JP4800549B2 - Optical sheet and backlight unit using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet which has remarkably high optical functions such as a light diffusing function, a function of refraction to a normal direction side, and a light converging function, and to provide a back light unit which can be improved more in quality such as, high luminance to its front direction and leveling of luminance and made thinner by using the optical sheet. <P>SOLUTION: The optical sheet 1 is equipped with a transparent base material layer 2 and an optical layer 3 laminated on the surface side of the base material layer 2 and the optical layer 3 has spherical resin beads 5 in a binder 4. The optical sheet is characterized in that (a) the mathematical mean roughness of three-dimensional surface roughness of the optical layer 3 is 5 to 14 &mu;m and (b) 10-point mean roughness of three-dimensional surface roughness of the optical layer 3 is 50 to 80 &mu;m. <P>COPYRIGHT: (C)2004,JPO&amp;NCIPI

Description

【００８４】
上記表１に示すように、比較例１及び２の光学シートと比較して、三次元表面粗さにおける算術平均粗さ（Ｒａ）が５μｍ以上１４μｍ以下で、十点平均粗さ（Ｒｚ）が５０μｍ以上８０μｍ以下の実施例１及び２の光学シートが高い正面輝度を示している。
【００８５】
【発明の効果】
以上説明したように、本発明の光学シートによれば、光拡散機能、法線方向側への屈折機能、集光機能等の光学的機能を格段に向上することができる。また、当該光学シートを用いたバックライトユニットによれば、正面方向の高輝度化、輝度の均一化等の品質の向上や薄型化を促進することができる。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る光学シートを示す模式的断面図である。
【図２】図１の光学シートとは異なる形態の光学シートを示す模式的断面図である。
【図３】（ａ）は一般的なエッジライト型バックライトユニットを示す模式的斜視図、（ｂ）は一般的な拡散性光学シートを示す模式的断面図である。
【符号の説明】
１ 光学シート
２ 基材層
３ 光学層
４ バインダー
５ 樹脂ビーズ
６ 凸部
７ 凹部
１１ 光学シート
１２ スティッキング防止層
１３ バインダー
１４ 樹脂ビーズ[0001]
BACKGROUND OF THE INVENTION
The present invention has a predetermined optical function (diffuse function, condensing function, refraction function, reflection function, etc.) for transmitted light, and is particularly suitable for a backlight unit of a liquid crystal display device, and this optical sheet. It relates to the backlight unit used.
[0002]
[Prior art]
In the liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back side is widely used, and a backlight unit such as an edge light type or a direct type is provided on the lower surface side of the liquid crystal layer. As shown in FIG. 3A, the edge light type backlight unit 20 generally has a rod-like lamp 21 as a light source, and a rectangular plate shape arranged so that the end of the lamp 21 is along the end. The light guide plate 22 and a plurality of optical sheets 23 stacked on the surface side of the light guide plate 22 are provided. The optical sheet 23 has specific optical functions such as refraction and diffusion. Specifically, (1) a diffusive optical element disposed on the surface side of the light guide plate 22 and mainly having a light diffusion function. The sheet 24, (2) a refractive optical sheet 25 disposed on the surface side of the diffusive optical sheet 24 and having a refractive function toward the normal line side, and the like.
[0003]
The function of the backlight unit 20 will be described. First, a light beam incident on the light guide plate 22 from the lamp 21 is reflected by a reflective dot or a reflection sheet (not shown) on the back surface of the light guide plate 22 and each side surface. Emitted from the surface. Light rays emitted from the light guide plate 22 enter the diffusive optical sheet 24, are diffused, and are emitted from the surface. Thereafter, the light beam emitted from the optical sheet 24 is incident on the refractive optical sheet 25, and is emitted as a light beam having a distribution having a peak in a substantially upward direction by the prism portion 25a formed on the surface. In this way, the light emitted from the lamp 21 is diffused by the optical sheets 24 and 25, refracted so as to show a peak in a substantially upward direction, and further illuminates the entire liquid crystal layer (not shown) above. is there.
[0004]
Although not shown, the back in which more optical sheets 23 such as a diffusive optical sheet and a refractive optical sheet are disposed in consideration of the light guide characteristics of the light guide plate 22 and the optical function of the optical sheet 23 described above. There is also a light unit.
[0005]
As shown in FIG. 3B, the diffusible optical sheet 24 is generally laminated on the surface of a transparent synthetic resin base material layer 26 and the surface of the base material layer 26, and mainly has light diffusibility. The optical layer 27 is provided. The optical layer 27 generally has a structure in which resin beads 29 are dispersed in a binder 28. Such a diffusive optical sheet 24 is disclosed in, for example, Japanese Patent Laid-Open No. 2000-89007.
[0006]
[Patent Document 1]
JP 2000-89007 A
[0007]
[Problems to be solved by the invention]
The diffusive optical sheet 24 disperses the transmitted light substantially uniformly by the resin beads 29 of the optical layer 27, and is used for the purpose of making the luminance uniform by the light diffusibility, increasing the luminance in the front direction, and the like. ing. However, even if the amount of the resin beads 29 is simply increased in order to increase the light diffusibility of the diffusive optical sheet 24, there is a limit to the improvement of the light diffusion function. Invite the decline. For this reason, the conventional diffusive optical sheet 24 alone cannot direct the peak direction of the luminance distribution of the emitted light in the normal direction (front direction), and the refractive optical sheet 25 and the plurality of diffusible optical sheets 24 are not aligned. The arrangement refracts the light rays in the normal direction direction to improve the front luminance.
[0008]
The present invention has been made in view of these disadvantages, and an optical sheet having a significantly high optical function such as a light diffusing function, a refraction function toward the normal direction side, and a condensing function, and a front direction using the optical sheet. An object of the present invention is to provide a backlight unit that can promote improvement in quality such as high brightness and uniform brightness and reduction in thickness.
