Patent Application
20230358931
The present invention relates to an optical sheet and a display device.
To improve the color purity of a display device, there is a known method of using a color filter to separate or correct white light or monochromatic light emitted from a light source of a display device to narrow a full width at half maximum.
For improving color purity by a color filter, it is necessary to increase the concentration of a coloring material and thicken the filter. High coloring material concentrations, however, may degrade photolithographic properties. Thickening a filter may deteriorate pixel shapes and viewing angle properties.
Furthermore, a color filter which improved color purity is generally low in transmittance and likely to lower luminance efficiency.
In view of the above, a method of improving color purity without using a color filter is proposed.
PTL 1 discloses an optical filter including an adhesive resin layer that contains a coloring material having strong absorption of light in a prescribed wavelength band.
[Citation List] [Patent Literature] [PTL 1] JP 2019-56865 A; [PTL 2] JP 5917659 B.
A functional colorant contained in a coloring material used in a color-correction layer is often not high in light resistance, heat resistance, and moist heat resistance. Therefore, in an optical filter including such a functional colorant, the function of the functional colorant may decrease with use, leading to a failure to sufficiently exert the color correction function.
PTL 2 discloses a technique of mixing, into an adhesive layer, an ultraviolet absorber based on benzophenone or benzotriazole, and others, to improve light resistance.
The inventors found that the method described in PTL 2 might not sufficiently improve light resistance. Furthermore, the inventors conducted research on the solution and accomplished the present invention.
An object of the present invention is to provide an optical sheet that has a good color correction function and can withstand long-term use.
For solving the above-described problem, an optical sheet according to a first aspect of the present invention includes:
A display device according to a second aspect of the present invention includes a light source and the optical sheet according to the first aspect which is disposed with the first adhesive layer being arranged to face the light source.
According to the above-described aspects of the present invention, there can be provided: an optical sheet that has a good color correction function and can withstand long-term use; and a display device including the optical sheet.
Hereinafter, the first embodiment of the present invention will be described with reference to
In the present embodiment, a direction in which the colored adhesive layer 10 and the ultraviolet shielding layer 20 are laminated is referred to as a thickness direction, one side in the thickness direction (an observer side when a display image on a display device is observed) is referred to as an upper side, and a side opposite the upper side is referred to as a lower side.
The colored adhesive layer 10 contains an adhesive and a colorant. The adhesive is a resin that has adhesive properties. The resin component of the adhesive is not particularly limited, and examples thereof include silicone-based adhesives, acryl-based adhesives, and urethane-based adhesives. The colorant selectively absorbs the wavelength range of visible light. The colored adhesive layer 10 has a structure in which the colorant is contained in a base adhesive that has adhesive properties.
The colorant contains at least one from the group of three types of coloring materials including first to third coloring materials described below. The number of types of coloring materials to be contained is not limited to one, and two or more types of coloring materials may be contained.
The first coloring material has a maximum absorption wavelength in a range of 470 nm to 530 nm and an absorption spectral half width (full width at half maximum) of 15 nm to 45 nm.
The second coloring material has a maximum absorption wavelength in a range of 560 nm to 620 nm and an absorption spectral half width (full width at half maximum) of 15 nm to 55 nm.
In the third coloring material, a wavelength having the lowest transmittance in a wavelength range of 400 to 800 nm is in a range of 650 to 800 nm.
In the following description, the absorption spectral half width denotes the full width at half maximum.
The colored adhesive layer 10 has absorption in which the transmittance at the maximum absorption wavelength of one of absorption wavelength bands of the coloring materials is 1% or more and less than 50%.
When the coloring materials having the above-described absorption characteristics are used as the first to third coloring materials to be contained in the colored adhesive layer 10, the colored adhesive layer 10 can absorb, of visible light emitted by a display device, visible light in a wavelength region in which the light emission intensity is relatively low. For example, the colored adhesive layer 10 can absorb, of visible light in a wavelength range of 400 to 800 nm, visible light in a range of 470 nm to 530 nm, 560 nm to 620 nm, and 650 to 800 nm using the first, second, and third coloring materials, respectively. The wavelengths absorbed by the first, second, and third coloring materials are, for example, ranges overlapping wavelength regions in which the light emission intensity is relatively low, of visible light emitted by a display device in the spectroscopic spectrum during white display of an OLED display device illustrated in
As the first to third coloring materials, there can be used a coloring material that contains one or more compounds selected from the group consisting of a compound having any of a porphyrin structure, merocyanine structure, phthalocyanine structure, azo structure, cyanine structure, squarylium structure, coumarin structure, polyene structure, quinone structure, tetraazaporphyrin structure, pyrromethene structure, and indigo structure, and a metal complex thereof. In particular, it is more preferable to use squarylium structure or a metal complex having, in the molecule, a porphyrin structure, pyrromethene structure, or phthalocyanine structure.
The colored adhesive layer 10 may contain at least one of a radical scavenger, a singlet oxygen quencher, and a peroxide decomposer.
The coloring material contained in the colored adhesive layer 10 is also degraded by light, heat, and other factors which are promoted under the influence of oxygen. When the radical scavenger is mixed in the colored adhesive layer 10, radicals produced during oxidative degradation of the colorant can be trapped to prevent degradation of the coloring material caused by autooxidation, which can further lengthen the period during which the color correction function is maintained.
Also, when the singlet oxygen quencher is present in the colored adhesive layer 10, it is possible to inactivate highly reactive singlet oxygen having the property of easily oxidatively degrading (fading) the colorant to suppress the oxidative degradation (color fading) of the colorant.
