JP2008304500A - Diffusion plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diffusion plate capable of emitting light brightly, uniformly and evenly over the whole surface independent of arrangement and shape of a light source, and capable of removing lamp irregularity. <P>SOLUTION: A plurality of elliptic cylinder lenses 7 of the same shape of which each cross-section takes the form of a part of an ellipse are arranged side by side on one side surface such that the major axis of the ellipse orthogonally crosses the face 8, wherein elliptical rate (major diameter/minor diameter) b/a of the ellipse and angle θ of a valley part formed by neighboring elliptic cylinder lenses 7 fall into the following ranges. The ranges are respectively 1.5≤b/a and 0°<θ≤70°. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a diffuser plate, a direct type backlight mounted with the diffuser plate, and a liquid crystal display.

  In recent years, flat-panel televisions such as liquid crystal televisions and plasma televisions have been expanded instead of cathode-ray tubes, and particularly liquid crystal televisions are growing rapidly. Since the liquid crystal is not self-luminous, a backlight (also referred to as a back light source device) is necessary, and two types of backlight, an edge light type and a direct type, are generally used.

  The edge light type is a method in which a linear light source is placed on the edge of a liquid crystal panel and surface light is emitted by a light guide plate. It is suitable for a thin and light personal computer monitor, but it is said that it is difficult to increase the screen size and brightness. On the other hand, the direct type is a method in which a large number of linear light sources are arranged directly under a liquid crystal panel and surface emission is performed with a diffusion plate. It is easily used for large screens and high brightness and is preferred for liquid crystal televisions.

  The direct-type backlight type liquid crystal display has a structure in which a reflector, a linear light source, a diffuser, an optical film, and a liquid crystal panel are sequentially arranged. Among the components, the diffuser diffuses the light from the linear light source, and it is important to improve the uniformity by blurring the linear light and darkness (so-called lamp unevenness) formed in the linear light source gap adjacent to the bright line directly above the linear light source. Have an optical role.

  In recent years, there has been a movement to reduce the number of linear light sources used in backlights for cost reduction, and there is a tendency to increase the spacing between adjacent linear light sources (so-called lamp pitch). It was a problem in terms of quality.

  As a method for eliminating the lamp unevenness, a method of thickening the light diffusing material in a resin diffusion plate containing a light diffusing material can be considered. However, this method has a problem in that the luminance is lowered.

  In Patent Documents 1 to 3, the development of a high-performance plate that has a prism shape, an elliptical column shape, or the like on the surface of the diffusion plate, prevents a decrease in brightness by a light condensing function of the lens, and eliminates lamp unevenness. Has been done.

  However, Patent Documents 1 to 3 do not completely eliminate the lamp unevenness. Furthermore, if the arrangement of the light sources (distance between the light sources, distance between the light source and the diffuser) is changed, the angle of light incident on the diffuser and the light flux density will change, and the conditions for satisfying uniform light output will change. There was also a problem that the shape of the diffusion plate had to be changed for each arrangement and shape.

JP 2007-18939 A JP 2006-162887 A Japanese Patent Publication No. 51-15418

  In the recent display industry, in addition to light source reduction for cost reduction, the layout of light sources has been changing rapidly due to the diversification of designs (eg, thinning) due to diversifying tastes, and the speed of change has changed. Accelerating. On the other hand, changing the shape of the diffusion plate is unavoidable, but changing the shape of the mold is inevitable, but it takes several months to manufacture the mold, making it increasingly difficult to keep up with the speed of changes in the industry. ing.

  Therefore, the present invention provides a diffuser plate that can emit light uniformly and uniformly without any unevenness regardless of the arrangement and shape of the light source, and can eliminate the lamp unevenness, and a direct backlight and liquid crystal display equipped with the diffuser plate The purpose is to provide.

  That is, in the diffusing plate of the present invention, on one surface, a plurality of elliptical cylindrical lenses having the same shape whose cross section forms a part of an ellipse are arranged side by side so that the major axis of the ellipse is orthogonal to the surface. The ellipticity (major axis / minor axis) b / a and the angle θ of the valley formed by the adjacent elliptic cylinder lens are in the following range.