[0009]
[Means for Solving the Problems]
As a result of earnestly studying which part of the optical layer in the conventional diffusible optical sheet contributes to the optical function such as the light diffusing function, reflection at the resin bead interface, Although the internal factors of the optical layer represented by refraction do not contribute much to the light diffusing function, there is a risk of adverse effects such as a decrease in light transmittance and a decrease in image clarity of transmission. On the other hand, it has been found that the fine irregularities formed on the surface of the optical layer by the resin beads exhibit an optical function such as a high light diffusion function due to its lens action.
[0010]
The invention made to solve the above-mentioned problems obtained as a result is provided with a transparent substrate layer and an optical layer laminated on the surface side of the substrate layer, and the optical layer is a spherical resin in the binder. An optical sheet having beads, wherein (a) the arithmetic average roughness in the three-dimensional surface roughness of the optical layer is 5 μm or more and 14 μm or less; and (b) the tertiary of the optical layer. The ten-point average roughness in the original surface roughness is 50 μm or more and 80 μm or less. In addition, the optical sheet has a resin bead blending amount of 200 parts or more and 280 parts or less with respect to 100 parts of the polymer content of the binder, and the coefficient of variation of the particle size distribution of the resin beads is 32% or more and 40% or less. And Further, this optical sheet is characterized in that the internal haze is 5% or more and 15% or less. Here, “three-dimensional surface roughness” refers to the surface roughness specified in JIS-B-0601, that is, the two-dimensional surface roughness based on the (X, Z) coordinates, and this standard (X, Y, Z) means a value expanded to coordinates.
[0011]
According to the optical sheet, fine irregularities are formed on the surface of the optical layer by the resin beads that are present, and each concave portion and convex portion constituting the fine irregularities have a lens-like curved surface shape. By setting the three-dimensional surface roughness of the optical layer surface within the above range, the convex and concave portions of fine irregularities on the optical layer surface function like a convex lens and a concave lens with respect to the transmitted light, compared with a conventional optical sheet. Thus, the optical functions of the optical sheet such as the light diffusing function, the refraction function toward the normal direction side, and the light collecting function are significantly improved.
[0012]
The average thickness of the optical layer may be 80% or more and 300% or less of the average particle diameter of the resin beads. Here, the “average thickness of the optical layer” is an average value of values measured by the A-2 method of 5.1.2 defined in JIS-K-7130. As this means, by controlling the average thickness of the optical layer within the above range in relation to the average particle diameter of the resin beads, lens-shaped concave and convex portions are remarkably formed on the optical layer surface by the resin beads that are present. The three-dimensional surface roughness of the formed optical layer can be easily controlled within the above range.
[0013]
The resin beads may have an average particle size of 18 μm or more and 22 μm or less. The variation coefficient of the particle size distribution of the resin beads is 32% or more and 40% or less, and the amount of the resin beads blended with respect to 100 parts of the polymer of the binder is 200 parts or more and 280 parts or less. By controlling the average particle diameter of the resin beads, the coefficient of variation of the particle diameter distribution, and the blending amount within the above ranges as in this means, fine irregularities are formed on the optical layer surface with a dense and substantially equal density by the resin beads that are present. The three-dimensional surface roughness of the optical layer surface can be easily and reliably controlled within the above range. Thus, the optical function of the optical sheet such as the light diffusing function, the refraction function toward the normal direction, and the condensing function is remarkably improved by the lens action of minute irregularities formed densely on the surface of the optical layer. .
[0014]
The binder may be formed from a polymer composition containing a polyol. In this way, when a polyol is used as the base polymer of the binder, the polyol is excellent in processability, moldability and adhesion with the resin beads, so that the adhesion between the binder and the resin beads is good by means such as coating, It is possible to easily and reliably form an optical layer that does not involve air inside and that has the fine irregularities on the surface. Further, according to the polyol, the coating layer physical properties such as surface hardness, abrasion resistance, weather resistance, heat resistance, and contamination resistance of the optical layer are enhanced, and the dispersion of the fine inorganic filler in the binder is facilitated. Therefore, it is possible to suppress the temporal deterioration of the optical function of the optical sheet.
[0015]
As the polyol, acrylic polyol or polyester polyol is preferable. Such an acrylic polyol or polyester polyol is excellent in transparency and has excellent film properties such as surface hardness, hydrophobicity, weather resistance, etc., so that the total light transmittance of the optical sheet is increased, yellowing due to ultraviolet rays, deterioration, etc. Can be reduced. As a result, the optical function of the optical sheet can be further promoted, and a decrease with time can be suppressed.
[0016]
In the polymer composition, a fine inorganic filler having an organic polymer fixed on its surface may be dispersedly contained. Here, “fixing” does not mean mere adhesion and adhesion, but means that a chemical bond is formed between the organic polymer and the minute inorganic filler, and therefore, the minute inorganic filler is bonded to any solvent. Organic polymer is not detected in the washing solution washed with. Since the optical sheet in the backlight unit is exposed to the heat of the lamp, a fine inorganic filler is often blended in the polymer composition constituting the binder for the purpose of improving heat resistance. When using a fine inorganic filler with an organic polymer fixed on the surface, it has a good affinity for the base polymer constituting the binder, and has surface hardness, heat resistance, wear resistance, weather resistance, and stain resistance. It is possible to form an optical layer having good film properties such as the above. As a result, the optical function of the optical sheet can be further promoted, and a decrease with time can be suppressed.
[0017]
The internal haze of the optical sheet is preferably 5% or more and 30% or less. Thus, by setting the internal haze of the optical sheet within the above range and making it relatively small, the light diffusing function resulting from the lens action of fine irregularities on the surface of the optical layer, the refraction function toward the normal direction, the light collection Optical functions such as functions can be made to function and be enhanced. Further, by controlling the internal haze within the above range, it is possible to reduce a decrease in the total light transmittance of the optical sheet, a decrease in transmitted image definition, and the like.
[0018]
It is good to further have a sticking prevention layer laminated on the back side of the base material layer and having resin beads in the binder. According to this means, it is possible to prevent sticking with a light guide plate, a prism sheet or the like superimposed on the optical sheet.
