JPWO2008050763A1 - Direct backlight unit - Google Patents

Abstract

Provided is a direct type backlight device capable of improving the luminance uniformity of a light emitting surface. A direct-type backlight device including a reflector, a light source, and a light diffusing plate, wherein an uneven structure of a predetermined Ra (max) is formed on the light emitting surface, and light is incident on a range MR on the light incident surface. A transmission suppression layer is provided, and the minimum value of MR transmittance is between the position where the center position of the light source is projected onto the light diffusion plate and the position where the intermediate position between the adjacent light sources is projected onto the light diffusion plate. 5% or more lower than the transmittance value of the portion including the light diffusing plate and the light transmission suppressing layer, the average distance a between the centers of the adjacent light sources, the center of the light sources, and the light incident surface The range MR is a region within a distance M from the reference line, where the reference line is a position where the center line of the light source is projected onto the incident surface of the light diffusing plate. , M and b satisfy a predetermined relationship .

Description

  The present invention relates to a direct-type backlight device, and more particularly to a direct-type backlight device that can increase the luminance uniformity of a light emitting surface.

  Conventionally, in a liquid crystal display device, a plurality of light sources, a reflecting plate that reflects light from these light sources, direct light from the light source and reflected light from the reflecting plate are incident from a light incident surface, and the incident light is received. A direct type backlight device including a light diffusing plate that diffuses and exits from a light emitting surface is used. In such a direct type backlight device, there is a problem that in the light emitting surface which is a light emitting surface, the portion directly above the light source is likely to have higher brightness than the other portions. For this reason, there is a demand for development of a technique that has sufficient luminance and uniformizes the luminance of the light emitting surface (suppresses luminance unevenness).

  For example, Patent Document 1 discloses a technique in which a pattern made of white ink dots is provided on a surface of a light diffusing plate that faces a linear light source so that the portion closer to the linear light source has a higher density. With such a configuration, the luminance uniformity of the light emitting surface can be increased. However, in such a configuration, when the distance between the linear light sources is increased or the distance between the linear light sources and the light incident surface is decreased, the light amount incident on the light diffusion plate is small at the linear light source intermediate position, and Since the light is diffused by the light diffusing plate, the luminance in the middle of the linear light source is lowered, and the luminance between the linear light source and the intermediate luminance cannot be balanced, resulting in luminance unevenness.

  Therefore, Patent Document 2 describes a configuration in which a plurality of lenticular or prism-like concavo-convex structures extending along the longitudinal direction of a linear light source are provided on a light incident surface of a light diffusing plate in a direct type backlight device. ing. In this case, an embodiment is disclosed in which the distance between the linear light sources is equal to the distance between the linear light sources and the light incident surface. According to such a configuration, it is possible to increase the luminance while increasing the luminance uniformity, but if the distance between the linear light sources is increased or the distance between the linear light source and the light incident surface is decreased, In the concavo-convex structure, there is a problem that light directly above the linear light source cannot be sufficiently suppressed, and the luminance in the middle of the linear light source cannot be balanced, resulting in uneven luminance.

  Further, in Patent Documents 3 and 4, in a direct type backlight device, a concavo-convex structure on a light exit surface of a light diffusing plate, and a light incident surface corresponding to the convex portion or a reflecting portion at a position inside the light diffusing plate Is described. According to such a configuration, it is possible to increase the brightness by suppressing the outgoing light in an unnecessary direction, but since the reflection portion exists evenly over the entire surface of the light diffusion plate, the brightness in the middle of the linear light source is also increased. If the distance between the linear light sources is increased, or the distance between the linear light sources and the light incident surface is decreased, the luminance between the light source directly above and the middle is not balanced, resulting in uneven brightness. There was a problem.

JP-A-6-273760 JP 2000-182418 A JP 2006-318886 A JP 2006-208930 A

  Incidentally, in recent years, there has been a demand for the development of a technology for reducing power consumption by reducing the number of linear light sources and a thinner backlight device. However, in the configurations shown in Patent Documents 1 to 4, the distance between the linear light sources is increased compared to the distance between the linear light source and the light incident surface, in other words, the number of linear light sources used is reduced, As the distance between the linear light source and the light incident surface decreases, the power consumption can be reduced and the backlight device can be made thinner. However, as described above, the pattern of white ink dots on the light diffusion plate There is a problem that luminance unevenness occurs only by providing a plurality of lenticular or prismatic uneven structures extending along the longitudinal direction of the linear light source. For this reason, there is a demand for the development of a technique that can sufficiently increase the luminance uniformity even when the number of linear light sources is reduced. Such a problem occurs not only in a linear light source but also in a point light source.

  An object of the present invention is to provide a direct type backlight device capable of increasing the luminance uniformity of a light emitting surface.

  The inventor is not limited to the type of light source, and in the light diffusion plate provided with an uneven structure on at least one surface, the distance between the light sources, the refractive index of the material constituting the light diffusion plate, the size of the light source, and It has been found that the above object can be achieved by highly relating the installation conditions of the light transmission suppressing layer that suppresses the light transmittance.

According to the present invention, the following direct type backlight device is provided.
[1] 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 incident from a light incident surface and diffused to obtain a light emitting surface. A direct-type backlight device comprising: a light diffusing plate that emits light from at least one of the light emitting surface and the light incident surface; A concavo-convex structure in which Ra (max), which is the maximum value of the center line average roughness Ra measured along various directions, is 3 μm to 1,000 μm is formed, and among the light emitting surface and the light incident surface of at least one surface, at least a range M _R inhibits light transmission suppressing layer the transmission of light is provided, in the range M _R, of the light diffuser plate and the transmittance of the portion including the light transmission suppressing layer The minimum value is the center position of the linear light source Of the portion including the light diffusing plate and the light transmission suppressing layer at a position intermediate between the position projected onto the light diffusing plate and the position where the center position of the adjacent linear light source is projected onto the light diffusing plate. The average distance between the centers of the adjacent linear light sources is a (mm), and the average distance between the center of the linear light sources and the light incident surface is b (mm). satisfy the relation of 1.7 ≦ a / b ≦ 23.0, the range M _R is a reference line position of the centerline is projected on the incident surface of the light diffuser plate of the linear light source, the reference line Is a region within a distance M (mm) from where M and b satisfy a relationship of 0 ≦ M <b × tan (2π / 9).
[2] Light diffusion in which a reflecting plate, a plurality of point light sources, direct light from these point light sources and reflected light from the reflecting plate are incident from a light incident surface and diffused to be emitted from a light emitting surface A at least one surface of the light exit surface and the light incident surface along at least a part thereof along various directions within the surface. An uneven structure having a maximum value Ra (max) of the average roughness Ra of the center line of 3 μm to 1,000 μm is formed, and at least one of the light emitting surface and the light incident surface , at least range M _R inhibits light transmission suppressing layer the transmission of light is provided, in the range M _R, the minimum value of the light diffuser plate and the transmittance of the portion including the light transmission suppressing layer, the The light diffusing plate is positioned at the center of the point light source. From the transmittance value of the portion including the light diffusing plate and the light transmission suppressing layer at a position intermediate between the position projected onto the light diffusing plate and the center position of the adjacent point light source projected onto the light diffusing plate Is 5% or more lower, the average distance a (mm) between the centers of the adjacent point light sources, and the average distance between the center of the point light sources and the light incident surface is b (mm), and 0.5 ≦ a satisfy the relationship of /B≦15.0, the range M _R is the center point of the point light source as a reference point the projection position on the incident surface of the light diffuser plate, the distance M from the reference point (mm) A direct-type backlight device in which M and b satisfy the relationship of 0 ≦ M <b × tan (2π / 9).
[3] In the direct type backlight device, the concavo-convex structure is a linear prism having a polygonal cross section extending substantially parallel to the longitudinal direction of the linear light source, or a shape in which the cross section includes a curved portion. Direct type backlight device with a structure in which multiple lenticulars are arranged.
[4] In the direct type backlight device, the light transmission suppressing layer is configured by a printing layer that reflects and / or absorbs incident light.
[5] The direct type backlight device, wherein the printing layer is provided so that the light transmittance increases continuously or stepwise as the distance from the light source increases.
[6] In the direct type backlight device, in the surface on which the printed layer is formed, the direct type backlight device having a center line average roughness Ra at a position where the printed layer is formed is 0.005 μm to 5 μm. .
[7] In the direct type backlight device, the concavo-convex structure is a direct type backlight device having a configuration in which a plurality of dot-like protrusions or dent-like structural units are arranged.
[8] In the direct type backlight device, the uneven structure is formed on the light emitting surface, and the light incident surface is a substantially flat surface having a center line average roughness Ra of less than 3 μm.
[9] In the direct type backlight device, θ (max) (degrees) is the maximum value of the arithmetic average inclination angles θ measured along various directions within the surface on which the uneven structure is formed. A direct-type backlight device satisfying a relationship of sin ⁻¹ (R / 2nb) + sin ⁻¹ (1 / n)> θmax, where n is the refractive index of the concavo-convex structure portion, and R is the outer diameter of the light source.
[10] In the direct-type backlight device, the light transmission suppression layer is provided at least at a predetermined position NO on either the light emitting surface or the light incident surface, and the position NO is obtained when light is emitted from the light source. A path that exits from the center of the light, passes through the light diffusing plate, and exits in a direction parallel to the thickness direction of the light diffusing plate, and a position where a light incident surface or a light emitting surface of the light diffusing plate intersects, The transmittance of the portion including the light diffusion plate and the light transmission suppressing layer at the position NO is the maximum value of the transmittance between the position NO and a position where an intermediate position of the adjacent light source is projected onto the light diffusion plate. Direct type backlight device that is 5% lower than
[11] In the direct-type backlight device, the minimum value TA of the light diffuser plate and the transmittance of the portion including the light transmission suppressing layer at a distance R / 2 within the range N _R of centering the position NO, When the average value TB of the transmittance of the portion including the light diffusing plate and the light transmission suppressing layer between the position N0 and the position where the center of the light source is projected onto the light diffusing plate, TA <TB Direct type backlight device that meets the requirements.
[12] In the direct type backlight device, the light diffusing plate is made of a resin composition containing a transparent resin, and the resin composition has a total light transmittance of 40% or more and 98% measured by normal incident light. Direct type backlight device which is the following.
[13] In the direct type backlight device, the light diffusion plate is made of a resin composition containing a transparent resin, and the water absorption rate of the resin composition is 0.25% or less.

  According to the present invention, the average distance between the centers of the light sources (linear light source and point light source) and the average distance between the center of the light source and the light incident surface satisfy a certain relationship, and at least one of the light diffusion plates. By forming a concavo-convex structure on at least a portion of the surface and providing a predetermined light transmission suppression layer on at least one surface of the light diffusing plate, the distance between the light diffusing plate and the light source can be reduced when the number of light sources used is reduced. Even in this case, it is possible to increase the luminance uniformity of the light emitting surface.

FIG. 1 is a longitudinal sectional view schematically showing a direct type backlight device according to a first embodiment of the present invention. FIG. 2 is a diagram for explaining Fresnel reflection on the light incident surface of the light diffusing plate. FIG. 3 is a diagram for explaining the influence of the concavo-convex structure on the light emission direction. FIG. 4 is a diagram for explaining the projected area of the light source onto the light incident surface of the light diffusion plate. FIG. 5 is a graph for explaining Fresnel reflection on the light incident surface of the light diffusion plate. FIG. 6 is a diagram for explaining the relationship between the incident angle of light from the light source to the light incident surface of the light diffusing plate and the projected area on the light incident surface of the light diffusing plate of the light source. FIG. 7 is a diagram illustrating how light enters the light incident surface of the light diffusion plate. FIG. 8 is a longitudinal sectional view schematically showing the shape of the lenticular. FIG. 9 is a diagram for explaining a light transmission suppressing layer provided on the light incident surface of the light diffusing plate. FIG. 10 is a diagram for explaining the effect of the printing layer provided on the light incident surface of the light diffusing plate. FIG. 11 is a diagram for explaining the effect when the print layer shown in FIG. 10 is not provided. FIG. 12 is a diagram for explaining how the light incident on the light diffusion plate from the linear light source travels. FIG. 13 is a diagram for explaining the path of light reaching the concavo-convex structure from the light source. FIG. 14 is a diagram for explaining the relationship between the critical angle and the perpendicularly incident light in the concavo-convex structure. FIG. 15 is a diagram for explaining an image of a linear light source observed through the light diffusion plate. FIG. 16 is a diagram for explaining the path of light from the linear light source. FIG. 17 is a diagram for explaining how the light incident from the linear light source enters the print layer provided on the light incident surface of the light diffusion plate. FIG. 18 is a diagram for explaining the relationship between the distances M and b. FIG. 19 is a longitudinal sectional view schematically showing a direct type backlight device according to the second embodiment of the present invention. FIG. 20 is a longitudinal sectional view schematically showing a first aspect of the linear prism. FIG. 21 is a longitudinal sectional view schematically showing a second aspect of the linear prism. FIG. 22 is a longitudinal sectional view schematically showing a direct type backlight device according to the third embodiment of the present invention. FIG. 23 is a plan view schematically showing a first mode of arrangement of point light sources. FIG. 24 is a plan view schematically showing a second aspect of the arrangement of the point light sources. FIG. 25 is a plan view schematically showing a third aspect of the arrangement of the point light sources. FIG. 26 is a diagram for explaining a light transmission suppressing layer provided on the light incident surface of the light diffusing plate. FIG. 27 is a cross-sectional view schematically showing the tip of the cutting tool. FIG. 28 is a perspective view showing the concavo-convex structure surface formed on the stamper. FIG. 29 is a longitudinal sectional view for explaining the shape of the reflecting plate. FIG. 30 is a diagram for explaining the light transmission suppressing layer provided on the light incident surface of the light diffusing plate. FIG. 31 is a diagram for explaining a light transmission suppressing layer provided on the light incident surface of the light diffusion plate. FIG. 32 is a longitudinal sectional view schematically showing the diffusion plate of Comparative Example 8.

