JP2007163810A - Light diffusion plate and direct backlight device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light diffusion plate capable of constituting a direct backlight device which has high brightness and is excellent in brightness uniformity without largely changing the constitution when being used for the direct backlight device. <P>SOLUTION: In the light diffusion plate 1, the light emission surface is an irregular surface with an irregular structure of which the center line average roughness Ra(Omax) measured in such a direction to obtain a maximum value is 3.0 μm to 1,000 μm and the light incident surface is a rough surface of which the center line average roughness Ra(Imax) measured in such a direction to obtain the maximum value is ≥0.1 μm and <3.0 μm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light diffusing plate and a direct type backlight device, and in particular, when used in a direct type backlight device, the direct type that has high luminance and excellent luminance uniformity without greatly changing its configuration. The present invention relates to providing a light diffusing plate that can be used as a backlight device, and to a direct type backlight device including the light diffusing plate.

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

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

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

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

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

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

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

  However, the luminance uniformity cannot be improved sufficiently by simply forming a prism pattern on the surface of the light diffusing plate. An object of the present invention is to provide a light diffusing plate that can be used as a direct type backlight device having high luminance and excellent luminance uniformity without greatly changing its configuration when used in a direct type backlight device. And providing a direct type backlight device including the light diffusion plate.

  As a result of studies to solve the above problems, the present inventor has obtained a light diffusing plate having a light incident surface on which light from a light source is incident and a light emitting surface on which light incident from the light incident surface is diffusely irradiated. The light exit surface is an uneven surface on which an uneven structure having a center line average roughness (Ra (Omax)) of 3 μm to 1,000 μm measured in the direction in which the maximum value is obtained, and light By making the incident surface a rough surface with a center line average roughness (Ra (Imax)) measured in the direction in which the obtained value is maximum, 0.1 μm or more and less than 3 μm, this light diffusion plate is made a direct type backlight. When used in a device, the present inventors have found that a direct-type backlight device having high luminance and excellent luminance uniformity can be obtained without greatly changing the configuration of the device itself, and the present invention is completed based on this finding. It came to.

That is, according to the present invention,
(1) A light diffusing plate having a light incident surface on which light from a light source is incident and a light emitting surface for diffusing and irradiating light incident from the light incident surface. It is a concavo-convex surface on which a concavo-convex structure with a center line average roughness (Ra (Omax)) measured in the maximum direction is 3.0 μm to 1,000 μm, and the light incident surface has the maximum value obtained A light diffusing plate characterized by a rough surface having a center line average roughness (Ra (Imax)) measured in a direction of 0.1 μm or more and less than 3.0 μm,
(2) On the light incident surface, the centerline average roughness (Ra (Imax)) measured in the maximum direction and the centerline average roughness (Ra (Imin) measured in the direction where the obtained value is the minimum. ))), A light diffusing plate characterized by satisfying a relationship of Ra (Imax)> Ra (Imin) × 1.5,
(3) The light diffusing plate, wherein the concavo-convex structure is a prism row in which a plurality of linear prisms each having a concave or convex cross section are arranged in parallel.
(4) Each of the linear prisms has a concave or convex cross-section and is formed of a triangle having an apex angle of 60 ° to 170 °, and an interval between adjacent linear prisms is 20 μm to 700 μm. And (5) each linear prism includes at least four surfaces, and two of the at least four surfaces and the other two surfaces are incident on the light. A light diffusing plate, wherein the light diffusing plate is inclined in directions opposite to each other with respect to a surface including a normal of the surface and a longitudinal direction of the linear prism;
Is provided.

