JP2008130488A - Light-diffusing plate, surface light source device, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light source device capable of preventing generation of an uncomfortable sound from a contacting point of a light-diffusing plate and a lamp box. <P>SOLUTION: This surface light source device 1 is the surface light source device in which a plurality of light sources 2 is mutually separated and arranged in the resin made lamp box 5 of which the front face side is opened, and in which in a state of contacting the front face 31a of a frame part 31 of the lamp box 5, the resin made light-diffusing plate 3 is arranged so as to shield an open face of the lamp box 5. A part contacting at least the frame part front face 31a on the rear face of the light-diffusing plate 3 is formed on a mat face, the arithmetic average roughness Ra of the mat face is 0.8 to 15 μm, and the average spacing Sm of unevenness of the mat face is 100 to 300 μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light diffusing plate, a surface light source device, and a liquid crystal display device that can prevent generation of unpleasant noise from a contact portion between a light diffusing plate and a lamp box.

  In this specification and claims, the term “arithmetic average roughness Ra” means an arithmetic average roughness Ra measured in accordance with JIS B0601-1994, and “an average interval Sm of unevenness”. "Means an average interval Sm of unevenness measured in accordance with JIS B0601-1994.

As a liquid crystal display device, for example, a configuration in which a surface light source device is disposed as a backlight on a lower surface side (back surface side) of an image display unit in which a pair of polarizing plates is disposed on both upper and lower surfaces of a liquid crystal cell is known. As the surface light source device for the backlight, a surface light source device having a configuration in which a plurality of light sources are arranged in a lamp box and a light diffusion plate is arranged on the front side of these light sources is known (Patent Document 1). reference).
Japanese Unexamined Patent Publication No. 7-141908 (paragraph 0012, FIG. 1)

  By the way, the light diffusing plate is arranged and fixed in contact with the front surface of the edge frame portion of the lamp box, and unpleasant noise is generated due to friction between the front surface of the edge frame portion and the light diffusing plate. There are things to do. For example, when the power is turned on, the light diffusing plate expands due to a temperature rise inside the surface light source device, and at this time, an unpleasant sound may be generated due to a rubbing phenomenon between the front surface of the edge frame and the light diffusing plate. Such generation of unpleasant noise was remarkable when the edge frame of the lamp box was made of polycarbonate.

  The present invention has been made in view of such a technical background, and provides a light diffusing plate, a surface light source device, and a liquid crystal display device that can prevent generation of unpleasant noise from a contact portion between a light diffusing plate and a lamp box. The purpose is to provide.

  In order to achieve the above object, the present invention provides the following means.

[1] In a state where a plurality of light sources are spaced apart from each other in a resin lamp box whose front side is open and a resin light diffusion plate is in contact with the front surface of the edge frame portion of the lamp box. A surface light source device arranged to close an open surface of the lamp box,
A portion of the back surface of the light diffusing plate that contacts at least the front surface of the edge frame portion is formed on the mat surface, the arithmetic average roughness Ra of the mat surface is 0.8 to 15 μm, and the average interval of the unevenness of the mat surface Sm is 100-300 micrometers, The surface light source device characterized by the above-mentioned.

  [2] A plurality of triangular convex portions having a triangular cross-sectional shape are projected on the front surface of the light diffusion plate, the apex angle of the triangular convex portions is set to 40 to 150 degrees, and the pitch between adjacent triangular convex portions is 2. The surface light source device according to item 1, wherein the interval is set to 10 to 500 μm.

[3] In a state in which a plurality of light sources are spaced apart from each other in a resin lamp box whose front side is open and a resin light diffusion plate is in contact with the front surface of the edge frame portion of the lamp box. A surface light source device arranged to close an open surface of the lamp box,
The entire back surface of the light diffusing plate is formed on the mat surface, the arithmetic average roughness Ra of the mat surface is 0.8 to 15 μm, and the average interval Sm of the unevenness of the mat surface is 100 to 300 μm. A characteristic surface light source device.

  [4] A plurality of triangular convex portions having a triangular cross-sectional shape are projected on the front surface of the light diffusion plate, the apex angle of the triangular convex portions is set to 40 to 150 degrees, and the pitch between adjacent triangular convex portions is 4. The surface light source device according to item 3, wherein the interval is set to 10 to 500 μm.

  [5] The surface light source device according to item 2 or 4, wherein the light diffusing plate has a total light transmittance of 55 to 75%.

  [6] A liquid crystal display device comprising: the surface light source device according to any one of items 1 to 5; and a liquid crystal panel disposed on a front surface side of the surface light source device.

  [7] The matte surface has an arithmetic mean roughness Ra of 0.8 to 15 μm, and the mat surface has irregularities. A light diffusing plate having an average interval Sm of 100 to 300 μm.

  [8] A plurality of triangular convex portions having a triangular cross-sectional shape are provided on the other surface of the light transmitting plate, the apex angle of the triangular convex portions is set to 40 to 150 degrees, and adjacent triangular convex portions are adjacent to each other. 8. The light diffusing plate according to 7 above, wherein the pitch interval is set to 10 to 500 μm.

  [9] The one surface is made of a resin light-transmitting plate formed on the mat surface, the arithmetic average roughness Ra of the mat surface is 0.8 to 15 μm, and the average roughness of the mat surface A light diffusing plate having a spacing Sm of 100 to 300 μm.

  [10] A plurality of triangular convex portions having a triangular cross-sectional shape are provided on the other surface of the light transmitting plate, the apex angle of the triangular convex portions is set to 40 to 150 degrees, and adjacent triangular convex portions are adjacent to each other. 10. The light diffusing plate according to 9 above, wherein the pitch interval is set to 10 to 500 μm.

  In the invention of [1], at least a portion of the back surface of the light diffusing plate that is in contact with the front surface of the edge frame portion is formed on the mat surface, and the arithmetic average roughness Ra of the mat surface is 0.8 to 15 μm. Since the average interval Sm is 100 to 300 μm, it is possible to prevent the generation of unpleasant noise due to the friction between the front surface of the edge frame portion of the lamp box and the light diffusion plate. In the conventional configuration, the generation of unpleasant noise was particularly noticeable when the edge frame portion of the lamp box was made of polycarbonate, but according to the present invention, when the edge frame portion of such a lamp box is made of polycarbonate, The generation of unpleasant noise can be sufficiently prevented.

  In the invention of [2], a plurality of triangular convex portions having a triangular cross-sectional shape are projected on the front surface of the light diffusing plate, the apex angle of the triangular convex portions is set to 40 to 150 degrees, and adjacent triangular convex portions Since the pitch interval between them is set to 10 to 500 μm, the luminance of the emitted light can be improved.

