WO2008111718A1 - Light guide panel for liquid crystal display having light diffusion material and back light unit using thereof - Google Patents

Light guide panel for liquid crystal display having light diffusion material and back light unit using thereof Download PDF

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Publication number
WO2008111718A1
WO2008111718A1 PCT/KR2007/005971 KR2007005971W WO2008111718A1 WO 2008111718 A1 WO2008111718 A1 WO 2008111718A1 KR 2007005971 W KR2007005971 W KR 2007005971W WO 2008111718 A1 WO2008111718 A1 WO 2008111718A1
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WO
WIPO (PCT)
Prior art keywords
light
guide plate
light guide
prisms
plate according
Prior art date
Application number
PCT/KR2007/005971
Other languages
French (fr)
Inventor
Sang Hum Lee
O Yong Jeong
Man Suk Kim
Original Assignee
Cheil Industries Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Cheil Industries Inc. filed Critical Cheil Industries Inc.
Priority to CN200780052144XA priority Critical patent/CN101641619B/en
Publication of WO2008111718A1 publication Critical patent/WO2008111718A1/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0033—Means for improving the coupling-out of light from the light guide
    • G02B6/0035—Means for improving the coupling-out of light from the light guide provided on the surface of the light guide or in the bulk of it
    • G02B6/0038—Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/02—Diffusing elements; Afocal elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0033—Means for improving the coupling-out of light from the light guide
    • G02B6/0035—Means for improving the coupling-out of light from the light guide provided on the surface of the light guide or in the bulk of it
    • G02B6/0036—2-D arrangement of prisms, protrusions, indentations or roughened surfaces
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0033—Means for improving the coupling-out of light from the light guide
    • G02B6/0035—Means for improving the coupling-out of light from the light guide provided on the surface of the light guide or in the bulk of it
    • G02B6/004—Scattering dots or dot-like elements, e.g. microbeads, scattering particles, nanoparticles
    • G02B6/0041—Scattering dots or dot-like elements, e.g. microbeads, scattering particles, nanoparticles provided in the bulk of the light guide
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0033—Means for improving the coupling-out of light from the light guide
    • G02B6/005—Means for improving the coupling-out of light from the light guide provided by one optical element, or plurality thereof, placed on the light output side of the light guide
    • G02B6/0051—Diffusing sheet or layer

Definitions

  • the present invention relates to a light guide plate for a back light unit of a liquid crystal display device, and more particularly to a light guide plate capable of improving visibility and brightness significantly by distributing a diffusion material in the overall volume of a front prism provided on the front surface of the light guide plate upon which light exits.
  • a liquid crystal display (hereinafter, referred to simply as a
  • LCD liquid crystal
  • the LCD device Since the LCD device is not a self-luminescent device, it must be provided with a back light unit as a light source to generate light. An image is displayed in such a manner that transmittance of light generated from the back light unit is adjusted in a liquid crystal panel, in which liquid crystals are uniformly arranged.
  • FIG. 1 is an exploded perspective view showing a back light unit of a conventional LCD device.
  • LCD back light units are classified into a direct-type back light unit in which the light source is disposed directly beneath an LCD panel 100, and an edge-type back light unit in which the light source is disposed at the side of the LCD panel 100.
  • the back light unit shown in FlG. 1 is an edge-type back light unit.
  • the conventional LCD back light unit includes a light source 105, a light guide plate 112, a reflection plate 115, a diffusion sheet 120, a prism sheet 125, and a protective sheet 130.
  • the light source 105 serves to emanate light initially in the LCD device.
  • Various types of light source 105 can be used, however the LCD device generally employs a cold cathode fluorescence lamp (CCFL) as the light source 105, which has a low power consumption and emits highly bright white light.
  • CCFL cold cathode fluorescence lamp
  • the light guide plate 112 is provided below an LCD panel 100 and near one side of the light source 105.
  • the light guide plate 112 serves to convert spot light generated from the light source 105 into plane light and then project the plane light forward to the LCD panel 100.
  • the reflection plate 115 is provided on a rear side of the light guide plate
  • the reflection plate 115 serves to reflect light emitted from the light source 105 toward the LCD panel 100 disposed in front of the reflection plate 112.
  • the diffusion sheet 120 is provided on a front side of the light guide plate 112.
  • the diffusion sheet 120 serves to uniformize light passing through the light guide plate 112.
  • the protective sheet 130 is provided above the prism sheets 125.
  • the protective sheet 130 serves to prevent scratches on the prism sheets 125, and to prevent Moire effect from occurring when using the prism sheets 125 arranged in two layers in the vertical and horizontal directions.
  • the conventional back light unit 10 further includes a frame or a housing, to which the respective components constituting the back light unit 10 are fixed, and a back cover or a lamp housing for protecting the back light unit 10 and supporting the back light unit 10 while maintaining the strength of the back light unit 10.
  • FIGs. 2 and 3 are enlarged sectional views of a light guide plate illustrating progress of light emitted from a light source 105 through the light guide plate 112.
  • the light source 105 is generally disposed at the edge of the back light unit 10 (in the case of LCD televisions, the light source 105 is directly disposed at the rear of the panel).
  • the light guide plate 112 is used.
  • the light guide plate 112 is generally made of a transparent acryl material, which has a high strength, and thus, is not easily broken or deformed, is light in weight, and has a high visible-ray transmissivity.
  • the light guide plate 112 serves to allow light emitted from the light source 105 to be uniformly projected to the overall surface of the light guide plate 112.
  • the light is not uniformly projected to the overall surface of the light guide plate 112, but concentrated on both ends of the light guide plate 112. This is because the light guide plate 112 guides the light from the light source 105 to the opposite side of the light guide plate 112.
  • the rear surface of the light guide plate 112 is subjected to a specific treatment to cause scattered reflection of light in the light guide plate 112 such that light can be transmitted through the overall surface of the light guide plate 112.
  • the rear surface of the light guide plate 112 is formed with prominence/depression parts 113 which have a predetermined shape designed in consideration of a distance from the light source 105 and the like.
  • the prominence/depression parts 113 is formed on the rear surface of the light guide plate 112, plane light having higher brightness and uniformity is emitted through the overall surface of the light guide panel of the liquid crystal display device.
  • the LCD device When the LCD device is manufactured according to the above-described method, however, there occurs a phenomenon that the intensity of the light is high at the areas at which the prominence/depression parts 113 are formed, and, on the other hand, the intensity of the light is low at the other areas at which the prominence/depression parts 113 are not formed, i.e., the panel is spotted. As a result, the visibility is decreased. Especially when the size of the panel is great, the amount of the light reaching the area far away from the light source 105 is not sufficient, and therefore, the intensity of light is low at the area far away from the light source 105.
  • the diffuser sheet 120 and the prism sheet 125 are used.
  • the use of the diffusion sheet 120 and the prism sheet 125 increases a thickness of the back light unit thereby causing difficulties in thinning the back light unit and increases the manufacturing costs of the back light unit.
  • the light guide plate having the dot prism pattern on its rear surface may have excellent brightness and uniformity without using the prism sheet, the light guide plate has an inferior structure for visibility observed in the back light state with bear eyes.
  • the light guide plate provided with the dot prisms allows light to exit perpendicularly due to its optical structure, thereby exhibiting a high brightness.
  • a diffusion sheet having a low haze (%) and a high transmittance (%) must be used in constituting the back light assembly.
  • the diffusion sheet when used, about 40% of the brightness is reduced, and the dark area and bright area generated in the edge or corner portion of the light guide plate cannot be eliminated completely.
  • the present invention has been made in view of the above problems, and it is an object of the present invention to provide a light guide plate for liquid crystal display (LCD) back light units having high brightness and excellent uniformity and visibility over the entire surface of a panel of the LCD device without using a diffusion sheet or a prism sheet. Another object of the present invention is to provide an LCD back light unit using the light guide plate according to the present invention.
  • LCD liquid crystal display
  • a light guide plate for an LCD device having a stripe pattern comprising: opposite side surfaces, upon which light is incident, and front and rear surfaces connected to the opposite side surfaces for allowing the light to exit therethrough and reflect, respectively, wherein the front surface is provided with a plurality of front prisms, having a predetermined sectional shape, disposed at the front surface of the main body, in which a diffusion material is distributed in the overall volume of the front prisms, and the rear surface is provided with an optical pattern for reflecting light.
