JP2010123348A - Light guide plate, and method of manufacturing light guide plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guide plate achieving an excellent light diffusion property when used in a backlight unit such as a liquid crystal display device, and to provide a method of manufacturing the light guide plate. <P>SOLUTION: The light guide plate includes a light diffusion layer on a rear surface. The light diffusion layer contains hollow resin fine particles having a single pore structure. The hollow resin fine particle has an average particle diameter of 0.1-20 μm, and a porosity of 50-95 vol%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a light guide plate capable of realizing excellent light diffusibility when used in a backlight unit such as a liquid crystal display device. Furthermore, this invention relates to the manufacturing method of this light-guide plate.

In a liquid crystal display device that displays an image using light incident from the outside, a backlight unit is usually separately installed as a light source for irradiating the display panel with light. Such a backlight unit is classified into a direct method and an edge method depending on the position of the light source lamp, but the direct method is thick and requires many parts, whereas the edge method is It is excellent in terms of weight reduction and the like and is expected to expand in the future.

The edge method has a configuration in which a straight tubular light source lamp is arranged along the edge (edge) of a transparent light guide plate made of acrylic or the like.For example, a light diffusion layer such as a dot shape pattern is provided on the back surface of the light guide plate. There is known a backlight unit in which a reflection plate is installed on the light diffusion layer side of the light guide plate, and a diffusion sheet is installed on the surface side of the light guide plate. In the edge type backlight unit, the light emitted from the light source lamp is diffused by the light diffusion layer, and then enters the display panel installed on the diffusion sheet via the diffusion sheet. As described above, the edge type backlight unit has a structure in which the traveling direction of light from the light source lamp is changed and incident on the surface side, and thus the light diffusion performance of the light diffusion layer is extremely important.

As an edge-type backlight unit, for example, Patent Document 1 discloses the manufacture of a surface-emitting light-guiding panel in which a light diffusion layer containing ultrafine titanium oxide coated with an organic fluorescent derivative is formed on the back surface of a light-guiding plate. A method is disclosed.
Patent Document 2 discloses a method for manufacturing a light guide plate for a backlight unit in which a light diffusion layer containing a light scattering or irregularly reflective material such as glass beads is formed on the back surface.

In such a light guide plate, as a method of forming a light diffusion layer, a method of applying a dispersion paste containing light diffusing particles on a light guide plate by screen printing is performed. The method of Document 2 has a problem in that the light diffusing particles in the dispersion paste are poorly dispersible, and as a result, the obtained light diffusing layer cannot exhibit a desired light diffusing effect.
JP-A-5-303017 JP 2003-344661 A

An object of this invention is to provide the light-guide plate which can implement | achieve the outstanding light diffusibility when it uses for backlight units, such as a liquid crystal display device. Furthermore, an object of this invention is to provide the manufacturing method of this light-guide plate.

The present invention is a light guide plate having a light diffusion layer on the back surface, wherein the light diffusion layer contains hollow resin fine particles having a single-hole structure, and the hollow resin fine particles have an average particle diameter of 0.1 to 20 μm. In addition, the light guide plate has a porosity of 50 to 95% by volume.
Hereinafter, the present invention will be described in detail.

When the hollow resin fine particles having a predetermined structure are used as the light diffusing particles used in the light diffusing layer, the present inventors remarkably improve the dispersibility in the dispersion paste for forming the light diffusing layer, As a result, it was found that the obtained light diffusion layer exhibits an excellent light diffusion effect, and the present invention has been completed.

The light guide plate of the present invention has a light diffusion layer on the back surface.
In this specification, in a light guide plate used in a backlight unit such as a liquid crystal display device, a surface on which a display panel displaying an image is located is referred to as a “front surface”, and a surface on the opposite side is referred to as a “back surface”. In the present specification, the “light diffusion layer” refers to a layer formed to diffuse light incident from the light source lamp into the light guide plate.

The light diffusion layer contains the hollow resin fine particles. By containing the hollow resin fine particles, the light diffusion layer exhibits excellent light diffusibility.

The hollow resin fine particles have a single pore structure.
In the present specification, the “single pore structure” refers to a structure having only one closed void, not including a plurality of voids such as a porous shape. Because of the single pore structure, the hollow resin fine particles have voids excellent in hermeticity, and when mixed with other components such as a binder for various uses, binders into the voids, etc. Intrusion of other components is suppressed. Therefore, for example, when the light guide plate of the present invention is produced using the hollow resin fine particles, the void ratio of the hollow resin fine particles contained in the obtained light diffusion layer is less likely to decrease due to the intrusion of other components. Therefore, the light diffusion layer can exhibit excellent light diffusibility.

The hollow resin fine particles have a lower limit of the average particle diameter of 0.1 μm and an upper limit of 20 μm. When the average particle size is less than 0.1 μm, the hollow resin fine particles are aggregated, making handling difficult. When the average particle diameter exceeds 20 μm, the particle diameter is too large, so that it is difficult to apply the fine particle-dispersed paste for screen printing thinly, which is not suitable for screen printing. A preferable lower limit of the average particle diameter is 0.2 μm, and a preferable upper limit is 10 μm. A more preferable lower limit is 0.5 μm, and a more preferable upper limit is 7 μm.