  In the invention of [3], the entire back surface of the light diffusing plate is formed on the mat surface, the arithmetic average roughness Ra of the mat surface is 0.8 to 15 μm, and the average interval Sm of the unevenness of the mat surface is 100 to 300 μm. Therefore, it is possible to prevent generation of unpleasant noise due to friction between the front surface of the edge frame portion of the lamp box and the light diffusion plate. In the conventional configuration, the generation of unpleasant noise was particularly noticeable when the edge frame portion of the lamp box was made of polycarbonate, but according to the present invention, when the edge frame portion of such a lamp box is made of polycarbonate, The generation of unpleasant noise can be sufficiently prevented. In addition, since the entire back surface of the light diffusing plate is formed on the mat surface, the manufacturing efficiency can be improved and it is easy to cope with production of different sizes.

  In the invention of [4], a plurality of triangular convex portions having a triangular cross-sectional shape are projected on the front surface of the light diffusing plate, the apex angle of the triangular convex portions is set to 40 to 150 degrees, and adjacent triangular convex portions Since the pitch interval between them is set to 10 to 500 μm, the luminance of the emitted light can be improved. Further, brightness unevenness is caused by a synergistic effect that the entire back surface of the light diffusing plate is formed on a specific mat surface and the triangular convex portion having the specific configuration is projected on the front surface of the light diffusing plate. It is possible to emit uniform light without any light. Note that the luminance unevenness suppressing effect due to the synergistic effect becomes larger when a configuration in which the total light transmittance of the light diffusion plate is high (for example, 55 to 75%) is adopted.

  In general, when a triangular convex portion is formed on the front surface of the light diffusing plate (particularly when the apex angle of the triangular convex portion is 90 degrees), the light diffusing plate is incident in the normal direction. The diffused light is returned to the back side (to the light source side) by total reflection, so that the diffusivity of the light diffusion plate is low. In the invention of [4], the entire back surface of the light diffusion plate is Further, even if the light is incident in the normal direction, it is sufficiently diffused by being formed on the mat surface having an arithmetic average roughness Ra of 0.8 to 15 μm and an average interval Sm of unevenness of 100 to 300 μm. Thus, it is possible to emit the diffused light to the front side without causing total reflection on the front surface of the light diffusing plate, so that the diffusivity of the light diffusing plate can be sufficiently improved. In other words, the light diffusion plate has a synergistic effect that the entire back surface of the light diffusion plate is formed on a specific mat surface and the triangular protrusion having the specific configuration is projected on the front surface of the light diffusion plate. The diffusion rate of the plate can also be sufficiently improved. This synergistic effect is particularly remarkable in a light diffusing plate having a structure containing a light diffusing agent (light diffusing particles). For example, in a light diffusing plate containing a light diffusing agent (light diffusing particles) having a particle size of submicron, a contour image of a colored light source (lamp) is easily transmitted to the front side and is easily seen. However, in the invention of [4], appearance of the contour image of the light source can be sufficiently suppressed by the synergistic effect.

  In the invention [5], since the total light transmittance of the light diffusing plate is 55 to 75%, sufficient luminance can be obtained, and the luminance unevenness suppressing effect by the synergistic effect can be sufficiently obtained.

  In the invention of [6], a liquid crystal display device capable of preventing generation of unpleasant noise from a contact portion between the light diffusion plate and the lamp box is provided.

  The invention (7) (light diffusing plate) comprises a resin-made light transmitting plate in which at least a peripheral portion of one surface is formed on a mat surface, and an arithmetic average roughness Ra of the mat surface is 0.8 to 15 μm. In addition, since the average interval Sm of the unevenness of the mat surface is 100 to 300 μm, it is possible to prevent generation of unpleasant noise due to friction between the front surface of the edge frame portion of the lamp box and the light diffusion plate.

  In the invention of [8], a plurality of triangular convex portions having a triangular cross-sectional shape are projected on the other surface of the light transmission plate, the apex angle of the triangular convex portions is set to 40 to 150 degrees, and adjacent triangles Since the pitch interval between the convex portions is set to 10 to 500 μm, the luminance of the emitted light can be improved.

  The invention of [9] comprises a resin light-transmitting plate in which the entire surface of one surface is formed on the mat surface, the arithmetic average roughness Ra of the mat surface is 0.8 to 15 μm, and the unevenness of the mat surface Since the average interval Sm is 100 to 300 μm, it is possible to prevent the generation of unpleasant noise due to the friction between the front surface of the edge frame portion of the lamp box and the light diffusion plate. In addition, since the entire surface of one surface is formed on the mat surface, the manufacturing efficiency can be improved, and it is very easy to cope with production of different sizes.

  In the invention of [10], a plurality of triangular convex portions having a triangular cross-sectional shape are projected on the other surface of the light transmission plate, the apex angle of the triangular convex portions is set to 40 to 150 degrees, and adjacent triangles Since the pitch interval between the convex portions is set to 10 to 500 μm, the luminance of the emitted light can be improved. Furthermore, a synergistic effect between the fact that the entire surface of one surface of the light diffusing plate is formed on a specific mat surface and the triangular protrusions of the specific configuration projecting on the other surface of the light diffusing plate. As a result, uniform light without uneven brightness can be emitted, and the diffusivity of the light diffusion plate can be sufficiently improved.

  An embodiment of a liquid crystal display device according to the present invention is shown in FIG. In FIG. 1, (1) is a surface light source device (backlight), (10) is a liquid crystal panel, and (20) is a liquid crystal display device. The liquid crystal panel (10) includes a liquid crystal cell (11) and polarizing plates (12) and (13) disposed on both upper and lower sides of the liquid crystal cell (11).

  The said surface light source device (1) is arrange | positioned at the lower surface side (back side) of the polarizing plate (13) below the said liquid crystal panel (10). The surface light source device (1) includes a thin box-shaped lamp box (5) having a substantially rectangular shape in plan view and an open front surface (upper surface), and a lamp box (5) spaced apart from each other. A plurality of linear light sources (2) arranged, and a resin light diffusing plate (3) arranged on the front side (upper side) of the plurality of linear light sources (2) are provided. As shown in FIG. 1, the lamp box (5) has an edge frame portion (31) made of a side plate extending from the periphery of the rear plate (32) having a rectangular shape in plan view and extending toward the front side. The front side is open. The light diffusing plate (3) is disposed and fixed to the lamp box (5) so as to close the open surface on the front side. That is, the light diffusing plate (3) is configured such that the peripheral portion of the back surface (3a) of the light diffusing plate (3) is in contact with the front surface (31a) of the edge frame portion (31) of the lamp box (5). ) Is fixed to the lamp box (5). A light reflecting layer (not shown) is provided on the inner surface of the lamp box (5).

