TWI416172B - An optical sheet and a backlight unit using the same - Google Patents

Abstract

The invention aims to provide an optical piece and a backlight unit using the same. The optical piece can control the optical functions of all the regions on the surface of the optical piece truly and easily, improves the brightness homogeneity of the backlight unit and promotes the thinning thereof. the optical piece of the present invention has a transparent base material layer and an optical layer deposited on the surface of the base material layer; and is characterized in that: the optical layer has a plurality of light diffusion units deposited on the surface of the base material layer by diffused points; the light diffusion unit contains light diffusion agent and binding agent; wherein the light diffusion unit is preferably formed into convex lens shaped, the mass ratio of the lightdiffusion agent to the binding agent is between 0.1 and 2; the average diameter (D) of the light diffusion unit is preferably between 10 mum and 300 mum; and the specific value (H1/D) of the average height (H1) to the average diameter (D) is preferably between 0.05 and 0.5.

Description

Optical sheet and backlight unit using the same

The present invention relates to an optical sheet and a backlight unit. In particular, the present invention relates to an optical sheet suitable for use in a liquid crystal display device and a backlight unit using the same.

A liquid crystal display device is widely used as a backlight in which a liquid crystal layer is irradiated from a rear surface to emit light, and a backlight of an edge light type or a bottom light type is provided on a lower surface side of the liquid crystal layer. unit. The sidelight type backlight unit 20 basically includes a linear light source 21 as a light source, a square plate-shaped light guide plate 22 disposed at an end portion along the light source 21, and a laminate as shown in FIG. Various optical sheets 23 on the surface side of the light guide plate 22. The optical sheet 23 has a specific optical function such as refraction and diffusion, and specifically corresponds to the light guide plate 22, the light diffusion sheet 24 mainly having a light diffusion function disposed on the surface side of the light guide plate 22, and the light diffusion sheet. The surface side of the surface 24 has a ruthenium sheet 25 or the like which is refracted toward the normal side.

The function of the backlight unit 20 will be described below. First, the light incident from the light source 21 to the light guide plate 22 is reflected by a reflection point or a reflection sheet (not shown) on the inner surface of the light guide plate 22, and is self-reflected from the surface of the light guide plate 22. Exit. The light emitted from the light guide plate 22 is incident on the light diffusion sheet 24, diffused by the light diffusion sheet 24, and then emitted from the surface of the light diffusion sheet 24. Thereafter, the light emitted from the surface of the light-diffusing sheet 24 is incident on the cymbal sheet 25, and is emitted as a light having a peak distribution in a substantially normal direction by the dam portion 25a formed on the surface of the cymbal sheet 25.

As described above, the light emitted from the light source 21 is diffused by the light diffusion sheet 24, and is refracted by the cymbal sheet 25 so as to show a peak in a substantially normal direction, thereby illuminating the liquid crystal layer on the surface side (not shown). ) The whole face. Further, although not shown, the ruthenium 25 is based on the relaxation of the condensing characteristics of the cymbal sheet 25 or the protection of the crotch portion 25a or the adhesion between the liquid crystal panel such as a polarizing plate and the cymbal sheet 25. The surface side is further provided with an optical sheet.

As the light-diffusing sheet 24 of the backlight unit 20, a bead coating type light-diffusing sheet having a bead coated with a surface of a transparent base material layer made of a synthetic resin is generally used (for example, reference is made to Japanese Patent Laid-Open No. Hei 7-5305, JP-A-2000-89007, and the like. The light-diffusing sheet can function as a light diffusion by the fine uneven shape of the surface.

In the above conventional light-diffusing sheet, the bead layer is laminated on the entire surface of the base material layer by coating, and the entire surface of the light-diffusing sheet exhibits a substantially uniform light diffusing function. The case of the cymbal is also the same as above. On the other hand, the backlight unit tends to increase the brightness in the vicinity of the light source 21 in the structure. Therefore, it is necessary to perform processing on the surface of the light guide plate 22 to ensure the average brightness of the entire surface of the liquid crystal panel. However, most of the processing of the surface of the light guide panel 22 is injection molding, and it takes time to form a metal mold for injection molding, so that the lead time required for correction of the surface pattern or the like is long, and there is also a need to manufacture a plurality of products. The problem of time.

[Patent Document 1] Japanese Patent Laid-Open No. Hei 7-5305

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2000-89007

The present invention has been made in view of the above problems, and an object thereof is to provide an optical sheet and a backlight unit using the same, which can easily and surely control optical functions of respective regions of the optical sheet surface, improve brightness uniformity of the backlight unit, and promote thinning. .

The present invention for solving the above problems is an optical sheet comprising a transparent substrate layer and an optical layer laminated on a surface of the substrate layer, wherein the optical layer has a layer of scatter on the surface of the substrate layer. a plurality of light diffusing portions; the light diffusing portion contains a light diffusing agent and a binder.

Since the optical sheet has a plurality of light diffusing portions which are layered on the surface of the base material layer, the optical sheet has a portion where the light is diffused and a portion where the light is not diffused, and the light diffusibility varies depending on the area on the sheet. different. In short, the optical sheet can be used to adjust the light diffusing property of each sheet surface by adjusting the position of the laminated portion of the optical layer or the like so that the desired position on the optical sheet is diffused by the light of the required intensity. Further, since the optical sheet can be laminated on the base material layer by printing, the adjustment of the arrangement of the laminated portions can be easily performed.

The light diffusing portion is preferably formed in a convex lens shape. By forming the light-diffusing portion into a convex lens shape, the light diffusibility can be improved, and the control of the light diffusibility can be easily performed.

