JP2007256368A - Light guiding plate and liquid crystal display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light guiding plate capable of guiding light from a light source with uniform and high luminance. <P>SOLUTION: This is a light guiding plate containing a transparent base resin and particles dispersed therein, wherein a refractive index difference between the particles and the transparent base resin is <0.01. Further, as the characteristic, the particle is a silica-combined polymer particle comprising a polymer ingredient derived from a polymerizable vinyl monomer and a silica ingredient, wherein the silica ingredient is a condensate derived from a polyalkoxysiloxane oligomer inert to the polymerizable vinyl monomer and the silica ingredient is unevenly present in the silica-combined polymer particle so that when the silica-combined polymer particle is burned to remove the polymer ingredient, then the resultant silica particle comprises a spherical or nearly spherical outer shell part which has a hollow structure and an inner shell part which is in contact with the outer shell part and forms a part projecting toward the center. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light guide plate and a liquid crystal display device. More specifically, the present invention relates to a light guide plate that can extract light from a light source incident on a certain surface from another surface without uniform attenuation and a liquid crystal display device including the light guide plate.

  The light guide plate is known as a constituent member of a liquid crystal display device, for example. This light guide plate is generally the same size as the display surface of the liquid crystal display panel constituting the liquid crystal display device, and is a thin plate made of transparent resin. An example of how to use the light guide plate is shown in FIG. In FIG. 1, a linear light source (cold cathode ray tube) 2 is disposed on the side surface of the light guide plate 1. Further, a diffusion sheet 4 is provided on the surface of the liquid crystal display panel (hereinafter referred to as “light emitting surface”), and a reflection sheet is provided on the opposite surface. The configuration of FIG. 1 is generally referred to as a backlight unit. The light incident on the side surface of the light guide plate is extracted from the light emitting surface of the light guide plate while being repeatedly reflected and refracted in the light guide plate. The light guide plate needs to extract light from the light source from the liquid crystal display panel side with uniform and high luminance.

  Conventionally, a transparent plate made of an acrylic resin, a polycarbonate resin, a polystyrene resin, or the like has been used as the light guide plate. However, a light guide plate made of such a material cannot sufficiently satisfy the above characteristics. In particular, it has been difficult to achieve uniform brightness.

  In order to eliminate such inconvenience, it has been proposed to provide a dot pattern on a reflection sheet constituting the backlight unit. However, in a backlight unit having a reflection sheet having a dot pattern, there is a problem that light and darkness derived from the dot pattern occurs in the light extracted from the light emitting surface of the light guide plate. In order to solve this problem, contrivances such as installing a plurality of types of light diffusion sheets have been made. However, this device has a problem that the cost increases because the number of members increases.

Furthermore, a technique for mixing particles in a transparent plate has been proposed for the purpose of achieving high luminance and uniformity. For example, JP-A-4-29290 (Patent Document 1) proposes a method of embedding transparent resin particles in a light guide plate. Japanese Patent Laid-Open No. 4-145485 (Patent Document 2) proposes a method of using a light scattering resin containing inorganic particles for a light guide plate.
Japanese Patent Laid-Open No. 4-29290 JP-A-4-145485

However, the technique described in the above publication has a problem that the luminance improvement effect is small. Further, when inorganic particles are used, there is a problem that it is difficult to make the luminance uniform because the inorganic particles have poor dispersibility in the resin.
Therefore, it has been desired to provide a light guide plate that can guide light from a light source uniformly and with high luminance.

  As a result of earnest research to solve the above problems, the inventors of the present invention have used silica composite polymer particles in which silica components derived from polyalkoxysiloxane oligomers are unevenly distributed inside and on the surface of the polymer component for the light guide plate. Surprisingly, it has been found that the light from the light source can be guided uniformly and with high brightness, and the present invention has been achieved.

Thus, according to the present invention, a light guide plate comprising a transparent base resin and particles dispersed in the transparent base resin,
The refractive index difference between the particles and the transparent base resin is less than 0.01,
The particles are silica composite polymer particles containing a polymer component derived from a polymerizable vinyl monomer and a silica component,
The silica component is a condensate derived from an inert polyalkoxysiloxane oligomer with respect to the polymerizable vinyl monomer, and
When the silica component is obtained by firing the silica composite polymer particles and removing the polymer component, a spherical or substantially spherical outer shell having a hollow structure, and a convex portion in contact with the outer shell and toward the center There is provided a light guide plate characterized by being unevenly distributed so as to be silica particles having an inner shell portion that forms.

  In addition, according to the present invention, it is provided with at least a liquid crystal display panel having a display surface and a back surface, the light guide plate disposed on the back surface side, and a light source that makes light incident on a side surface of the light guide plate. A liquid crystal display device is provided.

  In the light guide plate of the present invention, since the silica composite polymer particles having a special shape are blended in the transparent base resin, the light from the light source can be guided uniformly and with high luminance.

