JP7469889B2 - Optical laminate and method for manufacturing display device - Google Patents

Description

The present invention relates to an optical laminate and a method for manufacturing a display device.

JP 2010-188550 A (Patent Document 1) discloses a roll of optical film wound around a surface, in which a first base film is provided on a first surface via a first adhesive layer, and a second base film is provided on a second surface via a second adhesive layer. After being cut into a predetermined shape, the optical film is attached to a display substrate via the first adhesive layer exposed by peeling off the first base film.

JP 2010-188550 A

Patent Document 1 describes adjusting the magnitude relationship of the adhesive strength at the interface to suppress lifting that occurs between the substrate film and the optical film when wound on a roll.

The present invention aims to provide an optical laminate in which, when a release film attached to the surface of a pressure-sensitive adhesive layer for bonding the optical laminate is peeled off, peeling of a surface protection film provided on the surface opposite to the release film is suppressed, and a method for manufacturing a display device using the optical laminate.

The present invention provides the following methods for producing an optical laminate and a display device.
[1] A polarizing laminate, a first pressure-sensitive adhesive layer laminated on a first surface of the polarizing laminate, a first base film laminated on a surface of the first pressure-sensitive adhesive layer opposite to the polarizing laminate side, a second pressure-sensitive adhesive layer laminated on a second surface of the polarizing laminate, and a second base film laminated on a surface of the second pressure-sensitive adhesive layer opposite to the polarizing laminate side,
An optical laminate satisfying the following formula (1a):
(A/B)×C≧800 (1a)
[In formula (1a),
A is a value calculated by A1/A2, where A1 [gf/25 mm] is the 180° peel strength between the polarizing laminate and the second pressure-sensitive adhesive layer, and A2 [μm] is the total thickness of the second base film and the second pressure-sensitive adhesive layer,
B is a value calculated by B1/B2, where B1 [gf/25 mm] is the 180° peel strength between the first pressure-sensitive adhesive layer and the first base film and B2 [μm] is the thickness of the first base film,
C is the stiffness [Gurley unit] of the evaluation laminate in which the first pressure-sensitive adhesive layer, the polarizing laminate, the second pressure-sensitive adhesive layer, and the second base film are laminated in this order.
[2] The optical laminate according to [1], further satisfying the relationship of the following formula (2a):
(A/B)×C≦10000 (2a)
[3] The optical laminate according to [1] or [2], wherein A satisfies the following formula (3a):
0.1≦A≦1 (3a)
[4] The optical laminate according to any one of [1] to [3], wherein B satisfies the relationship of the following formula (4a):
0.08≦B≦0.8 (4a)
[5] The optical laminate according to any one of [1] to [4], wherein C satisfies the relationship of the following formula (5a):
200≦C≦3000 (5a)
[6] A first base film peeling step of peeling the first base film from the optical laminate according to any one of [1] to [5] to expose a surface of the first pressure-sensitive adhesive layer;
and a bonding step of bonding the exposed surface of the first pressure-sensitive adhesive layer to a display element.

The present invention provides an optical laminate in which, when a release film attached to the surface of a pressure-sensitive adhesive layer for bonding the optical laminate is peeled off, peeling of a surface protection film provided on the surface opposite to the release film is suppressed, and a method for manufacturing a display device using the optical laminate.

1 is a schematic cross-sectional view showing an example of an optical laminate of the present invention.

Below, an embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiment. In all of the drawings below, the scale of each component has been appropriately adjusted to make it easier to understand, and the scale of each component shown in the drawings does not necessarily match the scale of the actual component.

[Display Device]
FIG. 1 is a schematic cross-sectional view showing an aspect in which an optical laminate 100 ′ obtained by peeling off a first base film 22 from the optical laminate 100 is attached to a display element 200 to produce a display device 300 .

<Optical laminate>
The optical laminate 100 has a polarizing laminate 10, a first adhesive layer 21 laminated on a first surface of the polarizing laminate 10, a first substrate film 22 laminated on the surface of the first adhesive layer 21 opposite the polarizing laminate 10 side, a second adhesive layer 31 laminated on a second surface of the polarizing laminate 10, and a second substrate film 32 laminated on the surface of the second adhesive layer 31 opposite the polarizing laminate 10 side.

In the optical laminate 100, the surface of the first adhesive layer 21 becomes the surface to be bonded to the display element 200. The first base film 22 is a release film (separator) laminated on the surface of the first adhesive layer 21 opposite the polarizing laminate 10 side. The release film is peeled off from the optical laminate 100 when the optical laminate 100 is bonded to the display element 200. The laminate after the first base film 22 is peeled off from the optical laminate 100 is referred to as the optical laminate 100'.

The second substrate film 32 is laminated to the second surface of the polarizing laminate 10 via the second adhesive layer 31, and functions as a surface protection film 30 together with the second adhesive layer 31. The second adhesive layer 31 is usually provided in advance on the second substrate film 32 to form the surface protection film 30, and the surface of the second adhesive layer 31 in the surface protection film 30 is bonded to the polarizing laminate 10 to form the optical laminate 100. The surface protection film 30 is usually peeled off from the optical laminate 100' after the optical laminate 100 is bonded to the display element 200.

The polarizing laminate 10 includes at least a polarizing plate, and may further include a front plate, a touch sensor panel, etc. The polarizing plate includes at least a polarizing film, and may also include a protective film, a retardation film, a brightness enhancement film, an adhesive layer, etc.

The thickness of the optical laminate 100 is not particularly limited as it varies depending on the function required of the optical laminate and the application of the optical laminate, but is, for example, 20 μm or more and 2000 μm or less, preferably 50 μm or more and 1000 μm or less, and more preferably 100 μm or more and 500 μm or less.

The planar shape of the optical laminate 100 may be, for example, a square shape, preferably a square shape having long sides and short sides, and more preferably a rectangle. When the shape of the surface direction of the optical laminate 100 is rectangular, the length of the long side may be, for example, 10 mm or more and 1400 mm or less, and preferably 50 mm or more and 600 mm or less. The length of the short side is, for example, 5 mm or more and 800 mm or less, preferably 30 mm or more and 500 mm or less, and more preferably 50 mm or more and 300 mm or less. Each layer constituting the optical laminate 100 may have rounded corners, notched ends, or holes.