The mass ratio of the light diffusing agent to the binder is preferably 0.1 or more and 2 or less. By setting the mass ratio of the light diffusing agent to the above range, the light diffusibility can be effectively exhibited.

The average diameter (D) of the light diffusing portion is preferably 10 μm or more and 300 μm or less. By forming the optical layer by a convex lenticular light diffusing agent having the above diameter, the optical function of the optical sheet can be controlled simply and surely.

The height ratio (H ₁ /D) of the average height (H ₁ ) of the light diffusing portion to the average diameter (D) is preferably 0.05 or more and 0.5 or less. By setting the height ratio (H ₁ /D) of the light diffusing portion to the above range, an optical function such as diffusion and a variable angle toward the normal direction side can be improved.

Absolute value of the difference in refractive index of the light diffusing agent in the light diffusing portion refractive index (n ₁₎ and the binder (n ₂₎ of _{(| n 1 -n 2 |)} , is preferably 0.05 or more. By having the above-mentioned refractive index difference between the light diffusing agent and the binder, effective condensing, refracting toward the normal direction side, diffusion, and the like can be performed.

The particle diameter of the light diffusing agent in the light diffusing portion is preferably 0.1 μm or more and 20 μm or less. When the particle diameter of the light diffusing agent is less than the above range, the light diffusing effect may be insufficient. When the particle diameter of the light diffusing agent exceeds the above range, the arrangement of the binder forming the light diffusing portion may become difficult.

The layering ratio of the light diffusion portion in the optical layer is preferably 10% or more and 90% or less. By setting the layering ratio within the above range, optical functions such as diffusion can be easily controlled.

The arrangement pattern of the surface of the base material layer of the light diffusion portion is preferably a regular triangular lattice pattern. The regular triangular lattice pattern can more closely arrange the convex lens-shaped light diffusing portions. Therefore, the regular triangular lattice pattern can easily increase the filling rate of the convex lenticular light diffusing portion, and greatly enhance the optical functions such as refraction and diffusion toward the normal direction side.

Further, the arrangement pattern of the surface of the base material layer of the light diffusion portion may be a random pattern. The above-mentioned random pattern can reduce the embossing generated when the lenticular sheet is overlapped with other optical parts.

Preferably, the back surface of the base material layer has a corrugated crucible shape, and the height ratio (H ₂ /P) of the average height (H ₂ ) of the crucible to the crucible spacing (P) is 0.05 or more and 0.5. the following. By providing the back surface of the base material layer with the above-described height ratio, the optical function such as refraction and diffusion toward the normal direction side can be greatly enhanced.

Therefore, in the backlight unit for a liquid crystal display device which disperses the light emitted from the light source and guides the light to the surface side thereof, the brightness can be adjusted in each area, and if it has an optical function such as high diffusion and variable angle, In the optical sheet, the optical sheet can be used to adjust the brightness and improve the quality by unifying the brightness.

Here, the "convex lenticular shape" means that the cross-sectional shape has a convex shape, and the planar shape is not limited to a circular shape. The "average height (H ₁ )" means an average vertical distance from the base surface to the topmost portion of the light-diffusing portion of the convex lens shape. The "average diameter (D)" means the average diameter of the base of the convex lens-shaped light diffusion portion. The "layering ratio" means the ratio of the light diffusing portion per unit area in the surface projection shape of the optical sheet. The "triangular lattice pattern" means an equilateral triangle whose surface is divided into the same shape, and each vertex of the triangle is provided with a pattern of a light diffusion portion. The "average height (H ₂ )" means the average vertical distance from the base surface to the apex of the raft. In addition, the "pitch spacing (P)" means the distance between the average vertices in the cross-sectional shape of the crucible.

As described above, by using the optical sheet of the present invention and the backlight unit using the same, the optical function of each region of the optical sheet surface can be easily and surely controlled, and the brightness uniformity of the backlight unit can be improved and the thickness can be reduced.

Hereinafter, embodiments of the present invention will be described in detail with reference to the appropriate drawings. 1(a) and 1(b) are a schematic partial plan view and a schematic partial cross-sectional view showing an optical sheet according to a specific embodiment of the present invention; and Fig. 2 is a schematic view showing an optical sheet of a different form from the optical sheet of Fig. 1. FIG. 3 is a schematic cross-sectional view showing a backlight unit including the optical sheet of FIG. 2.

The optical sheet 1 of Fig. 1 includes a base material layer 2 and an optical layer 3 provided on the surface side of the base material layer 2.

The base material layer 2 is formed of a colorless transparent synthetic resin because it needs to penetrate light. 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, and polyolefin. Cellulose acetate, weather resistant vinyl chloride, active energy ray-curable resin, electron beam curing resin, and the like. Among them, polyethylene terephthalate having excellent transparency and high strength is preferable, and polyethylene terephthalate having improved flexural properties is particularly preferable.

The thickness (average thickness) of the base film 2 is not particularly limited, and may be, for example, 50 μm or more and 800 μm or less, and preferably 100 μm or more and 600 μm or less. When the thickness of the base film 2 is less than the above range, when the backlight unit or the like is exposed to a hot environment, curling and difficulty in use may occur. On the other hand, if the thickness of the base film 2 exceeds the above range, the brightness of the liquid crystal display device may decrease, and the thickness of the backlight unit may increase, which is also inconsistent with the thinning requirement of the liquid crystal display device.