  As shown in FIG. 3, the light diffusing plate (3) is made of a resin-made light transmitting plate having the entire back surface (3a) formed on the mat surface. That is, the light diffusion plate (3) is arranged so that the surface (3a) formed on the mat surface is on the light source (2) side (see FIG. 1). The arithmetic average roughness Ra of the mat surface is set to 0.8 to 15 μm, and the average interval Sm of the unevenness of the mat surface is set to 100 to 300 μm. In this embodiment, the entire back surface (3a) of the light diffusing plate (3) is formed on the mat surface. However, the present invention is not particularly limited to this configuration, and the light diffusing plate (3) It suffices that at least a portion of the back surface (3a) that contacts the front surface (31a) of the edge frame is formed on the mat surface (6). For example, as shown in FIG. 4, the back surface (3a) of the light diffusion plate (3) It is also possible to adopt a configuration in which only the portion in contact with the front surface (31a) of the edge frame portion is formed on the mat surface (6).

  Moreover, in this embodiment, the uneven | corrugated shaped part (4) in which the triangle convex part (7) which cross-sectional shape is a triangle protrudes in the front surface (3b) of the said light diffusing plate (3) is formed. Yes. That is, the surface (3b) on which the triangular protrusions (7) of the light diffusing plate (3) are formed is disposed on the liquid crystal panel (10) side (see FIG. 1). The apex angle (α) of the triangular convex portion (7) is set to 40 to 150 degrees, and the pitch interval (P) between adjacent triangular convex portions (7) is set to 10 to 500 μm. Moreover, in this embodiment, the cross-sectional shape of the said triangular convex part (7) is an isosceles triangle whose length of two sides which pinch | interpose an apex angle ((alpha)) is equal.

  Moreover, in this embodiment, the said triangular convex part (7) is formed in the protruding item | line part (8) where the cross-sectional shape extended along one direction parallel to the surface of the said light diffusing plate (3) is a triangle. The plurality of ridges (8) are arranged so that their length directions are substantially parallel to each other (see FIG. 2).

  In this embodiment, a linear light source is used as the light source (2), and the length direction of the linear light source (2) and the length of the ridge (8) of the light diffusion plate (3) are used. It arrange | positions so that a vertical direction may correspond substantially. Moreover, the length direction of the said protruding item | line part (8) is arrange | positioned so that it may correspond with the longitudinal direction (N) of the said light diffusing plate (3) (refer FIG. 2).

  In the surface light source device (1) according to the above configuration, at least a portion of the back surface (3a) of the light diffusing plate (3) that contacts the front surface (31a) of the edge frame portion of the lamp box (5) is formed on the mat surface (6). Since the arithmetic average roughness Ra of the mat surface (6) is 0.8 to 15 μm and the average interval Sm of the unevenness of the mat surface (6) is 100 to 300 μm, the edge of the lamp box (5) The contact between the frame front surface (31a) and the light diffusing plate (3) becomes a point contact or a state close to a point contact, and friction between both is reduced, thereby the edge frame front surface (31a) of the lamp box (5). ) And the light diffusion plate (3) can be prevented from generating unpleasant noise.

  Further, in the present embodiment, a plurality of triangular convex portions (7) having a triangular cross-sectional shape project from the front surface (3b) of the light diffusion plate (3), and the apex angle (α ) Is set to 40 to 150 degrees, and the pitch interval (P) between adjacent triangular protrusions (7) is set to 10 to 500 μm, the brightness of the emitted light can be sufficiently increased.

  In addition, in this embodiment, the entire back surface (3a) of the light diffusing plate (3) is formed on the mat surface (6) with Ra of 0.8 to 15 μm and Sm of 100 to 300 μm. Due to the synergistic effect with the triangular protrusion (7) protruding from the front surface (3b) of the light diffusing plate (3), uniform light without uneven brightness can be emitted. That is, the surface uniformity of luminance is excellent. Note that the degree of improvement in the surface uniformity of the luminance varies depending on the separation distance (L) of the light source (2) and the distance (d) between the light diffusion plate (3) and the light source (2). Depending on the value of the apex angle (α) of the part (7), it is possible to further improve the surface uniformity of luminance by setting the distance (d) between the light diffusing plate (3) and the light source (2) small. There is a case.

  Moreover, in this embodiment, since the whole surface of the back surface (3a) of the light diffusing plate (3) is formed on the mat surface (6), the manufacturing efficiency can be improved, and products of different sizes are produced. This has the advantage of being easy to handle.

  In the present invention, the mat surface (6) is formed on at least a portion of the back surface (3a) of the light diffusing plate (3) in contact with the front surface (31a) of the edge frame portion. The arithmetic average roughness Ra of 6) needs to be set in the range of 0.8 to 15 μm, and the average interval Sm of the unevenness of the mat surface (6) needs to be set in the range of 100 to 300 μm. If Ra is less than 0.8 μm or Sm exceeds 300 μm, the effect of preventing the generation of unpleasant noise cannot be sufficiently obtained. Further, a mat surface having an Ra of more than 15 μm and a mat surface having an Sm of less than 100 μm are difficult to manufacture and the productivity is deteriorated. Among them, the arithmetic average roughness Ra of the mat surface (6) is preferably set in the range of 1.0 to 10 μm, and the average interval Sm of the unevenness of the mat surface (6) is set in the range of 130 to 250 μm. It is preferable.

  Examples of the cross-sectional shape of the mat surface (6) include a substantially semicircular arc shape and a flat curve shape, but are not particularly limited thereto. That is, as long as the conditions of Ra: 0.8 to 15 μm and Sm: 100 to 300 μm are satisfied, the mat surface (6) may have any cross-sectional shape.

  The formation method of the mat surface (6) is not particularly limited. For example, the mat surface may be formed by transferring irregularities using an embossing roll on the surface, or the mat surface may be formed by particle bulging on the surface by adding fine particles to the constituent resin. In particular, it is not limited to these methods.