Moreover, according to the present invention,
(6) A plurality of light sources, a reflecting plate that reflects light from these light sources, and the light diffusion plate that diffuses and irradiates direct light from the light source and reflected light from the reflecting plate. Direct type backlight device,
(7) The concave-convex structure of the light diffusing plate is a prism array in which a plurality of linear prisms each having a concave or convex cross section are arranged in parallel, and each linear prism constitutes the triangle. The angle formed by two inclined surfaces and a plane substantially parallel to the light incident surface is made equal, and as the position of the linear prism moves away from the light source closest to the linear prism, the angle increases. The direct-type backlight device, characterized by being continuously or intermittently enlarged,
(8) The light source is a plurality of linear light sources arranged substantially in parallel, and the light diffusing plate is formed on at least one of the light incident surface and the light emitting surface. The three or more surfaces of the concave or convex structure in the cross section of the light diffusing plate in a direction perpendicular to the longitudinal direction of the linear light source. Includes a plurality of line segments with different inclinations, the inclination of the plurality of line segments is Xn (degree, n is an integer of 1 or more), and the distance between the centers of the adjacent linear light sources A (mm), where b (mm) is the distance between the center of the linear light source and the main surface of the light diffusing plate on the linear light source side, and the slopes Xn of the plurality of line segments are all n, 12.5-10 × (b / a) <Xn <85-25 × (b / a) The direct type backlight device, characterized by:
(9) The light source is a plurality of point light sources arranged, and the light diffusing plate includes three or more surfaces formed on at least one of the light incident surface and the light emitting surface. A line corresponding to the three or more surfaces of the concave structure or the convex structure in a cross section in a plane including the normal line of the light diffusion plate of the light diffusion plate. The minute includes two or more types of line segments having different inclinations, the inclination of the plurality of line segments is Xn (degree, n is an integer of 1 or more), and the adjacent point-like shapes in the plurality of point light sources The average distance between the light sources is a (mm), and the distance between the center of the point light source and the principal surface of the light diffusing plate on the point light source side is b (mm). 12.5-11 × (b / a) <x <85-28.5 × (for all n b / a), the direct type backlight device,
(10) The repeating unit has a convex structure, and the light diffusing plate having such a convex structure has a V shape in a direction different from the longitudinal direction of the linear prisms constituting the prism row. The direct type backlight device obtained by making a cut in the shape,
(11) The direct type backlight device, wherein the convex structure is a pyramid or a truncated pyramid shape,
(12) The repeating unit has a concave structure, and the light diffusing plate having such a concave structure has a V shape in a direction different from the longitudinal direction of the linear prisms constituting the prism row. The direct type backlight device, which is obtained by transferring the convex shape of a transfer member having a convex shape obtained by making a cut in a shape,
(13) The direct-type backlight device, wherein the concave structure is a pyramid or a truncated pyramid shape,
(14) The direct-type backlight device, wherein the light diffusing plate is formed by dispersing a light diffusing agent in a transparent resin, and the total light transmittance of the dispersion is 60% to 98%. ,and,
(15) The direct type backlight device, wherein the haze of the dispersion is 20% to 100%,
Is provided.

  According to the light diffusing plate of the present invention, when used in a direct type backlight device, a direct type backlight device having a simple structure with high luminance and excellent luminance uniformity can be obtained.

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

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

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

  The distance a between the centers of the adjacent linear light sources 2 is preferably 15 mm to 150 mm, and more preferably 20 mm to 100 mm. By setting the distance a within the above range, the power consumption of the direct type backlight device can be reduced, the assembly of the device can be facilitated, and the luminance unevenness of the light emitting surface can be suppressed.

  As a material of the reflector 3, a resin colored in white or silver, a metal, or the like can be used, and a resin is preferable from the viewpoint of weight reduction. The color of the reflector 3 is preferably white from the viewpoint of improving the luminance uniformity, but white and silver may be mixed in order to balance the luminance and the luminance uniformity highly.

The light diffusing plate 1 is a plate material that diffuses and irradiates incident light.
As a material constituting the light diffusing plate, glass, a mixture of two or more kinds of resins that are difficult to mix, a material in which a light diffusing agent is dispersed in a transparent resin, one kind of transparent resin, and the like can be used. Among these, a resin is preferable because it is lightweight and easy to mold, and one kind of transparent resin is preferable from the viewpoint that luminance can be easily improved, and adjustment of total light transmittance and haze is easy. From the viewpoint, a transparent resin in which a light diffusing agent is dispersed is preferable.