1.5 ≦ b / a
0 ° <θ ≦ 70 °

  When the diffusing plate of the present invention is used, in a direct-type backlight type liquid crystal display, it is possible to prevent a decrease in luminance and eliminate lamp unevenness. Even if the shape and arrangement of the light source of the direct type backlight are changed, the effect does not change.

  Hereinafter, the present invention will be described in detail.

<Backlight, liquid crystal display>
FIG. 1 shows an example of a direct backlight type liquid crystal display of the present invention.

  As shown in FIG. 1, in the liquid crystal display, a reflection plate 1, a linear light source 2, a diffusion plate 3, an optical film 4, and a liquid crystal panel 5 are sequentially arranged from the inside. Among these, the direct backlight 6 is composed of the reflector 1 to the optical film 4.

  The reflector 1 is made of a metal plate coated with a reflector, or a white or silver polyethylene terephthalate (PET) -based or polycarbonate (PC) -based reflective film.

  The linear light source 2 is a light source having a linear shape, and the most common linear light source used in a liquid crystal display is a fluorescent tube having a diameter of 2 to 4 mm called a cold cathode tube (abbreviated as CCFL). Cold cathode tubes include straight lines, U-shaped tubes, W-shaped tubes, etc., and the longer the linear portion, the more preferred for large screens.

  The diffuser plate 3 is an important optical member that scatters the light from the linear light source 2 and converts the linear light source into a planar light source. As shown in FIG. 1, the diffusing plate 3 is disposed such that the lens forming surface is opposite to the linear light source 2 and the longitudinal direction of the lens coincides with the longitudinal direction of the linear light source 4. Details of the diffusion plate 3 will be described later.

  The optical film 4 improves so-called luminance, such as a diffusion film 4-1 that further scatters or collects light transmitted through the diffusion plate 3, a prism film 4-2 that collects scattered light, and a reflective polarizing film 4-3. It is a group of a plurality of highly functional films such as a film to be made.

  As the liquid crystal panel 5, known ones such as VA type and IPS type can be used.

<Diffusion plate>
FIG. 2 shows a schematic perspective view of an example of the diffusion plate of the present invention. FIG. 3 is a schematic enlarged view of the elliptical lens portion of the diffusion plate of FIG.

  As shown in FIG. 2, the diffuser plate of the present invention has an elliptical cylindrical lens 7 having the same shape on one surface, and the generatrix is parallel with adjacent elliptical cylindrical lenses 7 in contact with each other at the sheet surface 8. A plurality are arranged in parallel. As shown in FIG. 3, the elliptical lens 7 is arranged such that its cross section forms part of the ellipse 9 and the major axis b of the ellipse 9 is orthogonal to the sheet surface 8.

  The ellipticity (major axis / minor axis) b / a of the ellipse 9 is 1.5 ≦ b / a, preferably 1.7 ≦ b / a, and more preferably 2.2 ≦ b / a. The light exit angle at the lens portion is determined by the angle of light transmitted through the diffuser plate, the exit surface angle, and the refractive index of the resin. When b / a is less than 1.5, the incident angle increases. Of the light emitted from the lens, the area of the light emitting part that emits light from the front is rapidly reduced. Therefore, when used in a direct type backlight, the luminance between the linear light sources is lower (a dark portion is generated) than that immediately above the linear light sources, and uniform light emission is not achieved.

  Further, the angle of the valley formed by the adjacent elliptic cylinder lenses 7, that is, the angle θ formed by the tangent lines at the points where the adjacent elliptic cylinder lenses 7 contact is 0 ° <θ ≦ 70 °, preferably 20 ° ≦ θ ≦ 70 °. As described above, the light emission angle at the lens portion is determined by the angle of light transmitted through the diffusion plate, the emission surface angle, and the refractive index of the resin, but when the angle θ of the valley exceeds 70 °. The emitted light suddenly decreases in the vicinity of the center between the linear light sources. Therefore, when used in a direct type backlight, the luminance between the linear light sources is lower (a dark portion is generated) than that immediately above the linear light sources, and uniform light emission is not achieved.

  The pitch of the elliptic lens 7 is preferably 50 μm to 500 μm. If the pitch is less than 50 μm, there is a possibility that the emitted light from the lens does not become the intended pattern due to the processing accuracy of the mold for molding the diffusion plate. If the pitch exceeds 500 μm, the incident light is generated even within a single lens. There is a possibility that the angle and the density of the light are remarkably different at the light receiving location and the intended emission pattern is not obtained.