  • a back light unit for an LCD device comprising a light guide plate of the present invention, and a light source arranged at one side or opposite sides of the light guide plate.
  • the light guide plate according to a preferred embodiment of the present invention allows sufficient diffusion of light in the light guide plate itself without using a prism sheet and a diffusion sheet. Especially, a dark area or a bright area that can be exhibited in the edge and corner portions of the light guide plate may be eliminated.
  • FIG. 1 is an exploded perspective view showing a back light unit of a conventional LCD device
  • FIGs. 2 and 3 are enlarged sectional views of a light guide plate illustrating progress of light emitted from a light source through the light guide plate;
  • FIG. 4 is a perspective view showing a light guide plate for LCD back light units according to a preferred embodiment of the present invention.
  • FIGs. 5 and 6 are respectively a sectional view along line A-B in FIG. 4;
  • FIGs. 7 through 9 are perspective views showing various different examples of sectional shapes of the front prisms of the light guide plate for LCD back light units according to the present invention;
  • FIG. 10 is an enlarged sectional view of one of the dot prisms according to the present invention shown in FlG. 4;
  • FIGs. 11 through 14 are views showing various different examples of the shapes of the dot prisms;
  • FIGs. 15 through 17 are plan views of the light guide plate for LCD back light units according to the present invention as seen from under the main body of the light guide plate showing the arrangement of the dot prisms;
  • FIGs. 18 and 19 are views showing other examples of an optical pattern formed on a rear surface of a main body of the present invention, and more particularly, views showing a light guide plate formed with a stripe pattern; and
  • FIGs. 20 and 21 are plan views showing other examples of the stripe pattern.
  • FlG. 4 is a perspective view showing a light guide plate for LCD back light units according to a preferred embodiment of the present invention.
  • the light guide plate 20 for LCD back light units is generally made of a transparent acryl material, which has a high strength, and thus, is not easily broken or deformed, is light in weight, and has a high visible-ray transmissivity.
  • the light guide plate 20 includes a main body 200, front prisms 210, and dot prisms 220.
  • the main body 200 includes first side surfaces 201, upon which light is incident, second side surfaces 202, upon which light is not incident, a front surface 203 connected to the first and second side surfaces 201 and 202 and disposed opposite to a panel (not shown) of an LCD device, and a rear surface 205 connected to the first and second side surfaces 201 and 202 and disposed opposite to the front surface 203.
  • the first side surfaces 201 correspond to opposite side surfaces of a main body 200 disposed adjacent to the light sources 206, i.e., the side surfaces upon which light emitted from light sources 206 is incident.
  • the first side surfaces 201 i.e., the surfaces of the light incident sides are subjected to a predetermined surface treatment, such as a treatment of forming a wedge-shaped pattern, a treatment of forming a prominence/depression pattern with a uniformed shape, or a sand blast process, to more effectively diffuse, refract and reflect the light emitted from the light sources 206 to be incident on the first side surfaces 201.
  • a predetermined surface treatment such as a treatment of forming a wedge-shaped pattern, a treatment of forming a prominence/depression pattern with a uniformed shape, or a sand blast process
  • the reason for the above-mentioned surface treatment on the first side surfaces 201 of the main body 200 is that the main body 200 accelerates diffusion, refraction and reflection of the light emitted from the light sources 206 from the moment the light is incident on the main body 200 so as to eliminate high light intensity lines and low light intensity lines generated in partial areas of the main body 200, thereby obtaining the light guide plate with even more uniformity and excellent visibility over the entire main body 200.
  • the second side, surface 202 is connected to the first side surfaces 201 and forms one side surface of the main body 200.
  • the second side surfaces are connected to the first side surfaces 201 and forms one side surface of the main body 200.
  • the second side surfaces are connected to the first side surfaces 201 and forms one side surface of the main body 200.
  • the first side surfaces 201 are different from the first side surfaces 201 in the point that they are not disposed adjacent to the light sources 206, and light emitted from the light sources 206 is not incident thereon.
  • light sources may be optionally disposed adjacent to the second side surfaces.
  • the front surface 203 and the rear surface 205 are surfaces for allowing the light emitted from the light sources 206 and incident upon the side surfaces 201 to exit therethrough.
  • the front surface 203 and the rear surface 205 are connected to the side surfaces 201.
  • the front surface 203 and the rear surface 205 have, respectively, one surface disposed in the main body 200 and the other surface forming one of outer surfaces of the main body 200.
  • front prisms 210 having a predetermined sectional shape and serving to uniformly diffract, refract, and diffuse the light exiting through the main body 200.
  • the front prisms 210 may be disposed over the entire front surface 203 tightly without any space apart from each other, or spaced a predetermined distance from each other.
  • each of the front prisms 210 extends lengthwise indicated by an arrow Q (the direction in which light is emitted from each of the light sources 206) in FIG. 4.
  • FIGs. 5 and 6 are respectively a sectional view along line A-B in FIG. 4. As shown in FIGs. 5 and 6, the light diffusion material 211 is distributed in overall surfaces or inside/outside of the front prisms 210.
  • the light diffusion material 211 is used to even more accelerate light diffusion during the process where light emitted from the light source (see reference numeral 206 in FIG. 4) and incident upon the first side surface 201 is reflected in the dot prisms 220 over the entire rear surface 205 or where light directly exits through the front surface 203.
  • the object of the present invention is to allow the light guide plate to have sufficient diffusivity by itself without using an addition diffusion sheet, the light diffusion material 211 is distributed inside of the front prisms 210 provided on the front surface 203 of the light guide plate 200.
  • the light guide plate of the present invention serves as a plane light source having excellent brightness and diffusivity in its overall surface.
  • the light diffusion material 211 is characterized by being distributed randomly on the overall surface or inside/outside of the front prisms 210. Since the light diffusion material 211 has a self-light-absorbing property, the brightness may be deteriorated when the distribution amount of the light diffusion material 211 is high. Thus, it is necessary to appropriately control the distribution amount of the light diffusion material 211 over the entire front prisms 210.
  • the light diffusion material 211 is preferably contained in an amount of 0.05 to 8% by volume based on the total components constituting the front prisms 210.
  • the light diffusion material may be applied only on the front surface of the light guide plate. If the light diffusion material 211 is contained in the above-mentioned range of volume ratio, the light guide plate can have a very advantageous effect in the point of brightness due to high light diffusivity, light absorbance and light resistance.
  • the light diffusion material 211 is at least one selected from inorganic diffusers, or organic diffusers of silicone-base, acryl-base, or styrene-base.
  • inorganic diffusers examples include SiO 2 , TiO 2 , CaCO 3 , BaSO 4 , AIOH 3 , glass, talc, mica, white carbon, MgO 2 , ZnO 2 , or the like.
  • Siloxane-based light diffusers are siloxane-based crosslinking particles which are solids at room temperature.
  • the siloxane-based light diffusers include both silicon rubber having a low crosslinking density as silicone-based resin particles and hardened silicon resins having a high crosslinking density.
  • silicone-based light diffusers include polyalkyl siloxane resins such as polydimethyl siloxane, polydiethyl siloxane, or silicon resins having a three dimensional network structure such as siloxane with an epoxy as a terminal group.
  • the siloxane-based crosslinking particles are excellent in the weather resistance. Thus, yellowing phenomenon is not generated in the final resin composition in that the composition exposed to light for a prolonged time turns yellow.
  • the siloxane-based diffusers have a refraction index of about
  • the siloxane-based diffusers have an advantage of obtaining light diffusivity and light transmittance in the similar level with the other light diffusers, even though only a small amount is added. It is preferable that the siloxane-based light diffusers used in the present invention use spherical crosslinking fine particles having an average diameter of 1 to 20 ⁇ m.
  • the acryl-based light diffuser used in the present invention is spherical crosslinking particles having an average diameter of 1 to 20 ⁇ m and a refraction index of 1.46 to 1.56.
  • the acryl-based light diffuser is acryl-based mono- functional monomers, and examples thereof include methacrylic acid esters such as ethyl methacrylate, methyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, or phenyl methacrylate; acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, or benzyl acrylate; and, if necessary, two or more thereof can be used in combination.
