JP2010157384A - Direct backlight device, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve superior optical characteristics and improve the yield upon manufacturing. <P>SOLUTION: The direct backlight device is provided with a plurality of linear light sources arranged nearly parallel mutually, a reflecting plate to reflect light from these linear light sources, and a light diffusion plate which has a light incident face into which direct light from the linear light sources and reflected light from the reflecting plate enter and a light outgoing face from which light incident from the incident face is diffused and emitted. At least a part of the light outgoing face has a convex structure group in which a repeating unit consisting of a plurality of convex stripes including two kinds or more of convex tripes 201a, 201b with different shape is periodically arranged, and out of the convex stripes included in the repeating unit, the difference of apex angle between one 201b with largest apex angle (θ2) and the one 201a with smallest apex angle (θ1) is 10° or more, and in the plurality of convex stripes 201a, 201b, the locations of the apexes of the respective convex stripes in thickness direction (Z direction) of the light diffusion plate are set within a range of 5 μm or less for their difference of locations in thickness direction. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a direct backlight device including a light diffusion plate and a liquid crystal display device including the direct backlight device.

  As a backlight device used in a liquid crystal display device, a direct type backlight device is known. A direct type backlight device generally includes a plurality of lamps (cold cathode tubes, etc.) as linear light sources arranged in parallel, and a reflector that is arranged behind the lamp and reflects light emitted from the lamps. A light diffusing plate having a light incident surface on which direct light from the lamp and reflected light from the reflecting plate are incident, a light emitting surface that diffuses and emits light incident from the light incident surface, and the light diffusing plate And an optical sheet (a diffusion sheet or the like) disposed in contact with the light exit surface.

  As a light diffusing plate used in such a direct type backlight device, in order to increase the luminance uniformity, a plurality of ridges having a triangular cross section are formed on the light exit surface according to the distance from the light source. A different arrangement (Patent Document 1), an arrangement in which two types of protrusions having different apex angles are alternately arranged (Patent Document 2), and the like are known.

  Here, the thing of patent document 2 is a convex part (henceforth a high convex part) whose apex angle of a protrusion is an acute angle (50-70 degrees), and comparatively tall, and an apex angle is an obtuse angle ( 110-130 °) and relatively short convex portions (hereinafter also referred to as low convex portions) are alternately combined. In this light diffusing plate, the position in the thickness direction of the diffusing plate in the valley portion of each ridge (the valley portion between adjacent ridges) is substantially the same between each high protruding portion and each low protruding portion. The position in the thickness direction of the top of the ridge (the portion of the ridge line of the ridge) is set so that the high protrusion is high and the low protrusion is low.

  However, since an optical sheet such as a light diffusing sheet or a brightness enhancement film may be disposed in contact with the light exit surface of the light diffusing plate, the optical sheet described in Patent Document 2 has a high convex portion. Since it will be supported by the top part and separated from the top part of the low convex part, there are few contact points with the optical sheet, and when vibration is applied when incorporating into the backlight device of the optical sheet or after incorporation, The friction between the optical sheet and the top of the high convex portion may cause scratches on the top of the optical sheet or the high convex portion, which may cause deterioration of optical characteristics.

  When the light diffusing plate is formed by resin injection molding, the light emitting surface may be taken out by vacuum (negative pressure) adsorption and taken out by a take-out device equipped with a suction cup when the mold is opened. In the thing of patent document 2, since the top part of a low convex part is in a position lower than the top part of a high convex part, when this position difference is large, it is not fully absorbed and falls from an extraction device. In some cases, it is not possible to perform stable conveyance such as failure to take out, and the yield (production amount per unit time) at the time of manufacture may be reduced. These problems can also occur in the same manner as described in Patent Document 1.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a backlight device that has excellent optical characteristics and can improve productivity, and a liquid crystal display device including the backlight device. Is to provide.

As a technique related to the light diffusing plate, a plurality of quadrangular pyramid-shaped convex portions are provided on the light exit surface side of the light diffusing sheet, and the inclination angles of the convex portions are varied stepwise according to the distance from the light source. And a plurality of ridges having different apex angles on the light incident surface side of the light diffusion plate (Patent Document 4, Patent Document 5), and the like.
JP 2005-338611 A JP 2008-146025 A JP 2007-114587 A Special table 2003-511735 gazette JP 2004-331312 A

  The direct type backlight device of the present invention includes a plurality of linear light sources arranged substantially parallel to each other, a reflecting plate that reflects light from these linear light sources, direct light from the linear light source, and the above-mentioned A direct-type backlight device comprising a light incident surface on which reflected light from a reflecting plate is incident and a light diffusing plate having a light emitting surface that diffuses and emits light incident from the light incident surface, wherein the light emission At least a part of the surface has a convex structure group in which repeating units composed of a plurality of convex stripes including two or more types of convex stripes having different shapes are periodically arranged, and the convex stripes included in the repeating unit Among these ridges, the top position of each ridge in the thickness direction of the light diffusing plate is the position in the thickness direction. The difference is within the range of 5 μm or less This is a lower backlight device.

  In the direct type backlight device of the present invention, the position of the bottom portion of each valley portion in the thickness direction of the light diffusing plate in the plurality of valley portions provided between the adjacent ridges is the position in the thickness direction. The difference can be within a range of 5 μm or less.

