KR102759292B1 - Optical films, optical laminates and flexible image display devices - Google Patents

Abstract

The purpose of the present invention is to provide an optical film having excellent visibility when suitably used as an optical film in a display device. An optical film comprising at least one selected from the group consisting of polyimide, polyamide and polyamideimide, wherein the optical film comprises a compound of formula (1)
1.1≤Transmission b*-Reflection(SCE) b*≤15 ··· (1)
[In formula (1), transmission b* represents b* in the L*a*b* colorimetric system of light transmitted through the optical film, and reflection (SCE) b* represents b* in the L*a*b* colorimetric system of light reflected from the optical film obtained by the SCE method.]
An optical film that satisfies the

Description

Optical films, optical laminates and flexible image display devices

The present invention relates to an optical film comprising at least one selected from the group consisting of polyimide, polyamide, and polyamideimide.

Recently, optical films containing polyimide resins have been used as functional films for imparting functions to image display devices such as televisions, personal computers, smart phones, tablets, and electronic papers. Since users of such image display devices directly view images displayed with the naked eye through the optical films applied to the display devices, extremely high visibility is required of the optical films. For example, Patent Document 1 discloses an optical film containing polyimide resin and silica particles.

Japanese Patent Publication No. 2009-215412

However, according to the inventor's review, it was found that even when an optical film containing such a polyimide-based resin is applied to an image display device, there are cases where sufficient visibility is not obtained.

Accordingly, an object of the present invention is to provide an optical film having excellent visibility, and an optical laminate including the optical film and a flexible image display device.

The present inventors, as a result of careful examination to solve the above-mentioned problem, have found that the above-mentioned problem can be solved by adjusting the transmission b*-reflection (SCE) b* within a predetermined range in an optical film comprising at least one selected from the group consisting of polyimide, polyamide and polyamideimide, thereby completing the present invention. That is, the present invention includes the following aspects.

[1] An optical film comprising at least one selected from the group consisting of polyimide, polyamide and polyamideimide, wherein the formula (1)

1.1≤Transmission b*-Reflection(SCE) b*≤15 ··· (1)

[In formula (1), transmission b* represents b* in the L*a*b* colorimetric system of light transmitted through the optical film, and reflection (SCE) b* represents b* in the L*a*b* colorimetric system of light reflected from the optical film obtained by the SCE method.]

An optical film that satisfies the

[2] Equation (2)

Transmission b*-reflection (SCI) b*≤4.5 ··· (2)

[In formula (2), transmission b* represents b* in the L*a*b* colorimetric system of light transmitted through the optical film, and reflection (SCI) b* represents b* in the L*a*b* colorimetric system of light reflected from the optical film obtained by the SCI method.]

An optical film as described in [1], which further satisfies the requirements.

[3] An optical film as described in [1] or [2] having a haze of 1% or less and a total light transmittance Tt of 85% or more.

[4] An optical film as described in any one of [1] to [3], further comprising silica particles.

[5] The optical film described in [4], wherein the silica particles are silica particles in which a water-soluble alcohol-dispersed silica sol is substituted as a solvent.

[6] An optical film as described in any one of [1] to [5], further comprising an ultraviolet absorber.

[7] Containing more silica particles,

The three-dimensional distance Ra determined by the Hansen melting method is given by Equation (3).

Ra≤8.0···(3)

[In formula (3), Ra represents a three-dimensional distance between the silica particles and at least one selected from the group consisting of the polyimide, the polyamide, and the polyamideimide in the solubility parameter space]

An optical film as described in any one of [1] to [6], which satisfies the following.

[8] An optical laminate comprising an optical film as described in any one of [1] to [7], and a hard coating layer on at least one surface of the optical film.

[9] A flexible image display device comprising an optical laminate as described in [8].

[10] A flexible display device as described in [9], additionally comprising a polarizing plate.

[11] A flexible image display device as described in [9] or [10], additionally comprising a touch sensor.

According to the present invention, when used as an optical film in an image display device, an optical film having excellent visibility can be provided. Furthermore, according to the present invention, an optical laminate including an optical film having excellent visibility and a flexible image display device can be provided.

Hereinafter, embodiments of the present invention will be described in detail. In addition, the scope of the present invention is not limited to the embodiments described herein, and various changes can be made without departing from the spirit of the present invention.

<Optical Film>

The optical film of the present invention is an optical film comprising at least one selected from the group consisting of polyimide, polyamide and polyamideimide, wherein the optical film is formed by the following formula (1):

1.1≤Transmission b*-Reflection(SCE) b*≤15 ··· (1)

[In formula (1), transmission b* represents b* in the L*a*b* colorimetric system of light transmitted through the optical film, and reflection (SCE) b* represents b* in the L*a*b* colorimetric system of light reflected from the optical film obtained by the SCE method.]

It satisfies.

[1. Equation (1)]

When the optical film satisfies formula (1), the optical film has excellent visibility. From a viewpoint of further improving the visibility of the optical film, the numerical value (transmission b*-reflection (SCE) b*) of formula (1) is preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, and particularly preferably 4 or less. From a viewpoint of further improving the clarity of the optical film, the numerical value (transmission b*-reflection (SCE) b*) of formula (1) is preferably 1.3 or more, more preferably 1.4 or more, more preferably 1.45 or more, and particularly preferably 1.5 or more.

(transmission b*)

The transmission b* of an optical film is b* in the L*a*b* chromaticity system of light transmitted through the optical film, and in this specification, refers to the b* value of the CIE 1976 L*a*b* chromaticity system of transmitted light for incident light (white light) in a wavelength range of 380 to 780 nm incident from a direction perpendicular to the plane of the optical film. The transmission b* is preferably 0.3 or more, more preferably 1.6 or less, and even more preferably 1.5 or less. These upper and lower limits can be arbitrarily combined. The transmission b* of an optical film can be measured using an ultraviolet-visible-near-infrared spectrophotometer, and can be measured, for example, by the method described in the Examples.

(Reflection (SCE) b*)

The reflection (SCE) b* of the optical film is the b* in the L*a*b* chromaticity of light reflected from the optical film, which is obtained by the SCE (Specular Component Excluded) method, and in this specification, refers to the b* value of the CIE 1976 L*a*b* chromaticity of diffusely reflected light excluding specular light among reflected light in a wavelength range of 380 to 780 nm, which is incident from a direction oblique to the vertical direction of the optical film plane at a predetermined angle. The reflection (SCE) b* is preferably -2.5 or more, preferably -2.4 or more, more preferably -2.3 or more. The reflection (SCE) b* is preferably -0.02 or less, preferably -0.05 or less, more preferably -0.07 or less, and particularly preferably -0.1 or less. These multiple upper and lower limits can be arbitrarily combined. The reflection (SCE) b* of an optical film can be measured using a spectrophotometer, for example, by the method described in the examples.

As a means for adjusting the numerical value of equation (1) to a predetermined numerical range, for example, a means for reducing the interaction between white light and components within the optical film can be mentioned. As a means for reducing the interaction, for example, a means for adjusting the film thickness of the optical film, addition of an additive (more specifically, silica particles, an ultraviolet absorber, a whitening agent, etc.), and characteristics of the additive (more specifically, particle diameter, surface modification, content, etc.) to a predetermined range can be mentioned. Among these, when the particle diameter, surface modification, and content of the silica particles are adjusted to a predetermined range, the silica particles are less likely to aggregate in the optical film, and it is possible to exist in the form of primary particles, so the silica particles are easily dispersed uniformly in the optical film. In addition, since the interaction with white light due to the uneven shape on the surface of the optical film is reduced, and furthermore, since the interaction between the aggregates and white light within the optical film is reduced, it is thought that this contributes to visibility.

[2. Equation (2)]

The optical film of the present invention,

Equation (2)

Transmission b*-reflection (SCI) b*≤4.5 ··· (2)

[In formula (2), transmission b* has the same meaning as formula (1), and reflection (SCI) b* represents b* in the L*a*b* colorimetric system of light reflected from the optical film obtained by the SCI method]

It is desirable to satisfy Equation (2). When the optical film satisfies Equation (2), the visibility of the optical film is further improved. The numerical value of Equation (2) (transmission b* - reflection (SCI) b*) is preferably 4.1 or less, more preferably 4.0 or less, and even more preferably 3.9 or less, from the viewpoint of further improving the visibility of the optical film.

(Reflective (SCI) b*)

The reflection (SCI) b* of the optical film is the b* in the L*a*b* chromaticity of light reflected from the optical film, which is obtained by the SCI (Specular Component Included: including specular reflection light) method, and in this specification, refers to the b* value of the CIE 1976 L*a*b* chromaticity of reflected light (reflected light including specular reflection light) for incident light in a wavelength range of 380 to 780 nm that is incident from a direction oblique to the vertical direction of the optical film plane at a predetermined angle. The reflection (SCI) b* is preferably -2.9 or more, more preferably -2.7 or more, and even more preferably -2.5 or more. The reflection (SCI) b* is preferably -1.2 or less, more preferably -1.4 or less, and even more preferably -1.6 or less. These multiple upper and lower limits can be arbitrarily combined. The reflection (SCI) b* of the optical film can be measured using a spectrophotometer, and can be measured, for example, by the method described in the Examples. As a means for adjusting the numerical value of formula (2) to within a predetermined numerical range, for example, a means for adjusting the numerical value of formula (1) above to within a predetermined numerical range can be exemplified.

[3. Haze]

The haze of the optical film of the present invention is preferably 1% or less, more preferably 0.8% or less, further preferably 0.5% or less, and particularly preferably 0.3% or less, from the viewpoint of further improving the visibility of the optical film. The haze of the optical film can be measured in accordance with JIS K 7136:2000, and can be measured, for example, by the method described in the Examples. Since the haze of the optical film indicates the degree of dispersibility of the additive in the optical film, when the haze of the optical film is within the above range, the visibility of the optical film is excellent.

[4. Light transmittance]

The total light transmittance of the optical film of the present invention is preferably 85% or more, more preferably 87% or more, and even more preferably 89% or more. The total light transmittance of the optical film can be measured in accordance with JIS K 7361-1:1997, and can be measured, for example, by the method described in the Examples. When the total light transmittance of the optical film is in the above numerical range, sufficient visibility can be secured when introduced into an image display device. In addition, when the total light transmittance of the optical film is in the above numerical range, it becomes easy to secure a constant brightness, so that, for example, it becomes possible to suppress the luminescence intensity of a display element, etc., and thus the power consumption of the image display device can be reduced.

[5. Yellowness (YI)]

The yellowness of the optical film of the present invention is preferably 3.0 or less, more preferably 2.7 or less, and even more preferably 2.5 or less. The yellowness of the optical film can be measured in accordance with JIS K 7373:2006, and can be measured, for example, by the method described in the Examples.

[6. Film thickness]

The film thickness of the optical film of the present invention is preferably 10 µm or more, more preferably 20 µm or more, and even more preferably 25 µm or more. In addition, the film thickness is preferably 120 µm or less, more preferably 100 µm or less, even more preferably 90 µm or less, and especially preferably 85 µm or less. If the film thickness is 30 µm or more, it is advantageous from the viewpoint of internal protection when the optical film is made into a device, and if the film thickness is 120 µm or less, it is advantageous from the viewpoints of fold resistance, cost, transparency, etc. The film thickness of the optical film can be measured, for example, by the method described in the Examples.

[7. Solubility parameters]

The inventor of the present invention found that a composition in an optical film causes agglomeration, etc. due to poor dispersion, thereby reducing visibility in a wide-angle direction, and therefore introduced the Hansen Solubility Parameter (hereinafter sometimes abbreviated as HSP) as an index for evaluating the compatibility between a solute (for example, an additive, more specifically, an ultraviolet absorber, silica particles, a whitening agent, etc.) and a medium (for example, a resin, more specifically, at least one resin selected from the group consisting of polyimide, polyamide, and polyamideimide) in a solid system such as an optical film. As a result of careful examination by the inventor of the present invention, the following formulas (3) to (5) were derived. That is, the optical film of the present invention, from the viewpoint of further improving visibility in a wide-angle direction (particularly, from the viewpoint of suppressing the occurrence of a problem of having a white taste in black display), has formula (3) regarding HSP.

Ra≤8.0···(3)

[In Equation (3), Ra represents the three-dimensional distance between the solute and the medium in the HSP space]

It is desirable to satisfy .

In addition, the optical film of the present invention, from the viewpoint of further improving visibility in a wide-angle direction, has equation (4) regarding HSP in addition to equation (3).

