CN113429609A

CN113429609A - Optical film and flexible display device

Info

Publication number: CN113429609A
Application number: CN202110276365.7A
Authority: CN
Inventors: 大松一喜; 福井仁之; 唐泽真义
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2020-03-18
Filing date: 2021-03-15
Publication date: 2021-09-24
Also published as: TW202140627A; JP2021148939A; KR20210117965A

Abstract

The invention provides a wide angle directionAn optical film having excellent visibility and sufficient mechanical properties even in a low-temperature environment, and a flexible display device provided with the same, wherein the optical film comprises at least 1 selected from polyimide-based resins and polyamide-based resins, has a total light transmittance of 85% or more and a haze of 0.5% or less, and has a 1 st transmission image clarity value C, which is obtained according to JIS K7374 when the comb width is 0.125mm and the film plane is inclined by 60 DEG from the perpendicular direction to the MD direction, wherein the MD direction is the direction parallel to the machine traveling direction during production, and the TD direction is the direction perpendicular to the machine traveling direction₆₀(MD) and a2 nd transmission image characteristic value C in a direction inclined by 60 DEG from the vertical direction to the TD direction₆₀(TD), 3 rd transmission image value C in vertical direction₀Satisfies the formulas (1) to (3), and the-40 ℃ breaking strain epsilon of the optical film₁Strain at break at 25 ℃ ∈₂Satisfies formula (4), and is more than or equal to 87 percent C₆₀(MD)≤100％(1)，87％≤C₆₀(TD)≤100％(2)，0.8≤C₆₀(MD)/C₀≤1.0(3)，0.70≤ε₁/ε₂≤1.20(4)。

Description

Optical film and flexible display device

Technical Field

The present invention relates to an optical film including at least 1 resin selected from the group consisting of polyimide-based resins and polyamide-based resins, and a flexible display device including the optical film.

Background

Conventionally, glass has been used as a material for display members such as solar cells and image display devices. However, glass does not have a sufficient material for the recent requirements of miniaturization, thinning, weight reduction, and flexibility, and various films have been studied as alternative materials for glass. Examples of such a film include polyimide films (for example, patent documents 1 and 2).

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2009-215412

Patent document 2: japanese patent laid-open No. 2020 and 3781

Disclosure of Invention

Problems to be solved by the invention

When the polyimide resin film is applied to a transparent member such as a front panel of a flexible display device, an image may be displayed in a state where an image display surface is curved, and therefore, excellent visibility in a wide angle direction is required as compared with a non-curved image display surface. However, according to the studies of the present inventors, the conventional polyimide resin film may not sufficiently satisfy visibility in a wide angle direction. In addition, when the optical film of the present invention is used in a low-temperature environment, sufficient mechanical properties of the optical film may not be obtained.

As a result of studies, for example, the optical films described in patent documents 1 and 2 may not sufficiently satisfy visibility in a wide angle direction.

Accordingly, an object of the present invention is to provide an optical film having excellent visibility in a wide angle direction and sufficient mechanical properties even in a low-temperature environment, and a flexible display device including the optical film.

Means for solving the problems

The present inventors have conducted intensive studies to solve the above problems and as a result, found that when an optical film comprising at least 1 resin selected from the group consisting of polyimide-based resins and polyamide-based resins is used, and the optical film has a total light transmittance of 85% or more and a haze of 0.5% or less, the optical film has a strain at break ∈ at-40 ℃₁Strain at break at 25 ℃ ∈₂Satisfies a predetermined relationship, and the transmission image value (C) of the optical film₆₀(MD)、C₆₀(TD) and C₀) The above problems can be solved by satisfying the predetermined relationship, and the present invention has been completed. That is, the present invention includes the following aspects.

An optical film comprising at least 1 resin selected from the group consisting of polyimide resins and polyamide resins, wherein the optical film has a total light transmittance of 85% or more and a haze of 0.5% or less,

when the direction parallel to the machine traveling direction during production is the MD direction and the direction perpendicular to the machine traveling direction is the TD direction in the optical film plane,

a 1 st transmission image value C in a direction inclined by 60 DEG from a perpendicular direction to the MD direction with respect to the plane of the optical film, which is obtained in accordance with JIS K7374 when the width of a light comb (Japanese: optical ) is 0.125mm₆₀(MD) from the vertical direction toward the TD directionThe 2 nd transmission image C in the direction inclined by 60 DEG₆₀(TD) and a 3 rd transmission image quality value C in the vertical direction₀Satisfies the following conditions:

mathematical formula (1):

87％≤C₆₀(MD)≤100％···(1)，

mathematical formula (2):

87％≤C₆₀(TD) 100% or less (2), and

mathematical formula (3):

0.8≤C₆₀(MD)/C₀≤1.0···(3)；

the breaking strain epsilon of the optical film at-40 DEG C₁Strain at break at 25 ℃ ∈₂Satisfies the following numerical formula (4):

0.70≤ε₁/ε₂≤1.20···(4)。

the optical film according to the above [ 1], wherein the 2 nd transmission image characteristic value and the 3 rd transmission image characteristic value further satisfy the following formula (5):

0.9≤C₆₀(TD)/C₀≤1.0···(5)。

[ 3] the optical film according to the above [ 1] or [ 2], wherein the Haze difference Δ Haze before and after the bending resistance test according to JIS K5600-5-1 is less than 0.3%.

[ 4] the optical film according to any one of [ 1] to [ 3] above, wherein the difference Δ C between the 1 st transmission image quality values before and after the bending resistance test according to JIS K5600-5-1₆₀(MD) and the difference Δ C between the 2 nd transmission image quality values₆₀(TD) and the difference Δ C between the transmission image values of the 3 rd image₀Each less than 15.

The optical film according to any one of [ 1] to [ 4] above, wherein a weight average molecular weight of a resin selected from the group consisting of a polyimide-based resin and a polyamide-based resin is 350,000 or less.

The optical film according to any one of [ 1] to [ 5] above, wherein the thickness is 10 to 150 μm.

The optical film according to any one of [ 1] to [ 6] above, which has a hard coat layer on at least one surface.

The optical film according to the above [ 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 [ 1] to [ 8] above.

The flexible display device according to [ 10] above [ 9], further comprising a polarizing plate.

The flexible display device according to the above [ 9] or [ 10], further comprising a touch sensor.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, an optical film having excellent visibility in a wide angle direction and sufficient mechanical properties even in a low-temperature environment, and a flexible display device including the optical film can be provided.

Drawings

Fig. 1 is a view showing an optical axis in the measurement of the 1 st transmission image characteristic value.

Fig. 2 is a view showing an optical axis in the measurement of the 2 nd transmission image characteristic value.

Fig. 3 is a view showing an optical axis in the measurement of the 3 rd transmission image characteristic value.

FIG. 4 is a process cross-sectional view schematically showing a preferred embodiment of the method for producing an optical film of the present invention.

FIG. 5 is a sectional view schematically showing a heating step in a preferred embodiment of the method for producing an optical film of the present invention.

FIG. 6 is a sectional view schematically showing a process in a tenter furnace in the method for producing an optical film of the present invention.

FIG. 7 is a schematic diagram for explaining a method for producing an optical film in examples.

FIG. 8 is a schematic diagram for explaining a method for producing an optical film in examples.

Description of the reference numerals

1 optical film

3 vertical axis

10 st 1 incident light

11 st incident position

12 st 1a transmitted light

14 1 st optical axis

16 st optical comb

18 th 1b transmitted light

19 st optical receiver

20 nd 2 incident light

21 nd 2 nd incident position

22 nd 2a transmitted light

24 nd 2 nd optical axis

26 nd 2 optical comb

28 nd 2b transmitted light

29 nd 2 nd optical receiver

30 rd incident light

31 3 rd incident position

32 No. 3a transmitted light

34 3 rd optical axis

36 rd 3 optical comb

38 the 3 rd b transmitted light

39 rd 3 optical receiver

40 region

Region 41

Region 42

43 gripping device

44 raw material film

45 resin film

46 Upper nozzle (nozzle)

47 underside nozzle (nozzle)

48 nozzle

49 IR heater

100 tenter oven

100a upper surface

100b lower surface

A direction of film conveyance

51 PET film substrate

521 spray nozzle

522 tank

53 drier

54 protective film

55 PET film substrate roll

56 laminate roll

57 protective film roll

58 tenter type dryer

201 nip roll

202 nip roll

59 slitting device

60 PET protective film

61 optical film

201-204 grip roller

101 to 109 guide rollers

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail. The scope of the present invention is not limited to the embodiments described herein, and various modifications can be made without departing from the scope of the present invention. When a plurality of upper and lower limits are described for a specific parameter, any of the upper and lower limits may be combined as a preferred range.

< optical film >

The optical film of the present invention comprises at least 1 resin selected from the group consisting of polyimide-based resins and polyamide-based resins, has a total light transmittance of 85% or more and a haze of 0.5% or less,

when the direction parallel to the machine traveling direction in the production of the optical film is the MD direction and the direction perpendicular to the machine traveling direction is the TD direction,

a 1 st transmission image value C in a direction inclined by 60 DEG from a perpendicular direction to the MD direction with respect to the plane of the optical film, the transmission image value C being obtained in accordance with JIS K7374 when the width of the optical comb is 0.125mm₆₀(MD) and a2 nd transmission image characteristic value C in a direction inclined by 60 DEG from the vertical direction to the TD direction₆₀(TD) and a 3 rd transmission image quality value C in the vertical direction₀Satisfies the following conditions:

mathematical formula (1):

87％≤C₆₀(MD)≤100％···(1)，

mathematical formula (2):

87％≤C₆₀(TD) 100% or less (2), and

mathematical formula (3):

0.8≤C₆₀(MD)/C₀≤1.0···(3)；

0.70≤ε₁/ε₂≤1.20··(4)。

the MD direction is a direction parallel to the machine traveling direction in the optical film surface at the time of production, and for example, indicates a direction parallel to the direction in which the optical film is conveyed in the case of production by a solution casting method. The TD direction is a direction perpendicular to the machine traveling direction, and for example, indicates a direction perpendicular to the direction of conveyance. The MD direction and the TD direction in the optical film plane are determined by the following method if the directions are unknown. With respect to MD and TD, cross-sectional sectioning of the optical film in at least 20 or more different directions is performed. More specifically, assuming a circle centered at 1 arbitrary point of the optical film, a semicircle thereof is cut out from the optical film, and the optical film is linearly cut out so that the central angles of the sectors obtained by cutting out the semicircle are substantially equal to each other, and 20 or more cross-sectional cuts are made. The center of the thickness of the obtained plurality of cross sections was measured based on Laser Raman (Laser Raman), and 1,620cm was measured^-1The direction in which the peak intensity in the vicinity is maximum is the MD direction.

The 1 st transmission image value C₆₀The (MD) is a transmission image clarity value in a direction inclined by 60 ° from the perpendicular direction to the MD direction with respect to the plane of the optical film, which is obtained in accordance with Japanese Industrial Standard (JIS) K7374. Referring to FIG. 1, the 1 st transmission image C is explained in more detail₆₀(MD). Fig. 1 is a view showing an optical axis in the measurement of the 1 st transmission image characteristic value. The optical film 1 is irradiated with 1 st incident light 10 (white light: indicated by a solid line in fig. 1) along an axis (1 st optical axis 14) inclined by an angle of 60 ° in the MD direction from an axis (vertical axis 3) perpendicular to the optical film 1, with an arbitrary point (1 st incident position 11) on the surface of the optical film 1 as a fulcrum. Then, let pass throughThe 1 st a transmitted light 12 (indicated by a dotted line in fig. 1) of the optical film 1 is transmitted from the 1 st optical comb 16 extending perpendicularly to the 1 st optical axis 14. Next, the 1 st b-th transmitted light 18 (indicated by a one-dot chain line in fig. 1) transmitted through the 1 st optical comb 16 is received by the 1 st optical receiver 19 extending perpendicularly to the 1 st optical axis 14. The 1 st optical comb 16 has an opening portion through which the 1 st transmitted light 12 is transmitted and a light shielding portion that shields the 1 st transmitted light 12. The 1 st optical comb 16 has a slit width (width of the opening) of 0.125 mm.

The operation of moving the 1 st optical comb 16 by a predetermined unit width and receiving the 1 b-th transmitted light 18 is repeated in a direction (direction of arrow a) parallel to the plane of the 1 st optical comb 16 and in the direction of arrangement of the slits in the 1 st optical comb 16, and a light receiving waveform is obtained. The maximum value M and the minimum value M of the relative light amount are obtained from the obtained light receiving waveform. From the obtained M and M, the 1 st transmission image C is calculated based on the formula (7)₆₀(MD). The transmission image value (1 st transmission image value, and the 2 nd transmission image value and the 3 rd transmission image value described later) can be measured using an image measuring instrument.

The 1 st transmission image value C₆₀When (MD) satisfies the formula (1), the wide-angle viewing properties in the MD direction of the optical film are excellent. The 1 st transmission image value C₆₀The content of (MD) in the formula (1) is 87% or more, and from the viewpoint of further improving the visibility of the optical film in the wide angle direction in the MD direction, it is preferably 88% or more, more preferably 89% or more, further preferably 90% or more, further preferably 91% or more, particularly preferably 93% or more, and usually 100% or less.

The 2 nd transmission image characteristic value C₆₀(TD) is a transmission image clarity value in a direction inclined by 60 DEG in the TD direction from the perpendicular direction to the plane of the optical film, which is obtained in accordance with JIS K7374. Referring to FIG. 2, the 2 nd transmission image C is explained in more detail₆₀(TD). Fig. 2 is a view showing an optical axis in the measurement of the 2 nd transmission reflectivity value. The optical film 1 is put on the surfaceThe optical film 1 is irradiated with the 2 nd incident light 20 (white light: indicated by a solid line in fig. 2) along an axis (2 nd optical axis 24) inclined by an angle of 60 ° in the TD direction from an axis (vertical axis 3) perpendicular to the optical film 1 as a fulcrum. Next, the 2 nd transmitted light 22 (indicated by a broken line in fig. 2) transmitted through the optical film 1 is transmitted through the 2 nd optical comb 26 extending perpendicularly to the 2 nd optical axis 24. Next, the 2 nd transmitted light 28 (indicated by a one-dot chain line in fig. 2) transmitted through the 2 nd optical comb 26 is received by a2 nd optical receiver 29 extending perpendicularly to the 2 nd optical axis 24. The 2 nd optical comb 26 has an opening portion through which the 2 nd transmitted light 22 is transmitted and a light shielding portion that shields the 2 nd transmitted light 22. The 2 nd comb 26 has a slit width (width of the opening) of 0.125 mm.

The operation of moving the 2 nd comb 26 by a predetermined unit width and receiving the 2 nd transmitted light 28 is repeated in a direction (direction of arrow B) parallel to the plane of the 2 nd comb 26 and in the direction of arrangement of the slits in the 2 nd comb 26, and a light receiving waveform is obtained. The maximum value M and the minimum value M of the relative light amount are obtained from the obtained light receiving waveform. From the obtained M and M, the 2 nd transmission image C is calculated based on the formula (7)₆₀(TD)。

The 2 nd transmission image characteristic value C₆₀When (TD) satisfies the formula (2), the optical film has excellent visibility in a wide angle direction in the TD direction. The 2 nd transmission image characteristic value C₆₀The content of (TD) in the formula (2) is 87% or more, and from the viewpoint of further improving the visibility of the optical film in the wide angle direction in the TD direction, it is preferably 88% or more, more preferably 89% or more, further preferably 90% or more, further preferably 91% or more, particularly preferably 92% or more, and usually 100% or less.

The 3 rd transmittance mapping value C₀The transmission image quality was measured in accordance with JIS K7374 in a direction perpendicular to the plane of the optical film. Referring to FIG. 3, the 3 rd transmission image C is explained in more detail₀. Fig. 3 is a diagram showing an optical axis in the measurement of the 3 rd image quality value. Irradiating an arbitrary point (3 rd incident position 31) on the surface of the optical film 1 with 3 rd incident light 30 (white light: figure) along an axis (3 rd optical axis 34) parallel to an axis (vertical axis 3) perpendicular to the optical film 13, indicated by a solid line). Next, the 3 rd transmitted light 32 (indicated by a broken line in fig. 3) transmitted through the optical film 1 is transmitted through a 3 rd optical comb 36 extending perpendicularly to the 3 rd optical axis 34. Next, the 3 rd b transmitted light 38 (indicated by a one-dot chain line in fig. 3) transmitted through the 3 rd optical comb 36 is received by a light receiver 39 extending perpendicularly to the 3 rd optical axis 34. The 3 rd optical comb 36 has an opening portion through which the 3 rd transmitted light 32 is transmitted and a light shielding portion that shields the 3 rd transmitted light 32. The 3 rd optical comb 36 has a slit width (width of the opening) of 0.125 mm.

The operation of moving the 3 rd optical comb 36 by a predetermined unit width and receiving the 3 rd transmitted light 38 is repeated in a direction (direction of arrow C) parallel to the plane of the 3 rd optical comb 36 and in the direction of arrangement of the slits in the 3 rd optical comb 36, and a light receiving waveform is obtained. The maximum value M and the minimum value M of the relative light amount are obtained from the obtained light receiving waveform. From the obtained M and M, the 3 rd transmission image C is calculated based on the formula (7)₀。

The 1 st transmission image value C₆₀(MD) and the 3 rd transmission image characteristic value C₀When the formula (3) is satisfied, the optical film is excellent in visibility in the MD direction perpendicular to the optical film. 1 st image value C₆₀(MD) relative to the 3 rd transmission map value C₀Ratio of (C)₆₀(MD)/C₀) In the formula (3), the value is 0.8 or more, and from the viewpoint of further improving the visibility in the MD direction, it is preferably 0.89 or more, more preferably 0.90 or more, still more preferably 0.93 or more, still more preferably 0.94 or more, and usually 1.0 or less.

The 3 rd transmittance mapping value C₀Preferably 97% or more, more preferably 98% or more. The 1 st transmission image value C₆₀The content (MD) is preferably 89% or more, more preferably 90% or more, and still more preferably 92% or more.

The transmission image value (more specifically, the 1 st transmission image value C)₆₀(MD) and 2 nd transmission image characteristic value C₆₀(TD) and a 3 rd transmission image characteristic value C₀) The adjustment can be performed by improving the smoothness of the surface of the optical film, suppressing the scattering of the transmitted light on the surface of the optical film, or the like. Further, the smoothness of the surface of the optical filmThe properties can be adjusted by, for example, the composition of the optical film (more specifically, the type, average primary particle diameter, content, and the like of the filler), and the conditions for producing the optical film (more specifically, the drying temperature, drying time, air flow in the drying system, the thickness of the coating film, the transport speed in the drying step, the amount of solvent in the varnish, and the like). In the case where the optical film further includes a hard coat layer, adjustment can be made by improving the smoothness of the surface of the hard coat layer, suppressing scattering in the surface of the hard coat layer, or the like. The smoothness of the hard coat layer can be adjusted by the method of adjusting the smoothness of the optical film, and by adjusting the kind of solvent, the component ratio, the solid content concentration, and the addition of the leveling agent, for example.

From the viewpoint of improving the visibility of the optical film of the present invention in the TD direction with respect to the perpendicular direction, the 2 nd transmission image characteristic value and the 3 rd transmission image characteristic value preferably further satisfy the formula (5):

0.9≤C₆₀(TD)/C₀≤1.0···(5)。

from the viewpoint of further improving the visibility in the TD direction of the present invention, the ratio (C) of the 1 st transmission image characteristic value to the 3 rd transmission image characteristic value₆₀(TD)/C₀) Preferably 0.9 or more, more preferably 0.91 or more, further preferably 0.92 or more, still more preferably 0.93 or more, particularly preferably 0.94 or more, and usually 1.0 or less.

The 2 nd transmission image characteristic value C₆₀The content of (TD) is preferably 89% or more, more preferably 90% or more, and still more preferably 92% or more. The 3 rd transmittance mapping value C₀Preferably 97% or more, more preferably 98% or more, and still more preferably 99% or more.

In the optical film of the present invention, it is sufficient that expressions (1) to (3) (and, in some cases, expression (5)) are satisfied when light is transmitted through at least any one surface of the optical film, and it is more preferable that expressions (1) to (3) (and, in some cases, expression (5)) are satisfied when light is transmitted through any one surface of the optical film. When the formula is satisfied when light is transmitted through any one surface, for example, when any one surface of the optical film is used for an image display surface of an electronic device, visibility in a wide angle direction is excellent.

In particular, when the optical film of the present invention is applied to a front panel of a flexible device, the absolute value Δ C of the difference between the 1 st transmission image values before and after the bending resistance test in accordance with JIS K5600-5-1 is considered from the viewpoint of further improving the visibility in the wide angle direction₆₀Absolute value Δ C of difference between (MD) and 2 nd transmission image characteristic values₆₀(TD) and the absolute value Δ C of the difference between the No. 3 transmission map values₀Preferably less than 15 each. When the difference in transmission image permeability values before and after the bend resistance test is less than 15, the flexible device has excellent visibility in a wide angle direction even when used in a state in which the image display surface of the flexible device is particularly bent and/or after used in a bent state. Delta C₆₀(MD) is more preferably less than 1.5, still more preferably less than 1.0, and still more preferably less than 0.5. Delta C₆₀(TD) is more preferably less than 2.8, still more preferably less than 2.3, still more preferably less than 2.1, and particularly preferably less than 1.5. Delta C₀More preferably less than 2, still more preferably less than 1, still more preferably less than 0.7, and particularly preferably less than 0.5.

The optical film of the present invention has a total light transmittance of 85% or more and a haze of 0.5% or less. When the total light transmittance is less than 85% or the haze is less than 0.5%, the initial optical properties of the optical film are low, and thus sufficient visibility of the optical film cannot be achieved. Further, the optical film of the present invention has a strain at break ε at-40 ℃₁Strain at break at 25 ℃ ∈₂Satisfies the following numerical formula (4):

0.70≤ε₁/ε₂≤1.20···(4)。

ε₁/ε₂if the amount is less than 0.70, the strain at break at low temperature is too low, and therefore sufficient mechanical properties of the optical film such as tensile modulus under low temperature environment cannot be obtained.

