KR102672540B1 - Optical laminates and image display devices - Google Patents

Abstract

An optical laminate having an optically anisotropic substrate (hereinafter also referred to as an anisotropic substrate) and having an excellent anti-reflection function is provided.
The optical laminate of the present invention has a polarizer, a polarizing plate including a protective layer disposed on at least one side of the polarizer, a first retardation layer, a second retardation layer, a conductive layer, and a base material in this order, and the in-plane retardation Re of the base material (550) is greater than 0 nm, and the angle formed between the slow axis of the substrate and the slow axis of the second phase difference layer is -5° to 5° or 85° to 95°.

Description

Optical laminates and image display devices

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

Recently, with the spread of thin displays, displays equipped with organic EL panels (organic EL displays) have been proposed. Since the organic EL panel has a highly reflective metal layer, it is prone to problems such as external light reflection and background mirroring. Therefore, it is known to prevent these problems by installing a circularly polarizing plate on the viewer's side. On the other hand, demand for so-called inner touch panel type input display devices in which a touch sensor is built between a display cell (for example, an organic EL cell) and a polarizing plate is increasing. In an input display device with such a configuration, the distance between the image display cell and the touch sensor is close, so it is possible to provide a natural input operation feeling to the user. Additionally, the input display device having the above configuration can reduce the influence of reflected light caused by a conductive pattern formed on the touch sensor.

Generally, the touch sensor in the input display device of the above configuration includes a sensor film including a substrate and a conductive layer formed on the substrate. Isotropic substrates are often used as the substrate. If this isotropic substrate is optically completely isotropic, the anti-reflection function of the circularly polarizing plate is sufficiently exerted. However, in reality, due to the influence of the conductive layer formation process, treatment to increase the toughness of the substrate, etc., even a substrate intended to be isotropic develops some anisotropy. As a result, there are cases where problems such as reflection of external light or reflection of the background are not solved even if the circular polarizer is placed.

Japanese Patent Application Publication No. 2003-311239 Japanese Patent Application Publication No. 2002-372622 Japanese Patent No. 3325560 Publication Japanese Patent Application Publication No. 2003-036143

The present invention was made to solve the above-described conventional problems, and its main purpose is to provide an optical laminate that has an optically anisotropic substrate (hereinafter also referred to as an anisotropic substrate) and has an excellent anti-reflection function.

The optical laminate of the present invention has a polarizing plate including a polarizer and a protective layer disposed on at least one side of the polarizer, a first retardation layer, a second retardation layer, a conductive layer, and a substrate in this order, and the substrate The in-plane phase difference Re (550) is greater than 0 nm, and the angle formed between the slow axis of the substrate and the slow axis of the second phase difference layer is -5° to 5° or 85° to 95°.

In one embodiment, the angle formed between the absorption axis of the polarizer and the slow axis of the first retardation layer is 10° to 20°, and the angle formed between the absorption axis and the slow axis of the second retardation layer is 65° to 65°. It is 85°.

In one embodiment, the first phase difference layer and the second phase difference layer are composed of a cyclic olefin resin film.

In one embodiment, the first phase difference layer and the second phase difference layer are alignment-fixed layers of a liquid crystal compound.

According to another aspect of the present invention, an image display device is provided. This image display device is provided with the above optical laminate.

According to the present invention, an optical laminate having an anisotropic substrate and excellent anti-reflection function can be provided by optimizing the slow axis angle of the anisotropic substrate.

1 is a schematic cross-sectional view of an optical laminate according to an embodiment of the present invention.
Figure 2 is a graph showing the results of examples and comparative examples.
Figure 3 is a graph showing the results of examples and comparative examples.

Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

(Definition of terms and symbols)

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

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

“nx” is the refractive index in the direction where the in-plane refractive index is maximum (i.e., slow axis direction), “ny” is the refractive index in the direction orthogonal to the slow axis in the plane (i.e., fast axis direction), and “nz” is It is the refractive index in the thickness direction.

(2) In-plane phase difference (Re)

“Re(λ)” is the in-plane retardation measured with light of wavelength λ nm at 23°C. For example, “Re(550)” is the in-plane retardation measured with light with a wavelength of 550 nm at 23°C. Re(λ) can be obtained by the formula: Re(λ)=(nx-ny)×d when the thickness of the layer (film) is d(nm).

(3) Thickness direction phase difference (Rth)

“Rth(λ)” is the phase difference in the thickness direction measured with light with a wavelength of λnm at 23°C. For example, “Rth(550)” is the phase difference in the thickness direction measured with light with a wavelength of 550 nm at 23°C. Rth(λ) can be obtained by the formula: Rth(λ)=(nx-nz)×d when the thickness of the layer (film) is d(nm).

(4) Nz coefficient

The Nz coefficient can be obtained by Nz=Rth/Re.

A. Overall composition of optical laminate

1 is a schematic cross-sectional view of an optical laminate according to an embodiment of the present invention. The optical laminate 100 of this embodiment includes a polarizing plate 11, a first phase difference layer 12, a second phase difference layer 13, a conductive layer 21, and a base material 22 in this order. have The polarizer 11 includes a polarizer 1, a first protective layer 2 disposed on one side of the polarizer 1, and a second protective layer 3 disposed on the other side of the polarizer 1. . Depending on the purpose, one of the first protective layer 2 and the second protective layer 3 may be omitted. For example, if the first phase difference layer 12 can also function as a protective layer of the polarizer 1, the second protective layer 3 may be omitted. The conductive layer 21 and the base material 22 may each be a single layer and be a component of the optical laminate 100, and the optical laminate 100 may be formed as a laminate of the base material 22 and the conductive layer 21. It may be introduced in . The laminate of the substrate 22 and the conductive layer 21 can function, for example, as the sensor film 20 of a touch sensor. Additionally, for ease of viewing, the thickness ratio of each layer in the drawing is different from the actual one. In addition, each layer constituting the optical laminate may be laminated with any suitable adhesive layer (adhesive layer or pressure-sensitive adhesive layer: not shown) interposed therebetween. On the other hand, the base material 22 may be laminated in close contact with the conductive layer 21. In this specification, "close lamination" means that two layers are laminated directly or in a fixed manner without an adhesive layer (eg, adhesive layer, pressure-sensitive adhesive layer) intervening.

