JPWO2008123280A1 - Direct backlight unit - Google Patents

Abstract

Provided is a direct type backlight device having high energy efficiency and less periodic luminance unevenness. A direct type backlight device including a plurality of linear light sources, a light diffusion plate, and the like, wherein the linear light source has an outer diameter of 5 mm to 30 mm, and is at least one of the light emitting surface and the light incident surface Has a concavo-convex structure formed in at least a part thereof, and the concavo-convex structure in a region obtained by projecting the outer diameter of the linear light source perpendicularly to the light diffusion plate and an intermediate position between the linear light sources adjacent to each other. And a concave-convex structure in a region having the same width as the outer diameter of the linear light source has a different shape.

Description

  The present invention relates to a direct type backlight device.

  Conventionally, as a backlight device for a liquid crystal display device, for example, a reflecting plate, a plurality of linear light sources arranged substantially in parallel, direct light from these linear light sources and reflected light from the reflecting plate are used. A direct type backlight device that includes a light diffusing plate that is incident from a light incident surface and is emitted from a light emitting surface to be a light emitting surface in this order is widely used. On the light emitting surface of such a direct type backlight device, high luminance can be easily obtained, while the luminance of the portion directly above the linear light source on the light emitting surface is high, and the luminance tends to decrease as the distance from the portion directly above is increased. , Periodic luminance unevenness may occur on the surface.

  Therefore, in a direct type backlight device, as a linear light source, cold cathode tubes, which are usually 4 mm or less in diameter, can be arranged in parallel as closely as possible to reduce the degree of periodic luminance unevenness. It is preferred. However, since the energy efficiency of the cold cathode fluorescent lamp itself is low, when the number of cold cathode fluorescent lamps arranged in this way reaches a large number, the energy efficiency of the backlight device is significantly lowered.

  As a measure for improving the energy efficiency, it is conceivable to use a hot cathode tube that is thicker and more energy efficient than a cold cathode tube. However, in that case, it is necessary to use a hot cathode tube thicker than the cold cathode tube at a distance from the cold cathode tube, and as a result, the periodic luminance unevenness becomes larger than when the cold cathode tube is used.

  As a method for reducing the luminance unevenness of a backlight device using a cold cathode tube, a light amount correction pattern in a striped pattern or a dot shape is printed on a light diffusion plate to reduce the amount of light irradiated on the portion directly above the linear light source. A method of relatively increasing the amount of light irradiated between linear light sources is disclosed (Patent Document 1: Japanese Patent Laid-Open No. 6-273760). However, this method does not sufficiently improve even the nonuniformity in the case where a hot cathode tube is used instead of the cold cathode tube.

  Accordingly, an object of the present invention is to provide a direct type backlight device having high energy efficiency and less periodic luminance unevenness.

  As a result of diligent research to solve the above problems, the present inventors have determined that the shape of the light diffusing plate is a specific shape even when a linear light source such as a hot cathode tube having a large diameter is used. As a result, it was found that the luminance unevenness can be reduced, and the present invention has been completed based on this finding.

That is, according to the present invention, the following is provided:
[1] A plurality of linear light sources arranged substantially parallel to each other, a reflecting plate that reflects light from these linear light sources, direct light from the linear light source, and reflected light from the reflecting plate A direct-type backlight device including a light diffusing plate that is incident from a light incident surface and that is diffusely irradiated from a light emitting surface, wherein the linear light source has an outer diameter of 5 mm to 30 mm, and the light emitting surface and the light emitting surface In at least one of the light incident surfaces, a concavo-convex structure is formed in at least a portion thereof, and in the light diffusing plate, when the outer diameter of the linear light source is projected perpendicularly to the light diffusing plate, The uneven structure of the projected portion is different from the uneven structure of the portion having the same width as the outer diameter of the linear light source in the light diffusing plate, the center being an intermediate position between adjacent linear light sources. Directly shaped bar characterized by its shape Cuck light device.
[2] The direct type backlight device, wherein the linear light source is a hot cathode tube.
[3] The concavo-convex structure is a prism row in which a plurality of linear prisms extending along the longitudinal direction of the linear light source are arranged substantially in parallel, and the linear prism is perpendicular to the longitudinal direction of the linear light source. The straight type backlight device is characterized in that the cross section is a curved or polygonal convex portion, a substantially flat portion, or a combination thereof.
[4] A cross section of the linear prism perpendicular to the longitudinal direction of the linear light source includes two or more types of convex portions having different shapes, and the abundance ratio of the two or more types of convex portions is the linear light source. The direct-type backlight device, which changes continuously or stepwise as it moves away from the display.
[5] The cross section of the linear prism perpendicular to the longitudinal direction of the linear light source includes both the convex portion and the substantially flat portion, and the abundance ratio thereof is continuous as the distance from the linear light source increases. The direct type backlight device, which changes in a stepwise or stepwise manner.
[6] An optical sheet provided on the light exit surface side of the light diffusing plate is further provided, and an arbitrary linear light source is defined as A in a cross section perpendicular to the longitudinal direction of the linear light source. An adjacent linear light source is set as B, an intermediate position between the linear light source A and the linear light source B projected on the light incident surface is set as X, and the linear light source A and the linear light source B are set as X. And an arbitrary point on the light incident surface closer to the linear light source A than the intermediate position X is P, the center of the linear light source A is C, and the center C The total light transmittance Tp at the point P of light incident from the center C to the direction of the point P is smaller than the total light transmittance Tx at the point X of light incident from the center C toward the intermediate position X. The direct type backlight device characterized by the above.
[7] The length of the line segment connecting the center C and the point P is LCP, the point where the center C is projected perpendicularly to the light incident surface is Q, and the center C and the point Q are connected. The length of the line segment is LCQ, and the total light transmittance at the point Q of the light incident from the center C in the direction of the point Q is Tq. 0.2 × (Tq · LCP / LCQ) ≦ Tp ≦ 5 0.0 × (Tq · LCP / LCQ) satisfying the relationship, the direct type backlight device.
[8] The direct-type backlight device, wherein the concavo-convex structure is formed on both at least a part of the light emitting surface and at least a part of the light incident surface of the light diffusing plate.
[9] The concavo-convex structure is a prism row in which a plurality of linear prisms extending along the longitudinal direction of the linear light source are arranged substantially in parallel, and at least a part thereof is perpendicular to the longitudinal direction of the linear light source. The direct-type backlight device is characterized in that a simple cross section is a polygonal shape, and the polygonal shape is symmetrical about an axis parallel to the thickness direction of the light diffusion plate in the cross section.
[10] The inclined surface of the linear prism on at least one of the light emitting surface and the light incident surface, and the light diffusion as it moves away from the linear light source and toward an intermediate position between the linear light sources adjacent to each other The direct type backlight device according to claim 1, wherein an angle formed by a plane perpendicular to the thickness direction of the plate increases continuously or stepwise.
[11] Two or more types of lines in the linear prism on at least one of the light emitting surface and the light incident surface as they move away from the linear light source and move toward an intermediate position between the linear light sources adjacent to each other. The mixing ratio of the linear prisms changes continuously or stepwise, and the ratio of the linear prisms having a large inclination angle increases continuously or stepwise toward the intermediate position of the linear light sources adjacent to each other. The direct type backlight device.
[12] A liquid crystal display device comprising the direct type backlight device. Since such a liquid crystal display device includes the direct type backlight device of the present invention, there is an effect that energy consumption is lower than luminance and luminance unevenness is small.

