preferably 15 nm or more, and particularly preferably 20 nm or more, and is preferably 100 nm or less, more preferably 90 nm or less, even more preferably 80 nm or less, even more preferably 70 nm or less, especially preferably 60 nm or less, especially more preferably 50 nm or less, and especially more preferably 40 nm or less. When the average primary particle diameter of the silica particles is within the above range, aggregation of the silica particles is suppressed, and the optical properties of the obtained optical film are easily improved. The average primary particle diameter of the filler can be measured by the BET method. The average primary particle diameter may also be measured by image analysis using a transmission electron microscope or a scanning electron microscope.

The content of the filler, for example, inorganic particles, especially silica particles, in the optical film of the present invention is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 45% by mass or less, even more preferably 40% by mass or less, and preferably 0% by mass or more, based on the total mass of the optical film. When the content of the filler is equal to or less than the above upper limit, it is easy to increase the elastic modulus of the obtained optical film and improve the optical properties of the optical film. Here, the tensile elastic modulus of the optical film tends to be increased by increasing the content of fillers such as silica particles, but if the content of fillers such as silica particles is too high, it is difficult for the obtained optical film to satisfy the above formulas (1) to (3). In addition, the puncture strength of the optical film is likely to decrease. Therefore, in the optical film of the present invention, it is preferable to set the content of silica particles to equal to or less than the above upper limit, from the viewpoint of increasing the tensile elastic modulus of the optical film, increasing the puncture strength, and easily maintaining high visibility in a wide angle direction. In this specification, for example, when the content of silica particles in an optical film is equal to or less than the upper limit relative to the total mass of the optical film, this means that the content of silica particles is 0% by mass, i.e., no silica particles are contained, or even if they are contained, the amount is equal to or less than the upper limit.

(Ultraviolet absorber)
The optical film of the present invention may further contain an ultraviolet absorber. The ultraviolet absorber may be appropriately selected from those that are commonly used as ultraviolet absorbers in the field of resin materials. The ultraviolet absorber may contain a compound that absorbs light with a wavelength of 400 nm or less. Examples of ultraviolet absorbers include triazine-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzoate-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, and salicylate-based ultraviolet absorbers. These may be used alone or in combination of two or more. When the optical film contains an ultraviolet absorber, deterioration of the resin is suppressed, so that the visibility can be improved when the optical film of the present invention is applied to a display device or the like. In this specification, the term "based compound" refers to a derivative of the compound to which the term "based compound" is attached. For example, the term "benzophenone-based compound" refers to a compound having benzophenone as a parent skeleton and a substituent bonded to benzophenone. Suitable commercially available ultraviolet absorbers include, for example, Sumisorb (registered trademark) 340 manufactured by Sumika Chemtex Co., Ltd., Adeka STAB (registered trademark) LA-31 manufactured by ADEKA Corporation, and Tinuvin (registered trademark) 1577 manufactured by BASF Japan Ltd.

When the optical film of the present invention contains an ultraviolet absorber, the content of the ultraviolet absorber is preferably 0.01 to 10 parts by mass, more preferably 1 to 8 parts by mass, and even more preferably 2 to 7 parts by mass, per 100 parts by mass of the polyamideimide resin contained in the optical film. When the content of the ultraviolet absorber is equal to or greater than the above lower limit, ultraviolet absorbency is easily improved. When the content of the ultraviolet absorber is equal to or less than the above upper limit, decomposition of the ultraviolet absorber due to heat during production of the substrate can be suppressed, and optical properties can be easily improved, for example, haze can be easily reduced.

The use of the optical film of the present invention is not particularly limited, and it may be used for various purposes. The optical film of the present invention may be a single layer or a laminate, and the optical film of the present invention may be used as it is, or may be used as a laminate with other films. The optical film of the present invention has excellent visibility in a wide angle direction, and is therefore useful as an optical film in image display devices and the like. When the optical film is a laminate, all layers laminated on one or both sides of the optical film are referred to as the optical film.

The use of the optical film of the present invention is not particularly limited, and it may be used for various purposes. The optical film of the present invention has excellent visibility in wide-angle directions, and is therefore useful as an optical film in image display devices and the like. In particular, the optical film of the present invention is useful as a front panel of an image display device, in particular a front panel (window film) of a flexible display. A flexible display has, for example, a flexible functional layer and the above-mentioned optical film that is layered on the flexible functional layer and functions as a front panel. That is, the front panel of the flexible display is placed on the viewing side above the flexible functional layer. This front panel has the function of protecting the flexible functional layer.

<Method of Manufacturing Optical Film>
The optical film of the present invention can be produced, but is not limited to, by the following process, for example:
(a) preparing a liquid containing the resin and optionally the filler (hereinafter, sometimes referred to as varnish) (varnish preparation step);
(b) a step of applying the varnish to a substrate to form a coating film (coating step); and (c) a step of drying the applied liquid (coating film) to form an optical film (optical film forming step).
The composition can be produced by a method comprising the steps of:

In the varnish preparation process, the resin is dissolved in a solvent, and the filler and other additives are added as necessary, followed by stirring and mixing to prepare the varnish.

The solvent used in preparing the varnish is not particularly limited as long as it can dissolve the resin. Examples of such solvents include amide-based solvents such as N,N-dimethylacetamide (hereinafter sometimes abbreviated as DMAc) and N,N-dimethylformamide (hereinafter sometimes abbreviated as DMF); lactone-based solvents such as γ-butyrolactone (hereinafter sometimes abbreviated as GBL) and γ-valerolactone; sulfur-containing solvents such as dimethylsulfone, dimethylsulfoxide, and sulfolane; carbonate-based solvents such as ethylene carbonate and propylene carbonate; and combinations thereof. Among these, from the viewpoint of easily producing an optical film that satisfies the formulas (1) to (3), the solvent used in the varnish is preferably an amide-based solvent or a lactone-based solvent. These solvents can be used alone or in combination of two or more kinds. The varnish may also contain water, alcohol-based solvents, ketone-based solvents, non-cyclic ester-based solvents, ether-based solvents, and the like. The solid content concentration of the varnish is preferably 1 to 25% by mass, more preferably 5 to 20% by mass.

In the coating process, the varnish is applied onto the substrate by a known coating method to form a coating film. Known coating methods include, for example, wire bar coating, roll coating methods such as reverse coating and gravure coating, die coating, comma coating, lip coating, screen coating, fountain coating, and drip molding.

In the optical film forming process, the coating film is dried (referred to as first drying), and after peeling from the substrate, the dried coating film is further dried (referred to as second drying or post-baking treatment) to form an optical film. The first drying may be performed under an inert atmosphere or reduced pressure conditions as necessary. The first drying is preferably performed under negative pressure conditions, such as in a negative tenter furnace, at a relatively low temperature over a long period of time. When the first drying is performed under negative pressure conditions, the transmission image clarity value of the optical film produced is likely to satisfy formulas (1) to (3), the total light transmittance of the optical film is likely to be increased, and the haze and YI are likely to be reduced, although the reason is not clear. This is thought to be because the solvent volatilized and removed from the optical film under the first drying conditions is prevented from remaining on the optical film surface, resulting in a uniform surface of the optical film. In addition, the surface of the optical film is likely to be uniform by performing the first drying over a long period of time at a relatively low temperature, and the transmission image clarity value of the optical film produced is likely to satisfy formulas (1) to (3). In addition, because the oxidative deterioration of the resin during drying is suppressed, it is easier to increase the total light transmittance of the optical film and to reduce the haze and YI.

Here, when the optical film of the present invention is industrially produced, the actual production environment is often unfavorable for increasing the visibility in the wide-angle direction compared to the production environment at the laboratory level, and as a result, it may be difficult to increase the visibility of the optical film in the wide-angle direction. As described above, it is preferable to perform the first drying under negative pressure conditions at a relatively low temperature for a long time. However, at the laboratory level, the first drying can be performed in a sealed dryer, so that the surface of the optical film is relatively unlikely to become rough due to external factors. In contrast, when the optical film is industrially produced, for example, a large area needs to be heated in the first drying, and a blower may be used during heating. As a result, the surface condition of the optical film is easily roughened, making it difficult to increase the visibility of the optical film in the wide-angle direction.

When drying is performed by heating, the temperature of the first drying is preferably 60 to 150°C, more preferably 60 to 130°C, and even more preferably 70 to 120°C, particularly when considering the above-mentioned external factors in industrial production of optical films. The time of the first drying is preferably 5 to 60 minutes, more preferably 10 to 40 minutes. Particularly when considering the above-mentioned external factors in industrial production of optical films, it is preferable to perform the first drying under drying temperature conditions of three or more stages. The multi-stage conditions can be performed under the same or different temperature conditions and/or drying times in each stage, and drying may be performed in, for example, 3 to 10 stages, preferably 3 to 8 stages. When the first drying is performed under multi-stage conditions of three or more stages, the transmission image clarity value of the optical film produced is more likely to satisfy the formulas (1) to (3), and the visibility in the wide-angle direction is improved. In an embodiment under multi-stage conditions of three or more stages, it is preferable that the temperature profile of the first drying includes a temperature rise and a temperature fall. That is, the first drying conditions in the optical film forming process are preferably heating temperature conditions with a temperature profile of three or more stages including temperature rise and temperature fall. In an example of a four-stage temperature profile, the temperatures of the first drying are 70 to 90°C (first temperature), 90 to 120°C (second temperature), 80 to 120°C (third temperature), and 80 to 100°C (fourth temperature) in that order. In this example, the temperature of the first drying is raised from the first temperature to the second temperature, then lowered from the second temperature to the third temperature, and further lowered from the third temperature to the fourth temperature. Here, the time of the first drying is, for example, 5 to 15 minutes in each stage. It is preferable that the first drying is performed so that the amount of the remaining solvent in the dried coating film is preferably 5 to 15 mass%, more preferably 6 to 12 mass%, based on the mass of the dried coating film. When the amount of remaining solvent is within the above range, the peelability of the dried coating film from the substrate is good, and the transmission image clarity value of the produced optical film is likely to satisfy formulas (1) to (3).

The temperature of the second drying is preferably 150 to 300°C, more preferably 180 to 250°C, and even more preferably 180 to 230°C. The time of the second drying is preferably 10 to 60 minutes, and more preferably 30 to 50 minutes.

The second drying may be performed by a sheet-by-sheet method, but in the case of industrial production, it is preferable to perform the second drying by a roll-to-roll method from the viewpoint of production efficiency. In the sheet-by-sheet method, it is preferable to dry the film in a state in which it is uniformly stretched in the in-plane direction.
In the roll-to-roll method, from the viewpoint that the obtained optical film easily satisfies the formulae (1) to (3), it is preferable to dry the dried coating film in a state stretched in the conveying direction, and the conveying speed is preferably 0.1 to 5 m/min, more preferably 0.2 to 3 m/min, and even more preferably 0.7 to 2.5 m/min. The second drying may be performed under one-stage or multi-stage conditions. The multi-stage conditions can be preferably performed under at least one selected from the same or different temperature conditions, drying time, and hot air speed in each stage, and drying may be performed in, for example, 3 to 10 stages, preferably 3 to 8 stages. From the viewpoint that the optical film easily satisfies the ranges of the formulae (1) to (3), it is preferable to perform the drying under multi-stage conditions. In addition, in each stage, the hot air speed is preferably 5 to 20 m/min, more preferably 10 to 15 m/min, and even more preferably 11 to 14 m/min, from the viewpoint that the transmission image clarity value of the produced optical film easily satisfies the formulae (1) to (3).

When the optical film of the present invention has a hard coat layer, the hard coat layer can be formed, for example, by applying a curable composition to at least one surface of the optical film to form a coating film, and then irradiating the coating film with high-energy radiation to cure the coating film.

Examples of the substrate include, for example, a metal-based SUS plate, and for example, a resin-based PET film, PEN film, other polyimide-based resin or polyamide-based resin film, cycloolefin polymer (COP) film, acrylic film, or the like, or a resin film having a hard coat layer, glass substrate, etc. Among them, from the viewpoint of excellent smoothness and heat resistance and from the viewpoint of the optical film's transmission image clarity value easily satisfying the mathematical formulas (1) to (3), PET film, COP film, resin film having a hard coat layer, SUS plate, glass plate, etc. are preferred, and further, from the viewpoint of adhesion to the optical film and cost, SUS plate and resin film having a hard coat layer are more preferred, and SUS plate and PET film having a hard coat layer are even more preferred.

