TWI849200B - Optical layered body and display device using the same - Google Patents

Abstract

An objective of the present invention is to provide an optical layered body which can have good visibility regardless of presence or absence of polarized sunglasses even after being placed in a high temperature environment.

As a solution, the present invention provides an optical layered body provided with a polarizing plate and a high retardation film in this order, the polarizing plate has a protective film laminated on the opposite side of the polarizer and the high retardation film side of the polarizer, the in-plane retardation value of the high retardation film is 3000 to 30,000 nm, the slow axis of the high retardation film and the absorption axis of the polarizer make an angle of 40° to 50°, the absolute value of the photoelastic coefficient of the protective film is 8×10^-12Pa^-1 or less.

Description

Optical laminate and display device using the same

The present invention relates to an optical multilayer body and a display device using the optical multilayer body.

In recent years, with the rapid popularization of liquid crystal display devices, the use of smart phones or car applications under strong sunlight has increased. When using such strong sunlight, wearing sunglasses with polarized characteristics (polarized sunglasses), when visually confirming the liquid crystal display device through polarized sunglasses, the liquid crystal display device will become darker due to different visual confirmation directions, and visual confirmation will be significantly reduced.

Patent document 1 describes a method for improving visual confirmation, which uses a white light-emitting diode as the backlight of a liquid crystal display device, and on the visual confirmation side of the polarizer, a polymer film with a delay of 3000 to 30000nm is configured and used in a manner such that the angle between the absorption axis of the polarizer and the slow axis of the polymer film is about 45°. According to the method for improving visual confirmation of patent document 1, the visual confirmation when observing the screen through polarized sunglasses can be improved. However, when using a polymer film with such a high phase difference value, when placed in a high temperature environment for a long time, the front brightness of the liquid crystal display device when it is displayed in black will increase, and when the screen is visually confirmed without wearing polarized sunglasses, the visual confirmation will decrease.

[Prior Art Literature]

[Patent Literature]

Patent document 1: Japanese Patent Publication No. 2011-215646.

The purpose of the present invention is to provide a solution to the above-mentioned problem, which is about an optical layered body that can have good visual confirmation even after being placed in a high temperature environment, regardless of the presence of polarized sunglasses.

As a result of diligent research, the inventors of the present invention have found that when a liquid crystal display device in which a polymer film with a phase difference value of 3000 to 30000nm (hereinafter referred to as "high phase difference film") is bonded to the surface of the polarizing plate used on the visual confirmation side of the liquid crystal display device via an adhesive in such a way that the angle between the absorption axis of the polarizing plate and the slow axis of the polymer film is about 45° is placed in a high temperature environment for a long time, the front brightness of the liquid crystal display device in black display will increase. The reason is believed to be as follows.

High phase difference film is made by stretching at high temperature and high stretching ratio, and cooling under residual stress. If the polarizing plate with such high phase difference film is stored in a high temperature environment for a long time, the oblique residual stress of the high phase difference film will be released. It is speculated that the oblique stress will also be applied to the protective film of the polarizing plate, especially the protective film arranged between the polarizer and the liquid crystal display device, which will produce a phase difference with an oblique optical axis relative to the absorption axis of the polarizer, and will cause light leakage.

Based on the above speculation, it is found that if the protective film on the liquid crystal device side has a low photoelastic modulus and a specific value, the above problem can be solved, thereby completing the present invention. It is speculated that a protective film with a low photoelastic modulus is less likely to produce a phase difference with a tilted optical axis.

The present invention provides the optical multilayer body exemplified below and a display device using the optical multilayer body.

[1] An optical stack comprises a polarizing plate and a high retardation film in sequence, wherein the polarizing plate comprises a polarizer and a protective film laminated on the surface of the polarizer opposite to the high retardation film, the in-plane retardation value of the high retardation film is 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°, and the absolute value of the photoelastic coefficient of the protective film is less than 8×10 ^-12 Pa ^-1 .

[2] The optical laminate as described in [1], wherein the protective film contains at least one selected from the group consisting of (meth)acrylic resin, polystyrene resin, and butylene diimide resin.

[3] The optical layered structure as described in [1], wherein the protective film contains a cyclic olefin resin.

[4] An optical multilayer as described in any one of [1] to [3], wherein the in-plane phase difference of the protective film is less than 10 nm.

[5] An optical multilayer as described in any one of [1] to [3], wherein the in-plane phase difference of the protective film is 50nm to 300nm.

[6] An optical multilayer as described in any one of [1] to [5], wherein the thickness of the high phase difference film is less than 200 μm.

[7] An optical laminate as described in any one of [1] to [6], wherein the high phase difference film and the polarizing plate are laminated via an adhesive layer.

[8] A display device having an optical multilayer body as described in any one of [1] to [7] stacked on a display element.

According to the present invention, an optical laminate can be provided, which can have good visual confirmation even after being placed in a high temperature environment, regardless of the presence of polarized sunglasses.

1: Polarizing plate

4:Front panel

10: Polarizer

11: 1st protective film

12: Second protective film

13: High phase difference film

14, 15, 16: Adhesive layer

100: Optical multilayers

Figure 1 is an example of a schematic cross-sectional view showing the layer structure of an optical laminate.

Figure 2 is an example of a schematic cross-sectional view showing the layer structure of the optical laminate of the laminate front panel.

(Definition of terms and symbols)

The definitions of terms and symbols in this manual are as follows.

(1) Refractive index (nx, ny, nz)

"nx" is the refractive index in the direction with the largest refractive index in the plane (i.e. the slow axis direction), "ny" is the refractive index in the direction orthogonal to the slow axis in the plane, and "nz" is the refractive index in the thickness direction.

(2) In-plane phase difference

The in-plane phase difference (Re[λ]) is the phase difference in the film plane at 23°C and wavelength λ (nm). Re[λ] is obtained by Re[λ]=(nx-ny)×d when the film thickness is d (nm).

(3) Phase difference in thickness direction

The phase difference in the thickness direction (Rth[λ]) is the phase difference in the film thickness direction at 23°C and wavelength λ(nm). Rth[λ] is obtained by Rth[λ]=((nx+ny)/2-nz)×d when the film thickness is d(nm).

<Optical layered structure>

The optical laminate of the present invention sequentially comprises a polarizing plate and a high phase difference film. The polarizer and the protective film constituting the polarizing plate can be laminated via a bonding layer, for example. The bonding layer can be, for example, an adhesive layer or a bonding agent layer described later.

An example of the layer structure of the optical laminate of the present invention is described below with reference to FIG1. In addition, FIG1 does not show the bonding layer for bonding the polarizer 10 and the protective films 11 and 12. The optical laminate 100 shown in FIG1 has the following layer structure: the polarizer 1 is a first protective film 11 laminated on one side of the polarizer 10 and a second protective film 12 laminated on the other side of the polarizer 10, and the polarizer 1 and the high phase difference film 13 are laminated via an adhesive layer 14. In addition, 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 used to adhere to a display element, etc.