<First Embodiment>
(Direct type backlight device)
A direct type backlight device according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view schematically showing a direct type backlight device 1 according to the present embodiment. As shown in FIG. 1, the direct type backlight device 1 includes a plurality of linear light sources 10, a reflecting plate 20 that reflects light from these linear light sources 10, and direct light and reflection from the linear light source 10. Reflected light from the plate 20 is incident from the light incident surface 30A, and the incident light is diffused from the light emitting surface 30B to be emitted, and the light diffusing plate 30 is provided on the light incident surface 30A. The light transmission suppression layer 50 is provided.

(Linear light source)
As the linear light source 10, a straight-tube cold cathode tube (CCFL) is used from the viewpoint of luminance uniformity. The linear light source 10 is not limited to a cold cathode tube, but includes, for example, an external electrode fluorescent tube (EEFL), a hot cathode tube, a xenon lamp, a mercury xenon lamp, and a light emitting diode (LED) arranged in a straight line. A combination of an LED and a light guide can also be used. In this embodiment, a straight light source is used as the linear light source, but a substantially U-shaped tube in which two substantially parallel tubes are connected by one semicircular tube, and a substantially parallel 3 Examples include an approximately N-shaped tube in which two tubes are connected by two semicircular tubes, and an approximately W-shaped tube in which four approximately parallel tubes are connected by three semicircular tubes. Can do.

  In the present invention, a combination of LEDs arranged in a straight line or a combination of an LED and a light guide is also considered as a single linear light source. Of those connected by a semicircular tube, the substantially U-shaped The tube is assumed to be two linear light sources, the substantially N-shaped tube is assumed to be three linear light sources, and the substantially W-shaped tube is assumed to be four.

  The number of linear light sources used 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 16, 14, 12, 8, or an odd number. It can be a book.

  In the present embodiment, the plurality of linear light sources 10 are arranged substantially parallel to each other. The average distance between the central axes of any adjacent linear light sources 10 is substantially constant at a (mm). Note that “substantially parallel” means within a range of ± 5 degrees from a truly parallel state. However, in the present invention, the plurality of linear light sources are not limited to this embodiment, and may be arranged in parallel. Further, the average distance between the central axes of the adjacent linear light sources may be random, or may have a regularity that increases or decreases toward a specific location. Here, the specific part is, for example, a central part including a line connecting one long side of a rectangular light diffusing plate or the central positions of opposing short sides.

  In the present embodiment, the relationship (A) of 1.7 ≦ a / b ≦ 23.0 is satisfied between the average distance a (mm) and the average distance b (mm). Furthermore, it is preferable to satisfy the relationship (B) of 3.5 ≦ a / b ≦ 17.0, and it is more preferable to satisfy the relationship (C) of 3.5 ≦ a / b ≦ 11.0. By satisfying such a preferable relationship, it is possible to reduce the number of linear light sources used while keeping the thickness of the backlight appropriate, and to suppress the power consumption of the apparatus. In addition, with the above configuration, the thickness of the backlight device can be further reduced.

  In order to reduce the number of light sources used in the direct type backlight device or to reduce the thickness of the device, it is only necessary to increase a / b. However, in order to suppress luminance unevenness, the configuration of the device is set to a specific range. It is important to. This will be described below.

FIG. 2 is a view for explaining Fresnel reflection on the light incident surface, and is a longitudinal sectional view schematically showing an adjacent light source and a light diffusion plate. FIG. 5 is a graph for explaining Fresnel reflection on the light incident surface of the light diffusion plate having a refractive index of 1.53, and shows the relationship between the incident angle (degrees) and the reflectance. Here, the average value of the reflectance of s-wave and p-wave light is shown.
As shown in FIG. 2, assuming that a position obtained by projecting the intermediate position of adjacent linear light sources onto the light incident surface is A, the incident angle of light from the linear light source toward position A (in this application, the incident angle is the incident surface) The angle between the normal direction and the incident direction is increased, and the amount of reflected light (Fresnel reflection) at position A increases. Further, as shown in FIG. 5, it can be seen that the reflectance increases when the incident angle exceeds 40 degrees (that is, a / b = 1.7). Therefore, in an aspect where the incident angle exceeds 40 degrees, the luminance at the position A is low. Further, when the incident angle exceeds 60 degrees (that is, a / b = 3.5), the reflectance value becomes nearly twice that of the incident angle of 40 degrees, and the tendency becomes remarkable. . For this reason, when the incident angle falls within the above range, the luminance at the position B (FIG. 2) where the linear light source is projected is higher than the position A, and the luminance unevenness occurs on the light emitting surface. Here, “projection” specifically means that the image of the light source is projected onto the surface at a viewpoint angle perpendicular to the surface.

  Therefore, in the light diffusing plate, by providing a light transmission suppressing layer at the position B where the linear light source is projected, the amount of light emitted from the light diffusing plate at the position B can be suppressed. In this way, by suppressing the amount of emitted light at the position B, it is possible to eliminate uneven brightness on the light emitting surface. However, as shown by the arrow on the left side of FIG. 3, when the uneven structure is not formed at the position A, the incident light is emitted from the light diffusion plate at the same angle as the incident angle. Therefore, a predetermined uneven structure is provided at the position A, and the direction of the emitted light is converted to the front direction as shown by the arrow on the right side of FIG. The luminance unevenness of the surface can be reduced.

  FIG. 4 is a diagram for explaining the projected area of light incident on the light incident surface from the linear light source. As shown in FIG. 4, at the position C where the light from the linear light source is incident at the incident angle θa, the light is incident from the linear light source compared to the position B where the light from the linear light source is incident at the incident angle of 0 degrees. The projected area of light incident on the surface is 1 / cos θa times. Here, since the luminance is the luminous intensity per unit area, the luminance on the light emitting surface decreases as the distance from the linear light source increases, that is, as the incident angle increases.

FIG. 6 is a graph for explaining the relationship between the incident angle (degrees) of light from the linear light source to the light incident surface and the projected area on the light incident surface. As shown in FIG. 6, when the value of 1 / cos θa starts to increase from 80 degrees (ie, a / b = 11.3) and exceeds 85 degrees (ie, a / b = 22.9), It grows rapidly. In other words, when the incident angle exceeds 85 degrees, the luminance between the linear light sources rapidly decreases, and it becomes difficult to suppress luminance unevenness.
For this reason, in this invention, it is necessary to satisfy | fill the relationship (A) mentioned above.

  The outer diameter R (mm) of the linear light source 10 is 2 ≦ R ≦ 30, preferably 2.5 ≦ R ≦ 25, and more preferably 2.5 ≦ R ≦ 20. The average distance b (mm) between the central axis of the linear light source 10 and the light incident surface 30A of the light diffusing plate 30 may be designed in consideration of the thickness and luminance uniformity of the direct type backlight device. 0.0 ≦ b ≦ 32.0, preferably 3.0 ≦ b ≦ 27.0, and more preferably 3.0 ≦ b ≦ 22.0. Thereby, the damage of the linear light source can be reduced, and the thickness of the direct type backlight device can be made appropriate. In this case, furthermore, by setting the average distance a (mm) between the centers of the adjacent linear light sources to 20 ≦ a ≦ 200, preferably 22 ≦ a ≦ 170, more preferably 23 ≦ a ≦ 150, By reducing the number of linear light sources used, the device can be easily assembled, power consumption can be reduced, or the thickness of the device can be reduced, and the angle difference between θb and θc in FIG. 7 can be reduced. The unevenness of brightness can be eliminated by the uneven structure of the light diffusing plate. When the angle difference between θb and θc becomes large, light at various angles enters the light diffusing plate from one point of the light source, making it difficult to control the optical path with the concavo-convex structure and making it difficult to suppress luminance unevenness.

In the present embodiment, the plurality of linear light sources 10 are of the same type having the same diameter. However, a plurality of types of linear light sources having different diameters can be used.
In the present embodiment, the plurality of linear light sources 10 are arranged such that the average distance b (mm) to the light incident surface 30A is substantially constant for all the linear light sources. Note that “almost constant” means that the maximum value of the average distance b (mm) / the minimum value of the average distance b (mm) ≦ 1.3. However, a plurality of linear light sources may be arranged so that some linear light sources are closer to the light incident surface 30A than other linear light sources. For example, it may be random or may have regularity that becomes larger or smaller as it goes to a specific location. Here, the specific location is, for example, a central location including a long side of a rectangular light diffusing plate or a line connecting the central locations of opposing short sides.

(a reflector)
For the reflecting plate 20, a resin colored in white or silver, a metal, or the like can be used. Among these, a resin can be preferably used for the reflecting plate 20 from the viewpoint of weight reduction. The color of the reflector 20 is preferably white from the viewpoint of improving the luminance uniformity. Moreover, what mixed white and silver can also be used from a viewpoint which balances a brightness | luminance and brightness | luminance uniformity highly.

  Projections that protrude toward the light diffusing plate and extend along the longitudinal direction of the plurality of linear light sources may be provided in a region of the reflecting plate located between the plurality of linear light sources. At this time, it is preferable that the protrusion is provided at a substantially middle position between adjacent linear light sources. Furthermore, the cross-sectional shape in the short direction of the protrusion is not particularly limited, but isosceles triangle, isosceles trapezoid, circular cut shape, elliptical shape cut by a line segment parallel to the short axis, and elliptical shape is long. Examples include a shape cut by a line segment parallel to the axis, a shape in which downward convex curves are connected so as to be a line object, and a shape in which upward convex curves are connected in line symmetry. The apex portions of these shapes may be pointed or rounded. From the viewpoint of brightness uniformity and ease of production, a triangular shape is preferable. Moreover, it is preferable that the cross-sectional shape of the protrusion is line symmetric with respect to a line segment perpendicular to the thickness direction of the light diffusion plate. By setting it as such a structure, the brightness nonuniformity in the light-projection surface of a light diffusing plate can be suppressed.

  The protrusions may be formed so as to extend continuously in a bowl shape, or may be formed such that a plurality of vertical bodies are connected in the longitudinal direction with or without spacing. However, it is preferable to make it continuous in a bowl shape in that the luminance uniformity can be further improved.

  As the method of installing the protrusion, a method of painting a metal frame with a protrusion in white or silver, a method of attaching a white or silver reflective sheet to a metal frame with a protrusion, a flat surface of white or silver Examples thereof include a method of bending a reflecting sheet and placing it on a flat metal frame, and a method of molding a white or silver resin using a mold having a predetermined shape.

(Light diffusion plate)
As a material constituting the light diffusion plate 30, glass and resin can be used. As the resin, a transparent resin, a resin composition of two or more resins that are difficult to mix, a resin composition in which a light diffusing agent is dispersed in the transparent resin, and the like can be used. Among these, the material constituting the light diffusing plate 30 is preferably a resin because it is lightweight and easy to mold, and a transparent resin is preferable from the viewpoint of easily improving luminance. From the viewpoint of easy adjustment of haze, a resin composition in which a light diffusing agent is dispersed in a transparent resin 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, a copolymer of an aromatic vinyl monomer and a (meth) acrylic acid alkyl ester having a lower alkyl group, polyethylene terephthalate, terephthalic acid-ethylene glycol-cyclohexanedimethanol copolymer, polycarbonate, acrylic resin, and Examples thereof include 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.
In particular, when a / b is smaller than 1.7, the distance between the light diffusing plate and the linear light source is short or the linear light sources are separated from each other, so that the light diffusing plate is easily heated locally. As a result, if the water absorption is greater than 0.25%, the local moisture content fluctuates greatly, resulting in a difference in expansion coefficient depending on the location, deformation is particularly likely to occur, and uneven brightness occurs. In this case, the water absorption is preferably 0.25% or less, and more preferably 0.15% or less.

