JP2004198743A - Optical sheet and backlight unit using the same - Google Patents

Abstract

An optical sheet having remarkably high optical functions such as a light diffusing function, a refraction function in a normal direction side, and a condensing function, and using the same to improve quality such as high brightness in the front direction and uniform brightness. It is an object of the present invention to provide a backlight unit capable of promoting improvement and thinning.
An optical sheet comprising a transparent base layer and an optical layer laminated on the surface side of the base layer, wherein the optical layer has spherical resin beads in a binder. (A) the three-dimensional surface roughness of the optical layer 3 having an arithmetic average roughness of 5 μm or more and 14 μm or less; and (b) the three-dimensional surface roughness of the optical layer 3. Is characterized by having a ten-point average roughness of 50 μm or more and 80 μm or less.
[Selection diagram] Fig. 1

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]
TECHNICAL FIELD OF THE INVENTION
The present invention has an optical sheet having a predetermined optical function (a diffusing function, a condensing function, a refracting function, a reflecting function, etc.) for transmitted light, and is particularly suitable for a backlight unit of a liquid crystal display device. This relates to the backlight unit used.
[0002]
[Prior art]
2. Description of the Related Art As a liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back to emit light has become widespread, and a backlight unit of an edge light type, a direct type or the like is provided on a lower surface side of the liquid crystal layer. As shown in FIG. 3A, such an edge light type backlight unit 20 generally has a rod-shaped lamp 21 as a light source, and a rectangular plate-shaped lamp 21 whose end is arranged along the lamp 21. And a plurality of optical sheets 23 laminated on the surface side of the light guide plate 22. The optical sheet 23 has a specific optical function such as refraction and diffusion. Specifically, (1) a diffusive optical element mainly disposed on the surface of the light guide plate 22 and mainly having a light diffusion function. The sheet 24, (2) a refraction optical sheet 25 which is disposed on the surface side of the diffusive optical sheet 24 and has a refraction function in the normal direction side, and the like.
[0003]
The function of the backlight unit 20 will be described. First, a light ray incident on the light guide plate 22 from the lamp 21 is reflected by a reflection dot or a reflection sheet (not shown) on the back surface of the light guide plate 22 and on each side surface. Emitted from the surface. Light emitted from the light guide plate 22 enters the diffusive optical sheet 24, is diffused, and is emitted from the surface. Thereafter, the light beam emitted from the optical sheet 24 enters the refracting optical sheet 25 and is emitted as a light beam having a distribution having a peak almost directly above by the prism portion 25a formed on the surface. In this manner, the light beam emitted from the lamp 21 is diffused by the optical sheets 24 and 25, refracted so as to show a peak almost directly above, and illuminates the entire liquid crystal layer (not shown) further above. is there.
[0004]
Although not shown, in consideration of the light guide characteristics of the light guide plate 22 and the optical function of the optical sheet 23, a back panel in which more optical sheets 23 such as a diffusive optical sheet and a refractive optical sheet are provided is provided. There is also a light unit.
[0005]
As shown in FIG. 3B, the diffusive optical sheet 24 generally has a base layer 26 made of a transparent synthetic resin, and is laminated on the surface of the base layer 26 and mainly has a light diffusing property. And an optical layer 27 having the same. 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, JP-A-2000-89007.
[0006]
[Patent Document 1]
JP 2000-89007 A
[Problems to be solved by the invention]
The diffusive optical sheet 24 is for uniformly dispersing the transmitted light by the resin beads 29 of the optical layer 27, and is used for the purpose of equalizing the luminance by the light diffusing property, 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 diffusivity of the diffusive optical sheet 24, the improvement of the light diffusing function is limited, and conversely, the reduction of light transmittance and other quality Leads to a decrease in
Therefore, the above-described conventional diffusive optical sheet 24 alone cannot direct the peak direction of the luminance distribution of the emitted light beam in the normal direction (front direction), and the refractive optical sheet 25 and a plurality of diffusive optical sheets The arrangement refracts light rays in the normal direction, thereby improving the front luminance.
[0008]
The present invention has been made in view of these inconveniences, an optical sheet having a significantly higher optical function such as a light diffusion function, a refraction function to a normal direction side, and a condensing function, and a frontal direction using the optical sheet. It is an object of the present invention to provide a backlight unit capable of improving quality such as high luminance and uniform luminance and promoting thinning.
