JPWO2010005051A1 - Direct type backlight device and liquid crystal display device - Google Patents

Abstract

A direct type backlight device comprising a plurality of linear light sources arranged substantially parallel to each other, a reflecting plate, and a light diffusing plate having a light incident surface and a light emitting surface, wherein the light incident surface and / or light The exit surface has a concavo-convex structure group in which repeating units composed of two or more different concavo-convex structures are arranged, and in the repeating unit, a range continuously occupied by the same concavo-convex structure is 350 μm or less, and the two types Of the two concavo-convex structures (a) and (b), the total light transmittance X (%) of light perpendicularly incident on the light diffusion plate in the region occupied by the concavo-convex structure (a). And a direct back that satisfies the relationship of 95 ≧ | X−Y | ≧ 20 in which the total light transmittance Y (%) of light perpendicularly incident on the light diffusion plate in the region occupied by the uneven structure (b) Light equipment.

Description

  The present invention relates to a direct backlight device and a liquid crystal display device.

  Conventionally, a direct backlight device has been used as one embodiment of a backlight device for a liquid crystal display. The direct type backlight device usually includes a plurality of light sources such as cold cathode fluorescent lamps arranged in parallel, a reflection plate provided on the back surface of the light source, and a light diffusion plate forming a light emission surface. The direct-type backlight device has an advantage that the light emission surface can be easily increased in brightness using a large number of light sources compared to the edge light type device, while the luminance uniformity of the light emission surface is poor, For example, there are many cases where luminance unevenness occurs such that a bright line of a cold cathode tube is visually recognized on the light emitting surface of the backlight device.

  As a means of improving the brightness uniformity, it is conceivable to reduce the interval between the light sources, but for this purpose, the number of light sources must be increased, resulting in a complicated manufacturing process of the backlight device and when the lamp is lit. Power consumption increases. As another means for improving the luminance uniformity, it is conceivable to increase the distance between the light source and the light diffusion plate, but in this case, the backlight device becomes undesirably thick.

  Conventionally, various measures have been taken to improve the luminance uniformity. For example, a striped pattern or dot-shaped light quantity correction pattern is printed on a light diffusing plate to reduce the luminous flux emitted directly above the cold cathode tube (FIG. 6 of JP-A-6-273760), or wave reflection There has been proposed a technique (Japanese Patent Laid-Open No. 2001-174813) that uses a plate to focus the reflected light from the reflection plate to a region corresponding to the middle of the cold cathode tube and the cold cathode tube.

  However, as a means of improving the brightness uniformity, when the light quantity correction pattern is printed on the light diffusing plate, this pattern blocks a part of the light beam, so that the utilization rate of the light beam emitted from the cold cathode tube is lowered and sufficient. High brightness cannot be obtained. In addition, when the wave reflector is used, the configuration of the apparatus becomes complicated.

  In addition, a light diffusing plate used in a direct type backlight device often uses a material in which a light diffusing agent is dispersed in a transparent resin, but the concentration of the light diffusing agent is increased to improve the luminance uniformity. There was a problem that the brightness would decrease. In order to solve such a decrease in luminance, 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 reducing the luminance (Japanese Patent Laid-Open No. 5-333333). JP, 8-297202, and 2000-182418). However, the luminance uniformity cannot be improved by simply forming a prismatic pattern on the surface of the light diffusing plate.

  Accordingly, an object of the present invention is to provide a direct type backlight device and a liquid crystal display device in which bright lines of a linear light source are effectively concealed and luminance uniformity is high.

  As a result of diligent research to solve the above problems, the inventors of the present invention can reduce luminance unevenness by setting the shape of the light diffusing plate in the direct type backlight device to a specific shape (brightness uniformity can be reduced). Based on this finding, the present invention has been completed.

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 reflector that reflects light from the linear light source;
A light diffusing plate having a light incident surface on which direct light from the linear light source and reflected light from the reflecting plate are incident, and a light emitting surface that diffuses and emits light incident from the light incident surface;
A direct-type backlight device comprising:
At least one of the light incident surface and the light emitting surface has a concavo-convex structure group in which repeating units composed of two or more different concavo-convex structures are periodically arranged in at least a part thereof,
A plane that passes through the center of each linear light source and is parallel to the normal of the light diffusing plate is used as a reference plane.
In a region passing through the center of each linear light source and included in a range within 45 ° of the polar angle as an angle with respect to the reference plane, the same repeat unit along the direction perpendicular to the reference plane The area occupied by the concavo-convex structure is 350 μm or less,
Of the two or more different concavo-convex structures (a) and (b) of the two or more different concavo-convex structures in the repeating unit, the light incident perpendicularly to the light diffusion plate in the region occupied by the concavo-convex structure (a) The total light transmittance X (%) and the total light transmittance Y (%) of light perpendicularly incident on the light diffusion plate in the region occupied by the uneven structure (b) are 95 ≧ | X−Y | ≧ A direct type backlight device satisfying the relationship of 20.
[2] The concavo-convex structure is a linear prism extending substantially parallel to the longitudinal direction of the linear light source,
The direct type backlight device, wherein a shape of a cross section of the linear prism perpendicular to the longitudinal direction of the linear light source is any of a polygonal convex portion, a flat portion, and a combination thereof.
[3] The light diffusion plate includes a transparent resin as a main component,
The concavo-convex structures (a) and (b) are linear prisms (a) and (b) having a triangular cross section formed on the light emitting surface, respectively.
The apex angle θa of the linear prism (a) is expressed by the following formula (1):
θa <180-2sin ⁻¹ (1 / n) (1a)
And the apex angle θb of the linear prism (b) is the following formula (1b):
θb ≧ 180−2 sin ⁻¹ (1 / n) (1b)
(In formulas (1a) and (1b), n represents the refractive index of the transparent resin)
The direct type backlight device satisfying the above.
[4] The direct-type backlight device, wherein the ratio A / B between the number A of the concavo-convex structure of the most existing species in the repeating unit and the number B of the concavo-convex structure of the least existing species is 10 or less. .
[5] The direct type backlight device in which the abundance ratio of the two types of concavo-convex structures (a) and (b) in the repeating unit changes stepwise as the distance from the linear light source increases.
[6] A liquid crystal display device comprising: the direct type backlight device; and a liquid crystal panel disposed on a light emitting side of the direct type backlight device.