The optical film of the present invention has a total light transmittance of 85% or more, and is preferably 87% or more, more preferably 88% or more, even more preferably 89% or more, and usually 100% or less, from the viewpoint of facilitating further improvement in visibility in the wide angle direction. The optical film may have a total light transmittance in accordance with JIS K7361-1: 1997, the haze can be measured by computer, for example, by the method described in the examples. The optical film of the present invention exhibits a high total light transmittance, and therefore, for example, can suppress the emission intensity of a display element or the like required to obtain a certain luminance, as compared with the case of using a film having a low transmittance. Therefore, power consumption can be reduced. For example, when the optical film of the present invention is incorporated into an image display device, bright display tends to be obtained even when the amount of light from a backlight is reduced, and this contributes to energy saving. The upper limit of the total light transmittance is usually 100% or less. The total light transmittance may be a total light transmittance within a thickness range of an optical film to be described later.

The haze of the optical film of the present invention is 0.5% or less, and is preferably 0.4% or less, and more preferably 0.3% or less, from the viewpoint of facilitating further improvement in visibility in the wide angle direction. The haze of the optical film may be measured according to JIS K7136: 2000 the assay was performed. The haze may be measured according to JIS K7136: the haze value can be measured by a haze computer at 2000, for example, by the method described in examples. The optical film of the present invention preferably has an absolute value Δ Haze of the difference between the Haze values before and after the bending resistance test in accordance with JIS K5600-5-1 of 0.3% or less, more preferably 0.2% or less.

The tensile elastic modulus at 25 ℃ of the optical film of the present invention is preferably 5.1GPa or more, more preferably 5.2GPa or more, and still more preferably 5.3GPa or more, from the viewpoint of easily improving the folding resistance of the optical film and hardly causing defects such as pits in the optical film. In addition, from the viewpoint of easily improving the flexibility of the optical film, the tensile elastic modulus is preferably 10GPa or less, more preferably 9GPa or less, and further preferably 8GPa or less. The elastic modulus can be measured by using a tensile tester (the distance between chucks is 50mm, and the tensile speed is 10 mm/min), and can be measured by the method described in examples, for example. When the tensile elastic modulus is within the above range, a pit defect is less likely to occur in the optical film. The tensile elastic modulus of the optical film can be measured using a tensile tester in accordance with JIS K7127, and can be measured, for example, by the method described in examples. The tensile elastic modulus can be set within the above range by, for example, increasing the stretch ratio in the production of the optical film, using a resin having a preferred structure described later, or the like.

In the optical film of the present invention, the strain at break ε at-40 ℃₁Strain at break at 25 ℃ ∈₂Satisfies the following numerical formula (4):

0.70≤ε₁/ε₂≤1.20···(4)。

ε in formula (4)₁/ε₂Is 0.70 or more, preferably 0.73 or more, and more preferably 0.75 or more, from the viewpoint of easily improving the mechanical properties of the optical film in a low-temperature environment. In addition, for ε in equation (4)₁/ε₂The plastic film is considered to be generally hard to elongate when the temperature is lowered, and to be capable of elongating even at a low temperature by adding a filler or the like, and therefore, is generally 1.20 or less, preferably 1.15 or less, more preferably 1.10 or less, and further preferably 1.05 or less. Note that the strain at break ε₁And epsilon₂The strain can be determined from the magnitude of strain at the time of breaking in the optical film in a stress-strain curve measured according to ASTM D638-14 at-40 ℃ or 25 ℃, respectively. The strain at break can be measured, for example, by using a tensile tester in accordance with ASTM D638-14A 2.6. The measurement method may be, for example, the method described in examples. As a result of₁/ε₂Examples of the method for adjusting the content to the above range include a method using a preferred resin described later.

Strain at break ε at-40 ℃ for the optical film of the present invention₁From the viewpoint of easily improving the mechanical properties and bending resistance of the film at low temperatures, it is preferably 5.0 or more, more preferably 6.0 or more, and still more preferably 7.0 or more, and from the viewpoint of the hardness of the film, it is preferably 50 or less, and more preferably 45 or less.

Strain at break at 25 ℃ ε to the optical film of the present invention₂In terms of the flexibility of the filmFrom the viewpoint of the hardness of the film, it is preferably 5.0 or more, more preferably 6.0 or more, and still more preferably 7.0 or more, and from the viewpoint of the hardness of the film, it is preferably 50 or less, and more preferably 45 or less.

From the viewpoint of further improving the visibility, the YI value (which is an index of the yellowness index) of the optical film of the present invention is preferably 4.0 or less, more preferably 3.0 or less, further preferably 2.5 or less, further preferably 2.0 or less, particularly preferably 1.9 or less, particularly preferably 1.8 or less, preferably-5 or more, and more preferably-2 or more. The YI value can be calculated by measuring the transmittance for light of 300 to 800nm using an ultraviolet-visible near-infrared spectrophotometer to obtain the tristimulus value (X, Y, Z) and calculating the YI value based on the formula of 100 × (1.2769X-1.0592Z)/Y.

From the viewpoint of improving folding resistance, the number of times of folding of the optical film of the present invention is preferably 20,000 or more, more preferably 100,000 or more, further preferably 200,000 or more, further preferably 350,000 or more, particularly preferably 400,000 or more, particularly preferably 500,000 or more, particularly preferably 600,000 or more, and particularly preferably 700,000 or more. When the number of times of bending is not less than the above lower limit, cracks, fractures, and the like are less likely 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 can be determined by the MIT bending fatigue test according to ASTM standard D2176-16. The MIT bending fatigue test is, for example, the test described in examples. The optical film of the present invention preferably has high wide-angle visibility even after the MIT folding fatigue test under the above-described conditions, and for example, the difference between the image quality values and/or the difference between the haze values before and after the MIT folding fatigue test under the above-described conditions is more preferably within the range of the difference between the image quality values and/or the difference between the haze values before and after the above-described bending resistance test.

The thickness of the optical film of the present invention may be appropriately adjusted depending on the application, and is preferably 10 μm or more, more preferably 20 μm or more, further preferably 25 μm or more, further preferably 30 μm or more, and preferably 200μ m or less, more preferably 150 μm or less, still more preferably 100 μm or less, and still more preferably 85 μm or less. When the thickness of the optical film is within the above range, the tensile elastic modulus of the optical film can be easily further increased, and ∈ can be easily adjusted₁/ε₂Adjusted to the above range. The thickness of the optical film can be measured by a micrometer, for example, by the method described in examples.

< polyimide-based resin and polyamide-based resin >

The optical film of the present invention contains at least 1 resin selected from the group consisting of polyimide-based resins and polyamide-based resins. In the present specification, the polyimide-based resin means at least 1 resin selected from the group consisting of a polyimide resin, a polyamideimide resin, a polyimide precursor resin, and a polyamideimide precursor resin. The polyimide resin is a resin containing a repeating structural unit containing an imide group, and the polyamideimide resin is a resin containing a repeating structural unit containing both an imide group and an amide group. The polyimide precursor resin and the polyamideimide precursor resin are precursors before imidization, which provide the polyimide resin and the polyamideimide resin, respectively, by imidization, and are also called polyamic acids. In the present specification, the polyamide resin is a resin containing a repeating structural unit containing an amide group. The optical film of the present invention may contain 1 kind of polyimide-based resin or polyamide-based resin, or may contain 2 or more kinds of polyimide-based resins and/or polyamide-based resins in combination. The optical film of the present invention can easily improve the tensile elastic modulus and the bending resistance of the optical film, easily improve the visibility in the wide angle direction, and easily adjust e₁/ε₂From the viewpoint of adjusting the amount to the above range, the polyimide resin is preferably contained, and the polyimide resin is preferably a polyimide resin or a polyamideimide resin, and more preferably a polyamideimide resin.

In a preferred embodiment of the present invention, the tensile modulus and the bending resistance of the optical film are easily improved, and the visibility in the wide angle direction is easily improvedEasy to separate epsilon₁/ε₂From the viewpoint of adjusting the amount to the above range, the polyimide-based resin and the polyamide-based resin are preferably aromatic resins. In the present specification, the aromatic resin means a resin in which the structural units contained in the polyimide resin and the polyamide resin are mainly aromatic structural units.

In the above-described preferred embodiment, the tensile modulus and the bending resistance of the optical film can be easily improved, the visibility in the wide angle direction can be easily improved, and ∈ can be easily reduced₁/ε₂From the viewpoint of adjusting the content to the above range, the proportion of the structural unit derived from the aromatic monomer to the total structural units contained in the polyimide-based resin and the polyamide-based resin is preferably 60 mol% or more, more preferably 70 mol% or more, still more preferably 80 mol% or more, and still more preferably 85 mol% or more. Here, the structural unit derived from an aromatic monomer is a structural unit derived from a monomer at least a part of which contains an aromatic structure (for example, an aromatic ring) and at least a part of which contains an aromatic structure (for example, an aromatic ring). Examples of the aromatic monomer include aromatic tetracarboxylic acid compounds, aromatic diamines, and aromatic dicarboxylic acids.

In a preferred embodiment of the present invention, the polyimide-based resin is preferably a polyimide resin having a structural unit represented by formula (1) or a polyamideimide resin having a structural unit represented by formula (1) and a structural unit represented by formula (2).

[ chemical formula 1]

[ in formula (1), Y represents a 4-valent organic group, X represents a 2-valent organic group, and X represents a bond ]

[ chemical formula 2]

[ in the formula (2), Z and X independently represent a 2-valent organic group and represent a bond ]

The polyamide resin is preferably a polyamide resin having a structural unit represented by formula (2). The following are descriptions of formula (1) and formula (2), the description of formula (1) relating to both polyimide resin and polyamideimide resin, and the description of formula (2) relating to both polyamide resin and polyamideimide resin.

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

In the formula (1), Y represents a 4-valent organic group, preferably a 4-valent organic group having 4 to 40 carbon atoms, and more preferably a 4-valent organic group having 4 to 40 carbon atoms and having a cyclic structure. Examples of the cyclic structure include alicyclic, aromatic ring, and heterocyclic structures, and the tensile elastic modulus and the bending resistance of the optical film can be easily improved, the visibility in the wide angle direction can be easily improved, and ∈ can be easily adjusted₁/ε₂From the viewpoint of adjusting the content to the above range, an aromatic ring is preferably used. The organic group is an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, and in this case, the number of carbon atoms in the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably 1 to 8. In one embodiment of the present invention, the polyimide-based resin may contain a plurality of kinds of Y, and the plurality of kinds of Y may be the same or different from each other. Examples of Y include groups represented by the following formulae (20), (21), (22), (23), (24), (25), (26), (27), (28) and (29); a group represented by the formulae (20) to (29) wherein a hydrogen atom is substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group; and a chain hydrocarbon group having a valence of 4 and 6 or less carbon atoms.

[ chemical formula 3]

In the formulae (20) to (29), W represents a bond¹Represents a single bond, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-Ar-、-SO₂-、-CO-、-O-Ar-O-、-Ar-O-Ar-、-Ar-CH₂-Ar-、-Ar-C(CH₃)₂-Ar-or-Ar-SO₂-Ar-. Ar represents an arylene group having 6 to 20 carbon atoms in which a hydrogen atom may be substituted with a fluorine atom, and specific examples thereof include phenylene groups. When a plurality of Ar's are present, Ar's may be the same or different from each other. The hydrogen atom on the ring in the formulas (20) to (29) may be substituted by an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms and the aryl group having 6 to 12 carbon atoms include groups exemplified by the following formula (3).

Among the groups represented by the formulae (20) to (29), the tensile modulus and the bending resistance of the optical film can be easily improved, the visibility in the wide angle direction can be easily improved, and epsilon can be easily expressed₁/ε₂From the viewpoint of adjusting the amount to the above range, a group represented by formula (26), formula (28) or formula (29) is preferable, and a group represented by formula (26) is more preferable. In addition, the tensile elastic modulus and the bending resistance of the optical film can be easily improved, the YI value of the optical film can be easily reduced, and epsilon can be easily reduced₁/ε₂In view of adjustment to the above range, W¹Independently of one another, are preferably single bonds, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-or-C (CF)₃)₂-, more preferably a single bond, -O-, -CH₂-、-CH(CH₃)-、-C(CH₃)₂-or-C (CF)₃)₂-is more preferably a single bond, -C (CH)₃)₂-or-C (CF)₃)₂-, particularly preferably a single bond or-C (CF)₃)₂-。

In a preferred embodiment of the present invention, Y in the polyimide resin is preferably 50 mol% or more,More preferably 60 mol% or more, and still more preferably 70 mol% or more, is represented by formula (26). Y in the above range in the polyimide resin is represented by the formula (26), preferably W¹Is a single bond, -C (CH)₃)₂-or-C (CF)₃)₂-formula (26), more preferably W¹Is a single bond or-C (CF)₃)₂When the formula (26) represents, the tensile modulus and the bending resistance of the optical film are easily improved, the YI value of the optical film is easily lowered, and ε is easily reduced₁/ε₂Adjusted to the above range. The proportion of the structural unit represented by the formula (26) for Y in the polyimide resin can be used, for example¹H-NMR was measured, or it was calculated from the charge ratio of the raw materials.

In a preferred embodiment of the present invention, the structural unit represented by formula (1) contains a group represented by formula (4) as Y.

[ chemical formula 4]

[ in the formula (4), R²～R⁷Independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, R²～R⁷Wherein the hydrogen atoms contained in (A) may be substituted independently by halogen atoms, and V represents a single bond, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-, -S-, -CO-or-N (R)⁸)-，R⁸Represents a hydrogen atom or a C1-valent hydrocarbon group which may be substituted with a halogen atom and has 1 to 12 carbon atoms, and represents a bond]

That is, in Y in the structural units represented by the formula (1), at least a part of Y is preferably a group represented by the formula (4). In such an embodiment, the tensile elastic modulus and the bending resistance of the optical film can be easily improved, the YI value of the optical film can be easily reduced, and ∈ can be easily reduced₁/ε₂Adjusted to the above range. The structural sheet represented by the formula (1)In the above formula (I), 1 or more groups represented by the formula (4) may be contained as Y.

In the formula (4), R²、R³、R⁴、R⁵、R⁶And R⁷Independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms or the aryl group having 6 to 12 carbon atoms include R in the formula (3)^3aWherein the alkyl group has 1 to 6 carbon atoms, the alkoxy group has 1 to 6 carbon atoms, or the aryl group has 6 to 12 carbon atoms. With respect to R in the formula (3)^3aExamples thereof include the groups exemplified above. R²～R⁷Independently of each other, preferably represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, wherein R²～R⁷The hydrogen atoms contained in (a) may be substituted by halogen atoms independently of each other. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. V represents a single bond, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-, -S-, -CO-or-N (R)⁸)-，R⁸Represents a hydrogen atom or a C1-valent hydrocarbon group which may be substituted with a halogen atom and has 1 to 12 carbon atoms. Examples of the 1-valent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom include those related to R in W in the formula (3) described later⁹And the groups exemplified above. Among these, the tensile modulus, optical properties, surface hardness and bending resistance of the optical film can be easily improved, and ε can be easily adjusted₁/ε₂From the viewpoint of adjusting the above range, V is preferably a single bond, -O-, -CH₂-、-CH(CH₃)-、-C(CH₃)₂-or-C (CF)₃)₂-, more preferably a single bond, -C (CH)₃)₂-or-C (CF)₃)₂-, more preferably a single bond or-C (CF)₃)₂-。

In a preferred embodiment of the present invention, at least a part of Y in the plurality of formulas (1) is represented by formula (5) and/or formula (9).

[ chemical formula 5]

[ in the formula (5), R¹⁸～R²⁵Independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, R¹⁸～R²⁵The hydrogen atoms contained in (A) may be substituted independently of each other by halogen atoms, representing a chemical bond]

[ chemical formula 6]

[ formula (9) wherein R³⁵～R⁴⁰Independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, R³⁵～R⁴⁰The hydrogen atoms contained in (A) may be substituted independently of each other by halogen atoms, representing a chemical bond]

When at least a part of Y in the plurality of formulae (1) is represented by formula (5) and/or formula (9), the tensile modulus and optical properties of the optical film are easily improved.

In the formula (5), R¹⁸、R¹⁹、R²⁰、R²¹、R²²、R²³、R²⁴And R²⁵Independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms or the aryl group having 6 to 12 carbon atoms include R in the formula (3)^3aWherein the alkyl group has 1 to 6 carbon atoms, the alkoxy group has 1 to 6 carbon atoms, or the aryl group has 6 to 12 carbon atoms. R¹⁸～R²⁵Independently of one another preferably represents a hydrogen atom or a carbon atomAn alkyl group having a number of 1 to 6, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, wherein R¹⁸～R²⁵The hydrogen atoms contained in (a) may be substituted by halogen atoms independently of each other. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom. From the viewpoint of easily improving the tensile elastic modulus and the bending resistance of the optical film, and from the viewpoint of easily improving the transparency and easily maintaining the transparency, R¹⁸～R²⁵Independently of each other, a hydrogen atom, a methyl group, a fluoro group, a chloro group or a trifluoromethyl group is more preferable, and R is further more preferable¹⁸、R¹⁹、R²⁰、R²³、R²⁴And R²⁵Is a hydrogen atom, R²¹And R²²Is hydrogen, methyl, fluoro, chloro or trifluoromethyl, particularly preferably R²¹And R²²Is methyl or trifluoromethyl.

In the formula (9), R is from the viewpoint of easily improving the tensile elastic modulus and the bending resistance of the optical film, and from the viewpoint of easily improving the transparency and easily maintaining the transparency³⁵～R⁴⁰Preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and still more preferably a hydrogen atom. Here, R³⁵～R⁴⁰The hydrogen atoms contained in (a) may be independently substituted with a halogen atom, and examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. As R³⁵～R⁴⁰In the above-mentioned examples, the alkyl group having 1 to 6 carbon atoms and the aryl group having 6 to 12 carbon atoms are exemplified as the above groups, respectively.

In a preferred embodiment of the present invention, formula (5) is represented by formula (5 '), and formula (9) is represented by formula (9').

[ chemical formula 7]

That is, at least a part of the plurality of Y is represented by formula (5 ') and/or formula (9'). In this case, the tensile modulus and the bending resistance of the optical film are easily improved. In the case where the formula (5) is represented by the formula (5'), the solubility of the polyimide resin in a solvent can be improved by the skeleton containing a fluorine element, the storage stability of the varnish containing the resin can be easily improved, the viscosity of the varnish can be easily reduced, and the processability of the optical film can be easily improved. As a result, the optical film of the present invention satisfying the expressions (1) to (3) can be easily produced. Further, the optical properties of the optical film are easily improved by the skeleton containing the fluorine element.

In a preferred embodiment of the present invention, preferably 50 mol% or more, more preferably 60 mol% or more, and still more preferably 70 mol% or more of Y in the polyimide-based resin is represented by formula (5), particularly formula (5'). When Y in the above range in the polyimide-based resin is represented by formula (5), particularly formula (5'), the solubility of the polyimide-based resin in a solvent can be improved by the fluorine element-containing skeleton, the viscosity of a varnish containing the resin can be easily reduced, and the processability of an optical film can be easily improved. As a result, the optical film of the present invention satisfying the expressions (1) to (3) can be easily produced. Further, the optical properties of the optical film are easily improved by the skeleton containing the fluorine element. Preferably, 100 mol% or less of Y in the polyimide-based resin is represented by formula (5), particularly formula (5'). Y in the polyimide-based resin may be formula (5), particularly formula (5'). The proportion of the structural unit represented by the formula (5) of Y in the polyimide resin can be used, for example¹H-NMR was measured, or it was calculated from the charge ratio of the raw materials.

In the formula (2), Z is a 2-valent organic group, preferably a 4-40 carbon-valent organic group which may be substituted with a C1-6 alkyl group, a C1-6 alkoxy group, or a C6-12 aryl group (hydrogen atoms of these groups may be substituted with a halogen atom (preferably a fluorine atom)), more preferably a C1-6 alkyl group, a C1-6 alkoxy group, or a C6-12 aryl group (hydrogen atoms of these groups may be substituted with a halogen atom (preferably a fluorine atom)), and has a cyclic structureA number of 4 to 40 of 2-valent organic groups. As examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, or the aryl group having 6 to 12 carbon atoms, R in the formula (3) described later can be similarly applied^3aAnd R^3bExamples of (2). Examples of the cyclic structure include alicyclic, aromatic ring, and heterocyclic structure. Examples of the organic group of Z include a group obtained by replacing non-adjacent 2 of the chemical bonds of the groups represented by formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28) and formula (29) with a hydrogen atom, and a 2-valent chain hydrocarbon group having 6 or less carbon atoms,

[ chemical formula 8]

In [ formula (20) to formula (29), W¹Represents a single bond, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-Ar-、-SO₂-、-CO-、-O-Ar-O-、-Ar-O-Ar-、-Ar-CH₂-Ar-、-Ar-C(CH₃)₂-Ar-or-Ar-SO₂Ar-wherein Ar independently represents an arylene group having 6 to 20 carbon atoms (for example, phenylene group) in which hydrogen atoms may be substituted with fluorine atoms, and represents a bond]

Examples of the heterocyclic structure of Z include a group having a thiophene ring skeleton. From the viewpoint of easily lowering the YI value of the optical film, easily improving the total light transmittance, and easily lowering the haze, the cyclic structure in Z is preferably a group represented by formulae (20) to (29) or a group having a thiophene ring skeleton, and more preferably a group represented by formulae (26), (28), and (29).

The organic group of Z is more preferably a 2-valent organic group represented by formula (20 '), formula (21'), formula (22 '), formula (23'), formula (24 '), formula (25'), formula (26 '), formula (27'), formula (28 ') and formula (29').

[ chemical formula 9]

In [ formulae (20 ') to (29'), W¹And as defined in formulas (20) to (29)]

The hydrogen atom on the ring in the formulae (20) to (29) and (20 ') to (29') may be substituted with an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, in which the hydrogen atom may be substituted with a halogen atom (preferably, a fluorine atom).

When the polyamide resin or polyamideimide resin has a structural unit wherein Z in formula (2) is represented by any one of formulae (20 ') to (29 '), and particularly when Z in formula (2) is represented by formula (3 ') described later, it is preferable that the polyamide resin or polyamideimide resin has not only the structural unit but also a structural unit derived from a carboxylic acid represented by formula (d1) described below from the viewpoint of easily improving the film-forming property of the varnish and easily improving the uniformity of the optical film.

