JP2011102917A - Optical sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color compensation sheet capable of solving a problem that, in a recent liquid crystal display device, displayable colors vary according to a viewing angle. <P>SOLUTION: The optical sheet contains 0.0001 to 1.0% of organic or inorganic fine particles having a specific diffusion and an average particle diameter of ≤0.4 μm in a transparent resin, the diffusion degree (a ratio of 30° exit-light to 0° exit-light when light is vertically made incident on the optical sheet, when measured by a goniometer) of the optical sheet is ≤0.3%, and when the light is vertically made incident on the optical sheet, a ratio of the straight advancing light to the total transmissive light varies according to wavelength, and the wavelength selectivity of the straight advancing light shown by the following expression 1 is a value larger than 2. The expression 1: (wavelength selectivity of straight advancing light)=((straight advancing light transmittance of 685 nm light)/(total transmittance of 685 nm light))/((straight advancing light transmittance of 470 nm light)/(total transmittance of 470 nm light)). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical sheet having wavelength selectivity in transmitted light distribution and effective in suppressing a change in color tone depending on a viewing angle of a liquid crystal display device.

  2. Description of the Related Art In recent years, liquid crystal display devices have been widely used as display devices used for personal computer monitors, portable terminals, televisions, and the like because they are thin, lightweight, and consume less power. The liquid crystal display device includes a backlight that emits light and a liquid crystal panel having a structure in which a liquid crystal cell is sandwiched between two substrates. This liquid crystal cell performs ON / OFF display depending on the alignment state of the liquid crystal molecules, and according to the type of liquid crystal molecules constituting the liquid crystal cell, TN (Twisted Nematic), IPS (In-Plane Switching), VA. Display modes such as (Vertically Aligned) and STN (Super Twisted Nematic) have been proposed. However, one of the problems of this liquid crystal display device is a phenomenon that the color tone changes depending on the viewing direction. This is because the transmittance of the liquid crystal cell has an angle dependency and a wavelength dependency.

  For example, in a TN mode liquid crystal display device in which the twist angle of liquid crystal molecules is 90 degrees, there is a problem that the light transmittance varies depending on the viewing angle or wavelength. The transmittance tends to be relatively low compared to the transmittance on the long wavelength side. That is, when viewed from the front direction, the color tone is bluish as a whole, and there is a problem that the yellowish color becomes stronger as the viewing angle increases.

In order to solve such problems relating to the color tone due to the viewing angle, a method of adding a dichroic dye for color compensation to the liquid crystal layer (Patent Document 1) or a film to which particles having shape anisotropy are added is used. A method (Patent Document 2) and the like have been proposed.
However, these methods not only are uneconomical because they add expensive dyes and anisotropic particles, but it is not easy to control the dispersibility and orientation of the additives during production, and they are put to practical use. It was difficult to do.

Japanese Patent No. 3974217 JP 2004-341308 A

  This invention is made in view of the above-mentioned problem, and makes it a subject to provide the optical sheet which can suppress the color tone change by the change of the viewing angle of a liquid crystal panel.

In solving the above problems, according to the present invention, there is provided an optical sheet having a specific average particle size and a predetermined amount of fine particles having a small degree of dispersion, and having a diffusivity (perpendicular to the optical sheet by a goniometer When light is incident from the direction, the ratio of 30 ° outgoing light to 0 ° outgoing light) is 0.3% or less. When light is incident from the vertical direction of the optical sheet, the light travels straight with respect to the total transmitted light. The optical sheet is provided in which the ratio is different depending on the wavelength, and the wavelength selectivity of the straight light represented by Formula 1 is a value larger than 2.
(Formula 1)
Wavelength selectivity of straight light = ((straight light transmittance of 685 nm light) / (total transmittance of 685 nm light) / ((straight light transmittance of 470 nm light) / (total transmittance of 470 nm light))

  As described above, according to the optical sheet of the present invention, the color tone change due to the change in the viewing angle of the liquid crystal panel can be reduced, and good visibility can be obtained at any viewing angle.