  The major axis of the ellipse 9 is not particularly limited, but is preferably 75 μm to 22800 μm. The minor axis of the ellipse 9 is not particularly limited, but is preferably 50 μm to 3600 μm, and more preferably 50 μm to 2800 μm. Further, the height of the elliptical lens 7 is not particularly limited, but is preferably 15 μm to 1020 μm, and more preferably 15 μm to 500 μm.

  The thickness of the diffusing plate is preferably 0.4 mm to 5 mm, and more preferably 1 mm to 3 mm.

  The diffusing plate is preferably one in which light diffusing fine particles are blended as a light diffusing material in a translucent resin.

  As the translucent resin, an acrylic resin, a styrene-methyl methacrylate copolymer resin (MS resin), a styrene resin, a PC resin, a cyclic olefin resin, etc., which have high optical characteristics, particularly high transmittance, are preferable. In order to prevent deformation due to water absorption, a resin having a low water absorption rate is more preferable. For example, styrene resin, MS resin, PC resin, and cyclic olefin resin are more preferable.

  The light diffusing fine particles preferably blended in the translucent resin may be either organic or inorganic fine particles, such as acrylic crosslinked fine particles, MS crosslinked fine particles, styrene crosslinked fine particles, silicone crosslinked fine particles, calcium carbonate, Examples thereof include titanium oxide, barium sulfate, talc, and mica.

  The light diffusing fine particles are preferably spherical, spherical, elliptical, flat, scaly, polygonal, cubic, and rectangular parallelepiped, and the particle diameter is preferably 1 to 30 μm with good light scattering performance.

  The blending amount of the light diffusing fine particles is preferably 3 parts by weight or less with respect to 100 parts by weight of the translucent resin in order to prevent a decrease in luminance.

  The diffuser plate may be a single sheet in which a light diffusing material (light diffusing fine particles) is blended with a translucent resin, but may be a laminated sheet for improving light resistance and improving surface hardness. In particular, it is more preferable to laminate a 10 to 100 μm surface layer containing an ultraviolet absorber for improving light resistance.

  Examples of the method for forming a lens on the surface of the diffusion plate include extrusion molding, UV molding, thermal transfer, compression molding, shaving, etching, and other various methods.

  Extrusion molding and thermal transfer are continuous molding processes in which the surface shape of a die roll engraved with a lens shape by cutting or etching is transferred to the surface of the diffusion plate and cooled and solidified during the extrusion process for producing the diffusion plate. . UV molding may be a continuous extrusion process or a single wafer batch process, but is a method of forming a lens shape on the surface of the diffusion plate by ultraviolet curing rather than cooling and solidification. Compression molding is a method of forming a shape by thermally compressing a planar mold engraved with a lens shape onto the surface of a diffusion plate.

  As a method for producing a mold roll or a planar mold, any method may be used as long as a predetermined lens shape can be dug, such as cutting, etching, and electrical discharge machining.

<Evaluation method>
(1) Measurement of lens shape The diffuser plate was cleaved to expose the lens cross section, and the pitch and height of the lens were measured under an optical microscope. Next, a cross-sectional photograph of the lens was taken, and the ellipticity of the lens was determined by comparing the cross-sectional photograph with the basic ellipse shape using image software. The obtained pitch, height, and ellipticity were substituted into the ellipse formula, and the tangent angle of the lens skirt was calculated. Furthermore, the angle θ of the valley portion was obtained from the tangential angle.

(2) Luminance and Visibility of Light Source Image The diffusion plate was mounted on a 32-inch direct backlight type evaluation liquid crystal display devices I to III, and the luminance and the visibility of the light source image were measured.

  As shown in FIG. 1, each evaluation liquid crystal display device has a white PET reflecting sheet (reflecting plate 1), a cold cathode tube having a diameter of 3 mm as a linear light source 2, and the number and pitch intervals shown in Table 1. Arranged in parallel, a diffusion plate 3 is provided at a distance shown in Table 1, and a diffusion film 4-1, a prism film 4-2, and a reflective polarizing film 4-3 are sequentially arranged as an optical film 4. On top of that, a VA type liquid crystal panel 5 is mounted. The diffusion plate 3 was mounted so that the lens forming surface was in contact with the optical film 4 and the longitudinal direction of the lens and the linear light source was matched.