  The direct type backlight device of the present invention includes a linear light source having a diameter equal to or larger than a specific diameter, such as a hot cathode tube, and has a specific light diffusing plate shape, so that energy efficiency can be improved, and There is an effect that periodic luminance unevenness is small.

FIG. 1 is a perspective view showing an outline of a direct type backlight device of the present invention. FIG. 2 is a partial cross-sectional view for specifically explaining an example of the surface shape of the light diffusion plate of the direct type backlight device of the present invention. FIG. 3 is a partial cross-sectional view showing an example of the uneven structure of the light diffusing plate. FIG. 4 is a partial cross-sectional view showing another example of the uneven structure of the light diffusing plate. FIG. 5 is a partial cross-sectional view showing another example of the uneven structure of the light diffusing plate. FIG. 6 is a partial cross-sectional view showing another example of the uneven structure of the light diffusing plate. FIG. 7 is a partial cross-sectional view showing another example of the uneven structure of the light diffusing plate. FIG. 8 is a partial cross-sectional view showing another example of the uneven structure of the light diffusing plate. FIG. 9 is a partial cross-sectional view showing another example of the uneven structure of the light diffusing plate. FIG. 10 is a partial cross-sectional view showing another example of the uneven structure of the light diffusing plate. FIG. 11 is a partial cross-sectional view showing another example of the uneven structure of the light diffusing plate. FIG. 12 is a partial cross-sectional view showing another example of the uneven structure of the light diffusing plate. FIG. 13 is a partial cross-sectional view showing another example of the uneven structure of the light diffusing plate. FIG. 14 is a cross-sectional view schematically illustrating the direct type backlight device according to Embodiment 1 of the present application. FIG. 15 is a partial cross-sectional view illustrating an outline of the light diffusion plate of the direct type backlight device according to the first embodiment of the present application. FIG. 16: is a fragmentary sectional view which shows the uneven structure of the light diffusing plate of the direct type backlight apparatus based on this-application Example 1. FIG. FIG. 17: is a fragmentary sectional view which shows the outline of the light diffusing plate of the direct type | mold backlight apparatus which concerns on this-application Example 2. FIG. FIG. 18 is a partial cross-sectional view showing the uneven structure of the light diffusing plate of the direct type backlight device according to Example 3 of the present application. FIG. 19 is a partial cross-sectional view for specifically explaining an example of optical properties of the light diffusion plate of the direct type backlight device of the present invention. FIG. 20 is a partial cross-sectional view illustrating an outline of the light diffusing plate of the direct type backlight device according to Embodiment 3 of the present application. FIG. 21 is a cross-sectional view schematically illustrating a direct type backlight device according to Embodiment 6 of the present application. FIG. 22 is a partial cross-sectional view illustrating an outline of a light diffusing plate of a direct type backlight device according to Embodiment 6 of the present application. FIG. 23 is a partial cross-sectional view showing the concavo-convex structure of the light diffusion plate of the direct type backlight device according to Example 6 of the present application.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a perspective view showing an outline of a direct type backlight device according to an embodiment of the present invention. The direct type backlight device according to the present embodiment includes a plurality of linear light sources 102 arranged substantially parallel to each other, a reflecting plate 103 that reflects light from these linear light sources 102, and linear light sources 102. A light diffusing plate 101 that diffuses and irradiates direct light and reflected light from the reflecting plate 103. Since the embodiment shown in FIG. 1 is a schematic diagram for showing these positional relationships, in FIG. 1, the light diffusing plate has a prismatic uneven structure having a sawtooth cross section only on the upper main surface, that is, the exit surface. Although shown, the direct type backlight device of the present invention has a specific structure to be described later on both the exit surface and the entrance surface of the light diffusion plate 101.

  In the present specification, unless otherwise specified, the “up” and “down” directions mean “up” and “down” in a state where the direct-type backlight device is placed so that its light emission surface is horizontally upward. It means the “down” direction and corresponds to the upward direction and the downward direction in the drawings of FIGS.

  In the direct type backlight device of the present embodiment, the linear light source 102 has an outer diameter of 5 mm to 30 mm, preferably a hot cathode tube. By adopting this structure, a backlight device with high energy efficiency can be obtained. Further, the linear light source 102 preferably has a luminous efficiency of 60 (Lm / W) or more, a length of 700 mm or more, and even when both ends thereof are supported, the bending does not occur by 2 mm or more. preferable.

  As the shape of the linear light source 102, in addition to a straight line shape, two parallel tubes are connected by one approximately semicircle to form a U-shape, and three parallel tubes are approximately two semicircles. N-shapes that are connected by one, and W-shapes that are formed by connecting four parallel pipes by three approximately semicircles.

  The distance between the centers of adjacent linear light sources 102 is preferably 35 mm to 200 mm, and more preferably 40 mm to 150 mm. By setting the distance within the above range, the power consumption of the direct type backlight device can be reduced, the assembly of the device can be facilitated, and the luminance unevenness of the light emitting surface can be suppressed.

  The number of the linear light sources 102 is not particularly limited. For example, when the direct type backlight device of the present invention is used for a 32-inch liquid crystal display device, the number of linear light sources is, for example, an even number such as 12, 8, 4, 2, or an odd number. It can be a book.

  As a material of the reflecting plate 103, 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 103 is preferably white from the viewpoint of improving the luminance uniformity, but white and silver may be mixed in order to highly balance the luminance and the luminance uniformity.

The light diffusion plate 101 is a plate material that diffuses and irradiates incident light.
As a material constituting the light diffusing plate, glass, a mixture of two or more kinds of resins that are difficult to mix, a material in which a light diffusing agent is dispersed in a transparent resin, one kind of transparent resin, and the like can be used. Among these, a resin is preferable because it is lightweight and easy to mold, and one kind of transparent resin is preferable from the viewpoint that luminance can be easily improved, and adjustment of total light transmittance and haze is easy. From the viewpoint, a transparent resin in which a light diffusing agent is dispersed is preferable.

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

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

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

  The resin having an alicyclic structure is a resin having an alicyclic structure in the main chain and / or side chain. From the viewpoint of mechanical strength, heat resistance, etc., a resin containing an alicyclic structure in the main chain is particularly preferred. Examples of the alicyclic structure include a saturated cyclic hydrocarbon (cycloalkane) structure and an unsaturated cyclic hydrocarbon (cycloalkene, cycloalkyne) structure. From the viewpoint of mechanical strength, heat resistance and the like, a cycloalkane structure and a cycloalkene structure are preferable, and among them, a cycloalkane structure is most preferable. When the number of carbon atoms constituting the alicyclic structure is usually in the range of 4 to 30, preferably 5 to 20, more preferably 5 to 15, the mechanical strength, heat resistance and light diffusion plate Formability characteristics are highly balanced and suitable.

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

  Specific examples of the resin having an alicyclic structure include (1) ring-opening polymer of norbornene monomer and ring-opening copolymer of 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 with other monomers copolymerizable with it Vinyl alicyclic hydrocarbon polymers such as hydrogenated products of the body of the aromatic ring; and the like.