The optical laminate 100 can be used in a display device 300. A method for manufacturing the display device 300 includes a step of peeling the first substrate film 22 from the optical laminate 100 to expose the surface of the first adhesive layer 21, and a step of bonding the exposed surface of the first adhesive layer 21 to a display element 200.

The display device 300 is not particularly limited, and examples thereof include an organic electroluminescence (organic EL) display device, an inorganic electroluminescence (inorganic EL) display device, a liquid crystal display device, and an electroluminescence display device. The optical laminate 100 is suitable for a display device that can be bent. When the optical laminate 100 is used in an organic EL display device, the polarizing laminate 10 in the optical laminate 100 is preferably a circular polarizing plate, and the first substrate film 22 is peeled off from the optical laminate 100 and then attached to the viewing side surface of the organic EL display element to suppress reflected light. When the optical laminate 100 is used in a liquid crystal display device, the polarizing laminate 10 in the optical laminate 100 is preferably a linear polarizing plate or a circular polarizing plate, and the first substrate film 22 is peeled off from the optical laminate 100 and then attached to both sides of the liquid crystal display element to form image light.

The optical laminate 100 satisfies the relationship of the following formula (1a), and preferably satisfies the relationship of the following formula (1b).
(A/B)×C≧800 (1a)
(A/B)×C≧820 (1b)

The values in formula (1a) and formula (1b) are as follows.
A is a value calculated by A1/A2, where A1 [gf/25 mm] is the 180° peel force between the polarizing laminate 10 and the second adhesive layer 31, and A2 [μm] is the total thickness of the second base film 32 and the second adhesive layer 31.
B is a value calculated by B1/B2, where B1 [gf/25 mm] is the 180° peel force between the first adhesive layer 21 and the first base film 22 and B2 [μm] is the thickness of the first base film 22.
C is the stiffness (Gurley units) of the evaluation laminate in which the first pressure-sensitive adhesive layer 21, the polarizing laminate 10, the second pressure-sensitive adhesive layer 31, and the second base film 32 are laminated in this order, where 1 mN=9.807×10 ⁻³ Gurley units.
Each value is measured according to the method described in the Examples section below.

The method for manufacturing a display device using the optical laminate 100 includes a first substrate film peeling step of peeling the first substrate film 22 from the optical laminate 100 to expose the surface of the first adhesive layer 21. The first substrate film peeling step includes, for example, an operation of adsorbing and holding the optical laminate 100 from the surface side on which the surface protective film 30 is laminated, attaching tape to the surface of the first substrate film 22, and raising the first substrate film 22 through the tape to peel off only the first substrate film 22. Although the first substrate film peeling step is intended to peel off the first substrate film 22, peeling of the surface protective film 30 may occur. If peeling of the surface protective film 30 occurs, it becomes difficult to continue the first substrate film peeling step.

In order to prevent peeling of the surface protection film 30 during the first substrate film peeling process, it is possible to consider a method of increasing the adhesive strength between the surface protection film 30 and the polarizing laminate 10 to increase the peeling strength. However, if the adhesive strength of the surface protection film 30 is increased, it may become difficult to peel the surface protection film 30 cleanly in a later process, or defects such as scratches may occur on the surface of the polarizing laminate 10 after peeling.

As a result of intensive research, the inventors have found that peeling of the surface protection film 30 during the first substrate film peeling step can be suppressed by making the optical laminate 100 satisfy the relationship of the above formula (1a).

The optical laminate 100 preferably satisfies the relationship of the following formula (2a), and more preferably satisfies the relationship of the following formula (2b).
(A/B)×C≦10000 (2a)
(A/B)×C≦2000 (2b)

When the optical laminate 100 satisfies the relationship of formula (2a) above, the surface protective film 30 can be peeled off easily and cleanly in the surface protective film peeling process in which the surface protective film 30 is peeled off after the first substrate film peeling process and the lamination process in which the optical laminate 100' is bonded to the display element 200, and peeling of the first substrate film 22 before the first substrate film peeling process can be suppressed.

From the viewpoint of enabling the surface protective film 30 to be peeled off easily and cleanly in the surface protective film peeling step, the A in the above formula (1a) preferably satisfies the relationship of the following formula (3a), and more preferably satisfies the relationship of the following formula (3b). The value of A can be adjusted by adjusting the value of A1 by adjusting at least one of the material of the second base film 32, the material of the second pressure-sensitive adhesive layer 31, and the surface treatment of the bonding surface between the second pressure-sensitive adhesive layer 31 and the polarizing laminate 10, or by adjusting the total thickness A2 of the second base film 32 and the second pressure-sensitive adhesive layer. Examples of the surface treatment of the bonding surface include corona treatment, plasma treatment, and saponification treatment.
0.1≦A≦1 (3a)
0.15≦A≦0.6 (3b)

From the viewpoint of enabling the first base film 22 to be peeled off easily and cleanly in the first base film peeling step, the B in the above formula (1a) preferably satisfies the relationship of the following formula (4a), and more preferably satisfies the relationship of the following formula (4b). The value of B can be adjusted by adjusting at least one of the material of the first base film 22, the material of the first pressure-sensitive adhesive layer 21, and the surface treatment of the bonding surface between the first pressure-sensitive adhesive layer 21 and the first base film 22 to adjust the value of B1, or by adjusting the thickness B2 of the first base film 22. Examples of the surface treatment of the bonding surface include corona treatment, plasma treatment, and saponification treatment.
0.08≦B≦0.8 (4a)
0.1≦B≦0.4 (4b)

From the viewpoint of being able to suppress peeling of the first base film 22 before the first base film peeling step and from the viewpoint of being able to impart flexibility to the optical laminate 100' or the polarizing laminate 10, the C in the above formula (1a) preferably satisfies the relationship of the following formula (5a), and more preferably satisfies the relationship of the following formula (5b). The optical laminate 100' or the polarizing laminate 10 has flexibility, so that it is possible to configure a display device having flexibility. The value of C can be adjusted by adjusting the material of the second base film 32, the laminate structure of the polarizing laminate 10, and the material and thickness of each layer used in the laminate structure.
200≦C≦3000 (5a)
300≦C≦2000 (5b)

The 180° peel strength A1 between the polarizing laminate 10 and the second adhesive layer 31 is preferably 10 gf/25 mm or more, more preferably 14 gf/25 mm or more, and may be 20 gf/25 mm or more. The 180° peel strength A1 is preferably 50 gf/25 mm or less, may be 40 gf/25 mm or less, or may be 30 gf/25 mm or less.