  Further, in the present invention, it is preferable to adopt a configuration in which a plurality of triangular convex portions (7) having a triangular cross-sectional shape are projected on the front surface (3b) of the light diffusing plate (3). In the case of adopting the configuration, the apex angle (α) of the triangular convex portion (7) is set to 40 to 150 degrees, and the pitch interval (P) between the adjacent triangular convex portions (7) is set to 10 to 500 μm. Must be set. By setting to such a range, the brightness | luminance of emitted light can fully be improved. When the apex angle (α) is less than 40 degrees, it is difficult to form the shape with high accuracy, and when the apex angle (α) exceeds 150 degrees, the light condensing characteristic is deteriorated. If the pitch interval (P) is less than 10 μm, it will be difficult to accurately shape the shape, and if the pitch interval (P) exceeds 500 μm, the shape (streaks) of the triangular protrusions (7) will be visually recognized. is there. Especially, it is preferable that the vertex angle ((alpha)) of the said triangular convex part (7) is set to 60-120 degree | times. The pitch interval (P) is preferably set to 30 to 100 μm.

  The height (h) of the triangular protrusion (7) is preferably set in the range of 1.0 to 800 μm. When the thickness is 1.0 μm or more, the brightness enhancement effect can be sufficiently exhibited, and when the thickness is 800 μm or less, the shape (streak) of the triangular convex portion (7) is not visually observed. .

  A method for forming the triangular convex portion (7) is not particularly limited. For example, a thermal transfer method using a mold, an injection molding method, a cutting method, a profile extrusion molding method, and a melt extrusion transfer molding method using an engraving roll. Etc.

  In addition, about the cross-sectional shape of the substantially V-shaped groove | channel between adjacent triangular convex parts (7), you may be R shape (arc shape) about 5 micrometers in radius, for example. Moreover, as long as the effect of this invention is not impaired, the vertex part of the said triangular convex part (7) may also be R shape (arc shape). Or the vertex part of the said triangular convex part (7) may be formed flat, if it is about 1/10 of the said pitch space | interval (P).

  Although the thickness (S) of the said light diffusing plate (3) is not specifically limited, It is preferable to set to the range of 1.0-5.0 mm.

  Moreover, it is preferable that the total light transmittance of the said light diffusing plate (3) is set to the range of 55 to 75%. By setting to such a range, sufficient luminance can be obtained, and the luminance unevenness suppressing effect by the above-described synergistic effect can be sufficiently obtained. Although such a total light transmittance is not specifically limited, For example, it can adjust by adding a light-diffusion agent. In addition, the said total light transmittance is a total light transmittance measured based on JISK7361-1 (1997).

  In the present invention, the light diffusing plate (3) is not particularly limited, but a single-layer plate made of a translucent resin and a different type of translucent resin on at least one surface of a base layer made of a translucent resin. A laminated plate or the like in which one or more other layers made of are laminated is used.

  Examples of the translucent resin include acrylic resin, styrene resin, polycarbonate, polyethylene, polypropylene, cyclic polyolefin, cyclic olefin copolymer, polyethylene terephthalate, MS resin (methyl methacrylate-styrene copolymer resin), Examples include ABS resin (acrylonitrile-butadiene-styrene copolymer resin), AS resin (acrylonitrile-styrene copolymer resin), and the like.

  The light diffusing plate (3) contains a light diffusing agent (light diffusing particles) as necessary. The light diffusing agent is not particularly limited as long as it is a particle having a refractive index different from that of the translucent resin constituting the light diffusing plate (3), and any material can be used. it can. The inorganic light diffusing agent is not particularly limited, and examples thereof include calcium carbonate, barium sulfate, titanium oxide, aluminum hydroxide, silica, glass, talc, mica, white carbon, magnesium oxide, and zinc oxide. May have been subjected to a surface treatment with a fatty acid or the like. The organic light diffusing agent is not particularly limited, and examples thereof include styrene polymer particles, acrylic polymer particles, and siloxane polymer particles. Among them, the weight average molecular weight is 500,000 to 5,000,000. High molecular weight polymer particles and crosslinked polymer particles having a gel fraction of 10% by mass or more when dissolved in acetone are preferably used. As the light diffusing agent, one of those exemplified above may be used, or a mixture of two or more of these may be used.

  The absolute value of the difference between the refractive index of the translucent resin and the refractive index of the light diffusing agent is preferably 0.02 or more from the viewpoint of light diffusibility, and the absolute value is 0.13 or less. Is preferable from the viewpoint of light transmittance. That is, the absolute value of the difference between the refractive index of the translucent resin and the refractive index of the light diffusing agent is preferably in the range of 0.02 to 0.13.

  The light diffusing plate (3) may contain various additives such as an ultraviolet absorber, a heat stabilizer, an antioxidant, a weathering agent, a light stabilizer, a fluorescent brightening agent, and a processing stabilizer. . In addition, when adding a ultraviolet absorber, it is preferable to add 0.1-3 mass parts of ultraviolet absorbers with respect to 100 mass parts of said translucent resins. By setting it in such a range, bleeding to the surface of the ultraviolet absorber can be suppressed, and the appearance can be favorably maintained. Further, when a heat stabilizer is also added, the heat stabilizer is preferably 2 parts by mass or less with respect to 1 part by mass of the UV absorber in the translucent resin, and in particular, the UV absorption in the translucent resin. It is particularly preferable to add 0.01 to 1 part by mass of a heat stabilizer with respect to 1 part by mass of the agent.

  Although it does not specifically limit as said light source (2), For example, point light sources, such as a light emitting diode, etc. other than linear light sources, such as a fluorescent tube, a halogen lamp, and a tungsten lamp, are mentioned.

  Moreover, it is preferable that the space | interval (L) of adjacent light sources (2) (2) is set to 10 mm or more from a viewpoint of power saving, and the said light diffusing plate (3) and the said light source (2). The distance (d) is preferably set to 50 mm or less from the viewpoint of thinning. D: L is preferably 1: 5 to 5: 1. Especially, it is more preferable that the space | interval (L) of the said adjacent light sources (2) (2) is set to 10-100 mm. The distance (d) between the light diffusing plate (3) and the light source (2) is particularly preferably set to 10 to 50 mm.

  In the above embodiment, the triangular convex portion (7) of the light diffusing plate (3) is formed by the convex strip portion (8) extending along one direction parallel to the surface (one-dimensional). The type (see FIG. 2) is not particularly limited to such a configuration. For example, the triangular protrusion (7) of the light diffusing plate has two different directions parallel to the surface (for example, two directions orthogonal to each other). ) May be formed by protruding ridges (8) extending along the line (that is, it may be a two-dimensional type).

  Moreover, in the said embodiment, as shown in FIG. 3, although the cross-sectional shape of a triangular convex part (7) is an isosceles triangle with the length of two sides which pinches | interposes an apex angle ((alpha)), especially such a triangle. It is not limited to the configuration, and may be a non-isosceles triangle as long as the triangle satisfies the condition of apex angle (α): 40 to 150 degrees.

