KR100524231B1 - Light diffusion sheet and backlight unit using the same - Google Patents

Abstract

A light diffusion sheet which can improve heat resistance, thermal dimensional stability and weather resistance while maintaining transparency, and which is hard to cause warpage or yellowing even when the lamp is heated or irradiated with ultraviolet rays, and the light scattering sheet It is an object of the present invention to provide a backlight unit that reduces generation.

The light-diffusion sheet of this invention is equipped with the transparent base material layer and the light-diffusion layer laminated | stacked on the surface side of this base material layer, This light-diffusion layer contains a light-diffusion agent in a binder, This binder contains a polyol and a micro inorganic filler. It is formed from a polymer composition, and has a glass transition temperature of 50 ° C. or higher and 80 ° C. or lower, and the average particle diameter of the fine inorganic filler is 5 nm or more and 50 nm or less.

Description

LIGHT DIFFUSION SHEET AND BACKLIGHT UNIT USING THE SAME}

The present invention relates to a light diffusing sheet having a function of diffusing transmitted light and particularly suitable for a backlight unit of a liquid crystal display device and a backlight unit using the light diffusing sheet.

Background Art A liquid crystal display device is widely used with a backlight system that emits light by illuminating a liquid crystal layer from a background, and a backlight unit such as an edge light layer or a direct type is provided on the lower surface side of the liquid crystal layer. The edge light type backlight unit 20 basically has a linear lamp 21 as a light source and a rectangular plate-shaped light guide plate disposed so that an end portion follows the lamp 21 as shown in FIG. 22), the light-diffusion sheet 23 arrange | positioned at the surface side of the light guide plate 22, and the prism sheet 24 arrange | positioned at the surface side of the light-diffusion sheet 23 is provided.

The function of the backlight unit 20 will be described. First, the light rays incident on the light guide plate 22 from the lamp 21 are reflected by a reflective dot or a reflection sheet (not shown) on the rear surface of the light guide plate 22, and the light guide plate ( 22) Emitted from the surface. Light rays emitted from the light guide plate 22 enter the light diffusion sheet 23, are diffused from the light diffusion sheet 23, and are emitted from the light diffusion sheet 23 surface. Thereafter, the light rays emitted from the light diffusing sheet 23 enter the prism sheet 24 and serve as light rays of a distribution showing peaks in a substantially normal direction by the prism portions 24a formed on the surface of the prism sheet 24. It is emitted.

In this way, the light rays emitted from the lamp 21 are diffused by the light diffusion sheet 23 and refracted by the prism sheet 24 to show a peak in a substantially normal direction, and furthermore, the liquid crystal layer on the surface side (not shown). Not to illuminate the front. Although not shown, the prism sheet (for the purpose of alleviating the light collection characteristics of the prism sheet 24 described above, protecting the prism portion 24a, or preventing sticking of the liquid crystal panel such as a polarizing plate and the prism sheet 24) The light-diffusion sheet is further arrange | positioned at the surface side of 24).

Generally, as shown in FIG.3 (b), the light-diffusion sheet 23 with which the said backlight unit 20 is equipped is the transparent base material layer 26 made of synthetic resin, and the surface of this base material layer 26. As shown in FIG. And a sticking prevention layer 28 laminated on the back surface of the substrate layer 26 (see, for example, Japanese Patent Laid-Open Nos. 7-5305 and 2000-89007). ). The light diffusing layer 27 generally contains a light diffusing agent 30 in the binder 29, and the light diffusing agent 30 functions to diffuse transparent light. Moreover, the sticking prevention layer 28 disperse | distributes a small amount of the beads 32 in the binder 31, and has the structure which the lower part of this bead 32 protruded from the back surface of the binder 31, and has light diffusion. The back surface of the sheet 23 is in close contact with the surface of the light guide plate 22 to prevent the problem of interference interference.

By the way, since the light-diffusion sheet 23 is generally formed with synthetic resin, it has a fault that it is easy to receive deformation | transformation and discoloration (yellowing etc.) by heat, an ultraviolet-ray, etc. On the other hand, the lamp 21, which is a light source, generates heat simultaneously with light emission. Generally, the lamp 21 vicinity of the light-diffusion sheet 23 is exposed under the temperature of about 80 degreeC to about 90 degreeC. For this reason, there exists a problem that the light-diffusion sheet 23 heat-transforms and partially bends, and as a result, the luminance unevenness of a screen will generate | occur | produce.

Therefore, by dispersing and containing the fine inorganic filler in the binder 29 of the light diffusion layer 27 in the light diffusion sheet 23, a technique for improving heat resistance has been developed (Japanese Patent Laid-Open No. 2000-89007). Reference), (a) the dispersibility of the micro inorganic filler is poor, sufficient heat resistance cannot be obtained, (b) the adhesion between the micro inorganic filler and the binder 29 is not sufficient, and a small gap is generated at the interface between them. There exists a problem that intensity | strength and light transmittance fall.

SUMMARY OF THE INVENTION The present invention has been made in view of these problems, and can improve heat resistance, thermal dimensional stability and weather resistance while maintaining a high light transmittance, and a light diffusion sheet which is less likely to cause warpage or yellowing even under heat generation or ultraviolet irradiation of a lamp, And the backlight unit for reducing the occurrence of luminance unevenness or luminance deterioration by using such a light diffusion sheet.

The invention made to solve the above problems comprises a transparent base layer and a light diffusing layer laminated on the surface side of the base layer, the light diffusing layer containing a light diffusing agent in a binder, the binder being a polyol and a micro inorganic filler It is formed from the polymer composition containing and is a light-diffusion sheet which has a glass transition temperature of 50 degreeC or more and 80 degrees C or less, and whose average particle diameter of this micro inorganic filler is 5 nm or more and 50 nm or less. Here, as a "glass transition temperature", the value measured by the preview scanning calorimetry (DSC) prescribed | regulated to JIS is employ | adopted.

