JP7345330B2 - Optical laminate and display device using the same - Google Patents

Description

The present invention relates to an optical laminate and a display device using the same.

In recent years, with the rapid spread of liquid crystal display devices, there has been an increase in the number of situations in which they are used under strong sunlight, such as in smartphones and in-vehicle applications. Under such strong sunlight, the user may wear sunglasses with polarizing properties (polarized sunglasses). There were times when the device became dark and visibility was significantly reduced.

Patent Document 1 discloses that a white light emitting diode is used as a backlight of a liquid crystal display device, and a polymer film having a retardation of 3000 to 30000 nm is placed on the viewer side of a polarizer so that the absorption axis of the polarizer and the polymer film are aligned. A visibility improvement method is described in which the display is arranged so that the angle with the slow axis is approximately 45°. According to the visibility improvement method disclosed in Patent Document 1, visibility when observing a screen through polarized sunglasses can be improved. However, when such a polymer film with a high retardation value is used, if it is left in a high-temperature environment for a long time, the front brightness of the liquid crystal display device when displaying black increases, making it difficult to wear polarized sunglasses. When viewing the screen, visibility sometimes deteriorated.

Japanese Patent Application Publication No. 2011-215646

An object of the present invention is to solve the above problems, and to provide an optical laminate that can provide good visibility regardless of the presence or absence of polarized sunglasses even after being placed in a high-temperature environment.

As a result of extensive studies, the present inventors have discovered that a polymer film (hereinafter simply referred to as "high retardation film") having a retardation value of 3000 to 30000 nm is attached to the surface of a polarizing plate used on the viewing side surface of a liquid crystal display device via an adhesive. ) is laminated so that the angle between the absorption axis of the polarizer and the slow axis of the polymer film is approximately 45°, and the liquid crystal display device is left in a high-temperature environment for a long time. The reason why the front luminance of the display device increases when displaying black is considered to be due to the following reasons.

A high retardation film is manufactured by being stretched at a high temperature and a high stretching ratio, and then cooled while residual stress remains. When a polarizing plate to which such a high retardation film is laminated obliquely is stored for a long time in a high temperature environment, residual stress in the oblique direction of the high retardation film is released. This diagonal stress is also applied to the protective film of the polarizer, and in particular, the protective film placed between the polarizer and the liquid crystal display device has a retardation that has an optical axis oblique to the absorption axis of the polarizer. It was assumed that this was due to light leakage.

Based on this estimation, we have found that the above problem can be solved by using a protective film on the liquid crystal device side that has a low photoelastic modulus and a specific value, and have completed the present invention. It is presumed that a protective film with a low photoelastic modulus is less likely to cause a retardation having an oblique optical axis.

The present invention provides an optical laminate and a display device using the same, as exemplified below.

[1] A polarizing plate and a high retardation film are provided in this order,
The polarizing plate has a polarizer and a protective film laminated on a surface of the polarizer opposite to the high retardation film side,
The high retardation film has an in-plane retardation value of 3000 to 30000 nm,
The angle between the slow axis of the high retardation film and the absorption axis of the polarizer is 40° to 50°,
An optical laminate, wherein the protective film has an absolute value of photoelastic coefficient of 8×10 ⁻¹² Pa ⁻¹ or less.

[2] The optical laminate according to [1], wherein the protective film contains at least one selected from the group consisting of (meth)acrylic resin, polystyrene resin, and maleimide resin.

[3] The optical laminate according to [1], wherein the protective film contains a cyclic olefin resin.

[4] The optical laminate according to any one of [1] to [3], wherein the protective film has an in-plane retardation value of 10 nm or less.

[5] The optical laminate according to any one of [1] to [3], wherein the protective film has an in-plane retardation value of 50 nm to 300 nm.

[6] The optical laminate according to any one of [1] to [5], wherein the high retardation film has a thickness of 200 μm or less.

[7] The optical laminate according to any one of [1] to [6], wherein the high retardation film and the polarizing plate are laminated via an adhesive layer.

[8] A display device, in which the optical laminate according to any one of [1] to [7] is laminated on a display element.

According to the present invention, it is possible to provide an optical laminate that can provide good visibility regardless of the presence or absence of polarized sunglasses even after being placed in a high-temperature environment.

It is an example of a schematic cross-sectional view showing the layer structure of an optical laminate. It is an example of a schematic cross-sectional view showing the layer structure of an optical laminate in which front plates are laminated.

(Definition of terms and symbols)
Definitions of terms and symbols used herein are as follows.

(1) Refractive index (nx, ny, nz)
"nx" is the refractive index in the direction in which the in-plane refractive index is maximum (that is, the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the plane, and "nz ” is the refractive index in the thickness direction.

(2) In-plane retardation value The in-plane retardation value (Re[λ]) refers to the in-plane retardation value of the film at 23° C. and wavelength λ (nm). Re[λ] is determined by Re[λ]=(nx−ny)×d, where d (nm) is the thickness of the film.

(3) Retardation value in the thickness direction The in-plane retardation value (Rth[λ]) refers to the retardation value in the thickness direction of the film at 23° C. and wavelength λ (nm). Rth[λ] is determined by Rth[λ]=((nx+ny)/2−nz)×d, where d (nm) is the thickness of the film.

<Optical laminate>
The optical laminate of the present invention includes a polarizing plate and a high retardation film in this order. The polarizer and protective film constituting the polarizing plate can be laminated, for example, via an adhesive layer. Examples of the adhesive layer include a pressure-sensitive adhesive layer and an adhesive layer described below.

Hereinafter, an example of the layer structure of the optical laminate of the present invention will be explained with reference to FIG. Note that, in FIG. 1, adhesive layers for bonding the polarizer 10 and the protective films 11 and 12, respectively, are not shown. The optical laminate 100 shown in FIG. 1 includes a polarizing plate 1 in which a first protective film 11 is laminated on one side of a polarizer 10 and a second protective film 12 is laminated on the other side of the polarizer 10. and a high retardation film 13 are laminated with an adhesive layer 14 in between. Furthermore, the optical laminate 100 has an adhesive layer 15 on the surface of the first protective film 11 opposite to the polarizer 10. The adhesive layer 15 can be an adhesive layer for bonding to a display element or the like.

<Polarizing plate>
In the present invention, a polarizing plate refers to a laminate having a polarizer and at least one protective film. The protective film included in the polarizing plate may have a surface treatment layer such as a hard coat layer, an antireflection layer, and an antistatic layer, which will be described later. The polarizer and the protective film can be laminated, for example, via an adhesive layer or a pressure-sensitive adhesive layer. The members included in the polarizing plate will be explained below.

(1) Polarizer The polarizer 10 included in the polarizing plate 1 absorbs linearly polarized light with a vibration plane parallel to its absorption axis, and absorbs linearly polarized light with a vibration plane perpendicular to the absorption axis (parallel to the transmission axis). It can be an absorptive polarizer that has the property of transmitting light. As the polarizer 10, a polarizer in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol resin film can be suitably used. The polarizer 10 can be produced, for example, through a step of uniaxially stretching a polyvinyl alcohol resin film; a step of dyeing the polyvinyl alcohol resin film with a dichroic dye to adsorb the dichroic dye; and a step in which the dichroic dye is adsorbed. It can be produced by a method including a step of treating a polyvinyl alcohol resin film with a crosslinking liquid such as a boric acid aqueous solution; and a step of washing with water after the treatment with the crosslinking liquid.