From the viewpoint of easily manufacturing an optical film satisfying the above formulas (1) to (3), it is preferable to perform the drying of the coating film in the above optical film forming process by a manufacturing method including a process of drying the coating film to a predetermined solvent amount, peeling off the substrate to obtain a raw film, and a heating process of heating the raw film in a tenter furnace whose inside is divided into a plurality of spaces. Furthermore, in the tenter furnace, it is preferable that the heating process is performed by a hot air treatment method in at least one space, and the heating process is performed by a radiation treatment method in at least one space. Note that the tenter furnace refers to a furnace in which both ends in the width direction of the film are fixed and heated. Note that the heating device for heating the raw film, including the tenter furnace, is also referred to as an oven in this specification. It is also preferable that the pressure inside the tenter furnace is adjusted so that the pressure inside the tenter furnace is negative relative to the pressure outside the tenter furnace.

The manufacturing method of the optical film of this embodiment will be described with reference to the drawings. FIG. 4 is a process cross-sectional view that shows a schematic diagram of a preferred embodiment of the manufacturing method of the optical film in one embodiment of the present invention. In FIG. 4, a raw material film 44 containing at least a polyimide resin and/or a polyamide resin is carried into a tenter furnace 100, heated in a heating zone in the tenter furnace 100, and then carried out from the tenter furnace 100. In this specification, the film before the heating process and the film during the heating process or being carried through the oven, although there are changes over time in the amount of solvent, etc., are referred to as the raw material film, and the film carried out of the oven after the heating process is referred to as the optical film.

The raw film 44 may be unwound from a roll and fed into the tenter furnace 100, or may be fed into the tenter furnace continuously from the immediately preceding step. FIG. 5 is a process cross-sectional view that shows a schematic diagram of a preferred embodiment of the heating step in the optical film manufacturing method of the present invention. As shown in FIG. 5, the raw film 44 is preferably fed through the tenter furnace with both ends of the film fixed in the direction perpendicular to the film feed direction (MD direction, also called the longitudinal direction). Fixing may be performed, for example, by a gripping device 43.

Both ends can be fixed using a gripping device such as a pin sheet, clip, or film chuck that is generally used in film manufacturing equipment. The fixed ends can be adjusted appropriately depending on the gripping device used, but it is preferable to fix them at a distance of 50 cm or less from the end of the film. As shown in FIG. 5, the raw film may be conveyed while being gripped at both ends by multiple gripping devices 43. The multiple gripping devices 43 installed at one end of the film are preferably spaced apart from each other such that defects such as cracks caused by flapping of the film or dimensional changes due to heating can be suppressed. The distance between adjacent gripping devices is preferably 1 to 50 mm, more preferably 3 to 25 mm, and even more preferably 5 to 10 mm. In addition, the gripping devices are preferably installed so that when a straight line perpendicular to the film transport axis is aligned with the center of the gripping part of any gripping device at one end of the film, the distance between the intersection of the straight line and the other end of the film and the center of the gripping part of the gripping device closest to the intersection is preferably 3 mm or less, more preferably 2 mm or less, and even more preferably 1 mm or less. This reduces the difference in stress between the opposing ends of the film, improving the homogeneity of the resulting optical film. In addition, by drying the film while fixing it using a gripping device under these conditions, flapping of the film during drying is suppressed, making it easier to produce the optical film of the present invention that satisfies the above formulas (1) to (3).

An example of an operation for fixing both ends of the film with a gripping device is a method in which both ends of the film in the width direction are fixed with multiple film chucks arranged opposite each other in the width direction of the film before or after the film is carried into the tenter furnace at an appropriate time. These operations suppress the flapping of the film, and an optical film can be obtained in which defects such as uneven thickness and scratches are sufficiently suppressed. In addition, it becomes easier to manufacture the optical film of the present invention that satisfies the above formulas (1) to (3). The fixing of both ends of the film may be performed inside the tenter furnace or after the film is carried out from the tenter furnace, as long as it is released at an appropriate time after the heating process is performed.

The total length of the tenter furnace used in the heating process in the film transport direction is usually 10 to 100 m, preferably 15 to 80 m, and more preferably 15 to 60 m. The inside of the tenter furnace may be one space or may be divided into multiple spaces, but in the embodiment of the present invention, a tenter furnace in which the heating process is performed is adopted in which the inside is divided into multiple spaces. The space may be a space in which the temperature conditions, wind speed conditions, etc. can be controlled, and it does not have to have a physical boundary such as a partition plate. When the inside of the tenter furnace is divided into multiple spaces, it may be divided into multiple spaces perpendicular or parallel to the film transport direction. The number of spaces is usually 2 to 20, preferably 3 to 18, more preferably 4 to 15, and even more preferably 5 to 10. Regardless of the internal structure of the tenter furnace, the entire tenter furnace may be a heating zone, or a part of the inside may be a heating zone. Referring to FIG. 4, all three of zones 40, 41, and 42 may be heating zones, or only one of them, for example, zone 42, may be a heating zone.

A plurality of tenter furnaces may be used. In this case, the number of tenter furnaces is not particularly limited, but may be, for example, 2 to 12. The inside of each tenter furnace may have the structure described above. A plurality of tenter furnaces may be installed in succession so that the film is transported without being exposed to the outside air. When a plurality of tenter furnaces are used, all of the tenter furnaces may be heating zones, or some of the tenter furnaces may be heating zones. In addition to the tenter furnaces, ovens may be used in combination as other equipment. In this specification, oven means equipment that can heat the film, and includes heating furnaces and drying furnaces. The heating furnace may be either a hot air treatment or a radiation treatment, or may be a heating furnace that uses both. When an oven is used in combination, the internal structure of the ovens, the number of ovens used, and the heating conditions may be appropriately adjusted within the range in which the optical film of the present invention can be obtained, but it is preferable that they are the same as the tenter furnaces described in this specification.

When the inside of the tenter furnace is divided into a plurality of spaces, the circulation and exhaust of air inside the tenter furnace is preferably performed in each space, and when there are a plurality of tenter furnaces, the circulation and exhaust of air inside the tenter furnace is preferably performed in each tenter furnace. From the viewpoint of facilitating the production of the optical film of the present invention that satisfies the above formulas (1) to (3), the pressure inside the tenter furnace is preferably adjusted so that the pressure inside the tenter furnace is negative relative to the pressure outside the tenter furnace. The temperature inside the tenter furnace is preferably adjustable for each tenter furnace, and when the inside of the tenter furnace is divided into a plurality of spaces, it is preferable that the temperature can be adjusted independently for each space. The temperature settings for each space may be the same or different. However, it is preferable that the temperature of each tenter furnace or space satisfies the temperature range described below.

In the tenter furnace 100 in which the heating process is carried out, the heating process is carried out by the hot air treatment method in at least one space, and the heating process is carried out by the radiation treatment method in at least one space. It is preferable that the heating process is carried out by the hot air treatment method in all spaces in which this process is carried out. The heating process by the radiation treatment method may be carried out in a space separate from the space by the hot air treatment method, but it is preferable that the heating process is carried out in combination with the hot air treatment method.

The heating process in the hot air treatment method can be carried out by installing a nozzle that blows out hot air inside the tenter oven. The heating process in the radiation treatment method can be carried out by installing an IR heater or the like inside the tenter oven and exposing the film to radiation.

As an example of an embodiment of the present invention, a hot air treatment method using a nozzle and a radiation treatment method using an IR heater will be described below, starting with the hot air treatment method using a nozzle.

Referring to FIG. 4, the tenter furnace 100 in which the heating step is performed has a plurality of upper nozzles 46 on its internal upper surface 100a, and a plurality of lower nozzles 47 on its internal lower surface 100b. The upper nozzles 46 and the lower nozzles 47 are provided so as to face each other in the vertical direction. For example, the nozzles may be provided in four pairs of nozzles (total of eight nozzles) as in zone 42 of FIG. 4, or in ten pairs of nozzles (total of twenty nozzles) as in zone 41 of FIG. 4, and can be appropriately installed according to the structure of the oven. The interval between adjacent nozzles is preferably 0.1 to 1 m, more preferably 0.1 to 0.5 m, and even more preferably 0.1 to 0.3 m, from the viewpoint of uniformly heating the raw material film while simplifying the structure of the tenter furnace, and from the viewpoint of easily manufacturing an optical film that satisfies the formulas (1) to (3).

When the inside of the tenter furnace is divided into multiple sections, the number of nozzles for blowing hot air provided in each space can usually be 5 to 30. From the viewpoint of facilitating the production of the optical film of the present invention that satisfies the above formula, the number of nozzles is preferably 8 to 20. When the number of nozzles is within the above range, the curvature of the floating film tends not to become too large, and the film tends to easily float between the nozzles, i.e., to float.

The upper nozzle 46 provided on the upper surface 100a of the tenter furnace 100 has an outlet at the bottom and can blow hot air downward (in the direction of arrow B). On the other hand, the lower nozzle 47 provided on the lower surface of the tenter furnace 100 has an outlet at the top and can blow hot air upward (in the direction of arrow C). Although not shown in FIG. 4, the upper nozzle 46 and the lower nozzle 47 have a depth of a predetermined size in the direction perpendicular to the paper surface of FIG. 4 so that the raw material film can be heated uniformly in the width direction. Here, it is also possible to set the nozzle direction horizontal to the film surface, but in that case, it is difficult to manufacture an optical film that satisfies formulas (1) to (3), although the reason is not clear.

In the optical film manufacturing method of this embodiment, the blowing speed of hot air from the outlets of all upper nozzles 46 and all lower nozzles 47 provided in the heating zone is preferably 2 to 25 m/sec. From the viewpoints of facilitating the production of the optical film of the present invention that satisfies the above formula and facilitating the improvement of the optical uniformity of the optical film, the blowing speed is more preferably 2 to 23 m/sec, and even more preferably 8 to 20 m/sec. From the same viewpoints, the blowing volume of air from the outlet of each nozzle 46 or 47 per meter of the nozzle length along the width direction of the raw material film is preferably 0.1 to 3 m ³ /sec, more preferably 0.1 to 2.5 m ³ /sec, and even more preferably 0.2 to 2 m ³ /sec.

When the heating process is performed under the above conditions, it is easy to produce the optical film of the present invention that satisfies the above formula, and since the film is heated uniformly, the variation in the amount of solvent remaining in the film is reduced, making it easier to obtain an optical film with a more uniform elastic modulus across the entire film surface. Therefore, variation in flexibility across the entire film surface is less likely to occur, and damage caused by differences in flexibility across the film surface can be suppressed.

In the tenter furnace, the raw film 44 is heated from room temperature to a temperature at which the solvent contained in the raw film evaporates, but since the raw film is held by the gripping device 43 so that its widthwise length remains almost unchanged, it tends to droop due to thermal expansion. If the blowing air speed and blowing air volume are within the above ranges, the raw film 44 can be heated sufficiently and drooping and flapping of the raw film 44 can be suppressed.

The hot air blowing speed can be measured at the hot air outlet of nozzles 46 and 47 using a commercially available thermal anemometer. The volume of air blown from the outlet can be calculated by multiplying the blowing air speed by the area of the outlet. From the viewpoint of measurement accuracy, it is preferable to measure the hot air blowing speed at about 10 points at the outlet of each nozzle and use the average value.

The blowing speed and blowing volume of the hot air may be appropriately adjusted depending on the physical properties (optical properties, mechanical properties, etc.) of the optical film to be produced, but in any embodiment, it is preferable that they are within the above range. This makes it easy to produce the optical film of the present invention that satisfies the above formulas (1) to (3), and makes it easy to improve the visibility of the optical film in a wide angle direction after a bending resistance test. It is more preferable that the blowing speed of the heating zone is 25 m/sec or less and the blowing volume of the heating zone is 2 ^m3 /sec or less in all heating zones.

In this embodiment, when the raw film 44 is not introduced into the tenter furnace 100, the wind speed of the hot air at the position where the raw film 44 is to be held is preferably 5 m/sec or less, and it is more preferable that the wind speed is at least in this range in the heating zone. By heating the raw film 44 using such hot air, it is easy to manufacture the optical film of the present invention that satisfies the above formulas (1) to (3), and it is easy to improve the visibility of the optical film in the wide-angle direction after the bending resistance test.

In the heating zone, the difference between the maximum and minimum values of the hot air blowing speed at the outlet of each nozzle 46, 47 in the width direction (direction perpendicular to the paper surface of FIG. 4) is preferably 4 m/sec or less. By using hot air with little variation in wind speed in the width direction in this way, it is easy to manufacture the optical film of the present invention that satisfies the above formulas (1) to (3), and it is easy to improve the visibility of the optical film in wide-angle directions after the bending resistance test.

