JP2021070315A - Optical laminate and display device - Google Patents

Abstract

To provide an optical laminate having excellent bend resistance and impact resistance.SOLUTION: The present invention provides an optical laminate 10 having a front plate 1, a first adhesive layer 2, an impact resistant layer 3, and a second adhesive layer 4 in this order, the second adhesive layer 4 having a tanδ of 1.20 or less at -20°C.SELECTED DRAWING: Figure 1

Description

The present invention relates to an optical laminate and a display device, and more particularly to an optical laminate that covers the display surface of a display panel and a display device having the optical laminate.

In recent years, flexible flexibility display devices have attracted attention. The flexibility display device can also be installed on a non-planar surface such as a curved surface and a bending surface. Further, the flexibility display device can be improved in portability by being folded or having a scroll shape. In such a flexibility display device, the optical laminate covering the display surface is also required to have flexibility.

The optical laminate used in the flexibility display device is required to have not only flexibility but also impact resistance. Furthermore, in addition to these, thinning and weight reduction of the optical laminate are desired not only for practical reasons but also for cost reduction and resource saving.

Patent Document 1 describes an optical laminate having a base material having a protective layer formed on one side thereof, a first transparent adhesive layer, and a first buffer layer (summary). A sample obtained by joining the optical laminate and the display panel with an adhesive sheet is said to have good impact resistance and bending resistance (paragraph [0118], paragraph [0125]).

JP-A-2018-55098

However, it cannot be said that the optical laminate of Patent Document 1 has sufficient characteristics, particularly bending resistance, and therefore, it is desired to introduce an optical laminate having further improved bending resistance.

The present invention solves the above problems, and an object of the present invention is to provide an optical laminate having excellent bending resistance and impact resistance.

The present invention is an optical laminate including a front plate, a first pressure-sensitive adhesive layer, an impact-resistant layer, and a second pressure-sensitive adhesive layer in this order from the visual side, and the second pressure-sensitive adhesive layer is 1.20 or less. An optical laminate having a tan δ at 20 ° C. is provided.

In one embodiment, the impact resistant layer and the second pressure-sensitive adhesive layer have the formula of 5.5 or less.

［式中、ａは耐衝撃層の厚さであり、ｃは第２粘着剤層の厚さである。］
で表される厚さ比ｒを有する。

[In the formula, a is the thickness of the impact resistant layer, and c is the thickness of the second pressure-sensitive adhesive layer. ]
It has a thickness ratio r represented by.

In one embodiment, the impact resistant layer has a tan δ at −20 ° C. of 0.001 to 0.020.

In one embodiment, the impact resistant layer has a tensile modulus of 0.1 to 10 GPa.

In one embodiment, the impact resistant layer material is selected from the group consisting of polycarbonate resins, polyimide resins and polyester resins.

In one embodiment, the first pressure-resistant layer, the impact-resistant layer, and the second pressure-resistant layer have a total thickness of 120 to 190 μm.

In one embodiment, the optical laminate has a thickness of 130-220 μm.

In one embodiment, the optical laminate is subjected to 180 ° bending and stretching with the front plate inside under the conditions of a temperature of 25 ° C., a bending speed of 30 rpm, and a bending radius of 1.00 mm in a continuous bending test of 150,000 times or more. Indicates the number of times of bending resistance.

The present invention also provides a display device including any of the above optical laminates and a display unit in the internal direction of the optical laminate.

According to the present invention, an optical laminate having excellent bending resistance and impact resistance, and further thinner is provided.

It is sectional drawing which shows an example of the structure of the optical laminated body of this invention. It is sectional drawing which shows an example of the structure of the display device of this invention.

[Optical laminate]
FIG. 1 is a cross-sectional view showing an example of the structure of the optical laminate of the present invention. The optical laminate 10 shown in FIG. 1 includes a front plate 1, a first adhesive layer 2, an impact resistant layer 3, and a second adhesive layer 4 in this order from the visual side. When bending the optical laminate 10, it is preferable that the front plate is on the inside.

The shape of the optical laminate in the plane direction may be, for example, a square shape, preferably a square shape having a long side and a short side, and more preferably a rectangle. When the shape of the optical laminate in the plane direction is rectangular, the length of the long side may be, for example, 10 to 1400 mm, preferably 50 to 600 mm. The length of the short side is, for example, 5 to 800 mm, preferably 30 to 500 mm, and more preferably 50 to 300 mm. Each layer constituting the optical laminate may have corners R-processed, end portions notched, or perforated.

The thickness of the optical laminate is preferably 100 to 200 μm. By adjusting the thickness of the optical laminate within this range, it becomes easy to improve the bending resistance while maintaining the impact resistance. The thickness of the optical laminate is more preferably 100 to 180 μm, still more preferably 120 to 150 μm. In one embodiment, the thickness of the optical laminate is preferably 130-220 μm, more preferably 150-210 μm. By adjusting the thickness of the optical laminate within the above range, good impact resistance and good flexibility can be obtained.

[Front plate]
The front plate 1 of the optical laminate is located in front of the optical laminate with reference to FIG. In FIG. 1, the upward direction indicates the external direction in which the optical laminate is visually recognized, and the downward direction indicates the internal direction in which the optical laminate is adhered to the display unit or the like.

The material of the front plate 1 is not limited as long as it is a plate-like body that can transmit light, but from the viewpoint of impact resistance and flexibility, a resin plate-like body (for example, a resin plate, a resin sheet, a resin) is used. It is preferable to use a film or the like). The front plate may be composed of only one layer, or may be composed of two or more layers.

When the front plate 1 is a resin plate-like body, the material may be, for example, an acrylic resin such as polymethyl (meth) acrylate and polyethyl (meth) acrylate; and a polyolefin-based material such as polyethylene, polypropylene, polymethylpentene and polystyrene. Resins: Cellular resins such as triacetyl cellulose, acetyl cellulose butyrate, propionyl cellulose, butyryl cellulose and acetyl propionyl cellulose; ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl acetal, etc. Polyvinyl resin; sulfone resin such as polysulfone and polyether sulfone; ketone resin such as polyether ketone and polyether ether ketone; polyetherimide; polycarbonate resin; polyester resin; polyimide resin; polyamideimide resin; And polyamide resin and the like. These polymers can be used alone or in admixture of two or more. Above all, from the viewpoint of improving strength and transparency, it is preferable to use a polycarbonate resin, a polyester resin, a polyimide resin, a polyamide-imide resin, or a polyamide resin.

The polycarbonate-based resin is a polymer containing a repeating structural unit having a carbonate group. Examples of the polycarbonate resin include bisphenol A type polycarbonate, branched polycarbonate obtained by polymerizing trivalent phenol, and copolymerized polycarbonate obtained by copolymerizing an aliphatic or aromatic dicarboxylic acid and an aliphatic or alicyclic divalent alcohol. In the embodiment of the present invention, it can be appropriately selected and used from these.

The polyester resin is a polymer containing a repeating structural unit containing an ester bond. Examples of the polyester resin include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polytrimethylene terephthalate, polytrimethylene naphthalate, polycyclohexanedimethylterephthalate, polycyclohexanedimethylnaphthalate and the like. , In the embodiment of the present invention, it can be appropriately selected and used from these.

In the present specification, the polyimide-based resin represents a polymer containing any one or more selected from polyimide and polyamide-imide. Polyimide represents a polymer containing a repeating structural unit having an imide group, and polyamide-imide represents a polymer containing a repeating structural unit having an imide group and a repeating structural unit having an amide group. The polyamide resin represents a polymer containing a repeating structural unit having an amide group.

The polyimide-based resin according to this embodiment has a repeating structural unit represented by the formula (10). Here, G represents a tetravalent organic group, and A represents a divalent organic group. G and / or A may include two or more different repeating structural units represented by the formula (10). Further, the polyimide-based resin according to the present embodiment has a repeating structure represented by any of the formulas (11), (12), and (13) as long as the various physical properties of the obtained transparent resin film are not impaired. It may contain any one or more of the units.

It is preferable that the main structural unit of the polyimide resin is the repeating structural unit represented by the formula (10) from the viewpoint of the strength and transparency of the transparent resin film. In the polyimide resin according to the present embodiment, the repeating structural unit represented by the formula (10) is preferably 40 mol% or more, more preferably 50 mol% or more, based on all the repeating structural units of the polyimide resin. It is even more preferably 70 mol% or more, even more preferably 90 mol% or more, and even more preferably 98 mol% or more. The repeating structural unit represented by the formula (10) may be 100 mol%.

G and G ¹ independently represent a tetravalent organic group, preferably a tetravalent organic group having 4 to 40 carbon atoms. The organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, in which case the hydrocarbon group and the fluorine-substituted hydrocarbon group preferably have 1 to 8 carbon atoms. Examples of G and G ¹ include formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), and formula (28). ) Or a group represented by the formula (29) and a chain hydrocarbon group having a tetravalent carbon number of 6 or less. Equation (20) to (29) in the * represents a bond, Z is a single _{bond, -O -, - CH 2 -} , - CH 2 -CH 2 -, - CH (CH 3) -, - C (CH ₃ ) _2- , -C (CF ₃ ) _2- , -Ar-, -SO _2- , -CO-, -O-Ar-O-, -Ar-O-Ar-, -Ar-CH ₂ -Ar-, -Ar-C (CH ₃ ) _{Represents 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 specific examples thereof include a phenylene group. Yellowness index of the transparent resin film obtained from the easily suppressed, as the G and ^{G 1,} preferably of formula (20), equation (21), equation (22), equation (23), equation (24), wherein (25), the group represented by the formula (26) or the formula (27) can be mentioned.

G ² represents a trivalent organic group, preferably a trivalent organic group having 4 to 40 carbon atoms. The organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, in which case the hydrocarbon group and the fluorine-substituted hydrocarbon group preferably have 1 to 8 carbon atoms. The G ^2, equation (20), equation (21), equation (22), equation (23), equation (24), equation (25), equation (26), equation (27), equation (28) or Examples thereof include a group in which any one of the bonds of the group represented by the formula (29) is replaced with a hydrogen atom, and a chain hydrocarbon group having a trivalent carbon number of 6 or less. The example of Z in the formulas (20) to (29) is the same as the example of Z in the description regarding G.