  Moreover, in the said embodiment, although the triangular convex part (7) is comprised so that all may become the same shape and the same magnitude | size, it is not limited to such a structure in particular, A triangular convex part (7 ) Vertex angle (α), height (h) of triangular convex portion (7), pitch interval (P) of triangular convex portion (7), etc. It may be configured as follows. For example, a configuration as shown in FIG. 5 may be adopted.

  Moreover, in the said embodiment, although the adjacent triangular convex part (7) is comprised so that it may continue, it is not limited to such a continuous structure in particular, In the range which does not inhibit the effect of this invention. If there is, for example, as shown in FIG. 6, it may be configured such that a flat surface exists between adjacent triangular convex portions (7).

  In addition, if it is a range which does not inhibit the effect of this invention, the said uneven | corrugated shaped part (4) includes other triangular convex parts other than the triangular convex part (7) whose apex angle ((alpha)) is 40-150 degree | times. The structure which becomes may be sufficient. Similarly, if it is a range which does not inhibit the effect of this invention, the said uneven | corrugated shaped part (4) is a structure which comprises the triangular convex part whose pitch space | interval (P) of adjacent triangular convex parts is not 10-500 micrometers. It may be.

  The light diffusing plate (3), the surface light source device (1) and the liquid crystal display device (20) according to the present invention are not particularly limited to those of the above-described embodiment, and the spirit thereof is within the scope of the claims. Any design changes are allowed as long as they do not deviate from.

  Next, specific examples of the present invention will be described, but the present invention is not particularly limited to these examples.

<Raw materials>
Translucent resin A: Styrene resin (Toyo Styrene "HRM40", refractive index 1.59)
Translucent resin B: MS resin (“MS200NT” manufactured by Nippon Steel Chemical Co., Ltd., refractive index 1.57, styrene / methyl methacrylate = 80 parts by mass / 20 parts by mass)
Light diffusing agent A: PMMA crosslinked particles (“SUMIPEX XC1A” manufactured by Sumitomo Chemical Co., Ltd., refractive index 1.49, weight average particle diameter 35 μm)
Light diffusing agent B: Cross-linked siloxane polymer particles (Toray Fill DY33-719, manufactured by Toray Dow Corning, refractive index 1.42, volume average particle diameter 2 μm)
Light diffusing agent C: “KE-P50” manufactured by Nippon Shokubai (refractive index 1.43, average particle size 0.54 μm).

  Light diffusing agent master batch A: 52.0 parts by mass of translucent resin A, 40.0 parts by mass of light diffusing agent A, 4.0 parts by mass of light diffusing agent B, SUMISORB 200 (Sumitomo) as an ultraviolet absorber (Chemical Co., Ltd.) 2.0 parts by mass, and heat stabilizer Sumilyzer GP (Sumitomo Chemical Co., Ltd.) 2.0 parts by mass, and then this blended product is put into a hopper of a 65 mm twin screw extruder. A light diffusing agent master batch A in the form of a pellet obtained by melting and mixing in a cylinder, and then extruding into a strand and pelletizing. Extrusion was carried out by setting the temperature in the cylinder from the lower part of the hopper: 200 ° C. to the vicinity of the extrusion die: 250 ° C. so that the temperature gradually increased toward the downstream.

  Light diffusing agent master batch B: 75.8 parts by mass of translucent resin B, 23.0 parts by mass of light diffusing agent A, and 1.0 of LA-31 (manufactured by Asahi Denka Kogyo Co., Ltd.) which is an ultraviolet absorber. After dry blending 0.2 parts by mass of Sumrizer GP (manufactured by Sumitomo Chemical Co., Ltd.) which is a mass part and a heat stabilizer, this blended product is put into a hopper of a 65 mm twin screw extruder and melt-mixed in a cylinder. A pellet-shaped light diffusing agent master batch B obtained by extruding into a strand and pelletizing. Extrusion was carried out by setting the temperature in the cylinder from the lower part of the hopper: 200 ° C. to the vicinity of the extrusion die: 250 ° C. so that the temperature gradually increased toward the downstream.

<Example 1>
After dry blending 97.0 parts by mass of translucent resin A and 3.0 parts by mass of light diffusing agent masterbatch A, the mixture is melt-kneaded with a first extruder having a temperature in the cylinder of 190 to 250 ° C. and supplied to the feed block. To do. On the other hand, the light diffusing agent master batch B is melt-kneaded by a second extruder having a temperature in the cylinder of 190 to 250 ° C. and supplied to the feed block.

  The resin supplied from the first extruder to the feed block becomes an intermediate layer (base layer), and the resin supplied from the second extruder to the feed block becomes a surface layer (both sides). By co-extrusion molding from a manifold die and clamping and cooling with a polishing roll, a three-layer laminate having a width of 23.0 cm and a thickness of 2.0 mm (intermediate layer 1.9 mm, surface layer 0.05 mm × 2 A light diffusion plate (3) made of

  In addition, since the gap between the intermediate roll and the lower roll of the three polishing rolls is set to be larger than the thickness of the laminated plate of 2.0 mm during the molding, the light diffusing agent particles added to the resin are raised. Allowed (without being smoothed), the entire surface of one surface (back surface) (3a) of the light diffusion plate (3) is formed on the mat surface (6). The arithmetic average roughness Ra of the mat surface (6) was 1.24 μm, and the average interval Sm of the unevenness of the mat surface (6) was 169.0 μm. The other surface (front surface) (3b) of the light diffusion plate (3) is formed as a smooth surface.

<Example 2>
After dry blending 97.0 parts by weight of translucent resin A and 4.5 parts by weight of light diffusing agent masterbatch A, the mixture is melt-kneaded with a first extruder having a temperature in the cylinder of 190 to 250 ° C. and supplied to the feed block. To do. On the other hand, the light diffusing agent master batch B is melt-kneaded by a second extruder having a temperature in the cylinder of 190 to 250 ° C. and supplied to the feed block.

  The resin supplied from the first extruder to the feed block becomes an intermediate layer (base layer), and the resin supplied from the second extruder to the feed block becomes a surface layer (both sides). By co-extrusion molding from a manifold die and clamping and cooling with a polishing roll, a three-layer laminate (intermediate layer 1.4 mm, surface layer 0.05 mm × 2) having a width of 23.0 cm and a thickness of 1.5 mm A light diffusion plate (3) made of

  In addition, since the gap between the intermediate roll and the lower roll of the three polishing rolls is set to be larger than the thickness of the laminated plate at 1.5 mm during the molding, the light diffusing agent particles added to the resin are raised. Allowed (not smoothed), the entire surface of one surface (back surface) (3a) of the light diffusion plate (3) is formed on the mat surface (6) (see FIG. 3). The arithmetic average roughness Ra of the mat surface (6) was 4.19 μm, and the average interval Sm of the unevenness of the mat surface (6) was 195.0 μm.