  In the direct type backlight device of the present invention, the convex stripes are linear prisms extending along the longitudinal direction of the linear light source, and the convex structure group is a prism array in which a plurality of linear prisms are arranged substantially in parallel. The cross section perpendicular to the longitudinal direction of the linear light source of the linear prism can be a polygonal shape.

  In the direct type backlight device of the present invention, the repeating unit may include a ridge whose apex angle is 100 ° or more and a ridge whose apex angle is less than 100 °.

  In the direct type backlight device of the present invention, the abundance ratio of two or more types of protrusions having different shapes included in the repeating unit can be changed continuously or stepwise as the distance from the linear light source increases.

  The direct type backlight device of the present invention may further include an optical film disposed in contact with the light emitting surface of the light diffusing plate.

  The liquid crystal display device of the present invention is a liquid crystal display device including a liquid crystal panel and the above-described direct type backlight device of the present invention that illuminates the liquid crystal panel from the back side.

  According to the present invention, the difference in position in the thickness direction of the light diffusing plate at the tops of the ridges is within a range of 5 μm or less. Therefore, the optical sheets arranged in contact with the light emitting surface of the light diffusing plate are It can be supported by almost all the tops of the ridges, that is, there are many contacts, and even when the optical sheet is assembled or when vibration is applied, the optical sheet and the convex part are scratched, and the optical characteristics Can be prevented from deteriorating. In addition, since the light diffusing plate can be sufficiently adsorbed to the light exit surface during manufacture, stable transfer can be achieved, yield during manufacture can be improved, and productivity can be improved.

  In addition, according to the present invention, excellent optical characteristics can be maintained over a long period of time, so that a high-quality and long-life liquid crystal display device can be provided at low cost.

  Hereinafter, a direct backlight device used in a transmissive liquid crystal display device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a schematic configuration of a direct type backlight device according to an embodiment of the present invention.

  As shown in FIG. 1, a direct type backlight device 100 according to this embodiment includes a plurality of linear light sources 102 arranged substantially in parallel to each other, and a reflector 103 that reflects light from these linear light sources 102. And a light diffusing plate 101 having a light incident surface 101A for receiving the direct light from the linear light source 102 and the reflected light from the reflecting plate 103 and a light emitting surface 101B for diffusing and emitting the light incident from the light incident surface 101A. And a housing (case) 105 for supporting them. On the light diffusion plate 101, an optical film 106 such as a brightness enhancement film (BEF) or a diffusion sheet is disposed. The light diffusing plate 101 and the optical film 106 are fixed to the housing 105 via a fixture 107 at the periphery.

  Although not shown, the direct type backlight device 100 uniformly transmits and illuminates a liquid crystal panel in which a polarizing plate, a liquid crystal cell, a retardation plate, and the like are appropriately arranged on the optical film 106 from the back side. Used for.

  In this embodiment, the XYZ orthogonal coordinate system shown in FIG. 1 is set, the thickness direction (vertical direction in FIG. 1) of the light diffusing plate 101 is set as the Z direction, and linear in a plane orthogonal to the Z direction. In the following description, the longitudinal direction of the light source 102 (the direction orthogonal to the paper surface in FIG. 1) is the X direction, and the arrangement direction of the linear light sources 102 (the left-right direction in FIG. 1) is the Y direction.

  As an example of the shape of the linear light source 102, in addition to a straight line shape, two parallel tubes are connected by one approximately semicircle to form one U-shape, and three parallel tubes are approximately two. Examples include an N-shape that is connected by a semicircle, and a W-shape that four parallel pipes are connected by three approximately semicircles.

  In this embodiment, a cold cathode tube (CCFL) is used as the linear light source 102. However, as the linear light source 102, for example, an external electrode fluorescent tube (EEFL), a xenon lamp, a xenon mercury lamp, a hot cathode tube, and a light emitting diode (LED) arranged in a straight line, an LED and a light guide are used. Combinations and the like can also be used.

  The outer diameter of the linear light source 102 is preferably 1.0 mm to 20.0 mm. The distance d1 between the centers of adjacent linear light sources 102 is preferably 20.0 mm to 200.0 mm. Here, in the case of LEDs arranged in a straight line, a combination of an LED and a light guide, a U-shaped light source, etc., each linear part is considered as one linear light source, and adjacent linear parts Is the distance between the centers of the linear light sources.

  The number of the linear light sources 102 is not particularly limited. For example, when this direct type backlight device is used for a 32-inch liquid crystal display device, the number of linear light sources is, for example, an even number, such as 12, 8, 4, or 2, or an odd number. can do.

  As a material of the reflecting plate 103, a resin colored in white or silver, metal, or the like can be used, and the resin is preferably used from the viewpoint of weight reduction. The color of the reflector 103 is preferably white from the viewpoint of improving the luminance uniformity, but white and silver may be mixed in order to highly balance the luminance and the luminance uniformity.

  The light diffusion plate 101 is a plate material that diffuses and irradiates incident light. As a material constituting the light diffusing plate 101, glass, a mixture of two or more kinds of resins that are difficult to mix, a material in which a light diffusing agent is dispersed in a transparent resin, one kind of transparent resin, and the like can be used. Among these, as the material, a resin is preferable because it is lightweight and easy to mold, and one kind of transparent resin is preferable from the viewpoint that luminance can be easily improved. From the viewpoint of easy adjustment, it is preferable to disperse a light diffusing agent in a transparent resin as a main component.