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

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

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

  The ratio of the light diffusing agent dispersed in the transparent resin can be appropriately selected according to the thickness of the light diffusing plate, the interval between the linear light sources, and the like. Usually, the total light transmittance of the dispersion is 60% to 98%. It is preferable to adjust the content of the light diffusing agent so as to be, and it is more preferable to adjust the content of the light diffusing agent to be 65% to 95%. By setting the total light transmittance within the above preferable range, 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 101 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 101 will be described.
FIG. 2 is an elevational partial sectional view for more specifically explaining the surface shape of the light diffusion plate 101 of the direct type backlight device according to the embodiment of FIG. For convenience of explanation, in FIG. 2, only two adjacent linear light sources 102 a and 102 b among the plurality of linear light sources 102 are partially illustrated.

  The light diffusing plate 101 includes a light incident surface S260 on which light from the linear light source 102 is incident, and a light emitting surface S250 that diffuses and irradiates light incident from the light incident surface, and includes the light emitting surface and the light. An uneven structure is formed on at least a part of the incident surface.

  In the light diffusing plate, when the outer diameter of the linear light source is projected perpendicularly to the light diffusing plate, the projected portion of the uneven structure and the light diffusing plate are adjacent to each other in the linear shape. The concavo-convex structure of the part having the same width as the outer diameter of the linear light source and having an intermediate position of the light source as a center has a different shape. Here, “with different shapes” includes a case where the shape of the concavo-convex structure is different on at least one of the light incident surface and the light emitting surface of the light diffusion plate. In addition, the “different shape” means, for example, that when the concavo-convex structure is composed of a plurality of convex portions (prism portions) and each convex portion is a polygon, the apex angle of the convex portion exceeds ± 1 degree. Such a shape. In this case, the aspect in which the shape of the concavo-convex structure is different includes a case in which at least one of the plurality of convex portions has a different shape.

In the example shown in FIG. 2, the uneven structure in the regions R271, R281, R273, and R283 obtained by projecting the outer diameters of the linear light sources 102a and 102b perpendicularly to the light diffusion plate 101, and the intermediate position 241 between the linear light sources 102a and 102b. The uneven structure in the regions R272 and R282 on the light diffusion plate having the same width as that of the linear light source 102 in the center is different. That is, the following conditions (i) and (ii):
(i) R272 has an uneven structure different from R271 and R273,
(ii) R282 has a concavo-convex structure different from that of R281 and R283, and therefore satisfies the following condition: “Concavity and convexity in the region where the outer diameter of the linear light source is projected perpendicularly to the light diffusion plate” The structure and the concavo-convex structure in the region on the light diffusing plate having the same width as the outer diameter of the linear light source and the center position between the adjacent linear light sources are different.

  The structure of other regions (that is, regions not included in the regions R271 to R273 and R281 to R283) of the light incident surface S260 and the light emitting surface S250 of the light diffusion plate 101 is not particularly limited. A region including a concavo-convex structure in a region group including a region obtained by projecting the outer diameter of the light source perpendicularly to the light diffusing plate, and a region on the light diffusing plate having the same width as the outer diameter of the linear light source, centered on the intermediate position of the linear light source The uneven structure in the group can be different.

  More specifically, for example, as shown in FIG. 2, each of the light incident surface S260 and the light emitting surface S250 includes a region group R251, R261, R253 including a region obtained by projecting the linear light source outer diameter perpendicularly to the light diffusion plate. R263 is equally divided into region groups R252 and R262 including the region on the light diffusion plate having the same width as the linear light source with the intermediate position of the linear light source as the center, and the uneven structure is different between these region groups Can be.

  Specifically, “the uneven structure is different” between the region groups R251, R261, R253, and R263 and the region groups R252 and R262 includes, for example, the following modes:

(1) R251-R252-R253: Uneven structure A-flat surface-uneven structure A
R261-R262-R263: Flat surface-Flat surface-Flat surface (2) R251-R252-R253: Flat surface-Uneven structure B-Flat surface R261-R262-R263: Flat surface-Flat surface-Flat surface (3) R251 -R252-R253: concavo-convex structure A- concavo-convex structure B- concavo-convex structure A
R261-R262-R263: Flat surface-Flat surface-Flat surface (4) R251-R252-R253: Flat surface-Uneven structure B-Flat surface R261-R262-R263: Uneven structure A-Flat surface-Uneven structure A
(5) R251-R252-R253: Uneven structure A- Uneven structure A- Uneven structure A
R261-R262-R263: Flat surface-Uneven structure B-Flat surface (6) R251-R252-R253: Uneven structure A-Uneven structure A-Uneven structure A
R261-R262-R263: Uneven structure B-flat surface-uneven structure B
(7) R251-R252-R253: Flat surface-Uneven structure B-Flat surface R261-R262-R263: Uneven structure A-Uneven structure A-Uneven structure A
(8) R251-R252-R253: Uneven structure B-flat surface-uneven structure B
R261-R262-R263: concavo-convex structure A- concavo-convex structure A- concavo-convex structure A
(9) R251-R252-R253: Uneven structure B- Uneven structure C- Uneven structure B
R261-R262-R263: concavo-convex structure A- concavo-convex structure A- concavo-convex structure A
(10) R251-R252-R253: Uneven structure A- Uneven structure A- Uneven structure A
R261-R262-R263: concavo-convex structure B- concavo-convex structure C- concavo-convex structure B
(11) R251-R252-R253: Uneven structure A-flat surface-uneven structure A
R261-R262-R263: concavo-convex structure B- concavo-convex structure C- concavo-convex structure B
(12) R251-R252-R253: Uneven structure A- Uneven structure D- Uneven structure A
R261-R262-R263: concavo-convex structure B- concavo-convex structure C- concavo-convex structure B
(13) In each of the above (1) to (12), the structure of R251-R252-R253 and the structure of R261-R262-R263 are interchanged

  In the above, the uneven structure A to the uneven structure D indicate different shapes.

The light diffusing plate may be provided with a concavo-convex structure only on one surface thereof as in the above aspects (1) to (3), but preferably the concavo-convex structure is at least one of the light exit surfaces of the light diffusing plate. And at least part of the light incident surface. In particular, on the light incident surface, a concavo-convex structure is provided at least in a region (region R282 in FIG. 2) on the light diffusion plate incident surface having the same width as that of the linear light source and centered on the intermediate position of the linear light source. It is preferable.
By providing a concavo-convex structure on the light incident surface side, the Fresnel reflection is reduced when light from the linear light source is incident on the region such as the region R282, and when light from the linear light source is incident on the region. It is possible to prevent an increase in the projected area of the linear light source. Thereby, the light incident amount per unit area of the light incident surface between the linear light sources can be improved, and the dark part between the linear light sources can be brightened.
On the other hand, by providing a concavo-convex structure on at least a part of the light emitting surface, light incident from the light incident surface can be refracted and emitted in a desired direction, and with respect to vertical incident light from a linear light source Light can be returned into the backlight device using total reflection, and the bright portion directly above the linear light source can be darkened. From the above, the luminance unevenness can be further reduced.