The 180° peel strength B1 between the first adhesive layer 21 and the first base film 22 is preferably 1 gf/25 mm or more, more preferably 5 gf/25 mm or more, and may be 6 gf/25 mm or more. The 180° peel strength B1 is preferably 20 gf/25 mm or less, may be 15 gf/25 mm or less, or may be 10 gf/25 mm or less.

It is preferable that the 180° peel force A1 between the polarizing laminate 10 and the second adhesive layer 31 is greater than the 180° peel force B1 between the first adhesive layer 21 and the first base film 22.

<First pressure-sensitive adhesive layer 21>
The first pressure-sensitive adhesive layer 21 is laminated on the first surface of the polarizing laminate 10 in the optical laminate 100, and functions as an attachment layer between the polarizing laminate 10 and the display element. The first pressure-sensitive adhesive layer 21 may be one layer or may be two or more layers, but is preferably one layer. The first pressure-sensitive adhesive layer 21 can be composed of a pressure-sensitive adhesive composition mainly composed of a (meth)acrylic resin, a rubber resin, a urethane resin, an ester resin, a silicone resin, or a polyvinyl ether resin. Among them, a pressure-sensitive adhesive composition having a (meth)acrylic resin as a base polymer, which is excellent in transparency, weather resistance, heat resistance, etc., is suitable. The pressure-sensitive adhesive composition may be an active energy ray curable type or a heat curable type.

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

The adhesive composition may contain only the base polymer, but usually further contains a crosslinking agent. Examples of crosslinking agents include divalent or higher metal ions that form metal carboxylates with carboxyl groups, polyamine compounds that form amide bonds with carboxyl groups, polyepoxy compounds or polyols that form ester bonds with carboxyl groups, and polyisocyanate compounds that form amide bonds with carboxyl groups. Among these, polyisocyanate compounds are preferred.

The active energy ray curable adhesive composition has the property of being cured by irradiation with active energy rays such as ultraviolet rays or electron beams, and has adhesiveness even before irradiation with active energy rays, allowing it to be adhered to an adherend such as a film, and has the property of being cured by irradiation with active energy rays, allowing the adhesive strength to be adjusted. The active energy ray curable adhesive composition is preferably an ultraviolet ray curable type. The active energy ray curable adhesive composition further contains an active energy ray polymerizable compound in addition to a base polymer and a crosslinking agent. If necessary, a photopolymerization initiator, a photosensitizer, etc. may be contained.

The adhesive composition may contain additives such as fine particles for imparting light scattering properties, beads (resin beads, glass beads, etc.), glass fibers, resins other than the base polymer, tackifiers, fillers (metal powders and other inorganic powders, etc.), antioxidants, UV absorbers, dyes, pigments, colorants, defoamers, corrosion inhibitors, and photopolymerization initiators.

The first adhesive layer 21 can be formed by applying an organic solvent dilution of the adhesive composition onto the first surface of the substrate film or the polarizing laminate 10 and drying it. The substrate film is generally a thermoplastic resin film, and a typical example of such a film is a separate film that has been subjected to a release treatment. The separate film can be, for example, a film made of a resin such as polyethylene terephthalate, polybutylene terephthalate, polycarbonate, or polyarene, and the surface on which the adhesive layer is to be formed is subjected to a release treatment such as silicone treatment.

For example, a separate film may be used as the first substrate film 22, and a pressure-sensitive adhesive composition may be directly applied to the release-treated surface to form a pressure-sensitive adhesive layer as the first pressure-sensitive adhesive layer 21, and this pressure-sensitive adhesive layer with separate film may be laminated onto the first surface of the polarizing laminate 10.
An adhesive composition may be directly applied to the first surface of the polarizing laminate 10 to form an adhesive layer as the first adhesive layer 21, and a separate film may be laminated on the outer surface of the first adhesive layer 21 as the first base film 22.
When providing the adhesive layer on the first surface of the polarizing laminate 10, it is preferable to subject the bonding surface of the polarizing laminate 10 and/or the bonding surface of the adhesive layer to a surface activation treatment, such as a plasma treatment, corona treatment, etc., and it is more preferable to subject the adhesive layer to a corona treatment.
Alternatively, a pressure-sensitive adhesive composition may be applied onto the second separate film to form the first pressure-sensitive adhesive layer 21, a pressure-sensitive adhesive sheet may be prepared by laminating a separate film (first base film 22) on the formed pressure-sensitive adhesive layer, and the pressure-sensitive adhesive layer with the separate film after peeling the second separate film from this pressure-sensitive adhesive sheet may be laminated on the polarizing laminate 10. The second separate film used has weaker adhesion to the first pressure-sensitive adhesive layer 21 than the separate film (first base film 22) and is easier to peel off.

The thickness of the first adhesive layer 21 is not particularly limited, but is preferably, for example, 1 μm or more and 100 μm or less, more preferably 3 μm or more and 50 μm or less, and may be 20 μm or more.

<First Base Film 22>
The first base film 22 is a release film (separator) laminated on the surface of the first pressure-sensitive adhesive layer 21 opposite to the polarizing laminate 10. The surface of the first base film 22 in contact with the first pressure-sensitive adhesive layer 21 is preferably subjected to a release treatment.

The first base film 22 is preferably a thermoplastic resin film. Examples of thermoplastic resin films include cyclic polyolefin resin films; cellulose acetate resin films made of resins such as triacetyl cellulose and diacetyl cellulose; polyester resin films made of resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; polycarbonate resin films; (meth)acrylic resin films; and polypropylene resin films. The first base film 22 is preferably a polyester resin film, and more preferably a polyethylene terephthalate film.