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

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

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

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

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

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

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

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

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

  The ratio of the light diffusing agent dispersed in the transparent resin can be appropriately selected according to the thickness of the light diffusing plate, the interval between the linear light sources, and the like. Usually, the total light transmittance of the dispersion is 60% to 98%. It is preferable to adjust the content of the light diffusing agent so as to be, and it is more preferable to adjust the content of the light diffusing agent to be 65% to 95%. Further, the content of the light diffusing agent is preferably adjusted so that the haze is 20% to 100%, and the content of the light diffusing agent is adjusted to be 25% to 100%. More preferably. By setting the total light transmittance and haze within the above-mentioned preferable ranges, the luminance and the luminance uniformity can be further improved.

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

  The thickness of the light diffusing plate 1 is preferably 0.4 mm to 5 mm, and more preferably 0.8 mm to 4 mm. By setting the thickness of the light diffusing plate within the above preferable range, it is possible to suppress bending due to its own weight and to facilitate the molding.

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

  The light incident surface 1A is a rough surface having a center line average roughness (Ra (Imax)) measured in a direction in which the obtained value is maximized in a range from 0.1 μm to less than 3 μm. Such a rough surface can increase the luminance uniformity of the light emitting surface. Further, on the light incident surface 1A, between the center line average roughness measured in the direction where the obtained value is the maximum and the center line average roughness (Ra (Imin)) measured in the direction where the obtained value is the minimum. And (Ra (Imax))> (Ra (Imin)) × 1.5 is preferably satisfied. With such a configuration, the luminance uniformity can be further increased.

  The light emitting surface 1B is a concavo-convex surface on which a concavo-convex structure having a center line average roughness (Ra (Omax)) of 3 μm to 1,000 μm measured in the direction in which the obtained value is maximized.

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

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

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

  FIG. 3 is a perspective view schematically showing a direct type backlight device according to the second embodiment of the present invention. The direct type backlight device of the present embodiment includes a plurality of point light sources 12, a reflector 3 that reflects light from the point light source 12, direct light from the point light source 12, and reflected light from the reflector 3. And a light diffusing plate 11 that diffuses and irradiates the light. In FIG. 3, the outer shape of the light diffusion plate 11 is schematically shown in the light diffusion plate 1 of FIG. 1.

  For each point light source 12, for example, a light emitting diode (LED) can be used. Examples of the configuration of each LED include (1) a configuration consisting of only white LEDs, (2) a configuration combining RGB primary colors, and (3) a configuration combining intermediate colors with RGB primary colors.

  Further, when the configuration combining the three primary colors of RGB (the configuration of (2) and (3)) is used, (A) at least one red LED, green LED, and blue LED are arranged close to each other, and each color And (B) a configuration in which a red LED, a green LED, and a blue LED are appropriately arranged, and a color cover is provided using a field sequential method in which each color LED is colored in a time-sharing manner. Can do.

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

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

  A plurality of convex structures or concave structures are formed on the light exit surface 11B of the light diffusing plate 11. Each convex structure or each concave structure is a structure having three or more faces as shown in FIG. 7A (in FIG. 7A, it is shown as a convex structure of a quadrangular pyramid), and brightness In terms of unevenness improvement, it is preferable that the light diffusion plate is periodically arranged in a direction different from the short direction. At this time, the period is preferably 20 μm to 700 μm, and more preferably 30 μm to 400 μm.

  The center line average roughness Ra (Omax) of the concave structure or the convex structure is preferably 3 μm to 1,000 μm, more preferably 3 μm to 800 μm, and still more preferably 4 μm to 500 μm. The concave structure or the convex structure may be formed on the entire light emitting surface, or may be formed only on a part of the light emitting surface (for example, an optically effective surface).