As the polyvinyl alcohol resin, a saponified polyvinyl acetate resin can be used. Examples of polyvinyl acetate-based resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate with other monomers that can be copolymerized. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having an ammonium group.

In this specification, "(meth)acrylic" means at least one selected from acrylic and methacryl. The same applies to "(meth)acryloyl", "(meth)acrylate", etc.

The degree of saponification of polyvinyl alcohol resin is usually 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol resin may be modified, and for example, polyvinyl formal or polyvinyl acetal modified with aldehydes can also be used. The average degree of polymerization of the polyvinyl alcohol resin is usually 1,000 to 10,000, preferably 1,500 to 5,000. The average degree of polymerization of polyvinyl alcohol resin can be determined in accordance with JIS K 6726.

A film formed from such a polyvinyl alcohol resin is used as an original film of a polarizer. The method of forming a polyvinyl alcohol resin into a film is not particularly limited, and any known method may be employed. The thickness of the polyvinyl alcohol base film is not particularly limited, but for example, in order to make the thickness of the polarizer 25 μm or less, it is preferable to use one having a thickness of 40 to 75 μm. More preferably, it is 45 μm or less.

The uniaxial stretching of the polyvinyl alcohol resin film can be performed before, simultaneously with, or after dyeing with the dichroic dye. When uniaxial stretching is performed after dyeing, this uniaxial stretching may be performed before or during crosslinking treatment. Further, uniaxial stretching may be performed in these plural steps.

In the uniaxial stretching, it may be uniaxially stretched between rolls having different circumferential speeds, or it may be uniaxially stretched using hot rolls. Further, the uniaxial stretching may be dry stretching in which the film is stretched in the atmosphere, or wet stretching in which the polyvinyl alcohol resin film is stretched in a swollen state using a solvent or water. The stretching ratio is usually 3 to 8 times.

As a method for dyeing a polyvinyl alcohol resin film with a dichroic dye, for example, a method of immersing the film in an aqueous solution containing a dichroic dye is adopted. Iodine and dichroic organic dyes are used as the dichroic dye. In addition, it is preferable that the polyvinyl alcohol resin film is subjected to a immersion treatment in water before the dyeing treatment.

As the crosslinking treatment after dyeing with a dichroic dye, a method of immersing the dyed polyvinyl alcohol resin film in an aqueous solution containing boric acid is usually adopted. When using iodine as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide.

The thickness of the polarizer is usually 50 μm or less, preferably 5 to 30 μm, more preferably 5 to 25 μm, and even more preferably 5 to 20 μm. By setting the thickness of the polarizer within these ranges, it is possible to maintain handleability while preventing breakage or cracking during manufacturing of the polarizer, and to achieve both high optical properties. Further, by setting the thickness of the polarizer to 20 μm or less, it is possible to further suppress a decrease in visibility when placed in a high temperature environment.

As the polarizer, for example, as described in JP-A No. 2016-170368, a polarizer in which a dichroic dye is oriented in a cured film in which a liquid crystal compound is polymerized may be used. As the dichroic dye, one having absorption within the wavelength range of 380 to 800 nm can be used, and it is preferable to use an organic dye. Examples of dichroic dyes include azo compounds. The liquid crystal compound is a liquid crystal compound that can be polymerized while being oriented, and can have a polymerizable group in the molecule. Further, as described in WO2011/024891, a polarizer may be formed from a dichroic dye having liquid crystallinity.

(2) Protective Film The polarizing plate 1 used in the present invention includes a polarizer 10 and a first protective film 11 laminated on the surface of the polarizer 10 opposite to the high retardation film 13 side. The polarizing plate 1 has at least one protective film corresponding to the first protective film 11, and further corresponds to the second protective film 12 laminated on the surface of the polarizer 10 on the high retardation film 13 side. It may have a protective film.

(First protective film 11)
The first protective film 11 has an absolute value of photoelastic coefficient of 8×10 ⁻¹² Pa ⁻¹ or less at a temperature of 23° C. By using the first protective film 11 with such a small photoelastic coefficient, distortion of the first protective film 11 caused by shrinkage stress of the high retardation film 13 when placed in a high-temperature environment causes distortion of the first protective film 11. It is thought that the retardation value is small, and as a result, visibility is good even after being placed in a high-temperature environment, regardless of the presence or absence of polarized sunglasses.

The first protective film 11 is not particularly limited, but may include a translucent (preferably optically transparent) thermoplastic resin having an absolute value of photoelastic coefficient of 8×10 ⁻¹² Pa ⁻¹ or less; For example, polyolefin resins such as chain polyolefin resins (polypropylene resins, etc.) and cyclic polyolefin resins (norbornene resins, etc.); cellulose resins such as triacetyl cellulose and diacetyl cellulose; polyethylene terephthalate, polybutylene terephthalate Polyester resins such as; polycarbonate resins; (meth)acrylic resins such as methyl methacrylate resins; polystyrene resins; polyvinyl chloride resins; acrylonitrile/butadiene/styrene resins; acrylonitrile/styrene resins; Polyvinyl acetate resin; Polyvinylidene chloride resin; Polyamide resin; Polyacetal resin; Modified polyphenylene ether resin; Polysulfone resin; Polyether sulfone resin; Polyarylate resin; Polyamide-imide resin; Polyimide resin; It can be a film made of maleimide resin or the like.

In particular, the first protective film 11 preferably has a small photoelastic coefficient. That is, it is preferable to use a film containing at least one selected from the group consisting of a cyclic polyolefin resin, a (meth)acrylic resin, a polystyrene resin, and a maleimide resin.

The photoelastic coefficient of the first protective film 11 at a temperature of 23° C. is preferably 0.05 to 8.0×10 ⁻¹² Pa ⁻¹ , more preferably 0.1 to 5.0×10 ⁻¹² Pa ^{− 1} , more preferably 0.2 to 3.0×10 ⁻¹² Pa ⁻¹ . Note that the photoelastic coefficient is a value measured by the method described in Examples described later.

The in-plane retardation value of the protective film 11 is preferably adjusted to 10 nm or less or 50 to 300 nm as long as the photoelastic coefficient is within the above range. In particular, it is preferable to use a film with a thickness of 10 nm or less to obtain higher effects. This is because it is estimated that in a film with a retardation, the retardation value changes due to the stress relaxation in the diagonal direction of the high retardation film, and the optical axis also changes, which increases light leakage during black display. Ru. When applying a retardation film as an optical compensation film to a liquid crystal display device, etc., it is also a useful design means to arrange the optical compensation film on another polarizing plate used as a pair.

Cyclic polyolefin resin is a general term for resins that are polymerized using cyclic olefins as polymerization units, and is described, for example, in JP-A-1-240517, JP-A-3-14882, JP-A-3-122137, etc. Examples include resins that are Specific examples of cyclic polyolefin resins include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, and copolymers of cyclic olefins with chain olefins such as ethylene and propylene (typically is a random copolymer), a graft polymer obtained by modifying these with an unsaturated carboxylic acid or a derivative thereof, and a hydrogenated product thereof. Among these, a norbornene resin using a norbornene monomer such as norbornene or a polycyclic norbornene monomer as the cyclic olefin is preferably used.