Δδ _t ≤2.0 ··· (4)

[In formula (4), Δδ _t represents the difference in the sum of the dispersion term, polarity term, and hydrogen bond term of HSP between the solute and the medium, δ _t ]

, or Equation (5)

Δδ _p ≤4.5 ··· (5)

[In formula (5), Δδ _p represents the difference in polarity term δ _p of HSP between the solute and the medium]

It is more desirable to satisfy .

In addition, it is more preferable that the optical film of the present invention satisfies all of equations (3) to (5) from the viewpoint of further improving visibility in a wide-angle direction.

(7-1. Method for calculating HSP value)

The HSP value is calculated using the Hansen Solubility Sphere method. The details are described below. The target composition (the solute and the medium) is dissolved or dispersed in a solvent having a known HSP value, and the solubility or dispersibility of the composition in a specific solvent is evaluated. The evaluation of solubility and dispersibility is performed by visually determining whether the target composition is dissolved and dispersed in the solvent, respectively. This is performed for a plurality of solvents. It is preferable to use solvents having widely different δ _t types, and more specifically, preferably 10 or more types, more preferably 15 or more types, and even more preferably 18 or more types. Next, the obtained solubility or dispersibility evaluation result is plotted in a three-dimensional space (HSP space) composed of the dispersion term δ _d , the polar term δ _{p ,} and the hydrogen bonding term δ _h of the HSP. A sphere (Hansen sphere) is created, which has a solvent inside which the composition of the target is dissolved or dispersed, a solvent outside which the composition of the target is not dissolved or dispersed, and a minimum radius. The center coordinates (δ _d , δ _p , δ _h ) of the obtained Hansen sphere are used as the HSP of the composition of the target.

(7-2. Calculation method of δ _t , Δδ _t , Δδ _p and Ra)

7-1. Using the method for calculating the HSP value, the HSP value (δ _d1 , δ _p1 , δ _h1 : HSP value of component 1, δ _d2 , δ _p2 , δ _h2 : HSP value of component 2) is calculated when two components in an optical film, for example, resin is used as component 1 and silica is used as component 2.

The sum δ _t of the dispersion term, polar term and hydrogen bond term of HSP and the difference Δδ _t of the sum between component 1 and component 2 are calculated using equations (6) and (7), respectively. The obtained δ _t corresponds to Hildebrand's HSP.

δ _t ² =δ _d ² +δ _p ² +δ _h ² ··· (6)

Δδ _t =|δ _t2 -δ _t1 | ··· (7)

From the viewpoint of further improving visibility in the wide-angle direction, Δδ _t is preferably 3.5 or less, more preferably 3.0 or less, further preferably 2.0 or less, even more preferably 1.0 or less, and particularly preferably 0.5 or less.

The difference Δδ _p of the polarity terms of HSP between components 1 and 2 is calculated using equation (8).

Δδ _p =|δ _p2 -δ _p1 | ··· (8)

From the viewpoint of further improving visibility in the wide-angle direction, Δδ _p is preferably 4.5 or less, more preferably 3.5 or less, even more preferably 3.0 or less, even more preferably 2.0 or less, and particularly preferably 1.0 or less.

The three-dimensional distance Ra(>0) between component 1 and component 2 in the HSP space is calculated using equation (9).

Ra ² =4(δ _d2 -δ _d1 ) ² +(δ _p2 -δ _p1 ) ² +(δ _h2 -δ _h1 ) ² ··· (9)

The smaller the Ra value, the better the affinity between component 1 and component 2. From the viewpoint of further improving the visibility in the wide-angle direction, the Ra value is preferably 8.0 or less, more preferably 7.0 or less, further preferably 6.0 or less, still more preferably 5.5 or less, and particularly preferably 5.0 or less.

[8. Polyimide, polyamide, polyamideimide]

The optical film of the present invention comprises at least one resin selected from the group consisting of a polyimide-based resin and a polyamide-based resin. The polyimide-based resin refers to at least one polymer selected from the group consisting of a polymer containing a repeating structural unit including an imide group (hereinafter, sometimes referred to as a polyimide) and a polymer containing a repeating structural unit including both an imide group and an amide group (hereinafter, sometimes referred to as a polyamideimide). In addition, the polyamide-based resin refers to a polymer containing a repeating structural unit including an amide group.

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

The polyimide resin may contain at least one selected from the group consisting of repeating structural units represented by formulae (11), (12), and (13), within a range that does not impair various physical properties of the optical film.

In formulas (10) and (11), G and G ¹ are each independently a tetravalent organic group, and are preferably organic groups which may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Examples of G and G ¹ include groups represented by formulas (20), (21), (22), (23), (24), (25), (26), (27), (28), or (29), and tetravalent chain hydrocarbon groups having 6 or fewer carbon atoms. From the viewpoint of easily suppressing the yellowness (YI value) of an optical film, among them, a group represented by formulas (20), (21), (22), (23), (24), (25), (26), or (27) is preferable.

Among equations (20) to (29),

* indicates a combined hand,

Z represents a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -Ar-, -SO ₂ -, -CO-, -O-Ar-O-, -Ar-O-Ar-, -Ar-CH ₂ -Ar-, -Ar-C(CH ₃ ) ₂ -Ar- or -Ar-SO ₂ -Ar-. Ar represents an arylene group having 6 to 20 carbon atoms which may be substituted with a fluorine atom, and a specific example includes a phenylene group.

In formula (12), G ² is a trivalent organic group, and is preferably an organic group which may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. As G ² , a group in which any one of the bonding hands of the group represented by formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28), or formula (29) is substituted with a hydrogen atom, and a trivalent chain hydrocarbon group having 6 or fewer carbon atoms are exemplified.

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

In formulas (10) to (13), A, A ¹ , A ^{2 ,} and A ³ are each independently a divalent organic group, and are preferably organic groups which may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. As A, A ¹ , A ² , and A ^{3 ,} groups represented by formula (30), formula (31), formula (32), formula (33), formula (34), formula (35), formula (36), formula (37), or formula (38) are exemplified; groups in which they are substituted with a methyl group, a fluoro group, a chloro group, or a trifluoromethyl group; and chain hydrocarbon groups having 6 or fewer carbon atoms.

Among equations (30) to (38),

* indicates a combined hand,

Z ¹ , Z ² and Z ³ each independently represent a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ - or -CO-.

One example is a compound in which Z ¹ and Z ³ are -O-, and further, Z ² is -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, or -SO ₂ -. It is preferred that the bonding positions of Z ¹ and Z ² to each ring, and the bonding positions of Z ² and Z ³ to each ring, are each a meta position or a para position with respect to each ring.

From the viewpoint of easily improving visibility, the polyimide-based resin is preferably a polyamideimide having at least a repeating structural unit represented by formula (10) and a repeating structural unit represented by formula (13). In addition, the polyamide-based resin preferably has at least a repeating structural unit represented by formula (13).

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

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

As the tetracarboxylic acid compound, examples thereof include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic dianhydride; and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic dianhydride. The tetracarboxylic acid compound may be used alone or in combination of two or more. In addition to the dianhydride, the tetracarboxylic acid compound may be a tetracarboxylic acid compound derivative such as an acid chloride compound.

Specific examples of aromatic tetracarboxylic dianhydrides include 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenoxyphenyl)propane dianhydride, Examples thereof include 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, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, and 4,4'-(p-phenylenedioxy)diphthalic dianhydride and 4,4'-(m-phenylenedioxy)diphthalic dianhydride. These can be used alone or in combination of two or more.

As the aliphatic tetracarboxylic dianhydride, cyclic or acyclic aliphatic tetracarboxylic dianhydride can be mentioned. The cyclic aliphatic tetracarboxylic dianhydride is a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure, and specific examples thereof include cycloalkane tetracarboxylic 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, dicyclohexyl-3,3',4,4'-tetracarboxylic dianhydride, and positional isomers thereof. These can be used alone or in combination of two or more. Specific examples of acyclic aliphatic tetracarboxylic dianhydrides include 1,2,3,4-butanetetracarboxylic dianhydride, 1,2,3,4-pentanetetracarboxylic dianhydride, etc., and these can be used alone or in combination of two or more. In addition, cyclic aliphatic tetracarboxylic dianhydride and acyclic aliphatic tetracarboxylic dianhydride may be used in combination.

Among the above tetracarboxylic dianhydrides, from the viewpoints of high transparency and low coloration, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride, and mixtures thereof are preferable. In addition, as the tetracarboxylic acid, an aqueous adduct of an anhydride of the above tetracarboxylic acid compound may be used.

Examples of the tricarboxylic acid compound include aromatic tricarboxylic acid, aliphatic tricarboxylic acid, and their flexible acid chloride compounds, acid anhydrides, etc., and two or more types may be used in combination. Specific examples include anhydride of 1,2,4-benzenetricarboxylic acid; 2,3,6-naphthalenetricarboxylic acid-2,3-anhydride; compounds in which phthalic anhydride and benzoic acid are linked by a single bond, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, or a phenylene group.

As the dicarboxylic acid compound, aromatic dicarboxylic acid, aliphatic dicarboxylic acid and their flexible acid chloride compounds, acid anhydrides, etc. can be mentioned, and two or more types of these can be used in combination. Their specific examples include terephthalic acid dichloride (terephthaloyl chloride (TPC)); isophthalic acid dichloride; naphthalenedicarboxylic acid dichloride; 4,4'-biphenyldicarboxylic acid dichloride; 3,3'-biphenyldicarboxylic acid dichloride; 4,4'-oxybis(benzoyl chloride) (OBBC); dicarboxylic acid compounds of chain hydrocarbons having 8 or less carbon atoms, and compounds in which two benzoic acids are linked by a single bond, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, or a phenylene group.

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

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

As aromatic diamines, for example, aromatic diamines having one aromatic ring, such as p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, and 2,6-diaminonaphthalene; 4,4'-Diaminodiphenylmethane, 4,4'-Diaminodiphenylpropane, 4,4'-Diaminodiphenylether, 3,4'-Diaminodiphenylether, 3,3'-Diaminodiphenylether, 4,4'-Diaminodiphenylsulfone, 3,4'-Diaminodiphenylsulfone, 3,3'-Diaminodiphenylsulfone, 1,4-Bis(4-aminophenoxy)benzene, 1,3-Bis(4-aminophenoxy)benzene, Bis〔4-(4-aminophenoxy)phenyl〕sulfone, Bis〔4-(3-aminophenoxy)phenyl〕sulfone, 2,2-Bis[4-(4-aminophenoxy)phenyl]propane, 2,2-Bis[4-(3-aminophenoxy)phenyl]propane, 2,2'-Dimethylbenzidine, Examples of aromatic diamines having two or more aromatic rings include 2,2'-bis(trifluoromethyl)benzidine (2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl (TFMB)), 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-diaminodiphenylmethane, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene, 9,9-bis(4-amino-3-chlorophenyl)fluorene, and 9,9-bis(4-amino-3-fluorophenyl)fluorene. These can be used alone or in combination of two or more.

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

Polyimide-based resins are obtained by mixing the respective raw materials, such as the diamine, tetracarboxylic acid compound, tricarboxylic acid compound, and dicarboxylic acid compound, by a conventional method, such as stirring, and then imidizing the resulting intermediate in the presence of an imidization catalyst and, if necessary, a dehydrating agent. Polyamide-based resins are obtained by mixing the respective raw materials, such as the diamine, dicarboxylic acid compound, and the like, by a conventional method, such as stirring.

Examples of the imidization catalyst used in the imidization process include, but are not particularly limited to, aliphatic amines such as tripropylamine, dibutylpropylamine, and ethyldibutylamine; alicyclic amines (monocyclic) such as N-ethylpiperidine, N-propylpiperidine, N-butylpyrrolidine, N-butylpiperidine, and N-propylhexahydroazepine; alicyclic amines (polycyclic) such as azabicyclo[2.2.1]heptane, azabicyclo[3.2.1]octane, azabicyclo[2.2.2]octane, and azabicyclo[3.2.2]nonane; and aromatic amines such as 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2,4-dimethylpyridine, 2,4,6-trimethylpyridine, 3,4-cyclopentenopyridine, 5,6,7,8-tetrahydroisoquinoline, and isoquinoline.

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

In the mixing and imidization process of each raw material, the reaction temperature is not particularly limited, but is, for example, 15 to 350°C, preferably 20 to 100°C. The reaction time is also not particularly limited, but is, for example, about 10 minutes to 10 hours. If necessary, the reaction may be performed under conditions of an inert atmosphere or reduced pressure. In addition, the reaction may be performed in a solvent, and examples of the solvent include solvents used in the preparation of varnish. After the reaction, the polyimide-based resin or polyamide-based resin is purified. As a purification method, for example, a method in which a poor solvent is added to the reaction solution, the resin is precipitated by a reprecipitation method, the resin is dried to remove the precipitate, and, if necessary, the precipitate is washed with a solvent such as methanol and dried.