[ chemical formula 10]

[ in the formula (d1), R⁴¹Independently of each other, R in the formula (3) described later^3aA group as defined or a hydrogen atom, R⁴²Represents R⁴¹or-C (═ O) -, denotes a bond]

Specific examples of the structural unit (d1) include R⁴¹And R⁴²Structural units each of which is a hydrogen atom (structural units derived from a dicarboxylic acid compound), R⁴¹Are all hydrogen atoms and R⁴²A structural unit (structural unit derived from a tricarboxylic acid compound) representing — C (═ O) -, and the like.

In the polyamide resin or the polyamideimide resin, a plurality of types of Z may be contained as Z in the formula (2), and the plurality of types of Z may be the same or different from each other. In particular, from the viewpoint of easily improving the tensile elastic modulus and easily improving the optical properties of the optical film of the present invention, it is preferable that Z in formula (2) has at least a structural unit represented by formula (3) or more preferably formula (3').

[ chemical formula 11]

[ in the formula (3), R^3aAnd R^3bIndependently represent an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, R^3aAnd R^3bWherein the hydrogen atoms contained in (A) may be substituted independently by halogen atoms, and W independently represents a single bond, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-, -S-, -CO-or-N (R)⁹)-，R⁹Represents a hydrogen atom, a C1-valent hydrocarbon group which may be substituted with a halogen atom and has 1 to 12 carbon atoms, s is an integer of 0 to 4, t is an integer of 0 to 4, u is an integer of 0 to 4, and represents a bond]

[ chemical formula 12]

[ formula (3') wherein R^3a、R^3bS, t, u, W and as defined in formula (3)]

In the present specification, the phrase "the polyamide resin or the polyamideimide resin has a structural unit represented by formula (3) in which Z in formula (2) is represented by" and the phrase "the polyamide resin or the polyamideimide resin has a structure represented by formula (3) as Z in formula (2)" has the same meaning means that Z in at least a part of the structural units is represented by formula (3) among the structural units represented by formula (2) that can be contained in the polyamide resin or the polyamideimide resin. This description is also applicable to other similar descriptions.

In the formulae (3) and (3'), W independently represents a single bond, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-, -S-, -CO-or-N (R)⁹) From the viewpoint of the bending resistance of the optical film, the compound preferably represents-O-or-S-, and more preferably represents-O-.

R^3aAnd R^3bIndependently represent an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 2-methyl-butyl group, a 3-methylbutyl group, a 2-ethyl-propyl group, and an n-hexyl group. Examples of the alkoxy group having 1 to 6 carbon atoms include a methoxy group, an ethoxy group, a propyloxy group, an isopropyloxy group, a butoxy group, an isobutoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group, a cyclohexyloxy group, and the like. Examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a biphenyl group. From the viewpoint of tensile modulus of elasticity, surface hardness and flexibility of the optical film, R^3aAnd R^3bIndependently of each other, the alkyl group preferably has 1 to 6 carbon atoms or the alkoxy group has 1 to 6 carbon atoms, and more preferably has 1 to 3 carbon atoms or the alkoxy group has 1 to 3 carbon atoms. Here, R^3aAnd R^3bThe hydrogen atoms contained in (a) may be substituted by halogen atoms independently of each other.

R⁹Represents a hydrogen atom, a C1-valent hydrocarbon group which may be substituted with a halogen atom and has 1 to 12 carbon atoms. Examples of the 1-valent hydrocarbon group having 1 to 12 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, 2-methyl-butyl, 3-methyl-butyl, 2-ethyl-propyl, n-hexyl, n-heptyl, n-octyl, tert-octyl, n-nonyl, and n-decyl groups, which may be substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom and the like.

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

In the formula (3) and the formula (3'), s is an integer in the range of 0 to 4, and when s is in this range, the tensile elastic modulus and the bending resistance of the optical film are easily improved. In the formulae (3) and (3'), s is preferably an integer in the range of 0 to 3, more preferably an integer in the range of 0 to 2, even more preferably 0 or 1, and even more preferably 0, from the viewpoint of facilitating further improvement in the tensile elastic modulus and the bending resistance of the optical film. The polyamideimide resin or the polyamide-based resin may contain 1 or 2 or more kinds of the structural unit represented by the formula (3) or the formula (3') in Z.

In a preferred embodiment of the present invention, Z is preferably represented by formula (3) or formula (3') where s is 0 and u is preferably 1 to 3, more preferably 1 or 2, from the viewpoints of improving the tensile elastic modulus, and bending resistance of the optical film and reducing the YI value. It is also preferable that the functional group has not only the structural unit represented by formula (2) containing Z represented by formula (3) or formula (3') in which s is 0 but also the structural unit represented by formula (d1) described above.

When the polyamideimide resin or the polyamide resin has the structural unit represented by the formula (3) or the formula (3'), the proportion thereof is preferably 20 mol% or more, more preferably 30 mol% or more, further preferably 40 mol% or more, further preferably 50 mol% or more, particularly preferably 60 mol% or more, preferably 90 mol% or less, more preferably 85 mol% or less, and further preferably 80 mol% or less, when the total of the structural unit represented by the formula (1) and the structural unit represented by the formula (2) of the polyamideimide resin or the polyamide resin is taken as 100 mol%. When the proportion of the structural unit represented by formula (3) or formula (3') is not less than the above lower limit, the tensile modulus of elasticity and the bending resistance of the optical film can be easily improved. When the proportion of the structural unit represented by formula (3) or formula (3') is not more than the above upper limit, the increase in viscosity of the varnish containing the resin due to hydrogen bonding between amide bonds derived from formula (3) is easily suppressed, and the film processability is easily improved. The compound of formula (1), (2), (3) or (3') The proportions of the structural units represented can be used, for example¹H-NMR was measured, or it was calculated from the charge ratio of the raw materials.

In a preferred embodiment of the present invention, Z in the polyamideimide resin or the polyamide resin is a structural unit represented by formula (3) or formula (3') wherein s is 0 to 4, preferably 30 mol% or more, more preferably 40 mol% or more, still more preferably 45 mol% or more, and still more preferably 50 mol% or more. When the lower limit of Z is not less than the above-mentioned range and s is 0 to 4, the tensile modulus and the bending resistance of the optical film are easily improved in the structural unit represented by the formula (3) or the formula (3'). Further, the structural unit represented by the formula (3) or (3') in which 100 mol% or less of Z in the polyamideimide resin or the polyamide resin is s 0 to 4 may be used. The proportion of the structural unit represented by the formula (3) or (3') wherein s is 0 to 4 in the resin can be used, for example¹H-NMR was measured, or it was calculated from the charge ratio of the raw materials.

In the formulae (1) and (2), X independently represents a 2-valent organic group, preferably a 2-valent organic group having 4 to 40 carbon atoms, and more preferably a 2-valent organic group having 4 to 40 carbon atoms and having a cyclic structure. Examples of the cyclic structure include alicyclic, aromatic ring, and heterocyclic structure. The organic group may have hydrogen atoms substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, and in this case, the number of carbon atoms in the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably 1 to 8. In one embodiment of the present invention, the polyamide resin and the polyimide resin of the present invention may contain a plurality of types of X, and the plurality of types of X may be the same or different. Examples of X include groups represented by formula (10), formula (11), formula (12), formula (13), formula (14), formula (15), formula (16), formula (17), and formula (18); a group obtained by substituting a hydrogen atom in the group represented by the formula (10) to the formula (18) 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.

[ chemical formula 13]

In the formulae (10) to (18), represents a bond,

V¹、V²and V³Independently of each other, represents a single bond, -O-, -S-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-, -CO-or-N (Q) -. Wherein Q represents a C1-12 hydrocarbon group which may be substituted with a halogen atom. Examples of the 1-valent hydrocarbon group having 1 to 12 carbon atoms include those for R⁹But the groups described hereinbefore.

1 example is, V¹And V³Is a single bond, -O-or-S-, and V²is-CH₂-、-C(CH₃)₂-、-C(CF₃)₂-or-SO₂-。V¹And V²Bonding position with respect to each ring, and V²And V³The bonding position to each ring is preferably meta-or para-position, and more preferably para-position, independently from each ring.

Among the groups represented by formulae (10) to (18), from the viewpoint of easily improving the tensile elastic modulus and the bending resistance of the optical film, the groups represented by formulae (13), (14), (15), (16) and (17) are preferable, and the groups represented by formulae (14), (15) and (16) are more preferable. In addition, from the viewpoint of easily improving the tensile elastic modulus and flexibility of the optical film, V¹、V²And V³Independently of one another, are preferably single bonds, -O-or-S-, more preferably single bonds or-O-.

In a preferred embodiment of the present invention, the polyamide resin and/or the polyimide resin contains a 2-valent organic group represented by formula (5) as X in formula (1) or X in formula (2).

[ chemical formula 14]

[ formula (5) wherein Ar is²Independently of one another may haveA substituent group of 2-valent aromatic group, V represents a single bond, -O-, diphenylmethylene, fluorenyl, 2-valent alkyl with 1-12 carbon atoms and-SO₂-、-S-、-CO-、-PO-、-PO₂-、-N(R^a) -or-Si (R)^b)₂Here, the hydrocarbon group may contain an alicyclic structure, the hydrogen atoms contained in the hydrocarbon group may be substituted with halogen atoms independently of each other, R^aAnd R^bIndependently represent a hydrogen atom or a C1-valent hydrocarbon group which may be substituted with a halogen atom and has 1 to 12 carbon atoms, m represents an integer of 0 to 3, and]

when the structural unit (1) and the structural unit (2) contain a 2-valent organic group represented by formula (5) as X, the structural unit (1) and the structural unit (2) may contain 1 or 2 or more 2-valent organic groups represented by formula (5) as X. In the structural unit (1) and the structural unit (2), X may include other 2-valent organic group not belonging to the 2-valent organic group represented by the formula (5) in addition to the 2-valent organic group represented by the formula (5).

Ar in formula (5)²Represents a 2-valent aromatic group which may have a substituent. The 2-valent aromatic group is a group obtained by replacing 2 hydrogen atoms of a monocyclic aromatic ring, a condensed polycyclic aromatic ring, or a ring-assembly aromatic ring with a chemical bond. The 2-valent aromatic group may include an aromatic ring having a ring (a single ring, a condensed multiple ring, or a ring assembly) formed only of carbon atoms, or may include a heteroaromatic ring having a ring formed by including an atom other than carbon atoms. Examples of the atom other than carbon atoms include a nitrogen atom, a sulfur atom and an oxygen atom. The total number of carbon atoms forming the aromatic ring and atoms other than carbon atoms is not particularly limited, but is preferably 5 to 18, more preferably 5 to 14, and still more preferably 5 to 12. In the formula (5), when m is 1 or more, Ar is present in plural²May be the same or different from each other.

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

Examples of the fused polycyclic aromatic ring include naphthalene, anthracene, phenanthrene, indole, benzothiazole, benzimidazole, and benzoxazole.

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

From the viewpoint of easily improving the tensile elastic modulus of the optical film, the 2-valent aromatic group which may have a substituent is preferably a group in which 2 hydrogen atoms of an aromatic hydrocarbon ring which may have a substituent are replaced with a chemical bond, more preferably a group in which 2 hydrogen atoms of benzene, biphenyl, terphenyl, or quaterphenyl which may have a substituent are replaced with a chemical bond, and even more preferably a group in which 2 hydrogen atoms of benzene or biphenyl which may have a substituent are replaced with a chemical bond.

As Ar²Examples of the substituent in (3) include a halogen group, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, and a group in which a hydrogen atom contained in these groups is substituted with a halogen atom.

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

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

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

Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom and the like.

As Ar²The substituent(s) in (1) is preferably a halogen group or an alkyl group having 1 to 12 carbon atoms in which a hydrogen atom may be substituted with a halogen atom, and more preferably a methyl group, a fluoro group, a chloro group or a trifluoromethyl group.

V in the formula (5) represents a single bond, -O-, diphenylmethylene, fluorenyl, 2-valent hydrocarbon group with 1-12 carbon atoms, -SO₂-、-S-、-CO-、-PO-、-PO₂-、-N(R^a) -or-Si (R)^b)₂-. Here, the hydrocarbon group may contain an alicyclic structure, the hydrogen atoms contained in the hydrocarbon group may be substituted with halogen atoms independently of each other, and R^aAnd R^bIndependently represent a hydrogen atom or a C1-valent hydrocarbon group which may be substituted with a halogen atom and has 1 to 12 carbon atoms. Examples of the 1-valent hydrocarbon group having 1 to 12 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, 2-methyl-butyl, 3-methylbutyl, 2-ethyl-propyl, n-hexyl, n-heptyl, n-octyl, tert-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl and the like, which may be substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom and the like. From the viewpoint of easily improving the tensile elastic modulus and the bending resistance of the optical film, V in formula (5) is preferably a single bond or a group obtained by substituting at least a part of hydrogen atoms contained in a 2-valent hydrocarbon group having 1 to 12 carbon atoms and a halogen atom for each of the hydrocarbon groups, and more preferably a single bond, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-or-C (CF)₃)₂-is more preferably a single bond, -C (CH)₃)₂-or-C (CF)₃)₂-, more preferably a single bond or-C (CF)₃)₂-。

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

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

In a preferred embodiment of the present invention, the structural unit represented by formula (1) and/or the structural unit represented by formula (2) contains a 2-valent organic group represented by formula (5a) as X, from the viewpoint of easily improving the tensile elastic modulus of the optical film.

[ chemical formula 15]

[ in the formula (5a), R²Represents a fluoroalkyl group having 1-12 carbon atoms, p and q independently represent an integer of 1-4, wherein when p and/or q represent an integer of 2-4, a plurality of R exist²May be the same or different from each other, and represent a chemical bond]

The 2-valent organic group represented by the formula (5a) is a group included in the 2-valent organic group represented by the formula (5), and specifically corresponds to the case where V in the formula (5) represents a single bond and Ar in the formula (5)²Represents a fluoroalkyl group (R) having 1 to 12 carbon atoms²) A substituted benzene ring, and m represents an integer of 0 to 3, namely a 2-valent organic group. When the structural unit (1) and the structural unit (2) contain a 2-valent organic group represented by the formula (5a) as X, the structural unit (1) and the structural unit (2) may contain 1 or 2 or more kinds of organic groups represented by the formula (5a)And a 2-valent organic group as X. In the structural unit (1) and/or the structural unit (2), X may contain, in addition to the 2-valent organic group represented by the formula (5a), another 2-valent organic group that does not belong to the 2-valent organic group represented by the formula (5 a).

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

p and q independently represent an integer of 1 to 4. From the viewpoint of easily improving the tensile elastic modulus of the optical film, p is preferably an integer of 1 or 2, and more preferably 2. From the viewpoint of easily improving the tensile elastic modulus of the optical film, q is preferably an integer of 1 or 2, and more preferably 1. Wherein when p and/or q represents an integer of 2 to 4, a plurality of R's are present²May be the same or different from each other, but a plurality of R's are present²Preferably identical to each other.

The 2 chemical bonds in the formula (5a) may be located at any of the ortho, meta, and para positions, but are preferably located at the para position from the viewpoint of easily improving the tensile elastic modulus of the optical film.

As a preferred example of the 2-valent aromatic group represented by the formula (5a), R in the formula (5a) may be mentioned²Represents a perfluoroalkyl group having 1 to 12 carbon atoms, p is 2, q is 1 or 2, and/or 2 chemical groupsAromatic groups with bonds para to each other.

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

In a preferred embodiment of the present invention, the polyamide resin and the polyimide resin contain a structure represented by formula (4) as X in formula (1) or X in formula (2).

[ chemical formula 16]

[ in the formula (4), R¹⁰～R¹⁷Independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, R¹⁰～R¹⁷The hydrogen atoms contained in (A) may be substituted independently of each other by halogen atoms, representing a chemical bond]

When at least a part of X in the plurality of structural units represented by formulas (1) and (2) is represented by formula (4), the tensile modulus and transparency of the optical film are easily improved.

In the formula (4), R¹⁰、R¹¹、R¹²、R¹³、R¹⁴、R¹⁵、R¹⁶And R¹⁷Independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. MakingExamples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, or the aryl group having 6 to 12 carbon atoms include alkyl groups having 1 to 6 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, and aryl groups having 6 to 12 carbon atoms in the formula (3). R¹⁰～R¹⁷Independently of each other, preferably represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, wherein R¹⁰～R¹⁷The hydrogen atoms contained in (a) may be substituted by halogen atoms independently of each other. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. From the viewpoint of tensile modulus, transparency and bending resistance of the optical film, R¹⁰～R¹⁷Independently of each other, a hydrogen atom, a methyl group, a fluoro group, a chloro group or a trifluoromethyl group is more preferable, and R is further more preferable¹⁰、R¹²、R¹³、R¹⁴、R¹⁵And R¹⁶Is a hydrogen atom, R¹¹And R¹⁷Is hydrogen, methyl, fluoro, chloro or trifluoromethyl, particularly preferably R¹¹And R¹⁷Is methyl or trifluoromethyl.

In a preferred embodiment of the present invention, the structural unit represented by formula (4) is a structural unit represented by formula (4'),

[ chemical formula 17]

That is, at least a part of X in the plurality of structural units represented by formulas (1) and (2) is a structural unit represented by formula (4'). In this case, the fluorine element-containing skeleton can improve the solubility of the polyimide-based resin or the polyamide-based resin in a solvent, easily improve the storage stability of the varnish containing the resin, easily reduce the viscosity of the varnish, and easily improve the processability of the optical film. As a result, the optical film of the present invention satisfying the expressions (1) to (3) can be easily produced. Further, the optical properties of the optical film are easily improved by the skeleton containing the fluorine element.

In a preferred embodiment of the present invention, preferably 30 mol% or more, more preferably 50 mol% or more, and still more preferably 70 mol% or more of X that can be contained in the polyimide-based resin or the polyamide-based resin is represented by formula (4), particularly formula (4'). When X in the above range in the polyimide-based resin or the polyamide-based resin is represented by formula (4), particularly formula (4'), the solubility of the resin in a solvent can be improved by the skeleton containing a fluorine element in the obtained optical film, the storage stability of a varnish containing the resin can be easily improved, the viscosity of the varnish can be easily reduced, and the optical film of the present invention satisfying formulae (1) to (3) can be easily produced. Further, the optical properties of the optical film are also easily improved by the skeleton containing the fluorine element. Preferably, 100 mol% or less of X in the polyimide-based resin or the polyamide-based resin is represented by formula (4), particularly formula (4'). X in the resin may be formula (4), particularly formula (4'). The proportion of the structural unit represented by the formula (4) of X in the resin can be used, for example¹H-NMR was measured, or it was calculated from the charge ratio of the raw materials.

The polyimide-based resin may be a polyimide-based resin containing a structural unit represented by formula (30) and/or a structural unit represented by formula (31), or may be a polyimide-based resin containing not only the structural unit represented by formula (1) and, optionally, formula (2), but also the structural unit represented by formula (30) and/or the structural unit represented by formula (31).

[ chemical formula 18]

In the formula (30), Y¹Is a 4-valent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. As Y¹Examples thereof include groups represented by formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28) and formula (29), and the hydrogen atom in the groups represented by formula (20) to formula (29)A group obtained by substituting a methyl group, a fluoro group, a chloro group or a trifluoromethyl group, and a chain hydrocarbon group having a 4-valent carbon number of 6 or less. In one embodiment of the present invention, the polyimide-based resin may contain a plurality of kinds of Y¹Plural kinds of Y¹May be the same or different from each other.

In the formula (31), Y²Is a 3-valent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. As Y²Examples thereof include a group obtained by replacing 1 of the chemical bonds of the groups represented by the above formulae (20), (21), (22), (23), (24), (25), (26), (27), (28) and (29) with a hydrogen atom, and a chain hydrocarbon group having 6 or less carbon atoms and having a valence of 3. In one embodiment of the present invention, the polyimide-based resin may contain a plurality of kinds of Y²Plural kinds of Y²May be the same or different from each other.

In the formulae (30) and (31), X¹And X²Independently of one another, are 2-valent organic groups, preferably organic groups in which the hydrogen atoms of the organic groups can be replaced by hydrocarbon groups or fluorine-substituted hydrocarbon groups. As X¹And X²Examples thereof include the groups represented by the above-mentioned formula (10), formula (11), formula (12), formula (13), formula (14), formula (15), formula (16), formula (17) and formula (18); a group obtained by substituting a hydrogen atom in the group represented by the formula (10) to the formula (18) 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.

In one embodiment of the present invention, the polyimide-based resin is formed from a structural unit represented by formula (1) and/or formula (2), and optionally a structural unit represented by formula (30) and/or formula (31). In addition, from the viewpoint of easily improving the tensile elastic modulus, optical properties, and bending resistance of the optical film, the proportion of the structural unit represented by formula (1) and formula (2) in the polyimide-based resin is preferably 80 mol% or more, more preferably 90 mol% or more, and still more preferably 95 mol% or more, based on all the structural units represented by formula (1) and formula (2) and, in some cases, formula (30) and formula (31). The polyimide resin isIn the formula (1), the ratio of the structural unit represented by the formula (1) or the formula (2) is usually 100% or less with respect to the total of all the structural units represented by the formula (1) or the formula (2) and, in some cases, the formula (30) and/or the formula (31). The above ratio can be used, for example¹H-NMR was measured, or it was calculated from the charge ratio of the raw materials.

In one embodiment of the present invention, the content of the polyimide-based resin and/or the polyamide-based resin in the optical film is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, further preferably 50 parts by mass or more, preferably 99.5 parts by mass or less, and more preferably 95 parts by mass or less, with respect to 100 parts by mass of the optical film. When the content of the polyimide-based resin and/or the polyamide-based resin is within the above range, the tensile elastic modulus, the optical characteristics, and the bending resistance of the optical film are easily improved.

From the viewpoint of easily improving the tensile modulus of elasticity and the bending resistance of the optical film, and₁/ε₂from the viewpoint of adjusting the weight average molecular weight to the above range, the weight average molecular weight of the polyimide-based resin and the polyamide-based resin is preferably 100,000 or more, more preferably 130,000 or more, further preferably 150,000 or more, further preferably 170,000 or more, particularly preferably 200,000 or more, particularly preferably 230,000 or more, particularly preferably 250,000 or more, and particularly preferably 260,000 or more in terms of standard polystyrene. In addition, from the viewpoint of easily improving the solubility of the resin in a solvent and easily improving the stretchability and processability of the optical film, the weight average molecular weight of the polyimide-based resin and the polyamide-based resin is preferably 800,000 or less, more preferably 700,000 or less, even more preferably 600,000 or less, even more preferably 500,000 or less, particularly preferably 400,000 or less, particularly preferably 350,000 or less, and particularly preferably 300,000 or less. The weight average molecular weight can be determined by GPC measurement, for example, in terms of standard polystyrene, and can be calculated by the method described in examples, for example. When the weight average molecular weight (Mw) of the polyimide-based resin and the polyamide-based resin is not more than the upper limit, the inclusion of the resin is easily increasedThe solid component of the varnish of the grease, and the viscosity of the varnish are easily reduced, and as a result, the optical film of the present invention satisfying the expressions (1) to (3) can be easily produced. Further, the visibility in the wide angle direction after the bending resistance test is easily maintained, and the folding resistance is easily improved.