  The direct type backlight device of the present invention and the liquid crystal display device of the present invention having the same have the effect that the bright line of the linear light source is effectively concealed and the luminance uniformity can be increased.

FIG. 1 is a perspective view showing an outline of a direct type backlight device according to a first embodiment of the present invention. FIG. 2 is a longitudinal sectional view showing an outline of a section obtained by cutting the apparatus shown in FIG. 1 along a plane perpendicular to the longitudinal direction of the linear light source 102. FIG. 3 is a longitudinal sectional view showing an outline of a section obtained by cutting a part of the light diffusing plate 101 of the apparatus shown in FIG. 1 along a plane perpendicular to the longitudinal direction of the linear light source 102. FIG. 4 is a longitudinal sectional view showing a schematic cross section of a part of the light diffusing plate 101 of the apparatus according to the second embodiment of the present invention. FIG. 5 is a vertical cross-sectional view showing a schematic cross section of a part of the light diffusion plate of the apparatus according to Embodiment 3 of the present application. FIG. 6 is a vertical cross-sectional view showing an outline of a cross section of another part of the light diffusing plate of the apparatus according to Embodiment 3 of the present application. FIG. 7 is a longitudinal sectional view showing an outline of the relationship between the light diffusing plate 101 and the linear light sources 102a and 102b in the direct type backlight device according to the third embodiment of the present invention. FIG. 8 is a longitudinal sectional view showing an outline of a section of a part of a light diffusion plate of an apparatus according to a modification of the present invention. FIG. 9 is a longitudinal sectional view showing an outline of a section of a part of a light diffusion plate of an apparatus according to another modification of the present invention.

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

(First embodiment)
FIG. 1 is a perspective view schematically showing a direct type backlight device according to the first embodiment of the present invention, and FIG. 2 is a plan view of the device shown in FIG. 1 perpendicular to the longitudinal direction of the linear light source 102. It is a longitudinal cross-sectional view which shows the outline of the cross section cut | disconnected by.

  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 reflective plate 103 having a reflective surface 103A that reflects light from these linear light sources 102, and a line And a light diffusing plate 101 having a light incident surface 101A for receiving direct light from the light source 102 and reflected light from the reflecting plate 103 and a light emitting surface 101B for diffusing and emitting the light incident from the light incident surface 101A. . Since FIG. 1 is a schematic diagram showing these positional relationships, the linear prisms 201a and 201b are shown enlarged in FIG. 1, but in reality, the linear prisms 201a and 201b are linear. The diameter of the light source 102 can be very small. In the present invention, the arrangement of the components being substantially parallel means that in addition to the parallel state, an error within a range not impairing the effect of the present invention may be included. The error can be preferably within a range of ± 10 ° from the parallel direction, more preferably within a range of ± 5 ° from the parallel direction, and further preferably within a range of ± 2 °.

  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 “down” direction, which corresponds to the upward direction and the downward direction in the drawings of FIGS.

  In the present embodiment, all the linear light sources 102 are arranged such that the distance 111 from the center of the linear light source 102 to the reflecting surface 103A is the same for all the linear light sources. In this embodiment, the linear light sources 102 are arranged so that the distances 111 are equal. In this case, a deviation within ± 2 mm is allowed as an error during assembly. The deviation is preferably within 1 mm. As an example of the shape of the light source 102, in addition to the linear shape shown in FIGS. 1 and 2, two substantially parallel tubes are connected by one approximately semicircle to form a single U-shape, approximately parallel There can be mentioned an N-shape in which three tubes are connected by two approximately semicircles, and a W-shape in which four approximately parallel tubes are connected by three approximately semicircles. .

  In the direct type backlight device of the present embodiment, the linear light source 102 includes, for example, an external electrode fluorescent tube (EEFL), a xenon lamp, a xenon mercury lamp, a hot cathode tube, and a light emitting diode (in addition to a cold cathode tube). LEDs) arranged in a straight line, a combination of LEDs and a light guide, and the like can also be used. The outer diameter of the tubular linear light source 102 is preferably 1.0 mm to 20.0 mm. The distance 113 between the centers of the adjacent linear light sources 102 is preferably 20.0 mm to 200.0 mm. The center of the linear light source is a line extending in the longitudinal direction through the central axis of the linear light source, that is, the center in the cross section of the linear light source cut by a plane perpendicular to the longitudinal direction of the linear light source. Here, in the case of LEDs arranged in a straight line, a combination of an LED and a light guide, a U-shaped light source, etc., each linear part is considered as one linear light source, The width of the light emitting region (in the vertical direction) is the outer diameter of the linear light source, and the distance between the centers of adjacent linear portions is the distance between the centers of the linear light sources.

  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 in 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 11 It can be an odd number such as 7, 7, 5 or 3.

