JP2005055861A - Optical member, light diffusing sheet, and reflector, light guide plate and prism sheet using optical member, and backlight unit using light diffusing sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical member having excellent light diffusing property, a light diffusing sheet having an excellent balance in light diffusing property and light transmitting property, and a backlight unit having both favorable light diffusing property and luminance. <P>SOLUTION: The optical member contains at least a resin and a silica-based material having 2 to 30 nm pore diameter and 0.3 to 3 ml/g pore volume. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical member and a light diffusion sheet, a reflector using the optical member, a light guide plate and a prism sheet, and a backlight unit using the light diffusion sheet. More specifically, the present invention relates to an optical member and a light diffusion sheet using a specific silica-based material, a reflection plate using the optical member, a light guide plate and a prism sheet, and a backlight unit for a liquid crystal display device using the light diffusion sheet. It is.

  In the liquid crystal display device, a backlight system in which a liquid crystal layer is illuminated from the back side is widely used, and a backlight unit such as an edge light type or a direct type is provided on the lower surface side of the liquid crystal layer. As shown in FIG. 1, the edge light type backlight unit basically includes a linear lamp 10 as a light source, and a rectangular plate-shaped light guide plate 12 arranged so that an end thereof is along the lamp 10. And a light diffusion sheet 13 disposed on the front surface side of the light guide plate 12 and a prism sheet 14 disposed on the upper side of the light diffusion sheet 13.

  The function of the backlight unit will be described. First, the light beam incident on the light guide plate 12 from the lamp 10 is reflected by the reflective dots or the reflection sheet 11 on the back surface of the light guide plate 12 and emitted from the surface of the light guide plate 12. The light beam emitted from the light guide plate 12 enters the light diffusion sheet 13, is diffused by the light diffusion sheet 13, and is emitted from the surface of the light diffusion sheet 13. Thereafter, the light beam emitted from the light diffusing sheet 13 enters the prism sheet 14 and is emitted as a light beam having a distribution that shows a peak in a substantially upward direction by the prism portion formed on the surface of the prism sheet 14. In this way, the light beam emitted from the lamp 10 is diffused by the light diffusion sheet 13 and refracted by the prism sheet 14 so as to show a peak in a substantially upward direction. Illuminate.

  In addition, on the surface side (liquid crystal panel side) of the prism sheet 14 for the purpose of relaxing the light condensing characteristics of the prism sheet 14 and protecting the prism portion or preventing sticking between the liquid crystal panel such as a polarizing plate and the prism sheet 14. Further, a light diffusion sheet 15 may be provided. Then, the light reaches the liquid crystal panel 17 through the bright line shading print 16 for adjusting the luminance, and the image of the liquid crystal panel is visually recognized.

The light diffusing sheets 13 and 15 are typically a laminate of a base material layer and a light diffusing layer. The light diffusing layer is a fine particle made of synthetic resin or glass in a synthetic resin binder. A structure in which is dispersed is generally used. And light diffusivity is expressed by the difference in refractive index between the binder resin and the fine particles. Conventionally, a diffusion material having an optical density (refractive index) higher than that of a binder resin has been generally used.
Several reports have recently been made on such light diffusion sheets and backlight units (for example, see Japanese Patent Application Nos. 2002-303708 and 2003-4912). However, when a material with a high refractive index is used, if the ratio of the diffusing material is increased in order to increase the light diffusibility, the optical density of the light diffusing sheet itself increases, and as a result, the light reflected to the light source side increases and the liquid crystal increases. There was a problem that the brightness on the panel side was lowered.

  An object of the present invention is to provide an optical member having excellent light diffusibility, a light diffusing sheet having a good balance between light diffusibility and light transmittance, a reflector, a light guide plate, and a prism sheet using the optical member. There is to do. Another object of the present invention is to provide a backlight unit in which both the light diffusibility and luminance of the light diffusion sheet are good.