The thickness B2 of the first base film 22 is preferably 15 μm or more, more preferably 20 μm or more, and even more preferably 25 μm or more. The thickness B2 of the first base film 22 is preferably 80 μm or less, and even more preferably 60 μm or less.

<Surface protection film 30>
The surface protective film 30 is composed of a second base film 32 and a second adhesive layer 31 laminated thereon. The surface protective film 30 has a function of protecting the second surface of the polarizing laminate 10, and is peeled off from the polarizing laminate 10 after, for example, the optical laminate 100′ is attached to the display element 200.

The above description of the first base film 22 applies to the resin that constitutes the second base film 32.

The above description of the adhesive composition constituting the first adhesive layer 21 applies to the adhesive composition constituting the second adhesive layer 31. The thickness of the second adhesive layer 31 is not particularly limited, but is preferably, for example, 1 μm or more and 100 μm or less, more preferably 3 μm or more and 50 μm or less, and may be 20 μm or more. A commercially available product can also be used as the surface protection film 30.

The total thickness A2 of the second base film 32 and the second adhesive layer 31 is preferably 30 μm or more, more preferably 40 μm or more, and may be 50 μm or more. The total thickness A2 of the second base film 32 and the second adhesive layer 31 is preferably 200 μm or less, and more preferably 150 μm or less.

<Polarizing laminate 10>
(Polarizer)
The polarizing laminate 10 includes at least a polarizing plate. The polarizing plate includes at least a linear polarizer layer. The polarizing plate is, for example, a circular polarizing plate, and the circular polarizing plate includes at least a retardation layer. The circular polarizing plate can absorb external light reflected in the display device, and therefore can provide the optical laminate with an anti-reflection function.

The thickness of the polarizing plate is usually 5 μm or more, and may be 20 μm or more, 25 μm or more, or 30 μm or more. The thickness of the polarizing plate is preferably 80 μm or less, and more preferably 60 μm or less.

(Linear Polarizer Layer)
The linear polarizer layer has a function of selectively transmitting linearly polarized light in one direction, which is made of unpolarized light such as natural light. The linear polarizer layer may include a stretched film or layer having a dichroic dye adsorbed thereon, a cured product of a polymerizable liquid crystal compound, and a dichroic dye, and the dichroic dye is dispersed in the cured product of the polymerizable liquid crystal compound and oriented in the cured product. When a dye is dispersed and oriented in an anisotropic medium, it may appear colored from a certain direction and almost colorless from a direction perpendicular to the direction. A dye that exhibits such a phenomenon is called a dichroic dye. A linear polarizer layer using a liquid crystal layer as a polarizer layer is preferable because there is no restriction on the bending direction compared to a stretched film or layer having a dichroic dye adsorbed thereon.

(Polarizer layer which is a stretched film or layer having a dichroic dye adsorbed thereon)
A polarizer layer, which is a stretched film having a dichroic dye adsorbed thereon, can usually be produced through a process of uniaxially stretching a polyvinyl alcohol-based resin film, a process of dyeing the polyvinyl alcohol-based resin film with a dichroic dye such as iodine to adsorb the dichroic dye, a process of treating the polyvinyl alcohol-based resin film having the dichroic dye adsorbed thereon with an aqueous boric acid solution, and a process of washing with water after the treatment with the aqueous boric acid solution.

The thickness of the polarizer layer is usually 30 μm or less, preferably 18 μm or less, and more preferably 15 μm or less. Reducing the thickness of the polarizer layer is advantageous for making the circular polarizer thinner. The thickness of the polarizer layer is usually 1 μm or more, and may be, for example, 5 μm or more.

Polyvinyl alcohol resins are obtained by saponifying polyvinyl acetate resins. Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as copolymers of vinyl acetate and other monomers that can be copolymerized with it. Examples of other monomers that can be copolymerized with vinyl acetate include unsaturated carboxylic acid compounds, olefin compounds, vinyl ether compounds, unsaturated sulfone compounds, and (meth)acrylamide compounds with ammonium groups.

The degree of saponification of polyvinyl alcohol resins is usually about 85 mol% or more and 100 mol% or less, and preferably 98 mol% or more. The polyvinyl alcohol resins may be modified, and polyvinyl formal, polyvinyl acetal, etc. modified with aldehydes can also be used. The degree of polymerization of polyvinyl alcohol resins is usually 1000 or more and 10000 or less, and preferably 1500 or more and 5000 or less.

The polarizer layer, which is a stretched layer having a dichroic dye adsorbed thereon, can usually be manufactured through the steps of applying a coating liquid containing the above-mentioned polyvinyl alcohol resin onto a substrate film, uniaxially stretching the resulting laminated film, dyeing the polyvinyl alcohol resin layer of the uniaxially stretched laminated film with a dichroic dye to adsorb the dichroic dye to form a polarizer layer, treating the film having the dichroic dye adsorbed thereon with an aqueous boric acid solution, and washing the film with water after the treatment with the aqueous boric acid solution. The substrate film used to form the polarizer layer may be used as a protective layer for the polarizer layer. If necessary, the substrate film may be peeled off and removed from the polarizer layer. The material and thickness of the substrate film may be the same as the material and thickness of the thermoplastic resin film described below.

The polarizer layer, which is a stretched film or layer with a dichroic dye adsorbed thereon, may be used as a linear polarizer layer as is, or a protective layer may be formed on one or both sides of the polarizer layer to be used as a linear polarizer layer. The protective layer may be a thermoplastic resin film as described below. The thickness of the resulting linear polarizer layer is preferably 2 μm or more and 40 μm or less.

Examples of thermoplastic resin films include films known in the art, such as cyclic polyolefin resin films; cellulose acetate resin films made of resins such as triacetyl cellulose and diacetyl cellulose; polyester resin films made of resins such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; polycarbonate resin films; (meth)acrylic resin films; and polypropylene resin films. The polarizer layer and protective layer can be laminated via an adhesive layer, which will be described later.

From the viewpoint of thinning, the thickness of the thermoplastic resin film is usually 100 μm or less, preferably 80 μm or less, more preferably 60 μm or less, even more preferably 40 μm or less, and even more preferably 30 μm or less, and is usually 5 μm or more, preferably 10 μm or more.

