JP2020184077A - Optical film - Google Patents

Abstract

To provide an optical film that excels in visibility in a wide-angle direction.SOLUTION: Provided is an optical film containing at least one kind of resin selected from the group consisting of a polyimide resin and a polyamide resin, the total light transmittance of which is 85% or greater and the haze 0.5% or less. A first transmission image clarity C60(MD) in a direction inclined 60° in an MD direction parallel to a machine flow direction during manufacturing from a vertical direction to the plane of the optical film, a second transmission image clarity C60(TD) in a direction inclined 60° in a TD direction perpendicular to the machine flow direction from the vertical direction, and a third transmission image clarity C0 in the vertical direction, as obtained in conformity with JIS-K-7374 when the width of an optical comb is 0.125 mm, satisfy equation (1): 87%≤C60(MD)≤100%, equation (2): 87%≤C60(TD)≤100%, and equation (3): 0.8≤C60(MD)/C0≤1.0.SELECTED DRAWING: Figure 1

Description

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

Conventionally, glass has been used as a material for display members such as solar cells and image display devices. However, it did not have sufficient materials to meet the recent demands for miniaturization, thinning, weight reduction and flexibility. Therefore, various films are being studied as alternative materials for glass. Examples of such a film include a polyimide film (for example, Patent Document 1).

JP-A-2009-2154412

When the polyimide film is applied to a transparent member such as the front plate of a flexible display device, the image may be displayed with the image display surface bent, so that the image display surface is wider than the non-flexible image display surface. Excellent visibility is required. However, according to the study of the present inventor, there are cases where the conventional polyimide resin film cannot sufficiently satisfy the visibility in the wide-angle direction.

Therefore, an object of the present invention is to provide an optical film having excellent visibility in a wide-angle direction, and a flexible display device including the optical film.

As a result of diligent studies to solve the above problems, the present inventors have included at least one resin selected from the group consisting of a polyimide resin and a polyamide resin, and have a total light transmittance of 85% or more. In an optical film having a haze of 0.5% or less, the transmissivity value {C ₆₀ (MD), C ₆₀ (TD)} and the ratio of the transmissivity value {C ₆₀ (MD) / C ₀ } are predetermined. We have found that the above problems can be solved by adjusting the range, and have completed the present invention. That is, the present invention includes the following aspects.

[1] An optical film containing at least one resin selected from the group consisting of a polyimide resin and a polyamide resin, having a total light transmittance of 85% or more and a haze of 0.5% or less.
When the direction parallel to the machine flow direction at the time of manufacture in the optical film plane is the MD direction and the direction perpendicular to the machine flow direction is the TD direction,
The first transmission mapping property value C in the direction inclined by 60 ° in the MD direction from the direction perpendicular to the plane of the optical film, which is obtained when the width of the optical comb is 0.125 mm in accordance with JIS K 7374. _{The 60} (MD), the second transmission mapping property value C ₆₀ (TD) in the direction inclined by 60 ° from the vertical direction to the TD direction, and the third transmission mapping property value C _{0 in} the vertical direction are
Equation (1):
87% ≤ C ₆₀ (MD) ≤ 100% ... (1),
Equation (2):
87% ≤ C ₆₀ (TD) ≤ 100% ... (2), and equation (3):
0.8 ≤ C ₆₀ (MD) / C ₀ ≤ 1.0 ... (3)
An optical film that meets the requirements.
[2] The second transmission mapping property value and the third transmission mapping property value are expressed by the formula (4):
0.9 ≤ C ₆₀ (TD) / C ₀ ≤ 1.0 ... (4)
The optical film according to [1], which further satisfies the above.
[3] The optical film according to [1] or [2], wherein the difference ΔHaze of the haze before and after the bending resistance test according to JIS K 5600-5-1 is less than 0.3%.
[4] The difference ΔC ₆₀ (MD) of the first transmission mapping property value before and after the bending resistance test according to JIS K 5600-5-1, the difference ΔC ₆₀ (TD) of the second transmission mapping property value, and The optical film according to any one of [1] to [3], wherein the difference ΔC ₀ of the third transmission mapping property value is less than 15.
[5] The optical film according to any one of [1] to [4], which has a thickness of 10 to 150 μm.
[6] The optical film according to any one of [1] to [5], wherein the tensile elastic modulus at 80 ° C. is 4,000 to 9,000 MPa.
[7] The optical film according to any one of [1] to [6], which has a hard coat layer on at least one surface.
[8] The optical film according to [7], wherein the hard coat layer has a thickness of 3 to 30 μm.
[9] A flexible display device including the optical film according to any one of [1] to [8].
[10] The flexible display device according to [9], further comprising a touch sensor.
[11] The flexible display device according to [9] or [10], further comprising a polarizing plate.

According to the present invention, it is possible to provide an optical film having excellent visibility in a wide-angle direction and a flexible display device including the optical film.

FIG. 1 is a diagram showing an optical axis in measuring the first transmission mapping property value. FIG. 2 is a diagram showing an optical axis in the measurement of the second transmission mapping property value. FIG. 3 is a diagram showing an optical axis in the measurement of the third transmission mapping property value.

Hereinafter, embodiments of the present invention will be described in detail. 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. Further, when a plurality of upper limit values and lower limit values are described for a specific parameter, any upper limit value and lower limit value among these upper limit values and lower limit values can be combined to form a suitable numerical range.

<Optical film>
The optical film of the present invention contains at least one resin selected from the group consisting of a polyimide resin and a polyamide resin, and has an total light transmittance of 85% or more and a haze of 0.5% or less. And
When the direction parallel to the machine flow direction at the time of manufacture in the optical film plane is the MD direction and the direction perpendicular to the machine flow direction is the TD direction,
The first transmission mapping property value C in the direction inclined by 60 ° in the MD direction from the direction perpendicular to the plane of the optical film, which is obtained when the width of the optical comb is 0.125 mm in accordance with JIS K 7374. _{The 60} (MD), the second transmission mapping property value C ₆₀ (TD) in the direction inclined by 60 ° from the vertical direction to the TD direction, and the third transmission mapping property value C _{0 in} the vertical direction are
Equation (1):
87% ≤ C ₆₀ (MD) ≤ 100% ... (1),
Equation (2):
87% ≤ C ₆₀ (TD) ≤ 100% ... (2), and equation (3):
0.8 ≤ C ₆₀ (MD) / C ₀ ≤ 1.0 ... (3)
Meet.

[1. Equation (1)]
(MD direction, TD direction)
The MD direction is a direction parallel to the mechanical flow direction at the time of manufacture in the plane of the optical film, and indicates, for example, a direction parallel to the direction in which the optical film is conveyed when manufactured by the solution casting method. The TD direction is a direction perpendicular to the machine flow direction, and indicates, for example, a direction perpendicular to the conveyed direction. When the directions are unknown, the MD direction and the TD direction in the optical film plane are determined by the following method. With respect to MD and TD, at least 20 points or more of the optical film are cross-sectioned in different directions. More specifically, assuming a circle centered on any one point of the optical film, the semicircle is cut out from the optical film, and the central angle of the sector after cutting the semicircle becomes substantially uniform. As described above, the optical film is cut in a straight line, and 20 or more cross sections are formed. The center of the thickness of the obtained plurality of cross sections is measured by laser Raman, and the one having the highest peak intensity near 1,620 cm ^{-1 is} defined 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。 (First transmission mapping property value C ₆₀ (MD))
The first transmission mapping property value C ₆₀ (MD) is obtained in accordance with Japanese Industrial Standards (JIS) K 7374, and is a transmission mapping property in a direction inclined by 60 ° from the vertical direction to the MD direction with respect to the plane of the optical film. The value. The first transmission mapping property value C ₆₀ (MD) will be described more specifically with reference to FIG. FIG. 1 is a diagram showing an optical axis in measuring the first transmission mapping property value. An axis (first optical axis) inclined at an angle of 60 ° in the MD direction from an axis perpendicular to the optical film 1 (vertical axis 3) with 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 the first incident light 10 (white light: indicated by a solid line in FIG. 1) along 14). Next, the first a transmitted light 12 (indicated by a broken line in FIG. 1) transmitted through the optical film 1 is transmitted to the first optical comb 16 extending perpendicularly to the first optical axis 14. Next, the first b transmitted light 18 (denoted by the alternate long and short dash line in FIG. 1) transmitted through the first optical comb 16 is received by the first receiver 19 extending perpendicular to the first optical axis 14. The first optical comb 16 has an opening for transmitting the first a transmitted light 12 and a light shielding portion for blocking the first a 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 by a predetermined unit width in the direction parallel to the plane of the first optical comb 16 and in which the slits in the first optical comb 16 are arranged (direction of arrow A) to transmit the first b. The light receiving waveform is obtained by repeating receiving the light 18. The maximum value M and the minimum value m of the relative light amount are obtained from the obtained received light waveform. Equation (5) from the obtained M and m

The first transmission mapping property value C ₆₀ (MD) is calculated based on the above. The transmission mapping property value (the first transmission mapping property value, and the second transmission mapping property value and the third transmission mapping property value described later) can be measured using a mapping property measuring device.

When the first transmission mapping property value C ₆₀ (MD) satisfies the equation (1), the optical film is excellent in visibility in the wide-angle direction in the MD direction. From the viewpoint of further improving the visibility of the optical film in the wide-angle direction in the MD direction, the first transmission mapping property value C ₆₀ (MD) is 87% or more, preferably 89% or more, more preferably 90 in the formula (1). % Or more, more preferably 92% or more, even more preferably 93% or more, and 100% or less.

[2. Equation (2)]
(Second transmission mapping property value C ₆₀ (TD))
The second transmission mapping property value C ₆₀ (TD) is a transmission mapping property value obtained in accordance with JIS K 7374 in a direction inclined by 60 ° in the TD direction from the direction perpendicular to the plane of the optical film. The second transmission mapping property value C ₆₀ (TD) will be described more specifically with reference to FIG. FIG. 2 is a diagram showing an optical axis in the measurement of the second transmission mapping property value. An axis (second optical axis) inclined at an angle of 60 ° in the TD direction from an axis perpendicular to the optical film 1 (vertical axis 3) with 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 the second incident light 20 (white light: indicated by a solid line in FIG. 2) along 24). Next, the second a transmitted light 22 (indicated by a broken line in FIG. 2) transmitted through the optical film 1 is transmitted to the second optical comb 26 extending perpendicularly to the second optical axis 24. Next, the second b transmitted light 28 (indicated by the alternate long and short dash line in FIG. 2) transmitted through the second optical comb 26 is received by the second light receiver 29 extending perpendicularly to the second optical axis 24. The second optical comb 26 has an opening for transmitting the second a transmitted light 22 and a light shielding portion for blocking the second a 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 by a predetermined unit width in the direction in which the slits are arranged in the second optical comb 26 (direction of arrow B) and is parallel to the plane of the second optical comb 26, and is transmitted through the second b. The light 28 is repeatedly received to obtain a light receiving waveform. The maximum value M and the minimum value m of the relative light amount are obtained from the obtained received light waveform. The second transmission mapping property value C ₆₀ (TD) is calculated from the obtained M and m based on the formula (5).

When the second transmission mapping property value C ₆₀ (TD) satisfies the equation (2), the optical film is excellent in visibility in the wide-angle direction in the TD direction. From the viewpoint of further improving the visibility of the optical film in the wide-angle direction in the TD direction, C ₆₀ (TD) is 87% or more, preferably 89% or more, more preferably 90% or more, still more preferably 90% or more in the formula (2). It is 92% or more, more preferably 93% or more, and 100% or less.