As a result of intensive studies in view of the above problems, the present inventors have obtained a light diffusing sheet that balances light diffusibility and light transmittance by using a specific silica material having a low optical density as a light diffusing material. The present invention was found.
That is, the gist of the present invention resides in an optical member comprising at least a binder resin and a silica-based material having a pore diameter of 2 to 30 nm and a pore volume of 0.3 to 3 ml / g. .
Another gist of the present invention resides in a light diffusion sheet comprising at least the optical member.
Still another subject matter of the present invention is a light diffusion sheet comprising at least a binder resin and a silica-based material having a pore diameter of 2 to 30 nm and a pore volume of 0.3 to 3 ml / g. Exist.
Still another subject matter of the present invention is that a light diffusing material containing a silica-based material having a pore diameter of 2 to 30 nm and a pore volume of 0.3 to 3 ml / g is coated on a substrate. It exists in the light-diffusion sheet characterized by this.
Still another subject matter of the present invention is a backlight unit for a liquid crystal display device in which light emitted from a lamp is dispersed and guided to the surface side, and is provided with the above-mentioned optical member or light diffusion sheet. It exists in the backlight unit for display devices.
Still another subject matter of the present invention lies in a reflecting plate comprising at least the optical member.
Still another subject matter of the present invention lies in a light guide plate comprising at least the optical member.
Still another subject matter of the present invention resides in a prism sheet characterized by comprising at least the optical member.

  According to the backlight unit using the optical member and the light diffusing sheet of the present invention, the reflector using the optical member, the light guide plate and the prism sheet, the luminance can be improved without reducing the light diffusibility of the light diffusing sheet. Can be promoted.

The optical member of the present invention is a member having light diffusibility, light transmission property, or light reflection property. For example, a backlight unit used in a liquid crystal television as shown in FIG. 1, a rear projection television, It is suitably used as a member of a screen used for a microfilm reader, a signboard or the like. The optical member of the present invention has a binder resin and a silica-based material as essential elements, and light diffusibility from the difference in refractive index between the binder resin and the silica-based material by dispersing silica particles in the resin sheet or plate. Optical properties such as light transmittance and light reflectivity can be obtained.
Examples of such an optical member include a light diffusion sheet, a reflection plate (reflection sheet), a light guide plate (light guide sheet), and a prism sheet. Hereinafter, the present invention will be described in detail by taking a light diffusion sheet as an example.
The light diffusion sheet of the present invention contains at least a silica-based material having a pore diameter of 2 to 30 nm and a pore volume of 0.3 to 3 ml / g as a light diffusion material. In order to hold this silica-based material in a sheet shape, the silica-based material is formed on a transparent base material (for example, a molded body of a binder resin) obtained by molding a composition containing the silica-based material and a binder resin into a sheet shape. The one coated with is used.
In the light diffusing sheet of the present invention, the reason why the excellent effect of the present invention is exhibited by using the silica material used as the light diffusing material is not necessarily clear, but the pore volume of the silica material and the pore diameter are large. By being small, the ratio of the binder resin entering the pores of the silica-based material when mixed with the binder resin is suppressed. As a result, the apparent refractive index of the silica-based material and the apparent refractive index of the light diffusion sheet itself are reduced. Estimated to remain low.
The pore volume is preferably 0.6 ml / g or more, more preferably 0.8 ml / g or more, and preferably 1.6 ml / g or less. The pore volume is measured by a nitrogen gas absorption / desorption method.

The specific surface area of the silica-based material used in the present invention is preferably 200 m ³ / g or more, more preferably 300 m ³ / g or more, and preferably 1000 m ³ / g or less, 900 m ³ / g or less is more preferable, and 800 m ³ / g or less is particularly preferable. By setting it as the above preferable range, light diffusibility is further improved. The specific surface area is measured by the BET method by nitrogen gas adsorption / desorption.
Further, the average particle diameter of the silica-based material is preferably 1 μm or more, more preferably 2 μm or more, further preferably 25 μm or less, and further preferably 10 μm or less. By setting it as the said preferable range, dust generation can be suppressed and it can reduce that the other member which touches a light-diffusion sheet is damaged.
Furthermore, the weight average particle diameter of the silica-based material is usually 1 μm or more, preferably 1.5 μm or more, more preferably 2 μm or more, and usually 100 μm or less, preferably 20 μm or less, more preferably 8 μm or less. By setting it as the said range, when it is set as a light-diffusion sheet, it can prevent that transmitted light is colored yellow by Rayleigh scattering, and can prevent see-through from generating. Furthermore, since the silica-based material can exhibit high light diffusivity within the above range, the amount of the silica-based material used in manufacturing the light diffusing sheet can be reduced, and the light diffusing sheet can be easily manufactured. While being able to make it, it can raise the impact strength of the manufactured light-diffusion sheet.