In addition, for the production of polyimide-based resins, reference may be made to the production methods described in, for example, Japanese Patent Application Laid-Open No. 2006-199945 or Japanese Patent Application Laid-Open No. 2008-163107. In addition, commercially available products may also be used as the polyimide-based resins, and specific examples thereof include Neopurim (registered trademark) manufactured by Mitsubishi Gas Chemical Co., Ltd., and KPI-MX300F manufactured by Kawamura Sangyo Co., Ltd.

The weight average molecular weight of the polyimide-based resin or polyamide-based resin is preferably 200,000 or more, more preferably 250,000 or more, more preferably 300,000 or more, and preferably 600,000 or less, more preferably 500,000 or less. The larger the weight average molecular weight of the polyimide-based resin or polyamide-based resin, the more likely it is to exhibit high bending resistance when formed into a film. Therefore, from the viewpoint of increasing the bending resistance of the optical film, it is preferable that the weight average molecular weight is equal to or more than the lower limit described above. On the other hand, the smaller the weight average molecular weight of the polyimide-based resin or polyamide-based resin, the more likely it is to lower the viscosity of the varnish and to improve the processability. In addition, the extensibility of the polyimide-based resin or polyamide-based resin tends to improve. Therefore, from the viewpoints of processability and extensibility, it is preferable that the weight average molecular weight is equal to or less than the upper limit described above. In addition, in the present invention, the weight average molecular weight can be obtained by performing gel permeation chromatography (GPC) measurement and converting to standard polystyrene, and can be calculated, for example, by the method described in the examples.

The imidization rate of the polyimide-based resin is preferably 95 to 100%, more preferably 97 to 100%, even more preferably 98 to 100%, and particularly preferably 100%. From the viewpoints of the stability of the varnish and the mechanical properties of the obtained optical film, it is preferable that the imidization rate is equal to or higher than the lower limit described above. In addition, the imidization rate can be obtained by the IR method, the NMR method, or the like. From the above viewpoint, it is preferable that the imidization rate of the polyimide-based resin contained in the varnish is within the above range.

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

The content of halogen atoms in the polyimide-based resin or polyamide-based resin is preferably 1 to 40 mass%, more preferably 5 to 40 mass%, and even more preferably 5 to 30 mass%, based on the mass of the polyimide-based resin or polyamide-based resin. When the content of halogen atoms is 1 mass% or more, the elastic modulus when formed into a film is further improved, the absorption rate is lowered, the yellowness index (YI value) is further reduced, and the transparency is easily improved. When the content of halogen atoms exceeds 40 mass%, synthesis may become difficult.

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 40 mass% or more, more preferably 50 mass% or more, and even more preferably 70 mass% or more, based on the total mass of the optical film. It is preferable that the content of the polyimide-based resin and/or the polyamide-based resin is equal to or more than the lower limit above, from the viewpoint of easily improving the bending resistance, etc. In addition, the content of the polyimide-based resin and/or the polyamide-based resin in the optical film is usually 100 mass% or less, based on the total mass of the optical film.

[9. Additives]

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

(silica particles)

The optical film of the present invention may further contain silica particles as an additive. The content of the silica particles is preferably 1 mass% or more, more preferably 3 mass% or more, and even more preferably 5 mass% or more, based on the total mass of the optical film. In addition, the content of the silica particles is preferably 60 mass% or less, more preferably 50 mass% or less, and even more preferably 45 mass% or less, based on the total mass of the optical film. In addition, the content of the silica particles can be combined by selecting any lower limit and upper limit among these upper limits and lower limits. When the content of the silica particles is within the numerical range of the upper limit and/or lower limit, in the optical film of the present invention, the silica particles are unlikely to aggregate and tend to be uniformly dispersed in the state of primary particles, so that a decrease in the visibility of the optical film of the present invention can be suppressed.

The particle size of the silica particles is preferably 1 nm or more, more preferably 3 nm or more, more preferably 5 nm or more, particularly preferably 8 nm, and preferably 30 nm or less, more preferably 28 nm or less, and more preferably 25 nm or less. The particle size of the silica particles can be combined by selecting any lower limit and upper limit from among these upper and lower limits. When the content of the silica particles is in the numerical range of the upper limit and/or lower limit, in the optical film of the present invention, it is difficult to interact with light of a specific wavelength in white light, so that the reduction in the visibility of the optical film of the present invention can be suppressed. In the present specification, the particle size of the silica particles represents the average primary particle size. The particle size of the silica particles in the optical film can be measured from an image taken using a transmission electron microscope (TEM). The particle size of the silica particles before producing the optical film (for example, before adding to a varnish) can be measured by a laser diffraction particle size distribution meter. The method for measuring the particle size of silica particles is described in detail in the examples.

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

The silica particles may be surface-treated, and may be silica particles substituted with a solvent (more specifically, γ-butyrolactone or the like) from, for example, a water-soluble alcohol-dispersed silica sol. The water-soluble alcohol is an alcohol having 3 or fewer carbon atoms per hydroxyl group in one water-soluble alcohol molecule, and examples thereof include methanol, ethanol, 1-propanol, and 2-propanol. Depending on the compatibility between the silica particles and the types of polyimide-based resin and polyamide-based resin, usually, when the silica particles are surface-treated, the affinity with the polyimide-based resin and polyamide-based resin included in the optical film improves, and the dispersibility of the silica particles tends to improve, so that the deterioration of the visibility of the present invention can be suppressed.

(UV absorber)

The optical film of the present invention may further contain an ultraviolet absorber. Examples thereof include a triazine-based ultraviolet absorber, a benzophenone-based ultraviolet absorber, a benzotriazole-based ultraviolet absorber, a benzoate-based ultraviolet absorber, and a cyanoacrylate-based ultraviolet absorber. These may be used alone or in combination of two or more. Preferred commercially available ultraviolet absorbers include Sumisorb (registered trademark) 340 manufactured by Sumika Chemtex Co., Ltd., Adekastab (registered trademark) LA-31 manufactured by ADEKA Co., Ltd., and Tinuvin (registered trademark) 1577 manufactured by BASF Japan Co., Ltd. The content of the ultraviolet absorber is preferably 1 phr or more and 10 phr or less, and more preferably 3 phr or more and 6 phr or less, based on the mass of the optical film of the present invention.

(whitening agent)

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

The use of the optical film of the present invention is not particularly limited, and may be used for various purposes. The optical film of the present invention may be a single layer as described above, or may be a laminate, and the optical film of the present invention may be used as is, or may be used as a laminate with another film. Since the optical film of the present invention has excellent surface quality, it is useful as an optical film for image display devices, etc.

The optical film of the present invention is useful as a front panel of an image display device, particularly as a front panel (window film) of a flexible display. The flexible display has, for example, a flexible functional layer and the polyimide-based film that functions as a front panel by being overlapped with the flexible functional layer. That is, the front panel of the flexible display is arranged on the viewing side of the flexible functional layer. This front panel has a function of protecting the flexible functional layer.

[10. Method for manufacturing optical film]

The optical film of the present invention is not particularly limited, but includes, for example, the following processes:

(a) a process for preparing a liquid containing the above resin and the above filler (hereinafter, sometimes referred to as varnish) (varnish preparation process);

(b) a process of forming a film by applying varnish to a substrate (application process), and

(c) Process of drying the applied liquid (film) to form an optical film (optical film formation process)

It can be manufactured by a method including:

In the varnish preparation process, the resin is dissolved in a solvent, and the filler and other additives are added as needed, and stirred and mixed to prepare the varnish. In addition, when silica is used as a filler, a dispersion of silica sol containing silica may be added to the resin, in which the silica sol is substituted with a solvent in which the resin is soluble, for example, a solvent used in the preparation of the varnish described below.

The solvent used in the preparation of the varnish is not particularly limited as long as it can dissolve the resin. Examples of such solvents include amide solvents such as N,N-dimethylacetamide and N,N-dimethylformamide; lactone solvents such as γ-butyrolactone (GBL) and γ-valerolactone; sulfur-containing solvents such as dimethylsulfone, dimethylsulfoxide and sulfolane; carbonate solvents such as ethylene carbonate and propylene carbonate; and combinations thereof. Of these, amide solvents or lactone solvents are preferable. These solvents can be used singly or in combination of two or more. In addition, the varnish may contain water, an alcohol solvent, a ketone solvent, an acyclic ester solvent, an ether solvent, or the like. The solid content concentration of the varnish is preferably 1 to 25 mass%, more preferably 5 to 20 mass%.

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

In the optical film forming process, the optical film can be formed by drying the coating film and peeling it off from the substrate. After peeling, a drying process for additionally drying the optical film may be performed. The drying of the coating film can usually be performed at a temperature of 50 to 350°C. If necessary, the drying of the coating film may be performed under conditions of an inert atmosphere or reduced pressure.

Examples of the substrate include, if it is metal, SUS board, and if it is resin, PET film, PEN film, other polyimide-based resin or polyamide-based resin film, cycloolefin-based polymer (COP) film, acrylic film, etc. Among them, PET film, COP film, etc. are preferable from the viewpoint of excellent smoothness and heat resistance, and PET film is more preferable from the viewpoint of adhesion to optical films and cost.

<Optical laminate>

The optical laminate of the present invention has an optical film of the present invention and a hard coating layer (protective film) on at least one of the optical films. The optical laminate may further have an adhesive layer. The optical laminate of the present invention may be configured, for example, by bonding the optical film of the present invention and the hard coating layer via an adhesive layer.

(hard coating layer)

The thickness of the hard coating layer is not particularly limited, and may be, for example, 2 to 100 μm. When the thickness of the hard coating layer is within the above range, sufficient scratch resistance can be secured, and further, the bending resistance is unlikely to deteriorate, and the problem of curling due to curing shrinkage tends to be unlikely to occur.

The above hard coating layer can be formed by curing a hard coating composition including a reactive material capable of forming a crosslinking structure by irradiation with active energy rays or by application of heat energy, and is preferably formed by irradiation with active energy rays. An active energy ray is defined as an energy ray capable of decomposing a compound that generates an active species to generate an active species, and examples thereof include visible light, ultraviolet rays, infrared rays, X-rays, α-rays, β-rays, γ-rays, and electron rays, and preferably ultraviolet rays. The hard coating composition contains at least one polymer of a radically polymerizable compound and a cationically polymerizable compound.

The above radical polymerizable compound is a compound having a radical polymerizable group. The radical polymerizable group possessed by the above radical polymerizable compound may be a functional group capable of causing a radical polymerization reaction, and examples thereof include a group including a carbon-carbon unsaturated double bond, and specific examples thereof include a vinyl group, a (meth)acryloyl group, and the like. In addition, when the above radical polymerizable compound has two or more radical polymerizable groups, these radical polymerizable groups may be the same or different. The number of radical polymerizable groups possessed by the above radical polymerizable compound in one molecule is preferably 2 or more from the viewpoint of improving the hardness of the hard coating layer. As the radical polymerizable compound, in terms of high reactivity, a compound having a (meth)acryloyl group is preferably exemplified, and specifically, a compound called a polyfunctional acrylate monomer having 2 to 6 (meth)acryloyl groups per molecule, or an oligomer having several (meth)acryloyl groups per molecule and having a molecular weight of hundreds to thousands, such as epoxy (meth)acrylate, urethane (meth)acrylate, and polyester (meth)acrylate, is exemplified, and preferably, at least one selected from epoxy (meth)acrylate, urethane (meth)acrylate, and polyester (meth)acrylate is exemplified.

The above cationic polymerizable compound is a compound having a cationic polymerizable group such as an epoxy group, an oxetanyl group, or a vinyl ether group. The number of cationic polymerizable groups that the above cationic polymerizable compound has in one molecule is preferably 2 or more, more preferably 3 or more, from the viewpoint of improving the hardness of the hard coating layer.

In addition, as the cation polymerizable compound, among them, a compound having at least one of an epoxy group and an oxetanyl group as a cation polymerizable group is preferable. A cyclic ether group such as an epoxy group or an oxetanyl group is preferable in that shrinkage due to a polymerization reaction is small. In addition, a compound having an epoxy group among the cyclic ether groups has the advantages that compounds having various structures are easy to obtain, do not adversely affect the durability of the obtained hard coating layer, and compatibility with the radical polymerizable compound is easy to control. In addition, among the cyclic ether groups, the oxetanyl group tends to have a high degree of polymerization compared to an epoxy group, and has the advantage of accelerating the network formation speed obtained from the cation polymerizable compound of the obtained hard coating layer, thereby forming an independent network without leaving unreacted monomers in the film even in a region mixed with the radical polymerizable compound.