[0019]
Accordingly, in a backlight unit for a liquid crystal display device that disperses light emitted from a lamp and guides it to the surface side, when the optical sheet is provided, the optical sheet has an excellent optical function (light diffusion function, method) as described above. Since it has a refraction function in the line direction side, a light condensing function, etc., there is no luminance unevenness, the viewing angle can be widened, and the front luminance can be increased. Therefore, according to the backlight unit, a refractive optical sheet such as a prism sheet can be omitted, or the number of optical sheets can be reduced, and as a result, the reduction in thickness can be promoted.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. FIG. 1 is a schematic cross-sectional view showing an optical sheet according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view showing an optical sheet having a different form from the optical sheet of FIG.
[0021]
The optical sheet 1 in FIG. 1 has the same configuration as the bead-coating type diffusive optical sheet. Specifically, the optical layer 3 and the optical layer 3 laminated on the surface of the base material layer 2 are used. It consists of and.
[0022]
Since the base material layer 2 needs to transmit light, it is made of a synthetic resin that is transparent, particularly colorless and transparent. The synthetic resin used for the base material layer 2 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather resistant vinyl chloride. . Among them, polyethylene terephthalate having excellent transparency and high strength is preferable, and polyethylene terephthalate having improved bending performance is particularly preferable.
[0023]
The thickness (average thickness) of the base material layer 2 is not particularly limited, but is, for example, 10 μm or more and 500 μm or less, preferably 35 μm or more and 250 μm or less, and particularly preferably 50 μm or more and 188 μm or less. When the thickness of the base material layer 2 is less than the above range, problems such as curl are likely to occur when the resin composition for forming the optical layer 3 is applied, and handling becomes difficult. To do. On the contrary, if the thickness of the base material layer 2 exceeds the above range, the luminance of the liquid crystal display device may decrease, and the thickness of the backlight unit becomes large, which is contrary to the demand for thinning of the liquid crystal display device. It will also be a thing.
[0024]
The optical layer 3 has resin beads 5 disposed on the surface of the base material layer 2 in a layered and substantially equal density, and a binder 4 filled around the resin beads 5. On the surface of the optical layer 3, fine irregularities (convex portions 6 and concave portions 7) that are smoothly continuous are formed densely and substantially uniformly by the binder 4 that covers the upper surface of the resin beads 5. The convex portion 6 and the concave portion 7 have a lens-like curved surface shape. The convex portion 6 acts as a convex lens on the transmitted light, and the concave portion 7 acts as a concave lens. Therefore, the optical sheet 1 can exhibit an excellent light diffusion function. Further, the optical sheet 1 has a remarkably improved refraction function for refracting transmitted light toward the normal direction due to the excellent light diffusion function. Furthermore, the optical sheet 1 also has a high light collecting function for condensing transmitted light in the normal direction macroscopically.
[0025]
The lower limit of the arithmetic average roughness (Ra) in the three-dimensional surface roughness of the surface of the optical layer 3 is 5 μm, and 7 μm is particularly preferable. On the other hand, the upper limit of the arithmetic average roughness (Ra) is 14 μm, and 12 μm is particularly preferable. By controlling the arrangement pitch, curvature, height, and the like of the lens-like convex portions 6 and the concave portions 7 so that the three-dimensional surface arithmetic average roughness (Ra) of the optical layer 3 falls within the above range, the convex portions 6 and the optical function such as the light diffusion function by the lens action of the concave portion 7 can be remarkably enhanced.
[0026]
Similarly, the lower limit of the ten-point average roughness (Rz) in the three-dimensional surface roughness of the surface of the optical layer 3 is 50 μm, and 60 μm is particularly preferable. On the other hand, the upper limit of the ten-point average roughness (Rz) is 80 μm, and 70 μm is particularly preferable.
[0027]
The lower limit of the average thickness of the optical layer 3 is preferably 80%, particularly 85%, more particularly 90% of the average particle diameter of the resin beads 5. On the other hand, the upper limit of the average thickness of the optical layer 3 is preferably 300%, particularly 290%, more particularly 280% of the average particle diameter of the resin beads 5. By setting the thickness of the optical layer 3 to this level, the surface of the optical layer 3 can be remarkably formed with fine unevenness that acts as a lens, and can effectively exhibit the light diffusion function, the refraction function, and the light collecting function. it can.
[0028]
The internal haze of the optical sheet 1 is 5% or more and 30% or less, and the upper limit thereof is preferably 15%, particularly 8%. This is because if the internal haze of the optical sheet 1 exceeds the above upper limit, the total light transmittance may decrease, the image clarity of transmission may decrease, and the internal haze may be reduced to the above lower limit. This is because making it smaller increases the difficulty in production and makes it difficult to develop the desired overall haze. The “internal haze” value was measured after the surface of the optical sheet 1 was coated with the same polymer composition as the binder 4 and the surface of the optical layer 3 was smoothed by filling the fine irregularities.
[0029]
Moreover, as a ratio of the internal haze with respect to the whole haze, 7% or more and 35% or less are preferable. By reducing the ratio of internal haze to the above range and making it relatively small, the reduction in total light transmittance, etc. is reduced, and the external haze, that is, the light diffusing function resulting from the lens action of the fine irregularities on the optical layer surface, etc. The optical function can be exhibited.
[0030]
The lower limit of the image sharpness of transmission with an optical comb width of 2 mm in the optical sheet 1 is 7%, and 7.4% is particularly preferable. On the other hand, the upper limit of the transmission image definition is 23%, and 20% is particularly preferable. This is because if the transmission image definition exceeds the above upper limit, the haze required for the diffusive optical sheet may not be obtained. Conversely, if the transmission image definition is less than the above lower limit, This is because the rate is lowered and there is a possibility that high luminance in the front direction cannot be achieved.
[0031]
The resin beads 5 are transparent spherical fine particles made of resin. Specific materials used for the resin beads 5 are not particularly limited, and examples thereof include acrylic resin, acrylonitrile resin, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, and polyamide. Among them, an acrylic resin having high transparency is preferable, and polymethyl methacrylate (PMMA) is particularly preferable.
