JP2007192950A - Light diffusing plate and direct type back light device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion plate capable of further improving the luminance in the front direction when being used for a direct type back light device, and to provide a direct type back light device provided with the light diffusing plate. <P>SOLUTION: In the light diffusing plate 21, at least either face in a light incidence surface 21A and a light emission surface 21B lies in a specular state in which the center line average roughness (Ra(maxl)) measured in a direction at which the obtained value reaches the maximum is 0.0001 to 0.1 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light diffusing plate and a direct backlight device, and more particularly to a light diffusing plate capable of further improving the brightness in the front direction when used in a direct backlight device, and a direct light provided with the light diffusing plate. The present invention relates to a type backlight device.

  Conventionally, as a backlight device for a liquid crystal display, for example, a plurality of cold-cathode tubes arranged in parallel, a reflector that reflects light from these cold-cathode tubes, direct light from the cold-cathode tubes and A direct type backlight device including a light diffusing plate that becomes a light emitting surface by diffusing and irradiating reflected light from a reflecting plate is widely used. In such a direct type backlight device, it is possible to increase the brightness of the exit surface of the light diffusion plate by increasing the number of cold cathode tubes used.

  However, in the direct type backlight device, the luminance directly above the cold cathode tube increases, and the luminance tends to decrease as the distance from the upper portion increases. For this reason, periodic luminance unevenness occurs on the light emitting surface, and there is a problem that the luminance uniformity of the light emitting surface is lowered. For this reason, a liquid crystal display using such a direct type backlight device has a problem that display unevenness occurs on the display screen.

  Therefore, in recent years, for example, a stripe-shaped or dot-shaped light amount correction pattern is printed on the light diffusion plate, the amount of light emitted directly above the cold cathode tubes is reduced, and the amount of light emitted between the cold cathode tubes is relative. A method of increasing the number of reflections (Patent Document 1) and a method of collecting reflected light from the reflection plate in a region corresponding to the middle of the cold cathode tube and the cold cathode tube using a wave reflector (Patent Document 2) Has been.

  However, the method shown in Patent Document 1 has a problem in that since a part of the light amount is blocked by the light amount correction pattern, the utilization rate of the light amount emitted from the cold cathode tube is reduced and sufficient luminance cannot be obtained. . Further, the method disclosed in Patent Document 2 has a problem that the configuration of the backlight device is complicated.

  By the way, a material in which a light diffusing agent is dispersed in a transparent resin is often used for a light diffusing plate used in a direct type backlight device. In the light diffusing plate using such a material, the concentration of the light diffusing agent is increased in order to improve the luminance uniformity, but in this case, there is a problem that the luminance is lowered.

  Therefore, in order to solve such problems, it has been proposed to form a pattern such as a prism shape on the surface of the light diffusing plate so as to have a diffusion effect due to the surface shape without lowering the luminance. (Patent Documents 3 to 5).

JP-A-6-273760 JP 2001-174813 A JP-A-5-333333 JP-A-8-297202 JP 2000-182418 A

  However, if a prismatic pattern is simply formed on the surface of the light diffusing plate, the luminance in the front direction of the direct type backlight device having the light diffusing plate may be insufficient. An object of the present invention is to provide a light diffusing plate capable of further improving the luminance in the front direction when used in a direct type backlight device, and a direct type backlight device provided with the light diffusing plate.

  As a result of studies to solve the above-mentioned problems, the present inventor has found a light diffusing plate having a light incident surface on which light from a light source is incident and a light emitting surface on which light incident from the light incident surface is diffusely irradiated. The center line average roughness (Ra (max1)) of at least one of the light incident surface and the light emitting surface measured in the direction in which the obtained value is maximum is 0.0001 μm to 0.1 μm. It was found that the brightness in the front direction can be further improved when this light diffusing plate is used in a direct type backlight device, and the present invention has been completed based on this finding.

That is, according to the present invention, the following light diffusion plate is provided.
(1) A light diffusing plate having a light incident surface on which light from a light source is incident and a light emitting surface for diffusing and irradiating light incident from the light incident surface, wherein the light incident surface and the light emitting surface Light diffusion characterized in that at least one of the surfaces is in a mirror state having a center line average roughness (Ra (max1)) of 0.0001 μm to 0.1 μm measured in a direction in which the obtained value is maximized Board.

(2) A light diffusing plate having a light incident surface on which light from a light source is incident and a light emitting surface for diffusing and irradiating light incident from the light incident surface, wherein the light incident surface or the light emitting surface is A concavo-convex surface on which a concavo-convex structure having a center line average roughness (Ra (max2)) measured in the direction in which the obtained value is maximum is 3.0 μm to 1,000 μm, and the surface of the concavo-convex surface, The center line average roughness (Ra (max1)) measured in the direction in which the obtained value is the maximum for at least one of the surfaces opposite to the surface having the concavo-convex surface is 0.0001 μm to 0 A light diffusing plate having a mirror surface state of 1 μm. The concavo-convex structure constituting the concavo-convex surface can include, for example, a configuration having a plurality of linear prisms having a polygonal cross section, a polygonal pyramid prism, or the like as structural units, which will be described using these configurations. In this case, the surface of the uneven surface is a surface corresponding to each side of the polygonal shape or each surface of the polygonal pyramid. The surface opposite to the surface having the concavo-convex surface is a light exit surface when the light incident surface is an uneven surface, and the light exit surface when the light exit surface is an uneven surface. That is. In the present invention, the specular state means that the center line average roughness (Ra (max1)) measured in the direction in which the obtained value is maximum on a certain surface is in the range of 0.0001 μm to 0.1 μm. It means a state.