Examples of the cationically polymerizable compound having an epoxy group include: an alicyclic epoxy resin obtained by epoxidizing a polyglycidyl ether of a polyhydric alcohol having an alicyclic ring, or a compound containing a cyclohexene ring or a cyclopentene ring, with a suitable oxidizing agent such as hydrogen peroxide or a peracid; an aliphatic epoxy resin such as a polyglycidyl ether of an aliphatic polyhydric alcohol or an alkylene oxide adduct thereof, a polyglycidyl ester of an aliphatic long-chain polybasic acid, a homopolymer or copolymer of glycidyl (meth)acrylate; a glycidyl ether produced by the reaction of bisphenols such as bisphenol A, bisphenol F, or hydrogenated bisphenol A, or derivatives such as their alkylene oxide adducts or caprolactone adducts with epichlorohydrin, and a novolac epoxy resin; and a glycidyl ether-type epoxy resin derived from bisphenols.

The hard coating composition may further contain a polymerization initiator. As the polymerization initiator, a radical polymerization initiator, a cationic polymerization initiator, a radical and cationic polymerization initiator, etc. may be mentioned, and they are appropriately selected and used. Such a polymerization initiator is decomposed by at least one of active energy ray irradiation and heating, and generates radicals or cations to promote radical polymerization and cationic polymerization.

The radical polymerization initiator can be a substance capable of initiating radical polymerization by at least one of irradiation with an active energy ray and heating. For example, examples of thermal radical polymerization initiators include organic peroxides such as hydrogen peroxide and perbenzoic acid, and azo compounds such as azobisbutyronitrile.

As active energy ray radical polymerization initiators, there are Type 1 radical polymerization initiators that generate radicals by decomposition of molecules, and Type 2 radical polymerization initiators that coexist with tertiary amines and generate radicals by hydrogen abstraction reaction, and they are used alone or in combination.

The cationic polymerization initiator can be a substance capable of initiating cationic polymerization by at least one of irradiation with an active energy ray and heating. As the cationic polymerization initiator, an aromatic iodonium salt, an aromatic sulfonium salt, a cyclopentadienyl iron (II) complex, or the like can be used. Depending on the difference in structure, these can initiate cationic polymerization by either or both irradiation with an active energy ray or heating.

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

The above hard coating composition may further comprise at least one selected from the group consisting of a solvent and an additive.

The above solvent can be used as long as it is capable of dissolving or dispersing the polymerizable compound and the polymerization initiator, and is known as a solvent for a hard coating composition in the technical field of the present invention, within a range that does not impede the effects of the present invention.

The above additives may further include inorganic particles, leveling agents, stabilizers, surfactants, antistatic agents, lubricants, antifouling agents, etc.

The optical laminate of the present invention can be used, for example, in a flexible image display device, and is particularly suitable for use in a foldable display device or a rollable display device.

<Flexible image display device>

The flexible image display device of the present invention comprises the optical laminate of the present invention. For example, the flexible image display device comprises an optical laminate (laminated body for a flexible image display device) and an organic EL display panel, and the laminate for a flexible image display device is arranged on the viewing side with respect to the organic EL display panel and is configured to be foldable. The laminate for a flexible image display device may further contain a window, a polarizing plate, and a touch sensor, and the order of lamination thereof is arbitrary, but it is preferable that the window, the polarizing plate, and the touch sensor or the window, the touch sensor, and the polarizing plate are laminated in this order from the viewing side. If the polarizing plate is present on the viewing side of the touch sensor, the pattern of the touch sensor becomes difficult to be recognized, which is preferable because the visibility of the displayed image improves. Each member can be laminated using an adhesive, a pressure-sensitive adhesive, or the like. In addition, a light-shielding pattern formed on at least one surface of any of the layers of the window, the polarizing plate, and the touch sensor may be a circular polarizing plate.

(Windows)

The window is arranged on the viewing side of the flexible image display device and plays a role in protecting other components from external impact or environmental changes such as temperature and humidity. Conventionally, glass has been used as such a protective layer, but the window in the flexible image display device is not rigid and hard like glass, but has flexible characteristics. The window is made of a flexible transparent substrate and may include a hard coating layer on at least one surface. The hard coating layer optionally included in the window has the same meaning as the hard coating layer included in the optical laminate described above.

(polarizing plate)

Polarizing plates, especially circular polarizing plates, are functional layers that have the function of transmitting only the right or left circularly polarized light component by laminating a λ/4 phase difference plate on a linear polarizing plate. For example, they are used to convert external light into right circularly polarized light, block external light that is reflected by an organic EL panel and becomes left circularly polarized light, and suppress the influence of reflected light by transmitting only the emission component of the organic EL, thereby making it easier to view images. In order to achieve the circular polarization function, the absorption axis of the linear polarizing plate and the slow axis of the λ/4 phase difference plate theoretically need to be 45°, but in practice, it is 45±10°. The linear polarizing plate and the λ/4 phase difference plate do not necessarily need to be laminated adjacently, and the relationship between the absorption axis and the slow axis should satisfies the above-mentioned range. Although it is desirable to achieve complete circular polarization over the entire wavelength, this is not necessarily the case in practice, so the circular polarizing plate in the present invention also includes an elliptically polarizing plate. It is also desirable to improve visibility when wearing polarizing sunglasses by additionally laminating a λ/4 phase difference film on the viewing side of a linear polarizing plate to make the emitted light circularly polarized.

A linear polarizing plate is a functional layer that allows light vibrating in the direction of the transmission axis to pass through, but blocks polarization of a vibration component perpendicular thereto. The linear polarizing plate may be configured to include only a linear polarizer, or a linear polarizer and a protective film attached to at least one surface thereof. The thickness of the linear polarizing plate may be 200 ㎛ or less, and is preferably 0.5 to 100 ㎛. If the thickness is within the above range, flexibility tends to be unlikely to decrease.

The above linear polarizer may be a film-type polarizer manufactured by dyeing and stretching a polyvinyl alcohol (PVA) film. A dichroic dye such as iodine is adsorbed onto the PVA film that has been oriented by stretching, or the dichroic dye is oriented by being stretched in a state in which the dichroic dye is adsorbed onto the PVA, thereby exhibiting polarization performance. In the manufacture of the film-type polarizer, other processes such as swelling, crosslinking with boric acid, washing with an aqueous solution, and drying may be included. The stretching and dyeing processes may be performed on the PVA film alone, or may be performed in a laminated state with another film such as polyethylene terephthalate. The thickness of the PVA film used is preferably 10 to 100 µm, and the stretching ratio is preferably 2 to 10 times.

In addition, as another example of the polarizer, a liquid crystal coating type polarizer formed by applying a liquid crystal polarizing composition may be used. The liquid crystal polarizing composition may include a liquid crystal compound and a dichroic dye compound. The liquid crystal compound may have a property of exhibiting a liquid crystal state, and in particular, it is preferable to have a high-order alignment state such as a smectic phase, because this can exhibit high polarizing performance. In addition, it is also preferable that the liquid crystal compound have a polymerizable functional group.

The above dichroic dye is a dye that is aligned with the above liquid crystal compound to exhibit dichroism. The dichroic dye itself may have liquid crystal properties and may also have a polymerizable functional group. Any compound in the liquid crystal polarizing composition has a polymerizable functional group.

The above liquid crystal polarizing composition may additionally 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 above circular polarizing plate may be a liquid crystal polarizing layer. The above liquid crystal polarizing layer is manufactured by applying a liquid crystal polarizing composition onto an alignment film to form a liquid crystal polarizing layer.

The liquid crystal polarizing layer can be formed to have a thinner thickness than a film-type polarizer. The thickness of the liquid crystal polarizing layer is preferably 0.5 to 10 ㎛, more preferably 1 to 5 ㎛.

The above-mentioned alignment film can be manufactured, for example, by applying an alignment film-forming composition on a substrate and imparting alignment by rubbing, polarizing irradiation, or the like. The above-mentioned alignment film-forming composition may contain, in addition to an alignment agent, a solvent, a crosslinking agent, an initiator, a dispersant, a leveling agent, a silane coupling agent, or the like. As the alignment agent, for example, polyvinyl alcohols, polyacrylates, polyamic acids, and polyimides can be used. When applying photoalignment, it is preferable to use an alignment agent containing a cinnamate group. The weight average molecular weight of the polymer used as the alignment agent may be about 10,000 to 1,000,000. The thickness of the alignment film is preferably 5 to 10,000 nm, more preferably 10 to 500 nm, from the viewpoint of alignment controllability. The above-mentioned liquid crystal polarizing layer may be laminated by peeling from the substrate and transferring it, or the substrate may be laminated as it is. It is also desirable for the above-mentioned material to serve as a protective film, a phase difference plate, or a transparent material for a window.

As the above protective film, any transparent polymer film may be used, and materials and additives used for the transparent substrate may be used. Cellulose-based films, olefin-based films, acrylic films, and polyester-based films are preferable. A coating-type protective film obtained by applying and curing a cationic curing composition such as an epoxy resin or a radical curing composition such as an acrylate may also be used. If necessary, a plasticizer, an ultraviolet absorber, an infrared absorber, a coloring agent such as a pigment or a dye, a fluorescent whitening agent, a dispersant, a heat stabilizer, a light stabilizer, an antistatic agent, an antioxidant, an activator, a solvent, etc. may be contained. The thickness of the above protective film may be 200 µm or less, and is preferably 1 to 100 µm. When the thickness of the above protective film is within the above range, the flexibility of the protective film is unlikely to decrease. The protective film may also serve as a transparent substrate for a window.

The above-mentioned λ/4 phase difference plate is a film that provides a phase difference of λ/4 in a direction orthogonal to the direction of propagation of incident light (in the direction within the plane of the film). The above-mentioned λ/4 phase difference plate may be a stretched phase difference plate manufactured by stretching a polymer film such as a cellulose-based film, an olefin-based film, or a polycarbonate-based film. If necessary, it may contain a phase difference regulator, a plasticizer, an ultraviolet absorber, an infrared absorber, a coloring agent such as a pigment or dye, a fluorescent whitening agent, a dispersant, a heat stabilizer, a light stabilizer, an antistatic agent, an antioxidant, an activator, a solvent, or the like. The thickness of the above-mentioned stretched phase difference plate may be 200 µm or less, and is preferably 1 to 100 µm. When the thickness is within the above range, the flexibility of the film tends not to decrease easily.

In addition, as another example of the above λ/4 phase difference plate, a liquid crystal coating type phase difference plate formed by coating a liquid crystal composition may be used. The liquid crystal composition includes a liquid crystal compound having a property of exhibiting a liquid crystal state such as nematic, cholesteric, or smectic. Any compound including the liquid crystal compound in the liquid crystal composition has a polymerizable functional group. The liquid crystal coating type phase difference plate may further include an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, etc. The liquid crystal coating type phase difference plate can be manufactured by coating and curing a liquid crystal composition on an alignment film, similar to the substrate in the liquid crystal polarizing layer, to form a liquid crystal phase difference layer. The liquid crystal coating type phase difference plate can be formed to have a thinner thickness than an elongated phase difference plate. The thickness of the liquid crystal polarizing layer may be usually 0.5 to 10 µm, preferably 1 to 5 µm. The above liquid crystal coating type phase difference plate can be laminated by peeling and transferring it from the substrate, or the substrate can be laminated as is. It is also preferable that the above substrate plays a role as a protective film, phase difference plate, or transparent substrate for a window.

In general, there are many materials that exhibit greater birefringence as the wavelength is shorter and smaller birefringence as the wavelength is longer. In this case, since it is impossible to achieve a phase difference of λ/4 in the entire visible light range, the in-plane phase difference is often designed to be 100 to 180 nm, preferably 130 to 150 nm, so as to achieve λ/4 around 560 nm, where visibility is high. It is preferable to use a reverse-dispersion λ/4 phase difference plate using a material that has wavelength dispersion characteristics of birefringence opposite to that of normal materials, as this can improve visibility. As such materials, it is also preferable to use those described in Japanese Unexamined Patent Publication No. 2007-232873 for an elongated phase difference plate, or in Japanese Unexamined Patent Publication No. 2010-30979 for a liquid crystal-coated phase difference plate.