  Moreover, since the sheet | seat with which the convex part was engraved on the surface was wound and fixed to the surrounding surface of the intermediate | middle roll of three polishing rolls, the other surface (front surface) (3b) of a light diffusing plate (3) A plurality of ridges (8) composed of triangular ridges (7) are formed in a protruding manner on the entire surface (see FIGS. 2 and 3). The apex angle (α) of the triangular convex portion (7) was 90.0 degrees, and the pitch interval (P) between adjacent triangular convex portions was 50.0 μm.

<Example 3>
On the entire front surface (smooth surface) of the light diffusing plate obtained in Example 1, a convex portion comprising triangular convex portions (7) using a heat press machine (Shindo ASF hydraulic press, manufactured by Shinto Metal Industry). A number of strips (8) were formed in a protruding manner (see FIG. 3) to produce a light diffusion plate (3) having a thickness of 2.0 mm. The heat press by the hot press machine is arranged with the front surface (smooth surface) of the light diffusing plate obtained in Example 1 facing up, and the prism film is placed on the front surface (smooth surface) with the prism portion facing down. The pressure was applied for about 3 minutes with the upper surface temperature of the hot press set at 160 ° C. and the lower surface temperature set at 70 ° C. Although the triangular convex part (7) was formed in the front surface (3b) by the said heat press, the mat surface (6) of the back surface (3a) was maintained as it was. The apex angle (α) of the triangular convex portion (7) was 90.0 degrees, and the pitch interval (P) between adjacent triangular convex portions was 50.0 μm.

<Example 4>
After 99.7 parts by mass of the light-transmitting resin A and 0.3 parts by mass of the light diffusing agent C are dry blended, the mixture is melt-kneaded by an extruder having a temperature in the cylinder of 190 to 250 ° C. and supplied to the feed block. The resin supplied to the feed block from the extruder is subjected to single layer extrusion molding from a multi-manifold die at an extrusion resin temperature of 250 ° C., and sandwiched and cooled by a polishing roll, whereby a width of 23.0 cm and a thickness of 2. A 0 mm resin plate (both sides were smooth surfaces) was produced.

  Next, a mat surface was formed on one surface of the resin plate using a heat press machine (Shindo ASF hydraulic press manufactured by Shindo Metal Industry Co., Ltd.). That is, in the hot press by the hot press machine, a copper plate (with a mat surface of Ra = 6.0 μm and Sm = 111.0 μm formed on the surface of the copper plate by the sand blast method) is provided below the resin plate. The mat surface was placed face up, and pressurization was performed for about 3 minutes with the upper surface temperature of the hot press set at 70 ° C. and the lower surface temperature set at 170 ° C. By this hot pressing, a light diffusion plate (3) in which the entire surface of one surface (back surface) (3a) was formed on the mat surface (6) was produced. The arithmetic average roughness Ra of the mat surface (6) was 5.75 μm, and the average interval Sm of the unevenness of the mat surface (6) was 163.0 μm. The other surface (front surface) (3b) of the light diffusing plate (3) is a smooth surface.

<Example 5>
After 99.7 parts by mass of the light-transmitting resin A and 0.3 parts by mass of the light diffusing agent C are dry blended, the mixture is melt-kneaded by an extruder having a temperature in the cylinder of 190 to 250 ° C. and supplied to the feed block. The resin supplied to the feed block from the extruder is subjected to single layer extrusion molding from a multi-manifold die at an extrusion resin temperature of 250 ° C., and sandwiched and cooled by a polishing roll, whereby a width of 23.0 cm and a thickness of 2. A 0 mm resin plate (both sides were smooth surfaces) was produced.

  Next, a mat surface is formed on one surface (rear surface) of the resin plate using a heat press machine (Shindo ASF hydraulic press manufactured by Shindo Metal Industry Co., Ltd.) and a triangular convex portion is formed on the other surface (front surface). A large number of ridges (8) made of (7) were formed to project. That is, in the hot press by the hot press machine, the prism film is placed on the resin plate with the prism portion facing down, while the copper plate is placed on the lower side of the resin plate (Ra = 3.15 μm, Sm = 170.0 μm mat surface formed) was placed with the mat surface facing up, and the upper surface temperature of the hot press was set to 160 ° C. and the lower surface temperature was set to 170 ° C. Pressure was applied for about 3 minutes in the state. By this hot pressing, the entire surface of one surface (back surface) (3a) is formed on the mat surface (6) and the entire surface of the other surface (front surface) (3b) is formed with a triangular protrusion (7). A light diffusing plate (3) in which a large number of (8) was formed in a protruding manner was produced (see FIG. 3). The arithmetic average roughness Ra of the mat surface (6) was 5.74 μm, and the average interval Sm of the unevenness of the mat surface (6) was 174.0 μm. Further, the apex angle (α) of the triangular convex portion (7) was 90.0 degrees, and the pitch interval (P) between adjacent triangular convex portions was 50.0 μm.

<Comparative Example 1>
After dry blending 97.0 parts by mass of translucent resin A and 3.0 parts by mass of light diffusing agent masterbatch A, the mixture is melt-kneaded with a first extruder having a temperature in the cylinder of 190 to 250 ° C. and supplied to the feed block. To do. On the other hand, the translucent resin A is melt-kneaded by a second extruder having a temperature in the cylinder of 190 to 250 ° C. and supplied to the feed block.

  The resin supplied from the first extruder to the feed block becomes an intermediate layer (base layer), and the resin supplied from the second extruder to the feed block becomes a surface layer (both sides). By co-extrusion molding from a manifold die and clamping and cooling with a polishing roll, a three-layer laminate having a width of 23.0 cm and a thickness of 2.0 mm (intermediate layer 1.9 mm, surface layer 0.05 mm × 2 A light diffusion plate made of

  The gap between the intermediate roll and the lower roll of the three polishing rolls is set to be larger than the thickness of the laminated plate at 2.0 mm during the molding, but the resin constituting the surface layer of the laminated plate is a light diffusing agent. Since it does not contain, the light diffusing agent particles do not rise, and both surfaces of the light diffusing plate are substantially smooth. That is, the surface (both sides) of the light diffusing plate had an arithmetic average roughness Ra of 0.21 μm, and an average unevenness interval Sm of 0.56 μm.