(2-1) Luminance The luminance at the center of the screen was measured from a position 50 cm away using a luminance meter (BM-7 manufactured by Topcon Corporation).

(2-2) Visibility of light source image It was confirmed whether the light source image was visually observed from the front of the screen, and evaluated according to the following criteria.
○: The light source image is not visible Δ: The light source image is somewhat visible ×: The light source image is clearly visible

<Example 1>
100 parts by weight of polystyrene resin (PSPS manufactured by PS Japan Co., Ltd.) as a translucent resin and 0.1 part by weight of silicone-based crosslinked fine particles (KMP manufactured by Shin-Etsu Chemical Co., Ltd., average particle size 2 μm) as a diffusing material are added to an extruder. did.

  The resin melt-kneaded by the extruder was widened and discharged by a mold called a sheet T-die, and wound around three cooling rolls to form a sheet having a thickness of 1.5 mm.

  This sheet was heated to about 150 ° C., and a die having a surface engraved with grooves in which elliptical columnar shapes were arranged in parallel was thermocompression bonded to obtain a diffusion plate shown in FIG. The evaluation results are shown in Table 2.

<Examples 2-12, Comparative Examples 1-6>
A diffusion plate was produced and evaluated in the same manner as in Example 1 except that the content of the diffusing material and the lens shape were changed as shown in Table 2. The results are shown in Table 2.

<Comparative Example 7>
A diffusing plate was produced and evaluated in the same manner as in Example 1 except that the diffusing material content was changed as shown in Table 3, and the lens shape was changed to a linear prism having an apex angle of 110 ° and a prism pitch of 120 μm. The results are shown in Table 3.

<Comparative Examples 8 and 9>
A diffusing plate was produced and evaluated in the same manner as in Example 1 except that the diffusing material content was changed as shown in Table 3, and no lens was formed. The results are shown in Table 3.

<Comparative Example 10>
A diffusion plate was produced in the same manner as in Example 1 except that the content of the diffusing material was changed as shown in Table 3 and the surface was roughened by sandblasting without forming a lens and the surface roughness was Ra = 15. And evaluated. The results are shown in Table 3.

  The diffusion plate of the present invention can be suitably used as a diffusion plate for a direct type backlight type liquid crystal display.

It is a schematic sectional drawing which shows an example of the liquid crystal display of this invention. It is a schematic perspective view of an example of the diffusion plate of the present invention. FIG. 3 is a schematic enlarged view of an elliptic cylindrical lens portion of the diffusion plate of FIG. 2.

Explanation of symbols

1 Reflector 2 Linear light source (cold cathode tube)
DESCRIPTION OF SYMBOLS 3 Diffusion plate 4 Optical film 4-1 Diffusion film 4-2 Prism film 4-3 Reflective polarizing film 5 Liquid crystal panel 6 Direct type backlight 7 Ellipsoidal column lens 8 Sheet surface 9 Ellipse

Claims (5)

On one surface, a plurality of elliptical cylindrical lenses having the same shape whose cross section forms a part of an ellipse are arranged side by side so that the major axis of the ellipse is orthogonal to the surface, and the ellipticity of the ellipse (major axis / minor axis) A diffuser plate characterized in that b / a and the angle θ of the valley formed by the adjacent elliptic cylinder lenses are in the following range.
1.5 ≦ b / a
0 ° <θ ≦ 70 °   The diffusion plate according to claim 1, wherein an angle θ of the valley portion is 20 ° ≦ θ ≦ 70 °.   The diffusion plate according to claim 1 or 2, wherein the pitch of the elliptical cylindrical lens is 50 µm to 500 µm.   It is a direct type backlight arrange | positioned in order of a reflecting plate, a linear light source, a diffuser plate, and an optical film, Comprising: The said diffusion slope is a diffuser plate in any one of Claims 1-3, The said elliptic cylinder A direct type backlight comprising: a lens disposed opposite to the linear light source; and the longitudinal direction of the elliptical lens and the longitudinal direction of the linear light source coincide with each other.   5. A liquid crystal display, wherein a liquid crystal panel is disposed on the direct type backlight according to claim 4.

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