  Furthermore, a resin having an alicyclic structure is more preferable because it has good fluidity and can efficiently produce a large light diffusion plate. Further, a resin composition in which a light diffusing agent is mixed with a resin having an alicyclic structure has both high permeability and high diffusibility necessary for a light diffusing plate, and can improve chromaticity. Can be 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, the alicyclic structure is preferably a cycloalkane structure or a cycloalkene structure, and more preferably a cycloalkane structure. The number of carbon atoms constituting the alicyclic structure is usually 4 to 30, preferably 5 to 20, and more preferably 5 to 15. In this case, it is preferable that the mechanical strength, heat resistance, and moldability of the light diffusion plate can be highly balanced.

  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 preferable. 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 aromatic hydrogenated copolymers of copolymers with other possible monomers.

  The light diffusing agent is a particle having a property of diffusing light, and examples thereof include 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. As an organic filler, polystyrene resin, polysiloxane resin, and fine particles composed of a crosslinked product thereof are preferable in terms of high dispersibility, high heat resistance, and no coloration (yellowing) during molding. Fine particles made of a cross-linked product of polysiloxane resin are more preferable in terms of excellent properties.

  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 preferably used in a state of being uniformly dispersed in the transparent resin.

  In the case where the light diffusing agent is dispersed in the transparent resin, the content ratio of the light diffusing agent can be appropriately selected according to the thickness of the light diffusing plate, the interval between the linear light sources, etc., but the light diffusing agent is dispersed in the transparent resin. The total light transmittance of the resin composition is preferably adjusted to be 40% to 98%, and more preferably adjusted to be 45% or more and 95% or less. By setting the total light transmittance to the above preferable range, the luminance and the luminance uniformity can be further improved.

  The total light transmittance is based on JIS K7361-1 (this standard is measured using a single beam photometer equipped with a light source and a photo detector specified by the CIE standard). It is a value measured with a smooth 2 mm thick plate.

  The thickness of the light diffusing plate 30 is preferably 0.4 mm to 5 mm, and more preferably 0.8 mm to 4 mm. By making the thickness of the light diffusing plate 30 within the above preferable range, it is possible to suppress the bending due to its own weight and to facilitate the molding.

  As shown in FIG. 1, a concavo-convex structure 40 is formed on a light emission surface 30B corresponding to one surface. In the present embodiment, the concavo-convex structure 40 is configured to include a plurality of lenticulars 41 having a convex arcuate cross section that extend substantially parallel to the longitudinal direction of the linear light source 10. Here, the center line average roughness Ra along the direction orthogonal to the longitudinal direction of the lenticular 41 (left-right direction in the figure) is 3 μm to 1,000 μm. In the light exit surface 30B, the center line average roughness Ra measured along the left-right direction of the center line average roughness Ra measured along various directions in the surface indicates the maximum value. . The center line average roughness Ra of the light exit surface 30B, which is the target surface, can be obtained by direct reading using an ultradeep shape measuring microscope based on JIS B0601. The light incident surface 30A corresponding to the other surface is a flat surface having a center line average roughness Ra of 3 μm or less in an arbitrary direction within the surface. Here, “the maximum value of the center line average roughness Ra measured along various directions” can be simply the maximum value of the center line average roughness measured along all directions.

  In addition, as a curve which comprises the cross section of the lenticular 41, it is good also as circular arc shape as mentioned above, and it is good also as elliptical arc shape, parabolic arc shape, etc. Moreover, as shown in FIG. 8, it can also be set as the shape which has the two hypotenuses S of a triangle, and the curved part C (for example, circular arc shape) formed in the shape of a curve by the vertex part of this triangle. The length of the curved portion C is 40% or more of the total length of the two oblique sides S and the curved portion C.

  The method for forming the concavo-convex structure on the surface of the light diffusing plate is not particularly limited. For example, a method of forming the concavo-convex structure on the surface of the flat light diffusing plate may be used, or it 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 a method for forming a concavo-convex structure on the surface of the flat light diffusion plate include a method of cutting the surface of the flat light diffusion plate, a prism sheet having a desired shape on the flat light diffusion plate, and the like. A method of laminating or pasting a sheet having a concavo-convex structure, applying a photo-curing resin or a thermosetting resin to the surface of a flat light diffusing plate, transferring a desired shape to the coating film with a roll or a die, and the state And a method of curing the coating film and an embossing method in which the surface of the flat light diffusion plate is pressed with a roll or a stamp having a desired shape.

  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 shape transfer rate, 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.

Next, the light transmission suppressing layer provided on the light incident surface of the light diffusion plate will be described.
FIG. 9 is a diagram for explaining a light transmission suppressing layer provided on the light incident surface. As shown in FIG. 9, in the direct type backlight device 1 of the present embodiment, a position X where the central axis of an arbitrary linear light source 10A is projected on the light incident surface 30A and a line adjacent to the linear light source 10A. A light transmission suppressing layer 50 that suppresses transmission of light is provided in a region between the position Y projected from the central axis of the light source 10B. In the present embodiment, the light transmission suppressing layer 50 is provided so that the light transmittance increases as the distance from the linear light source 10A located at the closest position increases.

  The light transmittance in the present invention is the total light transmittance of light incident from the center of the light source toward the position of interest unless otherwise specified.

The light transmission suppressing layer 50 is configured by a printed layer that reflects and / or absorbs incident light. By using a light transmission suppression layer as a printing layer, reflected light is scattered as shown in FIG. 10, and the amount of light at an intermediate position between adjacent linear light sources can be increased, thereby suppressing uneven brightness on the light emitting surface. Can do. When there is no printed layer and only the uneven structure of the light diffusing plate, the light that exits from the linear light source and enters the light diffusing plate perpendicularly as shown in FIG. Therefore, if the distance between the linear light sources is increased or the distance between the linear light sources and the light incident surface is reduced, the reflected light does not reach the middle of the linear light sources efficiently, and uneven brightness is suppressed. Can not.
In addition, if the number of linear light sources is reduced or the thickness of the backlight device is reduced, the position where the linear light source is projected becomes higher in brightness than other parts under certain conditions. Must be installed at the projection position of the linear light source to suppress uneven brightness. This will be described below.

FIG. 12 is a diagram for explaining how the light incident on the light diffusion plate from the linear light source travels, and FIG. 13 is a diagram for explaining the path of light reaching the concavo-convex structure from the linear light source. FIG. 14 is a diagram for explaining the relationship between the critical angle and the perpendicularly incident light in the concavo-convex structure.
As shown in FIG. 13, on the slope S1 of the concavo-convex structure of the light diffusing plate, there is light L1 that is perpendicularly incident on the light incident surface from the center of the linear light source and light L2 that is incident from the end of the linear light source. . The angle between the vertical direction of the main surface of the light diffusion plate and the light L2 incident on the light diffusion plate is θd, and the angle between the vertical direction of the main surface of the light diffusion plate and the light L2 incident on the light diffusion plate is θe. From the law of refraction, the relationship of formula (1) is satisfied.
θe = sin ⁻¹ ((1 / n) sin θd) (1)
Further, when the refractive index of the concavo-convex structure is n, the outer diameter of the linear light source is R (mm), and the distance between the center of the linear light source and the light incident surface is b (mm), the expression (1) is expressed by the expression (2). )
θe = sin ⁻¹ (R / 2nb) (2)
On the other hand, the critical angle θg of the material constituting the concavo-convex structure is represented by the formula (3).
θg = sin ⁻¹ (1 / n) (3)
Therefore, the arithmetic average inclination angle of the concavo-convex structure in the cross section parallel to the light source arrangement direction (left and right direction in FIGS. 12 to 14) and perpendicular to the main surface of the light diffusion plate is θ (max), and the light L1 and the slope of the concavo-convex structure Is the angle θf formed by the line 1401 indicating the critical angle θg direction and the light L1.
θf = 90−θg−θh
= 90−sin ⁻¹ (1 / n) − (90−θ (max))
= Θ (max) −sin ⁻¹ (1 / n) (4)
Here, when θe is larger than θf, that is, when the relationship of Expression (5) is satisfied, the light from the linear light source is emitted from the light diffusion plate without being reflected by the slope S1 of the concavo-convex structure.
θe> θf
When Expression 2 and Expression 4 are substituted, sin ⁻¹ (R / 2nb)> θ (max) −sin ⁻¹ (1 / n)
sin ⁻¹ (R / 2nb) + sin ⁻¹ (1 / n)> θ (max) (5)

  In order to prevent the position where the linear light source is projected on the light emitting surface, which is the light exit surface of the light diffusing plate, from being brighter than other parts, the light from the linear light source is In order to reflect and return the light into the backlight device, it is necessary to totally reflect the light on the slope S1. However, total reflection does not occur when the relationship of equation (5) is satisfied. Therefore, as shown in FIG. 17, it is necessary to suppress the transmission of light corresponding to the projection position of the linear light source by providing a printing layer in a range including the position where the linear light source is projected. Can be suppressed. This effect becomes more prominent as the outer diameter R of the light source increases or the distance b between the light source center and the light incident surface decreases. The arithmetic average inclination angle can be obtained based on JIS B0601-1994. In this embodiment, it is computable using ultra deep shape measuring microscope VK-9500 (made by Keyence Corporation).

Further, as described above, for a small range of the Fresnel reflection of the light source upper becomes higher luminance than the other portions, as shown in FIG. 18, providing a light transmission suppressing layer in a range M _R comprising at least the high luminance Thus, uneven brightness can be suppressed. That is, it is necessary to provide a light transmission suppression layer at least in a range where the incident angle to the light diffusion plate from directly above the light source is 40 °. Here, the range M _R is the reference line (when the light source is a linear light source) or the distance from a reference point (if the light source is a point-like light source) is a region within M (mm). When the light source is a linear light source, the reference line is the position where the center line of the linear light source is projected onto the incident surface of the light diffusing plate. When the light source is a point light source, the reference point is a position where the center point of the point light source is projected onto the incident surface of the light diffusion plate. Here, M and b must satisfy the following formula (6).
0 ≦ M <btan (2π / 9) (6)

In the range M _R, the minimum value of the light diffuser plate and the transmittance of the portion including the light transmission suppressing layer, a position where the center position projected onto the light diffuser plate of the linear light sources, adjacent the linear The center position of the light source is set to be 5% or more lower than the transmittance value of the portion including the light diffusion plate and the light transmission suppression layer at a position intermediate between the position projected on the light diffusion plate.
Here, “the transmittance of the portion including the light diffusing plate and the light transmission suppressing layer” is a transmittance of light that transmits both of them in a portion where the light suppressing plate is provided on the light diffusing plate. There is a transmittance of light that is transmitted only through the light diffusing plate at a location where the transmission suppression layer is not provided.

In the present application, the reference to the difference in transmittance such as “lower than 5%” as described above indicates a difference between a certain value of transmittance in percentage and another value. For example, if the transmittance at a certain point P _A is 50% and the transmittance at another certain point P _B is 55%, the transmittance at the point P _A is 5% lower than the transmittance at the point P _B.

  In general, it is sufficient that there is at least a printed layer at a position where the light source is projected perpendicularly to the light diffusing plate. However, such a mode is not necessarily optimal for a light diffusing plate provided with an uneven structure. This will be described below.