The laminate 10 of the polarizing plate 11, the first retardation layer 12, and the second retardation layer 13 may function as a circularly polarizing plate. Additionally, substrate 22 may be optically anisotropic. In the present invention, even if the anisotropic substrate 22 is provided, the angle formed between the slow axis of the substrate 22 and the second phase difference layer 13 is within a specific range (-5° to 5° or 85° to 95°), the anti-reflection function of the circularly polarizing plate is fully exhibited, and an optical laminate that can effectively prevent reflection of external light or reflection of the background can be provided. The substrate 22 has an in-plane retardation (e.g., an in-plane retardation Re(550) greater than 0 nm and less than or equal to 10 nm). Details will be described later.

The total thickness of the optical laminate is preferably 220 μm or less, and more preferably 40 μm to 180 μm.

The optical laminated body may be elongated (for example, roll-shaped) or may be sheet-shaped.

Below, each layer and optical film constituting the optical laminate will be described in more detail.

B. Polarizer

B-1. polarizer

As the polarizer 1, any suitable polarizer may be employed. For example, the resin film forming the polarizer may be a single-layer resin film or a laminate of two or more layers.

Specific examples of polarizers composed of a single-layer resin film include hydrophilic polymer films such as polyvinyl alcohol (PVA)-based films, partially formalized PVA-based films, and partially saponified ethylene-vinylacetate copolymer-based films, and iodine and dichroic films. Examples include those that have been dyed and stretched with dichroic substances such as dyes, and polyene-based oriented films, such as dehydrated PVA products and dehydrochloric acid-treated polyvinyl chloride products. Preferably, a polarizer obtained by dyeing a PVA-based film with iodine and uniaxially stretching it is used because it has excellent optical properties.

The dyeing with iodine is performed, for example, by immersing the PVA-based film in an aqueous iodine solution. The draw ratio of the uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after dyeing treatment or may be performed while dyeing. Additionally, it may be dyed after stretching. If necessary, the PVA-based film is subjected to swelling treatment, cross-linking treatment, washing treatment, drying treatment, etc. For example, by immersing the PVA-based film in water and washing it before dyeing, not only can contamination and anti-blocking agents on the surface of the PVA-based film be removed, but also the PVA-based film can be swelled to prevent dyeing stains.

Specific examples of a polarizer obtained using a laminate include a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or a PVA-based resin layer formed by applying a resin substrate to the resin substrate. A polarizer obtained using a laminated body of the following can be mentioned. A polarizer obtained using a laminate of a resin substrate and a PVA-based resin layer formed by applying to the resin substrate is, for example, applied by applying a PVA-based resin solution to the resin substrate and drying it to form a PVA-based resin layer on the resin substrate. Obtaining a laminate of a resin substrate and a PVA-based resin layer; It can be produced by stretching and dyeing the laminate and using the PVA-based resin layer as a polarizer. In this embodiment, stretching typically includes stretching the laminate by immersing it in an aqueous boric acid solution. In addition, if necessary, stretching may further include air stretching the laminate at a high temperature (eg, 95°C or higher) before stretching in an aqueous boric acid solution. The obtained resin substrate/polarizer laminate may be used as is (i.e., the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled from the resin substrate/polarizer laminate and applied to the peeled surface for the purpose. Accordingly, any appropriate protective layer may be laminated and used. Details of the manufacturing method of such a polarizer are described in, for example, Japanese Patent Application Publication No. 2012-73580. The entire disclosure of this publication is incorporated herein by reference.

The thickness of the polarizer is preferably 15 μm or less, more preferably 1 μm to 12 μm, further preferably 3 μm to 12 μm, and particularly preferably 5 μm to 12 μm.

The boric acid content of the polarizer is preferably 18% by weight or more, and more preferably 18% by weight to 25% by weight. If the boric acid content of the polarizer is within this range, the ease of curl adjustment during bonding is maintained satisfactorily and curling during heating is well suppressed due to a synergistic effect with the iodine content described later. Appearance durability during heating can be improved. The boric acid content can be calculated as the amount of boric acid contained in the polarizer per unit weight using the following formula, for example, using a neutralization method.

[Number 1]

The iodine content of the polarizer is preferably 2.1% by weight or more, and more preferably 2.1% by weight to 3.5% by weight. If the iodine content of the polarizer is in this range, the synergistic effect with the boric acid content described above maintains the ease of curl adjustment during bonding, and further suppresses curl during heating, while Appearance durability can be improved. In this specification, “iodine content” means the amount of all iodine contained in the polarizer (PVA-based resin film). More specifically, in the polarizer, iodine exists in the form of iodine ions (I ^- ), iodine molecules (I ₂ ), polyiodine ions (I ₃ ^- , I ₅ ^- ), etc., and the iodine content in this specification is It refers to the amount of iodine including all of its forms. Iodine content can be calculated by, for example, a calibration curve method of fluorescence X-ray analysis. In addition, the polyiodine ion exists in a state in which a PVA-iodine complex is formed in the polarizer. By forming such a complex, absorption dichroism can be expressed in the visible light wavelength range. Specifically, the complex of PVA and tri-iodide ions (PVA·I ₃ ^- ) has an absorption peak around 470 nm, and the complex of PVA and penta-iodide ions (PVA·I ₅ ^- ) has an absorption peak around 600 nm. has As a result, polyiodine ions can absorb light in a wide range of visible light depending on their shape. On the other hand, iodine ions (I ^- ) have an absorption peak around 230 nm and are not substantially involved in the absorption of visible light. Therefore, polyiodine ions present in a complex with PVA may be mainly involved in the absorption performance of the polarizer.