A hard coat layer may be formed on the thermoplastic resin film. The hard coat layer may be formed on one side of the thermoplastic resin film, or on both sides. By providing a hard coat layer, the thermoplastic resin film can be improved in hardness and scratch resistance. The hard coat layer can be formed in the same manner as the hard coat layer formed on the resin film described above.

(Liquid crystal layer, polarizer layer)
The polymerizable liquid crystal compound used to form the liquid crystal layer is a compound having a polymerizable reactive group and exhibiting liquid crystallinity. The polymerizable reactive group is a group involved in a polymerization reaction, and is preferably a photopolymerizable reactive group. The photopolymerizable reactive group refers to a group that can be involved in a polymerization reaction by an active radical or an acid generated from a photopolymerization initiator. Examples of the photopolymerizable functional group include a vinyl group, a vinyloxy group, a 1-chlorovinyl group, an isopropenyl group, a 4-vinylphenyl group, an acryloyloxy group, a methacryloyloxy group, an oxiranyl group, and an oxetanyl group. Among them, an acryloyloxy group, a methacryloyloxy group, a vinyloxy group, an oxiranyl group, and an oxetanyl group are preferred, and an acryloyloxy group is more preferred. The type of the polymerizable liquid crystal compound is not particularly limited, and a rod-shaped liquid crystal compound, a discotic liquid crystal compound, and a mixture thereof can be used. The liquid crystallinity of the polymerizable liquid crystal compound may be a thermotropic liquid crystal or a lyotropic liquid crystal, and the phase order structure may be a nematic liquid crystal or a smectic liquid crystal.

As the dichroic dye used in the polarizer layer, which is a liquid crystal layer, it is preferable that the dichroic dye has a maximum absorption wavelength (λMAX) in the range of 300 to 700 nm. Examples of such dichroic dyes include acridine dyes, oxazine dyes, cyanine dyes, naphthalene dyes, azo dyes, and anthraquinone dyes, among which azo dyes are preferable. Examples of azo dyes include monoazo dyes, bisazo dyes, trisazo dyes, tetrakisazo dyes, and stilbene azo dyes, and preferably bisazo dyes and trisazo dyes. The dichroic dyes may be used alone or in combination of two or more kinds, but it is preferable to combine three or more kinds. In particular, it is more preferable to combine three or more kinds of azo compounds. A part of the dichroic dye may have a reactive group and may have liquid crystal properties.

The polarizer layer, which is a liquid crystal layer, can be formed, for example, by applying a composition for forming a polarizer layer, which contains a polymerizable liquid crystal compound and a dichroic dye, onto an alignment film formed on a substrate film, and polymerizing and curing the polymerizable liquid crystal compound. The composition for forming a polarizer layer may be applied onto the substrate film to form a coating film, and the coating film may be stretched together with the substrate film to form a polarizer layer. The substrate film used to form the polarizer layer may be used as a protective layer for the polarizer layer. The material and thickness of the substrate film may be the same as those of the thermoplastic resin film described above.

Examples of a composition for forming a polarizer layer containing a polymerizable liquid crystal compound and a dichroic dye, and a method for manufacturing a polarizer layer using this composition, include those described in JP-A-2013-37353, JP-A-2013-33249, JP-A-2017-83843, etc. In addition to the polymerizable liquid crystal compound and the dichroic dye, the composition for forming a polarizer layer may further contain additives such as a solvent, a polymerization initiator, a crosslinking agent, a leveling agent, an antioxidant, a plasticizer, and a sensitizer. Each of these components may be used alone or in combination of two or more.

The polymerization initiator that may be contained in the composition for forming a polarizer layer is a compound that can initiate the polymerization reaction of a polymerizable liquid crystal compound, and a photopolymerization initiator is preferred because it can initiate the polymerization reaction under lower temperature conditions. Specifically, photopolymerization initiators that can generate active radicals or acids under the action of light are exemplified, and among these, photopolymerization initiators that generate radicals under the action of light are preferred. The content of the polymerization initiator is preferably 1 part by mass or more and 10 parts by mass or less, more preferably 3 parts by mass or more and 8 parts by mass or less, relative to 100 parts by weight of the total amount of the polymerizable liquid crystal compound. Within this range, the reaction of the polymerizable group proceeds sufficiently, and the alignment state of the liquid crystal compound is easily stabilized.

The thickness of the polarizer layer, which is the liquid crystal layer, is usually 10 μm or less, preferably 0.5 μm or more and 8 μm or less, and more preferably 1 μm or more and 5 μm or less.

The polarizer layer, which is a liquid crystal layer, may be used as a linear polarizer layer without peeling off the substrate film, or the substrate film may be peeled off and removed from the polarizer layer to form a linear polarizer layer. The polarizer layer, which is a liquid crystal layer, may be used as a linear polarizer layer by forming a protective layer on one or both sides. The above-mentioned thermoplastic resin film can be used as the protective layer.

The polarizer layer, which is a liquid crystal layer, may have an overcoat layer on one or both sides. The overcoat layer may be provided for the purpose of protecting the polarizer layer. The overcoat layer may be formed, for example, by applying a material (composition) for forming the overcoat layer onto the polarizer layer. Examples of materials constituting the overcoat layer include photocurable resins and water-soluble polymers. Examples of materials that can be used to form the overcoat layer include (meth)acrylic resins and polyvinyl alcohol resins.

(Retardation Layer)
In the circular polarizing plate, the retardation layer may be one layer or two or more layers. The retardation layer may have an overcoat layer that protects its surface, a substrate film that supports the retardation layer, or the like. The retardation layer may include a λ/4 layer, and may further include at least one of a λ/2 layer or a positive C layer. When the retardation layer includes a λ/2 layer, the λ/2 layer and the λ/4 layer are laminated in order from the linear polarizer layer side. When the retardation layer includes a positive C layer, the λ/4 layer and the positive C layer may be laminated in order from the linear polarizer layer side, or the positive C layer and the λ/4 layer may be laminated in order from the linear polarizer layer side. The thickness of the retardation layer is, for example, 0.1 μm or more and 10 μm or less, preferably 0.5 μm or more and 8 μm or less, and more preferably 1 μm or more and 6 μm or less.