It is explanatory drawing of the manufacturing process of the resin sheet by the conventional extrusion molding.

1: White LED
2: Reflective sheet 3: Light guide plate 4: Micro lens sheet 5: Prism sheet 6: Optical sheet 7 of the present invention: Liquid crystal cell 8: Polarizing plate

  Hereinafter, the best mode for carrying out the present invention will be described in detail, but the present invention is not limited thereto.

  The present invention relates to an optical sheet that can suppress a change in color tone due to a change in viewing angle of a liquid crystal panel.

  The optical sheet of the present invention (in the present invention, “sheet” and “film” are used synonymously and both refer to a resin molded body having a thickness of 0.05 to 3 mm (hereinafter collectively referred to as “sheet”).

<Transparent thermoplastic resin of optical sheet>
The transparent thermoplastic resin constituting the optical sheet according to the present invention is not particularly limited as long as it is transparent and has an appropriate strength as a main component of the optical sheet. For example, polycarbonate resin; acrylic resin such as polymethyl methacrylate; styrene resin such as polystyrene, polyvinyl toluene, and poly (p-methylstyrene); MS resin (copolymer of methyl methacrylate and styrene); norbornene resin; poly An arylate resin; a polyethersulfone resin; a mixed resin of two or more of these can be used. A polycarbonate resin, a styrene resin, or a norbornene resin is preferably used. Among these, polycarbonate resin is particularly preferable as a resin for an optical sheet because it is excellent in transparency, heat resistance, and workability and has a good balance.

  The polycarbonate resin is obtained by reacting a dihydric phenol and a carbonate precursor by an interfacial polycondensation method or a melting method. Representative examples of the dihydric phenol include 2,2-bis (4-hydroxyphenyl) propane [commonly known as bisphenol A], 1,1-bis (4-hydroxyphenyl) ethane, and 1,1-bis (4-hydroxy). Phenyl) cyclohexane, 2,2-bis (3-methyl-4-hydroxyphenyl) propane, 2,2-bis (3,5-dimethyl-4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfide, bis (4-Hydroxyphenyl) sulfone, 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bis (4-hydroxy-3-methylphenyl) fluorene and the like are mentioned, and among them, bisphenol A is preferable. These dihydric phenols can be used alone or in admixture of two or more.

  As the carbonate precursor, carbonyl halide, carbonate ester, haloformate or the like is used, and specific examples include phosgene, diphenyl carbonate, dihaloformate of dihydric phenol, and the like.

  When producing polycarbonate resin by reacting the above dihydric phenol and carbonate precursor by interfacial polycondensation method or melting method, use catalyst, terminal terminator, dihydric phenol antioxidant, etc. as necessary May be. The polycarbonate resin may be a branched polycarbonate resin copolymerized with a trifunctional or higher polyfunctional aromatic compound, or may be a polyester carbonate resin copolymerized with an aromatic or aliphatic difunctional carboxylic acid, Moreover, the mixture which mixed 2 or more types of the obtained polycarbonate resin may be sufficient. As the polycarbonate resin used in the present invention, a polycarbonate resin obtained by an interfacial polycondensation method (generic name: phosgene method) is preferably used. In addition, it is more preferable to perform sheet extrusion directly using a polycarbonate resin in which the resin is not melt-processed by an extruder, a kneader, or the like because coloring of the sheet due to heat history can be reduced.

The molecular weight of the polycarbonate resin is usually 15,000 to 40,000, preferably 18,000 to 35,000, expressed as a viscosity average molecular weight. The viscosity average molecular weight referred to in the present invention is obtained by inserting the specific viscosity (ηsp) obtained from a solution of 0.7 g of polycarbonate resin in 100 ml of methylene chloride at 20 ° C. into the following equation.
ηsp / c = [η] + 0.45 × [η] ² c
[Η] = 1.23 × 10 ⁻⁴ M ^0.83
(Where c = 0.7, [η] is the intrinsic viscosity).