<Comparative example 2>
After 99.7 parts by mass of the light-transmitting resin A and 0.3 parts by mass of the light diffusing agent C are dry blended, the mixture is melt-kneaded by an extruder having a temperature in the cylinder of 190 to 250 ° C. and supplied to the feed block. The resin supplied to the feed block from the extruder is subjected to single layer extrusion molding from a multi-manifold die at an extrusion resin temperature of 250 ° C., and sandwiched and cooled by a polishing roll, whereby a width of 23.0 cm and a thickness of 2. A 0 mm light diffusion plate (both sides were smooth surfaces) was produced.

  In addition, since the gap between the intermediate roll and the lower roll among the three polishing rolls is set to 2.0 mm at the time of molding, the light diffusing agent particles do not rise, and both surfaces of the light diffusing plate are substantially smooth surfaces. It has become. That is, the surface (both sides) of the light diffusing plate had an arithmetic average roughness Ra of 0.07 μm, and the average interval Sm of the unevenness was not measurable (Sm was smaller than the measurement lower limit 0.04 μm).

<Comparative Example 3>
On the entire surface of one side (substantially smooth surface) of the light diffusing plate obtained in Comparative Example 2, a ridge formed of triangular ridges using a heat press machine (Shindo ASF hydraulic press manufactured by Shindo Metal Industry Co., Ltd.) A large number of protrusions were formed to produce a light diffusing plate having a thickness of 2.0 mm. The hot press by the hot press machine is arranged with one side of the light diffusing plate obtained in Comparative Example 2 facing up, and a prism film is placed thereon with the prism portion down, and the upper surface side of the hot press machine Pressurization was carried out for about 3 minutes with the temperature set at 160 ° C. and the lower surface temperature set at 70 ° C. Triangular protrusions were formed on one side by the hot pressing, but the substantially smooth surface of the other side was maintained as it was. The apex angle (α) of the triangular convex portion (7) was 90.0 degrees, and the pitch interval (P) between adjacent triangular convex portions was 50.0 μm.

  Each light diffusion plate produced as described above was evaluated according to the following evaluation method. These results are shown in Table 1.

<Total light transmittance measurement method>
Based on JIS K7361-1 (1997), the total light transmittance (%) of the light diffusing plate was measured using a transmittance meter (“HR-100” manufactured by Murakami Color Research Laboratory).

<Luminance uniformity evaluation method>
After removing the liquid crystal panel, various optical films, and the light diffusing plate from the commercially available 20-inch type liquid crystal television, the frame of the polycarbonate lamp box (with a plurality of fluorescent tubes spaced apart from each other) The light diffusing plate (Example product / Comparative product) produced as described above was placed and fixed in a state where it was in contact with the front surface of the unit, thereby closing the open surface of the lamp box. Thereafter, the luminance was measured using a luminance meter (“Eye Scale-3WS” manufactured by I-System Co., Ltd.) with the light diffusing plate set. When the minimum luminance value is “C1” and the maximum luminance value is “C2”,
Brightness uniformity (%) = (C1 / C2) × 100
The value obtained by the above formula was defined as the luminance uniformity (%).

  The luminance measurement was performed as follows. That is, the liquid crystal television is placed on the floor in a dark room of constant temperature and humidity (temperature: 25.0 ° C., humidity: 50.0%) with the front side facing up (the back is in contact with the floor), The camera was placed facing downwards above the LCD TV so that the entire front surface of the LCD TV was reflected. At this time, the distance from the front surface of the liquid crystal television to the camera is set to 65.0 cm, and the measurement conditions of the luminance meter are set to SPEED: 1/500, GAIN: 1, aperture: 16, and the central portion of the front surface of the liquid crystal television is set. The luminance at each measurement spot was measured by designating a range of 60 mm × 60 mm centering on the measurement spot, and the luminance uniformity (%) was obtained from the minimum luminance value and the maximum luminance value among these measurement values.

  The commercially available 20-inch liquid crystal television has an interval (L) between adjacent light sources of 28.0 mm, a diameter of the light source of 3.0 mm, a distance (d) between the light diffusion plate and the light source of 11.0 mm, The distance (f) between the reflector and the reflector (the bottom of the lamp box) was 2.0 mm (see FIG. 1). In addition, a reflective triangular convex portion having a triangular cross-sectional shape protrudes from the reflecting plate (the bottom surface of the lamp box) at the center position between adjacent light sources, and the convex stripes of the reflective triangular convex portion extend in the length direction of the light source ( The vertical angle (β) of the reflective triangular convex portion is 90 degrees, and the base length (M) of the reflective triangular convex portion is 8.0 mm. (See FIG. 1).

<Measurement method of diffusivity D of light diffusion plate>
What is the intensity distribution of transmitted light when light is incident on the light diffuser plate (example product / comparative example product) at a specified angle using an automatic variable angle photometer ("GP230" manufactured by Murakami Color Research Laboratory)? The diffusivity D (%) was determined by measuring whether or not it changes. The measurement was performed with the back surface of the light diffusing plate facing the light source (emitted light) and the front surface of the light diffusing plate facing the integrating sphere. In the case where the light diffusing plate has a triangular projection on the front surface, the pitch (interval) direction of the triangular projection was arranged on the left and right sides, and measurement was performed. The measurement conditions were a light beam stop: 1.7 mmφ, the intensity of emitted light and the sensitivity of light reception were constant, and the incident angle of light was 0 degree.

<Method for evaluating the prevention of unpleasant noise (sound)>
After removing the liquid crystal panel and light diffusion plate of the same commercially available 20-inch liquid crystal television used in the luminance uniformity evaluation method, a polycarbonate lamp box (with a plurality of fluorescent tubes spaced apart from each other). The light diffusing plate (Example product / Comparative product) produced as described above was placed and fixed in a state where it was in contact with the front surface of the edge frame portion), and the open surface of the lamp box was closed. After that, the liquid crystal panel is reset in this lamp box to reconfigure the liquid crystal television, and the liquid crystal television is shaken in the front-rear direction about 180 times in one minute while holding the normal vertical support state with both hands, The presence or absence of unpleasant noise was examined. The case where no unpleasant noise was generated was indicated as “◯”, the case where slight unpleasant sound was generated was indicated as “Δ”, and the case where no unpleasant noise was generated was indicated as “X”.

<Arithmetic mean roughness Ra measurement method>
The arithmetic average roughness Ra was measured in accordance with JIS B0601-1994. That is, the arithmetic average roughness Ra of the mat surface of the light diffusion plate was measured using a surface roughness meter (“SJ-201P” manufactured by Mitutoyo). The measurement conditions of the surface roughness meter were set to cut-off value: 2.5 × 5 and measurement range: auto.