According to the said light-diffusion sheet, by using a polyol as a base polymer of the binder of a light-diffusion layer, transparency is high and it is excellent in weather resistance, workability, etc. Moreover, since the binder of a light-diffusion layer has a glass transition temperature of 50 degreeC or more and 80 degrees C or less, heat resistance of a light-diffusion layer can be improved. Furthermore, by containing the micro inorganic filler in the polymer composition, the heat resistance of the light diffusion layer can be further increased. Since the average particle diameter of the micro inorganic filler dispersed and contained for such heat resistance improvement is 5 nm or more and 50 nm or less, it is smaller than the wavelength of visible light, and transparency of a light-diffusion layer can be maintained. As a result, the light-diffusion sheet can significantly suppress warpage and yellowing due to heat and the like, and can also prevent a decrease in light transmittance due to the content of the micro inorganic filler.

It is further provided with the anti-sticking layer laminated | stacked on the back surface side of the said base material layer, This anti-sticking layer disperse | distributing beads in a binder, This binder is formed from the polymer composition containing a polyol and a micro inorganic filler, and also it is 50 It is good to have a glass transition temperature of 80 degreeC or more and 80 degrees C or less, and to make the average particle diameter of this micro inorganic filler into 5 nm or more and 50 nm or less. According to such means, weather resistance and heat resistance can be improved while maintaining the transparency of the anti-sticking layer in the same manner as the light diffusion layer described above. As a result, warpage and yellowing can be suppressed while maintaining the transparency of the light diffusion sheet.

As the fine inorganic filler, a fine inorganic filler in which an organic polymer is fixed on the surface thereof may be used. Herein, "fixed" does not mean only adhesion and adhesion, but means that a chemical bond is formed between the organic polymer and the micro inorganic filler, and thus, the organic solvent is organic in the washing solution of the micro inorganic filler with an arbitrary solvent. No polymer is detected. As such, when the micro inorganic filler having the organic polymer fixed to the surface is used, the light diffusion layer has good affinity for the base polymer constituting the binder and has good film properties such as surface hardness, heat resistance, abrasion resistance, weather resistance, and stain resistance. Can be formed.

In the micro inorganic filler to which the organic polymer is fixed, the alkoxy group may contain 0.01 mmol / g or more and 50 mmol / g or less. By containing an alkoxy group of such an amount in the organic polymer fixed to the micro inorganic filler, the affinity between the micro inorganic filler and the base polymer of the matrix and the dispersibility of the micro inorganic filler in the base polymer can be improved.

The organic polymer may have a hydroxyl group and may contain one or two or more selected from a polyfunctional isocyanate compound, a melamine compound and an aminoplast resin in the polymer composition. According to this means, since the organic polymer and the binder matrix fixed on the surface of the micro inorganic filler are bonded by a crosslinked structure, a coating film having good film properties such as storage stability, stain resistance, flexibility, weather resistance, and storage stability can be provided. .

The polyol may have a cycloalkyl group. Thus, by using the polyol which has a cycloalkyl group as a base polymer, the hydrophobicity (water repellency, water resistance) of a binder becomes high, and the curvature resistance, dimensional stability, etc. of the said light-diffusion sheet under high temperature, high humidity conditions are improved. Moreover, coating film basic performances, such as hardness, weather resistance, and solvent resistance of a light-diffusion layer, improve. In addition, the affinity with the micro inorganic filler having the organic polymer fixed to the surface and the uniform dispersibility of the micro inorganic filler become more favorable.

What is necessary is just to contain an aliphatic isocyanate as a hardening | curing agent in the said polymer composition. Thus, yellowing of a light-diffusion layer or a sticking prevention layer can be prevented by using aliphatic isocyanate as a hardening | curing agent contained in a polymer composition.

Therefore, in the backlight unit for a liquid crystal display device which disperses the light rays generated from the lamp and guides them to the surface side, as described above, when the light diffusion sheet is provided, the heat diffusion of the light diffusion sheet, warpage due to ultraviolet rays, yellowing, etc. are reduced. Therefore, it is possible to suppress the luminance unevenness and the decrease of the luminance of the liquid crystal display device.

(Detailed Description of Preferred Embodiments)

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described, referring an appropriate drawing.

The light-diffusion sheet 1 of FIG. 1 is equipped with the base material layer 2 and the light-diffusion layer 3 laminated | stacked on the surface of this base material layer 2.

Since the base material layer 2 needs to transmit a light ray, it is formed of transparent, especially colorless and transparent synthetic resin. The synthetic resin used for the base material layer 2 is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, weather resistant vinyl chloride, and the like. have. Among these, polyethylene terephthalate excellent in transparency and high in strength is preferable, and polyethylene terephthalate having improved warping performance is particularly preferable.

Although the thickness (average thickness) of the base material layer 2 is not specifically limited, For example, 10 micrometers or more and 500 micrometers or less, Preferably 35 micrometers or more and 250 micrometers or less, Especially preferably, they are 50 micrometers or more and 188 micrometers or less. Is done. When the thickness of the base material layer 2 is less than the said range, when coating the resin composition for forming the light-diffusion layer 3, curling will become easy to generate | occur | produce, and the problem of handling becomes difficult. On the contrary, when the thickness of the base material layer 2 exceeds the said range, the brightness of a liquid crystal display device may fall, and thickness of a backlight unit may become large and it may be contrary to the request of thinning a liquid crystal display device.