  In the present invention, the concavo-convex structure on the light diffusing plate is specifically a line extending substantially parallel to the longitudinal direction of the linear light source 102 (within a range of parallel ± 5 °) as shown in FIG. And prisms in which the prisms are arranged substantially in parallel, and the cross section perpendicular to the longitudinal direction of the linear light source 102 has various cross-sectional shapes. The angle formed between the linear light source 102 and the linear prism may be within the range of the parallel ± 60 °.

  Examples of the cross-sectional structure include a convex portion having a curved shape, a convex portion having a polygonal shape, a substantially flat portion, and a combination shape thereof. Examples of the convex portion including the curved line include a convex portion including a curved line such as an arc, an elliptical arc, a parabolic arc, and a curved line in which these are distorted. Examples of the polygonal convex portions include various polygonal convex portions such as triangles, trapezoids and other quadrangular shapes, pentagons, hexagons, heptagons, etc. Particularly, the left and right base angles are substantially equal (± 10 °). The cross-sectional structure is preferably symmetric about an axis parallel to the thickness direction of the light diffusion plate in the cross-section. By adopting such a cross-sectional structure, it is possible to obtain advantages such as easy design and no unevenness in luminance even when viewed from the left or right. Further, when the emission surface of the backlight device is upright in the direction in which the prism rows are horizontal, the vertical direction (that is, when the light emission surface is observed from the upper right direction in the drawing in FIG. 2 and the upper left direction) (When the light exit surface is observed), the luminance distribution can be made symmetric.

The following can be mentioned as an example of a more specific cross-sectional structure.
As shown in FIG. 3, in the first example of the cross-sectional structure, the polygonal convex portion is a triangle 321 having substantially equal left and right base angles 322 and 323, and the base corner portions of adjacent triangles 321 touch each other. It is the structure arranged so.

  As shown in FIG. 4, the second example of the cross-sectional structure is a trapezoid 421 in which the polygonal convex portion has a substantially flat flat portion (top carrier portion) 422 on the top, and the bottom of the adjacent trapezoid 421. It is the structure arrange | positioned so that a corner | angular part may mutually contact.

  As shown in FIG. 5, the third example of the cross-sectional structure is a triangle 521 in which the polygonal convex portions have substantially equal left and right base angles, and a substantially flat portion 522 is provided between adjacent triangles 521. This is a combined structure in which a triangle 521 and a substantially flat portion 522 are aligned.

  As shown in FIG. 6, the fourth example of the cross-sectional structure is a pentagon in which a polygonal convex portion is obtained by adding a triangle 621 having a base angle smaller than the base angle of the trapezoid 622 to the top support portion of the trapezoid 622. Thus, the base corner portions of adjacent trapezoids 622 are arranged so as to contact each other.

  As shown in FIG. 7, the fifth example of the cross-sectional structure is a pentagon in which a polygonal convex portion is obtained by adding a triangle 721 having a base angle wider than the base angle of the trapezoid 722 to the top support portion of the trapezoid 722. Thus, the base corners of adjacent trapezoids 722 are arranged so as to contact each other.

  As shown in FIG. 8, the sixth example of the cross-sectional structure is a structure in which convex portions having a curved shape are semicircular 821 and adjacent semicirculars 821 are in contact with each other.

  As shown in FIG. 9, the seventh example of the cross-sectional structure is a structure in which the convex portion including the curve is a semi-elliptical shape 921 and adjacent semi-elliptical shapes 921 are in contact with each other.

  As shown in FIG. 10, the eighth example of the cross-sectional structure is a structure in which a convex portion including a curve is a parabolic arc 1021 and adjacent parabolic arcs 1021 are in contact with each other.

  As shown in FIG. 11, the ninth example of the cross-sectional structure is a structure in which convex portions having a curved shape are alternately combined with a semicircular shape 1121 and a semielliptical shape 1122.

  As shown in FIG. 12, in the tenth example of the cross-sectional structure, the convex portion including the curve includes a semicircle 1221 and a semi-elliptical 1222, and a plurality of semi-circles 1221 and semi-elliptical 1222 are provided. It is a combined structure.

  As shown in FIG. 13, the eleventh example of the cross-sectional structure is a structure in which convex portions having a curved shape are alternately combined with a semicircle 1321 and a triangle 1322.

In the present invention, the preferable height of the concavo-convex structure is a maximum value of Ra (max) among the center line average roughness Ra measured along various directions on the light incident surface or light emitting surface of the light diffusion plate. ), Ra (max) is 1 μm to 1,000 μm.
In the present specification, the “substantially flat portion” may have fine irregularities on the surface. For example, in the shape shown in FIG. 5, no unevenness is shown on the substantially flat portion 522, but relatively fine unevenness may be provided in this portion as compared with the triangle 521. A preferable height of the fine irregularities is 0.0001 μm to 3 μm as Ra (max). Further, the height of the fine unevenness can be in the range of 0.0001% to 5% with respect to Ra of the uneven structure.

  In the embodiment, a region group including a region obtained by projecting the linear light source outer diameter perpendicularly to the light diffusing plate, and a light diffusing plate having the same width as the outer diameter of the linear light source with the intermediate position of the linear light source as the center. Different concavo-convex structures are provided in the two region groups including the region group including the regions. However, as another embodiment of the present invention, arrangement of the concavo-convex structure different from this can be performed. For example, the cross section of the concavo-convex structure perpendicular to the longitudinal direction of the linear light source includes two or more types of convex portions having different shapes, and the abundance ratio of the two or more types of convex portions is further away from the linear light source. It can be set as the aspect which changes. More preferably, at least one of the linear prisms on either the light exit surface or the light entrance surface is moved away from the linear light source and toward an intermediate position between the linear light sources adjacent to each other. The mixing ratio of linear prisms changes continuously or stepwise, and the ratio of linear prisms having a large inclination angle increases continuously or stepwise toward the intermediate position of the linear light sources adjacent to each other. be able to. By adopting such a linear prism arrangement, the change in the shape of the concavo-convex structure gradually changes as it moves away from the linear light source, and as a result, the luminance is higher than when the concavo-convex shape changes abruptly. Unevenness can be reduced.

  Specifically, for example, as shown in FIG. 16, the concavo-convex structure has a unit in which convex portions 1621a and 1621b having different shapes are arranged at a predetermined ratio (1: 4 in FIG. 16). The unit is repeated, and the abundance ratio of the convex portions 1621a and 1621b can be changed as the distance from the linear light source is further increased.

  The change in the abundance ratio can be continuous or stepwise. For example, as shown in FIG. 15, a distance corresponding to an intermediate position 1441 between the centers of adjacent linear light sources 1402a and 1402b and the center of the linear light source is set to a plurality of zones (in FIG. 15, A, B, C and D zones), and the abundance ratio of the two or more types of convex portions is set to a predetermined value for each region corresponding to each zone of the light incident surface and / or the light exit surface of the light diffusing plate 1401. Can be set. The number of these zones is not particularly limited, but is not limited to the above, and may be increased to 15 to 20 levels.

  As another arrangement of the concavo-convex structure, for example, a cross section of the concavo-convex structure perpendicular to the longitudinal direction of the linear light source includes both the convex portion and the substantially flat portion, and the abundance ratio thereof is determined by the linear light source. It can be set as the aspect which changes continuously or in steps as it distances from.