<Polarizing plate>

In the present invention, the polarizing plate refers to a laminate having a polarizer and at least one protective film. The protective film of the polarizing plate may have a surface treatment layer such as a hard coating layer, an anti-reflection layer, and an anti-static layer described below. The polarizer and the protective film may be laminated, for example, through a bonding agent layer or an adhesive layer. The components of the polarizing plate are described below.

(1) Polarizer

The polarizer 10 of the polarizing plate 1 may be an absorption-type polarizer, which has the property of absorbing linear polarization having a vibration plane parallel to its absorption axis and transmitting linear polarization having a vibration plane orthogonal to the absorption axis (parallel to the transmission axis). The polarizer 10 is suitable for use in a polarizer in which a dichroic dye is adsorbed and aligned through a uniaxially stretched polyvinyl alcohol resin film. The polarizer 10 may be manufactured, for example, by a method comprising the following steps, namely, a step of uniaxially stretching a polyvinyl alcohol resin film; a step of dyeing the polyvinyl alcohol resin film with a dichroic dye to thereby adsorb the dichroic dye; a step of treating the polyvinyl alcohol resin film adsorbing the dichroic dye with a crosslinking liquid such as a boric acid aqueous solution; and a step of washing with water after the crosslinking liquid treatment.

Polyvinyl alcohol resins can be saponified polyvinyl acetate resins. Polyvinyl acetate resins include copolymers with other monomers copolymerizable with vinyl acetate, in addition to polyvinyl acetate homopolymers. Examples of other monomers copolymerizable with vinyl acetate include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, and (meth)acrylamides having ammonium groups.

In this specification, "(meth)acrylic acid" refers to at least one selected from acrylic acid and methacrylic acid. The same applies to "(meth)acryl", "(meth)acrylate", etc.

The saponification degree of polyvinyl alcohol resin is usually 85 to 100 mol%, preferably 98 mol% or more. Polyvinyl alcohol resin can be modified, for example, polyvinyl formal or polyvinyl acetaldehyde modified with aldehydes can be used. The average polymerization degree of polyvinyl alcohol resin is usually 1000 to 10000, preferably 1500 to 5000. The average polymerization degree of polyvinyl alcohol resin can be obtained according to JIS K 6726.

The polyvinyl alcohol resin film is used as a raw material film for a polarizer. The method for making a polyvinyl alcohol resin film is not particularly limited, and a known method can be used. The thickness of the polyvinyl alcohol raw material film is not particularly limited, but for example, in order to make the thickness of the polarizer less than 25μm, it is preferably 40 to 75μm. More preferably, it is less than 45μm.

The uniaxial stretching of the polyvinyl alcohol-based resin film can be performed before, during, or after dyeing with a dichroic pigment. When the uniaxial stretching is performed after dyeing, the uniaxial stretching can be performed before or during the crosslinking treatment. Furthermore, the uniaxial stretching can be performed in multiple stages.

During uniaxial stretching, it can be done between rollers with different circumferential speeds, or it can be done using hot rollers. In addition, uniaxial stretching can be done by dry stretching in the atmosphere, or by wet stretching using a solvent or water to stretch the polyvinyl alcohol resin film in a swollen state. The stretching ratio is usually 3 to 8 times.

The method of dyeing the polyvinyl alcohol resin film with a dichroic dye can be, for example, a method of immersing the film in an aqueous solution containing a dichroic dye. The dichroic dye is iodine or a dichroic organic dye. In addition, the polyvinyl alcohol resin film is preferably subjected to a water immersion treatment before the dyeing treatment.

The crosslinking treatment after dichroic dyeing is usually carried out by immersing the dyed polyvinyl alcohol resin film in an aqueous solution containing boric acid. When iodine is used as the dichroic dye, the aqueous solution containing boric acid preferably contains potassium iodide.

The thickness of the polarizer is usually less than 50μm, preferably 5 to 30μm, more preferably 5 to 25μm, and even more preferably 5 to 20μm. By making the thickness of the polarizer within these ranges, cracks or breakages during the manufacture of the polarizer can be prevented and the handling properties can be maintained, and high optical properties can be achieved. In addition, by making the thickness of the polarizer less than 20μm, the reduction in visual confirmation when placed in a high temperature environment can be further suppressed.

Polarizers can use, for example, dichroic dyes aligned in a liquid crystal compound polymerization cured film as described in Japanese Patent Publication No. 2016-170368. Dichroic dyes can be used that have absorption in the wavelength range of 380 to 800nm, preferably organic dyes. Examples of dichroic dyes include azo compounds. Liquid crystal compounds are liquid crystal compounds that can be polymerized under alignment and can have polymerizable groups in the molecule. In addition, as described in WO2011/024891, polarizers can be formed from liquid crystal dichroic dyes.

(2) Protective film

The polarizing plate 1 used in the present invention has a polarizing plate 10 and a first protective film 11 laminated on the surface of the polarizing plate 10 opposite to the high phase difference film 13 side. The polarizing plate 1 has at least one protective film equivalent to the first protective film 11, and may further have another protective film equivalent to the second protective film 12 laminated on the surface of the polarizing plate 10 on the high phase difference film 13 side.

(1st protective film 11)

The absolute value of the photoelastic coefficient of the first protective film 11 at a temperature of 23°C is less than 8×10 ^-12 Pa ^-1 . It is considered that by using the first protective film 11 with such a small photoelastic coefficient, the retardation value caused by the strain of the first protective film 11 caused by the shrinkage stress of the high retardation film 13 when placed in a high temperature environment can be reduced. As a result, even after being placed in a high temperature environment, it can have good visual confirmation regardless of the presence or absence of polarized sunglasses.

The first protective film 11 is not particularly limited, and can be a light-transmitting (preferably optically transparent) thermoplastic resin having an absolute value of a photoelastic coefficient of 8×10 ^-12 Pa ^-1 or less, such as polyolefin resins such as chain polyolefin resins (polypropylene resins, etc.) and cyclic polyolefin resins (norbornene resins, etc.); cellulose resins such as cellulose triacetate and cellulose diacetate; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate resins; Films composed of (meth)acrylic resins such as methyl methacrylate resins; polystyrene resins; polyvinyl chloride resins; acrylonitrile/butadiene/styrene resins; acrylonitrile/styrene resins; polyvinyl acetate resins; polyvinylidene chloride resins; polyamide resins; polyacetal resins; modified polyphenylene ether resins; polysulfide resins; polyethersulfone resins; polyarylate resins; polyamide imide resins; polyimide resins; butenediimide resins, etc.