In this embodiment, the wind speed of the hot air blown onto the film immediately after it is carried into the oven is preferably higher than the wind speed of the other transport paths inside the oven. Immediately after it is carried into the oven (hereinafter referred to as "transport path 1") refers to a distance from the oven entrance to less than 1/10 of the oven length (the length from the oven entrance to the exit) if the inside of the oven is not divided into multiple spaces. Transport path 1 refers to the space through which the film passes first if the inside of the oven is divided into multiple spaces. If multiple ovens are used, the internal structure of the first oven to be used may be the same as described above, or the oven through which the film passes first may be set to a wind speed higher than the wind speed in the second and subsequent ovens.

If the inside of the oven is not divided into multiple sections, the other transport path refers to the transport path section located 1/10 of the oven length from the oven entrance or later. If the inside of the oven is divided into multiple spaces, it refers to any space from the second onwards through which the film passes. If multiple ovens are used, the internal structure of the oven used first may be as described above, or the air speed in any of the second and subsequent ovens may be set to be slower than the air speed in the first oven passed through.

The difference between the wind speed of the transport path 1 and the wind speed of the other transport paths in the oven is preferably in the range of 0.1 to 15 m/sec. The difference in wind speed is more preferably 0.2 m/sec or more, more preferably 12 m/sec or less, even more preferably 8 m/sec or less, even more preferably 5 m/sec or less, and particularly preferably 3 m/sec or less. If the wind speed immediately after the film is introduced into the oven is made higher than the wind speed of the other transport paths in the oven so that the difference in wind speed is in the above range, the solvent in the film tends to be removed more efficiently. If the difference in wind speed is too large, the film may flutter due to the difference in wind speed, and it may be difficult to manufacture the optical film of the present invention that satisfies the above formulas (1) to (3). In addition, this may cause defects in the surface shape of the obtained optical film or variations in optical properties such as phase difference.

The difference between the wind speed of transport path 1 and the wind speed of other transport paths in the oven can be found as the difference between the wind speed of hot air blown from the nozzle installed on transport path 1 and the wind speed of hot air blown from the nozzle installed on the other transport paths. If there is a difference of 2 m/sec or more between the wind speed of hot air blown onto the film and the wind speed of hot air blown from the nozzle, it may be found as the difference in wind speed of hot air near the film on transport path 1 and the other transport paths.

The other transport path is preferably the transport path next to transport path 1 (hereinafter referred to as "transport path 2"). When the inside of the oven is not divided into multiple sections, transport path 2 refers to the transport path section located 2/10 of the oven length from the oven entrance. When the inside of the oven is divided into multiple spaces, transport path 2 refers to the second space through which the film passes. When multiple ovens are used, the internal structure of the oven used first may be the same as described above, or the air speed of the second oven may be set to be slower than that of the oven passed through first.

When the difference in wind speed between conveying path 1 and conveying path 2 is set as described above, the wind speed of the conveying paths after conveying path 2 may be within the range of the hot air blowing speed. The wind speed of the conveying paths after conveying path 2 is preferably 0.1 to 12 m/sec different from the wind speed of conveying path 1 or conveying path 2, respectively, and more preferably 0.2 to 8 m/sec different from the wind speed of conveying path 1 or conveying path 2. If the wind speed difference is within such a range, the fluttering of the film caused by the wind speed difference can be suppressed, the optical film of the present invention that satisfies the above formulas (1) to (3) can be easily manufactured, and the weight reduction rate of the obtained optical film tends to be easily adjusted to a desired range.

If the inside of the oven is not divided into multiple spaces, the difference in the air speed may be adjusted by adjusting the nozzle position, the hot air blowing speed and volume of the nozzle, the air flow inside the oven, etc. If the inside of the oven is divided into multiple spaces, the difference in the air speed may be adjusted by adjusting the nozzle position, the hot air blowing speed and volume of the nozzle, the air flow inside the oven, etc. in the first space and in subsequent spaces. If multiple ovens are used, the same procedure as described above may be followed depending on the structure of the first oven, or the nozzle position, the hot air blowing speed and volume of the nozzle, the air flow inside the oven, etc. may be set so that the air speed is different between the first oven and the second or subsequent ovens.

In the heating zone of the tenter furnace 100, the distance L (shortest distance) between the opposing upper nozzle 46 and lower nozzle 47 is preferably 150 mm or more, more preferably 150 to 600 mm, and even more preferably 150 to 400 mm. By arranging the upper nozzle and the lower nozzle at such a distance L, it is possible to more reliably suppress the fluttering of the film in each process, and it becomes easier to manufacture the optical film of the present invention that satisfies the above formulas (1) to (3).

The difference (ΔT) between the maximum and minimum temperatures in the width direction (perpendicular to the paper surface of FIG. 4) of the hot air at the outlet of each nozzle 46, 47 provided in the heating zone is preferably 2°C or less, and more preferably 1°C or less. By heating the film using hot air with a sufficiently small temperature difference in the width direction in this way, it becomes easier to manufacture the optical film of the present invention that satisfies the above formulas (1) to (3). The temperature of the hot air is preferably 150 to 400°C, more preferably 150 to 300°C, and even more preferably 150 to 250°C.

Nozzles that can be used in the optical film manufacturing method include nozzles that are generally used in film manufacturing equipment, examples of which include a jet nozzle (also called a slit nozzle), which is a nozzle with a slit-shaped outlet that extends in the width direction of the raw material film, and a punching nozzle (also called a multi-hole nozzle), which is a nozzle with an outlet with multiple openings arranged in both the transport direction and width direction of the raw material film.

The nozzles are provided on the upper surface 100a of the tenter oven 100 and are structured to blow hot air downward toward the film, and on the lower surface 100b of the tenter oven 100 and are structured to blow hot air upward toward the film.

The jet nozzle has a slit extending in the width direction of the film as a hot air outlet. The slit width is preferably 5 mm or more, more preferably 5 to 20 mm. By making the slit width 5 mm or more, the optical uniformity of the obtained optical film can be further improved. The area of the outlet per jet nozzle can be calculated by multiplying the length of the nozzle in the width direction of the jet nozzle by the slit width. The product of the area of the outlet per nozzle and the blowing air speed is the amount of hot air blown per nozzle. The amount of hot air blown per meter of the nozzle length in the width direction of the film can be calculated by dividing the amount of hot air blown by the length of the slit along the width direction of the film.

The punching nozzle may have a rectangular cross section perpendicular to its longitudinal direction, or a trapezoidal cross section that widens toward the surface facing the raw film 44. The punching nozzle has multiple openings (e.g., circular openings) on the lower surface that faces the film. The hot air outlet of the punching nozzle is composed of multiple openings provided on the outlet surface. The multiple openings are hot air outlets, and hot air is blown out from the openings at a predetermined wind speed. Multiple openings are arranged in the longitudinal direction of the film, and multiple openings are also arranged in the width direction. The openings may be arranged, for example, in a staggered pattern.

The area of the outlet of each punching nozzle can be calculated by adding up the areas of all the openings in one punching nozzle. The product of the area of the outlet of each nozzle and the blowing air speed is the volume of hot air blown out from each nozzle. By dividing this volume of hot air blown out by the length of the slit along the width direction of the film, the volume of hot air blown out per meter of nozzle length along the width direction of the film can be calculated.

When a punching nozzle is used, the difference between the maximum and minimum blowing speeds of the hot air in the width direction at the nozzle outlet can be calculated as the difference between the maximum and minimum blowing speeds of the hot air blown from multiple openings provided on the same nozzle. The difference between the maximum and minimum temperatures in the width direction of the hot air at the nozzle outlet can also be calculated in a similar manner.

If all the nozzles installed in the tenter furnace 100 are punching nozzles, the total area of the hot air outlets in the entire tenter furnace 100 can be increased. This makes it possible to reduce the wind pressure of the hot air hitting the film, and further reduce the flapping of the film. This makes it easier to manufacture the optical film of the present invention that satisfies the above formulas (1) to (3). In the tenter furnace or heating zone, the raw material film 44 is heated from room temperature to a temperature at which the solvent contained in the raw material film evaporates, but since the raw material film 44 is held by the gripping device 43 so that the length in the width direction of the raw material film 44 does not change much, it tends to sag due to thermal expansion. By using punching nozzles in the heating zone, the sagging and flapping of the raw material film 44 can be further suppressed, making it easier to manufacture the optical film of the present invention that satisfies the above formulas (1) to (3).

The size and number of each opening on the surface of the punching nozzle can be appropriately adjusted within a range in which the hot air blowing speed at each opening is 2 to 25 m/sec and the air volume blown from each nozzle is 0.1 to ³ m3/sec per meter of the nozzle length along the width direction of the film.

From the viewpoint of making the blowing air speed from each opening of the punching nozzle more uniform, it is preferable that the shape of the opening is circular. In this case, the diameter of the opening is preferably 2 to 10 mm, more preferably 3 to 8 mm.

When punching nozzles are used, the length of the surface of each nozzle in the film transport direction is preferably 50 to 300 mm. Furthermore, the distance between adjacent punching nozzles is preferably 0.3 m or less. Moreover, the ratio of the sum of the opening areas of the punching nozzles (the area of the blowing port) to the length of the punching nozzles in the film width direction (sum of the opening areas of the punching nozzles (m ² )/length of the punching nozzles in the film width direction (m)) is preferably 0.008 m or more.

By using such a punching nozzle, the area of the hot air outlet can be increased. This makes it possible to sufficiently reduce the speed of the hot air and blow out a sufficient volume of hot air, allowing the film to be heated more uniformly. As a result, it becomes easier to manufacture the optical film of the present invention that satisfies the above formulas (1) to (3).

The tenter furnace 100 in which the heating process is carried out may have an IR heater on its internal upper surface 100a or its internal lower surface 100b, similar to the nozzle, and may be arranged so as to face each other in the vertical direction. Also, multiple IR heaters may be provided. As the IR heater, an IR heater generally used in film manufacturing equipment may be used.

The radiation irradiated to the film is preferably heat radiation with a wavelength of 3 to 7 μm. In addition, in the radiation treatment method, as long as the temperature of the space in which the heating process is carried out is within the above-mentioned temperature range, radiation at a temperature 30°C or more higher than the temperature of the space may be irradiated to the raw film.

In an embodiment of the present invention, it is preferable to use the nozzles (hot air treatment method) and IR heaters (radiation treatment method) in combination in the tenter furnace 100 where the heating process is performed. In that case, the IR heaters can be installed between adjacent nozzles or between the nozzles and the inner wall of the tenter furnace (including the wall that divides the space).

In this case, the temperature of the space in which the heating process is carried out needs only to be within the above-mentioned temperature range, and in the radiation treatment method, radiation at a temperature higher than the temperature of the space may be applied to the film. The temperature of the radiation may be, for example, 30°C or more higher than the temperature of the space, or 150°C or more higher. Here, the temperature of the radiation refers to the temperature set by a device that emits radiant heat, such as the set temperature of an IR heater. The difference between the temperature of the radiation and the temperature of the radiation that hits the film is preferably 5°C or less, more preferably 3°C or less, and even more preferably 1°C or less.

When a nozzle (hot air treatment method) and an IR heater (radiation treatment method) are used in combination in the tenter furnace 100, the raw film is exposed to radiation that is higher in temperature than the temperature (ambient temperature) in the heating zone or tenter furnace, but the heating process can be carried out while preventing the temperature in the heating zone or tenter furnace from becoming too high.

The heating process using both hot air and radiation treatment is preferably carried out between the space through which the raw film first passes and a space located approximately halfway along the length of the tenter furnace, among the multiple spaces in the tenter furnace where the heating process is carried out. This not only shortens the time required for the heating process, but also allows the production of an optical film with superior uniformity of in-plane retardation.

The heating step is preferably performed in the range of 150 to 350°C. When the heating step is performed in this temperature range in the embodiment of the present invention, it tends to be easier to adjust the raw material film to the weight loss rate M described below. This temperature range is more preferably 170°C or higher, even more preferably 180°C or higher, more preferably 300°C or lower, even more preferably 250°C or lower, and particularly preferably 230°C or lower. When the temperature of the heating step is in the above range, the YI value of the obtained optical film is easily adjusted to within the above preferred range. In addition, the temperature of the space in which the heating step is performed is more preferably 170°C or higher, even more preferably 180°C or higher. The temperature in the tenter furnace in which the heating step is performed may be within the above range in the heating zone. When there are multiple tenter furnaces or when the tenter furnace is divided into multiple spaces, it can be adjusted as appropriate, but it is preferable that all tenter furnaces or spaces are within the above range.