The retardation layer may be formed from a resin film exemplified as the material for the protective layer, or may be formed from a layer of a hardened polymerizable liquid crystal compound. The retardation layer may further include an alignment film. The retardation layer may have a lamination layer for laminating the λ/4 layer with the λ/2 layer and the positive C layer.

When the retardation layer is formed from a layer obtained by curing a polymerizable liquid crystal compound, it can be formed by applying a composition containing the polymerizable liquid crystal compound to a substrate film and curing it. An alignment layer may be formed between the substrate film and the coating layer. The material and thickness of the substrate film may be the same as the material and thickness of the thermoplastic resin film. When the retardation layer is formed from a layer obtained by curing a polymerizable liquid crystal compound, it may be incorporated into the optical laminate in a form having an alignment layer and a substrate film. The retardation layer can be bonded to the linear polarizer layer via a bonding layer.

(Laminating layer)
The attachment layer is a layer composed of a pressure-sensitive adhesive composition or an adhesive composition. The above description of the pressure-sensitive adhesive composition constituting the first pressure-sensitive adhesive layer 21 is applied to the pressure-sensitive adhesive composition that is the material of the attachment layer.

The adhesive composition that is the material of the lamination layer can be formed by combining one or more of, for example, water-based adhesives and active energy ray curing adhesives. Examples of water-based adhesives include polyvinyl alcohol-based resin aqueous solutions and water-based two-liquid urethane-based emulsion adhesives. Active energy ray curing adhesives are adhesives that are cured by irradiation with active energy rays such as ultraviolet rays, and examples of such adhesives include adhesives containing a polymerizable compound and a photopolymerization initiator, adhesives containing a photoreactive resin, and adhesives containing a binder resin and a photoreactive crosslinking agent. Examples of the polymerizable compound include photopolymerizable monomers such as photocurable epoxy monomers, photocurable acrylic monomers, and photocurable urethane monomers, and oligomers derived from these monomers. Examples of the photopolymerization initiator include compounds containing substances that generate active species such as neutral radicals, anion radicals, and cation radicals when irradiated with active energy rays such as ultraviolet rays.

The thickness of the lamination layer may be, for example, 1 μm or more, preferably 1 μm or more and 25 μm or less, more preferably 2 μm or more and 15 μm or less, and even more preferably 2.5 μm or more and 5 μm or less.

(Front panel)
The polarizing laminate 10 may or may not include a front panel. The material and thickness of the front panel are not limited as long as the front panel is a plate-like body capable of transmitting light, and the front panel may be composed of only one layer or two or more layers. Examples of the front panel 10 include a resin plate-like body (e.g., a resin plate, a resin sheet, a resin film, etc.) and a glass plate-like body (e.g., a glass plate, a glass film, etc.). The front panel 10 can constitute the outermost surface of the display device.

The thickness of the front panel may be, for example, 30 μm or more and 500 μm or less, preferably 40 μm or more and 200 μm or less, and more preferably 50 μm or more and 100 μm or less.

When the front panel is a resin plate, the resin plate is not limited as long as it is light-transmitting. Examples of resins constituting resin plates such as resin films include films formed of polymers such as triacetyl cellulose, acetyl cellulose butyrate, ethylene-vinyl acetate copolymer, propionyl cellulose, butyryl cellulose, acetyl propionyl cellulose, polyester, polystyrene, polyamide, polyetherimide, poly(meth)acrylic, polyimide, polyethersulfone, polysulfone, polyethylene, polypropylene, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl acetal, polyether ketone, polyether ether ketone, polyethersulfone, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate, and polyamideimide. These polymers can be used alone or in combination of two or more. From the viewpoint of improving strength and transparency, the resin film is preferably formed of a polymer such as polyimide, polyamide, or polyamideimide.

The front plate is preferably a resin film or a resin film having a hard coat layer on the resin film. The hard coat layer may be formed on one side of the resin film or on both sides. By providing a hard coat layer, the resin film can be improved in hardness and scratch resistance. The hard coat layer is, for example, a cured layer of an ultraviolet-curable resin. Examples of ultraviolet-curable resins include acrylic resins, silicone resins, polyester resins, urethane resins, amide resins, and epoxy resins. The hard coat layer may contain an additive to improve strength. The additive is not limited, and examples include inorganic fine particles, organic fine particles, and mixtures thereof. When the resin film has hard coat layers on both sides, the composition and thickness of each hard coat layer may be the same as each other or may be different from each other.

When the front panel is a glass plate, the glass plate is preferably tempered glass for displays. The thickness of the glass plate may be, for example, 50 μm or more and 1000 μm or less. By using a glass plate, a front panel having excellent mechanical strength and surface hardness can be formed.

When the optical laminate 100 is used in a display device, the front panel not only has a function of protecting the front surface (screen) of the display device (functions as a window film), but may also have a function as a touch sensor, a blue light blocking function, a viewing angle adjustment function, etc.

(Touch sensor panel)
The polarizing laminate 10 may further include a touch sensor panel. An example of the polarizing laminate 10 including a touch sensor panel is a polarizing laminate having a front plate, a circular polarizing plate, and a touch sensor in this order. The touch sensor panel is not limited as long as it is a panel having a sensor (i.e., a touch sensor) capable of detecting a touched position. The detection method of the touch sensor is not limited, and examples include touch sensor panels of a resistive film type, a capacitive coupling type, an optical sensor type, an ultrasonic type, an electromagnetic induction coupling type, and a surface acoustic wave type. Resistive film type and capacitive coupling type touch sensor panels are preferably used because of their low cost.

One example of a resistive touch sensor is a component that is made up of a pair of substrates arranged opposite each other, an insulating spacer sandwiched between the pair of substrates, a transparent conductive film provided as a resistive film on the inner front surface of each substrate, and a touch position detection circuit. In an image display device equipped with a resistive touch sensor, when the surface of the front panel is touched, the opposing resistive film shorts out and a current flows through the resistive film. The touch position detection circuit detects the change in voltage at this time, and the touched position is detected.