The hollow resin fine particles have a porosity lower limit of 50% by volume and an upper limit of 95% by volume. When the porosity is less than 50% by volume, it is difficult to obtain a light guide plate having desired luminance or light diffusibility. When the porosity exceeds 95% by volume, it is difficult to maintain the shape or strength of the hollow resin fine particles. The minimum with said preferable porosity is 60 volume%, a preferable upper limit is 90 volume%, a more preferable minimum is 65 volume%, and a more preferable upper limit is 85 volume%.
In the present specification, the “porosity” refers to the volume ratio of the void portion excluding the core agent in the total volume of the hollow resin fine particles. The porosity is measured, for example, based on a photograph taken with a transmission electron microscope, the average particle diameter (outer diameter) and the average inner pore diameter, and the ratio between the volume of the void portion and the volume of the hollow resin fine particles is determined. It is measured by calculating.

The hollow resin fine particles have a preferred lower limit of the aspect ratio of 0.99 and a preferred upper limit of 1.1. When the aspect ratio is outside the above range, when the light guide plate of the present invention is produced using the hollow resin fine particles, the hollow resin fine particles may be crushed and / or sag in the production process. The aspect ratio is a value obtained by dividing the length of the major axis by the length of the minor axis. The closer the value is to 1, the closer the shape of the hollow resin fine particle is to a true sphere. A more preferable lower limit of the aspect ratio is 1.00, and a more preferable upper limit is 1.05.

The hollow resin fine particles have a preferable lower limit of 1 N / mm ² and a preferable upper limit of 1000 N / mm ² when compressive modulus (hereinafter also referred to as 10% K value) when the diameter at 23 ° C. is displaced by 10%. When the 10% K value is less than 1 N / mm ² , when screen printing is performed using the dispersion paste of the hollow resin fine particles, the hollow resin fine particles are applied when the paste is applied or the coating film is dried. May be crushed. When the 10% K value exceeds 1000 N / mm ² , when screen printing is performed using the dispersion paste of hollow resin fine particles, the flexibility of the coating film may be lost and cracks may occur.

The 10% K value is a smooth end surface of a diamond column having a diameter of 50 μm using a micro compression tester (for example, “PCT-200” manufactured by Shimadzu Corporation), and the compression rate of the hollow resin fine particles is 0. Compressed with a maximum test load of 10 g at a rate of .27 g / sec and a value obtained by the following formula.
^{K = (3 / √2) ·} F · S -3/2 · R -1/2
In the formula, F represents a load value (kg) in 10% compression deformation of fine particles, S represents a compression displacement (mm) in 10% compression deformation of fine particles, and R represents a radius (mm) of the fine particles.

The hollow resin fine particles preferably do not change in average particle diameter without being heated and expanded at 30 to 200 ° C. When screen printing is performed using a dispersion paste of hollow resin fine particles that expands by heating at 30 to 200 ° C., when the core agent is removed by drying after printing, unevenness of the printed surface becomes severe due to the expanded hollow resin fine particles. In some cases, it may be difficult to control light diffusibility. Even if the hollow resin fine particles are heated at a predetermined temperature of 30 to 200 ° C. for 10 minutes or more, the change rate of the average particle diameter is preferably within 100 ± 5%.

The hollow resin fine particles may have a core agent.
A preferable lower limit of the boiling point of the core agent is 30 ° C, and a preferable upper limit is 200 ° C. When the boiling point of the core agent is less than 30 ° C., boiling occurs at room temperature, and handling may be extremely difficult. When the boiling point of the core agent exceeds 200 ° C., the core agent cannot be easily evaporated by heating or the like, and a desired single pore structure may not be produced. A more preferable lower limit of the boiling point of the core agent is 50 ° C., and a more preferable upper limit is 160 ° C. In the present specification, the boiling point refers to the boiling point at 1 atm.

The core agent is not particularly limited as long as it is a substance that can be easily evaporated by heating, for example, n-pentane, n-hexane, cyclohexane, n-heptane, n-octane, isooctane, benzene, toluene, Xylene, water, dichloromethane, chloroform, methanol, ethanol, n-propanol, isopropyl alcohol, 1-butanol, 2-butanol, isobutyl alcohol, t-butyl alcohol, n-pentanol, isopentyl alcohol, neopentyl alcohol, octanol, Diethyl ether, dioxane, tetrahydrofuran, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, nitromethane, nitroethane, acetone Nitrile, aniline, 2-pyrrolidone, and water.

The method for producing the hollow resin fine particles is not particularly limited. For example, a non-polymerizable substance is added to a monomer solution containing a crosslinkable monomer, a polymerizable monomer, and a polymerization initiator, and the mixture is stirred in the monomer solution. A primary emulsification step for preparing a primary emulsion in which droplets made of a non-polymerizable substance are dispersed, the primary emulsion is added to and stirred with a solution insoluble in the monomer solution, and the monomer solution is insoluble in the solution. And a secondary emulsifying step for preparing a secondary emulsified liquid in which droplets composed of the monomer solution containing the non-polymerizable substance are dispersed, and a polymerization step for polymerizing the monomers in the monomer solution. .