[3. Equation (3)]
(Third transmission mapping property value C ₀ )
The third transmission mapping property value C ₀ is a transmission mapping property value in the direction perpendicular to the plane of the optical film, which is obtained in accordance with JIS K 7374. Referring to FIG. 3, it illustrated by the third transmission image clarity value C _0. FIG. 3 is a diagram showing an optical axis in the measurement of the third mapping property value. The third incident light 30 (white light: represented by a solid line in FIG. 3) along the axis parallel to the axis (vertical axis 3) perpendicular to the optical film 1 (third optical axis 34) is the optical film 1. Irradiate an arbitrary point (third incident position 31) on the surface. Next, the third a transmitted light 32 (indicated by a broken line in FIG. 3) transmitted through the optical film 1 is transmitted to the third optical comb 36 extending perpendicularly to the third optical axis 34. Next, the third b transmitted light 38 (indicated by the alternate long and short dash line in FIG. 3) transmitted through the third optical comb 36 is received by the receiver 39 extending perpendicular to the third optical axis 34. The third optical comb 36 has an opening for transmitting the third a transmitted light 32 and a light shielding portion for blocking the third a transmitted light 32. The slit width (width of the opening) of the third optical comb 36 is 0.125 mm.
The third optical comb 36 is moved by a predetermined unit width in the direction parallel to the plane of the third optical comb 36 and in which the slits in the third optical comb 36 are arranged (direction of arrow C) to transmit the third b. The light 38 is repeatedly received to obtain a light receiving waveform. The maximum value M and the minimum value m of the relative light amount are obtained from the obtained received light waveform. From the obtained M and m, the third transmission mapping property value C ₀ is calculated based on the equation (5).

When the first transmission mapping property value C ₆₀ (MD) and the third transmission mapping property value C ₀ satisfy the equation (3), the optical film is excellent in visibility in the MD direction with respect to the vertical direction of the optical film. From the viewpoint of further improving the visibility in the MD direction, the ratio of the first mapping property value C ₆₀ (MD) to the third transmission mapping property value C ₀ (C ₆₀ (MD) / C ₀ ) is 0.8 or more. It is preferably 0.90 or more, more preferably 0.93 or more, still more preferably 0.94 or more, and 1.0 or less.

The third transmission mapping property value C ₀ is preferably 97% or more, more preferably 98% or more, still more preferably 99% or more in the formula (3). The first transmission mapping property value C ₆₀ (MD) is preferably 89% or more, more preferably 90% or more, still more preferably 92% or more, and particularly preferably 93% or more in the formula (3).

The transmission mapping property values (more specifically, the first transmission mapping property value C ₆₀ (MD), the second transmission mapping property value C ₆₀ (TD), and the third transmission mapping property value C ₀ ) are the optical film surfaces. It can be adjusted by improving the smoothness of the film and suppressing scattering of transmitted light on the surface of the optical film. Further, the smoothness of the optical film surface is determined by, for example, the composition of the optical film (more specifically, the type of filler, the particle size and the content, etc.), and the manufacturing conditions of the optical film (more specifically, the drying temperature). , Drying time, airflow in the drying system, thickness of the coating film, transport speed in the drying step, amount of solvent in the varnish, etc.). When the optical film further contains a hard coat layer, it can be adjusted by improving the smoothness of the surface of the hard coat layer and suppressing scattering on the surface of the hard coat layer. The smoothness of the hard coat layer can be adjusted by, for example, adjusting the type of solvent, component ratio, solid content concentration, adding a leveling agent, and the like, in addition to the method for adjusting the smoothness of the optical film.

[4. Equation (4)]
From the viewpoint of enhancing the visibility of the optical film of the present invention in the TD direction with respect to the vertical direction, the second transmission mapping property value and the third transmission mapping property value are expressed by the formula (4):
0.9 ≤ C ₆₀ (TD) / C ₀ ≤ 1.0 ... (4)
It is preferable to further satisfy. From the viewpoint of further enhancing the visibility in the TD direction of the present invention, the ratio of the first transmission mapping property value to the third transmission mapping property value (C ₆₀ (TD) / C ₀ ) is preferably 0.9 or more. It is more preferably 0.91 or more, still more preferably 0.92 or more, particularly preferably 0.93 or more, particularly preferably 0.94 or more, and 1.0 or less.

The second transmission mapping property value C ₆₀ (TD) is preferably 89% or more, more preferably 90% or more, still more preferably 92% or more, and particularly preferably 93% or more in the formula (4). The third transmission mapping property value C ₀ is preferably 97% or more, more preferably 98% or more, and even more preferably 99% or more in the formula (4).

[5. Flexibility of transmission mapping property value]
In particular, when the optical film of the present invention is applied to the front plate of a flexible device, the first transmission map before and after the bending resistance test based on JIS K 5600-5-1 from the viewpoint of further improving visibility in the wide angle direction. The absolute value ΔC ₆₀ (MD) of the difference between the sex values, the absolute value ΔC ₆₀ (TD) of the difference between the second transmission mapping properties, and the absolute value ΔC ₀ of the difference between the third transmission mapping values are preferably less than 15, respectively. Is. When the difference in the transmission mapping property value before and after the bending resistance test is less than 15, the image display surface of the flexible device is used in a bent state and / or even after being used in a bent state. Has excellent visibility in the wide-angle direction. ΔC ₆₀ (MD) is more preferably less than 1.5, still more preferably less than 1.0, and particularly preferably less than 0.5. ΔC ₆₀ (TD) is more preferably less than 2.8, still more preferably less than 2.3, particularly preferably less than 2.1, and very particularly preferably less than 1.5. ΔC ₀ is more preferably less than 2, still more preferably less than 1, particularly preferably less than 0.7, and very particularly preferably less than 0.5.

[6. Total light transmittance]
The total light transmittance of the optical film of the present invention is 85% or more, and from the viewpoint of further improving visibility, it is preferably 87% or more, more preferably 89% or more, still more preferably 90% or more, and particularly preferably 90% or more. It is 91% or more, particularly preferably 92% or more, and usually 100% or less. The total light transmittance of the optical film can be measured according to JIS K 7136-1: 1997. The method for measuring the total light transmittance will be described in detail in Examples.

[7. Haze, difference between haze]
The haze of the optical film of the present invention is 0.5% or less, preferably 0.4% or less, more preferably 0.3% or less, still more preferably 0.2%, from the viewpoint of further improving visibility. It is as follows.
From the viewpoint of further improving the bending resistance of the haze, the optical film of the present invention preferably has an absolute value ΔHaze of the difference between the haze before and after the bending resistance test based on JIS K 5600-5-1 of 0.3%. Less than, more preferably less than 0.2%, still more preferably less than 0.1%.
The haze of the optical film can be measured according to JIS K 7136: 2000. The haze measurement method and the haze difference calculation method will be described in detail in Examples.

[8. Yellowness (YI)]
From the viewpoint of further improving visibility, the yellowness (YI) of the optical film of the present invention is preferably 4.0 or less, more preferably 3.0 or less, still more preferably 2.5 or less, and particularly preferably 2. It is 0 or less. The method for measuring YI will be described in detail in Examples.

[9. Number of folds]
From the viewpoint of improving the folding resistance, the number of times the optical film of the present invention is bent is preferably 20,000 times or more, more preferably 100,000 times or more, still more preferably 200,000 times or more, and particularly preferably 350 times or more. 000 times or more, very particularly preferably 700,000 times or more. When the number of times of bending is equal to or more than the above lower limit, cracks and cracks are unlikely to occur even if the optical film is bent. The upper limit of the number of times of bending is usually 50,000,000 or less. The number of times the optical film is bent is measured by a MIT folding fatigue resistance test conforming to ASTM standard D2176-16. The MIT fold resistance fatigue test is, for example, the test described in Examples.

[10. thickness]
The thickness of the optical film of the present invention is preferably 10 μm or more, more preferably 20 μm or more, still more preferably 25 μm or more, particularly preferably 30 μm or more, preferably 150 μm or less, more preferably 100 μm or less, still more preferably 85 μm. It is as follows. The method for measuring the thickness of the optical film will be described in detail in Examples.

[11. Tensile modulus]
The tensile elastic modulus of the optical film of the present invention at 80 ° C. is preferably 4,000 to 9,000 MPa, more preferably 4,500 to 8,500 MPa. The method for measuring the elastic modulus will be described in detail in Examples. When the tensile elastic modulus is within the above range, dent defects are less likely to occur in the optical film. The tensile elasticity of the optical film can be measured in accordance with JIS K 7127. The method for measuring the tensile elastic modulus will be described in detail in Examples.

[12. Hard coat layer]
The optical film of the present invention preferably has a hard coat layer on at least one surface. When the hard coat layer is provided on both sides, the two hard coat layers may contain the same or different components.

Examples of the hard coat layer include known hard coat layers such as acrylic type, epoxy type, urethane type, benzyl chloride type, and vinyl type. Among these, an acrylic-based, urethane-based, or a combination thereof hard coat layer can be preferably used from the viewpoint of suppressing a decrease in visibility of the optical film in the wide-angle direction and improving bending resistance. The hard coat layer is formed by polymerizing and curing a curable compound by irradiation with active energy rays. Examples of the polymerizable compound include polyfunctional (meth) acrylate compounds. The polyfunctional (meth) acrylate-based compound is a compound having at least two (meth) acryloyloxy groups in the molecule.

Examples of the polyfunctional (meth) acrylate compound include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, and tri. Methylolpropantri (meth) acrylate, trimethylolethanetri (meth) acrylate, tetramethylolmethanetri (meth) acrylate, tetramethylolmethanetetra (meth) acrylate, pentaglyceroltri (meth) acrylate, pentaerythritol tri (meth) acrylate , Pentaerythritol tetra (meth) acrylate, glycerintri (meth) acrylate, dipentaerythritol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) Acrylate, tris ((meth) acryloyloxyethyl) isocyanurate; phosphazenic (meth) acrylate compound in which a (meth) acryloyloxy group is introduced into the phosphazenic ring of a phosphazene compound; having at least two isocyanate groups in the molecule. Urethane (meth) acrylate compound obtained by reacting polyisocyanate with a polyol compound having at least one (meth) acryloyloxy group and a hydroxyl group; at least two carboxylic acid halides in the molecule and at least one (meth) ) A polyester (meth) acrylate compound obtained by reacting with a polyol compound having an acryloyloxy group and a hydroxyl group; and an oligomer such as a dimer or a trimer of each of the above compounds. These compounds are used alone or in admixture of two or more.

The curable compound may include a monofunctional (meth) acrylate compound in addition to the above-mentioned polyfunctional (meth) acrylate compound. Examples of the monofunctional (meth) acrylate-based compound include hydroxyethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, and 2-hydroxy-3. -Phenoxypropyl (meth) acrylate, glycidyl (meth) acrylate and the like can be mentioned. These compounds are used alone or in admixture of two or more. The content of the monofunctional (meth) acrylate-based compound is preferably 10% by mass or less when the solid content of the compound contained in the curable composition is 100% by mass. In addition, in this specification, a solid content means all components except a solvent contained in a curable composition.

The curable composition forming the hard coat layer may contain an additive in addition to the polyfunctional (meth) acrylate compound and the polymerizable oligomer. Examples of the additive include a polymerization initiator, silica, a leveling agent, a solvent and the like. Examples of the solvent include methyl ethyl ketone, polypropylene glycol monomethyl ether and the like.

Moreover, the curable compound may contain a polymerizable oligomer. By containing the polymerizable oligomer, the hardness of the hard coat layer can be adjusted. Examples of the polymerizable oligomer include terminal (meth) acrylate polymethyl methacrylate, terminal styryl poly (meth) acrylate, terminal (meth) acrylate polystyrene, terminal (meth) acrylate polyethylene glycol, terminal (meth) acrylate acrylonitrile-styrene copolymer, and terminal. Macromonomers such as (meth) acrylate styrene-methyl (meth) acrylate copolymers can be mentioned. The content of the polymerizable oligomer is preferably 5 to 50% by mass when the solid content of the compound contained in the curable composition is 100% by mass.

The thickness of the hard coat layer is preferably 3 to 30 μm, more preferably 5 to 25 μm, and further preferably 5 to 20 μm from the viewpoint of improving the hardness of the optical film.

[13. 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 functional layer is provided on one side of the optical film, the protective film may be laminated on the surface on the optical film side or the surface on the functional layer side, and is laminated on both the optical film side and the functional layer side. You may. When the optical film has functional layers on both sides, the protective film may be laminated on the surface on one functional layer side or 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 capable of protecting the surface of the optical film or the functional layer. Examples of the protective film include polyester resin films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyolefin resin films such as polyethylene and polypropylene films, acrylic resin films, and the like, and polyolefin resin films and polyethylene. It is preferable to select from the group consisting of a terephthalate resin film and an acrylic resin film. 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 10 to 110 μm, and more preferably 15 to 100 μm. When the optical film has two protective films, the thickness of each protective film may be the same or different.