  In the polycarbonate resin that can be suitably used for the optical sheet of the present invention, a phosphorus-containing heat stabilizer can be further used in order to prevent a decrease in molecular weight and a deterioration in hue during molding. Examples of such heat stabilizers include phosphorous acid, phosphoric acid, phosphonous acid, phosphonic acid, and esters thereof.

  Specifically, triphenyl phosphite, tris (nonylphenyl) phosphite, tridecyl phosphite, trioctyl phosphite, trioctadecyl phosphite, didecyl monophenyl phosphite, dioctyl monophenyl phosphite, diisopropyl monophenyl Phosphite, monobutyl diphenyl phosphite, monodecyl diphenyl phosphite, monooctyl diphenyl phosphite, tris (2,4-di-tert-butylphenyl) phosphite, bis (2,6-di-tert-butyl-4) -Methylphenyl) pentaerythritol diphosphite, 2,2-methylenebis (4,6-di-tert-butylphenyl) octyl phosphite, bis (nonylphenyl) pentaerythritol diphosphite, bis 2,4-di-tert-butylphenyl) pentaerythritol diphosphite, distearyl pentaerythritol diphosphite, tributyl phosphate, triethyl phosphate, trimethyl phosphate, triphenyl phosphate, diphenyl monooxoxenyl phosphate, dibutyl phosphate, dioctyl phosphate , Diisopropyl phosphate, tetrakis (2,4-di-iso-propylphenyl) -4,4′-biphenylene diphosphonite, tetrakis (2,4-di-n-butylphenyl) -4,4′-biphenylene diphospho Knight, tetrakis (2,4-di-tert-butylphenyl) -4,4′-biphenylenediphosphonite, tetrakis (2,4-di-tert-butylphenyl) -4,3′-biphenyl Diphosphonite, tetrakis (2,4-di-tert-butylphenyl) -3,3'-biphenylenediphosphonite, tetrakis (2,6-di-iso-propylphenyl) -4,4'-biphenylenediphospho Knight, tetrakis (2,6-di-n-butylphenyl) -4,4'-biphenylenediphosphonite, tetrakis (2,6-di-tert-butylphenyl) -4,4'-biphenylenediphosphonite, Tetrakis (2,6-di-tert-butylphenyl) -4,3′-biphenylenediphosphonite, tetrakis (2,6-di-tert-butylphenyl) -3,3′-biphenylenediphosphonite, bis ( 2,4-di-tert-butylphenyl) -biphenylphosphonite, dimethyl benzenephosphonate, die benzenephosphonate And dipropyl benzenephosphonate, among others, tris (2,4-di-tert-butylphenyl) phosphite, tetrakis (2,4-di-tert-butylphenyl) -4,4′-biphenylenedi Phosphonite and bis (2,4-di-tert-butylphenyl) -biphenylphosphonite are preferred.

  These heat stabilizers may be used alone or in combination of two or more. The amount of the heat stabilizer used is preferably 0.001 to 0.15 parts by weight with respect to 100 parts by weight of the copolymer polycarbonate resin or polycarbonate resin blend.

  Furthermore, a fatty acid ester compound can be blended with the polycarbonate resin of the present invention for the purpose of improving mold release properties during extrusion molding or injection molding.

  Such a fatty acid ester is preferably a partial ester or a total ester of a monovalent or polyhydric alcohol having 1 to 20 carbon atoms and a saturated fatty acid having 10 to 30 carbon atoms. Such partial esters or total esters of monohydric or polyhydric alcohols and saturated fatty acids include stearic acid monoglyceride, stearic acid diglyceride, stearic acid triglyceride, stearic acid monosorbite, behenic acid monoglyceride, pentaerythritol monostearate, pentaerythritol. Tetrastearate, pentaerythritol tetrapelargonate, propylene glycol monostearate, stearyl stearate, palmityl palmitate, butyl stearate, methyl laurate, isopropyl palmitate, biphenyl biphenate, sorbitan monostearate, 2-ethylhexyl stearate Rate, etc. Among them, stearic acid monoglyceride, stearic acid triglyceride, pentaerythrito Le tetrastearate are preferably used. The amount of the fatty acid ester used is preferably 0.001 to 0.5 parts by weight with respect to 100 parts by weight of the copolymer polycarbonate resin or polycarbonate resin blend.