[0009]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on which portion of the optical layer in the conventional diffusive optical sheet contributes to an optical function such as a light diffusion function, and as a result, the reflection at the resin bead interface, Internal factors of the optical layer represented by refraction, etc., do not contribute much to the light diffusion function, and may cause adverse effects such as a decrease in light transmittance and a decrease in transmission image clarity. On the other hand, it has been found that the fine irregularities formed on the surface of the optical layer by the resin beads exert an optical function such as a high light diffusion function due to its lens-like action.
[0010]
The invention made in order to solve the above-mentioned problem obtained as a result includes a transparent base layer and an optical layer laminated on the surface side of the base layer, and the optical layer has a spherical resin in a 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 degree of the optical layer The ten-point average roughness of the original surface roughness is 50 μm or more and 80 μm or less. Here, the “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. (Y, Z) means a value extended to coordinates.
[0011]
According to the optical sheet, fine concaves and convexes are formed on the surface of the optical layer by the inherent resin beads, and each concave and convex portion forming the fine concaves and convexes has 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 the fine irregularities on the optical layer surface function as a convex lens and a concave lens with respect to transmitted light, and are compared with conventional optical sheets. As a result, optical functions of the optical sheet, such as a light diffusing function, a refracting function toward the normal direction, and a condensing function, are remarkably improved.
[0012]
It is preferable that the average thickness of the optical layer is 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 specified in JIS-K-7130. By controlling the average thickness of the optical layer to the above range in relation to the average particle diameter of the resin beads as in this means, lens-shaped concave portions and convex portions on the optical layer surface due to the internal resin beads are remarkably formed. The three-dimensional surface roughness of the formed optical layer surface can be easily controlled within the above range.
[0013]
The resin beads having an average particle diameter of 18 μm or more and 22 μm or less and a coefficient of variation in particle diameter distribution of 30% or more and 40% or less are used. It is good to be 300 copies or less. By controlling the average particle diameter of the resin beads, the variation coefficient of the particle diameter distribution, and the amount of the resin beads in the above range as in this means, fine irregularities are formed densely and substantially at the same density on the optical layer surface by the inherent resin beads. In addition, the three-dimensional surface roughness of the optical layer surface can be easily and reliably controlled within the above range. As described above, the optical function of the optical sheet, such as the light diffusion function, the refraction function toward the normal direction, and the light condensing function, is remarkably improved by the lens function of the fine unevenness formed densely on the optical layer surface. .
[0014]
The binder is preferably formed from a polymer composition containing a polyol. When the polyol is used as the base polymer of the binder in this manner, the polyol is excellent in processability, moldability and adhesiveness with the resin beads, so that the adhesiveness between the binder and the resin beads is good by means such as coating, It is possible to easily and surely form an optical layer having the above-mentioned fine irregularities on the surface without entraining air therein. According to the above polyol, the surface hardness of the optical layer, the wear resistance, the weather resistance, the heat resistance, the coating properties such as the stain resistance are enhanced, and the dispersed inorganic fine filler in the binder is easily contained. Therefore, it is possible to suppress the temporal deterioration of the optical function of the optical sheet.
[0015]
As the polyol, an acrylic polyol or a polyester polyol is preferable. Such acrylic polyol or polyester polyol is excellent in transparency, and the surface hardness, hydrophobicity, and coating properties such as weather resistance are excellent, so that the total light transmittance of the optical sheet is increased, and yellowing, deterioration, and the like due to ultraviolet rays are reduced. 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]
It is preferable that a fine inorganic filler having an organic polymer fixed on its surface is dispersed and contained in the polymer composition. Here, “fixed” does not mean mere adhesion and adhesion, but means that a chemical bond has been formed between the organic polymer and the fine inorganic filler, and therefore, the fine inorganic filler can be added to any solvent. Organic polymer is not detected in the washing solution washed in step 1. Since the optical sheet in the backlight unit is exposed to the heat of the lamp, a fine inorganic filler is often compounded in the polymer composition constituting the binder for the purpose of improving heat resistance. The use of a fine inorganic filler with an organic polymer fixed on the surface has good affinity for the base polymer that constitutes the binder, surface hardness, heat resistance, abrasion resistance, weather resistance, and stain resistance. An optical layer having good physical properties such as coating can be formed. 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 from 5% to 30%. As described above, by setting the internal haze of the optical sheet within the above range and making it relatively small, the light diffusion function, the refraction function toward the normal direction side, and the light condensing function due to the lens-like action of the fine unevenness on the optical layer surface are achieved. Optical functions such as functions can be independently activated and 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 image clarity of transmission, and the like.