  Examples of the convex structure or the concave structure may be a pyramid shape and a truncated pyramid shape. The pyramid may be a polygonal pyramid such as a triangular pyramid, a quadrangular pyramid, a pentagonal pyramid, or a hexagonal pyramid. The pyramid may be a polygonal frustum such as a triangular frustum, a quadrangular frustum, a pentagonal frustum, or a hexagonal frustum. By adopting such a polygonal pyramid or polygonal frustum shape, sufficient luminance can be exhibited even when the light emitting surface is observed from a position shifted from the front. The plurality of convex structures or concave structures may be composed of only one type of structure, or may be a combination of a plurality of types of structures.

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

  Also, the plurality of concave structures, for example, have a convex shape obtained by making V-shaped cuts in a direction different from the longitudinal direction of the linear prisms constituting the prism row because they are easy to mold. It can be obtained by transferring the convex shape of the member.

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

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

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

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

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

  In FIG. 7 of the present embodiment, the case where the repeating unit has a convex structure is described as an example. However, in the preferred configuration (for example, satisfying the relation 1), the repeating unit has a concave structure. It is preferable that the same holds true for the case of.

<Modification>
The present invention is not limited to the above embodiments.
For example, in the first embodiment, the prism row of the light diffusing plate 1 is a linear prism, the linear prism is a triangular prism having a triangular cross section, and a plurality of identical triangular prisms are arranged. For example, as shown in FIG. 8, the triangular prism is formed so that the angles formed by two inclined surfaces constituting the triangle and a plane substantially parallel to the light incident surface are equal to each other. However, the light diffusing plate 101 may be configured so that the angle increases continuously or intermittently as the distance from the linear light source 2 closest to the triangular prism increases. According to such a configuration, the luminance of the portion corresponding to the space between the linear light sources 2 on the light emitting surface can be improved, and the luminance uniformity of the light emitting surface can be increased.

  In each of the above embodiments, as the prism array, as shown in FIG. 9, a linear prism (hereinafter referred to as a composite prism) composed of a polygon having a concave or convex cross section including at least four surfaces. The light diffusing plate 102 may be adjacent to each other or arranged at intervals. In the composite prism, two of the at least four surfaces and the other two surfaces are opposite to each other with respect to the normal line of the light incident surface (a line along the thickness direction of the light diffusion plate). It is preferable that the configuration is inclined to the angle. According to such a configuration, when the light diffusing plate having the composite prism is arranged on the light sources arranged at appropriate intervals, the light emitting surface is based on the number of the surfaces between the adjacent light sources. As a result, a plurality of light source images are observed, so that the luminance uniformity of the light emitting surface can be increased.

  As the light diffusing plate of the second embodiment, the light diffusing plate 1 used in the first embodiment may be applied, and the light diffusing plate according to the modification of the first embodiment described above is applied. You can also Even in such a case, the luminance and the luminance uniformity can be increased.

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

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

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

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

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

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

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

Production Example 3 (Die part B)
The surface of the cutting surface of the mold part A was blasted, and the surface of the cutting surface was roughened to produce a mold part B.

<Example 1>
A reflective sheet (manufactured by Tsujiden Co., Ltd., RF188) is attached to the inner surface of a milky white plastic case having an inner dimension width of 700 mm, a depth of 400 mm, and a depth of 20 mm to form a reflective plate. Fourteen cold-cathode tubes having a length of 750 mm were arranged so that the distance a between the centers of the cold-cathode tubes was 28 mm, the vicinity of the electrode part was fixed with a silicone sealant, and an inverter was attached.

  Next, the mold part A obtained in Production Example 2 was used for one mold constituting the mold, and the cavity surface of the other mold was roughened by blasting or the like from an oblique direction. Using such a mold for an injection molding machine (clamping force 4,410 kN), using the light diffusion plate pellet obtained in Production Example 1 as a raw material, under conditions of a cylinder temperature of 280 degrees and a mold temperature of 85 degrees A light diffusion plate was molded. The obtained light diffusing plate had a rectangular shape with a thickness of 2 mm and 727.5 mm × 415 mm, and a prism row composed of a plurality of triangular prisms was formed on one surface thereof.