The optical layer 3 is composed of a plurality of convex lens-shaped light diffusing portions 4, and includes a light diffusing agent 5 and an adhesive 6. This light diffusing agent 5 is covered with the adhesive 6. As described above, the light diffusing agent 5 included in the light diffusing portion 4 can uniformly diffuse the light transmitted through the light diffusing portion 4. Further, the fine convex portion is formed on the surface of the light diffusing portion 4 in a substantially uniform and substantially tight manner by the light diffusing agent 5. The light can be further diffused by the refraction of the fine meniscus lens formed on the surface of the optical sheet 1.

The light diffusing portion 4 has a convex lens shape. According to this means, by having the shape of the convex lens, the angle of refraction of the light on the surface of the light diffusing portion 4 can be adjusted, and the light can be further diffused and angled toward the normal side.

The light diffusing portion 4 is disposed on the surface of the base material layer 2 in a relatively tight and geometric manner. The light diffusion layer 4 is disposed on the surface of the base material layer 2 in an equilateral triangle lattice pattern. Therefore, the arrangement intervals of the light diffusing portions 4 are all fixed. This arrangement pattern can dispose the light diffusing portion 4 in the most dense manner, and can enhance the optical functions such as the diffusion function and the variable angle function of the optical sheet 1.

The lower limit of the layering ratio of the light diffusing portion 4 is 10%, particularly preferably 15%, and most preferably 20%. By setting the layering ratio of the light-diffusing portion 4 to the lower limit or more, the area occupied by the light-diffusing sheet 4 on the surface of the optical sheet can be increased, and the optical function such as diffusion and angle change of the optical sheet 1 can be further enhanced.

The upper limit of the buildup ratio of the light diffusing portion 4 is 90%, particularly preferably 75%, and most preferably 60%. By setting the layering ratio of the light diffusing portion 4 to be equal to or less than the above upper limit, the arrangement of the light diffusing sheets 4 on the surface of the optical sheet can be freely moved, and the optical function can be easily controlled.

The average diameter (D) of the light diffusion portion 4 is 10 μm or more and 300 μm or less, and preferably 40 μm or more and 100 μm or less. By setting the diameter of the light diffusing portion 4 within the above range, it is possible to easily and surely control the optical function such as diffusion and angular variation of the optical sheet 1. Further, the diameter of the light diffusing portion 4 may be completely the same or may vary depending on the position on the sheet. For example, by adjusting the diameter of the light diffusing portion of the portion where the brightness is to be increased, fine adjustment of the brightness in the optical sheet can be performed. Further, the planar shape of the light diffusing portion 4 is not limited to a circular shape, and a polygonal shape such as an elliptical shape, a quadrangular shape, or a hexagonal shape may be suitably employed.

The height ratio (H ₁ /D) of the average height (H ₁ ) of the light diffusing portion 4 to the average diameter (D) is preferably 0.05 or more and 0.5 or less. By setting the height ratio of the light-diffusing portion 4 to the above range, the light-diffusing portion 4 having the convex lens shape can effectively function as a convex lens on the surface of the light-diffusing portion 4, and diffuse the light beam and change the angle toward the normal direction. Wait.

The light diffusing agent 5 is a particle having a property of diffusing light, and is roughly classified into a filler and an organic filler. As the filler, for example, cerium oxide, aluminum hydroxide, aluminum oxide, zinc oxide, cerium sulfide, magnesium citrate, or a mixture thereof can be used. As a material of the organic filler, for example, an acrylic resin, an acrylonitrile resin, a polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamine or the like can be used. Among them, an acrylic resin having high transparency is preferred, and polymethyl methacrylate (PMMA) is more preferred. In other aspects, it may also contain fluorescent materials.

The shape of the light diffusing agent 5 is not particularly limited, and examples thereof include a spherical shape, a spindle shape, a needle shape, a rod shape, a cubic shape, a plate shape, a scaly shape, and a fiber shape. Among them, a ball excellent in light diffusibility is preferable. Beads.

The lower limit of the average particle diameter of the light diffusing agent 5 is preferably 1 μm, more preferably 2 μm, and most preferably 5 μm. On the other hand, the upper limit of the average particle diameter of the light diffusing agent 5 is preferably 50 μm, more preferably 20 μm, and most preferably 15 μm. The reason for this is that if the average particle diameter of the light diffusing agent 5 is less than the above range, the unevenness of the surface of the optical layer 3 formed by the light diffusing agent 5 becomes small, and it may be impossible to satisfy the necessity as a light diffusing sheet. Light diffusivity. On the other hand, when the average particle diameter of the light diffusing agent 5 exceeds the above range, the thickness of the optical sheet 1 increases, and it is difficult to uniformly spread. The average particle diameter of the light diffusing agent 5 is obtained by amplifying the 1000 light diffusing agents 5 which are arbitrarily extracted by a microscope to obtain the diameter of the particles, and averaging them. Further, when the light diffusing agent 5 is aspherical, the length of the light diffusing agent 5 in an arbitrary direction and the length of the light diffusing agent 5 perpendicular to the above direction are averaged.

The mass ratio of the light diffusing agent 5 to the binder 6 is 0.1 or more and 2 or less, and particularly preferably 0.3 or more and 0.5 or less. The reason for this is that if the mass ratio of the light diffusing agent 5 is less than the above range, the light diffusibility is insufficient. On the other hand, when the mass ratio of the light diffusing agent 5 exceeds the above range, the effect of fixing the light diffusing agent 5 is lowered.

The absolute value of the refractive index difference between the refractive index of the light diffusing agent 5 (n ₁₎ and the binder 6 (n ₂₎ of (| n ₁ -n ₂ |) is preferably 0.05 or more. By having the refractive index difference between the light diffusing agent 5 and the binder 6, the interface between the light diffusing agent 5 and the bonding agent 6 can be effectively used not only at the interface between the substrate layer 2 and the optical layer 3 but also at the surface of the optical layer 3. Since the ground is refracted, it is possible to efficiently condense, refract or diffuse toward the normal direction side, and the like.