FIG. 15 is a diagram illustrating a position where an image of the linear light source is observed after passing through the light diffusing plate, and FIG. 16 is a diagram for explaining a light path from the linear light source. As shown in FIG. 15, the light emitted from the light source is refracted by the concavo-convex structure of the light incident surface and the light emitting surface of the light diffusing plate, and an image is observed at a position different from the position directly above the light source. In other words, since the luminance is highest at a position slightly shifted rather than immediately above the light source, it is necessary to block the light of this path with the printing layer, and thereby uneven luminance can be suppressed. In addition, it is preferable that the transmittance of the printed layer on this path is lower than the other parts (specifically, 2% or more lower). The position where the image of the light source is observed is when the emitted light in FIG. 16 is perpendicular to the light diffusing plate, in other words, θl becomes equal to θ (max). Here, from the law of refraction, the following formulas (7) and (8) are established.
sinθl = nsinθk (7)
nsinθj = sinθi (8)
Further, θk and θj have the following relationship.
θk = θ (max) −θj (9)
Substituting equations (7) and (9) into equation (8),
θi = sin ⁻¹ (n × sin θj)
= Sin ⁻¹ (n × sin (θ (max) −θk))
= Sin ⁻¹ (n × sin (θ (max) −sin ⁻¹ (1 / n × sin θl)))
Since θl = θ (max),
θi = sin ⁻¹ (n × sin (θ (max) −sin ⁻¹ (1 / n × sin θ (max)))) (10)
Therefore, the distance O between the position where the center of the linear light source is projected on the light incident surface and the position on the light incident surface of the optical path where the image of the linear light source is observed on the light diffusion plate is expressed by the following equation. .
O = b × tan θi (11)
Substituting equation (10) into equation (11),
O = b × tan (sin ⁻¹ (n × sin (θ (max) −sin ⁻¹ (1 / n × sin θ (max)))))
The position of the light path that is emitted from the center of the light source and parallel to the thickness direction of the light diffusing plate is a position away from the position where the center of the linear light source is projected onto the light incident surface. NO.
In consideration of the outer diameter of the linear light source, in order to block the image of the linear light source on the light diffusion plate with the printed layer, at least the distance N (from the position where the center of the linear light source is projected onto the light incident surface) the range N _R where mm) satisfies the following relationship, it is necessary to provide the printing layer. The range N _R is a region indicated by an arrow 1501 in the example shown in FIG.
b × tan (sin ⁻¹ (n × sin (θ (max) −sin ⁻¹ (1 / n × sin θ (max)))) − R / 2 ≦ N ≦ b × tan (sin ⁻¹ (n × sin (θ (max) −sin ⁻¹ (1 / n × sin θ (max))))) + R / 2 (12)

  Since the position NO is the brightest position on the diffusion plate, it is important to make the light transmittance at that portion the lowest. That is, the minimum value TA of the transmittance including the light diffusing plate and the light transmission suppressing layer at the position NO, and between the position NO and the position where the center of the light source is projected on the light diffusing plate, When the average value TB of the transmittance of the portion including the light diffusing plate and the light transmission suppressing layer is set to an aspect satisfying TA <TB, it is possible to further suppress luminance unevenness.

  This print layer can be formed in a dot shape with, for example, white ink. In the case of using a dot-like print layer in this way, in order to control so that the light transmittance increases as the distance from the nearest linear light source 10 increases, the linear light source 10 As the distance increases, the formation area of the printing layer decreases. The reduction in the formation area means that the number and area of dot-like print layers per unit area are reduced. As a method of reducing the formation area of the print layer, the print layer may be continuously reduced or gradually decreased as the distance from the linear light source is increased.

  Specifically, as shown in FIG. 9, a position X where the central axis of the linear light source 10A is projected, and a distance between the central axis of the linear light source 10B and the central axis of the linear light source 10B from this position X. The area between the half position Z is divided at equal intervals (shown in FIG. 9 when it is divided into 10 equal parts), and these equally divided areas are sequentially designated as areas A1 to A10 from the left side of FIG. To do. Formed so as to reduce the formation range (unit:%) per unit area in a stepwise manner from the region A1 closest to the central axis of the linear light source 10A to the region A10 farthest from the linear light source 10A. Has been. The formation range of the print layer in each region is, for example, region A1: 90%, region A2: 87%, region A3: 72%, region A4: 50%, region A5: 35%, region A6: 19%, region A7. : 11%, region A8: 7%, region A9: 3%, region A10: 0%. Although not shown in FIG. 9, a similar print layer that is symmetric about Z can be provided in a region from position Y to position Z.

  In the light incident surface 30A, the center line average roughness Ra at the position where the print layer is formed is 0.005 μm to 5 μm. By setting it as such a range, the light which injected into the printing layer can be further scattered, and the brightness nonuniformity of a light emission surface can further be reduced. Ra here can be set to the maximum value among the values measured along various directions in the surface, similarly to Ra on the light exit surface 30B.

  According to the present embodiment, the linear light source 10 and the light diffusing plate 30 are disposed so as to satisfy the relationship (1), and the distance from the linear light source 10 closest to the light incident surface 30A of the light diffusing plate 30 is the closest. As the distance from the linear light source 10 at the position increases, a light transmission suppression layer 50 is provided to control the light transmittance to increase. Further, the light exit surface 30B has a center line average roughness Ra. Since the concavo-convex structure 40 having a maximum value Ra (max) of 3 μm to 1,000 μm is formed, the transmittance of incident light is suppressed by the light transmission suppressing layer 50 in the region immediately above the linear light source 10. In addition, the power consumption can be suppressed and the luminance uniformity of the light emitting surface can be increased.

  Moreover, since the light transmission suppression layer 50 is comprised by the printing layer, the light transmission suppression layer 50 can be formed by easy operation. At this time, since the portion where the printing layer is provided on the light diffusion plate 30 is slightly roughened, the light scattering effect can be enhanced and the luminance uniformity of the light emitting surface can be further improved. Furthermore, as a material of the light diffusing plate 30, by using a resin having a water absorption rate of 0.25% or less, it is possible to suppress the displacement of the printed layer provided on the light incident surface 30A of the light diffusing plate 30, The optical function can be fully demonstrated.

<Second Embodiment>
Next, a direct type backlight device according to a second embodiment of the present invention will be described.
This embodiment is different from the first embodiment in the configuration of the concavo-convex structure. For this reason, in this embodiment, it demonstrates centering around this difference and the description is abbreviate | omitted or simplified about the component same as or similar to the said embodiment. FIG. 19 is a longitudinal sectional view schematically showing the direct type backlight device according to this embodiment. The direct type backlight device 2 includes a light diffusing plate 230 having a light incident surface 230A and a light emitting surface 230B. On the light emitting surface 230B, a line-like uneven structure 240 is formed in which a plurality of linear prisms 241 having a polygonal cross section are arranged in parallel.

  The linear prism 241 can be a linear prism having a triangular cross-sectional shape (sometimes referred to as a triangular prism in this specification). The apex angle of the triangle constituting the triangular prism can be set to 40 ° to 170 °, and the interval between adjacent triangular prisms in the same plane can be set to 20 μm to 700 μm. By setting the apex angle and the interval as described above, the luminance unevenness of the light emitting surface can be sufficiently suppressed.

  Here, as the plurality of triangular prisms constituting the concavo-convex structure, those having the same shape (including those that can be seen) are generally used, but a plurality of types can also be used.

  Examples of the configuration including a plurality of types of triangular prisms include the following configurations. For example, as shown in FIG. 20, the triangular prism is formed so that the angles formed by the two inclined surfaces constituting the triangle and the surface perpendicular to the thickness direction of the light diffusion plate are equal, Between a certain point P of the light diffusing plate and a point Q that is a predetermined distance away from the point P in the short direction of the triangular prism, the distance from the point P and the point Q decreases continuously or intermittently. You may form in. At this time, it is preferable to arrange the linear light source at the position where the point P and the point Q are projected. In the present specification, “equal angle” means that the difference is within 1 degree.

  Further, the triangular prism has a cross-sectional shape that is line-symmetric with respect to a plane including the thickness direction of the light diffusion plate and the longitudinal direction of the triangular prism, and the concavo-convex structure includes a plurality of types of triangular prisms having different shapes. Also good. At this time, it is preferable that all types of these plural types of triangular prisms are included in the range of the width dimension of the linear light source along the direction perpendicular to the longitudinal direction of the triangular prism.

  The linear prism may have a polygonal cross section other than a triangular cross section. Examples of polygons include pentagons and heptagons. For example, as shown in FIG. 21, the linear prism is formed in a polygonal cross-section including at least four planes, and two of the at least four planes and the other two planes are related to the light diffusion. With respect to a plane including the thickness direction of the plate and the longitudinal direction of the linear prism, a configuration having a pentagonal cross section inclined in opposite directions can be adopted.

  According to the direct type backlight device of this embodiment, the same effects as those of the first embodiment can be obtained.

<Third Embodiment>
Next, a direct type backlight device according to a third embodiment of the present invention will be described.
This embodiment is different from the first embodiment in that the light source is a point light source, the configuration of the concavo-convex structure, and the configuration of the light transmission suppression layer. For this reason, in this embodiment, it demonstrates centering around these differences. FIG. 22 is a longitudinal sectional view schematically showing the direct type backlight device according to the present embodiment. As shown in FIG. 22, the direct type backlight device 3 according to this embodiment includes a plurality of point light sources 310 and a light diffusion plate 330 having a light incident surface 330A and a light emitting surface 330B. In addition, an uneven structure 340 in which a plurality of structural units 341 are arranged is formed on the light emitting surface 330B. The light incident surface 330A is provided with a light transmission suppressing layer 350 formed of a printing layer.

(Light diffusion plate)
The structural unit 341 constituting the concavo-convex structure 340 includes a structure having a shape in which the inclined side surface including the pyramid and the truncated pyramid has three or more inclined side surfaces, a hemisphere, and a semi-elliptical sphere as a dot-like protrusion or a recess. Examples include hemispherical structures. Such a structural unit is preferably a protrusion or depression that narrows the light emission direction.

  As a specific shape of the structural unit 341, for example, as a structure having three or more inclined side surfaces, a pyramid shape, a truncated pyramid shape, and a lenticular row or a linear prism row may be V-shaped. And a shape with a U-shaped cut. Examples of the pyramid include a triangular pyramid, a quadrangular pyramid, a pentagonal pyramid, and a hexagonal pyramid. Examples of the pyramid frustum include a triangular frustum, a quadrangular pyramid, a pentagonal pyramid, and a hexagonal pyramid. Further, for example, the hemispherical structure may be a dome shape such as a hemisphere or a semi-elliptical sphere, or a dome shape such as a polygonal hemisphere or a semi-elliptical sphere. Note that FIG. 22 shows a case where a plurality of hemispherical structures are arranged.

  The plurality of structural units 341 constituting the concavo-convex structure 340 may be configured from only one type or may be configured by combining a plurality of types.

  In the present embodiment, it is preferable to periodically and regularly arrange a group including the structural unit 341 or the plurality of structural units 341 in order to improve luminance uniformity. The period of these structural units or group is more preferably 20 μm or more and 700 μm or less, and further preferably 40 μm or more and 400 μm or less. When the period is within the above range, it can be easily formed and the occurrence of uneven brightness can be suppressed.

(Point light source)
The point light source 310 has a point-like light emission part, for example, can mention LED and a laser. Some LEDs emit various colors such as white, red (R), green (G), and blue (B). In this embodiment, the color balance is adjusted such that (1) only white LEDs are used as point light sources, (2) RGB three primary colors are combined, and (3) RGB three primary colors are combined with an intermediate color or white. It can be appropriately selected and used in consideration.

  In the combination of the three primary colors of RGB ((2) and (3)), (A) at least one red LED, green LED and blue LED are arranged close to each other, and each color is mixed to emit white light. And (B) a red LED, a green LED, and a blue LED appropriately disposed. In the case of (A), a combination of LEDs arranged close to each other is regarded as one point light source.

In this embodiment, a value obtained by measuring the dimension of the point light source in the short side direction of the light diffusion plate is set as the outer diameter R of the point light source 310. The range N _R represented by the formula (12) not only has a width R in the short side direction of the light diffusing plate, measuring the dimensions of the point light sources in the longitudinal direction in the short side direction of the light diffusing plate Have the same width as

  In the present embodiment, the plurality of point light sources 310 are discretely arranged. As an arrangement mode of the point light sources, for example, the point light sources are arranged in a straight line; as shown in FIG. 23, they are arranged at predetermined intervals along the vertical direction and the horizontal direction of the direct type backlight device. 24; as shown in FIG. 24, the point light sources P1 to P4 in FIG. A point light source 310 is disposed on the top of the honeycomb structure in which regular hexagons are continuously formed, as shown in FIG. 25, and the like. Can do.

  In the present embodiment, the relationship 0.5 ≦ a / b ≦ 15.0 is satisfied between the average distance a (mm) and the average distance b (mm), and 0.6 ≦ a It is preferable that /b≦13.0 is satisfied. By satisfying such a relationship, the number of point light sources used can be reduced and the power consumption of the device can be suppressed.

  Here, the average distance between the centers of the point light sources may be uniform at all locations or may be partially changed. The case of partial change is, for example, the case where the average distance between the centers of the point light sources is narrowed at the center of the direct type backlight device.