When the obtained light diffusing plate was observed using an ultra-deep microscope, the surface on which the prism array was formed (light emitting surface) was the center line average in the maximum direction (longitudinal direction of the light diffusing plate) It was an uneven surface having an uneven structure with a roughness (Ra (Omax)) of 5.9 μm.
On the other hand, the surface (light incident surface) of the obtained light diffusing plate where the prism array is not formed has a center line average roughness (Ra (Imax)) measured in the maximum direction of 0.6 μm, The center line average roughness (Ra (Imin)) in the minimum direction (short direction of the light diffusion plate) was a rough surface of 0.086 μm. Therefore, Ra (Imax) / Ra (Imin) = 7, and the relationship of Ra (Imax)> Ra (Imin) × 1.5 was satisfied.

  Next, the obtained light diffusing plate is placed on the plastic case with the cold cathode tube attached so that the surface on which the prism row is formed is opposite to the cold cathode tube (anti-light source position), that is, the light emitting surface. Installed. At this time, the cold cathode tubes were arranged so that the longitudinal direction of the cold cathode tubes and the longitudinal direction of the triangular prisms constituting the prism row were substantially parallel. Then, two diffusion sheets (“188GM2”, manufactured by Kimoto Co.) were installed on this light diffusion plate.

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

Next, the cold cathode tube was turned on by applying a tube current of 5 mA to the obtained direct type backlight, and using a two-dimensional color distribution measuring apparatus, 100 frontal luminances were equally spaced on the short direction center line. The luminance average value La and luminance unevenness Lu were obtained according to the following formulas 1 and 2. At this time, the luminance average value was 4,000 cd / m ² and the luminance unevenness was 0.5%.
Luminance average value La = (L1 + L2) / 2 (Formula 1)
Luminance unevenness Lu = ((L1-L2) / La) × 100 (Formula 2)
L1: Average luminance maximum value just above a plurality of cold-cathode tubes installed L2: Average minimum value sandwiched between maximum values Note that luminance unevenness is an index indicating luminance uniformity, and luminance unevenness When it is bad, the figure increases.

<Example 2>
A light diffusing plate and a direct type backlight device were obtained in the same manner as in Example 1 except that the mold part B was used instead of the mold part A. In the obtained light diffusing plate, the surface on which the prism row is formed has a concavo-convex structure having a center line average roughness (Ra (Omax)) of 5.6 μm in the maximum direction (longitudinal direction of the light diffusing plate). It was an uneven surface having
On the other hand, the surface of the obtained light diffusing plate on which no prism array is formed has a center line average roughness (Ra (Imax)) measured in the maximum direction of 0.6 μm and the minimum direction. The center line average roughness (Ra (Imin)) in the (short side direction of the light diffusing plate) was a rough surface of 0.086 μm. Therefore, Ra (Imax) / Ra (Imin) = 7, and the relationship of Ra (Imax)> Ra (Imin) × 1.5 was satisfied. In the obtained direct type backlight device, the average luminance value was 3,960 cd / m ² and the luminance unevenness was 0.6%.

<Comparative Example 1>
In Example 1, a direct type backlight device was obtained in the same manner as in Example 1 except that the cavity surface of the mold to which the mold part A was not attached was polished to be a polished surface.
In the obtained light diffusing plate, the surface on which the prism rows are formed has a concavo-convex structure having a center line average roughness (Ra (Omax)) of 5.9 μm in the maximum direction (longitudinal direction of the light diffusing plate). It was an uneven surface having
On the other hand, the surface of the obtained light diffusing plate where the prism rows are not formed has a center line average roughness (Ra (Imax)) measured in the maximum direction of 0.003 μm and the minimum direction. The center line average roughness (Ra (Imin)) in the (short direction of the light diffusing plate) was 0.003 μm. Therefore, Ra (Imax) / Ra (Imin) = 1, and the relationship of Ra (Imax)> Ra (Imin) × 1.5 was not satisfied. In such a direct type backlight device, the average luminance value was 4,040 cd / m ² and the luminance unevenness was 1.5%.