  The transparent resin is a resin having a total light transmittance of 70% or more measured with a 2 mm-thick plate smooth on both sides based on JIS K7361-1, for example, polyethylene, propylene-ethylene copolymer, Polypropylene, polystyrene, polymethylpentene-1, polysulfone, polyarylate, copolymer of aromatic vinyl monomer and alkyl (meth) acrylate having a lower alkyl group, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate Terephthalic acid-ethylene glycol-cyclohexanedimethanol copolymer, polycarbonate, acrylic resin, and resin having an alicyclic structure. In addition, (meth) acrylic acid is acrylic acid and methacrylic acid.

  The light diffusing agent is a particle having a property of diffusing light, and can be roughly classified into an inorganic filler and an organic filler. Examples of the inorganic filler include silica, aluminum hydroxide, aluminum oxide, titanium oxide, zinc oxide, barium sulfate, magnesium silicate, and a mixture thereof. Examples of the organic filler include acrylic resin, polyurethane, polyvinyl chloride, polystyrene resin, polyacrylonitrile, polyamide, polysiloxane resin, melamine resin, and benzoguanamine resin. Among these, as the organic filler, fine particles composed of polystyrene resin, polysiloxane resin, and cross-linked products thereof are preferable in terms of high dispersibility, high heat resistance, and no coloration (yellowing) during molding. Among these, fine particles made of a cross-linked product of polysiloxane resin are more preferable from the viewpoint of more excellent heat resistance.

  The ratio of the light diffusing agent dispersed in the transparent resin can be appropriately selected according to the thickness of the light diffusing plate, the interval between the linear light sources, and the like. Usually, the total light transmittance of the dispersion is 60% to 98%. It is preferable to adjust the content of the light diffusing agent so as to be, and it is more preferable to adjust the content of the light diffusing agent to be 80% to 98%. By setting the total light transmittance within the above preferable range, the luminance and the luminance uniformity can be further improved.

  The total light transmittance is a value measured with a 2 mm-thick plate smooth on both sides based on JIS K7361-1, and the haze is a value measured on a 2 mm-thick plate smooth on both sides with JIS K7136. .

  The thickness of the light diffusing plate 101 is preferably 0.4 mm to 5 mm, and more preferably 0.8 mm to 4 mm. By setting the thickness of the light diffusing plate within the above preferable range, it is possible to suppress bending due to its own weight and to facilitate the molding.

  FIG. 2 is an enlarged cross-sectional view of a part of the light emission surface of the light diffusion plate 101 of FIG. As shown in FIG. 2, the light incident surface 101 </ b> A of the light diffusing plate 101 is a smooth surface, and the light emitting surface 101 </ b> B has a convex structure group 200. The convex structure group 200 of the light emission surface 101B is a row formed by periodically arranging repeating units composed of a plurality of convex stripes including two or more types of convex stripes on almost the entire surface of the light emission surface 101B. It is. In this embodiment, as shown in FIG. 2, the convex structure group 200 includes convex prisms having two different shapes (here, apex angles), in which linear prisms 201a and 201b are appropriately combined. As a repeating unit, it is a prism row that is periodically arranged in the Y direction.

  In this embodiment, the plurality of linear prisms 201 a and 201 b constituting the convex structure group 200 extend substantially parallel to the Y direction, that is, the longitudinal direction of the linear light source 102. Here, “substantially parallel” includes not only the case of being parallel without error but also the case of forming an angle within ± 10 ° with respect to the longitudinal direction of the linear light source 102.

  The convex structure group 200 of this embodiment is configured by periodically arranging repeating units U1 including two (two) linear prisms 201a and one (one) linear prism 201b. . Here, the repeating unit U1 has been illustrated as being composed of two rows of linear prisms 201a and one row of linear prisms 201b. However, the number of linear prisms 201a is one or three or more. Two or more prisms 201b may be provided. Further, the arrangement (order of arrangement in the Y direction) of the linear prism 201a and the linear prism 201b may be other as long as the optical characteristics required for the light diffusion plate are not impaired. Further, the types of linear prisms included in the repeating unit U1 are not limited to two types, and may be three or more types.

  The linear prisms 201a and 201b of this embodiment have two left-right symmetric (symmetric with respect to the ZX plane) inclined surfaces, and their cross-sectional shapes are isosceles triangles having equal left and right base angles. However, the cross-sectional shape may be a triangle having different left and right base angles, that is, a right and left inclined surface having different inclination angles. The apex angle θ1 of the linear prism 201a and the apex angle θ2 of the linear prism 201b are set to be different from each other, and in the relationship with the refractive index of the constituent material (for example, transparent resin) of the light diffusion plate 101, a desired value is obtained. The angle is set to an angle suitable for realizing optical characteristics (here, luminance uniformity, etc.). Here, the difference between the apex angle θ1 of the linear prism 201a and the apex angle θ2 of the linear prism 201b is preferably set to 10 ° or more. Thus, when the difference in apex angle is different by 10 degrees or more, the optical functions of these linear prisms are greatly different. Therefore, by changing the existence position and the existence ratio of these linear prisms, The brightness can be finely adjusted at each location on the light emitting surface, and the brightness unevenness can be further improved. In particular, when the distance between the linear light sources is large, or when the distance between the linear light source and the light diffusing plate is short, the effect of improving the luminance unevenness is more remarkable by setting the apex angle difference to 10 degrees or more. It is. More specifically, of the two types of linear prisms, one of the linear prisms is near the linear light source (at a location where the light source is projected perpendicularly to the light diffusion plate) from the linear light source. It has a function of recurring light to brighten the middle position of the adjacent linear light source, and the other linear prism can be configured to brighten the area immediately above the linear light source. In order to provide a difference in such functions, it is necessary that the difference in apex angle is 10 degrees or more.