(3) The light diffusing plate, wherein the concavo-convex structure is a prism row in which a plurality of linear prisms each having a polygonal shape with a concave or convex cross section are arranged in parallel.

(4) The cross section of each linear prism is concave or convex, and the apex angle is a triangle of 60 ° to 170 °, and the interval between adjacent linear prisms in the same plane is 20 μm to 700 μm. A light diffusion plate characterized by being.

(5) Each of the linear prisms includes at least four surfaces, and two of the at least four surfaces and the other two surfaces are in the thickness direction of the light diffusion plate and the line. The light diffusing plate is inclined in opposite directions with respect to a plane including the longitudinal direction of the prism.

Further, according to the present invention, the following direct type backlight device is provided.
(6) A plurality of light sources, a reflecting plate that reflects light from these light sources, and the light diffusion plate that diffuses and irradiates direct light from the light source and reflected light from the reflecting plate. A direct type backlight device.

(7) The concavo-convex structure of the light diffusing plate is a prism array in which a plurality of linear prisms each having a concave or convex cross section are arranged in parallel, and each linear prism constitutes the triangle. The angle formed by the two inclined surfaces and the plane perpendicular to the thickness direction of the light diffusing plate is equal, and the position of the linear prism moves away from the light source closest to the linear prism, The direct-type backlight device, wherein the angle increases continuously or intermittently.

(8) The light source is a plurality of linear light sources arranged substantially in parallel, and the uneven structure of the light diffusing plate has a concave structure or a convex structure having three or more planes as a repeating unit, In the cross section of the light diffusing plate in the direction perpendicular to the longitudinal direction of the linear light source, the line segments corresponding to the three or more planes of the concave structure or the convex structure include a plurality of line segments having different inclinations. The slope of the plurality of line segments is Xn (degree, n is an integer of 1 or more), the distance between the centers of the adjacent linear light sources is a (mm), the center of the linear light source and the light diffusion plate Where the distance X to the light incident surface is b (mm), and the inclination Xn of the plurality of line segments is 12.5-10 × (b / a) <Xn <85-25 × (b / The direct type backlight device satisfying the relationship a).

(9) The light source is a plurality of point light sources, and the uneven structure of the light diffusion plate has a concave structure or a convex structure having three or more planes as a repeating unit, and the light diffusion plate In the cross section in the plane including the normal line of the light diffusing plate, the line segments corresponding to the three or more planes of the concave structure or the convex structure include two or more types of line segments having different inclinations. The inclination of the plurality of line segments is Xn (degree, n is an integer of 1 or more), the average distance between the adjacent point light sources in the plurality of point light sources is a (mm), and the center of the point light source And the light incident surface of the light diffusing plate is b (mm), and the inclination Xn of the plurality of line segments is 12.5-11 × (b / a) <x <85− for all n. The direct type backlight device satisfying the relationship of 28.5 × (b / a) Place.

(10) The repeating unit has a convex structure, and the light diffusion plate having the convex structure has a V-shape in the prism row in a direction different from the longitudinal direction of the linear prisms constituting the prism row. The direct type backlight device obtained by making a cut.

(11) The direct-type backlight device in which the convex structure has a pyramid shape or a truncated pyramid shape.

(12) The repeating unit has a concave structure, and the light diffusing plate having the concave structure has a V-shape in the prism row in a direction different from the longitudinal direction of the linear prism constituting the prism row. The direct type backlight device obtained by transferring the convex shape of a transfer member having a convex shape obtained by cutting.

(13) The direct-type backlight device in which the concave structure has a pyramid shape or a truncated pyramid shape.

(14) The direct-type backlight device, wherein the light diffusing plate is formed by dispersing a light diffusing agent in a transparent resin, and the total light transmittance of the dispersion is 60% to 98%. .

(15) The direct type backlight device, wherein the haze of the dispersion is 20% to 100%.

  According to the light diffusion plate of the present invention, when used in a direct type backlight device, there is an effect that the luminance in the front direction can be further improved. For this reason, this light diffusing plate can be suitably used for a direct type backlight device.

<First Embodiment>
A direct type backlight device according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view schematically showing a direct type backlight device according to a first embodiment of the present invention. The direct type backlight device of this embodiment includes a plurality of linear light sources 2 arranged in parallel, a reflector 3 that reflects light from the linear light source 2, and direct light and reflectors from the linear light source 2. And a light diffusing plate 1 that diffuses and irradiates reflected light from 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 assumed 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.

  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 is preferable from the viewpoint of weight reduction. The color of the reflector 3 is preferably white from the viewpoint of improving the luminance uniformity, but white and silver may be mixed in order to balance the luminance and the luminance uniformity highly.

The light diffusing plate 1 is a plate material that diffuses and irradiates incident light.
As a material constituting the light diffusing plate, 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, 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, and adjustment of total light transmittance and haze is easy. From the viewpoint, a transparent resin in which a light diffusing agent is dispersed is preferable.

  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 has both high permeability and high diffusibility required for a light diffusing plate, and has good chromaticity, so that it can be suitably used.