[0018]
It is preferable to further include an anti-sticking layer laminated on the back surface side of the base material layer and having resin beads in a binder. According to this means, it is possible to prevent sticking between the optical sheet and the light guide plate, the prism sheet, and the like that are superimposed.
[0019]
Therefore, in a backlight unit for a liquid crystal display device in which a light beam emitted from a lamp is dispersed and guided to the front side, if the optical sheet is provided, the optical sheet has excellent optical functions (light diffusion function, (A linear refraction function, 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 or the like can be omitted, and the number of optical sheets provided can be reduced, and as a result, the thickness can be reduced.
[0020]
BEST MODE FOR CARRYING OUT 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 sectional view showing an optical sheet according to an embodiment of the present invention, and FIG. 2 is a schematic sectional view showing an optical sheet having a form different from that of the optical sheet of FIG.
[0021]
The optical sheet 1 in FIG. 1 has the same configuration as the above-mentioned bead-coated diffusive optical sheet. Specifically, the optical sheet 1 has a base layer 2 and an optical layer 3 laminated on the surface of the base layer 2. It is composed of
[0022]
The base material layer 2 is formed of a transparent, particularly colorless and transparent synthetic resin because it is necessary to transmit light. The synthetic resin used for the base layer 2 is not particularly limited, and includes, for example, polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, weather resistant vinyl chloride, and the like. . 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 layer 2 is not particularly limited, but is, for example, 10 μm to 500 μm, preferably 35 μm to 250 μm, and particularly preferably 50 μm to 188 μm. When the thickness of the base material layer 2 is less than the above range, inconveniences such as curling easily occurring when the resin composition for forming the optical layer 3 is applied and handling becomes difficult occur. I do. Conversely, if the thickness of the base material layer 2 exceeds the above range, the brightness of the liquid crystal display device may be reduced, and the thickness of the backlight unit may be increased, contradicting the demand for thinner liquid crystal display devices. It will be.
[0024]
The optical layer 3 has resin beads 5 disposed on the surface of the base material layer 2 at 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 and continuous irregularities (convex portions 6 and concave portions 7) are formed densely and substantially uniformly by a binder 4 covering 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. In addition, the optical sheet 1 has a remarkably improved refraction function of refracting transmitted light rays in the normal direction due to the excellent light diffusion function. Further, the optical sheet 1 also has a high light condensing function that condenses transmitted light rays 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 set to 5 μm, and particularly preferably 7 μm. On the other hand, the upper limit of the arithmetic average roughness (Ra) is set to 14 μm, and particularly preferably 12 μm. By controlling the arrangement pitch, curvature, height and the like of the lens-shaped convex portions 6 and 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 are formed. Optical functions such as a light diffusion function by the lens function of the concave portions 6 and the concave portions 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 set to 50 μm, and particularly preferably 60 μm. On the other hand, the upper limit of the ten-point average roughness (Rz) is set to 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 preferably 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 preferably 280% of the average particle diameter of the resin beads 5. By setting the thickness of the optical layer 3 to this level, fine irregularities having a lens-like effect are remarkably formed on the surface of the optical layer 3, and the light diffusion function, refraction function, and light collection function can be effectively performed. 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 preferably 8%. This is because, if the internal haze of the optical sheet 1 exceeds the upper limit, the total light transmittance may decrease, the image clarity of transmission may decrease, and the like. This is because the smaller the size, the more difficult it is to manufacture and the more difficult it is to develop a 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 fine irregularities.
[0029]
The ratio of the internal haze to the entire haze is preferably 7% or more and 35% or less. By keeping the ratio of the internal haze within the above range and making it relatively small, the reduction of the total light transmittance and the like are reduced, and the external haze, that is, good quality of the light diffusion function and the like due to the lens-like action of the fine irregularities on the optical layer surface. The optical function of can be exhibited.
[0030]
The lower limit of the image clarity of transmission of the optical sheet 1 with an optical comb width of 2 mm is set to 7%, and particularly preferably 7.4%. On the other hand, the upper limit of the image clarity of the transmission is set to 23%, and 20% is particularly preferable. This is because if the image clarity of transmission exceeds the above upper limit, haze required as a diffusive optical sheet may not be obtained. Conversely, if the image clarity of transmission is smaller than the above lower limit, total light transmission This is because the rate may decrease, and it may not be possible to increase the luminance in the front direction.