In particular, the first protective film 11 is preferably a film having a smaller photoelastic coefficient. That is, the cyclic polyolefin resin is preferably a film containing at least one selected from the group consisting of (meth) acrylic resin, polystyrene resin, and butylene imide resin.

The photoelastic coefficient of the first protective film 11 at a temperature of 23°C is preferably 0.05×10 ^-12 to 8.0×10 ^-12 Pa ^-1 , more preferably 0.1×10 ^-12 to 5.0×10 ^-12 Pa ^-1 , and even more preferably 0.2×10 ^-12 to 3.0×10 ^-12 Pa ^-1 . The photoelastic coefficient is a value measured by the method described in the examples below.

If the in-plane phase difference value of the protective film 11 is within the range of the aforementioned photoelastic coefficient, it is preferably adjusted to less than 10nm or 50 to 300nm. In particular, it is preferred to form a film less than 10nm, thereby achieving a higher effect. The reason is that the film with phase difference will change the phase difference value through the oblique stress relaxation of the high phase difference film, and its optical axis will also change, thereby increasing the light leakage during black display. When the phase difference film is used as an optical compensation film in a liquid crystal display device, the aforementioned optical compensation film can be configured on the other polarizing plate used in pair, which is also a useful design method. In addition, unless otherwise specified, the phase difference value is a value at a wavelength of 550nm, which is a value measured by the method described in the embodiment described later.

Cyclic polyolefin resins are a general term for resins that use cyclic olefins as polymerized units, and examples thereof include resins described in Japanese Patent Application Laid-Open No. 1-240517, Japanese Patent Application Laid-Open No. 3-14882, and Japanese Patent Application Laid-Open No. 3-122137. Specific examples of cyclic polyolefin resins include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and chain olefins such as ethylene and propylene (most typically random copolymers), graft polymers obtained by modifying these with unsaturated carboxylic acids or their derivatives, and hydrogenated products thereof. Among them, the preferred is a norbornene resin using a norbornene monomer such as norbornene or a polycyclic norbornene monomer as the cyclic olefin.

There is no particular limitation on the method of making a protective film from a cyclic olefin resin. You can choose a method that is appropriate for the resin. For example, a solvent casting method is used to cast a resin dissolved in a solvent onto a metal strip or a drum, and then the solvent is dried to remove the solvent to obtain a film; and a melt extrusion method is used to heat the resin to a temperature above its melting point, knead it, extrude it, and cool it with a cooling drum to obtain a film. From the perspective of productivity, the melt extrusion method is preferred.

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

Next, the control method for making the phase difference of the aforementioned cyclic olefin resin film satisfy the above conditions is described. In order to make the in-plane phase difference value less than 10nm, it is necessary to minimize the strain remaining in the in-plane direction during extension. In addition, in order to make the thickness direction phase difference less than the specific value of the present invention, it is necessary to minimize the strain remaining in the thickness direction.

For example, in the aforementioned solvent casting method, a method is adopted to relax the residual extension strain in the in-plane direction and the residual contraction strain in the thickness direction generated when the cast resin solution is dried by heat treatment. In addition, in the aforementioned melt extrusion method, in order to prevent the resin film from stretching between extrusion and cooling, a method is adopted in which the distance from the mold to the cooling drum is minimized, and the extrusion amount and the rotation speed of the cooling drum are controlled in a manner that does not stretch the film. In addition, a method of relaxing the strain remaining in the obtained film by heat treatment, similar to the aforementioned melt extrusion method, can also be adopted.

Furthermore, within the range of the photoelastic coefficient of the present invention, a phase difference film having the function of an optical compensation film for a liquid crystal display device can be formed. Such a phase difference film can be prepared by giving the aforementioned annular olefin resin film an in-plane phase difference value. Stretching can be performed by conventional longitudinal uniaxial stretching, horizontal uniaxial stretching on a tenter, simultaneous biaxial stretching, sequential biaxial stretching, etc., and stretching can be performed in a manner that obtains the desired phase difference value.

For example, a liquid crystal display device in a horizontal electric field effect mode preferably uses a phase difference film with an in-plane phase difference adjusted to 50 to 300 nm. Specifically, the phase difference film described in Japanese Patent Publication No. 2010-20287 or the phase difference film described in Japanese Patent No. 3880996 can be used.

The thickness of the aforementioned cyclic olefin resin film is preferably 10μm to 200μm, more preferably 10μm to 100μm, and most preferably 10μm to 65μm. If the thickness is less than 10μm, the strength may be reduced. If the thickness exceeds 200μm, the transparency may be reduced.

(Meth)acrylic resins are resins having a compound having a (meth)acryloyl group as a main constituent monomer. Specific examples of (meth)acrylic resins include: poly(meth)acrylates such as polymethyl methacrylate; methyl methacrylate-(meth)acrylic acid copolymers; methyl methacrylate-(meth)acrylic acid copolymers; methyl methacrylate-(meth)acrylic acid copolymers; methyl methacrylate-acrylic acid ester-(meth)acrylic acid copolymers; methyl (meth)acrylate-styrene copolymers (MS resins, etc.); copolymers of methyl methacrylate and compounds having alicyclic hydrocarbon groups (e.g. methyl methacrylate-cyclohexyl methacrylate copolymers, methyl methacrylate-norbornene (meth)acrylate copolymers, etc.). It is preferred to use a polymer containing poly(meth)acrylic acid C _1-6 alkyl esters such as poly(methyl)acrylate as a main component, and it is more preferred to use a methyl methacrylate-based resin containing methyl methacrylate as a main component (50 to 100% by weight, preferably 70 to 100% by weight).

The in-plane phase difference Re[550] of the aforementioned (meth) acrylic resin film at a wavelength of 550nm is preferably less than 10nm, more preferably less than 7nm, more preferably less than 5nm, particularly preferably less than 3nm, and most preferably less than 1nm. The thickness direction phase difference Rth[550] of the (meth) acrylic resin film at a wavelength of 550nm is preferably less than 15nm, more preferably less than 10nm, more preferably less than 5nm, particularly preferably less than 3nm, and most preferably less than 1nm. In order to make the in-plane phase difference and the thickness direction phase difference within this range, for example, the (meth) acrylic resin having a pentamidoamine structure described later can be used.

The aforementioned (meth) acrylic resin may further have other structural units. Other structural units include structural units constituting lactone rings, polycarbonates, polyvinyl alcohol, cellulose acetate, polyesters, polyarylates, polyimides, polyolefins, etc., and structural units represented by the general formula (1) described below. Structural units exhibiting negative birefringence include structural units derived from styrene monomers, styrene diimide monomers, etc., structural units of polymethyl methacrylate, and structural units represented by the general formula (3) described below.