The silica-based material is preferably crushed. The crushed state means that the particles are not spherical or substantially spherical, but more specifically, the 50% circularity corresponding to the cumulative particle size value obtained by the following formula is usually 0.1 or more, Preferably it is 0.3 or more, and usually 0.9 or less, preferably 0.8 or less.
Circularity = Circumference of a circle having the same area as the particle projection area / perimeter of the particle projection image By using a crushed silica-based material, the adhesion between the prism sheet and the light diffusion sheet can be weakened and interference occurs. Patterns can be reduced.

  Further, the mode diameter (Dmax) of the pores of the silica-based material is preferably 2 nm or more, preferably less than 20 nm, more preferably less than 15 nm, and still more preferably 13 nm or less. Further, the volume of the pores in the range of ± 20% of Dmax is preferably 50% or more of the total pore volume, and more preferably 60% or more. By setting it as the said preferable range, there is no unevenness by the place of a light-diffusion sheet, and it becomes a sheet | seat which has more uniform diffusibility. The most frequent diameter (Dmax) is determined from the isothermal desorption curve measured by the nitrogen gas adsorption / desorption method. P. Barrett, L.M. G. Joyner, P.M. H. Haklenda, J .; Amer. Chem. Soc. , Vol. 73, 373 (1951), the pore distribution curve calculated by the BJH method, that is, the differential nitrogen gas adsorption amount (ΔV / Δ (logd)) with respect to the pore diameter d (nm); It is obtained from the figure on which the volume is plotted. The silica-based material used in the present invention means that the pores are small and the pore distribution is sharp.

  The silica-based material used in the present invention is preferably an amorphous material, that is, a material that does not have a crystalline structure. By being amorphous, it means that when a silica-based material is analyzed by X-ray diffraction, a crystalline peak is not substantially observed. The term “crystalline” specifically refers to a substance having at least one crystal structure peak at a position exceeding 0.6 nanometer (nm Units d-spacing) in an X-ray diffraction pattern. By using an amorphous silica-based material, the water resistance of the light diffusion sheet is further improved.

Furthermore, the silica-based material has a molar ratio of Q ⁴ / Q ³ (Si (Q ³ ) in which ^three -OSi are bonded to Si (Q ⁴ ) in which ^four -OSi are bonded) in solid Si-NMR. The value of (shown) is preferably 1.3 or more. By using such a silica-based material, aggregation of the silica-based material is prevented, and a sheet having more uniform light diffusibility is obtained.

  Further, the metal impurity in the silica-based material is preferably 500 ppm or less, more preferably 100 ppm or less, and particularly preferably 10 ppm or less. By setting it as the said preferable range, even if it uses for a long period of time, colorless transparency can be maintained and the optical density as a sheet | seat can be restrained low. In the present invention, the metal impurity means a metal component excluding silicon constituting the skeleton of silica gel, and specifically includes an alkali metal, an alkaline earth metal, a transition metal, and the like. In particular, the total content of elements belonging to the group consisting of alkali metals and alkaline earth metals is preferably 300 ppm or less. In this specification, “ppm” represents a ratio based on mass.

  The optical density of the silica-based material is preferably 1.1 or more, more preferably 1.15 or more, and preferably 1.4 or less, more preferably 1.35 or less. Since the silica-based material used in the present invention is fine particles (particles) having voids, the refractive index cannot be measured directly. Therefore, in the present specification, a value calculated by the following method is used as a measure of the apparent refractive index (optical density) viewed as a bulk.

  The reason why the refractive index of the particles of the silica-based material can be reduced is that a large amount of air having a low refractive index is contained in the particles. The intra-particle air of the silica-based material of the present invention is equal to the total pore volume determined by nitrogen adsorption. Large voids between particles cannot be measured by nitrogen adsorption, and the pore volume measured by nitrogen adsorption is the pore volume in the particle. Therefore, when the refractive index of the silica-based material is 1.5, the refractive index of air is 1.0, and the true density of the silica-based material is 2, if the silica-based material has a pore volume a (ml / g) 1.5 * (1/2) / (a + 1/2) + 1.0 * a / (a + 1/2).

