JP2008117639A - Light diffusion plate, backlight, and transmission type image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion plate which is easy to produce and superior in productivity, and in which sufficient front luminance is obtained with less luminance unevenness. <P>SOLUTION: The light diffusion plate 3 is composed of a light transmission plate in which irregular shape parts 4 in which a plurality of protrusions 7 with a cross-sectional shape of triangle are installed are provided on both sides, and the vertex angle α of the triangular protrusion 7 on one side of the light transmission plate is established at 39-45° and the vertex angle β of the triangular protrusion 7 on the other side of the light transmission plate is established at 87-103°. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a light diffusing plate and backlight having sufficient front luminance, and a transmissive image display device capable of displaying an image having high front luminance.

  As the transmissive image display device, for example, a backlight composed of a surface light source device is disposed on the lower surface side (back surface side) of the transmissive image display portion in which a pair of polarizing plates are disposed on the upper and lower surfaces of the transmissive liquid crystal cell. Those of construction are known. As 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 (see Patent Document 1). As such a backlight, a backlight capable of uniformly illuminating the transmissive image display unit is required.

  By the way, the distance between adjacent light sources in the backlight is preferably set as long as possible from the viewpoint that the number of light sources can be reduced and power can be saved, and the distance between the light source and the light diffusing plate is transmissive. The type image display device is preferably set to be as short as possible in that it can be made thinner.

  However, the conventional backlight has a problem that it is difficult to ensure sufficient front luminance when the interval between the light sources is set long. Further, if the distance between the light source and the light diffusing plate is set short, it is difficult to sufficiently diffuse the light from the plurality of light sources with the light diffusing plate, and there is a problem that luminance unevenness easily occurs.

As a solution to such a problem, a lenticular lens portion is formed on one surface (surface on the transmission type display portion side) of the base material sheet, and on the other surface (surface on the light source side) of the base material sheet. An optical sheet (light diffusing plate) in which a pentagonal optical axis correcting unit having a first total reflection surface composed of two gentle slopes and a second total reflection surface composed of two steep slopes is proposed. (See Patent Document 2).
JP-A-7-141908 JP 2005-43611 A

  However, the light diffusing plate described in Patent Document 2 has a problem that the cross-sectional shape is very complicated, so that it is not easy to manufacture and inferior in productivity, and also has an effect of improving luminance and preventing luminance unevenness. It was not enough.

  The present invention has been made in view of such technical background, and is a light diffusing plate and a backlight that are easy to produce, excellent in productivity, have sufficient front luminance and have little luminance unevenness, and sufficient An object of the present invention is to provide a transmissive image display device that can display a high-quality display with high front luminance and little luminance unevenness.

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

  [1] A light-transmitting plate having convex and concave portions formed by projecting a plurality of convex portions having a triangular cross-sectional shape on both sides, and the apex angle of the triangular convex portion on one surface of the light-transmitting plate is A light diffusing plate characterized in that it is set to 39 to 45 degrees, and the apex angle of the triangular convex portion on the other surface of the light transmitting plate is set to 87 to 103 degrees.

  [2] The light diffusing plate according to item 1 above, wherein the height of the triangular convex portions is 0.01 to 1 mm, and the pitch interval between adjacent triangular convex portions is 0.03 to 2 mm.

  [3] The triangular convex portions are formed of convex strips having a triangular cross-sectional shape extending along one direction parallel to the surface of the light transmission plate, and the length directions of the convex strips are mutually connected. 3. The light diffusing plate according to item 1 or 2, which is disposed so as to be substantially parallel.

  [4] A plurality of light sources are disposed in the lamp box so as to be spaced apart from each other, and the light diffusion plate according to any one of items 1 to 3 is disposed on the front side of the plurality of light sources. A backlight characterized in that a surface on which a triangular convex portion having an apex angle of 39 to 45 degrees on a plate is formed is positioned on the back side.

  [5] A plurality of linear light sources are arranged in the lamp box so as to be separated from each other, and the light diffusing plate described in the preceding item 3 is arranged on the front side of the plurality of linear light sources. The surface on which the triangular protrusions with angles of 39 to 45 degrees are formed is positioned on the back side, and the length direction of the linear light source and the length direction of the protrusions of the light diffusion plate are approximately A backlight characterized by being arranged to match.

[6] A plurality of linear light sources are disposed in the lamp box so as to be spaced apart from each other, and the light diffusion plate described in the preceding item 3 is disposed on the front side of the plurality of light sources,
The spacing between the adjacent linear light sources is set to 10 mm or more, the distance between the light diffusion plate and the light source is set to 50 mm or less,
The light diffusion plate is configured such that a surface on which a triangular convex portion with an apex angle of 39 to 45 degrees is formed is located on the back side, and the length direction of the linear light source and the convex portion of the light diffusion plate are A backlight characterized by being arranged so that its length direction substantially coincides.

  [7] A transmissive image display device, wherein the backlight according to any one of items 4 to 6 is disposed on the back side of the image display unit.

  The light diffusing plate according to the invention of [1] comprises a light transmissive plate provided on both sides with a concavo-convex shape portion formed by projecting a plurality of convex portions having a triangular cross-sectional shape, and one of the light transmissive plates Since the apex angle of the triangular convex portion of the surface is set to 39 to 45 degrees and the apex angle of the triangular convex portion of the other surface of the light transmission plate is set to 87 to 103 degrees, sufficient front luminance is obtained. And there is little brightness unevenness. Moreover, since the cross-sectional shape of the concavo-convex shape portion is a triangle, the production is easy and the productivity is excellent.

  In the invention of [2], since the height of the triangular convex portions is 0.01 to 1 mm and the pitch interval between adjacent triangular convex portions is 0.03 to 2 mm, the luminance is improved while further improving the front luminance. Generation of unevenness can be more sufficiently prevented.

