JP2006108004A - Light guide plate, manufacturing method of light guide plate, backlight, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a light guide plate of a type using scattered particles so that its brightness is sufficient, and its brightness unevenness becomes small. <P>SOLUTION: The light guide plate 210 is formed by dispersing scattered particles composed of nanoparticles, first micro-particles and second micro-particles in an acrylic resin which is a transparent material, and molded in a plate state. The nanoparticles are yttrium oxide of which the maximum diameter is nearly 30 nm, and the first micro-particles are silicone of which the maximum diameter is nearly 3.5 μm, and the second micro-particles are silicone of which the maximum diameter is nearly 12 μm. Light which enters from a light source facing the end face of the light guide plate 210 into the light guide plate 210 is scattered by the scattered particles and emitted from the emitting surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light guide plate mainly used for a backlight of a liquid crystal display device.

Liquid crystal display devices are very popular.
The liquid crystal display device includes a liquid crystal panel that displays an image, and is configured so that an image displayed on the liquid crystal panel is placed on light from behind the liquid crystal panel and is visible to the human eye. Since the liquid crystal panel itself in the liquid crystal display device does not have a function of emitting light, in the liquid crystal display device, a mechanism for guiding light for viewing an image from the back to the liquid crystal panel is indispensable.
There are various mechanisms for guiding light from behind the liquid crystal panel in the liquid crystal display device. For example, a reflection-type liquid crystal display device having a mechanism for reflecting light taken from the outside behind the liquid crystal panel and guiding it to the liquid crystal panel is known. On the other hand, in almost all liquid crystal display devices other than the reflective liquid crystal display device (for example, a transmissive liquid crystal display device or a transflective liquid crystal display device), a backlight is used. The backlight is a planar light source that emits light spontaneously and is used behind the liquid crystal panel. By guiding the light from the backlight to the liquid crystal panel, the image displayed on the liquid crystal panel becomes visible to human eyes.

The backlight has a great influence on the performance of the liquid crystal display device such as the thickness and power consumption of the liquid crystal display device, and is a highly important component. Therefore, various technologies have been proposed and put into practical use for backlights.
A common backlight uses a light guide plate.
The light guide plate is formed by forming a transparent material into a plate shape, and emits light introduced into the inside from a light source facing the end surface from one of its wide surfaces. . A general light guide plate is provided with a sharp wave shape having a prism function on the emission surface or the surface opposite to the emission surface, and the direction of light introduced from the light source into the inside of the light guide plate is determined. By changing the shape of the light source (for example, by reflection), the light introduced into the light source from the light source can be emitted from the light emission surface of the light guide plate.

By the way, the wave-shaped portion described above is manufactured by performing processing that requires a very high accuracy with an allowable error of several μm level. Therefore, the manufacture of a light guide plate, which is mostly a resin product, requires a very advanced technique due to the “sink mark” inherent to the resin product. In fact, since a technique for performing very precise processing is required, the number of people who can manufacture a mold for manufacturing a light guide plate is limited, and a mold for manufacturing a light guide plate is manufactured. In order to do so, expenses of several hundred million yen are necessary.
All these costs rebound to the price of the light guide plate. Therefore, the light guide plate is an expensive part. Such circumstances hinder the price of a backlight using a light guide plate and a liquid crystal display device using the backlight from being lowered.
However, a light guide plate having no wave shape as described above has also been proposed. However, even with such a light guide plate, there is no change in that very precise processing is required. Therefore, the light guide plate is generally difficult to manufacture because it requires precise processing, and is very expensive.

From the above viewpoint, the present inventor disperses the scattering particles in the transparent material of the light guide plate in which the transparent material is formed in a plate shape, and scatters the light introduced into the inside from the light source with the scattering particles. We are studying a light guide plate that emits light from the emission surface.
Such a light guide plate changes the direction of light introduced from the light source into the interior by scattering particles, and does not require the processing for forming the wave shape described above. It is very easy to make and can be cheap.

