JP2007294411A - Direct backlight device and optic lens sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct backlight device in which the brightness ratio at a middle position of linear light sources mutually juxtaposed is improved, and in which homogeneous brightness distribution can be obtained. <P>SOLUTION: An optical lens sheet 3 to be used for the direct backlight device is provided with a plurality of cylindrical lenses 31 juxtaposed in the same direction as the juxtaposed direction of the plurality of linear light sources. A cross-sectional shape of the cylindrical lenses 31 is polygonal, and in the cross-sectional shape of a convex face 310, a difference between inclined angles (θ1 to θ5) of mutually neighboring two sides (S1 to S5) gradually becomes smaller toward the lens edge LE from the lens center LC. Moreover, if a spacing of the two linear light sources juxtaposed mutually is made 2L, and the height from the center axis of the linear light sources to the lower face of the optical lens sheet 3 is made H, the inclined angle θ1 satisfies a formula (1): 1.6×arctan (L/H)>θ1>1.2×arctan(L/H). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a direct-type backlight device and an optical lens sheet, and more particularly to a direct-type backlight device and an optical lens sheet used in a liquid crystal display device typified by a liquid crystal television.

  A liquid crystal display device typified by a liquid crystal television includes a backlight device for illuminating a liquid crystal panel. There are a sidelight type and a direct type backlight device, but a large type liquid crystal display device having a large illumination area uses a direct type backlight device capable of increasing the brightness.

  As shown in FIG. 25, the conventional direct type backlight device 100 includes a housing 101, a reflective film 105 laid on the inner surface of the housing 101, and a diffusion fitted in the opening 102 in parallel with the rear surface of the housing 101. A plate 103, a plurality of line light sources 104 arranged in parallel with the diffusion plate 103 between the reflection film 105 and the diffusion plate 103, and an optical lens sheet 106 laid on the diffusion plate 103 and controlling the viewing angle. With.

  The diffusion plate 103 contains particles such as barium sulfate and titanium oxide and is opaque. The diffuser plate 103 diffuses and transmits the light rays from the line light source 104 and the reflective film 105, thereby making the luminance distribution on the front of the direct type backlight device 100 uniform compared to the case where the diffuser plate 103 is not used. To do. However, when the diffusing plate 103 is used, the amount of transmitted light decreases because the light incident on the inside of the diffusing plate repeats reflection / refraction by particles inside the diffusing plate. Therefore, the illumination efficiency of the direct type backlight device 100 decreases.

  In order to make the luminance distribution uniform while preventing a reduction in illumination efficiency, a direct type back disclosed in Japanese Patent Laid-Open Nos. 10-283818 (Patent Document 1) and 2004-006256 (Patent Document 2) is disclosed. The light device replaces the conventional diffuser plate 103 with a prism sheet in which a plurality of prism lenses each having a triangular cross section are arranged in parallel, or a lenticular lens sheet in which a plurality of cylindrical lenses having convex cylindrical surfaces are arranged in parallel. It is used as Since the prism sheet and the lenticular lens sheet have a smaller number of times that the incident light beam is repeatedly reflected and refracted than the diffuser plate 103, a decrease in the amount of transmitted light can be prevented and the illumination efficiency can be improved.

However, the prism sheet has a limit in making the luminance distribution uniform. Although the lenticular lens sheet can also make the luminance distribution more uniform than the prism sheet, uneven luminance occurs. In particular, the luminance ratio at an intermediate point (corresponding to P in FIG. 25) between the line light sources (cold cathode tubes) arranged in parallel with each other is smaller than the luminance ratio at other positions.
Japanese Patent Laid-Open No. 10-283818 JP 2004006256 A JP-A-6-250178

  An object of the present invention is to provide a direct type backlight device capable of improving a luminance ratio at an intermediate point between line light sources arranged in parallel to each other and obtaining a uniform luminance distribution.