  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 and the like, a cycloalkane structure and a cycloalkene structure are preferable, and among them, a cycloalkane structure is most preferable. When the number of carbon atoms constituting the alicyclic structure is usually in the range of 4 to 30, preferably 5 to 20, more preferably 5 to 15, the mechanical strength, heat resistance and light diffusion plate Formability characteristics are highly balanced and suitable.

  The proportion of the repeating unit having an alicyclic structure in the resin having an alicyclic structure may be appropriately selected according to the purpose of use, but is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90%. % By weight or more. When the ratio of the repeating unit having an alicyclic structure is too small, the heat resistance is lowered, which is not preferable. In addition, repeating units other than the repeating unit which has an alicyclic structure in resin which has an alicyclic structure are suitably selected according to the intended purpose.

  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 viewpoints of heat resistance, mechanical strength, and the like, norbornene polymers and vinyl alicyclic hydrocarbon polymers are preferred, 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.

  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 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. .

  The thickness of the light diffusion plate 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.

Next, the outer shape of the light diffusing plate 1 will be described.
FIG. 2 is a longitudinal sectional view schematically showing the light diffusing plate 1. As shown in FIG. 2, the light diffusing plate 1 includes a light incident surface 1A on which light from the linear light source 2 is incident, and a light emitting surface 1B that diffuses and irradiates light incident from the light incident surface 1A. . In the light diffusing plate 1, the light emitted from the linear light source 2 is incident on the light incident surface 1 </ b> A close to the linear light source 2, then diffused in the light diffusing plate 1, and then diversified on the light emitting surface 1 </ b> B. Diffused in the direction and emitted.

  The light incident surface 1A is in a mirror state with a center line average roughness (Ra (max1)) measured in the direction in which the obtained value is maximized, 0.0001 μm to 0.1 μm. Thus, by making the light incident surface 1A into a mirror state, the luminance in the front direction on the light emitting surface can be improved. The light diffusing plate 1 having such a mirror-like light incident surface 1A is obtained by injection molding using a mold part whose cavity surface is polished into a mirror surface, light molded by extrusion molding, injection molding, or the like. Examples thereof include a method in which the light incident surface 1A of the diffusion plate 1 is polished into a mirror surface by post-processing.

  The light exit surface 1B is a concavo-convex surface on which a concavo-convex structure having a center line average roughness (Ra (max2)) of 3.0 μm to 1,000 μm measured in the direction in which the obtained value is maximum is formed. The concavo-convex structure can be, for example, a prism array in which a plurality of linear prisms each having a polygonal shape having a concave or convex cross section are arranged in parallel. In the present embodiment, the concavo-convex structure is a prism in which linear prisms 4 (hereinafter also referred to as triangular prisms 4) each having a concave or convex cross section are adjacent to each other or arranged at intervals. Row 5 As shown in FIG. 1, each triangular prism 4 is formed substantially parallel to the longitudinal direction of the linear light source 2. The cross-sectional shapes of the plurality of triangular prisms 4 are all substantially the same. At this time, it is preferable that the apex angle of the triangle constituting the triangular prism 4 is 60 ° to 170 °, and the interval between adjacent triangular prisms 4 in the same plane is 20 μm to 700 μm. With such a configuration, the luminance uniformity of the light emitting surface can be increased. Here, each inclined surface 4A of the triangular prism 4 may be in the mirror surface state, or may be in a rough surface state that is out of the range of the mirror surface state.

  The centerline average roughness Ra is a roughness curve obtained by removing a component longer than a predetermined wavelength by a phase compensation type high-pass filter from a curve of a cross-sectional view in a plane perpendicular to the target surface based on JIS B0601. Or can be read directly using an ultra-deep profile measuring microscope.

  According to the present embodiment, the luminance in the front direction can be further improved by setting the light incident surface 1A of the light diffusing plate 1 to the mirror state. Further, since the prism array 5 including the plurality of triangular prisms 4 is formed on the light emitting surface 1B, the luminance uniformity of the light emitting surface can be increased.

Second Embodiment
Next, a second embodiment of the present invention will be described. The direct type backlight device according to this embodiment is different from the first embodiment in that the light source is a point light source and the outer shape of the light diffusion plate is different. For this reason, it demonstrates below centering on these differences, the same code | symbol is attached | subjected about the component similar to or equivalent to 1st Embodiment, and the description is abbreviate | omitted or simplified.

  FIG. 3 is a perspective view schematically showing a direct type backlight device according to the second embodiment of the present invention. The direct type backlight device of the present embodiment includes a plurality of point light sources 12, a reflector 3 that reflects light from the point light source 12, direct light from the point light source 12, and reflected light from the reflector 3. And a light diffusing plate 11 that diffuses and irradiates the light.

  For each point light source 12, for example, a light emitting diode (LED) can be used. 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.

Next, an aspect of arrangement of a plurality of point light sources will be described.
4 to 6 are plan views schematically showing the arrangement of a plurality of point light sources. As shown in FIG. 4, as a first mode in which a plurality of point light sources 12 are arranged, a configuration in which they are arranged at predetermined intervals along the vertical direction and the horizontal direction of the direct type backlight device can be adopted. . Further, as shown in FIG. 5, as the second mode, the point light sources 12 are arranged at the four vertices of the quadrangle, that is, the configuration in which the point light sources P1 to P4 in FIG. 4 are removed, The point light source 12 may be arranged at the intersection of the rectangular diagonal lines. Furthermore, as shown in FIG. 6, the third mode may be configured such that the point light sources 12 are respectively arranged at the apexes of the honeycomb structure in which regular hexagons are continuously formed.