In the primary emulsification step, the crosslinkable monomer is not particularly limited. For example, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1,6-hexanediol di ( (Meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethane tri (meth) acrylate, tetramethylolpropane tetra (meth) acrylate, diallyl phthalate and its isomers, triallyl isocyan Examples include nurate and its derivatives, divinylbenzene. These crosslinkable monomers may be used independently and may use 2 or more types together. In the present specification, (meth) acrylate means methacrylate and / or acrylate.

In the primary emulsification step, the amount of the crosslinkable monomer added relative to the total amount of the primary emulsion is preferably 25% by weight and preferably 50% by weight. When the addition amount of the crosslinkable monomer with respect to the total amount of the primary emulsion is less than 25% by weight, crosslinking may be insufficient, and thus the obtained hollow resin fine particles may have a desired single-pore structure or strength. In some cases, the resulting hollow resin particles may be crushed or sag when heated.

In the primary emulsification step, the polymerizable monomer is not particularly limited. For example, alkyl (meth) acrylate monomer, polar group-containing (meth) acrylic monomer, aromatic vinyl monomer, vinyl ester monomer, halogen-containing monomer, polydimethylsiloxane Examples include macromonomer, vinyl pyridine, ethylene, propylene, polyoxyethylene glycol (meth) acrylate, polyoxypropylene glycol (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, and N-vinylpyrrolidone.
Examples of the alkyl (meth) acrylate monomer include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, cumyl (meth) acrylate, cyclohexyl (meth) acrylate, and myristyl (meth) ) Acrylate, palmityl (meth) acrylate, stearyl (meth) acrylate, and isobornyl (meth) acrylate. Examples of the polar group-containing (meth) acrylic monomer include (meth) acrylonitrile, (meth) acrylamide, (meth) acrylic acid, glycidyl (meth) acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate. . Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, p-methylstyrene, and p-chlorostyrene. Examples of the vinyl ester monomer include vinyl acetate and vinyl propionate. Examples of the halogen-containing monomer include vinyl chloride and vinylidene chloride.
Among these, since the refractive index is relatively low, an alkyl (meth) acrylate monomer and a polydimethylsiloxane macromonomer are preferable. These polymerizable monomers may be used alone or in combination of two or more.

In the primary emulsification step, the polymerization initiator is not particularly limited, and can be appropriately selected according to the type of monomer component used. Examples thereof include organic peroxides, azo initiators, and redox initiators. The organic peroxide is not particularly limited, and examples thereof include benzoyl peroxide, lauroyl peroxide, dibutyl peroxydicarbonate, and α-cumyl peroxyneodecanoate. The azo initiator is not particularly limited, and examples thereof include azobisisobutyronitrile.

In the primary emulsification step, the non-polymerizable substance is liquid at the reaction temperature between the crosslinkable monomer and the polymerizable monomer, does not polymerize by the polymerization reaction, and can be easily evaporated by heating or the like. If it is a substance, it will not specifically limit, For example, the substance similar to the said core agent is mentioned.

In the primary emulsification step, the amount of the non-polymerizable substance added to the total amount of the primary emulsion is preferably 50% by weight and preferably 95% by weight. When the amount of the non-polymerizable substance added to the total amount of the primary emulsion is less than 50% by weight, the outer shell of the resulting hollow resin fine particles becomes thick and the porosity decreases. When the addition amount of the non-polymerizable substance with respect to the total amount of the primary emulsion exceeds 95% by weight, it may be difficult to maintain the shape of the obtained hollow resin fine particles or to ensure the strength.

In the primary emulsification step, the monomer solution containing the crosslinkable monomer, polymerizable monomer and polymerization initiator preferably further contains a lipophilic emulsifier. The lipophilic emulsifier has a role of improving the emulsion stability of the monomer solution. The lipophilic emulsifier is not particularly limited, and examples thereof include polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, glycerin fatty acid ester, polyglycerin fatty acid ester, and propylene glycol fatty acid ester. It is done.

In the secondary emulsification step, the monomer solution and the insoluble solution are not particularly limited, and examples thereof include the same substances as the non-polymerizable substance. Further, as the solution insoluble in the monomer solution, a substance different from the non-polymerizable substance may be used.

In the primary emulsification step and the secondary emulsification step, the monomer solution or the solution insoluble in the monomer solution may further contain an inorganic salt or a water-soluble polymerization inhibitor. When the monomer solution or a solution insoluble in the monomer solution contains an inorganic salt or a water-soluble polymerization inhibitor, generation of new particles due to polymerization of the monomer solution at a place other than droplets is suppressed.
The said inorganic salt reduces the solubility of a monomer component and suppresses superposition | polymerization. The inorganic salt is not particularly limited, and examples thereof include sodium chloride, calcium chloride, and sodium carbonate. The water-soluble polymerization inhibitor suppresses polymerization of the monomer component in the solvent. The water-soluble polymerization inhibitor is not particularly limited, and examples thereof include sodium sulfite, copper chloride, iron chloride, titanium chloride, and hydroquinone.

In the primary emulsification step and the secondary emulsification step, the stirring method is not particularly limited, and examples thereof include conventionally known methods using a homomixer, a biomixer, an omni mixer, an ultrasonic homogenizer, and a microfluidizer.