Means for Solving the Problems and Effects of the Invention

A direct type backlight device according to the present invention includes a plurality of line light sources and an optical lens sheet. The plurality of line light sources are arranged side by side. The optical lens sheet includes a base material portion and a plurality of cylindrical lenses. The base material portion is disposed at a predetermined distance from the plurality of line light sources. The plurality of cylindrical lenses are formed on the base portion and are arranged in the same direction as the arrangement direction of the plurality of line light sources. The cross-sectional shape of the cylindrical lens is a polygon, and in the cross-sectional shape, the difference in the inclination angle that each of the sides adjacent to each other forms a virtual line segment connecting the lens edges of the cylindrical lens is from the lens center to the lens edge. It gets smaller gradually. The distance between the two line light sources arranged in parallel with each other is 2L, and the height from the central axis of the line light source to the lower surface of the optical lens sheet is H. Of the cross-sectional shape, the inclination angle θ1 of the side including the lens edge satisfies Expression (1).
1.6 × arctan (L / H)>θ1> 1.2 × arctan (L / H) (1)
Here, the base material portion is, for example, a sheet shape or a film shape. The base material portion may be plate-shaped.

  In the direct type backlight device according to the present invention, the inclination angle θ1 of the cylindrical lens constituting the optical lens sheet satisfies the formula (1). For this reason, the surface near the lens edge having the inclination angle θ1 can emit light incident on the lower surface of the optical lens sheet to the front surface at a position corresponding to an intermediate point between the line light sources arranged in parallel with each other. Further, among the sides in the transverse shape of the convex surface (lens surface), the difference in the inclination angle between the sides adjacent to each other and the virtual line segment connecting the lens edges gradually decreases from the lens center toward the lens edge. Become. That is, the inclination angle does not change so much in the vicinity of the lens edge that plays a role of emitting light incident on the intermediate point to the front. Therefore, the area | region which can radiate | emit the light ray incident on the intermediate point to the front among convex surfaces becomes larger than the conventional lenticular lens sheet. As a result, the rate at which light incident on the intermediate point can be emitted to the front increases, the luminance ratio at the intermediate point can be increased, and the luminance distribution becomes uniform.

A direct type backlight device according to the present invention includes a plurality of line light sources and an optical lens sheet. The plurality of line light sources are arranged side by side. The optical lens sheet includes a base material portion and a plurality of cylindrical lenses. The base material portion is disposed at a predetermined distance from the line light source. The plurality of cylindrical lenses are formed on the base portion and are arranged in the same direction as the arrangement direction of the plurality of line light sources. The convex shape of the cylindrical lens has a curved cross-section, and the curvature of the curve gradually decreases from the center of the lens toward the lens edge. The distance between the two line light sources arranged in parallel with each other is 2L, and the height from the central axis of the line light source to the lower surface of the optical lens sheet is H. At the lens edge of the cylindrical lens, an angle θ1 formed by the plane and the convex surface of the cylindrical lens satisfies Expression (1).
1.6 × arctan (L / H)>θ1> 1.2 × arctan (L / H) (1)
The direct type backlight device according to the present invention has the same effects as the direct type backlight device described above. That is, in the optical lens sheet, the angle θ1 satisfies the formula (1). Therefore, the convex surface in the vicinity of the lens edge can emit light incident on an intermediate point between the line light sources arranged in parallel to each other on the lower surface of the optical lens sheet. Furthermore, the curvature of the convex transverse shape gradually decreases from the center of the lens toward the lens edge. Therefore, the region where the light beam incident on the intermediate point can be emitted to the front is larger than that of the conventional lenticular lens sheet. As a result, the rate at which light incident on the intermediate point can be emitted to the front increases, the luminance ratio at the intermediate point can be increased, and the luminance distribution becomes uniform.

  The optical lens sheet according to the present invention is used in the above-described direct type backlight device. Preferably, the base material portion is light-transmissive and has a plate shape.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

[Configuration of direct type backlight device]
With reference to FIGS. 1 and 2, the liquid crystal display device 50 includes a direct type backlight device 10 and a liquid crystal panel 20 laid in front of the direct type backlight device 10.

  The direct type backlight device 10 includes a plurality of cold-cathode tubes 1 that are line light sources, a reflective film 2, an optical lens sheet 3 having a function of uniforming luminance distribution as an alternative to a conventional diffusion plate, and a housing 4 Is provided. Although not shown in FIG. 2, the direct backlight device 10 further includes a lenticular lens sheet, a microlens array, a prism sheet, etc. on the optical lens sheet 3 for the purpose of improving the luminance and controlling the viewing angle. A conventional optical lens sheet is laid.