The method for producing a protective film from a cyclic olefin resin is not particularly limited, and may be appropriately selected depending on the resin. For example, a solvent casting method involves casting a resin dissolved in a solvent onto a metal band or drum, drying and removing the solvent to obtain a film, and a method in which the resin is heated and kneaded to a temperature higher than its melting temperature and extruded through a die. A melt extrusion method is employed in which the film is obtained by cooling with a cooling drum. Among these, the melt extrusion method is preferably employed from the viewpoint of productivity.

The in-plane retardation value Re[550] of the cyclic olefin resin film at a wavelength of 550 nm is preferably 10 nm or less, more preferably 7 nm or less, still more preferably 5 nm or less, particularly preferably 3 nm or less. most preferably 1 nm or less. The thickness direction retardation value Rth[550] of the cyclic olefin resin film at a wavelength of 550 nm is preferably 15 nm or less, more preferably 10 nm or less, still more preferably 5 nm or less, particularly preferably 3 nm or less. , most preferably 1 nm or less.

Next, a method of controlling the retardation value of the cyclic olefin resin film so as to satisfy the above conditions will be explained. In order to make the in-plane retardation value 10 nm or less, it is necessary to minimize the distortion remaining in the in-plane direction during stretching, and in order to make the thickness direction retardation less than the value specified in the present invention. , it is necessary to minimize residual distortion in the thickness direction.

For example, in the solvent casting method, a method is employed in which residual stretching strain in the in-plane direction and residual shrinkage strain in the thickness direction, which occur when the cast resin solution is dried, is alleviated by heat treatment. In addition, in the melt extrusion method, in order to prevent the resin film from being stretched between extrusion from the die and cooling, the distance from the die to the cooling drum is shortened as much as possible, and the extrusion amount and rotational speed of the cooling drum are A method of controlling the film so that it is not stretched is adopted. Furthermore, a method in which residual distortion in the obtained film is alleviated by heat treatment, similar to the melt extrusion method described above, may also be adopted.

Further, a retardation film having a function as an optical compensation film for a liquid crystal display device may be used within a range that satisfies the photoelastic coefficient of the present invention. Such a retardation film can be produced by stretching the cyclic olefin resin film and imparting an in-plane retardation value. Stretching can be performed by known longitudinal uniaxial stretching, tenter transverse uniaxial stretching, simultaneous biaxial stretching, sequential biaxial stretching, etc., and the stretching may be performed so as to obtain a desired retardation value.

For example, in an in-plane switching mode liquid crystal display device, a retardation film with an in-plane retardation adjusted to 50 to 300 nm is preferably used. Specifically, the retardation film described in Japanese Patent Application Publication No. 2010-20287, the retardation film described in Japanese Patent No. 3880996, etc. can be used.

The thickness of the cyclic olefin resin film is preferably 10 μm to 200 μm, more preferably 10 μm to 100 μm, and most preferably 10 μm to 65 μm. If the thickness is less than 10 μm, the strength may decrease. If the thickness exceeds 200 μm, there is a risk that transparency may decrease.

A (meth)acrylic resin is a resin whose main constituent monomer is a compound having a (meth)acryloyl group. Specific examples of (meth)acrylic resins include poly(meth)acrylic esters such as polymethyl methacrylate; methyl methacrylate-(meth)acrylic acid copolymers; methyl methacrylate-(meth)acrylic acid Ester copolymer; Methyl methacrylate-acrylic ester-(meth)acrylic acid copolymer; Methyl (meth)acrylate-styrene copolymer (MS resin, etc.); Methyl methacrylate and alicyclic hydrocarbon group (eg, methyl methacrylate-cyclohexyl methacrylate copolymer, methyl methacrylate-norbornyl (meth)acrylate copolymer, etc.). Preferably, a polymer containing _methyl methacrylate as a main component (50 to 100 % by weight, preferably 70 to 100% by weight).

The in-plane retardation value Re[550] of the (meth)acrylic resin film at a wavelength of 550 nm is preferably 10 nm or less, more preferably 7 nm or less, still more preferably 5 nm or less, and particularly preferably 3 nm. or less, most preferably 1 nm or less. The thickness direction retardation value Rth[550] of the (meth)acrylic resin film at a wavelength of 550 nm is preferably 15 nm or less, more preferably 10 nm or less, even more preferably 5 nm or less, particularly preferably 3 nm or less. and most preferably 1 nm or less. In order to make the in-plane retardation and the thickness direction retardation within such ranges, for example, a (meth)acrylic resin having a glutarimide structure described below can be used.

The (meth)acrylic resin may further have another structural unit. Examples of other structural units include structural units constituting lactone rings, polycarbonates, polyvinyl alcohols, cellulose acetates, polyesters, polyarylates, polyimides, polyolefins, etc., and structural units represented by general formula (1) described below. . Examples of structural units that exhibit negative birefringence include structural units derived from styrene monomers, maleimide monomers, etc., structural units of polymethyl methacrylate, and structural units represented by general formula (3) described below. Can be mentioned.

As the (meth)acrylic resin, a (meth)acrylic resin having a lactone ring structure or a glutarimide structure is preferably used. (Meth)acrylic resins having a lactone ring structure or a glutarimide structure have excellent heat resistance. More preferably, it is a (meth)acrylic resin having a glutarimide structure. By using a (meth)acrylic resin having a glutarimide structure, it is possible to obtain a (meth)acrylic resin film with low moisture permeability, small retardation, and small ultraviolet transmittance, as described above. (Meth)acrylic resins having a glutarimide structure (hereinafter also referred to as glutarimide resins) are disclosed in, for example, JP-A No. 2006-309033, JP-A No. 2006-317560, JP-A No. 2006-328329, and JP-A No. 2006-328329. 2006-328334, 2006-337491, 2006-337492, 2006-337493, 2006-337569, 2007-009182, 2009- It is described in No. 161744. These descriptions are incorporated herein by reference.

Preferably, the glutarimide resin has a structural unit represented by the following general formula (1) (hereinafter also referred to as a glutarimide unit) and a structural unit represented by the following general formula (2) (hereinafter referred to as (meth)). (also referred to as acrylic acid ester unit).

In formula (1), R ¹ and R ² are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ³ is hydrogen, an alkyl group having 1 to 18 carbon atoms, or an alkyl group having 3 to 8 carbon atoms. 12 cycloalkyl group, or a substituent containing an aromatic ring having 5 to 15 carbon atoms. In formula (2), R ⁴ and R ⁵ are each independently hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁶ is hydrogen, an alkyl group having 1 to 18 carbon atoms, or an alkyl group having 3 to 18 carbon atoms. 12 cycloalkyl group, or a substituent containing an aromatic ring having 5 to 15 carbon atoms.

The glutarimide resin may further contain a structural unit represented by the following general formula (3) (hereinafter also referred to as an aromatic vinyl unit), if necessary.

In formula (3), R ⁷ is hydrogen or an alkyl group having 1 to 8 carbon atoms, and R ⁸ is an aryl group having 6 to 10 carbon atoms.