  Specifically, for example, as shown in FIG. 18, as the concavo-convex structure, the unit is a state in which convex portions 1821 a and flat portions 1821 b that are substantially flat portions are alternately arranged, and this unit is repeated, and further, As the distance from the light source increases, the width 1822b of the flat portion 1821b can be changed continuously or stepwise.

  Here, the width 1822b of the flat portion 1821b is set to a predetermined value for each of a plurality of zones on the light incident surface and / or the light exit surface of the light diffusing plate, as described above with reference to FIG. Can also achieve intermittent changes. The number of these zones is not particularly limited, but is not limited to four zones, and may be increased to 15 to 20 levels. For example, as shown in FIG. 19, the flat portion 1821 b has a flat portion 1821 b according to the distance Ln from the linear light source on the light diffusion plate or according to the angle θs with respect to the surface of the light diffusion plate and the nearest linear light source. The width 1822b can be continuously changed to achieve a continuous change.

  As another arrangement of the concavo-convex structure, the linear prism of at least one of the light exit surface and the light entrance surface is moved away from the linear light source and toward an intermediate position between the linear light sources adjacent to each other. The angle formed by the inclined surface and the plane perpendicular to the thickness direction of the light diffusing plate may be increased continuously or stepwise.

  Specifically, for example, as in the other examples described above, the light incident surface and / or light exit surface of the light diffusing plate is divided into a plurality of zones, and linear prisms having the same structure are arranged in each zone. However, as the zone farther from the linear light source is arranged so that the angle formed by the slope of the linear prism and the plane perpendicular to the thickness direction of the light diffusing plate increases, the angle increases stepwise. A configuration can be obtained. Even with such a configuration, the change in the shape of the concavo-convex structure gradually changes as the distance from the linear light source increases, and as a result, the luminance unevenness is reduced compared to the case where the concavo-convex shape changes suddenly. can do.

  As a further preferred embodiment of the direct type backlight device of the present invention, the optical sheet further provided on the light emitting surface side of the light diffusing plate, and the uneven structure has a predetermined preferable total light transmittance distribution described in detail below. Can be mentioned. That is, in the direct type backlight device, in the cross section perpendicular to the longitudinal direction of the linear light source, an arbitrary linear light source is A, a linear light source adjacent to the linear light source A is B, and the linear light source An intermediate position obtained by projecting an intermediate position between A and the linear light source B onto the light incident surface is X, and is positioned between the linear light source A and the linear light source B, and from the intermediate position X. Also, an arbitrary point on the light incident surface closer to the linear light source A is P, the center of the linear light source A is C, and the point of light incident in the direction of the point P from the center C The total light transmittance Tp at P is preferably smaller than the total light transmittance Tx at the point X of light incident from the center C toward the intermediate position X. At this time, it is more preferable that an uneven structure is provided on the surface of the light diffusing plate so that the point P becomes substantially higher as it approaches the point X. Note that “substantially higher” mainly includes a case where the level increases continuously or stepwise, but also includes a case where the level becomes slightly lower. Such a “substantially higher” aspect is preferably satisfied in a range of at least 50% of the entire area of the light incident surface.

  The preferred embodiment will be described with reference to FIG. FIG. 19 shows the relationship between the angles on a cross section perpendicular to the longitudinal direction of the linear light source. In the example of FIG. 19, the linear light source 102a and the linear light source 102b are illustrated as the linear light source A and the linear light source B mentioned above. A point of intersection between a line 1941 perpendicular to the light diffusing plate 101 and a light incident surface S1960, which is a bisector of a distance L between the center 1973a of the linear light source 102a (= the point C) and the center 1973b of the linear light source 102b. 1974 corresponds to the point X. The total light transmittance at the point X of light incident on the point X from the center 1973a (point C) of the linear light source 102a (linear light source A) is Tx. On the other hand, the total light transmittance at the point P of light incident from the center 1973a (point C) to the point P on the light incident surface closer to the linear light source 1973a (A) than the point X is Tp. Here, when Tp is smaller than Tx, the above-described preferable mode is obtained. Furthermore, as point P approaches X, Tp becomes substantially higher, which is a more preferable aspect. By setting it as such an aspect, a high brightness | luminance uniformity can be achieved.

  The optical sheet may be a single sheet or a plurality of sheets. The optical sheet preferably includes one or more sheets having a function as a light direction conversion element. A sheet having a function as a light beam direction conversion element is a sheet having a different incident angle of incident light and an outgoing angle of outgoing light, and it is sufficient that the incident light and the outgoing light have different peak directions. It may diffuse and have a distribution.

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

  In a more preferred embodiment of the direct type backlight device of the present invention, the length of the line segment connecting the center C and the point P is LCP, and the point obtained by projecting the center C perpendicularly to the light incident surface is Q LCQ is the length of the line segment connecting the center C and the point Q, Tq is the total light transmittance at the point Q of the light incident from the center C in the direction of the point Q, 0.2 It is preferable to satisfy the relationship of × (Tq · LCP / LCQ) ≦ Tp ≦ 5.0 × (Tq · LCP / LCQ).

  The further preferable aspect will be described with reference to FIG. 19 again. In the example of FIG. 19, the length of the line segment 1943 connecting the point P and the point 1973a (point C) corresponds to the above-described length LCP. On the other hand, the intersection of the straight line 1945 passing through the point 1973a (point C) and perpendicular to the light diffusing plate 101 and the light incident surface S1960 becomes the point Q, and all rays at the point Q of the light incident in the direction from the point C to the point Q. The transmittance is Tq, and the distance between CQs is LCQ. Here, when Tp, Tq, LCP, and LCQ satisfy the above relationship, the above-described preferred embodiment can be obtained, and a higher luminance uniformity can be achieved. The relationship is preferably established over the entire surface of the light diffusing plate, but a favorable effect can be obtained when the relationship is established with an area of 50% of the entire surface of the light diffusing plate.

  The direct type backlight device of the present invention is not limited to the above embodiment, and can be changed within an equivalent range. Moreover, other arbitrary components can be further included. For example, in the direct type backlight device according to each of the above embodiments, an optical member for further improving luminance and luminance uniformity may be appropriately disposed. Examples of such an optical member include a diffusion sheet and a prism sheet. These optical members can be provided on the light exit surface side of the light diffusion plate, for example. In addition, a housing for forming the backlight device, a power supply device, and the like can be provided as appropriate. The direct type backlight device of the present invention can also be suitably used for a method of controlling turning on and off of the light source according to the brightness in the screen of the liquid crystal display device.

  The liquid crystal display device of the present invention includes the direct type backlight device of the present invention. The liquid crystal display device of the present invention includes, for example, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a hybrid alignment nematic (HAN) mode, a vertical alignment (VA) mode, a multi-domain vertical alignment (MVA) mode, an in-plane It can be based on display modes such as switching (IPS) mode, optically compensated birefringence (OCB) mode.