The light diffusion layer 3 is provided with the binder 4 and the light-diffusion layer agent 5 contained in this binder 4. By containing the light diffusing agent 5 in the light diffusing layer 3 in this manner, the light diffusing layer 3 can be uniformly diffused from the back surface. In addition, a part of the light diffusing agent 5 has an upper end protruding from the binder 4. Thus, by providing the light diffusing agent 5 and the light diffusing agent 5 which protrude in the binder 4, a light ray can be spread more easily. Although the thickness (meaning the thickness of the part of the binder 4 except the light-diffusion agent 5) of the light-diffusion layer 3 is not specifically limited, For example, they are about 10 micrometers or more and 30 micrometers or less.

The light diffusion layer 5 is a particle having a property of diffusing light rays, and largely classified into an inorganic filler and an organic filler. As the inorganic filler, specifically, silica, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide, magnesium silicate, or a mixture thereof can be used. As a specific material of an organic filler, an acrylic resin, an acrylonitrile resin, polyurethane, polyvinyl chloride, polystyrene, polyacrylonitrile, polyamide, etc. can be used. Among these, acrylic resin with high transparency is preferable, and polymethyl methacrylate (PMMA) is especially preferable.

The shape of the light diffusing agent 5 is not particularly limited, and examples thereof include a spherical shape, a cubic shape, a needle shape, a rod shape, a fusiform shape, a plate shape, a flaky shape, a fiber shape, and the like. Spherical beads excellent in light diffusivity are preferable.

As a minimum of the average particle diameter of the light-diffusion agent 5, 1 micrometer, especially 2 micrometers and 5 micrometers are more preferable, and as an upper limit of the average particle diameter of the light-diffusion agent 5, 50 micrometers, especially 20 micrometers and 15 micrometers are More preferred. This means 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 light diffusing layer 3 formed by the light diffusing agent 5 becomes small, and the light diffusivity required as the light diffusing sheet is satisfied. This is because the thickness of the light diffusing sheet 1 increases and it becomes difficult to spread uniformly when the average particle diameter of the light diffusing agent 5 exceeds the above range.

As a minimum of the compounding quantity of the light-diffusion agent 5 (the compounding quantity of the solid content conversion with respect to 100 parts of base polymers in the polymer composition which is a formation material of the binder 4), 10 parts, especially 20 parts and 50 parts are more preferable, As an upper limit, 500 parts, especially 300 part and 200 part are more preferable. This results in insufficient light diffusivity when the compounding quantity of the light diffusing agent 5 is less than the above range, and on the other hand, when the compounding quantity of the light diffusing agent 5 exceeds the above range, the light diffusing agent 5 is fixed. This is because it decreases. In addition, in the case of the so-called commercial light diffusing sheet arranged on the surface side of the prism sheet, since high light diffusivity is not required, the blending amount of the light diffusing agent 5 is 10 parts or more and 40 parts or less, especially 10 parts or more. 30 parts or less are preferable.

The binder 4 is formed by crosslinking and curing the polymer composition. This polymer composition contains a polyol and a micro inorganic filler, and, for example, a hardening | curing agent, a plasticizer, a stabilizer, a deterioration inhibitor, a dispersing agent, an antistatic agent, etc. are mix | blended suitably. The glass transition temperature of this binder 4 is 50 degreeC or more and 80 degrees C or less, Preferably it is 60 degreeC or more and 70 degrees C or less. Therefore, weather resistance, heat resistance, strength, handleability, etc. of the light-diffusion sheet 3 become high further by the weather resistance, heat resistance, intensity | strength, etc. which the binder 4 is excellent. Moreover, since the binder 4 needs to transmit light, it becomes transparent, and colorless transparency is especially preferable.

As this polyol, the polyol obtained by superposing | polymerizing the monomer component containing a hydroxyl-containing unsaturated monomer, the polyester polyol obtained by the hydroxyl group excess condition, etc. are mentioned, for example, These can be used individually or in mixture of 2 or more types.

As this hydroxyl-containing unsaturated monomer, (a) 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, allyl alcohol, homoallyl Hydroxyl-containing unsaturated monomers such as alcohol, cinnamic alcohol and crotonyl alcohol, (b) for example, ethylene glycol, ethylene oxide, propylene glycol, propylene oxide, butylene glycol, butylene oxide, 1, 4-bis (hydr Hydroxymethyl) cyclohexane, phenylglycidyl ether, glycidyl decanoate, and dihydric alcohols or epoxy compounds such as Fraxel FM-1 (manufactured by Daicel Kagaku Kogyo KK), for example, acrylic acid, meta The hydroxyl group containing unsaturated monomer etc. which are obtained by reaction with unsaturated carboxylic acid, such as a acrylic acid, maleic acid, a fumaric acid, a crotonic acid, and itaconic acid, are mentioned. Polyol can be manufactured by superposing | polymerizing 1 type (s) or 2 or more types chosen from these hydroxyl-containing unsaturated monomers.

For example, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, ethylhexyl acrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, meta N-butyl methacrylate, tert-butyl methacrylate, ethylhexyl methacrylate, glycidyl methacrylate, cyclohexyl methacrylate, styrene, vinyltoluene, 1-methylstyrene, acrylic acid, methacrylic acid, acrylo Nitrile, vinyl acetate, vinyl propionate, vinyl stearate, allyl acetate, diallyl adipic acid, diallyl itaconic acid, diethyl maleate, vinyl chloride, vinylidene chloride, acrylamide, N-methylol acrylamide, N- 1 or 2 or more types of ethylenically unsaturated monomers chosen from butoxymethyl acrylamide, diacetone acrylamide, ethylene, propylene, isoprene, etc., and a hydroxyl group chosen from said (a) and (b) By the polymerization of unsaturated organic monomers it can be produced a polyol.