In the polymerization step, the method for polymerizing the monomer in the monomer solution is not particularly limited and can be appropriately selected according to the type of monomer component to be used, but heating is usually preferable. Through the polymerization step, the monomer in the monomer solution is polymerized to form the outer shell of the hollow resin fine particles.

According to the method for producing hollow resin fine particles having the primary emulsification step, the secondary emulsification step and the polymerization step, a slurry having the hollow resin fine particles in a solution insoluble in the monomer solution is obtained. You may perform the process of removing a solution insoluble with a monomer solution. The method for removing the monomer solution and the insoluble solution is not particularly limited, and examples thereof include a method of drying by heating and a method of reducing the pressure of the entire reaction system.

According to the method for producing hollow resin fine particles as described above, the hollow resin fine particles have a single-pore structure, the average particle diameter is 0.1 to 20 μm, and the porosity is 50 to 95% by volume. Hollow resin fine particles can be produced.

The light diffusion layer preferably contains a binder resin for forming a layer in addition to the hollow resin fine particles. Examples of the binder resin for forming the layer include acrylic resin, polyurethane, polyester, fluorine resin, silicone resin, polyamideimide, and epoxy resin.

The light diffusion layer is preferably formed of, for example, a dot-shaped pattern. The dot shape is not limited to a circular shape, and may be, for example, an elliptical shape or a polygonal shape.
In addition, since the brightness of light decreases as the distance from the light source lamp increases, the light diffusion of the light diffusion layer is usually increased as the distance from the light source lamp increases in order to make the brightness of the light guided to the display panel uniform over the entire display panel surface. Ingenuity to improve performance is made. Therefore, for example, it is preferable to increase the area of the dot shape as the distance from the light source lamp increases, or to increase the number of dot shapes per unit area as the distance from the light source lamp increases.

The preferable lower limit of the thickness of the light diffusion layer is 1 μm, and the preferable upper limit is 500 μm. When the thickness of the light diffusion layer is less than 1 μm, a light guide plate having sufficient light diffusibility may not be obtained. When the thickness of the light diffusion layer exceeds 500 μm, the luminance of the obtained light guide plate may be insufficient.

The light guide plate of the present invention is preferably made of, for example, a transparent synthetic resin. The transparent synthetic resin is not particularly limited, and examples thereof include (meth) acrylic resin, polycarbonate resin, polyester resin, and polystyrene resin.

As a method for producing the light guide plate of the present invention, for example, a step of preparing a fine particle dispersed paste containing hollow resin fine particles having a single-hole structure, a binder resin, and an organic solvent, and the fine particle dispersed paste of the light guide plate substrate Examples thereof include a method having a step of forming a light diffusion layer by screen printing on the back surface.
A method of manufacturing a light guide plate having a light diffusion layer on the back surface, the step of preparing a fine particle dispersed paste containing hollow resin fine particles having a single-hole structure, a binder resin and an organic solvent, and the fine particle dispersed paste as a light guide plate And having a step of forming a light diffusion layer by screen printing on the back surface of the substrate, and the hollow resin fine particles have an average particle diameter of 0.1 to 20 μm and a porosity of 50 to 95% by volume. A method for manufacturing the light guide plate is also one aspect of the present invention.

The method for producing a light guide plate of the present invention includes a step of preparing a fine particle-dispersed paste containing hollow resin fine particles having a single-hole structure, a binder resin, and an organic solvent.

The preferable lower limit of the content of the hollow resin fine particles in the fine particle dispersed paste is 10% by weight, and the preferable upper limit is 95% by weight. When the content of the hollow resin fine particles is less than 10% by weight, a light guide plate having sufficient light diffusibility may not be produced. When the content of the hollow resin fine particles exceeds 95% by weight, a light guide plate having sufficient luminance and uniform surface emission may not be produced.

The organic solvent is not particularly limited, and examples thereof include methanol, ethanol, n-butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, N, N-dimethylformamide, tetrahydrofuran, and toluene.

The method for preparing the fine particle-dispersed paste is not particularly limited, and examples thereof include conventionally known methods such as a method of mixing each component using a mixer such as a homogenizer, a ball mill, a blender mill, or a three roll mill. More specifically, for example, after the binder resin and the organic solvent are mixed using a mixer, the hollow resin fine particles are added and further mixed using a mixer.

The method for producing a light guide plate of the present invention includes a step of screen-printing the fine particle dispersed paste on the back surface of the light guide plate base material to form a light diffusion layer.
The light guide plate base material is not particularly limited as long as it is a light guide plate base material used in a backlight unit such as a liquid crystal display device. For example, a light guide plate base material made of a transparent synthetic resin such as (meth) acrylic resin is used. Can be mentioned.

As a method for forming a light diffusion layer by screen printing the fine particle dispersed paste on the back surface of the light guide plate base material, for example, a cloth made of silk, chemical fiber or the like is strongly stretched to form a screen, and the fine particle dispersed paste is used as the screen. And a method of forming a light diffusion layer composed of the hollow resin fine particles by applying to the printed portion on the back surface of the light guide plate substrate and then drying by heating.