  However, according to the research of the present inventor, the light guide plate using such scattering particles tends to have insufficient light from the emission surface (easily insufficient in luminance), and a portion near and far from the light source. In the case of using a point light source, there is a problem that a difference in light intensity from the emission surface is likely to occur (brightness unevenness is likely to occur) between the front and the front of the light source.

  The present invention solves such a problem. More specifically, the light guide plate of the type using scattering particles is improved so that the luminance is sufficient, or the luminance unevenness in each part of the emission surface. The problem is to improve so as to reduce the size.

The present invention for solving the above-described problems is as follows.
In the present invention, a transparent material in which scattering particles are dispersed is formed into a plate shape, and light introduced from the light source facing the end surface is scattered by the scattering particles and emitted from the emission surface. It is the light-guide plate adapted to do. And the said scattering particle | grain contains the nanoparticle.
Since the light guide plate emits light from the light source from the emission surface by the scattering particles, it is easy to manufacture the mold, and the cost for manufacturing the mold is low. Moreover, in this light guide plate, as the scattering particles, those containing nanoparticles are dispersed inside the light guide plate. In this way, the exact reason is not known at present, but the brightness unevenness in each part of the emission surface is reduced, and in some cases, the overall brightness can be increased as compared with the case where no nanoparticles are included. .

The “emission surface” in the present invention means any one or two of the widened two surfaces of the plate-shaped light guide plate, and means a surface from which light is emitted. If there are two emission surfaces, the light guide plate of the present invention can be used in a double-sided liquid crystal display device.
In the present invention, the light introduced into the light source from the light source is scattered by the scattering particles and emitted from the emission surface. This is because the light scattered by the scattering particles is emitted from the emission surface as it is. And the case where the light scattered by the scattering particles is emitted from the emission surface after being reflected by a surface other than the emission surface such as the bottom surface.
Any method may be used for dispersing the scattering particles inside the light guide plate. If scattering particles are mixed in a transparent material used for injection molding, extrusion molding, etc., and molding is performed using the transparent material, the scattering particles can be dispersed inside the light guide plate.
Any transparent material may be used as long as it can be formed into a plate shape and has a transparency that allows light to be introduced into the transparent material. The transparent material can be, for example, a transparent resin. The transparent resin can be, for example, PMMA (acrylic), PC (polycarbonate), or COP (cycloolefin polymer).

The term “nanoparticle” in the present invention refers to a particle having a maximum diameter in the order of so-called nm, that is, a particle having a maximum diameter of 1 nm to 1000 nm.
The maximum diameter of the nanoparticles may be 1 nm to 100 nm. Nanoparticles are often defined as those having such a size, but it has been found that the use of nanoparticles of such a size produces the above-described effects.
The nanoparticles may have a maximum diameter of approximately 30 nm. At present, it has been found that the use of nanoparticles having such a size sufficiently produces the above-described effects.
As long as the nanoparticles have the maximum diameter as described above, the shape, type and material are not particularly limited. However, it is better that the nanoparticles have a weak property of absorbing visible light.
Examples of the shape of the nanoparticles include a true sphere, an oval sphere, a rod, a plate, and a thin film, and the inside may be dense or hollow.
Examples of variations regarding the type and material of the nanoparticles include metal nanoparticles, inorganic nanoparticles, organic nanoparticles, semiconductor nanoparticles, inorganic-organic hybrid nanoparticles, and polymer nanoparticles. As more detailed examples, silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), titanium oxide (IV) (TiO ₂ ), yttrium oxide (Y ₂ O ₃ ), magnesium oxide (MgO), zinc oxide (ZnO), carbon (C), silicon (Si), magnesium (Mg), calcium (Ca), silver (Ag), platinum (Pt), titanium (Ti), nickel (Ni), ruthenium (Ru), rhodium (Rh), gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), zirconia (ZrO ₂ ), silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), zeolite, nanodiamond, nanocrystal, scumite, mica, Dendrimer, star polymer, hyperbranched polymer, microporous methylphosphonate Miniumu, and the like.