  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. The light diffusing plate is usually provided at a position farther from the reflecting surface of the reflecting plate than the linear light source. In the present embodiment, the light diffusing plate 101 is arranged such that the distance 112 from the light incident surface 101A to the center of the linear light source 102 is the same for all the linear light sources, and therefore the light incident surface 101A is the reflecting plate 103. It is arranged so as to be substantially parallel to the reflective surface 103A. In the present embodiment, the linear light sources 102 are arranged so that the distances 112 are equal. In this case, a deviation within ± 2 mm is allowed as an error during assembly. The deviation is preferably within 1 mm.

  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, as the material, 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. From the viewpoint of easy adjustment, it is preferable to disperse a light diffusing agent in a transparent resin as a main component.

  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, polymethylpentene-1, polysulfone, polyarylate, copolymer of aromatic vinyl monomer and (meth) acrylic acid alkyl ester having lower alkyl group, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate Terephthalic acid-ethylene glycol-cyclohexanedimethanol copolymer, polycarbonate, acrylic resin, and resin having an alicyclic structure. In addition, (meth) acrylic acid is acrylic acid and methacrylic acid.

  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.

  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 80% to 98%. 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. 3 is a longitudinal sectional view showing an outline of a section obtained by cutting a part of the light diffusing plate 101 of the apparatus according to the first embodiment of the present invention shown in FIG. 1 along a plane perpendicular to the longitudinal direction of the linear light source 102. It is. In the present embodiment, the light incident surface 101A of the light diffusing plate 101 is a smooth surface, while the light emitting surface 101B of the light diffusing plate 101 extends substantially parallel to the longitudinal direction of the linear light source 102 as an uneven structure group. The linear prisms 201a and 201b, which are two types of different concavo-convex structures, have a prism row in which a plurality of linear prisms are arranged substantially in parallel.

  In the present invention, in the concavo-convex structure group, repeating units composed of two different concavo-convex structures are periodically arranged. In the first embodiment, the linear prisms 201a and 201b having a concavo-convex structure are periodically arranged in the horizontal direction of the drawing, that is, in the direction perpendicular to the extending direction of the linear prism and substantially parallel to the light incident surface. The That is, the light exit surface 101B of the light diffusing plate 101 has a structure in which units 220 each having a range 221a occupied by two rows of linear prisms 201a and a range 221b occupied by two rows of linear prisms 201b are periodically arranged. have.

  In the present invention, a plane that passes through the center of each linear light source and is parallel to the normal line of the light diffusing plate is used as a reference plane, and a polar angle that passes through the center of the linear light source and is formed with respect to the reference plane. In a region included in a range of 45 degrees or less, a range in which the same concavo-convex structure continuously occupies a direction perpendicular to the reference plane in the repeating unit is 350 μm or less. Here, “a range that is parallel to the normal of the light diffusing plate as a reference plane, passes through the center of the linear light source, and is an angle of 45 degrees or less with respect to the reference plane” means a line This is a region separated by a pair of planes that pass through the center line of the light source and form an angle of 45 ° with respect to the axis (that is, the direction parallel to the normal line of the light diffusing plate). The “range in which the same concavo-convex structure continuously occupies” in this region can be a width in a direction parallel to the main surface of the light diffusion plate in a cross section perpendicular to the longitudinal direction of the linear light source. For example, in the first embodiment, this requirement is satisfied if both the range 213a and the range 213b are 350 μm or less, and more preferably 250 μm or less. Also, for example, in a mode in which three linear prisms a and b are included in each repeating unit, and these linear prisms a and b are arranged in the order of aabbab, a in each repeating unit The range occupied by 3 is for 3 prisms, but the range that a continuously occupies is for 2 prisms, so the width for 2 prisms corresponds to the “range that the same uneven structure occupies continuously” To do.

  In the present invention, the width dimension of one concavo-convex structure (linear prism) (the dimension in the short direction in the case of a linear prism) is preferably 20 μm or more and 350 μm or less, and more preferably 40 μm or more and 350 μm or less. preferable.

  The direct-type backlight device of the present invention satisfies the requirements for the range that the same concavo-convex structure continuously occupies, so that the light emission is uniform to the extent that no bright line based on the shape of the linear light source is visible on the light emission surface. Can be realized.

  In the present invention, two concavo-convex structures (a) and (b) of the two or more different concavo-convex structures in the repeating unit are perpendicularly incident on the light diffusion plate in the region occupied by the concavo-convex structure (a). The total light transmittance X (%) of light and the total light transmittance Y (%) of light perpendicularly incident on the light diffusion plate in the region occupied by the concavo-convex structure (b) are 95 ≧ | X−Y | ≧ Satisfy 20 relationships. Here, | X−Y |, that is, a difference in total light transmittance is a difference between two total light transmittances (unit:%). For example, a total light transmittance in a region occupied by the concavo-convex structure (a) is 60. %, And the total light transmittance in the region occupied by the concavo-convex structure (b) is 80%, the difference between these total light transmittances is 20% (80% -60%). Note that the upper limit of the difference | X−Y | in the total light transmittance is 95% in order to obtain the bright line concealing effect, preferably 60%, and more preferably 50%.

  Further, in the measurement of the total light transmittance, in each region occupied by the concavo-convex structure (a), (b), the light is incident perpendicularly to the light diffusing plate. In this case, “perpendicular to the light diffusing plate” Is to measure by making light incident perpendicularly to the light incident surface of the light diffusing plate (or in a direction parallel to the thickness direction of the light diffusing plate). In addition, in the measurement of the total light transmittance, when measurement is not possible because the area occupied by the uneven structure (a) or (b) in the light diffusion plate is narrow, a sample in which only the same uneven structure is arranged is prepared. Alternatively, it can be substituted by measuring the light incident from the same direction as that of the direct backlight device.