The aforementioned (meth) acrylic resin is preferably a (meth) acrylic resin having a lactone ring structure or a glutarimide structure. The (meth) acrylic resin having a lactone ring structure or a glutarimide structure has excellent heat resistance. A (meth) acrylic resin having a glutarimide structure is more preferred. If a (meth) acrylic resin having a glutarimide structure is used, a (meth) acrylic resin film having low moisture permeability and small phase difference and ultraviolet transmittance can be obtained as described above. The (meth) acrylic resin having a glutarimide structure (hereinafter referred to as glutarimide resin) is described in, for example, Japanese Patent Publication No. 2006-309033, Japanese Patent Publication No. 2006-317560, Japanese Patent Publication No. 2006-328329, Japanese Patent Publication No. 2006-328334, Japanese Patent Publication No. 2006-337491, Japanese Patent Publication No. 2006-337492, Japanese Patent Publication No. 2006-337493, Japanese Patent Publication No. 2006-337569, Japanese Patent Publication No. 2007-009182, and Japanese Patent Publication No. 2009-161744. These descriptions are applicable to this specification as a reference.

Preferably, the above-mentioned pentylene imide resin includes a structural unit represented by the following general formula (1) (hereinafter referred to as pentylene imide unit) and a structural unit represented by the following general formula (2) (hereinafter referred to as (meth)acrylate unit).

In formula (1), ^R1 and ^R2 are independently hydrogen or an alkyl group having 1 to 8 carbon atoms, and ^R3 is a substituent including hydrogen, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aromatic ring having 5 to 15 carbon atoms. In formula (2), ^R4 and ^R5 are independently hydrogen or an alkyl group having 1 to 8 carbon atoms, and ^R6 is a substituent including hydrogen, an alkyl group having 1 to 18 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, or an aromatic ring having 5 to 15 carbon atoms.

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

In formula (3), ^R7 is hydrogen or an alkyl group having 1 to 8 carbon atoms, and ^R8 is an aryl group having 6 to 10 carbon atoms.

In the above general formula (1), preferably, ^R1 and ^R2 are independently hydrogen or methyl, and ^R3 is hydrogen, methyl, butyl, or cyclohexyl. More preferably, ^R1 is methyl, ^R2 is hydrogen, and ^R3 is methyl.

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

The glutarimide unit can be formed by imidizing the (meth)acrylate unit represented by the above general formula (2). In addition, the glutarimide unit can also be formed by imidizing 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, maleic anhydride, itaconic acid, itaconic anhydride, crotonic acid, fumaric acid, citric acid, etc. α, β-ethylenically unsaturated carboxylic acids.

In the above general formula (2), preferably, ^R4 and ^R5 are independently hydrogen or methyl, and ^R6 is hydrogen or methyl. More preferably, ^R4 is hydrogen, ^R5 is methyl, and ^R6 is methyl.

The glutarimide resin may contain only a single type of (meth)acrylate unit, or may contain a plurality of types in which R ⁴ , R ⁵ , and R ⁶ in the general formula (2) are different.

In the above-mentioned pentylene imide resin, the aromatic vinyl unit represented by the above-mentioned general formula (3) preferably contains styrene, α-methylstyrene, etc., and more preferably contains styrene. By having such an aromatic vinyl unit, the positive birefringence of the pentylene imide structure can be reduced, and a (meth) acrylic resin film with a lower phase difference can be obtained.

The glutarimide resin may contain only a single aromatic vinyl unit or may contain a plurality of aromatic vinyl units in which ^R7 and ^R8 are different.

The content of the pentylimide unit in the pentylimide resin preferably varies depending on the structure of R ³ , etc. The content of the pentylimide unit is preferably 1 wt % to 80 wt %, more preferably 1 wt % to 70 wt %, even more preferably 1 wt % to 60 wt %, and particularly preferably 1 wt % to 50 wt % based on the total structural units of the pentylimide resin. If the content of the pentylimide unit is within such a range, a (meth) acrylic resin film having excellent heat resistance and low phase difference can be obtained.

The content of the above-mentioned aromatic vinyl unit in the above-mentioned pentylimide resin can be appropriately set according to the purpose or the desired characteristics. Depending on the application, the content of the aromatic vinyl unit can also be 0. When the aromatic vinyl unit is contained, its content is preferably 10% to 80% by weight based on the pentylimide unit of the pentylimide resin, more preferably 20% to 80% by weight, more preferably 20% to 60% by weight, and particularly preferably 20% to 50% by weight. If the content of the aromatic vinyl unit is within this range, a (meth) acrylic resin film with low phase difference and excellent heat resistance and mechanical strength can be obtained.

The above-mentioned pentylene imide resin may be further copolymerized with other structural units other than pentylene imide units, (meth)acrylate units, and aromatic vinyl units as needed. Other structural units include nitrile monomers such as acrylonitrile or methacrylonitrile, structural units composed of cis-butenediamide monomers such as succinimide, N-methylsuccinimide, N-phenylsuccinimide, and N-cyclohexylsuccinimide. These other structural units can be directly copolymerized or grafted in the above-mentioned pentylene imide resin.

The (meth)acrylic resin film may contain any appropriate additives according to the purpose. Additives include, for example, hindered phenol-based, phosphorus-based, sulfur-based antioxidants; stabilizers such as light stabilizers, ultraviolet absorbers, weathering stabilizers, and thermal stabilizers; reinforcing materials such as glass fiber and carbon fiber; near-infrared absorbers; flame retardants such as tris(dibromopropyl) phosphate, triallyl phosphate, and antimony oxide; antistatic agents such as anionic, cationic, and non-ionic surfactants; colorants such as inorganic pigments, organic pigments, and dyes; organic fillers or inorganic fillers; resin modifiers; plasticizers; lubricants; phase difference reducing agents, etc. The type, combination, and amount of additives contained can be appropriately set according to the purpose or desired characteristics.

The method for producing the (meth)acrylic resin film is not particularly limited. For example, the (meth)acrylic resin, the ultraviolet absorber, other polymers or additives as required, etc. can be fully mixed by any appropriate mixing method and used as a pre-prepared thermoplastic resin composition for film molding. Alternatively, the (meth)acrylic resin, the ultraviolet absorber, other polymers or additives as required can be formed into individual solutions and then mixed to form a uniform mixed solution before film molding.

When manufacturing the above-mentioned thermoplastic resin composition, the above-mentioned film raw materials are pre-mixed with any appropriate mixer such as a homogenizer, and the obtained mixture is extruded and kneaded. At this time, the mixer used for extrusion and kneading is not particularly limited, for example, an extruder such as a single-screw extruder, a double-screw extruder, or any appropriate mixer such as a pressure kneading machine can be used.

The above-mentioned film forming method can be any appropriate film forming method such as solution casting (solution casting), melt extrusion, calendering, compression molding, etc. The melt extrusion method is preferred. The melt extrusion method does not use solvents, so it can reduce the burden of manufacturing costs or solvents on the earth's environment or the working environment.