The scattering particles may be included in the transparent material in any state. The same applies to the nanoparticles contained in the scattering particles. A part of the nanoparticles may be aggregated. However, if the nanoparticles are in an independently dispersed state (a state where they are not aggregated and are independent) (such nanoparticles are referred to as independently dispersed nanoparticles), the above-described effects can be obtained. It is considered suitable. That is, it is considered that at least a part of the nanoparticles in the light guide plate of the present invention is in an independently dispersed state.
Therefore, the direct dispersion method in which the nanoparticles are dispersed as they are in the transparent material is the simplest method for dispersing the nanoparticles in the transparent material. However, it is desirable that the nanoparticles to be dispersed in the transparent material be subjected to an anti-aggregation treatment. Conceivable. This is because the nanoparticles have a surface energy much higher than that of a polymer which is a general transparent material, and thus are easily aggregated in the transparent material by the direct dispersion method. Examples of the method for the anti-aggregation treatment include silane coupling treatment, aluminum coupling treatment, titanate coupling treatment, and surfactant treatment.

  The scattering particles of the present invention may include microparticles having a maximum diameter of 1 μm to 100 μm in addition to the above-described nanoparticles. When such microparticles larger than the nanoparticles were put in a transparent material, the light emitted from the light guide plate increased particularly in the portion far from the light source, and the luminance was improved when viewed from the entire light guide plate.

There are no particular restrictions on the type and material of the microparticles as long as the size is as described above. However, it is preferable that the microparticles have a weak property of absorbing visible light, like the nanoparticles. The microparticles can be opaque, such as metal powder, or can be transparent, such as silicone powder or acrylic powder. If the microparticles are made transparent, it is considered that not only light reflection but also refraction occurs.
The microparticles may include a plurality of types of microparticles having different maximum diameters. For example, the microparticles may include first microparticles having a maximum diameter of 1 μm to 10 μm and second microparticles having a maximum diameter of 10 μm to 30 μm. By dispersing the two types of microparticles having different sizes in the transparent material, the light guide plate can have sufficient luminance, and an effect of reducing luminance unevenness can be obtained.
For example, the first microparticle may have a maximum diameter of approximately 3.5 μm, and the second microparticle may have a maximum diameter of approximately 12 μm.
There is no particular limitation on how much the first microparticles and the second microparticles are added to the transparent material. For example, the transparent material may contain the first microparticles in an amount of 0.1 wt% to 15 wt% and the second microparticles in an amount of 0.1 wt% to 30 wt%. The weight ratio of the first microparticles to the second microparticles can be approximately 1: 2. At present, it has been found that when such a blending is performed, the luminance of the light guide plate can be made sufficient and the luminance unevenness can be reduced.

  Although the microparticle is not as large as the nanoparticle, aggregation is likely to occur, and it is considered that the above-described effects are more likely to occur when the microparticle is not aggregated. Therefore, it is considered that the microparticles should be subjected to the same aggregation prevention treatment as in the case of nanoparticles.

The light guide plate of the present invention is obtained, for example, by the following manufacturing method.
Such a manufacturing method is a method of manufacturing a light guide plate in which a transparent material is formed into a plate shape, and light introduced into the inside from a light source facing the end surface is emitted from the emission surface. is there. Then, scattering particles that can scatter light and those containing nanoparticles are dispersed in a monomer, and the monomer containing the nanoparticles is formed into a plate shape and polymerized to form a plate in which scattering particles are dispersed. A light guide plate that is a polymer is obtained.

The light guide plate described above can be applied to a backlight having a light source facing the end of the light guide plate, and can also be applied to a liquid crystal display device having such a backlight.
The light source used in combination with the light guide plate in the present invention can be appropriately selected as necessary. For example, as the light source, an LED or other point light source can be used, or a small fluorescent lamp or other linear light source can be used. Further, the number of light sources may be singular or plural. When the light guide plate is rectangular, the light source generally faces at least one of the sides when the light guide plate is viewed perpendicular to the emission surface. In this case, the light source has two or more light sources. It may be of a shape straddling the side.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

The liquid crystal display device according to this embodiment is schematically configured as shown in FIG.
This liquid crystal display device is configured by combining a liquid crystal panel 100 and a backlight 200. The backlight 200 is disposed on the back side of the liquid crystal panel 100, that is, on the side far from the eyes of the viewer of the liquid crystal display device.
The liquid crystal display device allows a user to view a predetermined image by transmitting light from the backlight 200 to the liquid crystal panel 100.
The liquid crystal display device includes a case for housing the liquid crystal panel 100 and the backlight 200, a circuit board for controlling the driving of the liquid crystal panel 100, and the like. The illustration is also omitted.