In the first embodiment, the repeating unit 220 has only two types of concavo-convex structures (linear prisms 201a and 201b), and therefore in the region 221a occupied by one of these linear prisms 201a. The difference between the total light transmittance of light perpendicularly incident on the light diffusing plate 101 and the total light transmittance of light vertically incident on the light diffusing plate 101 in the region 221b occupied by the other linear prism 201b is 20%. If it is 95% or less, this requirement is satisfied.
Unlike the first embodiment, when the repeating unit has three or more types of concavo-convex structures, there are three or more pairs of concavo-convex structures (for example, concavo-convex structures A and B, A and C, and B and C, etc. However, this requirement is satisfied when the requirement of the total light transmittance is satisfied when any one of the concavo-convex structure is the concavo-convex structure (a) and (b).

  The direct type backlight device of the present invention can increase the luminance uniformity on the light exit surface by satisfying the requirement of the difference in total light transmittance.

In the direct type backlight device of the present invention, preferably, the light diffusing plate is configured to include a transparent resin as a main component, and the concavo-convex structures (a) and (b) of the concavo-convex structure group are each configured to emit light. The linear prisms (a) and (b), which are formed on the surface as in the first embodiment, have a cross-sectional triangle, more preferably a triangle having the same base angle, and more preferably an isosceles triangle. ) Is represented by the following formula (1a):
θa <180-2sin ⁻¹ (1 / n) (1a)
The apex angle θb of the linear prism (b) is expressed by the following formula (1b):
θb ≧ 180−2 sin ⁻¹ (1 / n) (1b)
(In formulas (1a) and (1b), n represents the refractive index of the transparent resin).

When only two linear prisms are included in one repeating unit, the apex angle of the linear prism with the smaller apex angle is θa, and the apex angle of the linear prism with the larger apex angle is θb. When these satisfy the above formulas (1a) and (1b), the above conditions are satisfied. For example, in the first embodiment, the repeating unit 220 has only two types of concavo-convex structures (linear prisms 201a and 201b), and the apex angles θ214a and θ214b have a relationship of θ214a <θ214b. Therefore, if the equation (1a) is established by substituting θ214a into θa in the equation (1a), and the equation (1b) is established by substituting θ214b into θb in the equation (1b), the above condition is satisfied. .
Unlike the first embodiment, when the repeating unit has three or more types of linear prisms, any one of the three or more pairs of linear prisms is replaced with the linear prism (a). And when it is set as (b) and the requirement of the said total light transmittance and said Formula (1a) and Formula (1b) are satisfy | filled, this requirement is satisfied.
By satisfying the condition that the apex angle is satisfied, it is possible to transmit a part of the light vertically incident on the light diffusing plate and to totally diffuse a part of the light by totally reflecting the light. The incident light can be diffused satisfactorily, and the brightness uniformity can be further improved.

In the direct type backlight device of the present invention, more preferably, the apex angle θm of the linear prism having the smallest apex angle among the linear prisms in the repeating unit satisfies the following formula (2).
θm / 2−sin ⁻¹ (n × sin (3 / 2θm−90)) <45 (2)
When only two linear prisms are included in one repeating unit, when the linear prism apex angle θa having the smaller apex angle is θm and the above formula (2) is satisfied, the above condition is satisfied. Satisfy. For example, in the first embodiment, if the equation (2) is satisfied by substituting θ214a into θm of the equation (2), the above condition is satisfied.
Unlike the first embodiment, when the repeating unit has three or more types of linear prisms, the apex angle of the linear prism having the smallest apex angle among the three or more types of linear prisms is expressed by the above formula (2). If this requirement is satisfied, this requirement is satisfied.
If the apex angle of the linear prism is too small, the light incident perpendicularly to the light diffusing plate and totally reflected by one surface of the linear prism is refracted and transmitted through the other surface, and is emitted in the front direction. As a result, the luminance in the front direction increases and luminance unevenness may occur, but when the vertex angle of the linear prism having the smallest vertex angle among the linear prisms in the repeating unit satisfies the above formula (2), Such emission can be suppressed, and a preferable backlight device with high luminance uniformity can be obtained.

(Second Embodiment)
Next, a direct type backlight device according to a second embodiment of the present invention will be described. The direct type backlight device according to the second embodiment has the same configuration as that of the first embodiment except that the arrangement of the linear prisms 201a and 201b in the light diffusion plate 101 is different. FIG. 4 is a longitudinal sectional view showing an outline of a section obtained by cutting a part of the light diffusion plate 101 of the apparatus according to the second embodiment of the present invention along a plane perpendicular to the longitudinal direction of the linear light source 102.

  As shown in FIG. 4, in the present embodiment, the light exit surface 101B of the light diffusing plate 101 is a prism array in which a plurality of linear prisms 201a and 201b similar to those in the first embodiment are arranged substantially in parallel as an uneven structure group. However, the repeating unit 420 includes a range 421a occupied by two rows of linear prisms 201a and a range 421b occupied by one row of linear prisms 201b. Since both of the widths 413a and 413b of these ranges 421a and 421b are 350 μm or less, the present embodiment satisfies the requirements of the range continuously occupied by the same uneven structure in the present invention.

(Third embodiment)
In the direct type backlight device of the present invention, in the periodic arrangement of the repeating units described above, one type of repeating unit may be arranged over the entire entrance surface and / or exit surface of the light diffusion plate. However, as in the third embodiment described below, a plurality of types of repeating units may be arranged in one plane.
FIG. 7 is a longitudinal sectional view showing an outline of the relationship between the light diffusing plate 101 and the linear light sources 102a and 102b in the direct type backlight device according to the third embodiment of the present invention. In the present embodiment, the distance corresponding to the distance from the center 141 between the centers of the adjacent linear light sources 102a and 102b to the center of the linear light source is set to a plurality of zones (A, B, C and D in FIG. 7). In other words, each of the regions corresponding to the zones of the light incident surface and / or the light emitting surface of the light diffusing plate 101 is provided with a concavo-convex structure group of different repeating units.