When the peroxide decomposer is present in the colored adhesive layer 10, the peroxide decomposer decomposes peroxides generated during oxidative degradation of the colorant, which can terminate the autooxidation cycle and suppress colorant degradation (color fading).
The radical scavenger and the singlet oxygen quencher may be used in combination. Furthermore, the peroxide decomposer may be combined therewith.
As the radical scavenger, a hindered amine photostabilizer can be used. A hindered amine photostabilizer having a molecular weight of 2,000 or more, with which high color fading suppression effects can be obtained, is particularly preferable. When the radical scavenger has a low molecular weight, it easily volatilizes with the result that the number of molecules remaining in the colored adhesive layer 10 is small, and thus it is sometimes difficult to obtain sufficient color fading suppression effects. Examples of a material suitably used as the radical scavenger include Chimassorb 2020FDL, Chimassorb 944FDL, and Tinuvin 622 manufactured by BASF, and LA-63P manufactured by ADEKA Corporation.
Examples of the singlet oxygen quencher include transition metal complexes, colorants, amines, phenols, and sulfides. Examples of particularly suitably used materials include transition metal complexes of dialkyl phosphates, dialkyl thiocarbarmates, or benzene dithiol or similar dithiols. As the central metal of these transition metal complexes, nickel, copper, or cobalt is suitably used.
The peroxide decomposer has the function of decomposing peroxides generated during oxidative degradation of the colorant, terminating the autooxidation cycle, and suppressing colorant degradation (color fading). As the peroxide decomposer, a phosphorus-based antioxidant and a sulfur-based antioxidant can be used.
Examples of the phosphorus-based antioxidant include 2,2′-methylenebis(4,6-di-t-butyl-1-phenyloxy)(2-ethylhexyloxy)phosphorus, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, and 6-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propoxy]-2,4,8,10-tetra-t-butyldibenz[d,F][1,3,2]dioxaphosphepine.
Examples of the sulfur-based antioxidant include 2,2-bis({[3-(dodecylthio)propionyl]oxy}methyl)-1,3-propanediyl-bis[3-(dodecylthio)propionate], 2-mercaptobenzimidazole, dilauryl-3,3′-thiodipropionate, dimyristyl-3,3′-thiodipropionate, distearyl-3,3′-thiodipropionate, pentaerythrityl-tetrakis(3-laurylthiopropionate), and 2-mercaptobenzothiazole.
The ultraviolet shielding layer 20 contains an ultraviolet absorber in order to suppress degradation of the colorant contained in the colored adhesive layer 10. Accordingly, the ultraviolet shielding layer 20 has an ultraviolet shielding rate of 85% or more. Here, the ultraviolet shielding rate is a value measured in accordance with JIS L 1925 and calculated according to the following equation:
ultraviolet shielding rate (%) = 100 - average transmittance (%) of ultraviolet light at wavelengths of 290 to 400 nm.
The absorption wavelength region in the ultraviolet region of the ultraviolet absorber contained in the ultraviolet shielding layer 20 is preferably in a range of 290 to 370 nm. Examples of such an ultraviolet absorber include benzophenone-based, benzotriazole-based, triazine-based, oxalic acid anilide-based, and cyanoacrylate-based compounds. The ultraviolet absorber is added for suppressing degradation of the colorant contained in the colored adhesive layer 10. Therefore, an ultraviolet absorber is used that has properties of absorbing light in a wavelength region that contributes to the degradation of the colorant contained in the colored adhesive layer 10, of the ultraviolet region.
The ultraviolet shielding layer 20 may further contain a resin that exerts adhesiveness. Hereinafter, when the ultraviolet shielding layer 20 contains a resin that exerts adhesiveness, it is also referred to as an “ultraviolet absorption adhesive layer 20” or a “second adhesive layer 20”. In the ultraviolet absorption adhesive layer 20, the resin component exerting adhesiveness is not particularly limited, and resins similar to in the colored adhesive layer 10 can be used.
The optical sheet 1 can be manufactured by forming one of the colored adhesive layer 10 and the ultraviolet shielding layer (ultraviolet absorption adhesive layer) 20 on a base film formed with resin or the like, forming the other thereon, and peeling the base film. The base film may not be peeled and used as the separator S.
The colored adhesive layer 10 and the ultraviolet shielding layer (ultraviolet absorption adhesive layer) 20 can be formed by, for example, coating with a coating liquid that contains constituent materials of each layer and drying the coat.
By peeling the separator S, the colored adhesive layer 10 or the ultraviolet shielding layer (ultraviolet absorption adhesive layer) 20 can be bonded and attached to various objects to impart a color correcting ability thereto.
Examples of objects to have the optical sheet 1 attached include various optical function films such as anti-reflection films and anti-glare films and display devices such as displays. The optical sheet 1 is attached in such a manner that externally incident light containing ultraviolet light passes through the ultraviolet shielding layer (ultraviolet absorption adhesive layer) 20 and then enters the colored adhesive layer 10.
When light emitted from a light source (light emitted from the display device side) passes through the colored adhesive layer 10, a wavelength component at and around the maximum absorption wavelength of the contained coloring material is absorbed. This can improve the color purity of the display device. Furthermore, unlike in a color filter, the concentration of the coloring material does not need to be increased very much, and thus color purity can be improved without excessively lowering the luminance of the display device.
The coloring material contained in the colored adhesive layer 10 is excellent in color correction function but sometimes has insufficient resistance to light, especially to ultraviolet light. Therefore, degradation proceeds with time in response to irradiation with ultraviolet light, with the result that light at and around the maximum absorption wavelength cannot be absorbed.