  • the acryl-based light diffusers have advantages in that it controls tactile sensation (touch feel) such as white surface or matt surface having unevenness of the light guide plate, and improves visual quality.
  • Examples of the styrene-based diffusers include styrene, ⁇ -methyl styrene, halogenated styrene, or the like.
  • Inside the front prisms 210 of the light guide plate 200 of the present invention further includes, if necessary, an impact resistance modifier, a light stabilizer, an antistatic agent, a UV absorber, or the like, in addition to the above- mentioned light diffusion material.
  • the impact resistance modifier preferably includes rubber components such as an acrylic rubber or a butadiene rubber, but it is not limited thereto.
  • the rubber component improves properties of the copolymerized methacrylic resin, because the rubber component has high impact resistance and bending elastic modulus.
  • the light stabilizer functions to improve durability of the resin composition even more by capturing free radicals.
  • hindered amines are used as the light stabilizer.
  • the light stabilizer is generally co-used with a UV absorber in a range of not impairing the properties of the present invention.
  • the antistatic agent serves to prevent the front prisms 210 and the light guide plate 200 from electrification by eliminating space charges formed in the front prisms 210 and light guide plate 200.
  • a polymer resin used for fabricating the light guide plate 200 and front prisms 210 is easily electrified by static electricity due to its high surface resistivity. As a result, dusts, or the like, are adhered onto the front prisms causing deterioration in the visual quality of light diffusion plate and reduction in lighting efficiency. Consequently, the antistatic agent is used to prevent change in the lamp color.
  • antistatic agent examples include at least one from poly(ether imide amide), poly(ether ester), poly(ether ester amide), polyalkylene glycol, dodecylbenzene sulfonic acid alkaline metal, tertiary amine, quaternary ammonium, salt, and alkyl amines.
  • the UV absorber is used to block UV emitted from the light source 206 (see FIG. 4). Any UV absorber capable of absorbing a wavelength in the range of
  • the UV absorber absorbs a maximum wavelength in the range of 250 to 320 nm, it is preferable in that the light resistance in the light guide plate 200 is improved, and the coloration of diffusion sheet caused by UV absorption can be inhibited.
  • Specific examples of the UV absorber include at least one from benzophenone, benzotriazole, cyanoacrylate, salicylate, and nickel complex.
  • the front prisms 210 have a triangular lateral sectional shape.
  • the front prisms 210 are not limited thereto and may have various different lateral sectional shapes.
  • FIGs. 7 through 9 are perspective views showing various different examples of sectional shapes of the front prisms 210 of the light guide plate for LCD back light units according to the present invention.
  • the front prisms 210 may be formed without having any predetermined space between one another.
  • the reason why the front prisms 210 are not adjacent to one another but spaced the predetermined distance from one another is to improve uniformity of light and visibility. However, the same effect can be obtained without having any space between one another, when a light diffusion material as in the present invention is used.
  • the front prisms 210 may have a trapezoidal lateral sectional shape as shown in FlG. 8.
  • the front prisms 210 may have a reverse-groove lateral sectional shape having a pointed end and side surfaces of a predetermined radius of curvature as shown in FlG. 9.
  • the lateral sectional shape of each of the front prisms 210 is trapezoidal as shown in FlG. 8, the light is progressed perpendicularly to the panel (not shown) of the LCD device through planes A formed at the upper parts of the respective trapezoidal front prisms 210.
  • each of the front prisms 210 has the reverse-groove lateral sectional shape as shown in FlG. 9, on the other hand, the predetermined radius of curvature of each of the side surfaces of each front prism 210 is preferably 0.01 to 1.0 mm.
  • the front prisms 210 may be formed at one side, which is adjacent to the panel (not shown) of the LCD device, of the front surface 203 or at the other side of the front surface 203.
  • FIGs. 7 through 9 illustrate only the front prism 210 patterns with all in prominent form, but the same or similar effect can be obtained with all in depression form.
  • the ratio of the area occupied by the front prisms 210 to the area occupied by the spaces between the front prisms 210 at the front surface 203 of the main body 200 is in a range of 1:0.5 to 1:10.
  • the ratio of the height h 2 to the pitch W 2 of each of the front prisms 210 shown in FIGs. 7 through 9 is in a range of 0.3 to 0.6. If the ratio of the height h 2 to the pitch w 2 of each of the front prisms 210 is less than 0.3, the horizontal viewing angle is unnecessarily increased, and therefore, the brightness is decreased. If the ratio of the height h 2 to the pitch w 2 of each of the front prisms 210 exceeds 0.5, on the other hand, the horizontal viewing angle is unnecessarily decreased, and therefore, the optical properties are not satisfactory.
  • the rear surface 205 of the main body 200 is provided with an optical pattern having a function to reflect light, emitted from the light source and incident into the main body 200, forward to the front surface 203.
  • the rear surface 205 of the main body 200 is provided with a plurality of dot-shaped prisms having a pattern with a certain arrangement such that the plurality of dot-shaped prisms are spaced a predetermined distance from one another.
  • the dot-shaped prisms are defined as dot prisms 220.
  • the dot prisms 220 are patterns for reflecting the light proceeding to the rear surface 205 through being incident into the light guide plate 200.
  • the arrangement of the patterns may be spaced a predetermine distance from one another, as shown in FIG. 4, or may have various different forms.
  • FIG. 10 is an enlarged sectional view of one of the dot prisms according to the present invention shown in FlG. 4.
  • each of the dot prisms 220 is provided at the surface thereof with prism parts 222 having a predetermined sectional shape (prism parts having a triangular sectional shape are illustrated in FlG. 10).
  • each of the prism parts 222 which are formed at the surface of each of the dot prisms 220, extends in the direction perpendicular to the direction in which light is emitted from each of the light sources 206 (the direction indicated by the arrow Q).
  • the prism parts 222 extend in the direction perpendicular to the direction in which light is emitted from each of the light sources 206 (the direction indicated by the arrow Q)
  • the light is properly refracted and diffused.
  • the prism parts 222 formed at each of the dot prisms 220 extend in the direction perpendicular to the longitudinal direction of the front prisms 210 (the direction perpendicular to the direction indicated by the arrow Q).
  • the light is refracted and diffused by the prism parts 222. Consequently, when the prism parts 222 extend in the direction perpendicular to the longitudinal direction of the front prisms 210, the light is uniformly refracted and diffused.
  • each of the prism parts 222 formed at the surface of each of the dot prisms 220 is triangular as shown in FlG. 10, it is preferable that the interior angle ⁇ i of the triangle is 75 to 90. If the interior angle ⁇ i is smaller than 75° or greater than 90°, the angle between the exiting light and the direction perpendicular to the front surface of the back light unit is increased, and therefore, the brightness at the center is decreased.
  • the ratio of the height hi to the pitch W 1 of each of the prism parts 222 formed at the surface of each of the dot prisms 220 is 0.5 to 0.7. If the ratio of the height hi to the pitch W 1 of each of the prism parts 222 is less than 0.5 or greater than 0.7, the angle between the exiting light and the direction perpendicular to the front surface of the back light unit is increased, and therefore, the brightness at the center is decreased.
  • FIGs. 11 through 14 are views showing various different examples of the shapes of the dot prisms.
  • each of the dot prisms 220 has a plurality of prism parts 222.
  • Each of the dot prisms 220 is formed in a circular shape (FlG. 11), an elliptical shape (FlG. 12), a diamond shape (FlG. 13), and a rectangular shape (FlG. 14).
  • dot prisms 220 may be formed in a combination of the circular shape, the elliptical shape, the diamond shape, and the rectangular shape.
  • the ratio of the minor axis b to the major axis of the elliptical shape is 0.5 to 0.9.
  • the ratio of the minor axis b to the major axis of the elliptical shape is less than 0.5, the optical properties, such as the refraction and the diffraction, are not satisfactory. If the ratio of the minor axis b to the major axis of the elliptical shape exceeds 0.9, on the other hand, the visibility is decreased.
  • each of the dot prisms 220 may have various different shapes, it is most preferable that each of the dot prisms 220 be formed in the elliptical shape as in FIG. 12.
  • the dot prisms 220 may be formed at one side part of the rear surface 205 of the main body 200 or at the other side part of the front surface 203 (when the inside surface of the main body is defined as one side part, the outside surface of the main body is defined as the other side part).