  In the polycarbonate resin of the present invention, in addition to the above components, other components, such as triazole-based, acetophenone-based, salicylic acid ester-based ultraviolet absorbers, olefin-based sulfates or their metal salts, etc. , Higher alcohol phosphate esters, cationic acrylic ester derivatives, fatty acid polyhydric alcohol esters, alkylamines such as polyoxyethylene adduct antistatic agents, bluing agents, tetrabromobisphenol A, tetrabromobisphenol A Additives such as flame retardants such as low molecular weight polycarbonate and decabromodiphenylene ether, and flame retardant aids such as antimony trioxide may be blended as needed.

  The thickness of the optical sheet of the present invention is not particularly limited as long as it is about 0.05 to 3 mm, but particularly when used as an optical sheet for a flat panel display, it is desired to reduce the weight and thickness of the panel itself. The thickness is preferably 2 mm or less, more preferably 1 mm or less, and still more preferably 0.5 mm or less. On the other hand, in order to ensure the rigidity necessary for the optical sheet, the lower limit of the sheet thickness is preferably 0.1 mm or more, more preferably 0.2 mm or more, and further preferably 0.3 mm or more.

<Fine particles>
The average particle size (measured with a Coulter counter) of the fine particles used in the optical sheet of the present invention is 0.4 μm or less, preferably 0.35 μm or less, and more preferably 0.32 μm or less. If the average particle diameter of the fine particles is larger than 0.4 μm, the wavelength selectivity of so-called straight light, which changes the diffusion state depending on the wavelength of light, may be insufficient.

  Examples of the material of the fine particles used in the optical sheet of the present invention include (meth) acrylic resins, styrene resins, polyurethane resins, polyester resins, silicone resins, fluorine resins, and copolymers thereof. Synthetic resins; glass; clay compounds such as smectite and kaolinite; inorganic oxides such as silica and alumina; and the like. Of these materials, (meth) acrylic resins, silicone resins, and silica are particularly preferable, and silica is most preferable.

  The fine particles may be uniformly added to the entire optical sheet of the present invention, but a fine particle layer may be provided on the light incident surface and / or light exit surface side.

  The blending amount of the fine particles needs to be appropriately adjusted depending on the thickness of the fine particle layer to be formed, the size of the fine particles, the refractive index difference from the transparent thermoplastic resin constituting the sheet, etc. Preferably it is 0.0001 mass part or more and 1 mass part or less with respect to 100 mass parts of transparent thermoplastic resins, More preferably, it is 0.0005 mass part or more and 5 mass parts or less. If the amount used is less than 0.0001 parts by mass, the desired wavelength selectivity of straight light may not be obtained. Conversely, if the amount used exceeds 1 part by mass, the amount of transmitted light decreases, There is a risk that the brightness may decrease.

  When organic fine particles obtained by radical polymerization are used as the fine particles, as raw material monomers for fine particles, (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso- Propyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, t-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, (Meth) acrylates such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate; styrenes such as styrene, p-methylstyrene, vinyltoluene and pt-butylstyrene; N-phenylmaleimide 1- of maleimides such as N-cyclohexylmaleimide and N-benzylmaleimide; (meth) acrylamides such as (meth) acrylamide and N-methylol (meth) acrylamide; acrylonitriles such as (meth) acrylonitrile; N-vinylpyrrolidone; Species or a mixture of two or more of these can be used.