The above-mentioned melt extrusion method can be exemplified by T-die method, inflation method, etc. The molding temperature is preferably 150 to 350°C, more preferably 200 to 300°C.

When the film is formed by the T-die method, a T-die is installed at the front end of a conventional single-axis extruder or a double-axis extruder, and the film extruded in a film-like state is wound up to obtain a roll-shaped film. At this time, by appropriately adjusting the temperature of the winding roll and stretching in the extrusion direction, uniaxial stretching can also be performed. In addition, by stretching the film in a direction perpendicular to the extrusion direction, simultaneous biaxial stretching, sequential biaxial stretching, etc. can also be performed.

In the range of obtaining the above-mentioned desired phase difference, the above-mentioned (meth) acrylic resin film can be either an unstretched film or a stretched film. In the case of a stretched film, it can be either a uniaxially stretched film or a biaxially stretched film. In the case of a biaxially stretched film, it can be either a simultaneously biaxially stretched film or a sequentially biaxially stretched film.

The above-mentioned stretching temperature is preferably near the glass transition temperature of the thermoplastic resin composition of the film raw material, specifically, preferably (glass transition temperature -30°C) to (glass transition temperature +30°C), and more preferably (glass transition temperature -20°C) to (glass transition temperature +20°C). If the stretching temperature does not reach (glass transition temperature -30°C), there is a risk that the fog of the obtained film will increase, or the film will break or tear and the specific stretching ratio cannot be obtained. On the contrary, if the stretching temperature exceeds (glass transition temperature +30°C), the uneven thickness of the obtained film will increase, and there is a tendency that the mechanical properties such as elongation, tear propagation strength, and flexural fatigue resistance cannot be fully improved. In addition, there is a tendency to easily cause the problem of film adhesion to the roller.

The above stretching ratio is preferably 1.1 to 3 times, and more preferably 1.3 to 2.5 times. If the stretching ratio is within this range, the mechanical properties of the film, such as elongation, tear propagation strength, and flexural fatigue resistance, can be greatly improved. As a result, the thickness unevenness can be reduced, the birefringence is substantially zero (so the phase difference is smaller), and a film with less haze can be produced.

In order to stabilize the optical isotropy or mechanical properties of the above-mentioned (meth) acrylic resin film, heat treatment (annealing) etc. may be performed after the stretching treatment. Any appropriate conditions may be adopted 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 be reduced. If the thickness exceeds 200 μm, the transparency may be reduced.

(Second protective film 12)

The second protective film 12 may use the resin film described as the film used as the first protective film 11, or other resin films may be used. For example, it is preferred to use a chain olefin resin film or a cellulose resin film.

Chain polyolefin resins include chain olefin homopolymers such as polyethylene resin (polyethylene resin of ethylene homopolymer or copolymer with ethylene as the main component) and polypropylene resin (polypropylene resin of propylene homopolymer or copolymer with propylene as the main component), as well as copolymers composed of two or more chain olefins.

Cellulose ester resins are esters of cellulose and fatty acids. Specific examples of cellulose ester resins include cellulose triacetate, cellulose diacetate, cellulose tripropionate, and cellulose dipropionate. In addition, copolymers of these resins or resins in which a portion of the hydroxyl groups is modified with other substituents can also be cited. Among these, triacetylcellulose is particularly preferred.

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

As mentioned above, the second protective film 12 may also have a surface treatment layer (coating) such as a hard coating layer, an anti-glare layer, a light diffusion layer, an anti-reflection layer, a low refractive index layer, an anti-static layer, and an anti-fouling layer on its outside (the side opposite to the polarizer). In addition, the thickness of the second protective film 12 includes the thickness of the surface treatment layer.

(3) Next layer

The protective film (the first protective film 11 and the second protective film 12) can be attached to the polarizer via a bonding layer, for example. The bonding layer is, for example, a bonding agent layer or an adhesive layer. The bonding agent forming the bonding agent layer can be a water-based bonding agent, an active energy ray-curable bonding agent, or a thermosetting bonding agent, preferably a water-based bonding agent or an active energy ray-curable bonding agent.

The adhesive layer may be the one described below.

Examples of water-based adhesives include adhesives composed of polyvinyl alcohol resin aqueous solutions and water-based two-component urethane emulsion adhesives. Among them, water-based adhesives composed of polyvinyl alcohol resin aqueous solutions are suitable. In addition to vinyl alcohol homopolymers obtained by saponifying polyvinyl acetate, which is a vinyl acetate homopolymer, polyvinyl alcohol copolymers obtained by saponifying copolymers of vinyl acetate and other monomers copolymerizable therewith, or modified polyvinyl alcohol polymers in which the hydroxyl groups of these monomers are modified can be used. Water-based adhesives may contain crosslinking agents such as aldehyde compounds (such as glyoxal), epoxy compounds, melamine compounds, hydroxymethyl compounds, isocyanate compounds, amine compounds, and polyvalent metal salts.

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

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

The curable compound may be a cationically polymerizable curable compound or a free radically polymerizable curable compound. Examples of cationically polymerizable curable compounds include epoxy compounds (compounds having one or more epoxy groups in the molecule), or cyclohexane compounds (compounds having one or more cyclohexane rings in the molecule), or combinations thereof. Examples of free radically polymerizable curable compounds include (meth)acrylic compounds (compounds having one or more (meth)acryloyloxy groups in the molecule), or other vinyl compounds having free radically polymerizable double bonds, or combinations thereof. Cationic polymerizable curable compounds and free radically polymerizable curable compounds may be used together. Active energy ray-curable adhesives usually further contain cationic polymerization initiators and/or free radical polymerization initiators that initiate the curing reaction of the above-mentioned curable compounds.

When laminating the polarizer and the protective film, in order to improve the adhesion, a surface activation treatment can be performed on the laminating surface of at least one of them. The surface activation treatment can include dry treatments such as corona treatment, plasma treatment, discharge treatment (fluorescence discharge treatment, etc.), flame treatment, ozone treatment, UV ozone treatment, ionizing active ray treatment (ultraviolet ray treatment, electron beam treatment, etc.); wet treatments such as ultrasonic treatment using solvents such as water or acetone, saponification treatment, and primer treatment. These surface activation treatments can be performed alone or in combination of two or more.

When the protective films are laminated on both sides of the polarizer, the adhesives used to laminate the protective films can be the same adhesive or different adhesives.

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

<High phase difference film 13>

The optical multilayer of the present invention has a high phase difference film 13 for ensuring visual confirmation through polarized sunglasses. The high phase difference film 13 is composed of a transparent thermoplastic resin film with birefringence. In this specification, "high phase difference" means that the in-plane phase difference value Re[550] at a wavelength of 550nm is greater than 3000nm. The in-plane phase difference value Re[550] of the high phase difference film 13 at a wavelength of 550nm is preferably greater than 3000nm, more preferably greater than 5000nm, and particularly preferably greater than 7000nm. The upper limit value of the in-plane phase difference Re[550] of the high phase difference film 13 is 30000nm. By using such a film, it is possible to suppress the change in hue due to viewing angle when viewing a liquid crystal display device through polarized sunglasses.