[0031]
The resin beads 5 are transparent fine spherical particles made of resin. Specific materials used for the resin beads 5 are not particularly limited, and include, for example, acrylic resin, acrylonitrile resin, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide and the like. Among them, acrylic resins having high transparency are 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, and more preferably 20 μm. If the average particle diameter of the resin beads 5 is less than the above range, the irregularities on the surface of the optical layer 3 formed by the resin beads 5 may be small, and the above-mentioned excellent optical function may not be exhibited. If the average particle size 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 variation coefficient of the particle size distribution of the resin beads 5 is preferably 30%, particularly 32%, more preferably 34%, and the upper limit of this variation coefficient is preferably 40%, particularly 38%, more preferably 36%. This is because, when the coefficient of variation of the resin beads 5 exceeds the above upper limit, the resin beads 5 buried in the inside that does not contribute to the formation of the fine irregularities on the surface of the optical layer 3 or the resin beads 5 protruding from the average surface of the optical layer 3 greatly. On the contrary, even if the coefficient of variation of the resin beads 5 is smaller than the lower limit, the light diffusion does not increase, and This is because the randomness of the particle diameter contributes to the light diffusing property and the quality is improved.
[0034]
The average particle size and the variation coefficient of the particle size distribution of the resin beads 5 are values measured by a Coulter counter method. The Coulter counter method is a method of electrically measuring the number and size of particles dispersed in a solution, in which the particles are dispersed in an electrolytic solution, and electricity flows using a suction force. In this method, the electrolyte is replaced by the volume of the particles when the particles pass through the pores, thereby increasing the resistance and measuring a voltage pulse proportional to the volume of the particles. Therefore, the number and the particle volume of each particle are measured by electrically measuring the height and the number of the voltage pulse, and the particle diameter and the particle diameter distribution are obtained from the measurement result. 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 by weight of the polymer in the polymer composition as the material for forming 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 more preferably 260 parts. If the amount of the resin beads 5 is less than the above range, the fine irregularities formed on the surface of the optical layer 3 are small, and the above-mentioned excellent optical function may not be exhibited. If the blending amount of the beads 5 exceeds the above range, the surface of the optical layer 3 will have severe irregularities, which may reduce the front luminance and the uniformity of the luminance.
[0036]
The binder 4 is made of a polymer composition containing a base polymer, and is formed by curing the polymer composition. In this polymer composition, for example, curing agents, plasticizers, dispersants, inorganic fillers, antistatic agents, various leveling agents, ultraviolet absorbers, antioxidants, viscosity modifiers, lubricants, light stabilization Agents and 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, polyamide imides, epoxy resins, and ultraviolet curable resins. Can be used alone or in combination of two or more. In particular, the base polymer is preferably a polyol which has high workability and can easily and surely form the optical layer 3 having fine irregularities by means such as coating. The base polymer is transparent because it is necessary to transmit light, and is preferably colorless and transparent.
[0038]
Examples of the polyol include a polyol obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer, and a polyester polyol obtained under the condition of an excess of hydroxyl groups. 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 and crotonyl alcohol; (b) for example, ethylene glycol, ethylene oxide, propylene glycol, propylene oxide, butylene glycol, butylene oxide, 1,4-bis (hydroxymethyl) cyclohexane, phenyl A dihydric alcohol or an epoxy compound such as glycidyl ether, glycidyl decanoate, or Praxel FM-1 (manufactured by Daicel Chemical Industries, Ltd.), for example, acrylic acid, methacrylic acid, maleic acid, or 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-containing unsaturated monomers can be polymerized to produce a polyol.
[0040]
Also, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, ethylhexyl acrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-methacrylate Butyl, tert-butyl methacrylate, ethylhexyl 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-methylolacrylamide, N-butoxymethylacryl One or more ethylenically unsaturated monomers selected from amide, diacetone acrylamide, ethylene, propylene, isoprene and the like, and a hydroxyl-containing unsaturated monomer selected from the above (a) and (b) A polyol can also be produced by polymerizing the polymer.
[0041]
The number average molecular weight of a polyol obtained by polymerizing a 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, and more preferably 20 or more and 150 or less.