In addition, a technology for obtaining a wideband λ/4 phase plate by combining it with a λ/2 phase plate is also known as another method (Japanese Patent Application Laid-Open No. 10-90521). The λ/2 phase plate is also manufactured using the same material method as the λ/4 phase plate. The combination of the stretched phase plate and the liquid crystal coating phase plate is arbitrary, but it is preferable to use a liquid crystal coating phase plate because the thickness can be reduced.

In order to improve visibility in the oblique direction, a method of laminating a positive C plate is also known for the above circular polarizing plate (Japanese Patent Application Laid-Open No. 2014-224837). The positive C plate may be a liquid crystal coating type phase difference plate or an elongated phase difference plate. The phase difference in the thickness direction is -200 to -20 nm, preferably -140 to -40 nm.

(Method for manufacturing circular polarizing plate)

An example of a method for manufacturing a circular polarizing plate is described. When manufacturing a circular polarizing plate having a polarizing layer/phase difference layer in this order, first, a polarizing layer and a phase difference layer are formed, respectively. For example, an orientation layer, a polarizer, and a protective layer are laminated in this order on a protective film as a base material to form a polarizing layer. In addition, a λ/4 phase difference plate and a positive C plate are bonded together using an adhesive to form a phase difference layer.

Next, using an adhesive, the formed polarizing layer and the phase difference layer are bonded together to manufacture a circular polarizing plate. In bonding the polarizing layer and the phase difference layer, the polarizing layer and the phase difference layer are bonded together so that the absorption axis of the polarizing layer becomes substantially 45° to the ground axis (optical axis) of the phase difference layer. In this way, a circular polarizing plate can be manufactured by laminating adhesive layer/polarizing layer (protective film/alignment layer/polarizer/protective layer)/adhesive layer/phase difference layer (λ/4 phase difference plate/positive C plate) in this order.

A laminate having a circular polarizing plate of the present invention (hereinafter, also referred to as an optical laminate) includes an optical film of the present invention.

(Formula (39))

An optical laminate having a circular polarizing plate of the present invention is formed by formula (39).

Transmission b*-reflection (SCE) b*≥4.0 ··· (39)

[In formula (39), transmission b* represents b* in the L*a*b* colorimetric system of light transmitted through the optical laminate, and reflection (SCE) b* represents b* in the L*a*b* colorimetric system of light reflected through the optical laminate obtained by the SCE method.]

The optical laminate having the circular polarizing plate of the present invention satisfies equation (39), so that the light transmittance from the light source is large and the reflection of external light is small, so that the reflected b* color is small and close to a neutral color, and therefore has excellent visibility.

The numerical value (transmission b* - reflection (SCE) b*) of equation (39) is preferably 4.2 or more, more preferably 4.5 or more, even more preferably 5.0 or more, and particularly preferably 6.5 or more, from the viewpoint of further improving the visibility of the optical laminate having a circular polarizing plate.

(Formula (40))

The optical laminate having the circular polarizing plate of the present invention is preferably formed according to formula (40) from the viewpoint of further improving visibility.

Transmission b*-reflection (SCI) b*≥4.5 ··· (40)

[In formula (40), transmission b* represents b* in the L*a*b* colorimetric system of light transmitted through the optical laminate, and reflection (SCI) b* represents b* in the L*a*b* colorimetric system of light reflected through the optical laminate obtained by the SCI method.]

The optical laminate having the circular polarizing plate of the present invention has excellent visibility because, when it satisfies equation (40), the reflected b* color becomes smaller and closer to a neutral color.

The numerical value (transmission b* - reflection (SCI) b*) of equation (40) is preferably 4.7 or more, more preferably 5.5 or more, and even more preferably 6.0 or more from the viewpoint of further improving the visibility of the optical laminate having a circular polarizing plate.

(transmission b*)

The transmission b* of an optical laminate having a circularly polarizing plate is the b* in the L*a*b* colorimetric system of light transmitted through the optical laminate, and in this specification refers to the b* value of the CIE 1976 L*a*b* colorimetric system of transmitted light (white light) in a wavelength range of 380 to 780 nm incident from a direction perpendicular to the plane of the optical laminate having a circularly polarizing plate. The transmission b* is preferably 4.0 or more, more preferably 5.0 or more, and even more preferably 6.0 or more. The transmission b* of an optical laminate having a circularly polarizing plate can be measured using an ultraviolet-visible-near-infrared spectrophotometer, and can be measured, for example, by the method described in the Examples.

(Reflection (SCE) b*)

The reflection (SCE) b* of an optical laminate having a circularly polarizing plate is b* in the L*a*b* colorimetric system of light reflected by the optical laminate obtained by the SCE method, and in this specification, refers to the b* value of the CIE 1976 L*a*b* colorimetric system of diffusely reflected light excluding regular reflected light among reflected light in a wavelength range of 380 to 780 nm, which is incident from a direction obliquely at a predetermined angle from the vertical direction of the plane of the optical laminate having a circularly polarizing plate. The reflection (SCE) b* is preferably 1.5 or less, preferably 1.0 or less, more preferably 0 or less, and particularly preferably -1.5 or less. The reflection (SCE) b* of an optical laminate having a circularly polarizing plate can be measured using a spectrophotometer, and can be measured, for example, by the method described in the Examples.

(Reflective (SCI) b*)

The reflection (SCI) b* of an optical laminate having a circularly polarizing plate is b* in the L*a*b* colorimetric system of light reflected from the optical laminate obtained by the SCI method, and in this specification, refers to the b* value of the CIE 1976 L*a*b* colorimetric system of reflected light (reflected light including regular reflected light) in a wavelength range of 380 to 780 nm, which is incident from a direction oblique to the vertical direction of a plane of the optical laminate having a circularly polarizing plate. The reflection (SCI) b* of an optical laminate having a circularly polarizing plate can be measured using a spectrophotometer, and can be measured, for example, by the method described in the Examples.

As a means for adjusting the transmission b*-reflection (SCE) b* in equation (39) to within a predetermined numerical range, examples thereof include a means for adjusting the transmission b*-reflection (SCE) b* of an optical film to within the numerical range of equation (1), and color control by changing the composition of a window.

In addition, as a means for adjusting the transmission b*-reflection (SCI) b* in equation (40) to within a predetermined numerical range, examples thereof include a means for adjusting the transmission b*-reflection (SCI) b* of an optical film to within the numerical range of equation (2), and color control by changing the composition of a window.

(Touch sensor)

A touch sensor is used as an input means. Various methods such as a resistive film method, a surface acoustic wave method, an infrared method, an electromagnetic induction method, and a capacitive method are proposed as touch sensors, and any method is acceptable. Among them, a capacitive method is preferable. A capacitive touch sensor is divided into an active region and an inactive region located on the outer side of the active region. The active region corresponds to an area where a screen is displayed (a display region) on a display panel, and is an area where a user's touch is detected, and the inactive region corresponds to an area where a screen is not displayed (a non-display region) on a display device. The touch sensor may include a substrate having flexible characteristics; a sensing pattern formed in the active region of the substrate; and each sensing line formed in the inactive region of the substrate and connected to an external driving circuit via the sensing pattern and a pad portion. As the substrate having flexible characteristics, a material similar to the transparent substrate of the window may be used. The substrate of the touch sensor is preferably one having a toughness of 2,000 MPa% or more in terms of crack suppression of the touch sensor. More preferably, the toughness may be 2,000 to 30,000 MPa%. Here, the toughness is defined as the area under the stress (MPa)-strain (%) curve obtained through a tensile test of a polymer material to the fracture point.

The above detection pattern may have a first pattern formed in a first direction and a second pattern formed in a second direction. The first pattern and the second pattern are arranged in different directions. The first pattern and the second pattern are formed on the same layer, and in order to detect a touched point, each pattern must be electrically connected. The first pattern has a structure in which each unit pattern is connected to each other with a seam, but the second pattern has a structure in which each unit pattern is separated from each other in an island shape, so a separate bridge electrode is required to electrically connect the second pattern. The detection pattern can apply a known transparent electrode material. For example, 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), poly(3,4-ethylenedioxythiophene) (PEDOT), carbon nanotubes (CNT), graphene, metal wires, etc., and these can be used alone or in combination of two or more. ITO is preferably used. The metal used in the metal wire is not particularly limited, and examples thereof include silver, gold, aluminum, copper, iron, nickel, titanium, and chromium. These can be used alone or in combination of two or more.

The bridge electrode can be formed on the upper part of the insulating layer by interposing an insulating layer on the upper part of the sensing pattern, and the bridge electrode can be formed on the substrate, and the insulating layer and the sensing pattern can be formed thereon. The bridge electrode can be formed of the same material as the sensing pattern, or can be formed of a metal such as molybdenum, silver, aluminum, copper, palladium, gold, platinum, zinc, tin, titanium, or an alloy of two or more thereof. Since the first pattern and the second pattern must be electrically insulated, an insulating layer is formed between the sensing pattern and the bridge electrode. The insulating layer can be formed only between the seam of the first pattern and the bridge electrode, or can be formed as a layer structure that covers the sensing pattern. In the latter case, the bridge electrode can connect to the second pattern by interposing a contact hole formed in the insulating layer. The above touch sensor may further include an optical control layer between the substrate and the electrode as a means for appropriately compensating for a difference in light transmittance caused by a difference in transmittance between a patterned area where a pattern is formed and a non-patterned area where a pattern is not formed, specifically, a difference in refractive index in these areas, and the optical control layer may include an inorganic insulating material or an organic insulating material. The optical control layer may be formed by coating a photocurable composition including a photocurable organic binder and a solvent onto the substrate. The photocurable composition may further include inorganic particles. The refractive index of the optical control layer can be increased by the inorganic particles.

The photocurable organic binder may include, for example, a copolymer of each monomer, such as an acrylate monomer, a styrene monomer, and a carboxylic acid monomer. The photocurable organic binder may also be, for example, a copolymer including different repeating units, such as an epoxy group-containing repeating unit, an acrylate repeating unit, and a carboxylic acid repeating unit.

The above inorganic particles may include, for example, zirconia particles, titania particles, alumina particles, etc. The photocurable composition may further include additives such as a photopolymerization initiator, a polymerizable monomer, and a curing assistant.

(Adhesive layer (adhesive layer))

Each layer (window, polarizing plate, touch sensor) forming the laminate for the above flexible image display device and the film member (linear polarizing plate, λ/4 phase difference plate, etc.) constituting each layer can be formed by an adhesive. As the adhesive, a generally used one can be used, such as an aqueous adhesive, an organic solvent-based adhesive, a solvent-free adhesive, a solid adhesive, a solvent vaporization adhesive, a moisture-curing adhesive, a heat-curing adhesive, an anaerobic curing adhesive, an active energy ray-curing adhesive, a curing agent mixture adhesive, a heat-melting adhesive, a pressure-sensitive adhesive (adhesive), a rewetting type adhesive. Among these, an aqueous solvent vaporization adhesive, an active energy ray-curing adhesive, and an adhesive are well used. The thickness of the adhesive layer can be appropriately adjusted depending on the required adhesive strength, etc., and is 0.01 to 500 μm, preferably 0.1 to 300 μm. Although there are multiple layers in the laminate for the flexible image display device, the thickness of each layer and the type of adhesive used may be the same or different.

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

The above-described active energy ray-curable adhesive can be formed by curing an active energy ray-curable composition including a reactive material that forms an adhesive layer by irradiating the composition with active energy rays. The above-described active energy ray-curable composition can contain at least one polymer of a radically polymerizable compound and a cationically polymerizable compound similar to those of the hard coating composition. The above-described radically polymerizable compound is similar to that of the hard coating composition, and those of the same type as those of the hard coating composition can be used. As the radically polymerizable compound used in the adhesive layer, a compound having an acryloyl group is preferable. It is also preferable to contain a monofunctional compound in order to lower the viscosity as an adhesive composition.

The above cationic polymerizable compound is the same as that of the hard coating composition, and the same type as that of the hard coating composition can be used. As the cationic polymerizable compound used in the active energy ray curing composition, an epoxy compound is particularly preferable. It is also preferable to include a monofunctional compound as a reactive diluent in order to lower the viscosity as an adhesive composition.

The active energy ray curable composition may further contain a polymerization initiator. As the polymerization initiator, a radical polymerization initiator, a cationic polymerization initiator, a radical and cationic polymerization initiator, etc. may be appropriately selected and used. Such a polymerization initiator is decomposed by at least one of active energy ray irradiation and heating to generate radicals or cations, thereby promoting radical polymerization and cationic polymerization. In the base material of the hard coating composition, an initiator capable of initiating at least one of radical polymerization and cationic polymerization by active energy ray irradiation may be used.