G ³ represents a divalent organic group, preferably a divalent organic group having 4 to 40 carbon atoms. The organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, in which case the hydrocarbon group and the fluorine-substituted hydrocarbon group preferably have 1 to 8 carbon atoms. The G ^3, equation (20), equation (21), equation (22), equation (23), equation (24), equation (25), equation (26), equation (27), equation (28) or Among the group bonds represented by the formula (29), a group in which two non-adjacent groups are replaced with a hydrogen atom and a divalent chain hydrocarbon group having 6 or less carbon atoms can be mentioned. The example of Z in the formulas (20) to (29) is the same as the example of Z in the description regarding G.

Examples ^{of the organic group of G 3} include formula (20'), formula (21'), formula (22'), formula (23'), formula (24'), formula (25'), formula (26'), Equation (27'), Equation (28') and Equation (29'):

［式（２０’）〜式（２９’）中、Ｗ^１は、式（２０）〜式（２９）において定義したＺと同義であり、＊は、式（２０）〜式（２９）において定義した通りである］で表される２価の有機基がより好ましい。

[In equations (20') to (29'), W ¹ is synonymous with Z defined in equations (20) to (29), and * is defined in equations (20) to (29). The divalent organic group represented by] is more preferable.

^{When the polyimide resin has a structural unit in which G 3} in the formula (2) is represented by any of the above formulas (20') to (29'), Z in the formula (2) will be described later. When the polyimide resin has a structural unit represented by the formula (101'), the polyimide resin has the following formula (100): In addition to the structural unit.

［式（１００）中、Ｒ^１は、互いに独立に、炭素数１〜６のアルキル基、炭素数１〜６のアルコキシ基又は炭素数６〜１２のアリール基を表し、Ｒ^２は、Ｒ^１又は−Ｃ（＝Ｏ）−＊を表し、＊は結合手を表す］
で表されるカルボン酸由来の構成単位をさらに有していてよい。この構造単位を有するポリイミド系樹脂は、透明樹脂フィルムを製造する際に使用する樹脂ワニスの流動性を高めやすいため好ましい。

[In the formula (100), R ¹ represents an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and R ² is R ^1. Or -C (= O)-*, * represents a bond]
It may further have a structural unit derived from a carboxylic acid represented by. A polyimide resin having this structural unit is preferable because it tends to increase the fluidity of the resin varnish used in producing the transparent resin film.

In R ^1, an alkyl group having 1 to 6 carbon atoms, the aryl group an alkoxy group and 6 to 12 carbon atoms having 1 to 6 carbon atoms, respectively, include those exemplified in Formula (101) described later. Specifically, as the structural unit (100), R ¹ and R ² are both hydrogen atoms (constituent units derived from the dicarboxylic acid compound), R ¹ is both hydrogen atoms, and R ^{2 is used.} Examples thereof include a structural unit (a structural unit derived from a tricarboxylic acid compound) representing −C (= O) − *.

Polyimide resin may include a plurality of types of G ³ as G ³ in formula (2), G ³ of plural kinds may being the same or different. In particular, easy to reduce the haze after the mandrel test of the optical film, and the yield point strain and elastic modulus from the enhanced easily standpoint, G ³ is preferably of the formula (101):

［式（１０１）中、Ｒ^３ａ及びＲ^３ｂは、互いに独立に、炭素数１〜６のアルキル基、炭素数１〜６のアルコキシ基、又は炭素数６〜１２のアリール基を表し、Ｒ^３ａ及びＲ^３ｂに含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、
Ｗは、互いに独立に、単結合、−Ｏ−、−ＣＨ_２−、−ＣＨ_２−ＣＨ_２−、−ＣＨ（ＣＨ_３）−、−Ｃ（ＣＨ_３）_２−、−Ｃ（ＣＦ_３）_２−、−ＳＯ_２−、−Ｓ−、−ＣＯ−又は−Ｎ（Ｒ^９）−を表し、Ｒ^９は水素原子、ハロゲン原子で置換されていてもよい炭素数１〜１２の１価の炭化水素基を表し、
ｓは０〜４の整数であり、
ｔは０〜４の整数であり、
ｕは０〜４の整数であり、
＊は結合手を表す］
で表され、より好ましくは式（１０１’）：

[In formula (101), R ^3a and R ^3b independently represent an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and R ^3a. And the ^{hydrogen atoms contained in R 3b} may be substituted with halogen atoms independently of each other.
W, independently of one another, a single _{bond, -O -, - CH 2 -} , - CH 2 -CH 2 -, - CH (CH 3) -, - C (CH 3) 2 -, - C (CF 3) _{2 -, - SO 2 -,} - S -, - CO- or -N ^{(R 9)} - represents, ^{R 9} is a hydrogen atom, monovalent 1-12 carbon atoms which may be substituted with a halogen atom Represents a hydrocarbon group
s is an integer from 0 to 4
t is an integer from 0 to 4
u is an integer from 0 to 4
* Represents a bond]
It is represented by, more preferably the formula (101') :.

［式（１０１’）中、Ｒ^３ａ、Ｒ^３ｂ、ｓ、ｔ、ｕ、Ｗ及び＊は、式（１０１）において定義した通りである］
で表される、式（２）で表される構成単位を少なくとも有することが好ましい。

[In equation (101'), R ^3a , R ^3b , s, t, u, W and * are as defined in equation (101)]
It is preferable to have at least the structural unit represented by the formula (2) represented by.

In the formula (101) and the formula (101 '), W, independently of one another, a single _{bond, -O -, - CH 2 -} , - CH 2 -CH 2 -, - CH (CH 3) -, - C ( CH ₃ ) _2- , -C (CF ₃ ) _2- , -SO _2- , -S-, -CO- or -N (R ⁹ )-, preferably from the viewpoint of bending resistance of the optical film. It represents −O− or −S−, more preferably −O−.

R ^3a and R ^3b independently represent an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of alkyl groups having 1 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group and 2-methyl-. Butyl group, 3-methyl-butyl group, 2-ethyl-propyl group, n-hexyl group and the like can be mentioned. Examples of the alkoxy group having 1 to 6 carbon atoms include a methoxy group, an ethoxy group, a propyloxy group, an isopropyloxy group, a butoxy group, an isobutoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group and a cyclohexyloxy group. Can be mentioned. Examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a tolyl group, a xsilyl group, a naphthyl group, a biphenyl group and the like. From the viewpoint of easily reducing the haze after the mandrel test of the optical film and easily increasing the breakdown point strain and the elastic modulus, R ^3a and R ^3b are independent of each other, preferably an alkyl group having 1 to 6 carbon atoms or a carbon number of carbon atoms. It represents 1 to 6 alkoxy groups, more preferably an alkyl group having 1 to 3 carbon atoms or an alkoxy group having 1 to 3 carbon atoms. Here, the ^{hydrogen atoms contained in R 3a} and R ^3b may be substituted with halogen atoms independently of each other.

R ⁹ represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a hydrogen atom or a halogen atom. Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group and an n-pentyl group. 2-Methyl-butyl group, 3-methylbutyl group, 2-ethyl-propyl group, n-hexyl, n-heptyl group, n-octyl group, tert-octyl group, n-nonyl group, n-decyl group and the like. These may be substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.

T and u in the formula (101) and the formula (101') are independently integers of 0 to 4, preferably an integer of 0 to 2, and more preferably 0 or 1.

The A, A ¹ , A ² and A ³ all represent a divalent organic group, preferably a divalent organic group having 4 to 40 carbon atoms. The organic group may be substituted with a hydrocarbon group or a hydrocarbon group having 1 to 8 carbon atoms substituted with fluorine, in which case the carbon number of the hydrocarbon group and the hydrocarbon group substituted with fluorine is preferable. 1 to 8. As A, A ¹ , A ² and A ³ , the formulas (30), formulas (31), formulas (32), formulas (33), formulas (34), formulas (35), formulas (36) and formulas (36), respectively. A group represented by (37) or the formula (38), a group in which these are substituted with one or more of a methyl group, a fluoro group, a chloro group or a trifluoromethyl group, and a chain hydrocarbon group having 6 or less carbon atoms. Can be mentioned.

Equation (30) to (38) in the * represents a ^bond, Z 1, ^{Z 2} and ^{Z 3,} independently of one another, a single _{bond, -O -, - CH 2 -} , - CH 2 -CH 2 _{-, - CH (CH 3)} -, - C (CH 3) 2 -, - C (CF 3) 2 -, - S -, - SO 2 -, - CO- or -N ^{(R 3)} - represents a .. Here, R ³ represents a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. Here, R ³ represents a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. Z ¹ and Z ² and Z ² and Z ³ are preferably located in the meta or para position with respect to each ring, respectively.

In the present invention, the resin composition forming the transparent resin film may be a polyamide-based resin. The polyamide-based resin according to this embodiment is a polymer mainly composed of a repeating structural unit represented by the formula (13). Preferred examples and specific examples of G ^3, and A ³ in the polyamide resin is the same as the preferable examples and specific examples of G ^3, and A ³ in the polyimide resin.
The polyamide resin may contain a repeating structural unit G ^3, and / or A ³ is represented by two or more different formula (13).

The polyimide resin can be obtained, for example, by polycondensation of a diamine and a tetracarboxylic dian compound (tetracarboxylic dianhydride, etc.). It can be synthesized according to the method described. Examples of commercially available polyimide products include "Neoprim" (registered trademark) manufactured by Mitsubishi Gas Chemical Company, Inc., "KPI-MX300F" (trade name) manufactured by Kawamura Sangyo Co., Ltd., and the like.

Examples of the tetracarboxylic acid compound used for the synthesis of the polyimide resin include an aromatic tetracarboxylic acid and its anhydride, preferably an aromatic tetracarboxylic acid compound such as a dianhydride thereof, and an aliphatic tetracarboxylic acid and its anhydride. , Preferably an aliphatic tetracarboxylic acid compound such as the dianhydride thereof. The tetracarboxylic acid compound may be a tetracarboxylic acid compound derivative such as a tetracarboxylic acid chloride compound as well as an anhydride, and these may be used alone or in combination of two or more.