ADVANTAGE OF THE INVENTION According to this invention, the light-guide plate which can implement | achieve the outstanding light diffusibility when it uses for backlight units, such as a liquid crystal display device, can be provided. Furthermore, according to this invention, the manufacturing method of this light-guide plate can be provided.

Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited only to these examples.

Example 1
(1) Production of hollow resin fine particles A 20 parts by weight of acrylonitrile as a polymerizable monomer and 50 parts by weight of polypropylene glycol dimethacrylate as a crosslinkable monomer (“Blenmer PDP-400”, manufactured by NOF Corporation, number of polyoxypropylene units = 7) And 30 parts by weight of trimethylolpropane triacrylate, 0.25 parts by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator, and 2 parts by weight of glycerin monostearate as a lipophilic emulsifier are mixed and stirred. A solution was prepared.

A sodium chloride / sodium nitrite aqueous solution was prepared by adding 1% by weight of sodium chloride to ion-exchanged water and 0.02% by weight of sodium nitrite as a water-soluble polymerization inhibitor. Next, 100 parts by weight of a sodium chloride / sodium nitrite aqueous solution was added to the monomer solution, and the mixture was stirred with a stirring and dispersing device to prepare a primary emulsion of water-in-oil (W / O) emulsion.

Thereafter, the obtained primary emulsion is added to 600 parts by weight of an ion exchange aqueous solution containing 1% by weight of polyvinyl alcohol (PVA) as a dispersing agent and 0.02% by weight of sodium nitrite as a water-soluble polymerization inhibitor, and stirred and dispersed. By stirring using the apparatus, a secondary emulsion of a (W / O / W) type composite emulsion in which oil droplets enclosing water was dispersed in an aqueous medium was obtained.

Using a 20-liter polymerization vessel equipped with a stirrer, jacket, reflux condenser and thermometer, the inside of the polymerization vessel was depressurized and deoxygenated in the vessel, and then the atmosphere inside the polymerization vessel was changed to a nitrogen atmosphere by purging with nitrogen. . Thereafter, the obtained secondary emulsion was added all at once, and the polymerization vessel was heated to 60 ° C. to initiate polymerization. After polymerization for 4 hours, the temperature was raised to 80 ° C., and after an aging period of 1 hour, the polymerization vessel was cooled to room temperature to obtain a slurry containing water-containing hollow resin fine particles A. The solvent of the obtained slurry was replaced with isopropanol (IPA) using a centrifuge to obtain an isopropanol (IPA) dispersion slurry of water-containing hollow resin fine particles A.

(2) Manufacture of light guide plate 100 parts by weight of slurry containing water-containing hollow resin fine particles A (30 parts by weight of hollow resin fine particles), 10 parts by weight of acrylic resin as binder resin, and 10 parts by weight of toluene as organic solvent Were mixed and stirred to obtain a fine particle dispersion paste for screen printing.
Using the obtained fine particle dispersion paste, the projections and depressions of the fine line stripes and the corrugated protrusions are printed on the back surface of a commercially available acrylic plate substrate by a screen printer, and then dried at 70 ° C. for 5 minutes to form a light diffusion layer A light guide plate having was obtained.

(Example 2)
(1) Preparation of hollow resin fine particle B 10 parts by weight of methacrylic acid as a polymerizable monomer, polyethylene glycol dimethacrylate (“Blenmer PDE-50R”, manufactured by NOF Corporation, number of polyoxyethylene units = 1) as a crosslinkable monomer 25 weight Parts, 25 parts by weight of neopentyl glycol diacrylate, 40 parts by weight of trimethylolpropane triacrylate, 400 parts by weight of normal hexane as a non-polymerizable substance, and 0.3 parts by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator The parts were mixed and stirred to prepare a normal hexane dispersion type primary emulsion.

Thereafter, the obtained primary emulsion was added to 370 parts by weight of an ion exchange aqueous solution containing 1% by weight of polyvinyl alcohol (PVA) as a dispersant and 0.02% by weight of sodium nitrite as a water-soluble polymerization inhibitor, and stirred and dispersed. By stirring using the apparatus, a secondary emulsion of a composite emulsion in which oil droplets containing normal hexane were dispersed in an aqueous medium was obtained.

Using a 20-liter polymerization vessel equipped with a stirrer, jacket, reflux condenser and thermometer, the inside of the polymerization vessel was depressurized and deoxygenated in the vessel, and then the atmosphere inside the polymerization vessel was changed to a nitrogen atmosphere by replacing with nitrogen. . Thereafter, the obtained secondary emulsion was added all at once, and the polymerization vessel was heated to 60 ° C. to initiate polymerization. After polymerization for 4 hours, the polymerization vessel was cooled to room temperature to obtain a slurry containing normal hexane-containing hollow resin fine particles B. The solvent of the obtained slurry was replaced with isopropanol (IPA) using a centrifuge, and an isopropanol (IPA) dispersion slurry of normal hexane-containing hollow resin fine particles B was obtained.