[14. Polyimide, polyamide resin]
The optical film of the present invention contains at least one resin selected from the group consisting of polyimide-based resins and polyamide-based resins. The polyimide-based resin is a resin containing a repeating structural unit containing an imide group (hereinafter, may be referred to as a polyimide resin) and a resin containing a repeating structural unit containing both an imide group and an amide group (hereinafter, referred to as a polyimide resin). Indicates at least one resin selected from the group consisting of (sometimes referred to as a polyamide-imide resin). Further, the polyamide-based resin refers to a resin containing a repeating structural unit containing an amide group (hereinafter, may be referred to as a polyamide-based resin).

The polyimide resin preferably has a repeating structural unit represented by the formula (10). Here, G is a tetravalent organic group and A is a divalent organic group. The polyimide-based resin may contain two or more types of repeating structural units represented by the formula (10), which differ in G and / or A.

The polyimide resin is one or more repeating structural units selected from the group consisting of repeating structural units represented by the formulas (11), (12) and (13) as long as the various physical properties of the optical film are not impaired. May include.

In formulas (10) and (11), G and G ¹ are independently tetravalent organic groups, and may be preferably substituted with a hydrocarbon group or a hydrocarbon group substituted with fluorine. It is an organic group. Examples of G and G ¹ include formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), and formula (28). ) Or a group represented by the formula (29) and a chain hydrocarbon group having a tetravalent carbon number of 6 or less. Since it is easy to suppress the yellowness (YI value) of the optical film, among them, the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25), the formula The group represented by (26) or the formula (27) is preferable.

In equations (20) to (29),
* Represents a bond
Z is 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 Represents −Ar−SO ₂ −Ar−. Ar represents an arylene group having 6 to 20 carbon atoms which may be substituted with a fluorine atom, and specific examples thereof include a phenylene group.

In formula (12), G ² is a trivalent organic group, preferably an organic group that may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. The G ^2, equation (20), equation (21), equation (22), equation (23), equation (24), equation (25), equation (26), equation (27), equation (28) or Examples thereof include a group in which any one of the bonds of the group represented by the formula (29) is replaced with a hydrogen atom, and a chain hydrocarbon group having a trivalent carbon number of 6 or less.

In formula (13), G ³ is a divalent organic group, preferably an organic group which may be substituted with a hydrocarbon group or a hydrocarbon group substituted with fluorine. The G ^3, equation (20), equation (21), equation (22), equation (23), equation (24), equation (25), equation (26), equation (27), equation (28) or Among the group bonds represented by the formula (29), a group in which two non-adjacent groups are replaced with hydrogen atoms and a chain hydrocarbon group having 6 or less carbon atoms are exemplified.

In formulas (10) to (13), A, A ¹ , A ² and A ³ are independently divalent organic groups, preferably hydrocarbon groups or fluorine-substituted hydrocarbon groups. It is an organic group that may be substituted. Examples of A, A ¹ , A ² and A ³ include formula (30), formula (31), formula (32), formula (33), formula (34), formula (35), formula (36) and formula ( 37) or a group represented by the formula (38); a group in which they are substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group; and a chain hydrocarbon group having 6 or less carbon atoms are exemplified.

In equations (30) to (38),
* Represents a bond
Z ^{1, Z 2} and ^{Z 3} are each independently a single _{bond, -O -, - CH 2 -} , - CH 2 -CH 2 -, - CH (CH 3) -, - C (CH 3) 2 _{-, - C (CF 3)} 2 -, - representing the or -CO- - SO _2.
In one example, Z ¹ and Z ³ are -O- and Z ² is -CH _2- , -C (CH ₃ ) _2- , -C (CF ₃ ) _2- or -SO _2- . is there. It is preferable that the bonding position of Z ¹ and Z ² with respect to each ring and the bonding position of Z ² and Z ³ with respect to each ring are in the meta position or the para position with respect to each ring, respectively.

The polyimide resin is preferably a polyamide-imide resin having at least a repeating structural unit represented by the formula (10) and a repeating structural unit represented by the formula (13) from the viewpoint of easily improving visibility. Further, the polyamide resin preferably has at least a repeating structural unit represented by the formula (13).

In one embodiment of the present invention, the polyimide-based resin is a diamine and a tetracarboxylic acid compound (a tetracarboxylic acid compound analog such as an acid chloride compound and a tetracarboxylic acid dianhydride), and, if necessary, a dicarboxylic acid compound. It is a condensed polymer obtained by reacting (hypercondensing) (dicarboxylic acid compound analogs such as acid chloride compounds), tricarboxylic acid compounds (tricarboxylic acid compound analogs such as acid chloride compounds and tricarboxylic acid anhydrides) and the like. .. The repeating structural unit represented by the formula (10) or the formula (11) is usually derived from a diamine and a tetracarboxylic acid compound. The repeating structural unit represented by the formula (12) is usually derived from a diamine and a tricarboxylic acid compound. The repeating structural unit represented by the formula (13) is usually derived from a diamine and a dicarboxylic acid compound.

In one embodiment of the present invention, the polyamide resin is a condensation type polymer obtained by reacting (polycondensing) a diamine and a dicarboxylic acid compound. That is, the repeating structural unit represented by the formula (13) is usually derived from a diamine and a dicarboxylic acid compound.

Examples of the tetracarboxylic acid compound include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic dianhydride; and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic dianhydride. The tetracarboxylic acid compound may be used alone or in combination of two or more. The tetracarboxylic dian compound may be a tetracarboxylic dian compound analog such as an acid chloride compound in addition to the dianhydride.

Specific examples of the aromatic tetracarboxylic dianhydride include 4,4'-oxydiphthalic dianhydride, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride, 2,2', 3,. 3'-benzophenonetetracarboxylic dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 2,2', 3,3'-biphenyltetracarboxylic dianhydride, 3,3 ', 4,4'-Diphenylsulfonetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane Dihydride, 2,2-bis (3,4-dicarboxyphenoxyphenyl) propane dianhydride, 4,4'-(hexafluoroisopropyridene) diphthalic acid dianhydride (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 and Examples thereof include 4,4'-(p-phenylenedioxy) diphthalic acid dianhydride and 4,4'-(m-phenylenedioxy) diphthalic acid dianhydride. These can be used alone or in combination of two or more.

Examples of the aliphatic tetracarboxylic dianhydride include cyclic or acyclic aliphatic tetracarboxylic dianhydride. The cyclic aliphatic tetracarboxylic dianhydride is a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure, and specific examples thereof include 1,2,4,5-cyclohexanetetracarboxylic dianhydride. Cycloalkanetetracarboxylic dianhydride such as 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, bicyclo [2.2] .2] Oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, dicyclohexyl-3,3', 4,4'-tetracarboxylic dianhydride and their positional isomers are listed. Be done. These can be used alone or in combination of two or more. Specific examples of the acyclic aliphatic tetracarboxylic dianhydride include 1,2,3,4-butanetetracarboxylic dianhydride, 1,2,3,4-pentanetetracarboxylic dianhydride and the like. These can be used alone or in combination of two or more. Further, a cyclic aliphatic tetracarboxylic dianhydride and an acyclic aliphatic tetracarboxylic dianhydride may be used in combination.

Among the above tetracarboxylic dianhydrides, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo [2.2.2] octo-7-ene, from the viewpoint of high transparency and low colorability. -2,3,5,6-tetracarboxylic dianhydride and 4,4'-(hexafluoroisopropyridene) diphthalic acid dianhydride, and mixtures thereof are preferred. Further, as the tetracarboxylic acid, a water adduct of the anhydride of the tetracarboxylic acid compound may be used.

Examples of the tricarboxylic acid compound include aromatic tricarboxylic acids, aliphatic tricarboxylic acids, acid chloride compounds related thereto, acid anhydrides, and the like, and two or more of them may be used in combination.
Specific examples include an anhydride of 1,2,4-benzenetricarboxylic acid; 2,3,6-naphthalentricarboxylic acid-2,3-anhydride; a single bond of phthalic anhydride and benzoic acid, -CH _{2 -, - C (CH 3)} 2 -, - C (CF 3) 2 -, - SO 2 - or a compound linked phenylene group.

Examples of the dicarboxylic acid compound include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, acid chloride compounds related thereto, acid anhydrides, and the like, and two or more of them may be used in combination. Specific examples thereof include terephthalic acid dichloride (terephthaloyl chloride (TPC)); isophthalic acid dichloride; naphthalenedicarboxylic acid dichloride; 4,4'-biphenyldicarboxylic acid dichloride; 3,3'-biphenyldicarboxylic acid dichloride; 4 , 4'-oxybis (benzoyl chloride) (OBBC); a dicarboxylic acid compound of a chain hydrocarbon having 8 or less carbon atoms and two benzoic acids in a single bond, -CH _2- , -C (CH ₃ ) _2- , Examples thereof include compounds linked by -C (CF ₃ ) _2- , -SO _2- or a phenylene group.

Examples of the diamine include aliphatic diamines, aromatic diamines, and mixtures thereof. In addition, in this embodiment, "aromatic diamine" represents a diamine in which an amino group is directly bonded to an aromatic ring, and an aliphatic group or other substituent may be contained in a part of the structure. The aromatic ring may be a monocyclic ring or a condensed ring, and examples thereof include, but are not limited to, a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring. Among these, it is preferable that the aromatic ring is a benzene ring. Further, the "aliphatic diamine" represents a diamine in which an amino group is directly bonded to an aliphatic group, and an aromatic ring or other substituent may be contained as a part of the structure thereof.

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

Examples of the aromatic diamine include p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylene diamine, p-xylylene diamine, 1,5-diaminonaphthalene, and 2,6-diaminonaphthalene. Aromatic amines having one aromatic ring, such as, 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, 4,4'-diaminodiphenyl sulfone, 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) benzidine (2,2'-bis (trifluoromethyl) -4,4'-diaminodiphenyl (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, 9,9-bis (4-amino-3-fluorophenyl) Examples thereof include aromatic amines having two or more aromatic rings, such as fluorene. These can be used alone or in combination of two or more.

Among the above diamines, from the viewpoint of high transparency and low colorability, it is preferable to use one or more selected from the group consisting of aromatic diamines having a biphenyl structure, and 2,2'-dimethylbenzidine, 2,2. It is more preferable to use one or more selected from the group consisting of'-bis (trifluoromethyl) benzidine, 4,4'-bis (4-aminophenoxy) biphenyl and 4,4'-diaminodiphenyl ether, more preferably 2,2. It is more preferred to use'-bis (trifluoromethyl) benzidine.

In the polyimide resin, each raw material such as the diamine, the tetracarboxylic acid compound, the tricarboxylic acid compound, and the dicarboxylic acid compound is mixed by a conventional method, for example, a method such as stirring, and then the obtained intermediate is used as an imidization catalyst and an imidization catalyst. It is obtained by imidization in the presence of a dehydrating agent, if necessary. The polyamide resin can be obtained by mixing each of the raw materials such as the diamine and the dicarboxylic acid compound by a conventional method, for example, a method such as stirring.

The imidization catalyst used in the imidization step is not particularly limited, and is, for example, an aliphatic amine such as tripropylamine, dibutylpropylamine, ethyldibutylamine; N-ethylpiperidine, N-propylpiperidin, N-butylpyrolidin. , N-butylpiperidin, and alicyclic amines such as N-propylhexahydroazepine (monocyclic); azabicyclo [2.2.1] heptane, azabicyclo [3.2.1] octane, azabicyclo [2.2] .2] Alicyclic amines (polycyclic) such as octane and azabicyclo [3.2.2] nonane; and 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2-ethylpyridine, 3- Fragrances such as ethylpyridine, 4-ethylpyridine, 2,4-dimethylpyridine, 2,4,6-trimethylpyridine, 3,4-cyclopentenopyridine, 5,6,7,8-tetrahydroisoquinoline, and isoquinolin. Amine can be mentioned.

The dehydrating agent used in the imidization step is not particularly limited, and examples thereof include acetic anhydride, propionic anhydride, isobutyric anhydride, pivalic acid anhydride, butyric anhydride, and isovaleric acid anhydride.