  The housing 4 is a housing having an opening 6 on the front surface, and houses the cold cathode tube 1 therein. A reflective film 2 is laid on the inner surface of the housing 4. The reflection film 2 diffusely reflects the light emitted from the cold cathode tube 1 and guides it to the opening 6.

  The plurality of cold cathode fluorescent lamps 1 are arranged in parallel in the vertical direction (y direction in the figure) in front of the rear surface of the housing 4. The cold cathode tube 1 is a line light source extending in the left-right direction (x direction in the figure), for example, a fluorescent tube.

  The optical lens sheet 3 is fitted into the opening 6 and is disposed at a predetermined distance from the cold cathode tube 1. The optical lens sheet 3 includes a plurality of cylindrical lenses 31 arranged in parallel in the same direction as the parallel arrangement direction of the cold cathode tubes 1. The optical lens sheet 3 emits light from the cold cathode fluorescent lamp 1 to the front surface of the direct type backlight to improve the front luminance. The optical lens sheet 3 further uniformizes the luminance distribution in front of the direct type backlight.

With reference to FIG. 3, the optical lens sheet 3 includes a base portion 32 and a plurality of cylindrical lenses 31 formed on the base portion 32. The base material part 32 has optical transparency. The base material portion 32 may be in the form of a sheet or a film. Moreover, plate shape may be sufficient. The cross-sectional shape of the convex surface (surface) 310 of the cylindrical lens 31 is a polygon. Among the sides S1 to S5 in the transverse shape of the convex surface 310, the difference in inclination angle between two sides adjacent to each other gradually decreases from the lens center LC toward the lens edge LE. Specifically, the inclination angles θ1 to θ5 of the sides S1 to S5 satisfy the following expression (A).
θ4-θ5>θ3-θ4>θ2-θ3> θ1-θ2 (A)
Here, the inclination angle θ is an angle formed between each side S and a virtual line segment PL connecting the lens edges LE. In other words, it is an angle formed by the plane of the cylindrical lens (that is, the surface of the base material portion 32) 320 and the surface including the sides S of the convex surface 310. For example, the inclination angle θ1 is an angle formed by the plane 320 and the surface including the side S1, and the inclination angle θ2 is an angle formed by the plane 320 and the surface including the side S2.

In FIG. 3, the number of sides from the lens edge LE to the lens center LC is five (S1 to S5), but the number of sides is not limited to this. When the number of sides from the lens edge LE to the lens center LC is n (S1 to Sn: n is a natural number), the inclination angle θn of each side Sn satisfies the following formula (B).
θ (n−1) −θn> θ (n−2) −θ (n−1) (B)
In short, in the cylindrical lens 31, the inclination angle θ in the vicinity of the lens center LC changes greatly toward the lens edge LE, but the inclination angle θn is not so great in the sides in the vicinity of the lens edge LE (for example, S1 and S2 in FIG. 3). It does not change.

Furthermore, the inclination angle θ1 of the side S1 including the lens edge LE satisfies the following expression (1).
1.6 × arctan (L / H)>θ1> 1.2 × arctan (L / H) (1)
Here, as shown in FIG. 2, L is a distance that is half the distance between the two cold-cathode tubes 1 arranged in parallel. As shown in FIG. 2, H is the height from the central axis C of the cold cathode tube 1 to the bottom surface of the optical lens sheet 3.

  The optical lens sheet 3 including the cylindrical lens 31 having the above cross-sectional shape can obtain a uniform luminance distribution as compared with the conventional lenticular lens sheet. More specifically, the difference between the inclination angles θn and θ (n−1) of two adjacent sides Sn and Sn−1 among the sides Sn in the transverse shape of the convex surface 310 is determined from the lens center LC to the lens. When the optical lens sheet 3 is gradually reduced toward the edge LE and the inclination angle θ1 of the side S1 including the lens edge LE satisfies the expression (1), the optical lens sheet 3 is positioned at the intermediate point P between the cold cathode tubes 1. The luminance ratio can be improved as compared with the conventional case. As a result, the direct type backlight device 10 can obtain a uniform luminance distribution.