The above-described active energy ray-curable composition may additionally contain an ion scavenger, an antioxidant, a chain transfer agent, an adhesion imparting agent, a thermoplastic resin, a filler, a fluid viscosity regulator, a plasticizer, an antifoaming solvent, an additive, and a solvent. In the case of bonding using the above-described active energy ray-curable adhesive, the above-described active energy ray-curable composition may be applied to one or both of the adherend layers, then bonded, and then cured by irradiating one or both adherend layers with an active energy ray. In the case of using the above-described active energy ray-curable adhesive, the thickness of the adhesive layer may be 0.01 to 20 μm, preferably 0.1 to 10 μm. In the case of using the above-described active energy ray-curable adhesive to form a plurality of layers, the thickness of each layer and the type of adhesive used may be the same or different.

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

(shading pattern)

The above-described shading pattern can be applied as at least a part of the bezel or housing of the flexible image display device. By hiding the wiring arranged in the periphery of the flexible image display device by the shading pattern and making it difficult to be recognized, the visibility of the image is improved. The shading pattern may be in the form of a single layer or multiple layers. The color of the shading pattern is not particularly limited, and may have various colors such as black, white, and metallic colors. The shading pattern can be formed of a pigment for implementing the color, and a polymer such as an acrylic resin, an ester resin, an epoxy resin, polyurethane, or silicone. These may be used alone or as a mixture of two or more types. The shading pattern can be formed by various methods such as printing, lithography, and inkjet. The thickness of the shading pattern is usually 1 to 100 μm, preferably 2 to 50 μm. In addition, it is also preferable to give a shape such as a slope in the thickness direction of the shading pattern.

Example

Hereinafter, the present invention will be described in more detail by examples. In the examples, “%” and “part” mean mass% and mass part, unless otherwise specified. First, the evaluation method will be described.

<1. Measurement method>

(Reflection (SCE) b* and reflection (SCI) b* of optical film)

The optical films obtained in the examples and comparative examples were cut to a size of 50 × 50 mm, and then bonded to black PET ("Goodkiri Mieru" manufactured by Tomoegawa Manufacturing Co., Ltd.) to obtain a sample for reflective optical measurement.

The colors of the obtained evaluation sample were measured using a spectrophotometer ("CM-3700A" manufactured by Konica Minolta Co., Ltd.) in the SCE method (excluding specular reflection) and the SCI method (including specular reflection). The measurement diameter was LAV: 8 mm in diameter, the measurement conditions were di: 8°, de: 8° (diffuse illumination, light receiving in 8° direction), the measurement field of view was 2°, the light source was a D65 light source, and the UV condition was 100% Full. Here, the color refers to a* and b* of the CIE 1976 L*a*b* color space. In addition, the reflection (SCE) a* and reflection (SCI) a* of the optical film were measured under the same conditions as above.

(Reflection (SCE) b* and reflection (SCI) b* of optical laminates having circular polarizing plates)

The reflection (SCE) b* and reflection (SCI) b* of an optical laminate having a circularly polarizing plate were measured in the same manner as the measurement method for an optical film, except that the measurement target was changed from an optical film to an optical laminate having a circularly polarizing plate. In addition, the reflection (SCE) a* and reflection (SCI) a* were also measured in the same manner.

(Y, the luminous transmittance of the laminate having a circular polarizing plate)

The luminous transmittance Y is a physical property value that represents the brightness of an object's color in the XYZ colorimetric system. The luminous transmittance Y of the SCI and SCE methods was measured using a spectrophotometer ("CM-2600d" manufactured by Konica Minolta Co., Ltd.).

(transmission b* of optical film)

The optical films obtained in the examples and comparative examples were cut to a size of 50 mm x 50 mm, and transmission optical measurements were performed using a spectrophotometer (“CM-3700A” manufactured by Konica Minolta Co., Ltd.). The measurement diameter was LAV: 25.4 mm in diameter, and the measurement field of view was 2°. In addition, the measurement light source used a D65 light source, and the UV condition was 100% Full. Here, the color refers to a* and b* of the CIE 1976 L*a*b* color space.

(Transmission b* of an optical laminate having a circular polarizing plate)

The transmission b* of an optical laminate having a circularly polarizing plate was measured in the same manner as the measurement method for an optical film, except that the measurement target was changed from an optical film to an optical laminate having a circularly polarizing plate. In addition, the transmission a* of an optical laminate having a circularly polarizing plate was also measured in the same manner.

(film thickness of optical film and adhesive layer)

Using a micrometer (Mitsutoyo Co., Ltd., “ID-C112XBS”), the film thickness of optical films at 10 points or more was measured, and the average value was calculated. Similarly, the thickness of the adhesive layer was measured, and the average value was calculated.

(Total light transmittance and haze of optical film)

The total light transmittance of the optical film was measured in accordance with JIS K 7361-1:1997, and the haze was measured in accordance with JIS K 7136:2000, using a fully automatic direct-reading haze computer HGM-2DP manufactured by Suga Test Equipment Co., Ltd. The measurement samples were produced by cutting the optical films of the examples and comparative examples into a size of 30 mm × 30 mm.

(yellowness of optical film)

The yellowness (YI value) of the optical film was measured using an ultraviolet-visible-near-infrared spectrophotometer (V-670, manufactured by Nippon Bunko Co., Ltd.). After performing background measurement in the absence of a sample, the optical films obtained in the examples and comparative examples were set in a sample holder, and the transmittance for light of 300 to 800 nm was measured, and the tristimulus values (X, Y, Z) were obtained. From the obtained tristimulus values, the YI value was calculated according to the following formula according to the standard of ASTM D1925.

YI=100×(1.2769X-1.0592Z)/Y

(particle size of silica particles)

The particle size of silica particles was calculated from the specific surface area measurement value by the BET adsorption method in accordance with JIS Z8830. The specific surface area of the powder of silica sol dried at 300°C was measured using a specific surface area measuring device (“Monosorb (registered trademark) MS-16” manufactured by Yuasa Ionics Co., Ltd.).

(weight average molecular weight)

Gel permeation chromatography (GPC) measurement

(1) Preprocessing method

The sample was dissolved in γ-butyrolactone (GBL) to make a 20 mass% solution, diluted 100-fold with DMF eluent, and filtered through a 0.45 μm membrane filter to prepare the measurement solution.

(2) Measurement conditions

Column: TSKgel Super AWM-H×2+Super AW2500×1(6.0mm I.D.×150mm×3)

Eluent: DMF (with 10 mmol of lithium bromide added)

Flow rate: 0.6mL/min

Detector: RI detector

Column temperature: 40℃

Injection volume: 20μL

Molecular weight standard: Standard polystyrene

(Imidization rate)

The imidization rate was obtained by ^1H -NMR measurement as follows.

(1) Preprocessing method

The measurement sample was a 2 mass% solution prepared by dissolving an optical film containing a polyimide resin in deuterated dimethyl sulfoxide (DMSO-d ₆ ).

(2) Measurement conditions

Measuring device: JEOL 400MHz NMR device JNM-ECZ400S/L1

Standard substance: DMSO-d ₆ (2.5 ppm)

Sample temperature: room temperature

Number of accumulations: 256

Relaxation time: 5 seconds

(3) Method for interpreting imidization rate

(Imidization rate of polyimide resin)

In the ^1H -NMR spectrum obtained by the measurement sample containing the polyimide resin, the integral of the benzene proton A derived from the structure that does not change before and after imidization among the observed benzene protons was referred to as Int _A. In addition, the integral of the amide proton derived from the amic acid structure remaining in the observed polyimide resin was referred to as Int _B. The imidization ratio of the polyimide resin was obtained from these integrals by the following equation.

Imidation rate (%) = 100 × (1-α × Int _B / Int _A )

In the above formula, α is the ratio of the number of benzene protons A to 1 amide proton in the case of polyamic acid (imidization degree 0%).

(Imidization rate of polyamideimide resin)

In the ^1H -NMR spectrum obtained by a measurement sample including a polyamideimide resin, the integral of benzene proton C, which originates from a structure that does not change before and after imidization among the observed benzene protons and is not affected by the structure derived from the amic acid structure remaining in the polyamideimide resin, was referred to as Int _C. In addition, the integral of benzene proton D, which originates from a structure that does not change before and after imidization among the observed benzene protons and is affected by the structure derived from the amic acid structure remaining in the polyamideimide resin, was referred to as Int _D. The β value was obtained from the obtained Int _C and Int _D by the following equation.

β=Int _D /Int _C

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

Imidation rate (%) = k × β + 100

In the above correlation, k is a constant.

The imidization rate (%) of the polyamide-imide resin was obtained by substituting β into the correlation equation.

(Calculation of HSP value of Suzy)

The solubility of polyamideimide resin 1 (PAI-1) in a solvent was evaluated. 10 mL of a solvent (Source: Polymer Handbook, 4th edition) having known solubility parameters as shown in Table 1 and 10.1 g of polyamideimide resin were placed in a transparent container to prepare a mixture. The obtained mixture was subjected to ultrasonic treatment for a total of 6 hours. The appearance of the mixture after the ultrasonic treatment was visually observed, and the solubility of polyamideimide resin 1 in a solvent was evaluated based on the evaluation criteria below from the obtained observation results. The evaluation results are shown in Table 1. In addition, the solubility in a solvent was evaluated in the same manner for polyamideimide resin 2 (PAI-2) and polyimide resin 1 (PI) except that the type of resin of polyamideimide resin 1 in the polyamideimide resin 1-solvent system was changed.

(metewand)

1: The appearance of the mixture is cloudy.

0: The appearance of the mixture is transparent.

From the results of evaluating the solubility of the obtained resin in the solvent, a Hansen sphere was created using the Hansen dissolution sphere method described above. The center coordinates of the obtained Hansen sphere were called HSP values. The results are shown in Table 2.

(Calculation of HSP value of silica)

The solvent was removed from silica sol 1, and silica 1 as a solid was extracted. The dispersibility of the silica 1 in the solvent was evaluated. 10 mL of a solvent having known solubility parameters as shown in Table 3 (Source: Polymer Handbook, 4th edition) and 10.1 g of silica were added to a transparent container to prepare a mixture. The obtained mixture was subjected to ultrasonic treatment for a total of 6 hours. The appearance of the mixture after the ultrasonic treatment was observed with the naked eye, and the dispersibility of silica 1 in the solvent was evaluated based on the following evaluation criteria from the obtained observation results. The evaluation results are shown in Table 3. In addition, similarly, the dispersibility in solvents was evaluated for methanol-dispersed silica sol ("MA-ST-L" manufactured by Nissan Chemical Industry Co., Ltd., primary particle size 20–25 nm) and methanol-dispersed silica sol (silica sol 2, primary particle size 10–12 nm) in the same manner, except that the type of silica sol, which is the raw material, was changed in the silica 1-solvent system.

(metewand)

1: The appearance of the mixture is cloudy.

0: The appearance of the mixture is transparent.

From the results of evaluating the dispersibility of each silica dispersed in the silica sol in the solvent, Hansen spheres were created using the Hansen dissolution sphere method described above. The center coordinates of the obtained Hansen spheres were used as the HSP values. The results are shown in Table 4.

(HSP value of resin-silica system)

From Tables 2 and 4, the HSP values of the resin-silica system were calculated using Equations (6) to (9). The results are shown in Table 5.

As shown in Table 5, Ra, Δδ _t , and Δδ _p of the silica 1, 2-resin system were smaller than Ra, Δδ _t , and Δδ _p of the silica (MA-ST-L)-resin system, respectively. In addition, Ra, Δδ _t , and Δδ _p of the silica 1, 2-resin system satisfied equations (3) to (5), respectively.

(elasticity)

The elastic modulus (tensile modulus) G' of the adhesive layer was measured using an electromechanical universal testing machine (manufactured by Instron) through a tensile test in accordance with JIS K 7127. The measurement conditions were a test speed of 5 m/min and a load cell of 5 kN.

<2. Evaluation method>

(Evaluation of the visibility of optical films)

A film was installed as a front panel on the surface of a liquid crystal display device, and a white display or a black display was made, and an observer observed the optical film with the naked eye from an angle tilted 45° from the vertical direction of the optical film plane. The visibility of the optical film was evaluated based on the evaluation criteria below from the observation results. They are indicated in order from the best to the worst as ◎, ○, △, and ×.

(Evaluation criteria for visibility of optical films)

◎: Both the white and black markings do not have any yellow tint at all.

○: Both the white and black markings have almost no yellow tint.

△: In at least one of the white and black marks, there is a slight yellowish tinge.

×: The white and black markings also have a yellowish tint. Also, the black marking has a white flavor.