In the mixing and imidization steps of each raw material, the reaction temperature is not particularly limited, but is, for example, 15 to 350 ° C, preferably 20 to 100 ° C. The reaction time is also not particularly limited, but is, for example, about 10 minutes to 10 hours. If necessary, the reaction may be carried out under conditions of an inert atmosphere or reduced pressure. The reaction may be carried out in a solvent, and examples of the solvent include those used for preparing a varnish. After the reaction, the polyimide resin or the polyamide resin is purified. Examples of the purification method include a method in which a poor solvent is added to the reaction solution to precipitate the resin by a reprecipitation method, the resin is dried to remove the precipitate, and if necessary, the precipitate is washed with a solvent such as methanol and dried. Can be mentioned.
For the production of the polyimide resin, for example, the production method described in JP-A-2006-199945 or JP-A-2008-163107 may be referred to. Commercially available products can also be used as the polyimide resin, and specific examples thereof include Neoprim (registered trademark) manufactured by Mitsubishi Gas Chemical Company, Inc., KPI-MX300F manufactured by Kawamura Sangyo Co., Ltd., and the like.

The weight average molecular weight of the polyimide resin or the polyamide resin is preferably 200,000 or more, more preferably 250,000 or more, still more preferably 300,000 or more, preferably 600,000 or less, more preferably 550, It is 000 or less, more preferably 500,000. The larger the weight average molecular weight of the polyimide resin or the polyamide resin, the more easily it tends to exhibit high bending resistance when formed into a film. Therefore, from the viewpoint of enhancing the bending resistance of the optical film, it is preferable that the weight average molecular weight is at least the above lower limit. On the other hand, the smaller the weight average molecular weight of the polyimide resin or the polyamide resin, the easier it is to lower the viscosity of the varnish and improve the processability. Further, the stretchability of the polyimide resin or the polyamide resin tends to be easily improved. Therefore, from the viewpoint of processability and stretchability, the weight average molecular weight is preferably not more than the above upper limit. In the present application, the weight average molecular weight can be obtained by gel permeation chromatography (GPC) measurement and converted to standard polystyrene, and can be calculated by, for example, the method described in Examples.

The imidization ratio of the polyimide resin in the optical film is preferably 95 to 100%, more preferably 97 to 100%, still more preferably 98 to 100%, and particularly preferably 100%. From the viewpoint of the stability of the varnish and the mechanical properties of the obtained optical film, the imidization ratio is preferably at least the above lower limit. The imidization rate can be determined by an IR method, an NMR method, or the like. From the above viewpoint, the imidization ratio of the polyimide resin contained in the varnish is preferably within the above range.

In a preferred embodiment of the present invention, the polyimide resin or polyamide resin contained in the optical film of the present invention contains a halogen atom such as a fluorine atom which can be introduced by, for example, the above-mentioned fluorine-containing substituent or the like. Good. When the polyimide resin or the polyamide resin contains halogen atoms, it is easy to improve the elastic modulus of the optical film and reduce the yellowness (YI value). When the elastic modulus of the optical film is high, it is easy to suppress the occurrence of scratches and wrinkles in the film, and when the yellowness of the optical film is low, it is easy to improve the transparency of the film. The halogen atom is preferably a fluorine atom. Preferred fluorine-containing substituents for containing a fluorine atom in the polyimide resin or the polyamide resin include, for example, a fluoro group and a trifluoromethyl group.

The content of the halogen atom in the polyimide resin or the polyamide resin is preferably 1 to 40% by mass, more preferably 5 to 40% by mass, and further, based on the mass of the polyimide resin or the polyamide resin. It is preferably 5 to 30% by mass. When the content of the halogen atom is 1% by mass or more, the elastic modulus at the time of film formation is further improved, the water absorption rate is lowered, the yellowness (YI value) is further reduced, and the transparency is more likely to be improved. If the halogen atom content exceeds 40% by mass, synthesis may become difficult.

In one embodiment of the present invention, the content of the polyimide resin and / or the polyamide resin in the optical film is preferably 40% by mass or more, more preferably 50% by mass, based on the total mass of the optical film. The above is more preferably 70% by mass or more. It is preferable that the content of the polyimide resin and / or the polyamide resin is at least the above lower limit from the viewpoint of easily improving the bending resistance and the like. The content of the polyimide resin and / or the polyamide resin in the optical film is usually 100% by mass or less based on the total mass of the optical film.

The optical film of the present invention preferably contains two or more resins selected from the group consisting of polyimide resins and polyamide resins. When the optical film contains the two or more resins, in other words, for example, when the varnish contains the two or more resins in the method for producing an optical film described later, the viscosity of the varnish is easily adjusted to an appropriate range. be able to. In particular, in the coating step of the manufacturing method, it becomes easy to apply the varnish to the base material to form a uniform coating film. As a result, it becomes easy to adjust the manufactured optical film to the range of the formulas (1) to (3). In such a case, the visibility of the optical film in the wide-angle direction is further improved.

The two or more resins are, for example, two or more polyimide resins, two or more polyamide resins, and a combination of one or more polyimide resins and one or more polyamide resins.
In particular, among the two or more resins, two or more polyimide resins or two or more polyamide resins having different weight average molecular weights are preferable. Of the two or more polyimide resins or the two or more polyamide resins, the weight average molecular weight of at least one polyimide resin or at least one polyamide resin may be 250,000 to 500,000. The weight average molecular weight of at least one polyimide-based resin or at least one polyamide-based resin may be 200,000 to 450,000.
In particular, among the two or more resins, more preferably, two polyimide-based resins or two polyamide-based resins having different weight average molecular weights from each other. Of the two polyimide resins or the two polyamide resins, the weight average molecular weight of one polyimide resin or one polyamide resin may be 250,000 to 500,000, and the other polyimide resin or the other The weight average molecular weight of the polyamide resin of the above may be 200,000 to 450,000.

When the optical film contains two polyimide resins or two polyamide resins, the weight ratio of one polyimide resin or one polyamide resin to the other polyimide resin or the other polyamide resin (former / latter). ) Can be appropriately selected depending on the type of resin and the desired solid content concentration of the varnish, and may be, for example, 5/95 to 95/5.

[15. Additive]
The optical film of the present invention may further contain additives. Examples of such additives include fillers (more specifically, silica particles and the like), ultraviolet absorbers, whitening agents, silica dispersants, antioxidants, pH adjusters and leveling agents.

(Silica particles)
The optical film of the present invention may further contain silica particles as an additive. The content of the silica particles is preferably 1% by mass or more, more preferably 3% by mass or more, still more preferably 5% by mass or more, based on the total mass of the optical film. The content of the silica particles is preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 45% by mass or less, based on the total mass of the optical film. Further, the content of the silica particles can be combined by selecting an arbitrary lower limit value and upper limit value among these upper limit values and lower limit values. When the content of the silica particles is within the numerical range of the upper limit value and / or the lower limit value, the silica particles are less likely to aggregate in the optical film of the present invention and tend to be uniformly dispersed in the state of the primary particles. It is possible to suppress a decrease in visibility of the optical film of the present invention.

The particle size of the silica particles is preferably 1 nm or more, more preferably 3 nm or more, further preferably 5 nm or more, particularly preferably 8 nm, preferably 30 nm or less, more preferably 28 nm or less, still more preferably 25 nm or less. When the content of silica particles is within the numerical range of the upper limit value and / or the lower limit value, it is difficult for the optical film of the present invention to interact with light of a specific wavelength in white light. It is possible to suppress a decrease in visibility. In the present specification, the particle size of the silica particles indicates the average primary particle size. The particle size of the silica particles in the optical film can be measured by imaging with a transmission electron microscope (TEM). The particle size of the silica particles before the optical film is produced (for example, before being added to the varnish) can be measured by a laser diffraction type particle size distribution meter. The method for measuring the particle size of the silica particles will be described in detail in Examples.

Examples of the form of the silica particles include a silica sol in which the silica particles are dispersed in an organic solvent and the like, and a silica powder prepared by a vapor phase method. Among these, silica sol is preferable from the viewpoint of workability.

The silica particles may be surface-treated, and may be, for example, silica particles obtained by substituting a solvent (more specifically, γ-butyrolactone, etc.) with a water-soluble alcohol-dispersed silica sol. The water-soluble alcohol is an alcohol having 3 or less carbon atoms per hydroxy group in one water-soluble alcohol molecule, and examples thereof include methanol, ethanol, 1-propanol, and 2-propanol. Although it depends on the compatibility between the silica particles and the types of the polyimide resin and the polyamide resin, usually, when the silica particles are surface-treated, the compatibility with the polyimide resin and the polyamide resin contained in the optical film is improved, and the silica Since the dispersibility of the particles tends to be improved, the decrease in visibility of the present invention can be suppressed.

(UV absorber)
The optical film of the present invention may further contain an ultraviolet absorber. Examples thereof include triazine-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzoate-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers. These may be used alone or in combination of two or more. Suitable commercially available UV 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 BASF Japan Ltd. Chinubin (registered trademark) 1577 and the like can be mentioned. The content of the ultraviolet absorber is preferably 1 phr or more and 10 phr or less, and more preferably 3 phr or more and 6 phr or less, based on the mass of the optical film of the present invention.

(Whitening agent)
The optical film of the present invention may further contain a whitening agent (hereinafter, may be abbreviated as BA). The whitening agent can be added to adjust the color when, for example, an additive other than the whitening agent is added. Examples of the whitening agent include monoazo dyes, triarylmethane dyes, phthalocyanine dyes, and anthraquinone dyes. Among these, anthraquinone dyes are preferable. Suitable commercially available whitening agents include, for example, Macrolex® Violet B manufactured by LANXESS, Sumiplast® Violet B manufactured by Sumika Chemtex Co., Ltd., and Diaresin manufactured by Mitsubishi Chemical Corporation. (Registered trademark) Blue G and the like can be mentioned. These may be used alone or in combination of two or more. The content of the whitening agent is preferably 5 ppm or more and 40 ppm or less based on the mass of the optical film of the present invention.

The use of the optical film of the present invention is not particularly limited, and it may be used for various purposes. As described above, the optical film of the present invention may be a single layer or a laminated body, the optical film of the present invention may be used as it is, or a laminated body with another film. May be used as. Since the optical film of the present invention has excellent surface quality, it is useful as an optical film in an image display device or the like. When the optical film is a laminated body, it is referred to as an optical film including all the layers laminated on one side or both sides of the optical film.

The use of the optical film of the present invention is not particularly limited, and may be used for various purposes. Since the optical film of the present invention is excellent in visibility in the wide-angle direction, it is useful as an optical film in an image display device or the like. In particular, the optical film of the present invention is useful as a front plate of an image display device, particularly a front plate (window film) of a flexible display. The flexible display has, for example, a flexible functional layer and the optical film that is superposed on the flexible functional layer and functions as a front plate. That is, the front plate of the flexible display is arranged on the visible side above the flexible functional layer. This front plate has a function of protecting the flexible functional layer.

[16. Optical film manufacturing method]
The optical film of the present invention is not particularly limited, but for example, the following steps:
(A) A step of preparing a liquid containing the resin and the filler (hereinafter, may be referred to as varnish) (varnish preparation step).
(B) A step of applying varnish to a base material 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). )
It can be manufactured by a method including.

In the varnish preparation step, the varnish is prepared by dissolving the resin in a solvent, adding the filler and, if necessary, other additives, and stirring and mixing. When silica is used as the filler, a silica sol obtained by substituting a dispersion of silica sol containing silica with a solvent in which the resin can be dissolved, for example, a solvent used for preparing the following varnish may be added to the resin.

The solvent used for preparing the varnish is not particularly limited as long as the resin can be dissolved. Examples of such a solvent include amide solvents such as N, N-dimethylacetamide (DMAc) and N, N-dimethylformamide; lactone solvents such as γ-butyrolactone (GBL) and γ-valerolactone; dimethyl sulfoxide and dimethyl sulfoxide. , Sulfolane and other sulfur-containing solvents; carbonate solvents such as ethylene carbonate and propylene carbonate; and combinations thereof. Among these, an amide solvent or a lactone solvent is preferable. These solvents can be used alone or in combination of two or more. Further, the varnish may contain water, an alcohol solvent, a ketone solvent, an acyclic ester solvent, an ether solvent 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 step, a 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 method, reverse coating, roll coating method such as gravure coating, die coating method, comma coating method, lip coating method, screen coating method, fountain coating method, salivation molding method and the like. ..