Further, when mixed with a binder resin, it is also effective to block the pores of the silica-based material so that the pores are not filled with the binder resin, thereby preventing the resin from entering the pores. Specifically, a method of coating the surface of silica-based material particles with colloidal inorganic nanoparticles made of silica, alumina, titania, zirconia, or a composite oxide thereof can be used. In addition to the above, it is also effective to use a silica sol produced by hydrolysis of alkoxysilane, various silane coupling agents or partial hydrolysates thereof alone or together with the above-mentioned oxide colloid. It is also effective to perform surface modification with a silane coupling agent having a large organic functional group having a molecular weight of 100 or more because the pore entrance / exit can be selectively blocked.
In addition, it is also effective to use a binder resin that does not easily enter the pores. A binder resin having a molecular size calculated from the molecular weight larger than the pore diameter is preferable.

The production method of the above-described silica-based material having each preferable physical property is not particularly limited, but is preferably produced through a step of hydrolyzing silicon alkoxide, more preferably tetramethoxysilane. Hereinafter, the production method of the silica-based material of the present invention will be described using silica gel as an example.
Further, it can be produced by applying a hydrothermal treatment method of a silica hydrogel obtained by hydrolyzing an alkali silicate or a silica hydrogel obtained by hydrolyzing a silicon alkoxide. It is something that does not mature before.

  As silicon alkoxide used as a raw material of the silica gel of the present invention, a lower alkyl group having 1 to 4 carbon atoms such as trimethoxysilane, tetramethoxysilane, triethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane and the like. Examples thereof include tri- or tetraalkoxysilane or oligomers thereof, and tetramethoxysilane, tetraethoxysilane and oligomers thereof are preferable. Since the above silicon alkoxide can be easily purified by distillation, it is suitable as a raw material for high-purity silica gel. The total content of metal impurities in the silicon alkoxide is usually preferably 100 ppm or less, more preferably 10 ppm or less. The content of metal impurities can be measured by the same method as the method for measuring impurities in silica gel.

  The hydrolysis of the silicon alkoxide is usually 2 mol or more, preferably 3 mol or more, particularly preferably 4 mol or more, and usually 20 mol or less, preferably 10 mol or less, particularly preferably 8 mol per mol of silicon alkoxide. It is carried out using submolar water. Hydrolysis of the silicon alkoxide produces silica hydrogel and alcohol. This hydrolysis reaction is usually from room temperature to about 100 ° C., but it can also be performed at a higher temperature by maintaining the liquid phase under pressure. The reaction time depends on the composition of the reaction solution (type of silicon alkoxide and molar ratio with water) and the reaction temperature, and since the time until gelation varies, it is not generally specified. The reaction time is the time when the fracture stress of the hydrogel does not exceed 6 MPa. In addition, hydrolysis can be accelerated | stimulated by adding an acid, an alkali, salts, etc. to a reaction system as a catalyst. However, the use of such additives is not very preferable in the production of the silica gel of the present invention because it causes aging of the produced hydrogel, as will be described later.

  In the above silicon alkoxide hydrolysis reaction, the silicon alkoxide is hydrolyzed to produce a silicate. Subsequently, a condensation reaction of the silicate occurs, the viscosity of the reaction solution rises, and finally gelates to form a silica hydrogel. Become. In order to produce the silica gel of the present invention, it is important to immediately perform a hydrothermal treatment without substantially aging so that the hardness of the hydrogel of silica produced by the above hydrolysis does not increase. Hydrolysis of silicon alkoxide produces a soft silica hydrogel. This hydrogel is stably aged or dried, and then hydrothermally treated to finally form a silica gel with controlled pore properties. In this method, silica gel having the physical property range defined in the present invention cannot be produced.

  Immediate hydrothermal treatment of the hydrogel of silica generated by hydrolysis without substantial aging described above means that the soft state immediately after the formation of the hydrogel of silica is maintained and the following conditions are maintained. It means to be subjected to hydrothermal treatment. It is not preferable to mix acid, alkali, salt, or the like into the silicon alkoxide hydrolysis reaction system or to make the hydrolysis reaction temperature too strict, since the aging of the hydrogel proceeds. Also, temperature and time should not be taken more than necessary in washing, drying, leaving, etc. in post-treatment after hydrolysis.

  As a means for specifically confirming the aging state of the hydrogel, the hardness of the hydrogel measured by a method as shown in the examples described later can be referred to. That is, silica gel having a physical property range defined in the present invention can be obtained by hydrothermally treating a soft hydrogel having a fracture stress of usually 6 MPa or less, preferably 3 MPa or less, more preferably 2 MPa or less.