  Hereinafter, with respect to the operation of the direct type backlight device according to the present embodiment, the brightness in the backlight device that does not use the diffusion plate and the optical lens sheet, the backlight device that uses the prism sheet, and the backlight device that uses the lenticular lens sheet This will be explained while comparing with the distribution.

[Brightness distribution of direct type backlight device without using optical lens sheet]
As shown in FIG. 4, the front luminance distribution of the direct type backlight device 200 that does not use the diffusion plate and the optical lens sheet as an alternative to the diffusion plate in the opening 6 is as shown in FIG. 5. The horizontal axis in FIG. 5 indicates the distance in the y direction when the front lower side of the direct type backlight device 200 is the origin (0), and the horizontal axis in FIG. 5 corresponds to the same reference numeral in FIG. To do. The vertical axis in FIG. 5 is the luminance ratio. The luminance ratio is the ratio of the luminance at each point to the maximum luminance among the measured luminances.
Referring to FIG. 5, the luminance distribution of direct type backlight device 200 is non-uniform. The luminance ratio is maximized at the points (LS1 to LS6) where the cold cathode fluorescent lamps 1 are disposed, and is minimized at the intermediate points (P1 to P5) between the cold cathode fluorescent tubes 1. The difference between the maximum value and the minimum value of the luminance ratio is 80% or more, and luminance unevenness occurs.

[Brightness distribution of direct type backlight device using prism sheet]
FIG. 8 shows the luminance distribution of the direct type backlight device 13 in which the prism sheet 12 shown in FIG. 6 is fitted into the opening 6 of the housing 4 as shown in FIG. Referring to FIG. 8, in direct type backlight device 13, the luminance ratio is minimum at points LS1 to LS6, and a point between intermediate points P1 to P5 and points LS1 to LS6 (for example, point LS1 and intermediate point P1) The luminance ratio becomes maximum at the point between Such luminance distribution is caused by the shape of the prism lens on the prism sheet 12. Hereinafter, this point will be described.
Referring to FIG. 9, a light beam 7a incident at an incident angle θa, a light beam 7b incident at an incident angle θb, and a light beam 7c incident at an incident angle θc from the cold cathode tube 1 at point LS to the lower surface of the prism sheet 12. Consider the trajectory of each ray 7d incident at an incident angle of 0 °. Each incident angle has a relationship of θa>θb> θc.

  First, the trajectory of the light ray 7a incident on the intermediate point P (P1 to P5) will be examined. As shown in FIG. 10, the light ray 7a incident at the incident angle θa is refracted on the lower surface of the prism sheet 12, travels through the prism sheet, and is incident on the prism surface 12a or 12b. The light ray 7a incident on the surface 12a is refracted and emitted in a direction shifted by θa1 ° from the normal line N0. The light ray 7b incident on the surface 12b is totally reflected because the incident angle exceeds the critical angle. The totally reflected light beam 7a is incident on the surface 12a and is emitted to the outside at a wide angle with respect to the normal line N0.

  In short, the light ray 7a incident on the intermediate point P is emitted in a direction shifted from the front direction (normal line N0). Therefore, the luminance ratio at the intermediate point P is low.

  Similarly, with reference to FIG. 11, at point R, a light beam 7 c incident on the lower surface of the prism sheet 12 at an incident angle θc is emitted in a direction shifted from the front direction. Therefore, the luminance ratio at the point R is also reduced.

  Referring to FIG. 12, at a point LS (LS1 to LS6) corresponding to the position where the cold cathode fluorescent lamp 1 is disposed, a light beam 7d incident on the lower surface of the prism sheet 12 at an incident angle of 0 ° is reflected on the prism surface 12a. And 12b. That is, in this case, the light beam 7d does not pass through the prism surfaces 12a and 12b. Therefore, the luminance ratio at the point LS is minimized.

  On the other hand, with reference to FIG. 13, at the point Q, among the light rays 7b incident on the prism sheet 12, the light rays incident on the surface 12a are emitted in parallel with the normal line N0. In the prism lens, the surface 12a has the same inclination angle from the lens edge LE to the lens center LC. Therefore, all the light rays 7b incident on the surface 12a are emitted in parallel with the normal line N0. As a result, the luminance ratio at the point Q is maximized.