  • FIGs. 15 through 17 are plan views of the light guide plate for LCD back light units according to the present invention as seen from under the main body 200 (FIG. 4) of the light guide plate showing the arrangement of the dot prisms 222.
  • FlG. 15 is a plan view showing the arrangement of the dot prisms 220 in the case where each of the dot prisms 220 is formed in the elliptical shape as shown in FlG. 12, and the light emitted from the light sources 206 (see FlG. 4) is incident upon the opposite side surfaces 201 of the main body 200 of the light guide plate.
  • the dot prisms 220 are arranged in a pattern in which the sizes (the areas occupied by the dot prisms at the rear surface) of the dot prisms 320 are gradually increased toward the middle from the side surfaces 201.
  • the dot prisms 220 are arranged such that the sizes of the dot prisms 220 are gradually increased toward the middle from the side surfaces 201 is that, if the light becomes more distant from the side surfaces 201, upon which the light is incident, the amount of the arrived light is decreased. For this reason, the sizes of the dot prisms 220, which serve to refract and reflect the light, are increased to increase the amount of the refracted light and the amount of the reflected light although the amount of the arrived light is small.
  • FlG. 16 is a plan view showing the arrangement of the dot prisms 220 in the case that each of the dot prisms 220 is formed in the elliptical shape as shown in FlG. 12, and the light emitted from one of the light sources 206 (see FlG. 4) is incident upon only one of the opposite side surfaces 201 of the main body 200 of the light guide plate.
  • the dot prisms 220 are arranged in a pattern in which the sizes of the dot prisms 220 are gradually increased toward the other side surface 201.
  • FlG. 17 is a plan view showing another arrangement of the dot prisms 220.
  • the main body 200 may be further provided at the rear surface 205 thereof with a plurality of second dot prisms 225, which are disposed at the spaces between the dot prisms 220, i.e., the lattice-shaped spaces, in addition to the dot prisms 220 shown in FIGs. 15 and 16.
  • Each of the second dot prisms 225 has prism parts formed at the surface thereof. The prism parts of each of the second dot prisms 225 extend in the direction not parallel with the longitudinal direction of the prism parts 222 (see FlG. 10) formed at the surface of each of the dot prisms 220.
  • the reason why the second dot prisms 225 are further formed is to increase the refractive and reflective indices of the light.
  • the dot prisms 220 are formed in the elliptical shape, although the dot prisms 220 may be formed in the circular shape, the diamond shape, or the rectangular shape as shown in FIGs. 11 through 14.
  • the dot prisms 220 are arranged in a pattern in which the sizes of the dot prisms 220 are gradually increased as the dot prisms 220 become more distant from the side surface 201, upon which the light is incident.
  • the second dot prisms 225 are formed in a circular shape as shown in FlG.
  • the second dot prisms 225 may be formed in another shape, such as a triangular shape, a rectangular shape, a pentagonal shape, a hexagonal shape, an elliptical shape, or a diamond shape.
  • the dot prisms 220 are arranged lengthwise and crosswise at the rear surface 205 of the main body 200 (see FlG. 4) of the light guide plate in a zigzag fashion, and therefore, the odd-numbered lows rows of the dot prisms 220 do not overlap with the even-numbered rows of the dot prisms 220.
  • the reason why the dot prisms 220 are arranged in the zigzag fashion as described above is to maximize the function of the dot prisms in consideration of the direction in which the light is progressed such that the uniformity of the exiting light is further increased, and the visibility is improved.
  • FIGs. 18 and 19 are views showing other examples of an optical pattern formed on a rear surface 205 of a main body 200 of the present invention, and more particularly, views showing a light guide plate provided with stripe patterns 320.
  • FIG. 18 is a plan view showing arrangement form of the stripe patterns 320 when light emitted from the light source 201 (see FIG. 4) is incident from opposite sides of the light guide plate 200. As shown in FIGs. 18 and 19, the rear surface 205 of the light guide plate
  • each stripe pattern 310 is provided with a plurality of prisms 322.
  • the function of the plurality of prisms 322 is the same as that of the dot prisms 222 as described above.
  • the width of the stripe patterns 320 increases as light proceeds from the opposite sides toward the center.
  • the reason for increasing the width of the stripes 320 as the incident light proceeds far from the side 201 is to increase light refraction and reflection amount by increasing the width of the stripe pattern 320, which serves to refract and reflect light, since the amount of light reaching the center away from the side 201 is small.
  • FIG. 19 is a plan view showing an arrangement form of the stripes 320 when light emitted from the light source 206 (see FIG. 4) is incident from one side of the light guide plate 200.
  • the width of the stripe pattern 320 increases as the light proceeds toward the opposite side passing the center.
  • FIGs. 20 and 21 are plan views showing other examples of the stripe pattern.
  • the stripe pattern 320 provided on the rear surface 205 of the light guide pattern 200 is formed such that the width of the stripes increases as the incident light proceeds far from the side 201.
  • the corner portion of the rear surface 205 that is, when light is incident from opposite sides as shown in FIG. 20, the width of the stripe patterns 320 or the length of the prisms 322 formed on the stripe patterns 320 is increased at four corner portion, to thereby overcome the deterioration in the visibility or brightness in the corner portions of the rear surface 205.
  • the width of the stripe patterns 320 at the corner portions of the rear surface is increased as it is close to the light source. This will serve to inhibit dark area generation at the corner portions.
  • prisms 322 formed on the surface of the stripe patterns 320 are spaced a certain distance from one another, and more preferable that the prisms 322 are formed adjacent to each other.
  • the space between the prisms 322 inside the stripe pattern 320 is adjusted, that is, by varying the pitch between the prisms 322 inside the stripes, it is possible to control the brightness and visibility precisely.

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Abstract

A light guide plate for an LCD back light unit having high brightness and excellent light uniformity and visibility in the overall panel of the LCD device without using additional diffusion sheet and prism sheet. The light guide plate includes opposite side surfaces, upon which light is incident, a front surface connected to the opposite side surfaces for allowing the light to exit therethrough, and a rear surface connected to the opposite side surfaces for allowing the light to reflect, in which the front surface is provided with a plurality of front prisms, having a predetermined sectional shape, in which a diffusion material is distributed in the overall volume of the front prisms, and the rear surface is provided with an optical pattern for reflecting light.

Description

[DESCRIPTION]
[Invention Title]
LIGHT GUIDE PANEL FOR LIQUID CRYSTAL DISPLAY HAVING LIGHT DIFFUSION MATERIAL AND BACK LIGHT UNIT USING THEREOF
[Technical Field]
The present invention relates to a light guide plate for a back light unit of a liquid crystal display device, and more particularly to a light guide plate capable of improving visibility and brightness significantly by distributing a diffusion material in the overall volume of a front prism provided on the front surface of the light guide plate upon which light exits.
[Background Art]
In general, a liquid crystal display (hereinafter, referred to simply as a
"LCD") device refers to a device which displays numerals or images through application of an electric field to liquid crystals disposed between two glass substrates, in which the liquid crystals are made of a material having an intermediate phase between a liquid and a solid.
Since the LCD device is not a self-luminescent device, it must be provided with a back light unit as a light source to generate light. An image is displayed in such a manner that transmittance of light generated from the back light unit is adjusted in a liquid crystal panel, in which liquid crystals are uniformly arranged.
FIG. 1 is an exploded perspective view showing a back light unit of a conventional LCD device.
Based on the position of the light source for emitting light, LCD back light units are classified into a direct-type back light unit in which the light source is disposed directly beneath an LCD panel 100, and an edge-type back light unit in which the light source is disposed at the side of the LCD panel 100. The back light unit shown in FlG. 1 is an edge-type back light unit.
As shown in FIG. 1, the conventional LCD back light unit includes a light source 105, a light guide plate 112, a reflection plate 115, a diffusion sheet 120, a prism sheet 125, and a protective sheet 130.
The light source 105 serves to emanate light initially in the LCD device. Various types of light source 105 can be used, however the LCD device generally employs a cold cathode fluorescence lamp (CCFL) as the light source 105, which has a low power consumption and emits highly bright white light.