In the optical film forming step, the coating film is dried (referred to as first drying), peeled from the substrate, and then 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 carried out under conditions of an inert atmosphere or reduced pressure, if necessary. The first drying is preferably carried out at a relatively low temperature over a long period of time. When the first drying is performed at a relatively low temperature for a long time, the reflection mapability value of the produced optical film easily satisfies the equations (1) to (3).

Here, when the optical film of the present invention is produced industrially, the actual manufacturing environment is often disadvantageous in improving the visibility in the wide-angle direction as compared with the manufacturing environment at the laboratory level, and as a result, It is difficult to improve the visibility of the optical film in the wide-angle direction. As mentioned above, it is preferable to carry out the first drying at a relatively low temperature for a long time, but at the laboratory level, when the first drying is carried out, the drying is carried out in a closed dryer. Therefore, the surface of the optical film is relatively less likely to be roughened due to external factors. On the other hand, in the case of industrially producing an optical film, for example, since it is necessary to heat a large area in the first drying, a blower may be used at the time of heating. As a result, the surface condition of the optical film tends to be rough, and it is difficult to improve the visibility of the optical film in the wide-angle direction.

When drying by heating, the temperature of the first drying is preferably 60 to 150 ° C., more preferably 60 to 140 ° C. in consideration of the above-mentioned external factors, especially when the optical film is industrially produced. More preferably, it is 70 to 140 ° C. The first drying time is preferably 1 to 60 minutes, more preferably 5 to 40 minutes. In particular, in consideration of the above-mentioned external factors in the industrial production of optical films, it is preferable that the first drying is carried out under three or more stages of drying temperature conditions. The multi-step conditions can be carried out at the same or different temperature conditions and / or drying times in each step, for example, drying may be carried out in 3 to 10 steps, preferably 3 to 8 steps. When the first drying is carried out under a multi-step condition of three or more steps, the reflection mapability value of the produced optical film easily satisfies the formulas (1) to (3), and the visibility in the wide-angle direction is improved. In aspects under multi-step conditions of three or more steps, it is preferred that the temperature profile of the first drying includes temperature rise and fall. That is, the first drying condition in the optical film forming step is preferably a heating temperature condition in which the temperature profile includes three or more steps including temperature raising and lowering. Taking the case of four stages as such a temperature profile as an example, the temperature of the first drying is 70 to 90 ° C (first temperature), 90 to 120 ° C (second temperature), and 80 to 120 ° C, respectively. (Third temperature) and 80-100 ° C. (fourth temperature). 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 from the third temperature to the fourth temperature. To lower the temperature. Here, the time of the first drying is, for example, 5 to 15 minutes in each step. The first drying is preferably carried out so that the residual amount of the solvent in the dry coating film is preferably 5 to 15% by mass, more preferably 6 to 12% by mass with respect to the mass of the dry coating film. When the residual amount of the solvent is in the above range, the peelability of the dry coating film from the substrate is good, and the reflection mapping property values of the produced optical film easily satisfy the 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 second drying time is preferably 10 to 60 minutes, more preferably 30 to 50 minutes.

The second drying may be carried out by a single-wafer method, but in the case of industrial production, it is preferably carried out by a roll-to-roll method from the viewpoint of production efficiency. In the single-wafer type, it is preferable to dry in a state of being uniformly extended in the in-plane direction.
In the roll-to-roll method, from the viewpoint of easily satisfying the range of the formulas (1) to (3), it is preferable to dry the dried coating film in a state of being stretched in the transport direction, and the transport speed is preferably 0. .1 to 5 m / min, more preferably 0.5 to 3 m / min, still more preferably 0.7 to 1.5 m / min. The second drying may be carried out under one-step or multi-step conditions. The multi-step conditions can preferably be carried out in each step with at least one selected from the same or different temperature conditions, drying time and hot air velocity, eg, 3-10 steps, preferably 3 steps. Drying may be performed in steps of ~ 8, and it is preferable to carry out the drying under a multi-step condition from the viewpoint that the optical film easily satisfies the range of the formulas (1) to (3). Further, at each stage, the wind speed of the hot air is preferably 5 to 20 m / min, more preferably 10 to 10 from the viewpoint that the reflection mapability value of the produced optical film easily satisfies the formulas (1) to (3). It is 15 m / min, more preferably 11-14 m / min.

When the optical film of the present invention includes a hard coat layer, for example, the hard coat layer is formed by applying a curable composition to at least one surface of the optical film to form a coating film, and high energy rays are applied to the coating film. It can be formed by irradiating and curing the coating film.

Examples of the base material are a SUS plate for metal, PET film, PEN film for resin, other polyimide resin or polyamide resin film, cycloolefin polymer (COP) film, acrylic film. And so on. Among them, PET film, COP film and the like are preferable from the viewpoint of excellent smoothness and heat resistance, and PET film is more preferable from the viewpoint of adhesion to an optical film and cost.

When the optical film of the present invention includes a hard coat layer, the hard coat layer is formed by using, for example, a composition for forming a hard coat layer. The composition for forming a hard coat layer contains, for example, a monomer and / or an oligomer, a photoinitiator, silica, a leveling agent, and a solvent. Examples of the monomer include a polyfunctional monomer (more specifically, a bifunctional monomer, a trifunctional monomer, etc.). Examples of the oligomer include a 10-functional urethane oligomer. Examples of the solvent include methyl ethyl ketone, polypropylene glycol monomethyl ether and the like.

In the hard coat layer forming step, the coating film is irradiated with high energy rays (for example, active energy rays) to cure the coating film to form a hard coat layer. The irradiation intensity is appropriately determined by 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 0.1~6,000mW / cm ^2, more preferably 10~1,000mW / cm ^2, more preferably from 20 to 500 mW / cm ^2. When the irradiation intensity is within the above range, an appropriate reaction time can be secured, 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 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 50~1,000mJ / cm ^2, more preferably is set to be 80~500mJ / cm ^2. When the integrated light amount is within the above range, a sufficient amount of active species derived from the polymerization initiator can be generated to allow the curing reaction to proceed more reliably, and the irradiation time does not become too long, resulting in good productivity. Can be maintained. Further, it is useful because the hardness of the hard coat layer can be further increased by undergoing the irradiation step in this range. From the viewpoint of improving the smoothness of the hard coat layer and further improving the visibility in the wide angle direction of the optical film, optimization of the type of solvent, component ratio, solid content concentration, addition of a leveling agent, and the like can be mentioned.

<Flexible image display device>
The present invention includes a flexible display device including the optical film. The optical film of the present invention is preferably used as a front plate in a flexible image display device, and the front plate may be referred to as a window film. The flexible image display device includes a laminate for a flexible image display device and an organic EL display panel, and the laminate for the flexible image display device is arranged on the visual side with respect to the organic EL display panel and is configured to be bendable. ing. The laminated body for the flexible image display device may further contain a polarizing plate and a touch sensor, and the stacking order thereof is arbitrary, but the window film, the polarizing plate, the touch sensor or the window film, and the touch are viewed from the visual side. It is preferable that the sensor and the polarizing plate are laminated in this order. If a polarizing plate is present on the visual side of the touch sensor, the pattern of the touch sensor is less likely to be visually recognized and the visibility of the displayed image is improved, which is preferable. Each member can be laminated using an adhesive, an adhesive, or the like. Further, a light-shielding pattern formed on at least one surface of any layer of the window film, the polarizing plate, and the touch sensor can be provided.

[Polarizer]
As described above, the flexible display device of the present invention preferably includes a polarizing plate, preferably a circular polarizing plate. The circular polarizing plate is a functional layer having a function of transmitting only the right or left circularly polarized light component by laminating a λ / 4 retardation plate on a linear polarizing plate. For example, the external light is converted to right circular polarization and reflected by the organic EL panel to block the left circular polarization, and only the light emitting component of the organic EL is transmitted to suppress the influence of the reflected light. It is used to make it 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 need to be theoretically 45 °, but practically 45 ± 10 °. The linear polarizing plate and the λ / 4 retardation plate do not necessarily have to be laminated adjacent to each other, and the relationship between the absorption axis and the slow phase axis may satisfy the above range. The circular polarizing plate in the present invention also includes an elliptical polarizing plate because it is preferable to achieve perfect circular polarization at all wavelengths, but it is not always necessary in practical use. It is also preferable to further laminate a λ / 4 retardation film on the visible side of the linear polarizing plate to convert the emitted light into circularly polarized light to improve the visibility when wearing polarized sunglasses.

The linear polarizing plate is a functional layer having a function of transmitting light vibrating in the transmission axis direction but blocking polarization of a vibration component perpendicular to the linear polarizing plate. The linear polarizing plate may be configured to include a linear polarizing element alone or a linear polarizing element and a protective film attached to at least one surface thereof. The thickness of the linear polarizing plate may be 200 μm or less, preferably 0.5 to 100 μm. When the thickness of the linear polarizing plate is within the above range, the flexibility of the linear polarizing plate tends to be difficult to decrease.

The linear polarizer may be a film-type polarizer produced by dyeing and stretching a polyvinyl alcohol (hereinafter, may be abbreviated as PVA) -based film. A dichroic dye such as iodine is adsorbed on the PVA-based film oriented by stretching, or the dichroic dye is oriented in a state of being adsorbed on the PVA to exhibit polarization performance. In the production of the film-type polarizer, other steps such as swelling, cross-linking with boric acid, washing with an aqueous solution, and drying may be included. The stretching and dyeing steps may be performed on the PVA-based film alone, or may be performed in a state of being laminated with another film such as polyethylene terephthalate. The thickness of the PVA-based film used is preferably 10 to 100 μm, and the draw ratio is preferably 2 to 10 times.

Further, as another example of the polarizer, there is a liquid crystal coating type polarizing element 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 particularly preferable when it has a higher-order orientation state such as a smectic phase because it can exhibit high polarization performance. Further, the liquid crystal compound preferably has a polymerizable functional group.
The dichroic dye compound is a dye that is oriented together with the liquid crystal compound and exhibits dichroism, and may have a polymerizable functional group, and the dichroic dye itself has a liquid crystal property. You may be.

Any of the compounds contained in the liquid crystal polarizing composition has a polymerizable functional group. The liquid crystal polarizing composition can further contain an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a cross-linking agent, a silane coupling agent and the like.

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

The alignment film is produced, for example, by applying an alignment film forming composition on a substrate and imparting orientation by rubbing, polarized light irradiation, or the like. The alignment film forming composition contains an alignment agent, and may further contain a solvent, a cross-linking agent, an initiator, a dispersant, a leveling agent, a silane coupling agent, and the like. Examples of the alignment agent include polyvinyl alcohols, polyacrylates, polyamic acids, and polyimides. When an orientation agent that imparts orientation by polarization irradiation is used, it is preferable to use an orientation agent containing a synnamate group. The weight average molecular weight of the polymer used as the alignment agent is, for example, about 10,000 to 1,000,000. The thickness of the alignment film is preferably 5 to 10,000 nm, and more preferably 10 to 500 nm in that the alignment regulating force is sufficiently exhibited.

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

As the protective film, any transparent polymer film may be used, and the same materials and additives used for the transparent base material of the window film can be used. Further, it may be a coating type protective film obtained by applying a cationic curing composition such as an epoxy resin or a radical curing composition such as acrylate and curing the film. The protective film may be 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 antioxidant, an antioxidant, if necessary. , Lubricants, solvents and the like may be contained. 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 within the above range, the flexibility of the film tends to be difficult to decrease.

The λ / 4 retardation plate is a film that gives a retardation of λ / 4 in a direction orthogonal to the traveling direction of incident light (in-plane direction of the film). The λ / 4 retardation plate may be a stretch-type 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 be used as a retardation adjuster, a plastic agent, an ultraviolet absorber, an infrared absorber, a colorant such as a pigment or a dye, a fluorescent whitening agent, a dispersant, a heat stabilizer, and a light stabilizer. It may contain an agent, an antioxidant, an antioxidant, a lubricant, a solvent and the like.