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

Production Example 1 (Pellet A for Light Diffusing Plate)
A resin having an alicyclic structure (Zeon Corporation, ZEONOR 1060R, water absorption 0.01%) as a transparent resin is kneaded with a twin-screw extruder, extruded into a strand, cut with a pelletizer, and used for a light diffusion plate Pellets A were produced. Using this light diffusing plate pellet A as a raw material, a 100 mm × 50 mm test plate having a smooth thickness of 2 mm on both sides was molded 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 92% and a haze of 0.3%.

Production Example 2 (Pellet B for Light Diffusing Plate)
Instead of the resin, 99.9 parts of the resin and 0.1 part of fine particles made of a cross-linked product of a polysiloxane polymer having an average particle diameter of 2 μm as a light diffusing agent were mixed, and the same method as in Production Example 1 Thus, a light diffusion plate pellet B was produced. A test plate similar to that of Production Example 1 was prepared using the light diffusion plate pellet B as a raw material, and the total light transmittance and haze were measured by the same method. The test plate had a total light transmittance of 94% and a haze of 89%.

<Example 1>
A backlight device schematically shown in FIG. 14 was produced. A reflective sheet (manufactured by Tsujiden Co., Ltd., RF188) is attached to the inner surface of an aluminum case (not shown) having an inner dimension width of 730 mm, a depth of 405 mm, and a depth of 32.5 mm to form a reflector 1403 having a diameter of 15.5 mm, Four 800 mm long hot-cathode tubes (manufactured by Elevum Co., Ltd.) 1402 were attached in parallel to the inner dimension width direction. The distance 1413 between the centers of the hot cathode tubes was 100 mm, and the distance 1411 from the reflector to the center of the hot cathode tubes was 8.75 mm. The vicinity of the electrode part was fixed with a silicone sealant, and an inverter was attached.

  Next, using a mold part of a predetermined shape for an injection molding machine (clamping force 4,410 kN), using the light diffusion plate pellet A obtained in Production Example 1 as a raw material, a cylinder temperature of 280 degrees, a mold temperature A light diffusion plate was molded under the condition of 85 degrees. The obtained light diffusing plate was a rectangular flat plate having a thickness of 2 mm and 750 mm × 430 mm, and a predetermined pattern of a concavo-convex structure in which a plurality of triangular prisms were arranged substantially in parallel was formed on one surface thereof. . The predetermined pattern will be described in detail below.

  Next, the obtained light diffusing plate was placed on an aluminum case to which a hot cathode tube was attached such that the other surface (surface having no uneven structure: light incident surface) was on the hot cathode tube side. At this time, the distance between the center of the hot cathode tube and the light incident surface of the light diffusion plate was 25 mm.

  The uneven structure on the light diffusion plate used in this example will be described with reference to FIGS. With the light diffusing plate 1401 attached, a distance corresponding to the center 1441 from the middle 1441 between the centers of adjacent hot cathode tubes (1402a and 1402b in FIG. 15) is A (4 mm), It was divided into four zones, B (30 mm), C (10 mm) and D (6 mm). Each zone of the light exit surface of the light diffusion plate 1401 has a prism-like convex portion 1621a having a triangular cross section with an apex angle of 60 ° as shown in FIG. 16, and a triangular cross section with an apex angle of 95 °. The prism-shaped convex part 1621b was provided in the aspect shown below.

A: 1621a / 1621b = 1/4
B: 1621a / 1621b = 1/3
C: 1621a / 1621b = 1/4
D: 1621a / 1621b = 1/5

  The above notation shows the arrangement of the convex portions 1621a and 1621b in the repeating unit of the concavo-convex structure pattern. For example, in the case of “1621a / 1621b = 1/4”, as shown in FIG. 16, one triangular convex portion 1621a having an apex angle of 60 ° and four triangular convex portions 1621b having an apex angle of 95 ° are arranged. An uneven structure is a unit, and this unit is repeated.

  The bases 1622a and 1622b of the convex portions 1621a and 1621b are both 70 μm. On the other hand, the light incident surface was a flat surface.

  Further, a diffusion sheet (“188GM3”, manufactured by Kimoto Co., Ltd.), a prism sheet (“BEFIII-10T”, manufactured by Sumitomo 3M Co.) as an optical sheet, and reflected polarized light are provided on the upper surface (light emitting surface) of the light diffusing plate. A child ("DBEF-D", manufactured by Sumitomo 3M) and a polarizing plate ("HCL2-2518", manufactured by Sanlitz) were installed in this order.

Next, the obtained direct type backlight device is energized at a tube current of 175 mA, the hot cathode tube is turned on, and a two-dimensional color distribution measuring device is used to equidistantly center the short direction (depth direction of the case) on the center line. The luminance of 100 points in the front direction was measured. The central brightness measurement was 8462 cd / m ² . Further, according to the following formulas 1 and 2, the brightness average value (front brightness) La and brightness unevenness Lu in the front direction were obtained. The luminance unevenness was 1.4%. The results are shown in Table 1.

Luminance average value La = (L1 + L2) / 2 (Formula 1)
Luminance unevenness Lu = ((L1-L2) / La) × 100 (Formula 2)
L1: Average brightness maximum value just above a plurality of installed hot cathode tubes L2: Average minimum value sandwiched between maximum values Note that brightness unevenness is an index indicating brightness uniformity, and brightness unevenness When it is bad, the figure increases.

<Example 2>
A direct type backlight device was produced in the same manner as in Example 1 except that the uneven structure pattern of the light diffusion plate was as described in detail below.

  The uneven structure on the light diffusion plate used in this example will be described with reference to FIGS. 17 and 18. With the light diffusing plate 1701 attached, a distance corresponding to the center 1441 between the centers of adjacent hot cathode tubes (1402d and 1402e in FIG. 17) to the center of the hot cathode tube is A (5 mm), Divided into 5 zones: B (5 mm), C (5 mm), D (20 mm) and E (15 mm). In each zone of the light emitting surface of the light diffusing plate 1701, prism-shaped convex portions 1821a having a triangular cross section with an apex angle of 90 ° as shown in FIG. 18 and flat portions 1821b are alternately provided. The base 1822a of the convex portion 1821a was 70 μm in all zones, while the width 1822b of the flat portion 1821b was as follows for each zone.

A: 46.67 μm
B: 35 μm
C: 17.5 μm
D: 7 μm
E: 0 μm

  On the other hand, the light incident surface was a flat surface. The obtained direct type backlight device was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Example 3>
A direct type backlight device was produced in the same manner as in Example 1 except that the uneven structure pattern of the light diffusion plate was as described in detail below.

  The uneven structure on the light diffusion plate used in this example will be described with reference to FIG. With the light diffusing plate 2001 attached, a distance corresponding to the center 1441 from the middle 1441 between the centers of adjacent hot cathode tubes (1402f and 1402g in FIG. 20) is A (15 mm), It was divided into three zones, B (10 mm) and C (25 mm).

  The light exit surface S2050 of the light diffusing plate 2001 has prism-shaped convex portions having a triangular cross section with an apex angle of 100 ° and a base of 70 μm on the entire surface, without a flat portion gap (there is no flat portion). In other words, the triangular base corner portions adjacent to each other are in contact with each other).