  In the invention of [3], it is possible to manufacture by, for example, extrusion molding, and there is an advantage that the productivity can be remarkably improved and thus the manufacturing cost can be reduced.

  In the invention of [4], a plurality of light sources are arranged apart from each other in the lamp box, and the light diffusion plate according to any one of [1] to [3] is arranged on the front side of the plurality of light sources. In addition, since the surface on which the triangular convex portion having an apex angle of 39 to 45 degrees is formed on the back side of the light diffusing plate, a sufficient front luminance can be obtained and the luminance unevenness can be reduced. A light is provided.

  In the invention of [5], a plurality of linear light sources are disposed in the lamp box so as to be spaced apart from each other, and the light diffusion plate described in [3] is disposed on the front side of the plurality of linear light sources, Since the light diffusing plate is configured such that the surface on which the triangular protrusions with an apex angle of 39 to 45 degrees are formed is located on the back side, a backlight with sufficient front luminance and less luminance unevenness is provided. Is done. Furthermore, since it is arranged so that the length direction of the linear light source and the length direction of the ridges of the light diffusing plate substantially coincide with each other, a larger front luminance can be obtained.

  In the invention of [6], since the interval between adjacent linear light sources is set to a long interval of 10 mm or more, power can be saved and the distance between the light diffusion plate and the light source can be as short as 50 mm or less. Since it is a set configuration, it can be made thinner. In addition, a plurality of linear light sources are arranged in the lamp box so as to be separated from each other, and the light diffusion plate described in [3] is arranged on the front side of the plurality of light sources, and the apex angle in the light diffusion plate is Since the surface on which the 39-45 degree triangular convex portion is formed is positioned on the back side, sufficient front luminance can be obtained even in such a power-saving and thinned configuration. And a backlight with less luminance unevenness. Furthermore, since it is arranged so that the length direction of the linear light source and the length direction of the ridges of the light diffusing plate substantially coincide with each other, a larger front luminance can be obtained.

  In the invention of [7], a transmissive image display device capable of providing a high quality display with sufficient front luminance and less luminance unevenness is provided.

  FIG. 1 shows a liquid crystal display device according to an embodiment of the transmissive image display device (10) of the present invention. In FIG. 1, (10) is a liquid crystal display device, (11) is a liquid crystal cell, (12) and (13) are polarizing plates, and (1) is a backlight (surface light source device). Polarizing plates (12) and (13) are respectively arranged on the upper and lower sides of the liquid crystal cell (11), and a transmissive image display unit is constituted by these constituent members (11), (12) and (13).

  The said backlight (1) is arrange | positioned at the lower surface side (back side) of the said lower polarizing plate (13). The backlight (1) has a rectangular shape in plan view and a thin box-shaped lamp box (5) whose upper surface (front side) is open, and the lamp box (5) are spaced apart from each other. A plurality of linear light sources (2), and a light diffusion plate (3) disposed above (front side) the plurality of linear light sources (2). The said light diffusing plate (3) is mounted and fixed with respect to the said lamp box (5) so that the open surface may be block | closed. A light reflecting layer is provided on the inner surface of the lamp box (5).

  As shown in FIGS. 2 and 3, the light diffusing plate (3) is a light having a concavo-convex shape portion (4) formed by projecting a plurality of convex portions (7) having a triangular cross-sectional shape on both sides. It consists of a transmission plate. The apex angle (α) of the triangular convex portion (7) on one surface of the light diffusing plate (3) is set to 39 to 45 degrees, and the triangular convex portion (7 on the other surface of the light diffusing plate (3)). ) Is set to 87 to 103 degrees. In the present embodiment, the surface (3a) on which the triangular convex portion (7) having an apex angle of 39 to 45 degrees in the light diffusing plate (3) is located on the back side (so as to be on the light source side). ) (See FIG. 1). That is, the surface (3b) on which the triangular convex portion (7) having an apex angle of 87 to 103 degrees in the light diffusing plate (3) is located on the front side (so as to be on the image display portion side). Is arranged (see FIG. 1). Moreover, in this embodiment, the cross-sectional shape of the said triangular convex part (7) is an isosceles triangle with equal length of two sides which pinch | interpose an apex angle (refer FIG. 3).

  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.

In the backlight (1) according to the above configuration, the light diffusing plate (3) is provided with concave and convex portions (4) formed by projecting a plurality of convex portions (7) having a triangular cross-sectional shape on both sides. The apex angle (α) of the triangular convex portion of one surface (light source side surface) (3a) of the light diffusing plate (3) is set to 39 to 45 degrees, and the other of the light diffusing plate (3) Since the apex angle (β) of the triangular convex portion of the surface (surface on the image display unit side) (3b) is set to 87 to 103 degrees, as shown in FIG. 1, from the plurality of light sources (2) Incident incident light (Q ₁ ) can be emitted toward the front side direction (substantially upward in the drawing) (F) substantially perpendicular to the surface of the light diffusing plate (3). The front luminance can be obtained and the luminance unevenness can be reduced. That is, according to the backlight (1), light having a large front luminance and little luminance unevenness can be emitted toward the liquid crystal cell (11). Moreover, since the cross-sectional shape of the uneven | corrugated shaped part (4) of a light diffusing plate (3) is a triangle, production is comparatively easy and it is excellent in productivity.

  Further, in the backlight (1), the distance (L) between the adjacent light sources (2) is set to 10 mm or more, and the distance (d) between the light diffusion plate (3) and the light source (2) is 50 mm. Even when the configuration set below, that is, a configuration in which power saving and thinning is adopted, sufficient front luminance can be obtained and luminance unevenness can be reduced. Therefore, by using the backlight (1), it is possible to provide a transmissive image display device (10) that can achieve a high-quality display with low luminance unevenness and sufficient front luminance with low thickness and power saving. It becomes.