The number average molecular weight of the polyol obtained by superposing | polymerizing the monomer component containing such a hydroxyl-containing unsaturated monomer is 1000 or more and 500000 or less, Preferably it is 5000 or more and 100000 or less. Moreover, the hydroxyl value is 5 or more and 300 or less, Preferably it is 10 or more and 200 or less, More preferably, it is 20 or more and 150 or less.

The polyester polyol obtained on the condition of hydroxyl excess is (c) 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 Polyhydric alcohols such as (hydroxymethyl) cyclohexane, hydroquinone bis (hydroxyethyl ether), tris (hydroxyethyl) isocinurate, xylene glycol, and (d) maleic acid, fumaric acid, succinic acid, The polybasic acids such as dific acid, sebacic acid, azelaic acid, trimethic acid, terephthalic acid, phthalic acid and isophthalic acid may be substituted by the number of hydroxyl groups in polyhydric alcohols such as propanediol, hexanediol, polyethylene glycol and trimethylolpropane. All carboxylic rider can be prepared by reacting a number of conditions.

The number average molecular weights of the polyester polyol obtained on such hydroxyl group excess conditions are 500 or more and 300000 or less, Preferably they are 2000 or more and 100000 or less. Moreover, the hydroxyl value is 5 or more and 300 or less, Preferably it is 10 or more and 200 or less, More preferably, it is 20 or more and 150 or less.

As a polyol used as a base polymer of the said polymer composition, the acryl polyol obtained by superposing | polymerizing the monomer component containing the said polyester polyol and the said hydroxyl-containing unsaturated monomer, and having a (meth) acryl unit etc. is preferable. Either of these polyester polyols and acrylic polyols may be used, or both may be used.

The number of hydroxyl groups in the polyester polyol and acrylic polyol is not particularly limited as long as the number of hydroxyl groups is 2 or more per molecule, but when the hydroxyl value in the solid content is 10 or less, the crosslinking score is decreased, and the solvent resistance, water resistance, heat resistance, and surface hardness are reduced. There exists a tendency for film physical properties, such as these, to fall.

Such a polyol has high workability and can easily form the light diffusion layer 3 by means of coating or the like. Moreover, the binder 4 which uses a polyester polyol or an acryl polyol as a base polymer has high weather resistance, and can suppress yellowing etc. of the light-diffusion layer 3, and the like. On the other hand, by dispersing the fine inorganic filler in the binder 4, the heat diffusion of the light diffusion layer 3 and further, the heat resistance of the light diffusion sheet 1 can be improved, and the warpage can be suppressed.

Moreover, what is necessary is just to use the polyol which has a cycloalkyl group as said polyol. Thus, by introducing a cycloalkyl group into the polyol constituting the binder 4, the hydrophobicity (water repellency, water resistance) of the binder 4 is increased, and the warpage resistance, dimensional stability, and the like of the light diffusion sheet at high temperature and high humidity conditions are improved. do. Moreover, coating film basic performances, such as hardness, solvent resistance, and weather resistance of the light-diffusion layer 3, improve.

The polyol which has the said cycloalkyl group is obtained by copolymerizing the polymerizable unsaturated monomer (a) which has a cycloalkyl group. The polymerizable unsaturated monomer (a) having this cycloalkyl group is a polymerizable unsaturated monomer having at least one cycloalkyl group in a molecule. It does not specifically limit as a polymerizable unsaturated monomer (a) which has this cycloalkyl group, For example, it is preferable that it is a polymerizable unsaturated monomer represented by following General formula (1). These may be used independently and may use 2 or more types together.

In Formula 1, R ¹ represents a hydrogen atom or a hydrocarbon group having 1 or 2 carbon atoms. Z represents the C1-C36 cycloalkyl group which may have a substituent. It does not specifically limit as said C1-C2 hydrocarbon group, For example, a methyl group, an ethyl group, etc. are mentioned.

It does not specifically limit as said substituent, For example, a C1-C18 hydrocarbon group etc. are mentioned. It does not specifically limit as said C1-C18 hydrocarbon group, For example, a methyl group, an ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert- butyl group, pentyl group, hexyl group , Heptyl group, octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group and the like.

It does not specifically limit as said cycloalkyl group, For example, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclononyl group, a cyclodecyl group, a cyclo undecyl group, a cyclododecyl group, a cyclo A tridecyl group, a cyclo tetradecyl group, a cyclopentadecyl group, a cyclohexadecyl group, a cycloheptadecyl group, a cyclooctadecyl group, etc. are mentioned.

It does not specifically limit as a polymerizable unsaturated monomer represented by the said General formula (1), For example, cyclohexyl (meth) acrylate, methylcyclohexyl (meth) acrylate, tert- butylcyclohexyl (meth) acrylate, cyclodode Thread (meth) acrylate etc. are mentioned.

As a copolymerization ratio of the polymerizable unsaturated monomer (a) which has the said cycloalkyl group, 5.0 mass% or more and 97.9 mass% or less are especially preferable 5.0 mass% or more and 80.0 mass% or less, 10.0 mass% or more and 70.0 mass% or less. When the copolymerization ratio of the polymerizable unsaturated monomer (a) having a cycloalkyl group is smaller than the above range, there is a possibility that the basic performance such as hardness, glossiness of the coating film may not be improved, and the polymerizable unsaturated monomer (a) is copolymerized. There exists a possibility that a polyol will not have an effect | action which forms the coating film which has extremely high weather resistance. On the other hand, when the copolymerization ratio of the polymerizable unsaturated monomer (a) having a cycloalkyl group exceeds the above range, in the polyol formed by copolymerizing the polymerizable unsaturated monomer (a), the polymerizable unsaturated monomer (a) having a cycloalkyl group is copolymerized. There exists a possibility that the balance of the effect which this has by having and the effect which other polymerizable unsaturated monomers have by copolymerizing may worsen.