The light guide plate 112 is provided below an LCD panel 100 and near one side of the light source 105. The light guide plate 112 serves to convert spot light generated from the light source 105 into plane light and then project the plane light forward to the LCD panel 100. The reflection plate 115 is provided on a rear side of the light guide plate
112. The reflection plate 115 serves to reflect light emitted from the light source 105 toward the LCD panel 100 disposed in front of the reflection plate 112.
The diffusion sheet 120 is provided on a front side of the light guide plate 112. The diffusion sheet 120 serves to uniformize light passing through the light guide plate 112.
While passing through the diffusion sheet 120, the light is diffused in horizontal and vertical directions, and brightness is rapidly deteriorated. In this regard, the prism sheets 125 are used to refract and concentrate the light, to thereby enhance brightness. The protective sheet 130 is provided above the prism sheets 125. The protective sheet 130 serves to prevent scratches on the prism sheets 125, and to prevent Moire effect from occurring when using the prism sheets 125 arranged in two layers in the vertical and horizontal directions.
In addition, although not shown in FIG. 1, the conventional back light unit 10 further includes a frame or a housing, to which the respective components constituting the back light unit 10 are fixed, and a back cover or a lamp housing for protecting the back light unit 10 and supporting the back light unit 10 while maintaining the strength of the back light unit 10. FIGs. 2 and 3 are enlarged sectional views of a light guide plate illustrating progress of light emitted from a light source 105 through the light guide plate 112.
As shown in FIG. 2, the light source 105 is generally disposed at the edge of the back light unit 10 (in the case of LCD televisions, the light source 105 is directly disposed at the rear of the panel). As a result, light is not uniformly transmitted over the entire area of the back light unit. Specifically, the edge of the back light unit is brighter than the other area of the back light unit. In order to prevent this phenomenon, the light guide plate 112 is used. The light guide plate 112 is generally made of a transparent acryl material, which has a high strength, and thus, is not easily broken or deformed, is light in weight, and has a high visible-ray transmissivity.
In other words, the light guide plate 112 serves to allow light emitted from the light source 105 to be uniformly projected to the overall surface of the light guide plate 112. In practice, however, in a case where the back light unit 10 is disassembled and light is allowed to emit from the light source 105 located at one side of the light guide plate 112, the light is not uniformly projected to the overall surface of the light guide plate 112, but concentrated on both ends of the light guide plate 112. This is because the light guide plate 112 guides the light from the light source 105 to the opposite side of the light guide plate 112.
Thus, the rear surface of the light guide plate 112 is subjected to a specific treatment to cause scattered reflection of light in the light guide plate 112 such that light can be transmitted through the overall surface of the light guide plate 112. Specifically, the rear surface of the light guide plate 112 is formed with prominence/depression parts 113 which have a predetermined shape designed in consideration of a distance from the light source 105 and the like. When the prominence/depression parts 113 is formed on the rear surface of the light guide plate 112, plane light having higher brightness and uniformity is emitted through the overall surface of the light guide panel of the liquid crystal display device.
When the LCD device is manufactured according to the above-described method, however, there occurs a phenomenon that the intensity of the light is high at the areas at which the prominence/depression parts 113 are formed, and, on the other hand, the intensity of the light is low at the other areas at which the prominence/depression parts 113 are not formed, i.e., the panel is spotted. As a result, the visibility is decreased. Especially when the size of the panel is great, the amount of the light reaching the area far away from the light source 105 is not sufficient, and therefore, the intensity of light is low at the area far away from the light source 105.
In addition, in order to increase the uniformity of the light, the diffuser sheet 120 and the prism sheet 125 are used. However, the use of the diffusion sheet 120 and the prism sheet 125 increases a thickness of the back light unit thereby causing difficulties in thinning the back light unit and increases the manufacturing costs of the back light unit.
In order to solve these problems, a technique for forming a certain pattern on the rear surface (reflective surface) of the light guide plate has been reported. The representative example of this technique is a technique for forming a dot prism pattern on the rear surface of the light guide plate.
Although the light guide plate having the dot prism pattern on its rear surface may have excellent brightness and uniformity without using the prism sheet, the light guide plate has an inferior structure for visibility observed in the back light state with bear eyes.
The light guide plate provided with the dot prisms allows light to exit perpendicularly due to its optical structure, thereby exhibiting a high brightness. In order to realize such advantages, a diffusion sheet having a low haze (%) and a high transmittance (%) must be used in constituting the back light assembly. However, when the diffusion sheet is used, about 40% of the brightness is reduced, and the dark area and bright area generated in the edge or corner portion of the light guide plate cannot be eliminated completely.
Consequently, it is required to carry out a great deal of research to obtain plane light having excellent visibility and high brightness and uniformity at the front surface of the panel of the LCD device without using additional diffusion sheet 120 and prism sheet 125.
[Disclosure] [Technical Problem]
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a light guide plate for liquid crystal display (LCD) back light units having high brightness and excellent uniformity and visibility over the entire surface of a panel of the LCD device without using a diffusion sheet or a prism sheet. Another object of the present invention is to provide an LCD back light unit using the light guide plate according to the present invention.
The present invention is not limited to the above-mentioned objects, and other objects will be apparently understood from the following description of the present invention by those skilled in the art to which the present invention pertains.
[Technical Solution]
In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a light guide plate for an LCD device having a stripe pattern according to a preferred embodiment of the present invention, comprising: opposite side surfaces, upon which light is incident, and front and rear surfaces connected to the opposite side surfaces for allowing the light to exit therethrough and reflect, respectively, wherein the front surface is provided with a plurality of front prisms, having a predetermined sectional shape, disposed at the front surface of the main body, in which a diffusion material is distributed in the overall volume of the front prisms, and the rear surface is provided with an optical pattern for reflecting light.
In accordance with another aspect of the present invention, there is provided a back light unit for an LCD device according to the present invention, comprising a light guide plate of the present invention, and a light source arranged at one side or opposite sides of the light guide plate.
[Advantageous Effects]
The light guide plate according to a preferred embodiment of the present invention allows sufficient diffusion of light in the light guide plate itself without using a prism sheet and a diffusion sheet. Especially, a dark area or a bright area that can be exhibited in the edge and corner portions of the light guide plate may be eliminated.
Therefore, since it is possible to constitute a back light unit through omitting at least a diffusion sheet or a prism sheet used in a conventional back light unit, reducing the production cost of the back light unit becomes possible.
[Description of Drawings]
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
FIG. 1 is an exploded perspective view showing a back light unit of a conventional LCD device; FIGs. 2 and 3 are enlarged sectional views of a light guide plate illustrating progress of light emitted from a light source through the light guide plate;
FIG. 4 is a perspective view showing a light guide plate for LCD back light units according to a preferred embodiment of the present invention;
FIGs. 5 and 6 are respectively a sectional view along line A-B in FIG. 4; FIGs. 7 through 9 are perspective views showing various different examples of sectional shapes of the front prisms of the light guide plate for LCD back light units according to the present invention;
FIG. 10 is an enlarged sectional view of one of the dot prisms according to the present invention shown in FlG. 4; FIGs. 11 through 14 are views showing various different examples of the shapes of the dot prisms;
FIGs. 15 through 17 are plan views of the light guide plate for LCD back light units according to the present invention as seen from under the main body of the light guide plate showing the arrangement of the dot prisms; FIGs. 18 and 19 are views showing other examples of an optical pattern formed on a rear surface of a main body of the present invention, and more particularly, views showing a light guide plate formed with a stripe pattern; and
FIGs. 20 and 21 are plan views showing other examples of the stripe pattern.
[Best Mode]
Now, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.
The advantages and features of the present invention and the method of accomplishing the advantages and features of the present invention will be clearly understood from the preferred embodiment of the present invention, which will be described hereinafter in detail in conjunction with the accompanying drawings. It should be noted, however, that the present invention is not limited to the embodiment but is embodied in various different forms. It should be noted, therefore, that the embodiment is provided merely to complete the disclosure of the present invention and to let those skilled in the art to which the present invention pertains to fully understand the scope of the present invention. The present invention is defined only by the accompanying claims. The same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings.
Furthermore, it should be noted that the sizes of components constituting the present invention are exaggerated in the accompanying drawings for the purpose of clarity. The description of "one of the components is present in or connected to another component" means that the components may be brought into contact with each other, or the components may be spaced a predetermined distance from each other. In the case that the components are spaced a predetermined distance from each other, the description of a third unit for fixing or connecting the two spaced components to another component may be omitted.
