JP2010066664A - Light diffusion plate, direct backlight device, and liquid crystal display device - Google Patents

Abstract

Provided is a light diffusing plate that can be molded using a relatively small existing injection molding machine, can suppress luminance unevenness of a light emitting surface, and can contribute to thinning of a direct type backlight device.
A light diffusing plate according to the present invention is made of injection molding so as to close an opening of a casing. The light diffusing plate includes a main body portion 10 having a rectangular shape in plan view, an outer peripheral portion 20 on the outer peripheral side of the main body portion, and a connection portion 30 that connects the main body portion and the outer peripheral portion. The main body portion is provided with an effective illumination region at a substantially central position of a rectangle, and a concavo-convex structure 12 having a maximum center line average roughness of 3 to 1000 μm is formed in a range including this region. The outer peripheral portion has a substantially constant thickness that is thinner than the thickness of the main body, and is supported by the housing. A connection part becomes thin as it goes to an outer peripheral part side from a main-body part.
[Selection] Figure 3

Description

  The present invention relates to a light diffusing plate, a direct type backlight device, and a liquid crystal display device. In particular, the present invention can be molded using a relatively small existing injection molding machine, suppresses uneven luminance on the light emitting surface, and when used in a direct backlight device, The present invention relates to a light diffusion plate that can contribute to a reduction in thickness, a direct backlight device including the light diffusion plate, and a liquid crystal display device including the direct backlight device.

  2. Description of the Related Art Conventionally, a liquid crystal display device includes a direct type backlight device and a liquid crystal panel that is an object to be illuminated by the direct type backlight device. As a direct type backlight device used in this liquid crystal display device, for example, a housing having an opening formed on at least one surface, and a plurality of light sources (for example, cold cathode tubes, for example) disposed in the internal space of the housing And LEDs) and a light diffusing plate arranged so as to close the opening of the housing are widely used.

  In recent years, since there is also a demand for a wall-hanging type or the like, further thinning of a liquid crystal display device is required. For this reason, the direct-type backlight device is also required to be thin. In order to reduce the thickness of the direct type backlight device, it is necessary to reduce the distance between the light source and the light diffusing plate. In this case, the luminance directly above the light source increases, and this directly above part Since the luminance decreases as the distance from the light source increases, there is a problem that periodic luminance unevenness occurs on the light emitting surface. Therefore, in recent years, a technology has been used in which a predetermined uneven structure such as a prism shape or a so-called lenticular shape is formed on the surface of the light diffusing plate, and the uneven brightness on the light emitting surface is reduced by these uneven structures (Patent Documents). 1).

  Moreover, as shown in Patent Document 1, the light diffusing plate having such a concavo-convex structure on its surface is thin because the concavo-convex structure formed on the surface of the light diffusing plate can be formed as desired. From the viewpoint of being able to cope with the manufacturing process and being easily mass-produced, a method in which a transparent resin is injection-molded using a mold in which a fine structure corresponding to the concavo-convex structure is formed is used.

JP 2006-66074 A

  However, in order to reduce the thickness of the direct type backlight device, if an attempt is made to obtain a light diffusing plate thinner than the conventional one by injection molding, the injection pressure is increased due to the reduced thickness (depth) of the cavity. An injection molding machine with a large clamping force that can withstand a large injection pressure must be prepared. For this reason, there is a possibility that an existing injection molding machine cannot mold a thin light diffusion plate.

  The object of the present invention is to use a relatively small existing injection molding machine without using a large injection molding machine, and to suppress uneven luminance on the light emitting surface and to be used for a direct type backlight device. At the same time, it is to provide a light diffusing plate that can contribute to thinning of the direct type backlight device. Another object of the present invention is to provide a thin direct type backlight device and a liquid crystal display device including such a light diffusion plate.

  In the present invention, an opening is formed on at least one surface and a light source is disposed in the internal space. The housing is disposed so as to close the opening, and light incident on the light source side surface. A light diffusing plate integrally formed by injection molding, having a surface and a light emitting surface opposite to the light incident surface, the plate having a substantially constant thickness. A main body portion having a rectangular shape in plan view, an outer peripheral portion provided on at least a part of the outer peripheral side of the main body portion, and a connecting portion that connects the main body portion and the outer peripheral portion. An effective illumination area having a rectangular shape in plan view for effectively irradiating the object to be illuminated is provided at a substantially central position of the rectangle, and at least one of the light incident surface and the light exit surface includes the effective illumination region The maximum centerline average roughness (Ra) is 3 in the range. An uneven structure having a thickness of 1000 μm is formed, the outer peripheral portion is a portion having a substantially constant thickness that is thinner than the thickness of the main body portion, and is supported by the housing, and the connecting portion is the main body portion It is the shape where the thickness becomes thin as it goes to the said outer peripheral part side from the side.

  According to the present invention, at least a part of the outer peripheral portion supported by the casing on the outer peripheral side, a main body portion on which a predetermined concavo-convex structure is formed, and a connection portion that connects between the outer peripheral portion and the main body portion. The thickness of the outer peripheral portion is thinner than that of the main body portion, and the thickness of the connecting portion is reduced from the main body portion side toward the outer peripheral portion side, so that the thickness of the outer peripheral portion supported by the housing is thin. Therefore, for example, by arranging the light diffusing plate on the housing so that the surface of the main body projecting side faces the light source, it is possible to reduce the thickness of the direct type backlight device, and thus the liquid crystal display The apparatus can also be thinned.

  In addition, according to the present invention, since the light diffusion plate has a thin configuration only at the outer peripheral portion, the thin portion is relatively thin only on the outer peripheral side as compared with the case where the thickness of the entire light diffusion plate is uniformly reduced. Since the area is small, a molded product by injection molding can be obtained using an injection molding machine having a relatively small clamping force. Furthermore, since only the outer peripheral portion of the light diffusing plate is thin, the rigidity as the light diffusing plate can be sufficiently exerted as compared with the case where the entire thickness of the light diffusing plate is uniformly reduced, and deformation or cracking can be achieved. Etc. can be suppressed.