(Evaluation of visibility of optical laminate having circular polarizing plate)

An optical laminate having a circular polarizing plate was installed on the surface of a reflector (aluminum plate, reflectivity 97%), and an observer observed the optical laminate with the naked eye from an angle inclined at 45° from the vertical direction of the plane of the optical laminate. The visibility of the optical laminate having a circular polarizing plate was evaluated based on the evaluation criteria below from the observation results. They are marked as ○, △, and × in order from best to worst.

(Evaluation criteria for visibility of optical laminates having circular polarizing plates)

○: Color change at a 45° angle compared to the vertical direction on the reflector. Front color on the reflector is neutral, and there is no color change due to the viewing angle.

△: Color change at a 45° angle compared to the vertical direction on the reflector. Front color on the reflector is neutral, and there is a slight color change depending on the viewing angle.

×: Color change at a 45° angle compared to the vertical on the reflector. The front color on the reflector is neutral. ×, the color change is large due to the viewing angle.

<3. Manufacturing of optical films>

[3-1. Manufacturing of polyimide resin]

〔Manufacturing Example 1: Polyimide Resin 1〕

A reaction vessel equipped with a silica gel tube, a stirring device, and a thermometer in a separable flask, and an oil bath were prepared. 75.52 g of 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA) and 54.44 g of 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl (TFMB) were charged into the reaction vessel installed in the oil bath. While stirring the contents of the reaction vessel at 400 rpm, 519.84 g of N,N-dimethylacetamide (DMAc) was additionally charged into the reaction vessel, and stirring was continued until the contents of the reaction vessel became a uniform solution. Subsequently, stirring was continued for an additional 20 hours while adjusting the temperature inside the vessel to a range of 20 to 30°C using the oil bath, and the reaction was performed to generate a polyamic acid. After 30 minutes, the stirring speed was changed to 100 rpm. After 20 hours of stirring, the reaction system temperature was returned to room temperature (25°C), and 649.8 g of DMAc was additionally charged into the reaction vessel to adjust the polymer concentration to 10 mass% based on the total mass of the contents of the reaction vessel. In addition, 32.27 g of pyridine and 41.65 g of acetic anhydride were charged into the reaction vessel, and imidization was performed by stirring at room temperature for 10 hours. The polyimide varnish was taken out from the reaction vessel. The obtained polyimide varnish was dropwise added to methanol to perform reprecipitation. The precipitate was taken out by filtration and dried to obtain a powder. The obtained powder was further heated and dried to remove the solvent, and polyimide resin 1 was obtained as a solid. The weight average molecular weight of the obtained polyimide resin 1 was 320,000, and the imidization ratio was 98.6%.

〔Manufacturing Example 2: Polyamideimide resin 1〕

Under a nitrogen gas atmosphere, a reaction vessel equipped with a stirring blade in a 1 L separable flask and an oil bath were prepared. 45 g (140.52 mmol) of TFMB and 768.55 g of DMAc were charged into the reaction vessel installed in the oil bath. The contents of the reaction vessel were stirred at room temperature to dissolve TFMB in DMAc. Next, 18.92 g (42.58 mmol) of 6FDA was additionally charged into the reaction vessel, and the contents of the reaction vessel were stirred at room temperature for 3 hours. Thereafter, 4.19 g (14.19 mmol) of 4,4'-oxybis(benzoyl chloride) (OBBC) and then 17.29 g (85.16 mmol) of terephthaloyl chloride (TPC) were charged into the reaction vessel, and the contents of the reaction vessel were stirred at room temperature for 1 hour. Next, 4.63 g (49.68 mmol) of 4-methylpyridine and 13.04 g (127.75 mmol) of acetic anhydride were additionally added to the reaction vessel, and the contents of the reaction vessel were stirred at room temperature for 30 minutes. After stirring, the temperature inside the vessel was increased to 70°C using an oil bath, and while maintaining it at 70°C, the contents of the reaction vessel were additionally stirred for 3 hours to obtain a reaction solution.

The obtained reaction solution was cooled to room temperature, poured into a large amount of methanol in a thread-like shape, and a precipitate was precipitated. The precipitated precipitate was taken out, soaked in methanol for 6 hours, and washed with methanol. Then, the precipitate was dried under reduced pressure at 100°C, and a polyamideimide resin was obtained. The weight average molecular weight of the polyamideimide resin was 400,000, and the imidization ratio was 98.8%.

〔Manufacturing Example 3: Polyamideimide resin 2〕

Under a nitrogen gas atmosphere, a reaction vessel equipped with a stirring blade in a 1 L separable flask and an oil bath were prepared. 45 g (140.52 mmol) of TFMB and 768.55 g of DMAc were placed in the reaction vessel installed in the oil bath. TFMB was dissolved in DMAc while stirring the contents of the reaction vessel at room temperature. Next, 19.01 g (42.79 mmol) of 6FDA was additionally placed in the reaction vessel, and the contents of the reaction vessel were stirred at room temperature for 3 hours. Thereafter, 4.21 g (14.26 mmol) of OBBC and then 17.30 g (85.59 mmol) of TPC were placed in the reaction vessel, and the contents of the reaction vessel were stirred at room temperature for 1 hour. Next, 4.63 g (49.68 mmol) of 4-methylpyridine and 13.04 g (127.75 mmol) of acetic anhydride were additionally added to the reaction vessel, and the contents of the reaction vessel were stirred at room temperature for 30 minutes. After stirring, the temperature inside the vessel was increased to 70°C using an oil bath, and stirred for an additional 3 hours while maintaining it at 70°C to obtain a reaction solution.

The obtained reaction solution was cooled to room temperature and poured into a large amount of methanol in a thread-like shape to precipitate a precipitate. The precipitated precipitate was taken out, soaked in methanol for 6 hours, and washed with methanol. Then, the precipitate was dried under reduced pressure at 100°C to obtain a polyamideimide resin. The weight average molecular weight of the obtained polyamideimide resin was 365,000, and the imidization ratio was 98.9%.

[3-2. Production of silica particles]

〔Manufacturing Example 4: Silica sol 1〕

A 1 L flask and a boiling water bath were prepared as a reaction vessel. 442.6 g of methanol-dispersed silica sol (primary particle size: 25 nm, silica solid content: 30.5%) and 301.6 g of γ-butyrolactone were charged into the reaction vessel installed in the boiling water bath. The temperature inside the vessel was adjusted to 45°C using the boiling water bath, the pressure inside the reaction vessel was adjusted to 400 hPa using an evaporator and maintained for 1 hour, and then the pressure inside the reaction vessel was adjusted to 250 hPa and maintained for 1 hour to evaporate the methanol. In addition, the pressure inside the reaction vessel was adjusted to 250 hPa, the temperature inside the vessel was increased to 70°C, and the mixture was heated for 30 minutes. As a result, γ-butyrolactone-dispersed silica sol (silica sol 1, SGS7#09) was obtained. The solid content of the obtained γ-butyrolactone-dispersed silica sol was 28.9%.

〔Manufacturing Example 5: Silica sol 2〕

Solvent replacement was performed in the same manner as in Manufacturing Example 4, except that the primary particle size of the methanol-dispersed silica sol was changed to 10 nm and the silica solid content was changed to 22%, thereby obtaining γ-butyrolactone-dispersed silica sol (silica sol 2) having a solid content of 20%.

〔Manufacturing Example 6: Silica sol 3〕

Except that the methanol-dispersed silica sol (primary particle size: 25 nm, silica solid content: 30.5%) was changed to methanol-dispersed silica sol ("MA-ST-L" manufactured by Nissan Chemical Industry Co., Ltd., primary particle size: 40-50 nm), solvent replacement was performed in the same manner as in Manufacturing Example 4 to obtain γ-butyrolactone-dispersed silica sol (silica sol 3) having a solid content of 30.5% and a primary particle size of 50 nm.

[3-3. Varnish production]

〔Manufacturing Example 7: Varnish 1〕

Varnish 1 was prepared by adding polyamideimide resin 1, silica sol 1, Sumisorb (registered trademark) 340 as an ultraviolet absorber, and Sumiplast (registered trademark) Violet B as a whitening agent to γ-butyrolactone with a composition shown in Table 6 so that the solid content would be 10.2%.

In Table 6, the unit wt% of the content of the column "Resin" and "Silica Particles" represents the ratio (mass%) to the total mass of the resin and silica particles. The unit phr of the content of the column "UV Absorbent" represents the ratio (mass%) to the total mass of the resin and silica particles.

〔Manufacturing examples 8~13: Varnish 2~8〕

Varnish 3 was prepared in the same manner as varnish 1, except that the composition (type and/or content of components) was changed to that shown in Table 6, the substituted solvent was changed from γ-butyrolactone to N,N-dimethylacetamide, and the solids concentration of the resin was changed to 11.0%. In addition, varnishes 2 and 4 to 8 were prepared, respectively, in the same manner as varnish 1, except that the composition (type and/or content of components) was changed to that shown in Table 6.

〔Example 1〕

[3-4. Manufacturing of optical films]

The obtained varnish 1 was subjected to flexible molding on a PET film ("Cosmoshine (registered trademark) A4100" manufactured by Toyobo Co., Ltd.) to form a coating film. The PET return speed in the flexible molding was 0.3 m/min. Thereafter, the coating film was dried by heating at 80°C for 20 minutes and at 90°C for 20 minutes, and the coating film was peeled off from the PET film. Thereafter, the coating film was heated at 200°C for 12 minutes while being stretched transversely using a tenter, to obtain a polyamideimide film 1 having a film thickness of 51 μm.

〔Example 2〕

A polyamide-imide film 2 having a film thickness of 29 μm was obtained in the same manner as in Example 1, except that the film thickness of the pottery was changed.

〔Example 3〕

A polyamideimide film 3 having a thickness of 50 μm was obtained in the same manner as Example 1, except that varnish 1 was changed to varnish 2.

〔Example 4〕

A polyamideimide film 4 having a thickness of 49 μm was obtained in the same manner as in Example 1, except that varnish 1 was changed to varnish 3.

〔Example 5〕

A polyamide-imide film 5 having a thickness of 48 μm was obtained in the same manner as in Example 1, except that varnish 1 was changed to varnish 4.

〔Example 6〕

A polyamide-imide film 6 having a thickness of 48 μm was obtained in the same manner as in Example 1, except that varnish 1 was changed to varnish 5.

〔Example 7〕

A polyimide film 7 having a thickness of 78 μm was obtained in the same manner as Example 1, except that varnish 1 was changed to varnish 6.

〔Comparative Example 1〕

A polyimide film 8 having a thickness of 52 μm was obtained in the same manner as in Example 1, except that varnish 1 was changed to varnish 7.

〔Comparative Example 2〕

A polyamideimide film 9 having a thickness of 50 μm was obtained in the same manner as in Example 1, except that varnish 1 was changed to varnish 8.

The optical films of Examples 1 to 7 satisfy formula (1), and their visibility evaluation results were ◎, ○, and △. The optical films of Comparative Examples 1 to 2 contain polyamideimide, do not satisfy formula (1), and their visibility evaluation results were ×.

It is clear that the optical films of Examples 1 to 7 have superior visibility compared to the optical films of Comparative Examples 1 to 2.

〔Example 8〕

[3-5. Manufacturing of adhesive layer]

(Preparation of a composition for forming an adhesive layer)

A composition for forming an adhesive layer was prepared based on the composition described in Table 8.

In Table 8, BA represents butylacrylate. MMA represents methyl methacrylate. HEA represents hydroxyethyl acrylate. AA represents acrylic acid. The amount of crosslinking agent and SC agent added is the mass relative to 100 mass parts of monomer.

(Formation of adhesive layer 1)

An adhesive layer-forming composition 1 was applied to the release-treated surface of a release-treated substrate (polyethylene terephthalate film, thickness 38 μm) using an applicator to form a coating layer. The coating layer was dried at 100°C for 1 minute to form an adhesive layer 1. The thickness of the adhesive layer 1 was 25 μm.

Next, a separate substrate (polyethylene terephthalate film, thickness 38 ㎛) that had undergone release treatment was bonded onto the adhesive layer 1. Thereafter, it was cured for 7 days under the conditions of a temperature of 23°C and a relative humidity of 50% RH. Accordingly, a film having the adhesive layer 1 was obtained. The elastic modulus G' and thickness of the obtained adhesive layer 1 were measured. The measurement results are summarized in Table 9.

In addition, in the case of laminating the adhesive layers as described below, the substrate that underwent release treatment was peeled off after laminating the adhesive layers.