  In addition, in the case of using crosslinked organic fine particles obtained by radical polymerization as fine particles, in addition to the above composition, as a raw material monomer of the crosslinked fine particles, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, propylene glycol di (meta) ) Acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, bishydroxyethylbisphenol A di (meth) acrylate and other polyfunctional (meth) acrylates; divinyloxyethoxy (meth) acrylate, diallyl Radical polymerizable crosslinking agents such as phthalate, allyl (meth) acrylate, divinylbenzene; bisphenol A diglycidyl ether, diethylene glycol diglycidyl ether, neopentyl Polyfunctional epoxy compounds such as recall diglycidyl ether; polyfunctional isocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate and isophorone diisocyanate; polyfunctional methylol compounds such as N-methylol melamine and N-methylol benzoguanamine; Two or more of them can be mixed and used.

<Wavelength selectivity of straight light>
The optical sheet of the present invention is characterized in that when light is incident from the vertical direction, the ratio of the straight light to the total transmitted light varies depending on the wavelength, and the wavelength selectivity of the straight light represented by Equation 1 is 2 or more. It is an optical sheet.

(Formula 1)
Wavelength selectivity of straight light = ((straight light transmittance of 685 nm light) / (total transmittance of 685 nm light) / ((straight light transmittance of 470 nm light) / (total transmittance of 470 nm light))
The value represented by Equation 1 indicates the wavelength selectivity of the straight light of the optical sheet of the present invention. The larger the value, the more the blue light of about 470 nm in the oblique viewing angle direction with respect to the red light of about 685 nm. This indicates that the liquid crystal display device has a blue front and a yellow color from an oblique viewing angle.
The wavelength selectivity value of straight light represented by the formula 1 is more preferably 2.5 or more, and further preferably 3.0 or more.

<Diffusion degree>
The optical sheet of the present invention has a diffusivity (a ratio of 30 ° outgoing light to 0 ° outgoing light when light is incident on the optical sheet from a vertical direction with a goniometer) of 0.3% or less. This diffusivity is an index indicating the diffusivity of the entire light incident on the optical sheet. The higher the value, the higher the diffusivity. Since the light is diffused, the wavelength selectivity of the straight light tends to be low. The diffusivity is more preferably 0.2% or less, and more preferably 0.1% or less.

  The refractive index of the fine particles according to the present invention is different from the refractive index of the transparent thermoplastic resin constituting the optical sheet of the present invention, and the refractive index difference is preferably 0.05 or more, more preferably 0.10 or more. preferable.

  An antioxidant may be further added to at least one of the organic fine particles or the thermoplastic resin of the present invention. Since the antioxidant can suppress coloring of the organic fine particles due to oxidation or deterioration during the heat molding, the luminance of the light source unit to which the optical sheet of the present invention is applied can be more reliably exhibited.

  A conventionally well-known thing can be used as antioxidant. For example, pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] or octadecyl-3- (3,5-di-t-butyl-1-hydroxyphenyl) propionate Hindered phenolic antioxidants; tris (2,4-di-t-butylphenyl) phosphite and tris [2-[[2,4,8,10-tetra-t-butyldibenzo [d, f] [ Phosphorous antioxidants such as 1,3,2] dioxaphosphin-6-yl] oxy] ethyl] amine; thiodiethylenebis [3- (3,5-di-t -Butyl-4-hydroxyphenyl) propionate] and the like having no aromatic ring, pentaerythrityltetrakis (3-laurylthiopropionate) Sulfur-based antioxidants such as; lactone-based antioxidants such as the reaction product of 3-hydroxy-5,7-di-t-butyl-furan-2-one and o-xylene; Hydroxylamine antioxidants such as oxidation products of alkylamines; 3,4-dihydro-2,5,7,8-tetramethyl-2- (4,8,12-trimethyltridecyl) -2H-benzopyran- Vitamin E antioxidants such as 6-ol can be used. Although the usage-amount of antioxidant may be adjusted suitably, normally, what is necessary is just to add about 0.005 mass% or more and 0.3 mass% or less with respect to the whole organic fine particle.