Hereinafter, the present invention will be described in more detail.
As illustrated in FIG. 2, the light guide plate of the present invention is composed of a transparent base resin 5 and silica composite polymer particles 6 blended in the resin 5.
As the transparent base resin and the silica composite polymer particles, resins and particles whose refractive index difference is less than 0.01 are used. A difference in refractive index of 0.01 or more is not preferable because the light diffusibility of the light guide plate is increased (total light transmittance is decreased), and the luminance of emitted light is decreased. A more preferable refractive index difference is less than 0.006. The lower limit of the refractive index difference is 0.

  Among the above components, the silica composite polymer particle 6 includes a polymer component derived from a polymerizable vinyl monomer and a silica component derived from a condensate of a polyalkoxysiloxane oligomer that is inactive with respect to the polymer vinyl monomer. . Furthermore, when the polymer component is removed by firing the silica composite polymer particles, a spherical or substantially spherical outer shell having a hollow structure, and a convex portion in contact with the outer shell and toward the center are formed. Silica particles having an inner shell portion to be obtained are obtained. A schematic cross-sectional view of the obtained silica particles is shown in FIG. The inventor of the present invention believes that the silica component is unevenly distributed in the silica composite polymer particles in a shape corresponding to the silica particles. A schematic view of the silica composite polymer particles is shown in FIG. In FIG. 4, 7 means a polymer component, and 8 means a silica component. In addition, the shape and size of the convex portion can be appropriately adjusted by changing the type and amount of the raw material.

  The inventor has found that the light guide plate including the silica composite polymer particles can exhibit uniform and high luminance as compared with the conventional light guide plate including inorganic particles such as alumina and transparent resin particles.

  In the silica composite polymer particles of the present invention, it is preferable that the silica component is unevenly distributed in the silica composite polymer particles so that the opening ratio of the outer shell portion of the silica particles after firing is 0.5 to 1. The opening ratio of the silica particles is strictly the same as the opening ratio of the silica component corresponding to the outer shell part due to shrinkage of the silica component during firing or lack of a thin area at the end of the silica component. Although it may differ, the inventor has confirmed that the opening ratio of the silica component of the silica composite polymer particles and the opening ratio of the outer shell portion of the silica particles are substantially the same. The opening ratio is a value calculated by dividing the area of the opening by the projected area of the silica particles.

  Further, in FIG. 3, the silica component has a silica composite weight so that the calcined silica particles have a relationship of 0.5 ≦ h / D <1 between the height h of the outer shell and the diameter D of the silica particles. It is preferably present in the coalesced particles. Strictly speaking, the h / D of the silica particles is shrunk at the time of firing, or the thin area at the end of the silica component is missing, so that the h / D of the silica component in the silica composite polymer particles is strictly Although the value may be different, the inventor has confirmed that h / D of the silica component corresponding to the outer shell portion and h / D of the silica particles are substantially the same.

  In the light guide plate of the present invention, the blending ratio of the silica composite polymer particles is preferably 0.01 to 20 parts by weight with respect to 100 parts by weight of the transparent base resin. The brightness improvement effect is exhibited satisfactorily when the blending ratio is 0.01 parts by weight or more. In addition, when the blending ratio is up to 20 parts by weight, the ratio of light incident from the light source being converted in the direction perpendicular to the light emitting surface in the vicinity of the light source can be reduced, and the light can be sufficiently transmitted to the central portion of the light guide plate Can be reached. As a result, the light emission distribution on the light emitting surface can be appropriately balanced. Such an appropriate balance is desired particularly in a large liquid crystal display device of 15 inches or more. Furthermore, when the blending ratio is up to 20 parts by weight, there is little change in the color tone in the vicinity of the light source of the light guide plate due to scattering, and the color tone distribution of the emitted light in the light emitting surface can be suppressed. A more preferable blending ratio is 0.03 to 15 parts by weight.

  Moreover, it is preferable that the silica component in a silica composite polymer particle is contained in the light-guide plate in 0.001-15 weight part with respect to 100 weight part of light-guide plates, 0.005-10 weight More preferably, it is contained within the range of parts. By including the silica component in this range, both light guiding properties and light diffusing properties can be achieved at a high level. In addition, content of the silica component here means the value estimated from the usage-amount of the raw material polyalkoxysiloxane oligomer.

  The light guide plate usually comprises a light emitting surface, an opposite surface facing the light emitting surface, and a side surface defined by the light emitting surface and the opposite surface. For example, a light source for causing light to enter the light guide plate is disposed on a side surface of a liquid crystal display device of a notebook personal computer or a thin liquid crystal TV. Specifically, when the light emitting surface is a square and there are four corresponding side surfaces, the light source may be arranged on at least one side surface. In addition, a pair of light sources may be arranged on two opposing side surfaces, or a light source may be arranged on all four side surfaces. The wavelength of light guided and diffused in the light guide plate may be in the visible light region, the infrared region, or the ultraviolet region. In particular, in the use of a liquid crystal display device, it is preferable to include at least a visible light region.