  Here, the abundance ratio of the two types of concavo-convex structures (a) and (b) in each repeating unit is preferably changed stepwise as the distance from the linear light source increases. For example, in zone A, the number of linear prisms 201a and 201b is arranged in a repeating unit with a ratio of 1: 1, and in zone B, it is arranged in a repeating unit with an abundance ratio of 2: 1. It is possible to provide a concavo-convex structure group in which the abundance ratio changes in four stages, in which the abundance ratio is 3: 1 in the zone C and only the linear prism 201a is arranged in the zone D. In addition, the number of these zones is not particularly limited, but may be 2 to 10 stages, for example.

(Other embodiments)
In the first embodiment described above, the repeating unit is composed of the same number of two types of uneven structures, and in the second embodiment, the ratio of the uneven structures (a) and (b) was 2: 1. In the direct type backlight device of the present invention, the ratio of the number of each type of concavo-convex structure in the repeating unit is not limited to this and can be any ratio. The ratio A / B between the number A of the concavo-convex structures of the most abundant species in the repeating unit and the number B of the concavo-convex structures of the least abundant species is preferably 10 or less from the viewpoint of further increasing the luminance uniformity. More preferably, it is 5 or less.

  In the first embodiment and the second embodiment described above, the cross section of the linear prism perpendicular to the longitudinal direction of the linear light source has a triangular convex shape. The cross-sectional shape of the linear prism on the light diffusing plate in the direct type backlight device is not limited to this, but may be various polygonal shapes such as a trapezoidal quadrangle, pentagon, hexagon, heptagon, etc. in addition to a triangle. In particular, it is preferable that the left and right base angles are substantially equal (within a range of ± 10 °) in a polygonal shape because it is easy to design and the luminance does not vary even when viewed from the left or right. Specifically, for example, a pentagonal cross-sectional shape such as a linear prism 201c shown in FIG.

  In the present invention, the surface of the light-diffusing plate with the concavo-convex structure roughened and emitted can be more diversified within an appropriate range, and the releasability from the mold during molding can be improved. In that case, the arithmetic average height Ra of the concavo-convex structure surface is preferably 0.01 μm or more and 3 μm or less, more preferably 0.02 μm or more and 2 μm or less, and further preferably 0.05 μm or more and 1 μm or less. . By making Ra 0.01 μm or more, the light emission direction can be made more diverse, and the releasability from the mold at the time of molding can be improved, and by making it 3 μm or less, It is possible to prevent the emission direction of the light from being diversified. Such roughening of the surface of the concavo-convex structure may be performed on the entire light emitting surface having the concavo-convex structure, may be performed on a part thereof, or may be performed on the entire surface of one concavo-convex structure, It may be applied to some parts.

  Further, one of the multiple types of uneven structures included in the repeating unit is a flat structure such as the flat portion 201d shown in FIG. 9, and constitutes a combination of a polygonal convex portion and a flat portion. It may be. In the case shown in FIG. 9, the repeating unit 920 includes a range 921a occupied by the linear prism 201a and a range 921b occupied by the flat portion 201d. Since both of the widths 913a and 913b of these ranges 921a and 921b are 350 μm or less, the present embodiment satisfies the requirements of the range continuously occupied by the same uneven structure in the present invention. Further, when the flat portion 201d is a linear prism having an apex angle of 180 °, it is more preferable that the repeating unit 920 satisfies the requirements of the above formulas (1a), (1b), (2) and the like.

  In the present invention, the concavo-convex structure group in which predetermined repeating units are periodically arranged may be formed only on the light emitting surface as in the above embodiments, but is not limited thereto, and only the light incident surface. The concavo-convex structure group may be formed on both the light incident surface and the light emitting surface. Further, the predetermined repeating unit may be periodically arranged not on the entire surface of the light incident surface and / or the light emitting surface. For example, “a method of a light diffusing plate passing through the center of each linear light source” In a region other than a region including a plane parallel to the line as a reference plane and passing through the center of the linear light source and within an angle of 45 ° or less as an angle formed with respect to the reference plane, the same unevenness Repeating units in which the structure continuously occupies more than 350 μm may be arranged.

  The method for forming the concavo-convex structure on the surface of the light diffusing plate is not particularly limited. For example, the method may be a method of forming the concavo-convex structure on the surface of the flat light diffusing plate, or may be a base material for the light diffusing plate. It is good also as a method of forming a concavo-convex structure integrally with formation of a flat part (it may be called a light diffusing plate base in this specification).

  Examples of the method for forming the concavo-convex structure on the surface of the flat light diffusing plate include a method of cutting the surface of the flat light diffusing plate, a prism sheet having a desired concavo-convex structure on the flat light diffusing plate, etc. A method of laminating or pasting a sheet having a concavo-convex structure, applying a photocurable resin or a thermosetting resin to the surface of a flat light diffusing plate, and transferring the desired concavo-convex structure to the coating film with a roll or a die, Examples thereof include a method of curing the coating film in this state, and an embossing method in which the surface of the plate-shaped light diffusion plate is pressed with a roll or a stamp having a desired uneven structure.