(2) Manufacture of light guide plate 350 parts by weight of slurry containing normal hexane-containing hollow resin fine particles B (42 parts by weight of hollow resin fine particles B), 15 parts by weight of acrylic resin as binder resin, and 13 parts by weight of toluene as organic solvent The parts were mixed and stirred to obtain a fine particle dispersion paste for screen printing.
Using the obtained fine particle dispersion paste, the projections and depressions of the fine line stripes and the corrugated protrusions are printed on the back surface of a commercially available acrylic plate substrate by a screen printer, and then dried at 70 ° C. for 5 minutes to form a light diffusion layer A light guide plate having was obtained.

(Example 3)
(1) Preparation of hollow resin fine particles C 15 parts by weight of methacrylonitrile and 15 parts by weight of methyl methacrylate as polymerizable monomers, and polyethylene glycol dimethacrylate (“Blenmer PDE-50R”, manufactured by NOF Corporation, polyoxy as a crosslinkable monomer Number of ethylene units = 1) 10 parts by weight, 30 parts by weight of neopentyl glycol diacrylate, 30 parts by weight of trimethylolpropane triacrylate, 145 parts by weight of cyclohexane as a non-polymerizable substance, 40 parts by weight of ethyl acetate, and as a polymerization initiator 0.3 parts by weight of azobisisobutyronitrile (AIBN) was mixed and stirred to prepare a cyclohexane-ethyl acetate dispersion type primary emulsion.

Thereafter, the obtained primary emulsion is added to 300 parts by weight of an ion exchange aqueous solution containing 1% by weight of polyvinyl alcohol (PVA) as a dispersing agent and 0.02% by weight of sodium nitrite as a water-soluble polymerization inhibitor, and stirred and dispersed. By stirring using an apparatus, a secondary emulsion of a composite emulsion in which oil droplets containing cyclohexane-ethyl acetate were dispersed in an aqueous medium was obtained.

Using a 20-liter polymerization vessel equipped with a stirrer, jacket, reflux condenser and thermometer, the inside of the polymerization vessel was depressurized and deoxygenated in the vessel, and then the atmosphere inside the polymerization vessel was changed to a nitrogen atmosphere by purging with nitrogen. . Thereafter, the obtained secondary emulsion was added all at once, and the polymerization vessel was heated to 60 ° C. to initiate polymerization. After polymerization for 4 hours, the polymerization vessel was cooled to room temperature to obtain a slurry containing cyclohexane-ethyl acetate-containing hollow resin fine particles C. The obtained dispersion was dried using a spray dryer to obtain dry hollow resin fine particles C that did not enclose the liquid.

(2) Manufacture of light guide plate 40 parts by weight of dry hollow resin fine particles C obtained, 10 parts by weight of acrylic resin as binder resin, and 10 parts by weight of toluene as organic solvent were mixed, and stirred, for screen printing. A fine particle dispersion paste was obtained.
Using the obtained fine particle dispersion paste, the projections and depressions of the fine line stripes and the corrugated protrusions are printed on the back surface of a commercially available acrylic plate substrate by a screen printer, and then dried at 70 ° C. for 5 minutes to form a light diffusion layer A light guide plate having was obtained.

(Comparative Example 1)
40 parts by weight of a true spherical hollow glass bubble (“Microcell” manufactured by SOViTEC, average particle diameter of 15 μm), 30 parts by weight of an acrylic resin as a binder resin, and 30 parts by weight of toluene as an organic solvent are mixed and stirred. As a result, a fine particle dispersion paste for screen printing was obtained.
Using the obtained fine particle dispersion paste, the projections and depressions of the fine line stripes and the corrugated protrusions are printed on the back surface of a commercially available acrylic plate substrate by a screen printer, and then dried at 70 ° C. for 5 minutes to form a light diffusion layer A light guide plate having was obtained.

(Comparative Example 2)
(1) Preparation of hollow resin fine particles D: 50 parts by weight of methacrylic acid as a polymerizable monomer, polyethylene glycol dimethacrylate (“Blenmer PDE-50R”, manufactured by NOF Corporation, number of polyoxyethylene units = 1) as a crosslinkable monomer And 40 parts by weight of trimethylolpropane triacrylate, 50 parts by weight of ethyl acetate and 50 parts by weight of heptane as a non-polymerizable substance, and 0.3 parts by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator are mixed. The mixture was stirred to prepare an ethyl acetate-heptane dispersion type primary emulsion.

Thereafter, the obtained primary emulsion is added to 400 parts by weight of an ion exchange aqueous solution containing 1% by weight of polyvinyl alcohol (PVA) as a dispersing agent and 0.02% by weight of sodium nitrite as a water-soluble polymerization inhibitor, followed by stirring and dispersing. By stirring using an apparatus, a secondary emulsion of a composite emulsion in which oil droplets containing ethyl acetate-heptane were dispersed in an aqueous medium was obtained.

Using a 20-liter polymerization vessel equipped with a stirrer, jacket, reflux condenser and thermometer, the inside of the polymerization vessel was depressurized and deoxygenated in the vessel, and then the atmosphere inside the polymerization vessel was changed to a nitrogen atmosphere by purging with nitrogen. . Thereafter, the obtained secondary emulsion was added all at once, and the polymerization vessel was heated to 60 ° C. to initiate polymerization. After polymerization for 8 hours, the polymerization vessel was cooled to room temperature to obtain a slurry containing ethyl acetate-heptane-containing hollow resin fine particles D. The solvent of the obtained slurry was replaced with isopropanol (IPA) using a centrifuge, and an isopropanol (IPA) dispersion slurry of ethyl acetate-heptane-containing hollow resin fine particles D was obtained.