In the polyamide-imide resin, the content of the structural unit represented by formula (2) is preferably 0.1 mol or more, more preferably 0.5 mol or more, further preferably 1.0 mol or more, further preferably 1.5 mol or more, preferably 6.0 mol or less, more preferably 5.0 mol or less, and further preferably 4.5 mol or less, relative to 1mol of the structural unit represented by formula (1). When the content of the structural unit represented by formula (2) is not less than the above lower limit, the tensile elastic modulus of the optical film is easily increased. When the content of the structural unit represented by formula (2) is not more than the above upper limit, thickening due to hydrogen bonds between amide bonds in formula (2) is easily suppressed, and the viscosity of the varnish in the production of the optical film is easily reduced, so that the optical film of the present invention satisfying formulae (1) to (3) can be easily produced.

In a preferred embodiment of the present invention, the polyimide-based resin and/or the polyamide-based resin contained in the optical film may contain a halogen atom such as a fluorine atom which can be introduced, for example, through the above-mentioned fluorine-containing substituent or the like. When the polyimide-based resin and/or the polyamide-based resin contains a halogen atom, the tensile elastic modulus of the optical film is easily increased, and the YI value is easily decreased. When the tensile elastic modulus of the optical film is high, the generation of scratches, wrinkles, and the like is easily suppressed, and the mechanical properties in a low-temperature environment are easily improved. In addition, when the YI value of the optical film is low, the transparency and visibility of the film are easily improved. The halogen atom is preferably a fluorine atom. Examples of the preferable fluorine-containing substituent for containing a fluorine atom in the polyimide resin include a fluorine group and a trifluoromethyl group.

The content of the halogen atom in the polyimide-based resin and the polyamide-based resin is preferably 1 to 40% by mass, more preferably 5 to 40% by mass, and still more preferably 5 to 30% by mass, based on the mass of the polyimide-based resin and the polyamide-based resin. When the content of the halogen atom is not less than the lower limit, the tensile elastic modulus of the optical film tends to be further increased, and the YI value tends to be further decreased. When the content of the halogen atom is not more than the above upper limit, the synthesis becomes easy.

The imidization ratio of the polyimide-based resin and the polyamideimide resin is preferably 90% or more, more preferably 93% or more, and further preferably 96% or more. The imidization ratio is preferably not less than the above-described lower limit from the viewpoint of easily improving the optical properties of the optical film. The upper limit of the imidization rate is 100% or less. The imidization ratio indicates a ratio of a molar amount of imide bonds in the polyimide-based resin to a value 2 times a molar amount of structural units derived from a tetracarboxylic acid compound in the polyimide-based resin. When the polyimide resin contains a tricarboxylic acid compound, the molar amount of the imide bond in the polyimide resin is represented by the ratio of a value 2 times the molar amount of the structural unit derived from the tetracarboxylic acid compound in the polyimide resin to the total molar amount of the structural unit derived from the tricarboxylic acid compound. The imidization ratio can be determined by an IR method, an NMR method, or the like.

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

(method for producing resin)

The method for producing the polyimide-based resin and the polyamide-based resin included in the optical film of the present invention is not particularly limited. The polyimide resin and the polyimide precursor resin can be produced, for example, from tetracarboxylic acid compounds and diamine compounds as main raw materials, the polyamideimide resin and the polyamideimide precursor resin can be produced, for example, from tetracarboxylic acid compounds, dicarboxylic acid compounds and diamine compounds as main raw materials, and the polyamide resin can be produced, for example, from diamine compounds and dicarboxylic acid compounds as main raw materials.

The structural units represented by the formulae (1) and (30) can be derived from a diamine compound and a tetracarboxylic acid compound. The structural unit represented by the formula (2) may be generally derived from a diamine compound and a dicarboxylic acid compound. The structural unit represented by formula (31) may be generally derived from a diamine compound and a tricarboxylic acid compound.

Examples of the diamine compound that can be used for producing the resin include aliphatic diamines, aromatic diamines, and mixtures thereof. In the present embodiment, the "aromatic diamine" refers to a diamine in which an amino group is directly bonded to an aromatic ring, and may include an aliphatic group or other substituent in a part of the structure. The aromatic ring may be a monocyclic ring or a condensed ring, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring, but are not limited thereto. Of these, benzene rings are preferably exemplified. The "aliphatic diamine" refers to a diamine in which an amino group is directly bonded to an aliphatic group, and may contain an aromatic ring or other substituent in a part of the structure.

Examples of the aliphatic diamine include acyclic aliphatic diamines such as 1, 6-hexamethylenediamine, and cyclic aliphatic diamines such as 1, 3-bis (aminomethyl) cyclohexane, 1, 4-bis (aminomethyl) cyclohexane, norbornanediamine, and 4, 4' -diaminodicyclohexylmethane. These can be used alone or in combination of 2 or more.

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

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

Among the diamine compounds, from the viewpoint of easily improving the tensile elastic modulus, transparency, flexibility, bending resistance, and easily lowering the YI value of the optical film, it is preferable to use 1 or more selected from the group consisting of aromatic diamines having a biphenyl structure. More preferably, 1 or more selected from the group consisting of 2,2 '-dimethylbenzidine, 2' -bis (trifluoromethyl) benzidine, 4 '-bis (4-aminophenoxy) biphenyl, and 4, 4' -diaminodiphenyl ether is used, and still more preferably, 2 '-bis (trifluoromethyl) -4, 4' -diaminobiphenyl (TFMB) is used.

Examples of the tetracarboxylic acid compound that can be used for producing the resin 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 2 or more. The tetracarboxylic acid compound may be a tetracarboxylic acid compound analog such as an acid chloride compound, in addition to a dianhydride.

Specific examples of the aromatic tetracarboxylic dianhydride include non-condensed polycyclic aromatic tetracarboxylic dianhydrides, monocyclic aromatic tetracarboxylic dianhydrides, and condensed polycyclic aromatic tetracarboxylic dianhydrides. Examples of the non-condensed polycyclic aromatic tetracarboxylic acid dianhydride include 4,4 '-oxydiphthalic dianhydride, 3, 3', 4,4 '-benzophenonetetracarboxylic acid dianhydride, 2', 3,3 '-benzophenonetetracarboxylic acid dianhydride, 3, 3', 4,4 '-biphenyltetracarboxylic acid dianhydride (sometimes referred to as BPDA), 2', 3,3 '-biphenyltetracarboxylic acid dianhydride, 3, 3', 4,4 '-diphenylsulfonetetracarboxylic acid dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 2-bis (2, 3-dicarboxyphenyl) propane dianhydride, 2-bis (3, 4-dicarboxyphenoxyphenyl) propane dianhydride, 4, 4' - (hexafluoroisopropylidene) diphthalic acid dianhydride (4,4 ' - (hexafluoroisopropylidene) dicarboxylic dianhydride, which is sometimes referred to as 6FDA), 1, 2-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1, 2-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, 4 ' - (p-phenylenedioxy) diphthalic dianhydride, 4 ' - (m-phenylenedioxy) diphthalic dianhydride. Examples of the monocyclic aromatic tetracarboxylic acid dianhydride include 1,2,4, 5-benzenetetracarboxylic acid dianhydride, and examples of the condensed polycyclic aromatic tetracarboxylic acid dianhydride include 2,3,6, 7-naphthalenetetracarboxylic acid dianhydride.

Among these, preferred examples include 4,4 '-oxydiphthalic dianhydride, 3, 3', 4,4 '-benzophenonetetracarboxylic dianhydride, 2', 3,3 '-benzophenonetetracarboxylic dianhydride, 3, 3', 4,4 '-biphenyltetracarboxylic dianhydride, 2', 3,3 '-biphenyltetracarboxylic dianhydride, 3, 3', 4,4 '-diphenylsulfonetetracarboxylic dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 2-bis (2, 3-dicarboxyphenyl) propane dianhydride, 2-bis (3, 4-dicarboxyphenoxyphenyl) propane dianhydride, 4, 4' - (hexafluoroisopropylidene) diphthalic dianhydride (6FDA), 1, 2-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1, 1-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1, 2-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, 4,4 '- (terephthaloxy) diphthalic dianhydride and 4, 4' - (isophthaloxy) diphthalic dianhydride, more preferably 4,4 '-oxydiphthalic dianhydride, 3, 3', 4,4 '-biphenyltetracarboxylic dianhydride, 2', 3,3 '-biphenyltetracarboxylic dianhydride, 4, 4' - (hexafluoroisopropylidene) diphthalic dianhydride (6FDA), bis (3, 4-dicarboxyphenyl) methane dianhydride and 4, 4' - (p-phenylenedioxy) diphthalic dianhydride. These can be used alone or in combination of 2 or more.

Examples of the aliphatic tetracarboxylic dianhydride include cyclic and acyclic aliphatic tetracarboxylic dianhydrides. The cyclic aliphatic tetracarboxylic dianhydride is a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure, and specific examples thereof include cycloalkanetetracarboxylic dianhydrides such as 1,2,4, 5-cyclohexanetetracarboxylic dianhydride, 1,2,3, 4-cyclobutanetetracarboxylic dianhydride and 1,2,3, 4-cyclopentanetetracarboxylic dianhydride, bicyclo [2.2.2] oct-7-ene-2, 3,5, 6-tetracarboxylic dianhydride, bicyclohexane-3, 3 ', 4, 4' -tetracarboxylic dianhydride, and positional isomers thereof. These can be used alone or in combination of 2 or more. Specific examples of the acyclic aliphatic tetracarboxylic acid dianhydride include 1,2,3, 4-butanetetracarboxylic acid dianhydride, and 1,2,3, 4-pentanedicarboxylic acid dianhydride, and these can be used alone or in combination of 2 or more. In addition, cyclic aliphatic tetracarboxylic dianhydride and acyclic aliphatic tetracarboxylic dianhydride can be used in combination.

Among the tetracarboxylic dianhydrides, from the viewpoint of easily improving the tensile elastic modulus, surface hardness, transparency, flexibility and bending resistance of the optical film and easily lowering the YI value, preferred are 4,4 ' -oxydiphthalic dianhydride, 3,3 ', 4,4 ' -benzophenone tetracarboxylic dianhydride, 3,3 ', 4,4 ' -biphenyl tetracarboxylic dianhydride, 2 ', 3,3 ' -biphenyl tetracarboxylic dianhydride, 3,3 ', 4,4 ' -diphenylsulfone tetracarboxylic dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 4,4 ' - (hexafluoroisopropylidene) diphthalic dianhydride and mixtures thereof, and more preferred are 3,3 ', 4,4 ' -biphenyl tetracarboxylic dianhydride and 4,4 ' - (hexafluoroisopropylidene) diphthalic dianhydride, And mixtures thereof, more preferably 4,4 ' - (hexafluoroisopropylidene) diphthalic dianhydride (6FDA) and 3,3 ', 4,4 ' -biphenyltetracarboxylic dianhydride (BPDA).

Examples of the dicarboxylic acid compound that can be used for the synthesis of the resin include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and their analogous acid chloride compounds, acid anhydrides, and 2 or more kinds thereof may be used in combination. Specific examples thereof include terephthalic acid, isophthalic acid, 2-methoxyphthalic acid, 2-methylterephthalic acid; 2, 5-bis (trifluoromethyl) terephthalic acid; isophthalic acid; 2, 5-dimethyl terephthalic acid; 2, 5-dimethoxyterephthalic acid; naphthalenedicarboxylic acid; 4, 4' -biphenyldicarboxylic acid; 3, 3' -biphenyldicarboxylic acid; 2,2 '-bis (trifluoromethyl) -4, 4' -biphenyldicarboxylic acid; by single bonds, -CH₂-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂Or a compound in which a dicarboxylic acid compound of a chain hydrocarbon having 8 or less carbon atoms and 2 benzoic acids are linked to each other through a phenylene group, and an acid chloride compound thereof. Among these dicarboxylic acid compounds, from the viewpoint of easily improving the tensile elastic modulus and the bending resistance of the optical film, 4 ' -oxybis benzoic acid, terephthalic acid, isophthalic acid, 2-methoxy terephthalic acid, 2-methyl terephthalic acid, 2, 5-dimethyl terephthalic acid, 2, 5-dimethoxy terephthalic acid, 2, 5-bis (trifluoromethyl) terephthalic acid, 2 ' -bis (trifluoromethyl) -4,4 ' -biphenyl dicarboxylic acid and acid chlorides thereof are preferable, and 2-methoxy terephthalic acid, 2-methyl terephthalic acid, 2, 5-dimethyl terephthalate (DMTPC), 2, 5-dimethoxy terephthalate (MOTPC), 2, 5-bis (trifluoromethyl) terephthalate (6FTPC) are more preferable, Terephthaloyl chloride (TPC), isophthaloyl chloride, more preferably terephthaloyl chloride (TPC), 2-methoxy terephthalic acid, 2-methyl terephthalic acid, 2, 5-dimethyl terephthaloyl chlorideChlorine (DMTPC), 2, 5-dimethoxyterephthaloyl chloride (MOTPC), particularly preferably 2-methoxyterephthalic acid, 2-methylterephthalic acid, 2, 5-dimethylterephthaloyl chloride (DMTPC) and 2, 5-dimethoxyterephthaloyl chloride (MOTPC).

The polyimide resin may be a product obtained by reacting other tetracarboxylic acids, tricarboxylic acids, anhydrides thereof, and derivatives thereof in addition to the tetracarboxylic acid compound usable in the resin synthesis, within a range that does not impair various physical properties of the optical film.

Examples of the other tetracarboxylic acid include water adducts of anhydrides of the above tetracarboxylic acid compounds.

Examples of the tricarboxylic acid compound include an aromatic tricarboxylic acid, an aliphatic tricarboxylic acid, and a similar acid chloride compound or acid anhydride thereof, and 2 or more kinds thereof may be used in combination. Specific examples thereof include anhydrides of 1,2, 4-benzenetricarboxylic acid; acid chloride compounds of 1,3, 5-benzenetricarboxylic acid; 2,3, 6-naphthalene tricarboxylic acid-2, 3-anhydride; phthalic anhydride and benzoic acid through single bond, -O-, -CH₂-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-or phenylene groups.

In the production of the resin, the amount of the diamine compound, the tetracarboxylic acid compound and/or the dicarboxylic acid compound to be used may be appropriately selected depending on the ratio of the respective constituent units of the desired resin.

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

In the imidization step in the production of the polyimide-based resin, imidization may be performed in the presence of an imidization catalyst. Examples of the imidization catalyst include aliphatic amines such as tripropylamine, dibutylpropylamine, and ethyldibutylamine; n-ethylpiperidine, N-propylpiperidine, N-butylpyrrolidine, N-butylpiperidine, and N-propylhexahydroazepino

Alicyclic amines (monocyclic); azabicyclo [2.2.1]Heptane, azabicyclo [3.2.1]Octane, azabicyclo [2.2.2]Octane, and azabicyclo [3.2.2]Alicyclic amines (polycyclic) such as nonane; and aromatic amines such as pyridine, 2-methylpyridine (2-picoline), 3-methylpyridine (3-picoline), 4-methylpyridine (4-picoline), 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2, 4-dimethylpyridine, 2,4, 6-trimethylpyridine, 3, 4-cyclopentenopyridine, 5,6,7, 8-tetrahydroisoquinoline, and isoquinoline. In addition, from the viewpoint of facilitating the imidization reaction, it is preferable to use not only the imidization catalyst but also an acid anhydride. As the acid anhydride, a conventional acid anhydride which can be used in the imidization reaction can be mentionedSpecific examples thereof include aliphatic acid anhydrides such as acetic anhydride, propionic anhydride and butyric anhydride, and aromatic acid anhydrides such as phthalic acid.

The polyimide-based resin and the polyamide-based resin can be separated by separation and purification by a conventional method, for example, separation means such as filtration, concentration, extraction, crystallization, recrystallization, column chromatography, or a combination thereof, and in a preferred embodiment, the separation can be carried out by adding a large amount of an alcohol such as methanol to a reaction solution containing a transparent polyamide-imide resin, precipitating the resin, concentrating, filtering, drying, or the like.

< additive >

The optical film of the present invention may further comprise an additive. Examples of such additives include fillers, ultraviolet absorbers, brighteners, antioxidants, pH adjusters, and leveling agents.

(Filler)

The optical film of the present invention may contain at least 1 filler. Examples of the filler include organic particles and inorganic particles, and preferably inorganic particles. Examples of the inorganic particles include metal oxide particles such as silica, zirconia, alumina, titania, zinc oxide, germanium oxide, indium oxide, tin oxide, indium tin oxide, antimony oxide, and cerium oxide, and metal fluoride particles such as magnesium fluoride and sodium fluoride, and among these, silica particles, zirconia particles, and alumina particles are preferable, and silica particles are more preferable, from the viewpoint of improving the elastic modulus and/or tear strength of the optical film and easily improving the impact resistance. These fillers may be used alone or in combination of 2 or more.

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

The content of the filler (for example, inorganic particles, particularly silica particles) in the optical film of the present invention is preferably 60% by mass or less, more preferably 50% by mass or less, further preferably 45% by mass or less, further preferably 40% by mass or less, and preferably 0% by mass or more, based on the total mass of the optical film. When the content of the filler is not more than the above upper limit, the elastic modulus of the obtained optical film is easily improved, and the optical characteristics of the optical film are easily improved. Here, the tensile elastic modulus of the optical film tends to be high by increasing the content of the filler such as silica particles, but when the content of the filler such as silica particles is too large, the obtained optical film may be difficult to satisfy the above expressions (1) to (3). Therefore, in the optical film of the present invention, it is preferable that the content of the silica particles is not more than the above-described upper limit from the viewpoint of increasing the tensile elastic modulus of the optical film and easily obtaining high visibility in a wide angle direction. In the present specification, the content of, for example, silica particles in the optical film is, for example, the upper limit described above or less with respect to the total mass of the optical film, and represents: the content of the silica particles is 0 mass%, that is, the silica particles are not contained, or the silica particles are contained in an amount of not more than the above upper limit.

(ultraviolet absorber)

The optical film of the present invention may further comprise an ultraviolet absorber. The ultraviolet absorber can be appropriately selected from those generally used as ultraviolet absorbers in the field of resin materials. The ultraviolet absorber may contain a compound that absorbs light having a wavelength of 400nm or less. Examples of the ultraviolet absorber include triazine-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzoate-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, and the like. These can be used alone, also can be used in combination of more than 2. Since the optical film contains the ultraviolet absorber, deterioration of the resin can be suppressed, and thus, when the optical film of the present invention is applied to a display device or the like, visibility can be improved. In the present specification, the term "related compound" refers to a derivative of a compound having the "related compound". For example, the "benzophenone-based compound" refers to a compound having benzophenone as a matrix skeleton and a substituent bonded to benzophenone. Preferable examples of the commercially available ultraviolet absorber include Sumisorb (registered trademark) 340 manufactured by Sumika Chemtex Company, Limited, ADK STAB (registered trademark) LA-31 manufactured by ADEKA, and TINUVIN (registered trademark) 1577 manufactured by BASF Japan Ltd.

When the optical film of the present invention contains an ultraviolet absorber, the content of the ultraviolet absorber is preferably 0.01 to 10 parts by mass, more preferably 1 to 8 parts by mass, and still more preferably 2 to 7 parts by mass, based on 100 parts by mass of the polyamideimide resin contained in the optical film. When the content of the ultraviolet absorber is not less than the above lower limit, the ultraviolet absorbability is easily improved. When the content of the ultraviolet absorber is not more than the upper limit, decomposition of the ultraviolet absorber due to heat in the production of the base material can be suppressed, and optical characteristics, for example, haze can be easily improved.

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

The use of the optical film of the present invention is not particularly limited, and the optical film can be used for various applications. The optical film of the present invention is excellent in visibility in a wide angle direction, and therefore 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 panel of an image display device, particularly a front panel of a flexible display (window film). The flexible display includes, for example, a flexible functional layer and the optical film that overlaps the flexible functional layer and functions as a front panel. That is, the front panel of the flexible display is arranged on the viewing side on the flexible functional layer. The front panel has the function of protecting the flexible functional layer.

< method for producing optical film >

The optical film of the present invention is not particularly limited, but can be produced, for example, by a method including the following steps.

(a) A step of preparing a liquid (hereinafter, sometimes referred to as a varnish) containing the resin and the optional filler (varnish preparation step);

(b) a step (coating step) of applying a varnish to a substrate to form a coating film; and

(c) a step of drying the applied liquid (coating film) to form an optical film (optical film forming step)

In the varnish preparation step, the resin is dissolved in a solvent, and the filler and other additives are added as necessary, and stirred and mixed to prepare a varnish.

The solvent used for the preparation of the varnish is not particularly limited as long as it can dissolve the resin. Examples of the solvent include amide solvents such as N, N-dimethylacetamide (hereinafter, sometimes abbreviated as DMAc) and N, N-dimethylformamide (hereinafter, sometimes abbreviated as DMF); lactone solvents such as γ -butyrolactone (hereinafter, may be abbreviated as GBL) and γ -valerolactone; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide and sulfolane; carbonate solvents such as ethylene carbonate and propylene carbonate; and combinations thereof. Among these, the solvent used in the varnish is preferably an amide-based solvent or a lactone-based solvent, from the viewpoint of facilitating the production of an optical film satisfying the formulas (1) to (3). These solvents may be used alone or in combination of two or more. 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 mass%, more preferably 5 to 20 mass%.

In the coating step, a varnish is applied to the substrate by a known coating method to form a coating film. Examples of known coating methods include roll coating methods such as wire bar coating, reverse coating, and gravure coating, die coating, comma coating, lip coating, screen coating, spray coating, and casting.