  The apex angle θ1 of the linear prism 201a is preferably 60 ° or more and less than 100 °, and the apex angle θ2 of the linear prism 201b is preferably 100 ° or more and 175 ° or less. The apex angle θ1 of the linear prism 201a is more preferably 70 ° or more and less than 100 °, and the apex angle θ2 of the linear prism 201b is more preferably 100 ° or more and 155 ° or less. As an example, the apex angle θ1 of the linear prism 201a can be set to 85 °, and the apex angle θ2 of the linear prism 201b can be set to 125 ° or 145 °.

  The positions in the Z direction (thickness direction of the light diffusing plate 101) of the apexes (ridge lines) of the plurality of linear prisms 201a and 201b constituting the convex structure group 200 substantially coincide with each other. Here, substantially matching means that the difference in the position in the Z direction of each apex is 5 μm or less. Further, the positions in the Z direction (thickness direction of the light diffusing plate 101) of the valley portions (valley lines) of the plurality of linear prisms 201a and 201b constituting the convex structure group 200 substantially coincide with each other. Here, substantially matching means that the difference in the position of each valley in the Z direction is 5 μm or less. Accordingly, the heights h1 of the linear prisms 201a and 201b (difference in position in the Z direction between the top and the valley) are all set to be substantially equal.

  In the present embodiment, as a method of forming the above-described convex structure group 200 on the light emitting surface 101B of the light diffusing plate 101, an injection molding method using a mold having a shape corresponding to the above-described convex structure group 200 is used. The light diffusion plate 101 is formed integrally with the main body portion. In the injection molding method, in order to increase the shape transfer rate, it is preferable to raise the mold temperature at the time of injecting the resin and rapidly cool the mold during cooling. Moreover, you may apply the injection compression molding method which expands a type | mold when injecting resin and closes a type | mold after that.

  As an example, a mold used for injection molding includes a fixed mold and a movable mold that advances and retreats with respect to the fixed mold. The movable mold is provided with a stamper on which a pattern (convex structure group) having a shape corresponding to the above-described convex structure group 200 is formed. At the time of mold clamping, a cavity for molding a light diffusion plate, which is a molded product, is defined by the movable side mold and the fixed side mold, and this cavity is filled with molten resin and solidified. Thereafter, the mold is opened, and the light diffusion plate 101 remaining in the fixed mold with the light emitting surface 101B on which the convex structure group 200 is formed exposed has a plurality of suction pads P (see FIG. 5). It is taken out by the take-out device and conveyed to a predetermined position. The suction pad P is a device that sucks vacuum (negative pressure) inside the pad, and a plurality of suction pads P are arranged so as to suck a predetermined plurality of locations on the light exit surface 101B of the light diffusion plate 101.

  Here, FIG. 3 is a diagram showing a conventional convex structure group, which is optically equivalent to the convex structure group 200 of the present embodiment shown in FIG. In FIG. 3, the repeating unit U2 is configured by two rows of linear prisms 202a having a height h1 and two rows of linear prisms 202b having a height h2 (here, h2 = h1 / 2). The linear prism 202a in FIG. 3 and the linear prism 201a in FIG. 2 have substantially the same configuration. That is, the apex angle θ1 is equal to the width of the bottom (the width in the Y direction).

  Further, the two rows of linear prisms 202b in FIG. 3 and the one linear prism 201b in FIG. 2 are optically equivalent. That is, the linear prism 202b of FIG. 3 and the linear prism 201b of FIG. 2 have substantially the same apex angle θ2, whereas the linear prism 202a of FIG. 3 has a height of h2. The height of the linear prism 201b in FIG. 2 is h1. The inclination angle of the inclined surface of the linear prism 202a in FIG. 3 is equal to the inclination angle of the inclined surface of the linear prism 202b in FIG. 2, and the area of the inclined surface of the two rows of linear prisms 202a in FIG. Since the areas of the inclined surfaces of the linear prisms 202b in one row are equal, they are optically equivalent.

  FIG. 4 is a diagram illustrating another configuration example of the convex structure group according to the present embodiment. Compared to the conventional convex structure group illustrated in FIG. 3 (or the convex structure group according to the present embodiment illustrated in FIG. 2). Thus, it has an optically equivalent configuration. In FIG. 4, the repeating unit U3 is configured by four rows of linear prisms 203a having a height h2 and two rows of linear prisms 203b having a height h2. The linear prism 202b in FIG. 3 and the linear prism 203b in FIG. 4 have the same apex angle and height. Also, the two rows of linear prisms 202a in FIG. 3 and the four linear prisms 203a in FIG. 4 are optically equivalent. That is, the linear prism 202a of FIG. 3 and the linear prism 203a of FIG. 4 have substantially the same apex angle θ1, and the height of the linear prism 202a of FIG. The height of the linear prism 203a in FIG. 4 is h2. Therefore, the area of the inclined surfaces of the two rows of linear prisms 202a in FIG. 3 and the area of the inclined surfaces of the four rows of linear prisms 203a in FIG. 4 are equal, so they are optically equivalent. .