As an inorganic substance which comprises a micro inorganic filler, it does not specifically limit but an inorganic oxide is preferable. The inorganic oxide is defined as various oxygen-containing metal compounds in which metal elements mainly form a three-dimensional network through bonding with oxygen atoms. As the metal element constituting the inorganic oxide, for example, an element selected from group II to VI of the periodic table of the elements is preferable, and an element selected from group III to V of the periodic table of the elements is more preferable. Especially, the element chosen from Si, Al, Ti, and Zr is especially preferable, and the colloidal silica whose metal element is Si is the most preferable from a heat resistant improvement effect and a light transmittance. Moreover, the shape of a micro inorganic filler may be arbitrary particle shapes, such as spherical shape, needle shape, plate shape, flaky shape, and crushing shape, and is not specifically limited.

As a minimum of the average particle diameter of a micro inorganic filler, it becomes 5 nm and 10 nm is especially preferable. On the other hand, as an upper limit of the average particle diameter of a micro inorganic filler, it is set to 50 nm and 25 nm is preferable. This is because when the average particle diameter of the micro inorganic filler is less than the above range, the surface energy of the micro inorganic filler becomes high, and aggregation or the like tends to occur. On the contrary, when the average particle diameter exceeds the above range, the effect of short wavelength It is because it becomes cloudy and the transparency of the light-diffusion sheet 1 cannot fully be maintained.

As a minimum of the compounding quantity (solid content conversion amount of only an inorganic component only) of the micro inorganic filler with respect to 100 parts of base polymers of a polymer composition, 5 parts are preferable and 50 parts are especially preferable. On the other hand, as an upper limit of the said compounding quantity of a micro inorganic filler, 500 parts are preferable, 200 parts are more preferable, 100 parts are especially preferable. If the compounding quantity of the micro inorganic filler is less than the above range, thermal deformation of the light diffusion sheet 1 may not be sufficiently prevented. Conversely, if the compounding quantity exceeds the above range, This is because the compounding becomes difficult, and the light transmittance of the light diffusing layer 3 may decrease.

As a micro inorganic filler, what fixed organic polymer on the surface may be used. Thus, by using an organic polymer fixed micro inorganic filler, the dispersibility in the binder 4 and the affinity with the binder 4 are aimed at. The organic polymer is not particularly limited in terms of its molecular weight, shape, composition, presence or absence of functional groups, and any organic polymer can be used. Moreover, about the shape of an organic polymer, the thing of arbitrary shapes, such as linear form, a branch form, and a crosslinked structure, can be used.

As specific resin which comprises such an organic polymer, For example, polyester, such as (meth) acrylic resin, polystyrene, polyolefin, such as polyvinyl acetate, polyethylene, and polypropylene, polyvinyl chloride, polyvinylidene chloride, polyethylene terephthalate, etc. And resins partially modified with functional groups such as these copolymers, amino groups, epoxy groups, hydroxyl groups, and carboxyl groups. Especially, it is suitable to have an organic polymer containing (meth) acryl units, such as (meth) acrylic resin, (meth) acrylstyrene resin, and (meth) acrylic polyester resin as an essential component, and has a film forming ability. . On the other hand, a resin having compatibility with a polyol which is a base polymer of the polymer composition is preferable, and therefore, it is most preferable to have the same composition as the polyol included in the polymer composition.

In addition, the micro inorganic filler may contain the organic polymer in microparticles | fine-particles. As a result, a moderate degree of ductility and toughness can be imparted to the core mineral of the fine inorganic filler.

The organic polymer may contain an alkoxy group, and the content thereof is preferably 0.01 mmol or more and 50 mmol or less per 1 g of the micro inorganic filler to which the organic polymer is fixed. By such an alkoxy group, the affinity with the matrix resin which comprises the binder 4 and the dispersibility in the binder 4 can be improved.

The alkoxy group mentioned here represents the RO group couple | bonded with the metal element which forms a fine particle skeleton. R is an alkyl group which may be substituted, and the RO group 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.

The content rate of the organic polymer in the micro inorganic filler to which the organic polymer is fixed is not particularly limited, but 0.5 to 50 mass% is preferable based on the micro inorganic filler.

As described above, a polyfunctional isocyanate compound, a melamine compound, and an amino plastic having two or more functional groups reacting with a hydroxyl group in the polymer composition constituting the binder (4) using an organic polymer fixed to the micro inorganic filler. What is necessary is just to contain at least 1 sort (s) of thing chosen from resin. As a result, the micro inorganic filler and the matrix resin of the binder 4 are bonded in a crosslinked structure, so that the storage stability, contamination resistance, flexibility, weather resistance, storage stability, and the like become good, and the resulting film has glossiness.

As said polyfunctional isocyanate compound, aliphatic, cycloaliphatic, aromatic, other polyfunctional isocyanate compounds, and these modified compounds are mentioned. As a specific example of a polyfunctional isocyanate compound, for example, tolylene diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, lysine diisocyanate, 2,2,4-trimethylhexyl methane Trimers such as diisocyanate, methylcyclohexanediisocyanate, biuret of 1,6-hexamethylene diisocyanate, isocyanurate and the like; Compounds in which two or more isocyanate groups formed by reaction of these polyfunctional isocyanates with polyhydric alcohols such as propanediol, hexanediol, polyethylene glycol, and trimethylolpropane are present; These polyfunctional isocyanate compounds include alcohols such as ethanol and hexanol, compounds having phenolic hydroxyl groups such as phenol and cresol, oximes such as acetoxime and methyl ethyl ketoxime, lactams such as ε-caprolactam and γ-caprolactam. The blocked polyfunctional isocyanate compound etc. which were sealed by blocking agents, such as the like, are mentioned. In addition, the said polyfunctional isocyanate compound can be used 1 type or in mixture of 2 or more types. Especially, in order to prevent the yellowing of a film, the yellowing-denatured polyfunctional isocyanate compound which does not have an isocyanate group directly bonded to the aromatic ring is preferable.