Specific examples of the aromatic tetracarboxylic dianhydride include a non-condensed polycyclic aromatic tetracarboxylic dianhydride, a monocyclic aromatic tetracarboxylic dianhydride, and a condensed polycyclic aromatic tetra. Examples include carboxylic dianhydride. Examples of the non-condensed polycyclic aromatic tetracarboxylic dianhydride include 4,4'-oxydiphthalic acid dianhydride, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride and 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) Phenyl) propane dianhydride, 2,2-bis (3,4-dicarboxyphenoxyphenyl) propane dianhydride, 4,4'-(hexafluoroisopropyridene) diphthalic dianhydride (6FDA) may be described. Yes), 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-) Examples thereof include dicarboxyphenyl) methane dianhydride, 4,4'-(p-phenylenedioxy) diphthalic acid dianhydride, and 4,4'-(m-phenylenedioxy) diphthalic acid dianhydride. Further, as the monocyclic aromatic tetracarboxylic dianhydride, 1,2,4,5-benzenetetracarboxylic dianhydride is used, and as the condensed polycyclic aromatic tetracarboxylic dianhydride, 1,2,4,5-benzenetetracarboxylic dianhydride is used. Examples thereof include 2,3,6,7-naphthalenetetracarboxylic dianhydride.

Among these, preferably 4,4'-oxydiphthalic acid dianhydride, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride, 2,2', 3,3'-benzophenonetetracarboxylic dianhydride. Anhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 2,2', 3,3'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'-diphenyl Sulfontetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, 2,2- Bis (3,4-dicarboxyphenoxyphenyl) propanedianhydride, 4,4'-(hexafluoroisopropyridene) diphthalic acid dianhydride (6FDA), 1,2-bis (2,3-dicarboxyphenyl) Etan dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,2-bis (3,4-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3) , 4-dicarboxyphenyl) ethane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, 4,4'-(p-) Examples thereof include phenylenedioxy) diphthalic dianhydride and 4,4'-(m-phenylenedioxy) diphthalic dianhydride, more preferably 4,4'-oxydiphthalic dianhydride, 3,3',. 4,4'-biphenyltetracarboxylic dianhydride, 2,2', 3,3'-biphenyltetracarboxylic dianhydride, 4,4'-(hexafluoroisopropyridene) diphthalic acid dianhydride (6FDA) , Bis (3,4-dicarboxyphenyl) methane dianhydride and 4,4'-(p-phenylenedioxy) diphthalic dianhydride. These can be used alone or in combination of two or more.

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

Among the tetracarboxylic acid compounds, the alicyclic tetracarboxylic dianhydride or non-condensation polycyclic aromatic is preferable from the viewpoint of easily improving the tensile elasticity, bending resistance, and optical properties of the transparent resin film. Examples include tetracarboxylic dianhydride. More preferred specific examples are 3,3', 4,4'-biphenyltetracarboxylic dianhydride, 2,2', 3,3'-biphenyltetracarboxylic dianhydride, 2,2-bis (3). , 4-Dicarboxyphenyl) propane dianhydride, 4,4'-(hexafluoroisopropylidene) diphthalic acid dianhydride (6FDA). These can be used alone or in combination of two or more.

The polyimide-based resin according to the present embodiment has a tetracarboxylic acid, a tricarboxylic acid compound, and a dicarboxylic acid in addition to the tetracarboxylic acid anhydride used in the above-mentioned polyimide synthesis, as long as the various physical properties of the obtained transparent resin film are not impaired. Acid compounds, their anhydrides and their derivatives may be further reacted.

Examples of the tricarboxylic acid compound include aromatic tricarboxylic acids, aliphatic tricarboxylic acids, acid chloride compounds related thereto, acid anhydrides, and the like, and two or more of these may be used in combination. Specific examples thereof include an anhydride of 1,2,4-benzenetricarboxylic acid, an acid chloride compound of 1,3,5-benzenetricarboxylic acid, and 2,3,6-naphthalenetricarboxylic acid-2,3-anhydride. Examples thereof include compounds in which phthalic anhydride and benzoic acid are single-bonded, -CH _2- , -C (CH ₃ ) _2- , -C (CF ₃ ) _2- , -SO _2- or phenylene group linked. ..

Examples of the dicarboxylic acid compound include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, acid chloride compounds related thereto, acid anhydrides, and the like, and two or more of these may be used in combination.
Specific examples thereof include dicarboxylic acid compounds of terephthalic acid; isophthalic acid; naphthalenedicarboxylic acid; 4,4'-biphenyldicarboxylic acid; 3,3'-biphenyldicarboxylic acid; chain hydrocarbons having 8 or less carbon atoms. The two benzoic acid skeletons are -CH _2- , -S-, -C (CH ₃ ) _2- , -C (CF ₃ ) _2- , -O-, -N (R ⁹ )-, -C (= O) )-, -SO _2- or compounds linked by a phenylene group. These can be used alone or in combination of two or more. Here, R ⁹ represents a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom.

The dicarboxylic acid compounds are preferably terephthalic acid; isophthalic acid; 4,4'-biphenyldicarboxylic acid; 3,3'-biphenyldicarboxylic acid; and two benzoic acid skeletons -CH _2- , -C (= O). -, -O-, -N (R ⁹ )-, -SO _2- or phenylene group-linked compounds, more preferably terephthalic acid; 4,4'-biphenyldicarboxylic acid; and two benzoic acids. backbone ^{-O -, - N (R 9} ) -, - compounds linked by - C (= O) - or -SO _2. These can be used alone or in combination of two or more.

The ratio of the tetracarboxylic acid compound to the total of the tetracarboxylic acid compound, the tricarboxylic acid compound, and the dicarboxylic acid compound is preferably 40 mol% or more, more preferably 50 mol% or more, still more preferably 70 mol%. The above is more preferably 90 mol% or more, and particularly preferably 98 mol% or more.

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

Specific examples of the aliphatic diamine include an acyclic aliphatic diamine such as hexamethylenediamine, 1,3-bis (aminomethyl) cyclohexane, 1,4-bis (aminomethyl) cyclohexane, norbornanediamine, 4,4'. -Cyclic aliphatic diamines such as diaminodicyclohexylmethane can be mentioned, and these can be used alone or in combination of two or more.

Specific examples of aromatic diamines include p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylene diamine, p-xylylene diamine, 1,5-diaminonaphthalene, and 2,6-diamino. Aromatic amines with one aromatic ring, such as naphthalene, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3 '-Diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-Aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (4-aminophenoxy)) Phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2'-dimethylbenzidine, 2,2'-bis (trifluoromethyl) -4,4'-diaminodiphenyl ( TFMB), 4,4'-bis (4-aminophenoxy) biphenyl, 9,9-bis (4-aminophenyl) fluorene, 9,9-bis (4-amino-3-methylphenyl) ) Aromatic diamines having two or more aromatic rings, such as fluorene, 9,9-bis (4-amino-3-chlorophenyl) fluorene, 9,9-bis (4-amino-3-fluorophenyl) fluorene, etc. Be done. These can be used alone or in combination of two or more.

As the aromatic diamine, preferably 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenylsulfone, 3,3'-Diaminodiphenyl sulfone, 1,4-bis (4-aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2'-dimethylbenzidine, 2,2'-bis (Trifluoromethyl) -4,4'-diaminodiphenyl (TFMB), 4,4'-bis (4-aminophenoxy) biphenyl, and more preferably 4,4'-diaminodiphenylmethane, 4,4'-. Diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylsulfone, 1,4-bis (4-aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl] sulfone, 2, 2-Bis [4- (4-aminophenoxy) phenyl] propane, 2,2'-dimethylbenzidine, 2,2'-bis (trifluoromethyl) -4,4'-diaminodiphenyl (TFMB), 4,4 '-Bis (4-aminophenoxy) biphenyl can be mentioned. These can be used alone or in combination of two or more.

The diamine may also have a fluorine-based substituent. Examples of the fluorine-based substituent include a perfluoroalkyl group having 1 to 5 carbon atoms such as a trifluoromethyl group and a fluoro group.

Among the above diamines, from the viewpoint of high transparency and low colorability, one or more selected from the group consisting of aromatic diamines having a biphenyl structure are preferably mentioned, and specific examples thereof include 2,2'-. One or more selected from the group consisting of dimethylbenzidine, 2,2'-bis (trifluoromethyl) -4,4'-diaminodiphenyl (TFMB) and 4,4'-bis (4-aminophenoxy) biphenyl Can be mentioned. More preferably, a diamine having a biphenyl structure and a fluorine-based substituent can be mentioned, and specific examples thereof include 2,2'-bis (trifluoromethyl) -4,4'-diaminodiphenyl (TFMB).

The polyimide-based resin is represented by the formula (10), which is formed by polycondensation of a diamine and a tetracarboxylic acid compound (including a tetracarboxylic acid compound derivative such as an acid chloride compound and a tetracarboxylic acid dianhydride). It is a condensation type polymer containing a repeating structural unit. In addition to these, tricarboxylic acid compounds (including tricarboxylic acid compound derivatives such as acid chloride compounds and tricarboxylic acid anhydrides) and dicarboxylic acid compounds (including derivatives such as acid chloride compounds) can also be used as starting materials. is there. The polyamide resin is a condensed polymer containing a repeating structural unit represented by the formula (13), which is formed by polycondensation of a diamine and a dicarboxylic acid compound (including a derivative such as an acid chloride compound). is there.

The repeating structural units represented by the formulas (10) and (11) are usually derived from diamines and tetracarboxylic acid compounds. The repeating structural unit represented by the formula (12) is usually derived from a diamine and a tricarboxylic acid compound. The repeating structural unit represented by the formula (13) is usually derived from a diamine and a dicarboxylic acid compound. Specific examples of the diamine, the tetracarboxylic acid compound, the tricarboxylic acid compound and the dicarboxylic acid compound are as described above.

The molar ratio of the diamine to the carboxylic acid compound such as the tetracarboxylic acid compound can be appropriately adjusted in the range of 0.9 mol or more and 1.1 mol or less of the tetracarboxylic acid with respect to 1.00 mol of the diamine. Since the obtained polyimide resin preferably has a high molecular weight in order to exhibit high folding resistance, it is more preferably 0.98 mol or more and 1.02 mol of tetracarboxylic acid with respect to 1.00 mol of diamine. It is more preferably 0.99 mol or more and 1.01 mol or less.

Further, from the viewpoint of suppressing the yellowness of the obtained transparent resin film, it is preferable that the ratio of amino groups in the obtained polymer terminal is low, and the carboxylic acid compound such as the tetracarboxylic acid compound with respect to 1.00 mol of diamine It is preferably 1.00 mol or more.