  In the present invention, the distance (L) between the adjacent light sources (2) and (2) is preferably set to 10 mm or more from the viewpoint of power saving, and the light diffusion plate (3) and the light source ( The distance (d) to 2) is preferably set to 50 mm or less from the viewpoint of thinning. D: L is preferably 1: 5 to 5: 1. Among these, the distance (L) between the adjacent light sources (2) and (2) is more preferably set to 10 to 100 mm, and particularly preferably 10 to 60 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 present invention, the apex angle (α) of the triangular convex portion (7) of one surface (surface on the light source side) (3a) of the light diffusing plate (3) is set in a range of 39 to 45 degrees. Need to be. When the apex angle (α) is less than 39 degrees, the front luminance decreases, and when the apex angle (α) exceeds 45 degrees, the front luminance decreases. Among them, the apex angle (α) of the triangular convex portion (7) of the light source side surface (3a) of the light diffusing plate (3) is preferably set to 40 to 44 degrees, and a particularly preferable range is 41. ~ 43 degrees.

  Further, the apex angle (β) of the triangular convex portion (7) of the other surface (surface on the image display portion side) (3b) of the light diffusing plate (3) needs to be set in the range of 87 to 103 degrees. There is. When the apex angle (β) is less than 87 degrees, the front luminance decreases. When the apex angle (β) exceeds 103 degrees, the front luminance decreases. Among them, the apex angle (β) of the triangular convex portion (7) of the surface (3b) on the image display portion side of the light diffusing plate (3) is preferably set to 88 to 92 degrees, and particularly suitable range. Is 89-91 degrees.

  Further, the triangular convex portion (7) may have a structure (triangular shape in a strict sense) in which corner portions constituting apex angles (α) and (β) are angular as shown in FIGS. Alternatively, as shown in FIG. 9, the corners constituting the apex angle (α) may have a rounded structure (configuration in which the corners are curved). Of course, the corner portion constituting the apex angle (β) may have a rounded structure (configuration in which the corner portion has a curved surface shape). In the claims and the specification of the present application, the term “triangular protrusion” includes such a configuration in which the apex angle (α) and / or the apex angle (β) is rounded. It is used in meaning.

When adopting a configuration in which the corners constituting the apex angle (α) and / or apex angle (β) are rounded, the transfer rate calculated by the following calculation formula is preferably 70% or more. ,
Transfer rate (%) = f ÷ h × 100
f: height of straight line portion of constituent side h: imaginary line height h of triangular convex portion
A configuration with a transfer rate of 80% or more is particularly preferable (see FIG. 9).

  Moreover, in this invention, it is preferable that the height (h) of the triangular convex part (7) which comprises the said uneven | corrugated shaped part (4) is set to the range of 0.01-1 mm. By being 0.01 mm or more, it is possible to emit light toward the front side direction (F) substantially perpendicular to the surface of the light diffusion plate (3), and when it is 1 mm or less, The uneven shape portion (4) is not visually observed, and the uniformity can be improved. Especially, it is more preferable that the height (h) of the triangular convex part (7) which comprises the said uneven | corrugated shaped part (4) is set to the range of 0.01-0.1 mm.

  Moreover, it is preferable that the pitch interval (P) of adjacent triangular convex parts (7) is set in the range of 0.03 to 2 mm. When it is 0.03 mm or more, the triangular protrusion (7) can be easily processed with respect to the surface of the light diffusion plate (3), and when it is 2 mm or less, luminance unevenness can be sufficiently suppressed. Especially, it is more preferable that the pitch interval (P) between the adjacent triangular convex portions (7) is set in the range of 0.03 to 0.1 mm.

  The thickness (S) of the light diffusing plate (3) is not particularly limited, but is preferably set in the range of 1 to 10 mm. By setting the thickness within such a range, it is possible to further reduce the thickness while sufficiently securing the front luminance. Especially, it is more preferable that the thickness (S) of the light diffusing plate (3) is set to 2 to 5 mm.

  In the above-described embodiment, the triangular convex portion (7) of the light diffusing plate is formed by a convex strip portion (8) extending along one direction parallel to the surface (one-dimensional type). (Refer to FIG. 2) is not particularly limited to such a configuration. For example, the triangular convex portion (7) of the light diffusion plate has two different directions parallel to the surface (for example, two directions orthogonal to each other). It may be formed by a protruding line portion (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 the said triangular convex part (7) is an isosceles triangle with the same length of the two sides which pinch | interpose an apex angle, especially in such a structure. The triangle is not limited, and may be a non-isosceles triangle as long as the triangle satisfies the condition of apex angle (α): 39 to 45 degrees or apex angle (β): 87 to 103 degrees.

  Moreover, in the said embodiment, as shown in FIG. 3, the position of the vertex of the triangle convex part (7) of the light source side surface (3a) in the light diffusing plate (3) and the surface (3b) on the image display unit side. The positions of the vertices of the triangular protrusions (7) are configured to coincide with each other, but are not particularly limited to such regular arrangements, for example, as shown in FIGS. In this way, the relationship between the two positions may be configured to partially match and not to match the rest, or as illustrated in FIG. 7, the positions may not be matched over the entire region. May be.

In the embodiment shown in FIGS. 3 to 5 and 7, the triangular protrusions (7) on the light source side surface (3 a) are all configured to have the same shape and size, and the image display unit side All the triangular protrusions (7) on the surface (3b) are also configured to have the same shape and the same size, but are not particularly limited to such a configuration, and the triangular protrusions on the light source side The apex angle (α) of (7), the apex angle (β) of the triangular convex part (7) on the image display unit side, the height (h ₁ ) of the triangular convex part (7) on the light source side, The height (h ₂ ) of the triangular convex portion (7), the pitch interval (P ₁ ) of the triangular convex portion (7) on the light source side, the pitch interval (P ₂ ) of the triangular convex portion (7) on the image display portion side, etc. The numerical value of at least one of the elements may vary and be different. For example, in the configuration shown in FIG. 6, the vertex angle (α) of the triangular convex portion (7) on the light source side is the same in all, but the height (h ₁ ) of the triangular convex portion (7) on the light source side is different. The pitch interval (P ₁ ) of the triangular convex portion (7) on the light source side is set to a plurality of different numerical values, while the apex angle (7) of the triangular convex portion (7) on the image display portion side is set. β) is the same in all cases, but the height (h ₂ ) of the triangular convex portion (7) on the image display portion side is set to a plurality of different numerical values, and the pitch of the triangular convex portion (7) on the image display portion side The interval (P ₂ ) is set to a plurality of different numerical values.