  As described above, in the convex structure group of the present embodiment shown in FIG. 2 or FIG. 4, the positions of the tops of the linear prisms in the Z direction substantially coincide, that is, the difference between the positions is 5 μm or less. Therefore, the optical sheet 106 disposed thereon is supported by all these tops. As a result, the load on each top from the optical sheet 106 is dispersed. Therefore, during the assembly work of the light diffusion plate 101 and the optical sheet 106 to the housing 105 via the fixture 107 in the assembly of the backlight device 100, Alternatively, even when vibration is applied after assembly vibration testing or after shipping as a product, the back surface of the optical sheet 106 (the surface on the light diffusion plate 101 side) is scratched or the linear prism 201a, When the tops of 201b, 203a, and 203b wear, it is suppressed that the optical characteristics are deteriorated.

  Further, in the light diffusing plate having the convex structure group of the conventional configuration, as shown in FIG. 5, when the light diffusing plate is manufactured by injection molding, or when the light diffusing plate is conveyed, the light diffusing plate has a light emitting surface. When the suction pad P is sucked, a relatively large space S is formed in a portion between the low linear prism 202b and the suction pad P, and air enters through this portion, thereby reducing the suction property. It was. On the other hand, in the present embodiment, since the positions of the tops of the linear prisms 201a and 201b (or 203a and 203b) are aligned (substantially match), they are formed between the suction pads P. The space to be formed is small, and the adsorptivity can be improved. Accordingly, problems such as failure of taking out the light diffusing plate or dropping of the light diffusing plate during taking out from the mold or during conveyance are reduced, and production with a high yield becomes possible.

  Furthermore, in the convex structure group of the present embodiment, not only the tops of the linear prisms 201a and 201b (or 203a and 203b) but also the positions of the valleys in the Z direction substantially coincide, that is, the difference in position is 5 μm or less. Therefore, the above-described effects can be achieved while maintaining the optical characteristics of the conventional convex structure group. Therefore, it is not necessary to change the optical specification employed in the conventional configuration, and the design work can be simplified.

  FIG. 6 is a diagram showing still another example of the convex structure group of the present embodiment, and FIG. 7 is a diagram showing a conventional convex structure group for comparison. The configuration shown in FIG. 6 is obtained by changing the configuration of some linear prisms without changing the angle and area of the inclined surface of each linear prism with respect to the conventional convex structure group shown in FIG. , The positions in the Z direction of the tops of the linear prisms are all aligned. The positions in the Z direction of the valley portions of the linear prism are not uniform. Even with such a configuration, the above-described effects of preventing damage and improving the reliability of conveyance can be realized.

  However, in the convex structure group of FIG. 6, since the positions of the valleys in the Z direction do not match, the incident efficiency of the oblique light incident on the inclined surface of the linear prism obliquely with respect to the light exit surface Changes. For example, in FIG. 7, the oblique light L1 to be emitted through the inclined surface P1 is emitted through the inclined surface P2 having a different inclination angle from that in FIG. 6, and the optical characteristics are changed. Therefore, in order to realize the same optical characteristics as the prior art shown in FIG. 7, it is necessary to change the optical design of the light diffusing plate in consideration of this point, and this embodiment shown in FIG. 2 or FIG. It can be said that the convex structure group according to is advantageous in design.

  In the convex structure group of the present embodiment, the shape of the vicinity of the top in the cross-sectional shape of the linear prism (cross-sectional shape cut along the ZY plane) is a certain degree of partial arc or quadratic curve, as shown in FIG. You may have roundness. In addition, the cross-sectional shape of the linear prism is not limited to a triangle, and can be various polygonal shapes such as a quadrangle such as a trapezoid (see FIG. 9), a pentagon (see FIG. 10), a hexagon, a heptagon, Particularly, it is preferable that the left and right base angles are substantially equal (within a range of ± 10 °) from the viewpoint of easy design, uneven brightness even when observed from either the left or right side, and the like. In the above-described embodiment, the linear prisms constituting the repeating unit are all triangular in cross section, but may be configured by combining two or more of various polygons including a triangle. . The width dimension of each linear prism is usually 10 to 500 μm, preferably 20 to 400 μm, and more preferably 30 to 300 μm.

  By roughening the surface of the inclined surface of the convex structure group of the light diffusing plate, the direction of emission can be made more diverse within an appropriate range, or the mold releasability from the mold during molding can be improved. it can. In that case, the arithmetic average height Ra of the surface of the convex structure group is preferably 0.01 μm or more and 3 μm or less, more preferably 0.02 μm or more and 2 μm or less, and 0.05 μm or more and 1 μm or less. Further preferred. By making Ra 0.01 μm or more, the light emission direction can be made more diverse, and the releasability from the mold at the time of molding can be improved, and by making it 3 μm or less, It is possible to prevent the emission direction of the light from being diversified. Such roughening of the surface of the convex structure group may be performed on the entire surface of the convex structure group or a part thereof.

  In the above-described embodiment, the connecting portion between the linear prism and the adjacent linear prism is a linear valley (valley line), but as shown in FIG. The surface (valley surface) F may be inserted and arranged. When providing a flat surface, the width dimension of the flat surface is usually 10 to 500 μm, preferably 20 to 400 μm, and more preferably 30 to 300 μm.