  Furthermore, since the concavo-convex structure in which the maximum value of the center line average roughness (Ra) is 3 to 1000 μm is formed in the range including the effective illumination area of the main body portion, the concavo-convex structure allows the light incident from this light source to By collecting and scattering the light in the direction, the luminance unevenness of the light emitting surface can be reduced. At this time, since the light diffusing plate is formed by injection molding, for example, the tip portion of the concavo-convex structure can be formed more accurately than in the case of obtaining a molded product by extrusion molding, so that a molded product as designed can be obtained. As a result, luminance unevenness can be further reduced. The maximum value of the center line average roughness (Ra) is the maximum value when Ra is measured along all directions of the surface.

  Here, in the diffusing plate, the light emitting surface is preferably a flat surface having no step between the connecting portion and the outer peripheral portion. At this time, the light emitting surface is more preferably a flat surface having no step between the main body portion, the connection portion, and the outer peripheral portion as described above. Thus, when the light emission surface is a flat surface without a step, for example, when an optical sheet such as a diffusion sheet or a prism sheet or an optical member is arranged on the light emission side of the light diffusion plate, Therefore, it is possible to arrange these optical sheets in a stable posture, to maintain the quality of the direct type backlight device and the liquid crystal display device, and to prevent the reduction in thickness. Note that the flat surface includes not only the case where the surface is a truly flat surface but also the case where the uneven structure (fine uneven structure) is formed on the surface. When the concavo-convex structure is formed on the surface, it indicates that there is no step on the plane excluding the concavo-convex structure.

  In the light diffusing plate, a recessed portion that is recessed toward the light incident surface may be formed in a range including the effective illumination region on the light emitting surface. According to such a configuration, for example, by forming a recess having a size corresponding to the size of the optical sheet, the optical sheet can be prevented from being displaced from the light diffusion plate. The quality of the display device can be further improved and the thickness thereof can be reduced.

  In the light diffusion plate, the outer peripheral portion is formed corresponding to a pair of long side portions formed corresponding to a pair of long side portions of the main body portion or a pair of short side portions of the main body portion. It can be set as the structure comprised by a pair of short side part. According to such a configuration, the size of the outer peripheral portion can be suppressed, and injection molding becomes easier. Moreover, the light diffusing plate supported by the housing can be maintained in a stable posture by providing the outer peripheral portion with a pair of configurations corresponding to the pair of sides of the main body.

  Moreover, the said light diffusing plate WHEREIN: The said outer peripheral part can also be set as the structure which is an edge-shaped part formed corresponding to the four sides of the said main-body part. According to such a structure, since the shape of the whole light diffusing plate can be made into a comparatively simple shape, shaping | molding becomes easy and productivity of a light diffusing plate can be improved. Moreover, the light-diffusion plate supported by a housing | casing can be maintained in the more stable attitude | position by making an outer peripheral part into the edge-shaped part corresponding to the four sides of a main-body part.

  In the light diffusing plate, the thickness of the support portion is preferably 20 to 90% of the thickness of the main body portion. Thus, by setting the thickness of the support portion to 20 to 90% of the main body portion, it is possible to achieve a balance between the rigidity as the light diffusion plate and the reduction in thickness of the direct type backlight device and the like.

  The present invention includes a housing having an opening formed on at least one surface thereof, a light source disposed in an internal space of the housing, and the light diffusion plate disposed so as to close the opening. This is a direct type backlight device. Further, the present invention is a liquid crystal display device comprising the direct type backlight device and a liquid crystal panel to be illuminated by the direct type backlight device.

  According to the present invention, it can be molded using a relatively small existing injection molding machine without using a large injection molding machine, and it is used for a direct type backlight device while suppressing luminance unevenness of the light emitting surface. At this time, there is an effect that the direct type backlight device can be reduced in thickness, and further, the liquid crystal display device can be reduced in thickness.

A liquid crystal display device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a longitudinal sectional view schematically showing a liquid crystal display device according to an embodiment of the present invention. The liquid crystal display device 100 according to the present embodiment includes a direct-type backlight device 120 and a liquid crystal panel 140 that is disposed on the light emission side of the direct-type backlight device 120 as an illumination target. The liquid crystal panel 140 is formed in a rectangular shape in plan view, and a general transmission type or semi-transmission type can be used. Examples of the operation mode of the liquid crystal panel include TN type, VA type, and IPS type.

  The direct type backlight device 120 includes a housing 4 having an opening formed on one surface, a plurality of linear light sources 2 disposed in an internal space of the housing 4, and the opening being closed. The light diffusing plate 1 to be disposed and the reflecting plate 3 provided on the inner surface of the housing 4 are provided. Note that the inner surface of the housing 4 may also serve as the reflector 3.

  Examples of the linear light source 2 include a cold cathode tube, a hot cathode tube, a linearly arranged LED (light emitting diode), and a combination of an LED and a light guide. The shape of the cold cathode tube and the hot cathode tube is, in addition to a straight line, two parallel tubes connected by one semi-circle and formed into one U-shape and three parallel tubes. Examples include an N-shape that is connected by a substantially semicircle and a single W shape, and a W-shape that is formed by connecting four parallel pipes by three approximately semicircles. Among these, as the linear light source 2, a cold cathode tube is preferable from the viewpoint of luminance uniformity, and from the viewpoint of color reproducibility, a linear array of LEDs, and a combination of an LED and a light guide are used. preferable.

  In the present invention, a plurality of linear light sources are provided. However, in the case of using a linearly arranged LED or a combination of an LED and a light guide, a series of arranged LEDs or a LED and a light guide are arranged. When there are a plurality of combinations of bodies, it is considered that there are a plurality of linear light sources.

  The distance a between the centers of the adjacent linear light sources 2 is preferably 15 mm to 150 mm, and more preferably 20 mm to 100 mm. By setting the distance a within the above range, the power consumption of the direct type backlight device can be reduced, the assembly of the device can be facilitated, and the luminance unevenness of the light emitting surface can be suppressed. The distance b between the center of the linear light source 2 and the light incident surface (described later) of the light diffusing plate 1 can be 2 mm to 100 mm, and preferably 3 mm to 75 mm.