[0042]
Polyester polyols obtained under the condition of excess hydroxyl groups include (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) isocinurate and xylylene glycol; and (d) maleic And polybasic acids such as fumaric acid, succinic acid, adipic acid, sebacic acid, azelaic acid, trimetic acid, terephthalic acid, phthalic acid, and isophthalic acid; and propanediol, hexanediol, polyethylene glycol, and trimethylolpropane. It can be produced by reacting under conditions where the number of hydroxyl groups in the polyhydric 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 hydroxyl group excess conditions is from 500 to 300,000, preferably from 2,000 to 100,000. The hydroxyl value is 5 or more and 300 or less, preferably 10 or more and 200 or less, and 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 the above-mentioned polyester polyol and a monomer component containing the above-mentioned hydroxyl group-containing unsaturated monomer, and (meth) acrylic unit. Is preferred. The binder 4 using such a polyester polyol or acrylic polyol as a base polymer has high weather resistance and can suppress yellowing of the optical layer 3 and the like. Note that either one of the polyester polyol and the acrylic polyol may be used, or 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 when the hydroxyl value in the solid content is 10 or less, the number of crosslinking points decreases, and the solvent resistance is reduced. In addition, the coating properties such as water resistance, heat resistance, and surface hardness tend to decrease.
[0046]
As the polyol, those having a cycloalkyl group are preferable. As described above, by introducing the cycloalkyl group into the base polymer (polyol) constituting the binder 4, the hydrophobicity such as the water repellency and the water resistance of the binder 4 is increased, and the binder 4 is obtained under a high temperature and high humidity condition. The deflection resistance and dimensional stability of the optical sheet 1 are improved. In addition, 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. Further, 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, for example, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, cyclononyl group, cyclodecyl group, cycloundecyl group, cyclododecyl group, cyclotridecyl group, Examples include a cyclotetradecyl group, a cyclopentadecyl group, a cyclohexadecyl group, a cycloheptadecyl group, and a cyclooctadecyl group.
[0048]
The polyol having a cycloalkyl group is 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 a molecule. The polymerizable unsaturated monomer is not particularly limited, and includes, for example, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, tert-butylcyclohexyl (meth) acrylate, cyclododecyl (meth) acrylate, and the like.
[0049]
When a polyol is used as the base polymer as described above, the polymer composition may contain a polyisocyanate compound as a curing agent. The polyisocyanate compound is a derivative such as a dimer, trimer, or tetramer obtained by polymerizing diisocyanate. The curing reaction rate of the polymer composition is increased by the incorporation of the polyisocyanate compound. Therefore, even if a cationic antistatic agent contributing to the dispersion stability of the fine inorganic filler is contained in the polymer composition, the cationic antistatic agent can be used. This can sufficiently compensate for the decrease in the curing reaction rate due to the agent, and can further enhance the productivity.
[0050]
The polyisocyanate compound is preferably a xylene diisocyanate derivative or a mixture of the xylene diisocyanate derivative and an aliphatic diisocyanate derivative. Since the xylene diisocyanate derivative has a large effect of improving the reaction rate of the polymer composition, and among the aromatic diisocyanate derivatives, yellowing and deterioration due to heat or ultraviolet rays are relatively small, the light transmittance of the optical sheet 1 with time is reduced. Reduction can be reduced. On the other hand, the aliphatic diisocyanate derivative has a small effect of improving the reaction rate as compared with the aromatic diisocyanate derivative, but the yellowing and deterioration due to ultraviolet rays and the like are remarkably small. And the effect of preventing yellowing and the like can be achieved in a well-balanced manner.
[0051]
As the aliphatic diisocyanate derivative, an isophorone diisocyanate derivative and a hexamethylene diisocyanate derivative are preferable. Among the aliphatic diisocyanate derivatives, the isophorone diisocyanate derivative and the hexamethylene diisocyanate derivative have a relatively large effect of improving the curing reaction rate, and can promote the above-described productivity and heat resistance.
[0052]
The type of the derivative of the diisocyanate is preferably a TMP adduct type, an isocyanurate type, or a burette type. According to these types of derivatives, the above-mentioned 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 component 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, and particularly preferably 40 parts. By setting the amount of the polyisocyanate compound in the above range, the effect of improving the curing reaction rate of the polymer composition can be effectively exerted.
[0054]
Further, the polymer composition may contain a fine inorganic filler. The dispersion and inclusion of the fine inorganic filler in the binder 4 can increase the heat resistance of the optical layer 3 and thus of the optical sheet 1 as a whole. As a result, the backlight unit is exposed to the heat of the lamp or moisture in the air. Even so, the deformation of the optical sheet 1 can be remarkably suppressed.