  In the embodiment described above, the light incident surface 101A of the light diffusing plate 101 is a flat surface, but a convex structure group as shown in FIGS. 2 to 7 may be provided.

  In the embodiment described above, the injection molding method using a mold is used as a method for forming the convex structure group described above on the light exit surface of the light diffusion plate. However, a casting mold that can form a desired convex structure group. A casting method using may be used. The casting method can be performed in a mold capable of forming a plate, or can be performed continuously while pouring a raw material between two continuous belts and moving the belt. In addition, as a method of forming the above-described convex structure group on the light exit surface of the light diffusion plate, a method of cutting the surface of a flat plate, a sheet having a convex structure group such as a prism sheet having a desired shape on the flat plate is used. A method of laminating or pasting, a method of applying a photocurable resin or a thermosetting resin to the surface of a flat plate, transferring a desired shape to the coating film by a roll or a die, and curing the coating film in that state, and a flat plate For example, an embossing method in which the surface is pressed with a roll having a desired shape or a pressing die, or the like, which is used to form a convex structure group on the surface of the flat plate later, may be used.

  The liquid crystal display device of the present invention comprises the above-described direct type backlight device of the present invention. Specifically, in addition to the direct type backlight device, a liquid crystal cell having various display modes can be provided, and light emitted from the backlight device can be emitted from the display surface through the liquid crystal cell. The liquid crystal display device of the present invention includes, for example, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a hybrid alignment nematic (HAN) mode, a vertical alignment (VA) mode, a multi-domain vertical alignment (MVA) mode, an in-plane It can be based on a display mode such as a switching (IPS) mode, an optically compensated birefringence (OCB) mode.

  In the above-described embodiment, the periodic arrangement of the repeating units is such that one type of repeating unit is disposed over the entire light exit surface of the light diffusion plate. However, as will be described below, a plurality of types of repeating units may be arranged.

  FIG. 12 is a cross-sectional view showing a main part of the light diffusing plate 101 in a direct type backlight device according to another embodiment of the present invention. In the present embodiment, the distance corresponding to the center of the linear light source 102 from the middle position of the distance between the centers of the linear light source 102 and the adjacent linear light source (not shown in FIG. 12) is set to a plurality of distances. Divided into zones (three zones Z1, Z2, and Z3), a convex structure group of different repeating units is provided for each region corresponding to each zone of the light exit surface 101B of the light diffusion plate 101.

  Here, it is preferable that the abundance ratio of the two types of protrusions (linear prisms 201a and 201b) in each repeating unit changes stepwise (or continuously) as the distance from the linear light source 102 increases. For example, in zone Z1, the number of linear prisms 201a and 201b is arranged in a repeating unit with a ratio of 2: 1, and in zone Z2, it is arranged in a repeating unit with an abundance ratio of 4: 1. In the zone Z3, it is possible to provide a convex structure group in which the abundance ratio is changed in three steps in such a manner that the abundance ratio is 6: 1. In addition, the number of these zones is not particularly limited, but may be 2 to 10 stages, for example.

  Thus, the brightness uniformity can be improved by increasing the number of linear prisms having a small apex angle as the distance from the linear light source 102 increases. However, as disclosed in Patent Document 1, the farther the distance from the linear light source 102 is, the more uniformly the prism apex angle is, the worse the luminance uniformity when observed obliquely. Therefore, when the distance from the linear light source 102 is increased as in the above-described aspect, the luminance uniformity when observed from an oblique direction is provided by providing a portion that increases the apex angle in addition to the portion that reduces the apex angle. Can be improved.

  Hereinafter, the present invention will be described in more detail based on examples.

<Pellets for light diffusion plates>
To a resin having an alicyclic structure (manufactured by Nippon Zeon Co., Ltd., trade name: ZEONOR 1060R, water absorption 0.01%), 0.05 μm of a diffusing agent comprising fine particles of a cross-linked polysiloxane polymer having an average particle diameter of 2 μm is added. %, Kneaded with a twin screw extruder, extruded into a strand, and cut with a pelletizer to produce a light diffusion plate pellet.

<Example 1>
A direct type backlight device schematically shown in FIG. 1 was produced. A reflective sheet (RF188, manufactured by Tsujiden Co., Ltd.) is attached to the inner surface of an aluminum case (housing 105) having an inner length of 700 mm, a width of 400 mm, and a depth of 22.8 mm to form a reflector 103 having a diameter of 4 mm and a length of Seven 700 mm cold cathode fluorescent lamps (Harrison Toshiba Lighting Co., Ltd.) 102 were attached in parallel. The distance between the centers of the cold cathode tubes (lamp pitch) d1 was 56.5 mm, and the distance from the light diffusion plate 101 to the center of the cold cathode tube 102 (lamp-diffusion plate distance) d2 was 19 mm. The vicinity of the electrode part was fixed with a silicone sealant, and an inverter was attached.

  Next, a mold having a predetermined shape is set in an injection molding machine (clamping force 4,410 kN), and the above-described light diffusion plate pellets are used as raw materials under conditions of a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. A light diffusing plate having a rectangular structure having a length of 710 mm, a width of 410 mm, and a thickness of 2 mm and having a convex structure group (prism array) in which a plurality of triangular prisms to be described later are arranged substantially in parallel on the light output surface thereof was manufactured.