By adjusting the number of fluorine in the molecule of the diamine and the carboxylic acid compound (for example, the tetracarboxylic acid compound), the amount of fluorine in the obtained polyimide resin is 1% by mass or more and 5 by mass based on the mass of the polyimide resin. It can be mass% or more, 10 mass% or more, and 20 mass% or more. Since the raw material cost tends to increase as the proportion of fluorine increases, the upper limit of the amount of fluorine is preferably 40% by mass or less. The fluorinated substituents may be present in either the diamine or the carboxylic acid compound, or in both. In particular, the YI value may be reduced by including a fluorine-based substituent.

The polyimide-based resin according to the present embodiment may be a copolymer containing a plurality of the above-mentioned repeating structural units of different types. The weight average molecular weight of the polyimide resin in terms of standard polystyrene is usually 100,000 to 800,000. When the weight average molecular weight of the polyimide resin is large, the flexibility at the time of film formation is improved, so that it is preferably 200,000 or more, more preferably 250,000 or more, and further preferably 280,000 or more. Is. Further, since a varnish having an appropriate concentration and viscosity can be obtained and the film forming property tends to be improved, it is preferably 750,000 or less, more preferably 600,000 or less, and further preferably 500,000. It is as follows. Two or more types of polyimide resins having different weight average molecular weights may be used in combination. Further, other polymer materials may be mixed as long as the physical properties are not impaired.

Since the polyimide-based resin and the polyamide-based resin contain a fluorine-containing substituent, the tensile elastic modulus at the time of film formation tends to be improved and the YI value tends to be reduced. When the tensile elastic modulus of the film is high, the occurrence of scratches and wrinkles tends to be suppressed. From the viewpoint of film transparency, the polyimide resin and the polyamide resin preferably have a fluorine-containing substituent. Specific examples of the fluorine-containing substituent include a fluoro group and a trifluoromethyl group.

The content of fluorine atoms in the polyimide resin and the mixture of the polyimide resin and the polyamide resin is preferably based on the mass of the polyimide resin or the total of the mass of the polyimide resin and the mass of the polyamide resin, respectively. It is 1% by mass or more and 40% by mass or less, and more preferably 5% by mass or more and 40% by mass or less. When the content of fluorine atoms is in the above range, the YI value at the time of film formation tends to be further reduced and the transparency tends to be further improved.

In the present invention, the content of the polyimide resin and / or the polyamide resin in the resin composition constituting the transparent resin film is preferably 40% by mass or more, more preferably 50% by mass, based on the solid content of the resin composition. % Or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and may be 100% by mass. When the content of the polyimide resin and / or the polyamide resin is at least the above lower limit value, the flexibility of the transparent resin film is good. The solid content refers to the total amount of the components excluding the solvent from the resin composition.

The imidization ratio of the polyimide resin and the polyamide-imide resin is preferably 90% or more, more preferably 93% or more, still more preferably 96% or more. From the viewpoint of easily increasing the optical homogeneity of the optical film and / or the optical laminate, the imidization ratio is preferably at least the above lower limit. The upper limit of the imidization rate is 100% or less. The imidization ratio indicates the ratio of the molar amount of imide bond in the polyimide resin and the polyamide-imide resin to the value twice the molar amount of the structural unit derived from the tetracarboxylic acid compound in the polyimide resin or the polyamide-imide resin. When the polyimide resin and the polyamide-imide resin contain a tricarboxylic acid compound, the value is twice the molar amount of the structural unit derived from the tetracarboxylic acid compound in the polyimide resin and the polyamide-imide resin, and the value is derived from the tricarboxylic acid compound. The ratio of the molar amount of the imide bond in the polyimide resin and the polyamide-imide resin to the total amount of the molar amount of the constituent unit is shown. The imidization rate can be determined by an IR method, an NMR method, or the like. For example, in the NMR method, it can be measured by the method described in Examples.

In the present invention, the resin composition for forming the transparent resin film may further contain an inorganic material such as inorganic particles in addition to the above-mentioned polyimide-based resin and / or polyamide-based resin. Examples of the inorganic material include inorganic particles such as silica particles, titanium particles, aluminum hydroxide, zirconia particles, and barium titanate particles, and silicon compounds such as quaternary alkoxysilane such as tetraethyl orthosilicate. From the viewpoint of the stability of the varnish and the dispersibility of the inorganic material, silica particles, aluminum hydroxide, zirconia particles, and more preferably silica particles are preferable.

The average primary particle size of the inorganic material particles is preferably 10 to 100 nm, more preferably 10 to 90 nm, still more preferably 10 to 50 nm, and even more preferably 10 to 30 nm. When the average primary particle size of the silica particles is 100 nm or less, the transparency tends to be improved. When the average primary particle size of the silica particles is 10 nm or more, the cohesive force of the silica particles is weakened, so that the silica particles tend to be easy to handle.

In the present invention, the silica particles may be a silica sol in which silica particles are dispersed in a solvent or the like, or silica fine particle powder produced by the vapor phase method may be used, but the silica particles are produced by the liquid phase method because they are easy to handle. It is preferably a silica sol.

The average primary particle size of the silica particles in the transparent resin film can be determined by observation with a transmission electron microscope (TEM). The particle size distribution of the silica particles before forming the transparent resin film can be obtained by a commercially available laser diffraction type particle size distribution meter.

In the present invention, when the resin composition contains an inorganic material, the content thereof is preferably 0.001% by mass or more and 90% by mass or less, more preferably 0.% by mass, based on the solid content of the resin composition. It is 001% by mass or more and 60% by mass or less, and more preferably 0.001% by mass or more and 40% by mass or less. When the content of the inorganic material in the resin composition is within the above range, the transparency and mechanical strength of the transparent resin film tend to be compatible with each other. The solid content refers to the total amount of the components excluding the solvent from the resin composition.

The resin composition constituting the transparent resin film may further contain other components in addition to the components described above. Other components include, for example, antioxidants, mold release agents, light stabilizers, bluing agents, flame retardants, lubricants and leveling agents.

In the present invention, when the resin composition contains a resin component such as a polyimide resin and other components other than the inorganic material, the content of the other components is preferably 0.001% or more with respect to the total mass of the transparent resin film. It is 20% by mass or less, more preferably 0.001% or more and 10% by mass or less.

In the present invention, the transparent resin film is, for example, a reaction solution of a polyimide resin and / or a polyamide resin obtained by selecting and reacting with the tetracarboxylic acid compound, the diamine and the other raw materials, if necessary. It can be produced from a resin varnish prepared by adding a solvent to a resin composition containing an inorganic material and other components, mixing and stirring. In the resin composition, a solution of the purchased polyimide resin or the like or a solution of the purchased solid polyimide resin or the like may be used instead of the reaction solution of the polyimide resin or the like.

As the solvent that can be used for preparing the resin varnish, a solvent capable of dissolving or dispersing a resin component such as a polyimide resin can be appropriately selected. From the viewpoint of solubility, coatability, drying property and the like of the resin component, the boiling point of the solvent is preferably 120 to 300 ° C., more preferably 120 to 270 ° C., still more preferably 120 to 250 ° C., and particularly preferably 120 to 120 ° C. It is 230 ° C. Specific examples of such a solvent include amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide and N-methylpyrrolidone; and lactone solvents such as γ-butyrolactone and γ-valerolactone; Ketone solvents such as cyclohexanone, cyclopentanone and methyl ethyl ketone; acetate solvents such as butyl acetate and amyl acetate; sulfur-containing solvents such as dimethyl sulfoxide, dimethyl sulfoxide and sulfolane, carbonate solvents such as ethylene carbonate and propylene carbonate, etc. Can be mentioned. Among them, N, N-dimethylacetamide (boiling point: 165 ° C.), γ-butyrolactone (boiling point: 204 ° C.), N-methylpyrrolidone (boiling point: 202 ° C.) because of its excellent solubility in polyimide-based resin and polyamide-based resin. , Butyl acetate (boiling point: 126 ° C.), cyclopentanone (boiling point: 131 ° C.) and amyl acetate (boiling point: 149 ° C.). As the solvent, one type may be used alone, or two or more types may be used in combination.
When two or more kinds of solvents are used, it is preferable to select the type of solvent so that the boiling point of the solvent having the highest boiling point among the solvents used falls within the above range.

The amount of the solvent may be selected so as to have a viscosity that allows the resin varnish to be handled, and is not particularly limited. For example, the amount of the solvent is preferably 50 to 95% by mass, more preferably 70 to 95, based on the total amount of the resin varnish. It is by mass, more preferably 80 to 95% by mass.

The transparent resin film of the present invention can be obtained by applying the above resin varnish on a support and pre-drying it. The transparent resin film is releasably laminated on the support. The fact that the film can be peeled off means that the shape of the film can be maintained and the film can be peeled off from the support without breaking. Specifically, it means that the solvent is dried by pre-drying so that an appropriate amount of solvent remains. Here, if the amount of residual solvent is too large, the shape of the film cannot be maintained, and if the amount of residual solvent is too small, the adhesion to the support becomes too high and the film breaks at the time of peeling. The appropriate amount of residual solvent varies depending on the type of resin composition, solvent, and support of the transparent resin film, and needs to be adjusted as appropriate. However, usually, the content of the solvent in the transparent resin film is 0.1% by mass or more with respect to the total mass of the transparent resin film. The upper limit of the solvent content in the transparent resin film is not particularly limited as long as the shape can be maintained as a film, but is usually 50% by mass or less with respect to the total mass of the transparent resin film.

The thickness of the resin plate-like body is preferably 10 to 200 μm. By adjusting the thickness of the resin plate-like body within this range, it becomes easy to improve the bending resistance while maintaining the impact resistance. The thickness of the resin plate-like body is more preferably 20 to 100 μm, still more preferably 30 to 80 μm.

The yellowness (YI value) of the transparent resin film is preferably 3.0 or less, more preferably 2.7 or less, still more preferably 2.5 or less, and particularly preferably 2.0 or less. When the yellowness of the optical laminate is not more than the above upper limit, the transparency is likely to be improved, and for example, the visibility is easily improved when used for the front plate of a display device. The yellowness is usually -5 or more, preferably -2 or more, more preferably 0 or more, still more preferably 0.3 or more, still more preferably 0.5 or more, and particularly preferably 0.7 or more. The yellowness (YI) is determined by measuring the transmittance of light at 300 to 800 nm using an ultraviolet-visible near-infrared spectrophotometer in accordance with JIS K 7373: 2006, and tristimulating values (X, Y, Z). Can be calculated based on the formula of YI = 100 × (1.2769X-1.0592Z) / Y.