The moving speed of the raw material film 44 in the tenter furnace 100 can be adjusted appropriately within the range of usually 0.1 to 50 m/min. The upper limit of the moving speed is preferably 20 m/min, more preferably 15 m/min. The lower limit of the moving speed is preferably 0.2 m/min, more preferably 0.5 m/min, even more preferably 0.7 m/min, and particularly preferably 0.8 m/min. If the moving speed is fast, the tenter furnace length will be long in order to ensure the desired drying time, and the equipment will tend to be large. In an embodiment of the present invention, when the moving speed of the raw material film 44 in the tenter furnace 100 is within the above range, it tends to be easy to adjust the raw material film to have the weight loss rate M described below. In addition, it is easy to manufacture an optical film that satisfies the mathematical formulas (1) to (3).

The processing time for the heating step is usually 60 seconds to 2 hours, and preferably 10 minutes to 1 hour. The processing time may be adjusted appropriately taking into consideration the conditions such as the temperature of the tenter oven, the moving speed, and the speed and volume of the hot air.

In one embodiment of the present invention, the method for producing an optical film may include an operation of changing the width of the film or an operation of conveying the film while maintaining the width during the heating step. An example of an operation of changing the width of the film includes an operation of stretching the film in the width direction. The stretching ratio is preferably 0.7 to 1.5 times, more preferably 0.8 to 1.4 times, and even more preferably 0.8 to 1.3 times. An example of an operation of conveying the film while maintaining the width includes an operation of maintaining the film so that the length in the width direction remains almost unchanged. The optical film obtained through these operations may have a length of about 0.7 to 1.5 times the length in the width direction of the raw material film, and may be stretched, equal to, or shrunk from the length in the width direction of the raw material film. The stretching ratio is determined as the ratio of the width of the film after stretching (excluding the portion to be gripped) to the width of the film excluding the portion to be gripped.
In FIG. 5, in the operation of stretching the film in the width direction, the stretching ratio exceeding 1 is shown by a solid line, and the stretching ratio being equal to or less than 1 is shown by a dotted line.

After the heating process, the optical film is removed from the tenter furnace and may be continuously supplied to the next process, or may be wound into a roll and supplied to the next process. When the optical film is wound into a roll, it may be wound with a surface protective film and other films such as other optical films laminated thereon. The surface protective film laminated on the optical film may be the same as the surface protective film laminated on the raw material film described below. The thickness of the surface protective film laminated on the optical film is usually 10 to 100 μm, preferably 10 to 80 μm.

<Raw film>
The raw film supplied to the heating step contains at least a polyimide resin and/or a polyamide resin. The raw film preferably contains the same components as those contained in the varnish used to form the raw film described below, but they do not have to be the same because structural changes of the components and evaporation of a part of the solvent may occur. The raw film may be a self-supporting film or may be a gel film.

From the viewpoint of facilitating the production of an optical film that satisfies the formulas (1) to (3), it is preferable that a part of the solvent is removed from the varnish so that the weight loss rate M from 120°C to 250°C determined by thermogravimetry-differential thermal analysis (hereinafter sometimes referred to as "TG-DTA measurement") is preferably about 1 to 40%, more preferably 3 to 20%, even more preferably 5 to 15%, and particularly preferably 5 to 12%, regardless of whether the raw material film contains an inorganic material. The weight loss rate M of the raw material film can be measured by the following method using a commercially available TG-DTA measuring device. As the TG-DTA measuring device, a TG/DTA6300 manufactured by Hitachi High-Tech Science Corporation can be used.

First, about 20 mg of a sample is obtained from the raw material film, and the sample is heated from room temperature to 120° C. at a heating rate of 10° C./min, held at 120° C. for 5 minutes, and then heated to 400° C. at a heating rate of 10° C./min while measuring the change in weight of the sample. Next, from the results of the TG-DTA measurement, the weight loss rate M (%) from 120° C. to 250° C. can be calculated using the following formula. In the formula, W ₀ represents the weight of the sample after being held at 120° C. for 5 minutes, and W ₁ represents the weight of the sample at 250° C.
M(%)=100−(W ₁ /W ₀ )×100

If the weight loss rate M of the raw material film is relatively large, when the raw material film is wound up as a laminate with a substrate or a surface protection film, deformation of the laminate such as bending is suppressed, and the winding properties of the laminate tend to improve. In addition, it becomes easier to manufacture an optical film that satisfies the formulas (1) to (3).

If the weight loss rate M of the raw film is relatively small, when the raw film is wound up as a laminate with a substrate or a surface protective film, the raw film tends not to stick to the substrate or the surface protective film. Therefore, the laminate can be easily unwound from the roll while maintaining the uniform transparency of the raw film.

The raw film can be formed by drying the coating film and peeling it off from the substrate. The coating film can usually be dried at a temperature of 50 to 350°C. If necessary, the coating film may be dried in an inert atmosphere or under reduced pressure. The raw film obtained as described above can be supplied to the heating step to produce the optical film of the present invention. The raw film may be continuously transported and supplied to the heating step, or may be wound up and then supplied.

<Functional layer>
At least one surface of the optical film of the present invention may be laminated with one or more functional layers. Examples of the functional layer include an ultraviolet absorbing layer, a hard coat layer, a primer layer, a gas barrier layer, an adhesive layer, a hue adjusting layer, and a refractive index adjusting layer. The functional layers may be used alone or in combination of two or more kinds.

(Ultraviolet absorbing layer)
The ultraviolet absorbing layer is a layer having the function of absorbing ultraviolet rays, and is composed of a main material selected from, for example, an ultraviolet curing type transparent resin, an electron beam curing type transparent resin, and a thermosetting type transparent resin, and an ultraviolet absorbing agent dispersed in this main material.

(Hard Coat Layer)
The hard coat layer is, for example, a layer that can be formed by curing a composition for forming a hard coat (hereinafter also referred to as a "hard coat composition") containing a reactive material that can form a crosslinked structure by irradiation with active energy rays or by applying thermal energy, and a layer that can be formed by irradiation with active energy rays is preferable. The active energy rays are defined as energy rays that can decompose a compound that generates active species to generate active species, and examples of such rays include visible light, ultraviolet rays, infrared rays, X-rays, α rays, β rays, γ rays, and electron beams, and preferably ultraviolet rays. The hard coat composition contains at least one polymer of a radical polymerizable compound and a cationic polymerizable compound. The thickness of the hard coat layer is not particularly limited, but from the viewpoint of easily preventing cracks in the hard coat layer or at the interface between the hard coat layer and the optical film, it is preferably 2 to 50 μm, more preferably 2 to 40 μm, even more preferably 3 to 20 μm, and even more preferably 3 to 15 μm. When the thickness of the hard coat layer is in the above range, sufficient scratch resistance can be ensured, and bending resistance is less likely to decrease, and curling problems due to curing shrinkage tend to be less likely to occur.

In the hard coat layer forming step, the coating film is irradiated with high energy rays (e.g., active energy rays) to cure the coating film to form a hard coat layer. The irradiation intensity is appropriately determined depending on the composition of the curable composition and is not particularly limited, but irradiation in a wavelength region effective for activating the polymerization initiator is preferable. The irradiation intensity is preferably 0.1 to 6,000 mW/cm ² , more preferably 10 to 1,000 mW/cm ² , and even more preferably 20 to 500 mW/cm ² . When the irradiation intensity is within the above range, an appropriate reaction time can be ensured, and yellowing and deterioration of the resin due to heat radiated from the light source and heat generated during the curing reaction can be suppressed. The irradiation time may be appropriately selected depending on the composition of the curable composition and is not particularly limited, but is set so that the integrated light amount expressed as the product of the irradiation intensity and the irradiation time is preferably 10 to 10,000 mJ/cm ² , more preferably 50 to 1,000 mJ/cm ² , and even more preferably 80 to 500 mJ/cm ² . When the accumulated light amount is within the above range, a sufficient amount of active species derived from the polymerization initiator can be generated, and the curing reaction can be more reliably promoted, and the irradiation time is not too long, so that good productivity can be maintained. In addition, by undergoing an irradiation process within this range, the hardness of the hard coat layer can be further increased, which is useful. In order to improve the smoothness of the hard coat layer and further improve the visibility of the optical film in the wide angle direction, optimization of the type of solvent, component ratio, solid content concentration, and addition of a leveling agent can be mentioned.

The radical polymerizable compound is a compound having a radical polymerizable group. The radical polymerizable group of the radical polymerizable compound may be any functional group capable of generating a radical polymerization reaction, and may include a group containing a carbon-carbon unsaturated double bond, and specifically includes a vinyl group and a (meth)acryloyl group. When the radical polymerizable compound has two or more radical polymerizable groups, these radical polymerizable groups may be the same or different from each other. The number of radical polymerizable groups that the radical polymerizable compound has in one molecule is preferably 2 or more from the viewpoint of improving the hardness of the hard coat layer. From the viewpoint of high reactivity, the radical polymerizable compound is preferably a compound having a (meth)acryloyl group, specifically, a compound called a polyfunctional acrylate monomer having 2 to 6 (meth)acryloyl groups in one molecule, or an oligomer having a molecular weight of several hundred to several thousand and having several (meth)acryloyl groups in the molecule, called an epoxy (meth)acrylate, a urethane (meth)acrylate, or a polyester (meth)acrylate, is preferably one or more selected from an epoxy (meth)acrylate, a urethane (meth)acrylate, and a polyester (meth)acrylate.

The cationic polymerizable compound is a compound having a cationic polymerizable group such as an epoxy group, an oxetanyl group, a vinyl ether group, etc. The number of cationic polymerizable groups that the cationic polymerizable compound has in one molecule is preferably 2 or more, more preferably 3 or more, from the viewpoint of improving the hardness of the hard coat layer.
In addition, among the cationic polymerizable compounds, compounds having at least one of epoxy group and oxetanyl group as cationic polymerizable group are preferred. Cyclic ether groups such as epoxy group and oxetanyl group are preferred because they have small shrinkage associated with polymerization reaction. In addition, compounds having epoxy group among cyclic ether groups have the advantage that compounds with various structures are easily available, they do not adversely affect the durability of the obtained hard coat layer, and the compatibility with radical polymerizable compound is easy to control. In addition, oxetanyl group among cyclic ether groups has the advantage that the degree of polymerization is easily high compared with epoxy group, and it has the advantage of accelerating the network formation rate obtained from the cationic polymerizable compound of the obtained hard coat layer, and forming an independent network without leaving unreacted monomer in the film even in the region mixed with radical polymerizable compound.
Examples of the cationically polymerizable compound having an epoxy group include alicyclic epoxy resins obtained by epoxidizing a polyglycidyl ether of a polyhydric alcohol having an alicyclic ring or a compound containing a cyclohexene ring or a cyclopentene ring with a suitable oxidizing agent such as hydrogen peroxide or a peracid; aliphatic epoxy resins such as polyglycidyl ethers of aliphatic polyhydric alcohols or their alkylene oxide adducts, polyglycidyl esters of aliphatic long-chain polybasic acids, and homopolymers and copolymers of glycidyl (meth)acrylate; glycidyl ethers produced by reacting bisphenols such as bisphenol A, bisphenol F, and hydrogenated bisphenol A, or derivatives thereof such as alkylene oxide adducts or caprolactone adducts, with epichlorohydrin, and novolak epoxy resins, and the like, which are derived from bisphenols.

The hard coat composition may further include a polymerization initiator. The polymerization initiator may be a radical polymerization initiator, a cationic polymerization initiator, a radical and cationic polymerization initiator, etc., and may be appropriately selected and used. These polymerization initiators are decomposed by at least one of active energy ray irradiation and heating, generating radicals or cations to advance radical polymerization and cationic polymerization.
The radical polymerization initiator may be any initiator capable of releasing a substance that initiates radical polymerization by at least one of irradiation with active energy rays and heating. For example, examples of thermal radical polymerization initiators include organic peroxides such as hydrogen peroxide and perbenzoic acid, and azo compounds such as azobisbutyronitrile.
The active energy ray radical polymerization initiator includes a Type 1 radical polymerization initiator in which radicals are generated by molecular decomposition, and a Type 2 radical polymerization initiator in which radicals are generated by a hydrogen abstraction reaction in the presence of a tertiary amine, and these are used alone or in combination.
The cationic polymerization initiator may be any one that can release a substance that initiates cationic polymerization by at least one of active energy ray irradiation and heating. As the cationic polymerization initiator, aromatic iodonium salts, aromatic sulfonium salts, cyclopentadienyl iron (II) complexes, etc. can be used. These can initiate cationic polymerization by either active energy ray irradiation or heating or both, depending on the difference in structure.