  In the above-described aspect, the distance between the point light sources may be uniform at all locations or may be partially changed. The case of partial change is, for example, the case where the interval between the point light sources is narrowed at the center of the direct type backlight device.

  The light diffusion plate 11 includes a light incident surface 11A and a light emitting surface 11B. The light exit surface 11B is an uneven surface on which an uneven structure is formed. This uneven structure is a structure in which a plurality of convex structures 13 as repeating units are formed. Each convex structure 13 is a structure having three or more planes as shown in FIG. 7A (shown as a convex structure of a quadrangular pyramid in FIG. 7A), which improves luminance unevenness. In this respect, it is preferable that the light diffusing plate is periodically arranged in a direction different from the short direction. At this time, the period is preferably 20 μm to 700 μm, and more preferably 30 μm to 400 μm.

  The convex structure 13 has a center line average roughness (Ra (max2)) measured in the direction in which the obtained value is maximum, 3 μm to 1,000 μm, preferably 3 μm to 800 μm, and preferably 4 μm to 500 μm. It is more preferable that Further, the convex structure may be formed on the entire light emitting surface, or may be formed only on a part of the light emitting surface (for example, an optically effective surface). Note that the direction in which the obtained value is the maximum is the direction passing between the apexes of adjacent quadrangular pyramids.

  Here, in the present embodiment, the surface 13A of the convex structure 13 is a mirror surface having a center line average roughness (Ra (max1)) measured in the direction in which the obtained value is maximum 0.0001 μm to 0.1 μm. State. Examples of a method for making the surface 13A of the convex structure 13 into a mirror state include a method of injection molding using a mold part whose cavity surface is polished into a mirror surface.

  Further, the light incident surface 11A of the light diffusing plate 11 is configured as a substantially flat surface. The light incident surface 11A may be in the mirror surface state or may be in a rough surface state that is out of the range of the mirror surface state. When the light incident surface 11A is intentionally roughened, for example, it can be performed by injection molding using a mold part whose surface is roughened by sandblasting or the like.

  Examples of the convex structure include a pyramid shape and a truncated pyramid shape. The pyramid may be a polygonal pyramid such as a triangular pyramid, a quadrangular pyramid, a pentagonal pyramid, or 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. With such a pyramid shape or a truncated pyramid shape, sufficient luminance is obtained even when observed from a position deviated from the front. The plurality of convex structures may be composed of only one type of structure, or may be a combination of a plurality of types of structures.

  In addition, the plurality of convex structures may have a shape obtained by making V-shaped cuts in a direction different from the longitudinal direction of the linear prisms constituting the prism row, for example, because they are easy to mold. it can. At this time, the shape of the linear prism can be, for example, a polygonal cross section.

  The concavo-convex structure having three or more planes may be a concave structure having the same shape as the convex structure. In this case, the plurality of concave structures have, for example, a convex shape obtained by making V-shaped cuts in a direction different from the longitudinal direction of the linear prisms constituting the prism row from the viewpoint that molding is easy. It can be obtained by transferring the convex shape of the transfer member.

  As shown in FIG. 7B, in the concavo-convex structure, in the cross section parallel to the thickness direction of the light diffusing plate 11, the line segment corresponding to the surface 13A of the convex structure 13 has an inclination (X1, X2; degree). There are two different types of line segments. In the present invention, as indicated by X1 in FIG. 7B, the same type is used if the angle is the same numerical value, regardless of whether the angle is right-up or left-up.

  In the light diffusing plate having such a configuration, as a result of intensive studies by the present inventors, the inclinations X1 and X2 indicate that the distance between the centers of the adjacent point light sources 12 is a (mm), and the center of the point light source 12 is When the distance from the light incident surface of the light diffusion plate 11 is b (mm), the relation 1 of 12.5-11 × (b / a) <X1 or X2 <85-28.5 × (b / a) is satisfied. It was found that this is preferable. With such a configuration, both luminance and luminance uniformity can be improved.

  Here, the adjacent point light sources are two point light sources in a state where no other point light sources exist on the line segment connecting the centers of the two point light sources. is there. Here, the distance between the centers of adjacent point light sources is the smaller value of the distance between the center position of a point light source and the center position of another point light source adjacent to this point light source. These are values obtained by selecting four in order and calculating the arithmetic average of these four numerical values.

  The distances a and b are preferably constant values in the direct type backlight device, but may not be constant values. When the values of the distances a and b are not constant, the relationship 1 is established when the distances a and b are the smallest values.

  The distance b may be designed in consideration of the thickness and luminance uniformity of the direct type backlight device, but is preferably 2 mm to 30 mm, and more preferably 3 mm to 25 mm. By setting the distance b in the above range, luminance unevenness can be reduced and a reduction in the luminous efficiency of the lamp can be prevented. In addition, the overall thickness of the backlight can be reduced.

  In FIG. 7 of the present embodiment, the case where the concavo-convex structure is a convex structure is described as an example. However, in the above preferable configuration (for example, satisfying the relation 1), the concavo-convex structure is concave. The same holds true for the structure.