  As described above, in the prism sheet 12, although the light ray 7b is emitted in the normal line N0 direction at the point Q, the light rays 7a, 7c, and 7d are in the normal line N0 direction at other intermediate points P, LS, and point R. Is not emitted. In short, the prism surfaces (12a, 12b) have a constant inclination angle, so that only light beams having a specific incident angle are emitted to the front surface, and other light beams cannot be emitted to the front surface. Therefore, as shown in FIG. 8, a luminance peak appears remarkably, and the luminance distribution becomes non-uniform.

[Brightness distribution of backlight device using lenticular lens sheet]
In place of the prism sheet 12, a lenticular lens sheet 14 having a plurality of cylindrical lenses 141 whose convex cross section is an arc is fitted in the direct type backlight device 13 shown in FIG. 7 instead of the prism sheet 12. The luminance distribution of the direct type backlight device is shown in FIG.

  Referring to FIG. 15, when the lenticular lens sheet 14 is used, the luminance distribution is uniform as compared with the prism sheet 12. However, the luminance ratio at the intermediate points P1 to P5 is about 20% lower than the luminance ratio at the points LS1 to LS6, and luminance unevenness still occurs. This luminance unevenness is presumed to be caused by the following principle.

  Referring to FIG. 16, the transverse shape of convex surface 142 of cylindrical lens 141 is an arc having a constant curvature. When the light beam 7a incident on the lower surface 144 of the lenticular lens sheet 14 at the incident angle θa is incident on the point S100 on the convex surface 142 of the cylindrical lens 141, the light beam 7a is emitted to the outside in parallel with the normal line N0. . At this time, an angle formed by the boundary surface BP100 including the point S100 and the plane 143 (here, referred to as an inclination angle) is defined as θ100. In short, the light ray 7a is emitted to the front at the boundary surface BP100 having the inclination angle θ100.

  As described above, the lenticular lens sheet 14 can also emit the light ray 7a incident on the intermediate point P to the front. However, the area of the convex surface 142 where the light beam 7a can be emitted to the front is small. Since the transverse shape of the convex surface 142 is an arc having a constant curvature, the inclination angle θ of the boundary surface BP including an arbitrary point S on the arc rapidly decreases from the lens edge LE toward the lens center LC. That is, the fluctuation of the inclination angle θ is large even near the lens edge LE. As a result, as shown in FIG. 16, when the light beam 7a is incident on the point S101 slightly shifted from the point S100 in the lens center LC direction, the inclination angle θ101 becomes smaller than the inclination angle θ100. Therefore, the light ray 7a is emitted with a predetermined angle deviation from the normal line N0.

In short, the light beam 7a is emitted to the front only at the point S100 and the area in the vicinity thereof, and is not emitted to the front if entering the other area. As a result, the luminance ratio at the intermediate point P becomes small.
The luminance ratio at the intermediate point P decreases as the interval 2L between the cold cathode fluorescent lamps 1 increases or as the height H decreases. In short, as the incident angle θa of the light beam 7a increases, the luminance ratio at the intermediate point P decreases, and the luminance unevenness becomes remarkable.

[Luminance Distribution of Backlight Device Using Optical Lens Sheet of the Present Invention]
The direct type backlight device 10 provided with the optical lens sheet 3 according to the present embodiment is an improvement of the above-described drawbacks of the lenticular lens sheet 14.
As shown in FIG. 3, in the transverse shape of the convex surface 310 of the cylindrical lens 31, the inclination angle θ1 of the side S1 including the lens edge LE satisfies the following expression (1).
1.6 × arctan (L / H)>θ1> 1.2 × arctan (L / H) (1)
Since the inclination angle θ1 satisfies the expression (1), the light ray 7a incident on the intermediate point P can be emitted to the front. Hereinafter, this point will be described.

  Referring to FIG. 17, a light ray 7a incident on the lower surface of the optical lens sheet 3 at an incident angle θa is emitted into the optical lens sheet 3 at a refraction angle α2. The light ray 7a that has traveled through the optical lens sheet 3 enters the side S1 of the convex shape 310 across the side S1 at an incident angle α3, and exits to the outside at a refraction angle α4.