The total light transmittance of the transparent resin film is preferably 80% or more, more preferably 85% or more, still more preferably 89%, and even more preferably 90% or more. When the total light transmittance is equal to or higher than the above lower limit, it is easy to improve the visibility when the front plate is incorporated into the image display device. The upper limit of the total light transmittance is usually 100% or less. The total light transmittance can be measured using a haze computer in accordance with, for example, JIS K 7361-1: 1997.

The haze of the transparent resin film is preferably 3.0% or less, more preferably 2.0% or less, still more preferably 1.0% or less, even more preferably 0.5% or less, and particularly preferably 0.3%. It is as follows. When the haze of the transparent resin film is not more than the above upper limit, the transparency is good, and when it is used for the front plate of an image display device, for example, the visibility of an image can be easily improved. The lower limit of haze is usually 0.01% or more. The haze can be measured using a haze computer in accordance with JIS K 7136: 2000.

The front plate 1 may be a film having a hard coat layer provided on at least one surface of the base film to further improve the hardness. As the base film, a film made of the above resin can be used. The hard coat layer may be formed on one surface of the base film or may be formed on both surfaces. By providing the hard coat layer, a resin film having improved hardness and scratchability can be obtained. The hard coat layer is, for example, a cured layer of an ultraviolet curable resin. Examples of the ultraviolet curable resin include acrylic resin, silicone resin, polyester resin, urethane resin, amide resin, epoxy resin and the like. The hard coat layer may contain additives to improve strength. Additives are not limited, and examples thereof include inorganic fine particles, organic fine particles, and mixtures thereof.

When the optical laminate is used in the display device, the front plate 1 may have a function as a window film in the display device. The front plate 1 may have a blue light cut function, a viewing angle adjusting function, and the like. The front plate 1 can be a layer constituting the outermost surface of the display device.

The thickness of the front plate 1 is preferably 20 to 220 μm. By adjusting the thickness of the front plate 1 within this range, it becomes easy to improve the bending resistance while maintaining the impact resistance, and it is also possible to impart hardness. The thickness of the front plate 1 is more preferably 35 to 110 μm, still more preferably 40 to 90 μm.

The tensile elastic modulus of the front plate is preferably 3 GPa or more, more preferably 4 GPa or more, further preferably 5 GPa or more, preferably 10 GPa or less, and more preferably 9 GPa or less. When the tensile elastic modulus is at least the above lower limit value, defects such as dents are less likely to occur in the front plate when an impact is received from the outside, and the strength of the front plate is likely to be increased. Further, when the tensile elastic modulus is not more than the above upper limit value, it is easy to improve the bending resistance of the front plate. The tensile elastic modulus may satisfy the above range at least one of MD (Machine Direction, film forming direction) or TD (Transverse Direction, direction perpendicular to MD), and it is preferable that both satisfy the above range.

[Adhesive layer]
The pressure-sensitive adhesive layer is located between the non-adhesive layers constituting the optical laminate or between the non-adhesive layer constituting the optical laminate and an adherend such as a display unit. The pressure-sensitive adhesive layer is a layer that connects members existing on both sides thereof. In one embodiment, with reference to FIG. 1, the optical laminate 10 has a first pressure-sensitive adhesive layer 2 and a second pressure-sensitive adhesive layer 4. The first pressure-sensitive adhesive layer 2 is located between the front plate 1 and the impact-resistant layer 3 described later, and binds the two. The second pressure-sensitive adhesive layer is located on the inner surface of the impact-resistant layer 3 and bonds the impact-resistant layer and the adherend. Examples of the adherend include a polarizing plate of a display unit, a circular polarizing plate, a touch sensor, and the like. Each pressure-sensitive adhesive layer may be made of the same material or different materials.

The pressure-sensitive adhesive layer can be composed of a pressure-sensitive adhesive composition containing a resin as a main component, such as (meth) acrylic-based, rubber-based, urethane-based, ester-based, silicone-based, and polyvinyl ether-based. Among them, a pressure-sensitive adhesive composition using a (meth) acrylic resin having excellent transparency, weather resistance, heat resistance and the like as a base polymer is preferable. The pressure-sensitive adhesive composition may be an active energy ray-curable type or a thermosetting type.

Examples of the (meth) acrylic resin (base polymer) used in the pressure-sensitive adhesive composition include butyl (meth) acrylate, ethyl (meth) acrylate, isooctyl (meth) acrylate, and 2- (meth) acrylate. A polymer or copolymer containing one or more (meth) acrylic acid esters such as ethylhexyl as a monomer is preferably used. It is preferable that the base polymer is copolymerized with a polar monomer. Examples of the polar monomer include (meth) acrylic acid, 2-hydroxypropyl (meth) acrylate, hydroxyethyl (meth) acrylate, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, and glycidyl (). Examples thereof include monomers having a carboxyl group, a hydroxyl group, an amide group, an amino group, an epoxy group and the like, such as meta) acrylate.

The pressure-sensitive adhesive composition may contain only the above-mentioned base polymer, but usually further contains a cross-linking agent. The cross-linking agent is a divalent or higher metal ion that forms a carboxylic acid metal salt with a carboxyl group; a polyamine compound that forms an amide bond with a carboxyl group; poly. Epoxy compounds and polyols that form an ester bond with a carboxyl group; polyisocyanate compounds that form an amide bond with a carboxyl group, preferably polyisocyanate compounds. Can be mentioned.

The active energy ray-curable pressure-sensitive adhesive composition has a property of being cured by being irradiated with active energy rays such as ultraviolet rays and electron beams, and has adhesiveness even before irradiation with active energy rays. It is a pressure-sensitive adhesive composition having the property of being able to adhere to an adherend such as, etc., and being cured by irradiation with active energy rays to adjust the adhesion force. The active energy ray-curable pressure-sensitive adhesive composition is preferably an ultraviolet-curable type. The active energy ray-curable pressure-sensitive adhesive composition further contains an active energy ray-polymerizable compound in addition to the base polymer and the cross-linking agent. Further, if necessary, a photopolymerization initiator, a photosensitizer, or the like may be contained.

The pressure-sensitive adhesive composition includes fine particles for imparting light scattering, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, pressure-sensitive adhesives, fillers (metal powders and other inorganic powders). Etc.), antioxidants, UV absorbers, dyes, pigments, colorants, antifoaming agents, corrosion inhibitors, photopolymerization initiators and other additives may be included.

It can be formed by applying an organic solvent diluent of the pressure-sensitive adhesive composition on a substrate and drying it. When the active energy ray-curable pressure-sensitive adhesive composition is used, the formed pressure-sensitive adhesive layer can be irradiated with active energy rays to obtain a cured product having a desired degree of curing.

The pressure-sensitive adhesive layer has viscoelasticity and has a function of cushioning an impact applied to the optical laminate. In the optical laminate of the present invention, the bending resistance is improved by appropriately adjusting the viscoelasticity of the pressure-sensitive adhesive layer or selecting a pressure-sensitive adhesive layer having appropriate viscoelasticity.

Here, as a method for evaluating viscoelasticity, there are a static viscoelasticity measurement method and a dynamic viscoelasticity measurement method.
The static viscoelasticity measurement method is a method for measuring the response time and temperature change in response to steady strain and stress, and specifically. There are stress relaxation measurement, which measures the stress by applying a constant strain to the measurement sample, and creep & recovery method, which measures the strain by applying a constant stress. Further, the dynamic viscoelasticity measurement is a method of applying a strain of a sinusoidal waveform to a measurement sample and measuring the corresponding strain or stress signal. In the dynamic viscoelasticity measurement, the temperature dependence of the glass transition temperature and elastic modulus can be analyzed by the temperature dispersion measurement. Furthermore, by simultaneously measuring the temperature dispersion and frequency dispersion, various relaxation phenomena including glass transition can be observed, and knowledge about the molecular structure and molecular motion of the polymer can be obtained.

In the above dynamic viscous measurement, the elastic modulus G ^*, which is the ratio of stress and strain, is expressed by the following equation in the range where response signals of the same frequency are observed.

［式中、Ｇ’は貯蔵弾性率、Ｇ”は損失弾性率を表す。ωは測定周波数を表す。］

[In the formula, G'represents the storage elastic modulus, G'represents the loss elastic modulus. Ω represents the measurement frequency.]

G'(ω) is a measure of the energy stored in a given strain, and G'(ω) is a measure of the rate at which energy is dissipated due to phase shift due to the viscous behavior of the sample. , The ratio of G "and G',

［式中、Ｇ’は貯蔵弾性率を表し、Ｇ”は損失弾性率を表す。］

[In the formula, G'represents the storage modulus and G'represents the loss modulus.]

Is called the mechanical loss tangent tan δ.

In the above equation, when tan δ is larger than 1, the viscous property of the measurement sample is larger than the elastic property, and conversely, when tan δ is smaller than 1, the elastic property is larger than the elastic property.

Generally, the energy applied to the system by repeated dynamic deformation such as a bending resistance test is consumed as the deformation energy of the system or dissipated as heat. The deformation energy of the system is partially consumed as elastic energy, and the other part is spent on the destruction of the system.

In the case of tan δ of the pressure-sensitive adhesive layer, that is, when the viscosity is high, the energy that is mechanically dissipated as elastic energy or the like as described above is usually released by molecular relaxation of the pressure-sensitive adhesive composition constituting the pressure-sensitive adhesive layer. It is stored in the stratified system. This causes the temperature of the pressure-sensitive adhesive layer to rise, and as a result and / or the stored energy contributes to the destruction of the system as interfacial peeling energy, so that the pressure-sensitive adhesive layer and the adherend layer are separated from each other. Is considered to be even more likely to occur.

In view of the above, it has been clarified by diligent studies by the inventor of the present application that the bending resistance of the optical laminate of the present invention is affected by the tan δ of the pressure-sensitive adhesive layer and its position in the laminated structure. That is, it was found that the lower the tan δ of the pressure-sensitive adhesive layer located on the outer side when bending the optical laminate, the more effective it is for improving the bending resistance.

The tan δ of the second pressure-sensitive adhesive layer of the optical laminate of the present invention at −20 ° C. is less than 1.23. When the tan δ of the second pressure-sensitive adhesive layer at −20 ° C. is smaller than 1.23, the pressure-sensitive adhesive layer is likely to suppress peeling from the adherend due to thermal deterioration. The tan δ of the second pressure-sensitive adhesive layer at −20 ° C. is preferably 0.01 to 1.20, more preferably 0.06 to 0.8. In one embodiment, the tan δ of the second pressure-sensitive adhesive layer of the optical laminate at −20 ° C. is preferably 0.03 to 1.00, more preferably 0.05 to 0.80, still more preferably 0.06 to 0.06. It is 0.70.