In the optical sheet 1 of the present embodiment, the ultraviolet shielding layer (ultraviolet absorption adhesive layer) 20 has a high ultraviolet shielding rate. Therefore, when the optical sheet 1 is attached in the above-described manner, a major portion of ultraviolet light contained in external light does not pass through the ultraviolet shielding layer (ultraviolet absorption adhesive layer) 20 and fails to reach the colored adhesive layer 10. Accordingly, ΔE * ab, which is a chromaticity difference between before and after a light resistance test (irradiation for 120 hours under the conditions of a xenon lamp illuminance of 60 W/cm2 (300 to 400 nm), a temperature of 45° C., and a humidity of 50% RH), can satisfy Equation (1) below:
In brief, degradation of the coloring material contained in the colored adhesive layer 10 can be prevented, and the color correction function can be maintained for a long time. It is noted that ΔE * ab of Equation (1) is a chromaticity difference standardized by the CIE (Commission International del’Eclairage).
The second embodiment of the present invention will be described with reference to
The transparent substrate 30 has an ultraviolet shielding rate of 85% or more and functions as an ultraviolet shielding layer. The definition of the ultraviolet shielding rate is the same as that explained regarding the ultraviolet shielding layer (ultraviolet absorption adhesive layer) 20.
Examples of usable materials of the transparent substrate 30 include polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate, polyacrylates such as polymethyl methacrylate, polyamides such as nylon 6 and nylon 66, transparent resins such as polyimide, polyarylate, polycarbonate, triacetyl cellulose, polyacrylates, polyvinyl alcohols, polyvinyl chloride, cycloolefin copolymers, norbornene-containing resins, polyether sulfones, and polysulfone, and inorganic glasses. Among these, a film formed of polyethylene terephthalate (PET), a film formed of triacetyl cellulose (TAC), a film formed of polymethyl methacrylate (PMMA), and a film formed of polyester can be suitably used. The thickness of the transparent substrate 30 is not particularly limited but preferably 10 to 100 µm.
In
The ultraviolet shielding rate of the transparent substrate is not particularly limited, and may depend on the absorption characteristics of resin, or the ultraviolet absorber described as an example for the ultraviolet shielding layer (ultraviolet absorption adhesive layer) 20 may be used.
In the optical sheet 1A according to the present embodiment, the transparent substrate 30 suppresses deterioration of the coloring material contained in the colored adhesive layer 10 caused by ultraviolet light. As a result, the same effects as those of the optical sheet 1 according to the first embodiment can be exerted.
In the optical sheet 1A, a transparent adhesive layer may be disposed on a side of the transparent substrate 30 where the colored adhesive layer 10 is not disposed (on the upper side of the transparent substrate 30). This allows an object to be bonded to a side where the colored adhesive layer 10 is not disposed and thus enhances versatility.
The third embodiment of the present invention will be described with reference to
The separator S is disposed only on a surface of the colored adhesive layer 10 opposite the surface on which the ultraviolet shielding layer (ultraviolet absorption adhesive layer) 20 is disposed (on the lower surface of the colored adhesive layer 10).
In the optical sheet 1B according to the present embodiment, the transparent substrate 30 and the ultraviolet shielding layer (ultraviolet absorption adhesive layer) 20 suppress deterioration of the coloring material contained in the colored adhesive layer 10 caused by ultraviolet light. As a result, effects that are the same as or more than those of the optical sheet 1 according to the first embodiment and/or the optical sheet 1A according to the second embodiment are exerted.
In the optical sheet 1B, a transparent adhesive layer may be disposed on a side of the transparent substrate 30 where the colored adhesive layer 10 is not disposed (on the upper side of the transparent substrate 30). This allows an object to be bonded to a side where the colored adhesive layer 10 is not disposed (to the upper side of the transparent substrate 30) and thus enhances versatility.
The fourth embodiment of the present invention will be described with reference to
The oxygen barrier layer 40 is an optically transmissive, transparent layer and has an oxygen permeability of 10 cc/(m2·day·atm) or less, more preferably 5 cc/(m2·day·atm) or less, and further preferably 1 cc/(m2·day·atm) or less. A material for forming the oxygen barrier layer 40 preferably contains polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymers (EVOH), vinylidene chloride, siloxane resin, and others, and Maxive (registered trademark) manufactured by Mitsubishi Gas Chemical Company, Inc., EVAL manufactured by Kuraray Co., Ltd., Saran Latex and Saran Resin manufactured by Asahi Kasei Corp., and others can be used. The thickness of the oxygen barrier layer 40 is not particularly limited and has only to be a thickness that enables desired oxygen barrier properties to be obtained.
Also, inorganic particles (particles including an inorganic compound) may be dispersed in the oxygen barrier layer 40. The inorganic particles can further lower the oxygen permeability and can further suppress the oxidative degradation (color fading) of the colored adhesive layer 10. The size and content of the inorganic particles are not particularly limited and have only to be appropriately set depending on, for example, the thickness of the oxygen barrier layer 40. The size (maximum length) of the inorganic particles dispersed in the oxygen barrier layer 40 is preferably less than the thickness of the oxygen barrier layer 40 and advantageously as small as possible. The size of the inorganic particles dispersed in the oxygen barrier layer 40 may be either uniform or non-uniform. Specific examples of the inorganic particles dispersed in the oxygen barrier layer 40 include silica particles, alumina particles, silver particles, copper particles, titanium particles, zirconia particles, and tin particles.