The thickness of the stretched retardation plate is preferably 200 μm or less, and more preferably 1 to 100 μm. When the thickness of the stretchable retardation plate is within the above range, the flexibility of the stretchable retardation plate tends to be difficult to decrease.

Further, as another example of the λ / 4 retardation plate, there is a liquid crystal coating type retardation plate formed by coating a liquid crystal composition.

The liquid crystal composition contains a liquid crystal compound exhibiting a liquid crystal state such as nematic, cholesteric, and smectic. The liquid crystal compound has a polymerizable functional group.

The liquid crystal composition can further contain an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a cross-linking agent, a silane coupling agent, and the like.

The liquid crystal coating type retardation plate can be manufactured by applying a liquid crystal composition on a substrate and curing the liquid crystal composition to form a liquid crystal retardation layer, similarly to the liquid crystal polarizing layer. The liquid crystal coating type retardation plate can be formed to be thinner than the stretch 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 base material, transferred and laminated, or the base material can be laminated as it is. It is also preferable that the base material serves as a transparent base material for a protective film, a retardation plate, and 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 region, the in-plane phase difference is preferably 100 to 4 so that it becomes λ / 4 with respect to the vicinity of 560 nm, which has high luminosity factor. It is designed to be 180 nm, more preferably 130-150 nm. A reverse dispersion λ / 4 retardation plate using a material having a birefringence wavelength dispersion characteristic opposite to the usual one is preferable in that visibility is good. As such a material, for example, a stretchable retardation plate can be used as described in JP-A-2007-232873, and a liquid crystal-coated retardation plate can be used as described in JP-A-2010-30979. ..

Further, as another method, a technique for obtaining a wideband λ / 4 retardation plate by combining with a λ / 2 retardation plate is also known (for example, Japanese Patent Application Laid-Open No. 10-90521). The λ / 2 retardation plate is also manufactured by the same material method as the λ / 4 retardation plate. The combination of the stretchable retardation plate and the liquid crystal coating type retardation plate is arbitrary, but the thickness can be reduced by using the liquid crystal coating type retardation plate in both cases.

A method of laminating a positive C plate on the circular polarizing plate in order to improve visibility in an oblique direction is known (for example, Japanese Patent Application Laid-Open No. 2014-224738). The positive C plate may be a liquid crystal coating type retardation plate or a stretched retardation plate. The phase difference in the thickness direction of the retardation plate is preferably −200 to −20 nm, more preferably −140 to −40 nm.

[Touch sensor]
As described above, the flexible display device of the present invention preferably includes a touch sensor. The touch sensor is used as an input means. Examples of the touch sensor include various types such as a resistive film method, a surface acoustic wave method, an infrared method, an electromagnetic induction method, and a capacitance method, and a capacitance method is preferable.

The capacitive touch sensor is divided into an active region and an inactive region located outside the active region. The active area is an area corresponding to the area where the screen is displayed on the display panel (display unit), the area where the user's touch is sensed, and the inactive area is the area where the screen is not displayed on the display device (non-active area). This is the area corresponding to the display unit). The touch sensor is formed in a substrate having flexible characteristics, a sensing pattern formed in an active region of the substrate, and an inactive region of the substrate, and is connected to an external drive circuit via the sensing pattern and a pad portion. Each sensing line for can be included. As the substrate having flexible characteristics, the same material as the transparent substrate of the window film can be used.

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

The bridge electrode can be formed on the upper part of the insulating layer via the insulating layer on the upper part of the sensing pattern, the bridge electrode is formed on the substrate, and the insulating layer and the sensing pattern can be formed on the bridge electrode. The bridge electrode can be made of the same material as the sensing pattern, or it can be made of molybdenum, silver, aluminum, copper, palladium, gold, platinum, zinc, tin, titanium or two or more alloys of these. it can.

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 may be formed only between the joint of the first pattern and the bridge electrode, or may be formed as a layer covering the entire sensing pattern. In the case of a layer that covers the entire sensing pattern, the bridge electrode can connect the second pattern through a contact hole formed in the insulating layer.

The touch sensor is induced by a difference in transmittance between a pattern region in which a sensing pattern is formed and a non-pattern region in which a sensing pattern is not formed, specifically, a difference in refractive index in these regions. An optical adjustment layer may be further included between the substrate and the electrode as a means for appropriately compensating for the difference in light transmittance. The optical control layer may contain an inorganic insulating material or an organic insulating material. The optical control layer can be formed by coating a photocurable composition containing a photocurable organic binder and a solvent on a substrate. The photocurable composition may further contain inorganic particles. The refractive index of the optical control layer can be increased by the inorganic particles.

The photocurable organic binder contains a copolymer of each monomer such as an acrylate-based monomer, a styrene-based monomer, and a carboxylic acid-based monomer, as long as the effects of the present invention are not impaired. be able to. The photocurable organic binder may be, for example, a copolymer containing different repeating units such as an epoxy group-containing repeating unit, an acrylate repeating unit, and a carboxylic acid repeating unit.

Examples of the inorganic particles include zirconia particles, titania particles, alumina particles and the like.

The photocuring composition may further contain each additive such as a photopolymerization initiator, a polymerizable monomer, and a curing aid.

[Adhesive layer]
Each layer (window film, circular polarizing plate, touch sensor) forming the laminate for the flexible image display device and the film member (straight polarizing plate, λ / 4 retardation plate, etc.) constituting each layer are joined by an adhesive. Can be done. Examples of the adhesive include water-based adhesives, water-based solvent volatilization adhesives, organic solvent-based adhesives, solvent-free adhesives, solid adhesives, solvent volatilization adhesives, moisture-curable adhesives, heat-curable adhesives, and anaerobic adhesives. Uses commonly used adhesives such as curable type, active energy ray curable type adhesive, hardener mixed type adhesive, heat melt type adhesive, pressure sensitive type adhesive (adhesive), rewet type adhesive, etc. A water-based solvent volatilization type adhesive, an active energy ray-curable adhesive, and an adhesive can be preferably used. The thickness of the adhesive layer can be appropriately adjusted according to the required adhesive force and the like, and is preferably 0.01 to 500 μm, more preferably 0.1 to 300 μm. The laminated body for a flexible image display device has a plurality of adhesive layers, and the thickness and type of each may be the same or different.

As the water-based solvent volatilization type adhesive, a polyvinyl alcohol-based polymer, a water-soluble polymer such as starch, an ethylene-vinyl acetate-based emulsion, a styrene-butadiene-based emulsion, or the like in an aqueous-dispersed state can be used as the main component polymer. In addition to the main polymer and water, a cross-linking agent, a silane compound, an ionic compound, a cross-linking catalyst, an antioxidant, a dye, a pigment, an inorganic filler, an organic solvent and the like may be blended. When adhering with the water-based solvent volatilization type adhesive, the water-based solvent volatilization type adhesive can be injected between the layers to be adhered, the adherend layers are bonded, and then dried to impart adhesiveness. When the water-based solvent volatilization type adhesive is used, the thickness of the adhesive layer is preferably 0.01 to 10 μm, more preferably 0.1 to 1 μm. When the water-based solvent volatilization type adhesive is used in a plurality of layers, the thickness and type of each layer 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 is irradiated with active energy rays to form an adhesive layer. The active energy ray-curable composition can contain at least one polymer of a radically polymerizable compound and a cationically polymerizable compound similar to those contained in the hard coat composition. As the radically polymerizable compound, the same compound as the radically polymerizable compound in the hard coat composition can be used.

As the cationically polymerizable compound, the same compound as the cationically polymerizable compound in the hard coat composition can be used.

As the cationically polymerizable compound used in the active energy ray-curing composition, an epoxy compound is particularly preferable. It is also preferable to include a monofunctional compound as a reactive diluent in order to reduce the viscosity of the adhesive composition.

The active energy ray composition can contain a monofunctional compound in order to reduce the viscosity. Examples of the monofunctional compound include an acrylate-based monomer having one (meth) acryloyl group in one molecule and a compound having one epoxy group or oxetanyl group in one molecule, for example, glycidyl (meth). ) Acrylate and the like can be mentioned.

The active energy ray composition can further contain a polymerization initiator. Examples of the polymerization initiator include radical polymerization initiators, cationic polymerization initiators, radicals and cationic polymerization initiators, and these are 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 to promote radical polymerization and cation polymerization. In the description of the hard coat composition, an initiator that can initiate at least one of radical polymerization or cationic polymerization by irradiation with active energy rays can be used.

The active energy ray-curing composition further comprises an ion scavenger, an antioxidant, a chain transfer agent, an adhesion imparting agent, a thermoplastic resin, a filler, a fluid viscosity modifier, a plasticizer, a defoaming agent solvent, an additive, and a solvent. Can be included. When two layers to be adhered are bonded by the active energy ray-curable adhesive, the active energy ray-curable composition is applied to either or both of the layers to be adhered, and then bonded to each layer. Alternatively, both layers to be adhered can be adhered by irradiating them with active energy rays and curing them. 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 for forming a plurality of adhesive layers, the thickness and type of the respective layers may be the same or different.

The pressure-sensitive adhesive is classified into an acrylic pressure-sensitive adhesive, a urethane-based pressure-sensitive adhesive, a rubber-based pressure-sensitive adhesive, a silicone-based pressure-sensitive adhesive, and the like according to the main polymer, and any of them can be used. In addition to the main polymer, the pressure-sensitive adhesive may contain a cross-linking agent, a silane compound, an ionic compound, a cross-linking catalyst, an antioxidant, a tackifier, a plasticizer, a dye, a pigment, an inorganic filler and the like. A pressure-sensitive adhesive layer is formed by dissolving and dispersing each component constituting the pressure-sensitive adhesive in a solvent to obtain a pressure-sensitive adhesive composition, applying the pressure-sensitive adhesive composition onto a substrate, and then drying the mixture. To. The adhesive layer may be directly formed, or a separately formed base material may be transferred. It is also preferable to use a release film to cover the adhesive surface before bonding. When the active energy ray-curable adhesive is used, the thickness of the adhesive layer is preferably 0.1 to 500 μm, more preferably 1 to 300 μm. When a plurality of layers of the pressure-sensitive adhesive are used, the thickness and type of each layer may be the same or different.

[Shading pattern]
The shading pattern can be applied as at least part of the bezel or housing of the flexible image display device. The light-shielding pattern hides the wiring arranged at the edge of the flexible image display device to make it difficult to see, thereby improving the visibility of the image. The shading 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 be various colors such as black, white, and metallic. The light-shielding pattern can be formed of a pigment for embodying color and a polymer such as an acrylic resin, an ester resin, an epoxy resin, polyurethane, or silicone. They can also be used alone or in admixture of two or more. The shading pattern can be formed by various methods such as printing, lithography, and inkjet. The thickness of the shading pattern is preferably 1 to 100 μm, more preferably 2 to 50 μm. It is also preferable to give a shape such as an inclination in the thickness direction of the light-shielding pattern.

Hereinafter, the present invention will be described in more detail with reference to Examples. Unless otherwise specified, "%" and "part" in the example mean mass% and parts by mass. First, the evaluation method will be described.

<1. Manufacturing of optical film>
[1-1. Resin preparation]
(Production Example 1: Preparation of Polyimide Resin 1)
A reaction vessel equipped with a silica gel tube, a stirrer, and a thermometer in a separable flask, and an oil bath were prepared. 75.6 g of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 2,2'-bis (trifluoromethyl) -4,4'-in a reaction vessel installed in an oil bath. 54.5 g of diaminodiphenyl (TFMB) was added. While stirring the contents in the reaction vessel at 400 rpm, 530 g of N, N-dimethylacetamide (DMAc) was further added into the reaction vessel, and stirring was continued until the contents in the reaction vessel became a uniform solution. Subsequently, stirring was continued for another 20 hours while adjusting the temperature inside the container to be in the range of 20 to 30 ° C. using an oil bath, and the reaction was carried out to generate a polyamic acid. After 30 minutes, the stirring speed was changed to 100 rpm. After stirring for 20 hours, the reaction system temperature was returned to room temperature (25 ° C.), and 650 g of DMAc was further added into the reaction vessel so that the polymer concentration became 10% by mass based on the total mass of the contents in the reaction vessel. It was adjusted. Further, 32.3 g of pyridine and 41.7 g of acetic anhydride were further charged into the reaction vessel, and the contents in the reaction vessel were stirred at room temperature for 10 hours for imidization. The polyimide varnish was taken out from the reaction vessel. The obtained polyimide varnish was added dropwise to methanol for reprecipitation. The precipitate was taken out by filtration, and the obtained precipitate was dried by heating to remove the solvent to obtain a polyimide resin 1 as a solid content (powder). When the obtained polyimide resin 1 was subjected to GPC measurement, the weight average molecular weight was 350,000. The imidization ratio of the polyimide resin 1 was 98.8%.