[0032]
The lower limit of the average particle diameter of the resin beads 5 is preferably 18 μm, particularly 19 μm, more preferably 20 μm, and the upper limit of the average particle diameter of the resin beads 5 is preferably 22 μm, particularly 21 μm, more particularly 20 μm. If the average particle diameter of the resin beads 5 is less than the above range, the unevenness of the surface of the optical layer 3 formed by the resin beads 5 is small, and the above-described excellent optical function may not be achieved. If the average particle diameter of the resin beads 5 exceeds the above range, the thickness of the optical sheet 1 increases and uniform diffusion becomes difficult.
[0033]
The lower limit of the coefficient of variation of the particle size distribution of the resin beads 5 is preferably 30%, particularly 32%, more particularly 34%, and the upper limit of this coefficient of variation is preferably 40%, particularly 38%, more particularly 36%. This is because if the coefficient of variation of the resin beads 5 exceeds the above upper limit, the resin beads 5 buried inside that do not contribute to the formation of fine irregularities on the surface of the optical layer 3 or the resin beads 5 protruding greatly from the average surface of the optical layer 3 This is because the total light transmittance and the light diffusibility may be lowered, and conversely, even if the coefficient of variation of the resin beads 5 is smaller than the above lower limit, the light diffusibility does not increase, and to some extent. This is because the random particle size contributes to the light diffusibility and increases the quality.
[0034]
In addition, the variation coefficient of the average particle diameter and particle diameter distribution of the resin beads 5 is a value measured by a Coulter counter method. The Coulter counter method is a method for electrically measuring the number and size of particles dispersed in a solution, in which particles are dispersed in an electrolyte solution and electricity flows using suction force. This is a method of measuring a voltage pulse in proportion to the volume of the particle by replacing the electrolyte by the volume of the particle when passing the particle through the pores, increasing the resistance. Therefore, the number and individual particle volume are measured by electrically measuring the height and number of the voltage pulse, and the particle size and particle size distribution are obtained from the measurement results, and the average particle size of the resin beads 5 and A coefficient of variation is determined.
[0035]
The lower limit of the blending amount of the resin beads 5 (the blending amount in terms of solid content with respect to 100 parts of the polymer in the polymer composition that is the forming material of the binder 4) is preferably 200 parts, particularly 220 parts, and more preferably 240 parts. The upper limit of the amount is preferably 300 parts, particularly 280 parts, and further 260 parts. This is because if the blending amount of the resin beads 5 is less than the above range, there are few fine irregularities formed on the surface of the optical layer 3 and the above-mentioned excellent optical function may not be achieved. This is because, if the blending amount of the beads 5 exceeds the above range, the unevenness of the surface of the optical layer 3 becomes severe, so that the front luminance and the uniformity of the luminance may decrease.
[0036]
The binder 4 consists of a polymer composition containing a base polymer, and is formed by curing this polymer composition. In addition to this polymer composition, for example, curing agents, plasticizers, dispersants, inorganic fillers, antistatic agents, various leveling agents, ultraviolet absorbers, antioxidants, viscosity modifiers, lubricants, light stabilization An agent or the like may be appropriately blended.
[0037]
The base polymer is not particularly limited, and examples thereof include acrylic resins, polyurethanes, polyesters, fluorine resins, silicone resins, polyamideimides, epoxy resins, ultraviolet curable resins, and the like. Can be used singly or in combination of two or more. In particular, the base polymer is preferably a polyol that has high processability and can form the optical layer 3 having fine irregularities easily and reliably by means such as coating. The base polymer is transparent because it is necessary to transmit light, and colorless and transparent is particularly preferable.
[0038]
Examples of the polyol include a polyol obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer, a polyester polyol obtained under conditions of excess hydroxyl group, etc., and these may be used alone or in combination of two or more. Can be used.
[0039]
Examples of the hydroxyl group-containing unsaturated monomer include (a) 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, allyl alcohol, homoallyl alcohol, Hydroxyl group-containing unsaturated monomers such as cinnamon alcohol, crotonyl alcohol, (b) for example ethylene glycol, ethylene oxide, propylene glycol, propylene oxide, butylene glycol, butylene oxide, 1,4-bis (hydroxymethyl) cyclohexane, phenyl Dihydric alcohols or epoxy compounds such as glycidyl ether, glycidyl decanoate, Plaxel FM-1 (manufactured by Daicel Chemical Industries, Ltd.) and, for example, acrylic acid, methacrylic acid, maleic acid, fumaric acid Crotonic acid, and the like react with the resulting hydroxyl group-containing unsaturated monomer with an unsaturated carboxylic acid such as itaconic acid. One or more selected from these hydroxyl group-containing unsaturated monomers can be polymerized to produce a polyol.
[0040]
In addition, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, ethyl hexyl acrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-methacrylic acid n- Butyl, tert-butyl methacrylate, ethyl hexyl methacrylate, glycidyl methacrylate, cyclohexyl methacrylate, styrene, vinyl toluene, 1-methylstyrene, acrylic acid, methacrylic acid, acrylonitrile, vinyl acetate, vinyl propionate, vinyl stearate, acetic acid Allyl, diallyl adipate, diallyl itaconate, diethyl maleate, vinyl chloride, vinylidene chloride, acrylamide, N-methylol acrylamide, N-butoxymethyl acrylate One or more ethylenically unsaturated monomers selected from amide, diacetone acrylamide, ethylene, propylene, isoprene and the like, and a hydroxyl group-containing unsaturated monomer selected from the above (a) and (b) A polyol can also be produced by polymerizing the product.
[0041]
The number average molecular weight of the polyol obtained by polymerizing the monomer component containing such a hydroxyl group-containing unsaturated monomer is from 1,000 to 500,000, preferably from 5,000 to 100,000. The hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, more preferably 20 or more and 150 or less.