In the optical sheet 1C according to the present embodiment, the oxygen barrier layer 40 can suppress degradation of the coloring material contained in the colored adhesive layer 10 caused by light, heat, and other factors which are promoted under the influence of oxygen in external air, so that the color correction function can be maintained for a further long time.
In the present embodiment, the number of oxygen barrier layers 40 and the position thereof can be appropriately set. For example, the oxygen barrier layer 40 has only to be laminated on the viewer side as a layer above the colored adhesive layer 10. Also, in the optical sheets 1A and 1C according to the second and fourth embodiments, the oxygen barrier layer 40 may be disposed between the colored adhesive layer 10 and the transparent substrate 30. Also, in the optical sheet 1B according to the third embodiment, the oxygen barrier layer 40 may be disposed between the colored adhesive layer 10 and the ultraviolet absorption adhesive layer 20 or between the ultraviolet absorption adhesive layer 20 and the transparent substrate 30. When the oxygen barrier layer 40 is provided, oxygen contained in external air does not reach the colored adhesive layer 10 as long as it does not pass through the oxygen barrier layer 40, similarly to in the fourth embodiment. This can suppress degradation of the coloring material caused by oxygen in the external air, so that the color correction function can be maintained for a further long time.
In the optical sheet 1C, a transparent adhesive layer may be disposed on the oxygen barrier layer 40. This allows an object to be bonded to the oxygen barrier layer 40 side and thus enhances versatility.
The fifth embodiment of the present invention will be described with reference to
The hardness of the hardcoat layer 51 is preferably H or above in pencil hardness at a surface load of 500 g.
The hardcoat layer 51 is a hard resin layer and enhances the scratch resistance of the optical sheet 1D. Also, the hardcoat layer 51 may have a refractive index higher than that of the low refractive index layer 52. A resin constituting the hardcoat layer 51 is a resin curable by polymerization with the irradiation of active energy rays such as ultraviolet light and electron beams. Examples of such a resin to be used include monofunctional, bifunctional, or trifunctional or higher (meth)acrylate monomers. As described herein, “(meth)acrylate ” is a generic name for both acrylate and methacrylate, and “(meth)acryloyl” is a generic name for both acryloyl and methacryloyl.
Examples of the monofunctional (meth)acrylate compound include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, glycidyl (meth)acrylate, acryloylmorpholine, N-vinylpyrrolidone, tetrahydrofurfuryl acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, cetyl (meth)acrylate, stearyl (meth)acrylate, benzyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, ethyl carbitol (meth)acrylate, phosphate (meth)acrylate, ethylene-oxide-modified phosphate (meth)acrylate, phenoxy (meth)acrylate, ethylene-oxide-modified phenoxy (meth)acrylate, propylene-oxide-modified phenoxy (meth)acrylate, nonyl phenol (meth)acrylate, ethylene-oxide-modified nonyl phenol (meth)acrylate, propylene-oxide-modified nonyl phenol (meth)acrylate, methoxy diethylene glycol (meth)acrylate, methoxy polyethylene glycol (meth)acrylate, methoxy propylene glycol (meth)acrylate, 2-(meth)acryloyl oxyethyl-2-hydroxy propyl phthalate, 2-hydroxy-3-phenoxy propyl (meth)acrylate, 2-(meth)acryloyl oxyethyl hydrogen phthalate, 2-(meth)acryloyl oxypropyl hydrogen phthalate, 2-(meth)acryloyl oxypropyl hexahydro hydrogen phthalate, 2-(meth)acryloyl oxypropyl tetrahydro hydrogen phthalate, dimethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, tetrafluoropropyl (meth)acrylate, hexafluoropropyl (meth)acrylate, octafluoropropyl (meth)acrylate, and adamantine derivatives of mono(meth)acrylates, such as adamantyl acrylate having monovalent mono(meth)acrylate derived from 2-adamantane and an adamantine diol.
Examples of the difunctional (meth)acrylate compound include di(meth)acrylates such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, butanediol di(meth)acrylate, hexanediol di(meth)acrylate, nonanediol di(meth)acrylate, ethoxylated hexanediol di(meth)acrylate, propoxylated hexanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, neopentyl glycol di(meth)acrylate, ethoxylated neopentyl glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and hydroxy pivalic acid neopentyl glycol di(meth)acrylate.
Examples of the trifunctional or higher (meth)acrylate compound include tri(meth)acrylates such as trimethylolpropane tri(meth)acrylate, ethoxylated trimethylolpropane tri(meth)acrylate, propoxylated trimethylolpropane tri(meth)acrylate, tris-2-hydroxyethyl isocyanurate tri(meth)acrylate, and glycerol tri(meth)acrylate, trifunctional (meth)acrylate compounds such as pentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, and ditrimethylolpropane tri(meth)acrylate, trifunctional or higher polyfunctional (meth)acrylate compounds such as pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, ditrimethylolpropane penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and ditrimethylolpropane hexa(meth)acrylate, and polyfunctional (meth)acrylate compounds in which a part of each of these (meth)acrylates is substituted with an alkyl group or ε-caprolactone.
As the active energy ray-curing resin, urethane (meth)acrylate can also be used. An example of the urethane (meth)acrylate is one obtained by allowing a product obtained by allowing polyester polyol to react with an isocyanate monomer or prepolymer to react with a (meth)acrylate monomer having a hydroxyl group.