The liquid crystal panel 100 may be any existing liquid crystal panel, but in this embodiment, has a structure as shown in FIG. The liquid crystal panel 100 includes a liquid crystal layer 110 in the middle thereof. The liquid crystal layer 110 is sandwiched between the alignment film layers 120. A transparent electrode layer 130 is provided outside the alignment film layers 120. Further, a glass substrate 140 is provided outside the transparent electrode layers 130, and a polarizing plate 150 is provided outside the both glass substrates 140. Note that a color filter layer 160 is provided between the glass substrate 140 and the transparent electrode layer 130 closer to the front side of the liquid crystal panel 100, that is, from the viewer's eyes.
In this embodiment, the liquid crystal layer 110, the alignment film layer 120, the transparent electrode layer 130, the glass substrate 140, the polarizing plate 150, and the color filter layer 160 all have the same shape, more specifically, the same rectangular shape. ing.
The liquid crystal layer 110, the alignment film layer 120, the transparent electrode layer 130, the glass substrate 140, the polarizing plate 150, and the color filter layer 160 described above are as follows.
Both the two polarizing plates 150 have a function of changing the light transmitted therethrough into linearly polarized light in a predetermined direction. Among the polarizing plates 150 in this embodiment, the one on the back side has a role of polarizing light emitted from the backlight 200. On the other hand, the polarizing plate 150 on the front side passes through the liquid crystal layer 110 after being polarized after passing through the polarizing plate 150 on the back side, and allows light whose polarization plane is rotated as necessary. Or have a role to block. The liquid crystal layer 110 is driven as necessary to pass light polarized through the polarizing plate 150 on the back side while maintaining the polarization plane as it is or rotating 90 degrees. Control of driving of the liquid crystal layer 110 performed to rotate the polarization plane is realized by a change in potential difference between the transparent electrode layers 130.
The color filter layer 160 is a layer formed by a color filter for coloring the light passing therethrough. In general, the color filter layer 160 includes fine filters of R (red), G (green), and B (blue) arranged in a matrix, and in this embodiment, this is the case.

On the other hand, the backlight 200 is configured as shown in FIG.
The backlight 200 in this embodiment includes a light guide plate 210 and a light source 220. The light guide plate 210 is configured by dispersing scattering particles in a transparent material. The transparent material of the light guide plate 210, details of the scattering particles, and the manufacturing method of the light guide plate 210 will be described later.
The light guide plate 210 has a rectangular shape when viewed from a direction perpendicular to its wide surface, and is formed in a thin plate shape (cuboid shape). Note that the emission surface in this embodiment, that is, the surface from which light introduced from the light source 220 is emitted into the light guide plate 210 is the upper surface of the light guide plate 210 in FIG.

A light source 220 is provided at the center of the portion of the light guide plate 210 corresponding to one side of the rectangle described above. The light source 220 in this embodiment is not necessarily so, but is an LED. The light source 220 is controlled to be lit as necessary. The light source 220 is opposed to a portion (end face) corresponding to one side of the rectangle described above, and light emitted from the light source 220 is introduced into the light guide plate 210.
The light source 220 is a point light source in this embodiment, but may be a linear light source such as a fluorescent lamp. Note that although there is one light source 220 in this embodiment, a plurality of light sources 220 may be arranged on an end surface corresponding to a portion corresponding to one side of the rectangle or on other end surfaces.
In addition, the light guide plate 210 according to this embodiment does not necessarily have to be so, but guides light that is intended to go out of the light guide plate 210 from the inside of the light guide plate 210 except for the end face facing the light source 220 and the emission face. The light plate 210 is covered with a reflecting material. For example, the reflector may be configured by attaching a mirror-like member different from the light guide plate 210 around the light guide plate 210, or by depositing a metal such as aluminum on a necessary portion of the light guide plate 210. It may be manufactured.