<Uneven shape on optical sheet>
The optical sheet of the present invention may be a sheet having smooth surfaces, but a plurality of fine irregularities may be formed on at least one surface. The fine concavo-convex shape includes a cut sphere concavo-convex shape, a cut ellipsoid concavo-convex shape, a cone concavo-convex shape, a cut cone concavo-convex shape, a triangular pyramid concavo-convex shape, a cut triangular pyramid concavo-convex shape, a cut quadrangular pyramid concavo-convex shape, It may be an independent shape such as a pyramid uneven shape or a cut polygonal pyramid uneven shape, or may be a shape in which straight bowl-like shapes are continuously arranged.

<Addition of functions other than optical elements of optical sheet>
In the optical sheet of the present invention, an ultraviolet absorber, an antistatic agent, a lubricant, and a near infrared absorber can be used within a range that does not impair the gist of the present invention. Preferably, a layer containing an agent, a layer containing an antistatic agent, or both an ultraviolet absorber-containing layer and an antistatic agent-containing layer are formed.

  Conventionally known UV absorbers and antistatic agents can be used. For example, as a UV absorber, a salicylic acid phenyl ester UV absorber; a benzophenone UV absorber; a triazine UV absorber; a benzotriazole UV absorber; a cyclic imino ester UV absorber; and a hindered phenol structure in the molecule Low molecular ultraviolet absorbers such as hybrid ultraviolet absorbers having a hindered amine structure; triphenylcyanoacrylate ultraviolet absorbers; oxalic anilide ultraviolet absorbers; malonic ester ultraviolet absorbers; and these low molecular ultraviolet absorbers Can be used, such as a polymer ultraviolet absorber (eg, Halus Hybrid (registered trademark) manufactured by Nippon Shokubai Co., Ltd.). Of these, triphenylcyanoacrylate ultraviolet absorbers; oxalic anilide ultraviolet absorbers; malonic ester ultraviolet absorbers are preferred because they absorb less light in the visible light region. When used for a polycarbonate resin, an oxalic anilide ultraviolet absorber; a malonic ester ultraviolet absorber is more preferable.

  Antistatic agents include alkyl sulfonic acids, alkyl benzene sulfonic acids, olefinic sulfates such as Li, Na, Ca, Mg, and Zn salts thereof or metal salts thereof; anionic surface activity such as phosphate esters of higher alcohols. Agents; Cationic surfactants such as tertiary amines, quaternary ammonium salts, cationic acrylic ester derivatives, cationic vinyl ether derivatives; amphoteric salts of alkylamine betaines, amphoteric salts of alanine carboxylates or sulfonates, Amphoteric surfactants such as amphoteric salts of alkyl imidazolines; Nonionic surfactants such as fatty acid polyhydric alcohol esters, polyoxyethylene adducts of alkyl (amines); Polyamide elastomers such as polyether ester amides and polyester amides This Can. In addition, conductive resins such as polyvinyl benzyl type cationic resins and polyacrylic acid type cationic resins can also be used as an antistatic agent.

  Although the usage-amount of a ultraviolet absorber and an antistatic agent can be suitably adjusted according to each function, Usually, it is about 1-50 mass parts with respect to 100 mass parts of resin which comprises each layer.

  These layers having different functions can be obtained by bonding a sheet in which a UV absorber or an antistatic agent is uniformly dispersed in the same resin as the thermoplastic resin constituting the sheet to the optical sheet or the like by thermocompression bonding or an adhesive. Good. Or you may dry or cool, after apply | coating the paste containing an ultraviolet absorber etc. on an optical sheet. Moreover, you may coextrude the thermoplastic resin which comprises a sheet | seat, and the thermoplastic resin which mix | blended the ultraviolet absorber and the antistatic agent.

  The thickness of the layer having these different functions may be appropriately adjusted according to each function, etc., but can usually be about 1 to 50 μm.