Examples of the urethane (meth)acrylate include a pentaerythritol triacrylate hexamethylene diisocyanate urethane prepolymer, a dipentaerythritol pentaacrylate hexamethylene diisocyanate urethane prepolymer, a pentaerythritol triacrylate toluene diisocyanate urethane prepolymer, a dipentaerythritol pentaacrylate toluene diisocyanate urethane prepolymer, a pentaerythritol triacrylate isophorone diisocyanate urethane prepolymer, and a dipentaerythritol pentaacrylate isophorone diisocyanate urethane prepolymer.
The above-described resins may be used singly or in combination of two or more. Also, the above-described resins may be a monomer in a composition for forming a hardcoat layer or a partially polymerized oligomer.
The hardcoat layer 51 may contain the previously described ultraviolet absorber, in order to suppress degradation of the colorant contained in the colored adhesive layer 10. However, when the amount of ultraviolet light absorbed by the ultraviolet absorber is excessively large during curing of the composition that contains the ultraviolet absorber, curing of the composition becomes insufficient, and the obtained optical sheet sometimes has insufficient surface hardness. Therefore, it is preferable to use an ultraviolet absorber in which the absorption wavelength region in the ultraviolet region is in a range that is different from the absorption wavelength region in the ultraviolet region of the photoinitiator to suppress inhibition of curing when an ultraviolet absorber is present, and an acylphosphine oxide-based photoinitiator can be suitably used. Examples of the acylphosphine oxide-based photoinitiator include diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.
Also, a composition for forming the hardcoat layer 51 may contain metal oxide fine particles for purposes of adjusting the refractive index and imparting hardness. Examples of the metal oxide fine particles include zirconium oxide, titanium oxide, niobium oxide, antimony trioxide, antimony pentoxide, tin oxide, indium oxide, indium tin oxide, and zinc oxide.
The hardcoat layer 51 can be simply formed when formed with an energy ray-curing type compound such as an ultraviolet light-curing resin. In this case, the hardcoat layer 51 can be formed by coating with a coating liquid that contains an energy ray-curing type compound, a photoinitiator, and an ultraviolet absorber and irradiating the coat with the corresponding energy ray.
When the optical sheet 1D is applied to a display device, the low refractive index layer 52 is disposed on a side that is closest to a user (viewer) who views a display. The low refractive index layer 52 prevents the strong reflection of external light and improves the visibility of a display device.
The low refractive index layer 52 may be a layer that includes an inorganic material or an inorganic compound. Examples of the inorganic material and the inorganic compound include fine particles of LiF, MgF, 3NaF·AIF, AIF, Na3AlF6, and others as well as silica fine particles. Also, when silica fine particles have voids inside the particles, such as porous silica fine particles and hollow silica fine particles, the refractive index of the low refractive index layer can be effectively lowered. Also, the composition for forming the low refractive index layer 52 may be appropriately formulated with the photoinitiator, the solvent, and other additives described for the hardcoat layer 51.
The refractive index of the low refractive index layer 52 has only to be lower than the refractive index of the transparent substrate 30 and preferably 1.55 or less. Also, the film thickness of the low refractive index layer 52 is not particularly limited but preferably 40 nm to 1 µm.
The low refractive index layer 52 may contain any of silicon oxide, fluorine-containing silane compounds, fluoroalkyl silazane, fluoroalkyl silane, fluorine-containing silicon-based compounds, and perfluoropolyether group-containing silane coupling agents. Since these materials can impart water and/or oil repellency to the low refractive index layer 52, anti-fouling properties can be enhanced.
The low refractive index layer 52 may be formed by, for example, vapor deposition or sputtering. Also, it may be formed by coating with a coating liquid that contains constituent materials of the low refractive index layer 52 and drying the coat.
The optical sheet 1D according to the present embodiment can exert the same effects as those of the above-described embodiments and the optical function based on the optical function layer 50.
The sixth embodiment of the present invention will be described with reference to
Also, when the transparent substrate 30 has ultraviolet shielding properties by having the absorption characteristics of resin and containing the ultraviolet absorber described as an example for the ultraviolet absorption adhesive layer 20, the optical sheet 1E has only to include the colored adhesive layer 10, the transparent substrate 30, and the optical function layer 50.
The anti-glare layer 53 is a layer that has microscopic asperities on the surface and scatters external light by the microscopic asperities to reduce reflected glare of external light. The anti-glare layer 53 can be formed by coating with a composition for forming an anti-glare layer that contains an active energy ray-curing resin and, as necessary, organic fine particles and/or inorganic fine particles. Examples of the active energy ray-curing resin used in the composition for forming an anti-glare layer include the resins described with regard to the hardcoat layer 51. The film thickness of the anti-glare layer 53 is not particularly limited but preferably 1 to 10 µm.
The organic fine particles used in the composition for forming an anti-glare layer are a material that mainly forms microscopic asperities on the surface of the anti-glare layer 53 to impart the function of scattering external light. Examples of usable organic fine particles include resin particles constituted by a translucent resin material such as acrylic resin, polystyrene resin, styrene-(meth)acrylic acid ester copolymers, polyethylene resin, epoxy resin, silicone resin, polyvinylidene fluoride, and polyethylene fluoride-based resin. For adjusting the refractive index and the dispersibility of resin particles, two or more types of resin particles having different material properties (refractive indices) may be mixed and used.