The polymerization initiator may preferably be contained in an amount of 0.1 to 10% by mass relative to 100% by mass of the entire hard coat composition. When the content of the polymerization initiator is within the above range, curing can be sufficiently advanced, the mechanical properties and adhesion of the final coating film can be in a good range, and poor adhesion, cracking, and curling due to cure shrinkage tend to be less likely to occur.

The hard coat composition may further include at least one selected from the group consisting of a solvent and an additive.
The solvent can dissolve or disperse the polymerizable compound and the polymerization initiator, and any solvent known in the art as a solvent for hard coat compositions can be used as long as it does not impair the effects of the present invention.
The additives may further include inorganic particles, leveling agents, stabilizers, surfactants, antistatic agents, lubricants, antifouling agents, and the like.

(Adhesive layer)
The adhesive layer is a layer having an adhesive function, and has a function of adhering the optical film to other members. As a material for forming the adhesive layer, a commonly known material can be used. For example, a thermosetting resin composition or a photocurable resin composition can be used. In this case, the resin composition can be polymerized and cured by supplying energy thereto afterwards.

The adhesive layer may be a layer called a pressure sensitive adhesive (PSA), which is attached to an object by pressing. The pressure sensitive adhesive may be a pressure sensitive adhesive that is "a substance that has adhesiveness at room temperature and adheres to an adherend with light pressure" (JIS K6800), or it may be a capsule type adhesive that is "an adhesive that contains specific components in a protective coating (microcapsules) and maintains stability until the coating is destroyed by appropriate means (pressure, heat, etc.)" (JIS K6800).

(Hue Adjustment Layer)
The hue adjustment layer is a layer having a function of adjusting the hue, and is a layer capable of adjusting the laminate including the optical film to a desired hue. The hue adjustment layer is, for example, a layer containing a resin and a colorant. Examples of the colorant include inorganic pigments such as titanium oxide, zinc oxide, red iron oxide, titanium oxide-based calcined pigments, ultramarine, cobalt aluminate, and carbon black; organic pigments such as azo compounds, quinacridone compounds, anthraquinone compounds, perylene compounds, isoindolinone compounds, phthalocyanine compounds, quinophthalone compounds, threne compounds, and diketopyrrolopyrrole compounds; extender pigments such as barium sulfate and calcium carbonate; and dyes such as basic dyes, acid dyes, and mordant dyes.

(Refractive index adjusting layer)
The refractive index adjustment layer is a layer having a function of adjusting the refractive index, and is, for example, a layer having a refractive index different from that of an optical film, and capable of imparting a predetermined refractive index to the optical laminate. The refractive index adjustment layer may be, for example, a resin layer containing an appropriately selected resin and, if necessary, a pigment, or may be a thin metal film. Examples of pigments for adjusting the refractive index include silicon oxide, aluminum oxide, antimony oxide, tin oxide, titanium oxide, zirconium oxide, and tantalum oxide. The average primary particle diameter of the pigment may be 0.1 μm or less. By setting the average primary particle diameter of the pigment to 0.1 μm or less, diffuse reflection of light passing through the refractive index adjustment layer can be prevented, and a decrease in transparency can be prevented. Examples of metals used in the refractive index adjustment layer include metal oxides or metal nitrides such as titanium oxide, tantalum oxide, zirconium oxide, zinc oxide, tin oxide, silicon oxide, indium oxide, titanium oxynitride, titanium nitride, silicon oxynitride, and silicon nitride.

(Protective film)
In one embodiment of the present invention, the optical film may have a protective film on at least one side (one side or both sides). For example, when the optical film has a functional layer on one side, the protective film may be laminated on the surface on the optical film side or the surface on the functional layer side, or may be laminated on both the optical film side and the functional layer side. When the optical film has a functional layer on both sides, the protective film may be laminated on the surface on one functional layer side, or may be laminated on the surfaces on both functional layer sides. The protective film is a film for temporarily protecting the surface of the optical film or the functional layer, and is not particularly limited as long as it is a peelable film that can protect the surface of the optical film or the functional layer. Examples of the protective film include polyester-based resin films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyolefin-based resin films such as polyethylene and polypropylene films, and acrylic resin films, and are preferably selected from the group consisting of polyolefin-based resin films, polyethylene terephthalate-based resin films, and acrylic resin films. When the optical film has two protective films, each protective film may be the same or different.

The thickness of the protective film is not particularly limited, but is usually 10 to 120 μm, preferably 15 to 110 μm, and more preferably 20 to 100 μm. When the optical film has two protective films, the thicknesses of the protective films may be the same or different.

The optical film of the present invention may be a single layer or a laminate. For example, the optical film produced as described above may be used as it is, or may be used as a laminate with other films.

In a preferred embodiment of the present invention, the optical film of the present invention is very useful as a front panel of an image display device, particularly a front panel of a flexible display device (hereinafter also referred to as a "window film"), particularly a front panel of a rollable display or a foldable display. A flexible display device has, for example, a flexible functional layer and an optical film that is overlaid on the flexible functional layer and functions as a front panel. That is, the front panel of a flexible display device is disposed on the viewing side above the flexible functional layer. This front panel has the function of protecting the flexible functional layer.

Examples of image display devices include televisions, smartphones, mobile phones, car navigation systems, tablet PCs, portable game consoles, electronic paper, indicators, bulletin boards, watches, and wearable devices such as smart watches. Examples of flexible display devices include all image display devices that have flexible properties.

[Flexible display device]
The present invention also provides a flexible display device comprising the optical film of the present invention. The optical film of the present invention is preferably used as a front plate in a flexible display device, and the front plate may be called a window film. The flexible display device is composed of a laminate for a flexible display device and an organic EL display panel, and the laminate for a flexible display device is arranged on the viewing side of the organic EL display panel and is configured to be foldable. The laminate for a flexible display device may contain the optical film (window film) of the present invention, a circular polarizing plate, and a touch sensor, and although the order of lamination of these is arbitrary, it is preferable that the window film, the circular polarizing plate, the touch sensor, or the window film, the touch sensor, and the circular polarizing plate are laminated from the viewing side. If a circular polarizing plate is present on the viewing side of the touch sensor, the pattern of the touch sensor is less visible, and the visibility of the displayed image is improved, which is preferable. Each member can be laminated using an adhesive, a pressure-sensitive adhesive, or the like. In addition, a light-shielding pattern formed on at least one surface of any of the layers of the window film, the circular polarizing plate, and the touch sensor can be provided.

[Polarizer]
The flexible display device of the present invention may further include a polarizing plate, preferably a circular polarizing plate. The circular polarizing plate is a functional layer having a function of transmitting only right-handed or left-handed circularly polarized components by laminating a λ/4 retardation plate on a linear polarizing plate. For example, the circular polarizing plate is used to convert external light into right-handed circularly polarized light, block the external light that is reflected by the organic EL panel and becomes left-handed circularly polarized light, and transmit only the light-emitting component of the organic EL, thereby suppressing the influence of reflected light and making the image easier to see. In order to achieve the circular polarization function, the absorption axis of the linear polarizing plate and the slow axis of the λ/4 retardation plate theoretically need to be 45°, but in practice, they are 45±10°. The linear polarizing plate and the λ/4 retardation plate do not necessarily need to be laminated adjacent to each other, and it is sufficient that the relationship between the absorption axis and the slow axis satisfies the above-mentioned range. It is preferable to achieve complete circular polarization at all wavelengths, but this is not necessarily required in practice, so the circular polarizing plate in the present invention also includes an elliptical polarizing plate. It is also preferable to further laminate a λ/4 phase difference film on the viewing side of the linear polarizing plate to make the emerging light circularly polarized, thereby improving visibility when wearing polarized sunglasses.

A linear polarizing plate is a functional layer that transmits light vibrating in the transmission axis direction but blocks polarized light of vibration components perpendicular to the transmission axis. The linear polarizing plate may be a linear polarizer alone or a linear polarizer and a protective film attached to at least one surface of the linear polarizer. The thickness of the linear polarizing plate may be 200 μm or less, and is preferably 0.5 to 100 μm. When the thickness of the linear polarizing plate is within the above range, the flexibility tends not to decrease.

The linear polarizer may be a film-type polarizer manufactured by dyeing and stretching a polyvinyl alcohol (hereinafter also referred to as "PVA")-based film. A dichroic dye such as iodine is adsorbed to the PVA-based film oriented by stretching, or the dichroic dye is oriented by stretching the film while adsorbed to the PVA, thereby exhibiting polarization performance. The manufacture of the film-type polarizer may include other steps such as swelling, crosslinking with boric acid, washing with an aqueous solution, and drying. The stretching and dyeing steps may be performed on the PVA-based film alone, or may be performed on the PVA-based film laminated with another film such as polyethylene terephthalate. The thickness of the PVA-based film used is preferably 10 to 100 μm, and the stretching ratio is preferably 2 to 10 times.

Another example of the polarizer is a liquid crystal coating type polarizer formed by coating a liquid crystal polarizing composition. The liquid crystal polarizing composition may contain a liquid crystal compound and a dichroic dye compound. The liquid crystal compound may have a property of exhibiting a liquid crystal state, and is preferably in a highly oriented state such as a smectic phase, since it can exhibit high polarization performance. It is also preferable that the liquid crystal compound has a polymerizable functional group.
The dichroic dye is a dye that exhibits dichroism by being aligned together with the liquid crystal compound, and may have a polymerizable functional group, or the dichroic dye itself may have liquid crystallinity. Any of the compounds in the liquid crystal polarizing composition has a polymerizable functional group.

The liquid crystal polarizing composition may further include an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, etc.

The liquid crystal polarizing layer is manufactured by applying a liquid crystal polarizing composition onto an alignment film to form a liquid crystal polarizing layer. The liquid crystal polarizing layer can be formed to be thinner than a film-type polarizer. The thickness of the liquid crystal polarizing layer is preferably 0.5 to 10 μm, more preferably 1 to 5 μm.

The alignment film can be produced, for example, by applying an alignment film-forming composition onto a substrate and imparting alignment by rubbing, polarized light irradiation, or the like. The alignment film-forming composition may contain, in addition to the alignment agent, a solvent, a crosslinking agent, an initiator, a dispersant, a leveling agent, a silane coupling agent, or the like. Examples of the alignment agent include polyvinyl alcohols, polyacrylates, polyamic acids, and polyimides. When applying photoalignment, it is preferable to use an alignment agent containing a cinnamate group. The weight-average molecular weight of the polymer used as the alignment agent may be, for example, about 10,000 to 1,000,000. The thickness of the alignment film is preferably 5 to 10,000 nm, more preferably 10 to 500 nm, from the viewpoint of alignment control force.

The liquid crystal polarizing layer can be peeled off from the substrate and transferred and laminated, or the substrate can be laminated as is. It is also preferable that the substrate serves as a transparent substrate for a protective film, retardation film, or window film.

The protective film may be any transparent polymer film. Specifically, examples of the polymer film that can be used include polyolefins such as polyethylene, polypropylene, polymethylpentene, norbornene, or cycloolefin derivatives having monomer units containing cycloolefin; (modified) celluloses such as diacetyl cellulose, triacetyl cellulose, and propionyl cellulose; acrylics such as methyl methacrylate (co)polymers; polystyrenes such as styrene (co)polymers; acrylonitrile-butadiene-styrene copolymers, acrylonitrile-styrene copolymers, ethylene-vinyl acetate copolymers; polyvinyl chlorides; polyvinylidene chlorides; polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, and polyarylate; polyamides such as nylon; polyimides; polyamideimides; polyetherimides; polyethersulfones; polysulfones; polyvinyl alcohols; polyvinyl acetals; polyurethanes; and epoxy resins. In terms of excellent transparency and heat resistance, preferred are polyamide, polyamideimide, polyimide, polyester, olefin, acrylic, or cellulose-based films. These polymers can be used alone or in combination of two or more. These films are used as unstretched films or as uniaxially or biaxially stretched films. Cellulose-based films, olefin-based films, acrylic films, and polyester-based films are preferred. The protective film may be a coating type film obtained by applying and curing a cationic curing composition such as an epoxy resin or a radical curing composition such as an acrylate. If necessary, the protective film may contain a plasticizer, an ultraviolet absorber, an infrared absorber, a colorant such as a pigment or dye, a fluorescent brightener, a dispersant, a heat stabilizer, a light stabilizer, an antistatic agent, an antioxidant, a lubricant, a solvent, etc. The thickness of the protective film is preferably 200 μm or less, more preferably 1 to 100 μm. When the thickness of the protective film is in the above range, the flexibility of the protective film is less likely to decrease.