The binder 6 is formed by crosslinking and hardening a polymer composition containing a base polymer. The light diffusing agent 5 can be disposed and fixed to the surface of the substrate layer 2 by the binder 6. Further, the polymer composition for forming the binder 6 may be appropriately blended with, for example, a micro inorganic filler, a hardener, a plasticizer, a dispersant, various leveling agents, and an ultraviolet absorber in addition to the base polymer. , antioxidants, viscous modifiers, lubricants, light stabilizers, fluorescent materials, etc.

The base polymer is not particularly limited, and examples thereof include an acrylic resin, an urethane resin, a polyester resin, a fluorine resin, an anthraquinone resin, a polyamide amide, an epoxy resin, and an ultraviolet ray. Hardened resin, etc. These polymers may be used in combination of one type or two or more types. Among them, the above-mentioned base polymer is preferably a polyol which is highly processable and can be simply formed into the optical layer 3 by means of coating or the like. Further, the base polymer itself for the adhesive 6 is preferably transparent, particularly preferably colorless and transparent, from the viewpoint of improving light transmittance.

Examples of the polyhydric alcohol include a polyhydric alcohol obtained by polymerizing a monomer component containing a hydroxyl group-containing unsaturated monomer, or a polyester polyol obtained under conditions of an excess of a hydroxyl group, and the like, which may be used alone. Alternatively, two or more types may be used in combination.

Examples of the hydroxyl group-containing unsaturated monomer include (a) 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and propylene alcohol. a hydroxyl group-containing unsaturated monomer such as propylene alcohol, cinnamyl alcohol or crotyl alcohol; (b) for example, ethylene glycol, ethylene oxide, propylene glycol, propylene oxide, butylene glycol, butylene oxide, 1,4- a dihydric alcohol or an epoxy compound such as bis(hydroxymethyl)cyclohexane, phenyl glycidyl ether, glycidyl decanoate, Placcel FM-1 (manufactured by Daicel Chemical Industries, Inc.), and, for example, acrylic acid, A hydroxyl group-containing unsaturated monomer obtained by reacting an unsaturated carboxylic acid such as methacrylic acid, maleic acid, fumaric acid, crotonic acid or itaconic acid. One or two or more selected from the group of the hydroxyl group-containing unsaturated monomers may be polymerized to produce the above polyol.

Further, the above polyol may also be selected from the group consisting of ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, ethyl hexyl acrylate, ethyl methacrylate, methacrylic acid. N-propyl ester, isopropyl methacrylate, n-butyl methacrylate, 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, propylene acetate, diallyl adipate, itacon Diallyl acrylate, diethyl maleate, vinyl chloride, vinylidene chloride, acrylamide, N-methylol acrylamide, N-butoxymethyl acrylamide, diacetone propylene One or two or more kinds of ethylenically unsaturated monomers of decylamine, ethylene, propylene, and isobutylene are produced by polymerizing a hydroxyl group-containing unsaturated monomer selected from the above (a) and (b).

The number average molecular weight of the polyol obtained by polymerizing the monomer component containing a hydroxyl group-containing unsaturated monomer is 1,000 or more and 500,000 or less, preferably 5,000 or more and 100,000 or less. Further, 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.

As the polyester polyol obtained under the condition of excess hydroxyl group, (c) such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butylene glycol, 1,4-butanediol 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,10-decanediol, 2,2,4-trimethyl-1,3-pentanediol, trishydroxy Methylpropane, hexanetriol, glycerol, pentaerythritol, cyclohexanediol, hydrogenated bisphenol A, bis(hydroxymethyl)cyclohexane, hydroquinone bis(hydroxyethyl ether), isocyanuric acid tris(hydroxyl) Polyhydric alcohols such as ethyl esters and phthalic acid, and (d), for example, maleic acid, fumaric acid, succinic acid, adipic acid, sebacic acid, sebacic acid, trimellitic acid And polybasic acids such as terephthalic acid, phthalic acid, and isophthalic acid, and the number of hydroxyl groups in the polyols such as propylene glycol, hexanediol, polyethylene glycol, and trimethylolpropane is more than the carboxyl group of the above polybasic acid The reaction was carried out under the conditions of several conditions.

The polyester polyol obtained by the excess of the hydroxyl group has a number average molecular weight of 500 or more and 300,000 or less, preferably 2,000 or more and 100,000 or less. Further, 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.

The polyol used as the base polymer of the polymer composition is preferably a (meth) propylene obtained by polymerizing a monomer component containing the polyester polyol and the hydroxyl group-containing unsaturated monomer. An acrylic polyol such as a mercapto unit. The polyester 6 or the acrylic polyol as the binder of the base polymer 6 has high transparency and weather resistance, and can suppress yellowing of the release layer 3 and the like. In particular, by using an acrylic polyol as a base polymer and a diffusing agent 5 made of an acrylic resin, the unnecessary refraction, reflection, and the like of the interface of the diffusing agent 5 can be reduced, and the direction of the optical sheet 1 can be improved. Optical function such as light diffusion function and light transmission. Further, either of the polyester polyol and the acrylic polyol may be used, or both may be used.

In addition, the number of the hydroxyl groups in the polyester polyol and the acrylic polyol is not particularly limited as long as it is contained in two or more molecules per molecule, but the hydroxyl value in the solid component is 10 or less. In addition, the number of crosslinking points decreases, and the physical properties of the film such as solvent resistance, water resistance, heat resistance, and surface hardness tend to decrease.