The storage elastic modulus of the second pressure-sensitive adhesive layer at −20 ° C. is preferably 0.01 to 25.00 MPa. When the storage elastic modulus of the second pressure-sensitive adhesive layer at −20 ° C. is 0.01 MPa or more, the impact resistance of the optical laminate is improved, and when it is 25.00 MPa or less, the bending resistance of the optical laminate is improved. To do. The storage elastic modulus of the second pressure-sensitive adhesive layer at −20 ° C. is preferably 0.01 to 25.00 MPa, more preferably 0.10 to 25.00 MPa. The storage elastic modulus of the second pressure-sensitive adhesive layer at 25 ° C. has a storage elastic modulus of 0.01 to 0.80 MPa. When the storage elastic modulus of the pressure-sensitive adhesive layer is 0.01 MPa or more, the impact resistance of the optical laminate is improved, and when it is 0.80 MPa or less, the flexibility of the optical laminate is improved. It is preferably 0.02 to 0.75 MPa, more preferably 0.03 to 0.70 MPa.

The thickness of the second pressure-sensitive adhesive layer is preferably 5 to 100 μm. When the thickness of the second pressure-sensitive adhesive layer is 5 μm or more, the impact resistance of the optical laminate is improved, and when the thickness of the second pressure-sensitive adhesive layer is 100 μm or less, the flexibility is improved. The thickness of the second pressure-sensitive adhesive layer is more preferably 5 to 85 μm, still more preferably 15 to 85 μm, and may be 25 to 50 μm.

The tan δ of the first pressure-sensitive adhesive layer at −20 ° C. is preferably 0.1 to 1.2, more preferably 0.1 to 1.0. The storage elastic modulus of the first pressure-sensitive adhesive layer at −20 ° C. is preferably 0.01 to 25.00 MPa, more preferably 0.10 to 25.00 MPa.
The storage elastic modulus of the first pressure-sensitive adhesive layer at 25 ° C. has a storage elastic modulus of 0.01 to 0.80 MPa. The thickness of the first pressure-sensitive adhesive layer is preferably 5.0 to 50.0 μm, more preferably 5.0 to 25.0 μm.

[Impact resistant layer]
The impact-resistant layer 3 is located in the internal direction of the front plate, and has a function of alleviating the impact when an impact is applied to the front surface of the display device and preventing damage to the wiring of the display panel, elements, and the like. The impact resistant layer 3 preferably has a function of improving the bending resistance of the optical laminate.

When the material is bent, the deformation energy applied to the material reaches a threshold value, so that the material is damaged such as fracture, crack or wrinkle.

Therefore, the impact-resistant layer is preferably a material having a large tolerance for deformation energy, and for example, a thermoplastic resin that is hard and tenacious (that is, has a large toughness) is preferable. Examples of such resins include polycarbonate-based resins, polyimide-based resins, polyamide-based resins, polyamide-imide-based resins, and polyester-based resins. Further, since the present invention is intended to be used in a display device, it is preferable to use a resin having excellent translucency (preferably optically transparent).

The impact resistant layer preferably has a tensile modulus of elasticity of 0.1 to 10 GPa. When the tensile elastic modulus of the impact-resistant layer is 0.1 GPa or more, the impact resistance of the optical laminate is improved, and when it is 10 GPa or less, the flexibility of the optical laminate is improved. The tensile elastic modulus of the impact-resistant layer is preferably 1.0 to 8.0 GPa, and more preferably 3.0 to 7.0 GPa. The tensile elastic modulus may satisfy the above range at least one of MD (Machine Direction, film forming direction) or TD (Transverse Direction, direction perpendicular to MD), and it is preferable that both satisfy the above range.

The impact resistant layer may be an impact resistant layer having an optical function such as a retardation film or a brightness improving film. For example, a retardation film to which an arbitrary retardation value is imparted by stretching a film made of the thermoplastic resin (uniaxial stretching, biaxial stretching, etc.) or forming a liquid crystal layer or the like on the film. Can be.

The tan δ of the impact resistant layer at −20 ° C. is 0.001 to 0.020. If the tan δ of the impact-resistant layer at −20 ° C. is less than 0.001, the impact resistance of the optical laminate tends to decrease, and if it exceeds 0.020, the bending resistance of the optical laminate tends to decrease. The tan δ of the impact resistant layer at −20 ° C. is preferably 0.005 to 0.020 rather than 0.001 to 0.020.

The impact resistant layer has a thickness of 5 to 140 μm. When the thickness of the impact-resistant layer is 5 μm or more, the impact resistance of the optical laminate is improved, and when it is 140 μm or less, the flexibility of the optical laminate is improved. The thickness of the impact resistant layer is preferably 10 to 120 μm, more preferably 40 to 100 μm.

[Manufacturing method of optical laminate]
The optical laminate of the present invention is produced by bonding a front plate and an impact-resistant layer using an adhesive layer and forming an adhesive layer on the inner surface of the impact-resistant layer.

As a method of bonding the front plate and the impact resistant layer, an adhesive layer may be formed on the bonding surface of one layer and then the other layer may be laminated, or the adhesive layer may be adhered to the bonding surface of both layers. After forming the agent layer, the pressure-sensitive adhesive layers may be combined with each other. The method of forming the pressure-sensitive adhesive layer on the surface to which the layers are bonded may be formed by using the pressure-sensitive adhesive composition as described above, or a sheet-like pressure-sensitive adhesive that can be handled independently is prepared and used. It may be formed by sticking it on the surface.

As shown in FIG. 1, when the optical laminate includes, for example, a front plate 1, a first adhesive layer 2, an impact resistant layer 3, and a second adhesive layer 4 in this order from the visual side, it is resistant. The ratio r of the impact layer thickness a to the thickness c of the second pressure-sensitive adhesive layer is preferably 5.5 or less from the viewpoint of bending resistance of the optical laminate. The ratio r is preferably 5.5 or less, more preferably 5.0 or less, and even more preferably 1 to 4.

In a preferred embodiment, the total thickness of the first pressure-resistant layer, the impact-resistant layer, and the second pressure-sensitive adhesive layer is 100 to 200 μm. When the total thickness of the pressure-sensitive adhesive layer and the impact-resistant layer is 100 μm or more, the impact resistance of the optical laminate is improved, and when it is 200 μm or less, the bending resistance of the optical laminate is improved. The total thickness is preferably 100 μm to 190 μm, more preferably 120 to 180 μm, and may be 120 to 190 μm.

The optical laminate has excellent bending resistance. In the present specification, the bending resistance refers to a characteristic that the adhesive layer does not peel or break at the bent portion when the front plate of the optical laminate is bent inside. The bending radius at the time of bending is, for example, 5 mm or less, preferably 3 mm or less, and more preferably 1 mm or less. The bending speed at the time of bending is, for example, 30 to 60 rpm, preferably 30 rpm or less. The number of times of bending may decrease when the bending speed is slow, but the optical laminate in the present invention has high bending resistance even when the bending speed is slow.

The optical laminate is usually 100,000 times when a continuous flexibility test is performed in which the impact resistant layer and the second pressure-sensitive adhesive layer are continuously bent and stretched by 180 ° with the front plate inside until peeling occurs. As described above, the bending resistance is preferably 150,000 times or more, more preferably 200,000 times or more. In this case, the conditions of the continuous bending test are a temperature of 25 ° C., a bending speed of 30 rpm, and a bending radius of 1.00 mm.

[Display device]
FIG. 2 is a cross-sectional view showing an example of the structure of the display device of the present invention. The display device 20 has an optical laminate 10 arranged on the front surface (visual side) thereof, and a display unit 5. The display unit may be configured to be foldable with the surface on the viewing side inside, or may be configured to be retractable. Further, the display unit may be configured as a touch panel type display device. Specific examples of the display unit include a laminated body in which a touch sensor layer and a polarizing layer are formed on the display surface of the display element. Specific examples of the display element include a liquid crystal display element, an organic EL display element, an inorganic EL display element, a plasma display element, and a field emission type display element.

The display device 20 can be used as a mobile device such as a smartphone or tablet, a television, a digital photo frame, an electronic signage, a measuring instrument or an instrument, an office device, a medical device, a computer device, or the like.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. In this example, the unit "part" of the ratio of the substance to be blended is based on mass unless otherwise specified.

<Manufacturing example 1>
Synthesis of Polyamide-imide Resin Under a nitrogen gas atmosphere, a reaction vessel equipped with a stirring blade in a separable flask and an oil bath were prepared. In a reaction vessel installed in an oil bath, 45 parts of 2,2'-bis (trifluoromethyl) -4,4'-diaminodiphenyl (TFMB) and 768.55 parts of N, N-dimethylacetamide (DMAc) were added. I put it in. TFMB was dissolved in DMAc while stirring the contents in the reaction vessel at room temperature. Next, 19.01 parts of 4,4'-(hexafluoroisopropyridene) diphthalic acid dianhydride (6FDA) was further charged into the reaction vessel, and the contents in the reaction vessel were stirred at room temperature for 3 hours. Then, 4.21 parts of 4,4'-oxybis (benzoyl chloride) (OBBC) and then 17.30 parts of terephthaloyl chloride (TPC) were put into the reaction vessel, and the contents in the reaction vessel were charged at room temperature for 1 hour. Stirred. Next, 4.63 parts of 4-methylpyridine and 13.04 parts of acetic anhydride were further added to the reaction vessel, and the contents in the reaction vessel were stirred at room temperature for 30 minutes. After stirring, the temperature inside the container was raised to 70 ° C. using an oil bath, maintained at 70 ° C., and stirred for another 3 hours to obtain a reaction solution. The obtained reaction solution was cooled to room temperature and poured into a large amount of methanol in the form of filaments to precipitate a precipitate. The precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyamide-imide resin 1. The weight average molecular weight of the obtained polyamide-imide resin 1 was 400,000, and the imidization rate was 99.0%.

[Weight average molecular weight]
Gel Permeation Chromatography (GPC) Measurement (1) Pretreatment Method The sample was dissolved in γ-butyrolactone (GBL) to prepare a 20% by mass solution, and this solution was diluted 100-fold with a DMF eluent. The diluted solution was filtered through a membrane filter having a pore size of 0.45 μm to prepare a measurement solution.