  In addition, as a method of integrally forming the concavo-convex structure simultaneously with the formation of the light diffusion plate base, a casting method using a casting mold capable of forming a desired concavo-convex structure, and injection using a mold capable of forming a desired concavo-convex structure Examples thereof include a molding method. As described above, the injection molding method and the casting method have a simple process because the concavo-convex structure can be formed simultaneously with the formation of the light diffusion plate base. The casting method can be performed in a mold capable of forming a plate, or can be performed continuously while pouring a raw material between two continuous belts and moving the belt. In the injection molding method, in order to increase the transfer rate of the concavo-convex structure, it is preferable to raise the mold temperature at the time of injecting the resin and rapidly cool the mold during cooling. Moreover, you may apply the injection compression molding method which expands a type | mold when injecting resin and closes a type | mold after that.

  The liquid crystal display device of the present invention includes the direct type backlight device of the present invention. Specifically, in addition to the direct type backlight device, a liquid crystal cell having various display modes can be provided, and light emitted from the backlight device can be emitted from the display surface through the liquid crystal cell. 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.

  The direct type backlight device of the present invention and the liquid crystal display device of the present invention are not limited to the above-described embodiments, and can be modified within the scope of the claims of the present application and within the equivalent scope thereof. 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 appropriately provided. 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.

  Hereinafter, the present invention will be described in more detail based on examples. In addition, this invention is not limited to the following Example. In the following, “parts” and “%” relating to the quantity ratio of the components represent parts by weight and% by weight unless otherwise specified.

<Production Example 1 (Light Diffusion Plate Pellet A)>
99.9 parts of resin having an alicyclic structure (Zeon Corporation, ZEONOR 1060R, water absorption of 0.01%) and 0.1 part of fine particles composed of a crosslinked product of polysiloxane polymer having an average particle diameter of 2 μm are mixed. Then, the mixture was kneaded with a twin-screw extruder, extruded into a strand shape, and cut with a pelletizer to produce a light diffusion plate pellet A. 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 94% and a haze of 89%.

<Example 1>
A direct type backlight device schematically shown in FIG. 1 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 length of 700 mm, a width of 400 mm, and a depth of 22.8 mm to form a reflector 103 having a diameter of 4 mm Seven 700 mm cold cathode fluorescent lamps (manufactured by Harrison Toshiba Lighting Co., Ltd.) 102 were attached in parallel to the inner dimension length direction. The distance 113 between the centers of the cold cathode tubes was 56.4 mm, and the distance 112 from the diffusion plate to the center of the cold cathode tubes was 19.3 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 in an injection molding machine (clamping force 4,410 kN), using the light diffusion plate pellet A obtained in Production Example 1 as a raw material, a cylinder temperature of 280 ° C., a mold temperature A light diffusion plate was molded under the condition of 85 ° C. The obtained light diffusing plate is a rectangular flat plate having a length of 710 mm, a width of 410 mm, and a thickness of 2 mm, and on one surface thereof, has a concavo-convex structure in which a plurality of triangular prisms described in detail below are arranged substantially in parallel. A predetermined pattern was formed.

As shown in FIG. 4, the light exit surface 101B of the light diffusion plate 101 has a linear prism 201a having a triangular cross section with an apex angle θ214a of 85 ° and a triangular cross section with an apex angle θ214b of 125 °. The linear prisms 201b having them are provided side by side. In other words, the concavo-convex structure in which two rows of linear prisms 201a and one row of 201b are arranged as one repeating unit 420, and the unit 420 is repeated. The widths 211a and 211b of the linear prisms 201a and 201b are both 100 μm. In the repeating unit 420, the width 213a of the range continuously occupied by the linear prism 201a was 200 μm, and the width 213b of the range continuously occupied by the linear prism 201b was 100 μm, similar to 211b.
In the region 421a occupied by the linear prism 201a, the total light transmittance of light perpendicularly incident on the light diffusion plate is 35.6%, and in the region 421b occupied by the linear prism 201b, the light incident perpendicularly to the light diffusion plate is obtained. The total light transmittance was 70.5%, and the difference was 34.9%. The total light transmittance is obtained by preparing a sample in which concave and convex structures having the same structure are continuously arranged, and using an integrating sphere type turbidimeter based on JIS K7361-1, a direct type backlight device It was measured by making light incident from the light incident surface side when the same arrangement as that used in the above was used. Also in the following examples and comparative examples, the total light transmittance was measured in the same manner.

  Next, the obtained light diffusing plate was placed on an aluminum case to which the cold cathode tube was attached such that the other surface (surface having no uneven structure: light incident surface) was on the cold cathode tube side. At this time, the distance between the center of the cold cathode tube and the light incident surface of the light diffusion plate was 19.3 mm.

  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 to obtain a direct type backlight device.

Next, the obtained direct type backlight device was energized at a tube current of 6.0 mA, the cold cathode tube was turned on, and the short-side direction (CA1500W, manufactured by Konica Minolta Co., Ltd.) was used. Case width direction) The luminance in the front direction of 100 points was measured at equal intervals on the center line. Further, according to the following formulas A and B, a luminance average value (front luminance) La and luminance uniformity Lu in the front direction were obtained. The luminance uniformity was 2.8%.
Luminance average value La = (L1 + L2) / 2 (Formula A)
Luminance uniformity Lu = ((L1-L2) / La) × 100 (Formula B)
L1: Average brightness maximum value just above a plurality of cold-cathode tubes installed L2: Average minimum value sandwiched between maximum values Note that brightness uniformity is an indicator of brightness uniformity, and brightness uniformity When the degree is bad, the value increases.

Furthermore, the light emission surface was observed from the front, and whether or not the bright line of the cold cathode tube was concealed was visually evaluated based on the following evaluation criteria.
Good: The bright line is not visible Good: The bright line is slightly visible Not possible: The bright line is visible The results are shown in Table 1.