When the refractive index of the optical lens sheet 3 is ns, the following expressions (2) and (3) are established according to Snell's law.
sin θa = ns × sin α2 (2)
ns × sin α3 = sin α4 (3)

Here, in order to emit the light beam 7a to the front, it is necessary to satisfy the following formula (4).
α2 + α3 = α4 = θ1 (4)
Since the refractive index ns of a general optical lens sheet is 1.45 to 1.65, if the inclination angle θ1 satisfies the following expression (5) from the expressions (2) to (4), the light beam 7a is It is emitted to the front.
1.6 × θa>θ1> 1.2 × θa (5)

Here, since the light ray 7a is a light ray incident on the intermediate point P, the angle θa is expressed by Expression (6).
θa = arctan (L / H) (6)

  From Expressions (5) and (6), if the tilt angle θ1 satisfies Expression (1), the light beam 7a can be emitted to the front. If the inclination angle θ1 is out of the range of the expression (1), the light ray 7a is emitted at an angle deviated from the front, and the luminance ratio at the intermediate point P is lowered. Specifically, the difference between the luminance ratio at the point LS and the luminance ratio at the intermediate point P exceeds 10%.

Furthermore, as shown in FIG. 3, the difference between the inclination angles of two sides adjacent to each other among the sides Sn in the transverse shape of the convex surface 310 gradually decreases from the lens center LC toward the lens edge LE. That is, the inclination angle θn does not change so much in the vicinity of the lens edge LE (for example, S1 and S2) that plays the role of collimating the light beam 7a. Thereby, the area | region which can radiate | emit the light ray 7a to the front among the convex surfaces 310 becomes larger than the cylindrical lens 141 of the lenticular lens sheet 14. FIG. As a result, the ratio at which the light beam 7a can be emitted to the front is greater than that of the lenticular lens sheet 14.
Based on the above actions, the trajectories of the light beams 7a to 7d in the direct type backlight 10 are examined.

18 to 21 are schematic diagrams showing the trajectories of the light rays 7a to 7d when the cylindrical lens 31 has an octagonal cross-sectional shape. In these drawings, as an example, the cross-sectional shape of the cylindrical lens 31 is an octagon, but the same result can be obtained even when the cross-sectional shape is another polygon different from the octagon.
Referring to FIG. 18, among the light rays 7a incident on the optical lens sheet 3, the light rays incident on the surface corresponding to the side S1 having the inclination angle θ1 are emitted to the front. That is, a part of the light beam 7a is emitted to the front. Referring to FIG. 19, out of the light beam 7 b incident on the optical lens sheet 3, the light beam incident on the surface corresponding to the side S <b> 2 is emitted to the front. Therefore, a part of the light beam 7b is collimated to the front. Similarly, referring to FIG. 20 and FIG. 21, the light ray incident on the surface corresponding to the side S3 of the light ray 7c is emitted to the front, and the light ray incident on the surface corresponding to the side S4 of the light ray 7d is emitted. It is emitted to the front.

  As described above, when the optical lens sheet 3 is used, a part of each of the light beams 7a to 7d is emitted to the front. A light beam having a larger incident angle on the optical lens sheet 3 is less likely to be emitted to the front, but the cylindrical lens 31 of the optical lens sheet 3 has an inclination angle θ1 at the lens edge LE that can emit the light 7a to the front, and In the vicinity of the lens edge LE, the inclination angle is set so as not to change so much. Thereby, the ratio of the light ray 7a which can be emitted to the front can be increased, and the luminance ratio of the intermediate point P can be increased until it becomes the same as the luminance ratio of other points.