  According to this embodiment, since the light incident surface 11A of the light diffusing plate 11 is in a mirror state, the luminance in the front direction of the light emitting surface can be further increased. Moreover, since the several convex structure 13 was formed in the light-projection surface 11B, the brightness | luminance uniformity of a light emission surface can be raised.

<Third Embodiment>
The third embodiment of the present invention is different from the first embodiment in the outer shape of the light diffusing plate. Therefore, this difference will be mainly described below. FIG. 8 is a perspective view schematically showing a direct type backlight device according to the third embodiment of the present invention. As shown in FIG. 8, the direct type backlight device of this embodiment includes the light source 2, the reflection plate 3, and a light diffusion plate 21.

  The light diffusion plate 21 includes a light incident surface 21A and a light emitting surface 21B. The light incident surface 21A and the light emitting surface 21B are each configured as a substantially flat surface. At least one of these surfaces 21A and 21B is in a mirror surface state with a center line average roughness (Ra (max1)) measured in the direction in which the obtained value is maximized, 0.0001 μm to 0.1 μm. . The method of polishing the surface to a mirror surface state can be performed by the same method as the light incident surface of the first embodiment. According to the present embodiment, since at least one of the light incident surface 21A and the light emitting surface 21B is in the mirror state, the luminance in the front direction of the light emitting surface can be further increased.

<Modification>
The present invention is not limited to the above embodiments.
For example, in the first embodiment, the prism row of the light diffusing plate 1 is a linear prism, the linear prism is a triangular prism having a triangular cross section, and a plurality of identical triangular prisms are arranged. For example, as shown in FIG. 9, the triangular prism is formed so that the angles formed by two inclined surfaces constituting the triangle and a plane substantially parallel to the light incident surface are equal. However, the light diffusing plate 101 may be configured so that the angle increases continuously or intermittently as the distance from the linear light source 2 closest to the triangular prism increases. According to such a configuration, the luminance of the portion corresponding to the space between the linear light sources 2 on the light emitting surface can be improved, and the luminance uniformity of the light emitting surface can be increased.

  Further, in the first embodiment, as the prism row, as shown in FIG. 10, a linear prism (hereinafter referred to as a composite) having a concave or convex polygonal section including at least four surfaces. The light diffusing plate 102 may be configured to be adjacent to each other or may be arranged at intervals.

  As the composite prism, two of the at least four surfaces and the other two surfaces are inclined in opposite directions with respect to a plane including the thickness direction of the light diffusion plate and the longitudinal direction of the linear prism. It is preferable that it is the structure. According to such a configuration, when the light diffusing plate having the composite prism is arranged on the light sources arranged at appropriate intervals, the light emitting surface is based on the number of the surfaces between the adjacent light sources. As a result, a plurality of light source images are observed, so that the luminance uniformity of the light emitting surface can be increased.

  In the first embodiment, the light incident surface 1A is in a mirror surface state and the light emitting surface 1B is in a mirror surface state or a rough surface state, but the light incident surface 1A is in a rough surface state and is formed on the light emitting surface 1B. The inclined surface of the triangular prism may be in the mirror state.

  In the second embodiment, the light incident surface 11A is in a mirror surface state or a rough surface state, and the surface of the convex structure formed on the light emitting surface 11B is in a mirror surface state, but the light incident surface 11A is in a mirror surface state. The surface of the convex structure formed on the light emitting surface 11B may be a rough surface state.

  Further, as the light diffusion plate of the second embodiment, the light diffusion plate 1 used in the first embodiment may be applied, and the light diffusion plate according to the modification of the first embodiment described above. Can also be applied. Similarly, as the light diffusing plate of the first embodiment, the light diffusing plate 11 used in the second embodiment may be applied, and according to a modification of the second embodiment described above or later. A light diffusing plate can also be applied.

  In the first embodiment, when the light diffusing plate 11 used in the second embodiment is applied, a cross section in a direction perpendicular to the longitudinal direction of the linear light source 2 in the convex structure formed on the light diffusing plate. Then, it is preferable that two types of line segments having different inclinations (X1, X2; degrees) exist in the line segments corresponding to the surface of the convex structure. In this case, the inclinations X1 and X2 are expressed as follows: 12. The distance between the centers of adjacent linear light sources is a (mm), and the distance between the center of the linear light source and the light incident surface of the light diffusion plate is b (mm). It is preferable to satisfy the relationship 2 of 5-10 × (b / a) <X1, X2 <85-25.0 × (b / a), and 15-10 × (b / a) <X1, X2 <80− It is more preferable to satisfy the relationship 3 of 25 × (b / a). The present inventors have found that the luminance and the luminance uniformity can be improved by adopting such a configuration.

  Further, in the direct type backlight device of each of the above embodiments, an optical member for further improving luminance and luminance uniformity may be appropriately arranged. Examples of such an optical member include a diffusion sheet and a prism sheet. These optical members are provided, for example, on the side far from the light source in the light diffusion plate.

  Further, for the purpose of further improving the luminance of the light emitting surface, a reflective polarizer shown below may be arranged, and this reflective polarizer can be provided on the side far from the light source of the optical member.

  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.