The λ/4 retardation plate is a film that imparts a phase difference of λ/4 in a direction perpendicular to the direction of propagation of incident light, i.e., in the in-plane direction of the film. The λ/4 retardation plate may be a stretched retardation plate manufactured by stretching a polymer film such as a cellulose-based film, an olefin-based film, or a polycarbonate-based film. The λ/4 retardation plate may contain a retardation regulator, a plasticizer, an ultraviolet absorber, an infrared absorber, a colorant such as a pigment or a dye, a fluorescent whitening agent, a dispersant, a heat stabilizer, a light stabilizer, an antistatic agent, an antioxidant, a lubricant, a solvent, etc., as necessary. The thickness of the stretched retardation plate is preferably 200 μm or less, more preferably 1 to 100 μm. If the thickness is within the above range, the flexibility of the film tends not to decrease.

Another example of the λ/4 retardation plate is a liquid crystal coating type retardation plate formed by coating a liquid crystal composition. The liquid crystal composition contains a liquid crystal compound having a property of exhibiting a liquid crystal state such as nematic, cholesteric, or smectic. Any compound in the liquid crystal composition, including the liquid crystal compound, has a polymerizable functional group. The liquid crystal composition may further contain an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, or the like. The liquid crystal coating type retardation plate can be manufactured by coating and curing a liquid crystal composition on an alignment film to form a liquid crystal retardation layer in the same manner as described for the liquid crystal polarizing layer. The liquid crystal coating type retardation plate can be formed to have a smaller thickness than a stretched type retardation plate. The thickness of the liquid crystal polarizing layer is preferably 0.5 to 10 μm, more preferably 1 to 5 μm. The liquid crystal coating type retardation plate can be peeled off from the substrate, transferred, and laminated, or the substrate can be laminated as it is. It is also preferable that the substrate serves as a transparent substrate for a protective film, a retardation plate, or a window film.

In general, there are many materials that exhibit larger birefringence at shorter wavelengths and smaller birefringence at longer wavelengths. In this case, since it is not possible to achieve a phase difference of λ/4 in the entire visible light range, it is often designed to have an in-plane phase difference of λ/4 around 560 nm where visibility is high, that is, preferably 100 to 180 nm, more preferably 130 to 150 nm. A reverse dispersion λ/4 retardation plate using a material with birefringence wavelength dispersion characteristics reverse to those of normal retardation plates is preferable because it can improve visibility. As such materials, it is also preferable to use those described in JP-A-2007-232873 for stretched retardation plates and JP-A-2010-30979 for liquid crystal coated retardation plates.

As another method, a technique is known in which a wideband λ/4 retardation plate is obtained by combining it with a λ/2 retardation plate (JP Patent Publication No. 10-90521). The λ/2 retardation plate is manufactured using the same materials and methods as the λ/4 retardation plate. The combination of a stretched retardation plate and a liquid crystal-coated retardation plate is arbitrary, but in either case, it is preferable to use a liquid crystal-coated retardation plate because it allows for a thinner plate.

A method of laminating a positive C plate on the circular polarizer to improve visibility in oblique directions is also known (JP Patent Publication 2014-224837). The positive C plate may be a liquid crystal-coated retardation plate or a stretched retardation plate. The retardation in the thickness direction of the retardation plate is preferably -200 to -20 nm, more preferably -140 to -40 nm.

[Touch sensor]
The flexible display device of the present invention may further include a touch sensor. The touch sensor is used as an input means. Various types of touch sensors have been proposed, such as a resistive film type, a surface acoustic wave type, an infrared type, an electromagnetic induction type, and a capacitive type, and any type may be used, but the capacitive type is preferred. The capacitive touch sensor is divided into an active area and a non-active area located on the outer periphery of the active area. The active area is an area corresponding to a display part where a screen is displayed in a display panel, and is an area where a user's touch is sensed, and the non-active area is an area corresponding to a non-display part where a screen is not displayed in a display device. The touch sensor may include a substrate having a flexible characteristic; a sensing pattern formed in the active area of the substrate; and each sensing line formed in the non-active area of the substrate for connecting to an external driving circuit via the sensing pattern and a pad part. The substrate having a flexible characteristic may be made of the same material as the polymer film. The substrate of the touch sensor is preferably one having a toughness of 2,000 MPa% or more in terms of suppressing cracks in the touch sensor. More preferably, the toughness may be 2,000 to 30,000 MPa%. Here, toughness is defined as the area under the curve up to the breaking point in a stress (MPa)-strain (%) curve obtained through a tensile test of a polymer material.

The sensing pattern may include a first pattern formed in a first direction and a second pattern formed in a second direction. The first and second patterns are arranged in different directions. The first and second patterns are formed in the same layer, and the patterns must be electrically connected to each other in order to sense a touch point. The first pattern has unit patterns connected to each other via joints, but the second pattern has a structure in which the unit patterns are separated from each other in an island form, so a separate bridge electrode is required to electrically connect the second pattern. A well-known transparent electrode material may be used as the electrode for electrically connecting the second pattern. Examples of the transparent electrode material include indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium zinc tin oxide (IZTO), indium gallium zinc oxide (IGZO), cadmium tin oxide (CTO), PEDOT (poly(3,4-ethylenedioxythiophene)), carbon nanotubes (CNT), graphene, and metal wires, which can be used alone or in combination of two or more. ITO can be preferably used as the transparent electrode material. The metal used for the metal wire is not particularly limited, and examples of the metal include silver, gold, aluminum, copper, iron, nickel, titanium, selenium, and chromium, which can be used alone or in combination of two or more.

The bridge electrode can be formed on the insulating layer on the sensing pattern, and the bridge electrode can be formed on the substrate, and the insulating layer and the sensing pattern can be formed thereon. The bridge electrode can be formed of the same material as the sensing pattern, or can be formed of a metal such as molybdenum, silver, aluminum, copper, palladium, gold, platinum, zinc, tin, titanium, or an alloy of two or more of these. Since the first pattern and the second pattern must be electrically insulated, an insulating layer is formed between the sensing pattern and the bridge electrode. The insulating layer can be formed only between the joint of the first pattern and the bridge electrode, or can be formed as a layer that covers the entire sensing pattern. When formed as a layer that covers the entire sensing pattern, the bridge electrode can connect to the second pattern through a contact hole formed in the insulating layer.

The touch sensor may further include an optical adjustment layer between the substrate and the electrode as a means for appropriately compensating for a difference in transmittance between a patterned region where a pattern is formed and a non-patterned region where a pattern is not formed, specifically, a difference in light transmittance caused by a difference in refractive index between these regions. The optical adjustment layer may include an inorganic insulating material or an organic insulating material. The optical adjustment layer may be formed by coating a photocurable composition including a photocurable organic binder and a solvent on a substrate. The photocurable composition may further include inorganic particles. The inorganic particles may increase the refractive index of the optical adjustment layer.
The photocurable organic binder may include a copolymer of each monomer, such as an acrylate monomer, a styrene monomer, a carboxylic acid monomer, etc. The photocurable organic binder may be a copolymer including different repeating units, such as an epoxy group-containing repeating unit, an acrylate repeating unit, a carboxylic acid repeating unit, etc.
Examples of the inorganic particles include zirconia particles, titania particles, alumina particles, etc. The photocurable composition may further contain various additives such as a photopolymerization initiator, a polymerizable monomer, and a curing assistant.

[Adhesive layer]
Each layer such as a window film, a polarizing plate, and a touch sensor, which form the laminate for a flexible display device, and each film member such as a linear polarizing plate and a λ/4 retardation plate which form the laminate for a flexible display device, can be bonded by an adhesive. As the adhesive, a water-based adhesive, an organic solvent-based adhesive, a solvent-free adhesive, a solid adhesive, a solvent volatilization type adhesive, a moisture-curing type adhesive, a heat-curing type adhesive, an anaerobic curing type adhesive, a water-based solvent volatilization type adhesive, an active energy ray curing type adhesive, a curing agent mixed type adhesive, a hot melt type adhesive, a pressure-sensitive adhesive, a pressure-sensitive adhesive, a re-moistening type adhesive, and the like, which are generally used, can be used. Among them, a water-based solvent volatilization type adhesive, an active energy ray curing type adhesive, and an adhesive are often used. The thickness of the adhesive layer can be appropriately adjusted according to the required adhesive strength, and is preferably 0.01 to 500 μm, more preferably 0.1 to 300 μm. The laminate for a flexible image display device may have a plurality of adhesive layers, and the thickness of each adhesive layer and the type of adhesive used may be the same or different.

The aqueous solvent volatile adhesive may be a polyvinyl alcohol polymer, a water-soluble polymer such as starch, or an aqueous dispersion polymer such as an ethylene-vinyl acetate emulsion or a styrene-butadiene emulsion. In addition to water and the aqueous polymer, a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, a dye, a pigment, an inorganic filler, an organic solvent, or the like may be blended. When bonding is performed using the aqueous solvent volatile adhesive, the aqueous solvent volatile adhesive is injected between the layers to be bonded, the layers are laminated, and the layers are dried to impart adhesiveness. When the aqueous solvent volatile adhesive is used, the thickness of the adhesive layer may be 0.01 to 10 μm, preferably 0.1 to 1 μm. When the aqueous solvent volatile adhesive is used to form multiple layers, the thickness of each layer and the type of adhesive may be the same or different.

The active energy ray curable adhesive can be formed by curing an active energy ray curable composition containing a reactive material that forms an adhesive layer by irradiating with active energy rays. The active energy ray curable composition can contain at least one polymer of a radical polymerizable compound and a cationic polymerizable compound similar to the compounds described for the hard coat composition. As the radical polymerizable compound, the same type of compound as described for the hard coat composition can be used. As the radical polymerizable compound used in the adhesive layer, a compound having an acryloyl group is preferable. In order to reduce the viscosity of the adhesive composition, it is also preferable that the composition contains a monofunctional compound.

As the cationic polymerizable compound, the same types of compounds as those described for the hard coat composition can be used. As the cationic polymerizable compound used in the active energy ray curable composition, an epoxy compound is more preferable. In order to reduce the viscosity of the adhesive composition, it is also preferable that the composition contains a monofunctional compound as a reactive diluent.

The active energy ray composition may further contain a polymerization initiator. Examples of the polymerization initiator include radical polymerization initiators, cationic polymerization initiators, and radical and cationic polymerization initiators, which may be appropriately selected and used. These polymerization initiators are decomposed by at least one of active energy ray irradiation and heating to generate radicals or cations, thereby proceeding with radical polymerization and cationic polymerization. In the description of the hard coat composition, an initiator that can initiate at least either radical polymerization or cationic polymerization by active energy ray irradiation may be used.

The active energy ray curable composition may further contain an ion trapping agent, an antioxidant, a chain transfer agent, an adhesion imparting agent, a thermoplastic resin, a filler, a flow viscosity modifier, a plasticizer, an antifoaming agent solvent, an additive, and a solvent. When two adherend layers are bonded using the active energy ray curable adhesive, the active energy ray curable composition is applied to one or both of the adherend layers, and then the layers are laminated together, and the composition is irradiated with active energy rays through one or both of the adherend layers to cure the composition, thereby bonding the layers together. When the active energy ray curable adhesive is used, the thickness of the adhesive layer is preferably 0.01 to 20 μm, more preferably 0.1 to 10 μm. When the active energy ray curable adhesive is used to form multiple layers, the thickness of each layer and the type of adhesive used may be the same or different.

The adhesive is classified into acrylic adhesives, urethane adhesives, rubber adhesives, silicone adhesives, etc. according to the main polymer, and any of these can be used. In addition to the main polymer, the adhesive may contain a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, a tackifier, a plasticizer, a dye, a pigment, an inorganic filler, etc. The components constituting the adhesive are dissolved and dispersed in a solvent to obtain an adhesive composition, and the adhesive composition is applied to a substrate and then dried to form an adhesive layer (adhesive layer). The adhesive layer may be formed directly, or a layer formed separately on a substrate may be transferred. It is also preferable to use a release film to cover the adhesive surface before adhesion. The thickness of the adhesive layer when the adhesive is used is preferably 1 to 500 μm, more preferably 2 to 300 μm. When the adhesive is used to form multiple layers, the thickness of each layer and the type of adhesive used may be the same or different.