  Here, the adjacent point light sources are two point light sources in a state where no other point light sources exist on the line connecting the centers of the two point light sources. The average distance between the centers of adjacent point light sources is a certain point light source L1 and a plurality of point light sources L2 to Ln (n is an integer of 4 or more) adjacent to the point light source L1. Three points are selected in order from the shortest distance between the centers of the point light source L1 and the other point light sources L2 to Ln, and are average values of these three numerical values.

  Further, when the average distance between the centers of the point light sources partially changes, a direct type backlight device is configured as follows. That is, an average distance between centers of adjacent point light sources by selecting three point light sources from a point light source and a point light source adjacent to the point light source at a certain location in advance. Ask for. Then, with respect to the range in which the area surrounded by these four point light sources whose average distance is measured is projected onto the light incident surface of the light diffusion plate, the light diffusion is performed so as to satisfy the relationship described later based on the obtained average distance. Design the board.

  In the case of the combination of the RGB primary colors (A), the center of the point light source regarded as one is specified based on the centers of the LEDs arranged close to each other, and based on this center, The distance between adjacent point light sources is obtained. In the case of the configuration (B) combining the three primary colors of RGB, the distance between adjacent point light sources is determined according to the above definition regardless of the color.

Next, the light transmission suppressing layer 350 will be described.
FIG. 26 is a diagram for explaining the light transmission suppressing layer 350 provided on the light incident surface 330A. As shown in FIG. 26, in the direct type backlight device 3 of the present embodiment, a position S where the central axis of an arbitrary point light source 310A is projected on the light incident surface 330A and a point adjacent to the point light source 310A. A light transmission suppression layer 350 is provided in a region between the position T projected from the central axis of the light source 310B. The light transmission suppressing layer 350 is provided so that the light transmittance increases as the distance from the point light source 310A located at the closest position increases.

  Specifically, for example, as shown in FIG. 26, when a plurality of point light sources 310 are arranged in a square lattice shape, first, the point light sources 310 </ b> A along the vertical direction and the horizontal direction of the square lattice. Axis S1, S2 passing through the center of the light source, Axis S1, T2 passing through the center of the point light source 310B laterally adjacent to the point light source 310A, and the center of the point light source 310C adjacent to the point light source 310A in the vertical direction Let us consider axes S2 and T1 passing through. Then, an axis TC indicating an intermediate position between the axes T1 and T2 and an axis SC indicating an intermediate position between the axes S1 and S2 are considered. For example, in the point light source 310A, the area between the axis T1 and the axis TC, which is the right side area of the point light source 310A, is divided into, for example, five equal parts, and similarly, the area below the point light source 310A. The axis S1 and the axis SC are divided into, for example, five equal parts. Further, although not shown, the left and upper regions of the point light source 310A are also divided into, for example, five equal parts. The five divided lines are connected to each other, and the formed rectangular area is referred to as areas A11 to A15 in order from the side closer to the point light source 310A. The formation range (unit:%) of the printing layer per unit area is reduced stepwise from the region A11 closest to the center of the point light source 310A to the region A15 farthest from the point light source 310A. For example, the formation range of the print layer in each region can be, for example, region A11: 90%, region A12: 75%, region A13: 30%, region A14: 10%, and region A15: 0%.

  As another method, the center position of the point light source LS1 passes through the midpoint of the line connecting the center position of a certain point light source LS1 and the center position of the point light source LS2 adjacent to the point light source LS1. And the center of the point light source LS1 are divided into five concentric circles (in this case, each region divided into five is extended from the side closer to the center of the point light source LS1 to the side away from the center of the point light source LS1). To B15), the formation range (unit:%) of the printing layer per unit area is gradually reduced from the region B11 to the region B15. For example, the formation range of the print layer in each region can be, for example, region B11: 90%, region B12: 75%, region B13: 30%, region B14: 10%, and region B15: 0%.

  In this manner, a predetermined print layer is formed in a direction with respect to one point light source among a plurality of point light sources adjacent to a certain point light source. And a printing layer is formed similarly to the above also with respect to the other point light sources among several adjacent point light sources. As described above, the light transmission suppressing layer 350 is formed.

  According to the direct type backlight device of this embodiment, the same effects as those of the first embodiment can be obtained. Further, by using an LED which is a point light source as the light source, the color gamut can be expanded as compared with the case where a linear light source is used.

<Modification>
The present invention is not limited to the above-described embodiment, and modifications can be made within the scope of the claims of the present application and equivalents thereof.
For example, in the above-described embodiment, the light transmission suppressing layer is provided so that the light transmittance increases as the distance from the light source increases (such an arrangement is referred to as configuration A). It does not have to be. For example, there may be a portion that does not partially satisfy the relational configuration A. At this time, as a method other than the above method for forming the print layer so as to satisfy the above configuration A, for example, a configuration in which the thickness of the print layer is reduced as the distance from the light source is reduced, or a method having a low ink concentration constituting the print layer is used. And the like. In the embodiment, the light transmittance is increased stepwise as the distance from the light source is increased. However, the light transmittance may be increased continuously.

  Moreover, in the said embodiment, although white ink was used as an ink which comprises a printing layer, a white pigment and a white dye can be used as such a white ink. A transparent pigment can also be used as the ink constituting the printing layer.

  Moreover, in the said embodiment, although the light transmission suppression layer was provided in the light-incidence surface of the light diffusing plate, you may provide in a light-projection surface, and you may provide in both surfaces of a light-incidence surface and a light-projection surface.

  Moreover, in the said embodiment, although the light-transmission suppression layer was provided in the whole surface of one side of a light diffusing plate, it does not necessarily need to provide in the whole surface and should just be provided in the part directly above a light source.

  In the embodiment, the concavo-convex structure is provided on the entire surface of the light exit surface of the light diffusing plate. However, it is not necessarily provided on the entire surface of the light exit surface. At least one of the light exit surface and the light entrance surface is not necessarily provided. It suffices if it is formed at least at a part of the surface. Here, at least a part of the portion means that the area where the concavo-convex structure is formed is 30% or more of the area of the light emitting surface.

  Further, in the direct type backlight device, in order to further improve the luminance and the luminance uniformity, for example, an optical member such as a diffusion sheet or a prism sheet can be disposed downstream of the light exit surface. Further, for the purpose of further improving the luminance of the light emitting surface, for example, a reflective polarizer shown below can be arranged at the rear stage of the light emitting surface.

  As the reflective polarizer, a reflective polarizer using the difference in reflectance of the polarization component depending on the Brewster angle (for example, the one described in JP-A-6-508449); using selective reflection characteristics by cholesteric liquid crystal 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); reflection type polarized light using at least two kinds of polymer films and utilizing the reflectance anisotropy due to the refractive index anisotropy Child (for example, those described in JP-A-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 A reflective polarizer (for example, as described in US Pat. No. 5,825,543); particles are dispersed in a polymer film, and the reflectance anisotropy due to refractive index anisotropy is reduced. Reflective polarizer to be used (for example, those described in JP-A-11-509014); inorganic particles are dispersed in a polymer film, and anisotropy of reflectance based on a scattering ability difference depending on size is used. Reflective polarizers (for example, those described in JP-A-9-297204) can be used.

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

(Production Example 1: Light Diffusing Plate Pellets P1)
99.7 parts of a resin having an alicyclic structure as a transparent resin (Nippon Zeon Co., Ltd., ZEONOR 1060R, water absorption 0.01%) and a cross-linked product of a polysiloxane polymer having an average particle diameter of 2 μm as a light diffusing agent Were mixed with 0.3 part of fine particles, extruded with a twin-screw extruder, extruded into a strand, and cut with a pelletizer to produce a light diffusion plate pellet P1. From this light diffusion plate pellet P1, a 100 mm × 50 mm test plate with 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 according to JIS K7361-1 and JIS K7136. The total light transmittance was 85%, and the haze was 99%.

(Production Example 2: Light Pellet Pellets P2)
99.9 parts of resin having the alicyclic structure as a transparent resin (Nippon Zeon Co., Ltd., ZEONOR 1060R) and 0.1 part of fine particles composed of a crosslinked product of the polysiloxane polymer as a light diffusing agent 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 P2. From this light diffusion plate pellet P2, a 100 mm × 50 mm test plate with a smooth thickness of 2 mm on both sides was molded using the injection molding machine. When the total light transmittance and haze of this test plate were measured in the same manner as described above, the total light transmittance was 94% and the haze was 89%.

(Production Example 3: Light Diffusing Plate Pellets P3)
97.5 parts of a resin having an alicyclic structure (Nippon Zeon Co., Ltd., ZEONOR 1060R) as a transparent resin and 2.5 parts of fine particles made of a crosslinked product of the polysiloxane polymer as a light diffusing agent 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 P3. From this light diffusion plate pellet P3, a test plate of 100 mm × 50 mm having a smooth thickness of 2 mm on both sides was molded using the injection molding machine. When the total light transmittance and haze of this test plate were measured in the same manner as described above, the total light transmittance was 55% and the haze was 99%.

(Production Example 4: Light Diffusing Plate Pellets P4)
99.9 parts of polystyrene (PS Japan Co., Ltd., G9504) as a transparent resin and 0.1 part of fine particles made of a cross-linked product of the polysiloxane polymer as a light diffusing agent are mixed and kneaded with a twin screw extruder. Then, it was extruded into a strand shape and cut with a pelletizer to produce a light diffusion plate pellet P4. From this light diffusion plate pellet P4, a test plate having a thickness of 2 mm and a smooth surface of 100 mm × 50 mm was formed using the injection molding machine. When the total light transmittance and haze of this test plate were measured in the same manner as described above, the total light transmittance was 86%, and the haze was 99%.

(Production Example 5: Stamper S1)
100 mm thick nickel-phosphorous electroless plating is applied to the entire surface of stainless steel SUS430 (hereinafter sometimes referred to as “metal member”) having a size of 800 mm × 500 mm and a thickness of 100 mm, and a semicircular cross section having a radius of 38.6 μm. Using a diamond cutting tool, a nickel-phosphorous electroless plating surface having a width of 70 μm, a depth of 22.3 μm, a pitch of 70 μm and a radius of 38.6 μm in a direction parallel to a side having a length of 800 mm (longitudinal) A groove having a cross-sectional shape of a part of the circle (a part slightly smaller than the semicircle) was formed by cutting.

(Production Example 6: Stamper S2)
The entire surface of the metal member having the same dimensions as above was subjected to nickel-phosphorus electroless plating having a thickness of 100 μm, and a diamond cutting tool having a vertex angle of 100 degrees and a triangular cross section was used. A prism array having a sawtooth-like cross section with a width of 70 μm, a height of 29.4 μm, a pitch of 70 μm, and an apex angle of 100 degrees was formed by cutting in a direction parallel to a side having a length of 800 mm (longitudinal).

(Production Example 7: Stamper S3)
A cutting tool TX having a cross-sectional shape shown in FIG. 27 was created using a focused ion beam device (manufactured by Hitachi High-Technologies Corporation) with a diamond cutting tool having an apex angle of 115 degrees. Next, nickel-phosphorus electroless plating with a thickness of 100 μm was applied to the entire surface of the metal member having the same dimensions as described above. A shape of a part of a cylinder having a width of 70 μm, a height of 22.3 μm, a pitch of 70 μm, and a radius of 38.6 μm extending on the nickel-phosphorous electroless plating surface in parallel with the longitudinal side using the cutting tool TX ( A semi-cylindrical shape, but the cross section is slightly smaller than the semicircle) was formed by cutting.

  Further, using the same cutting tool TX, cutting was performed in a direction (short direction) perpendicular to the longitudinal direction of the shape with a width of 70 μm, a height of 22.3 μm, and a pitch of 70 μm. In this way, as shown in FIG. 28, a concavo-convex structure surface was created in which a plurality of structures whose periodic pyramid-shaped inclined side surfaces bulge outward were periodically arranged. Next, nickel is formed to a thickness of 500 μm by electroforming using a nickel sulfamate aqueous solution on the nickel-phosphorus electroless plating surface of the metal member on which the concavo-convex structure surface is formed. The stamper S3 was obtained by peeling off the surface.

(Production Example 8: Stamper S4)
A photoresist (Nippon Zeon Co., Ltd., ZPP1700PG-30) is applied to the entire surface of a glass substrate having a diameter of 900 mm, and exposed and developed to form a square lattice with a radius of 31 μm and a height of 30 μm and a pitch of 80 μm. It was formed to be arranged in a shape. The glass substrate provided with the columnar convex portion was post-baked at 140 ° C. to deform the shape of the convex portion to obtain a substantially hemispherical convex portion having a bottom radius of 35 μm and a height of 35 μm. Next, electroless nickel plating was performed on the substantially hemispherical convex portions provided on the glass substrate. Next, nickel is formed thereon with a thickness of 500 μm by electroforming using a nickel sulfamate aqueous solution, and this formed product is peeled off from the glass substrate provided with the projections, and cut to a size of 800 mm × 500 mm. A stamper S4 was obtained.