  Moreover, in embodiment shown to FIGS. 3-7, 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, The effect of this invention For example, as shown in FIG. 8, a flat surface may exist between adjacent triangular convex portions (7).

  In the embodiments shown in FIGS. 3 to 5, 7, and 8, the triangular protrusions (7) are integrally formed on both surfaces of the light transmission plate. For example, a configuration may be adopted in which concave and convex portions (4) each including a plurality of triangular convex portions (7) are overlapped in a non-joined manner on both surfaces of the light transmission plate. . Alternatively, as shown in FIG. 6, a smooth lower surface of the first light transmission plate (21) in which a concave and convex portion (4) formed by projecting a plurality of triangular convex portions (7) is integrally formed on the upper surface; A configuration in which the smooth upper surface of the second light transmission plate (22) in which the concave and convex portion (4) formed by projecting a plurality of triangular convex portions (7) is integrally formed on the lower surface is superposed in a non-bonding manner. May be adopted.

  Although it does not specifically limit as a manufacturing method of the light diffusing plate (3) based on this invention, For example, an extrusion method, a press method, a cutting method etc. are mentioned. Especially, it is preferable to manufacture by an extrusion method from a viewpoint of production efficiency.

  The light diffusing plate (3) is not particularly limited as long as it is a plate made of a light transmissive material, and any material can be used. For example, a glass plate, an optical glass plate, a translucent resin plate, etc. are mentioned. Examples of the translucent resin plate include acrylic resin plates, polycarbonate plates, polystyrene plates, cyclic polyolefin plates, MS resin plates (methyl methacrylate-styrene copolymer resin plates), ABS resin plates, AS resin plates ( Acrylonitrile-styrene copolymer resin plate). Among these, a light transmission plate having a refractive index of 1.40 to 1.55 is preferably used.

  The light diffusing plate (3) of the present invention is provided with the light diffusing function by providing the concavo-convex portion (4) on both sides, but imparts light diffusibility to the plate itself as necessary. By doing so, you may comprise so that the light-diffusion function by the said uneven | corrugated shaped part (4) may be supplemented. That is, for example, light diffusing particles such as polystyrene particles, resin particles such as silicone particles, inorganic particles such as calcium carbonate particles, barium sulfate particles, titanium oxide particles, and alumina particles are added to translucent resins such as acrylic resins. A light diffusing plate formed by molding the contained composition may be used, or a light diffusing plate obtained by orientationally containing particles having refractive index anisotropy in an acrylic resin.

  The light source (2) is not particularly limited, and examples thereof include a linear light source such as a fluorescent tube, a halogen lamp, and a tungsten lamp, and a point light source such as a light emitting diode.

  In the backlight (1) of the present invention, the distance (e) between the light source (2) and the light reflecting layer (5a) on the bottom surface of the lamp box (5) is not particularly limited, but is usually 2.5. It is set to ˜8.5 mm (see FIG. 1). The interval (e) between the light source (2) and the light reflecting layer (5a) is a component that does not significantly affect the brightness enhancement effect.

  The light diffusing plate (3), the backlight (1), and the transmissive image display device (10) according to the present invention are not particularly limited to those of the above-described embodiment. Any design changes are permitted as long as they do not depart from the spirit.

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

<Example 1>
The luminance improvement rate (%) when the backlight (1) shown in FIG. 1 is configured using the light diffusion plate (3) made of transparent acrylic resin (PMMA) shown in FIGS. 2 and 3 was calculated by Monte Carlo simulation. . The thickness (S) of the light diffusing plate (3) is 4.0 mm, the apex angle (α) of the triangular convex portion on the light source side is 42 degrees, and the height (h ₁ ) of the triangular convex portion on the light source side is 0.0. 39 mm, the pitch interval (P ₁ ) of the triangular convex portion on the light source side is 300 μm, the apex angle (β) of the triangular convex portion on the image display portion side is 90 degrees, and the height (h ₂ ) of the triangular convex portion on the image display portion side ) Is set to 0.15 mm, the pitch interval (P ₂ ) between the triangular convex portions on the image display unit side is set to 300 μm, and the mutual separation interval (L) between adjacent linear light sources is set to 21.0 mm. . At this time, the distance (d) between the light diffusion plate and the light source is set to 9.0 mm, 10.0 mm, 11.0 mm, 12.0 mm, 13.0 mm, 14.0 mm, and 15.0 mm. The brightness improvement rate was calculated. The comparison target of the luminance improvement rate is a flat plate made of transparent acrylic resin (PMMA) having a thickness of 4.0 mm. The calculation results by these simulations are shown in Table 1, and a graph plotted based on the data in Table 1 is shown in FIG. The Monte Carlo simulation is a simulation method for obtaining an approximate solution by performing a simulation using random numbers many times.

<Comparative Example 1>
The light diffusing plate is the same as in Example 1 except that the light diffusing plate of the light diffusing plate of Example 1 having a configuration in which the triangular protrusions on the image display unit side are not formed (deleted configuration) is used. When the distance (d) between the diffusion plate and the light source is set to 9.0 mm, 10.0 mm, 11.0 mm, 12.0 mm, 13.0 mm, 14.0 mm, and 15.0 mm, the luminance improvement rate is Calculated. The calculation results by these simulations are shown in Table 1, and a graph plotted based on the data in Table 1 is shown in FIG.