[0055]
The inorganic substance 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 a bond with an oxygen atom. As the metal element constituting the inorganic oxide, for example, an element selected from Groups II to VI of the Periodic Table of the Elements is preferable, and an element selected from Groups III to V of the Periodic Table of the Elements is more preferable. Among them, an element selected from Si, Al, Ti and Zr is particularly preferable, and colloidal silica in which the 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 sphere, a needle, a plate, a scale, 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, particularly preferably 10 nm. On the other hand, the upper limit of the average particle diameter of the fine inorganic filler is preferably 50 nm, particularly preferably 25 nm. This is because when the average particle diameter of the fine inorganic filler is less than the above range, the surface energy of the fine inorganic filler is increased, and aggregation or the like is likely to occur.Conversely, when the average particle diameter exceeds the above range, This is because the optical sheet 1 may become cloudy due to the influence of the short wavelength and the transparency of the optical sheet 1 may be reduced.
[0057]
The lower limit of the blending amount of the fine inorganic filler (only the inorganic component) (the blending amount in terms of solid content with respect to 100 parts of the polymer component in the polymer composition) is preferably 10 parts, and particularly preferably 50 parts. On the other hand, the upper limit of the amount of the fine inorganic filler is preferably 500 parts, and particularly preferably 200 parts. This is because if the amount of the fine inorganic filler is less than the above range, the heat resistance of the optical sheet 1 may not be sufficiently exhibited, and conversely, if the amount exceeds the above range. This is because compounding into the polymer composition becomes difficult, and the light transmittance of the optical layer 3 may decrease.
[0058]
As the fine inorganic filler, a material having an organic polymer fixed on its surface is preferably used. By using the organic polymer-fixed fine inorganic filler as described above, the dispersibility in the binder 4 and the affinity with the binder 4 are improved. Therefore, the influence of the dispersed content of the fine inorganic filler on the formability of the lens-shaped convex portions 6 and concave portions 7 can be reduced. This organic polymer is not particularly limited with respect to its molecular weight, shape, composition, presence or absence of a functional group and the like, and any organic polymer can be used. Regarding the shape of the organic polymer, any shape such as a linear, branched, or crosslinked structure can be used.
[0059]
Specific resins constituting such an organic polymer include, for example, (meth) acrylic resin, polystyrene, polyvinyl acetate, polyolefins such as polyethylene and polypropylene, polyvinyl chloride, polyvinylidene chloride, polyesters such as polyethylene terephthalate and the like. Examples include copolymers and resins partially modified with functional groups such as amino groups, epoxy groups, hydroxyl groups, and carboxyl groups. Among them, those having an organic polymer containing a (meth) acrylic unit as an essential component such as a (meth) acrylic resin, a (meth) acryl-styrene resin, and a (meth) acryl-polyester resin have a film forming ability. It is suitable. On the other hand, a resin having compatibility with the base polymer of the polymer composition is preferable, and therefore, a resin having the same composition as the base polymer contained in the polymer composition is most preferable.
[0060]
In addition, the fine inorganic filler may include an organic polymer in the fine particles. This makes it possible to impart appropriate softness and toughness to the inorganic substance as the core of the fine inorganic filler.
[0061]
The organic polymer preferably contains an alkoxy group, and the content thereof is preferably 0.01 mmol or more and 50 mmol or less per 1 g of the fine inorganic filler to which the organic polymer is fixed. With such an alkoxy group, affinity with the matrix resin constituting the binder 4 and dispersibility in the binder 4 can be improved.
[0062]
Here, the alkoxy group refers to an RO group bonded to a metal element forming the skeleton of the fine particles. 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 containing 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]
As described above, a polymer having a hydroxyl group is used as the organic polymer fixed to the fine inorganic filler, and a polyfunctional isocyanate compound having two or more functional groups that react with the hydroxyl group in the polymer composition constituting the binder 4, melamine It is preferable to contain at least one selected from a compound and an aminoplast resin. Thereby, the fine inorganic filler and the matrix resin of the binder 4 are bonded in a crosslinked structure, and the storage stability, stain resistance, flexibility, weather resistance, storage stability, and the like are improved, and the obtained coating film is further improved. 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, for example, tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, lysine diisocyanate, 2,2,4-trimethylhexylmethane diisocyanate, methylcyclohexane diisocyanate, 1,6 A trimer such as a biuret or isocyanurate of hexamethylene diisocyanate; and 2 formed by the reaction of these polyfunctional isocyanates with polyhydric alcohols such as propanediol, hexanediol, polyethylene glycol and trimethylolpropane. Compounds in which at least two isocyanate groups remain; these polyfunctional isocyanate compounds are Choles, compounds having a phenolic hydroxyl group such as phenol and cresol, acetoximes, oximes such as methyl ethyl ketoxime, ε-caprolactam, blocked polyfunctional isocyanate compounds blocked with a lactam such as γ-caprolactam and the like. Can be mentioned. In addition, the said polyfunctional isocyanate compound can be used individually by 1 type or in mixture of 2 or more types. Among them, 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 coating.