(Production Example 9: Stamper S5)
100 mm thick nickel-phosphorus electroless plating is applied to the entire surface of a metal member having dimensions of 800 mm × 500 mm and thickness 100 mm, and nickel-phosphorus electroless plating is performed using a diamond cutting tool having a vertex angle of 130 degrees and a triangular section. A prism row having a sawtooth-shaped cross section having a width of 100 μm, a height of 23.3 μm, a pitch of 100 μm, and an apex angle of 130 degrees was formed by cutting on a surface in a direction parallel to a side having a length of 800 mm (longitudinal). .

(Production Example 10: Stamper S6)
100 mm thick nickel-phosphorus electroless plating is applied to the entire surface of a metal member having dimensions of 800 mm × 500 mm and thickness 100 mm, and nickel-phosphorus electroless plating is performed using a diamond cutting tool having a vertex angle of 130 degrees and a triangular section. A prism row having a sawtooth-shaped cross section having a width of 100 μm, a height of 23.3 μm, a pitch of 100 μm, and an apex angle of 130 degrees was formed by cutting on a surface in a direction parallel to a side having a length of 800 mm (longitudinal). . Here, the prism rows were not formed on the entire plated surface, but were formed so that four strip-like regions having a width of 30 mm were formed at intervals of 90 mm. That is, a region having a width of 60 mm in which no prism row was formed was provided between regions having a width of 30 mm in which the prism row was formed.

(Production Example 11: Stamper S7)
Nickel-phosphorus electroless plating surface with a semi-circular diamond cutting tool with a radius of 115 μm and nickel-phosphorus electroless plating with a thickness of 100 μm on the entire surface of a metal member having dimensions of 800 mm × 500 mm and a thickness of 10 mm Further, a groove having a width of 150 μm, a depth of 50 μm, a pitch of 150 μm, and a part of a circle having a radius of 115 μm (a portion smaller than a semicircle) in a direction parallel to a side having a length of 800 mm (long) Was formed by cutting.

(Production Example 12: Stamper S8)
100 mm thick nickel-phosphorus electroless plating is applied to the entire surface of a metal member having dimensions of 800 mm × 500 mm and thickness 100 mm, and nickel-phosphorus electroless plating is performed using a diamond cutting tool having a vertex angle of 40 degrees and a triangular section. A prism row with a sawtooth-like cross section having a width of 100 μm, a height of 68.7 μm, a pitch of 50 μm, and an apex angle of 40 degrees was formed by cutting on the surface in a direction parallel to a side having a length of 800 mm (longitudinal). .

<Example 1>
A reflective sheet (manufactured by Tsujiden Co., Ltd., RF188) is attached to the inner surface of a milky white plastic case having an inner dimension width of 700 mm, a depth of 400 mm, and a depth of 20 mm to make a reflector, and the diameter is 3.5 mm away from the bottom of the reflector. Twelve cold-cathode tubes having a length of 3 mm and a length of 430 mm were arranged such that the distance a between the centers of the cold-cathode tubes was 33 mm, the vicinity of the electrode portion was fixed with a silicone sealant, and an inverter was attached. In the backlight of this design, the distance b between the cold cathode tube center and the light incident surface of the light diffusion plate (surface on the cold cathode tube side) was 15 mm. For this reason, a / b was 2.20.

  Next, a mold to which the stamper S1 obtained in Production Example 5 was attached was prepared, and using this and the light diffusion plate pellet P1 obtained in Production Example 1, an injection molding machine (clamping force 4,410 kN) Was molded at a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. Accordingly, a light having a thickness of 2 mm and a thickness of 730 mm × 430 mm having a concavo-convex structure in which a plurality of substantially semi-cylindrical lenticulars are arranged in parallel so as to extend in the longitudinal direction on one surface and the other surface is a flat surface. A diffusion plate D1 was obtained. When the center line average roughness Ra was measured along various directions in the surface of the one surface on which the concavo-convex structure was formed using an ultra-deep microscope, the short direction (430 mm) of the light diffusion plate D1 was measured. The centerline average roughness Ra measured in the direction) was the maximum value, and the maximum value Ra (max) was 5.0 μm. Further, when the centerline average roughness Ra was measured in the same manner for the other surface which is a flat surface, Ra was constant and 0.6 μm regardless of the direction in the surface.

  Next, the white ink is printed on the other surface of the light diffusing plate D1 where the uneven structure is not formed, and printing is performed so that the formation range decreases as the distance from the central axis of the cold cathode tube increases. A layer was formed. Specifically, as shown in FIG. 9, a position X where the central axis of the linear light source 10A is projected, and a distance between the central axis of the linear light source 10B and the central axis of the linear light source 10B from this position X. The area between the half of the positions Z is divided into 10 at equal intervals, and these equally divided areas are referred to as areas A1 to A10 in order from the left side of FIG. From the region A1 closest to the central axis of the linear light source 10A to the region A10 farthest from the linear light source 10A, the print layer formation range (unit:%) per unit area is stepwise as follows. Formed to reduce. The formation range of the printing layer in each region is as follows: region A1: 90%, region A2: 87%, region A3: 72%, region A4: 50%, region A5: 35%, region A6: 19%, region A7: 11 %, Area A8: 7%, area A9: 3%, and area A10: 0%.

  Such a light diffusing plate D1 was disposed on the plastic case so that the concavo-convex structure was the light emitting surface on the opposite side of the cold cathode tube. Furthermore, a diffusion sheet (Kimoto Co., Ltd., 188GM3) is installed on top of this, and a prism sheet (Sumitomo 3M Co., Ltd., BEF3) is placed thereon. It was installed so as to be parallel and far from the light diffusion plate. A direct-type backlight device was fabricated by installing a reflective polarizer (DBEF-D, manufactured by Sumitomo 3M Co., Ltd.) using birefringence thereon.

  In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 60%, the total light transmittance of light incident from the center of the light source in the position NO direction is 64%, and an intermediate position between adjacent light sources is The total light transmittance of the light incident on the projected position was 72%.

Next, the cold cathode tube is turned on by applying a tube current of 5 mA to the produced direct type backlight, and 100 points are equally spaced in the short direction on the center line of the light diffusion plate using a two-dimensional color distribution measuring device. The brightness in the front direction was measured, and the brightness average value La and brightness unevenness Lu were obtained according to the following formulas 1 and 2. In this example, the average luminance value was 4690 cd / m ² and the luminance unevenness was 0.8%.
Luminance average value La = (L1 + L2) / 2 (Formula 1)
Luminance unevenness Lu = ((L1-L2) / La) × 100 (Formula 2)
L1: Average brightness maximum value directly above a plurality of cold cathode fluorescent lamps installed L2: Average brightness minimum value sandwiched between brightness maximum values Note that brightness unevenness is an indicator of brightness uniformity and brightness When the unevenness is bad, the value increases.

<Example 2>
The 16 cold-cathode tubes are arranged so that the distance a between the centers of the cold-cathode tubes is 23 mm, the distance b between the cold-cathode tube center and the light incident surface of the light diffusion plate is 8 mm, and the applied current Was performed in the same manner as in Example 1 except that the current was set to 4 mA. At this time, a / b was 2.88. In this example, the average luminance value was 5350 cd / m ² and the luminance unevenness was 0.95%.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 60%, the total light transmittance of light incident from the center of the light source in the position NO direction is 64%, and an intermediate position between adjacent light sources is The total light transmittance of the light incident on the projected position was 74%.

<Example 3>
The ten cold cathode tubes are arranged so that the distance a between the centers of the cold cathode tubes is 40 mm, the distance b between the cold cathode tube center and the light incident surface of the light diffusion plate is 18 mm, and the applied current Was carried out in the same manner as in Example 1 except that the current was 6 mA. At this time, a / b was 2.22. In this example, the luminance average value was 4086 cd / m ² and the luminance unevenness was 0.90%.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 60%, the total light transmittance of light incident from the center of the light source in the position NO direction is 64%, and an intermediate position between adjacent light sources is The total light transmittance of the light incident on the projected position was 72%.

<Example 4>
A mold to which the stamper S2 obtained in Production Example 6 was attached was prepared, and using this and the light diffusion plate pellet P1 obtained in Production Example 1, an injection molding machine (clamping force 4,410 kN) was used. Molding was performed at a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. Thus, one surface has a concavo-convex structure in which a plurality of linear prisms (triangular prisms) having a triangular cross section extend in the longitudinal direction substantially in parallel, and the other surface is a flat surface with a thickness of 2 mm. A light diffusion plate D2 of 730 mm × 430 mm was obtained. The one surface on which the concavo-convex structure was formed was measured for the center line average roughness Ra along various directions in the surface using an ultra-deep microscope, and as a result, the short direction (430 mm) of the light diffusing plate D2 was measured. The center line average roughness Ra measured in the direction) was the maximum value, and the maximum value Ra (max) was 6.6 μm. Further, when the centerline average roughness Ra was measured in the same manner for the other surface which is a flat surface, Ra was constant and 0.6 μm regardless of the direction in the surface.

The eight cold-cathode tubes are arranged so that the distance a between the centers of the cold-cathode tubes is 50 mm, and the distance b between the cold-cathode tube center and the light incident surface of the light diffusion plate is 23 mm. Example 1 was performed except that the current to be applied was 8 mA. At this time, a / b was 2.17. In this example, the average luminance was 4067 cd / m ² and the luminance unevenness was 0.65%.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 60%, the total light transmittance of light incident from the center of the light source in the position NO direction is 64%, and an intermediate position between adjacent light sources is The total light transmittance of the light incident on the projected position was 77%.

<Example 5>
Example 4 was the same as Example 4 except that the light diffusion plate D2 was changed to the light diffusion plate D1. In this example, the luminance average value was 3864 cd / m ² and the luminance unevenness was 0.75%.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 60%, the total light transmittance of light incident from the center of the light source in the position NO direction is 64%, and an intermediate position between adjacent light sources is The total light transmittance of the light incident on the projected position was 72%.

<Example 6>
Lay a 0.5mm aluminum plate for heat dissipation on the bottom of a milky white plastic case with an inner dimension width of 700mm, depth of 400mm, and depth of 20mm, and paste a reflective sheet (E-60L made by Toray Industries, Inc.) on it. A reflector was used. Next, a white chip type LED (manufactured by Nichia Corporation, NSSM025T: size: 3.0 × 3.0 × 1.8 mm), which is a point light source, is provided at the bottom of the reflector plate at a center and length of 26 mm. Were arranged so as to have a square lattice shape (as shown in FIG. 23) and wired so that a direct current could be supplied to the electrode portion. In the backlight of this design, the distance b between the LED center and the light incident surface of the light diffusing plate was 19.1 mm. For this reason, a / b was 1.36.

  A mold to which the stamper S4 obtained in Production Example 8 was attached was prepared, and using this and the light diffusion plate pellet P2 obtained in Production Example 2, an injection molding machine (clamping force 4,410 kN) was used. Molding was performed at a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. As a result, a light diffusing plate having a thickness of 2 mm and a thickness of 730 mm × 430 mm has a concavo-convex structure in which a plurality of substantially hemispherical structures are periodically arranged in a square lattice pattern on one surface and the other surface is a flat surface. D3 was obtained. When the center line average roughness Ra is measured along various directions in the surface of the one surface on which the concavo-convex structure is formed using an ultra-deep microscope, the direction passing through the apex portion of the structure The centerline average roughness Ra measured in (1) was the maximum value, and the maximum value Ra (max) was 8.5 μm. Further, when the centerline average roughness Ra was measured in the same manner for the other surface which is a flat surface, Ra was constant and 0.6 μm regardless of the direction in the surface.

  Next, white ink is printed on the other surface of the light diffusion plate D3 where the uneven structure is not formed, and a printing layer is formed so that the formation range decreases as the distance from the center of the LED increases. did. Specifically, as shown in FIG. 26, a certain rectangular LED is selected, and a total of four line segments are created by connecting the center positions of adjacent LEDs in the vertical and horizontal directions of the LED. . Next, a rectangular line connecting intermediate positions of these line segments was set. The region between the rectangular line and the rectangular LED is divided into five equal parts as shown in FIG. 26 along the direction away from the center of the LED, and these regions are designated as regions A11 to A15 in order from the center of the LED. . From the region A11 closest to the center of the LED to the region A15 farthest from the LED, the formation range (unit:%) of the printing layer per unit area was gradually reduced. Specifically, the region A11 was 90%, the region A12 was 75%, the region A13 was 30%, the region A14 was 10%, and the region A15 was 0%.