The polymer composition forming the binder 6 may contain a minute inorganic filler. The heat resistance of the optical layer 3 and the optical sheet 1 is improved by including the fine inorganic filler in the binder 6. The inorganic substance constituting the fine inorganic filler is not particularly limited, and is preferably an inorganic oxide. The inorganic oxide is defined as a metal element that forms a three-dimensional network structure of a plurality of oxygen-containing metal compounds mainly via bonding with oxygen atoms. The metal element constituting the inorganic oxide is preferably, for example, an element selected from Groups 2 to 6 of the periodic table, and more preferably an element selected from Groups 3 to 5 of the periodic table. It is preferably an element selected from the group consisting of Si, Al, Ti, and Zr, and in terms of an effect of improving heat resistance and uniform dispersibility, a colloidal ceria having a metal element of Si is preferable as a fine inorganic filler. Further, the shape of the fine inorganic filler may be any particle shape such as a spherical shape, a needle shape, a plate shape, a scaly shape, or a crushed shape, and is not particularly limited.

The lower limit of the average particle diameter of the fine inorganic filler is preferably 5 nm, more preferably 10 nm. On the other hand, the upper limit of the average particle diameter of the fine inorganic filler is preferably 50 nm, more preferably 25 nm. The reason for this is that if the average particle diameter 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 liable to occur. On the other hand, if the average particle diameter exceeds the above range, the short wavelength is obtained. The influence is white turbid, so that the transparency of the optical sheet 1 cannot be completely maintained.

The lower limit of the mass ratio of the fine inorganic filler (only the mass ratio of the inorganic component to 100 parts of the base polymer of the binder 6) is preferably 5 parts, more preferably 50 parts, in terms of solid content. On the other hand, the upper limit of the mass ratio of the fine inorganic filler is preferably 500 parts, more preferably 200 parts, and most preferably 100 parts. The reason for this is that if the mass ratio of the fine inorganic filler is less than the above range, the heat resistance of the optical sheet 1 may not be sufficiently exhibited. On the other hand, if the mass ratio exceeds the above range, it is difficult to blend into the polymer composition. It is possible to lower the light transmittance of the optical layer 3.

As the above fine inorganic filler, those in which an organic polymer is fixed on the surface can be used. By using a fine inorganic filler to which the above organic polymer is fixed, the dispersibility of the inorganic filler in the binder 6 or the affinity of the inorganic filler and the binder 6 can be improved. The organic polymer is not particularly limited in terms of its molecular weight, shape, composition, presence or absence of a functional group, and any organic polymer can be used. Further, the shape of the organic polymer may be any shape such as a linear chain, a branched shape or a crosslinked structure.

Specific examples of the specific resin constituting the above organic polymer include (meth)acrylic resin, polystyrene, polyvinyl acetate, polyolefin such as polyethylene or polypropylene, polyvinyl chloride, vinylidene chloride, and polypair. A polyester such as ethylene phthalate or a copolymer thereof; or a resin obtained by partially modifying a functional group such as an amine group, an epoxy group, a hydroxyl group or a carboxyl group. In particular, an organic polymer containing a (meth)acrylic acid unit such as a (meth)acrylic resin, a (meth)acrylic acid-styrene resin, or a (meth)acrylic acid-polyester resin is used as an essential component. It is preferred that the film forms a function. On the other hand, a resin having compatibility with the base polymer of the above polymer composition is preferred, and therefore, it is preferably one having the same composition as the base polymer contained in the polymer composition.

Further, the fine inorganic filler may also contain an organic polymer in the fine particles. Thereby, it is possible to impart moderate softness and toughness to the inorganic material of the core which is a minute inorganic filler.

The organic polymer may be used in an amount of 0.01 mmol or more and 50 mmol or less per 1 g of the organic inorganic polymer. By the alkoxy group, the affinity with the matrix resin constituting the binder 6 and the dispersibility in the binder 6 can be improved.

The above alkoxy group means an RO group bonded to a metal element forming a fine particle skeleton. The 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 a methyl group, an ethyl group, a n-propyl group, an isopropyl group, and an n-butyl group. It is preferred to use an alkoxy group of the same metal as the metal constituting the minute inorganic filler, and when the minute inorganic filler is colloidal cerium oxide, it is preferred to use an alkoxy group having ruthenium as a metal.

The content of the organic polymer in the fine inorganic filler to which the organic polymer is immobilized 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.

The above-mentioned organic polymer to be immobilized on a fine inorganic filler is a polymer composition containing a hydroxyl group and constituting the binder 6, and may contain a polyfunctional isocyanate selected from two or more functional groups reactive with a hydroxyl group. At least one of a compound, a melamine compound, and an amine resin. Thereby, the micro inorganic filler and the matrix resin of the binder 6 are bonded by a crosslinked structure, thereby improving storage stability, stain resistance, flexibility, weather resistance, storage stability, and the like, and further obtaining the obtained film. Has a luster.

The base polymer of the above binder 6 is preferably a polyol having a cycloalkyl group. As described above, by introducing a cycloalkyl group into the polyol constituting the binder 6 as the base polymer, the water repellency and water resistance of the binder 6 can be made high, and under high temperature and high humidity conditions, The bending resistance, dimensional stability, and the like of the optical sheet 1 are improved. Further, the basic properties of the coating film such as weather resistance, hardness, thickness feeling, and solvent resistance of the optical layer 3 are improved. Further, the affinity between the binder 6 and the fine inorganic filler to which the organic polymer is fixed on the surface, and the uniform dispersibility of the fine inorganic filler are further improved.