The inorganic fine particles used in the composition for forming an anti-glare layer are a material for mainly adjusting the sedimentation and aggregation of organic fine particles in the anti-glare layer 53. Examples of usable inorganic fine particles include silica fine particles, metal oxide fine particles, and various mineral fine particles. Examples of usable silica fine particles include colloidal silica and silica fine particles surface-modified with a reactive functional group such as a (meth)acryloyl group. Examples of usable metal oxide fine particles include alumina, zinc oxide, tin oxide, antimony oxide, indium oxide, titania, and zirconia. Examples of usable mineral fine particles include mica, synthetic mica, vermiculite, montmorillonite, iron montmorillonite, bentonite, beidellite, saponite, hectorite, stevensite, nontronite, magadiite, ilerite, kanemite, layered titanic acid, smectite, and synthetic smectite. The mineral fine particles to be used may be either a natural product or a synthetic product (including a substituted body and a derivative) and may be a mixture of both. Among the mineral fine particles, a layered organic clay is more preferable. Layered organic clay refers to swellable clay including organic onium ions introduced in the interlayer. The organic onium ion may be any one that can convert the swellable clay into an organic form by utilizing the cation exchangeability of the swellable clay. When layered organic clay mineral is used as mineral fine particles, the above-mentioned synthetic smectite can be suitably used. The synthetic smectite has the function of increasing the viscosity of the coating liquid for forming an anti-glare layer, suppressing the sedimentation of resin particles and inorganic fine particles, and adjusting the concavo-convex shape of the surface of the optical function layer.
The composition for forming an anti-glare layer may contain any of silicon oxide, fluorine-containing silane compounds, fluoroalkyl silazane, fluoroalkyl silane, fluorine-containing silicon-based compounds, and perfluoropolyether group-containing silane coupling agents. Since these materials can impart water and/or oil repellency to the anti-glare layer 53, anti-fouling properties can be enhanced.
The anti-glare layer 53 may be formed as a layer in which a layer having a relatively high refractive index and a layer having a relatively low refractive index are laminated sequentially from the colored adhesive layer 10 side (from the lower side), by allowing the materials to be unevenly distributed. The anti-glare layer 53 in which the materials are unevenly distributed can be formed by, for example, coating with a composition including a high refractive index material and a low refractive index material that contains surface-treated silica fine particles or hollow silica fine particles, and phase-separating the coat by taking advantage of a difference in surface free energy between both materials. When the anti-glare layer 53 is constituted by the two phase-separated layers, it is preferable that the layer having a relatively high refractive index on the transparent substrate 30 side has a refractive index of 1.50 to 2.40, and the layer having a relatively low refractive index on the surface side of the optical sheet 1E has a refractive index of 1.20 to 1.55. The anti-glare layer 53 can be formed by, for example, coating with a coating liquid that contains constituent materials of each layer and drying the coat.
The optical sheet 1E according to the present embodiment can exert the same effects as those of the above-described embodiments and the optical function based on the optical function layer 50.
The seventh embodiment of the present invention will be described with reference to
Also, when the transparent substrate 30 has the absorption characteristics of resin and contains the ultraviolet absorber described as an example for the ultraviolet absorption adhesive layer 20 to have ultraviolet shielding properties, the optical sheet 1F has only to include the colored adhesive layer 10, the transparent substrate 30, and the optical function layer 50.
The optical sheet 1F can be manufactured by laminating the ultraviolet shielding layer 20 and the colored adhesive layer 10, or the colored adhesive layer 10, to the first surface side of the transparent substrate 30 (to the lower surface side of the transparent substrate 30), and sequentially forming the anti-glare layer 53 and the low refractive index layer 52 on the second surface opposite the first surface on the transparent substrate 30 (on the upper surface side of the transparent substrate 30).
In the optical sheet 1F according to the present embodiment, the anti-glare layer 53 and the low refractive index layer 52 can prevent reflected glare and strong reflection of external light and improve the visibility of a display device.
In the present embodiment, the optical function layer 50 is not limited to the above-described structures, and the exerted optical function also changes by changing the structure.
For example, an anti-reflection layer including a combination of a low refractive index layer and a high refractive index layer is also an example of the optical function layer 50 in the present invention. The low refractive index layer may be the same structure as the low refractive index layer 52 described in the fifth embodiment. The high refractive index layer may be disposed on a surface below the low refractive index layer and have a refractive index that is higher than that of the low refractive index layer. According to the anti-reflection layer including a combination of a low refractive index layer and a high refractive index layer, strong reflection of external light can be prevented, and visibility of a display device can be improved.
Also, an anti-reflection layer including a high refractive index layer and an anti-glare layer is an example of the optical function layer 50 in the present invention. The anti-glare layer may be the same structure as the anti-glare layer 53 described in the sixth embodiment. The high refractive index layer may be disposed on a surface below the anti-glare layer 53 and have a refractive index higher than that of the anti-glare layer 53. Also, the anti-reflection layer including a high refractive index layer and an anti-glare layer may further include the low refractive index layer 52. These structures can further improve the visibility of a display device.
Also, in the present embodiment, an ultraviolet shielding function (ultraviolet absorption properties) may be imparted to the optical function layer 50 to allow the optical function layer 50 to function as an ultraviolet shielding layer. In this case, the transparent substrate 30 may not have an ultraviolet shielding function. When the optical function layer 50 has an ultraviolet shielding function, an ultraviolet absorber has only to be added to the hardcoat layer 51 and the anti-glare layer 53. When an ultraviolet absorber is contained in the hardcoat layer 51 including an ultraviolet light-curing resin, it is preferable that the absorption wavelength region in the ultraviolet region of the photoinitiator is different from the absorption wavelength region in the ultraviolet region of the ultraviolet absorber.
The optical sheet according to the present invention will be further described using examples and comparative examples. The present invention is not limited in any way by the specific contents of the following examples.
In the following examples and comparative examples, optical sheets 1 to 22 having layer structures illustrated in Tables 1 to 3 were prepared, and properties of the prepared optical sheets were evaluated. Also, optical properties of OLED display devices 1 to 7 which include the optical sheets 6, 11, 12, and 19 to 22 were confirmed by simulation.