The polarizer preferably exhibits absorption dichroism at any wavelength from 380 nm to 780 nm. The single transmittance of the polarizer is 43.0% to 46.0% as described above, and is preferably 44.5% to 46.0%. The polarization degree of the polarizer is preferably 97.0% or more, more preferably 99.0% or more, and even more preferably 99.9% or more.

B-2. first protective layer

The first protective layer 2 is formed from any suitable film that can be used as a protective layer for a polarizer. Specific examples of materials that are the main components of the film include cellulose resins such as triacetylcellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, Transparent resins such as polysulfone-based, polystyrene-based, polynorbornene-based, polyolefin-based, (meth)acrylic-based, and acetate-based resins can be mentioned. Additionally, thermosetting resins or ultraviolet curing resins such as (meth)acrylic, urethane, (meth)acrylic urethane, epoxy, silicone, etc. are also included. In addition, for example, glassy polymers such as siloxane polymers can also be mentioned. Additionally, the polymer film described in Japanese Patent Application Laid-Open No. 2001-343529 (WO01/37007) can also be used. As a material for this film, for example, a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain can be used, for example, isobutene and A resin composition containing an alternating copolymer made of N-methylmaleimide and an acrylonitrile/styrene copolymer can be mentioned. The polymer film may be, for example, an extrusion molded product of the resin composition.

As will be described later, the optical laminate of the present invention is typically placed on the viewer side of an image display device, and the first protective layer 2 is typically placed on the viewer side. Accordingly, the first protective layer 2 may be subjected to surface treatment such as hard coat treatment, anti-reflection treatment, anti-sticking treatment, or anti-glare treatment as necessary. Additionally, the first protective layer 2 may be treated, if necessary, to improve visibility when viewed through polarized sunglasses (typically, imparting an (alternative) circular polarization function or imparting an ultra-high phase difference. ) may be used. By performing such processing, excellent visibility can be achieved even when the display screen is viewed through a polarizing lens such as polarized sunglasses. Therefore, the optical laminate can also be preferably applied to image display devices that can be used outdoors.

The thickness of the first protective layer may be any suitable thickness. The thickness of the first protective layer is, for example, 10 μm to 50 μm, and is preferably 15 μm to 40 μm. In addition, when surface treatment is applied, the thickness of the first protective layer is a thickness including the thickness of the surface treatment layer.

B-3. second protective layer

The second protective layer 3 is also formed of any suitable film that can be used as a protective layer for a polarizer. The material that constitutes the main component of the film is the same as described in Section B-2 above regarding the first protective layer. The second protective layer 3 is preferably optically substantially isotropic. In this specification, "optically substantially isotropic" means that the in-plane retardation Re(550) is 0 nm to 10 nm and the thickness direction retardation Rth(550) is -10 nm to +10 nm.

The thickness of the second protective layer is, for example, 15 μm to 35 μm, and is preferably 20 μm to 30 μm. The difference between the thickness of the first protective layer and the thickness of the second protective layer is preferably 15 μm or less, and more preferably 10 μm or less. If the difference in thickness is within this range, curling during bonding can be well suppressed. The thickness of the first protective layer and the thickness of the second protective layer may be the same, the first protective layer may be thicker, and the second protective layer may be thicker. Typically, the first protective layer is thicker than the second protective layer.

C. First phase contrast layer

C-1. Characteristics of the first phase difference layer

The first retardation layer 12 may have any suitable optical and/or mechanical properties depending on the purpose. The first phase difference layer 12 typically has a slow axis. In one embodiment, the angle formed by the slow axis of the first retardation layer 12 and the absorption axis of the polarizer 1 is preferably 10° to 20°, more preferably 13° to 17°, and further. Preferably it is about 15°. If the angle between the slow axis of the first retardation layer 12 and the absorption axis of the polarizer 1 is in this range, the in-plane retardation of the first retardation layer and the second retardation layer are each set to a predetermined range, as described later. And, by arranging the slow axis of the second retardation layer at a predetermined angle with respect to the absorption axis of the polarizer, an optical laminate having excellent circular polarization properties (as a result, excellent anti-reflection properties) in a wide band can be obtained.

The first retardation layer preferably exhibits a refractive index characteristic of nx>ny≥nz. The in-plane retardation Re(550) of the first retardation layer is preferably 180 nm to 320 nm, more preferably 200 nm to 290 nm, and still more preferably 230 nm to 280 nm. Additionally, here, “ny=nz” includes not only the case where ny and nz are completely the same, but also the case where they are substantially the same. Therefore, there may be cases where ny < nz within a range that does not impair the effect of the present invention.

The Nz coefficient of the first phase difference layer is preferably 0.1 to 3, more preferably 0.2 to 1.5, and still more preferably 0.3 to 1.3. When the optical laminate obtained by satisfying this relationship is used in an image display device, very excellent reflected color can be achieved.

The first phase difference layer may exhibit inverse dispersion wavelength characteristics in which the phase difference value increases depending on the wavelength of the measurement light, or may exhibit positive wavelength dispersion characteristics in which the phase difference value decreases depending on the wavelength of the measurement light. Accordingly, it may exhibit flat wavelength dispersion characteristics that rarely change. In one embodiment, the first phase difference layer exhibits flat wavelength dispersion characteristics in which the phase difference value hardly changes depending on the wavelength of the measurement light. In this case, Re(450)/Re(550) of the retardation layer is preferably 0.99 to 1.03, and Re(650)/Re(550) is preferably 0.98 to 1.02. By using a combination of a first phase contrast layer that exhibits flat wavelength dispersion characteristics and a predetermined in-plane retardation and a second retardation layer that exhibits flat wavelength dispersion characteristics and a predetermined in-plane retardation at a predetermined slow axis angle, Very excellent anti-reflection properties can be achieved.