  Furthermore, a liquid crystal display device is configured by placing a liquid crystal panel taken out from a liquid crystal television (manufactured by Sony Corporation) on the obtained direct backlight device, and when displayed, an image can be displayed with uniform brightness. It was.

<Example 2>
The linear prisms 201a and 201b have a width of 150 μm, the width 413a of the region 421a where the linear prism 201a continues is 300 μm, and the width 413b of the region 421b where the linear prism 201b continues is 150 μm. By operating in the same manner as in Example 1, a direct type backlight device as shown in FIG. 3 was manufactured and evaluated. The results are shown in Table 1. In the region 421a occupied by the linear prism 201a, the total light transmittance of light perpendicularly incident on the light diffusion plate is 35.6%, and in the region 421b occupied by the linear prism 201b, the light incident perpendicularly to the light diffusion plate is obtained. The total light transmittance was 70.5%, and the difference was 34.9%.

<Example 3>
A direct type backlight device was manufactured 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 diffusing plate used in this example will be described with reference to FIG. With the light diffusion plate 101 attached, adjacent cold cathode fluorescent lamps (in FIG. 7, the distance corresponding to the middle 141 between the centers of 102a and 102b and the center of the cold cathode fluorescent lamps are A (10 mm), B 4 zones (7.2 mm), C (6 mm), and D (5 mm), each zone on the light exit surface of the light diffusing plate 101 has an apex angle of 85 ° as shown in FIGS. A prismatic linear prism 201a having a triangular cross section and a prismatic linear prism 201b having a triangular cross section with an apex angle of 125 ° are provided in a mixed manner and the width of the linear prisms 201a and 201b. 211a and 211b were set to 70 μm in all zones, and the mode of mixing linear prisms 201a and 201b was as follows for each zone.

A: As shown in FIG. 5, 201a and 201b are alternately arranged in a row.
B: As shown in FIG. 4, an uneven structure in which two rows 201a and one row 201b are arranged as one unit, and this unit is repeated.
C: As shown in FIG. 6, a concavo-convex structure in which three rows of 201a and one row of 201b are arranged as one unit, and this unit is repeated.
D: Only 201a.

  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. The total light transmittance of light perpendicularly incident on the light diffusion plate in the region occupied by the linear prism 201a is 35.6%, and the total light ray of light incident perpendicularly on the light diffusion plate in the region occupied by the linear prism 201b. The transmittance was 70.5%, and the difference was 34.9%.

<Example 4>
The linear prism 201b has an apex angle of 110 ° and a width of 100 μm (the apex angle and width of the linear prism 201a are 85 ° and 100 μm, respectively, as in the first embodiment), and the linear prisms 201a are arranged in three consecutive rows. A direct-type backlight device was manufactured and evaluated in the same manner as in Example 1 except that the concavo-convex structure having the portion and the portion in which the linear prisms 201b are arranged in a row was taken as one unit, and this unit was repeated. did. The results are shown in Table 2. The total light transmittance of light perpendicularly incident on the light diffusion plate in the region occupied by the linear prism 201a is 35.6%, and the total light ray of light incident perpendicularly on the light diffusion plate in the region occupied by the linear prism 201b. The transmittance was 56.5%, and the difference was 20.9%.

<Example 5>
The apex angle of the linear prism 201b is 140 ° and the width is 100 μm (the apex angle and width of the linear prism 201a are 85 ° and 100 μm, respectively, as in the first embodiment), and these linear prisms 201a and 201b are arranged in a row. A direct type backlight device was manufactured and evaluated in the same manner as in Example 1 except that they were alternately arranged. The results are shown in Table 2. The total light transmittance of light perpendicularly incident on the light diffusion plate in the region occupied by the linear prism 201a is 35.6%, and the total light ray of light incident perpendicularly on the light diffusion plate in the region occupied by the linear prism 201b. The transmittance was 78.5%, and the difference was 50.5%.

<Example 6>
A direct type backlight device was manufactured in the same manner as in Example 1 except that the shape of the light exit surface 101B of the light diffusion plate 101 was changed as described below. On the light exit surface 101B, the apex angle and width of the linear prism 201a were set to 85 ° and 100 μm, respectively, as in Example 1, the linear prism 201b was not provided, and the flat portion 201d shown in FIG. 9 was provided. The width of the flat part 201d was 100 μm, and the linear prisms 201a and the flat parts 201d were alternately arranged in a line.
The obtained direct type backlight device was evaluated in the same manner as in Example 1. The results are shown in Table 2. The total light transmittance of light perpendicularly incident on the light diffusion plate in the region occupied by the linear prism 201a is 35.6%, and the total light ray of light incident perpendicularly on the light diffusion plate in the region occupied by the linear prism 201b. The transmittance was 88.6%, and the difference was 53.0%.

<Comparative Example 1>
The linear prism is operated in the same manner as in Example 1 except that only the linear prisms having a triangular cross section with an apex angle of 100 ° and a width of 70 μm are arranged on the entire surface. The device was manufactured and evaluated. The results are shown in Table 3. In the region occupied by the linear prisms, the total light transmittance of light perpendicularly incident on the light diffusion plate was 45.4%.

<Comparative example 2>
The linear prism 201a has an apex angle of 105 ° and a width of 100 μm, and the linear prism 201b has an apex angle of 120 ° and a width of 100 μm. In operation, a direct backlight device was manufactured and evaluated. The results are shown in Table 3. In the region 421a occupied by the linear prism 201a, the total light transmittance of light vertically incident on the light diffusing plate is 52.4%, and in the region 421b occupied by the linear prism 201b, the light incident perpendicularly on the light diffusing plate The total light transmittance was 68.9%, and the difference was 16.5%.