Hereinafter, a method of forming each layer will be described.
The following transparent substrates were used.
An 80% aqueous solution of PVA 117 (manufactured by Kuraray Co., Ltd.) was applied on the transparent substrate of Example 7 illustrated in Table 1 and dried to form an oxygen barrier layer having an oxygen permeability of 1 cc/(m2·day·atm).
The compositions illustrated in Table 4 were prepared with the following materials of a composition for forming a hardcoat layer.
The transparent substrate or the oxygen barrier layer illustrated in Table 1 to Table 3 was coated with the composition for forming a hardcoat layer illustrated in Table 4. The coat was dried in an oven at 80° C. for 60 seconds and thereafter irradiated with ultraviolet light at an irradiation dose of 150 mJ/cm2 using an ultraviolet light irradiation device (manufactured by Fusion UV Systems Japan K.K., light source: H bulb). Accordingly, the coat was cured to form hardcoat layers 1 and 2 having a film thickness after curing of 5.0 µm illustrated in Table 1 to Table 3. It is noted that the hardcoat layer 2 contains an ultraviolet absorber and thus also serves as an ultraviolet shielding layer.
As a composition for forming a low refractive index layer, the following materials were used.
The hardcoat layer illustrated in Table 1 to Table 3 was coated with a composition for forming a low refractive index layer, having the above-described make-up. The coat was dried in an oven at 80° C. for 60 seconds and thereafter irradiated with ultraviolet light at an irradiation dose of 200 mJ/cm2 using an ultraviolet light irradiation device (manufactured by Fusion UV Systems Japan KK, light source: H bulb). Accordingly, the coat was cured to form a low refractive index layer having a film thickness after curing of 100 nm illustrated in Table 1 to Table 3.
The following materials were used as a composition for forming an anti-glare layer to prepare the composition illustrated in Table 5.
The transparent substrate of Example 13 illustrated in Table 2 was coated with the composition for forming an anti-glare layer illustrated in Table 5. The coat was dried in an oven at 80° C. for 60 seconds and thereafter irradiated with ultraviolet light at an irradiation dose of 150 mJ/cm2 using an ultraviolet light irradiation device (manufactured by Fusion UV Systems Japan KK, light source: H bulb). Accordingly, the coat was cured to form the anti-glare layer having a film thickness after curing of 5.0 µm illustrated in Table 2.
The following composition was used as a base adhesive.
The following materials of a composition for forming an adhesive layer used in forming the below-described first and second adhesive layers were used to prepare the compositions illustrated in Table 6. It is noted that for the maximum absorption wavelength and half width of the coloring material, characteristic values in the adhesive layer were calculated from a spectral transmittance.
The composition for forming an adhesive layer obtained as described above was applied on a release substrate film so as to have a dried film thickness of 25 µm. The coat was sufficiently dried and thereafter laminated with a release film to obtain an adhesive layer. One of the release films of the obtained adhesive layer was peeled away, and the exposed surface was bonded to a non-alkali glass support body (adherend) having a thickness of 0.7 mm.
Thereafter, the other of the release films of the adhesive layer was peeled away, and the exposed surface was bonded to a substrate laminated with the functional layer illustrated in Table 1 to Table 3 to obtain each of the optical sheets 1 to 22. It is noted that the samples of Examples 1 to 14 and Comparative Examples 1 to 8 are each constituted by bonding the optical sheet to an adherend. The adherend is not particularly limited as long as it is a material that does not hinder the characteristic evaluation of the optical sheet. Materials other than non-alkali glass may also be used.
For a laminate as a layer above the first adhesive layer in each of the obtained optical sheets 1 to 18, the transmittance was measured using an automatic spectrophotometer (U-4100, manufactured by Hitachi, Ltd.). Using the transmittance, the average transmittance in the ultraviolet region (290 to 400 nm) was calculated, and the ultraviolet shielding rate illustrated in Equation (2) was calculated.
The reliability test of the obtained optical sheets 1 to 18 was performed as follows. Using a xenon weather meter tester (manufactured by Suga Test Instruments Co., Ltd., X75), the test was performed for 120 hours under the conditions of a xenon lamp illuminance of 60 W/cm2 (300 to 400 nm), a tester chamber temperature of 45° C. and humidity of 50% RH. The transmittance was measured before and after the test using an automatic spectrophotometer (U-4100, manufactured by Hitachi, Ltd.) to calculate transmittance difference Δtλ between before and after the test at wavelength λ that exhibits the smallest transmittance in the wavelength ranges of the first coloring material to the third coloring material and color difference ΔE * ab with illuminant C between before and after the test. The transmittance difference and color difference are good when closer to zero and preferably achieve ΔE * ab ≤ 5.
The evaluation results of the above-described items are illustrated in Table 7 and Table 8.
The optical sheets of Examples 1 to 14 include a first adhesive layer (colored adhesive layer) and a layer that is disposed on a side above the first adhesive layer and that has ultraviolet absorption properties. For example, an ultraviolet absorber is contained in the adhesive layer 8 as the second adhesive layer in Example 1 and in the hardcoat layer 2 in Example 2. In Examples 3 to 14, the substrate has an ultraviolet absorption properties. Also, as illustrated in Tables 7 and 8, the layer disposed on a side above the first adhesive layer has an ultraviolet shielding rate of 85% or more.