(2) Production of light guide plate 100 parts by weight of the obtained ethyl acetate-heptane-containing hollow resin fine particle D-containing slurry (55 parts by weight of hollow resin fine particle D), 20 parts by weight of acrylic resin as binder resin, and as organic solvent 25 parts by weight of toluene was mixed and stirred to obtain a fine particle dispersion paste for screen printing.
Using the obtained fine particle dispersion paste, the projections and depressions of the fine line stripes and the corrugated protrusions are printed on the back surface of a commercially available acrylic plate substrate by a screen printer, and then dried at 70 ° C. for 5 minutes to form a light diffusion layer A light guide plate having was obtained.

(Comparative Example 3)
(1) Preparation of hollow resin fine particles E 25 parts by weight of acrylonitrile as a polymerizable monomer, 25 parts by weight of polyethylene glycol dimethacrylate (“Blenmer PDE-50R”, manufactured by NOF Corporation, polyoxyethylene unit number = 1) as a crosslinkable monomer And 50 parts by weight of trimethylolpropane triacrylate, 40 parts by weight of ethyl acetate and 145 parts by weight of cyclohexane as a non-polymerizable substance, and 0.3 part by weight of azobisisobutyronitrile (AIBN) as a polymerization initiator The mixture was stirred to prepare an ethyl acetate-cyclohexane dispersed primary emulsion.

Thereafter, the obtained primary emulsion was added to 455 parts by weight of an ion exchange aqueous solution containing 1% by weight of polyvinyl alcohol (PVA) as a dispersing agent and 0.02% by weight of sodium nitrite as a water-soluble polymerization inhibitor, and stirred and dispersed. By stirring using an apparatus, a secondary emulsion of a composite emulsion in which oil droplets containing ethyl acetate-cyclohexane were dispersed in an aqueous medium was obtained.

Using a 20-liter polymerization vessel equipped with a stirrer, jacket, reflux condenser and thermometer, the inside of the polymerization vessel was depressurized and deoxygenated in the vessel, and then the atmosphere inside the polymerization vessel was changed to a nitrogen atmosphere by purging with nitrogen. . Thereafter, the obtained secondary emulsion was added all at once, and the polymerization vessel was heated to 60 ° C. to initiate polymerization. After polymerization for 8 hours, the polymerization vessel was cooled to room temperature to obtain a slurry containing ethyl acetate-cyclohexane-encapsulated hollow resin fine particles E. The solvent of the obtained slurry was replaced with isopropanol (IPA) using a centrifuge, and an isopropanol (IPA) dispersion slurry of ethyl acetate-cyclohexane-encapsulated hollow resin fine particles E was obtained.

(2) Production of light guide plate Ethyl acetate-cyclohexane-encapsulated hollow resin fine particle E-containing slurry 200 parts by weight (hollow resin fine particle E 90 parts by weight), acrylic resin 30 parts by weight as binder resin, and toluene as organic solvent 30 parts by weight was mixed and stirred to obtain a fine particle dispersion paste for screen printing.
Using the obtained fine particle dispersion paste, the projections and depressions of the fine line stripes and the corrugated protrusions are printed on the back surface of a commercially available acrylic plate substrate by a screen printer, and then dried at 70 ° C. for 5 minutes to form a light diffusion layer A light guide plate having was obtained.

(Comparative Example 4)
(1) Preparation of hollow resin fine particles F 20 parts by weight of methacrylonitrile and 10 parts by weight of methyl methacrylate as polymerizable monomers, and polypropylene glycol dimethacrylate (“Blenmer PDP-400”, manufactured by NOF Corporation, polyoxy Number of propylene units = 7) 10 parts by weight and polyethylene glycol dimethacrylate (“Blenmer PDE-50R”, manufactured by NOF Corporation, polyoxyethylene unit number = 1) 25 parts by weight and 35 parts by weight of neopentyl glycol diacrylate, non-polymerized 50 parts by weight of ethyl acetate and 150 parts by weight of heptane as the active substance, and 0.3 parts by weight of azobisisobutyronitrile (AIBN) as the polymerization initiator are mixed and stirred, and the primary emulsification dispersed in ethyl acetate-heptane A liquid was prepared.

Thereafter, the obtained primary emulsion is added to 400 parts by weight of an ion exchange aqueous solution containing 1% by weight of polyvinyl alcohol (PVA) as a dispersing agent and 0.02% by weight of sodium nitrite as a water-soluble polymerization inhibitor, followed by stirring and dispersing. By stirring using an apparatus, a secondary emulsion of a composite emulsion in which oil droplets containing ethyl acetate-heptane were dispersed in an aqueous medium was obtained.