FlG. 4 is a perspective view showing a light guide plate for LCD back light units according to a preferred embodiment of the present invention.
As shown in FlG. 4, the light guide plate 20 for LCD back light units according to the preferred embodiment of the present invention is generally made of a transparent acryl material, which has a high strength, and thus, is not easily broken or deformed, is light in weight, and has a high visible-ray transmissivity. The light guide plate 20 includes a main body 200, front prisms 210, and dot prisms 220.
The main body 200 includes first side surfaces 201, upon which light is incident, second side surfaces 202, upon which light is not incident, a front surface 203 connected to the first and second side surfaces 201 and 202 and disposed opposite to a panel (not shown) of an LCD device, and a rear surface 205 connected to the first and second side surfaces 201 and 202 and disposed opposite to the front surface 203.
The first side surfaces 201 correspond to opposite side surfaces of a main body 200 disposed adjacent to the light sources 206, i.e., the side surfaces upon which light emitted from light sources 206 is incident.
The first side surfaces 201, i.e., the surfaces of the light incident sides are subjected to a predetermined surface treatment, such as a treatment of forming a wedge-shaped pattern, a treatment of forming a prominence/depression pattern with a uniformed shape, or a sand blast process, to more effectively diffuse, refract and reflect the light emitted from the light sources 206 to be incident on the first side surfaces 201.
The reason for the above-mentioned surface treatment on the first side surfaces 201 of the main body 200 is that the main body 200 accelerates diffusion, refraction and reflection of the light emitted from the light sources 206 from the moment the light is incident on the main body 200 so as to eliminate high light intensity lines and low light intensity lines generated in partial areas of the main body 200, thereby obtaining the light guide plate with even more uniformity and excellent visibility over the entire main body 200.
The second side, surface 202 is connected to the first side surfaces 201 and forms one side surface of the main body 200. However, the second side surfaces
202 are different from the first side surfaces 201 in the point that they are not disposed adjacent to the light sources 206, and light emitted from the light sources 206 is not incident thereon.
However, light sources may be optionally disposed adjacent to the second side surfaces.
The front surface 203 and the rear surface 205 are surfaces for allowing the light emitted from the light sources 206 and incident upon the side surfaces 201 to exit therethrough. The front surface 203 and the rear surface 205 are connected to the side surfaces 201. The front surface 203 and the rear surface 205 have, respectively, one surface disposed in the main body 200 and the other surface forming one of outer surfaces of the main body 200.
At the front surface 203 are formed front prisms 210 having a predetermined sectional shape and serving to uniformly diffract, refract, and diffuse the light exiting through the main body 200.
The front prisms 210 may be disposed over the entire front surface 203 tightly without any space apart from each other, or spaced a predetermined distance from each other.
In addition, each of the front prisms 210 extends lengthwise indicated by an arrow Q (the direction in which light is emitted from each of the light sources 206) in FIG. 4.
FIGs. 5 and 6 are respectively a sectional view along line A-B in FIG. 4. As shown in FIGs. 5 and 6, the light diffusion material 211 is distributed in overall surfaces or inside/outside of the front prisms 210.
The light diffusion material 211 is used to even more accelerate light diffusion during the process where light emitted from the light source (see reference numeral 206 in FIG. 4) and incident upon the first side surface 201 is reflected in the dot prisms 220 over the entire rear surface 205 or where light directly exits through the front surface 203.
Since the object of the present invention is to allow the light guide plate to have sufficient diffusivity by itself without using an addition diffusion sheet, the light diffusion material 211 is distributed inside of the front prisms 210 provided on the front surface 203 of the light guide plate 200.
Accordingly, the light guide plate of the present invention serves as a plane light source having excellent brightness and diffusivity in its overall surface.
The light diffusion material 211 is characterized by being distributed randomly on the overall surface or inside/outside of the front prisms 210. Since the light diffusion material 211 has a self-light-absorbing property, the brightness may be deteriorated when the distribution amount of the light diffusion material 211 is high. Thus, it is necessary to appropriately control the distribution amount of the light diffusion material 211 over the entire front prisms 210. The light diffusion material 211 is preferably contained in an amount of 0.05 to 8% by volume based on the total components constituting the front prisms 210. In addition, the light diffusion material may be applied only on the front surface of the light guide plate. If the light diffusion material 211 is contained in the above-mentioned range of volume ratio, the light guide plate can have a very advantageous effect in the point of brightness due to high light diffusivity, light absorbance and light resistance.
The light diffusion material 211 is at least one selected from inorganic diffusers, or organic diffusers of silicone-base, acryl-base, or styrene-base.
Examples of the inorganic diffusers include SiO2, TiO2, CaCO3, BaSO4, AIOH3, glass, talc, mica, white carbon, MgO2, ZnO2, or the like.
Siloxane-based light diffusers are siloxane-based crosslinking particles which are solids at room temperature. The siloxane-based light diffusers include both silicon rubber having a low crosslinking density as silicone-based resin particles and hardened silicon resins having a high crosslinking density.
Specific examples of the silicone-based light diffusers include polyalkyl siloxane resins such as polydimethyl siloxane, polydiethyl siloxane, or silicon resins having a three dimensional network structure such as siloxane with an epoxy as a terminal group.
The siloxane-based crosslinking particles are excellent in the weather resistance. Thus, yellowing phenomenon is not generated in the final resin composition in that the composition exposed to light for a prolonged time turns yellow. In addition, the siloxane-based diffusers have a refraction index of about
1.40 to 1.43 which is lower than the other organic crosslinking particles. Thus, the siloxane-based diffusers have an advantage of obtaining light diffusivity and light transmittance in the similar level with the other light diffusers, even though only a small amount is added. It is preferable that the siloxane-based light diffusers used in the present invention use spherical crosslinking fine particles having an average diameter of 1 to 20 μm.
The acryl-based light diffuser used in the present invention is spherical crosslinking particles having an average diameter of 1 to 20 μm and a refraction index of 1.46 to 1.56. The acryl-based light diffuser is acryl-based mono- functional monomers, and examples thereof include methacrylic acid esters such as ethyl methacrylate, methyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, or phenyl methacrylate; acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, or benzyl acrylate; and, if necessary, two or more thereof can be used in combination.
The acryl-based light diffusers have advantages in that it controls tactile sensation (touch feel) such as white surface or matt surface having unevenness of the light guide plate, and improves visual quality. Examples of the styrene-based diffusers include styrene, α-methyl styrene, halogenated styrene, or the like.
Inside the front prisms 210 of the light guide plate 200 of the present invention further includes, if necessary, an impact resistance modifier, a light stabilizer, an antistatic agent, a UV absorber, or the like, in addition to the above- mentioned light diffusion material.
The impact resistance modifier preferably includes rubber components such as an acrylic rubber or a butadiene rubber, but it is not limited thereto.
When copolymerizing a methacrylic resin with a rubber component, the rubber component improves properties of the copolymerized methacrylic resin, because the rubber component has high impact resistance and bending elastic modulus.
The light stabilizer functions to improve durability of the resin composition even more by capturing free radicals. Thus, hindered amines are used as the light stabilizer. The light stabilizer is generally co-used with a UV absorber in a range of not impairing the properties of the present invention.
The antistatic agent serves to prevent the front prisms 210 and the light guide plate 200 from electrification by eliminating space charges formed in the front prisms 210 and light guide plate 200. In addition, a polymer resin used for fabricating the light guide plate 200 and front prisms 210 is easily electrified by static electricity due to its high surface resistivity. As a result, dusts, or the like, are adhered onto the front prisms causing deterioration in the visual quality of light diffusion plate and reduction in lighting efficiency. Consequently, the antistatic agent is used to prevent change in the lamp color. Specific examples of the antistatic agent include at least one from poly(ether imide amide), poly(ether ester), poly(ether ester amide), polyalkylene glycol, dodecylbenzene sulfonic acid alkaline metal, tertiary amine, quaternary ammonium, salt, and alkyl amines.