In the above general formula (1), preferably R ¹ and R ² are each independently hydrogen or a methyl group, and R ³ is hydrogen, a methyl group, a butyl group, or a cyclohexyl group, and more preferably , R ¹ is a methyl group, R ² is hydrogen, and R ³ is a methyl group.

The glutarimide resin may contain only a single type of glutarimide unit, or may contain multiple types in which R ¹ , R ² , and R ³ in the general formula (1) are different. good.

The glutarimide unit can be formed by imidizing the (meth)acrylic acid ester unit represented by the above general formula (2). In addition, the glutarimide unit is an acid anhydride such as maleic anhydride, or a half ester of such an acid anhydride and a linear or branched alcohol having 1 to 20 carbon atoms; acrylic acid, methacrylic acid, maleic acid. It can also be formed by imidizing α,β-ethylenically unsaturated carboxylic acids such as , maleic anhydride, itaconic acid, itaconic anhydride, crotonic acid, fumaric acid, and citraconic acid.

In the above general formula (2), preferably R ⁴ and R ⁵ are each independently hydrogen or a methyl group, R ⁶ is hydrogen or a methyl group, and more preferably R ⁴ is hydrogen. , R ⁵ is a methyl group, and R ⁶ is a methyl group.

The above glutarimide resin may contain only a single type of (meth)acrylic acid ester unit, or may contain multiple types in which R ⁴ , R ⁵ and R ⁶ in the above general formula (2) are different. May contain.

The glutarimide resin preferably contains styrene, α-methylstyrene, etc., and more preferably styrene as the aromatic vinyl unit represented by the general formula (3). By having such an aromatic vinyl unit, the positive birefringence of the glutarimide structure can be reduced, and a (meth)acrylic resin film with a lower retardation can be obtained.

The above-mentioned glutarimide resin may contain only a single type of aromatic vinyl unit, or may contain a plurality of types in which R ⁷ and R ⁸ are different.

The content of the glutarimide unit in the glutarimide resin is preferably varied depending on, for example, the structure of ^R3 . The content of glutarimide units is preferably 1% to 80% by weight, more preferably 1% to 70% by weight, even more preferably 1% by weight, based on the total structural units of the glutarimide resin. 60% by weight, particularly preferably 1% to 50% by weight. If the content of glutarimide units is within this range, a (meth)acrylic resin film with excellent heat resistance and low retardation can be obtained.

The content of the aromatic vinyl unit in the glutarimide resin can be appropriately set depending on the purpose and desired properties. Depending on the application, the content of aromatic vinyl units may be zero. When an aromatic vinyl unit is included, its content is preferably 10% to 80% by weight, more preferably 20% to 80% by weight, based on the glutarimide unit of the glutarimide resin. The amount is more preferably 20% to 60% by weight, particularly preferably 20% to 50% by weight. If the content of aromatic vinyl units is within this range, a (meth)acrylic resin film with low retardation and excellent heat resistance and mechanical strength can be obtained.

The above-mentioned glutarimide resin may further be copolymerized with other structural units other than glutarimide units, (meth)acrylic acid ester units, and aromatic vinyl units, if necessary. Other structural units include, for example, structures composed of nitrile monomers such as acrylonitrile and methacrylonitrile, maleimide monomers such as maleimide, N-methylmaleimide, N-phenylmaleimide, and N-cyclohexylmaleimide. Units are listed. These other structural units may be directly copolymerized or graft copolymerized in the glutarimide resin.

The (meth)acrylic resin film may contain any suitable additives depending on the purpose. Examples of additives include antioxidants such as hindered phenol, phosphorus, and sulfur; stabilizers such as light stabilizers, ultraviolet absorbers, weather stabilizers, and heat stabilizers; glass fibers, carbon fibers, etc. Reinforcing materials; near-infrared absorbers; flame retardants such as tris(dibromopropyl) phosphate, triallyl phosphate, and antimony oxide; antistatic agents such as anionic, cationic, and nonionic surfactants; inorganic pigments, organic pigments, Coloring agents such as dyes; organic fillers and inorganic fillers; resin modifiers; plasticizers; lubricants; retardation reducing agents and the like. The types, combinations, contents, etc. of the additives contained can be appropriately set depending on the purpose and desired characteristics.

The method for producing the above (meth)acrylic resin film is not particularly limited, but includes, for example, a (meth)acrylic resin, an ultraviolet absorber, and other polymers and additives as necessary. These can be thoroughly mixed using any appropriate mixing method to form a thermoplastic resin composition in advance, which can then be formed into a film. Alternatively, the (meth)acrylic resin, the ultraviolet absorber, and other polymers and additives as necessary are made into separate solutions and then mixed to form a uniform mixture, and then formed into a film. You may.

To produce the thermoplastic resin composition, the film raw materials are preblended using any appropriate mixer such as an omnimixer, and then the resulting mixture is extruded and kneaded. In this case, the mixer used for extrusion kneading is not particularly limited, and any suitable mixer may be used, such as an extruder such as a single-screw extruder or twin-screw extruder, or a pressure kneader. I can do it.

Examples of the film forming method include any suitable film forming method, such as a solution casting method (solution casting method), a melt extrusion method, a calendar method, a compression molding method, and the like. Melt extrusion methods are preferred. Since the melt extrusion method does not use a solvent, it is possible to reduce manufacturing costs and the impact of solvents on the global environment and work environment.

Examples of the melt extrusion method include the T-die method and the inflation method. The molding temperature is preferably 150 to 350°C, more preferably 200 to 300°C.

When forming a film using the above T-die method, attach a T-die to the tip of a known single-screw extruder or twin-screw extruder, and wind up the extruded film to obtain a roll-shaped film. I can do it. At this time, it is also possible to perform uniaxial stretching by appropriately adjusting the temperature of the winding roll and applying stretching in the extrusion direction. Moreover, simultaneous biaxial stretching, sequential biaxial stretching, etc. can also be performed by stretching the film in a direction perpendicular to the extrusion direction.

The (meth)acrylic resin film may be either an unstretched film or a stretched film as long as the desired retardation can be obtained. If it is a stretched film, it may be either a uniaxially stretched film or a biaxially stretched film. In the case of a biaxially stretched film, it may be either a simultaneous biaxially stretched film or a sequentially biaxially stretched film.

The above-mentioned stretching temperature is preferably close to the glass transition temperature of the thermoplastic resin composition that is the raw material for the film, and specifically, preferably (glass transition temperature -30°C) to (glass transition temperature +30°C), more It is preferably within the range of (glass transition temperature -20°C) to (glass transition temperature +20°C). If the stretching temperature is lower than (glass transition temperature - 30° C.), there is a risk that the obtained film will have a large haze, or the film will tear or crack, making it impossible to obtain a predetermined stretching ratio. On the other hand, if the stretching temperature exceeds (glass transition temperature + 30°C), the resulting film may have large thickness unevenness, and mechanical properties such as elongation, tear propagation strength, and rolling fatigue resistance may not be sufficiently improved. There is a tendency to Furthermore, troubles such as the film sticking to the roll tend to occur more easily.