  The light diffusing plate is taken out from the fixed mold after injection molding, and the take-out robot RZ-manufactured by Sailor Fountain Pen Co., Ltd. having 16 φ30 mm silicon rubber vacuum pads (PATK-30-S manufactured by Myokutoku Co., Ltd.) 700 VE was used. The arrangement of each suction pad was set at the center of each rectangular area obtained by dividing the light diffusing plate into four parts vertically and four parts horizontally.

  The extraction of the light diffusion plate from the mold using this extraction robot was performed for 100 sheets, and the number of adsorption failures (falling) at that time was counted.

  As the convex structure group on the light exit surface of the light diffusion plate, the one shown in FIG. 13 was used. That is, two rows of linear prisms 201a having a triangular cross section with apex angle θ1 (vertical angle 1) of 85 ° and one row having a triangular cross section with apex angle θb (vertical angle 2) of 125 °. The repeating unit composed of the linear prisms 201b is periodically arranged. The width (width 1) of the bottom side of the linear prism 201a was 100 μm, and the width (width 2) of the bottom side of the linear prism 201b was 200 μm. The difference E1 in the Z-direction position (peak height) of the tops of the linear prisms 201a and 201b of the light diffusing plate is 2.5 μm, and the difference in the Z-direction position (valley height) of each valley is 0 μm. It was.

  Next, the obtained light diffusing plate was placed on an aluminum case (housing) to which a cold cathode tube was attached such that the light incident surface was on the cold cathode tube side. At this time, the distance between the center of the cold cathode tube and the light incident surface of the light diffusion plate was 19.0 mm.

  Further, a diffusion sheet (“188GM3”, manufactured by Kimoto Co., Ltd.), a prism sheet (“BEFIII-10T”, manufactured by Sumitomo 3M Co.) as an optical sheet, and reflected polarized light are provided on the upper surface (light emitting surface) of the light diffusing plate. A child (“DBEF-D”, manufactured by Sumitomo 3M) and a polarizing plate (“HCL2-2518”, manufactured by Sanlitz) were installed in this order to obtain a direct type backlight device.

  Next, the obtained direct type backlight device was energized at a tube current of 6.0 mA, the cold cathode tube was turned on, and the short-side direction (CA1500W, manufactured by Konica Minolta Co., Ltd.) was used. The luminance in the front direction of 100 points was measured at equal intervals on the center line in the width direction of the case. Further, according to the following formulas A and B, a luminance average value (front luminance) La and luminance uniformity Lu in the front direction were obtained.

Brightness average value La = (L1 + L2) / 2 (Formula A)
Luminance uniformity Lu = ((L1-L2) / La) × 100 (Formula B)
L1: Average brightness maximum value just above a plurality of cold-cathode tubes installed L2: Average minimum value sandwiched between maximum values Note that brightness uniformity is an indicator of brightness uniformity, and brightness uniformity When the degree is bad, the value increases.

  Further, a vibration test was performed on the obtained direct backlight device using a vibration tester (product name: EMICF 600 BA / FAE08, manufactured by Emic Co., Ltd.). The frequency was 50 Hz, the vibration direction was (x, y, z), and the test time was 30 minutes each. After the test, the optical sheet was removed and the contact surface with the light diffusing plate was visually observed to evaluate the presence or absence of scratches on the sheet. The evaluation criteria are as follows.

◯: No scratches can be confirmed Δ: Scratches can be slightly confirmed ×: Scratches can be confirmed Table 1 shows the results.

  As shown in Table 1, in Example 1, the brightness uniformity, the sheet damage, and the number of adsorption failures were each free of problems.

<Example 2>
Using the convex structure group shown in FIG. 14, the difference in the Z-direction position (peak height) of each apex of the linear prism of the light diffusing plate is 0 μm, and the Z-direction position (valley height) of each trough ), Except that the difference E2 was set to 28.5 μm. The results are shown in Table 1.

  As shown in Table 1, in Example 2, the brightness uniformity, the sheet damage, and the number of adsorption failures were not problematic.

<Example 3>
The same as Example 1 described above, except that the difference in the Z-direction position (peak height) of each apex of the linear prism of the light diffusion plate was 1.3 μm. The results are shown in Table 1.

  As shown in Table 1, in Example 3, the brightness uniformity, the sheet damage, and the number of adsorption failures were not problematic.

<Example 4>
The apex angle θ1 (vertex angle 1) of the linear prism 201a is 105 °, the apex angle θ2 (vertex angle 2) of the linear prism 201b is 125 °, and the width (width 1) of the base of the linear prism 201a is 100 μm. The same as Example 1 described above, except that the width (width 2) of the base of the linear prism 201b was 140 μm. The results are shown in Table 1.

  As shown in Table 1, in Example 4, the brightness uniformity, the sheet damage, and the number of adsorption failures were not problematic.

<Example 5>
The convex structure group shown in FIG. 12 was used. That is, as the distance from the linear light source 102 increases, the mixing ratio of the linear prism 201a having the apex angle θ1 (vertical angle 1) and the linear prism having the apex angle θ2 (vertical angle 2) included in the repeating unit is 2: 1. , 4: 1, 6: 1, except for the above-described Example 1. The results are shown in Table 1.

  As shown in Table 1, in Example 5, the luminance uniformity, the sheet damage, and the number of adsorption failures were each free of problems.