  The size and shape of the optical sheet of the present invention are not particularly limited, and may be used according to the size of a light source unit for a liquid crystal display, for example.

Next, examples of the present invention will be described, but the present invention is not limited to these examples.

<Measurement method of wavelength selectivity of straight light>
A sample sheet is set on a spectrophotometer (Shimadzu Corporation UV-3100) that is not equipped with a light-transmitting light integrating sphere, and the light transmittance from 300 nm to 800 nm is obtained.

A sample sheet is set on a spectrophotometer (Shimadzu UV-3100) equipped with a total transmittance integrating sphere, and the light transmittance from 300 nm to 800 nm is obtained.

Calculate the wavelength selectivity of the straight light of the sample from the following formula (Formula 1)
((Straight transmittance of 685 nm light) / (Total transmittance of 685 nm light)) / ((Straight light transmittance of 470 nm light) / (Total transmittance of 470 nm light))> 2.

<Diffusion degree measurement method>
Using a goniometer (Murakami Color Research Laboratory GP-5), set the sample so that the incident angle of light is 0 ° (perpendicular to the sample), and measure the diffused emitted light in the range of -90 to 90 ° To do. The diffusivity is obtained from the following equation.
Diffusivity = (30 ° emission angle light intensity) / (0 ° emission angle light intensity) × 100

In the measurement of the wavelength selectivity and diffusivity of the straight light described above, when the surface of the optical sheet of the present invention has a concavo-convex shape as described above, in order to eliminate the diffusion of light derived from the concavo-convex shape, It is filled with a contact liquid having the same refractive index as that of the transparent thermoplastic resin used for the measurement and sandwiched between glass plates for measurement. For example, when polycarbonate is used as the transparent thermoplastic resin, the uneven shape is filled with a contact liquid having a refractive index of 1.585 for measurement.

<Evaluation method of color compensation>
With the configuration shown in FIG. 1, the liquid crystal display device was displayed in white, and the color tone from the front and the color tone from 45 ° were confirmed visually.

<Example 1>
100 parts of polycarbonate resin (“Iupilon E2000FN”: manufactured by Mitsubishi Engineering Plastics), 0.1 part of a phosphorus-based heat stabilizer (“Irgaphos 168”: manufactured by Ciba Specialty Chemicals), and an average particle size of 0.3 μm 0.5 parts of silica-based fine particles (Nippon Catalyst Seahoster KE-P30) were melted at 265 ° C., and a flat sheet having a thickness of 0.5 mm was obtained by extrusion molding.
The obtained sheet was evaluated for wavelength selectivity, diffusivity, and color compensation of straight light, and the results shown in Table 1 were obtained.

<Comparative Example 1>
A flat sheet having a thickness of 0.5 mm was obtained in the same manner as in Example 1 except that silica fine particles having an average particle diameter of 1.0 μm (Nippon Catalyst Seahoster P100) were used.
The obtained sheet was evaluated for wavelength selectivity, diffusivity, and color compensation of straight light, and the results shown in Table 1 were obtained.

  The color compensation sheet of the present invention can solve the problem that the color that can be displayed by the liquid crystal display device changes depending on the viewing angle.

Claims (1)

An optical sheet comprising 0.0001 to 1.0% of organic or inorganic fine particles having an average particle diameter of 0.4 μm or less in a transparent thermoplastic resin with respect to the transparent thermoplastic resin. (When light is incident on the optical sheet from the vertical direction with a goniometer, the ratio of 30 ° outgoing light to 0 ° outgoing light) is 0.3% or less, and the light is incident from the vertical direction of the optical sheet. In this case, the optical sheet is characterized in that the ratio of the straight light to the total transmitted light is different depending on the wavelength, and the wavelength selectivity of the straight light represented by Formula 1 is a value larger than 2.
(Formula 1)
Wavelength selectivity of straight light = ((straight light transmittance of 685 nm light) / (total transmittance of 685 nm light) / ((straight light transmittance of 470 nm light) / (total transmittance of 470 nm light))

Images