  The casing 4 includes a box-shaped casing main body 42 having an opening 42A on the top surface side, and an overhanging piece 44 protruding outward from an edge portion near the opening 42A of the casing main body 42. The casing main body 42 is formed in an inverted trapezoidal shape in vertical section. The upper base side of the trapezoid (the length is longer than the lower base) opens to form an opening 42A. The overhanging piece 44 is an L-shaped section that supports the outer peripheral portion of the light diffusing plate 1, and is erected from the horizontal portion 46 that supports the outer peripheral portion of the light diffusing plate 1 and the outer peripheral end of the horizontal portion 46. And a regulating portion 48 that regulates the positional deviation of the light diffusing plate 1, the liquid crystal panel 140, and the like.

  The reflecting plate 3 is a member that reflects the light emitted from the linear light source 2. As a material of the reflector 3, a resin colored in white or silver, a metal, or the like can be used, and a resin can be preferably used from the viewpoint of weight reduction. Moreover, it is preferable that the color of the reflecting plate 3 is white from a viewpoint which can improve a brightness | luminance uniformity. However, from the viewpoint of highly balancing the luminance and the luminance uniformity, the color of the reflector 3 may be a color obtained by mixing white and silver.

The light diffusing plate 1 is a plate material that diffuses and irradiates incident light.
As a material constituting the light diffusing plate, 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, it is preferable to use one kind of transparent resin from the viewpoint of easy luminance improvement. Further, from the viewpoint of easy adjustment of the total light transmittance and haze, a transparent resin in which a light diffusing agent is dispersed can be used.

  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, copolymer of aromatic vinyl monomer and (meth) acrylic acid alkyl ester having a lower alkyl group, polyethylene terephthalate, terephthalic acid-ethylene glycol-cyclohexanedimethanol copolymer, polycarbonate, acrylic resin, And a resin having an alicyclic structure. In addition, (meth) acrylic acid is acrylic acid and methacrylic acid. Among these, as a transparent resin, a copolymer of polycarbonate, polystyrene, an aromatic vinyl monomer containing 10% or more of an aromatic vinyl monomer, and a (meth) acrylic acid alkyl ester having a lower alkyl group Further, a resin having a water absorption of 0.25% or less, such as a resin having an alicyclic structure, is preferable in that a large light diffusion plate with little warpage can be obtained because deformation due to moisture absorption is small.

  A resin having an alicyclic structure is more preferable because it has good fluidity and can efficiently produce a large light diffusion plate. A mixture of a resin having an alicyclic structure and a light diffusing agent can be suitably used because it has both high permeability and high diffusibility required for a light diffusing plate and good chromaticity.

  The resin having an alicyclic structure is a resin having an alicyclic structure in the main chain and / or side chain. From the viewpoint of mechanical strength, heat resistance, etc., a resin containing an alicyclic structure in the main chain is particularly preferred. Examples of the alicyclic structure include a saturated cyclic hydrocarbon (cycloalkane) structure and an unsaturated cyclic hydrocarbon (cycloalkene, cycloalkyne) structure. From the viewpoint of mechanical strength, heat resistance, etc., a cycloalkane structure or a cycloalkene structure is preferable, and among them, a cycloalkane structure is most preferable. The number of carbon atoms constituting the alicyclic structure is not particularly limited, but is usually 4 to 30, preferably 5 to 20, more preferably 5 to 15 in the mechanical strength, The properties of heat resistance and moldability of the light diffusing plate are highly balanced and suitable.

  Specific examples of the resin having an alicyclic structure include (1) a ring-opening polymer of a norbornene monomer and a ring-opening copolymer of the norbornene monomer and other monomers capable of ring-opening copolymerization Norbornene polymers such as hydrogenated products, addition polymers of norbornene monomers, and addition copolymers of norbornene monomers with other monomers copolymerizable therewith; (2) Monocyclic olefin polymer and hydrogenated product thereof; (3) Cyclic conjugated diene polymer and hydrogenated product thereof; (4) Polymer of vinyl alicyclic hydrocarbon monomer and vinyl alicyclic hydrocarbon Copolymers of monomers and other monomers copolymerizable therewith, as well as hydrogenated products thereof, aromatic ring hydrogenated products of vinyl aromatic monomers, and vinyl aromatic monomers. Copolymerization of the monomer and other monomers copolymerizable therewith Vinyl alicyclic hydrocarbon polymers such as hydrogenated products of the body of the aromatic ring; and the like.

  Among these, from the viewpoint of heat resistance, mechanical strength, and the like, norbornene polymers and vinyl alicyclic hydrocarbon polymers are preferable, and ring-opening polymer hydrogenated products of norbornene monomers, norbornene monomers, and Hydrogenation of ring-opening copolymer with other monomers capable of ring-opening copolymerization, hydrogenation of aromatic ring of polymer of vinyl aromatic monomer, and copolymerization with vinyl aromatic monomer and this More preferred are hydrogenated aromatic rings of copolymers with other possible monomers.

  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.

  Examples of the shape of the light diffusing agent include a spherical shape, a cubic shape, a needle shape, a rod shape, a spindle shape, a plate shape, a scale shape, and a fiber shape. Among these, the light diffusing direction can be exemplified. Spherical shape is preferable in that it can be squarely. The light diffusing agent is used in a state of being uniformly dispersed in the transparent resin.

  When a light diffusing agent is added to the transparent resin, 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, etc. It is preferable to adjust the content of the light diffusing agent so that the light transmittance is 60% to 98%, and it is more preferable to adjust the content of the light diffusing agent to be 65% to 95%. Further, the content of the light diffusing agent is preferably adjusted so that the haze is 20% to 100%, and the content of the light diffusing agent is adjusted to be 25% to 100%. More preferably. By setting the total light transmittance and haze within the above-mentioned preferable ranges, the luminance and the luminance uniformity can be further improved.