The absolute value of the photoelastic coefficient of the first phase difference layer is preferably 2 × 10 ^-11 m ² /N or less, more preferably 2.0 × 10 ^-13 m ^{2 /N} to 1.5 × ^{10 -11} m ² /N, More preferably, it contains 1.0×10 ^-12 m ^{2 /N} to 1.2× ^{10 -11} m ² /N of resin. If the absolute value of the photoelastic coefficient is in this range, it is difficult for a phase difference change to occur when shrinkage stress occurs during heating. As a result, heat spots in the resulting image display device can be well prevented.

C-2. First retardation layer composed of resin film

When the first retardation layer is composed of a resin film, its thickness is preferably 40 μm or less, and preferably 25 μm to 35 μm. If the thickness of the first retardation layer is within this range, the desired in-plane retardation can be obtained.

The first retardation layer 12 may be made of any suitable resin film that can satisfy the above characteristics. Representative examples of such resins include cyclic olefin-based resin, polycarbonate-based resin, cellulose-based resin, polyester-based resin, polyvinyl alcohol-based resin, polyamide-based resin, polyimide-based resin, polyether-based resin, and polystyrene-based resin. and acrylic resin. When the first retardation layer is composed of a resin film exhibiting flat wavelength characteristics, a cyclic olefin-based resin can be preferably used.

Cyclic olefin resin is a general term for resins that polymerize cyclic olefins as polymerization units, and are described, for example, 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. Resin can be mentioned. Specific examples include ring-opening (co)polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins and α-olefins such as ethylene and propylene (typically random copolymers), and these as unsaturated carboxylic acids or Examples include graft-modified products modified with their derivatives, and their hydrides. Specific examples of cyclic olefins include norbornene monomers. Norbornene-based monomers include, for example, norbornene and its alkyl and/or alkylidene substituents, such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene, 5-ethyl-2-norbornene, 5 -Butyl-2-norbornene, 5-ethylidene-2-norbornene, etc., and polar group substitutes thereof such as halogen; Dicyclopentadiene, 2,3-dihydrodicyclopentadiene, etc.; Dimethanooctahydronaphthalene, its alkyl and/or alkylidene substituent and polar group substituent such as halogen, such as 6-methyl-1,4:5,8-dimethano-1,4,4a,5,6, 7,8,8a-octahydronaphthalene, 6-ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-ethylidene -1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-chloro-1,4:5,8-dimethano-1 ,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8, 8a-octahydronaphthalene, 6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, 6-methoxycarbonyl- 1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphthalene, etc.; Tri-tetramers of cyclopentadiene, such as 4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octahydro-1H-benzoindene, 4,11 :5,10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclopentaanthracene, etc. there is.

In the present invention, other cycloolefins capable of ring-opening polymerization can be used together within the range that does not impair the purpose of the present invention. Specific examples of such cycloolefins include compounds having one reactive double bond, such as cyclopentene, cyclooctene, and 5,6-dihydrodicyclopentadiene.

The cyclic olefin resin preferably has a number average molecular weight (Mn) of 25,000 to 200,000, more preferably 30,000 to 100,000, and most preferably 40,000 to 80,000, as measured by gel permeation chromatography (GPC) using a toluene solvent. am. If the number average molecular weight is within the above range, mechanical strength can be excellent, and solubility, moldability, and flexible handling properties can be improved.

When the cyclic olefin resin is obtained by hydrogenating a ring-opening polymer of norbornene monomer, the hydrogenation rate is preferably 90% or more, more preferably 95% or more, and most preferably 99% or more. Within this range, heat deterioration resistance, light deterioration resistance, etc. are excellent.

As the cyclic olefin resin film, a commercially available film may be used. Specific examples include the brand names "Zeonex" and "Zeonoa" manufactured by Nippon Zeon, the brand names "Arton" manufactured by JSR, the brand name "Topas" manufactured by TICONA, and the brand name "APEL" manufactured by Mitsui Chemicals. I can hear it.

The first retardation layer 12 can be obtained, for example, by stretching a film formed of the cyclic olefin resin. As a method of forming a film from a cyclic olefin resin, any appropriate molding processing method can be employed. Specific examples include compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, cast coating (eg, casting method), calendar molding, and heat pressing. Extrusion molding or cast coating method is preferred. This is because the smoothness of the resulting film can be increased and good optical uniformity can be obtained. Molding conditions can be appropriately set depending on the composition or type of the resin used, the characteristics desired for the retardation layer, etc. In addition, as mentioned above, since many film products of cyclic olefin resin are commercially available, the commercial film may be subjected to stretching treatment as is.

The thickness of the resin film (unstretched film) can be set to any appropriate value depending on the desired thickness of the first retardation layer, desired optical properties, stretching conditions described later, etc. Preferably it is 50㎛ to 300㎛.

For the stretching, any appropriate stretching method and stretching conditions (eg, stretching temperature, stretching ratio, stretching direction) may be employed. Specifically, various stretching methods such as free end stretching, fixed end stretching, free end shrinking, and fixed end shrinking may be used singly, simultaneously, or sequentially. Regarding the stretching direction, it can be carried out in various directions or dimensions, such as the longitudinal direction, the width direction, the thickness direction, and the oblique direction. The stretching temperature is preferably Tg-30°C to Tg+60°C, more preferably Tg-30°C to Tg+50°C, relative to the glass transition temperature (Tg) of the resin film, and Tg-15°C to Tg. It is more preferable that Tg+30°C.