<Comparative example 2>
In Example 2, the direct-type backlight is the same as in Example 2 except that the cavity surface of the mold to which the mold part B is not attached is further roughened by blasting from the direction perpendicular to the cavity surface. Got the device.
In the obtained light diffusing plate, the surface on which the prism row is formed has a concavo-convex structure having a center line average roughness (Ra (Omax)) of 5.6 μm in the maximum direction (longitudinal direction of the light diffusing plate). It was an uneven surface having
On the other hand, the surface of the obtained light diffusing plate on which no prism array is formed has a center line average roughness (Ra (Imax)) measured in the maximum direction of 10 μm, and the minimum direction (light The center line average roughness (Ra (Imin)) in the short direction of the diffuser plate was 10 μm. Therefore, Ra (Imax) / Ra (Imin) = 1, and the relationship of Ra (Imax)> Ra (Imin) × 1.5 was not satisfied. In such a direct type backlight device, the average luminance value was 3,564 cd / m ² and the luminance unevenness was 2.0%.

<Comparative Example 3>
In Comparative Example 2, a direct type backlight device was obtained in the same manner as in Comparative Example 2 except that the cavity surface was further roughened. In the obtained light diffusing plate, the surface on which the prism row is formed has a concavo-convex structure having a center line average roughness (Ra (Omax)) of 5.6 μm in the maximum direction (longitudinal direction of the light diffusing plate). It was an uneven surface having
On the other hand, the surface of the obtained light diffusing plate on which no prism array is formed has a center line average roughness (Ra (Imax)) measured in the maximum direction of 23 μm and the minimum direction (light The center line average roughness (Ra (Imin)) in the short direction of the diffusion plate was 23 μm. Therefore, Ra (Imax) / Ra (Imin) = 1, and the relationship of Ra (Imax)> Ra (Imin) × 1.5 was not satisfied. In such a direct type backlight device, the average luminance value was 3,366 cd / m ² and the luminance unevenness was 2.5%.

  Table 1 shows the results of Examples 1 and 2 and Comparative Examples 1 to 3.

  As shown in Table 1, in Examples 1 and 2, since the center line average roughness (Ra (Imax)) of the light incident surface satisfies the above relationship, both the average luminance and the luminance unevenness are good. all right. On the other hand, as shown in Comparative Examples 1 to 3, the center line average roughness (Ra (Imax)) of the light incident surface does not satisfy the above relationship, which indicates that the luminance unevenness is insufficient. In particular, in Comparative Examples 2 and 3, the luminance was insufficient.

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

Explanation of symbols

1, 11, 101, 102 Light diffusing plate 1A Light incident surface 1B, 11B Light emitting surface 2 Linear light source 3 Reflecting plate 12 Point light source

Claims (16)