[Shading pattern]
The light-shielding pattern may be applied as at least a part of a bezel or a housing of the flexible image display device. The light-shielding pattern hides wiring arranged at the edge of the flexible image display device, making it difficult to see, thereby improving the visibility of an image. The light-shielding pattern may be in the form of a single layer or multiple layers. The color of the light-shielding pattern is not particularly limited, and may have various colors such as black, white, and metallic colors. The light-shielding pattern may be formed of a pigment for realizing a color and a polymer such as an acrylic resin, an ester resin, an epoxy resin, a polyurethane, or a silicone. These may be used alone or in a mixture of two or more kinds. The light-shielding pattern may be formed by various methods such as printing, lithography, and inkjet. The thickness of the light-shielding pattern is preferably 1 to 100 μm, more preferably 2 to 50 μm. It is also preferable to impart a shape such as a slope in the thickness direction of the light-shielding pattern.

The present invention will be described in more detail below with reference to examples. In the examples, "%" and "parts" refer to mass% and mass parts unless otherwise specified. First, the evaluation method will be described.

<Measurement of total light transmittance>
The total light transmittance (Tt) of the optical film was measured in accordance with JIS K 7105:1981 using a fully automatic direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd.

<Haze>
In accordance with JIS K 7136:2000, the optical films obtained in the examples and comparative examples were cut to a size of 30 mm x 30 mm, and the haze (%) was measured using a haze computer (manufactured by Suga Test Instruments Co., Ltd., "HGM-2DP").

<YI value>
The YI value (Yellow Index) of the optical film was measured in accordance with JIS K 7373:2006 using an ultraviolet, visible, near infrared spectrophotometer "V-670" manufactured by JASCO Corporation. After background measurement was performed without a sample, the optical film was set in a sample holder and transmittance measurement was performed for light of 300 to 800 nm to determine tristimulus values (X, Y, Z), and the YI value was calculated based on the following formula.
YI = 100 x (1.2769X - 1.0592Z) / Y

<Measurement of weight average molecular weight>
Gel Permeation Chromatography (GPC) Measurement (1) Pretreatment Method A DMF eluent (10 mmol/L lithium bromide solution) was added to a polyamideimide film to give a concentration of 2 mg/mL, and the film was heated at 80° C. for 30 minutes with stirring. After cooling, the film was filtered through a 0.45 μm membrane filter to obtain a measurement solution.
(2) Measurement Conditions Column: Tosoh Corporation TSKgel α-2500 ((7) 7.8 mm diameter × 300 mm) × 1, α-M ((13) 7.8 mm diameter × 300 mm) × 2 Eluent: DMF (10 mmol/L lithium bromide added)
Flow rate: 1.0 mL/min Detector: RI detector Column temperature: 40° C.
Injection volume: 100 μL
Molecular weight standards: Standard polystyrene

<Thickness Measurement>
The thickness of the optical film was measured using an ABS Digimatic Indicator (manufactured by Mitutoyo Corporation, "ID-C112BS").

<Tensile modulus>
The elastic modulus of the optical films obtained in the Examples and Comparative Examples was measured at a temperature of 25° C. and a relative humidity of 50% using an “Autograph AG-IS” manufactured by Shimadzu Corporation. More specifically, a film having a length and width of 10 mm was prepared, and a stress-strain curve (S-S curve) was measured under conditions of a chuck distance of 50 mm and a tensile speed of 10 mm/min, and the elastic modulus was calculated from the slope of the curve.

<Puncture strength>
A puncture test was carried out in an environment of 25°C temperature and 55% relative humidity using an InSTRON 5982 universal testing machine in accordance with JIS Z 1707. Using a test piece having a width of 50 mm, a length of 50 mm, and a thickness of 0.05 mm, a test was carried out using a needle pressure probe having a diameter of 2.5 mm and a semicircular tip shape of 2.5 mm, a load cell of 5 kN, and a test speed of 10 mm/min, and the fracture displacement was measured. The maximum load at that time was taken as the puncture strength.

<Measurement of Transmission Image Clarity Value of Optical Film>
The transmission image clarity value of the optical film was measured by a transmission method in accordance with JIS K 7345 using an image clarity measuring instrument ("ICM-1" manufactured by Suga Test Instruments Co., Ltd.) as follows.
The optical film was placed in the image clarity measuring device. Before the optical film was placed, both sides were lightly wiped with ethanol, dried, and foreign matter was removed from the surface. Then, the light amount and cross-sectional area were adjusted, and white light adjusted to parallel light was irradiated onto the placed optical film from an angle (incident angle) inclined at 60° in the MD direction with respect to the optical film plane. The transmitted light that had passed through the optical film was passed through an optical comb that had an adjusted cross-sectional area and extended perpendicular to the optical axis of the irradiated light, and the light that had passed through the optical comb was received by a light receiver.
The optical comb (slit width: 0.125 mm) was moved by a predetermined unit width in the direction parallel to the plane of the optical comb and in the direction in which the slits in the optical comb were arranged, and the transmitted light of the optical comb was repeatedly received. As a result, a received light waveform was obtained. The maximum value M and minimum value m of the relative light amount were obtained from the obtained received light waveform. The first transmission image clarity value C ₆₀ (MD) was calculated based on the obtained M and m according to the formula (7).

A second transmission image clarity value C 60 (TD) and a third transmission image clarity value C 0 were calculated in the same manner as the first transmission image clarity value, except that the incident angle was changed to an angle inclined by ₆₀ ° in the TD direction from the perpendicular direction to the optical film plane, and to an angle perpendicular to the optical film plane (an angle inclined by ₀ °).

<Imidization rate>
The imidization rate was determined by ¹ H-NMR measurement as follows.
(1) Pretreatment Method An optical film containing a polyimide resin was dissolved in deuterated dimethyl sulfoxide (DMSO-d ₆ ) to prepare a 2% by mass solution, which was used as a measurement sample.
(2) Measurement conditions Measurement device: JEOL 400MHz NMR device JNM-ECZ400S/L1
Standard: DMSO- _d6 (2.5 ppm)
Sample temperature: room temperature Number of accumulated times: 256 Relaxation time: 5 seconds (3) Imidization rate analysis method (imidization rate of polyimide resin)
In the ¹ H-NMR spectrum obtained from the measurement sample containing the polyimide resin, the integral value of benzene proton A derived from a structure that does not change before and after imidization among the observed benzene protons was taken as Int _A. Furthermore, the integral value of amide protons derived from an amic acid structure remaining in the observed polyimide resin was taken as Int _B. From these integral values, the imidization rate of the polyimide resin was calculated based on the following formula.
Imidization rate (%)=100×(1−Int _B / Int _A )

(Imidization rate of polyamide-imide resin)
In the ¹ H-NMR spectrum obtained from the measurement sample containing the polyamideimide resin, the integral value of benzene proton C, which is derived from a structure that does not change before and after imidization among the observed benzene protons and is not affected by a structure derived from an amic acid structure remaining in the polyamideimide resin, was defined as Int _C. Furthermore, the integral value of benzene proton D, which is derived from a structure that does not change before and after imidization among the observed benzene protons and is affected by a structure derived from an amic acid structure remaining in the polyamideimide resin, was defined as Int _D. The β value was calculated from the obtained Int _C and Int _D according to the following formula.
β=Int _D /Int _C
Next, the β value of the above formula and the imidization ratio of the polyimide resin of the above formula were determined for a plurality of polyamide-imide resins, and the following correlation formula was obtained from these results.
Imidization rate (%) = k × β + 100
In the above correlation equation, k is a constant.
The imidization rate (%) of the polyamide-imide resin was obtained by substituting β into the correlation equation.

<Viscosity of Varnish>
The measurement was performed using a Brookfield E-type viscometer DV-II+Pro in accordance with JIS K 8803:2011. The measurement temperature was 25°C.

<Flexibility test>
The optical film was subjected to a bending resistance test in accordance with JIS K 5600-5-1. The bending resistance test was performed using a small tabletop bending resistance tester (manufactured by Yuasa System Co., Ltd.). The optical film after the bending resistance test was measured for transmission image clarity and haze in the same manner as in the above-mentioned measurement method. The absolute values of the differences in transmission image clarity and haze before and after the bending resistance test were taken, and the differences in transmission image clarity (first transmission image clarity value difference ΔC ₆₀ (MD), second transmission image clarity value difference ΔC ₆₀ (TD), and third transmission image clarity value difference ΔC ₀ ) and the difference in haze (ΔHaze) were calculated.

<Folding endurance test (MIT)>
In accordance with ASTM standard D2176-16, the number of times the optical film was folded in the examples and comparative examples was determined as follows. The optical film was cut into a strip of 15 mm width and 100 mm length using a dumbbell cutter to prepare a measurement sample. The measurement sample was set in the main body of an MIT folding fatigue tester ("Model 0530" manufactured by Toyo Seiki Seisakusho Co., Ltd.). Specifically, one end of the measurement sample was fixed to a load clamp, the other end was fixed to a folding clamp, and tension was applied to the measurement sample. In this state, the measurement sample was folded back and forth in the front and back directions until it broke under the conditions of a test speed of 175 cpm, a folding angle of 135°, a load of 0.75 kgf, and a bending radius R of the folding clamp of 3 mm. The number of foldings was measured.

<Visibility>
The optical film was cut into a 10 cm square. The MD direction of a polarizing plate with an adhesive layer of the same size was aligned with the MD direction of the cut optical film, and the polarizing plate with an adhesive layer was attached to the optical film to prepare an evaluation sample. Two evaluation samples were prepared for each of the optical films of the examples and comparative examples. In addition, two evaluation samples were prepared for each of the optical films of the examples and comparative examples after the bending resistance test.
One of the two evaluation samples was fixed on a stand so that the fluorescent lamp was positioned vertically to the plane of the evaluation sample and the longitudinal direction of the fluorescent lamp was parallel to the MD direction of the evaluation sample.
An observer visually observed the image of the fluorescent lamp reflected on the surface of the evaluation sample from an angle of 30° with respect to the vertical direction of the plane of the evaluation sample.
The other evaluation sample was fixed to the stand in the same manner, except that the longitudinal direction of the fluorescent lamp was changed from horizontal to vertical, and the image of the fluorescent lamp was observed.
From the observation results, visibility was evaluated based on the following evaluation criteria.
(Visibility evaluation criteria)
.circle.: Almost no distortion of the fluorescent light image is visible.
◯: Some distortion of the fluorescent light image is visible.
Δ: Distortion of the fluorescent light image is visible.
×: Distortion of the fluorescent light image is clearly visible.

(Production Example 1: Preparation of polyamideimide resin (1))
Under a nitrogen atmosphere, TFMB and DMAc were added to a separable flask equipped with a stirring blade so that the solid content of TFMB was 6.08 mass%, and TFMB was dissolved in DMAc while stirring at room temperature. Next, 6FDA was added to the flask so that it was 40.82 mol% relative to TFMB, and stirred at room temperature for 16 hours. After that, it was cooled to 10 ° C., and OMTPC was added so that it was 27.55 mol% relative to TFMB, and after stirring for 10 minutes, OMTPC was further added so that it was 27.55 mol% relative to TFMB, and stirred for 20 minutes. Then, the same amount of DMAc as the DMAc added initially was added, and after stirring for 10 minutes, OMTPC was added so that it was 6.12 mol% relative to TFMB, and stirred for 2 hours. Next, diisopropylethylamine and 4-picoline were added to the flask in an amount of 61.22 mol % each relative to TFMB, and acetic anhydride was added in an amount of 285.71 mol % relative to TFMB. After stirring for 30 minutes, the internal temperature was raised to 70° C. and stirring was continued for a further 3 hours to obtain a reaction liquid.
The reaction solution obtained was cooled to room temperature and poured into a large amount of methanol in the form of a filament, and the precipitate was taken out and immersed in methanol for 6 hours, and then washed with methanol. The precipitate was then dried under reduced pressure at 60°C to obtain polyamideimide resin (1). The weight average molecular weight of the obtained polyamideimide resin (1) was 300,000, and the imidization ratio was 99.1.