By appropriately selecting the stretching method and stretching conditions, a retardation film having the desired optical properties (eg, refractive index properties, in-plane retardation, Nz coefficient) can be obtained.

In one embodiment, the retardation film is produced by uniaxial stretching or fixed-end uniaxial stretching of a resin film. A specific example of fixed-end uniaxial stretching is a method of stretching a resin film in the width direction (transverse direction) while running it in the longitudinal direction. The stretching ratio is preferably 1.1 to 3.5 times.

In another embodiment, the retardation film can be produced by continuously obliquely stretching a long resin film in a direction at a predetermined angle with respect to the longitudinal direction. By employing oblique stretching, a long stretched film having an orientation angle of a predetermined angle (slow axis in the direction of the angle) with respect to the longitudinal direction of the film is obtained, making roll-to-roll possible, for example, when laminated with a polarizer. This makes it possible to simplify the manufacturing process. Additionally, the angle may be the angle formed between the absorption axis of the polarizer and the slow axis of the first retardation layer in the optical laminate. As mentioned above, the angle is preferably 10° to 20°, more preferably 13° to 17°, and even more preferably about 15°.

Stretching machines used for diagonal stretching include, for example, tenter-type stretching machines that can apply feed force, tension force, or pull force at different speeds on the left and right in the horizontal and/or vertical directions. Tenter-type stretching machines include transverse uniaxial stretching machines and simultaneous biaxial stretching machines, but any suitable stretching machine can be used as long as it can continuously diagonally stretch a long resin film.

By appropriately controlling the left and right speeds in the stretching machine, it is possible to obtain a first retardation layer (substantially a long retardation film) having the desired in-plane retardation and having a slow axis in the desired direction.

The stretching temperature of the film may vary depending on the in-plane retardation value and thickness desired for the first retardation layer, the type of resin used, the thickness of the film used, the stretching ratio, etc. Specifically, the stretching temperature is preferably Tg-30°C to Tg+60°C, more preferably Tg-30°C to Tg+50°C, and even more preferably Tg-15°C to Tg+30°C. By stretching at such a temperature, a first retardation layer having appropriate properties in the present invention can be obtained. Additionally, Tg is the glass transition temperature of the film's constituent materials.

C-3. A first phase difference layer composed of an orientation-solidified layer of a liquid crystal compound

The first phase difference layer 12 may be an alignment-fixed layer of a liquid crystal compound. Since the difference between nx and ny of the retardation layer obtained by using a liquid crystal compound can be significantly increased compared to a non-liquid crystal material, the thickness of the first retardation layer for obtaining the desired in-plane retardation can be significantly reduced. As a result, further thinning of the optical laminate can be realized. When the first phase difference layer 12 is composed of an alignment-fixed layer of a liquid crystal compound, its thickness is preferably 7 μm or less, and more preferably 5 μm or less. By using a liquid crystal compound, it is possible to realize an in-plane retardation equivalent to that of a resin film with a thickness significantly thinner than that of a resin film.

In this specification, the term “alignment-fixed layer” refers to a layer in which a liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state is fixed. In addition, the “alignment hardening layer” is a concept that includes an alignment hardening layer obtained by curing a liquid crystal monomer, as will be described later. In this embodiment, the liquid crystal compounds in the form of rods are typically aligned in the slow axis direction of the first retardation layer (homogeneous orientation). Examples of the liquid crystal compound include a liquid crystal compound (nematic liquid crystal) whose liquid crystal phase is a nematic phase. As such a liquid crystal compound, for example, liquid crystal polymer or liquid crystal monomer can be used. The mechanism for expressing liquid crystallinity of the liquid crystal compound may be lyotropic or thermotropic. The liquid crystal polymer and liquid crystal monomer may be used individually or in combination.

When the liquid crystal compound is a liquid crystal monomer, the liquid crystal monomer is preferably a polymerizable monomer or a crosslinkable monomer. This is because the alignment state of the liquid crystal monomer can be fixed by polymerizing or crosslinking (i.e., curing) the liquid crystal monomer. After aligning the liquid crystal monomers, for example, by polymerizing or crosslinking the liquid crystal monomers, the alignment state can be thereby fixed. Here, a polymer is formed by polymerization, and a three-dimensional network structure is formed by crosslinking, which is non-liquid crystalline. Accordingly, the formed first phase contrast layer does not transition into a liquid crystal phase, a glass phase, or a crystal phase due to temperature changes characteristic of liquid crystal compounds, for example. As a result, the first phase difference layer becomes a phase difference layer that is not affected by temperature changes and has extremely excellent stability.

The temperature range where a liquid crystal monomer exhibits liquid crystallinity varies depending on its type. Specifically, the temperature range is preferably 40°C to 120°C, more preferably 50°C to 100°C, and most preferably 60°C to 90°C.

Any appropriate liquid crystal monomer may be employed as the liquid crystal monomer. For example, polymerization methods described in Japanese Patent Application No. 2002-533742 (WO00/37585), EP358208 (US5211877), EP66137 (US4388453), WO93/22397, EP0261712, DE19504224, DE4408171 and GB2280445. gen compounds, etc. can be used. Specific examples of such polymerizable mesogenic compounds include, for example, product name LC242 manufactured by BASF, brand name E7 manufactured by Merck, and brand name LC-Sillicon-CC3767 manufactured by Wacker-Chem. As the liquid crystal monomer, for example, a nematic liquid crystal monomer is preferable.