The high phase difference 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 resins such as polymethyl (meth)acrylate; cellulose triacetate, cellulose diacetate, and cellulose acetate propionate. Cellulose ester resins such as cellulose; vinyl alcohol resins such as polyvinyl alcohol and polyvinyl acetate; polycarbonate resins; polystyrene resins; polyarylate resins; polysulfone resins; polyethersulfone resins; polyamide resins; polyimide resins; polyetherketone resins; polyphenylene sulfide resins; polyphenylene ether resins, and mixtures and copolymers thereof. From the viewpoint of availability or transparency, polyethylene terephthalate, cellulose ester, cyclic olefin resin or polycarbonate is preferred.

The thermoplastic resins can be subjected to uniaxial or biaxial heat stretching to form a film with the desired phase difference. The stretching ratio is usually 1.1 to 6 times, preferably 1.1 to 4 times.

Furthermore, it is preferable to use a method that can be stretched in an oblique direction by roll-to-roll manufacturing. The oblique stretching method is not particularly limited as long as the alignment axis can be continuously tilted to the desired angle, and a known stretching method can be adopted. Such a stretching method can be exemplified by the method described in Japanese Patent Publication No. 50-83482 or Japanese Patent Publication No. 2-113920. When the film is given a phase difference by stretching, the thickness after stretching is determined by the thickness before stretching or the stretching ratio.

The angle between the slow axis of the high phase difference film 13 and the absorption axis of the polarizer 10 is 40° to 50°, preferably 42° to 48°, and particularly preferably about 45°. This can suppress the reduction of the front brightness when visually confirming the liquid crystal display device through polarized sunglasses.

The thickness of the high phase difference film 13 is preferably less than 200μm, more preferably less than 150μm, and particularly preferably less than 100μm. By making the thickness of the high phase difference film 13 less than 200μm, the warping of the optical multilayer 100 can be suppressed, and defects such as bubbles when attached to a liquid crystal display device can be suppressed. The thickness of the high phase difference film 13 can be more than 10μm, and can also be more than 30μm.

The optical laminate 100 is arranged on the visual confirmation side of the liquid crystal unit of the liquid crystal display device, thereby suppressing the reduction of visual confirmation when visually confirming the liquid crystal display device through polarized sunglasses without the need for other high phase difference films. Specifically, it can suppress the reduction of front brightness and the hue change (color shift) corresponding to the viewing angle. A hard coating layer or an anti-glare layer can be laminated in the high phase difference film 13 as needed.

<Adhesive layer 14>

The adhesive layer 14 is a laminate of the polarizing plate 1 and the high phase difference film 13. The adhesive layer 14 can be composed of an adhesive composition with a resin such as (meth) acrylic resin, rubber resin, urethane resin, ester resin, silicone resin, and polyvinyl ether resin as the main component. Among them, the adhesive composition with (meth) acrylic resin having excellent transparency, weather resistance, heat resistance, etc. as the base polymer is preferred. The adhesive composition can be active energy ray curing type or heat curing type. The thickness of the adhesive layer is usually 3 to 30μm, preferably 3 to 25μm.

The (meth)acrylic resin (base polymer) used in the adhesive composition is suitable for using a polymer or copolymer with one or more (meth)acrylates such as butyl (meth)acrylate, ethyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate as monomers. The base polymer is preferably a copolymerized polar monomer. Examples of polar monomers include monomers having carboxyl, hydroxyl, amide, amino, epoxy, etc., such as (meth)acrylic acid, 2-hydroxypropyl (meth)acrylate, hydroxyethyl (meth)acrylate, (meth)acrylamide, N, N-dimethylaminoethyl (meth)acrylate, and glycidyl (meth)acrylate.

The adhesive composition may contain only the above-mentioned base polymer, but usually further contains a crosslinking agent. Examples of the crosslinking agent include metal ions with a valence of two or more and forming carboxyl metal salts between carboxyl groups; polyamine compounds and forming amide bonds between carboxyl groups; polyepoxide compounds or polyols and forming ester bonds between carboxyl groups; polyisocyanate compounds and forming amide bonds between carboxyl groups. Polyisocyanate compounds are preferred.

The storage elastic modulus of the adhesive layer 14 is preferably 0.001 to 0.350 MPa at a frequency of 1 Hz and a temperature of 23°C, more preferably 0.001 to 0.200 MPa, even more preferably 0.001 to 0.100 MPa, and particularly preferably 0.010 to 0.100 MPa. If the storage elastic modulus exceeds the aforementioned range, the shrinkage stress of the high phase difference film 13 in a high temperature environment is not sufficiently alleviated, which will induce the strain of the first protective film 11 and reduce the general visual confirmation of the non-polarized sunglasses. Moreover, if it is lower than the aforementioned range, problems such as peeling in a high temperature environment will occur.

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 multilayer of the present invention can be laminated on the liquid crystal unit via the adhesive 15 to form a liquid crystal display device. The adhesive 15 can use the above-mentioned composition, characteristics, and thickness recorded in the adhesive 14, and can be the same as or different from the adhesive layer 14.

<Front panel>

The optical laminate 100 can be used by configuring a front panel on its visual confirmation side surface. The front panel can be laminated on the optical laminate 100 via an intermediate layer. The intermediate layer can be, for example, the aforementioned adhesive layer or adhesive layer. FIG. 2 is a cross-sectional view showing the laminate structure in which the front panel 4 is configured on the visual confirmation side surface of the optical laminate 100. As shown in FIG. 2, the front panel 4 can be laminated on the high phase difference film 13 in the optical laminate 100 via an adhesive layer 16.

The front panel may be made of glass or a resin film with a hard coating on at least one side. For example, high-transmittance glass or reinforced glass may be used. In particular, when using a thin transparent surface material, chemically reinforced glass is preferred. The glass thickness may be, for example, 100 μm to 5 mm.

The front panel having a hard coating layer on at least one side of the resin film is not rigid like the existing glass, but can have flexible properties. The thickness of the hard coating layer is not particularly limited, for example, it can be 5 to 100μm.