A light diffusing plate having a light incident surface on which light from a light source is incident and a light emitting surface on which light incident from the light incident surface is diffusely irradiated;
The light exit surface is a concavo-convex surface on which a concavo-convex structure having a center line average roughness (Ra (Omax)) of 3.0 μm to 1,000 μm measured in a direction in which the obtained value is maximum,
The light diffusing plate is characterized in that the light incident surface is a rough surface having a center line average roughness (Ra (Imax)) measured in the direction in which the obtained value is maximized, in a range from 0.1 μm to less than 3.0 μm. . The light diffusing plate according to claim 1,
On the light incident surface, the center line average roughness (Ra (Imax)) measured in the maximum direction and the center line average roughness (Ra (Imin)) measured in the direction where the obtained value is the minimum. A light diffusing plate characterized by satisfying the relationship Ra (Imax)> Ra (Imin) × 1.5. In the light diffusing plate according to claim 1 or 2,
The light diffusing plate is characterized in that the concavo-convex structure is a prism row in which a plurality of linear prisms each having a polygonal shape having a concave or convex cross section are arranged in parallel. The light diffusing plate according to claim 3.
Each of the linear prisms has a concave or convex cross section and is formed of a triangle having an apex angle of 60 ° to 170 °, and an interval between the adjacent linear prisms is 20 μm to 700 μm. Board. The light diffusing plate according to claim 3.
Each of the linear prisms includes at least four surfaces,
Of the at least four surfaces, two surfaces and the other two surfaces are inclined in directions opposite to each other with respect to the surface including the normal line of the light incident surface and the longitudinal direction of the linear prism. A light diffusing plate characterized by   The light diffusing plate according to claim 1 or 2, wherein a plurality of light sources are disposed, a reflecting plate that reflects light from these light sources, and direct light from the light source and reflected light from the reflecting plate are diffusely irradiated. A direct-type backlight device comprising:   The light source arranged in multiple numbers, the reflecting plate which reflects the light from these light sources, and the direct light from the said light source, and the reflected light from the said reflecting plate are diffused and radiate | emitted in any one of Claims 3-5 A direct-type backlight device comprising the light diffusion plate described above. The direct type backlight device according to claim 6,
The concavo-convex structure of the light diffusing plate is a prism row in which a plurality of linear prisms each having a concave or convex cross section are arranged in parallel.
Each of the linear prisms is formed so that angles formed by two inclined surfaces constituting the triangle and a plane substantially parallel to the light incident surface are equal.
The direct-type backlight device, wherein the angle increases continuously or intermittently as the position of the linear prism moves away from the light source closest to the linear prism. The direct type backlight device according to claim 6,
The light source is a linear light source arranged in a plurality substantially parallel,
The light diffusion plate has, as a repeating unit, a concave structure or a convex structure having three or more surfaces formed on at least one of the light incident surface and the light emitting surface,
In the cross section of the light diffusing plate in the direction perpendicular to the longitudinal direction of the linear light source, the line segments corresponding to the three or more surfaces of the concave structure or the convex structure include a plurality of line segments having different inclinations. Included,
The inclination of the plurality of line segments is Xn (degree, n is an integer of 1 or more), the distance between the centers of the adjacent linear light sources is a (mm), the center of the linear light source and the light diffusion plate Assuming that the distance from the light incident surface is b (mm),
The direct-type backlight, wherein the inclination Xn of the plurality of line segments satisfies the relationship of 12.5-10 × (b / a) <Xn <85-25 × (b / a) in all n apparatus. The direct type backlight device according to claim 6,
The light source is a plurality of point light sources arranged,
The light diffusion plate has, as a repeating unit, a concave structure or a convex structure having three or more surfaces formed on at least one of the light incident surface and the light emitting surface,
In a cross section of the light diffusing plate in a plane including the normal line of the light diffusing plate, the line segments corresponding to the three or more surfaces of the concave structure or the convex structure include two or more types of line segments having different inclinations. Contains
The inclination of the plurality of line segments is Xn (degree, n is an integer of 1 or more), the average distance between the adjacent point light sources in the plurality of point light sources is a (mm), and the center of the point light source And the distance between the light incident surface of the light diffusion plate and b (mm),
The direct type, wherein the slopes Xn of the plurality of line segments satisfy the relationship of 12.5-11 × (b / a) <x <85-28.5 × (b / a) in all n Backlight device. The direct type backlight device according to claim 9 or 10,
The repeating unit is a convex structure;
The light diffusing plate having such a convex structure is obtained by making a V-shaped cut in the prism row in a direction different from the longitudinal direction of the linear prism constituting the prism row. Type backlight device. The direct type backlight device according to claim 11,
The direct-type backlight device, wherein the convex structure is a pyramid or a truncated pyramid. The direct type backlight device according to claim 9 or 10,
The repeating unit is a concave structure;
The light diffusing plate having such a concave structure has a convex shape obtained by making a V-shaped cut in the prism row in a direction different from the longitudinal direction of the linear prism constituting the prism row. A direct-type backlight device obtained by transferring the convex shape of a transfer member. The direct type backlight device according to claim 13,
The direct-type backlight device, wherein the concave structure is a pyramid or a truncated pyramid shape. The direct type backlight device according to any one of claims 6 to 14,
The light diffusing plate is made of a transparent resin in which a light diffusing agent is dispersed, and the total light transmittance of the dispersion is 60% to 98%. The direct type backlight device according to claim 15,
A direct type backlight device, wherein the haze of the dispersion is 20% to 100%.

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