The alignment-fixed layer of the liquid crystal compound is made by subjecting the surface of a predetermined substrate to an orientation treatment, coating the surface with a coating solution containing the liquid crystal compound, and aligning the liquid crystal compound in a direction corresponding to the orientation treatment, thereby maintaining the orientation state. It can be formed by fixing . By using such an orientation treatment, the liquid crystal compound can be oriented in a predetermined direction with respect to the long direction of the long-length substrate, and as a result, the slow axis can be expressed in the predetermined direction of the formed retardation layer. For example, a retardation layer having a slow axis oriented at 15° with respect to the long direction can be formed on a long substrate. Even when such a retardation layer is desired to have a slow axis in the oblique direction, since it can be laminated using roll-to-roll, the productivity of the optical laminate can be significantly improved. In one embodiment, the substrate is any suitable resin film, and the orientation solidification layer formed on the substrate can be transferred to the surface of the polarizing plate. In other embodiments, the substrate may be a second protective layer. In this case, the transfer process is omitted and lamination can be performed continuously from roll-to-roll from the formation of the orientation solidification layer (first phase difference layer), thereby further improving productivity.

As the orientation treatment, any suitable orientation treatment may be employed. Specifically, mechanical orientation treatment, physical orientation treatment, and chemical orientation treatment may be mentioned. Specific examples of mechanical orientation treatment include rubbing treatment and stretching treatment. Specific examples of physical alignment treatment include magnetic field alignment treatment and electric field alignment treatment. Specific examples of chemical alignment treatment include oblique vapor deposition and photo-alignment treatment. As for the treatment conditions for various orientation treatments, any appropriate conditions may be adopted depending on the purpose.

The alignment of the liquid crystal compound is achieved by treatment at a temperature that exhibits a liquid crystal phase depending on the type of the liquid crystal compound. By performing such temperature treatment, the liquid crystal compound assumes a liquid crystal state and is aligned in accordance with the orientation treatment direction of the substrate surface.

In one embodiment, the alignment state is fixed by cooling the liquid crystal compound aligned as described above. When the liquid crystal compound is a polymerizable monomer or a crosslinkable monomer, the alignment state is fixed by subjecting the liquid crystal compound oriented as described above to polymerization treatment or crosslinking treatment.

Specific examples of the liquid crystal compound and details of the method for forming the alignment solidification layer are described in Japanese Patent Application Laid-Open No. 2006-163343. The description in this publication is incorporated herein by reference.

D. Second phase contrast layer

D-1. Characteristics of the second phase difference layer

The second retardation layer 13 may have any suitable optical and/or mechanical properties depending on the purpose. The second phase difference layer 13 typically has a slow axis. In one embodiment, the angle formed by the slow axis of the second retardation layer 13 and the absorption axis of the polarizer 1 is preferably 65° to 85°, more preferably 72° to 78°, and further. Preferably it is about 75°. The angle formed by the slow axis of the second retardation layer 13 and the slow axis of the first retardation layer 12 is preferably 52° to 68°, more preferably 57° to 63°, and even more preferably It is about 60°. If the angle formed by the slow axis of the second retardation layer 13 and the absorption axis of the polarizer 1 is in this range, the in-plane retardation of the first retardation layer is set to a predetermined range as described above, and the By arranging the slow axis at a predetermined angle with respect to the absorption axis of the polarizer and setting the in-plane retardation of the second retardation layer to a predetermined range as described later, very excellent circular polarization properties in a wide band (as a result, very excellent anti-reflection properties) ) can be obtained.

The second retardation layer preferably exhibits a refractive index characteristic of nx>ny≥nz. The in-plane retardation Re(550) of the second retardation layer is preferably 80 nm to 200 nm, more preferably 100 nm to 180 nm, and even more preferably 110 nm to 170 nm.

Other characteristics of the second phase difference layer are the same as those described in Section C above with respect to the first phase difference layer.

D-2. Second retardation layer composed of resin film

When the second retardation layer is made of a resin film, its thickness is preferably 40 μm or less, and preferably 25 μm to 35 μm. If the thickness of the second retardation layer is within this range, the desired in-plane retardation can be obtained. The material, characteristics, manufacturing method, etc. of the second phase difference layer are the same as described in Section C-2 above with respect to the first phase difference layer.

D-3. A second phase contrast layer composed of an orientation-solidified layer of a liquid crystal compound.

The second phase difference layer 13 may be an alignment-fixed layer of a liquid crystal compound, similar to the first phase difference layer. When the second retardation layer 13 is composed of an alignment-fixed layer of a liquid crystal compound, its thickness is preferably 7 μm or less, and more preferably 5 μm or less. When the second retardation layer is composed of an alignment-fixed layer of a liquid crystal compound, its material, characteristics, manufacturing method, etc. are the same as those described in Section C-3 above with respect to the first retardation layer.

D-4. Combination of the first phase difference layer and the second phase difference layer

The first retardation layer and the second retardation layer may be used in any appropriate combination. Specifically, the first retardation layer may be comprised of a resin film, and the second retardation layer may be comprised of an alignment-fixed layer of a liquid crystal compound; The first retardation layer may be composed of an alignment-fixed layer of a liquid crystal compound, and the second retardation layer may be composed of a resin film; Both the first retardation layer and the second retardation layer may be composed of a resin film; Both the first retardation layer and the second retardation layer may be composed of an alignment-fixed layer of a liquid crystal compound. Preferably, when the first retardation layer is composed of a resin film, the second retardation layer is also composed of a resin film; When the first retardation layer is composed of an alignment-fixed layer of a liquid crystal compound, the second retardation layer is also composed of an alignment-fixed layer of a liquid crystal compound. In addition, when both the first phase difference layer and the second phase difference layer are comprised of a resin film, the first phase difference layer and the second phase difference layer may be the same or may have different detailed structures. The same applies to the case where both the first retardation layer and the second retardation layer are composed of an alignment-fixed layer of a liquid crystal compound.