<Comparative example 2>
As the light diffusing plate, a light diffusing plate having a configuration in which the triangular convex portions on the light source side and the image display unit side in the light diffusing plate of Example 1 are not formed (the configuration in which the both sides are smooth, that is, a configuration in which both surfaces are smooth surfaces) was used. The distance (d) between the light diffusing plate and the light source is 9.0 mm, 10.0 mm, 11.0 mm, 12.0 mm, 13.0 mm, 14.0 mm, 15.0 mm in the same manner as in Example 1. The brightness improvement rate when each value was set was calculated. The calculation results by these simulations are shown in Table 1, and a graph plotted based on the data in Table 1 is shown in FIG.

  As is apparent from Table 1 and FIG. 10, the backlight of Example 1 constructed using the light diffusion plate of the present invention was found to have a sufficient luminance improvement. On the other hand, in the backlight of Comparative Example 1 configured using a light diffusing plate having a configuration in which no triangular convex portion is formed on the image display unit side, the luminance improvement was insufficient. Further, in the backlight of Comparative Example 2 configured using the light diffusing plate whose upper and lower surfaces are smooth surfaces, the luminance improvement was further insufficient.

<Example 2>
The luminance improvement rate (%) when the backlight (1) shown in FIG. 1 is configured using the light diffusion plate (3) made of transparent acrylic resin (PMMA) shown in FIGS. 2 and 3 was calculated by Monte Carlo simulation. . The thickness (S) of the light diffusing plate (3) is 2.5 mm, the apex angle (α) of the triangular convex portion on the light source side is 39 degrees, and the height (h ₁ ) of the triangular convex portion on the light source side is 0. 424 mm, the pitch interval (P ₁ ) of the triangular convex portion on the light source side is 300 μm, the apex angle (β) of the triangular convex portion on the image display portion side is 90 degrees, and the height (h ₂ ) of the triangular convex portion on the image display portion side ) Is set to 0.15 mm, the pitch interval (P ₂ ) of the triangular projections on the image display unit side is set to 300 μm, and the spacing between adjacent linear light sources (L) is set to 21.0 mm, and light diffusion is performed. Calculation was performed by setting the distance (d) between the plate and the light source to 13.0 mm. The comparison target of the luminance improvement rate is a flat plate made of a transparent acrylic resin (PMMA) having a thickness of 2.5 mm. Table 2 shows the calculation results by simulation.

<Example 3>
The luminance improvement rate was calculated in the same manner as in Example 2 except that the apex angle (α) of the triangular convex portion on the light source side in the light diffusion plate (3) was set to 40 degrees. Table 2 shows the calculation results.

<Example 4>
The luminance improvement rate was calculated in the same manner as in Example 2 except that the apex angle (α) of the triangular convex portion on the light source side in the light diffusion plate (3) was set to 41 degrees. Table 2 shows the calculation results.

<Example 5>
The luminance improvement rate was calculated in the same manner as in Example 2 except that the apex angle (α) of the triangular convex portion on the light source side in the light diffusion plate (3) was set to 42 degrees. Table 2 shows the calculation results.

<Example 6>
The luminance improvement rate was calculated in the same manner as in Example 2 except that the apex angle (α) of the triangular convex portion on the light source side in the light diffusion plate (3) was set to 43 degrees. Table 2 shows the calculation results.

<Example 7>
The luminance improvement rate was calculated in the same manner as in Example 2 except that the apex angle (α) of the triangular convex portion on the light source side in the light diffusion plate (3) was set to 44 degrees. Table 2 shows the calculation results.

<Comparative Example 3>
The luminance improvement rate was calculated in the same manner as in Example 2 except that the apex angle (α) of the triangular convex portion on the light source side in the light diffusion plate (3) was set to 30 degrees. Table 2 shows the calculation results.

<Comparative Example 4>
The luminance improvement rate was calculated in the same manner as in Example 2 except that the apex angle (α) of the triangular convex portion on the light source side in the light diffusion plate (3) was set to 50 degrees. Table 2 shows the calculation results.

<Comparative Example 5>
The luminance improvement rate was calculated in the same manner as in Example 2 except that the apex angle (α) of the triangular convex portion on the light source side in the light diffusion plate (3) was set to 60 degrees. Table 2 shows the calculation results.

<Comparative Example 6>
The luminance improvement rate was calculated in the same manner as in Example 2 except that the apex angle (α) of the triangular convex portion on the light source side in the light diffusion plate (3) was set to 90 degrees. Table 2 shows the calculation results.

<Comparative Example 7>
The luminance improvement rate was calculated in the same manner as in Example 2 except that the apex angle (α) of the triangular convex portion on the light source side in the light diffusion plate (3) was set to 120 degrees. Table 2 shows the calculation results.

  A graph plotted based on the data in Table 2 is shown in FIG. As is apparent from Table 2 and FIG. 11, the backlights of Examples 2 to 7 configured using the light diffusion plate of the present invention (the apex angle α is 39 to 45 degrees) have a sufficient luminance improvement. It was. On the other hand, in the backlights of Comparative Examples 3 to 7 where the apex angle (α) deviates from the specified range (39 to 45 degrees) of the present invention, the improvement in luminance was insufficient.