  The shape of the light guide plate is not particularly limited, and can be appropriately determined according to the intended use. For example, examples of the shape of the light emitting surface include a rectangle, a square, a polygon, a circle, and an ellipse. Specifically, the length of the side surface perpendicular to the light emitting surface is preferably 1: 500 to 1: 4 with respect to the maximum length of the light emitting surface. More specifically, the length of the side surface is preferably 1 to 5 mm, and the maximum length of the light emitting surface is preferably 2 to 50 cm.

  The light guide plate of the present invention is usually obtained by molding a kneaded product obtained by melt-kneading silica composite polymer particles and a transparent base resin into a desired shape by extrusion molding, injection molding or the like. it can. Here, since the silica composite polymer particles have good dispersibility with respect to the transparent base resin, they can be mixed uniformly without particularly setting the kneading conditions severely.

Next, constituent materials of the light guide plate will be described.
First, a thermoplastic resin can usually be used for the transparent base resin constituting the light guide plate. Examples of the thermoplastic resin include (meth) acrylic resin, (meth) alkyl acrylate-styrene copolymer resin, polycarbonate resin, polyester resin, polyethylene resin, polypropylene resin, polystyrene resin, and the like. The above resins may be used alone or in combination of two or more. (Meth) acryl means methacryl or acrylic.

Among these, (meth) acrylic resin, (meth) acrylic acid acrylic-styrene copolymer resin, polycarbonate resin, polyester resin, and polystyrene resin are preferable because they have excellent transparency.
Next, the silica composite polymer particle is composed of a polymer component and a silica component. The compounding amount of the silica component is preferably 10 to 500 parts by weight and more preferably 20 to 300 parts by weight with respect to 100 parts by weight of the polymer component.

  This silica composite polymer particle is obtained by, for example, suspending a monomer composition containing a polymerizable vinyl monomer and a polyalkoxysiloxane oligomer in an aqueous medium, polymerizing the polymerizable vinyl monomer, Obtained by condensation.

  The polymerizable vinyl monomer that can be used in the present invention is not particularly limited. For example, styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, pn-butylstyrene, p-tert-butylstyrene, pn-hexyl Styrene, pn-octyl styrene, pn-nonyl styrene, pn-decyl styrene, pn-dodecyl styrene, p-methoxy styrene, p-phenyl styrene, p-chloro styrene, 3,4-di Styrene and its derivatives such as chlorostyrene,

Vinyl esters such as vinyl acetate, vinyl propionate and vinyl butyrate,
Methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, lauryl acrylate, 2-acrylate Chlorethyl, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate , Stearyl methacrylate, lauryl methacrylate, phenyl methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethyl methacrylate α- methylene aliphatic monocarboxylic acid esters such as aminoethyl,

There are acrylic acid or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and the like. In some cases, acrylic acid, methacrylic acid, maleic acid, fumaric acid and the like can also be used. Further, two or more of these may be used in combination.

  Further, vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether, vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, methyl isopropenyl ketone, N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, N-vinyl compounds such as N-vinylpyrrolidone, vinyl naphthalene salts, and the like can be used alone or in combination of two or more in a range not impeding the effects of the present invention.

Among the polymerizable vinyl monomers, styrene, methyl methacrylate, etc., which are inexpensive in terms of cost, are preferable.
The polymer component may be crosslinked with a monomer having two or more functional groups such as ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, divinylbenzene and the like.
The polyalkoxysiloxane oligomer, which is a precursor of the silica component, is inert to the polymerizable vinyl monomer (meaning that it is not copolymerized), and those having the following structural formula can be used.

In the formula, R may be the same or different.
Among the above structural formulas, for example, oligomers such as polymethoxysiloxane, polyethoxysiloxane, polypropoxysiloxane, polybutoxysiloxane, and the like can be given. Among these, polymethoxysiloxane oligomers and polybutoxysiloxane oligomers that are poorly water-soluble and have good phase separation from the resin are preferable. Particularly preferred are polymethoxysiloxane oligomers and polybutoxysiloxane oligomers having a weight average molecular weight of 300 to 3000, more preferably 300 to 2000. When the weight average molecular weight is less than 300 or more than 3000, it is not preferable because it is difficult to form silica composite polymer particles having the specific structure.

In addition, a weight average molecular weight is measured on condition of the following using GPC.
Column: “TSK GEL” (manufactured by Tosoh Corporation)
G-1000H,
G-2000H
G-4000H
Effluent: Tetrahydrofuran Outflow rate: 1 ml / min Outflow temperature: 40 ° C

  In low molecular weight alkoxysiloxanes such as tetramethoxysilane and tetraethoxysilane where n = 1-2 in the above molecular formula, the water solubility becomes stronger due to hydrolysis of the functional group, so it should be stably present in the monomer droplets. Is difficult and undesirable. In addition, a polyalkoxysiloxane oligomer in which n = 40 or more in the above molecular formula is not preferable because compatibility and condensability with a polymerizable vinyl monomer are lowered.