The resin film may be a cycloolefin derivative having a monomer unit containing a cycloolefin such as norbornene or a polycyclic norbornene monomer, cellulose (cellulose diacetate, cellulose triacetate, cellulose acetate butyrate, isobutyl cellulose, propylene cellulose, butyryl cellulose, acetylacetyl cellulose), ethylene-vinyl acetate copolymer, polycycloolefin, polyester, polystyrene, polyamide, polyetherimide, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, polyvinyl acetate, Films formed from polymers such as acrylate, polyimide, polyamide imide, polyether sulfone, polysulfone, polyethylene, polypropylene, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl acetal, polyether ketone, polyether ether ketone, polymethyl methacrylate, polyethylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyurethane, and epoxy. The resin film may be an unstretched, uniaxially or biaxially stretched film. These polymers may be used alone or in combination of two or more. The resin film is preferably a polyamide imide film or polyimide film with excellent transparency and heat resistance, a uniaxially or biaxially stretched polyester film, a cycloolefin derivative film with excellent transparency and heat resistance and capable of supporting large-scale film, a polymethyl methacrylate film, and a transparent cellulose triacetate and isobutyl cellulose film with no optical anisotropy. The thickness of the resin film can be 5 to 200 μm, preferably 20 to 100 μm.

The hard coat composition contains a reactive material that forms a cross-linked structure by irradiating light or heat energy, and the hard coat composition is cured to form the aforementioned hard coat layer. The aforementioned hard coat layer can be formed by curing a hard coat composition that contains a photocurable (meth)acrylate monomer or oligomer and a photocurable epoxy monomer or oligomer at the same time. The aforementioned photocurable (meth)acrylate monomer can contain one or more selected from the group consisting of epoxy (meth)acrylate, urethane (meth)acrylate and polyester (meth)acrylate. The aforementioned epoxy (meth)acrylate can react with a carboxylic acid having a (meth)acryloyl group relative to an epoxy compound.

The hard coating composition may further contain one or more selected from the group consisting of solvents, photoinitiators and additives. The additive may contain one or more selected from the group consisting of inorganic nanoparticles, levelers and stabilizers, and may further contain various components generally used in the technical field, such as antioxidants, UV absorbers, surfactants, lubricants, antifouling agents, etc.

(Implementation example)

The present invention is further described in detail below with examples, but the present invention is not limited to these examples. In the examples, the content or usage amount is expressed in parts and %, and is based on weight unless otherwise specified. In addition, in the following examples, the determination of each physical property is carried out using the following method.

[Measurement method]

(1) Film thickness measurement method

Measured using the MH-15M digital micrometer manufactured by Nikon Corporation.

(2) Phase difference measurement method

The phase difference measurement device KOBRA-WPR (manufactured by Oji Measuring Instruments Co., Ltd.) was used for measurement. Unless otherwise specified, the phase difference value refers to the value at a wavelength of 550nm.

(3) Determination method of photoelastic coefficient

Using the phase difference measuring device KOBRA-WPR (manufactured by Oji Measuring Instruments Co., Ltd.), the sample (size 1.5cm×6cm) is clamped and stress (0.5N to 8N) is applied at both ends, while the phase difference value (23℃/wavelength 550nm) at the center of the sample is measured and calculated from the functional inclination of stress and phase difference value.

(4) Determination method of storage elastic modulus:

The storage elastic modulus (G’) of the adhesive layer is measured according to the following (I) to (III).

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

(II) The two samples obtained in (I) above are attached to the upper and lower surfaces of the I-type jig, and the upper and lower surfaces are clamped by the L-type jig. The structure of the test sample is L-type jig/adhesive/I-type jig/adhesive/L-type jig.

(III) The sample prepared in this way is used to measure the storage elastic modulus (G') at a temperature of 23°C, a frequency of 1 Hz, and an initial strain of 1 N using a dynamic viscoelasticity measuring device [DVA-220, manufactured by IT Measurement & Control Co., Ltd.].

(5) Luminance measurement method:

The measurement was performed using the SR-UL1 spectroradiometer manufactured by Topcon Co., Ltd. The measurement was performed in a 2° field of view.

[Manufacturing Example 1] Manufacturing of polarizer 1

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

[Manufacturing Example 2] Manufacturing of Polarizer 2

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

[Preparation of protective film]

Protective film A:

Cellulose triacetate membrane with a thickness of 40μm [KC4UYW manufactured by KONICA MINOLTA OPTO Co., Ltd.].

Protective film B:

100 parts by weight of imidized MS resin particles (weight average molecular weight: 105,000) described in Production Example 1 of Japanese Patent Publication No. 2010-284840 were dried at 100.5 kPa and 100°C for 12 hours, extruded from a T die at a die temperature of 270°C in a uniaxial extruder and formed into a film (thickness 160 μm). The film was further stretched in an environment of 150°C in its conveying direction (thickness 80 μm), and then stretched in an environment of 150°C in a direction orthogonal to the film conveying direction, to obtain a protective film B ((meth) acrylic resin film) with a thickness of 40 μm. The in-plane phase difference Re of the protective film B at a wavelength of 550 nm was 0.5 nm, and the phase difference 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 ((meth) acrylic resin film) with a thickness of 40 μm was obtained in the same manner as protective film B, except that the imidized MS resin particles were replaced with transparent particles of an acrylic copolymer described in Comparative Example 1 of Japanese Patent Application Laid-Open No. 2008-191426. The in-plane phase difference Re of protective film C at a wavelength of 550 nm was 0.8 nm, and the phase difference 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:

In contrast to protective film B, a protective film D ((meth)acrylic resin film) with a thickness of 40 μm was obtained in the same manner except that the imidized MS resin particles were replaced with transparent particles of an acrylic copolymer described in Example 1 of Japanese Patent Application Laid-Open No. 2008-191426. The in-plane phase difference Re of protective film D at a wavelength of 550 nm was 0.4 nm, and the phase difference 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:

A 23μm thick norbornene resin film [ZF14-023 manufactured by ZEON Co., Ltd., Japan]. The in-plane phase difference Re of the protective film E at a wavelength of 550nm is 0.7nm, and the phase difference Rth in the thickness direction is 4.2nm. The photoelastic coefficient is 1.6×10 ^-12 Pa ^-1 .

Protective film F:

Compared with the 1/4 wavelength plate A1 stretched in an oblique direction as described in Manufacturing Example 3 of International Publication No. 2017/094485, a rolled 1/4 wavelength plate was prepared in the same manner except that the stretching direction was the long direction. The thickness of the 1/4 wavelength plate (protective film F) was 35 μm, the slow axis was the long direction, and the in-plane phase difference Re was 136 nm. In addition, the photoelastic coefficient of the obtained film was 4.0×10 ^-12 Pa ^-1 .

Protective film G:

Compared with the obliquely extended 1/4 wavelength plate B4 described in Manufacturing Example 5 of International Publication No. 2017/094485, a rolled 1/4 wavelength plate was produced in the same manner except that the extending direction was the long direction. The thickness of the 1/4 wavelength plate (protective film G) was 47 μm, the slow axis was the long direction, and the in-plane phase difference Re was 140 nm. In addition, the photoelastic coefficient of the obtained film was 6.0×10 ^-12 Pa ^-1 .