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

Next, the outer shape of the light diffusing plate 1 will be described.
FIG. 2 is a plan view schematically showing the light diffusing plate 1. FIG. 3 is a longitudinal sectional view of the light diffusing plate 1. As shown in FIGS. 2 and 3, the light diffusing plate 1 is formed in a rectangular shape in plan view that is formed so that its substantially central portion protrudes toward one side. The light diffusing plate 1 includes a main body portion 10 having a rectangular shape in plan view, an outer peripheral portion 20 that constitutes an outer peripheral edge of the main body portion 10, and a connection portion 30 that connects the main body portion 10 and the outer peripheral portion 20. In FIG. 3, for convenience of explanation, a wavy line indicating a boundary between the main body portion 10, the outer peripheral portion 20, and the connection portion 30 is virtually provided.

  As shown in FIG. 3, the main body 10 is formed so that its thickness TA is substantially constant. Note that “substantially constant” means that the thickness is within a range of designed thickness ± 0.2 mm. The thickness TA of the main body 10 is preferably 0.4 mm to 5 mm, more preferably 0.8 mm to 4.0 mm, and still more preferably 1.0 mm to 3.0 mm. By making the thickness of the light diffusing plate 1 within the above preferred range, it is possible to suppress bending due to its own weight, and it is not necessary to increase the injection pressure more than necessary during injection molding, thereby facilitating molding. be able to.

  As shown in FIG. 2, the main body unit 10 is provided with a size that allows an effective illumination region 11 as a region for effectively illuminating the liquid crystal panel 140 to be contained in the main body unit 10. The effective illumination area 11 is provided at a substantially central position of the rectangular main body 10.

  As shown in FIGS. 1 and 3, the light diffusing plate 1 has a light incident surface 1A that is a surface on the linear light source 2 side and a light emitting surface 1B that is a surface opposite to the light incident surface 1A. is doing. In the light diffusing plate 1, the direct light emitted from the linear light source 2 and the reflected light reflected by the reflecting plate 3 enter the light incident surface 1 </ b> A close to the linear light source 2 and then diffuse in the light diffusing plate 1. Then, it is diffused and emitted in various directions on the light exit surface 1B.

  In the present embodiment, the light incident surface 1A is formed as a substantially flat surface having a maximum center line average roughness (Ra) of less than 3.0 μm. In the present embodiment, a flat surface is used as described above, but a structure similar to a concavo-convex structure 12 described later formed on the light emitting surface 1B may be provided as necessary. With such a configuration, it is possible to further reduce the thickness of the direct type backlight device.

  On the light emitting surface 1B, a concavo-convex structure 12 having a maximum centerline average roughness (Ra) of 3 to 1000 μm is formed. The centerline average roughness Ra is obtained based on JIS B0601 for a roughness curve obtained by removing a component longer than a predetermined wavelength with a phase compensation type high-pass filter from a curve of a cross-sectional view in a plane perpendicular to the target surface. Or can be read directly using an ultra-deep profile measuring microscope or the like. Here, the concavo-convex structure preferably has a maximum center line average roughness (Ra) of 3 to 500 μm, and more preferably 3 to 100 μm.

  As such a concavo-convex structure 12, for example, a prism array in which a plurality of linear prisms each having a polygonal shape with a concave or convex cross section are arranged substantially in parallel can be used. These linear prisms are preferably formed substantially parallel to the longitudinal direction of the linear light source 2. The prism array of the present embodiment has a configuration in which linear prisms (hereinafter sometimes referred to as triangular prisms) each having a concave or convex cross section are adjacent to each other or arranged at intervals. Here, in this embodiment, all the cross-sectional shapes of the plurality of triangular prisms are substantially the same isosceles triangular shape. At this time, it is preferable that the apex angle of the triangle constituting the triangular prism is 60 ° to 170 °, and the interval between adjacent linear prisms is 20 μm to 700 μm. With such a configuration, the luminance uniformity of the light emitting surface can be increased.

  In this embodiment, all the triangular prisms have substantially the same shape, but a plurality of types of shapes may be mixed. Further, the triangular prism may not be an isosceles triangle.

  As shown in FIG. 2, the outer peripheral portion 20 is formed in an edge shape (four-circular shape) provided on the outer periphery of the rectangular main body portion 10. The outer peripheral portion 20 has a pair of long side portions 20L corresponding to the long side portion 10L of the main body portion 10 and a pair of short side portions 20S corresponding to the short side portion 10S of the main body portion 10. The outer peripheral portion 20 is disposed on the horizontal portion 46 of the housing 4 and is supported by the horizontal portion 46.

  As shown in FIG. 3, the outer peripheral portion 20 is formed so that its thickness TB is substantially constant. The thickness TB of the outer peripheral portion 20 can be appropriately set according to the thickness of the direct type backlight device 120, but is preferably 0.2 mm to 4.5 mm from the viewpoint of rigidity and the like, and is preferably 0.3 mm to 4 mm. 0.0 mm is more preferable. Moreover, it is preferable that thickness TB of the outer peripheral part 20 is 20 to 90% of thickness TA of the main-body part 10, and 40 to 80% is more preferable. By setting the thickness relationship as described above, it is possible to achieve a balance between the rigidity as the light diffusion plate and the reduction in thickness of the direct type backlight device or the like.

  In the outer peripheral part 20, it forms so that the width dimension WS of a pair of short side part 20S may become fixed. Further, the width dimension WL of the pair of long side portions 20L is also made constant. Furthermore, in the present embodiment, the width dimension WS and the width dimension WL are formed to be the same dimension. However, the width dimension WS and the width dimension WL may not be the same dimension.

  The width dimension WS is preferably 3 mm to 50 mm, and more preferably 5 mm to 30 mm. In addition, the width dimension WS is 0. 0 of the width dimension in the longitudinal direction of the main body 10 from the viewpoint of the rigidity, formability, linear expansion coefficient, temperature when used as a direct type backlight device, and the like. It is preferable to set it as 3%-5.0%. Furthermore, the width dimension WS is preferably 50 times or less the thickness TB of the outer peripheral portion because the flow path length of the outer peripheral portion 20 is not unnecessarily long during injection molding and the moldability is good.