  As conditions for this hydrothermal treatment, the state of water may be either liquid or gas, and it may be diluted with a solvent or other gas, but preferably liquid water is used. It is usually 0.1 times by weight or more, preferably 0.5 times by weight or more, particularly preferably 1 by weight or more, and usually 10 times by weight or less, preferably 5 times by weight or less, particularly preferably to silica hydrogel. 3 weight times or less of water is added to form a slurry, which is usually 40 ° C. or higher, preferably 50 ° C. or higher, and usually 250 ° C. or lower, preferably 200 ° C. or lower, usually 0.1 hours or longer, preferably 1 It is carried out for not less than time, usually not more than 100 hours, preferably not more than 10 hours. The water used for the hydrothermal treatment may contain lower alcohols, methanol, ethanol, propanol and the like. The hydrothermal treatment method is also applied to a material in which silica gel is formed on a substrate such as a particle, a substrate, or a tube in the form of a film or a layer for the purpose of making a membrane reactor or the like. It is also possible to perform hydrothermal treatment by changing the temperature conditions using a hydrolysis reaction reactor, but the optimum conditions are usually different between the hydrolysis reaction and the subsequent hydrothermal treatment. It is generally difficult to obtain the silica gel of the present invention.

  Under the above hydrothermal treatment conditions, increasing the temperature tends to increase the pore diameter and pore volume of the silica gel obtained. Further, with the treatment time, the specific surface area of the silica gel obtained tends to decrease gradually after reaching the maximum once. Based on the above tendency, it is necessary to appropriately select the conditions according to the desired physical property values, but since hydrothermal treatment is intended to change the physical properties of silica gel, it is usually at a higher temperature than the hydrolysis reaction conditions described above. It is preferable to do.

If the hydrothermal treatment temperature and time are set outside the above ranges, it will be difficult to obtain the silica gel of the present invention. For example, if the hydrothermal treatment temperature is too high, the pore diameter and pore volume of the silica gel become too large, and the pore distribution is also widened. Conversely, if the hydrothermal treatment temperature is too low, the resulting silica gel has a low degree of crosslinking, poor thermal stability, no peaks in the pore distribution, or the above-mentioned Q ^{4 in} solid Si-NMR. / Q ³ value becomes extremely small.

  When the hydrothermal treatment is performed in ammonia water, the same effect can be obtained at a lower temperature than in pure water. In addition, when hydrothermal treatment is performed in ammonia water, the silica gel finally obtained is generally hydrophobic as compared with the case of treatment in pure water, but is usually 30 ° C. or higher, preferably 40 ° C. or higher, and usually 250 Hydrophobic treatment at a relatively high temperature of not higher than ° C., preferably not higher than 200 ° C., particularly increases hydrophobicity. The ammonia concentration here is preferably 0.001% by weight or more, particularly preferably 0.005% by weight or more, and usually 10% by weight or less, particularly preferably 5% by weight or less.

  The hydrothermally treated silica hydrogel is usually dried at 40 ° C. or higher, preferably 60 ° C. or higher, and usually 200 ° C. or lower, preferably 120 ° C. or lower. The drying method is not particularly limited, and it may be a batch type or a continuous type, and can be dried under normal pressure or reduced pressure. If necessary, when a carbon component derived from the raw material silicon alkoxide is contained, it can be usually removed by baking at 400 to 600 ° C. Moreover, in order to control a surface state, it may bake at the temperature of a maximum of 900 degreeC. Furthermore, the final silica gel of the present invention is obtained by pulverizing and classifying as necessary.

  Silica gel with a crystal structure tends to have poor thermal stability in water, and gels are easy to hydrolyze silicon alkoxide in the presence of a template such as a surfactant used to form pores in the gel. Includes a crystal structure. Therefore, in the present invention, it is preferable to hydrolyze in the absence of a template such as a surfactant, that is, in a condition where there is no such an amount that it functions as a template.

The light diffusing material described above can be used by being applied to a substrate by being present in a binder resin, or can be used by being dispersed in a base material.
When the silica-based material is used by being applied to the substrate in the presence of the binder resin, the mass ratio of the silica-based material to the binder resin is usually 0.5% or more, preferably 1% or more, in addition, Preferably, it is used in the range of 3% or more, usually 50% or less, preferably 40% or less, more preferably 20% or less.