The addition amount of the polyalkoxysiloxane oligomer is preferably 10 to 500 parts by weight, more preferably 20 to 300 parts by weight with respect to 100 parts by weight of the polymerizable vinyl monomer. When the amount is less than 10 parts by weight or more than 500 parts by weight, it is difficult to obtain a composite state of the present invention, which is not preferable.
In addition, hydrolysable alkoxy metal compounds other than silicon-based compounds can be added to these polyalkoxysiloxane oligomers for the purpose of adding functions such as ultraviolet absorption.

  A polymerization initiator can be used for the polymerization of the polymerizable vinyl monomer. Examples of the polymerization initiator include oil-soluble peroxide polymerization initiators and azo polymerization initiators that are usually used in aqueous suspension polymerization. Specific examples include benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, orthochlorobenzoyl peroxide, orthomethoxybenzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxydicarbonate, cumene hydroperoxide, cyclohexanone peroxide, t-butyl. Peroxide polymerization initiators such as hydroperoxide, diisopropylbenzene hydroperoxide,

2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2,3-dimethylbutyronitrile), 2,2′- Azobis (2-methylbutyronitrile), 2,2′-azobis (2,3,3-trimethylbutyronitrile), 2,2′-azobis (2-isopropylbutyronitrile), 1,1′-azobis (Cyclohexane-1-carbonitrile), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile, (2-carbamoylazo) isobutyronitrile, 4,4′-azobis (4-cyanovaleric acid) ), And azo initiators such as dimethyl-2,2′-azobisisobutyrate.

Among these, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), benzoyl peroxide, lauroyl peroxide, and the like are in terms of the decomposition rate of the polymerization initiator. Is preferable.
The polymerization initiator is preferably used in an amount of 0.01 to 10 parts by weight, more preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the polymerizable vinyl monomer. If the polymerization initiator is less than 0.01 part by weight, it is difficult to achieve the function of initiating the polymerization, and if it exceeds 10 parts by weight, it is not preferable because it is uneconomical in terms of cost.

In order to color the silica component, metal oxide pigments such as titanium oxide, zinc oxide, magnesium oxide, chromium oxide, and zirconium oxide may be used.
The polymerizable vinyl monomer, the polyalkoxysiloxane oligomer, and optionally the polymerization initiator and other components are uniformly mixed by a known method to obtain a monomer composition.

Next, examples of the aqueous medium for aqueous suspension polymerization of the monomer composition include water or a mixed medium of water and a water-soluble solvent such as alcohol (for example, methanol, ethanol). The amount of the aqueous medium used is usually 100 to 1000 parts by weight with respect to a total of 100 parts by weight of the polymerizable vinyl monomer and polyalkoxysiloxane oligomer in order to stabilize the suspension polymerized particles.
In order to suppress the generation of emulsified particles in an aqueous system, water-soluble polymerization inhibitors such as nitrites, sulfites, hydroquinones, ascorbic acids, water-soluble vitamin Bs, citric acid, and polyphenols may be used. Good.

As the suspension stabilizer, colloidal silica having an average particle diameter of 150 nm or less is preferably used. If it is 150 nm or less, silica composite polymer particles having a structure in which the silica component is unevenly distributed on the surface and inside of the polymer component can be easily obtained. Furthermore, the average particle diameter is preferably as small as possible, and the more preferable average particle diameter is 0.1 to 70 nm.
Here, the average particle diameter of colloidal silica is a specific surface area diameter obtained by measurement by a nitrogen adsorption method (BET method). The average particle diameter (specific surface area diameter) (Dnm) is given by the formula D = 2720 / S from the specific surface area Sm ² / g as measured by the nitrogen adsorption method.

  As the colloidal silica, powdered colloidal silica such as precipitated silica powder and vapor phase method silica powder, or colloidal silica sol stably dispersed to the primary particle level in a medium can be used. Of these, the latter is preferred. Colloidal silica sols include aqueous silica sols and organosilica sols, both of which are applicable. In particular, since an aqueous medium is used for the production of silica composite polymer particles, it is most preferable to use aqueous colloidal silica from the viewpoint of dispersion stability of colloidal silica sol. The silica concentration in the colloidal silica sol is preferably 5 to 50% by weight because it is generally commercially available and can be easily obtained.

The colloidal silica is preferably contained in the aqueous suspension at a concentration of 0.5 to 20% by weight.
Furthermore, you may add another suspension stabilizer as needed. For example, phosphates such as calcium phosphate, magnesium phosphate, aluminum phosphate, zinc phosphate, pyrophosphates such as calcium pyrophosphate, magnesium pyrophosphate, aluminum pyrophosphate, zinc pyrophosphate, calcium carbonate, magnesium carbonate, calcium hydroxide And dispersion stabilizers of poorly water-soluble inorganic compounds such as magnesium hydroxide, aluminum hydroxide, calcium metasilicate, calcium sulfate, and barium sulfate. Of these, tricalcium phosphate, magnesium pyrophosphate and calcium pyrophosphate produced by the metathesis method are preferable because the polymer component can be stably obtained.