Protective film H:

Thick 20μm cellulose triacetate film [product name "ZRG20SL" manufactured by FUJIFILM Co., Ltd.]. The in-plane phase difference Re of the protective film H at a wavelength of 550nm is 1.1nm, and the phase difference Rth in the thickness direction is 1.3nm. The photoelastic coefficient is 9.4×10 ^-12 Pa ^-1 .

[Preparation of follow-up agent]

Dissolve 50g of modified PVA resin containing acetyl group (GOHSENX Z-410 manufactured by Mitsubishi Chemical Co., Ltd.) in 950g of pure water, heat at 90℃ for 2 hours and then cool to room temperature to obtain PVA solution A.

Then, the aforementioned PVA solution A, maleic acid, glyoxal, and pure water are mixed in such a way that each compound has the following concentrations to prepare a PVA-based adhesive.

[Preparing high phase difference film]

COSMOSHINE SRF (Super Retardation Film) (thickness 80μm) manufactured by Toyobo Co., Ltd. was used. The in-plane phase difference value Re[550] is 8400nm.

[Prepare adhesive]

Adhesive A: Commercially available 15μm thick sheet-like acrylic adhesive (storage elastic modulus 0.06MPa)

Adhesive B: Commercially available 25μm thick sheet-like acrylic adhesive (storage elastic modulus 0.06MPa)

[Implementation Example 1]

Adhesive A is applied to one side of the polarizer 1 obtained in Manufacturing Example 1 and a protective film A (second protective film) is attached thereto. Adhesive A is applied to the other side of the polarizer and a protective film B (first protective film) is attached thereto. After drying, a polarizing plate A is obtained. In addition, when attaching these materials, a corona treatment can be performed on the attaching surfaces of each material.

Adhesive A is applied to one side of the high phase difference film. In addition, when attaching these materials, a corona treatment can be performed on the bonding surface of each material.

The protective film A surface of the polarizing plate and the adhesive surface of the high phase difference film are bonded together in such a way that the angle θ between the absorption axis of the polarizing plate and the slow axis of the high phase difference film becomes 45°, thereby manufacturing the optical laminate A. In addition, when bonding these materials, the bonding surfaces of each material can be subjected to a corona treatment.

Finally, adhesive B is bonded to the protective film B surface of the obtained optical laminate A. In addition, when bonding these materials, corona treatment can be performed on the bonding surface of each material.

[Examples 2 to 8 and Comparative Example 1]

Compared to the optical laminate A prepared in the above-mentioned Example 1, in addition to using the first protective film and/or polarizer described in Table 1, optical laminates B to I (Examples 2 to 8 and Comparative Example 1) bonded with adhesive B are prepared in the same manner as in Example 1.

[Reference Example 1]

Compared to the optical laminate A with adhesive B in the above-mentioned Example 1, an optical laminate J with adhesive B is prepared in the same manner except that the absorption axis of the polarizing plate and the slow axis of the high phase difference film are bonded so that the angle between them becomes 90° (reference example 1).

[Reference Example 2]

The polarizer obtained in Manufacturing Example 1 is coated with adhesive A on one side and laminated with protective film A, and the other side of the polarizer is coated with adhesive A and laminated with protective film H. After drying, a polarizing plate K is obtained. In addition, when laminating these materials, a corona treatment can be performed on the laminating surface of each material.

Adhesive B is bonded to the protective film H surface of the obtained optical laminate K to obtain an inner polarizing plate with an adhesive layer. In addition, when bonding these materials, a corona treatment can be performed on the bonding surface of each material.

(Preparation of sample A for evaluation)

The optical laminate A with adhesive B was cut into a size of 20mm×20mm, and was bonded to an alkali-free glass with a thickness of 0.7mm and a size of 30mm×30mm via adhesive B. The optical laminate K with adhesive B (without high phase difference film bonded) was cut into a size of 20mm×20mm, and was bonded to the side of the alkali-free glass where the optical laminate A was not bonded via adhesive B in such a way that the absorption axes of the polarizing plates formed orthogonal polarizers, thereby producing the evaluation sample A.

(Preparation of evaluation samples B to K)

Evaluation samples B to K were prepared in the same manner as evaluation sample A, except that optical laminate A was replaced by optical laminates B to K, respectively.

(Evaluation of blackness change)

The optical multilayer K of the evaluation samples A to K prepared above was bonded to the irradiation surface of a white backlight module with a brightness of 20000 cd/ ^m2 . The brightness (black brightness 1) was measured from the evaluation sample side (high phase difference film) side. After being stored in a heated environment at a temperature of 95°C for 240 hours, the brightness (black brightness 2) was measured again after being cooled to room temperature. The change rate (%) of black brightness 2 relative to black brightness 1 was calculated and taken as black brightness change.

Specifically:

Darkness change (%) = {|Darkness 2 - Darkness 1|/Darkness 1}×100

This is used to determine the change in blackness. The evaluation results are shown in Table 1.

From the results shown in Table 1, we can see that:

1. The black brightness of the optical multilayer body with high retardation film laminated at 45° will increase after the high temperature durability test. However, by using the first protective film with a photoelastic coefficient of 8.0×10 ^-12 Pa ^-1 or less, the increase in black brightness after the high temperature durability test can be suppressed.

2. In addition, by making the thickness of the polarizer less than 20μm (using polarizer 2), the increase in black brightness after the high-temperature durability test can be further suppressed.

1: Polarizing plate

4:Front panel

10: Polarizer

11: 1st protective film

12: Second protective film

13: High phase difference film

14, 15, 16: Adhesive layer

100: Optical multilayers

Claims (7)

An optical laminate comprises a polarizing plate and a high retardation film in sequence. The polarizing plate comprises a polarizer and a protective film laminated on the surface of the polarizer opposite to the high retardation film. The in-plane retardation value of the high retardation film at a wavelength of 550nm is 3000 to 30000nm, 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 less than 8× ^10-12 Pa ^-1 , and the high retardation film and the polarizing plate are laminated via an adhesive layer having a storage elastic modulus of 0.010 to 0.100MPa. The optical laminate as described in claim 1, wherein the protective film contains at least one selected from the group consisting of (meth) acrylic resin, polystyrene resin, and butylene diimide resin. The optical layered body as described in claim 1, wherein the protective film contains a cyclic olefin resin. An optical multilayer as described in any one of claims 1 to 3, wherein the in-plane phase difference of the aforementioned protective film is less than 10nm. An optical layered body as described in any one of claims 1 to 3, wherein the in-plane phase difference of the aforementioned protective film is 50nm to 300nm. An optical multilayer as described in any one of claims 1 to 3, wherein the thickness of the high phase difference film is less than 200 μm. A display device having an optical layer stacked on a display element as described in any one of claims 1 to 6.

Images