  Such a light diffusing plate D3 was disposed on the plastic case so that the concavo-convex structure was the light emitting surface on the opposite side of the LED. Furthermore, a diffusion sheet (manufactured by Kimoto Co., Ltd., 188GM3) is installed thereon, a prism sheet (manufactured by Sumitomo 3M Co., Ltd., BEF3) is disposed thereon, and the longitudinal direction of the prism row of the prism sheet is the plastic case. It was installed parallel to the long side direction and on the side far from the light diffusion plate. A direct-type backlight device was fabricated by installing a reflective polarizer (DBEF-D, manufactured by Sumitomo 3M Co., Ltd.) using birefringence thereon.

Next, with respect to the direct type backlight thus obtained, currents of 2.2 V, 3.5 V, and 3.6 V were applied to the red chip, the green chip, and the blue chip constituting the white chip type LED, respectively. The LED is turned on, and the luminance in the front direction of 100 points is measured at equal intervals in the short direction on the center line of the light diffusing plate using a two-dimensional color distribution measuring device. An average value La and luminance unevenness Lu were obtained. In this example, the average luminance value was 1415 cd / m ² and the luminance unevenness was 0.95%.
Luminance average value La = (L1 + L2) / 2 (Formula 1)
Luminance unevenness Lu = ((L1-L2) / La) × 100 (Formula 2)
L1: Average luminance maximum value directly above the LED L2: Average luminance minimum value sandwiched between two luminance maximum values Note that the luminance unevenness is an index indicating the uniformity of luminance, and when the luminance unevenness is bad, That number will increase.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 43%, the total light transmittance of light incident from the center of the light source in the position NO direction is 58%, and an intermediate position between adjacent light sources is The total light transmittance of the light incident on the projected position was 63%.

<Example 7>
The light diffusing plate D1 is changed to the light diffusing plate D2, and the distance a between the centers of the cold cathode tubes is set to 24 mm, and the distance b between the cold cathode tube center and the light incident surface of the light diffusing plate is 6.5 mm. Then, RF188 (manufactured by Tsujiden Co., Ltd.) was changed to a reflective sheet described later, and the same procedure as in Example 2 was performed except that white ink was printed in the form described below. At this time, a / b was 3.69. In this example, the average luminance value was 5400 cd / m ² and the luminance unevenness was 0.73%.

As shown in FIG. 29, the reflection sheet is formed by bending MCPET (manufactured by Furukawa Electric Co., Ltd.) in 15 regions between the cold cathode fluorescent lamps 2910 so that the convex portions 2950 are arranged just in the middle of the cold cathode fluorescent lamps. Created. The shape of the convex part was a triangular section with a height of 4 mm and a width of 8 mm.
In addition, the white ink is printed on the other surface of the light diffusing plate D2 where the uneven structure is not formed, and the printing layer is reduced so that the formation range decreases as the distance from the position directly above the central axis of the cold cathode tube is increased. Formed. Specifically, as shown in FIG. 30, the formation range of the print layer in the area A1 from the position X projected from the central axis of the linear light source 10A to 2.5 mm is 75%, from 2.5 mm to 7.5 mm. The formation range of the printing layer in the area A2 was set to 20%.
In the backlight before installing the optical sheet, the total light transmittance just above the light source is 61%, the total light transmittance of light incident in the position NO direction from the center of the light source is 58%, and the intermediate position between adjacent light sources is The total light transmittance of the light incident on the projected position was 76%.

<Example 8>
A reflective sheet (manufactured by Tsujiden Co., Ltd., RF188) is attached to the inner surface of a milky white plastic case with an inner width of 700 mm, a depth of 400 mm, and a depth of 25 mm to make a reflector, and the diameter is 9.75 mm away from the bottom of the reflector. Four 15.5 mm long and 800 mm long hot cathode tubes (manufactured by Elevum Co., Ltd.) were placed so that the distance a between the centers of the hot cathode tubes was 90 mm, and the vicinity of the electrode part was fixed with a silicone sealant, An inverter was installed. In the backlight of this design, the distance b between the center of the hot cathode tube and the light incident surface of the light diffusing plate was 15.25 mm. For this reason, a / b was 5.90.

  Next, a mold to which the stamper S2 obtained in Production Example 6 was attached was prepared, and using this and a resin having an alicyclic structure (Nippon Zeon Co., Ltd., ZEONOR 1060R), an injection molding machine (clamping force) 4,410 kN), and was molded at a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. Thus, one surface has a concavo-convex structure in which a plurality of linear prisms (triangular prisms) having a triangular cross section extend in the longitudinal direction substantially in parallel, and the other surface is a flat surface with a thickness of 2 mm. A light diffusion plate D4 of 730 mm × 430 mm was obtained. When the center line average roughness Ra was measured along various directions in the surface of the one surface on which the concavo-convex structure was formed using an ultra-deep microscope, the short direction (430 mm) of the light diffusion plate D4 was measured. The center line average roughness Ra measured in the direction) was the maximum value, and the maximum value Ra (max) was 6.6 μm. Moreover, when centerline average roughness Ra was similarly measured about the other surface which is a flat surface, Ra was 0.6 micrometer.

  Next, white ink is printed on the other surface of the light diffusing plate D4 where the uneven structure is not formed, and printing is performed so that the formation range decreases as the distance from the position directly above the central axis of the hot cathode tube is increased. A layer was formed. Specifically, as shown in FIG. 30, the print layer formation range in the area A1 from the position X projected from the central axis of the linear light source 10A to 10.0 mm is 50%, from 10.0 mm to 20.0 mm. The formation range of the printing layer in the area A2 was set to 20%.

  Such a light diffusing plate D4 was disposed on the plastic case so that the concavo-convex structure was a light emitting surface on the opposite side of the hot cathode tube. Further, a diffusion sheet (188GM3 manufactured by Kimoto Co., Ltd.) is installed thereon, and a prism sheet (BEF3 manufactured by Sumitomo 3M Co., Ltd.) is disposed thereon, and the longitudinal direction of the prism rows of the prism sheet is parallel to the hot cathode tube. Then, it was installed on the side far from the light diffusion plate. A direct-type backlight device was produced by installing a diffusion sheet (188GM3 manufactured by Kimoto Co., Ltd.) thereon.

In this example, the luminance average value was 8030 cd / m ² and the luminance unevenness was 0.90%.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 55%, the total light transmittance of light incident from the center of the light source in the position NO direction is 65%, and an intermediate position between adjacent light sources is The total light transmittance of the light incident on the projected position was 78%.

<Example 9>
A resin having an alicyclic structure (Nippon ZEON Co., Ltd., ZEONOR 1060R) is changed to the light diffusion plate pellet P4 obtained in Production Example 4, and light diffusion is performed using the stamper S1 obtained in Production Example 5. The same procedure as in Example 8 was performed except that the plate D5 was prepared, and the light diffusion plate D5 and RF188 (manufactured by Tsujiden Co., Ltd.) were changed to a reflection sheet described later. At this time, a / b was 5.90. In this example, the luminance average value was 8190 cd / m ² and the luminance unevenness was 0.70%.

The reflection sheet was prepared by bending MCPET (manufactured by Furukawa Electric Co., Ltd.) in three regions between the hot cathode tubes so that the convex portions are arranged just in the middle of the hot cathode tubes. The shape of the convex portion was a triangular cross section having a height of 20 mm and a width of 40 mm.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 63%, the total light transmittance of light incident from the center of the light source in the position NO direction is 60%, and the intermediate position between adjacent light sources is The total light transmittance of the light incident on the projected position was 65%.

<Example 10>
The same operation as in Example 7 was performed except that the method for forming the printing layer was changed.
White ink is printed on the other surface of the light diffusing plate D2 where the uneven structure is not formed, and a printed layer is formed so that the forming range decreases as the distance from the center axis of the cold cathode tube is increased. did. Specifically, with reference to FIG. 31, the formation range of the printed layer in the area A1 from the position X projected from the central axis of the linear light source 10A to 1.0 mm is 60%, 1.0 mm to 2.5 mm. The formation range of the printing layer in the region A2 was 75%, and the formation range of the printing layer in the region A3 from 2.5 mm to 7.5 mm was 20%. In addition, the printing layer was not provided in area | region A4 in FIG. At this time, a / b was 3.69. In this example, the luminance average value was 5420 cd / m ² and the luminance unevenness was 0.52%.
In the backlight before installing the optical sheet, the total light transmittance just above the light source is 65%, and the total light transmittance of light incident from the center of the light source in the position NO direction is 58%. The total light transmittance of the light incident on the projected position was 76%.

<Comparative Example 1>
The light diffusion plate pellet P1 obtained in Production Example 1 was used and molded using an injection molding machine (clamping force 4,410 kN) at a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. Thus, a flat light diffusion plate D6 having a thickness of 2 mm and a thickness of 730 mm × 430 mm was obtained. For each surface of the light diffusing plate D6, the centerline average roughness Ra was measured in the same manner, and Ra was 0.6 μm.

A light diffusing plate D6 is used instead of the light diffusing plate D1, and white ink is printed on the light incident surface of the light diffusing plate D6, and the formation range decreases as the distance from the central axis of the cold cathode tube is increased. A direct type backlight device was obtained in the same manner as in Example 1 except that a printing layer similar to the printing layer in Example 1 was formed. In this example, the luminance average value was 4737 cd / m ² and the luminance unevenness was 5.3%.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 40%, the total light transmittance of light incident from the center of the light source in the position NO direction is 40%, and an intermediate position between adjacent light sources is The total light transmittance of the light incident on the projected position was 80%.

<Comparative Example 2>
A flat light diffusing plate D7 is produced using the light diffusing plate pellet P3 instead of the light diffusing plate pellet P1, and a direct type back is formed in the same manner as in Comparative Example 1 except that this light diffusing plate D7 is used. A light device was obtained. In this example, the luminance average value was 3863 cd / m ² and the luminance unevenness was 2.0%.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 35%, the total light transmittance of light incident from the center of the light source in the position NO direction is 35%, and an intermediate position between adjacent light sources is determined. The total light transmittance of the light incident on the projected position was 45%.

<Comparative Example 3>
The same as in Example 2 except that the distance a between the centers of the cold cathode tubes is 23.0 mm and the distance b between the center of the cold cathode tubes and the light incident surface of the light diffusion plate is 15 mm. went. At this time, a / b was 1.53. In this example, the luminance average value was 5296 cd / m ² and the luminance unevenness was 1.90%.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 60%, the total light transmittance of light incident from the center of the light source in the position NO direction is 64%, and an intermediate position between adjacent light sources is The total light transmittance of the light incident on the projected position was 73%.

<Comparative example 4>
The same operation as in Example 8 was performed except that printing was not performed on the light diffusion plate D4. At this time, a / b was 5.90. In this example, the average luminance value was 7560 cd / m ² and the luminance unevenness was 10.1%.

<Comparative Example 5>
A light diffusing plate D1 is installed instead of the light diffusing plate D4, and two are arranged so that the distance a between the centers of the hot cathode tubes is 300 mm, and the distance between the center of the hot cathode tube and the light incident surface of the light diffusing plate. The same operation as in Example 8 was performed except that b was 10.25 mm and printing described later was performed. At this time, a / b was 29.27. In this example, the luminance average value was 3825 cd / m ² and the luminance unevenness was 118.6%.

White ink is printed on the other surface of the light diffusing plate D1 where the concavo-convex structure is not formed, and a printed layer is formed so that the forming range decreases as the distance from the central axis of the hot cathode tube increases. did. Specifically, as shown in FIG. 31, the formation range of the print layer in the area A1 from the position X to 10.0 m projected from the central axis of the linear light source 10A is 75%, from 10.0 mm to 25.0 mm. The formation range of the printing layer in the region A2 is 60%, the formation range of the printing layer in the region A3 from 25.0 mm to 40.0 mm is 35%, the formation of the printing layer in the region A4 from 40.0 mm to 65.0 mm. The range was 20%.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 62%, the total light transmittance of light incident from the center of the light source in the position NO direction is 62%, and the intermediate position between adjacent light sources is The total light transmittance of the light incident on the projected position was 30%.