Using a 20-liter polymerization vessel equipped with a stirrer, jacket, reflux condenser and thermometer, the inside of the polymerization vessel was depressurized and deoxygenated in the vessel, and then the atmosphere inside the polymerization vessel was changed to a nitrogen atmosphere by purging with nitrogen. . Thereafter, the obtained secondary emulsion was added all at once, and the polymerization vessel was heated to 70 ° C. to initiate polymerization. Polymerization was completed in 30 minutes, and then a aging period of 1 hour was performed, and then the polymerization vessel was cooled to room temperature to obtain a slurry containing ethyl acetate-heptane-containing hollow resin fine particles F. The solvent of the obtained slurry was replaced with isopropanol (IPA) using a centrifuge, and an isopropanol (IPA) dispersion slurry of ethyl acetate-heptane-containing hollow resin fine particles F was obtained.

(2) Manufacture of light guide plate Ethyl acetate / heptane inclusion type hollow resin fine particle F containing slurry 200 parts by weight (hollow resin fine particle F 36 parts by weight), acrylic resin 18 parts by weight as binder resin, and toluene as organic solvent By mixing 20 parts by weight and stirring, a fine particle dispersion paste for screen printing was obtained.
Using the obtained fine particle dispersion paste, the projections and depressions of the fine line stripes and the corrugated protrusions are printed on the back surface of a commercially available acrylic plate substrate by a screen printer, and then dried at 70 ° C. for 5 minutes to form a light diffusion layer A light guide plate having was obtained.

(Evaluation)
The following evaluation was performed about the hollow resin microparticles | fine-particles obtained by the Example and the comparative example, microparticle dispersion | distribution paste, and a light-guide plate. The results are shown in Table 1.

(1) The average particle diameter of the hollow resin fine particles, the rate of change in the average particle diameter after heating, and the hollow resin fine particles obtained in the aspect ratio examples and comparative examples, and heated in an oven at an internal temperature of 200 ° C. for 10 minutes The hollow resin fine particles thus obtained were photographed with a transmission electron microscope, 350 photographs were randomly extracted from the obtained photographs, and the major axis and minor axis were measured.
The major axis was taken as the particle diameter, and the number average was taken as the average particle diameter. Moreover, the aspect ratio was calculated by dividing the major axis by the minor axis, and the number average was calculated.
Moreover, the change rate of the average particle diameter by heating was computed by following formula (1).
Rate of change in average particle size after heating at 200 ° C for 10 minutes (%)
= (Average particle diameter after heating / Average particle diameter before heating) × 100 (1)

(2) Porosity of hollow resin fine particles The hollow resin fine particles were photographed with a transmission electron microscope, 350 photographs were randomly extracted from the obtained photographs, the pore diameters in the particles were measured, and the number average was calculated. Asked.
Then, assuming that the hollow resin fine particles are true spheres, and calculating the volume from the average particle diameter (outer diameter) and the average inner pore diameter, respectively, {(hole volume / volume of hollow resin fine particles) × 100} is calculated. Thus, the porosity was obtained.

(3) Hollow resin fine particles The hollow resin fine particles from which the liquid agent contained in the inner pore structure was removed were embedded in an epoxy resin and cut, and the cross section was observed with a scanning electron microscope.

(4) 10% K value of hollow resin fine particles “PCT-200” manufactured by Shimadzu Corporation was used to obtain the 10% K value of the hollow resin fine particles by the following formula (2).
K value (N / mm ² ) = (3/2 ^1/2 ) · F · S ⁻³ / ² · R ^−1/2 (2)
F: Load value at 10% compression deformation of hollow resin fine particles (N)
S: Compression displacement (mm) in 10% compression deformation of hollow resin fine particles
R: Radius of hollow resin fine particles (mm)

(5) State of fine particle dispersed paste The state of the fine particle dispersed paste was visually observed.

(6) Cross-sectional state of light diffusion layer The cross-sections of the light guide plates obtained in the examples and comparative examples were observed using a scanning electron microscope (SEM) to evaluate the state of the holes in the light guide plate.

(7) Luminance and luminance unevenness of the light guide plate The backlight unit (manufactured by Nippon Lights Co., Ltd.) is mounted with the light guide plate obtained instead of the existing acrylic light guide plate (thickness 10 mm), and the milky white plate of the display surface is mounted. After removing, a luminance meter (“CS-100” manufactured by Konica Minolta) was fixed at a position 30 cm away from the light guide plate, and the luminance was measured. Further, luminance unevenness was visually observed.

ADVANTAGE OF THE INVENTION According to this invention, the light-guide plate which can implement | achieve the outstanding light diffusibility when it uses for backlight units, such as a liquid crystal display device, can be provided. Furthermore, according to this invention, the manufacturing method of this light-guide plate can be provided.

Claims (2)

A light guide plate having a light diffusion layer on the back surface,
The light diffusion layer contains hollow resin fine particles having a single pore structure,
The hollow resin fine particles have an average particle diameter of 0.1 to 20 μm and a porosity of 50 to 95% by volume. A method of manufacturing a light guide plate having a light diffusion layer on the back surface,
A step of preparing a fine particle-dispersed paste containing a hollow resin fine particle having a single pore structure, a binder resin and an organic solvent, and
A step of screen-printing the fine particle-dispersed paste on the back surface of the light guide plate substrate to form a light diffusion layer;
The hollow resin fine particles have an average particle diameter of 0.1 to 20 μm and a porosity of 50 to 95% by volume.