[0042]
The polyester polyol obtained under the condition of excess hydroxyl group is (c), for example, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, neopentyl. Glycol, hexamethylene glycol, decamethylene glycol, 2,2,4-trimethyl-1,3-pentanediol, trimethylolpropane, hexanetriol, glycerin, pentaerythritol, cyclohexanediol, hydrogenated bisphenol A, bis (hydroxymethyl) Polyhydric alcohols such as cyclohexane, hydroquinone bis (hydroxyethyl ether), tris (hydroxyethyl) isosinurate, xylylene glycol, and (d) for example malee , Fumaric acid, succinic acid, adipic acid, sebacic acid, azelaic acid, trimetic acid, terephthalic acid, phthalic acid, isophthalic acid and other polybasic acids, and propanediol, hexanediol, polyethylene glycol, trimethylolpropane, etc. It can be produced by reacting under the condition that the number of hydroxyl groups in the monohydric alcohol is larger than the number of carboxyl groups of the polybasic acid.
[0043]
The number average molecular weight of the polyester polyol obtained under such an excessive hydroxyl group condition is 500 or more and 300,000 or less, and preferably 2000 or more and 100,000 or less. The hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, more preferably 20 or more and 150 or less.
[0044]
The polyol used as the base polymer of the polymer composition is obtained by polymerizing a monomer component containing the polyester polyol and the hydroxyl group-containing unsaturated monomer, and is a (meth) acryl unit or the like. An acrylic polyol having The binder 4 having such a polyester polyol or acrylic polyol as a base polymer has high weather resistance, and can suppress yellowing or the like of the optical layer 3. In addition, any one of this polyester polyol and acrylic polyol may be used, and both may be used.
[0045]
The number of hydroxyl groups in the polyester polyol and acrylic polyol is not particularly limited as long as it is 2 or more per molecule, but if the hydroxyl value in the solid content is 10 or less, the number of crosslinking points decreases, and the solvent resistance , Film properties such as water resistance, heat resistance and surface hardness tend to decrease.
[0046]
As said polyol, what has a cycloalkyl group is preferable. Thus, by introducing a cycloalkyl group into the base polymer (polyol) constituting the binder 4, the hydrophobicity such as water repellency and water resistance of the binder 4 is increased, and the said polymer under high temperature and high humidity conditions. The bending resistance and dimensional stability of the optical sheet 1 are improved. Further, the basic properties of the coating film such as hardness, weather resistance, feeling of holding, and solvent resistance of the optical layer 3 are improved. Furthermore, the affinity with the fine inorganic filler having the organic polymer fixed on the surface and the uniform dispersibility of the fine inorganic filler are further improved.
[0047]
The cycloalkyl group is not particularly limited, and examples thereof include a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclononyl group, a cyclodecyl group, a cycloundecyl group, a cyclododecyl group, a cyclotridecyl group, Examples thereof include a cyclotetradecyl group, a cyclopentadecyl group, a cyclohexadecyl group, a cycloheptadecyl group, and a cyclooctadecyl group.
[0048]
The polyol having a cycloalkyl group can be obtained by copolymerizing a polymerizable unsaturated monomer having a cycloalkyl group. The polymerizable unsaturated monomer having a cycloalkyl group is a polymerizable unsaturated monomer having at least one cycloalkyl group in the molecule. The polymerizable unsaturated monomer is not particularly limited, and examples thereof include cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, tert-butylcyclohexyl (meth) acrylate, and cyclododecyl (meth) acrylate.
[0049]
As described above, when a polyol is used as the base polymer, a polyisocyanate compound may be contained as a curing agent in the polymer composition. This polyisocyanate compound is a derivative of dimer, trimer, tetramer or the like obtained by polymerizing diisocyanate. Since the curing reaction rate of the polymer composition is increased by blending the polyisocyanate compound, even if a cationic antistatic agent that contributes to the dispersion stability of the fine inorganic filler is contained in the polymer composition, the cationic antistatic agent is used. The decrease in the curing reaction rate due to the agent can be sufficiently compensated, and the productivity can be further increased.
[0050]
The polyisocyanate compound is preferably a xylene diisocyanate derivative or a mixture of this xylene diisocyanate derivative and an aliphatic diisocyanate derivative. This xylene diisocyanate derivative has a large effect of improving the reaction rate of the polymer composition, and among aromatic diisocyanate derivatives, yellowing and deterioration due to heat and ultraviolet rays are relatively small. Therefore, the light transmittance of the optical sheet 1 with time is reduced. Reduction can be reduced. On the other hand, aliphatic diisocyanate derivatives have a smaller reaction rate improvement effect than aromatic diisocyanate derivatives, but yellowing, deterioration, etc. due to ultraviolet rays etc. are much smaller, so mixing with xylene diisocyanate derivatives can improve reaction rate. And the effect of preventing yellowing and the like can be achieved in a balanced manner.
[0051]
As this aliphatic diisocyanate derivative, an isophorone diisocyanate derivative and a hexamethylene diisocyanate derivative are preferable. Such isophorone diisocyanate derivatives and hexamethylene diisocyanate derivatives have a relatively large effect of improving the curing reaction rate among aliphatic diisocyanate derivatives, and can promote the above-described productivity and heat resistance.
[0052]
The type of the diisocyanate derivative is preferably TMP adduct type, isocyanurate type or burette type. According to these types of derivatives, the above-described curing reaction rate can be effectively increased.
[0053]
The lower limit of the blending amount of the polyisocyanate compound (the blending amount in terms of solid content with respect to 100 parts of the polymer in the polymer composition) is preferably 20 parts, and particularly preferably 25 parts. On the other hand, the upper limit of the amount of the curing agent is preferably 45 parts, particularly preferably 40 parts. Thus, by making the compounding quantity of a polyisocyanate compound into the said range, the above-mentioned hardening reaction rate improvement effect | action of a polymer composition can be show | played effectively.
[0054]
Moreover, it is good to contain a fine inorganic filler in the polymer composition. The dispersion of the minute inorganic filler in the binder 4 can increase the heat resistance of the optical layer 3 and the optical sheet 1 as a whole. As a result, the backlight unit is exposed to the heat of the lamp and moisture in the air. However, the deformation of the optical sheet 1 can be remarkably suppressed.