<Comparative Example 1>
As the convex structure group, as shown in FIG. 15, a linear prism 204 having an apex angle θ3 of 100 ° and a base width (width 1) of 100 μm is used. Example 1 was the same as Example 1 described above except that the difference in the position (peak height) in the Z direction of the top portion was 0 μm and the difference in the position (valley height) in the Z direction of each valley portion was 0 μm. The results are shown in Table 1.

  As shown in Table 1, in Comparative Example 1, since the positions (peak heights) of the linear prisms in the Z direction were aligned, there was no problem with the sheet damage and the number of suction failures. However, the luminance uniformity was extremely low.

<Comparative example 2>
Example 1 described above except that the convex structure group shown in FIG. 16 is adopted and the difference E1 in the Z-direction position (peak height) of each linear prism of the light diffusing plate is set to 28.5 μm. And the same. The results are shown in Table 1.

As shown in Table 1, in Comparative Example 2, although the luminance uniformity was good, the position of the linear prism in the Z direction (the height of the peaks) was not uniform, so that the sheet was significantly damaged, There were also many adsorption failures.

  The embodiments and examples described above are described for easy understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the embodiment described above is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

It is sectional drawing which shows the outline of the direct type | mold backlight apparatus which concerns on embodiment of this invention. It is a figure which shows the convex structure group arrange | positioned at the light-projection surface of the light diffusing plate in embodiment of this invention. It is a figure which shows the convex structure group of the light-projection surface of the light diffusing plate used for the conventional direct type | mold backlight apparatus. It is a figure which shows the other structure of the convex structure group arrange | positioned at the light-projection surface of the light diffusing plate in embodiment of this invention. It is a figure for demonstrating the problem regarding adsorption | suction of the light diffusing plate used for the conventional direct type | mold backlight apparatus. It is a figure for demonstrating the optical characteristic of the convex structure group arrange | positioned at the light-projection surface of the light diffusing plate in embodiment of this invention. It is a figure for demonstrating the optical characteristic of the light diffusing plate used for the conventional direct type | mold backlight apparatus. It is a figure which shows the other example of the cross-sectional shape of the linear prism which comprises the convex structure group arrange | positioned at the light-projection surface of the light diffusing plate in embodiment of this invention. It is a figure which shows the other example of the cross-sectional shape of the linear prism which comprises the convex structure group arrange | positioned at the light-projection surface of the light diffusing plate in embodiment of this invention. It is a figure which shows the other example of the cross-sectional shape of the linear prism which comprises the convex structure group arrange | positioned at the light-projection surface of the light diffusing plate in embodiment of this invention. It is a figure which shows the other example of arrangement | positioning of the linear prism which comprises the convex structure group arrange | positioned at the light-projection surface of the light diffusing plate in embodiment of this invention. It is a figure which shows the convex structure group arrange | positioned at the light-projection surface of the light diffusing plate in other embodiment of this invention. It is a figure which shows the convex structure group employ | adopted in Example 1 or Example 3 of this invention. It is a figure which shows the convex structure group employ | adopted in Example 2 of this invention. 6 is a diagram illustrating a convex structure group employed in Comparative Example 1. FIG. 6 is a diagram illustrating a convex structure group employed in Comparative Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Light diffusing plate 101A ... Light incident surface 101B ... Light emission surface 102 ... Linear light source 103 ... Reflecting plates 201a, 201b, 203a, 203b ... Linear prisms [theta] 1, [theta] 2 ... Apex angle P of linear prism ... Adsorption pad

Claims (7)

A plurality of linear light sources arranged substantially parallel to each other, a reflecting plate that reflects light from these linear light sources, and light that receives direct light from the linear light source and reflected light from the reflecting plate A direct-type backlight device comprising an incident surface and a light diffusing plate having a light exit surface that diffuses and emits light incident from the light incident surface;
At least part of the light exit surface has a convex structure group in which repeating units composed of a plurality of convex stripes including two or more types of convex stripes having different shapes are periodically arranged,
The difference between the largest and smallest vertexes of the ridges included in the repeating unit is 10 ° or more,
In the plurality of ridges, the top position of each ridge in the thickness direction of the light diffusing plate is a direct type backlight device in which a difference in position in the thickness direction is within a range of 5 μm or less.   In the plurality of valley portions provided between the adjacent ridges, the position of the bottom portion of each valley portion in the thickness direction of the light diffusing plate has a difference in position in the thickness direction within a range of 5 μm or less. Item 2. The direct type backlight device according to Item 1. The ridge is a linear prism extending along the longitudinal direction of the linear light source,
The convex structure group is a prism row in which a plurality of the linear prisms are arranged substantially in parallel.
The direct type backlight device according to claim 1 or 2, wherein a cross section of the linear prism perpendicular to the longitudinal direction of the linear light source is polygonal.   The direct type backlight device according to any one of claims 1 to 3, wherein the repeating unit includes a ridge having an apex angle of 100 ° or more and a ridge having an apex angle of less than 100 °.   The direct lower according to any one of claims 1 to 4, wherein the abundance ratio of two or more types of protrusions having different shapes included in the repeating unit changes continuously or stepwise as the distance from the linear light source increases. Type backlight device.   The direct type backlight device according to claim 1, further comprising an optical film disposed in contact with the light emitting surface of the light diffusing plate. LCD panel,
A liquid crystal display device comprising the direct type backlight device according to claim 1, wherein the liquid crystal panel is illuminated from the back surface side.

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