E. Conductive layer

The conductive layer can be formed by forming a metal oxide film on any suitable substrate by any suitable film forming method (eg, vacuum deposition, sputtering, CVD, ion plating, spraying, etc.). After film formation, heat treatment (for example, 100°C to 200°C) may be performed as needed. An amorphous film can be crystallized by performing heat treatment. Examples of metal oxides include indium oxide, tin oxide, zinc oxide, indium-tin composite oxide, tin-antimony composite oxide, zinc-aluminum composite oxide, and indium-zinc composite oxide. Indium oxide may be doped with divalent metal ions or tetravalent metal ions. Preferably, it is indium-based complex oxide, and more preferably, it is indium-tin complex oxide (ITO). Indium-based complex oxide has the characteristics of having high transmittance (e.g., 80% or more) in the visible light region (380 nm to 780 nm) and low surface resistance per unit area.

When the conductive layer contains a metal oxide, the thickness of the conductive layer is preferably 50 nm or less, and more preferably 35 nm or less. The lower limit of the thickness of the conductive layer is preferably 10 nm.

The surface resistance value of the conductive layer is preferably 300 Ω/□ or less, more preferably 150 Ω/□ or less, and still more preferably 100 Ω/□ or less.

The conductive layer can be patterned as needed. A conductive part and an insulating part can be formed by patterning. Any suitable method may be adopted as the patterning method. Specific examples of the patterning method include wet etching and screen printing.

F. Description

The base material has a slow axis. In the present invention, even when using a substrate having a slow axis, that is, an anisotropic substrate, the anti-reflection function of the circular polarizer is sufficiently demonstrated, and an optical laminate can be provided that can effectively prevent reflection of external light or reflection of the background. . Therefore, according to the present invention, there is no need to select materials constituting the base material with emphasis on optical isotropy as in the past, and various materials can be selected according to desired properties.

In addition, the substrate may be a substrate that is produced with the goal of being optically isotropic (in-plane retardation Re(550) is 0 nm) and unavoidably has a slow axis. When forming a conductive layer on a substrate (i.e., when the substrate and the conductive layer are stacked by close contact lamination), unnecessary slow axes may occur in the substrate due to heating during the film formation process. The slow axis created in this way inhibits the anti-reflection function of the circularly polarizing plate, makes it difficult to control its direction, and may also cause a decrease in production stability. In the present invention, even if the slow axis is a substrate, the anti-reflection function of the circularly polarizing plate is sufficiently exhibited. In the present invention, a conductive layer can be formed by allowing the occurrence of a slow axis, and restrictions on the conditions for forming a conductive layer can be reduced.

The above effect is obtained by optimizing the angle between the slow axis of the substrate and the slow axis of the second retardation layer. The present invention is particularly useful in that the anti-reflection function of the circularly polarizing plate is sufficiently exercised no matter what direction the slow axis of the substrate is oriented.

The angle formed by the slow axis of the substrate and the slow axis of the second retardation layer is -5° to 5° or 85° to 95°, preferably -3° to 3° or 87° to 93°, and more preferably is -1° to 1° or 89° to 91°, and is particularly preferably 0° or 90°. Within this range, the anti-reflection function of the circularly polarizing plate is sufficiently exhibited, and an optical laminate that can effectively prevent reflection of external light, reflection of the background, etc. can be provided. In addition, in this specification, a clockwise angle with respect to the slow axis of the substrate is regarded as a positive angle, and a counterclockwise angle is regarded as a negative angle.

The angle formed by the slow axis of the substrate and the slow axis of the first retardation layer is 55° to 65° or 145° to 155°, preferably 57° to 63° or 147° to 153°, and more preferably 59° to 59°. ° to 61° or 149° to 151°, and particularly preferably 60° or 150°. Within this range, the anti-reflection function of the circularly polarizing plate is sufficiently exhibited, and an optical laminate that can effectively prevent reflection of external light, reflection of the background, etc. can be provided.

The substrate preferably exhibits the relationship nx>ny≥nz in its refractive index properties. The in-plane retardation Re(550) of the substrate is greater than 0 nm. According to the present invention, even when using a substrate having an in-plane retardation Re, an optical laminate in which the anti-reflection function of the circularly polarizing plate is sufficiently exhibited as described above can be obtained. In one embodiment, the in-plane retardation Re(550) of the substrate is 3 nm or more. In another embodiment, the in-plane retardation Re (550) of the substrate is 5 nm or more. The upper limit of the in-plane retardation Re(550) of the substrate is, for example, 10 nm. If the in-plane retardation Re(550) of the substrate is 10 nm or less (more preferably 8 nm or less, even more preferably 6 nm or less), the anti-reflection function of the circular polarizer is further improved.

Any suitable resin film can be used as the substrate. Specific examples of constituent materials include cyclic olefin resin, polycarbonate resin, cellulose resin, polyester resin, and acrylic resin.

The thickness of the base material is preferably 10 μm to 200 μm, and more preferably 20 μm to 60 μm.

If necessary, a hard coat layer (not shown) may be provided between the conductive layer 21 and the base material 22. As the hard coat layer, a hard coat layer having any suitable structure may be used. The thickness of the hard coat layer is, for example, 0.5 μm to 2 μm. If the haze is within an acceptable range, fine particles to reduce Newton rings may be added to the hard coat layer. Additionally, if necessary, an anchor coat layer to increase the adhesion of the conductive layer and/or a refractive index adjustment layer to adjust the reflectance are provided between the conductive layer 21 and the substrate 22 (hard coat layer, if present). It's okay. Any suitable configuration may be employed as the anchor coat layer and the refractive index adjustment layer. The anchor coat layer and the refractive index adjustment layer may be thin layers of several nm to tens of nm.

If necessary, another hard coat layer may be provided on the side of the substrate 22 opposite to the conductive layer 21 (outermost side of the optical laminate). The hard coat layer typically includes a binder resin layer and spherical particles, and the spherical particles protrude from the binder resin layer to form convex portions. The details of such a hard coating layer are described in Japanese Patent Application Laid-Open No. 2013-145547, the description of which is incorporated herein by reference.