The UV absorber is used to block UV emitted from the light source 206 (see FIG. 4). Any UV absorber capable of absorbing a wavelength in the range of
250 to 280 nm can be utilized. When the UV absorber absorbs a maximum wavelength in the range of 250 to 320 nm, it is preferable in that the light resistance in the light guide plate 200 is improved, and the coloration of diffusion sheet caused by UV absorption can be inhibited. Specific examples of the UV absorber include at least one from benzophenone, benzotriazole, cyanoacrylate, salicylate, and nickel complex.
Referring back to FlG. 4, the front prisms 210 have a triangular lateral sectional shape. However, the front prisms 210 are not limited thereto and may have various different lateral sectional shapes. FIGs. 7 through 9 are perspective views showing various different examples of sectional shapes of the front prisms 210 of the light guide plate for LCD back light units according to the present invention.
As shown in FIG. 7, the front prisms 210 may be formed without having any predetermined space between one another. The reason why the front prisms 210 are not adjacent to one another but spaced the predetermined distance from one another is to improve uniformity of light and visibility. However, the same effect can be obtained without having any space between one another, when a light diffusion material as in the present invention is used.
The front prisms 210 may have a trapezoidal lateral sectional shape as shown in FlG. 8. Alternatively, the front prisms 210 may have a reverse-groove lateral sectional shape having a pointed end and side surfaces of a predetermined radius of curvature as shown in FlG. 9. In the case that the lateral sectional shape of each of the front prisms 210 is trapezoidal as shown in FlG. 8, the light is progressed perpendicularly to the panel (not shown) of the LCD device through planes A formed at the upper parts of the respective trapezoidal front prisms 210.
In the case where each of the front prisms 210 has the reverse-groove lateral sectional shape as shown in FlG. 9, on the other hand, the predetermined radius of curvature of each of the side surfaces of each front prism 210 is preferably 0.01 to 1.0 mm.
The front prisms 210 may be formed at one side, which is adjacent to the panel (not shown) of the LCD device, of the front surface 203 or at the other side of the front surface 203.
FIGs. 7 through 9 illustrate only the front prism 210 patterns with all in prominent form, but the same or similar effect can be obtained with all in depression form.
Preferably, the ratio of the area occupied by the front prisms 210 to the area occupied by the spaces between the front prisms 210 at the front surface 203 of the main body 200 is in a range of 1:0.5 to 1:10.
Also preferably, the ratio of the height h2 to the pitch W2 of each of the front prisms 210 shown in FIGs. 7 through 9 is in a range of 0.3 to 0.6. If the ratio of the height h2 to the pitch w2 of each of the front prisms 210 is less than 0.3, the horizontal viewing angle is unnecessarily increased, and therefore, the brightness is decreased. If the ratio of the height h2 to the pitch w2 of each of the front prisms 210 exceeds 0.5, on the other hand, the horizontal viewing angle is unnecessarily decreased, and therefore, the optical properties are not satisfactory. The rear surface 205 of the main body 200 is provided with an optical pattern having a function to reflect light, emitted from the light source and incident into the main body 200, forward to the front surface 203.
Referring back to FlG. 4, the rear surface 205 of the main body 200 is provided with a plurality of dot-shaped prisms having a pattern with a certain arrangement such that the plurality of dot-shaped prisms are spaced a predetermined distance from one another. Hereinafter, the dot-shaped prisms are defined as dot prisms 220.
The dot prisms 220 are patterns for reflecting the light proceeding to the rear surface 205 through being incident into the light guide plate 200. The arrangement of the patterns may be spaced a predetermine distance from one another, as shown in FIG. 4, or may have various different forms.
FIG. 10 is an enlarged sectional view of one of the dot prisms according to the present invention shown in FlG. 4.
As shown in FlG. 10, each of the dot prisms 220 is provided at the surface thereof with prism parts 222 having a predetermined sectional shape (prism parts having a triangular sectional shape are illustrated in FlG. 10).
Preferably, each of the prism parts 222, which are formed at the surface of each of the dot prisms 220, extends in the direction perpendicular to the direction in which light is emitted from each of the light sources 206 (the direction indicated by the arrow Q). When the prism parts 222 extend in the direction perpendicular to the direction in which light is emitted from each of the light sources 206 (the direction indicated by the arrow Q), the light is properly refracted and diffused.
As described above, it is also preferable that the prism parts 222 formed at each of the dot prisms 220 extend in the direction perpendicular to the longitudinal direction of the front prisms 210 (the direction perpendicular to the direction indicated by the arrow Q). The light is refracted and diffused by the prism parts 222. Consequently, when the prism parts 222 extend in the direction perpendicular to the longitudinal direction of the front prisms 210, the light is uniformly refracted and diffused.
When the lateral sectional shape of each of the prism parts 222 formed at the surface of each of the dot prisms 220 is triangular as shown in FlG. 10, it is preferable that the interior angle θi of the triangle is 75 to 90. If the interior angle θi is smaller than 75° or greater than 90°, the angle between the exiting light and the direction perpendicular to the front surface of the back light unit is increased, and therefore, the brightness at the center is decreased.
Also, it is preferable that the ratio of the height hi to the pitch W1 of each of the prism parts 222 formed at the surface of each of the dot prisms 220 is 0.5 to 0.7. If the ratio of the height hi to the pitch W1 of each of the prism parts 222 is less than 0.5 or greater than 0.7, the angle between the exiting light and the direction perpendicular to the front surface of the back light unit is increased, and therefore, the brightness at the center is decreased.
FIGs. 11 through 14 are views showing various different examples of the shapes of the dot prisms. As shown in FIGs. 11 to 14, each of the dot prisms 220 has a plurality of prism parts 222. Each of the dot prisms 220 is formed in a circular shape (FlG. 11), an elliptical shape (FlG. 12), a diamond shape (FlG. 13), and a rectangular shape (FlG. 14). Alternatively, dot prisms 220 may be formed in a combination of the circular shape, the elliptical shape, the diamond shape, and the rectangular shape. When each of the dot prisms 220 is formed in the elliptical shape as shown in FlG. 12, it is preferable that the ratio of the minor axis b to the major axis of the elliptical shape is 0.5 to 0.9.
If the ratio of the minor axis b to the major axis of the elliptical shape is less than 0.5, the optical properties, such as the refraction and the diffraction, are not satisfactory. If the ratio of the minor axis b to the major axis of the elliptical shape exceeds 0.9, on the other hand, the visibility is decreased.
Although the dot prisms 220 may have various different shapes, it is most preferable that each of the dot prisms 220 be formed in the elliptical shape as in FIG. 12.
The dot prisms 220 may be formed at one side part of the rear surface 205 of the main body 200 or at the other side part of the front surface 203 (when the inside surface of the main body is defined as one side part, the outside surface of the main body is defined as the other side part). FIGs. 15 through 17 are plan views of the light guide plate for LCD back light units according to the present invention as seen from under the main body 200 (FIG. 4) of the light guide plate showing the arrangement of the dot prisms 222.
FlG. 15 is a plan view showing the arrangement of the dot prisms 220 in the case where each of the dot prisms 220 is formed in the elliptical shape as shown in FlG. 12, and the light emitted from the light sources 206 (see FlG. 4) is incident upon the opposite side surfaces 201 of the main body 200 of the light guide plate.
When the light emitted from the light sources 206 is incident upon the side surfaces 201 as shown in FlG. 15, the dot prisms 220 are arranged in a pattern in which the sizes (the areas occupied by the dot prisms at the rear surface) of the dot prisms 320 are gradually increased toward the middle from the side surfaces 201.
The reason why the dot prisms 220 are arranged such that the sizes of the dot prisms 220 are gradually increased toward the middle from the side surfaces 201 is that, if the light becomes more distant from the side surfaces 201, upon which the light is incident, the amount of the arrived light is decreased. For this reason, the sizes of the dot prisms 220, which serve to refract and reflect the light, are increased to increase the amount of the refracted light and the amount of the reflected light although the amount of the arrived light is small.
FlG. 16 is a plan view showing the arrangement of the dot prisms 220 in the case that each of the dot prisms 220 is formed in the elliptical shape as shown in FlG. 12, and the light emitted from one of the light sources 206 (see FlG. 4) is incident upon only one of the opposite side surfaces 201 of the main body 200 of the light guide plate.