[0066]
Examples of the melamine compound include dimethylol melamine, trimethylol melamine, tetramethylol melamine, pentamethylol melamine, hexamethylol melamine, isobutyl ether melamine, n-butyl ether melamine, and butylated benzoguanamine.
[0067]
Examples of the aminoplast resin include an alkyl etherified melamine resin, a urea resin, a benzoguanamine resin, and the like. 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 an aminotriazine and alkyl etherifying it with cyclohexanol or an alkanol having 1 to 6 carbon atoms. Resin is a typical one. Further, a sulfonic acid-based catalyst for accelerating curing, for example, paratoluenesulfonic acid and its amine salt can be used.
[0068]
Further, an antistatic agent may be contained in the polymer composition. The antistatic agent is not particularly limited. For example, anionic antistatic agents such as alkyl sulfates and alkyl phosphates, quaternary ammonium salts, cationic antistatic agents such as imidazoline compounds, polyethylene glycol-based Nonionic antistatic agents such as polyoxyethylene sorbitan monostearate and ethanolamide, and high molecular antistatic agents such as polyacrylic acid are used. Among them, a cationic antistatic agent which has a relatively large antistatic effect and does not impair the stability of the dispersed state of the fine inorganic filler is preferable. Among these cationic antistatic agents, ammonium salts and betaines, which can further promote the antistatic property of the above-mentioned highly hydrophobic binder 4, are particularly preferable.
[0069]
The lower limit of the compounding amount of the antistatic agent (the compounding 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, more preferably 10 parts. This is because if the amount of the antistatic agent is smaller than the lower limit, the above-described antistatic effect may not be sufficiently exhibited, and conversely, if the amount of the antistatic agent exceeds the upper limit, the charge may be reduced. This is because the incorporation of the inhibitor may cause inconveniences such as a decrease in total light transmittance and a decrease in strength.
[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. 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. By reducing the size, it is possible to promote an optical function such as a light diffusion function by the lens function of the convex portion 6 and the concave portion 7.
[0071]
Next, a method for manufacturing the optical sheet 1 will be described. The method for producing the optical sheet 1 includes: (a) a step of producing a coating liquid for an optical layer by mixing resin beads 5 with a polymer composition constituting the binder 4; Coating the liquid on the surface of the base material layer 2 to laminate the optical layer 3.
[0072]
The optical sheet 11 in FIG. 2 includes a base layer 2, an optical layer 3 stacked on the front side of the base layer 2, and an anti-sticking layer 12 stacked on the back surface of the base layer 2. . Since the base layer 2 and the optical layer 3 are the same as those of the embodiment shown in FIG. 1, the same reference numerals are given and the description is omitted. Therefore, the optical sheet 11 also has a very excellent optical function like the optical sheet 1.
[0073]
The sticking prevention layer 12 includes 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. The same material as the resin beads 5 of the optical layer 3 is used as the material of the resin beads 14. The thickness of the sticking prevention layer 12 (the thickness of the binder 13 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 compounding 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 most of the resin beads 14 have a lower end projecting from the binder 13 by a very small amount. Therefore, when the optical sheet 11 is laminated on the light guide plate, the lower ends of the protruding resin beads 14 are in contact with the surface of the light guide plate or the like, and the entire rear surface of the optical sheet 11 is not in contact with the light guide plate or the like. Thereby, 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 a coating liquid for an optical layer by mixing resin beads 5 with a polymer composition constituting the binder 4, and (b) a coating liquid for the optical layer. A step of laminating the optical layer 3 by applying a liquid onto the surface of the base material layer 2, and (c) a coating liquid for sticking prevention layer by mixing resin beads 14 with a polymer composition constituting the binder 13. And (d) a step of coating the anti-sticking layer coating liquid on the back surface of the base material layer 2 to laminate the anti-sticking layer 12.
[0076]
Therefore, a lamp 21, a light guide plate 22, and an optical sheet 23 (a diffusive optical sheet 24 and a refractive optical sheet 25) are provided as shown in FIG. When the optical sheets 1 and 11 are used as the optical sheets 23 in the guiding backlight unit 20 for a liquid crystal display device, the optical sheets 1 and 11 have excellent optical functions. , The front luminance can be increased. In addition, the excellent optical functions of the optical sheets 1 and 11 make it possible to omit the prism type refractive optical sheet 25 and to reduce the number of optical sheets to be installed, thereby promoting thinning.