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 cyclodecyl group, a cyclodecyl group, a cyclodecyl group, and a ring twelve. Alkyl, cyclotridecyl, cyclotetradecyl, cyclopentadecyl, cyclohexadecyl, cycloheptadecyl, cyclooctadecyl, and the like.

The polyol having the above cycloalkyl group is obtained by copolymerizing a polymerizable unsaturated monomer having a cycloalkyl group. The polymerizable unsaturated monomer having a cycloalkyl group means 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, and t-butylcyclohexyl (meth)acrylate. Cyclododecyl (meth)acrylate or the like.

Further, the polymer composition may also contain an isocyanate as a hardener. By containing an isocyanate curing agent in the polymer composition, a more stable crosslinked structure can be obtained, and the film properties of the optical layer 3 can be further improved. As the isocyanate, the same ones as the above polyfunctional isocyanate compound can be used. Among them, an aliphatic isocyanate which prevents yellowing of the film is preferred.

In particular, when a polyol is used as the base polymer, one type of hexamethylene diisocyanate, isophorone diisocyanate, and xylene diisocyanate may be used as the curing agent to be blended in the polymer composition, or two kinds may be used in combination. the above. When such a curing agent is used, since the curing reaction rate of the polymer composition becomes large, even if a cationic substance which imparts dispersion stability to the fine inorganic filler is used as an antistatic agent, the cationic resistance can be sufficiently remedied. The reduction in the rate of hardening reaction caused by the electrostatic agent. Further, an increase in the curing reaction rate of the polymer composition imparts uniform dispersibility of the minute inorganic filler in the binder. As a result, the optical sheet 1 can significantly suppress the deflection and yellowing caused by heat, ultraviolet rays, and the like.

Further, the above polymer composition may also contain an antistatic agent. By forming the binder 6 with the polymer composition in which the antistatic agent is mixed, the optical sheet 1 can exhibit an antistatic effect, thereby preventing adsorption of dust or being difficult to overlap with the ruthenium or the like due to static electricity. The problem. Further, if an antistatic agent is applied to the surface, the surface may be sticky or dirty, but by dissipating the antistatic agent in the polymer composition as described above, the disadvantage can be reduced. The antistatic agent is not particularly limited, and examples thereof include an anionic antistatic agent such as an alkyl sulfate or an alkyl phosphate, a cationic antistatic agent such as a quaternary ammonium salt or an imidazoline compound, and a polyethylene glycol system. A nonionic antistatic agent such as polyoxyethylene sorbitan monostearate or ethanol decylamine, or a polymer antistatic agent such as polyacrylic acid. Among them, a cationic antistatic agent having a large antistatic effect is preferable, and an antistatic effect can be exhibited by adding a small amount of the cationic antistatic agent.

Further, the above polymer composition may also contain an ultraviolet absorber. By forming the bonding agent 6 with the polymer composition containing the above ultraviolet absorbing agent, the optical sheet 1 can be provided with an ultraviolet ray-proof function, and the ultraviolet ray emitted from the light source of the backlight unit can be isolated to prevent the destruction of the liquid crystal layer caused by the ultraviolet ray. .

The ultraviolet absorber is not particularly limited as long as it is a known compound which can absorb ultraviolet rays and efficiently convert it into heat energy and is stable to light. Among them, a salicylic acid-based ultraviolet absorber or a benzophenone-based ultraviolet absorber which has a high ultraviolet absorption function and is compatible with the above-mentioned base polymer and which can be stably present in the base polymer is preferable. , benzotriazole-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorber and ^can be used in more of those selected from a group of one or two kinds. Further, as the ultraviolet absorber, a polymer having an ultraviolet absorbing group in a molecular chain (for example, "Yudaburu UV" series manufactured by Nippon Shokubai Co., Ltd.) can be preferably used. By using a polymer having an ultraviolet absorbing group in the molecular chain, the compatibility with the main polymer of the binder 5 is improved, and deterioration of the ultraviolet absorbing function due to bleeding of the ultraviolet absorbing agent or the like can be prevented. Further, a polymer having an ultraviolet absorbing group in a molecular chain may be used as a base polymer of the binder 5. Further, the polymer having the ultraviolet absorbing group bonded thereto may be used as the base polymer of the binder 5, and the base polymer may further contain an ultraviolet absorber, thereby further improving the ultraviolet absorbing function.

The lower limit of the content of the ultraviolet absorber relative to the base polymer of the binder 6 is preferably 0.1% by mass, more preferably 1% by mass, most preferably 3% by mass; and the upper limit of the above content of the ultraviolet absorber is Preferably, it is 10% by mass, more preferably 8% by mass, most preferably 5% by mass. The reason for this is that when the mass ratio of the ultraviolet absorber to the base polymer is less than the lower limit, the substrate sheet for an optical sheet cannot effectively exhibit the ultraviolet absorbing function, and if the mass ratio of the ultraviolet absorber exceeds the upper limit, The base polymer is adversely affected, and the strength, durability, and the like of the adhesive 6 are lowered.

Instead of the above ultraviolet absorber, a UV stabilizer (including a base polymer having an ultraviolet stabilizing group bonded to a molecular chain) may be used, or a UV stabilizer may be used together with the ultraviolet absorber. By the ultraviolet stabilizer, radicals generated by ultraviolet rays, active oxygen, and the like can be deactivated, thereby improving ultraviolet stability, weather resistance, and the like. As the ultraviolet stabilizer, a hindered amine-based ultraviolet stabilizer having high stability to ultraviolet rays can be suitably used. Further, by using the ultraviolet absorber together with the ultraviolet stabilizer, the deterioration of the ultraviolet rays and the weather resistance can be remarkably improved.