[0055]
The inorganic material constituting the fine inorganic filler is not particularly limited, but an inorganic oxide is particularly preferable. This inorganic oxide is defined as various oxygen-containing metal compounds in which a metal element mainly forms a three-dimensional network through bonds with oxygen atoms. Moreover, as a metal element which comprises an inorganic oxide, the element chosen from the element periodic table II-VI group is preferable, for example, and the element chosen from the element periodic table III-V group is more preferable. Among them, an element selected from Si, Al, Ti, and Zr is particularly preferable, and colloidal silica whose metal element is Si is most preferable as the fine inorganic filler. The shape of the fine inorganic filler may be any particle shape such as a spherical shape, a needle shape, a plate shape, a scale shape, and a crushed shape, and is not particularly limited.
[0056]
The lower limit of the average particle size of the fine inorganic filler is preferably 5 nm, and particularly preferably 10 nm. On the other hand, the upper limit of the average particle size of the fine inorganic filler is preferably 50 nm, particularly preferably 25 nm. This is because if the average particle size of the fine inorganic filler is less than the above range, the surface energy of the fine inorganic filler becomes high and aggregation or the like is likely to occur. Conversely, if the average particle size exceeds the above range, This is because it may become cloudy due to the influence of a short wavelength and the transparency of the optical sheet 1 may be lowered.
[0057]
The lower limit of the compounding amount of the fine inorganic filler (only the inorganic component) (the compounding amount in terms of solid content with respect to 100 parts of the polymer in the polymer composition) is preferably 10 parts, particularly preferably 50 parts. On the other hand, the upper limit of the amount of the fine inorganic filler is preferably 500 parts, particularly preferably 200 parts. This is because if the blending amount of the fine inorganic filler is less than the above range, the heat resistance of the optical sheet 1 may not be sufficiently expressed, and conversely if the blending amount exceeds the above range. This is because blending into the polymer composition becomes difficult and the light transmittance of the optical layer 3 may be lowered.
[0058]
As the fine inorganic filler, a material having an organic polymer fixed on its surface may be used. As described above, by using the organic polymer-fixed fine inorganic filler, the dispersibility in the binder 4 and the affinity with the binder 4 can be improved. Therefore, the influence which dispersion | distribution content of a fine inorganic filler has on the formability of the lens-shaped convex part 6 and the recessed part 7 can be reduced. The organic polymer is not particularly limited with respect to its molecular weight, shape, composition, presence or absence of a functional group, and any organic polymer can be used. Moreover, about the shape of an organic polymer, the thing of arbitrary shapes, such as a linear form, a branched form, and a crosslinked structure, can be used.
[0059]
Specific resins constituting such an organic polymer include, for example, (meth) acrylic resins, polystyrene, polyvinyl acetate, polyolefins such as polyethylene and polypropylene, polyesters such as polyvinyl chloride, polyvinylidene chloride, polyethylene terephthalate, and the like. Examples thereof include a resin partially modified with a functional group such as a copolymer, an amino group, an epoxy group, a hydroxyl group, or a carboxyl group. Among them, those having an organic polymer containing a (meth) acryl unit such as a (meth) acrylic resin, a (meth) acrylic-styrene resin, and a (meth) acrylic-polyester resin have a film forming ability. Is preferred. On the other hand, a resin having compatibility with the base polymer of the polymer composition is preferred, and therefore, the resin having the same composition as the base polymer contained in the polymer composition is most preferred.
[0060]
The fine inorganic filler may contain an organic polymer in the fine particles. As a result, moderate softness and toughness can be imparted to the inorganic material that is the core of the fine inorganic filler.
[0061]
As the organic polymer, one containing an alkoxy group may be used, and the content is preferably 0.01 mmol or more and 50 mmol or less per 1 g of the fine inorganic filler on which the organic polymer is fixed. Such an alkoxy group can improve the affinity with the matrix resin constituting the binder 4 and the dispersibility in the binder 4.
[0062]
The alkoxy group here refers to an RO group bonded to a metal element forming a fine particle skeleton. R is an alkyl group which may be substituted, and the RO groups in the fine particles may be the same or different. Specific examples of R include methyl, ethyl, n-propyl, isopropyl, n-butyl and the like. It is preferable to use the same metal alkoxy group as the metal constituting the fine inorganic filler. When the fine inorganic filler is colloidal silica, it is preferable to use an alkoxy group having silicon as a metal.
[0063]
The content of the organic polymer in the fine inorganic filler to which the organic polymer is fixed is not particularly limited, but is preferably 0.5% by mass or more and 50% by mass or less based on the fine inorganic filler.
[0064]
A polyfunctional isocyanate compound having two or more functional groups capable of reacting with a hydroxyl group in the polymer composition constituting the binder 4, using an organic polymer having a hydroxyl group as the organic polymer fixed to the fine inorganic filler as described above, melamine It is preferable to contain at least one selected from a compound and an aminoplast resin. As a result, the fine inorganic filler and the matrix resin of the binder 4 are bonded in a cross-linked structure, and the storage stability, stain resistance, flexibility, weather resistance, storage stability, etc. are improved, and the resulting film is further obtained. It becomes glossy.
[0065]
Examples of the polyfunctional isocyanate compound include aliphatic, alicyclic, aromatic and other polyfunctional isocyanate compounds and modified compounds thereof. Specific examples of the polyfunctional isocyanate compound include tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, lysine diisocyanate, 2,2,4-trimethylhexylmethane diisocyanate, methylcyclohexane diisocyanate, 1,6. -Trimer such as biuret and isocyanurate of hexamethylene diisocyanate; produced by reaction of these polyfunctional isocyanates with polyhydric alcohols such as propanediol, hexanediol, polyethylene glycol and trimethylolpropane Compounds in which at least one isocyanate group remains; these polyfunctional isocyanate compounds can be combined with ethanol, hexanol, etc. Blocked polyfunctional isocyanate compounds blocked with blocking agents such as chols, compounds having phenolic hydroxyl groups such as phenol and cresol, oximes such as acetooxime and methylethylketoxime, and lactams such as ε-caprolactam and γ-caprolactam Can be mentioned. In addition, the said polyfunctional isocyanate compound can be used 1 type or in mixture of 2 or more types. Among these, a non-yellowing polyfunctional isocyanate compound having no isocyanate group directly bonded to an aromatic ring is preferable in order to prevent yellowing of the film.