  On the other hand, among the zones of the light incident surface S2060 of the light diffusing plate 2001, the zone A is a flat surface. In the zone B, prismatic convex portions having a triangular cross section as shown in FIG. 18 and flat portions are alternately provided. However, the apex angle of the triangle was 130 °, the base was 70 μm, and the width of the flat portion was 70 μm. In the zone C, prism-shaped convex portions having a triangular cross section having an apex angle of 130 ° and a base of 70 μm were provided without a flat portion gap.

The obtained direct type backlight device was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Example 4>
Example 2 except that the linear light source is a hot cathode tube having a diameter of 8.0 mm and a length of 800 mm (manufactured by Elevum Co., Ltd.), and the distance 1411 from the reflector to the center of the hot cathode tube is 8.75 mm. Similarly, a direct type backlight device was created. The obtained direct type backlight device was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Example 5>
The linear light source was a hot cathode tube (made by Elevum Co., Ltd.) having a diameter of 8.0 mm and a length of 800 mm, and the distance 1411 from the reflector to the center of the hot cathode tube was 5.0 mm. Similarly, a direct type backlight device was created. The obtained direct type backlight device was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<Comparative Example 1>
A direct type backlight device was created and evaluated in the same manner as in Example 1 except that the uneven structure pattern of the light diffusion plate was as follows. The results are shown in Table 1.
A prism-like convex portion having a triangular cross section with an apex angle of 130 ° and a base of 70 μm is provided on the incident side without a gap in a flat portion, and a triangular cross section with an apex angle of 100 ° and a base of 70 μm is provided on the output side. The prism-shaped convex part was provided without a gap in the flat part.

<Comparative example 2>
A direct type backlight device was created and evaluated in the same manner as in Example 1 except that the uneven structure pattern of the light diffusion plate was as follows. The results are shown in Table 1.
A prism-like convex portion having a triangular cross section with an apex angle of 90 ° and a base of 70 μm was provided only on the output side without a flat portion gap.

<Comparative Example 3>
A direct type backlight device was created and evaluated in the same manner as in Comparative Example 1 except that the linear light source was the same as in Example 4. The results are shown in Table 1.

<Comparative example 4>
A direct type backlight device was prepared and evaluated in the same manner as in Comparative Example 2 except that the linear light source was the same as in Example 4. The results are shown in Table 1.

<Example 6>
A backlight device schematically shown in FIG. 21 was produced. A reflector sheet (RF188, manufactured by Tsujiden Co., Ltd.) is attached to the inner surface of an aluminum case (not shown) having an inner dimension width of 730 mm, a depth of 405 mm, and a depth of 25 mm to form a reflector 2103 having a diameter of 15.5 mm and a length. Four 800 mm hot-cathode tubes (manufactured by Elevum Co., Ltd.) 1402 were attached in parallel to the inner dimension width direction. The distance 2113 between the centers of the hot cathode tubes was 90 mm, and the distance 2111 from the reflector plate to the center of the hot cathode tubes was 9.75 mm. The vicinity of the electrode part was fixed with a silicone sealant, and an inverter was attached.

  Next, using a mold part of a predetermined shape for an injection molding machine (clamping force 4,410 kN), using the light diffusion plate pellet A obtained in Production Example 1 as a raw material, a cylinder temperature of 280 degrees, a mold temperature A light diffusion plate was molded under the condition of 85 degrees. The obtained light diffusing plate is a rectangular flat plate having a thickness of 2 mm and 750 mm × 430 mm, and a predetermined pattern of a concavo-convex structure in which a plurality of triangular prisms are arranged in a uniform manner in parallel is formed on one surface thereof. On the other surface, a predetermined pattern in which triangular prisms are mixed with a predetermined gradation is formed. The predetermined pattern will be described in detail below.

  Next, the obtained light diffusing plate was placed on an aluminum case to which a hot cathode tube was attached such that the other surface was on the hot cathode tube side. At this time, the distance between the center of the hot cathode tube and the light incident surface of the light diffusion plate was 15.25 mm. The distance (2111 + 2112) between the reflecting plate 2003 and the light incident surface of the diffusing plate 2001 was 25 mm.

  The uneven structure on the light diffusion plate used in this example will be described with reference to FIGS. With the light diffusing plate 2101 attached, a distance corresponding to the center 2141 between the centers of adjacent hot cathode tubes (2102a and 2102b in FIG. 22) to the center of the hot cathode tube is A (20 mm), N of B (1.5 mm), C (1 mm), D (1.5 mm), E (6 mm), F (1.5 mm), G (1 mm), H (1.5 mm) and I (11 mm) Divided into zones. Each zone of the light incident surface of the light diffusion plate 2101 has a prism-like convex portion 2321a having a triangular cross section with an apex angle of 170 ° as shown in FIG. 23 and a triangular cross section with an apex angle of 160 °. A prism-shaped convex portion 2321b and a prism-shaped convex portion 2321c having a triangular cross section with an apex angle of 150 ° were provided in the following manner.

A: 2321a / 2321b / 2321c = 1/0/0
B: 2321a / 2321b / 2321c = 3/1/0
C: 2321a / 2321b / 2321c = 1/1/0
D: 2321a / 2321b / 2321c = 1/3/0
E: 2321a / 2321b / 2321c = 0/1/0
F: 2321a / 2321b / 2321c = 0/3/1
G: 2321a / 2321b / 2321c = 0/1/1
H: 2321a / 2321b / 2321c = 0/1/3
I: 2321a / 2321b / 2321c = 0/0/1

  The above notation shows the arrangement of the convex portions 2321a, 2321b, and 2321c in the repeating unit of the concavo-convex structure pattern. For example, in the case of “2321a / 2321b / 2321c = 1/0/0”, a structure in which only the triangular convex portion 2321a having an apex angle of 170 ° is repeated is shown. In the case of “2321a / 2321b / 2321c = 3/1/0”, a concavo-convex structure in which three triangular convex portions 2321a having an apex angle of 170 ° and one triangular convex portion 2321b having an apex angle of 160 ° are arranged side by side Represents a structure in which this unit is repeated. In the case of “2321a / 2321b / 2321c = 0/3/1”, the concavo-convex structure in which three triangular convex portions 2321b having an apex angle of 160 ° and one triangular convex portion 2321c having an apex angle of 150 ° are arranged side by side 1 represents a structure in which this unit is repeated.

  The bases 2322a, 2322b, and 2322c of the convex portion 2321a, the convex portion 2321b, and the convex portion 2321c are all 70 μm.

  On the other hand, a prism-shaped convex part having an apex angle of 100 ° and a base of 70 μm was provided on the entire surface of the light emitting surface in the manner shown in FIG.

  Further, a diffusion sheet (“188GM3”, manufactured by Kimoto Co., Ltd.), a prism sheet (“BEFIII-10T”, manufactured by Sumitomo 3M Co.) as an optical sheet, and reflected polarized light are provided on the upper surface (light emitting surface) of the light diffusing plate. A child ("DBEF-D", manufactured by Sumitomo 3M) and a polarizing plate ("HCL2-2518", manufactured by Sanlitz) were installed in this order.

Next, the obtained direct type backlight device is energized at a tube current of 175 mA, the hot cathode tube is turned on, and a two-dimensional color distribution measuring device is used to equidistantly center the short direction (depth direction of the case) on the center line. The luminance of 100 points in the front direction was measured. The measured value of the central brightness was 8261 cd / m ² . Further, according to the above formulas 1 and 2, the brightness average value (front brightness) La and brightness unevenness Lu in the front direction were obtained. The luminance unevenness was 1.5%.