<Measuring method of average interval Sm of unevenness>
Based on JIS B0601-1994, the average interval Sm of unevenness was measured. That is, the average interval Sm of the unevenness of the mat surface of the light diffusion plate was measured using a surface roughness meter (“SJ-201P” manufactured by Mitutoyo). The measurement conditions of the surface roughness meter were set to cut-off value: 2.5 × 5 and measurement range: auto.

  As is apparent from the table, the surface light source device and the liquid crystal display device configured using the light diffusion plates of Examples 1 to 5 of the present invention were able to sufficiently suppress the generation of unpleasant noise.

  On the other hand, in Comparative Examples 1 to 3 that depart from the scope of the present invention, the generation of unpleasant noise could not be prevented.

  Next, the spectral transmittance of the light diffusing plates of Example 4, Example 5, Comparative Example 2, and Comparative Example 3 was measured based on the following spectral transmittance measurement method. The result is shown in FIG.

<Spectral transmittance measurement method>
Spectral transmittance was measured using a self-recording spectrophotometer ("U-4000 type" manufactured by Hitachi Instrument Service Co., Ltd.). Spectral transmittance was measured in the visible light region with the back of the light diffuser facing the light source (emitted light) and the front of the light diffuser facing the integrating sphere. When the light diffusing plate has a triangular convex portion on the front surface, the pitch (interval) direction of the triangular convex portion was arranged on the left and right sides, and the measurement was performed.

  From the comparison between Example 4 and Comparative Example 2 in FIG. 7, in the light diffusing plate having no triangular convex portion, the transmittance in the visible light region is the presence or absence of formation of the mat surface (Example 4: present, It is recognized that they are almost the same regardless of (Comparative Example 2: None).

  On the other hand, from the comparison between Example 5 and Comparative Example 3 in FIG. 7, the light diffusion plate having a triangular convex portion has a mat surface so that the transmittance in the visible light region is increased. A marked improvement is observed (Example 5). That is, in Comparative Example 3, since the mat surface was not formed, the transmittance in the visible light region was low.

  The light diffusing plate of the present invention is suitably used as a light diffusing plate for a surface light source device, but is not particularly limited to such applications. The surface light source device of the present invention is preferably used as a backlight for a liquid crystal display device, but is not particularly limited to such applications.

1 is a schematic view showing an embodiment of a liquid crystal display device according to the present invention. It is a typical perspective view which shows one Embodiment of the light diffusing plate which concerns on this invention. FIG. 3 is a schematic cross-sectional view of the light diffusing plate of FIG. 2. It is typical sectional drawing which shows other embodiment of the light diffusing plate of this invention. It is typical sectional drawing which shows other embodiment of the light diffusing plate of this invention. It is typical sectional drawing which shows other embodiment of the light diffusing plate of this invention. It is a graph which shows a spectral transmittance measurement result. In the graph, Example 4 is indicated by a solid line, Example 5 is indicated by a dotted line, Comparative Example 2 is indicated by a one-dot chain line, and Comparative Example 3 is indicated by a two-dot chain line.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface light source device 2 ... Light source 3 ... Light diffusing plate 3a ... Back surface (one surface)
3b ... Front side (the other side)
DESCRIPTION OF SYMBOLS 5 ... Lamp box 6 ... Matte surface 7 ... Triangular convex part 10 ... Liquid crystal panel 20 ... Liquid crystal display device 31 ... Edge frame part (side plate)
31a ... front (front side end face of side plate)
α ... Vertical angle of triangular convex part P ... Pitch interval between adjacent triangular convex parts

Claims (10)

A plurality of light sources are disposed apart from each other in a resin lamp box whose front side is open, and the light box made of resin is in contact with the front surface of the edge frame portion of the lamp box. A surface light source device arranged so as to block the open surface of
A portion of the back surface of the light diffusing plate that contacts at least the front surface of the edge frame portion is formed on the mat surface, the arithmetic average roughness Ra of the mat surface is 0.8 to 15 μm, and the average interval of the unevenness of the mat surface Sm is 100-300 micrometers, The surface light source device characterized by the above-mentioned.   A plurality of triangular convex portions having a triangular cross-sectional shape are projected on the front surface of the light diffusion plate, the apex angle of the triangular convex portions is set to 40 to 150 degrees, and the pitch interval between adjacent triangular convex portions is 10. The surface light source device according to claim 1, which is set to ˜500 μm. A plurality of light sources are disposed apart from each other in a resin lamp box whose front side is open, and the light box made of resin is in contact with the front surface of the edge frame portion of the lamp box. A surface light source device arranged so as to block the open surface of
The entire back surface of the light diffusing plate is formed on the mat surface, the arithmetic average roughness Ra of the mat surface is 0.8 to 15 μm, and the average interval Sm of the unevenness of the mat surface is 100 to 300 μm. A characteristic surface light source device.   A plurality of triangular convex portions having a triangular cross-sectional shape are projected on the front surface of the light diffusion plate, the apex angle of the triangular convex portions is set to 40 to 150 degrees, and the pitch interval between adjacent triangular convex portions is 10. The surface light source device according to claim 3, which is set to ˜500 μm.   The surface light source device according to claim 2 or 4, wherein the light diffusing plate has a total light transmittance of 55 to 75%.   A liquid crystal display device comprising: the surface light source device according to claim 1; and a liquid crystal panel disposed on a front side of the surface light source device.   The matte surface has an arithmetic mean roughness Ra of 0.8 to 15 [mu] m, and an average interval of the irregularities on the mat surface. Sm is 100-300 micrometers, The light diffusing plate characterized by the above-mentioned.   A plurality of triangular protrusions having a triangular cross-sectional shape are projected on the other surface of the light transmission plate, the apex angle of the triangular protrusions is set to 40 to 150 degrees, and the pitch interval between adjacent triangular protrusions The light diffusing plate according to claim 7, wherein is set to 10 to 500 μm.   The one surface is made of a resin light-transmitting plate formed on the mat surface, the arithmetic average roughness Ra of the mat surface is 0.8 to 15 μm, and the average interval Sm of the unevenness of the mat surface is A light diffusing plate having a thickness of 100 to 300 μm.   A plurality of triangular protrusions having a triangular cross-sectional shape are projected on the other surface of the light transmission plate, the apex angle of the triangular protrusions is set to 40 to 150 degrees, and the pitch interval between adjacent triangular protrusions The light diffusing plate according to claim 9, wherein is set to 10 to 500 μm.

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