[0077]
【Example】
Hereinafter, the present invention will be described in detail with reference to Examples. However, the present invention should not be construed as being limited based on the description of Examples.
[0078]
[Example 1]
128 parts of acrylic polyol ("Udouble S-2840" manufactured by Nippon Shokubai Co., Ltd .; solid content 50%), 18 parts of isocyanate ("Coronate HL" manufactured by Nippon Polyurethane Industry Co., Ltd .; solid content 75%), antistatic In a polymer composition (refractive index after curing: 1.53) consisting of 42 parts of an 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. And 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 the coefficient of variation of the particle diameter distribution adjusted to 35%. An optical layer coating solution was prepared, and this optical layer coating solution was applied to the surface of a 100 μm-thick transparent polyester base material layer at a rate of 17 g / m ² (in terms of solid content). Get an optical sheet .
[0079]
[Example 2]
An optical sheet of Example 2 was obtained in the same manner as in Example 1 except that the variation coefficient was adjusted to 32% and the blending amount of the acrylic beads was changed to 178 parts.
[0080]
[Comparative Example 1]
An 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 changed to 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 the acrylic beads was changed to 162 parts.
[0082]
[Evaluation of properties]
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 the ten-point average roughness (Rz) of these optical sheets were measured. The sheet was provided on the surface side of the light guide plate of the edge light type backlight unit, and the front luminance was measured. The results are shown in Table 1 below.
[0083]
[Table 1]

[0084]
As shown in Table 1, as compared with the optical sheets of Comparative Examples 1 and 2, the arithmetic average roughness (Ra) in three-dimensional surface roughness is 5 μm or more and 14 μm or less, and the ten-point average roughness (Rz) is 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 diffusion function, a refraction function toward the normal direction, and a light collection function can be remarkably improved. Further, according to the backlight unit using the optical sheet, it is possible to improve the quality such as high luminance in the front direction and uniform luminance, and to promote the reduction in thickness.
[Brief description of the drawings]
FIG. 1 is a schematic 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 the optical sheet of FIG.
3A is a schematic perspective view illustrating a general edge light type backlight unit, and FIG. 3B is a schematic cross-sectional view illustrating a general diffusive optical sheet.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Optical sheet 2 Base layer 3 Optical layer 4 Binder 5 Resin beads 6 Convex part 7 Concave part 11 Optical sheet 12 Sticking prevention layer 13 Binder 14 Resin beads

Claims (10)

An optical sheet having a transparent base layer and an optical layer laminated on the surface side of the base layer, the optical layer having spherical resin beads in a binder,
An optical sheet, wherein the arithmetic average roughness of the optical layer in three-dimensional surface roughness is 5 μm or more and 14 μm or less. An optical sheet having a transparent base layer and an optical layer laminated on the surface side of the base layer, the optical layer having spherical resin beads in a binder,
An optical sheet characterized in that the optical layer has a ten-point average roughness in the three-dimensional surface roughness of 50 μm or more and 80 μm or less. The optical sheet according to claim 1, wherein an average thickness of the optical layer is 80% or more and 300% or less of an average particle diameter of the resin beads. As the resin beads, those having an average particle diameter of 18 μm or more and 22 μm or less, and a variation coefficient of the particle diameter distribution of 30% or more and 40% or less are used. The optical sheet according to claim 1, wherein the amount of the optical sheet is 300 parts or less. The optical sheet according to any one of claims 1 to 4, wherein the binder is formed from a polymer composition containing a polyol. The optical sheet according to claim 5, wherein an acrylic polyol or a polyester polyol is used as the polyol. The optical sheet according to claim 5, wherein a fine inorganic filler is dispersed and contained in the polymer composition, and an organic polymer is fixed on a surface of the fine inorganic filler. The optical sheet according to any one of claims 1 to 7, wherein the internal haze is 5% or more and 30% or less. The optical sheet according to any one of claims 1 to 8, further comprising a sticking prevention layer laminated on the back side of the base material layer, wherein the sticking prevention layer has resin beads in a binder. 10. A backlight unit for a liquid crystal display device, which disperses a light beam emitted from a lamp and guides the light beam to a front surface side, comprising the optical sheet according to any one of claims 1 to 9. Backlight unit for display device.

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