  Any resin can be used as the binder resin used in the light diffusion sheet, and examples thereof include acrylic resins, polyurethanes, polyesters, fluorine resins, silicone resins, polyamideimides, and epoxy resins. In this binder resin, for example, a reinforcing filler, a plasticizer, a stabilizer, a deterioration preventing agent, a dispersing agent, an antistatic agent and the like may be blended in addition to the above polymer. Since the binder resin needs to transmit light, it is transparent, and colorless and transparent is particularly preferable.

  In addition, when a silica-based material is coated on a transparent base material (binder resin molding) to form a light diffusion sheet, examples of the transparent base material include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene. It is made of synthetic resin such as polyolefin, cellulose acetate, weather resistant vinyl chloride. The transparent substrate is transparent because it is necessary to transmit light, and colorless and transparent is particularly preferable. The thickness of the transparent substrate is not particularly limited, but is preferably 50 μm or more and 250 μm or less.

The thickness of the layer containing the light diffusing material (that is, the silica-based material of the present invention) (hereinafter sometimes referred to as a light diffusing layer) is not particularly limited, but is preferably 1 μm or more and 30 μm or less.
Even in the case of forming a light diffusing layer by mixing a binder resin and a light diffusing material, in order to ensure its strength, in addition to the layer composed of the binder resin and the light diffusing material, it is transparent and hard. A base material may be laminated and used. As this base material, the same one as the above-mentioned transparent base material is used.
Moreover, you may have a light-diffusion layer on both sides of a base material layer.

  The light diffusing material can also be used by being dispersed in a transparent substrate. The transparent substrate is formed from a synthetic resin such as polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather-resistant vinyl chloride. The transparent substrate is transparent because it is necessary to transmit light, and colorless and transparent is particularly preferable. Moreover, the above-mentioned light diffusion layer obtained by further mixing a binder resin and a light diffusion material on a substrate containing such a light diffusion material can also be used in combination.

  The method for producing the light diffusing sheet is not particularly limited, but a method in which a silica-based material is blended into a polymer and melt-kneaded and molded using this as a base material. A base material containing material: a binder resin molded body) and drying to form a sheet; a method of applying a silica-based material together with fine particles such as colloidal silica onto a binder resin and a base material; Examples thereof include a method in which a silica-based material is dispersed in a monomer to be formed, this is coated on a substrate, and then the monomer is polymerized. Preferably, a silica-based material that is a light diffusing material is mixed with the resin composition constituting the binder resin to obtain a light diffusing layer coating solution, and this light diffusing layer coating solution is applied to the surface of the base material layer. To obtain a light diffusion sheet.

Among the light diffusion sheets thus obtained, the light diffusion sheet 15 installed on the upper part of the prism sheet (when the light reaches the light diffusion sheet 15, the light beam is directed almost directly above), a direct type If the light diffusion sheet installed on the surface side of the backlight unit is too diffusive, the brightness is reduced. Further, in order to facilitate gradation printing on the sheet surface, the surface is also required to be smooth. In that application, the haze value of the light diffusing sheet is usually 5% or more, preferably 7% or more, more preferably 10% or more, and usually 20% or less, preferably 18% or less, more preferably 15% or less. desirable.
Moreover, in the light diffusion sheet 13 installed on the upper part of the light guide plate 12, it is necessary that the light from the light source is sufficiently diffused and taken out to the surface. A desirable haze value in this case is usually 50% or more, preferably 60% or more, more preferably 65% or more, and usually 98% or less, preferably 95% or less, more preferably 92% or less.
Further, in various optical members other than the light diffusion sheets 13 and 15, a desirable haze value is usually 5% or more, preferably 7% or more, more preferably 10% or more, and usually 98% or less, preferably 95% or less, More preferably, it is 90% or less.
In addition, the “haze value” in the present specification is a value measured according to JIS-K-7105. The haze value in the above range of the light diffusing sheet 1 shows necessary and sufficient light diffusibility as a light diffusing sheet applied to today's backlight unit as described above.
Further, the optical density of the light diffusion sheet as a whole is preferably 1.8 or less, more preferably 1.7 or less, and preferably 1.3 or more, more preferably 1.4 or more. It is.