The suspension stabilizer can be used in combination with a surfactant such as an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant.
Examples of the anionic surfactant include fatty acid oils such as sodium oleate and castor oil potassium, alkyl sulfate salts such as sodium lauryl sulfate and ammonium lauryl sulfate, alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, and alkylnaphthalene sulfone. Acid salts, alkane sulfonates, dialkyl sulfosuccinates, alkyl phosphate esters, naphthalene sulfonate formalin condensates, polyoxyethylene alkyl phenyl ether sulfates, polyoxyethylene alkyl sulfates and the like.

  Nonionic surfactants include, for example, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxysorbitan fatty acid ester, polyoxyethylene alkylamine, glycerin fatty acid ester, oxy Examples include ethylene-oxypropylene block polymers.

Examples of the cationic surfactant include alkylamine salts such as laurylamine acetate and stearylamine acetate, and quaternary ammonium salts such as lauryltrimethylammonium chloride.
Examples of the zwitterionic surfactant include lauryl dimethylamine oxide and phosphate ester or phosphite ester surfactants.

  These suspension stabilizers and surfactants may be used alone or in combination of two or more. However, in consideration of the diameter of the obtained polymer component and the dispersion stability at the time of polymerization, the suspension stabilizer It is used by appropriately adjusting the selection and usage. Usually, the addition amount of the suspension stabilizer is 0.5 to 15 parts by weight with respect to 100 parts by weight of the polymerizable vinyl monomer, and the addition amount of the surfactant is 0.00 with respect to 100 parts by weight of the aqueous medium. 001 to 0.1 parts by weight.

The monomer composition is added to the aqueous medium thus prepared, and aqueous suspension polymerization is performed.
As a method for dispersing the monomer composition, for example, a method in which the monomer composition is directly added to an aqueous medium and dispersed in the aqueous medium as monomer droplets by a stirring force of a propeller blade or the like, a high shear force composed of a rotor and a stator is used. Examples thereof include a method of dispersing using a homomixer that is a dispersing machine to be used, an ultrasonic dispersing machine, or the like. Among these, the monomer composition is pressed into an aqueous medium through a high-pressure type disperser or MPG (microporous glass) porous film using collision of monomer droplets such as microfluidizer and nanomizer and collision force to the machine wall. It is preferable to disperse by a method such as that because the particle diameters can be made more uniform.

  Subsequently, suspension polymerization is started by heating the aqueous suspension in which the monomer composition is dispersed as spherical monomer droplets. During the polymerization reaction, it is preferable to stir the aqueous suspension, and the stirring may be performed so gently as to prevent the monomer droplets from floating and the particles from being settled after the polymerization.

In the suspension polymerization, the polymerization temperature is preferably about 30 to 100 ° C, more preferably about 40 to 80 ° C. The time for maintaining this polymerization temperature is preferably about 0.1 to 20 hours.
In addition, when the boiling point of the polymerizable vinyl monomer and the polyalkoxysiloxane oligomer is near the polymerization temperature or higher than the polymerization temperature, the pressure resistant polymerization equipment such as an autoclave is prevented so that the polymerizable vinyl monomer and the polyalkoxysiloxane oligomer do not volatilize. It is preferable to polymerize under sealing or under pressure.

  Next, silica composite polymer particles can be obtained by condensing the polyalkoxysiloxane oligomer. Examples of the condensation method of the polyalkoxysiloxane oligomer include dehydration condensation using an acid catalyst or a base catalyst. As the acid catalyst and the base catalyst, hydrochloric acid, sulfuric acid, nitric acid, ammonia, sodium hydroxide, potassium hydroxide, ammonium nitrate, sodium pyrophosphate and the like can be used. When the production container is made of steel or stainless steel, basic sodium hydroxide, ammonia, sodium pyrophosphate and the like are preferable from the viewpoint of corrosion and the like. The addition amount of the catalyst is preferably 0.01 to 30 parts by weight with respect to 100 parts by weight of the polyalkoxysiloxane oligomer. More preferably, it is 1 to 15 parts by weight.

After the condensation, the silica composite polymer particles are separated as a water-containing cake by a method such as suction filtration, centrifugal dehydration, centrifugal separation, pressure dehydration, and the obtained water-containing cake is washed with water and dried to obtain the desired silica composite weight. Combined particles can be obtained.
The size and shape of the silica composite polymer particles of the present invention are not particularly limited. According to the method for producing silica composite polymer particles, particles having an average particle diameter of 1 to 100 μm can be obtained.
Here, the adjustment of the average particle diameter of the particles can be performed by adjusting the mixing conditions of the monomer composition and water, the addition amount of the suspension stabilizer, the surfactant and the like, the stirring conditions of the agitator, and the dispersion conditions. is there.