One example of a capacitive coupling touch sensor is a component that is composed of a substrate, a transparent electrode for position detection provided on the entire surface of the substrate, and a touch position detection circuit. In an image display device equipped with a capacitive coupling touch sensor, when the surface of the front panel is touched, the transparent electrode is grounded at the touched point via the capacitance of the human body. The touch position detection circuit detects the grounding of the transparent electrode, and detects the touched position.

The thickness of the touch sensor panel may be, for example, 5 μm or more and 2000 μm or less, preferably 5 μm or more and 100 μm or less, and more preferably 5 μm or more and 50 μm or less.

The touch sensor panel may be a member in which a touch sensor pattern is formed on a substrate film. Examples of the substrate film may be the same as those in the description of the thermoplastic resin film above. The thickness of the touch sensor pattern may be, for example, 1 μm or more and 20 μm or less.

[Method of manufacturing optical laminate]
The optical laminate 100 can be manufactured by a method including a step of bonding each layer. The optical laminate 100 may be manufactured by first constructing the polarizing laminate 10 and then providing a pressure-sensitive adhesive layer on the first surface and the second surface of the polarizing laminate. Alternatively, the optical laminate 100 having the polarizing laminate 10 may be manufactured by a step of providing a pressure-sensitive adhesive layer in advance on a precursor having a surface that forms the first surface of the polarizing laminate, or a step of providing a pressure-sensitive adhesive layer in advance on a precursor having a surface that forms the second surface of the polarizing laminate, and then laminating the precursors.

[Use of display device]
The display device according to the present invention can be used as mobile devices such as smartphones and tablets, televisions, digital photo frames, electronic signs, measuring instruments and gauges, office equipment, medical equipment, computing equipment, and the like.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these.

[Preparation of Polarizing Stack Components]
(Liquid crystal polarizing plate having a polarizer layer which is a liquid crystal layer)
An alignment film composition was applied to one side of a 25 μm-thick TAC film, and the alignment film was formed by drying and exposing to polarized light. A liquid crystal composition containing a liquid crystal polymerizable compound and a dye was applied to the alignment film and dried. Curing was performed by UV irradiation to form a polarizer layer, which is a liquid crystal layer, to obtain a liquid crystal polarizing plate.

(Stretchable polarizing plate having a polarizer layer as a stretched layer)
The PVA film was uniaxially stretched while being immersed in a solution containing iodine to dye it, and then immersed in a solution containing boric acid to crosslink it and dry it to obtain a polarizer layer. A 13 μm-thick transparent film made of COP was attached to one side of the polarizer layer with an adhesive to obtain a stretched polarizing plate.

(1/4 Wave Plate)
An alignment film composition was applied to one side of a PET film, and the alignment film was formed by drying and exposing to polarized light. A liquid crystal composition containing a polymerizable liquid crystal compound was applied to the alignment film and dried. Curing was performed by UV irradiation to form a retardation layer (1/4 wavelength layer), and a 1/4 wavelength plate with a PET film was obtained. A laminate consisting of the alignment film and the retardation layer (1/4 wavelength layer) was used as a 1/4 wavelength plate.

(Half-wave plate)
An alignment film composition was applied to one side of a PET film, and the composition was dried and exposed to polarized light to form an alignment film. A liquid crystal composition containing a polymerizable liquid crystal compound was applied to the alignment film and dried. Curing was performed by UV irradiation to form a retardation layer (1/2 wavelength layer), and a 1/2 wavelength plate with a PET film was obtained. A laminate consisting of the alignment film and the retardation layer (1/2 wavelength layer) was used as a 1/2 wavelength plate.

(Positive C layer)
A vertical alignment film composition was applied to one side of a PET film, and the composition was dried and exposed to light to form an alignment film. A liquid crystal composition containing a polymerizable liquid crystal compound was applied to the alignment film and dried. Curing was performed by ultraviolet irradiation to form a retardation layer (positive C layer), and a positive C layer with a PET film was obtained. The laminate consisting of the alignment film and the retardation layer was also made into a positive C layer.

(Anti-reflection liquid crystal polarizing plate)
A 1/4 wavelength plate with a PET film was attached to the surface of the liquid crystal polarizing plate other than the TAC film side using an adhesive, and then the PET film was peeled off. A positive C retardation layer with a PET film was attached to the surface of the 1/4 wavelength plate using an adhesive, and then the PET film was peeled off. An adhesive composition was applied to the surface of the positive C layer to form an adhesive layer (first adhesive layer), and an anti-reflection liquid crystal polarizing plate (circular polarizing plate) with an adhesive layer was obtained.

(Anti-reflection stretchable polarizing plate)
A 1/2 wavelength plate with a PET film was attached to the surface of the stretched polarizing plate that was not the COP film side using an adhesive layer, and then the PET film was peeled off. A 1/4 wavelength plate with a PET film was attached to the surface of the 1/2 wavelength plate using an adhesive, and then the PET film was peeled off. An adhesive composition was applied to the surface of the 1/4 wavelength plate to form an adhesive layer (first adhesive layer), and an anti-reflection stretched polarizing plate with an adhesive layer (circular polarizing plate) was obtained.

[Example 1]
A surface protection film A (a polyethylene terephthalate (PET) film with an acrylic adhesive layer (second adhesive layer), Fujimori Kogyo Co., Ltd., AY-4212) was laminated to the TAC surface of the anti-reflection liquid crystal polarizing plate with an adhesive layer, and a release film F (50 μm thick PET with a release treatment) was laminated to the adhesive layer surface to produce the optical laminate of Example 1.

<Measurement of each parameter>
(Measurement of 180° peel force A1 and thickness A2 of surface protection film)
A measurement sample was cut out from the overall configuration of the optical laminate of Example 1 with a width of 2.5 cm. The release film was peeled off and removed from the cut optical laminate, and the surface of the adhesive layer (first adhesive layer) was attached to glass. The glass was fixed to a tensile force measuring device (Shimadzu Corporation "AG-1S"). A part of the surface protective film A was peeled off and fixed to the jig of the tensile force measuring device. In a 25°C environment, the surface protective film A was peeled off at a speed of 3.0 m/min so that the peeling angle was 180°, and the peeling force A1 [gf/25 mm] was measured. The peeled surface protective film A was measured for thickness A2 [μm] using a contact film thickness measuring device (Nikon Corporation "MS-5C"). Table 1 shows the values of the 180° peeling force A1, the thickness A2 of the surface protective film, and the parameter A calculated from A1/A2.