Next, a description will be given of a method of manufacturing the optical sheet 1. The manufacturing method of the optical sheet 1 has the steps of: producing a polymer composition for an optical layer, mixing the light diffusing agent 5 in a polymer composition constituting the bonding agent 6; and forming the optical layer 3 by The surface area of the substrate layer 2 is a polymer composition for the optical layer and is hardened. As a method of forming a polymer composition for an optical layer on the surface layer of the base material layer 2, there is a method of laminating a polymer composition for light diffusion by printing. The printing method is not particularly limited, and gravure printing, screen printing, inkjet printing, laser printing, or the like can be used.

The optical sheet 11 of FIG. 2 includes a base material layer 12 and an optical layer 3 provided on the surface side of the base material layer 12. A corrugated crotch portion 13 is provided on the back side of the base material layer 12. Since the optical layer 3 is the same as the optical sheet 1 described above, the same reference numerals are used, and the description thereof is omitted.

The crotch portion 13 is provided on the entire back surface of the optical sheet 11, and has a corrugated rib shape in cross section. The height ratio (H ₂ /P) of the average height (H ₂ ) of the crucible to the crucible pitch (P) is preferably 0.05 or more and 0.5 or less, and particularly preferably 0.1 or more and 0.2 or less. In the optical sheet 11, the light is reflected, diffused, refracted, and the like in the crotch portion 13, so that an optical function such as refraction and diffusion toward the normal direction side of the entire optical sheet 11 can be enhanced.

The crotch portion 13 may be integrally formed with the base material layer 12 or may be formed separately from the base material layer 12. Since the crotch portion 13 needs to pass light, it is formed of a transparent, particularly colorless, transparent synthetic resin. Specifically, the same synthetic resin as the base material layer 12 can be used.

The side light type backlight unit shown in FIG. 3 includes a light guide plate 7, and a pair of linear light sources 8 disposed on both sides of the light guide plate 7 and an optical sheet 11 disposed on the surface side of the light guide plate 7 in a superposed manner. The light emitted from the light source 8 and emitted from the surface of the light guide plate 7 has a strong peak inclined at a predetermined angle with respect to the normal direction, but the backlight unit is diffused toward the front side by the light diffusing function toward the front side. The optical sheet 11 having a relatively high optical function such as a variable angle function on the direction side can achieve high brightness on the front side and uniform brightness. In addition, the edge type backlight unit is sometimes equipped with four, six, etc. light sources 8.

Further, the optical sheet of the present invention is not limited to the above embodiment, and for example, the dot arrangement pattern is not limited to the above-mentioned equilateral triangle lattice pattern which can be densely filled, and may be a square lattice pattern or a random pattern. The random pattern can reduce the fold generated when the optical sheet is overlapped with other optical parts. In addition, the diameter of the dot can be made smaller in the vicinity of the light source, and larger as the distance from the light source, and the density of the dots is set lower as the distance from the light source, and the layer is unevenly distributed on the sheet. Light diffusing section. The brightness of the diffused light on the sheet can be adjusted by the change of the light diffusing portion. Further, the optical sheet can also be used as a light guide plate. By using the light guide plate, it is possible to shorten the lead time required for the thinning and shape correction of the backlight unit.

Example

Hereinafter, the present invention will be described in detail based on examples, but the present invention is not limited to the description of the examples.

[Comparative Example 1]

As the substrate layer, a film made of transparent polyethylene terephthalate having a thickness of 300 μm was used. As the polymer composition for a light diffusion layer, a polymer composition composed of beads made of an acrylic resin, an acrylic polyol (adhesive), and a solvent is used. The mass ratio of the acrylic resin beads to the acrylic polyol was 0.2. As the above bead system, only small-diameter monodisperse beads having an average particle diameter of 10 μm and a coefficient of variation of 0.1 were used. The polymer composition for a light-diffusion layer was deposited on the surface of the base material layer by a gravure coating method by 6 g/m ² (converted solid content) to prepare an optical sheet of Comparative Example 1.

[Comparative Example 2]

The polymer composition for a light-diffusion layer and an acrylic polyol were laminated on the surface of the base material layer by a screen printing and a lenticular shape to obtain an optical sheet of Comparative Example 2. The light diffusion portion of the optical sheet of Comparative Example 2 had an average diameter of 60 μm, a laminate ratio of 50%, and an arrangement pattern of a regular triangular lattice pattern. Other than the above, it was the same as Comparative Example 1 described above.

[Examples 1 to 8]

The mass ratio of the acrylic resin beads as the polymer composition for the light diffusion layer to the acrylic polyol (adhesive) is 0.1, 0.2, 0.3, 0.4, 0.5, 1, 1.5, and 2, respectively. The sheet was printed and laminated on the surface of the base material layer in the form of a convex lens or a scatter, and the optical sheets of Examples 1 to 8 were obtained. Other than the above, it was the same as Comparative Example 2 described above.

[Examples 9 to 19]

The back surface of the base material layer is processed to form a 稜鏡 shape having a wavy shape with a 稜鏡 height ratio (H ₂ /P) of 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, respectively. . The mass ratio of the acrylic resin beads as the polymer composition for the light diffusion layer to the acrylic polyol (adhesive) was 0.2, and the laminate was laminated in a convex lens shape or a scatter pattern by screen printing. On the surface of the substrate layer, the optical sheets of Examples 9 to 19 were obtained. The light-diffusing portions of the optical sheets of Examples 9 to 19 had an average diameter of 60 μm and a laminate ratio of 50%, and the arrangement pattern was a regular triangular lattice pattern. Other than the above, it was the same as Comparative Example 1 described above.