The above stretching ratio is preferably 1.1 to 3 times, more preferably 1.3 to 2.5 times. When the stretching ratio is within this range, the mechanical properties such as elongation rate, tear propagation strength, and rolling fatigue resistance of the film can be significantly improved. As a result, it is possible to produce a film with small thickness unevenness, substantially zero birefringence (therefore, small retardation), and low haze.

The above (meth)acrylic resin film can be subjected to heat treatment (annealing) etc. after the stretching treatment in order to stabilize its optical isotropy and mechanical properties. Any suitable conditions may be adopted as the conditions for the heat treatment.

The thickness of the (meth)acrylic resin film is preferably 10 μm to 200 μm, more preferably 15 μm to 100 μm, and most preferably 15 μm to 65 μm. If the thickness is less than 10 μm, the strength may decrease. If the thickness exceeds 200 μm, there is a risk that transparency may decrease.

(Second protective film 12)
As the second protective film 12, the above-mentioned resin film described as a film that can be used as the first protective film 11 may be used, or other resin films may be used. For example, chain olefin resin films and cellulose resin films are preferably used.

Chain polyolefin resins include polyethylene resins (polyethylene resins that are homopolymers of ethylene and copolymers mainly composed of ethylene), polypropylene resins (polypropylene resins that are homopolymers of propylene, and copolymers mainly composed of propylene). In addition to homopolymers of chain olefins such as (copolymers), copolymers consisting of two or more types of chain olefins can be mentioned.

Cellulose ester resin is an ester of cellulose and fatty acid. Specific examples of cellulose ester resins include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. Also included are copolymers of these and those in which some of the hydroxyl groups are modified with other substituents. Among these, cellulose triacetate (triacetylcellulose) is particularly preferred.

The thickness of the second protective film 12 is usually 1 to 100 μm, but from the viewpoint of strength and handleability, it is preferably 5 to 60 μm, more preferably 10 to 55 μm, and 15 to 50 μm. is even more preferable.

As described above, the second protective film 12 has a hard coat layer, an antiglare layer, a light diffusion layer, an antireflection layer, a low refractive index layer, and an antistatic layer on its outer surface (the surface opposite to the polarizer). It may be provided with a surface treatment layer (coating layer) such as a layer or an antifouling layer. Note that the thickness of the second protective film 12 includes the thickness of the surface treatment layer.

(3) Adhesive layer The protective films (first protective film 11 and second protective film 12) can be bonded to the polarizer via an adhesive layer that is, for example, an adhesive layer or a pressure-sensitive adhesive layer. As the adhesive forming the adhesive layer, a water-based adhesive, an active energy ray-curable adhesive, or a thermosetting adhesive can be used, and preferably a water-based adhesive or an active energy ray-curable adhesive. As the adhesive layer, those described below can be used.

Examples of the water-based adhesive include adhesives made of polyvinyl alcohol resin aqueous solutions, water-based two-component urethane emulsion adhesives, and the like. Among them, a water-based adhesive made of an aqueous solution of a polyvinyl alcohol resin is preferably used. Polyvinyl alcohol-based resins include vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a homopolymer of vinyl acetate, as well as vinyl alcohol homopolymers obtained by saponifying vinyl acetate and other monomers that can be copolymerized with vinyl acetate. A polyvinyl alcohol copolymer obtained by saponifying a polymer, a modified polyvinyl alcohol copolymer obtained by partially modifying the hydroxyl groups thereof, or the like can be used. The water-based adhesive can contain a crosslinking agent such as an aldehyde compound (such as glyoxal), an epoxy compound, a melamine compound, a methylol compound, an isocyanate compound, an amine compound, or a polyvalent metal salt.

When using a water-based adhesive, it is preferable to perform a drying step to remove water contained in the water-based adhesive after bonding the polarizer and the protective film. After the drying step, a curing step of curing at a temperature of, for example, 20 to 45° C. may be provided.

The above-mentioned active energy ray-curable adhesive is an adhesive containing a curable compound that is cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays, and preferably an ultraviolet curable adhesive. It is.

The curable compound may be a cationically polymerizable curable compound or a radically polymerizable curable compound. Examples of cationic polymerizable curable compounds include epoxy compounds (compounds having one or more epoxy groups in the molecule) and oxetane compounds (compounds having one or more oxetane rings in the molecule). ) or a combination thereof. Examples of radically polymerizable curable compounds include (meth)acrylic compounds (compounds having one or more (meth)acryloyloxy groups in the molecule) and radically polymerizable double bonds. Other vinyl compounds or combinations thereof can be mentioned. A cationically polymerizable curable compound and a radically polymerizable curable compound may be used together. The active energy ray-curable adhesive usually further contains a cationic polymerization initiator and/or a radical polymerization initiator for initiating the curing reaction of the curable compound.

When bonding the polarizer and the protective film, at least one of the bonding surfaces thereof may be subjected to surface activation treatment in order to improve adhesiveness. Surface activation treatments include dry treatments such as corona treatment, plasma treatment, discharge treatment (glow discharge treatment, etc.), flame treatment, ozone treatment, UV ozone treatment, ionizing active ray treatment (ultraviolet treatment, electron beam treatment, etc.) Examples include wet treatments such as ultrasonic treatment using a solvent such as water or acetone, saponification treatment, and anchor coating treatment. These surface activation treatments may be performed alone or in combination of two or more.

When protective films are pasted on both sides of the polarizer, the adhesives for pasting these protective films may be the same type of adhesive or different types of adhesives.

The optical laminate of the present invention may have a structure in which a high retardation film is directly laminated on the polarizer 10 via the adhesive 14. In that case, the second protective film 12 can be omitted.

<High retardation film 13>
The optical laminate of the present invention has a high retardation film 13 to ensure visibility through polarized sunglasses. The high retardation film 13 is made of a transparent thermoplastic resin film having birefringence. The in-plane retardation value Re[550] of the high retardation film 13 at a wavelength of 550 nm is preferably 3000 nm or more, more preferably 5000 nm or more, particularly preferably 7000 nm or more. The upper limit of the in-plane retardation Re[550] of the high retardation film 13 is 30000 nm. By using such a film, it is possible to suppress hue changes depending on the viewing angle when viewing the liquid crystal display device through polarized sunglasses.

The high retardation film 13 can be obtained, for example, by stretching a thermoplastic resin film. Specific thermoplastic resins include polyolefin resins such as polyethylene and polypropylene; cyclic polyolefin resins such as norbornene polymers; polyester resins such as polyethylene terephthalate and polyethylene naphthalate; (meth)acrylic acid, poly(meth) (meth)acrylic acid resins such as methyl acrylate; cellulose ester resins such as triacetyl cellulose, diacetyl cellulose and cellulose acetate propionate; vinyl alcohol resins such as polyvinyl alcohol and polyvinyl acetate; polycarbonate resins; polystyrene Polyarylate resin; Polysulfone resin; Polyether sulfone resin; Polyamide resin; Polyimide resin; Polyether ketone resin; Polyphenylene sulfide resin; Polyphenylene oxide resin, and mixtures and copolymers thereof. etc. can be mentioned. From the viewpoint of availability and transparency, polyethylene terephthalate, cellulose ester, cyclic olefin resin, or polycarbonate are preferred.

A film having a desired retardation value may be obtained by subjecting these thermoplastic resins to a uniaxial or biaxial hot stretching process. The stretching ratio is usually 1.1 to 6 times, preferably 1.1 to 4 times.