From the results of Tables 7 and 8, the optical sheet including the colored adhesive layer in the present invention includes, as the upper layer, the ultraviolet shielding layer having an ultraviolet shielding rate of 85% or more, and thus light resistance was drastically improved. Also, as understood from the result of Comparative Example 2, it is difficult to improve light resistance even when an ultraviolet absorber is added to the colored adhesive layer. In this manner, ultraviolet absorption properties have only a small effect when provided to the colored adhesive layer, and another layer needs to be provided as the upper layer.
Light resistance was further improved by further laminating an oxygen barrier layer or by containing, in the colored adhesive layer, at least one of a hindered amine photostabilizer having a high molecular weight as the radical scavenger and a dialkyl dithiocarbamate nickel complex as the singlet oxygen quencher. It is noted that as understood from the results on the light resistance of the optical sheets containing the adhesive layers 3, 4, and 5, either one or both of the radical scavenger and the singlet oxygen quencher may be added.
In Examples 15 to 17 and Comparative Examples 9 to 12 below, display device characteristics were evaluated by simulation in the following manner for the display devices 1 to 7 which include the obtained optical sheets 6, 11, 12, and 19 to 22. In the simulation, the display devices 1 to 7 were configured such that the optical sheet was bonded to an OLED display device (object).
It is noted that the OLED display device as an object to have the optical sheet bonded has a spectrum illustrated in
The transmittance of the optical sheet obtained was measured using an automatic spectrophotometer (U-4100, manufactured by Hitachi, Ltd.), and the spectrum after transmission through the optical sheet was calculated by multiplying the transmittance of the optical sheet by the single spectrum (shown in
The transmittance of the obtained optical sheet was measured using an automatic spectrophotometer (U-4100, manufactured by Hitachi, Ltd.). This transmittance of the optical sheet was multiplied by the individual spectra (illustrated in
As characteristic evaluation with the display devices, white display transmission characteristics and color reproducibility are illustrated in Table 9.
From the results of Table 9, the display devices 1 to 3 (Examples 15 to 17) including the colored adhesive layer as the first adhesive layer in the present invention had an sRGB chromaticity coverage ratio of 99% or more and improved color reproducibility compared to Comparative Example 9 in which a coloring material is not contained in the adhesive layer (the colored adhesive layer is not included).
In Comparative Example 10 having deep absorption in a plurality of wavelength ranges of the first coloring material and the second coloring material, white display transmission characteristics are low. This means that when multiple types of coloring materials are contained in the first adhesive layer, it is preferable that the transmittance is 1% or more and less than 50% in only one of the maximum absorption wavelengths of the coloring materials. Also, in Comparative Examples 11 and 12 including a coloring material that has a wavelength range and a half width that do not meet the requirements, white display transmission characteristics are low. In contrast to these, in Examples 15 to 17, it was demonstrated that white display transmission characteristics are excellent while exhibiting a certain color correction function.
It is noted that the technical scope of the present invention is not limited to the above-described embodiments, which can be variously modified within a scope that does not depart from the spirit of the present invention.
For example, the optical sheet has only to include a first adhesive layer (colored adhesive layer) 10 and a layer that is disposed on a side above the first adhesive layer and has ultraviolet absorption properties. The layer having ultraviolet absorption properties may be the ultraviolet shielding layer 20 or may be the transparent substrate 30 or the optical function layer 50. The layer that is disposed on a side above the first adhesive layer 10 and has ultraviolet absorption properties preferably has an ultraviolet shielding rate according to JIS L 1925 of 85% or more.
Also, the optical sheet may further include an anti-static layer and an anti-fouling layer.
Also, the anti-reflection layer in the optical function layer 50 of the optical sheet may include the high refractive index layer, the anti-glare layer 53, and the low refractive index layer 52. At least one of the high refractive index layer, the anti-glare layer 53, and the low refractive index layer 52 may have anti-static properties, and at least one of the high refractive index layer, the anti-glare layer 53, and the low refractive index layer 52 may have anti-fouling properties. For example, an anti-static agent may be added in the high refractive index layer and the anti-glare layer 53 in order to impart anti-static properties. A material having water and/or oil repellency may be contained in the low refractive index layer 52 in order to impart anti-fouling properties to the function of the low refractive index layer 52. Also, anti-fouling properties may be imparted to the high refractive index layer and the anti-glare layer 53. It is noted that both of anti-static properties and anti-fouling properties may be imparted to at least one of the high refractive index layer, the anti-glare layer 53, and the low refractive index layer 52.
This can impart further functions to the optical function layer.
In addition, constituent elements in the above-described embodiments can be appropriately replaced with known constituent elements, or the above-described embodiments and modifications may be appropriately combined, within a scope that does not depart from the spirit of the present invention.
The present invention can be used as an optical sheet used in a display device.
[Reference Signs List] 1, 1A, 1B, 1C, 1D, 1E, 1F Optical sheet; 10 Colored adhesive layer (first adhesive layer); 20 Ultraviolet shielding layer (ultraviolet absorption adhesive layer, second adhesive layer); 30 Transparent substrate (ultraviolet shielding layer); 40 Oxygen barrier layer; 50 Optical function layer; 51 Hardcoat layer; 52 Low refractive index layer; 53 Anti-glare layer; S Separator.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-006750 | Jan 2021 | JP | national |
This application is a continuation application filed under 35 U.S.C. § 111(a) claiming the benefit under 35 U.S.C. §§ 120 and 365(c) of International Patent Application No. PCT/JP2021/026647, filed on Jul. 15, 2021, which in turn claims the benefit of JP 2021-006750, filed Jan. 19, 2021, the disclosures of which are all incorporated herein by reference in its entirety.