  The width dimension WL is preferably 2 mm to 50 mm, and more preferably 3 mm to 30 mm. Further, the width dimension WL is preferably set to 0.3% to 5.0% of the width dimension in the longitudinal direction of the main body 10 from the viewpoint of the rigidity, moldability, and the like of the light diffusing plate 1. Furthermore, the width dimension WL is preferably 50 times or less the thickness TB of the outer peripheral portion because the flow path length of the outer peripheral portion 20 is not longer than necessary during injection molding and the moldability is good.

  As shown in FIG. 1, in the present embodiment, a gap of about 0.5 to 20 mm is provided between the outer peripheral portion 20 and the regulating portion 48. By providing such a gap, there is an advantage that it is possible to prevent problems when the light diffusing plate expands while preventing positional deviation and rattling of the light diffusing plate.

  As shown in FIG. 3, the connection part 30 is formed so that the thickness becomes thin as it goes to the outer peripheral part 20 side from the main-body part 10 side. Specifically, the connection part 30 is light-incident as it goes to the outer peripheral part 20 from the main body part 10 side and the upper surface 32 which comprises the flat surface without a level | step difference with the light emission side surface of the main body part 10 and the outer peripheral part 20. And a lower surface 34 as an inclined surface inclined so as to be close to the surface side. The inclination angle of the inclined surface 34 is preferably 15 degrees to 90 degrees, and more preferably 20 degrees to 87 degrees, from the viewpoints of the filling property of the molten resin, the releasability from the mold, and the like. Moreover, it is preferable that the connection part X of the main body part 10 and the connection part 30 on the light incident side surface is formed in a curved surface from the viewpoint of preventing chipping, stress concentration, and the like.

  As described above, in the light diffusion plate 1, the light incident surface 1A has a shape such that the central portion thereof swells toward the light source side, and the light exit surface 1B is uneven in a range including the effective illumination area. Although the structure is formed, it is formed as a generally flat surface.

Next, a method for manufacturing the light diffusing plate 1 will be described.
FIG. 4 is a longitudinal sectional view schematically showing an injection mold. The light diffusing plate used in the present invention is integrally formed by injection molding using an injection mold 50 shown in FIG. As shown in FIG. 4, the injection mold 50 includes a fixed mold 52 and a movable mold 54 that moves forward and backward with respect to the fixed mold 52. A cavity 72 for molding the light diffusing plate 1 that is a molded product is provided between the movable side mold 54 and the fixed side mold 52.

  The movable mold 54 includes a mold base 56 and a stamper 58 disposed on the surface (tip surface) of the mold base 56 on the fixed mold 52 side. On the surface 58A of the stamper 58, an uneven shape for forming the uneven structure 12 formed on the surface of the light diffusion plate 1 is formed.

  The fixed-side mold 52 includes a mold base 60, a mold plate 62 disposed on a surface (tip surface) of the mold base 60 on the movable-side mold 54 side, and a movable-side mold 54 side of the mold plate 62. A core plate 64 disposed at a substantially central position of the surface (front surface) and a frame member 66 disposed on four sides of the core plate 64 are provided. A hot runner portion 68 having a hot runner as a passage for supplying the molten resin P is provided in the mold base 60 and the core plate 64.

  The cavity surface 64A, which is the main surface of the core plate 64, is formed with a dimension that is one step lower than the surface (tip surface) of the frame member 66 on the movable mold 54 side. For this reason, when the mold is closed, a space X is provided between the stamper 58 and the core plate 64. When the resin P flows into the space X, the main body portion 10 of the light diffusing plate 1 is formed.

  The frame member 66 has a recess 70 formed on the surface (tip surface) on the movable mold 54 side. When the mold 50 is closed, the recess 70 provides a space Y corresponding to the recess 70 between the stamper 58 and the frame member 66. When the resin P flows into the space Y, the outer peripheral portion 20 and the connection portion 30 of the light diffusing plate 1 are formed.

  Therefore, the cavity 72 is formed by the space X and the space Y. The core plate 64 is formed with a plurality of gates (in-plane gates) 65 that communicate with the cavity surface 64A and serve as openings for injecting the molten resin P from the hot runner portion 68 to the cavity 72.

Next, the manufacturing procedure of the light diffusing plate 1 using the injection mold 50 will be described.
First, the mold 50 is clamped with a predetermined clamping force (4410 N) using a mold clamping device (not shown). Next, the gate 65 is opened, the molten resin P is injected from the gate 65 into the cavity 72, and after a predetermined amount of molten resin P is injected into the cavity 72, the gate 65 is closed. The molten resin P injected into the cavity 72 is cooled by the mold 50 and formed into a predetermined shape, and the light diffusion plate 1 having a predetermined shape is manufactured by taking out from the mold 50 in this state.

The present invention has the following effects.
(1) Since the thickness of the outer peripheral portion 20 is thinner than that of the main body portion 10 and the thickness of the connecting portion 30 is reduced from the main body portion 10 side toward the outer peripheral portion 20 side, the outer peripheral portion 20 is supported by the casing 4. Therefore, the direct-type backlight device 120 can be thinned, and the liquid crystal display device 100 can be thinned.

(2) Since only the outer peripheral portion 20 of the light diffusing plate 1 is thin, compared with a case where the entire thickness of the light diffusing plate is uniformly reduced, the thin portion is only on the outer peripheral side. A molded product by injection molding can be obtained using an injection molding machine having a small fastening force.

(3) Since only the outer peripheral portion 20 of the light diffusing plate 1 is thin, the rigidity as the light diffusing plate 1 can be sufficiently achieved as compared with the case where the entire light diffusing plate is uniformly thinned. Occurrence of deformation and cracking can be suppressed.