(Measurement of 180° peel force B1 and release film thickness B2)
A measurement sample was cut out from the overall configuration of the optical laminate of Example 1 with a width of 2.5 cm. The surface protective film A was removed from the cut optical laminate, and the surface on which the surface protective film A was located was attached to glass. The glass was fixed to a tensile force measuring device (Shimadzu Corporation "AG-1S"), and a part of the release film F (first base film) was peeled off and fixed to the jig of the tensile force measuring device. In a 25°C environment, the release film F was peeled off at a speed of 3.0 m/min so that the peeling angle was 180°, and the peeling force B1 [gf/25 mm] was measured. The peeled release film F was also measured for thickness B2 [μm] using a contact film thickness measuring device (Nikon Corporation "MS-5C"). Table 1 shows the 180° peeling force B1, the thickness B2 of the release film, and the values of the parameter B calculated from B1/B2.

(Measurement of stiffness C)
A measurement sample having a width of 2.54 cm and a length of 8.89 cm was cut from the overall structure of the optical laminate of Example 1. The release film F was removed from the measurement sample to obtain an evaluation laminate, and the evaluation laminate stiffness C [Gurley unit] was measured using a stiffness measuring device (Gurley Bending Stiffness Tester). Table 1 shows the stiffness C and the calculated value of (A/B)×C.

[Example 2]
The optical laminate of Example 2 was prepared in the same manner as in Example 1, except that surface protective film B (PET film with acrylic adhesive layer (second adhesive layer), Fujimori Kogyo Co., Ltd., AY-638) was used instead of surface protective film A, and each parameter was measured.

[Example 3]
An optical laminate of Example 3 was produced in the same manner as in Example 1, except that a surface protective film C (PET film with an acrylic adhesive layer (second adhesive layer), Fujimori Kogyo Co., Ltd., AY(75)-638) was used instead of the surface protective film A, and each parameter was measured.

[Example 4]
The optical laminate of Example 4 was prepared in the same manner as in Example 1, except that surface protective film D (a 125 μm-thick PET (second base film) was coated with a pressure-sensitive adhesive composition to form a 15 μm-thick acrylic pressure-sensitive adhesive layer (second pressure-sensitive adhesive layer)) was used instead of surface protective film A, and each parameter was measured.

[Example 5]
An optical laminate of Example 5 was produced in the same manner as in Example 1, except that release film G, which was a release-treated PET film having a thickness of 38 μm, was used instead of release film F, and each parameter was measured.

[Example 6]
An optical laminate of Example 6 was prepared in the same manner as in Example 3, except that an anti-reflection stretchable polarizing plate with an adhesive layer was used instead of the anti-reflection liquid crystal polarizing plate with an adhesive layer, and each parameter was measured.

[Comparative Example 1]
An optical laminate of Comparative Example 1 was prepared in the same manner as in Example 1, except that a surface protective film E (PET film with an acrylic adhesive layer (second adhesive layer), Fujimori Kogyo Co., Ltd., AY(75)-4212) was used instead of the surface protective film A, and each parameter was measured.

[Comparative Example 2]
An optical laminate of Comparative Example 2 was prepared in the same manner as in Example 5, except that an anti-reflection stretchable polarizing plate with an adhesive layer was used instead of the anti-reflection liquid crystal polarizing plate with an adhesive layer, and each parameter was measured.

[Peeling evaluation]
The optical laminates made in each Example and Comparative Example were placed on an adsorption stage so that the surface protective film was in contact with the surface and fixed by suction. A peeling tape was attached to the corner of the release film (first base film) and lifted so that the peeling angle was 90° from the surface of the optical laminate. When the release film was separated from the surface of the adhesive layer (first adhesive layer), it was judged as normal peeling, and when the surface protective film was peeled from the surface of the polarizing laminate, it was judged as poor peeling (reverse peeling). The results are shown in Table 1.

100, 100' Optical laminate, 10 Polarizing laminate, 21 First adhesive layer, 22 First base film, 30 Surface protective film, 31 Second adhesive layer, 32 Second base film, 200 Display element, 300 Display device.

Claims (4)

a polarizing laminate; a first pressure-sensitive adhesive layer laminated on a first surface of the polarizing laminate; a first base film laminated on a surface of the first pressure-sensitive adhesive layer opposite to the polarizing laminate side; a second pressure-sensitive adhesive layer laminated on a second surface of the polarizing laminate; and a second base film laminated on a surface of the second pressure-sensitive adhesive layer opposite to the polarizing laminate side,
An optical laminate satisfying the relationships of the following formulae (1a) , (2b), and (5b) :
(A/B)×C≧800 (1a)
(A/B)×C≦2000 (2b)
300≦C≦2000 (5b)
[In the formula (1a) , the formula (2b), and the formula (5b) ,
A is a value calculated by A1/A2, where A1 [gf/25 mm] is the 180° peel strength between the polarizing laminate and the second pressure-sensitive adhesive layer, and A2 [μm] is the total thickness of the second base film and the second pressure-sensitive adhesive layer,
B is a value calculated by B1/B2, where B1 [gf/25 mm] is the 180° peel strength between the first pressure-sensitive adhesive layer and the first base film and B2 [μm] is the thickness of the first base film,
C is the stiffness [Gurley unit] of the evaluation laminate in which the first pressure-sensitive adhesive layer, the polarizing laminate, the second pressure-sensitive adhesive layer, and the second base film are laminated in this order. The optical laminate according to claim 1 , wherein A satisfies the following formula (3a):
0.1≦A≦1 (3a) The optical laminate according to claim 1 or 2 , wherein B satisfies the following formula (4a):
0.08≦B≦0.8 (4a) A first base film peeling step of peeling the first base film from the optical laminate according to any one of claims 1 to 3 to expose a surface of the first pressure-sensitive adhesive layer;
and a bonding step of bonding the exposed surface of the first pressure-sensitive adhesive layer to a display element.