(2) Measurement conditions Column: TSKgel SuperAWM-H x 2 + SuperAW2500 x 1 (6.0 mm ID x 150 mm x 3)
Eluent: DMF (10 mM lithium bromide added)
Flow rate: 0.6 mL / min Detector: RI detector Column temperature: 40 ° C
Injection volume: 20 μL
Molecular weight standard: Standard polystyrene

[Immidization rate]
The imidization ratio was ^{determined by 1} H-NMR measurement as follows.
(1) Pretreatment method A sample _{was dissolved in deuterated dimethyl sulfoxide (DMSO-d 6} ) to prepare a 2% by mass solution, which was used as a measurement solution.

(2) Measurement conditions Measuring device: JEOL 400 MHz NMR device JNM-ECZ400S / L1 Standard substance: DMSO-d ₆ (2.5 ppm)
Sample temperature: Room temperature Accumulation number: 256 times Relaxation time: 5 seconds

^{(3) Imidization rate analysis method Of the benzene protons observed in the 1} H-NMR spectrum obtained for the measurement solution containing the polyamide-imide resin A, it is derived from the structure that does not change before and after imidization, and is contained in the polyamide-imide resin. The integrated value of benzene proton C, which is not affected by the structure derived from the remaining amic acid structure, was defined as IntC. Further, among the observed benzene protons, the integrated value of benzene proton D, which is derived from the structure that does not change before and after imidization and is influenced by the structure derived from the amic acid structure remaining in the polyamide-imide resin A, was defined as IntD. From these integral values, the β value was calculated based on the following equation.

次に、βをイミド化率に換算する相関式を得るために、イミド化率の異なる複数のポリアミドイミド樹脂について、上記と同様にしてβ値を求めると共に、ＨＳＱＣスペクトルを用いてイミド化率を求め、これらの結果から以下の相関式を得た。

Next, in order to obtain a correlation equation for converting β into an imidization rate, the β value of a plurality of polyamide-imide resins having different imidization rates is obtained in the same manner as above, and the imidization rate is determined using the HSQC spectrum. The following correlation equation was obtained from these results.

[式中、ｋは定数である。]
次いで、ポリアミドイミド樹脂Ａについて得たβを、上記相関式に代入してポリアミドイミド樹脂Ａのイミド化率（％）を得た。

[In the equation, k is a constant. ]
Next, β obtained for the polyamide-imide resin A was substituted into the above correlation equation to obtain the imidization ratio (%) of the polyamide-imide resin A.

<Manufacturing example 2>
Production of Optical Film for Front Plate The polyamide-imide resin (TPC / 6FDA / OBBC / TFMB = 60/30/10/100) obtained in Production Example 1 was diluted with γ-butyrolactone (GBL), and a GBL-substituted silica sol was added. And thoroughly mixed to obtain a resin / silica particle mixed varnish. At that time, a mixed varnish was prepared so that the concentration of the resin and the silica particles was 9.7% by mass. After filtering the obtained polyamide-imide varnish with a filter having an opening of 10 μm, the thickness of the self-supporting film is 55 μm on the smooth surface of the polyester base material (“A4100” (trade name) manufactured by Toyobo Co., Ltd.). It was applied, saliva-molded, and a varnish coating was formed. At this time, the linear velocity was 0.8 m / min. The varnish coating was heated at 80 ° C. for 10 minutes, at 100 ° C. for 10 minutes, and at 90 ° C. for 10 minutes. Then, by heating (post-baking) the coating film at 200 ° C. for 25 minutes, the thickness was 50 μm, the total light transmittance was 89.9 (%), YI = 1.6, and Haze = 0.2 (%). Polyamide-imide film was obtained.

<Manufacturing example 3>
Preparation of photocurable resin composition for hard coat Trimethylolpropane triacrylate (“A-TMPT” (trade name) manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) 28.4 parts by mass, pentaerythritol tetraacrylate (New Nakamura Chemical Industry Co., Ltd.) 28.4 parts by mass of "A-TMMT" (trade name) manufactured by BASF Co., Ltd., 1.8 parts by mass of 1-hydroxycyclohexylphenyl ketone ("Irgacure" (registered trademark) 184 manufactured by BASF) as a photopolymerization initiator. , 0.1 part by mass of leveling agent ("BYK" (registered trademark) -307 manufactured by Big Chemy Japan Co., Ltd.) and 39 parts by mass of propylene glycol 1-monomethyl ether (manufactured by Tokyo Kasei Kogyo Co., Ltd.) are stirred and mixed. , A photocurable resin composition was obtained.

<Manufacturing example 4>
Manufacture of front plate Roll-to-roll the photocurable resin composition prepared in Production Example 3 on one side of the polyamide-imide film (optical film) produced in Production Example 2 so that the thickness after drying is 10 μm. It was painted by the method. Then, the coating film was dried in an oven at 80 ° C. for 3 minutes, and the coating film was irradiated with ultraviolet rays using a high-pressure mercury lamp to cure the photocurable resin composition to obtain a front plate. The integrated light intensity of the irradiated ultraviolet rays was set to 500 mJ / cm ² . The thickness of the hard coat layer on the front plate was 10 μm. The tensile elastic modulus of the obtained front plate (including the hard coat layer) was 6.5 GPa.

<Manufacturing example 5>
A reactor equipped with a silica gel tube, a stirrer and a thermometer in a synthetic separable flask made of polyimide (PI) resin, and an oil bath were prepared. In this flask, 75.52 g of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 2,2'-bis (trifluoromethyl) -4,4'-diaminodiphenyl (TFMB) 54.44 g was added. While stirring this at 400 rpm, 519.84 g of N, N-dimethylacetamide (DMAc) was added, and stirring was continued until the contents of the flask became a uniform solution. Subsequently, stirring was continued for another 20 hours while adjusting the temperature inside the container to be in the range of 20 to 30 ° C. using an oil bath, and the reaction was carried out to generate a polyamic acid. After 30 minutes, the stirring speed was changed to 100 rpm. After stirring for 20 hours, the reaction system temperature was returned to room temperature, and 649.8 g of DMAc was added to adjust the polymer concentration to 10% by mass. Further, 32.27 g of pyridine and 41.65 g of acetic anhydride were added, and the mixture was stirred at room temperature for 10 hours for imidization. The polyimide varnish was taken out from the reaction vessel. The obtained polyimide varnish was dropped into methanol for reprecipitation, and the obtained powder was heated and dried to remove the solvent to obtain a transparent polyimide resin as a solid content. When the GPC measurement of the obtained polyimide resin was performed, the weight average molecular weight was 360,000.
<Manufacturing example 6>
Production of Polyimide (PI) Film for Impact Resistant Layer The polyimide resin (6FDA / TFMB = 100/100) obtained in Production Example 5 is diluted with a GBL / DMAc = 10/90 ratio to a polyimide having a concentration of 15.7% by mass. A varnish was prepared. After filtering the obtained polyimide varnish with a filter having an opening of 10 μm micrometer, the thickness of the free-standing film is 85 μm on the smooth surface of the polyester base material (“A4100” (trade name) manufactured by Toyobo Co., Ltd.). Was coated with an applicator and dried at 50 ° C. for 30 minutes and then at 140 ° C. for 15 minutes, and then the obtained coating film was peeled off from the polyester substrate to obtain a self-supporting film. The free-standing film was fixed to a gold frame and further dried in the atmosphere at 200 ° C. for 40 minutes to obtain a polyimide film (optical film) having a thickness of 80 μm.

<Example 1>
Production of Optical Laminate A polyimide (PI) film having a thickness of 80 μm and a tensile elastic modulus of 4.0 GPa obtained in Production Example 6 was prepared as an impact resistant layer. The PI film had a tan δ of 0.014 at −20 ° C.

As the first pressure-sensitive adhesive layer, a (meth) acrylic pressure-sensitive adhesive layer having a storage elastic modulus of 0.1 MPa at 25 ° C. was prepared. The pressure-sensitive adhesive layer had a thickness of 25 μm, a storage elastic modulus at −20 ° C. of 0.21 MPa, and a tan δ at −20 ° C. of 0.64.

As the second pressure-sensitive adhesive layer, a (meth) acrylic pressure-sensitive adhesive layer having a storage elastic modulus of 0.1 MPa at 25 ° C. was prepared. The pressure-sensitive adhesive layer had a thickness of 25 μm, a storage elastic modulus at −20 ° C. of 0.21 MPa, and a tan δ at −20 ° C. of 0.64.

The front plate obtained in Production Example 4 and the impact resistant layer were laminated via the first pressure-sensitive adhesive layer. The second pressure-sensitive adhesive layer was laminated on the surface on which the first pressure-sensitive adhesive layer of the impact-resistant layer was not laminated to prepare an optical laminate.

<Example 2>
Example 1 and Example 1 except that a polyethylene terephthalate (PET) film having a thickness of 80 μm (tensile elastic modulus 4.6 GPa, tan δ at -20 ° C: 0.007) was used as the impact resistant layer instead of the polyimide film. In the same manner, an optical laminate was produced.

<Example 3>
As the second pressure-sensitive adhesive layer, a layer having a storage elastic modulus at −20 ° C. of 0.11 MPa and a tan δ at −20 ° C. of 0.63 was used in the same manner as in Example 2. An optical laminate was produced.

<Example 4>
As the second pressure-sensitive adhesive layer, a layer having a storage elastic modulus at −20 ° C. of 0.19 MPa and a tan δ at −20 ° C. of 0.06 was used in the same manner as in Example 2. An optical laminate was produced.

<Example 5>
As the second pressure-sensitive adhesive layer, a layer having a storage elastic modulus at −20 ° C. of 4.03 MPa and a tan δ at −20 ° C. of 0.80 was used in the same manner as in Example 2. An optical laminate was produced.

<Example 6>
As the first pressure-sensitive adhesive layer, a layer having a storage elastic modulus at −20 ° C. of 28.06 MPa and a tan δ at −20 ° C. of 1.23 was used in the same manner as in Example 2. An optical laminate was produced.

<Example 7>
As the impact resistant layer, a PET film having a thickness of 50 μm and a tensile elastic modulus of 4.6 GPa was used instead of the polyimide film, and as the second adhesive layer, the storage elastic modulus at −20 ° C. was 0.09 MPa. , An optical laminate was produced in the same manner as in Example 1 except that the tan δ at −20 ° C. was 0.52.