(Manufacturing Example 2: Preparation of Polyimide Resin 2)
A polyimide resin 2 having a weight average molecular weight of 280,000 and an imidization ratio of 98.3% was produced in the same manner as in Production Example 1 except that the reaction time was changed from 20 hours to 16 hours.

(Production Example 3: Preparation of Polyamide-imide Resin 1)
A reaction vessel in which a stirring blade was attached to a separable flask having a capacity of 1 L and an oil bath were prepared. 45 g (140.52 mmol) of TFMB and 768.55 g of DMAc were put into a reaction vessel installed in an oil bath. Under a nitrogen gas atmosphere, the contents in the reaction vessel were stirred at room temperature to dissolve TFMB in DMAc. Then, 18.92 g (42.58 mmol) of 6FDA was further charged into the reaction vessel, and the contents in the reaction vessel were continuously stirred at room temperature for 3 hours. Then, 4.19 g (14.19 mmol) of 4,4'-oxybis (benzoyl chloride) (OBBC) and then 17.29 g (85.16 mmol) of terephthaloyl chloride (TPC) were further added to the reaction vessel at room temperature. Stirring was continued for 1 hour. Next, 4.63 g (49.68 mmol) of 4-methylpyridine and 13.04 g (127.75 mmol) of acetic anhydride were further added to the reaction vessel, and the contents in the reaction vessel were stirred at room temperature for 30 minutes. Then, the temperature inside the container was raised to 70 ° C. using an oil bath. The temperature inside the vessel was maintained at 70 ° C., and the contents in the reaction vessel were further stirred for 3 hours to obtain a reaction solution.
The obtained reaction solution was cooled to room temperature and poured into a large amount of methanol in the form of filaments. The precipitated precipitate was taken out and immersed in methanol for 6 hours. The precipitate was then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyamide-imide resin 1. The weight average molecular weight of the polyamide-imide resin 1 was 400,000, and the imidization rate was 98.1%.

(Production Example 4: Preparation of Polyamide-imide Resin 2)
A reaction vessel in which a stirring blade was attached to a separable flask having a capacity of 1 L and an oil bath were prepared. 45 g (140.52 mmol) of TFMB and 768.55 g of DMAc were put into a reaction vessel installed in an oil bath. The contents in the reaction vessel were stirred at room temperature in a nitrogen gas atmosphere to dissolve TFMB in DMAc. Next, 19.01 g (42.79 mmol) of 6FDA was further charged into the reaction vessel, and the contents in the reaction vessel were stirred at room temperature for 3 hours. Then, 4.21 g (14.26 mmol) of OBBC and then 17.30 g (85.59 mmol) of TPC were further added into the reaction vessel, and the contents in the reaction vessel were stirred at room temperature for 1 hour. Next, 4.63 g (49.68 mmol) of 4-methylpyridine and 13.04 g (127.75 mmol) of acetic anhydride were further added to the reaction vessel, and the contents in the reaction vessel were stirred at room temperature for 30 minutes. Then, the temperature inside the container was raised to 70 ° C. using an oil bath. The temperature inside the container was maintained at 70 ° C. and the mixture was further stirred for 3 hours to obtain a reaction solution.
The obtained reaction solution was cooled to room temperature, poured into a large amount of methanol in the form of filaments, the precipitated precipitate was taken out, and the mixture was immersed in methanol for 6 hours. The precipitate was then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyamide-imide resin 2. The weight average molecular weight of the obtained polyamide-imide resin 2 was 365,000, and the imidization ratio was 98.3%.

[1-2. Preparation of silica dispersion]
(Production Example 5: Preparation of Dispersion Solution 1)
Methanol-dispersed organic-treated silica (particle size 25 nm) was replaced with γ-butyrolactone (GBL) to obtain GBL-dispersed organic-treated silica (solid content 30.5%). This dispersion was designated as dispersion 1.

[1-3. Production of composition for forming hard coat layer]
(Production Example 6: Production of Composition 1 for Forming Hard Coat Layer)
Isopropanol silica sol (“IPA-ST-L” manufactured by Nissan Chemical Industries, Ltd., particle size 20 to 30 nm) 25% by mass, 10-functional urethane acrylate oligomer (“UV1000” manufactured by Shina T & C) 15% by mass, trifunctional monomer ( M340, MIRAMER) 18.5% by mass, photoinitiator (BASF "Irgacure (registered trademark) -184") 1.2% by mass, leveling agent (BYK "BYK-3530") 0.3% by mass , And 40% by mass of methyl ethyl ketone (MEK) were mixed to prepare a composition 1 for forming a hard coat layer.

(Production Example 7: Production of composition for forming a hard coat layer)
10% by mass of 10-functional urethane acrylate oligomer (“UV1000” manufactured by Shina T & C), 38.5% by mass of bifunctional monomer (M200, MIRAMER), 1.2% by mass of photoinitiator (“Irgacure 184” manufactured by BASF), A composition 2 for forming a hard coat layer was produced by mixing 0.3% by mass of a leveling agent (“BYK-3530” manufactured by BYK) and 53% by mass of methyl ethyl ketone (MEK).

[1-4. Preparation of varnish]
(Production Example 8: Preparation of varnishes (1) and (2))
The varnishes (1) and (2) were produced by dissolving a polyimide resin in a solvent with the compositions shown in Table 1.
In Table 1, the content (unit: mass%) of the column "solvent" indicates the ratio of the mass of the specific solvent to the total mass of the solvent (unit: mass%). The content (unit: mass%) of the column "polyimide-based resin" indicates the ratio (unit: mass%) of the mass of the specific polyimide-based resin to the total mass of all the polyimide-based resins. PI-1, PI-2, PAI-1, and PAI-2 in the column "Polyimide-based resin" indicate polyimide resin 1, polyimide resin 2, polyamide-imide resin 1, and polyamide-imide resin 2, respectively. The content (unit:%) in the column "solid content ratio" indicates the ratio (unit: mass%) of the total mass of the components other than the solvent to the mass of the varnish.

(Production Example 9: Preparation of varnish (3))
The varnish (3) was produced with the composition shown in Table 1. Specifically, the varnish (3) is mixed with the GBL solvent at room temperature so that the composition ratio (mass ratio) of the polymer and the filler (contained in the dispersion liquid 1) is 60:40, and further, an ultraviolet absorber. Sumisorb 340 (UVA) manufactured by Sumika Chemtex Co., Ltd. as a whitening agent and Sumiplast® Violet B (BA) manufactured by Sumika Chemtex Co., Ltd. as a whitening agent with respect to the total mass of polymer and silica. It was added so as to be 5.7 phr and 35 ppm, respectively, and stirred until uniform to obtain a varnish (3).
In Table 1, the content (unit: wt%) of the column “filler” indicates the ratio of the mass of the filler to the total mass of the total filler dispersion (unit: mass%). The content (unit: Phr) of the column “additive UVA” indicates the ratio (unit: mass%) of the mass of UVA to the total mass of the solid content (silica) of the polyimide resin and the dispersion liquid 1. The content (unit: ppm) of the column “additive BA” indicates the ratio (unit: ppm) of the mass of BA to the total mass of the solid content (silica) of the polyimide resin and the dispersion liquid 1.

[1-5. Manufacturing of optical film]
(Example 1: Production of optical film 1)
A coating film of the varnish (1) was formed on a PET (polyethylene terephthalate) film (“A4100” manufactured by Toyobo Co., Ltd., thickness 188 μm, thickness distribution ± 2 μm) by salivation molding. The linear velocity was 0.4 m / min. The coating film was dried by heating at 70 ° C. for 8 minutes, 100 ° C. for 10 minutes, 90 ° C. for 8 minutes, and 80 ° C. for 8 minutes, respectively, and the coating film was peeled off from the PET film. Using the obtained raw material film 1 (width 700 mm) as a gripper and using a tenter type dryer (1 to 6 chamber configuration) using a clip, the solvent was removed to obtain a polyimide film 1 having a thickness of 79 μm. The temperature inside the dryer is set to 200 ° C, and the ratio of the clip gripping width 25 mm, the film transport speed 1.0 m / min, the film width at the dryer inlet (distance between clips) and the film width at the dryer outlet is 1.0. The wind speed in each room of the tenter type dryer was adjusted to 13.5 m / sec in one room, 13 m / sec in two rooms, and 11 m / sec in three to six rooms. After the film was separated from the clip, the clip portion was slit, a PET-based protective film was attached to the film, and the film was wound around an ABS 6-inch core to obtain a roll film.

(Example 2: Production of optical film 2)
The hard coat layer forming composition 1 produced in Production Example 6 was applied to the surface of the optical film 1 obtained in Example 1 that was in contact with the PET film of the base material at the time of film formation to a thickness of 20 μm after curing (hard coat). The film was applied in layers) and dried in an oven at 80 ° C. for 1 minute. Then, a high-pressure mercury lamp was used to irradiate light with a light amount of 350 mJ / cm ² , and the coating film was cured to form a first hard coat layer. The hard coat layer forming composition 2 prepared in Production Example 7 was applied to the other surface so as to be 15 μm after curing, and dried in an oven at 80 ° C. for 2 minutes. Then, light was irradiated with a light amount of 350 mJ / cm ² using a high-pressure mercury lamp to cure the coating film to form a second hard coat layer, thereby producing an optical film 2 including the hard coat layer.

(Example 3: Production of optical film 3)
The varnish (1) was changed to the varnish (2), the linear velocity was changed from 0.4 m / min to 0.3 m / min, and the heating conditions of the coating film were sequentially changed to 70 ° C. for 8 minutes, 100 ° C. for 10 minutes, 90. The same as the method for producing the optical film 1 except that the temperature was changed from 8 minutes at 80 ° C. to 10 minutes at 80 ° C., 10 minutes at 100 ° C., 10 minutes at 90 ° C., and 10 minutes at 80 ° C. An optical film 3 having a thickness of 49 μm was produced.

(Example 4: Production of optical film 4)
The optical film 4 having a thickness of 79 μm is similar to the manufacturing method of the optical film 1 except that the varnish (1) is changed to the varnish (3) and the linear velocity is changed from 0.4 m / min to 0.2 m / min. Manufactured.

(Example 5: Production of optical film 5)
The heating conditions are 70 ° C. for 8 minutes, 100 ° C. for 10 minutes, 90 ° C. for 8 minutes, 80 ° C. for 8 minutes to 70 ° C. for 8 minutes, 90 ° C. for 10 minutes, 85 ° C. for 8 minutes, and 80 ° C. for 8 minutes. An optical film 5 having a thickness of 30 μm was produced in the same manner as in the production of the optical film 4, except that the optical film 5 was changed to.

(Comparative Example 1: Preparation of Optical Film 6)
A polyimide film (“UPILEX” manufactured by Ube Industries, Ltd., thickness 50 μm) was prepared as the optical film 6.

The formulation of the composition and the composition of the optical film are summarized in Table 2. In Table 2, the column "with or without HC" indicates whether or not a hard coat layer is provided (yes) or not (no).