<Example 8>
The luminance improvement rate (%) when the backlight (1) shown in FIG. 1 is configured using the light diffusion plate (3) made of transparent acrylic resin (PMMA) shown in FIGS. 2 and 3 was calculated by Monte Carlo simulation. . The thickness (S) of the light diffusion plate (3) is 2.5 mm, the apex angle (α) of the triangular convex portion on the light source side is 42 degrees, and the height (h ₁ ) of the triangular convex portion on the light source side is 0. 391 mm, the pitch interval (P ₁ ) of the triangular convex part on the light source side is 300 μm, the apex angle (β) of the triangular convex part on the image display part side is 87 degrees, and the height (h ₂ ) of the triangular convex part on the image display part side ) Is set to 0.158 mm, the pitch interval (P ₂ ) between the triangular projections on the image display unit side is set to 300 μm, and the spacing between adjacent linear light sources (L) is set to 21.0 mm, and light diffusion is performed. Calculation was performed by setting the distance (d) between the plate and the light source to 13.0 mm. The comparison target of the luminance improvement rate is a flat plate made of a transparent acrylic resin (PMMA) having a thickness of 2.5 mm. Table 3 shows the calculation results by simulation.

<Example 9>
The luminance improvement rate was calculated in the same manner as in Example 10 except that the apex angle (β) of the triangular convex portion on the image display portion side in the light diffusion plate (3) was set to 88 degrees. Table 3 shows the calculation results.

<Example 10>
The luminance improvement rate was calculated in the same manner as in Example 10 except that the apex angle (β) of the triangular convex part on the image display part side in the light diffusion plate (3) was set to 89 degrees. Table 3 shows the calculation results.

<Example 11>
The brightness improvement rate was calculated in the same manner as in Example 10 except that the apex angle (β) of the triangular protrusion on the image display unit side in the light diffusion plate (3) was set to 91 degrees. Table 3 shows the calculation results.

<Example 12>
The luminance improvement rate was calculated in the same manner as in Example 10 except that the apex angle (β) of the triangular convex part on the image display part side in the light diffusion plate (3) was set to 92 degrees. Table 3 shows the calculation results.

<Example 13>
The luminance improvement rate was calculated in the same manner as in Example 10 except that the apex angle (β) of the triangular convex part on the image display part side in the light diffusion plate (3) was set to 93 degrees. Table 3 shows the calculation results.

<Example 14>
The luminance improvement rate was calculated in the same manner as in Example 10 except that the apex angle (β) of the triangular protrusion on the image display unit side in the light diffusion plate (3) was set to 100 degrees. Table 3 shows the calculation results.

<Comparative Example 8>
The luminance improvement rate was calculated in the same manner as in Example 10 except that the apex angle (β) of the triangular convex part on the image display part side in the light diffusion plate (3) was set to 30 degrees. Table 3 shows the calculation results.

<Comparative Example 9>
The luminance improvement rate was calculated in the same manner as in Example 10 except that the apex angle (β) of the triangular convex part on the image display part side in the light diffusion plate (3) was set to 60 degrees. Table 3 shows the calculation results.

<Comparative Example 10>
The luminance improvement rate was calculated in the same manner as in Example 10 except that the apex angle (β) of the triangular convex part on the image display part side in the light diffusion plate (3) was set to 80 degrees. Table 3 shows the calculation results.

<Comparative Example 11>
The luminance improvement rate was calculated in the same manner as in Example 10 except that the apex angle (β) of the triangular convex part on the image display part side in the light diffusion plate (3) was set to 120 degrees. Table 3 shows the calculation results.

  A graph plotted based on the data in Table 3 is shown in FIG. As apparent from Table 3 and FIG. 12, the backlights of Examples 5 and 8 to 14 configured using the light diffusion plate of the present invention (the apex angle β is 87 to 103 degrees) sufficiently improve the luminance. Was recognized. On the other hand, in the backlights of Comparative Examples 8 to 11 where the apex angle (β) deviates from the specified range (87 to 103 degrees) of the present invention, the improvement in luminance was insufficient.

<Example 15>
The luminance improvement rate was calculated in the same manner as in Example 5 except that the thickness (S) of the light diffusion plate (3) was set to 2.0 mm. Table 4 shows the calculation results.

<Example 16>
The luminance improvement rate was calculated in the same manner as in Example 5 except that the thickness (S) of the light diffusion plate (3) was set to 2.8 mm. Table 4 shows the calculation results.

<Example 17>
The luminance improvement rate was calculated in the same manner as in Example 5 except that the thickness (S) of the light diffusing plate (3) was set to 3.0 mm. Table 4 shows the calculation results.

<Example 18>
The luminance improvement rate was calculated in the same manner as in Example 5 except that the thickness (S) of the light diffusing plate (3) was set to 4.0 mm. Table 4 shows the calculation results.

<Example 19>
The luminance improvement rate was calculated in the same manner as in Example 5 except that the thickness (S) of the light diffusion plate (3) was set to 5.0 mm. Table 4 shows the calculation results.

  A graph plotted based on the data in Table 4 is shown in FIG. As apparent from Table 4 and FIG. 13, the backlight constructed using the light diffusing plate of the present invention was sufficiently improved in luminance even when the thickness of the light diffusing plate was changed. Therefore, it can be seen that the thickness of the light diffusing plate is a component that does not significantly affect the brightness enhancement effect.

<Example 20>
The luminance improvement rate was calculated in the same manner as in Example 5 except that the spacing (L) between the adjacent linear light sources was set to 20.0 mm. Table 5 shows the calculation results.

<Example 21>
The luminance improvement rate was calculated in the same manner as in Example 5 except that the spacing (L) between the adjacent linear light sources was set to 22.0 mm. Table 5 shows the calculation results.

<Example 22>
The luminance improvement rate was calculated in the same manner as in Example 5 except that the spacing (L) between the adjacent linear light sources was set to 23.0 mm. Table 5 shows the calculation results.

<Example 23>
The luminance improvement rate was calculated in the same manner as in Example 5 except that the spacing (L) between the adjacent linear light sources was set to 24.0 mm. Table 5 shows the calculation results.

<Example 24>
The luminance improvement rate was calculated in the same manner as in Example 5 except that the spacing (L) between the adjacent linear light sources was set to 25.0 mm. Table 5 shows the calculation results.