[Feature evaluation]

The optical sheets of the above-described Examples 1 to 8 and the optical sheets of Comparative Examples 1 and 2 were incorporated in an edge-light type backlight unit as an actual light-diffusing sheet, and the surface uniformity of the front luminance and the average front luminance were measured. The surface uniformity is determined by measuring the front luminance in the plane of the optical sheet by the ratio of the minimum value of the luminance to the maximum luminance. The results are shown in Table 1 below.

As shown in the above Table 1, the optical sheets of Examples 1 to 8 had surface uniformity which was not inferior to that of the optical sheet of Comparative Example 1 in which the light diffusion layer was formed over the entire surface of the base material layer, and had high front luminance. Further, the optical sheets of Examples 1 to 8 had higher surface uniformity than the optical sheets of Comparative Example 2 which did not contain the light diffusion layer, and had a front luminance which was not inferior to Comparative Example 2. Further, when the optical sheets of Examples 1 to 8 were compared, it was revealed that the mass ratio of the light diffusing agent to the binder was 0.1 or more, and the surface uniformity was improved, and when the mass ratio was 0.3 or more, the surface uniformity was particularly improved.

Next, using the optical sheets of Examples 9 to 19, the optical sheets were incorporated in a direct type backlight unit as an actual light diffusion sheet, and the light diffusibility was evaluated. The evaluation of the light diffusibility was performed by visually confirming the degree of disappearance of the lamp image from the front side when the backlight was irradiated, and evaluated based on the following criteria:

(a) almost no light image ◎

(b) It is not easy to see the light image ○

(c) slightly visible light image △

(d) Clearly visible light image ╳

The results are shown in Table 2 below.

As shown in the above Table 2, the optical sheets of Examples 9 to 19 were compared, and it was revealed that the yttrium height ratio was 0.05 or more and 0.5 or less, and the light diffusibility was improved. When the height ratio was 0.1 or more and 0.2 or less, the light diffusion was particularly improved. Sex.

Industrial availability

As described above, the optical sheet of the present invention can be used as a constituent element of a backlight unit of a liquid crystal display device, and is particularly suitable for a transmissive liquid crystal display device.

1. . . Optical sheet

2. . . Substrate layer

3. . . Optical layer

4. . . Light diffusing section

5. . . Light diffusing agent

6. . . Adhesive

7. . . Light guide

8. . . Light source

11. . . Optical sheet

12. . . Substrate layer

13. . . Crotch

20. . . Backlight unit

twenty one. . . Light source

twenty two. . . Light guide

twenty three. . . Optical sheet

twenty four. . . Light diffuser

25. . . Bract

25a. . . Crotch

Fig. 1 is a schematic partial plan view (a) and a schematic partial cross-sectional view (b) showing an optical sheet according to a specific embodiment of the present invention.

Fig. 2 is a schematic partial cross-sectional view showing an optical sheet of a different form from the optical sheet of Fig. 1.

3 is a schematic cross-sectional view showing a backlight unit including the optical sheet of FIG. 2.

4 is a schematic partial perspective view showing a conventional general edge type backlight unit.

1. . . Optical sheet

2. . . Substrate layer

3. . . Optical layer

4. . . Light diffusing section

5. . . Light diffusing agent

6. . . Adhesive

7. . . Light guide

Claims (11)

An optical sheet comprising: a transparent substrate layer and an optical layer laminated on a surface of the substrate layer, wherein the optical layer has a plurality of light diffusion portions which are layered on the surface of the substrate layer; the light diffusion The portion contains a light diffusing agent and a binder thereof, and a fine convex portion is formed on the surface by the light diffusing agent, and a height ratio of the average height (H ₁ ) of the light diffusing portion to the average diameter (D) (H ₁ / D) is 0.05 or more and 0.5 or less. The optical sheet of claim 1, wherein the light diffusing portion is formed in a convex lens shape. The optical sheet of claim 1, wherein the mass ratio of the light diffusing agent to the binder is 0.1 or more and 2 or less. The optical sheet of claim 1, wherein the light diffusing portion has an average diameter (D) of 10 μm or more and 300 μm or less. The patent application range of the optical sheet, Paragraph 1, wherein the absolute value of difference in the refractive index of the light diffusing portion of the light diffusing agent _(n-1) and the refractive index of the binder (n ₂₎ of (| n ₁ -n ₂ | ) is 0.05 or more. The optical sheet of the first aspect of the invention, wherein the light diffusing agent in the light diffusing portion has an average particle diameter of 0.1 μm or more and 20 μm or less. The optical sheet of claim 1, wherein a laminate ratio of the light diffusion portion in the optical layer is 10% or more and 90% or less. The optical sheet of claim 1, wherein the arrangement pattern of the surface of the substrate layer of the light diffusion portion is a regular triangular lattice pattern. The optical sheet of claim 1, wherein the pattern of the surface of the substrate layer of the light diffusing portion is a random pattern. The optical sheet of claim 1, wherein the back surface of the base material layer has a corrugated crucible shape, and the height ratio of the average height (H ₂ ) of the crucible to the crucible spacing (P) (H ₂ / P) is 0.05 or more and 0.5 or less. A backlight unit for a liquid crystal display device that disperses light emitted from a light source and guides the light to the surface side thereof, and is characterized by comprising the optical sheet according to any one of claims 1 to 10.