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

Production Example 1 (Pellet A for Light Diffusing Plate)
99.2 parts of 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 Then, 0.8 parts of the resulting fine particles were mixed, kneaded with a twin-screw extruder, extruded into a strand, and cut with a pelletizer to produce a light diffusion plate pellet A. Using this light diffusion plate pellet A as a raw material, an injection molding machine (clamping force 1000 kN) was used to mold a 100 mm × 50 mm test plate with a smooth thickness of 2 mm on both sides. 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 65% and a haze of 99%.

Production Example 2 (Pellet B for Light Diffusing Plate)
A light diffusion plate pellet B was produced in the same manner as in Production Example 1 except that the amount of the resin was 99.7 parts and the amount of the light diffusing agent was 0.3 parts. A test plate similar to that of Production Example 1 was prepared using the light diffusion plate pellet B as a raw material, and the total light transmittance and haze were measured by the same method. The test plate had a total light transmittance of 85% and a haze of 99%.

Production example 3 (mold part X)
100 mm thick nickel-phosphorous electroless plating was applied to the entire surface of stainless steel SUS430 with dimensions 387 mm x 308 mm and thickness 100 mm, and the nickel-phosphorous electroless plating surface was applied using a diamond cutting tool with a vertex angle of 110 degrees. A plurality of triangular grooves with a pitch of 70 μm and an apex angle of 110 degrees were cut along a side having a length of 387 mm (long side direction) to produce a mold part X.

Production example 4 (mold part Y)
The surface of the cutting surface of the mold part X was blasted, and the surface of the cutting surface was roughened to produce a mold part Y.

<Example 1>
A reflective sheet (manufactured by Tsujiden Co., Ltd., RF188) is attached to the inner surface of a milky white plastic case having an inner dimension width of 300 mm, a depth of 200 mm, and a depth of 20 mm to form a reflector, 5 mm away from the bottom of the reflector, Eight cold-cathode tubes having a length of 360 mm were arranged such that the distance a between the centers of the cold-cathode tubes was 25 mm, the vicinity of the electrode part was fixed with a silicone sealant, and an inverter was attached.

  The movable cavity surface and the fixed cavity surface were each polished into a mirror surface state. Using these molds in an injection molding machine (clamping force 4,410 kN), using the light diffusion plate pellet A 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 was a rectangular flat plate having a thickness of 2 mm, 315 mm × 237 mm.

  When the obtained light diffusing plate was observed using an ultra-deep microscope, one surface had a center line average roughness (Ra (max1)) measured in the direction in which the obtained value was maximum 0.005 μm. The other surface had a center line average roughness (Ra (max 1)) measured in the direction in which the obtained value was maximum, and was 0.003 μm.

  Next, the obtained light diffusing plate was placed on a plastic case with a cold cathode tube attached so that the other surface was on the cold cathode tube side. Furthermore, on this light diffusion plate, a diffusion sheet (“188GM3”, manufactured by Kimoto), a prism sheet (“BEFIII-10T”, manufactured by Sumitomo 3M), and a diffusion sheet (“188GM3”, manufactured by Kimoto) Were installed in this order. Further, a direct type backlight device was produced by attaching a polarizing plate on the diffusion sheet.

Next, the cold cathode tube was turned on by applying a tube current of 5 mA to the obtained direct type backlight, and using a two-dimensional color distribution measuring apparatus, 100 frontal luminances were equally spaced on the short direction center line. The luminance average value (front luminance) La and luminance unevenness Lu in the front direction were obtained according to the following formulas 1 and 2. At this time, the front luminance was 4,871 cd / m ² and the luminance unevenness was 0.4%.
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.

<Example 2>
A light diffusing plate was obtained in the same manner as in Example 1 except that one of the movable cavity surface and the fixed cavity surface was not roughened and was made rough. In the obtained light diffusing plate, one surface has a center line average roughness (Ra (max1)) measured in the direction in which the obtained value is maximum, and is 0.16 μm, and the other surface is obtained. The centerline average roughness (Ra (max1)) measured in the direction in which the measured value was the maximum was 0.003 μm.

The obtained light diffusing plate was arranged so that the other surface was on the cold cathode tube side, and a direct type backlight device was produced in the same manner as in Example 1. In the obtained direct backlight device, the front luminance was 4,823 cd / m ² and the luminance unevenness was 0.3%.

<Example 3>
A light diffusing plate was obtained in the same manner as in Example 1 except that either the movable cavity surface or the fixed cavity surface was roughened by sandblasting without polishing as described above. . In the obtained light diffusing plate, one surface has a center line average roughness (Ra (max1)) measured in the direction in which the obtained value is maximized, and the other surface is obtained. The centerline average roughness (Ra (max1)) measured in the direction in which the measured value was maximum was 0.6 μm.

The obtained light diffusing plate was arranged so that the other surface was on the cold cathode tube side, and a direct type backlight device was produced in the same manner as in Example 1. In the obtained direct type backlight device, the front luminance was 4,847 cd / m ² and the luminance unevenness was 0.3%.

<Example 4>
The mold part X obtained in Production Example 3 was used for one mold constituting the mold, and the cavity surface of the other mold was polished into a mirror surface state. Such a mold is used in an injection molding machine (clamping force 4,410 kN), and the light diffusion plate pellet B obtained in Production Example 2 is used as a raw material under conditions of a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. The light diffusing plate was molded with The obtained light diffusing plate had a rectangular shape with a thickness of 2 mm, 315 mm × 237 mm, and a prism row composed of a plurality of triangular prisms was formed on one surface thereof.