(Production Example 2: Preparation of polyamideimide resin (2))
Under a nitrogen atmosphere, TFMB and DMAc were added to a separable flask equipped with a stirring blade so that the solid content of TFMB was 5.22 mass%, and TFMB was dissolved in DMAc while stirring at room temperature. Next, 6FDA was added to the flask so that it was 41.24 mol% relative to TFMB, and stirred at room temperature for 16 hours. After that, after cooling to 10°C, 2,5-dimethylterephthalic acid chloride (hereinafter sometimes abbreviated as DMTPC) was added so that it was 27.84 mol% relative to TFMB, and after stirring for 10 minutes, DMTPC was further added so that it was 27.84 mol% relative to TFMB, and stirred for 20 minutes. Then, the same amount of DMAc as the DMAc added initially was added, and after stirring for 10 minutes, DMTPC was added so that it was 6.19 mol% relative to TFMB, and stirred for 2 hours. Next, diisopropylethylamine and 4-picoline were added to the flask in an amount of 61.86 mol % each relative to TFMB, and acetic anhydride was added in an amount of 288.66 mol % relative to TFMB. After stirring for 30 minutes, the internal temperature was raised to 70° C. and stirring was continued for a further 3 hours to obtain a reaction liquid.
The reaction solution obtained was cooled to room temperature and poured into a large amount of methanol in the form of a filament, and the precipitate was taken out and immersed in methanol for 6 hours, and then washed with methanol. The precipitate was then dried under reduced pressure at 60°C to obtain polyamideimide resin (2). The weight average molecular weight of the obtained polyamideimide resin (2) was 280,000, and the imidization ratio was 98.9.

(Production Example 3: Preparation of Silica Dispersion)
The solvent methanol in the methanol-dispersed organically modified silica (particle size 25 nm) was replaced with γ-butyrolactone (GBL) to obtain GBL-dispersed organically modified silica (solid content 30.5%). This dispersion was named dispersion (1).

(Production Example 4: Preparation of varnish)
Varnishes (1) and (2) were obtained by adding polyamideimide resin to GBL so as to obtain a solid content shown in Table 1, and completely dissolving the resin by stirring at room temperature for 24 hours.
Varnish (3) was obtained by adding polyamideimide resin and dispersion liquid 1 to a GBL solvent at room temperature so as to obtain the solid content shown in Table 1, and stirring until homogenous. The mass ratio of the polyamideimide resin in varnish (3) to the filler (silica) contained in dispersion liquid 1 was set to 60:40.

(Production Example 5: Production of composition for forming hard coat layer)
A hard coat layer-forming composition (1) was produced by mixing 35 parts by mass of urethane acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.; UA-122P), 35 parts by mass of urethane acrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.; UA-232P), 25 parts by mass of methyl ethyl ketone, 4.5 parts by mass of a photoinitiator (1-hydroxycyclohexyl phenyl ketone), and 0.5 parts by mass of a leveling agent (manufactured by BYK-Chemie Co., Ltd.; BYK-3570).

Example 1
(Production of Optical Film (1))
The manufacture of the optical film (1) will be described with reference to Figures 7 and 8. First, as shown in Figure 7, a polyethylene terephthalate film substrate 51 (Cosmoshine (registered trademark) A4100, manufactured by Toyobo Co., Ltd., hereinafter sometimes referred to as PET film substrate 51) having a thickness of 188 μm was unwound and conveyed at a linear speed of 0.30 m/min, while the varnish (1) contained in a tank 522 was applied onto the PET film substrate 51 by drip molding from a nozzle 521 to a width of 500 mm. Thereafter, while conveying at the same linear speed, the applied varnish was dried by heating in a dryer 53 at 120°C for 20 minutes, 95°C for 10 minutes, and 85°C for 10 minutes. Next, protective film 54 (NSA-33T, manufactured by San-A Chemical Co., Ltd.) was unwound from the roll and attached to the surface of the dried coating film opposite to the surface in contact with PET film substrate 51. Then, PET film substrate 51 was peeled off from the dried coating film and taken up as PET film substrate roll 55, and the remaining laminate was obtained as laminate roll 56 having a length of 100 m.

Next, as shown in Fig. 8, the laminate film was unwound from the obtained laminate roll 56 at a transport speed of 0.5 m/sec, the protective film 54 was peeled off from the laminate film and taken up as a protective film roll 57, and the remaining dried coating film was passed through nip rolls 201 and 202, and then dried in a tenter dryer 58 under the following conditions. The tenter dryer 58 is equipped with a mechanism for holding both ends of the film with clips. The inside is divided into a first chamber to a sixth chamber in order from the inlet side of the film.
<Tenter Dryer 58>
Clip gripping width (distance from one end of the film to the corresponding clip gripping part): 25 mm
Ratio of the distance between clips at both ends of the film at the inlet of the dryer to the distance between clips at the outlet of the dryer: 1.0
Dryer temperature: 200°C
Air speed in each chamber in the dryer: Chamber 1 13.5 m/sec, Chamber 2 13 m/sec, Chambers 3 to 6 11 m/sec

After leaving the tenter dryer 58, the clips on the film ends were released. After passing through the nip rolls 203 and 204, the clipped portions of the film were slit by the slitting device 59, and then a PET protective film 60 was laminated and wound around a 6-inch ABS core to obtain a roll of optical film 61 with a thickness of 50 μm. The amount of solvent remaining in the optical film 61 obtained was 1.0% by mass.

Example 2
An optical film (2) having a thickness of 49 μm and a residual solvent content of 1.0 mass% in the film was produced in the same manner as in the production method of the optical film (1), except that the varnish (1) was changed to the varnish (2) and the drying conditions in the dryer 53 were changed to heating at 120° C. for 20 minutes, at 100° C. for 10 minutes, and at 90° C. for 10 minutes.

Example 3
(Production of Optical Film (3))
The composition for forming a hard coat layer (1) prepared in Production Example 5 was applied to the surface of the optical film (2) obtained in Example 2 that had been in contact with the PET substrate film during film formation so that the thickness of the first hard coat layer after curing was 3 μm, and the coating was dried for 1 minute in an oven at 80° C. Thereafter, light was irradiated using a high-pressure mercury lamp at a light intensity of 350 mJ/cm ² to cure the coating film and form a first hard coat layer, thereby producing an optical film (3) including a hard coat layer.

Example 4
An optical film (4) having a thickness of 51 μm and a residual amount of the solvent in the film of 1.0 mass% was produced in the same manner as in the production method of the optical film (1), except that the varnish (1) was changed to the varnish (3) and the linear speed was changed from 0.30 m/min to 0.50 m/min.

<Comparative Example 1>
As the optical film (5), a polyimide film (UPILEX, manufactured by Ube Industries, Ltd.) having a thickness of 50 μm was prepared.

The formulation of the composition and the composition of the optical film are summarized in Table 2. In Table 2, the column "HC presence/absence" indicates that the optical film has a hard coat layer and that the optical film does not have a hard coat layer.

The physical properties of the films obtained in the examples and comparative examples were measured according to the methods described above. The results are shown in Tables 3 to 6.

The optical films of Examples 1 to 4, in which the total light transmittance, haze, and puncture strength are within the specified range and satisfy the formulas (1) to (3), are excellent in visibility in the wide-angle direction, and in particular, the difference in image clarity and the difference in haze before and after the bending resistance test are small, so that it was confirmed that the optical films have excellent visibility in the wide-angle direction even after repeated folding operations. In this example, it was confirmed that the visibility in the wide-angle direction is excellent even after repeated folding operations because the difference in image clarity and the difference in haze before and after the bending resistance test are small. However, for example, the above folding resistance test may be performed any number of times, and the difference in image clarity and the difference in haze before and after the test may be evaluated, or the visibility in the wide-angle direction before and after the test may be evaluated according to the above evaluation criteria, to evaluate the visibility after repeated folding operations. In contrast, the optical film of Comparative Example 1, in which the total light transmittance and haze are not within the specified range and do not satisfy the formulas (1) to (3), did not have excellent visibility in the wide-angle direction.

1 Optical film 3 Vertical axis 10 First incident light 11 First incident position 12 1a transmitted light 14 First optical axis 16 First optical comb 18 1b transmitted light 19 First receiver 20 Second incident light 21 Second incident position 22 2a transmitted light 24 Second optical axis 26 Second optical comb 28 2b transmitted light 29 Second receiver 30 Third incident light 31 Third incident position 32 3a transmitted light 34 Third optical axis 36 Third optical comb 38 3b transmitted light 39 Third receiver 40 Zone 41 Zone 42 Zone 43 Holding device 44 Raw material film 45 Resin film 46 Upper nozzle (nozzle)
47 Lower nozzle (nozzle)
48 Nozzle 49 IR heater 100 Tenter furnace 100a Upper surface 100b Lower surface A Film transport direction 51 PET film substrate 521 Nozzle 522 Tank 53 Dryer 54 Protective film 55 PET film substrate roll 56 Laminate roll 57 Protective film roll 58 Tenter dryer 201 Nip roll 202 Nip roll 59 Slit device 60 PET protective film 61 Optical film 201 to 204 Nip roll 101 to 109 Guide roll

Claims (13)

An optical film comprising at least one polyimide-based resin selected from the group consisting of polyimide resins and polyamideimide resins , the optical film having a total light transmittance of 85% or more, a haze of 0.5% or less, and a puncture strength according to JIS Z 1707 of 10 to 100 N;
In the plane of the optical film, a direction parallel to the machine flow direction during production is defined as an MD direction, and a direction perpendicular to the machine flow direction is defined as a TD direction.
a first transmission image clarity value C _{60 (MD) in a direction inclined at 60° from a perpendicular direction to a plane of the optical film toward the MD direction, a second transmission image clarity value C 60} (TD) in a direction inclined at ₆₀ ° from the perpendicular direction toward the TD direction, and a third transmission image clarity value C ₀ in the perpendicular direction, which are obtained in accordance with JIS K 7374 when the width of an optical comb is 0.125 mm,
Formula (1):
87%≦ _C60 (MD)≦100%... (1),
Formula (2):
87%≦C ₆₀ (TD)≦100% (2), and the formula (3):
0.8≦ _C60 (MD) _/C0≦1.0 ... (3)
The filling,
The polyimide resin has the formula (1):

[In formula (1), Y represents a tetravalent organic group having 4 to 40 carbon atoms and an aromatic ring, X represents a divalent organic group having 4 to 40 carbon atoms and a cyclic structure, and * represents a bond.]
The polyamide-imide resin has a constitutional unit represented by the formula (1) and a constitutional unit represented by the formula (2):

[In formula (2), Z and X each independently represent a divalent organic group having a cyclic structure and having 4 to 40 carbon atoms, and * represents a bond.]
The optical film is a polyamide-imide resin having a structural unit represented by the formula : The second transmission image clarity value and the third transmission image clarity value are calculated using Equation (4):
0.9≦ _C60 (TD) _/C0≦1.0 (4)
The optical film of claim 1 further comprising: The fracture displacement L (mm) and the tensile modulus E (GPa) of the optical film in a puncture strength test in accordance with JIS Z 1707 are expressed by the following mathematical formula (5):
0.10≦L/E≦1.00 (5)
The optical film according to claim 1 or 2, which satisfies the above. The puncture strength S (N) of the optical film in accordance with JIS Z1707 and the thickness T (μm) are expressed by the following mathematical formula (6):
0.10≦S/T≦2.00 (6)
The optical film according to any one of claims 1 to 3, The optical film according to any one of claims 1 to 4, in which the difference in haze ΔHaze before and after a bending resistance test conforming to JIS K 5600-5-1 is less than 0.3%. 6. The optical film according to claim 1, wherein the first transmission image clarity value difference ΔC ₆₀ (MD), the second transmission image clarity value difference ΔC ₆₀ (TD), and the third transmission image clarity value difference ΔC ₀ before and after a bending resistance test in accordance with JIS K 5600-5-1 are each less than 15. 7. The optical film according to claim 1, wherein the weight average molecular weight of the polyimide resin is 350,000 or less. The optical film according to any one of claims 1 to 7, having a thickness of 10 to 150 μm. The optical film according to any one of claims 1 to 8, having a hard coat layer on at least one surface. The optical film according to claim 9, wherein the thickness of the hard coat layer is 3 to 30 μm. A flexible display device comprising the optical film according to any one of claims 1 to 10. The flexible display device of claim 11 further comprising a polarizing plate. The flexible display device according to claim 11 or 12, further comprising a touch sensor.

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