  When light is introduced from the light source 220 into the light guide plate 210 according to this embodiment, the light travels through the light guide plate 210 and is scattered by hitting the scattering particles contained in the light guide plate 210. The scattered light is either directly or after being reflected by a reflector, and then emitted to the outside from the emission surface of the light guide plate 210. Thus, the backlight 200 including the light guide plate 210 and the light source 220 functions as a planar light source.

Next, the transparent material of the light guide plate 210, the details of the scattering particles, and the manufacturing method of the light guide plate 210 will be described.
The light guide plate 210 is manufactured as follows.
First, the scattering particles are adjusted. In this embodiment, the following three types of scattering particles are used: nanoparticles, first microparticles, and second microparticles.

Nanoparticles are, for example, silicon dioxide (SiO ₂ ), aluminum oxide (Al ₂ O ₃ ), titanium (IV) (TiO ₂ ), yttrium oxide (Y ₂ O ₃ ), magnesium oxide (MgO), zinc oxide ( ZnO), carbon (C), silicon (Si), magnesium (Mg), calcium (Ca), silver (Ag), platinum (Pt), titanium (Ti), nickel (Ni), ruthenium (Ru), rhodium ( Rh), gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), zirconia (ZrO ₂ ), silicon carbide (SiC), silicon nitride (Si ₃ N ₄ ), zeolite, nanodiamond, nanocrystal, scumite, mica, dendrimer , Star polymer, hyperbranched polymer, microporous methylphosphonic acid It can be a chloride, in this embodiment, a yttrium oxide thereto.
The nanoparticles have a maximum diameter of 1 nm to 1000 nm, more preferably 1 nm to 100 nm, but in this embodiment, those having a maximum diameter of about 30 nm are used.
In this embodiment, it is not necessary to do so, but the aggregation prevention process is performed on the nanoparticles. Specifically, one of silane coupling treatment, aluminum coupling treatment, titanate coupling treatment, and surfactant treatment may be performed. In this embodiment, silane coupling treatment is performed on the nanoparticles. .

In this embodiment, both the first microparticle and the second microparticle are silicone particles. The maximum diameter of both the first microparticle and the second microparticle is 1 μm to 100 μm. In this embodiment, the former maximum diameter is 1 μm to 10 μm, and the latter maximum diameter is 10 μm to 30 μm. More specifically, the maximum diameter of the first microparticle is approximately 3.5 μm, and the maximum diameter of the second microparticle is approximately 12 μm.
In this embodiment, it is not always necessary to do so, but the aggregation preventing process is performed on the first microparticle and the second microparticle. Specifically, one of silane coupling treatment, aluminum coupling treatment, titanate coupling treatment, and surfactant treatment may be performed. In this embodiment, the first microparticles and the second microparticles are applied. Then, silane coupling treatment is performed.
In this embodiment, the silane coupling treatment is collectively performed on the nanoparticles, the first microparticles, and the second microparticles. Specifically, a solution obtained by adding nanoparticles, first microparticles, and second microparticles to an aqueous solution obtained by adding 10% by weight of alcohol to a 1-2% by weight acetic acid aqueous solution is ultrasonically stirred. Next, trialkoxysilane is dropped over time while stirring the solution at high speed with a magnetic stirrer. After such dripping, the mixture is stirred for several hours at room temperature, and when hydrolysis is completed, the liquid is neutralized and filtered through a filter to collect particles.
In this manner, nanoparticles, first microparticles, and second microparticles that have been subjected to silane coupling treatment are obtained.
In addition, it is also possible to perform the process similar to the above individually with respect to a nanoparticle, a 1st microparticle, and a 2nd microparticle.