(4) Since the predetermined concavo-convex structure 12 is formed in the range including the effective illumination area 11 of the main body 10, the concavo-convex structure 12 collects and scatters light incident from the light source 2 in a desired direction to emit light. The brightness unevenness of the surface can be reduced.

(5) Since the light diffusing plate 1 is formed by injection molding, for example, the tip portion of the concavo-convex structure can be formed more accurately than in the case of obtaining a molded product by extrusion molding, so that a molded product as designed can be obtained. Brightness unevenness can be further reduced.

(6) Since the outer peripheral portion 20 is formed in an edge shape and supported by the horizontal portion of the housing 4 at these edge portions, the posture (position) of the light diffusion plate 1 with respect to the housing 4 is stable. Can be maintained.

<Modification>
The present invention is not limited to the embodiment.
In the embodiment, the light source housed in the housing is a linear light source, but a point light source may be used. In this case, for example, a light emitting diode (LED) can be used as the point light source. Examples of the configuration of each LED include (1) a configuration consisting of only white LEDs, (2) a configuration combining RGB primary colors, and (3) a configuration combining intermediate colors with RGB primary colors.

  Further, when the configuration combining the three primary colors of RGB (the configuration of (2) and (3)) is used, (A) at least one red LED, green LED, and blue LED are arranged close to each other, and each color And (B) a configuration in which a red LED, a green LED, and a blue LED are appropriately arranged and color display is performed using a field sequential method in which each color LED is colored in a time-sharing manner. Can do. These point light sources can be arranged in a lattice, a staggered lattice, or a honeycomb.

  Further, in the above-described embodiment, the concavo-convex structure formed on the light diffusing plate is provided with a triangular prism, but a so-called lenticular lens-like linear structure including a curved line such as an arc, an elliptical arc, and a parabolic arc in a cross section. You can also Further, the concavo-convex structure is not limited to a linear structure, and may be, for example, a pyramid shape and a truncated pyramid shape. The pyramid can be a polygonal pyramid such as a triangular pyramid, a quadrangular pyramid, a pentagonal pyramid, and a hexagonal pyramid. The pyramid may be a polygonal frustum such as a triangular frustum, a quadrangular frustum, a pentagonal frustum, or a hexagonal frustum. By using such a polygonal pyramid or a polygonal frustum shape, when a point light source is used as the light source, there is an advantage that unevenness in luminance of the light emitting surface can be reduced.

  In the said embodiment, although the outer peripheral part was formed in the edge shape containing a pair of short side part 20S and a pair of long side part 20L, it is good also as a structure which made only one of a pair of opposing sides an outer peripheral part, for example. Good. In this case, the pair of sides on which the outer peripheral portion is formed may be a pair of long sides or a pair of short sides.

  Moreover, it is good also as a structure which provides an outer peripheral part only in the four corner part of a main-body part. At this time, it may be provided at all four corners, or may be provided at a part of the four corners. In this case, it is preferably provided at the corners at diagonal positions. Furthermore, instead of the configuration provided at the corner as described above, it may be provided at an intermediate position of the four sides other than the corner.

  In the embodiment, a notch may be formed in a part of the outer peripheral portion from the viewpoint of preventing the outer peripheral portion from wavy (deformed). In this case, it is particularly preferable that notches are formed in the pair of long side portions in the quadrangular outer peripheral portion. In addition, the number of notches, a position, a dimension, etc. are not specifically limited. Further, the outer shape of the outer peripheral portion 20 can be changed as appropriate in accordance with the shape or the like of the overhanging piece 44 of the housing 4.

  In the above embodiment, the lower surface 34 of the connecting portion 30 is an inclined surface, but it may be a stepped shape that gradually decreases in thickness. However, in the case of a stepped shape, there is a possibility that a crack or the like is likely to occur in the light diffusing plate.

  In the above embodiment, the body plate 10 of the light diffusing plate 1 is formed with the core plate 64, and the outer peripheral portion 20 and the connecting portion 30 of the light diffusing plate 1 are formed with the recesses 70 formed in the frame member 66. Although it is configured by the mold members 64 and 66, the core plate 64 and the frame member 66 may be configured as one mold member. However, in the above-described embodiment in which the mold member is a separate member, only the frame member 66 can be replaced and molded even when different types of light diffusion plates are molded according to the shape of the housing 4. There is an advantage that the molding operation can be facilitated.

  In the direct type backlight device 120 of each of the above embodiments, an optical sheet may be appropriately disposed in order to further improve luminance and luminance uniformity. Examples of such an optical sheet include a diffusion sheet and a prism sheet. These optical sheets are generally provided on the light exit side of the light diffusion plate.

  Further, for the purpose of further improving the luminance of the light emitting surface, a reflective polarizer as another optical sheet shown below may be arranged. This reflective polarizer can be used by being disposed on the light exit side of the optical sheet.

  As the reflective polarizer, a reflective polarizer that utilizes the difference in reflectance of the polarization component depending on the Brewster angle (for example, the one described in JP-T-6-508449); selective reflection characteristics by cholesteric liquid crystal are used. Reflective polarizer; specifically, a laminate of a film made of cholesteric liquid crystal and a quarter-wave plate (for example, one described in JP-A-3-45906); a fine metal linear pattern is applied Reflective polarizers (for example, those described in JP-A-2-308106); at least two kinds of polymer films are laminated, and the reflective polarization using the anisotropy of the reflectance due to the refractive index anisotropy Child (for example, those described in Japanese Patent Publication No. 9-506837); having a sea-island structure formed of at least two kinds of polymers in a polymer film, and anisotropy of reflectance due to refractive index anisotropy Profit Reflective polarizer used (for example, those described in US Pat. No. 5,825,543); particles are dispersed in a polymer film, and anisotropy of reflectance due to refractive index anisotropy is utilized Reflective polarizer (for example, the one described in JP-A-11-509014); reflection utilizing anisotropy of reflectance based on scattering ability difference depending on size, in which inorganic particles are dispersed in a polymer film Type polarizers (for example, those described in JP-A-9-297204) can be used.