Examples of the melamine compound include dimethylol melamine, trimethylolmelamine, tetramethylolmelamine, pentamethylolmelamine, hexamethylolmelamine, isobutylether type melamine, n-butylether type melamine, butylated benzoguanamine and the like. Can be mentioned.

Examples of the aminoplast resins include alkyl etherified melamine resins, urea resins, benzoguanamine resins, and the like, or mixtures or co-condensates of these aminoplast resins can be used. This alkylether-ized melamine resin is obtained by methylolating an aminotriazine, and alkylating into cyclohexanol or a C1-C6 alkanol, and a butylether melamine resin, a methylether melamine resin, and a methylbutyl mixture. Melamine resin is typical. Moreover, a sulfonic acid catalyst for promoting hardening, for example, paratoluenesulfonic acid and its amine salt, can be used.

Moreover, what is necessary is just to contain isocyanate as a hardening | curing agent in a polymer composition. Thus, by containing an isocyanate hardener in a polymer composition, it becomes a stronger crosslinked structure and the film physical property of the light-diffusion layer 3 further improves. As this isocyanate, the same substance as the polyfunctional isocyanate compound is used. Especially, the aliphatic isocyanate which prevents yellow discoloration of a film is preferable.

Furthermore, the antistatic agent may be kneaded in the polymer composition. By forming the binder 4 from the polymer composition in which the antistatic agent is kneaded in this way, an antistatic effect is expressed on the light diffusion sheet 1, and thus, static electricity such as attracting dust and difficulty in stacking the prism sheet or the like is difficult. Problems caused by charging can be prevented. In addition, when the antistatic agent is coated on the surface, stickiness and soiling of the surface are produced. However, such harmful effects are reduced by kneading in the polymer composition. The antistatic agent is not particularly limited, and examples thereof include anionic antistatic agents such as alkyl sulfates and alkyl phosphates, cationic antistatic agents such as quaternary ammonium salts and imidazoline compounds, polyethylene glycols, and polyoxyethylene sorbitan. Nonionic antistatic agents, such as a monostearic acid ester and ethanolamides, and polymeric antistatic agents, such as polyacrylic acid, etc. are used. Among them, a cationic antistatic agent having a relatively high antistatic effect is preferable, and an antistatic effect can be achieved by addition of a small amount.

Next, the manufacturing method of the said light-diffusion sheet 1 is demonstrated. The manufacturing method of the said light-diffusion sheet 1 is a process of manufacturing the coating liquid for light-diffusion layer by mixing (a) the light-diffusion agent 5 with the polymer composition which comprises the binder 4, and (b) is light It has the process of laminating | stacking the light-diffusion layer 3 by apply | coating the coating liquid for diffusion layers on the surface of the base material layer 2. FIG.

The light diffusion sheet 11 of FIG. 2 includes a base layer 2, a light diffusion layer 3 laminated on the front side of the base layer 2, and a sticking prevention layer laminated on the back surface of the base layer 2 ( 12). Since this base material layer 2 and the light-diffusion layer 3 are the same as the light-diffusion sheet 1 shown in FIG. 1, the same code | symbol is attached | subjected and description is abbreviate | omitted. Therefore, the said light-diffusion sheet 11 can also improve weather resistance and heat resistance, maintaining transparency.

The sticking prevention layer 12 is provided with the binder 13 and the beads 14 disperse | distributing in this binder 13. This binder 13 also contains the same polymer composition as the binder 4 of the light diffusing layer 3 (that is, a polymer containing a polyol and a fine inorganic filler and having a glass transition temperature of 50 ° C. or higher and 80 ° C. or lower after curing). It is formed by crosslinking and curing the composition). As the material of the bead 14, the same one as the light diffusing agent 5 of the light diffusing layer 3 is used. In addition, although the thickness (thickness of the binder 13 part except the bead 14) of this sticking prevention layer 12 is not specifically limited, For example, it is about 1 micrometer or more and about 10 micrometers or less.

The blending amount of the beads 14 is relatively small, the beads 14 are separated from each other and dispersed in the binder 13, and many of the beads 14 protrude very little from the binder 13 at the lower end thereof. Therefore, when this light-diffusion sheet 11 is laminated | stacked with the light guide plate, the lower end of the protruding bead 14 will contact with the surface of a light guide plate, etc., and the front surface of the back surface of the light diffusion sheet 11 will not contact with a light guide plate. . As a result, sticking of the light diffusion sheet 11, the light guide plate, and the like is prevented, and the luminance unevenness of the screen of the liquid crystal display device is suppressed.

Since the light diffusion sheet 11 contains a micro inorganic filler in the polymer composition constituting the binder 13 of the anti-sticking layer 12, the heat diffusion, abrasion resistance, weather resistance, stain resistance, etc. of the light diffusion sheet 11 are included. It is possible to further increase the film physical properties of the film, thereby significantly suppressing warpage. Moreover, since the polymer composition which comprises the said binder 13 also contains a polyol as a base polymer, and since the glass transition temperature after hardening is 50 degreeC or more and 80 degrees C or less, heat resistance and weather resistance can be improved significantly.