  Furthermore, the present invention provides a liquid crystal display device provided with the light guide plate. The configuration of the liquid crystal display device is not particularly limited as long as it includes the light guide plate. For example, as shown in FIG. 5, the liquid crystal display device includes a liquid crystal display panel 10 having a display surface and a back surface, a light guide plate 1 disposed on the back surface side of the panel, and a light source that makes light incident on the side surface of the light guide plate. 2 at least. In addition, the reflective sheet 3 is provided on the side of the light guide plate 1 opposite to the surface facing the liquid crystal display panel 10. This arrangement of the light sources 2 is generally referred to as an edge light type backlight arrangement.

The liquid crystal display panel has a configuration in which a liquid crystal layer 13 is sandwiched between a pair of substrates (11, 12). On the liquid crystal layer side of the substrate, electrodes (14, 15) and alignment films (16, 17) covering the electrodes are provided. Here, the electrode may include a thin film transistor. Further, the liquid crystal display panel may include a polarizing sheet, an antireflection sheet, and the like.
A diffusion sheet, a prism sheet, or the like may be disposed on the light emitting surface of the light guide plate on the liquid crystal panel side. In addition, a reflective sheet may be disposed on the back surface facing the light emitting surface.

Hereinafter, although an example and a comparative example explain the present invention, the present invention is not limited to this. In addition, the evaluation method of each property in an Example and a comparative example is described below.
(Measurement of average particle size)
The average particle diameter is a value measured with Multisizer II (manufactured by Beckman Coulter). The measurement is carried out by performing calibration using a 50 μm aperture according to Reference MANUAL FOR THE COULTER MULTISIZER (1987) published by Coulter Electronics Limited.
Specifically, 0.1 g of particles were predispersed in 10 ml of a 0.1% nonionic surfactant solution using a touch mixer and ultrasonic waves, and this was equipped with an ISOTON II (manufactured by Beckman Coulter, Inc .: measurement) In a beaker filled with an electrolytic solution), dripping with a dropper while gently stirring, adjust the reading of the densitometer on the main body screen to about 10%. Next, an aperture size of 50 μm, a current of 800, a gain of 4, and a polarity of + are input to the Multisizer II main body (the aperture size and the like can be changed as required) and measured manually. During the measurement, the beaker is stirred gently to the extent that bubbles do not enter, and the measurement is terminated when 100,000 particles are measured. The average particle diameter is an average value of the measured values.

(Refractive index measurement method)
(1) Refractive index measurement method of silica composite polymer particles 0.001 g of polymer particles on a slide glass, a liquid having a refractive index arbitrarily selected according to the publication “Atago Refractometer Data Book” (published by Atago Co., Ltd.) Disperse the particles with 0.2 ml of organic compound to prepare a sample plate.
Next, each sample plate was set in an optical microscope and observed using a sodium lamp as a light source, and it was confirmed that the outline of the particles became invisible at a temperature where the refractive index of each liquid organic compound was known. Let the refractive index of a liquid organic compound be a refractive index of particle | grains.

In addition, as a liquid organic compound and its refractive index, the above-mentioned publication includes, for example,
“Furifurylamine (17 ° C.): refractive index 1.4900,
p-diethylbenzene ... refractive index 1.4948 "
However, the refractive index is rounded off to the fourth decimal place. In addition, for the case where the temperature is not particularly described such as p-diethylbenzene, the presence or absence of the outline of the particle is confirmed at 20 ° C.

  In the following production method, a monomer composition prepared separately in the same manner as in each production example was used, and after the monomers were radically polymerized into polymer particles, the polymer particles were taken out without condensing the polysiloxane oligomer. Then, the refractive index is measured as described above with respect to an object obtained by washing with toluene and completely washing away the polysiloxane oligomer.

(2) Method for measuring refractive index of transparent base resin A material obtained by pulverizing a transparent base resin into particles (about 1 mg or less per particle) is measured by the same method as in the case of the silica composite polymer particles.
(Measurement of luminance of light guide plate and visual evaluation method of luminance unevenness)
A cold cathode fluorescent tube with a thickness of 4 mm is placed on the side surface of the light guide plate with a thickness of 4 mm, and a prism sheet (“BEF II” product name: manufactured by Sumitomo 3M) and a light diffusion film (“light up 100S” product) are further provided on the light guide plate. (Name: manufactured by Kimoto Co., Ltd.) are stacked in this order, and a reflection sheet under the light guide plate ("Lumirror E60L" product name: manufactured by Toray Industries, Inc.) is placed and fixed at a position 30 cm away from the light guide plate. A light quantity (luminance) passing through the light guide plate is measured with a meter (“CS-100”, trade name: manufactured by Konica Minolta). Also, luminance unevenness is evaluated by visual observation.

(1) Production Example and Comparative Production Example of Silica Composite Polymer Particle Production Example 1
A polymerization vessel having a stirrer with a dispersion medium in which 250 g of Snowtex O-40 (manufactured by Nissan Chemical Co., Ltd .: colloidal silica 40 wt% solution having an average particle size of 20 to 30 nm) is mixed as a suspension stabilizer with 1750 g of water. Put in.