  In the said embodiment, although the light-projection surface 1B of the light diffusing plate 1 was formed as a flat surface without a level | step difference, it is not restricted to this, For example, between the outer peripheral part 20 and the connection part 30, or the main-body part 10 and A certain level difference may be provided between the connecting portion 20 and the connecting portion 20. However, when there is a step, chipping or the like may occur, and therefore, it is preferable that the surface is flat as in the above-described embodiment.

  In addition, the outer peripheral portion 20 and the connection portion 30 may be formed as a flat surface without a step, and a step may be provided between the main body portion 10 and the connection portion 20. Moreover, it can also be set as the structure which formed the level | step difference between the outer peripheral part 20 and the connection part 30, and formed between the main-body part 10 and the connection part 20 on the flat surface without a level | step difference. At this time, the step is preferably a step in which the light emitting surface of the main body 10 is lowered to the light incident side by one step compared to the light emitting surfaces of the outer peripheral portion 20 and the connecting portion 30. In other words, the region including the effective illumination region 11 of the main body 10 can be configured to have a step which is lowered to the one-stage light incident side as compared to the outer peripheral side. According to such a configuration, a recessed portion is provided on the light emitting surface of the main body portion 10 due to the step lowered by one step, and the optical sheet can be disposed in the recessed portion. For this reason, the position of the optical sheet is regulated by this step, so that the position of the optical sheet relative to the light diffusing plate can be prevented from shifting, and the thickness of the optical backlight can be reduced by the thickness of the optical sheet. is there.

  Moreover, when providing a level | step difference between a main-body part and a connection part or between a connection part and an outer peripheral part, you may provide in the location corresponding to all four sides of a rectangular shape, but a pair of 2 facing each other You may provide only in the location corresponding to a side.

  Further, without providing a step between the main body portion and the connection portion, in the main body portion, in a range including the effective illumination area on the light emitting surface, for example, a dent portion recessed toward the light incident surface side according to the external dimensions of the optical sheet. It is good also as a structure in which is formed. According to such a configuration, there is an advantage that the optical sheet can be reliably prevented from being displaced from the light diffusion plate.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples. Parts and% are based on weight unless otherwise specified.

<Production Example 1: Light Diffusing Plate Pellets>
99.7 parts of a resin having an alicyclic structure as a transparent resin (Nippon Zeon Co., Ltd., ZEONOR 1060R, water absorption 0.01%) and a crosslinked product of a polysiloxane polymer having an average particle diameter of 2 μm as a light diffusing agent The resulting fine particles (0.3 parts) were mixed, kneaded with a twin-screw extruder, extruded into a strand shape, and cut with a pelletizer to produce a light diffusion plate pellet. Using this light diffusion plate pellet as a raw material, a 100 mm × 50 mm test plate having a smooth thickness of 2 mm on both sides was formed using an injection molding machine (clamping force 1000 kN). The total light transmittance and haze of the test plate were measured using an integrating sphere type color difference turbidimeter based on JIS K7361-1 and JIS K7136. The test plate had a total light transmittance of 85% and a haze of 99%.

<Production Example 2: Stamper>
The entire surface of stainless steel SUS430 having dimensions of 800 mm × 500 mm and a thickness of 100 mm was subjected to nickel-phosphorus electroless plating with a thickness of 100 μm, and a diamond cutting tool with an apex angle of 110 degrees was used on the nickel-phosphorus electroless plating surface. A plurality of triangular prism-shaped grooves having a width of 70 μm, a height of 24.5 μm, a pitch of 70 μm, and an apex angle of 110 degrees were cut along a side having a length of 800 mm (long side direction) to produce a stamper.

<Production Example 3: Injection Mold>
The same structure as the injection mold shown in FIG. 4 described above, that is, the core plate 64 and the frame member 66 arranged on the outer periphery of the core plate 64 were prepared using stainless steel. In the prepared frame member 66, a recess 70 corresponding to the outer peripheral portion 20 and the connection portion 30 was formed.

<Example 1>
Horizontal (inner dimension width) 700mm, length 400mm, depth 20mm, the same as shown in Fig. 1, the upper surface is open and the trapezoidal cross section of the main body, and projecting outward from the edge near the opening of the main body A milky white plastic case provided with a protruding piece to be prepared was prepared. Next, a reflecting sheet (manufactured by Tsujiden Co., Ltd., RF188) was attached to the inner side surface of the case to form a reflecting plate. Next, 14 cold cathode fluorescent lamps having a diameter of 3 mm and a length of 750 mm were arranged 5 mm away from the bottom of the case so that the distance a between the centers of the cold cathode fluorescent lamps was 28 mm. Next, the vicinity of the pole portion of the cold cathode tube was fixed to the case with a silicone sealant, and an inverter was attached.

  Next, the stamper obtained in Production Example 2 was placed on a fixed mold constituting the injection mold, and the core plate and frame member obtained in Production Example 3 were further placed on the movable mold side. Using such a mold for an injection molding machine (clamping force 4,410 kN), using the light diffusion plate pellet obtained in Production Example 1 as a raw material, under conditions of a cylinder temperature of 280 degrees and a mold temperature of 85 degrees A light diffusion plate was molded. The obtained light diffusing plate has a main body portion having a rectangular shape in plan view with a thickness TA = 2.0 mm and 727.5 mm × 415 mm, and a connecting portion continuously from a thickness 2.0 mm to 1.5 mm. It has a changed inclined surface, has a planar view edge shape with a width of 0.5 mm, and the outer peripheral portion has a thickness TB = 1.5 mm and a width WL = WS = 5.0 mm at all points in plan view. It was rim-like. The obtained light diffusing plate was a substantially flat surface having no step on the surface on which the inclined surface was not provided. However, a prism array including a plurality of triangular prisms extending along the longitudinal direction of the main body portion is formed on the surface on the light emitting side of the main body portion in a range including the effective illumination region.