Next, the manufacturing method of the light-diffusion sheet 11 is demonstrated. The manufacturing method of the light-diffusion sheet 11 includes the steps of (a) mixing the light-diffusing agent 5 with the polymer composition constituting the binder 4 to produce a coating liquid for the light-diffusion layer, and (b) Coating the light-diffusion layer coating liquid on the surface of the base material layer 2 to laminate the light-diffusion layer 3, and (c) mixing the beads 14 with the polymer composition constituting the binder 13 to prevent the sticking layer. And a step of laminating the sticking prevention layer 12 by coating the coating liquid for the anti-sticking layer on the back surface of the base layer 2.

Therefore, in the backlight unit for a liquid crystal display device having a lamp, a light guide plate, a light diffusion sheet, a prism sheet, and the like, which disperse light rays generated from the lamp and guide them to the surface side, the light diffusion sheet 1 is used as this light diffusion sheet. And 11), the light diffusion sheets 1 and 11 have high film properties such as high heat resistance and weather resistance, so that even when exposed to heating by a lamp or ultraviolet irradiation from the outside, it is difficult to cause warpage or yellowing. As a result, the glossiness of the screen of a liquid crystal display device and the fall of brightness are suppressed.

(Example)

Hereinafter, although this invention is explained based on an Example, this invention is not interpreted limitedly based on description of this Example.

Example 1

100 parts of binder resin blends ("Byron" of Toyo Boseki Co., Ltd.) of glass transition temperature 50 degrees C. which makes polyester polyol the base polymer, colloidal silica (Fuso Kagaku Kogyo Co., Ltd.) of 20 nm of average particle diameters "PLX" of acrylic resin bead (Sekisui Kasei Kogyo Co., Ltd.) of 15 micrometers of average particle diameters in the polymer containing 50 parts and 5 parts of hardening agents ("Colonate HX" of Nippon Polyurethane Co., Ltd.) -15 ") 50 parts are mixed, the coating liquid is produced, and this coating liquid is the surface of the 100-micrometer-thick transparent polyester base material layer (" A-4300 "of Toyo Boseki Co., Ltd.) by the roll coating method. 15 g / m <^2> (solid content conversion) was apply | coated to it, and the light-diffusion layer was formed by hardening. Moreover, in the said polymer composition, 10 parts of acrylic resin beads ("MBX-5" of Sekisui Kasehin Kogyo Co., Ltd.) of average particle diameter are mixed, a coating liquid is produced, and this coating liquid is roll-coated by the roll coating method. 3 g / m <^2> (solid content conversion) was apply | coated to the back surface of the said base material layer, and the sticking prevention layer was formed by hardening. This obtained the light-diffusion sheet of Example 1.

Example 2

Light diffusion of Example 2 in the same manner as in Example 1, except that a binder resin compound having a glass transition temperature of 60 ° C. using a polyester polyol as a base polymer (“Bylon” Series of Toyo Boseki Co., Ltd.) was used. A sheet was obtained.

Example 3

Light diffusion of Example 3 in the same manner as in Example 1, except that a binder resin compound having a glass transition temperature of 70 ° C. using a polyester polyol as a base polymer (“Byron” Series of Toyo Boseki Co., Ltd.) was used. A sheet was obtained.

[Example 4]

Light diffusion of Example 4 in the same manner as in Example 1, except that a binder resin compound having a glass transition temperature of 80 ° C. using a polyester polyol as a base polymer (“Byron” series of Toyo Boseki Co., Ltd.) was used. A sheet was obtained.

[Example 5]

100 parts of binder resin blend (50% of Daiichi Seka Kogyo Co., Ltd. "RUB memagium" series) after curing with acrylic polyol as a base polymer, colloidal silica (Fuso Kagaku) having an average particle diameter of 20 nm In the polymer composition containing 50 parts of "PL-1" of Kogyo Co., Ltd., and 5 parts of hardening agents ("PCTLN hardening agent of Daiichi Seka Kogyo Co., Ltd."), acrylic resin beads (Keshisei Sekisui of 15 micrometers of average particle diameters) A coating solution was prepared by mixing 3O parts of "MBX-15" manufactured by Kogyo Co., Ltd., and the coating solution was prepared by a roll coating method of a base material layer made of a transparent polyester having a thickness of 100 μm (Toyo Boseki Co., Ltd.) A-4300 ') was coated on the surface of 15 g / m ² (solid content conversion) and cured to form a light diffusion layer.In the polymer composition, acrylic resin beads (Sekisui Kasehin Kogyo Co., Ltd. Mix 10 parts of MBX-15 of Note) to make coating liquid. , By the coating liquid on a roll coating method and coating 3g / m ² (solid content conversion) on the back surface of the base layer, by curing to form a sticking layer. To obtain a fifth embodiment of the light-diffusing sheet by this.

Example 6

Example 6 was carried out in the same manner as in Example 5 except that a binder resin compound having a glass transition temperature of 60 ° C. using an acrylic polyol as a base polymer (“RUB memagium” series of Daiichi Seka Kogyo Co., Ltd.) was used. A light diffusion sheet was obtained.

Example 7

Example 7 was carried out in the same manner as in Example 5 except that a binder resin compound having a glass transition temperature of 70 ° C. using an acrylic polyol as a base polymer (“RUB memagium” series of Daiichi Seka Kogyo Co., Ltd.) was used. A light diffusion sheet was obtained.

Example 8

Example 8 was carried out in the same manner as in Example 5 except that a binder resin compound having a glass transition temperature of 80 ° C. using an acrylic polyol as a base polymer (“RUB memagium” series of Daiichi Seka Kogyo Co., Ltd.) was used. A light diffusion sheet was obtained.

Comparative Example 1

Light diffusion of Comparative Example 1 in the same manner as in Example 1, except that a binder resin compound having a glass transition temperature of 40 ° C. using a polyester polyol as a base polymer (“Byron” series of Toyo Boseki Co., Ltd.) was used. A sheet was obtained.