G. Other

The optical laminate according to the embodiment of the present invention may further include other layers. In practical terms, an adhesive layer (not shown) for bonding to the display cell is provided on the surface of the substrate 22. It is preferable that a release film is bonded to the surface of the adhesive layer until the optical laminated body is provided for use.

H. Image display device

The optical laminate described in items A to G above can be applied to an image display device. Accordingly, the present invention includes an image display device using such an optical laminate. Representative examples of image display devices include liquid crystal display devices and organic EL display devices. An image display device according to an embodiment of the present invention is provided with the optical laminate described in items A to G above on its viewing side. The optical laminate is laminated so that the conductive layer is on the display cell (eg, liquid crystal cell, organic EL cell) side (so that the polarizer is on the visible side). That is, the image display device according to the embodiment of the present invention may be a so-called inner touch panel type input display device in which a touch sensor is embedded between a display cell (eg, liquid crystal cell, organic EL cell) and a polarizing plate. In this case, the touch sensor may be disposed between the conductive layer (or conductive layer with a base material) and the display cell. As for the configuration of the touch sensor, a configuration known in the industry may be adopted, so a detailed description is omitted.

[Example]

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

For the optical laminate with the configuration shown in Table 1 below, the reflection characteristics of the optical laminate were evaluated from the front colors a and b using an optical simulator (manufactured by Shintec, brand name "LCD Master V8").

In addition, a light source (D65 light source registered in "LCD Master V8") is placed on the side opposite to the first retardation layer of the polarizer, and a reflector (registered in "LCD Master V8") is placed on the side opposite to the second retardation layer of the substrate. It was configured to place a registered ideal reflector (Idea-Reflector).

In addition, the front colors a and b were derived with the same configuration as Table 1 except that the base material was not included, and the results were used as a reference.

In this evaluation, as described later, a simulation is performed by changing the slow axis angle of the substrate, and the reflection characteristics of the optical laminate are evaluated through comparison with the reference.

[Table 1]

[Example 1]

The angle between the slow axis of the substrate and the absorption axis of the polarizer of the polarizing plate was set to 75°. That is, the angle formed between the slow axis of the substrate and the slow axis of the second phase difference layer was set to 0°.

[Example 2]

The angle formed between the slow axis of the substrate and the absorption axis of the polarizer of the polarizing plate was set to 165°. That is, the angle formed between the slow axis of the substrate and the slow axis of the second phase difference layer was set to 90°.

[Example 3]

The angle formed between the slow axis of the substrate and the absorption axis of the polarizer of the polarizing plate was set to 70°. That is, the angle formed between the slow axis of the substrate and the slow axis of the second retardation layer was set to -5°.

[Example 4]

The angle formed between the slow axis of the substrate and the absorption axis of the polarizer of the polarizing plate was set to 80°. That is, the angle formed between the slow axis of the substrate and the slow axis of the second retardation layer was set to 5°.

[Example 5]

The angle formed between the slow axis of the substrate and the absorption axis of the polarizer of the polarizing plate was set to 160°. That is, the angle formed between the slow axis of the substrate and the slow axis of the second phase difference layer was set to 85°.

[Example 6]

The angle formed between the slow axis of the substrate and the absorption axis of the polarizer of the polarizing plate was set to 170°. That is, the angle formed between the slow axis of the substrate and the slow axis of the second phase difference layer was set to 95°.

[Comparative example]

The angle between the slow axis of the substrate and the absorption axis of the polarizer of the polarizing plate was changed within the range of 0° to 65°, 85° to 155°, and 175° to 180°, and the reflection characteristics at each angle were evaluated.

Regarding the results of Examples and Comparative Examples, plots of front colors a and b are shown in Figure 2. Additionally, a graph showing the axis angle dependence of Δab is shown in Figure 3. Additionally, △ab is calculated by △ab={(front color a - front color a of reference) ² + (front color b - front color b of reference) ² } ^1/2 . The lower Δab, the less the influence of the isotropic substrate and the better the anti-reflection properties.

As is clear from Figures 2 and 3, the optical laminate of the present invention has an excellent anti-reflection function.

[Industrial applicability]

The optical laminate of the present invention is preferably used in image display devices such as liquid crystal displays and organic EL display devices, and can be particularly preferably used as an anti-reflection film for organic EL display devices. Additionally, the optical laminate of the present invention can be suitably used in an inner touch panel type input display device.

1: Polarizer
2: first protective layer
3: second protective layer
11: Polarizer
12: first phase difference layer
13: second phase difference layer
21: conductive layer
22: Description
100: Optical laminate

Claims (7)

It has a polarizing plate including a polarizer and a protective layer disposed on at least one side of the polarizer, a first phase difference layer, a second phase difference layer, a conductive layer, and a substrate in this order,
The in-plane retardation Re(550) of the substrate is greater than 0 nm and 10 nm or less,
The angle between the slow axis of the substrate and the slow axis of the second retardation layer is -5° to 5° or 85° to 95°,
The angle formed between the absorption axis of the polarizer and the slow axis of the first retardation layer is 10° to 20°, and the angle formed between the absorption axis and the slow axis of the second retardation layer is 65° to 85°,
The in-plane phase difference Re (550) of the first phase difference layer is 180 nm to 320 nm,
The in-plane phase difference Re (550) of the second phase difference layer is 80 nm to 200 nm,
Optical laminate.
delete According to claim 1,
An optical laminate in which the first phase difference layer and the second phase difference layer are composed of a cyclic olefin resin film.
delete According to claim 1,
An optical laminate wherein the first retardation layer and the second retardation layer are an alignment-fixed layer of a liquid crystal compound.
delete An image display device comprising the optical laminated body according to claim 1.

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