  When the obtained light diffusing plate was observed using an ultra-deep microscope, the surface on which the prism array was formed (light emitting surface) had a maximum centerline average roughness Ra (in the longitudinal direction of the light diffusing plate). Ra) along the surface was an uneven surface of 5.9 μm. On the other hand, in the obtained light diffusing plate, the maximum value of the center line average roughness Ra was 0.6 μm on the surface (light incident surface) where the prism row of the main body portion was not formed.

  Next, the obtained light diffusing plate was placed on the projecting piece of the case so that the surface on which the prism row was formed faced the light emitting side, that is, the light emitting surface. . At this time, the cold cathode tubes were arranged so that the longitudinal direction of the cold cathode tubes and the longitudinal direction of the triangular prisms constituting the prism row were substantially parallel. Further, two diffusion sheets (“188GM2”, manufactured by Kimoto Co., Ltd.) were installed on this light diffusion plate.

  Further, a prism sheet having a prism array (“Thick-RBEF”, manufactured by Sumitomo 3M Limited) was disposed on the diffusion sheet. At this time, the prism rows formed on the prism sheet were arranged on the light emission side, and the longitudinal direction of the prism was arranged substantially parallel to the cold cathode tube. Further, a reflective polarizer using birefringence (“DBEF-D”, manufactured by Sumitomo 3M) was installed on the prism sheet to produce a direct type backlight device.

Next, with respect to the obtained direct type backlight device, a tube current of 5 mA was applied to light the cold cathode tube, and a two-dimensional color distribution measuring device was used to measure 100 front directions at equal intervals on the short direction center line. The luminance average value La and luminance unevenness Lu were obtained according to the following formulas 1 and 2. At this time, the luminance average value was 4,000 cd / m ² and the luminance unevenness was 0.5%. For this reason, the luminance unevenness of the light emitting surface was good.
Luminance average value La = (L1 + L2) / 2 (Formula 1)
Luminance unevenness Lu = ((L1-L2) / La) × 100 (Formula 2)
L1: Average luminance maximum value just above a plurality of cold-cathode tubes installed L2: Average minimum value sandwiched between maximum values Note that luminance unevenness is an index indicating luminance uniformity, and luminance unevenness When it is bad, the figure increases.

  Further, a liquid crystal display device was produced by arranging a commercial liquid crystal panel to be illuminated on the light emitting side of the direct type backlight device.

It is a longitudinal cross-sectional view which shows the liquid crystal display device which concerns on one Embodiment of this invention. It is a top view which shows the light diffusing plate used for the said liquid crystal display device. It is a longitudinal cross-sectional view which shows the said light diffusing plate. It is a longitudinal cross-sectional view which shows the injection die which shape | molds the said light diffusing plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light diffusing plate 1A Light incident surface 1B Light output surface 2 Linear light source 3 Reflecting plate 4 Housing | casing 10 Main body part 10L Long side part 10S Short side part 11 Effective illumination area 12 Uneven structure 20 Outer part 20L A pair of long side part 30S A pair of short side portions 30 Connection portion 32 Upper surface 34 Lower surface 42 Housing main body 42A Opening portion 44 Overhanging piece 46 Horizontal portion 48 Restriction portion 50 Injection mold 52 Fixed side mold 54 Movable side mold 56 Mold base 58 Stamper 58A Surface 60 Mold base 62 Mold plate 64 Core plate 65 Gate 66 Frame member 68 Hot runner portion 70 Recess 72 Cavity 100 Liquid crystal display device 120 Direct type backlight device 140 Liquid crystal panel (illuminated object)
a, b Distance P Molten resin TA, TB Thickness WL, WS Width X, Y Space

Claims (9)

An opening is formed on at least one surface, and the housing in which the light source is disposed in the internal space is disposed so as to close the opening, and a light incident surface that is a surface on the light source side, A light diffusing plate integrally formed by injection molding, having a light emitting surface opposite to the light incident surface,
A main body having a rectangular shape in plan view formed in a plate shape whose thickness is substantially constant;
An outer periphery provided on at least a part of the outer periphery of the main body,
A connecting portion for connecting the main body portion and the outer peripheral portion,
The main body portion is provided with an effective illumination area having a rectangular shape in a plan view that effectively irradiates an object to be illuminated at a substantially central position of the rectangle,
An uneven structure having a maximum center line average roughness (Ra) of 3 to 1000 μm is formed in a range including the effective illumination region on at least one of the light incident surface and the light emitting surface,
The outer peripheral portion is a portion that has a substantially constant thickness that is thinner than the thickness of the main body portion, and is supported by the housing,
The connection part is a light diffusing plate having a shape in which the thickness thereof becomes thinner from the main body part side toward the outer peripheral part side. The light diffusing plate according to claim 1,
The light emitting surface is a light diffusing plate that is a flat surface having no step between the connecting portion and the outer peripheral portion. The light diffusing plate according to claim 2,
The light emitting surface is a light diffusing plate that is a flat surface having no step between the main body portion, the connection portion, and the outer peripheral portion. The light diffusing plate according to claim 2,
A light diffusing plate in which a recessed portion recessed toward the light incident surface is formed in a range including the effective illumination region on the light emitting surface. In the light diffusing plate in any one of Claims 1-4,
The outer peripheral portion is a pair of long side portions formed corresponding to a pair of long side portions of the main body portion, or a pair of short side portions formed corresponding to a pair of short side portions of the main body portion. The light diffusing plate comprised by this. In the light diffusing plate in any one of Claims 1-4,
The said outer peripheral part is a light diffusing plate which is an edge-shaped part formed corresponding to four sides of the said main-body part. In the light diffusing plate in any one of Claims 1-6,
The thickness of the said outer peripheral part is a light diffusing plate which is 20 to 90% of the thickness of the said main-body part.   The housing according to any one of claims 1 to 7, wherein the housing has an opening formed on at least one surface thereof, the light source disposed in the internal space of the housing, and the opening. A direct type backlight device comprising a light diffusing plate.   A liquid crystal display device comprising the direct type backlight device according to claim 8 and a liquid crystal panel to be illuminated by the direct type backlight device.

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