  Separately, 700 g of methyl methacrylate as a monofunctional polymerizable vinyl monomer, and MKC silicate MS57 (manufactured by Mitsubishi Chemical Corporation: average molecular weight 1300 to 1500, R is methyl, n is 15 to 18 in average) as a polyalkoxysiloxane oligomer 300 g A monomer composition prepared by uniformly dissolving 0.5 g of 2,2′-azobis (2,4-dimethylvaleronitrile) as a polymerization initiator was prepared.

This monomer composition was added to the dispersion medium and stirred at 6000 rpm for about 10 minutes with a homomixer to finely disperse the monomer composition.
Thereafter, stirring is continued at a stirring speed of 300 rpm, and the polymerizable vinyl monomer is polymerized by performing suspension polymerization for 4 hours after the temperature of the dispersion medium to which the monomer composition is added reaches 60 ° C. to obtain a polymer component. Further, 60 g of sodium pyrophosphate was added to condense the polyalkoxysiloxane oligomer.

  Next, the reaction liquid in the polymerization vessel was cooled to room temperature (about 30 ° C.) while stirring to obtain silica composite polymer particles in which the surface of the polymer component was locally coated with the silica component derived from the polyalkoxysiloxane oligomer. . The target particles were taken out by dehydrating and drying the obtained particles. The average particle diameter of the obtained silica composite polymer particles is 8.6 μm.

  In order to confirm the composite state of the polymer component and the silica component, the silica composite polymer particles were baked in an electric furnace at 500 ° C. to remove the polymer component, thereby obtaining silica particles. The shape of the obtained silica particles was observed with an electron micrograph. The shape of the silica particles had a shape with a spherical protrusion (seed) inside the hemisphere bowl. Therefore, the silica component was unevenly distributed in the silica composite polymer particle, in other words, the first silica component corresponding to the outer shell portion of the silica particle located on the surface of the silica composite polymer particle and the surface layer. And it was confirmed that it was composed of a second silica component corresponding to the inner shell portion of the silica particles forming the convex portion toward the center of the silica composite polymer particle. An electron micrograph is shown in FIG.

Production Example 2
Silica composite polymer particles were obtained in the same manner as in Production Example 1 except that 900 g of methyl methacrylate and 100 g of MKC silicate MS57 were used. The average particle diameter of the obtained particles was 8.1 μm. When fired in the same manner as in Production Example 1, the shape of the silica particles has a shape with spherical protrusions inside the hemispherical bowl, and the silica component is unevenly distributed in the silica composite polymer particles as in Production Example 1. I was able to confirm.

Production Example 3
Silica composite polymer particles were obtained in the same manner as in Production Example 1 except that 200 g of methyl methacrylate and 800 g of MKC silicate MS57 were used. The average particle diameter of the obtained particles was 7.9 μm. When fired in the same manner as in Production Example 1, the shape of the silica particles has a shape with spherical protrusions inside the hemispherical bowl, and the silica component is unevenly distributed in the silica composite polymer particles as in Production Example 1. I was able to confirm.

Comparative production example 1
A dispersion medium in which 50 g of magnesium pyrophosphate by metathesis method is mixed with 2000 g of water as a suspension stabilizer is placed in a polymerization vessel having a stirrer, and 0.4 g of sodium lauryl sulfate is used as a surfactant, and sub-polymer is used as a polymerization inhibitor. Sodium nitrate (0.2 g) was dissolved in the dispersion medium.

  Separately, 700 g of methyl methacrylate as a monofunctional polymerizable vinyl monomer, 300 g of MKC silicate MS57 as a polyalkoxysiloxane oligomer, 0.5 g of 2,2′-azobis (2,4-dimethylvaleronitrile) as a polymerization initiator A monomer composition prepared by uniformly dissolving was prepared.

This monomer composition was added to the dispersion medium and stirred at 7000 rpm for about 10 minutes with a homomixer to finely disperse the monomer composition.
Then, stirring is continued at a stirring speed of 300 rpm, and the polymerization vinyl monomer is polymerized by performing suspension polymerization for 4 hours after the temperature of the dispersion medium to which the monomer composition is added reaches 60 ° C. Further, 20 g of sodium hydroxide was added to condense the polyalkoxysiloxane oligomer.

  Next, the reaction solution in the polymerization vessel was cooled to room temperature while stirring, and hydrochloric acid was added until the pH of the slurry was about 2, whereby the suspension stabilizer was decomposed to obtain silica composite polymer particles. The target particles were taken out by dehydrating and drying the obtained particles. The average particle diameter of the obtained silica composite polymer particles is 8.8 μm.

  In order to confirm the composite state of the polymer component and the silica component, the silica composite polymer particles were baked in an electric furnace at 500 ° C. to remove the polymer component, thereby obtaining silica particles. The shape of the obtained silica particles was observed with an electron micrograph. It can be seen that the silica particles had a hemispherical bowl shape with no protrusions inside and coated the polymer component.