Moreover, a method of stretching in an oblique direction is also preferably used so that roll-to-roll manufacturing can be performed. The method for stretching in the diagonal direction is not particularly limited as long as it can continuously tilt the orientation axis at a desired angle, and any known stretching method can be used. Examples of such stretching methods include the methods described in JP-A-50-83482 and JP-A-2-113920. When imparting retardation properties to a film by stretching, the thickness after stretching is determined by the thickness before stretching and the stretching ratio.

The angle between the slow axis of the high retardation film 13 and the absorption axis of the polarizer 10 is 40° to 50°, more preferably 42° to 48°, particularly preferably about 45°. Thereby, when the liquid crystal display device is viewed through polarized sunglasses, a decrease in front brightness can be suppressed.

The thickness of the high retardation film 13 is preferably 200 μm or less, more preferably 150 μm or less, particularly preferably 100 μm or less. By setting the thickness of the high retardation film 13 to 200 μm or less, it is possible to suppress curling of the optical laminate 100, and it is possible to suppress defects such as air bubbles entering during bonding to a liquid crystal display device.

By providing the optical laminate 100 on the viewer side of the liquid crystal cell of the liquid crystal display device, a decrease in visibility when viewing the liquid crystal display device through polarized sunglasses is suppressed without requiring any other film with a high retardation. can do. Specifically, it is possible to suppress a decrease in front brightness and a change in hue (color shift) depending on the viewing angle. A hard coat layer or an anti-glare layer may be laminated on the high retardation film 13 if necessary.

<Adhesive layer 14>
The adhesive layer 14 is a layer on which the polarizing plate 1 and the high retardation film 13 are laminated. The adhesive layer 14 can be composed of an adhesive composition whose main component is a resin such as (meth)acrylic, rubber, urethane, ester, silicone, or polyvinyl ether. Among these, a pressure-sensitive adhesive composition whose base polymer is a (meth)acrylic resin having excellent transparency, weather resistance, heat resistance, etc. is suitable. The adhesive composition may be of an active energy ray curable type or a thermosetting type. The thickness of the adhesive layer is usually 3 to 30 μm, preferably 3 to 25 μm.

Examples of the (meth)acrylic resin (base polymer) used in the adhesive composition include butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, and 2-(meth)acrylate. Polymers or copolymers containing one or more types of (meth)acrylic esters such as ethylhexyl as monomers are preferably used. It is preferable to copolymerize a polar monomer with the base polymer. 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 include monomers having carboxyl groups, hydroxyl groups, amide groups, amino groups, epoxy groups, etc., such as meth)acrylates.

The pressure-sensitive adhesive composition may contain only the above base polymer, but usually further contains a crosslinking agent. Examples of crosslinking agents include metal ions with a valence of two or more that form carboxylic acid metal salts with carboxyl groups; polyamine compounds that form amide bonds with carboxyl groups; polyamine compounds that form amide bonds with carboxyl groups; Examples include epoxy compounds and polyols that form ester bonds with carboxyl groups; polyisocyanate compounds that form amide bonds with carboxyl groups. Among these, polyisocyanate compounds are preferred.

The storage modulus of the adhesive layer 14 is preferably 0.001 to 0.350 MPa, more preferably 0.001 to 0.200 MPa, even more preferably 0.001 to 0.100 MPa, at a frequency of 1 Hz and a temperature of 23° C. Particularly preferred is 0.010 to 0.100 MPa. If the storage elastic modulus exceeds the above range, the shrinkage stress of the high retardation film 13 under high temperature environment will not be sufficiently relaxed, causing distortion of the first protective film 11, and normal visibility without polarized sunglasses will be impaired. descend. Moreover, if it falls below the above range, problems such as peeling may occur in a high temperature environment.

The thickness of the adhesive layer 14 is preferably 5 to 200 μm, more preferably 7 to 100 μm, even more preferably 8 to 80 μm, and particularly preferably 10 to 50 μm.

<Display device>
The optical laminate of the present invention can be laminated onto a liquid crystal cell via an adhesive 15 to form a liquid crystal display device. The adhesive 15 may have the composition, characteristics, and thickness described above as the adhesive 14, and may be the same as or different from the adhesive layer 14.

<Front board>
The optical laminate 100 may be used with a front plate disposed on its viewing side surface. The front plate can be laminated to the optical laminate 100 via an adhesive layer. Examples of the adhesive layer include the above-mentioned pressure-sensitive adhesive layer and adhesive layer. FIG. 2 is a sectional view showing the structure of a laminate in which a front plate 4 is disposed on the viewing side surface of the optical laminate 100. As shown in FIG. 2, the front plate 4 can be laminated on the high retardation film 13 in the optical laminate 100 with an adhesive layer 16 interposed therebetween.

Examples of the front plate include glass or a resin film that includes a hard coat layer on at least one surface. As the glass, for example, high transmittance glass or tempered glass can be used. Especially when using a thin transparent surface material, chemically strengthened glass is preferable. The thickness of the glass can be, for example, 100 μm to 5 mm.

The front panel, which includes a hard coat layer on at least one surface of the resin film, is not rigid like existing glass, but can have flexible characteristics. The thickness of the hard coat layer is not particularly limited, and may be, for example, 5 to 100 μm.

Examples of resin films include cycloolefin derivatives having monomer units containing cycloolefins such as norbornene or polycyclic norbornene monomers, cellulose (diacetyl cellulose, triacetyl cellulose, acetyl cellulose butyrate, isobutyl ester cellulose) , propionylcellulose, butyrylcellulose, acetylpropionylcellulose) ethylene-vinyl acetate copolymer, polycycloolefin, polyester, polystyrene, polyamide, polyetherimide, polyacrylic, polyimide, polyamideimide, polyethersulfone, polysulfone, polyethylene, Polypropylene, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl acetal, polyetherketone, polyetheretherketone, polyethersulfone, polymethylmethacrylate, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycarbonate It may also be a film made of a polymer such as polyurethane, epoxy, or the like. As the resin film, an unstretched, uniaxially or biaxially stretched film can be used. These polymers can be used alone or in a mixture of two or more. Examples of resin films include polyamide-imide films or polyimide films that have excellent transparency and heat resistance, uniaxially or biaxially stretched polyester films, and cycloolefin derivative films that have excellent transparency and heat resistance and can accommodate larger films. , polymethyl methacrylate films, and triacetyl cellulose and isobutyl ester cellulose films that are transparent and optically free of anisotropy are preferred. The thickness of the resin film may be 5 to 200 μm, preferably 20 to 100 μm.

The hard coat layer can be formed by curing a hard coat composition containing a reactive material that forms a crosslinked structure by irradiating light or thermal energy. The hard coat layer can be formed by curing a hard coat composition that simultaneously contains a photocurable (meth)acrylate monomer or oligomer and a photocurable epoxy monomer or oligomer. The photocurable (meth)acrylate monomer may include one or more selected from the group consisting of epoxy (meth)acrylate, urethane (meth)acrylate, and polyester (meth)acrylate. The epoxy (meth)acrylate can be obtained by reacting an epoxy compound with a carboxylic acid having a (meth)acryloyl group.