The light diffusion sheet of the present invention may include other optical functional layers (for example, an anisotropic diffusion layer, a prism layer, etc.) in addition to the base layer, the light diffusion layer, and another light diffusion layer. Is possible.
This light diffusion sheet is suitably used for a backlight unit.
When the light diffusing sheets 13 and 15 are provided in the backlight unit for a liquid crystal display device that guides the light emitted from the lamp 10 to the surface side, the necessary and sufficient light diffusibility of the light diffusing sheets 13 and 15 is provided. Accordingly, it is possible to prevent a decrease in luminance due to excessive diffusion and to improve the luminance as compared with the backlight unit including the conventional light diffusion sheets 13 and 15. Further, according to the backlight unit in which the light diffusion sheets 13 and 15 are disposed on the surface side of the prism sheet 14, sticking with the liquid crystal panel 17 on the surface side can be effectively prevented. Further, uniform brightness can be promoted by accurate brightness prevention printing. Further, the reduction of the thickness of the light diffusion sheets 13 and 15 promotes a reduction in the thickness of the backlight unit.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited to a following example, unless the summary is exceeded.

(1) Analysis method of silica gel 1) Pore volume and specific surface area BET nitrogen adsorption isotherm was measured by AS-6 manufactured by Cantachrome Co., and the pore volume and specific surface area were determined. Specifically, the pore volume is a value when the relative pressure P / P0 = 0.98, and the specific surface area is P / P0 = 0.1, 0.2, 0.3 nitrogen adsorption amount at three points. It was calculated using the BET multipoint method. Further, the pore distribution curve and the differential pore volume at the mode diameter (Dmax) were determined by the BJH method. The interval between each point of the relative pressure to be measured was 0.025.

2) Powder X-ray diffraction Using a RAD-RB apparatus manufactured by Rigaku Corporation, measurement was performed using CuKα as a radiation source.
The divergence slit was ½ deg, the scattering slit was ½ deg, and the light receiving slit was 0.15 mm.
3) Content of metal impurities To 2.5 g of sample, hydrofluoric acid was added and heated to dryness, and then water was added to make 50 ml. ICP emission analysis was performed using this aqueous solution. Sodium and potassium were analyzed by flame flame light method.

4) Solid Si-NMR (Q ⁴ / Q ³ value)
Measurement was performed using a Bruker MSL300 solid-state NMR apparatus with a resonance frequency of 59.2 MHz (7.05 Tesla) and a 7 mm CP / MAS (Cross Polarization / Magic Angle Spinning) probe. The rotation speed of the sample was 5000 rps.
(2) Evaluation method of sheet | seat The transmittance | permeability and haze value were measured using the Nippon Denshoku Industries haze meter (NDH-1001DP), and the average value of three points | pieces was used.

[Example 1]
(A) Manufacture and Evaluation of Silica Gel 1000 g of pure water was charged into a 5 L separable flask (with a jacket) made of glass and fitted with a water-cooled condenser open to the atmosphere at the top. While stirring at 80 rpm, 1400 g of tetramethoxysilane was charged into this over 3 minutes. The water / tetramethoxysilane molar ratio is about 6/1. Warm water at 50 ° C. was passed through the jacket of the separable flask. Stirring was continued, and the stirring was stopped when the contents reached the boiling point. Subsequently, hot water of 50 ° C. was passed through the jacket for about 0.5 hour to gel the sol produced. Thereafter, the gel was quickly taken out and pulverized through a nylon net having an opening of 600 microns to obtain a powdery wet gel (silica hydrogel). 450 g of this hydrogel and 450 g of pure water were charged into a 1 L glass autoclave and hydrothermally treated at 170 ° C. After hydrothermal treatment for a predetermined time, the liquid was cut through a nylon net having an opening of 100 microns, and the filter cake was dried under reduced pressure at 150 ° C. until it became a constant weight without washing with water to obtain silica gel as the silica-based material of the present invention.

The obtained silica gel was pulverized with a Hosokawa Micron AFG-200 machine, and a powder having an average particle diameter of 20 μm was obtained by aerodynamic classification.
When the obtained powder was observed with a scanning electron microscope, the particles were crushed particles having a fracture surface.

Table 1 shows the physical properties of the obtained silica gel. Further, no crystalline peak appeared in the powder X-ray diffraction diagram, and no peak on the low angle side (2θ ≦ 5 deg) due to the periodic structure was observed.
The impurity concentration of the obtained silica gel was 1 ppm or less for sodium, potassium, calcium, magnesium, titanium, chromium and zirconium, except that iron and aluminum were each detected at 2 ppm.