In the optical film forming step, the coating film is dried (referred to as "1 st drying") and peeled off from the substrate, and then the dried coating film is further dried (referred to as "2 nd drying" or "post-baking" treatment), thereby forming an optical film. The drying step 1 may be carried out in an inert atmosphere or under reduced pressure, if necessary. The 1 st drying is preferably performed under an underpressure condition such as an underpressure in a tenter oven at a relatively low temperature and taking time. When the first drying is performed under the negative pressure condition, the reason is not clear, but the transmission image value of the optical film to be produced easily satisfies the expressions (1) to (3), and the total light transmittance of the optical film is easily increased, and the haze and YI are easily reduced. This is considered to be because the solvent that is evaporated from the optical film and removed under the first drying condition can be prevented from staying on the surface of the optical film, and as a result, the surface of the optical film becomes uniform. Further, by performing the 1 st drying at a relatively low temperature, the surface of the optical film is easily made uniform, and the transmission image value of the manufactured optical film easily satisfies the expressions (1) to (3). In addition, since oxidative deterioration of the resin during drying is suppressed, the total light transmittance of the optical film is easily increased, and the haze and YI are easily reduced.

Here, in the case of industrially producing the optical film of the present invention, the actual production environment is often disadvantageous in terms of improving the visibility in the wide angle direction compared to the laboratory-scale production environment, and as a result, it may be difficult to improve the visibility in the wide angle direction of the optical film. Although it takes time to perform the 1 st drying at a relatively low temperature under a negative pressure condition as described above, in the laboratory level, the 1 st drying may be performed in a sealed dryer, and thus, the roughness of the surface of the optical film caused by external factors is less likely to be generated. On the other hand, in the case of industrially producing an optical film, for example, in the 1 st drying, heating of a large area is required, and therefore, an air blowing device may be used in heating. As a result, the surface state of the optical film is easily roughened, and it is difficult to improve the visibility of the optical film in the wide angle direction.

When the drying is performed by heating, the temperature of the 1 st drying is preferably 60 to 150 ℃, more preferably 60 to 130 ℃, and further preferably 70 to 120 ℃ in consideration of the above-mentioned external factors particularly in the industrial production of the optical film. The drying time of the No. 1 is preferably 5 to 60 minutes, and more preferably 10 to 40 minutes. In particular, in the case of industrially producing an optical film, the 1 st drying is preferably carried out under a drying temperature condition of 3 stages or more in consideration of the above-mentioned external factors. The multistage conditions may be carried out under the same or different temperature conditions and/or drying times in each stage, and the drying may be carried out in 3 to 10 stages, for example, preferably 3 to 8 stages. When the 1 st drying is performed under the multi-stage condition of 3 stages or more, the transmission image value of the manufactured optical film easily satisfies the expressions (1) to (3), and the visibility in the wide angle direction is improved. In the multi-stage condition of 3 stages or more, the temperature profile (temperature profile) of the 1 st drying preferably includes a temperature rise and a temperature fall. That is, the 1 st drying condition in the optical film forming step is preferably a heating temperature condition in which the temperature distribution includes 3 stages of temperature increase and temperature decrease. In the case of 4 stages as an example of such a temperature distribution, the temperature of the 1 st drying is 70 to 90 ℃ (1 st temperature), 90 to 120 ℃ (2 nd temperature), 80 to 120 ℃ (3 rd temperature), and 80 to 100 ℃ (4 th temperature) in this order. In this example, the temperature of the 1 st drying is raised from the 1 st temperature to the 2 nd temperature, then lowered from the 2 nd temperature to the 3 rd temperature, and further lowered from the 3 rd temperature to the 4 th temperature. Here, the 1 st drying time is, for example, 5 to 15 minutes in each stage. Preferably, the drying of the 1 st stage is performed so that the residual solvent content of the dried coating film is preferably 5 to 15 mass%, more preferably 6 to 12 mass%, based on the mass of the dried coating film. When the solvent residual amount is within the above range, the peeling property of the dried coating film from the substrate becomes good, and the transmission image value of the optical film to be produced easily satisfies the expressions (1) to (3).

The temperature of the second drying is preferably 150 to 300 ℃, more preferably 180 to 250 ℃, and further preferably 180 to 230 ℃. The drying time of the 2 nd drying is preferably 10 to 60 minutes, and more preferably 30 to 50 minutes.

The 2 nd drying may be performed in a single-sheet manner, but in the case of industrial production, it is preferably performed in a roll-to-roll (roll) manner from the viewpoint of production efficiency. In the case of the single-sheet system, it is preferable to dry the sheet in a state of being uniformly elongated in the in-plane direction.

In the roll-to-roll method, from the viewpoint that the optical film to be obtained easily satisfies expressions (1) to (3), the dried coating film is preferably dried in a state of being elongated in the transport direction, and the transport speed is preferably 0.1 to 5 m/min, more preferably 0.2 to 3 m/min, and further preferably 0.7 to 2.5 m/min. The 2 nd drying may be carried out under 1 stage or multi-stage conditions. The multistage conditions are preferably performed in each stage under at least 1 selected from the group consisting of the same or different temperature conditions, drying time, and wind speed of hot air, for example, in 3 to 10 stages, preferably 3 to 8 stages, and are preferably performed under multistage conditions in view of easily satisfying the ranges of the expressions (1) to (3) of the optical film. In each stage, the wind speed of the hot wind is preferably 5 to 20 m/min, more preferably 10 to 15 m/min, and even more preferably 11 to 14 m/min, from the viewpoint that the transmission image clarity value of the optical film to be produced easily satisfies expressions (1) to (3).

When the optical film of the present invention includes a hard coat layer, the hard coat layer can be formed, for example, as follows: the curable composition is applied to at least one surface of an optical film to form a coating film, and the coating film is irradiated with high-energy rays to cure the coating film.

Examples of the substrate include a SUS plate in the case of a metal, and a PET film, a PEN film, another polyimide resin film, a polyamide resin film, a cycloolefin polymer (COP) film, an acrylic film, and the like in the case of a resin, or these resin films having a hard coat layer, a glass substrate, and the like. Among them, from the viewpoint of excellent smoothness and heat resistance and the viewpoint of the optical film having a transmission image value that easily satisfies expressions (1) to (3), a PET film, a COP film, a resin film having a hard coat layer, an SUS plate, a glass plate, and the like are preferable, and from the viewpoint of adhesion to the optical film and cost, an SUS plate and a resin film having a hard coat layer are more preferable, and an SUS plate and a PET film having a hard coat layer are even more preferable.

From the viewpoint of facilitating the production of an optical film satisfying the above expressions (1) to (3), the coating film in the above optical film forming step is preferably dried by a production method including the following steps: a step of drying the coating film to a predetermined solvent amount, and then peeling the base material to obtain a raw material film; and a heating step of heating the raw material film by a tenter furnace having an interior divided into a plurality of spaces. In the tenter oven, it is preferable that the heating step is performed by a hot air treatment method in at least one space, and the heating step is performed by a radiation treatment method in at least one space. The tenter oven is an oven that fixes and heats both ends in the film width direction. In this specification, a heating device for heating a raw material film including a tenter oven is also referred to as an oven. The pressure inside the tenter furnace is preferably adjusted so that the pressure inside the tenter furnace becomes negative with respect to the pressure outside the tenter furnace.

The method for manufacturing the optical film of the present embodiment is explained with reference to the drawings. Fig. 4 is a process cross-sectional view schematically showing a preferred embodiment of the method for manufacturing an optical film according to one embodiment of the present invention. In fig. 4, the raw material film 44 containing at least a polyimide-based resin and/or a polyamide-based resin is carried into the tenter 100, heated in a heating zone (zone) in the tenter 100, and then carried out of the tenter 100. In the present specification, a film that is subjected to a heating step and is conveyed in the heating step or an oven while the amount of a solvent or the like is changed with time before the heating step is referred to as a raw film, and a film that has been subjected to the heating step and is carried out of the oven is referred to as an optical film.

The raw material film 44 may be discharged from a roll in which the raw material film is wound and carried into the tenter oven 100, or may be continuously carried into the tenter oven from a step immediately before the discharge. Fig. 5 is a process cross-sectional view schematically showing a preferred embodiment of the heating process in the method for producing an optical film of the present invention. As shown in fig. 5, the raw material film 44 is preferably transported in a tenter furnace in a state in which both ends of the film are fixed in a direction (TD direction, also referred to as a width direction) perpendicular to a transport direction (MD direction, also referred to as a length direction) of the film. The fixing can be performed by, for example, the holding device 43.

The both ends can be fixed by using a holding device such as a pin seat (pin seat), a clip, and a film chuck which are generally used in a film manufacturing apparatus. The fixed ends can be adjusted as appropriate by the gripping means used, preferably fixed at a distance of within 50cm from the ends of the membrane. As shown in fig. 5, the raw material film may be conveyed while gripping both ends thereof by a plurality of gripping devices 43. The plurality of gripping devices 43 provided at one end of the film are preferably arranged at such a distance that the distance between adjacent gripping devices can suppress defects such as cracks generated by chattering or dimensional changes (which are caused by heating) of the film. The distance between adjacent gripping devices is preferably 1 to 50mm, more preferably 3 to 25mm, and still more preferably 5 to 10 mm. Further, the gripping device is preferably provided in the following manner: when a straight line orthogonal to the film transport axis is aligned with the center of the gripping portion of any gripping device at one end of the film, the distance between the intersection of the straight line with the other end of the film and the center of the gripping portion of the gripping device closest to the intersection is preferably 3mm or less, more preferably 2mm or less, and still more preferably 1mm or less. This makes it possible to reduce the difference in stress applied to the opposing film ends, and thus to improve the homogeneity of the optical film obtained. Further, by drying the film while fixing it by using the holding means under such conditions, chattering at the time of drying the film is suppressed, and the optical film of the present invention satisfying the above expressions (1) to (3) can be easily produced.

Examples of the operation of fixing both ends of the film by the holding means include the following methods: at an appropriate timing before or after the carrying into the tenter furnace, both ends in the width direction of the film are fixed by a plurality of film chucks provided in an opposing manner in the width direction of the film. By these operations, film flutter and the like are suppressed, and an optical film in which defects such as thickness unevenness and damage are sufficiently suppressed can be obtained. In addition, the optical film of the present invention satisfying the above expressions (1) to (3) can be easily produced. The fixing of both ends of the film may be released at an appropriate time after the heating step, and may be performed in a tenter oven or after being carried out from the tenter oven.

The whole length of the tenter used in the heating step in the film conveying direction is usually 10 to

100m, preferably 15 to 80m, and more preferably 15 to 60 m. The interior of the tenter may be 1 space or may be divided into a plurality of spaces, but in the embodiment of the present invention, the following tenter is used: the inside of the tenter furnace in which the heating step is performed is divided into a plurality of spaces. The space may be a space in which temperature conditions, wind speed conditions, and the like can be controlled, or may not have a physical boundary such as a partition plate. When the interior of the tenter oven is divided into a plurality of spaces, the plurality of spaces may be divided perpendicularly or in parallel to the film conveyance direction. The number of the spaces is usually 2 to 20, preferably 3 to 18, more preferably 4 to 15, and further preferably 5 to 10. Regardless of the internal structure of the tenter, the entire tenter may be a heating region, or a part of the inside may be a heating region. Referring to fig. 4, all of the three

regions

40, 41, and 42 may be heating regions, or one of them, for example, the region 42 may be a heating region.

Multiple tenter frames may also be used. The number of the tenter is not particularly limited, and may be, for example, 2 to 12. The inside of each tenter oven may be the structure described above. The plurality of tenter ovens may be continuously arranged in such a manner that the film is conveyed without contacting with the outside air. When a plurality of tenter furnaces are used, all tenter furnaces may be heated, or a part of tenter furnaces may be heated. In addition, an oven may be used as other equipment in addition to the tenter. In the present specification, the oven refers to a device capable of heating the film, and includes a heating furnace and a drying furnace. The heating furnace may be either hot air treatment or radiation treatment, or may be a heating furnace using both of them. When the optical film of the present invention is used in combination with an oven, the internal structure of the oven, the number of the ovens used, and the heating conditions may be appropriately adjusted within the range in which the optical film of the present invention can be obtained, and the same is preferable as the tenter oven described in the present specification.

In the case where the inside of the tenter furnace is divided into a plurality of spaces, it is preferable to perform the circulation and exhaust of the air inside the tenter furnace in each space, and in the case where there are a plurality of tenter furnaces, it is preferable to perform the circulation and exhaust of the air inside the tenter furnace in each tenter furnace. From the viewpoint of facilitating the production of the optical film of the present invention satisfying the above-described expressions (1) to (3), the pressure inside the tenter furnace is preferably adjusted so that the pressure inside the tenter furnace becomes a negative pressure with respect to the pressure outside the tenter furnace. The temperature inside the tenter furnace is preferably adjustable for each tenter furnace, and in the case where the inside of the tenter furnace is divided into a plurality of spaces, it is preferable that the temperature adjustment can be independently performed in each space. The temperature setting of each space may be the same or different. Among them, the temperature of each tenter oven or space preferably satisfies a temperature range described later.

In the tenter oven 100 in which the heating step is performed, the heating step is performed by a hot air treatment method in at least one space, and the heating step is performed by a radiation treatment method in at least one space. In the heating step, it is preferable that the entire space for performing the heating step is subjected to a hot air treatment. The heating step of the radiation processing system may be performed in a space different from that of the hot air processing system, but is preferably performed in combination with the hot air processing system.

The heating step of the hot air treatment system may be performed by providing a nozzle for blowing hot air in the tenter furnace. The heating step in the radiation treatment method may be performed by providing an IR heater or the like in a tenter oven and irradiating the film with radiation.

As an example of the embodiment of the present invention, the hot air processing method using a nozzle and the radiation processing method using an IR heater are described below in order from the hot air processing method using a nozzle.

Referring to fig. 4, in the tenter oven 100 that performs the heating step, a plurality of upper nozzles 46 are provided on an upper surface 100a inside thereof, and a plurality of lower nozzles 47 are provided on a lower surface 100b inside thereof. The upper nozzle 46 and the lower nozzle 47 are disposed so as to face each other in the vertical direction. For example, as shown in a region 42 of fig. 4,4 pairs of nozzles (8 nozzles in total) may be provided, or as shown in a region 41 of fig. 4, 10 pairs of nozzles (20 nozzles in total) may be provided, and the nozzles may be appropriately provided according to the structure of the oven. The interval between adjacent nozzles is preferably 0.1 to 1m, more preferably 0.1 to 0.5m, and still more preferably 0.1 to 0.3m, from the viewpoint of simplifying the structure of the tenter and uniformly heating the raw material film, and from the viewpoint of facilitating the production of an optical film satisfying the expressions (1) to (3).

When the interior of the tenter furnace is divided into a plurality of sections, the number of the nozzles for blowing out the hot air provided in each space may be usually 5 to 30. The number of nozzles is preferably 8 to 20 from the viewpoint of easy production of the optical film of the present invention satisfying the above formula. When the number of nozzles is within the above range, the curvature of the floating film tends not to be excessively large, and the film tends to easily float between the nozzles, that is, tends to easily float.

The upper nozzle 46 provided on the upper surface 100a of the tenter oven 100 has a blow-out port at the lower portion, and can blow out hot air downward (in the direction of arrow B). On the other hand, the lower side nozzles 47 provided on the lower surface of the tenter 100 have outlets at the upper portions thereof, and can blow out hot air upward (in the direction of arrow C). Although not shown in fig. 4, the upper nozzle 46 and the lower nozzle 47 have a depth of a predetermined size in a direction perpendicular to the paper surface of fig. 4 so that the raw material film can be uniformly heated in the width direction. Here, it is also conceivable that the orientation of the nozzle is set to be transverse to the film surface, and in this case, although the reason is not clear, it is difficult to make the tensile elastic modulus at 25 ℃ equal to or higher than the above-described lower limit value, and it is difficult to produce an optical film satisfying the expressions (1) to (3).

In the method for producing an optical film according to the present embodiment, the blowing speed of hot air from the blowing outlets of all the upper nozzles 46 and all the lower nozzles 47 provided in the heating area is preferably 2 to 25 m/sec. The blowing air speed is more preferably 2 to 23 m/sec, and still more preferably 8 to 20 m/sec, from the viewpoint of facilitating the production of the optical film of the present invention satisfying the above-mentioned numerical expression and facilitating the improvement of the optical uniformity of the optical film. From the same viewpoint, the air volume blown out from the outlet of each

nozzle

46 or 47 per 1m length of the nozzle along the width direction of the raw material film is preferably 0.1 to 3m³Second, more preferably 0.1 to 2.5m³Second, more preferably 0.2 to 2m³In seconds.

Further, when the heating step is performed under the above conditions, the optical film of the present invention satisfying the above formula can be easily produced and can be uniformly heated, so that variation in the amount of the solvent remaining in the film is reduced, and an optical film having a more uniform elastic modulus over the entire surface of the film can be easily obtained. Therefore, unevenness in the bendability is less likely to occur over the entire surface of the film, and the occurrence of damage due to a difference in the bendability in the film surface can be suppressed.

In the tenter furnace, the raw material film 44 is heated from room temperature to a temperature at which the solvent contained in the raw material film evaporates, but the raw material film tends to easily sag due to thermal expansion because it is held by the holding device 43 so that the length of the raw material film in the width direction is substantially constant. When the blowing air speed and the blowing air volume are within the above ranges, the raw material film 44 can be sufficiently heated, and sagging and fluttering of the raw material film 44 can be suppressed.

The blowing speed of the hot air can be measured by using a commercially available thermal anemometer at the hot air outlet of the

nozzles

46 and 47. The volume of air blown out from the air outlet can be determined by the product of the air blowing speed and the area of the air outlet. From the viewpoint of measurement accuracy, it is preferable that the blowing speed of hot air is measured at about 10 points at the blowing port of each nozzle, and the average value is taken.

The blowing speed and blowing volume of the hot air can be appropriately adjusted according to the physical properties (optical properties, mechanical properties, etc.) of the optical film to be produced, and are preferably within the above ranges in any of the embodiments. This makes it easy to manufacture the optical film of the present invention that satisfies the above equations (1) to (3), and to improve the visibility in the wide angle direction after the bending resistance test of the optical film. More preferably, the heating zone has a blowing air speed of 25 m/sec or less and a blowing air volume of 2m in all the heating zones³And less than second.

In the present embodiment, in a state where the raw material film 44 is not introduced into the tenter furnace 100, the wind speed of the hot wind at the position where the raw material film 44 is to be held is preferably 5 m/sec or less, and more preferably such a wind speed at least in the heating region. By heating the base film 44 with such hot air, the optical film of the present invention satisfying the above expressions (1) to (3) can be easily produced, and the visibility in the wide angle direction after the bending resistance test of the optical film can be easily improved.

In the heating area, the difference between the maximum value and the minimum value in the width direction (direction perpendicular to the paper surface of fig. 4) of the blowing wind speed of the hot air at the blowing outlets of the

nozzles

46 and 47 is preferably 4 m/sec or less. By using such hot air with little variation in air velocity in the width direction, the optical film of the present invention satisfying the above expressions (1) to (3) can be easily produced, and the visibility in the wide angle direction after the bending resistance test of the optical film can be easily improved.

In the present embodiment, the wind speed of the hot wind blown to the film is preferably higher immediately after the film is carried into the oven than the wind speed of the other transport path in the oven. When the inside of the oven is not divided into a plurality of areas immediately after the oven is carried into the oven (hereinafter referred to as "conveying path 1"), the distance is 1/10, which is less than the oven length (the length from the oven carrying-in port to the oven carrying-out port). In the case where the inside of the oven is divided into a plurality of spaces, the conveying path 1 refers to a space through which the film initially passes. When a plurality of ovens are used, depending on the internal structure of the oven used first, the first pass oven may be set to have a wind speed higher than the wind speed in the ovens of the 2 nd and subsequent ovens, as described above.

The other transport path means a transport path portion located after 1/10 in the oven length from the oven entrance when the inside of the oven is not divided into a plurality of areas. When the inside of the oven is divided into a plurality of spaces, the space is any space after the 2 nd space through which the film passes. When a plurality of ovens are used, the air speed in any of the ovens from among the 2 nd to subsequent ovens may be set to be lower than the air speed in the oven that first passes through, as described above, depending on the internal structure of the oven that first uses.

The difference between the wind speed of the conveying path 1 and the wind speed of the other conveying paths in the oven is preferably in the range of 0.1 to 15 m/sec. The difference in wind speed is more preferably 0.2 m/sec or more. Further, it is more preferably 12 m/sec or less, further preferably 8 m/sec or less, further more preferably 5 m/sec or less, and particularly preferably 3 m/sec or less. When the air speed immediately after the film is carried into the oven is made larger than the air speed of the other transport path in the oven so that the difference in air speed falls within the above range, the solvent in the film tends to be removed more efficiently. If the difference in wind speed is too large, film flutter due to the difference in wind speed may occur, and it may be difficult to manufacture the optical film of the present invention that satisfies the above equations (1) to (3). Further, the surface shape of the obtained optical film may be defective or cause optical property unevenness such as retardation.

The difference between the wind speed of the conveying path 1 and the wind speed of the other conveying path in the oven can be determined as the difference between the wind speed of the hot wind from the nozzle provided in the conveying path 1 and the wind speed of the hot wind from the nozzle provided in the other conveying path. When there is a difference of 2 m/sec or more between the wind speed of the hot air blown to the film and the wind speed of the hot air blown from the nozzle, the difference can be obtained as the difference between the wind speeds of the hot air in the film vicinity of the transport path 1 and the other transport paths.

The other conveyance path is preferably a conveyance path (hereinafter referred to as "conveyance path 2") located at a position subsequent to the conveyance path 1. When the inside of the oven is not divided into a plurality of areas, the conveyance path 2 is a conveyance path portion located at a position 2/10 that is the oven length from the oven entrance. In the case where the inside of the oven is divided into a plurality of spaces, the conveying path 2 refers to the 2 nd space through which the film passes. When a plurality of ovens are used, the wind speed of the 2 nd oven may be set to be lower than that of the oven that first passes, as described above, depending on the internal structure of the oven that first uses.

When the difference between the wind speeds of the conveyance path 1 and the conveyance path 2 is set as described above, the wind speeds of the conveyance paths subsequent to the conveyance path 2 may be within the range of the blowing wind speed of the hot wind. The wind speed of the transport path after the transport path 2 and the wind speed of the transport path 1 or the transport path 2 are preferably different from each other by 0.1 to 12 m/sec, and more preferably 0.2 to 8 m/sec. In the case of the difference in wind speed within such a range, the flutter of the film due to the difference in wind speed can be suppressed, and the optical film of the present invention satisfying the above expressions (1) to (3) tends to be easily manufactured, and the weight reduction rate of the obtained optical film tends to be easily adjusted within a desired range.