When the light emitted from one of the light sources 206 is incident upon only one of the side surfaces 201 as shown in FlG. 16, the dot prisms 220 are arranged in a pattern in which the sizes of the dot prisms 220 are gradually increased toward the other side surface 201.
FlG. 17 is a plan view showing another arrangement of the dot prisms 220.
As shown in FlG. 17, the main body 200 (see FlG. 4) may be further provided at the rear surface 205 thereof with a plurality of second dot prisms 225, which are disposed at the spaces between the dot prisms 220, i.e., the lattice-shaped spaces, in addition to the dot prisms 220 shown in FIGs. 15 and 16. Each of the second dot prisms 225 has prism parts formed at the surface thereof. The prism parts of each of the second dot prisms 225 extend in the direction not parallel with the longitudinal direction of the prism parts 222 (see FlG. 10) formed at the surface of each of the dot prisms 220.
The reason why the second dot prisms 225 are further formed is to increase the refractive and reflective indices of the light.
As shown in FIGs. 15 through 17, the dot prisms 220 are formed in the elliptical shape, although the dot prisms 220 may be formed in the circular shape, the diamond shape, or the rectangular shape as shown in FIGs. 11 through 14. In this case, the dot prisms 220 are arranged in a pattern in which the sizes of the dot prisms 220 are gradually increased as the dot prisms 220 become more distant from the side surface 201, upon which the light is incident. The second dot prisms 225 are formed in a circular shape as shown in FlG.
17, although the second dot prisms 225 may be formed in another shape, such as a triangular shape, a rectangular shape, a pentagonal shape, a hexagonal shape, an elliptical shape, or a diamond shape.
As shown in FIGs. 15 through 17 the dot prisms 220 are arranged lengthwise and crosswise at the rear surface 205 of the main body 200 (see FlG. 4) of the light guide plate in a zigzag fashion, and therefore, the odd-numbered lows rows of the dot prisms 220 do not overlap with the even-numbered rows of the dot prisms 220. The reason why the dot prisms 220 are arranged in the zigzag fashion as described above is to maximize the function of the dot prisms in consideration of the direction in which the light is progressed such that the uniformity of the exiting light is further increased, and the visibility is improved.
FIGs. 18 and 19 are views showing other examples of an optical pattern formed on a rear surface 205 of a main body 200 of the present invention, and more particularly, views showing a light guide plate provided with stripe patterns 320.
FIG. 18 is a plan view showing arrangement form of the stripe patterns 320 when light emitted from the light source 201 (see FIG. 4) is incident from opposite sides of the light guide plate 200. As shown in FIGs. 18 and 19, the rear surface 205 of the light guide plate
200 is provided with the stripe patterns 320, and inside each stripe pattern 310 is provided with a plurality of prisms 322.
Here, the function of the plurality of prisms 322 is the same as that of the dot prisms 222 as described above. Hereinafter, the reason for having the stripe patterns 320 as shown in FIGs.
18 and 19 will be described.
As shown in FIG. 18, when light is incident from the opposite sides 201 of the light source, the width of the stripe patterns 320 increases as light proceeds from the opposite sides toward the center. The reason for increasing the width of the stripes 320 as the incident light proceeds far from the side 201 is to increase light refraction and reflection amount by increasing the width of the stripe pattern 320, which serves to refract and reflect light, since the amount of light reaching the center away from the side 201 is small.
FIG. 19 is a plan view showing an arrangement form of the stripes 320 when light emitted from the light source 206 (see FIG. 4) is incident from one side of the light guide plate 200.
As shown in FIG. 19, when the light is incident from only one side of the light guide plate, the width of the stripe pattern 320 increases as the light proceeds toward the opposite side passing the center.
FIGs. 20 and 21 are plan views showing other examples of the stripe pattern.
First, referring to FIG. 20, the stripe pattern 320 provided on the rear surface 205 of the light guide pattern 200 is formed such that the width of the stripes increases as the incident light proceeds far from the side 201. However, the corner portion of the rear surface 205, that is, when light is incident from opposite sides as shown in FIG. 20, the width of the stripe patterns 320 or the length of the prisms 322 formed on the stripe patterns 320 is increased at four corner portion, to thereby overcome the deterioration in the visibility or brightness in the corner portions of the rear surface 205.
Consequently, the width of the stripe patterns 320 at the corner portions of the rear surface is increased as it is close to the light source. This will serve to inhibit dark area generation at the corner portions.
Next, referring to FIG. 21, it is preferable that prisms 322 formed on the surface of the stripe patterns 320 are spaced a certain distance from one another, and more preferable that the prisms 322 are formed adjacent to each other. However, in cases, the space between the prisms 322 inside the stripe pattern 320 is adjusted, that is, by varying the pitch between the prisms 322 inside the stripes, it is possible to control the brightness and visibility precisely. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[CLAIMS]
[Claim 1] A light guide plate for an LCD back light unit comprising: opposite side surfaces, upon which light is incident; a front surface connected to the opposite side surfaces for allowing the light to exit therethrough; and a rear surface connected to the opposite side surfaces for allowing the light to reflect, wherein the front surface is provided with a plurality of front prisms, having a predetermined sectional shape, in which a diffusion material is distributed in the overall volume of the front prisms, and wherein the rear surface is provided with an optical pattern for reflecting light.
[Claim 2] The light guide plate according to claim 1, wherein the diffusion material is at least one selected from an inorganic diffuser or an organic diffuser of silicone-base, acryl-base or styrene-base.
[Claim 3] The light guide plate according to claim 2, wherein the inorganic diffuser is selected from SiO2, TiO2, CaCO3, BaSO4, AlOH3, glass, talc, mica, white carbon, MgO2, or ZnO2.
[Claim 4] The light guide plate according to claim 2, wherein the silicone - based light diffuser is polyalkyl siloxane resins such as polydimethyl siloxane, polydiethyl siloxane, or silicon resins having a three dimensional network structure such as siloxane with an epoxy as a terminal group.
[Claim 5] The light guide plate according to claim 2, wherein the acryl- based light diffuser is methacrylic acid esters such as ethyl methacrylate, methyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, or phenyl methacrylate; or acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, or benzyl acrylate.
[Claim 6] The light guide plate according to claim 2, wherein the styrene- based diffuser is styrene, α-methyl styrene, or halogenated styrene.
[Claim 7] The light guide plate according to claim 1, wherein the light diffusion material is contained in a volume ratio of 0.05 to 8.0% based on the front prism.
[Claim 8] The light guide plate according to claim 1, wherein the front prism has a lateral sectional shape of a triangle, a trapezoid, or a reverse-groove having a predetermined radius of curvature.
[Claim 9] The light guide plate according to claim 1, wherein the front prisms are disposed with a predetermined space apart from one another.
[Claim 10] The light guide plate according to claim 1, wherein the ratio of the area occupied by the front prisms to the area occupied by the spaces between the front prisms at the front surface is in a range of 1:0.5 to 1:10.
[Claim 11] The light guide plate according to claim 1, wherein the ratio of height h2 to pitch w2 of each of the prism parts in each of the dot prisms formed at the rear surface is 0.3 to 0.6.
[Claim 12] The light guide plate according to claim 1, wherein the optical pattern provided on the rear surface is a dot pattern prism or a stripe pattern prism.
[Claim 13] The light guide plate according to claim 12, wherein the dot pattern is any one of a circular shape, an elliptical shape, a diamond shape, and a rectangular shape.
[Claim 14] The light guide plate according to claim 12, wherein the stripe pattern is formed such that the width of the stripes increases as the light proceeds far from the side of incident.
[Claim 15] A back light unit for an LCD device comprising: a light guide plate according to claim 1; and a light source disposed at one side or opposite sides of the light guide plate.
PCT/KR2007/005971 2007-03-14 2007-11-26 Light guide panel for liquid crystal display having light diffusion material and back light unit using thereof WO2008111718A1 (en)

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KR1020070025241A KR100880724B1 (en) 2007-03-14 2007-03-14 Light guide panel for liquid crystal display having light diffusion material and back light unit using thereof

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Also Published As

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TWI461761B (en) 2014-11-21
CN101641619A (en) 2010-02-03
TW200837409A (en) 2008-09-16
KR20080084090A (en) 2008-09-19
KR100880724B1 (en) 2009-02-02

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