[0066]
Examples of the melamine compound include dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, hexamethylol melamine, isobutyl ether type melamine, n-butyl ether type melamine, butylated benzoguanamine and the like.
[0067]
Examples of the aminoplast resin include alkyl etherified melamine resins, urea resins, and benzoguanamine resins. These aminoplast resins can be used alone or as a mixture or cocondensate of two or more. The alkyl etherified melamine resin is obtained by methylolating aminotriazine and alkyl etherifying with cyclohexanol or alkanol having 1 to 6 carbon atoms. The butyl etherified melamine resin, methyl etherified melamine resin, methylbutyl mixed melamine Resin is representative. In addition, a sulfonic acid catalyst for promoting curing, for example, paratoluenesulfonic acid and its amine salt can be used.
[0068]
Moreover, it is good to contain an antistatic agent in a polymer composition. The antistatic agent is not particularly limited. For example, anionic antistatic agents such as alkyl sulfates and alkyl phosphates, cationic antistatic agents such as quaternary ammonium salts and imidazoline compounds, polyethylene glycol type Nonionic antistatic agents such as polyoxyethylene sorbitan monostearic acid ester and ethanolamides, and high molecular antistatic agents such as polyacrylic acid are used. Among these, cationic antistatic agents that have a relatively large antistatic effect and do not inhibit the stability of the dispersion state of the fine inorganic filler are preferable. Among these cationic antistatic agents, ammonium salts and betaines that can further promote the antistatic property to the above-mentioned highly hydrophobic binder 4 are particularly preferable.
[0069]
The lower limit of the blending amount of the antistatic agent (blending amount in terms of solid content with respect to 100 parts of the polymer in the polymer composition) is preferably 0.5 part, and particularly preferably 3 parts. On the other hand, the upper limit of the amount of the antistatic agent is preferably 15 parts, particularly preferably 10 parts. This is because if the blending amount of the antistatic agent is smaller than the above lower limit, the above-mentioned antistatic effect may not be sufficiently exhibited. Conversely, if the blending amount of the antistatic agent exceeds the above upper limit, This is because inconveniences such as a decrease in total light transmittance and a decrease in strength due to the blending of the inhibitor may occur.
[0070]
The refractive index ratio between the binder 4 and the resin beads 5 is preferably 0.95 or more and 1.05 or less, particularly preferably 0.97 or more and 1.03 or less. Thus, by making the refractive index ratio between the binder 4 and the resin beads 5 relatively small, irregular reflection at the interface between the binder 4 and the resin beads 5 is reduced, and as a result, the internal haze of the optical sheet 1 is reduced. The optical function such as the light diffusion function by the lens action of the convex part 6 and the concave part 7 can be reduced.
[0071]
Next, a method for manufacturing the optical sheet 1 will be described. The manufacturing method of the optical sheet 1 includes: (a) a process of manufacturing an optical layer coating liquid by mixing resin beads 5 with a polymer composition constituting the binder 4; and (b) this optical layer coating. A step of laminating the optical layer 3 by applying the liquid onto the surface of the base material layer 2.
[0072]
The optical sheet 11 in FIG. 2 includes a base material layer 2, an optical layer 3 laminated on the front side of the base material layer 2, and a sticking prevention layer 12 laminated on the back surface of the base material layer 2. . The base material layer 2 and the optical layer 3 are the same as those in the embodiment shown in FIG. Therefore, the optical sheet 11 also has a very excellent optical function like the optical sheet 1.
[0073]
The anti-sticking layer 12 is composed of a binder 13 and resin beads 14 dispersed in the binder 13. The binder 13 is also formed by curing the same polymer composition as the binder 4 of the optical layer 3. Further, as the material of the resin beads 14, the same material as the resin beads 5 of the optical layer 3 is used. The thickness of the anti-sticking layer 12 (the thickness of the binder 13 portion excluding the resin beads 14) is not particularly limited, but is, for example, about 1 μm or more and 10 μm or less.
[0074]
The blending amount of the resin beads 14 is relatively small, the resin beads 14 are separated from each other and dispersed in the binder 13, and many of the resin beads 14 have a very small lower end protruding from the binder 13. Therefore, when this optical sheet 11 is laminated with the light guide plate, the lower end of the protruding resin beads 14 contacts the surface of the light guide plate or the like, and the entire back surface of the optical sheet 11 does not contact the light guide plate or the like. As a result, sticking between the optical sheet 11 and the light guide plate or the like is prevented, and uneven brightness on the screen of the liquid crystal display device is suppressed.
[0075]
Next, a method for manufacturing the optical sheet 11 will be described. The method for producing the optical sheet 11 includes: (a) a step of producing an optical layer coating liquid by mixing the resin beads 5 with the polymer composition constituting the binder 4; and (b) this optical layer coating. A step of laminating the optical layer 3 by coating the liquid on the surface of the base material layer 2; and (c) a coating solution for an anti-sticking layer by mixing the resin beads 14 with the polymer composition constituting the binder 13. And (d) a step of laminating the anti-sticking layer 12 by applying the coating solution for the anti-sticking layer to the back surface of the base material layer 2.