In the case where the inside of the oven is not divided into a plurality of spaces, the difference in the wind speeds may be adjusted by adjusting the position where the nozzle is provided, the blowing speed and the wind volume of hot air from the nozzle, the flow of air in the oven, and the like. When the interior of the oven is divided into a plurality of spaces, the position of the nozzle, the blowing speed and the air volume of hot air from the nozzle, the flow of air in the oven, and the like may be adjusted in the first space and the subsequent space. When a plurality of ovens are used, the setting may be performed in the same manner as described above depending on the configuration of the first oven, or the position of the nozzle, the blowing speed and the air volume of hot air from the nozzle, the airflow in the oven, and the like may be set so that the flow rate differs between the first oven and the ovens of the second and subsequent ovens.

In the heating area in the tenter furnace 100, the interval L (shortest distance) between the upper nozzles 46 and the lower nozzles 47 facing each other is preferably 150mm or more, more preferably 150 to 600mm, and further preferably 150 to 400 mm. By disposing the upper nozzles and the lower nozzles at such intervals L, the fluttering of the film in each step can be further reliably suppressed, and the optical film of the present invention satisfying the above expressions (1) to (3) can be easily produced.

The difference (Δ T) between the maximum temperature and the minimum temperature in the width direction (direction perpendicular to the paper surface of fig. 4) of the hot air at the outlet of each of the

nozzles

46 and 47 provided in the heating area is preferably 2 ℃ or less, and more preferably 1 ℃ or less. By heating the film with hot air having a sufficiently small temperature difference in the width direction, the optical film of the present invention satisfying the above expressions (1) to (3) can be easily produced. The temperature of the hot air is preferably 150 to 400 ℃, more preferably 150 to 300 ℃, and further preferably 150 to 250 ℃.

As the nozzle that can be used in the method for producing an optical film, a nozzle that is generally used in a film production apparatus can be used, and examples thereof include: a jet nozzle (also referred to as a slit nozzle) which is a nozzle having a slit-shaped outlet extending in the width direction of the raw material film; and a punching nozzle (also referred to as a multi-hole nozzle) which is a nozzle having a plurality of blow-out ports each having an opening in the conveyance direction of the raw material film and in the width direction of the raw material film.

The nozzles are of a structure that is disposed on the upper surface 100a in the tenter oven 100 and blows hot air downward toward the film, and of a structure that is disposed on the lower surface 100b in the tenter oven 100 and blows hot air upward toward the film.

The jet nozzle (jet nozzle) has a slit extending in the width direction of the film as a blowing port of hot air. The slit width of the slit is preferably 5mm or more, more preferably 5 to 20 mm. By setting the slit width to 5mm or more, the optical uniformity of the optical film obtained can be further improved. The area of the outlet port of each jet nozzle can be determined by the product of the length of the jet nozzle in the nozzle width direction and the slit width. The product of the area of the outlet of each nozzle and the blowing air speed is the blowing air volume of the hot air of each nozzle. The blowing rate of the hot air per 1m length of the nozzle in the film width direction can be obtained by dividing the blowing rate of the hot air by the length of the slit in the film width direction.

The punching nozzle (punching nozzle) may have a rectangular shape in cross section perpendicular to the longitudinal direction thereof, or may have a trapezoidal shape which is a shape gradually expanding toward the surface facing the raw material film 44. The punching nozzle has a plurality of openings (for example, circular openings) on a lower surface that is a surface facing the film. The outlet port of the hot air from the punching nozzle is formed by a plurality of openings provided in the outlet face. The plurality of openings are outlets for hot air, and the hot air is blown out from the openings at a predetermined wind speed. The plurality of openings are arranged in the longitudinal direction of the film, and the plurality of openings are also arranged in the width direction. The openings may be arranged, for example, in a meandering manner.

The area of the air outlet of each of the punching nozzles can be determined by the sum of the areas of all the openings provided in one punching nozzle. The product of the area of the outlet of each nozzle and the blowing air speed is the blowing air volume of the hot air of each nozzle. The blowing rate of the hot air per 1m length of the nozzle in the film width direction can be obtained by dividing the blowing rate of the hot air by the length of the slit in the film width direction.

When the punching nozzle is used, the difference between the maximum blowing-out wind speed and the minimum blowing-out wind speed in the width direction of the hot wind at the outlet of the nozzle can be obtained as the difference between the maximum blowing-out speed and the minimum blowing-out speed of the hot wind blown out from the plurality of openings provided in the same nozzle. The difference between the maximum temperature and the minimum temperature in the width direction of the hot air at the blowing port of the nozzle can be similarly determined.

When all the nozzles provided in the tenter oven 100 are punching nozzles, the total area of the hot air blow-out ports in the whole tenter oven 100 can be increased. Therefore, the wind pressure of the hot air blown to the film can be reduced, and the fluttering of the film can be further reduced. This makes it easy to manufacture the optical film of the present invention that satisfies the above expressions (1) to (3). In the tenter furnace or the heating zone, the raw material film 44 is heated from room temperature to a temperature at which the solvent contained in the raw material film evaporates, but the raw material film 44 tends to easily sag due to thermal expansion because it is held by the holding device 43 so that the length of the raw material film 44 in the width direction is substantially constant. By using a punching nozzle in the heating zone, sagging and chattering of the raw material film 44 can be further suppressed, and the optical film of the present invention satisfying the above expressions (1) to (3) can be easily produced.

The size and number of the openings provided on the surface of the punching nozzle can be adjusted so that the blowing speed of hot air at each opening is 2 to 25 m/sec and the blowing air quantity from each nozzle is 0.1 to 3m per 1m length of the nozzle along the film width direction³The appropriate adjustment is made in the range of/sec.

The shape of the opening is preferably circular from the viewpoint of making the blowing air velocity from each opening of the punching nozzle more uniform. In this case, the diameter of the opening is preferably 2 to 10mm, and more preferably 3 to 8 mm.

When the punching nozzles are used, the length of the surface of each nozzle in the film conveying direction is preferably 50 to 300 mm. Further, the interval between the punching nozzles adjacent to each other is preferably 0.3m or less. Further, the ratio of the total opening area of the punching nozzles (the area of the blowing port) to the length of the punching nozzles in the film width direction (the total opening area of the punching nozzles (m))²) The length (m)) of the punching nozzle in the film width direction is preferably 0.008m or more.

By using such a punching nozzle, the area of the outlet port of the hot air can be increased. This makes it possible to sufficiently reduce the wind speed of the hot air and blow the hot air with a sufficient air volume, thereby heating the film more uniformly. As a result, the optical film of the present invention satisfying the above expressions (1) to (3) can be easily produced.

The tenter 100 that performs the heating step may be provided with an IR heater on its inner upper surface 100a or its inner lower surface 100b so as to face each other in the vertical direction, similarly to the nozzle. In addition, a plurality of IR heaters may be provided. As the IR heater, an IR heater generally used in a film manufacturing apparatus may be used.

The radiation ray irradiated to the film is preferably a heat ray having a wavelength of 3 to 7 μm. In the radiation processing method, when the temperature of the space where the heating step is performed is within the above-described temperature range, the raw material film may be irradiated with radiation having a temperature higher by 30 ℃.

In the embodiment of the present invention, it is preferable to use the nozzle (hot air processing method) and the IR heater (radiation processing method) in combination in the tenter 100 that performs the heating step. In this case, the IR heater may be provided between adjacent nozzles or between the nozzle and the inner wall (including the wall of the partition space) of the tenter oven.

In this case, the temperature of the space in which the heating step is performed may be within the above-described temperature range, and in the radiation treatment system, the film may be irradiated with radiation having a temperature higher than the temperature of the space. The temperature of the radiation ray may be, for example, a temperature higher by 30 ℃ or more than the temperature of the space, or may be a temperature higher by 150 ℃ or more. The temperature of the radiation ray is a temperature set in a device that emits radiant heat, for example, a set temperature of an IR heater. The difference between the temperature of the radiation and the temperature of the radiation irradiated to the film is preferably 5 ℃ or less, more preferably 3 ℃ or less, and still more preferably 1 ℃ or less.

When the nozzle (hot air processing method) and the IR heater (radiation processing method) are used in combination in the tenter furnace 100, the heating step can be performed while suppressing the temperature in the heating region or the tenter furnace from becoming excessively high, even if the raw material film is irradiated with radiation having a temperature higher than the temperature in the heating region or the tenter furnace (the temperature of the atmosphere).

The heating step using the hot air treatment method and the radiation treatment method in combination is preferably performed between a space through which the raw material film first passes and a space located at the middle left and right positions of the entire length of the tenter furnace, among the plurality of spaces in the tenter furnace in which the heating step is performed. This can shorten the time required for the heating step and can produce an optical film having more excellent uniformity of in-plane retardation.

The heating step is preferably carried out at a temperature of 150 to 350 ℃. In the embodiment of the present invention, when the heating step is in this temperature range, the raw material film tends to be easily adjusted to the weight reduction rate M described later. The temperature range is more preferably 170 ℃ or higher, still more preferably 180 ℃ or higher, still more preferably 300 ℃ or lower, yet still more preferably 250 ℃ or lower, and particularly preferably 230 ℃ or lower. When the temperature in the heating step is within the above range, the YI value of the obtained optical film can be easily adjusted to the above preferred range. The temperature of the space in which the heating step is performed is more preferably 170 ℃ or higher, and still more preferably 180 ℃ or higher. The temperature in the tenter furnace in which the heating step is performed may be within the above range as long as the heating zone is within the above range. When there are a plurality of tenter furnaces and when the tenter furnace is divided into a plurality of spaces, the adjustment can be appropriately performed, and it is preferable that all of the tenter furnaces and the spaces are within the above range.

The moving speed of the raw material film 44 in the tenter 100 can be suitably adjusted usually within the range of 0.1 to 50 m/min. The upper limit of the moving speed is preferably 20 m/min, and more preferably 15 m/min. The lower limit of the moving speed is preferably 0.2 m/min, more preferably 0.5 m/min, still more preferably 0.7 m/min, and particularly preferably 0.8 m/min. If the moving speed is high, the length of the tenter furnace tends to be long and the facility tends to be large in order to secure a desired drying time. In the embodiment of the present invention, when the moving speed of the raw material film 44 in the tenter 100 is within the above range, the raw material film tends to be easily adjusted to the weight reduction rate M described later. In addition, an optical film satisfying the expressions (1) to (3) can be easily produced.

The treatment time in the heating step is usually 60 seconds to 2 hours, preferably 10 minutes to 1 hour. The treatment time may be appropriately adjusted in consideration of the conditions such as the temperature of the tenter, the moving speed, the wind speed and the wind amount of the hot wind.

In one embodiment of the present invention, the method for manufacturing an optical film may perform an operation of changing the film width in the heating step or an operation of holding the film width and conveying the same. As an example of the operation of changing the film width, an operation of stretching the film in the width direction can be cited. The stretching ratio is preferably 0.7 to 1.5 times, more preferably 0.8 to 1.4 times, and still more preferably 0.8 to 1.3 times. As an example of the operation of conveying while maintaining the film width, there is an operation of maintaining the film so that the length of the film in the width direction is substantially constant. The optical film obtained by these operations may have a length of about 0.7 to 1.5 times the length of the raw material film in the width direction, and may be a length obtained by stretching, equi-multiplying, or shrinking the raw material film from the length in the width direction. The stretch ratio is determined as the ratio of the width of the stretched film (excluding the gripped portion) to the width of the film excluding the gripped portion.

In fig. 5, in the operation of stretching the film in the width direction, the case where the stretching magnification exceeds 1 time is shown by a solid line, and the case where the stretching magnification is equal to or less than 1 time is shown by a broken line.

The optical film subjected to the heating step may be continuously fed to the next step after being carried out from the tenter, or may be fed to the next step after being wound in a roll. When the optical film is wound into a roll, the optical film may be wound after laminating a surface protective film and another film such as another optical film. As the surface protective film to be laminated on the optical film, the same film as a surface protective film to be laminated on a base film described later can be used. The thickness of the surface protective film laminated on the optical film is usually 10 to 100 μm, preferably 10 to 80 μm.

< raw Material film >

The raw material film supplied to the heating step contains at least a polyimide-based resin and/or a polyamide-based resin. The raw material film preferably contains the same components as those contained in the varnish used for forming the raw material film described later, but may be different in that structural changes of the components and evaporation of a part of the solvent may occur. The raw material film can be a self-supporting film or a gel film.

From the viewpoint of easy production of an optical film satisfying the expressions (1) to (3), the raw material film preferably has a weight loss rate M of preferably about 1 to 40%, more preferably 3 to 20%, further preferably 5 to 15%, and particularly preferably 5 to 12%, at 120 ℃ to 250 ℃ as determined by thermogravimetric-differential thermal measurement (hereinafter sometimes referred to as "TG-DTA measurement"), and a part of the solvent is removed from the varnish so that the weight loss rate M is preferably about 1 to 40%, more preferably 3 to 20%, further preferably 5 to 15%, and particularly preferably 5 to 12%, regardless of the presence or absence of the inorganic material. The weight loss rate M of the raw material film can be measured by the following method using a commercially available TG-DTA measuring apparatus. As the TG-DTA measuring device, TG/DTA6300 manufactured by Hitachi High-Tech Science Corporation can be used.

First, about 20mg of a sample was taken from a raw material film, the sample was heated from room temperature to 120 ℃ at a temperature increase rate of 10 ℃/min, and after being held at 120 ℃ for 5 minutes, the sample was heated to 400 ℃ at a temperature increase rate of 10 ℃/min, and the change in weight of the sample was measured while heating under these conditions. Then, from the results of TG-DTA measurement, the weight loss rate M (%) from 120 ℃ to 250 ℃ was calculated by the following formula. In the following formula, W₀The weight, W, of the sample after being held at 120 ℃ for 5 minutes is shown₁The weight of the sample at 250 ℃ is shown.

M(％)＝100-(W₁/W₀)×100

When the raw material film weight loss rate M is large to a certain extent, the raw material film tends to be wound as a laminate with a substrate or a surface protective film as follows: deformation such as bending of the laminate is suppressed, and the winding properties of the laminate are improved. In addition, an optical film satisfying the expressions (1) to (3) can be easily produced.

When the weight reduction rate M of the raw material film is small to a certain extent, the raw material film tends to be wound as a laminate with a substrate or a surface protective film as follows: the raw material film is not easily attached to the base material or the surface protective film. Therefore, the laminate can be easily unwound from the roll while maintaining uniform transparency of the raw material film.

The raw material film can be formed by drying the above coating film and peeling it from the substrate. The drying of the coating film may be carried out at a temperature of 50 to 350 ℃. If necessary, the coating film may be dried in an inert atmosphere or under reduced pressure. The raw material film obtained in the above manner is supplied to the above heating step, whereby the optical film of the present invention can be produced. The raw material film may be continuously conveyed and supplied to the heating step, or may be supplied after being temporarily wound.

< functional layer >

At least one functional layer of 1 or more may be laminated on at least one surface of the optical film of the present invention. Examples of the functional layer include an ultraviolet absorbing layer, a hard coat layer, an undercoat layer, a gas barrier layer, an adhesive layer, a hue adjusting layer, and a refractive index adjusting layer. The functional layers may be used alone or in combination of two or more.

(ultraviolet ray absorption layer)

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

(hard coating)

The hard coat layer is, for example, a layer which can be formed by curing a composition for forming a hard coat layer (hereinafter, also referred to as "hard coat layer composition") containing a reactive material capable of forming a crosslinked structure by irradiation with active energy rays or application of thermal energy, and is preferably a layer which can be formed by irradiation with active energy rays. The active energy ray is defined as an energy ray capable of decomposing a compound capable of generating an active species to generate an active species, and examples thereof include visible light, ultraviolet light, infrared light, X-ray, α -ray, β -ray, γ -ray, electron beam, and the like, and preferable examples thereof include ultraviolet light. The hard coat composition contains a polymer of at least 1 of a radical polymerizable compound and a cation polymerizable compound. The thickness of the hard coat layer is not particularly limited, but is preferably 2 to 50 μm, more preferably 2 to 40 μm, further preferably 3 to 20 μm, and further preferably 3 to 15 μm, from the viewpoint of easily preventing cracking at the interface between the hard coat layer or the hard coat layer and the optical film. When the thickness of the hard coat layer is within the above range, the following tendency is observed: sufficient scratch resistance can be ensured, and the bending resistance is not easily reduced, and the problem of curling due to curing shrinkage is not easily generated.

In the hard coat layer forming step, the coating film is coatedThe coating film is cured by irradiation with high-energy rays (e.g., active energy rays) to form a hard coating layer. The irradiation intensity is not particularly limited, and is preferably irradiation in a wavelength region effective for activation of the polymerization initiator. The irradiation intensity is preferably 0.1-6,000 mW/cm²More preferably 10 to 1,000mW/cm²More preferably 20 to 500mW/cm². 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 generation during the curing reaction can be suppressed. The irradiation time is not particularly limited, and may be suitably selected depending on the composition of the curable composition, and the cumulative light amount represented by the product of the irradiation intensity and the irradiation time is preferably 10 to 10,000mJ/cm²More preferably 50 to 1,000mJ/cm²More preferably 80 to 500mJ/cm²The mode of (2) is set. When the cumulative light amount is within the above range, a sufficient amount of active species derived from the polymerization initiator can be generated, so that the curing reaction can be more reliably performed, and the irradiation time does not become excessively long, so that good productivity can be maintained. In addition, the hard coat layer can be further increased in hardness by the irradiation step in this range, and therefore, this is useful. From the viewpoint of improving the smoothness of the hard coat layer and further improving the visibility of the optical film in the wide angle direction, the kind of solvent, the component ratio, the optimization of the solid content concentration, the addition of the leveling agent, and the like can be mentioned.

The radical polymerizable compound is a compound having a radical polymerizable group. The radical polymerizable group of the radical polymerizable compound may be a functional group capable of undergoing a radical polymerization reaction, and examples thereof include a group containing a carbon-carbon unsaturated double bond, specifically, a vinyl group and a (meth) acryloyl group. When the radical polymerizable compound has 2 or more radical polymerizable groups, the radical polymerizable groups may be the same or different from each other. The number of radical polymerizable groups contained in 1 molecule of the radical polymerizable compound is preferably 2 or more in terms of increasing the hardness of the hard coat layer. The radical polymerizable compound preferably includes a compound having a (meth) acryloyl group in view of high reactivity, specifically, a compound called a multifunctional acrylate monomer having 2 to 6 (meth) acryloyl groups in 1 molecule, an epoxy (meth) acrylate, a urethane (meth) acrylate, and an oligomer called a polyester (meth) acrylate having several (meth) acryloyl groups in a molecule and having a molecular weight of several hundred to several thousand, and preferably 1 or more selected from the group consisting of an epoxy (meth) acrylate, a urethane (meth) acrylate, and a polyester (meth) acrylate.

The cationically polymerizable compound is a compound having a cationically polymerizable group such as an epoxy group, an oxetane group, or a vinyl ether group. The number of the cationically polymerizable groups contained in 1 molecule of the cationically polymerizable compound is preferably 2 or more, and more preferably 3 or more, from the viewpoint of improving the hardness of the hard coat layer.

Among the above cationically polymerizable compounds, preferred are compounds having at least 1 of an epoxy group and an oxetane group as a cationically polymerizable group. A cyclic ether group such as an epoxy group or an oxetane group is preferable in that shrinkage accompanying the polymerization reaction is small. Among cyclic ether groups, compounds having an epoxy group have the following advantages: it is easy to obtain compounds having various structures, to exert no adverse effect on the durability of the obtained hard coat layer, and to control the compatibility with the radical polymerizable compound. Among cyclic ether groups, an oxetanyl group has the following advantages over an epoxy group: the polymerization degree is easily increased, the formation speed of the network of the cationic polymerizable compound in the obtained hard coat layer is increased, and even in the region where the hard coat layer is mixed with the radical polymerizable compound, the unreacted monomer is not left in the film, and an independent network can be formed; and so on.

Examples of the cationically polymerizable compound having an epoxy group include polyglycidyl ethers of polyhydric alcohols having an alicyclic ring, and alicyclic epoxy resins obtained by epoxidizing compounds having a cyclohexene ring or cyclopentene ring with an appropriate oxidizing agent such as hydrogen peroxide or a peroxy acid; aliphatic epoxy resins such as polyglycidyl ethers of aliphatic polyols or alkylene oxide adducts thereof, polyglycidyl esters of aliphatic long-chain polybasic acids, homopolymers and copolymers of glycidyl (meth) acrylate; glycidyl ethers produced by the reaction of bisphenols such as bisphenol a, bisphenol F and hydrogenated bisphenol a, or derivatives thereof such as alkylene oxide adducts and caprolactone adducts with epichlorohydrin, and glycidyl ether type epoxy resins derived from bisphenols such as Novolac epoxy resins.

The above hard coating composition may further comprise a polymerization initiator. Examples of the polymerization initiator include a radical polymerization initiator, a cationic polymerization initiator, a radical and cationic polymerization initiator, and they can be appropriately selected and used. These polymerization initiators are those which are decomposed by at least one of irradiation with active energy rays and heating to generate radicals or cations, thereby causing radical polymerization and cationic polymerization.

The radical polymerization initiator may be one that can release a substance that initiates radical polymerization by at least one of irradiation with active energy rays and heating. Examples of the thermal radical polymerization initiator include organic peroxides such as hydrogen peroxide and perbenzoic acid, and azo compounds such as azobisisobutyronitrile.

The active energy ray radical polymerization initiator includes a Type1 radical polymerization initiator which generates radicals by decomposition of molecules and a Type2 radical polymerization initiator which generates radicals by a hydrogen abstraction-Type reaction in the coexistence of a tertiary amine, and these may be used alone or in combination.

The cationic polymerization initiator may be one which can release a substance for initiating cationic polymerization by at least one of irradiation with active energy rays and heating. As the cationic polymerization initiator, aromatic iodonium salts, aromatic sulfonium salts, cyclopentadienyl iron (II) complexes, and the like can be used. For them, cationic polymerization can be initiated by either or both of irradiation with active energy rays or heating, depending on the structural difference.

The polymerization initiator may be preferably contained in an amount of 0.1 to 10% by mass based on 100% by mass of the entire hard coat composition. When the content of the polymerization initiator is within the above range, the curing can be sufficiently performed, the mechanical properties and the adhesion force of the finally obtained coating film can be in a good range, and poor adhesion, a crack phenomenon, and a curl phenomenon due to curing shrinkage tend to be less likely to occur.