The hard coat composition may further include one or more selected from the group consisting of a solvent, a photoinitiator, and an additive. The additive may include one or more selected from the group consisting of inorganic nanoparticles, leveling agents, and stabilizers, as well as other components commonly used in the art, such as antiseptics. It may further contain oxidizing agents, UV absorbers, surfactants, lubricants, antifouling agents, and the like.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. In the examples, parts and percentages indicating content or amount used are based on weight unless otherwise specified. In addition, the measurement of each physical property in the following examples was performed by the following method.

[Measuring method]
(1) Method for measuring film thickness The film thickness was measured using a digital micrometer MH-15M manufactured by Nikon Corporation.

(2) Method for measuring phase difference value Measurement was performed using a phase difference measuring device KOBRA-WPR (manufactured by Oji Scientific Instruments Co., Ltd.).

(3) Method for measuring photoelastic coefficient Using a phase difference measuring device KOBRA-WPR (manufactured by Oji Scientific Instruments Co., Ltd.), a sample (size 1.5 cm x 6 cm) was held at both ends and subjected to stress (0.5 N to 8 N). ), the retardation value at the center of the sample (23° C./wavelength 550 nm) was measured and calculated from the slope of the function of stress and retardation value.

(4) Measuring method of storage modulus:
The storage modulus (G') of the adhesive layer was measured according to (I) to (III) below.

(I) Take out two samples of 25±1 mg each from the adhesive layer and shape each sample into a roughly ball shape.

(II) The two samples obtained in the above (I) are attached to the upper and lower surfaces of an I-shaped jig, and both the upper and lower surfaces are sandwiched between the L-shaped jig. The configuration of the measurement sample is L-shaped jig/adhesive/I-shaped jig/adhesive/L-shaped jig.

(III) The storage modulus (G') of the sample prepared in this way was measured using a dynamic viscoelasticity measurement device [DVA-220, manufactured by IT Keisaku Control Co., Ltd.] at a temperature of 23°C, a frequency of 1Hz, and an initial temperature of 1Hz. Measurement was carried out under the condition of 1N strain.

(5) How to measure brightness:
Measurement was performed using a spectral radiance meter SR-UL1 manufactured by Topcon Corporation. Note that the measurement was performed in a 2° field of view.

[Production Example 1] Production of Polarizer 1 A 75 μm thick polyvinyl alcohol film made of polyvinyl alcohol with an average degree of polymerization of about 2,400 and a degree of saponification of 99.9 mol% or more was uniaxially stretched to about 5 times in a dry manner. Then, while maintaining the tension state, it was immersed in pure water at 60°C for 1 minute, and then immersed in an aqueous solution with a weight ratio of iodine/potassium iodide/water of 0.05/5/100 at 28°C for 60 seconds. . Thereafter, it was immersed in an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 8.5/8.5/100 at 72°C for 300 seconds. Subsequently, it was washed with pure water at 26° C. for 20 seconds and then dried at 65° C. to obtain a polarizer 1 with a thickness of 28 μm in which iodine was adsorbed and oriented on polyvinyl alcohol.

[Production Example 2] Production of Polarizer 2 A 50 μm thick polyvinyl alcohol film made of polyvinyl alcohol with an average degree of polymerization of about 2,400 and a degree of saponification of 99.9 mol% or more was uniaxially stretched to about 5 times in a dry manner. Then, while maintaining the tension state, it was immersed in pure water at 60°C for 1 minute, and then immersed in an aqueous solution with a weight ratio of iodine/potassium iodide/water of 0.05/5/100 at 28°C for 60 seconds. . Thereafter, it was immersed in an aqueous solution having a weight ratio of potassium iodide/boric acid/water of 8.5/8.5/100 at 72°C for 300 seconds. Subsequently, it was washed with pure water at 26° C. for 20 seconds and then dried at 65° C. to obtain a polarizer 2 with a thickness of 18 μm in which iodine was adsorbed and oriented on polyvinyl alcohol.

[Preparation of protective film]
Protective film A:
Triacetyl cellulose film with a thickness of 40 μm [trade name “KC4UYW” manufactured by Konica Minolta Opto Co., Ltd.].

Protective film B:
100 parts by weight of the imidized MS resin pellets (weight average molecular weight: 105,000) described in Production Example 1 of JP-A No. 2010-284840 were dried at 100.5 kPa and 100° C. for 12 hours, and then dried in a single-screw extruder. It was extruded from a T-die at a die temperature of 270° C. to form a film (thickness: 160 μm). Further, the film was stretched in an atmosphere at 150°C in the direction of transport (thickness: 80 μm), and then stretched in an atmosphere at 150°C in a direction perpendicular to the direction of transport of the film. ) Acrylic resin film) was obtained. The in-plane retardation value Re of the protective film B at a wavelength of 550 nm was 0.5 nm, and the retardation value Rth in the thickness direction was 0.82 nm. The photoelastic coefficient of the obtained film was 2.0×10 ⁻¹² Pa ⁻¹ .

Protective film C:
A protective film C with a thickness of 40 μm was prepared in the same manner as the protective film B except that the imidized MS resin pellets were replaced with transparent pellets of the acrylic copolymer described in Comparative Example 1 of JP-A No. 2008-191426. ((meth)acrylic resin film) was obtained. The in-plane retardation value Re of the protective film C at a wavelength of 550 nm was 0.8 nm, and the retardation value Rth in the thickness direction was 1.02 nm. The photoelastic coefficient of the obtained film was 2.1×10 ⁻¹² Pa ⁻¹ .

Protective film D:
A protective film D with a thickness of 40 μm was prepared in the same manner as the protective film B except that the imidized MS resin pellets were replaced with transparent pellets of the acrylic copolymer described in Example 1 of JP-A No. 2008-191426. ((meth)acrylic resin film) was obtained. The in-plane retardation value Re of the protective film D at a wavelength of 550 nm was 0.4 nm, and the retardation value Rth in the thickness direction was 0.73 nm. The photoelastic coefficient of the obtained film was 1.3×10 ⁻¹² Pa ⁻¹ .

Protective film E:
Norbornene-based resin film with a thickness of 23 μm [trade name "ZF14-023" manufactured by Nippon Zeon Co., Ltd.]. The in-plane retardation value Re of the protective film E at a wavelength of 550 nm was 0.7 nm, and the retardation value Rth in the thickness direction was 4.2 nm. The photoelastic coefficient was 1.6×10 ⁻¹² Pa ⁻¹ .

Protective film F:
A roll-shaped quarter-wave plate was produced in the same manner as the 45° oblique quarter-wave plate A1 described in Production Example 3 of International Publication 2017/094485, except that the stretching direction was changed to the longitudinal direction. This quarter wavelength plate (protective film F) had a thickness of 35 μm, a slow axis in the longitudinal direction, and an in-plane retardation Re of 136 nm. Further, the photoelastic coefficient of the obtained film was 4.0×10 ⁻¹² Pa ⁻¹ .

Protective film G:
A roll-shaped quarter-wave plate was produced in the same manner as the 45° oblique quarter-wave plate B4 described in Production Example 5 of International Publication 2017/094485, except that the stretching direction was changed to the longitudinal direction. The thickness of this quarter-wave plate (protective film G) was 47 μm, the slow axis was in the longitudinal direction, and the in-plane retardation Re was 140 nm. Further, the photoelastic coefficient of the obtained film was 6.0×10 ⁻¹² Pa ⁻¹ .