<Example 7>
A backlight device schematically shown in FIG. 21 was produced in the same manner as in Example 6 except that the pattern of the light diffusing plate was changed to the one described below.

  The uneven structure on the light diffusion plate used in this example will be described with reference to FIG. With the light diffusing plate (2001 in FIG. 20) attached, it corresponds to the middle of the distance between the centers of adjacent hot cathode tubes (1402f and 1402g in FIG. 20) to the center of the hot cathode tube in FIG. The distance was divided into three zones: A (5 mm), B (5 mm), and C (80 mm) Each zone on the light exit surface of the light diffusing plate (2001 in FIG. 20) has a triangle with an apex angle of 105 °. The prism-shaped convex part which has a cross section of a shape, and the prism-shaped convex part which has a triangular-shaped cross section with an apex angle of 160 degrees were provided in the aspect shown below.

In zone A, a concavo-convex structure in which one triangular convex portion having an apex angle of 105 ° and one triangular convex portion having an apex angle of 160 ° are arranged as one unit, and this unit is repeated.
In zone B, a concavo-convex structure in which two triangular convex portions having an apex angle of 105 ° and one triangular convex portion having an apex angle of 160 ° are arranged as one unit, and this unit is repeated.
In the zone C, a concavo-convex structure in which three triangular convex portions having an apex angle of 105 ° and one triangular convex portion having an apex angle of 160 ° are arranged as one unit, and this unit is repeated.

  The bases of the triangular shape with an apex angle of 105 ° and the triangular shape with an apex angle of 160 ° were both set to 70 μm.

  On the other hand, on the light incident surface, prism-shaped convex portions having an apex angle of 130 ° and a base of 70 μm were provided on the entire surface in the manner shown in FIG.

Next, the obtained direct type backlight device is energized at a tube current of 175 mA, the hot cathode tube is turned on, and a two-dimensional color distribution measuring device is used to equidistantly center the short direction (depth direction of the case) on the center line. The luminance of 100 points in the front direction was measured. Further, according to the above formulas 1 and 2, the brightness average value (front brightness) La and brightness unevenness Lu in the front direction were obtained. The central brightness measurement was 8344 cd / m ² . The luminance unevenness was 1.9%.

<Comparative Example 5>
As in Example 6, except that the linear light source was a cold cathode tube having a diameter of 3.0 mm and a length of 800 mm (made by Harrison Toshiba Lighting Co., Ltd.), and the cold cathode tube was turned on by energizing with a tube current of 4 mA. A direct type backlight device was created and evaluated. The central brightness measurement was 2615 cd / m ² . The luminance unevenness was 5.2%.

Claims (11)

A plurality of linear light sources arranged substantially parallel to each other, a reflecting plate that reflects light from these linear light sources, direct light from the linear light source and reflected light from the reflecting plate as a light incident surface A direct-type backlight device comprising a light diffusing plate that is incident from and diffused from a light exit surface,
The linear light source has an outer diameter of 5 mm to 30 mm,
At least one of the light emitting surface and the light incident surface is formed with a concavo-convex structure at least at a part thereof,
In the light diffusing plate, when the outer diameter of the linear light source is projected perpendicularly to the light diffusing plate, the uneven structure of the projected portion;
In the light diffusing plate, a direct type characterized in that the concave-convex structure of the portion having the same width as the outer diameter of the linear light source has a different shape centering on an intermediate position between adjacent linear light sources Backlight device. In the direct type backlight device according to claim 1,
The direct-type backlight device, wherein the linear light source is a hot cathode tube. In the direct type backlight device according to claim 1,
The concavo-convex structure is a prism row in which a plurality of linear prisms extending along the longitudinal direction of the linear light source are arranged substantially in parallel.
A direct type backlight device characterized in that a cross section of the linear prism perpendicular to the longitudinal direction of the linear light source is a curved or polygonal convex portion, a substantially flat portion, or a combination thereof. In the direct type backlight device according to claim 3,
The cross section of the linear prism perpendicular to the longitudinal direction of the linear light source includes two or more types of convex portions having different shapes, and the abundance ratio of the two or more types of convex portions moves away from the linear light source. A direct-type backlight device that changes continuously or stepwise. In the direct type backlight device according to claim 3,
The cross section of the linear prism perpendicular to the longitudinal direction of the linear light source includes both the convex portion and the substantially flat portion, and these abundance ratios are continuous or stepped as they move away from the linear light source. Directly-type backlight device characterized by a change. In the direct type backlight device according to claim 1,
Further comprising an optical sheet provided on the light exit surface side of the light diffusing plate,
In a cross section perpendicular to the longitudinal direction of the linear light source,
Arbitrary linear light source is A, linear light source adjacent to this linear light source A is B,
An intermediate position obtained by projecting an intermediate position between the linear light source A and the linear light source B onto the light incident surface is X,
P is an arbitrary point on the light incident surface located between the linear light source A and the linear light source B and closer to the linear light source A than the intermediate position X,
The center of the linear light source A is C,
The total light transmittance Tp at the point P of light incident in the direction of the point P from the center C is based on the total light transmittance Tx at the point X of light incident from the center C in the direction of the intermediate position X. Directly-type backlight device characterized by being small. The direct type backlight device according to claim 6,
The length of the line segment connecting the center C and the point P is LCP,
Let Q be the point at which the center C is projected perpendicularly to the light incident surface.
LCQ is the length of the line connecting the center C and the point Q,
Tq is the total light transmittance at the point Q of light incident in the direction of the point Q from the center C,
A direct-type backlight device satisfying a relationship of 0.2 × (Tq · LCP / LCQ) ≦ Tp ≦ 5.0 × (Tq · LCP / LCQ). In the direct type backlight device according to claim 1,
The direct-type backlight device, wherein the concavo-convex structure is formed on both at least a part of the light emitting surface and at least a part of the light incident surface of the light diffusing plate. The direct type backlight device according to claim 8,
The concavo-convex structure is a prism row in which a plurality of linear prisms extending along the longitudinal direction of the linear light source are arranged substantially in parallel, and a cross section perpendicular to the longitudinal direction of the linear light source is at least a part thereof. The direct-type backlight device is a polygonal shape, and the polygonal shape is symmetric about an axis parallel to the thickness direction of the light diffusion plate in the cross section. The direct type backlight device according to claim 8,
As moving away from the linear light source and toward the intermediate position of the linear light sources adjacent to each other,
An angle formed by the slope of the linear prism on at least one of the light exit surface and the light entrance surface and a plane perpendicular to the thickness direction of the light diffusion plate is increased continuously or stepwise. A direct type backlight device. The direct type backlight device according to claim 8,
As moving away from the linear light source and toward the intermediate position of the linear light sources adjacent to each other,
In the linear prism on at least one of the light exit surface and the light entrance surface, the mixing ratio of two or more types of linear prisms changes continuously or stepwise, so that they are intermediate between the adjacent linear light sources. A direct type backlight device characterized in that the ratio of linear prisms having a large inclination angle increases continuously or stepwise as it goes to a position.

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