  When the obtained light diffusing plate was observed using an ultra-deep microscope, the surface on which the prism array having the concavo-convex structure was formed had a maximum value (the longitudinal direction of the light diffusing plate). The center line average roughness (Ra (max2)) was 5.9 μm. Further, each surface of the triangular prism had a center line average roughness (Ra (max1)) measured in the direction in which the obtained value was maximum, and was 0.005 μm. On the other hand, the surface on which the prism row was not formed had a center line average roughness (Ra (max1)) measured in the direction in which the obtained value was maximum, and was 0.003 μm.

Next, the obtained light diffusing plate was disposed so that the other surface was on the cold cathode tube side, and a direct type backlight device was produced in the same manner as in Example 1. At this time, the longitudinal direction of the triangular prism and the longitudinal direction of the cold cathode tube were made substantially parallel. In the obtained direct type backlight device, the front luminance was 5,002 cd / m ² and the luminance unevenness was 0.3%.

<Example 5>
A light diffusing plate was obtained in the same manner as in Example 4 except that the mold part X was replaced with the mold part Y. In the obtained light diffusing plate, the surface on which the prism array is formed has a center line average roughness (Ra (max2)) in the direction in which the obtained value is maximum (longitudinal direction of the light diffusing plate). It was 5 μm. Further, each surface of the triangular prism had a center line average roughness (Ra (max1)) measured in the direction in which the obtained value was maximum, and was 0.16 μm. On the other hand, the surface on which the prism row was not formed had a center line average roughness (Ra (max1)) measured in the direction in which the obtained value was maximum, and was 0.003 μm.

Next, the obtained light diffusing plate was disposed so that the other surface was on the cold cathode tube side, and a direct type backlight device was produced in the same manner as in Example 1. In the obtained direct type backlight device, the front luminance was 4,952 cd / m ² and the luminance unevenness was 0.5%.

<Example 6>
A light diffusing plate was obtained in the same manner as in Example 4 except that the cavity surface of the other mold was roughened by sandblasting. In the obtained light diffusing plate, the surface on which the prism array is formed has a center line average roughness (Ra (max2)) in the direction in which the obtained value is maximum (longitudinal direction of the light diffusing plate). It was 9 μm. Further, each surface of the triangular prism had a center line average roughness (Ra (max1)) measured in the direction in which the obtained value was maximum, and was 0.005 μm. On the other hand, the surface on which the prism array was not formed had a center line average roughness (Ra (max1)) of 0.6 μm measured in the direction in which the obtained value was maximum.

Next, the obtained light diffusing plate was disposed so that the other surface was on the cold cathode tube side, and a direct type backlight device was produced in the same manner as in Example 1. In the obtained direct type backlight device, the front luminance was 4,977 cd / m ² and the luminance unevenness was 0.4%.

<Comparative Example 1>
A light diffusing plate was obtained in the same manner as in Example 5 except that the cavity surface of the other mold was roughened by sandblasting. In the obtained light diffusing plate, the surface on which the prism array is formed has a center line average roughness (Ra (max2)) in the direction in which the obtained value is maximum (longitudinal direction of the light diffusing plate). It was 5 μm. Each surface of the triangular prism had a center line average roughness (Ra (max1)) of 0.5 μm measured in the direction in which the obtained value was maximum. On the other hand, the surface on which the prism array was not formed had a center line average roughness (Ra (max1)) of 3.0 μm measured in the direction in which the obtained value was maximum.

Next, the obtained light diffusing plate was disposed so that the other surface was on the cold cathode tube side, and a direct type backlight device was produced in the same manner as in Example 1. In the obtained direct type backlight device, the front luminance was 4,479 cd / m ² and the luminance unevenness was 0.6%.

  The results of Examples 1 to 6 and Comparative Example 1 are shown in Table 1.

  As shown in Table 1, in Examples 1 to 6, it was found that the luminance unevenness was small and the front luminance could be further increased. On the other hand, as shown in Comparative Example 1, when both surfaces of the light incident surface and the light exit surface were roughened, the front luminance was insufficient.

1 is a perspective view schematically showing a direct type backlight device according to a first embodiment of the present invention. It is sectional drawing which shows typically the light-projection surface of the light diffusing plate used for 1st Embodiment. It is a perspective view which shows typically the direct type | mold backlight apparatus which concerns on 2nd Embodiment of this invention. It is a top view which shows typically the arrangement | positioning aspect of a some point light source. It is a top view which shows typically the arrangement | positioning aspect of a some point light source. It is a top view which shows typically the arrangement | positioning aspect of a some point light source. It is a figure for demonstrating the structure of the light-projection surface of the light diffusing plate used for 2nd Embodiment, (A) is the perspective view, (B) is the sectional drawing. It is a perspective view which shows typically the direct type | mold backlight apparatus which concerns on 3rd Embodiment of this invention. It is sectional drawing which shows typically the light diffusing plate which concerns on the 1st modification of the said embodiment. It is sectional drawing which shows typically the light diffusing plate which concerns on the 2nd modification of the said embodiment.