<Comparative Example 6>
A mold having the stamper S2 obtained in Production Example 6 and the stamper S5 obtained in Production Example 9 was prepared, and this and a resin having an alicyclic structure (Zeon Corporation, Zeonore 1060R) were used. Using an injection molding machine (clamping force 4,410 kN), molding was performed at a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. Thus, one surface has a concavo-convex structure in which a plurality of linear prisms (triangular prisms) having an apex angle of 100 degrees are arranged in parallel so as to extend in the longitudinal direction, and the other surface has an apex angle of 130. A light diffusing plate D8 having a thickness of 2 mm and a thickness of 730 mm × 430 mm was obtained having a concavo-convex structure in which a plurality of linear prisms (triangular prisms) having a triangular cross section extending in the longitudinal direction substantially parallel to each other. When the one surface on which the concavo-convex structure with an apex angle of 100 degrees was formed was measured for the center line average roughness Ra along various directions in the surface using an ultradeep microscope, the short side of the light diffusion plate D8 was measured. The centerline average roughness Ra measured in the hand direction (430 mm direction) was the maximum value, and the maximum value Ra (max) was 6.6 μm. Further, when the other surface on which the concavo-convex structure with an apex angle of 130 degrees was formed was measured for the center line average roughness Ra along various directions in the surface using an ultra-deep microscope, the light diffusion plate D8 The center line average roughness Ra measured in the short direction (430 mm direction) was the maximum value, and the maximum value Ra (max) was 5.5 μm. Using this light diffusing plate D8, the same procedure as in Example 8 was carried out except that the surface having the concavo-convex structure with an apex angle of 100 degrees was arranged on the plastic case so as to be the light emitting surface opposite to the hot cathode tube. Thus, a direct type backlight device was obtained. In this example, the luminance average value was 7950 cd / m ² and the luminance unevenness was 1.9%.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 53%, the total light transmittance of light incident from the center of the light source in the position NO direction is 66%, and an intermediate position between adjacent light sources is determined. The total light transmittance of the light incident on the projected position was 77%.

<Comparative Example 7>
A mold having the stamper S2 obtained in Production Example 6 and the stamper S6 obtained in Production Example 10 was prepared, and this and a resin having an alicyclic structure (Nippon Zeon Co., Ltd., Zeonore 1060R) were used. Using an injection molding machine (clamping force 4,410 kN), molding was performed at a cylinder temperature of 280 degrees and a mold temperature of 85 degrees. Thus, one surface has a concavo-convex structure in which a plurality of linear prisms (triangular prisms) having an apex angle of 100 degrees are arranged in parallel so as to extend in the longitudinal direction, and the other surface has an apex angle of 130. A light diffusion plate D9 having a thickness of 2 mm and a thickness of 730 mm × 430 mm having a concavo-convex structure in which four strips each having a width of 30 mm of a linear prism having a triangular cross section (triangular prism) extending in parallel and extending in the longitudinal direction Got. When the one surface on which the concavo-convex structure with an apex angle of 100 degrees was formed was measured for the center line average roughness Ra along various directions in the surface using an ultradeep microscope, the short side of the light diffusing plate D9 was measured. The centerline average roughness Ra measured in the hand direction (430 mm direction) was the maximum value, and the maximum value Ra (max) was 6.6 μm. Further, when the other surface on which the concavo-convex structure having an apex angle of 130 degrees was formed was measured for center line average roughness Ra along various directions in the surface using an ultradeep microscope, the apex angle 130 was measured. The center line average roughness Ra measured in the short direction (430 mm direction) of the light diffusion plate D8 is the maximum value, and the maximum value Ra (max) is 5.5 μm. It was. Using this light diffusing plate D9, the concavo-convex structure with the apex angle of 130 degrees is formed on the hot cathode tube so that the surface with the concavo-convex structure with the apex angle of 100 degrees becomes the light emitting surface opposite to the hot cathode tube. A direct type backlight device was obtained in the same manner as in Example 8 except that the direct type backlight device was placed on the plastic case. Here, the arrangement of the light diffusing plate is such that the center line in the width direction of the 30 mm wide region having a concavo-convex structure with an apex angle of 130 degrees coincides with the line obtained by projecting the center line of each hot cathode tube onto the light diffusing plate. The position was adjusted.
In this example, the luminance average value was 7880 cd / m ² and the luminance unevenness was 2.8%.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 53%, the total light transmittance of light incident from the center of the light source in the position NO direction is 66%, and an intermediate position between adjacent light sources is determined. The total light transmittance of the light incident on the projected position was 75%.

<Comparative Example 8>
On the concavo-convex structure surface of the stamper S7 obtained in Production Example 11, an ultraviolet curable resin (manufactured by Shin-Nakamura Chemical Co., Ltd., NK ester AMP-20GY) 95% by weight and a polymerization initiator (Ciba Specialty Chemicals Co., Ltd., Irgacure 184) 5 By applying a mixture of weight percent, placing a 900 mm x 600 mm size base material film (made by Teijin Limited, Teijin Tetron film (brand: O3, 50 μm thickness)) and pressing the film from above Air bubbles were removed. This was cured by irradiating with 600 mJ / cm ^{2 of} ultraviolet rays from the film side. Thereafter, the film was peeled off from the stamper S7 and cut into an 800 mm × 500 mm size to obtain a film 1 composed of a UV curable resin layer 3205 and a base film 3204. The white ink 3201 was printed on the surface opposite to the concavo-convex structure surface of the film 1 so as to form a belt having a width of 100 μm and a height of 100 μm in a direction parallel to the concavo-convex structure at a position facing the valley of the concavo-convex structure. . Further, an adhesive layer 3203 was applied to this surface so as to be 150 μm in height from the surface opposite to the uneven structure of the film 1. This was adhered to the light diffusing plate D7 (3202) so that the concavo-convex structure was on the outside to obtain a light diffusing plate D10. A cross-sectional structure is shown in FIG. When the center line average roughness Ra was measured along various directions in the surface of the surface on which the concavo-convex structure was formed using an ultra-deep microscope, it was in the short direction (430 mm direction) of the light diffusion plate D10. The measured centerline average roughness Ra was the maximum value, and the maximum value Ra (max) was 12.5 μm. Moreover, when the centerline average roughness Ra was similarly measured about the other surface which is a flat surface, Ra was 0.6 micrometer. Using this light diffusing plate D10, a direct type back is formed in the same manner as in Example 8 except that the surface having the concavo-convex structure is disposed on the plastic case so as to be the light emitting surface opposite to the hot cathode tube. A light device was obtained. In this example, the luminance average value was 6680 cd / m ² and the luminance unevenness was 3.5%.
In the backlight before installing the optical sheet, the total light transmittance directly above the light source is 31%, the total light transmittance of light incident from the center of the light source in the position NO direction is 30%, and the intermediate position between adjacent light sources is The total light transmittance of the light incident on the projected position was 30%.

  The results of Examples 1 to 10 and Comparative Examples 1 to 8 are shown in Tables 1 to 4.

  As shown in Tables 1 to 4, as in Examples 1 to 10, the average distance between the centers of the light sources and the average distance between the centers of the light sources and the light incident surface satisfy a certain relationship, and the antireflection layer is provided. Proper installation can prevent uneven brightness from occurring on the light emitting surface. On the other hand, as shown in Comparative Examples 1 to 8, when the predetermined relationship is not satisfied, uneven luminance occurs on the light emitting surface.

Claims (13)

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 incident from the light incident surface, diffused, and emitted from the light emitting surface. A direct-type backlight device comprising a light diffusing plate,
At least one of the light exit surface and the light entrance surface has a maximum value of center line average roughness Ra measured along various directions in the surface at least at a part thereof. A concavo-convex structure having Ra (max) of 3 μm to 1,000 μm is formed,
On at least one surface of said light emitting surface and the light incident surface is light transmission suppressing layer for suppressing the transmission of light is provided in at least a range M _R,
In the range M _R, the minimum value of the light diffuser plate and the transmittance of the portion including the light transmission suppressing layer, a position where the center position projected onto the light diffuser plate of the linear light sources, adjacent the linear 5% or more lower than the transmittance value of the portion including the light diffusing plate and the light transmission suppressing layer at a position intermediate between the position of the center of the light source projected on the light diffusing plate,
The average distance between the centers of the adjacent linear light sources is a (mm), and the average distance between the center of the linear light sources and the light incident surface is b (mm). 1.7 ≦ a / b ≦ 23. Satisfy the relationship of 0,
The range M _R is the position where the center line projected on the incident surface of the light diffuser plate of the linear light source and the reference line is an area within a distance M (mm) from the reference line, where M and b Is a direct type backlight device satisfying the relationship of 0 ≦ M <b × tan (2π / 9). A reflecting plate, a plurality of point light sources, a light diffusing plate that directs incident light from these point light sources and reflected light from the reflecting plate from a light incident surface, diffuses the light, and exits from the light emitting surface; A direct-type backlight device comprising:
At least one of the light exit surface and the light entrance surface has a maximum value of center line average roughness Ra measured along various directions in the surface at least at a part thereof. A concavo-convex structure having Ra (max) of 3 μm to 1,000 μm is formed,
On at least one surface of said light emitting surface and the light incident surface is light transmission suppressing layer for suppressing the transmission of light is provided in at least a range M _R,
In the range M _R, the minimum value of the transmittance of the portion including the light diffusing plate and the light transmission suppressing layer, a position where the center position projected onto the light diffuser plate of the point light source, like the points adjacent 5% or more lower than the transmittance value of the portion including the light diffusing plate and the light transmission suppressing layer at a position intermediate between the position of the center of the light source projected on the light diffusing plate,
The average distance a (mm) between the centers of the adjacent point light sources and the average distance between the center of the point light sources and the light incident surface are b (mm), and 0.5 ≦ a / b ≦ 15.0 Satisfy the relationship
The range M _R is the position where the center point obtained by projecting the incident surface of the light diffuser plate of the point light source as a reference point, a region within a distance M (mm) from the reference point, wherein M and b Is a direct type backlight device satisfying the relationship of 0 ≦ M <b × tan (2π / 9). In the direct type backlight device according to claim 1,
The concavo-convex structure is a direct type in which a plurality of linear prisms having a polygonal cross section extending in substantially the longitudinal direction of the linear light source, or a plurality of lenticulars having a cross section including a curved portion are arranged. Backlight device. The direct type backlight device according to claim 1 or 2,
The light transmission suppressing layer is a direct type backlight device configured by a printing layer that reflects and / or absorbs incident light. In the direct type backlight device according to claim 4,
The direct-type backlight device, wherein the printing layer is provided so that the light transmittance increases continuously or stepwise as the distance from the light source increases. The direct type backlight device according to claim 1 or 2,
A direct-type backlight device having a center line average roughness Ra of 0.005 μm to 5 μm at a position where the printed layer is formed on the surface on which the printed layer is formed.   The direct type backlight device according to claim 1, wherein the concavo-convex structure has a configuration in which a plurality of dot-like protrusions or dent-like structural units are arranged. The direct type backlight device according to claim 1 or 2,
The uneven structure is formed on the light exit surface,
The light incident surface is a direct type backlight device having a substantially flat surface with a center line average roughness Ra of less than 3 μm. The direct type backlight device according to claim 1 or 2,
The maximum value of the arithmetic mean inclination angle θ measured along various directions in the surface on which the uneven structure is formed is θ (max) (degrees), the refractive index of the uneven structure portion is n, and the light source The direct-type backlight device satisfying the relationship of sin ⁻¹ (R / 2nb) + sin ⁻¹ (1 / n)> θmax, where R (mm) is the outer diameter. The direct type backlight device according to claim 9,
The light transmission suppressing layer is provided at least at a predetermined position NO in any of the light emitting surface and the light incident surface,
The position NO includes a path where light is emitted from the center of the light source, passes through the light diffusion plate, and is emitted in a direction parallel to the thickness direction of the light diffusion plate, and a light incident surface of the light diffusion plate or It is the position where the light exit surface intersects,
The transmittance of the portion including the light diffusion plate and the light transmission suppressing layer at the position NO is the maximum value of the transmittance between the position NO and a position where an intermediate position of the adjacent light source is projected onto the light diffusion plate. Direct type backlight device that is 5% lower than The direct type backlight device according to claim 10,
The minimum value TA of the transmittance of the portion including the light diffusion plate and the light transmission suppressing layer in a range N _R within a distance R / 2 centered on the position NO,
When the average value TB of the transmittance of the portion including the light diffusion plate and the light transmission suppressing layer between the position N0 and the position where the center of the light source is projected onto the light diffusion plate,
Direct type backlight device satisfying TA <TB. The direct type backlight device according to claim 1 or 2,
The light diffusion plate is composed of a resin composition containing a transparent resin,
This resin composition is a direct type backlight device having a total light transmittance of 40% or more and 98% or less measured with normal incident light. The direct type backlight device according to claim 1 or 2,
The said light diffusing plate is comprised by the resin composition containing transparent resin, The direct-type backlight apparatus whose water absorption rate of this resin composition is 0.25% or less.

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