<Example 25>
The luminance improvement rate was calculated in the same manner as in Example 5 except that the spacing (L) between the adjacent linear light sources was set to 26.0 mm. Table 5 shows the calculation results.

  A graph plotted based on the data in Table 5 is shown in FIG. As is apparent from Table 5 and FIG. 14, the backlight configured using the light diffusion plate of the present invention has a power saving design in which the spacing between adjacent linear light sources is set to a length of 10 mm or more. Even with this configuration, a sufficient improvement in luminance was observed.

<Example 26>
Brightness is improved in the same manner as in Example 5 except that the pitch interval (P ₁ ) of the triangular convex portions on the light source side is set to 30 μm and the pitch interval (P ₂ ) of the triangular convex portions on the image display portion side is set to 30 μm. The rate was calculated. Table 6 shows the calculation results.

<Example 27>
Brightness is improved in the same manner as in Example 5 except that the pitch interval (P ₁ ) of the triangular convex portions on the light source side is set to 50 μm and the pitch interval (P ₂ ) of the triangular convex portions on the image display portion side is set to 50 μm. The rate was calculated. Table 6 shows the calculation results.

<Example 28>
Brightness is improved in the same manner as in Example 5 except that the pitch interval (P ₁ ) of the triangular convex portions on the light source side is set to 80 μm and the pitch interval (P ₂ ) of the triangular convex portions on the image display portion side is set to 80 μm. The rate was calculated. Table 6 shows the calculation results.

<Example 29>
Brightness is improved in the same manner as in Example 5 except that the pitch interval (P ₁ ) of the triangular convex portions on the light source side is set to 100 μm and the pitch interval (P ₂ ) of the triangular convex portions on the image display portion side is set to 100 μm. The rate was calculated. Table 6 shows the calculation results.

<Example 30>
Brightness is improved in the same manner as in Example 5 except that the pitch interval (P ₁ ) of the triangular projections on the light source side is set to 1000 μm and the pitch interval (P ₂ ) of the triangle projections on the image display unit side is set to 1000 μm. The rate was calculated. Table 6 shows the calculation results.

  A graph plotted based on the data in Table 6 is shown in FIG. As can be seen from Table 6 and FIG. 15, the backlight constructed using the light diffusion plate of the present invention was found to have a sufficient brightness improvement even when the pitch interval of the triangular convex portions was changed. Therefore, it can be seen that the pitch interval of the triangular convex portions is a component that does not significantly affect the brightness enhancement effect.

<Example 31>
The luminance improvement rate (%) when the backlight (1) shown in FIG. 1 was configured using the light diffusion plate (3) made of the transparent acrylic resin (PMMA) shown in FIG. 7 was calculated by Monte Carlo simulation. The thickness (S) of the light diffusion plate (3) is 2.5 mm, the apex angle (α) of the triangular convex portion on the light source side is 42 degrees, and the height (h ₁ ) of the triangular convex portion on the light source side is 0. 391 mm, the pitch interval (P ₁ ) of the triangular convex portion on the light source side is 300 μm, the apex angle (β) of the triangular convex portion on the image display portion side is 90 degrees, and the height (h ₂ ) of the triangular convex portion on the image display portion side ) Is set to 0.15 mm, the pitch interval (P ₂ ) of the triangular projections on the image display unit side is set to 300 μm, and the spacing between adjacent linear light sources (L) is set to 21.0 mm, and light diffusion is performed. The distance (d) between the plate and the light source is set to 13.0 mm, and the deviation width (J) between the vertex position of the triangular convex portion on the light source side and the vertex position of the triangular convex portion on the image display section side is set to 50 μm. Set and calculated. The comparison target of the luminance improvement rate is a flat plate made of a transparent acrylic resin (PMMA) having a thickness of 2.5 mm. Table 7 shows the calculation results by simulation.

<Example 32>
The luminance improvement rate was calculated in the same manner as in Example 31 except that the deviation width (J) was set to 100 μm. Table 7 shows the calculation results.

<Example 33>
The luminance improvement rate was calculated in the same manner as in Example 31 except that the deviation width (J) was set to 150 μm. Table 7 shows the calculation results.

<Example 34>
The luminance improvement rate was calculated in the same manner as in Example 31 except that the deviation width (J) was set to 200 μm. Table 7 shows the calculation results.

<Example 35>
The luminance improvement rate was calculated in the same manner as in Example 31 except that the deviation width (J) was set to 250 μm. Table 7 shows the calculation results.

  A graph plotted based on the data in Table 7 is shown in FIG. As apparent from Table 7 and FIG. 16, the backlight constructed using the light diffusing plate of the present invention was sufficiently improved in luminance even when the shift width (J) was changed. Therefore, it can be seen that the shift width (J) is a component that does not significantly affect the magnitude of the brightness enhancement effect.

<Example 36>
The luminance improvement rate (%) when the backlight (1) shown in FIG. 1 was configured using the light diffusion plate (3) made of the transparent acrylic resin (PMMA) shown in FIG. 9 was calculated by Monte Carlo simulation. The thickness (S) of the light diffusion plate (3) is 2.5 mm, the apex angle (α) of the triangular convex portion on the light source side is 42 degrees, and the height (h ₁ ) of the triangular convex portion on the light source side is 0. 391 mm, the pitch interval (P ₁ ) of the triangular convex portion on the light source side is 300 μm, the apex angle (β) of the triangular convex portion on the image display portion side is 90 degrees, and the height (h ₂ ) of the triangular convex portion on the image display portion side ) Is set to 0.15 mm, the pitch interval (P ₂ ) of the triangular projections on the image display unit side is set to 300 μm, and the spacing between adjacent linear light sources (L) is set to 21.0 mm, and light diffusion is performed. Calculation was performed by setting the distance (d) between the plate and the light source to 13.0 mm. At this time, the luminance improvement rate was calculated when the transfer rate of the triangular convex portion on the light source side was set to 79%, 90%, and 93%. The comparison target of the luminance improvement rate is a flat plate made of a transparent acrylic resin (PMMA) having a thickness of 2.5 mm. The calculation results by these simulations are shown in Table 8, and a graph plotted based on the data in Table 8 is shown in FIG.