Explanation of symbols

1, 11, 21, 101, 102 Light diffusing plates 1A, 11A, 21A Light incident surfaces 1B, 11B, 21B Light emitting surfaces 2 Linear light source 3 Reflecting plate 4 Triangular prism (linear prism)
4A slope 5 prism array 12 point light source 13 convex structure 13A surface

Claims (15)

A light diffusing plate having a light incident surface on which light from a light source is incident and a light emitting surface on which light incident from the light incident surface is diffusely irradiated;
At least one of the light incident surface and the light emitting surface is a mirror surface having a center line average roughness (Ra (max1)) of 0.0001 μm to 0.1 μm measured in a direction in which the obtained value is maximum. A light diffusion plate characterized by being in a state. A light diffusing plate having a light incident surface on which light from a light source is incident and a light emitting surface on which light incident from the light incident surface is diffusely irradiated;
The light incident surface or the light incident / exit surface is a concavo-convex surface on which a concavo-convex structure having a center line average roughness (Ra (max2)) of 3 μm to 1,000 μm measured in the direction in which the obtained value is maximum is formed. Yes,
Centerline average roughness (Ra (max1)) measured in the direction in which the obtained value is the maximum for at least one of the surface of the uneven surface and the surface opposite to the surface having the uneven surface Is a mirror surface state of 0.0001 μm to 0.1 μm. The light diffusing plate according to claim 2,
The light diffusing plate is characterized in that the concavo-convex structure is a prism array in which a plurality of linear prisms each having a polygonal shape having a concave or convex cross section are arranged in parallel. The light diffusing plate according to claim 3.
The cross section of each linear prism is concave or convex, and its apex angle is a triangle of 60 ° to 170 °,
The light diffusing plate according to claim 1, wherein a distance between the linear prisms adjacent in the same plane is 20 μm to 700 μm. The light diffusing plate according to claim 3.
Each of the linear prisms includes at least four surfaces,
Of the at least four surfaces, two surfaces and the other two surfaces are inclined in opposite directions with respect to a plane including the thickness direction of the light diffusion plate and the longitudinal direction of the linear prism. A light diffusion plate characterized by that.   The light diffusing plate according to claim 1 or 2, wherein a plurality of light sources are disposed, a reflecting plate that reflects light from these light sources, and direct light from the light source and reflected light from the reflecting plate are diffusely irradiated. A direct-type backlight device comprising: The direct type backlight device according to claim 6,
The concavo-convex structure of the light diffusing plate is a prism array in which a plurality of linear prisms having a concave or convex triangular cross section are arranged in parallel.
Each of the linear prisms is formed so that the angles formed by two inclined surfaces constituting the triangle and a plane perpendicular to the thickness direction of the light diffusion plate are equal.
The direct-type backlight device, wherein the angle increases continuously or intermittently as the position of the linear prism moves away from the light source closest to the linear prism. The direct type backlight device according to claim 6,
The light source is a linear light source arranged in a plurality substantially parallel,
The concavo-convex structure of the light diffusing plate has a concave structure or a convex structure having three or more planes as a repeating unit,
In the cross section of the light diffusing plate in the direction orthogonal to the longitudinal direction of the linear light source, the line segments corresponding to the three or more planes of the concave structure or the convex structure include a plurality of line segments having different inclinations. Included,
The inclination of the plurality of line segments is Xn (degree, n is an integer of 1 or more), the distance between the centers of the adjacent linear light sources is a (mm), the center of the linear light source and the light diffusion plate Assuming that the distance from the light incident surface is b (mm),
The direct-type backlight, wherein the inclination Xn of the plurality of line segments satisfies the relationship of 12.5-10 × (b / a) <Xn <85-25 × (b / a) in all n apparatus. The direct type backlight device according to claim 6,
The light source is a plurality of point light sources arranged,
The concavo-convex structure of the light diffusing plate has a concave structure or a convex structure having three or more planes as a repeating unit,
In a cross section of the light diffusing plate in a plane including the normal line of the light diffusing plate, line segments corresponding to the three or more planes of the concave structure or the convex structure include two or more types of line segments having different inclinations. Contains
The inclination of the plurality of line segments is Xn (degree, n is an integer of 1 or more), the average distance between the adjacent point light sources in the plurality of point light sources is a (mm), and the center of the point light source And the distance between the light incident surface of the light diffusion plate and b (mm),
The direct type, wherein the slopes Xn of the plurality of line segments satisfy the relationship of 12.5-11 × (b / a) <x <85-28.5 × (b / a) in all n Backlight device. The direct type backlight device according to claim 8 or 9,
The repeating unit is a convex structure;
The light diffusing plate having this convex structure is obtained by making a V-shaped notch in the prism row in a direction different from the longitudinal direction of the linear prism constituting the prism row. Light equipment. The direct type backlight device according to claim 10,
The direct-type backlight device, wherein the convex structure is a pyramid or a truncated pyramid. The direct type backlight device according to claim 8 or 9,
The repeating unit is a concave structure;
The light diffusion plate having this concave structure is a transfer member having a convex shape obtained by making a V-shaped cut in the prism row in a direction different from the longitudinal direction of the linear prism constituting the prism row. A direct type backlight device obtained by transferring the convex shape. The direct type backlight device according to claim 12,
The direct-type backlight device, wherein the concave structure is a pyramid or a truncated pyramid. The direct type backlight device according to any one of claims 6 to 13,
The light diffusing plate is made of a transparent resin in which a light diffusing agent is dispersed, and the total light transmittance of the dispersion is 60% to 98%. The direct type backlight device according to claim 14,
A direct type backlight device, wherein the haze of the dispersion is 20% to 100%.

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