Next, the nanoparticles, the first microparticles, and the second microparticles that have been subjected to the silane coupling treatment as described above are mixed in an acrylic monomer as a transparent material.
In this embodiment, the mixing amount of the nanoparticles, the first microparticles, and the second microparticles is an appropriate amount between 0.03 to 0.2 wt%, 1.16 wt%, and 2.32 wt%, respectively. %. In this embodiment, the weight ratio of the first microparticles to the second microparticles is 1: 2.
An acrylic monomer mixed with nanoparticles, first microparticles, and second microparticles was molded into a plate shape and polymerized to obtain a light guide plate 210 in which scattering particles were dispersed.
Such polymerization is performed as follows. First, 0.5% by weight of benzoyl peroxide (BPO) as a polymerization catalyst is added to the monomer methyl metal acrylate (MMA), and 3000 ppm of normal octyl mercaptan is added to the chain transfer agent to obtain a mixed solution. Next, the nanoparticles, the first microparticles, and the second microparticles are added to the mixed solution so as to be 0.10 wt%, 1.16 wt%, and 2.32 wt%, respectively. Next, this is agitated ultrasonically and then deaerated, and then placed in a water bath and prepolymerized at 70 ° C. for 70 minutes. When sol is formed and the viscosity is increased, it is poured into a mold and left in an oven. The polymerization reaction was carried out by placing at 75 ° C. for 40 hours.

  As described above, it was possible to obtain the light guide plate 210 in which at least a part of the nanoparticles are independently dispersed nanoparticles and the scattering particles are dispersed therein.

1 is a perspective view schematically showing a configuration of a liquid crystal display device according to an embodiment of the present invention. The perspective view which shows schematically the structure of the backlight of the liquid crystal display device shown in FIG.

Explanation of symbols

100 liquid crystal panel 200 backlight 210 light guide plate 220 light source

Claims (15)

A transparent material in which scattering particles are dispersed is formed into a plate shape, and light introduced from the light source facing the end surface is scattered by the scattering particles and emitted from the emission surface. A light guide plate,
The scattering particles include nanoparticles,
Light guide plate. The nanoparticles have a maximum diameter of 1 nm to 100 nm.
The light guide plate according to claim 1. The nanoparticles have a maximum diameter of approximately 30 nm.
The light guide plate according to claim 1 or 2. The scattering particles include microparticles having a maximum diameter of 1 μm to 100 μm.
The light guide plate according to claim 1. The microparticles include a plurality of types of microparticles having different maximum diameters.
The light guide plate according to claim 4. The microparticles include first microparticles having a maximum diameter of 1 μm to 10 μm and second microparticles having a maximum diameter of 10 μm to 30 μm.
The light guide plate according to claim 5. The first microparticle has a maximum diameter of approximately 3.5 μm, and the second microparticle has a maximum diameter of approximately 12 μm.
The light guide plate according to claim 6. In the transparent material, the first microparticles are contained in an amount of 0.1 wt% or more and 15 wt% or less, and the second microparticles are contained in an amount of 0.1 wt% or more and 30 wt% or less.
The light guide plate according to claim 6. The weight ratio of the first microparticles to the second microparticles is approximately 1: 2.
The light guide plate according to claim 6. The nanoparticles are at least a part of independently dispersed nanoparticles,
The light guide plate according to claim 1. The nanoparticles are those subjected to anti-aggregation treatment.
The light guide plate according to claim 1. The microparticles are those that have undergone anti-aggregation treatment.
The light guide plate according to claim 4. A transparent material is formed in a plate shape, and is a method of manufacturing a light guide plate that emits light introduced into the light source from a light source facing the end surface from the emission surface,
Disperse the particles containing nanoparticles that can scatter light in the monomer,
By forming and polymerizing the monomer containing the nanoparticles into a plate shape, a light guide plate that is a plate-like polymer in which scattering particles are dispersed is obtained.
Manufacturing method of light guide plate.   The backlight which makes a light source face the edge part of the light-guide plate in any one of Claims 1-12.   A liquid crystal display device comprising the backlight according to claim 14.

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