Protective film H:
Triacetyl cellulose film with a thickness of 20 μm [product name “ZRG20SL” manufactured by Fuji Film Corporation]. The in-plane retardation value Re of the protective film B at a wavelength of 550 nm was 1.1 nm, and the retardation value Rth in the thickness direction was 1.3 nm. The photoelastic coefficient was 9.4×10 ⁻¹² Pa ⁻¹ .

[Preparation of adhesive]
50 g of modified PVA resin containing an acetoacetyl group (manufactured by Mitsubishi Chemical Corporation: Gosenex Z-410) was dissolved in 950 g of pure water, heated at 90°C for 2 hours, cooled to room temperature, and PVA solution A was dissolved. Obtained.

Next, the PVA solution A, maleic acid, glyoxal, and pure water were blended so that each compound had the following concentration to prepare a PVA adhesive.

PVA concentration 3.0% by weight
Maleic acid 0.01% by weight
Glyoxal 0.15% by weight
[Preparation of high retardation film]
Cosmoshine SRF (Super Retardation Film) manufactured by Toyobo Co., Ltd. (thickness: 80 μm) was used. The in-plane retardation value Re[550] was 8400 nm.

[Preparation of adhesive]
Adhesive A: Commercially available sheet-like acrylic adhesive with a thickness of 15 μm (storage modulus 0.06 MPa)
Adhesive B: Commercially available sheet-like acrylic adhesive with a thickness of 25 μm (storage modulus 0.06 MPa)
[Example 1]
Adhesive A was applied to one side of the polarizer 1 obtained in Production Example 1 to form a protective film A (second protective film), and adhesive A was applied to the other side of the polarizer to form a protective film B (second protective film). 1 protective film) were bonded to each other. Thereafter, the polarizing plate A was obtained by drying. Note that when these materials were bonded together, corona treatment was applied to the bonding surfaces of each material.

Adhesive A was laminated on one side of the high retardation film. Note that when these materials were bonded together, corona treatment was applied to the bonding surfaces of each material.

The surface of the protective film A of the polarizing plate thus produced and the adhesive surface of the high retardation film are laminated together so that the angle θ between the absorption axis of the polarizer and the slow axis of the high retardation film is 45°. Laminated body A was produced. Note that when these materials were bonded together, corona treatment was applied to the bonding surfaces of each material.

Finally, adhesive B was bonded to the protective film B surface of the obtained optical laminate A. Note that when these materials were bonded together, corona treatment was applied to the bonding surfaces of each material.

[Examples 2 to 8 and Comparative Example 1]
Adhesive B Optical laminates B to I (Examples 2 to 8 and Comparative Example 1) were produced.

[Reference example 1]
Adhering was carried out in the same manner as above, except that the optical laminate A with adhesive B of Example 1 was laminated so that the angle between the absorption axis of the polarizing plate and the slow axis of the high retardation film was 90°. An optical laminate J with Agent B (Reference Example 1) was produced.

[Reference example 2]
Adhesive A was applied to one side of the polarizer obtained in Production Example 1 to attach protective film A, and adhesive A was applied to the other side of the polarizer to attach protective film H. Thereafter, the polarizing plate K was obtained by drying. Note that when these materials were bonded together, corona treatment was applied to the bonding surfaces of each material.

Adhesive B was bonded to the protective film H side of the obtained optical laminate K to obtain a back polarizing plate with an adhesive layer. Note that when these materials were bonded together, corona treatment was applied to the bonding surfaces of each material.

(Preparation of evaluation sample A)
The optical laminate A with adhesive B was cut into a size of 20 mm x 20 mm, and was bonded to a non-alkali glass with a thickness of 0.7 mm and a size of 30 mm x 30 mm via adhesive B. Optical laminate K with adhesive B (without high retardation film laminated) was cut into a size of 20 mm x 20 mm, and a polarizing plate was placed on the side of the above sample on which the alkali-free glass optical laminate A was not laminated. An evaluation sample A was prepared by bonding the optical laminate K through the adhesive B so that the absorption axes were crossed nicols.

(Preparation of evaluation samples B to K)
Evaluation samples B to K were produced in the same manner as in evaluation sample A except that optical laminate A was replaced with optical laminates B to K, respectively.

(Evaluation of black luminance change)
The side to which the optical laminate K of the evaluation samples A to K prepared above was attached was placed on the irradiation surface of a white backlight module with a brightness of 20,000 cd/m ² , and the brightness was adjusted from the evaluation sample side (high retardation film) side. After measurement (black brightness 1), it was stored in a heated environment at a temperature of 95°C for 240 hours, and after cooling to room temperature, the brightness was measured again (black brightness 2), and the rate of change (%) of black brightness 2 relative to black brightness 1 was calculated. This was calculated and defined as the change in black luminance. in particular,
Black brightness change (%) = {|Black brightness 2 - Black brightness 1|/Black brightness 1} x 100
The change in black luminance was determined by The evaluation results are shown in Table 1.

The following is clear from the results shown in Table 1.

1. An optical laminate with a high retardation film laminated at 45° may have increased black brightness after a high-temperature durability test, but the first protective film with a photoelastic coefficient of 8.0×10 ⁻¹² Pa ⁻¹ or less By using this, it is possible to suppress an increase in black brightness after a high-temperature durability test.

2. In addition to the above, by setting the thickness of the polarizer to 20 μm or less (using polarizer 2), it is possible to further suppress an increase in black brightness after the high temperature durability test.

Reference Signs List 1 polarizing plate, 4 front plate, 10 polarizer, 11 first protective film, 12 second protective film, 13 high retardation film, 14, 15, 16 adhesive layer, 100 optical laminate.

Claims (6)

A display device in which an optical laminate is laminated on a display element via an adhesive layer,
The optical laminate includes:
A polarizing plate and a high retardation film are provided in this order,
The polarizing plate has a polarizer with a thickness of 20 μm or less and a protective film laminated on the surface of the polarizer opposite to the high retardation film side,
The high retardation film has an in-plane retardation value of 3000 to 30000 nm at a wavelength of 550 nm,
The angle between the slow axis of the high retardation film and the absorption axis of the polarizer is 40° to 50°,
The absolute value of the photoelastic coefficient of the protective film is 3.0×10 ⁻¹² Pa ⁻¹ or less ,
The high retardation film and the polarizing plate are laminated via an adhesive layer having a storage modulus of 0.010 to 0.100 MPa,
The optical laminate is a display device, wherein the protective film is arranged closer to the display element than the high retardation film. The display device according to claim 1, wherein the protective film contains at least one selected from the group consisting of (meth)acrylic resin, polystyrene resin, and maleimide resin. The display device according to claim 1, wherein the protective film contains a cyclic olefin resin. The display device according to claim 1, wherein the protective film has an in-plane retardation value of 10 nm or less at a wavelength of 550 nm. The display device according to claim 1, wherein the protective film has an in-plane retardation value of 50 nm to 300 nm at a wavelength of 550 nm. The display device according to claim 1, wherein the high retardation film has a thickness of 200 μm or less.

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