(2) Examples and Comparative Examples of Light Guide Plate Example 1
3 g of the silica composite polymer particles of Production Example 1 were added to 300 g of methyl methacrylate resin (Sumipex EXA manufactured by Sumitomo Chemical Co., Ltd.), blended for 3 minutes in a food mixer, supplied to an injection molding machine, and injection molded. A light guide plate having a length of 300 mm, a width of 275 mm, and a thickness of 4 mm was obtained.
The luminance of this light guide plate was measured, and the luminance unevenness was visually observed. The results are shown in Table 1 below.

Example 2
A light guide plate was obtained in the same manner as in Example 1 except that 45 g of the silica composite polymer particles of Production Example 2 was added to 300 g of methyl methacrylate resin. Further, the luminance was measured in the same manner as in Example 1, and the luminance unevenness was visually observed. The results are shown in Table 1 below.

Example 3
A light guide plate was obtained in the same manner as in Example 1 except that 0.15 g of the silica composite polymer particles of Production Example 3 was added to 300 g of methyl methacrylate resin. Further, the luminance was measured in the same manner as in Example 1, and the luminance unevenness was visually observed. The results are shown in Table 1 below.

Example 4
A light guide plate was obtained in the same manner as in Example 1 except that the silica composite polymer particles of Production Example 4 were used. Further, the luminance was measured in the same manner as in Example 1, and the luminance unevenness was visually observed. The results are shown in Table 1 below.

Comparative Example 1
Example 1 except that 3 g of spherical polymer particles (“MBX-12” product name: manufactured by Sekisui Plastics Co., Ltd.) was added to 300 g of methyl methacrylate resin instead of silica composite polymer particles. A light guide plate was obtained in the same manner. Further, the luminance was measured in the same manner as in Example 1, and the luminance unevenness was visually observed. The results are shown in Table 1 below.

Comparative Example 2
A light guide plate was obtained in the same manner as in Example 1 except that alumina particles (primary particle diameter 0.5 μm) were used instead of the silica composite polymer particles. Further, the luminance was measured in the same manner as in Example 1, and the luminance unevenness was visually observed. The results are shown in Table 1 below.

Comparative Example 3
A light guide plate was obtained in the same manner as in Example 1 except that the silica composite polymer particles of Comparative Production Example 1 were used. Further, the luminance was measured in the same manner as in Example 1, and the luminance unevenness was visually observed. The results are shown in Table 1 below.

From Table 1, the light guide plates of Examples 1 to 4 can guide light from a light source with uniform and high luminance as compared with a light guide plate containing polymer particles alone (Comparative Example 1) and inorganic particles (Comparative Example 2). I understand that I can do it.
Moreover, from Example 1 and Comparative Example 3, it can be seen that the luminance can be further improved by the silica component having the inner shell portion.

It is the schematic of a backlight unit. It is the schematic of the light-guide plate of this invention. It is a schematic sectional drawing of a silica particle. It is the schematic of a silica composite polymer particle. It is a schematic sectional drawing of a liquid crystal display device. 2 is an electron micrograph of silica particles of Production Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light guide plate 2 Light source 3 Reflective sheet 4 Diffusion sheet 5 Transparent base resin 6 Silica composite polymer particle 7 Polymer component 8 Silica component 10 Liquid crystal display panel 11, 12 Substrate 13 Liquid crystal layer 14, 15 Electrode 16, 17 Alignment film

Claims (5)

A light guide plate comprising a transparent base resin and particles dispersed in the transparent base resin,
The refractive index difference between the particles and the transparent base resin is less than 0.01,
The particles are silica composite polymer particles containing a polymer component derived from a polymerizable vinyl monomer and a silica component,
The silica component is a condensate derived from an inert polyalkoxysiloxane oligomer with respect to the polymerizable vinyl monomer, and
When the silica component is obtained by firing the silica composite polymer particles and removing the polymer component, a spherical or substantially spherical outer shell having a hollow structure, and a convex portion in contact with the outer shell and toward the center A light guide plate characterized by being unevenly distributed so as to be silica particles having an inner shell portion that forms a surface.   The light guide plate according to claim 1, wherein the silica composite polymer particles are dispersed in the transparent base resin so that light incident from a side surface of the light guide plate can be extracted from the surface.   The light guide plate according to claim 1 or 2, wherein the silica composite polymer particles are contained in an amount of 0.01 to 20 parts by weight with respect to 100 parts by weight of the transparent base resin.   The light guide plate according to claim 1, wherein the silica component is contained in a range of 0.001 to 15 parts by weight with respect to 100 parts by weight of the light guide plate.   A liquid crystal display panel having a display surface and a back surface, at least a light guide plate according to any one of claims 1 to 4 disposed on the back surface side, and a light source that makes light incident on a side surface of the light guide plate. A liquid crystal display device characterized by that.