The hard coating composition may further include one or more selected from the group consisting of a solvent and an additive.

The solvent is a solvent capable of dissolving or dispersing the polymerizable compound and the polymerization initiator, and any solvent known as a solvent for a hard coat composition in the art may be used as long as the effect of the present invention is not impaired.

The above additives may further contain inorganic particles, leveling agents, stabilizers, surfactants, antistatic agents, lubricants, antifouling agents, and the like.

(adhesive layer)

The pressure-sensitive adhesive layer is a layer having a pressure-sensitive adhesive function and has a function of bonding the optical film to another member. As a material for forming the adhesive layer, a generally known material can be used. For example, a thermosetting resin composition or a photocurable resin composition may be used. In this case, the resin composition can be polymerized and cured by supplying energy afterwards.

The Pressure-Sensitive Adhesive layer may be a layer called a Pressure-Sensitive Adhesive (PSA) that is pressed and attached to an object. The pressure-sensitive adhesive may be a capsule adhesive as "a substance having adhesiveness at normal temperature and adhering to an adherend under light pressure" (JIS K6800), or as "an adhesive which contains a specific component in a protective film (microcapsule) and can maintain stability until the film is broken by an appropriate means (pressure, heat, etc.)" (JIS K6800).

(color phase adjusting layer)

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

(refractive index adjusting layer)

The refractive index adjustment layer is a layer having a function of adjusting the refractive index, and is, for example, a layer having a refractive index different from that of the optical film and capable of providing a predetermined refractive index to the optical laminate. The refractive index adjusting layer may be, for example, a resin selected as appropriate, a resin layer containing a pigment as the case may be, or a thin film of a metal. Examples of the pigment for adjusting the refractive index include silica, alumina, antimony oxide, tin oxide, titanium oxide, zirconium oxide, and tantalum oxide. The average primary particle diameter of the pigment may be 0.1 μm or less. By setting the average primary particle diameter of the pigment to 0.1 μm or less, diffuse reflection of light transmitted through the refractive index adjustment layer can be prevented, and a decrease in transparency can be prevented. Examples of the metal used for the refractive index adjustment layer include metal oxides and metal nitrides such as titanium oxide, tantalum oxide, zirconium oxide, zinc oxide, tin oxide, silicon oxide, indium oxide, titanium oxynitride, titanium nitride, silicon oxynitride, and silicon nitride.

(protective film)

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

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

The optical film of the present invention may be a single layer or a laminate, and for example, the optical film produced as described above may be used as it is, or may be further used as a laminate with another film.

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

Examples of the image display device include wearable devices such as a television, a smartphone, a mobile phone, a car navigation system, a tablet computer, a portable game machine, electronic paper, a pointer, a bulletin board, a clock, and a smart watch. As the flexible display device, all image display devices having a flexible characteristic can be cited.

[ Flexible display device ]

The invention also provides a flexible display device provided with the optical film. The optical film of the present invention is preferably used as a front panel in a flexible display device, which is sometimes referred to as a window film. The flexible display device is formed of a laminate for flexible display device and an organic EL display panel, and the laminate for flexible display device is disposed on the viewing side of the organic EL display panel and is configured to be foldable. The laminate for a flexible display device may contain the optical film (window film), circularly polarizing plate, and touch sensor of the present invention in any order, and preferably the window film, circularly polarizing plate, and touch sensor are laminated in this order or the window film, touch sensor, and circularly polarizing plate are laminated in this order from the viewing side. The presence of the circularly polarizing plate on the viewing side of the touch sensor is preferable because the pattern of the touch sensor is less likely to be observed and the visibility of the display image is good. The members may be laminated using an adhesive, or the like. The touch panel may further include a light-shielding pattern formed on at least one surface of any one of the window film, the circularly polarizing plate, and the touch sensor.

[ polarizing plate ]

The flexible display device of the present invention may further include a polarizing plate, preferably a circular polarizing plate. The circularly polarizing plate is a functional layer having a function of transmitting only a right-circularly polarized light component or a left-circularly polarized light component by laminating a λ/4 phase difference plate on a linearly polarizing plate. For example, can be used for: the external light is converted into right-handed circularly polarized light, the external light which is reflected by the organic EL panel and becomes left-handed circularly polarized light is blocked, only the light-emitting component of the organic EL is transmitted, and therefore the influence of reflected light is inhibited, and the image can be easily viewed. In order to achieve the circularly polarized light function, the absorption axis of the linear polarizer and the slow axis of the λ/4 phase difference plate need to be 45 ° in theory, but in practical applications, 45 ± 10 °. The linear polarizing plate and the λ/4 phase difference plate do not necessarily have to be stacked adjacent to each other, and the relationship between the absorption axis and the slow axis may satisfy the above range. It is preferable to achieve completely circularly polarized light at all wavelengths, but this is not necessarily the case in practical applications, and therefore, the circularly polarizing plate in the present invention also includes an elliptically polarizing plate. It is also preferable to further laminate a λ/4 retardation film on the viewing side of the linear polarizing plate to convert the emitted light into circularly polarized light, thereby improving visibility in a state where the polarized sunglasses are worn.

The linear polarizing plate is a functional layer having the following functions: light vibrating in the direction of the transmission axis is passed through, and polarized light of a vibration component perpendicular to the light is blocked. The linear polarizing plate may be a single linear polarizer or a structure including a linear polarizer and a protective film attached to at least one surface of the linear polarizer. The thickness of the linearly polarizing plate may be 200 μm or less, and preferably 0.5 to 100 μm. When the thickness of the linearly polarizing plate is within the above range, flexibility tends to be less likely to decrease.

The linear polarizer may be a film-type polarizer manufactured by dyeing and stretching a polyvinyl alcohol (hereinafter, also referred to as "PVA") film. The polarizing performance can be exhibited by adsorbing a dichroic dye such as iodine to a PVA film that has been stretched to be oriented, or by stretching the PVA film in a state of being adsorbed to the dichroic dye to orient the dichroic dye. The film-type polarizer may be produced by steps such as swelling, crosslinking with boric acid, washing with an aqueous solution, and drying. The stretching and dyeing step may be performed as a PVA film alone or in a state of being laminated with another film such as polyethylene terephthalate. The thickness of the PVA film to be used is preferably 10 to 100 μm, and the stretch ratio is preferably 2 to 10 times.

In addition, another example of the polarizer is a liquid crystal coating type polarizer formed by coating a liquid crystal polarizing composition. The liquid crystal polarizing composition may include a liquid crystal compound and a dichroic dye compound. The liquid crystalline compound is preferably used because it has a property of exhibiting a liquid crystal state, and particularly, when it has a high-order alignment state such as smectic, it can exhibit high polarizing performance. The liquid crystalline compound preferably has a polymerizable functional group.

The dichroic dye may have a polymerizable functional group, and may have liquid crystal properties, in addition to being aligned with the liquid crystal compound to exhibit dichroism. Any of the compounds in the liquid crystal polarizing composition has a polymerizable functional group.

The liquid crystal polarizing composition may further include an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, 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 liquid crystal polarizing layer can be formed to a thinner thickness than the film type polarizer. The thickness of the liquid crystal polarizing layer is preferably 0.5 to 10 μm, and more preferably 1 to 5 μm.

The above-described alignment film can be produced, for example, by: the alignment film-forming composition is applied to a substrate, and alignment properties are imparted by rubbing, polarized light irradiation, or the like. The above-mentioned alignment film forming composition may contain a solvent, a crosslinking agent, an initiator, a dispersant, a leveling agent, a silane coupling agent, and the like in addition to the alignment agent. Examples of the orientation agent include polyvinyl alcohols, polyacrylates, polyamide acids, and polyimides. In the case of applying photo-alignment, an alignment agent containing a cinnamate group (cinnamate group) is preferably used. The weight average molecular weight of the polymer that can be used as the orientation agent may be, for example, about 10,000 to 1,000,000. The thickness of the alignment film is preferably 5 to 10,000nm, more preferably 10 to 500nm, from the viewpoint of alignment regulating force.

The liquid crystal polarizing layer may be laminated by being peeled off from the substrate and then transferred, or the substrate may be directly laminated. The substrate preferably functions as a transparent substrate for a protective film, a retardation plate, and a window film.

The protective film may be a transparent polymer film, and specific examples of the polymer film to be used include polyolefins such as polyethylene, polypropylene, polymethylpentene, cycloolefin derivatives of cycloolefin having a unit containing a norbornene or cycloolefin monomer, (modified) celluloses such as diacetylcellulose, triacetylcellulose and propionylcellulose, acrylics such as methyl methacrylate (co) polymers, polystyrenes such as styrene (co) polymers, acrylonitrile-butadiene-styrene copolymers, acrylonitrile-styrene copolymers, ethylene-vinyl acetate copolymers, polyvinyl chlorides, polyvinylidene chlorides, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate and polyarylates, polyamides such as nylon, polyesters, polyamides, polyesters, polyamides, polyesters, and the like, polyesters, and the like, Films such as polyimides, polyamideimides, polyetherimides, polyethersulfones, polysulfones, polyvinyl alcohols, polyvinyl acetals, polyurethanes, and epoxy resins are preferably films of polyamides, polyamideimides, polyimides, polyesters, olefins, acrylic resins, or cellulose resins, from the viewpoint of excellent transparency and heat resistance. These polymers may be used alone or in combination of 2 or more. These films may be used in an unstretched state, or as uniaxially or biaxially stretched films. Cellulose-based films, olefin-based films, acrylic films, and polyester films are preferable. The protective film may be a coating type protective film obtained by applying and curing a cationically curable composition such as an epoxy resin or a radically curable composition such as an acrylate. If necessary, a plasticizer, an ultraviolet absorber, an infrared absorber, a pigment, a colorant such as a dye, a fluorescent brightener, a dispersant, a heat stabilizer, a light stabilizer, an antistatic agent, an antioxidant, a lubricant, a solvent, or the like may be included. The thickness of the protective film is preferably 200 μm or less, and more preferably 1 to 100 μm. When the thickness of the protective film is within the above range, the flexibility of the protective film is not easily reduced.

The λ/4 phase difference plate is a film that imparts a phase difference of λ/4 in a direction orthogonal to the traveling direction of incident light (i.e., in-plane direction of the film). The λ/4 retardation plate may be a stretched retardation plate produced by stretching a polymer film such as a cellulose film, an olefin film, or a polycarbonate film. The λ/4 phase difference plate may contain, if necessary, a phase difference adjuster, a plasticizer, an ultraviolet absorber, an infrared absorber, a pigment, a colorant such as a dye, a fluorescent brightener, a dispersant, a heat stabilizer, a light stabilizer, an antistatic agent, an antioxidant, a lubricant, a solvent, and the like. The thickness of the stretched phase difference plate is preferably 200 μm or less, and more preferably 1 to 100 μm. When the thickness is within the above range, the flexibility of the film tends not to be easily lowered.

Another example of the λ/4 retardation plate is a liquid crystal coating type retardation plate formed by coating a liquid crystal composition. The liquid crystal composition contains a liquid crystalline compound having a property of exhibiting a liquid crystal state such as a nematic state, a cholesteric state, or a smectic state. Any compound including a liquid crystalline compound in the liquid crystal composition has a polymerizable functional group. The liquid crystal composition may further include an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, and the like. The liquid crystal coating type retardation plate can be produced by coating a liquid crystal composition on an alignment film and curing the coating to form a liquid crystal retardation layer, as described in the liquid crystal polarizing layer. The liquid crystal coating type retardation plate can be formed to a smaller thickness than the stretching type retardation plate. The thickness of the liquid crystal polarizing layer is preferably 0.5 to 10 μm, and more preferably 1 to 5 μm. The liquid crystal coated retardation film may be laminated by being peeled from a substrate and then transferred, or the substrate may be directly laminated. The substrate preferably functions as a transparent substrate for a protective film, a retardation plate, and a window film.

In general, the birefringence is large as the wavelength is shorter, and the birefringence is small as the wavelength is longer. In this case, since a retardation of λ/4 cannot be achieved in all visible light regions, an in-plane retardation of λ/4, that is, an in-plane retardation of preferably 100 to 180nm, more preferably 130 to 150nm, is often designed in the vicinity of 560nm, which has high visibility. An inverse dispersion λ/4 phase difference plate using a material having a birefringence wavelength dispersion characteristic opposite to that of the usual one is preferable in view of being able to improve visibility. As such a material, the material described in japanese patent application laid-open No. 2007-232873 and the like is preferably used also in the case of a stretched phase difference plate, and the material described in japanese patent application laid-open No. 2010-30979 is preferably used also in the case of a liquid crystal coated phase difference plate.

As another method, a technique of obtaining a wide-band λ/4 phase difference plate by combining with a λ/2 phase difference plate is also known (japanese patent application laid-open No. h 10-90521). The λ/2 phase difference plate can be manufactured by the same material and method as the λ/4 phase difference plate. The combination of the stretching type retardation plate and the liquid crystal coating type retardation plate is optional, but in any case, when the liquid crystal coating type retardation plate is used, the thickness can be made thin, which is preferable from the viewpoint of the above.

For the circularly polarizing plate, a method of laminating a positive C plate is also known in order to improve visibility in an oblique direction (japanese patent application laid-open No. 2014-224837). The positive C plate may be a liquid crystal coated retardation plate or a stretched retardation plate. The retardation in the thickness direction of the retardation plate is preferably from-200 to-20 nm, more preferably from-140 to-40 nm.

[ touch sensor ]

The flexible display device of the present invention may further include a touch sensor. The touch sensor may be used as an input mechanism. As the touch sensor, various types such as a resistive film type, a surface acoustic wave type, an infrared ray type, an electromagnetic induction type, and a capacitance type have been proposed, and any type may be used, but the capacitance type is preferable. The capacitive touch sensor may be divided into an active region and an inactive region located at a peripheral portion of the active region. The active region is a region corresponding to a display portion, which is a region on the display panel where a screen is displayed, and is a region where a user's touch is sensed, and the inactive region is a region corresponding to a non-display portion, which is a region on the display device where a screen is not displayed. The touch sensor may include: a substrate having flexible properties; a sensing pattern formed in an active region of the substrate; and each sensing line formed in the inactive region of the substrate and used for connecting the sensing pattern with an external driving circuit through a pad (pad) portion. As the substrate having a flexible property, the same material as the polymer film can be used. The substrate of the touch sensor preferably has a toughness of 2,000 MPa% or more in terms of suppressing cracks in the touch sensor. The toughness may be more preferably 2,000 to 30,000 MPa%. Here, the toughness is defined as the area of the lower part of a Stress (MPa) -strain (%) curve (Stress-strain curve) obtained by a tensile test of a polymer material up to a failure point.

The sensing pattern may include a 1 st pattern formed along a 1 st direction and a2 nd pattern formed along a2 nd direction. The 1 st pattern and the 2 nd pattern are arranged in mutually different directions. The 1 st pattern and the 2 nd pattern are formed in the same layer, and in order to sense a touched position, the patterns must be electrically connected. The 1 st pattern is a form in which the unit patterns are connected to each other via a terminal, and the 2 nd pattern is a structure in which the unit patterns are separated from each other into islands, and therefore, in order to electrically connect the 2 nd pattern, a separate bridge electrode is required. As the electrode for electrically connecting the 2 nd pattern, a known transparent electrode material can be applied. Examples of the transparent electrode material include Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), zinc oxide (ZnO), Indium Zinc Tin Oxide (IZTO), Indium Gallium Zinc Oxide (IGZO), Cadmium Tin Oxide (CTO), PEDOT (poly (3,4-ethylenedioxythiophene), poly (3, 4-ethylenedioxythiophene)), Carbon Nanotube (CNT), graphene, and a metal wire, and these may be used alone or in combination of 2 or more. ITO is preferably used as the transparent electrode material. The metal usable for the wire is not particularly limited, and examples thereof include silver, gold, aluminum, copper, iron, nickel, titanium, selenium, chromium, and the like, and these metals may be used alone or in combination of 2 or more.

The bridge electrode may be formed on the insulating layer with an insulating layer interposed therebetween on the sensing pattern, the bridge electrode may be formed on the substrate, and the insulating layer and the sensing pattern may be formed thereon. The bridge electrode may be formed of the same material as the sensing pattern, or may be formed of a metal such as molybdenum, silver, aluminum, copper, palladium, gold, platinum, zinc, tin, titanium, or an alloy of 2 or more of these metals. The 1 st pattern and the 2 nd pattern must be electrically insulated, and thus, an insulating layer is formed between the sensing pattern and the bridge electrode. The insulating layer may be formed only between the tab of the 1 st pattern and the bridge electrode, or may be formed as a layer covering the entire sensing pattern. In the case of forming a layer covering the entire sensing pattern, the bridge electrode may connect the 2 nd pattern via a contact hole formed in the insulating layer.

The touch sensor may further include an optical adjustment layer between the substrate and the electrode as a means for appropriately compensating for a difference in transmittance between a pattern region where a pattern is formed and a non-pattern region where no pattern is formed (specifically, a difference in transmittance due to a difference in refractive index in these regions). The optical adjustment layer may contain an inorganic insulating substance or an organic insulating substance. The optical adjustment layer can be formed by applying a photocurable composition containing a photocurable organic binder and a solvent onto a substrate. The above-mentioned photocurable composition may further comprise inorganic particles. The refractive index of the optical adjustment layer can be increased by the inorganic particles.

The photocurable organic binder may include, for example, a copolymer of monomers such as an acrylate monomer, a styrene monomer, and a carboxylic acid monomer. The photocurable organic binder may be, for example, a copolymer containing repeating units different from each other, such as repeating units containing an epoxy group, repeating units containing an acrylate, repeating units containing a carboxylic acid, and the like.

Examples of the inorganic particles include zirconium dioxide particles, titanium dioxide particles, and aluminum oxide particles. The photocurable composition may further contain various additives such as a photopolymerization initiator, a polymerizable monomer, and a curing assistant.

[ adhesive layer ]

Each layer of the laminate for a flexible display device, such as a window film, a polarizing plate, and a touch sensor, and a film member constituting each layer, such as a linear polarizing plate and a λ/4 retardation plate, may be bonded with an adhesive. As the adhesive, a commonly used adhesive such as an aqueous adhesive, an organic solvent adhesive, a solventless adhesive, a solid adhesive, a solvent-volatile adhesive, a moisture-curable adhesive, a heat-curable adhesive, an anaerobic curable adhesive, an aqueous solvent-volatile adhesive, an active energy ray-curable adhesive, a curing agent-mixed adhesive, a hot-melt adhesive, a pressure-sensitive adhesive, and a remoistenable adhesive can be used. Among them, water-based solvent-volatile adhesives, active energy ray-curable adhesives, and adhesives are generally used. The thickness of the adhesive layer can be adjusted as appropriate according to the required adhesive strength, and is preferably 0.01 to 500 μm, and more preferably 0.1 to 300 μm. The laminate for a flexible image display device may have a plurality of adhesive layers, and the thickness and the type of the adhesive used may be the same or different.

The aqueous solvent-volatile adhesive may be a polyvinyl alcohol polymer, a water-soluble polymer such as starch, or a water-dispersed polymer such as an ethylene-vinyl acetate emulsion or a styrene-butadiene emulsion. In addition to water and the above-mentioned main agent polymer, a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, a dye, a pigment, an inorganic filler, an organic solvent, and the like may be blended. In the case of bonding with the aqueous solvent volatile adhesive, the aqueous solvent volatile adhesive may be injected between the layers to be bonded, and the layers to be bonded may be bonded and then dried to impart adhesiveness. The thickness of the adhesive layer when the aqueous solvent volatile adhesive is used may be 0.01 to 10 μm, preferably 0.1 to 1 μm. When the aqueous solvent-volatile adhesive is used for forming a plurality of layers, the thickness of each layer and the type of the adhesive may be the same or different.

The active energy ray-curable adhesive can be formed by curing an active energy ray-curable composition containing a reactive material capable of forming an adhesive layer by irradiation with an active energy ray. The active energy ray-curable composition may contain at least 1 polymer of a radical polymerizable compound and a cation polymerizable compound similar to the compounds described for the hard coat composition. As the radical polymerizable compound, the same type of radical polymerizable compound as described for the hard coat composition can be used. As the radical polymerizable compound that can be used in the adhesive layer, a compound having an acryloyl group is preferable. In order to reduce the viscosity as an adhesive composition, the composition preferably further contains a monofunctional compound.

As the cationic polymerizable compound, the same kind of cationic polymerizable compound as described for the hard coat composition can be used. The cationically polymerizable compound used in the active energy ray-curable composition is preferably an epoxy compound. In order to reduce the viscosity of the adhesive composition, the composition preferably also comprises a monofunctional compound as reactive diluent.

The active energy ray composition may further include a polymerization initiator. Examples of the polymerization initiator include a radical polymerization initiator, a cationic polymerization initiator, a radical and cationic polymerization initiator, and they can be appropriately selected and used. These polymerization initiators are those which can be decomposed by at least one of irradiation with active energy rays and heating to generate radicals or cations, thereby allowing radical polymerization and cationic polymerization to proceed. The initiator described in the description of the hard coat composition, which can initiate at least either radical polymerization or cationic polymerization by irradiation with active energy rays, may be used.

The active energy ray-curable composition may further contain an ion scavenger, an antioxidant, a chain transfer agent, an adhesion-imparting agent, a thermoplastic resin, a filler, a flow viscosity modifier, a plasticizer, an antifoaming agent, an additive, and a solvent. When 2 layers to be bonded are bonded with the active energy ray-curable adhesive, the layers can be bonded by: the active energy ray-curable composition is applied to one or both of the adhesive layers, and then the adhesive layers are bonded to each other, and the composition is cured by irradiation with active energy rays through one or both of the adhesive layers. The thickness of the adhesive layer when the active energy ray-curable adhesive is used 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 layers, the thickness of each layer and the type of the adhesive used may be the same or different.