<2. Measurement method>
When the optical films obtained in Examples and Comparative Examples had a protective film, the following measurements and evaluations were carried out using the optical film with the protective film peeled off.
(2-1. Measurement of transmission mapping property value of optical film)
The transmission mapping property value of the optical film was measured by the transmission method as follows using a mapping property measuring device (“ICM-1” manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K 7345.
The optical film was placed on the image quality measuring instrument. Before installation, both sides of this optical film were lightly wiped with ethanol and dried to remove foreign matter from the surface before installation. Next, the amount of light and the cross-sectional area were adjusted, and white light adjusted to parallel light was applied to the optical film installed from an angle (incident angle) inclined by 60 ° in the MD direction with respect to the optical film plane. The transmitted light transmitted through the optical film was transmitted to an optical comb extending perpendicular to the optical axis of the irradiation light by adjusting the cross-sectional area, and the light transmitted through the optical comb was received by the receiver.
The optical comb (slit width: 0.125 mm) is moved by a predetermined unit width in the direction parallel to the plane of the optical comb and the slits in the optical comb are arranged, and the transmitted light of the optical comb is repeatedly received. It was. As a result, a received light waveform was obtained. From the obtained received light waveform, the maximum value M and the minimum value m of the relative light amount were obtained. The first transmission mapping property value C ₆₀ (MD) was calculated from the obtained M and m based on the formula (5).

The first transmission mapping property value except that the angle of incidence was changed from a direction perpendicular to the optical film plane to an angle inclined by 60 ° in the TD direction and an angle perpendicular to the optical film plane (an angle inclined by 0 °). In the same manner as in the above, the second transmission mapping property value C ₆₀ (TD) and the third transmission mapping property value C ₀ were calculated, respectively.

(2-2. Total light transmittance and haze of optical film)
The total light transmittance of the optical film conforms to JIS K 7361-1: 1997, and the haze conforms to JIS K 7136: 2000, using the fully automatic direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd. Was measured. The measurement sample was prepared by cutting the optical films of Examples and Comparative Examples into a size of 30 mm × 30 mm.

(2-3. Yellowness of optical film)
The yellow index (yellowness: YI value) of the optical film was measured by an ultraviolet-visible near-infrared spectrophotometer V-670 manufactured by JASCO Corporation. After performing background measurement in the absence of a sample, an optical film was set in a sample holder, transmittance was measured for light of 300 to 800 nm, and tristimulus values (X, Y, Z) were determined. The YI value was calculated based on the following formula. When the protective film is laminated on the surface opposite to the support of the optical film, the protective film is peeled off and the yellow index is measured.
YI value = 100 × (1.2769X-1.0592Z) / Y

(2-4. Tensile elastic modulus of optical film)
The tensile elastic modulus of the optical film was measured by performing a tensile test at a test speed of 5 m / min and a load cell of 5 kN using an electromechanical universal tester (manufactured by Instron) in accordance with JIS K 7127.

(2-5. Thickness of optical film)
Using a micrometer (“ID-C112XBS” manufactured by Mitutoyo Co., Ltd.), the thickness of 10 or more optical films was measured, and the average value was calculated.

(2-6. Molecular weight of polyimide resin (weight average molecular weight))
Gel permeation chromatography (GPC) measurement was performed using a liquid chromatograph LC-10ATvp manufactured by Shimadzu Corporation.
(1) Pretreatment method A sample was dissolved in γ-butyrolactone (GBL) to prepare a 20% by mass solution, diluted 100-fold with a DMF eluent, and filtered through a 0.45 μm membrane filter to prepare a measurement solution. ..
(2) Measurement condition column: TSKgel SuperAWM-H × 2 + SuperAW2500 × 1 (6.0 mm ID × 150 mm × 3)
Eluent: DMF (10 mmol lithium bromide added)
Flow rate: 0.6 mL / min Detector: RI detector Column temperature: 40 ° C
Injection volume: 20 μL
Molecular weight standard: Standard polystyrene

(2-7. Particle size of silica particles)
The particle size of the silica particles was calculated from the specific surface area measurement value by the BET adsorption method according to JIS Z 8830. The specific surface area of the powder obtained by drying the silica sol at 300 ° C. was measured using a specific surface area measuring device (“Monosorb (registered trademark) MS-16” manufactured by Yuasa Ionics Co., Ltd.).

(2-8. Imidization rate)
The imidization ratio 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 Measuring device: JEOL 400MHz NMR device JNM-ECZ400S / L1
Standard substance: DMSO-d ₆ (2.5 ppm)
Sample temperature: Room temperature Accumulation number: 256 times 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 integrated value of the benzene proton A derived from the structure that does not change before and after imidization among the observed benzene protons was defined as Int _A. Further, the integral value of the amide proton derived from the amic acid structure remaining in the observed polyimide resin was defined as Int _B. From these integrated values, the imidization rate of the polyimide resin was determined 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 polyamide-imide resin, the structure derived from the structure of the observed benzene protons that does not change before and after imidization and the structure derived from the amic acid structure remaining in the polyamide-imide resin. The integrated value of benzene proton C, which is not affected by the above, was defined as Int _C. Further, among the observed benzene protons, the integral value of benzene proton D, which is derived from the structure that does not change before and after imidization and is influenced by the structure derived from the amic acid structure remaining in the polyamide-imide resin, was defined as Int _D. The β value was calculated from the obtained Int _C and Int _D by the following formula.
β = Int _D / Int _C
Next, the β value of the above formula and the imidization rate of the polyimide resin of the above formula were obtained 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.

(2-9. Flex resistance test)
A bending resistance test was carried out on the optical film in accordance with JIS K 5600-5-1. The bending resistance test was carried out using a small desktop durability tester (manufactured by Yuasa System Co., Ltd.). For the optical film after the bending resistance test, the transmission mapability value and the haze were measured in the same manner as in the above-mentioned measuring method. The absolute values of the difference between the transmission mapability value and the haze before and after the bending resistance test are taken, and the difference between the transmission mapping property values (the difference between the first transmission mapping property values ΔC ₆₀ (MD) and the difference between the second transmission mapping properties values ΔC). The difference between ₆₀ (TD) and the third transmission mapability value ΔC ₀ ) and the difference in haze (ΔHaze) were obtained and calculated, respectively.

(2-10. Fold resistance test (MIT))
Based on ASTM standard D2176-16, the number of times the optical film was bent in Examples and Comparative Examples was determined as follows. The optical film was cut into strips of 15 mm × 100 mm using a dumbbell cutter to prepare a measurement sample. The measurement sample was set in the main body of the MIT folding fatigue tester (“Model 0530” manufactured by Toyo Seiki Seisakusho Co., Ltd.). Specifically, one end of the measurement sample was fixed to the load clamp, the other end was fixed to the bending clamp, and tension was applied to the measurement sample. In this state, under the conditions of a test speed of 175 cpm, a bending angle of 135 °, a load of 0.75 kgf, and a bending radius of the bending clamp R = 1 mm, a reciprocating bending motion was performed in the front and back directions until the measurement sample broke. The number of bends was measured.

<3. Evaluation method>
(3-1. Visibility)
The optical film was cut into 10 cm squares. The MD direction of the polarizing plate with an adhesive layer of the same size (10 cm square) and the MD direction of the cut optical film were aligned, and the polarizing plate with an adhesive layer was attached to the cut optical film to prepare a sample for evaluation. Two evaluation samples were prepared for each of the optical films of one example and the comparative example.
For one of the two evaluation samples, the fluorescent lamp is located in the direction perpendicular to the evaluation sample plane, and the longitudinal direction of the fluorescent lamp is horizontal to the MD direction of the evaluation sample. Fixed on the table.
The observer visually observed the fluorescent lamp image reflected on the surface of the evaluation sample from an angle of 30 ° with respect to the vertical direction of the evaluation sample plane.
In the same manner except that the longitudinal direction of the fluorescent lamp was changed from horizontal to vertical, the other evaluation sample was fixed on a table and the fluorescent lamp image was observed.
From the observation results, the visibility was evaluated based on the following evaluation criteria.
(Evaluation criteria for visibility)
⊚: The distortion of the fluorescent lamp image is hardly visible.
◯: The distortion of the fluorescent lamp image is slightly visible.
Δ: Distortion of the fluorescent lamp image is visually recognized.
X: Distortion of the fluorescent lamp image is clearly visible.

<4. Evaluation result>
For the optical films of Examples 1 to 5 and Comparative Example 1, the total light transmittance, haze, transmission mapability value, yellowness and number of bends were measured, and the visibility was evaluated. The measurement and evaluation results are summarized in Tables 3-5. The column "Tt (%)" in Table 3 indicates the total light transmittance (unit:%) of the optical film. “Haze (%)” in Table 3 indicates the haze (unit:%) of the optical film.

The optical films 1 to 5 of Examples 1 to 5 all contained a polyimide resin, and had a total light transmittance of 85% or more and a haze of 0.5% or less. Further, the optical films 1 to 5 have a first transmission mapping property value and a second transmission mapping property value of 87% or more and 100% or less, and a ratio C ₆₀ (MD) / C ₀ of 0.8 or more. It was 0 or less. That is, the optical films 1 to 5 satisfy the formulas (1) to (3).
Further, the visibility evaluation results of the optical films 1 to 5 were any of ⊚, ◯, and Δ.

The optical film 6 of Comparative Example 1 had a total light transmittance of less than 85%, a haze of more than 0.5%, and a second transmission reproducibility value of less than 87%.
Further, the visibility of the optical film 6 was evaluated as x.

It is clear that the optical films of Examples 1 to 5 are superior in visibility in the wide-angle direction and have less angle dependence of visibility than the optical films of Comparative Example 1.

It was also confirmed that the optical films of Examples 1 to 5 had a low yellowness and excellent folding resistance.

1 Optical film 3 Vertical axis 10 1st incident light 11 1st incident position 12 1st a transmitted light 14 1st optical axis 16 1st optical comb 18 1st b transmitted light 19 1st receiver 20 2nd incident light 21 2nd incident Position 22 2nd a transmitted light 24 2nd optical axis 26 2nd optical comb 28 2nd b transmitted light 29 2nd receiver 30 3rd incident light 31 3rd incident position 32 3a transmitted light 34 3rd optical axis 36 3rd optical Comb 38 3b transmitted light 39 3rd receiver

Claims (11)

An optical film containing at least one resin selected from the group consisting of a polyimide resin and a polyamide resin, having a total light transmittance of 85% or more and a haze of 0.5% or less.
When the direction parallel to the machine flow direction at the time of manufacture in the optical film plane is the MD direction and the direction perpendicular to the machine flow direction is the TD direction,
The first transmission mapping property value C in the direction inclined by 60 ° in the MD direction from the direction perpendicular to the plane of the optical film, which is obtained when the width of the optical comb is 0.125 mm in accordance with JIS K 7374. _{The 60} (MD), the second transmission mapping property value C ₆₀ (TD) in the direction inclined by 60 ° from the vertical direction to the TD direction, and the third transmission mapping property value C _{0 in} the vertical direction are
Equation (1):
87% ≤ C ₆₀ (MD) ≤ 100% ... (1),
Equation (2):
87% ≤ C ₆₀ (TD) ≤ 100% ... (2), and equation (3):
0.8 ≤ C ₆₀ (MD) / C ₀ ≤ 1.0 ... (3)
An optical film that meets the requirements. The second transmission mapping property value and the third transmission mapping property value are expressed by the formula (4):
0.9 ≤ C ₆₀ (TD) / C ₀ ≤ 1.0 ... (4)
The optical film according to claim 1, further satisfying the above. The optical film according to claim 1 or 2, wherein the difference ΔHaze of the haze before and after the bending resistance test according to JIS K 5600-5-1 is less than 0.3%. The difference in the first transmission mapping property value before and after the bending resistance test according to JIS K 5600-5-1 ΔC ₆₀ (MD), the difference in the second transmission mapping property value ΔC ₆₀ (TD), and the third. The optical film according to any one of claims 1 to 3, wherein the difference ΔC ₀ of the transmission mapping property values is less than 15, respectively. The optical film according to any one of claims 1 to 4, which has a thickness of 10 to 150 μm. The optical film according to any one of claims 1 to 5, wherein the tensile elastic modulus at 80 ° C. is 4,000 to 9,000 MPa. The optical film according to any one of claims 1 to 6, which has a hard coat layer on at least one surface. The optical film according to claim 7, wherein the hard coat layer has a thickness of 3 to 30 μm. A flexible display device comprising the optical film according to any one of claims 1 to 8. The flexible display device according to claim 9, further comprising a touch sensor. The flexible display device according to claim 9 or 10, further comprising a polarizing plate.

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