[0076]
Accordingly, the lamp 21, the light guide plate 22, and the optical sheet 23 (diffusive optical sheet 24, refractive optical sheet 25) as shown in FIG. 3A are provided, and the light emitted from the lamp 21 is dispersed to the surface side. When the optical sheet 1 or 11 is used as the optical sheet 23 in the guiding backlight unit 20 for the liquid crystal display device, since the optical sheet 1 or 11 has an excellent optical function, the occurrence of luminance unevenness is prevented, and The front brightness can be increased. Further, the excellent optical functions of the optical sheets 1 and 11 enable the prism-type refractive optical sheet 25 to be omitted and the number of optical sheets to be reduced, thereby facilitating the reduction in thickness.
[0077]
【Example】
EXAMPLES Hereinafter, although this invention is explained in full detail based on an Example, this invention is not interpreted limitedly based on description of this Example.
[0078]
[Example 1]
Acrylic polyol (Nippon Shokubai Co., Ltd. “Udouble S-2840”; solid content 50%) 128 parts, isocyanate (Japan Polyurethane Industry Co., Ltd. “Coronate HL”; solid content 75%) 18 parts, antistatic In a polymer composition (refractive index after curing: 1.53) consisting of 42 parts of agent ("RUB antistatic agent" manufactured by Dainichi Seika Kogyo Co., Ltd .; solid content 50%), 105 parts of methyl ethyl ketone and 105 parts of toluene In addition, 192 parts of acrylic beads having an average particle diameter of 20 μm (“MBX-20” manufactured by Sekisui Plastics Co., Ltd .; refractive index: 1.50) with a coefficient of variation of particle diameter distribution adjusted to 35% were mixed. An optical layer coating solution was prepared, and this optical layer coating solution was applied to the surface of a transparent polyester base layer having a thickness of 100 μm at 17 g / m. ² (Solid content conversion) The optical sheet of Example 1 was obtained by coating.
[0079]
[Example 2]
An optical sheet of Example 2 was obtained in the same manner as in Example 1 except that the coefficient of variation was adjusted to 32% and the blending amount of acrylic beads was 178 parts.
[0080]
[Comparative Example 1]
The optical sheet of Comparative Example 1 was obtained in the same manner as in Example 1 except that the coefficient of variation was adjusted to 45% and the blending amount of acrylic beads was 206 parts.
[0081]
[Comparative Example 2]
An optical sheet of Comparative Example 2 was obtained in the same manner as in Example 1 except that the coefficient of variation was adjusted to 20% and the blending amount of acrylic beads was 162 parts.
[0082]
[Evaluation of characteristics]
Using the optical sheets of Examples 1 and 2 and the optical sheets of Comparative Examples 1 and 2, the arithmetic average roughness (Ra) and ten-point average roughness (Rz) of these optical sheets were measured, and these optical sheets were also measured. The front luminance was measured by mounting the sheet on the surface side of the light guide plate of the edge light type backlight unit. The results are shown in Table 1 below.
[0083]
[Table 1]

[0084]
As shown in Table 1, the arithmetic average roughness (Ra) in the three-dimensional surface roughness is 5 μm or more and 14 μm or less, and the ten-point average roughness (Rz) is compared with the optical sheets of Comparative Examples 1 and 2. The optical sheets of Examples 1 and 2 having a size of 50 μm or more and 80 μm or less show high front luminance.
[0085]
【The invention's effect】
As described above, according to the optical sheet of the present invention, optical functions such as a light diffusing function, a refraction function toward the normal direction, and a light collecting function can be remarkably improved. Moreover, according to the backlight unit using the optical sheet, it is possible to promote quality improvement and thinning such as high brightness in the front direction and uniform brightness.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an optical sheet according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view showing an optical sheet having a form different from that of the optical sheet in FIG.
3A is a schematic perspective view showing a general edge light type backlight unit, and FIG. 3B is a schematic cross-sectional view showing a general diffusive optical sheet.
[Explanation of symbols]
1 Optical sheet
2 Base material layer
3 Optical layer
4 Binder
5 Resin beads
6 Convex
7 recess
11 Optical sheet
12 Anti-sticking layer
13 Binder
14 Resin beads

Claims (7)

An optical sheet comprising a transparent substrate layer and an optical layer laminated on the surface side of the substrate layer, the optical layer having spherical resin beads in a binder,
The arithmetic average roughness in the three-dimensional surface roughness of this optical layer is 5 μm or more and 14 μm or less,
The blending amount of the resin beads with respect to 100 parts of the polymer content of the binder is 200 parts or more and 280 parts or less,
The coefficient of variation of the particle size distribution of the resin beads is 32% or more and 40% or less,
Ri der internal haze of 5% to 15% or less,
The average thickness of the optical layer is 80% or more and 300% or less of the average particle diameter of the resin beads,
An optical sheet having an average particle diameter of 18 μm to 22 μm as the resin beads . An optical sheet comprising a transparent substrate layer and an optical layer laminated on the surface side of the substrate layer, the optical layer having spherical resin beads in a binder,
The ten-point average roughness in the three-dimensional surface roughness of this optical layer is 50 μm or more and 80 μm or less,
The blending amount of the resin beads with respect to 100 parts of the polymer content of the binder is 200 parts or more and 280 parts or less,
The coefficient of variation of the particle size distribution of the resin beads is 32% or more and 40% or less,
Ri der internal haze of 5% to 15% or less,
The average thickness of the optical layer is 80% or more and 300% or less of the average particle diameter of the resin beads,
An optical sheet having an average particle diameter of 18 μm to 22 μm as the resin beads . The optical sheet according to claim 1, wherein the binder is formed from a polymer composition containing a polyol. The optical sheet according to claim 3 , wherein an acrylic polyol or a polyester polyol is used as the polyol. The optical sheet according to claim 3 or 4 , wherein a fine inorganic filler is dispersed and contained in the polymer composition, and an organic polymer is fixed on the surface of the fine inorganic filler. The optical sheet according to any one of claims 1 to 5 , further comprising an anti-sticking layer laminated on the back side of the base material layer, wherein the anti-sticking layer has resin beads in a binder. 7. A backlight unit for a liquid crystal display device that guides light emitted from a lamp to the surface side by dispersing the light, comprising the optical sheet according to any one of claims 1 to 6. Backlight unit for display devices.

Images