<Example 8>
As the impact resistant layer, a PET film having a thickness of 100 μm and a tensile elastic modulus of 4.6 GPa was used instead of the polyimide film, and as the second adhesive layer, the storage elastic modulus at −20 ° C. was 0.18 MPa. , An optical laminate was produced in the same manner as in Example 1 except that the tan δ at −20 ° C. was 0.93.

<Comparative example 1>
As the second pressure-sensitive adhesive layer, a layer having a storage elastic modulus at −20 ° C. of 28.06 MPa and a tan δ at −20 ° C. of 1.23 was used in the same manner as in Example 2. An optical laminate was produced.

<Comparative example 2>
As the impact resistant layer, a thermoplastic polyurethane (TPU) film was prepared instead of the polyethylene terephthalate film. This TPU film had a thickness of 150 μm, a tensile elastic modulus of 0.03 GPa, and a tan δ of 0.022 at −20 ° C.

As the first pressure-sensitive adhesive layer, a (meth) acrylic pressure-sensitive adhesive layer having a storage elastic modulus of 0.14 MPa at 25 ° C. was prepared. The pressure-sensitive adhesive layer had a thickness of 25 μm, a storage elastic modulus at −20 ° C. of 28.06 MPa, and a tan δ at −20 ° C. of 1.23.

As the second pressure-sensitive adhesive layer, a (meth) acrylic pressure-sensitive adhesive layer having a storage elastic modulus of 0.1 MPa at 25 ° C. was prepared. The pressure-sensitive adhesive layer had a thickness of 25 μm, a storage elastic modulus at −20 ° C. of 28.06 MPa, and a tan δ at −20 ° C. of 1.23.

The front plate obtained in Production Example 4 and the impact resistant layer were laminated via the first pressure-sensitive adhesive layer. The second pressure-sensitive adhesive layer was laminated on the surface on which the first pressure-sensitive adhesive layer of the impact-resistant layer was not laminated to prepare an optical laminate.

<Evaluation of optical characteristics of optical film for front plate>
[Yellowness of film]
The yellowness (Yellow Index: YI value) of the optical film was measured using a spectrocolorimeter CM-3700A manufactured by Konica Minolta Co., Ltd. Specifically, after performing background measurement in the absence of a sample, the optical laminate is set in the sample holder, the transmittance for light of 300 to 800 nm is measured, and the tristimulus values (X, Y, Z) are measured. ) Was calculated, and the YI value was calculated based on the following formula.

YI = 100 × (1.2769X-1.0592Z) / Y

[Total light transmittance]
The total light transmittance (Tt) was measured by a fully automatic direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd. in accordance with JIS K 7105: 1981.

[Haze]
In accordance with JIS K 7136: 2000, the optical films obtained in Examples and Comparative Examples were cut into a size of 30 mm × 30 mm, and a haze computer (manufactured by Suga Test Instruments Co., Ltd., “HGM-2DP”) was used. Haze (%) was measured using.

<Performance evaluation of optical laminate>
[Impact resistance test]
A polyimide substrate having a thickness of 125 μm was placed on a stone surface plate (manufactured by Uniseiki Co., Ltd., first grade). A pressure measurement film (“Prescale” grade: HS (trade name) manufactured by FUJIFILM Corporation) was placed on this polyimide substrate. The optical laminates produced in Examples 1 to 5 and Comparative Examples 1 and 2 were placed on the pressure measuring film. A weight was dropped from a height of 10 cm onto the optical laminate, and the bottom pressure was measured from the discoloration of the pressure-sensitive paper at the dropped portion. A pressure image analysis system (“FPD-8010J” (trade name) manufactured by FUJIFILM Corporation) was used to measure the bottom pressure. The weight had a mass of 5.6 g and was spherical. The point where the weight collided with the optical laminate was a circle with a diameter of 0.75 mm. This test was performed 3 times. The average value of the bottom pressure obtained in the three measurements was evaluated according to the following criteria.

〇… 100 MPa or less ×… 100 MPa or more

[Flex resistance test]
The bending resistance test was performed at a temperature of 25 ° C. The optical laminates obtained in Examples and Comparative Examples were cut into a size of 10 mm width using a dumbbell cutter. The cut optical laminate is set on the jig of a surface-state no-load U-shaped expansion / contraction tester ("DMLHB-FS" (trade name) manufactured by Yuasa System Co., Ltd.) so that it can be bent with the front plate inside. Then, the operation of bending and extending by 180 ° was repeated so that the distance between the facing front plates was 2.0 mm (bending radius of 1 mm). The bending speed was 30 rpm. The number of bends until the optical laminate peeled between the impact-resistant layer and the pressure-sensitive adhesive layer and whitened was recorded as the number of bends. The number of bending resistances was evaluated as follows.

◎… Bending resistance is 200,000 or more 〇… Bending resistance is 150,000 or more and less than 200,000 △… Bending resistance is 100,000 or more and less than 150,000 ×… Bending resistance is less than 100,000

<Tension modulus>
The impact-resistant layer and the front plate used in Examples and Comparative Examples were cut into strips of 10 mm × 100 mm using a dumbbell cutter to obtain samples. Using "Autograph AG-IS" (trade name) manufactured by Shimadzu Corporation, the tensile elastic modulus of this sample was measured by measuring the SS curve under the conditions of a distance between chucks of 500 mm and a tensile speed of 10 mm / min, and its inclination. The tensile elastic modulus of the impact-resistant layer was calculated from. The tensile elastic modulus was measured in an environment with a temperature of 23 ° C. and a relative humidity of 55%.

<Dynamic viscoelastic property (tan δ of impact resistant layer)>
From the tan δ curve of the loss elastic modulus and the storage elastic modulus measured in the following measurement modes using a dynamic viscoelasticity measuring device (“DMA Q800” (trade name) manufactured by TA Instrument), at -20 ° C. The tan δ was calculated.
Sample: Length 5-15 mm, Width 5 mm
Experimental mode: DMA Multi-Frequency-Strin

Detailed experimental mode conditions:
(1) Clamp: Tension: Film
(2) Amplitude: 5 μm
(3) Frequency: 0.1Hz (no fluctuation in all temperature sections)
(4) Preload Force: 0.01N
(5) Force Track: 125N

Temperature conditions:
(1) -25 ° C to 30 ° C
(2) Temperature rise rate: 5 ° C / min

Main data collected:
(1) Storage modulus (Storage modulus, E')
(2) Loss elastic modulus (Loss modulus, E'')
(3) tan δ (E'' / E')

<Dynamic viscoelastic property (storage elastic modulus of adhesive layer, tan δ)>
[Storage modulus]
The measurement was performed using a viscoelasticity measuring device (“MCR-301” (trade name) manufactured by Antonio Par). The same pressure-sensitive adhesive layer used in Examples and Comparative Examples was cut into a width of 20 mm and a length of 20 mm, and a plurality of layers were laminated so as to have a thickness of 150 μm. After bonding the laminated adhesive layer to the glass plate, the condition is that the frequency is 1.0 Hz, the deformation amount is 1%, and the temperature rise rate is 5 ° C / min in the temperature range of -20 ° C to 100 ° C in the state of being adhered to the measurement chip. The storage elastic modulus values at −20 ° C. and 25 ° C. were confirmed.

[Tanδ]
The tan δ at a temperature of −20 ° C. was measured using a viscoelasticity measuring device (“MCR-301” (trade name) manufactured by Antonio Par). The same pressure-sensitive adhesive layer used in Examples and Comparative Examples was cut into a width of 30 mm and a length of 30 mm, and a plurality of layers were laminated so as to have a thickness of 150 μm. After bonding the laminated adhesive layer to the glass plate, the temperature range is 1.0 Hz to 100 ° C., the deformation amount is 1%, and the temperature rise rate is 5 ° C./min in the state of being adhered to the measurement chip. The measured value of tan δ at a temperature of −20 ° C. was confirmed. It should be noted that tan δ has the following relationship between the storage elastic modulus G'and the loss elastic modulus G''.

<Measuring method of layer thickness>
[Film thickness]
Using "ID-C112XBS" (trade name) manufactured by Mitutoyo Co., Ltd., the thickness of 10 or more films was measured, and the average value was calculated.

[Thickness of hard coat layer]
The thickness of the hard coat layer was measured using a "F20 desktop film thickness system" (trade name) manufactured by Filmetics.

The above results are shown in Table 1.

In Example 6, a pressure-sensitive adhesive composition having a tan δ of 1.23 at −20 ° C. was used for the first pressure-sensitive adhesive layer, but no decrease in bending resistance was observed.

1 ... Front plate,
2 ... 1st adhesive layer,
3 ... Impact resistant layer,
4 ... Second adhesive layer,
5 ... Display unit,
10 ... Optical laminate,
20 ... Display device.

Claims (9)

An optical laminate having a front plate, a first pressure-sensitive adhesive layer, an impact-resistant layer, and a second pressure-sensitive adhesive layer in this order from the visual side, in which the second pressure-sensitive adhesive layer is 1.20 or less and tan δ at −20 ° C. An optical laminate having. The formula in which the impact resistant layer and the second pressure-sensitive adhesive layer are 5.5 or less.

[In the formula, a is the thickness of the impact resistant layer, and c is the thickness of the second pressure-sensitive adhesive layer. ]
The optical laminate according to claim 1, which has a thickness ratio r represented by. The optical laminate according to claim 1 or 2, wherein the impact resistant layer has a tan δ at −20 ° C. of 0.001 to 0.020. The optical laminate according to any one of claims 1 to 3, wherein the impact resistant layer has a tensile elastic modulus of 0.1 to 10 GPa. The optical laminate according to any one of claims 1 to 4, wherein the material of the impact resistant layer is selected from the group consisting of a polycarbonate resin, a polyimide resin, and a polyester resin. The optical laminate according to any one of claims 1 to 5, wherein the first pressure-sensitive adhesive layer, the impact-resistant layer, and the second pressure-sensitive adhesive layer have a total thickness of 120 to 190 μm. The optical laminate according to any one of claims 1 to 6, which has a thickness of 130 to 220 μm. Claims 1 to 1 show a bending resistance of 150,000 times or more in a continuous bending test in which the front plate is turned inside and 180 ° is bent and stretched under the conditions of a temperature of 25 ° C., a bending speed of 30 rpm and a bending radius of 1.00 mm. 7. The optical laminate according to any one of 7. A display device including the optical laminate according to any one of claims 1 to 8 and a display unit in the internal direction of the optical laminate.

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