  It can be seen from Table 8 and FIG. 17 that the luminance improvement rate (%) increases substantially linearly as the transfer rate (%) of the triangular convex portion on the light source side increases.

  The light diffusing plate of the present invention is preferably used as a light diffusing plate for a backlight, but is not particularly limited to such applications. The backlight of the present invention is suitably used as a backlight for a transmissive image 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 perspective view which shows 1st Embodiment of the light diffusing plate which concerns on this invention. It is sectional drawing which shows 1st Embodiment of the light diffusing plate which concerns on this invention. It is sectional drawing which shows 2nd Embodiment of the light diffusing plate which concerns on this invention. It is sectional drawing which shows 3rd Embodiment of the light diffusing plate which concerns on this invention. It is sectional drawing which shows 4th Embodiment of the light diffusing plate which concerns on this invention. It is sectional drawing which shows 5th Embodiment of the light diffusing plate which concerns on this invention. It is sectional drawing which shows 6th Embodiment of the light diffusing plate which concerns on this invention. It is sectional drawing which shows 7th Embodiment of the light diffusing plate which concerns on this invention. It is the graph (horizontal axis: distance d of a light diffusing plate and a light source, vertical axis | shaft: luminance improvement rate) which plotted the data of Example 1 and Comparative Examples 1 and 2. It is the graph (Horizontal axis: The apex angle (alpha) of the triangular convex part by the side of a light source, A vertical axis | shaft: Luminance improvement rate) which plotted the data of Examples 2-7 and Comparative Examples 3-7. It is the graph (Horizontal axis: The apex angle (beta) of the triangular convex part by the side of an image display part, Vertical axis: Luminance improvement rate) which plotted the data of Example 5, 8-14, and Comparative Examples 8-11. It is the graph (Horizontal axis: Thickness S of a light diffusing plate, vertical axis | shaft: Luminance improvement rate) which plotted the data of Example 5, 15-19. It is the graph (The horizontal axis | shaft: The mutual space | interval space | interval L of an adjacent linear light source, the vertical axis | shaft: Luminance improvement rate) which plotted the data of Example 5, 20-25. Example graph data plots of 5,26～30 (horizontal axis: pitch P ₁ of the triangular ridges, P _2, the vertical axis: brightness improvement ratio) is. Graph in which data of Examples 5, 31 to 35 are plotted (horizontal axis: deviation width J between the position of the vertex of the triangular convex portion on the light source side and the position of the vertex of the triangular convex portion on the image display unit side, vertical axis: luminance Improvement rate). It is the graph (The horizontal axis | shaft: The transfer rate of a triangular convex part, the vertical axis | shaft: Brightness improvement rate) which plotted the data of Example 36.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Backlight 2 ... Light source 3 ... Light diffusing plate 3a ... One surface (surface on the light source side)
3b ... the other surface (surface on the image display unit side)
DESCRIPTION OF SYMBOLS 4 ... Uneven shape part 5 ... Lamp box 7 ... Triangular convex part 8 ... Convex line part 10 ... Liquid crystal display device (transmission type image display apparatus)
11 ... Liquid crystal cell L ... Spacing distance of light source d ... Distance between light diffusion plate and light source α ... Apex angle of triangular convex part on back side (light source side) β ... Triangular convex part on front side (image display side) Vertex angle h: Triangular convex height P: Pitch interval between adjacent triangular convex portions

Claims (7)

  The concave and convex portion formed by projecting a plurality of convex portions having a triangular cross-sectional shape is composed of a light transmitting plate provided on both surfaces, and the apex angle of the triangular convex portion on one surface of the light transmitting plate is 39 to 45. The light diffusing plate is characterized in that the apex angle of the triangular convex portion on the other surface of the light transmitting plate is set to 87 to 103 degrees.   2. The light diffusing plate according to claim 1, wherein a height of the triangular convex portion is 0.01 to 1 mm, and a pitch interval between adjacent triangular convex portions is 0.03 to 2 mm.   The triangular convex portion is formed of a convex portion having a triangular cross section extending along one direction parallel to the surface of the light transmission plate, and the length directions of the convex portions are substantially parallel to each other. The light diffusing plate according to claim 1, wherein the light diffusing plate is arranged to be.   A plurality of light sources are disposed in the lamp box so as to be spaced apart from each other, and the light diffusing plate according to any one of claims 1 to 3 is disposed on a front side of the plurality of light sources. A backlight characterized in that a surface on which a triangular convex portion having an apex angle of 39 to 45 degrees is formed is positioned on the back side.   A plurality of linear light sources are spaced apart from each other in the lamp box, and the light diffusing plate according to claim 3 is disposed on the front side of the plurality of linear light sources. The surface on which the 39-45 degree triangular convex part is formed is configured to be located on the back side, and the length direction of the linear light source and the length direction of the convex part of the light diffusing plate substantially coincide. Backlight characterized by being arranged like this. A plurality of linear light sources are disposed in the lamp box so as to be spaced apart from each other, and the light diffusion plate according to claim 3 is disposed on the front side of the plurality of light sources,
The spacing between the adjacent linear light sources is set to 10 mm or more, the distance between the light diffusion plate and the light source is set to 50 mm or less,
The light diffusion plate is configured such that a surface on which a triangular convex portion with an apex angle of 39 to 45 degrees is formed is located on the back side, and the length direction of the linear light source and the convex portion of the light diffusion plate are A backlight characterized by being arranged so that its length direction substantially coincides.   A transmissive image display device, wherein the backlight according to any one of claims 4 to 6 is disposed on the back side of the image display unit.

Images