The pressure-sensitive adhesive may be classified into an acrylic pressure-sensitive adhesive, a urethane pressure-sensitive adhesive, a rubber pressure-sensitive adhesive, a silicone pressure-sensitive adhesive, and the like according to the base polymer, and any of them may be used. The binder may contain a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, an adhesion promoter, a plasticizer, a dye, a pigment, an inorganic filler, and the like in addition to the main polymer. The adhesive layer (adhesive layer) can be formed by dissolving and dispersing the components constituting the adhesive in a solvent to obtain an adhesive composition, applying the adhesive composition to a substrate, and then drying the adhesive composition. The adhesive layer may be formed directly or by transferring an adhesive layer separately formed on the substrate. A release film is also preferably used to cover the pressure-sensitive adhesive surface before bonding. The thickness of the adhesive layer when the adhesive is used is preferably 1 to 500 μm, more preferably 2 to 300 μm. When the above-mentioned adhesive is used for forming a plurality of layers, the thickness of each layer and the kind of the adhesive used may be the same or different.

[ light-shielding pattern ]

The light shielding pattern may be applied as at least a part of a bezel (bezel) or a housing of the flexible image display device. The wiring disposed at the edge of the flexible image display device is hidden by the light-shielding pattern and is not easily viewed, thereby improving visibility of an image. The light-shielding pattern may be in the form of a single layer or a plurality of layers. The color of the light-shielding pattern is not particularly limited, and may have various colors such as black, white, metallic color, and the like. The light-shielding pattern may be formed of a pigment for color, and polymers such as acrylic resin, ester resin, epoxy resin, polyurethane, silicone, and the like. They may be used alone or in the form of a mixture of 2 or more. The light-shielding pattern can be formed by various methods such as printing, photolithography, and inkjet. The thickness of the light-shielding pattern is preferably 1 to 100 μm, and more preferably 2 to 50 μm. Further, it is preferable to provide a shape such as an inclination in the thickness direction of the light-shielding pattern.

Examples

The present invention will be described in more detail below with reference to examples. Unless otherwise specified, "%" and "parts" in the examples mean mass% and parts by mass. First, the evaluation method will be explained.

< measurement of Total light transmittance >

The total light transmittance (Tt) of the optical film was measured in accordance with JIS K7105: 1981, using a fully automated direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd.

< haze >

According to JIS K7136: the optical films obtained in examples and comparative examples were cut into a size of 30mm × 30mm, and the haze (%) was measured using a haze computer (Suga Test Instruments co., ltd., "HGM-2 DP").

< YI value >

According to JIS K7373: the YI value of the optical film was measured by using an ultraviolet-visible near-infrared spectrophotometer "V-670" manufactured by Nippon spectral Co., Ltd. After background measurement in the absence of a sample, an optical film was placed on a sample holder, transmittance for light of 300 to 800nm was measured to obtain a tristimulus value (X, Y, Z), and a YI value was calculated based on the following formula.

YI＝100×(1.2769X-1.0592Z)/Y

< determination of weight average molecular weight >

Gel Permeation Chromatography (GPC) measurement

(1) Pretreatment method

A DMF eluent (10mmol/L lithium bromide solution) was added to a polyamideimide membrane so that the concentration thereof became 2mg/mL, and the mixture was heated while stirring at 80 ℃ for 30 minutes, cooled, and then filtered through a 0.45 μm membrane filter to obtain a solution as a measurement solution.

(2) Measurement conditions

Column: TSKgel α -2500 (7)7.8mm diameter. times.300 mm. times.1 and α -M ((13)7.8mm diameter. times.300 mm). times.2 from TOSOH Ltd

Eluent: DMF (with addition of 10mmol/L lithium bromide)

Flow rate: 1.0 mL/min

A detector: RI detector

Column temperature: 40 deg.C

Sample introduction amount: 100 μ L

Molecular weight standard: standard polystyrene

< measurement of thickness >

The thickness of the optical film was measured using an ABS number dial gauge ("ID-C112 BS", manufactured by Mitutoyo Co., Ltd.).

< tensile elastic modulus >

The elastic modulus of the optical films obtained in examples and comparative examples was measured at a temperature of 25 ℃ and a relative humidity of 50% by using "Autograph AG-IS" manufactured by Shimadzu corporation. More specifically, a film having a width of 10mm in length and width was prepared, a stress-strain curve (S-S curve) was measured under conditions that the distance between chucks was 50mm and the stretching speed was 10 mm/min, and the elastic modulus and the strain at break ε were calculated from the slopes of the stress-strain curve₂。

< Low temperature tensile test >

The elastic modulus of the optical films obtained in examples and comparative examples was measured at-40 ℃ by using "Autograph AG-IS" manufactured by Shimadzu corporation. More specifically, a film having a width of 10mm in length and width was prepared, a stress-strain curve (S-S curve) was measured under conditions that the distance between chucks was 50mm and the stretching speed was 10 mm/min, and the elastic modulus and the strain at break ε were calculated from the slopes of the stress-strain curve₁。

< measurement of Transmission image Property of optical film >

The transmission image value of the optical film was measured by the transmission method as described below using an image measuring instrument (ICM-1 manufactured by Suga Test Instruments co., ltd.) according to JIS K7345.

The optical film was set in a mapper. The optical film was set in a state where foreign matters were removed from the surface by lightly wiping both surfaces with ethanol and drying the surfaces before setting. Then, the light quantity and the cross-sectional area were adjusted, and white light adjusted to be parallel light was irradiated to the optical film from an angle (incident angle) inclined by 60 ° in the MD direction with respect to the plane of the optical film. The cross-sectional area of the transmitted light transmitted through the optical film is adjusted to be transmitted through an optical comb extending perpendicular to the optical axis of the irradiation light, and the light transmitted through the optical comb is received by an optical receiver.

The following operations were repeated: the optical comb (slit width: 0.125mm) is moved by a predetermined unit width in a direction parallel to the plane of the optical comb and in the direction of arrangement of the slits in the optical comb, and receives the transmitted light of the optical comb. As a result, a received light waveform was obtained. The maximum value M and the minimum value M of the relative light amount are obtained from the obtained light receiving waveform. From the obtained M and M, the 1 st transmission image C is calculated based on the formula (7)₆₀(MD)。

The 2 nd transmission image quality value C was calculated in the same manner as the 1 st transmission image quality value except that the incident angle was changed to an angle inclined by 60 degrees in the TD direction from the direction perpendicular to the optical film plane and an angle perpendicular to the optical film plane (an angle inclined by 0 degrees), respectively₆₀(TD) and a 3 rd transmission image value C₀。

< imidization ratio >

Utilization of imidization ratio¹H-NMR was measured in the following manner.

(1) Pretreatment method

Dissolving an optical film comprising a polyimide-based resin in deuterated dimethyl sulfoxide (DMSO-d)₆) In (3), a2 mass% solution was prepared, and the obtained solution was used as a measurement sample.

(2) Measurement conditions

A measuring device: 400MHz NMR device JNM-ECZ400S/L1 manufactured by JEOL

Standard substance: DMSO-d₆(2.5ppm)

Temperature of the sample: at room temperature

And (4) accumulating times: 256 times

Relaxation time: 5 seconds

(3) Method for analyzing imidization rate

(imidization ratio of polyimide resin)

Obtained from a measurement sample containing a polyimide resin¹In the H-NMR spectrum, the integral value of a benzene proton A derived from a structure which does not change before and after imidization in the observed benzene protons was defined as Int_A. In addition, the integral of the amide proton from the amic acid structure remaining in the polyimide resin was measuredValue as Int_B. From these integrated values, the imidization ratio of the polyimide resin was determined based on the following formula.

Imidization rate (%) < 100 × (1-Int)_B/Int_A)

(imidization ratio of Polyamide-imide resin)

Obtained from a measurement sample containing a polyamideimide resin¹In the H-NMR spectrum, the integral value of the benzene proton C derived from the structure which does not change before and after imidization and which is not affected by the structure derived from the amic acid structure remaining in the polyamideimide resin among the observed benzene protons was defined as Int_C. Further, Int represents the integral value of benzene proton D, which is observed in benzene protons, derived from a structure that does not change before and after imidization and influenced by a structure derived from an amic acid structure remaining in a polyamideimide resin_D. According to the obtained Int_CAnd Int_DThe β value is obtained by the following equation.

β＝Int_D/Int_C

Next, the β value of the above formula and the imidization ratio of the polyimide resin of the above formula were obtained for a plurality of polyamide-imide resins, and based on these results, the following correlation formula was obtained.

Imidization ratio (%) ═ kxbeta +100

In the above correlation, k is a constant.

Substituting β into the correlation equation gives the imidization ratio (%) of the polyamide-imide resin.

Viscosity of varnish

According to JIS K8803: 2011, measurement was performed using a Brookfield viscometer DV-II + Pro model E. The measurement temperature was set to 25 ℃.

< bending resistance test >

The optical film was subjected to a bending resistance test in accordance with JIS K5600-5-1. The bending resistance test was carried out using a bench bending tester (manufactured by YUASA SYSTEM). The optical film after the bending resistance test was subjected to the same measurement method as described above, and the transmission image value and the haze value were measured. Absolute values of the difference between the transmission image value and the haze before and after the flex resistance test were obtained, and the difference between the transmission image values (difference Δ C between the 1 st transmission image values) was calculated₆₀Difference Δ C between transmission map values of (MD) and 2 nd₆₀(TD) and No. 3 transmission image characteristic value difference Δ C₀) And the difference in Haze (Δ Haze).

< folding endurance test (MIT) >

The number of times of bending of the optical films in examples and comparative examples was determined as follows in accordance with ASTM standard D2176-16. The optical film was cut into a long strip having a width of 15mm and a length of 100mm by a dumbbell cutter to prepare a measurement sample. The measurement sample was set in a body of an MIT bending fatigue tester ("model 0530" manufactured by Toyo Seiki Seisaku-Sho Ltd.). Specifically, one end of the measurement sample is fixed to a load clamp, the other end is fixed to a bending clamp (clamp), and tension (tension) is applied to the measurement sample. In this state, the test speed was 175cpm, the bending angle was 135 °, the load was 0.75kgf, and the bending radius R of the bending jig was 3mm, and the reciprocating bending movement was performed in the front-back direction until the test specimen broke. The number of times of bending was measured.

< visibility >

The optical film was cut into 10cm squares. The MD direction of the polarizing plate with an adhesive layer of the same size was aligned with the MD direction of the optical film obtained by cutting, and the polarizing plate with an adhesive layer was laminated on the optical film to prepare a sample for evaluation. For 1 optical film of each of the examples and comparative examples, 2 evaluation samples were prepared. In addition, 2 evaluation samples were also prepared for each of the optical films of examples and comparative examples after the bending resistance test.

One of the 2 evaluation samples was fixed to a stage so that the fluorescent lamp was positioned in the direction perpendicular to the plane of the evaluation sample and the longitudinal direction of the fluorescent lamp was horizontal to the MD direction of the evaluation sample.

The fluorescent lamp image reflected on the surface of the evaluation sample was visually observed by an observer from an angle inclined by 30 ° to the perpendicular direction of the plane of the evaluation sample.

In the same manner as above, except that the longitudinal direction of the fluorescent lamp was changed from horizontal to vertical, another evaluation sample was fixed to the stage, and an image of the fluorescent lamp was observed.

From the observation results, the visibility was evaluated based on the following evaluation criteria.

(evaluation criteria for visibility)

Very good: little distortion of the fluorescent lamp image was seen.

O: distortion of the fluorescent lamp image was slightly visible.

And (delta): distortion of the fluorescent lamp image is seen.

X: distortion of the fluorescent lamp image is clearly seen.

Production example 1 preparation of polyamideimide resin (1)

In a separable flask equipped with a stirring blade, TFMB and DMAc were charged under a nitrogen atmosphere so that the solid content of TFMB became 6.08 mass%, and TFMB was dissolved in DMAc while stirring at room temperature. Then, 6FDA was added to the flask so that it became 40.82 mol% based on TFMB, and the mixture was stirred at room temperature for 16 hours. Then, after cooling to 10 ℃, OMTPC was added to make it 27.55 mol% with respect to TFMB, and after stirring for 10 minutes, OMTPC was further added to make it 27.55m o l% with respect to TFMB, and stirred for 20 minutes. Then, DMAc was added in an amount equivalent to that of the initially added DMAc, and after stirring for 10 minutes, OMTPC was added so that the concentration of the mixture became 6.12 mol% with respect to TFMB, and the mixture was stirred for 2 hours. Subsequently, diisopropylethylamine and 4-methylpyridine, each 61.22 mol% based on TFMB, and acetic anhydride 285.71 mol% based on TFMB were added to the flask, and the mixture was stirred for 30 minutes, then the internal temperature was increased to 70 ℃, and the mixture was further stirred for 3 hours to obtain a reaction solution.

The obtained reaction solution was cooled to room temperature, and put into a large amount of methanol in a linear form, and the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Then, the precipitate was dried under reduced pressure at 60 ℃ to obtain a polyamideimide resin (1). The weight-average molecular weight of the obtained polyamideimide resin (1) was 300,000, and the imidization ratio was 99.1%.

Production example 2 preparation of polyamideimide resin (2)

In a separable flask equipped with a stirring blade, TFMB and DMAc were charged under a nitrogen atmosphere so that the solid content of TFMB became 5.22 mass%, and TFMB was dissolved in DMAc while stirring at room temperature. Then, 6FDA was added to the flask so that it became 41.24 mol% based on TFMB, and the mixture was stirred at room temperature for 16 hours. Then, after cooling to 10 ℃,2, 5-dimethylterephthaloyl chloride (hereinafter, sometimes abbreviated as DMTPC) was added so as to be 27.84 mol% with respect to TFMB, and after stirring for 10 minutes, DMTPC was further added so as to be 27.84m o/l% with respect to TFMB, and stirring for 20 minutes. Then, DMAc was added in an amount equivalent to that of the initially added DMAc, and after stirring for 10 minutes, DMTPC was added so that it became 6.19 mol% with respect to TFMB, and the mixture was stirred for 2 hours. Subsequently, diisopropylethylamine and 4-methylpyridine, each in an amount of 61.86 mol% based on TFMB, and acetic anhydride in an amount of 288.66 mol% based on TFMB were added to the flask, and the mixture was stirred for 30 minutes, then the internal temperature was increased to 70 ℃, and the mixture was further stirred for 3 hours to obtain a reaction solution.

The obtained reaction solution was cooled to room temperature, and put into a large amount of methanol in a linear form, and the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Then, the precipitate was dried under reduced pressure at 60 ℃ to obtain a polyamideimide resin (2). The weight-average molecular weight of the obtained polyamideimide resin (2) was 280,000, and the imidization ratio was 98.9%.

Production example 3 preparation of silica Dispersion

The solvent methanol in the methanol-dispersed organically treated silica (average primary particle diameter of 25nm) was replaced with γ -butyrolactone (GBL), to obtain GBL-dispersed organically treated silica (solid content: 30.5%). This dispersion was used as a dispersion (1).

Production example 4 preparation of varnish

Varnishes (1) and (2) were obtained as follows: the polyamideimide resin was added to GBL so as to be a solid component shown in table 1, and was completely dissolved by stirring at room temperature for 24 hours.

Varnish (3) was obtained as follows: the polyamideimide resin and dispersion 1 were added to the GBL solvent at room temperature so as to be solid components shown in table 1, and stirred until they became homogeneous. The mass ratio of the polyamideimide resin in the varnish (3) to the silica as a filler contained in the dispersion liquid 1 was set to 60: 40.

[ Table 1]

Production example 5 production of composition for Forming hard coat layer

A composition (1) for forming a hard coat layer was prepared by mixing 35 parts by mass of urethane acrylate (UA-122P, manufactured by Ningmura chemical Co., Ltd.), 35 parts by mass of urethane acrylate (UA-232P, manufactured by Ningmura chemical Co., Ltd.), 25 parts by mass of methyl ethyl ketone, 4.5 parts by mass of photoinitiator (1-hydroxycyclohexyl phenyl ketone) and 0.5 part by mass of leveling agent (BYK-Chemie, manufactured by BYK-3570).

< example 1 >

(production of optical film (1))

The production of the optical film (1) will be described with reference to fig. 7 and 8. First, as shown in FIG. 7, a polyethylene terephthalate film base 51 (manufactured by Toyobo Co., Ltd.: Cosmo Shine (registered trademark) A4100, hereinafter, sometimes referred to as PET film base 51) having a thickness of 188 μm was unwound, and while being conveyed at a linear speed of 0.30 m/min, a varnish (1) charged in a tank 522 was applied to the PET film base 51 in a width of 500mm by casting from a nozzle 521. Then, the coated varnish was dried by heating at 120 ℃ for 20 minutes, 95 ℃ for 10 minutes and 85 ℃ for 10 minutes in the dryer 53 while being conveyed at the same linear speed. Next, a protective film 54(Sun a. kaken co., ltd.; NSA-33T) was unwound from the roll, and was laminated on the surface of the dry coating film opposite to the surface in contact with the PET film substrate 51, and then the PET film substrate 51 was peeled off from the dry coating film, and was wound into a PET film substrate roll 55, and the remaining laminate was obtained as a laminate roll 56 having a length of 100 m.

Next, as shown in fig. 8, from the obtained laminate roll 56, the laminate film was unwound at a transport speed of 0.5 m/sec, the protective film 54 was peeled off from the laminate film, the laminate film was wound into a protective film roll 57, and after the remaining dry coating film passed through the nip rolls 201 and 202, the laminate film was dried in a tenter dryer 58 under the following conditions. The tenter dryer 58 includes a mechanism for gripping both ends of the film using clips. The interior of the membrane is divided into 1 st to 6 th chambers in order from the inlet side of the membrane.

< tenter type dryer 58 >

Clip gripping width (distance from one end of the film to the corresponding clip gripping portion): 25mm

Ratio of distance between clips at dryer outlet to distance between clips at both ends of membrane at dryer inlet: 1.0

Temperature in the dryer: 200 deg.C

Air speed of each chamber in the dryer: 13.5 m/s in the 1 st chamber, 13 m/s in the 2 nd chamber, and 11 m/s in the 3 rd to 6 th chambers

After exiting the tenter dryer 58, the clips at the film ends are released from the hold. The obtained film was passed through nip

rollers

203 and 204, and then the clip-holding portion of the film was slit (slit) by a slitting device 59, and a PET protective film 60 was laminated and wound on a 6-inch core made of ABS to obtain an optical film 61 having a thickness of 50 μm in a roll form. The solvent remaining amount in the obtained optical film 61 was 1.0 mass%.

< example 2 >

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

< example 3 >

(production of optical film (3))

The composition (1) for forming a hard coat layer prepared in production example 5 was applied to the surface of the optical film (2) obtained in example 2, which was in contact with the PET substrate film during film production, so that the thickness of the 1 st hard coat layer after curing became 3 μm, and dried in an oven at 80 ℃ for 1 minute. Then, the mercury lamp was used at 350mJ/cm²Irradiating the film with light of the above light amount to cure the film to form a 1 st hard coat layer, thereby producing an optical film (3) including the hard coat layer.

< example 4 >

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

< comparative example 1 >

As the optical film (5), a polyimide film (UPILEX, manufactured by UK corporation) having a thickness of 50 μm was prepared.

The formulations of the compositions and the composition of the optical films are summarized in table 2. In table 2, in the column "presence or absence of HC", the case where the optical film has the hard coat layer is described as presence, and the case where the optical film does not have the hard coat layer is described as absence.

[ Table 2]

The film obtained in examples and comparative examples was measured for each physical property value by the method described above. The results obtained are shown in tables 3 to 6.

[ Table 3]

[ Table 4]

[ Table 5]

[ Table 6]

It was confirmed that the optical films of examples 1 to 4 having a total light transmittance and a haze within predetermined ranges and satisfying the expressions (1) to (3) were excellent in visibility in a wide angle direction. In addition, it was confirmed that the optical film of the present invention has a small difference in image clarity value and haze before and after the bending resistance test in a preferred embodiment of the present invention, and has excellent visibility in a wide angle direction even after repeated bending operations. In addition, it was confirmed that the optical film of the present invention has the above-mentioned characteristics and epsilon₁/ε₂In the range of 0.70 to 1.20, the mechanical properties are excellent even in a low-temperature environment. On the other hand, the optical film of comparative example 1, which had a total light transmittance and a haze value out of the predetermined ranges and did not satisfy the expressions (1) to (3), was not a film excellent in visibility in the wide angle direction.

Claims

1. An optical film comprising at least 1 resin selected from the group consisting of polyimide-based resins and polyamide-based resins, wherein the optical film has a total light transmittance of 85% or more and a haze of 0.5% or less,

a 1 st transmission image value C in a direction inclined by 60 DEG from a perpendicular direction to the MD direction with respect to the plane of the optical film, obtained in accordance with JIS K7374 with an optical comb width of 0.125mm₆₀(MD) a2 nd transmission image characteristic value C in a direction inclined by 60 DEG from the vertical direction to the TD direction₆₀(TD) and a 3 rd transmission image characteristic value C in the vertical direction₀Satisfies the following conditions:

mathematical formula (1):

87％≤C₆₀(MD)≤100％···(1)，

mathematical formula (2):

87％≤C₆₀(TD) 100% or less (2), and

mathematical formula (3):

0.8≤C₆₀(MD)/C₀≤1.0···(3)；

strain at break epsilon of said optical film at-40 DEG C₁Strain at break at 25 ℃ ∈₂Satisfies the following numerical formula (4):

0.70≤ε₁/ε₂≤1.20···(4)。

2. the optical film according to claim 1, wherein the 2 nd transmission image value and the 3 rd transmission image value further satisfy the numerical expression (5):

0.9≤C₆₀(TD)/C₀≤1.0···(5)。

3. the optical film according to claim 1 or 2, wherein the difference Δ Haze between before and after the bending resistance test according to JIS K5600-5-1 is less than 0.3%.

4. The optical film according to any one of claims 1 to 3, wherein a difference Δ C between the 1 st transmission image values before and after the bending resistance test according to JIS K5600-5-1₆₀(MD) and the difference Δ C between the 2 nd transmission image characteristic values₆₀(TD) and the difference Δ C between the 3 rd transmission image characteristic values₀Each less than 15.

5. The optical film according to any one of claims 1 to 4, wherein a weight average molecular weight of a resin selected from the group consisting of a polyimide-based resin and a polyamide-based resin is 350,000 or less.

6. The optical film according to any one of claims 1 to 5, which has a thickness of 10 to 150 μm.

7. An optical film according to any one of claims 1 to 6, which has a hard coat layer on at least one side.

8. The optical film according to claim 7, wherein the hard coat layer has a thickness of 3 to 30 μm.

9. A flexible display device comprising the optical film according to any one of claims 1 to 8.

10. The flexible display device according to claim 9, further comprising a polarizing plate.

11. The flexible display device according to claim 9 or 10, further provided with a touch sensor.