[Comparative Example 2]

Light diffusion of Comparative Example 2 in the same manner as in Example 1, except that a binder resin compound having a glass transition temperature of 85 ° C. using a polyester polyol as a base polymer (“Byron” series of Toyo Boseki Co., Ltd.) was used. A sheet was obtained.

Comparative Example 3

Comparative Example 3 was carried out in the same manner as in Example 5 except that a binder resin compound having a glass transition temperature of 45 ° C. using an acrylic polyol as a base polymer (“RUB memagium” series from Daiichi Seka Kogyo Co., Ltd.) was used. A light diffusion sheet was obtained.

[Comparative Example 4]

Comparative Example 4 was carried out in the same manner as in Example 5 except that a binder resin compound having a glass transition temperature of 85 ° C. using an acrylic polyol as a base polymer (“RUB memagium” series of Daiichi Seka Kogyo Co., Ltd.) was used. A light diffusion sheet was obtained.

[Evaluation of characteristics]

Using the light-diffusion sheets of Examples 1 to 8 and Comparative Examples 1 to 4, the handleability and heat resistance of these light-diffusion sheets were evaluated. The results are shown in Table 1 below.

The handleability is applied to the light diffusion sheet in the process of inspection, conveyance, assembly to the backlight unit, etc.

(1) ◎ When a wound or a film crack does not occur,

(2) Almost no scratches or film cracks occur.

(3) △ if the surface is likely to cause scratches,

(4) The case where a film crack occurs from a cross section ×

Evaluated as.

Heat resistance incorporates a light diffusion sheet into a 12.3 inch backlight unit, puts it into an environmental tester at 60 ° C. and 90% RH, turns on the lamp, and is for 1 hour, 2 hours, 4 hours, 8 hours, 12 hours and 24 hours. The light-diffusion sheet after elapses is judged from the occurrence state of the luminance unevenness of the backlight unit, and the presence or absence of warpage,

(1) When there is no luminance unevenness and warping does not occur at all,

(2) There is almost no luminance unevenness and very small warpage occurs.

It evaluated as.

As shown in Table 1, the higher the glass transition temperature of the binder, the better the heat resistance. On the other hand, the light diffusion sheets of Comparative Examples 1 and 3 having a glass transition temperature of less than 50 ° C. are easily scratched on the surface, and the film diffusion of the light diffusion sheets of Comparative Examples 2 and 4 having a glass transition temperature of more than 80 ° C. And handleability is falling. Therefore, the light diffusion sheets of Examples 1 to 8 having a glass transition temperature of 50 ° C. or higher and 80 ° C. or lower, in particular, the light diffusion sheets of Examples 2, 3, 6 and 7 whose glass transition temperature is 60 ° C. or higher and 70 ° C. or lower, have high heat resistance and handling. Showing a castle.

The light diffusing sheet of the present invention can improve heat resistance, thermal dimensional stability and weather resistance while maintaining high light transmittance, and it is difficult to cause warpage or yellowing even under heat generation or ultraviolet irradiation of a lamp, and the backlight using the light diffusing sheet The unit reduces the occurrence of luminance unevenness or luminance deterioration.

BRIEF DESCRIPTION OF THE DRAWINGS It is typical sectional drawing which shows the light-diffusion sheet which concerns on one Embodiment of this invention.

FIG. 2 is a schematic cross-sectional view showing a light diffusion sheet having a form different from that of FIG. 1.

3 (a) is a schematic perspective view showing a general edge light type backlight unit.

FIG.3 (b) is typical sectional drawing which shows a general light-diffusion sheet.

Claims (8)

It is provided with a transparent base material layer and the light-diffusion layer laminated | stacked on the surface side of this base material layer, This light diffusing layer contains a light diffusing agent in the binder, This binder is formed from a polymer composition containing a polyol and a micro inorganic filler, and has a glass transition temperature of 50 ° C or more and 80 ° C or less, The light diffusing sheet of which the average particle diameter of this micro inorganic filler is 5 nm or more and 5 Onm or less. The method according to claim 1, further comprising a sticking prevention layer laminated on the back side of the base material layer, This sticking prevention layer disperse | distributes beads in a binder, This binder is formed from a polymer composition containing a polyol and a micro inorganic filler, and has a glass transition temperature of 50 ° C or more and 80 ° C or less, The light-diffusion sheet characterized by the average particle diameter of this micro inorganic filler being 5 nm or more and 50 nm or less. The light diffusion sheet according to claim 1, wherein an organic polymer is fixed to a surface of the micro inorganic filler. 4. The light diffusion sheet according to claim 3, wherein the organic polymer contains 0.1 mmol / g or more and 50 mmol / g or less of an alkoxy group in the immobilized micro inorganic filler. 4. The light diffusion sheet according to claim 3, wherein the organic polymer has a hydroxyl group and contains one or two or more selected from a polyfunctional isocyanate compound, a melamine compound, and an amino flask resin in the polymer composition. The light diffusion sheet according to claim 1, wherein the polyol has a cycloalkyl group. The light diffusing sheet according to claim 1, wherein the polymer composition contains an aliphatic isocyanate as a curing agent. A backlight unit for a liquid crystal display device comprising a light diffusion sheet and dispersing light rays generated from a lamp to guide the surface side thereof. This light-diffusion sheet is equipped with the transparent base material layer and the light-diffusion layer laminated | stacked on the surface side of this base material layer, This light diffusing layer contains a light diffusing agent in the binder, This binder is formed from the polymer composition containing a polyol and a micro inorganic filler, and also has a glass transition temperature of 50 degreeC or more and 80 degrees C or less, The average particle diameter of this micro inorganic filler is 5 nm or more and 50 nm or less, The backlight unit for liquid crystal display devices characterized by the above-mentioned.