(Formation of adhesive layer 2)

Adhesive layer 2 was formed in the same manner as the formation of adhesive layer 1, except that the adhesive layer forming composition 1 was changed to adhesive layer forming composition 2 and the adhesive layer forming composition was applied so that the thickness of the adhesive layer became 5 ㎛. The elastic modulus and thickness of adhesive layer 2 are summarized in Table 9.

[3-6. Manufacturing of polarizing plate]

(Preparation of a composition for forming an alignment film)

Polymer 1 is a polymer having a photoreactive group including the following structural units.

As measured by GPC, the molecular weight of the obtained polymer 1 was a number-average molecular weight of 28,200, a polydispersity (Mw/Mn) of 1.82, and a monomer content of 0.5%. A solution of polymer 1 dissolved in cyclopentanone at a concentration of 5 mass% was used as a composition for forming an alignment film.

(Formation of alignment film)

The above-mentioned alignment film-forming composition was applied onto a protective film (triacetyl cellulose: TAC) by a bar coating method to form a coating film. The coating film was dried at 80° C. for 1 minute. Next, using a UV irradiation device (SPOT CURE SP-7, manufactured by Ushio Electric Co., Ltd.) and a wire grid ("UIS-27132##" manufactured by Ushio Electric Co., Ltd.), the coating film was irradiated with polarized UV under the conditions of an exposure dose of 100 mJ/cm ² (based on 365 nm). Thus, an alignment film was formed on the protective film. The alignment film had alignment performance, and its thickness was 100 nm.

(Preparation of a composition for forming a polarizer)

A composition for forming a polarizer comprises a polymerizable liquid crystal compound and a dichroic dye.

(polymerizable liquid crystal compound)

The polymerizable liquid crystal compound used was a polymerizable liquid crystal compound represented by formula (5) [hereinafter also referred to as compound (5)] and a polymerizable liquid crystal compound represented by formula (6) [hereinafter also referred to as compound (6)].

Compounds (5) and (6) were synthesized by the method described in Lub et al. Recl. Trav. Chim. Pays-Bas, 115, 321-328 (1996).

(Dichromatic pigment)

For the dichroic dye, an azo dye described in the examples of Japanese Patent Application Laid-Open No. 2013-101328, represented by the following formulas (7), (8), and (9), was used.

(Preparation of a composition for forming a polarizer)

A composition for forming a polarizer was prepared by mixing 75 parts by mass of compound (5), 25 parts by mass of compound (6), 2.5 parts by mass of each of the azo dyes represented by the above formulae (7), (8) and (9) as dichroic dyes, 6 parts by mass of 2-dimethylamino-2-benzyl-1-(4-morpholinophenyl)butan-1-one (Irgacure 369, manufactured by BASF Japan) as a polymerization initiator, and 1.2 parts by mass of a polyacrylate compound (BYK-361N, manufactured by BYK-Chemie) as a leveling agent, with 400 parts by mass of toluene, and stirring the obtained mixture at 80°C for 1 hour.

(Manufacture of polarizer)

On the formed alignment film, the polarizer-forming composition was applied by the bar coating method to form a coating film. The coating film was dried by heating at 100° C. for 2 minutes. Then, it was cooled to room temperature. Using the UV irradiation device, the coating film was irradiated with ultraviolet rays under the condition of an accumulated light amount of 1200 mJ/cm ² (based on 365 nm). Accordingly, a polarizer was formed on the alignment film. The thickness of the polarizer was 3 μm.

(Formation of a protective layer)

A composition containing polyvinyl alcohol and water was applied onto a polarizer to form a film. The film was dried at a temperature of 80°C for 3 minutes. Accordingly, a protective layer was formed on the polarizer. The thickness of the protective layer was 0.5 μm.

As described above, a polarizing layer was manufactured by laminating a protective film, an alignment film, a polarizer, and a protective layer in that order.

(Formation of λ/4 phase plate and positive C plate)

The λ/4 phase difference plate was formed as follows.

Each component shown below was mixed and the resulting mixture was stirred at 80°C for 1 hour, thereby obtaining a composition for forming a λ/4 phase difference layer.

Compound b-1 represented by the following formula: 80 parts by mass

Compound b-2 represented by the following formula: 20 parts by mass

Polymerization initiator (Irgacure369, 2-dimethylamino-2-benzyl-1-(4-morpholinophenyl)butan-1-one, manufactured by BASF Japan): 6 parts by mass

Leveling agent (BYK-361N, polyacrylate compound, manufactured by BYK-Chemie): 0.1 part by mass

Cyclopentanone: 400 parts by mass

The above-described composition for forming an alignment film was applied onto a first base film (thickness 100 ㎛, polyethylene terephthalate film (PET)) by a bar coating method, and dried by heating in an oven at 80° C. for 1 minute. The obtained dried film was subjected to polarized UV irradiation treatment to form a second alignment film. The polarized UV treatment was performed using the above-described UV irradiation device under the condition that the accumulated light amount measured at a wavelength of 365 nm was 100 mJ/cm ² . In addition, the polarization direction of the polarized UV was performed so as to be 45° with respect to the absorption axis of the polarizing layer. In this way, a laminate composed of “first base film/second alignment film” was obtained. The thickness of the second alignment film was 100 nm.

A composition for forming a λ/4 phase difference layer was applied onto the second alignment film of the laminate composed of the "first base film/second alignment film" by the bar coating method, dried by heating in a drying oven at 120°C for 1 minute, and then cooled to room temperature. The obtained dried film was irradiated with ultraviolet rays having an accumulated light quantity of 1000 mJ/ ^cm2 (based on 365 nm) using the above-described UV irradiation device, thereby forming a phase difference layer. The thickness of the obtained phase difference layer was measured using a laser microscope (OLS3000 manufactured by Olympus Co., Ltd.) and was found to be 2.0 μm. The phase difference layer was a λ/4 plate exhibiting a phase difference value of λ/4 in the in-plane direction. In this way, a laminate composed of the "first base film/second alignment film/λ/4 phase difference layer" was obtained.

Each component shown below was mixed and the resulting mixture was stirred at 80°C for 1 hour, thereby obtaining a composition for forming a positive C phase difference layer.

Compound represented by the following formula (LC242, manufactured by BASF Japan): 100 parts by mass

Polymerization initiator (Irgacure907, 2-methyl-4'-(methylthio)-2-morpholinopropiophenone, manufactured by BASF Japan): 2.6 parts by mass

Leveling agent (BYK-361N, polyacrylate compound, manufactured by BYK-Chemie): 0.5 mass part

Additive (LR9000, manufactured by BASF Japan): 5.7 parts by mass

Solvent (propylene glycol 1-monomethyl ether 2-acetate): 412 parts by mass

As with the above-mentioned λ/4 phase difference plate, the composition for forming the alignment film was applied onto a second base film (100 µm thick, polyethylene terephthalate film (PET)) by the bar coating method, and dried by heating in a drying oven at 90°C for 1 minute to form a third alignment film. Thereafter, the composition for forming a positive C phase difference layer was applied onto the third alignment film by the bar coating method, and dried by heating in a drying oven at 90°C for 1 minute, and then irradiated with ultraviolet rays at an accumulated light amount of 1000 mJ/ ^cm2 (based on 365 nm) using the above-mentioned UV irradiation device in a nitrogen atmosphere, thereby forming a positive C plate. The thickness of the obtained positive C plate, as measured by a laser microscope (OLS3000 manufactured by Olympus Co., Ltd.), was 1.8 µm.

Thereafter, a phase difference layer was produced by bonding the peeled surface of the second base film of the positive C plate to the opposite side of the first base film of the above λ/4 phase difference plate using an adhesive layer 2.

The formed λ/4 phase shift plate and positive C plate both contained a layer in which the polymerizable liquid crystal compound was cured in an aligned state.

[3-7. Manufacturing of optical laminate having circular polarizing plate]

An optical laminate 1 was manufactured using a polyamide-imide film 1, a polarizing layer, an adhesive layer 1, and an adhesive layer 2. The laminate 1 had polyamide-imide film 1/adhesive layer 1/polarizing layer (protective film/alignment film/polarizer/protective layer)/adhesive layer 2 in this order. On the side opposite to the protective film side of the polarizing layer, the side from which the first base film of the phase difference layer was peeled was bonded with the adhesive layer 2 interposed. The phase difference layer is a layer in which a λ/4 phase difference plate (RWP) and a positive C plate (PosiC) are laminated. Thereafter, an adhesive layer 1 was provided on the side opposite to the polarizing layer of the phase difference layer. Thus, a laminate 1 including a circular polarizing plate was manufactured. Laminate 1 had polyamide-imide film 1/adhesive layer 1/polarizing layer (protective film/alignment film/polarizer/protective layer)/adhesive layer 2/phase difference layer (λ/4 phase difference plate/positive C plate)/adhesive layer 1 in this order. Here, the notation of the alignment film in the phase difference layer is omitted.

In addition, in bonding the polarizing layer and the phase difference layer, the polarizing layer and the phase difference layer were bonded via an adhesive layer 2 such that the absorption axis of the polarizing layer is substantially 45° to the ground axis (optical axis) of the phase difference layer.

For an optical laminate having a circular polarizing plate, optical characteristic values were measured and calculated. Specifically, transmission b*, transmission a*, reflection (SCE) mode a*, b* and Y, and reflection (SCI mode) a*, b* and Y were measured. From the obtained transmission b* and reflection (SCE) b*, transmission b*-reflection (SCE) b* was calculated. The measurement results and calculated results are summarized in Table 10.

〔Example 9〕

An optical laminate 2 having a circular polarizing plate was manufactured in the same manner as Example 8, except that polyamideimide film 5 was applied to the front plate instead of polyamideimide film 1, and the optical characteristic values were measured and calculated.

〔Example 10〕

An optical laminate 3 having a circular polarizing plate was manufactured in the same manner as Example 8, except that polyimide film 7 was applied to the front plate instead of polyamideimide film 1, and the optical characteristic values were measured and calculated.

〔Comparative Example 3〕

An optical laminate 4 having a circular polarizing plate was manufactured in the same manner as Example 8, except that polyimide film 8 was applied to the front plate instead of polyamideimide film 1, and the optical characteristic values were measured and calculated.

The optical laminates having the circular polarizing plates of Examples 8 to 10 satisfied Equation (39), and their visibility evaluations were either ○ or △. In addition, the optical laminates having the circular polarizing plates of Examples 8 to 10 also satisfied Equation (40).

The optical laminate having the circular polarizing plate of Comparative Example 3 did not satisfy Equation (39), and its visibility was evaluated as ×. In addition, the optical laminate having the circular polarizing plate of Comparative Example 3 did not satisfy Equation (40) either.

It is clear that the optical laminate having the circular polarizing plate of Examples 8 to 10 has superior visibility compared to the optical laminate having the circular polarizing plate of Comparative Example 3.

Claims (10)

An optical film comprising at least one selected from the group consisting of polyimide, polyamide and polyamideimide, wherein the formula (1)
1.1≤Transmission b*-Reflection(SCE) b*≤15 ··· (1)
[In formula (1), transmission b* represents b* in the L*a*b* colorimetric system of light transmitted through the optical film, and reflection (SCE) b* represents b* in the L*a*b* colorimetric system of light reflected from the optical film obtained by the SCE method.]
To satisfy,
The above polyimide and the above polyamideimide have a repeating structural unit represented by formula (10),

[In formula (10), G is a tetravalent organic group and A is a divalent organic group.]
The above polyamide is an optical film having a repeating structural unit represented by formula (13).

[In formula (13), G ³ is a divalent organic group and A ³ is a divalent organic group.] In paragraph 1,
Equation (2)
Transmission b*-reflection (SCI) b*≤4.5 ··· (2)
[In formula (2), transmission b* represents b* in the L*a*b* colorimetric system of light transmitted through the optical film, and reflection (SCI) b* represents b* in the L*a*b* colorimetric system of light reflected from the optical film obtained by the SCI method.]
Optical films that better satisfy the needs of the user. In paragraph 1,
An optical film having a haze of 1% or less and a light transmittance Tt of 85% or more. In paragraph 1,
An optical film further comprising silica particles. In paragraph 4,
The above silica particles are optical films in which the silica particles are solvent-substituted with a water-soluble alcohol-dispersed silica sol. In paragraph 1,
An optical film further comprising an ultraviolet absorber. An optical laminate comprising an optical film according to any one of claims 1 to 6, and a hard coating layer on at least one surface of the optical film. A flexible image display device comprising the optical laminate described in claim 7. In Article 8,
A flexible display device additionally equipped with a polarizing plate. In Article 8,
A flexible display device additionally equipped with a touch sensor.