<Comparative Example 3>
A direct type backlight device was manufactured and evaluated in the same manner as in Example 1 except that the linear prism 201b had an apex angle of 95 ° and a width of 100 μm. The results are shown in Table 3.
In the region 421a occupied by the linear prism 201a, the total light transmittance of light perpendicularly incident on the light diffusion plate is 35.6%, and in the region 421b occupied by the linear prism 201b, the light incident perpendicularly to the light diffusion plate is obtained. The total light transmittance was 40.3%, and the difference was 4.7%.

<Comparative example 4>
The apex angle of the linear prism 201a is 85 ° and the width is 200 μm, the apex angle of the linear prism 201b is 125 ° and the width is 200 μm, the width 413a of the region 421a where the linear prism 201a is continuous is 400 μm, A direct type backlight device was manufactured and evaluated in the same manner as in Example 1 except that the width 413b of the region 421b where the prisms 201b are continuous was set to 200 μm. The results are shown in Table 3.
In the region 421a occupied by the linear prism 201a, the total light transmittance of light perpendicularly incident on the light diffusion plate is 35.6%, and in the region 421b occupied by the linear prism 201b, the light incident perpendicularly to the light diffusion plate is obtained. The total light transmittance was 70.5%, and the difference was 34.9%.

<Comparative Example 5>
The arrangement of the linear prisms 201a and 201b is such that the concavo-convex structure in which the linear prisms 201a arranged in four rows and the two rows 201b are arranged as one repeating unit, and this unit is repeated. Were operated in the same manner as in Example 1 to produce and evaluate a direct type backlight device. The results are shown in Table 3. The total light transmittance of light perpendicularly incident on the light diffusion plate in the region occupied by the linear prism 201a is 35.6%, and the total light ray of light incident perpendicularly on the light diffusion plate in the region occupied by the linear prism 201b. The transmittance was 70.5%, and the difference was 34.9%.

  As is apparent from the results of Examples and Comparative Examples, Comparative Example 1 having only one type of linear prism on the light diffusion plate, and total light transmittance difference in the region occupied by two types of linear prisms, but occupied by them. However, compared with Comparative Examples 2 and 3, which are outside the specified range of the present invention, the direct-type backlight devices of Examples 1 to 6 according to the present invention were remarkably superior in luminance uniformity. Also, the direct type backlight devices of Examples 1 to 6 according to the present invention are compared with Comparative Examples 4 and 5 in which the range in which the same linear prism continuously occupies the light exit surface is outside the specified range of the present invention. The hiding of the bright lines was very good.

DESCRIPTION OF SYMBOLS 101 Light diffusing plate 101A Light incident surface 101B Light output surface 102 Linear light source 103 Reflector 201a, 201b Linear prism

Claims (6)

A plurality of linear light sources arranged substantially parallel to each other;
A reflector that reflects light from the linear light source;
A light diffusing plate having a light incident surface on which direct light from the linear light source and reflected light from the reflecting plate are incident, and a light emitting surface that diffuses and emits light incident from the light incident surface;
A direct-type backlight device comprising:
At least one of the light incident surface and the light emitting surface has a concavo-convex structure group in which repeating units composed of two or more different concavo-convex structures are periodically arranged in at least a part thereof,
A plane that passes through the center of each linear light source and is parallel to the normal of the light diffusing plate is used as a reference plane.
In a region passing through the center of each linear light source and included in a range within 45 ° of the polar angle as an angle with respect to the reference plane, the same repeat unit along the direction perpendicular to the reference plane The area occupied by the concavo-convex structure is 350 μm or less,
Of the two or more different concavo-convex structures (a) and (b) of the two or more different concavo-convex structures in the repeating unit, the light incident perpendicularly to the light diffusion plate in the region occupied by the concavo-convex structure (a) The total light transmittance X (%) and the total light transmittance Y (%) of light perpendicularly incident on the light diffusion plate in the region occupied by the uneven structure (b) are 95 ≧ | X−Y | ≧ A direct type backlight device satisfying the relationship of 20. The direct type backlight device according to claim 1,
The concavo-convex structure is a linear prism extending substantially parallel to the longitudinal direction of the linear light source;
The direct type backlight device in which the shape of the cross section of the linear prism perpendicular to the longitudinal direction of the linear light source is any of a polygonal convex portion, a flat portion, and a combination thereof. The direct type backlight device according to claim 1,
The light diffusion plate is configured to include a transparent resin as a main component,
The concavo-convex structures (a) and (b) are linear prisms (a) and (b) having a triangular cross section formed on the light emitting surface, respectively.
The apex angle θa of the linear prism (a) is expressed by the following formula (1):
θa <180-2sin ⁻¹ (1 / n) (1a)
And the apex angle θb of the linear prism (b) is the following formula (1b):
θb ≧ 180−2 sin ⁻¹ (1 / n) (1b)
(In formulas (1a) and (1b), n represents the refractive index of the transparent resin)
Direct type backlight device that meets the requirements. The direct type backlight device according to claim 1,
A direct type backlight device in which the ratio A / B between the number A of the most uneven structures of the seeds present in the repeating unit and the number B of the most uneven structures of the seeds is 10 or less. The direct type backlight device according to claim 1,
A direct type backlight device in which the abundance ratio of the two types of concavo-convex structures (a) and (b) in the repeating unit changes stepwise as the distance from the linear light source increases.   A liquid crystal display device comprising: the direct type backlight device according to claim 1; and a liquid crystal panel disposed on a light emitting side of the direct type backlight device.

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