(B) Production and Evaluation of Light Diffusing Sheet 1) Production of Light Diffusing Sheet by Kneading Method To 495 g of polycarbonate resin, 0.12 g of heat stabilizer (ADK STAB 2112, Asahi Denka Kogyo Co., Ltd.) and 5 g of silica gel are mixed, The mixture was kneaded with a single screw extruder set at 280 ° C., extruded into a strand shape, and cut into pellets. A sheet of 15 cm × 15 cm × 0.5 cm (thickness) was produced from the pellets using a hot press machine under conditions of a press temperature of 250 ° C., a press pressure of 490 N / cm ² , and a press time of 5 minutes.
2) Manufacture of light diffusing sheet by coating method Acrylic resin (Dianar BR-80, Mitsubishi Rayon Co., Ltd.) 0.54 g was dissolved in 9.1 g of solvent mixed with dimethoxyethane: toluene = 3: 1, and further silica gel 0.36 g (40% by weight in the solid content) was added to obtain a solution having a solid content of 9% by weight. This was applied to a PET film (Diafoil T600E, 50 μm, Mitsubishi Chemical Polyester Film Co., Ltd.) using a bar coater # 14. The coated film was dried for 1 minute by a normal pressure dryer at 130 ° C.
3) Evaluation of light diffusion sheet As described above, the transmittance and haze value of each of the light diffusion sheet produced by the kneading method and the light diffusion sheet produced by the coating method were measured by the above-described methods.
The evaluation results are shown in Table 2.

[Example 2]
The same operation as in Example 1 was performed except that the hydrothermal treatment temperature was 50 ° C. Table 1 shows the physical properties of the obtained silica gel (silica-based material of the present invention). Table 2 shows the evaluation results of the produced light diffusion sheet.

In addition, the light-diffusion sheet of this invention is obtained also by melt-mixing said silica with a polyester resin and obtaining a sheet-like molded object.
Furthermore, the light-diffusion sheet of this invention is obtained also by expand | deploying the liquid which mixed the said silica and urethane resin on the board | substrate of a polyester sheet.

It is a schematic diagram which shows the backlight unit which concerns on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Light source lamp 11 Reflection sheet 12 Light guide plate 13 Light diffusion sheet on light source side 14 Prism sheet 15 Light diffusion sheet on liquid crystal panel side 16 Bright line shading printing 17 Liquid crystal panel

Claims (15)

  An optical member comprising at least a binder resin and a silica-based material having a pore diameter of 2 to 30 nm and a pore volume of 0.3 to 3 ml / g.   The optical member according to claim 1, wherein a resin composition containing at least the binder resin and the silica-based material is molded.   The optical member according to claim 1, wherein the silica-based material is coated on the binder resin molded body.   The optical member according to claim 1, wherein the silica-based material has a weight average particle diameter of 1 to 100 μm.   A light diffusion sheet comprising at least the optical member according to claim 1.   A light diffusion sheet comprising at least a binder resin and a silica-based material having a pore diameter of 2 to 30 nm and a pore volume of 0.3 to 3 ml / g.   A light diffusing sheet comprising a base material and a light diffusing material comprising a silica-based material having a pore diameter of 2 to 30 nm and a pore volume of 0.3 to 3 ml / g. The specific surface area of this silica type material is 200-1000 m < ³ > / g, The light-diffusion sheet of any one of Claims 5-7 characterized by the above-mentioned.   The light diffusion sheet according to any one of claims 5 to 8, wherein the silica-based material has an average particle diameter of 1 µm or more and 25 µm or less.   The light diffusion sheet according to any one of claims 5 to 9, wherein the silica-based material is crushed.   The optical diffusion sheet according to any one of claims 5 to 10, wherein the silica-based material has an optical density of 1.4 to 1.1.   A backlight unit for a liquid crystal display device for guiding light emitted from a lamp to the surface side by dispersing the light, comprising the light diffusing sheet according to any one of claims 5 to 11. Backlight unit for equipment.   A reflector comprising at least the optical member according to claim 1.   A light guide plate comprising at least the optical member according to claim 1. A prism sheet comprising at least the optical member according to claim 1.

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