The luminance distribution of the direct type backlight device 10 is shown in FIG. FIG. 22 shows, as an example of the optical lens sheet 3, a portion from the lens vertex LC to the lens edge LE in the transverse shape of the convex surface 310 from the lens edge LE to the lens center LC is constituted by four sides (S1 to S4). This is a luminance distribution when a lens provided with the cylindrical lens 31 is used. In the cylindrical lens of the optical lens sheet used for the investigation of the luminance distribution, the inclination angle θ1 of the side S1 is 60 °, the inclination angle θ2 of the side S2 is 50 °, the inclination θ3 of the side S3 is 30 °, and the side S4 The inclination angle θ4 was 5 ° and satisfied the formula (B). Further, since the distance 2L between the line light sources was 36 mm and the height H was 18 mm, the formula (1) was satisfied.
Referring to FIG. 22, the luminance distribution is more uniform than the direct type backlight device using the lenticular lens sheet 14, and the difference between the maximum value and the minimum value of the luminance ratio is less than 10%. It has become.

[Other forms of optical lens sheet]
FIG. 23 shows an optical lens sheet 40 having another configuration different from that of the optical lens sheet 3 shown in FIG. Referring to FIG. 23, the optical lens sheet 40 includes a base material portion 42 and a plurality of cylindrical lenses 41 formed on the base material portion 42. The base material part 42 has optical transparency. The base material portion 42 may be in the form of a sheet or a film. Moreover, plate shape may be sufficient. The plurality of cylindrical lenses 41 are arranged side by side in the same direction as the direction in which the cold cathode tubes 1 are arranged.

The transverse shape of the convex surface 410 of the cylindrical lens 41 is an arcuate curve. The curvature CU defined by the following equation (7) gradually decreases from the lens center LC toward the lens edge LE.
CU = 1 / Rc (7)
Here, Rc is the radius of curvature at an arbitrary point A on the curve which is the transverse shape of the convex surface 410.

  This is synonymous with the following matters. Referring to FIG. 24, a curve 410a between the lens edge LE and the lens center LC is equally divided in a direction parallel to the transverse shape (that is, straight line) 411a of the plane 411 of the cylindrical lens 41. When the angles formed by the convex surfaces at the respective dividing points A1 to An and the plane parallel to the plane 411 are θ1 to θn, the angles θ1 to θn satisfy the above-described formula (B). In short, when the number of sides Sn in the transverse shape of the convex surface 310 in FIG. 3 is infinite, the convex surface 410 shown in FIG. 23 is obtained.

  Furthermore, the angle θ1 described above, that is, the angle formed by the convex surface 410 and the plane 411 at the lens edge LE satisfies the formula (1).

  With the above configuration, the optical lens sheet 40 has the same effect as the optical lens sheet 3. In other words, the convex surface 410 has an angle θ1 at which the light ray 7a incident on the intermediate point P can be emitted to the front, and the curvature gradually decreases from the lens center LC toward the lens edge LE. In other words, the change in the angle θn in the vicinity of the lens edge LE is not so large, and the change in the angle θn increases as it goes toward the lens center LC. For this reason, compared with a lenticular lens sheet, the area | region which can radiate | emit the light ray 7a can be enlarged, and the luminance ratio of the intermediate point P can be raised until it becomes comparable with the luminance ratio of another point. .

[Production method]
A method for manufacturing the optical lens sheet 3 shown in FIG. 3 will be described.
First, the distance 2L between the cold cathode tubes 1 arranged in parallel in the direct type backlight device 10 using the optical lens sheet 3 and the height H from the central axis C of the cold cathode tube 1 to the lower surface of the optical lens sheet 3 are set. decide.

  After determining the interval 2L and the height H, the inclination angle θ1 is determined based on the determined interval 2L, the height H, and the equation (1).

  After determining the inclination angle θ1, based on the determined inclination angle θ1, in the transverse shape of the convex surface 310 of the cylindrical lens 31, the inclination angles θn, θ (n−1) of two adjacent sides Sn, Sn−1 The lens shape of the cylindrical lens 31 is determined so that the difference between the lens center LC and the lens edge LE gradually decreases.

  After determining the lens shape, a roll plate having a groove having the same cross-sectional shape as that of the cylindrical lens 31 is produced. An optical lens sheet 3 including a plurality of cylindrical lenses 31 is manufactured using the manufactured roll plate.

  In the manufacturing method described above, the roll plate is used for manufacturing, but after determining the lens shape, the optical lens sheet 3 may be manufactured by another method without using the roll plate. For example, when the plate-like optical lens sheet 3 is manufactured, a lithographic plate (flat mold) having a plurality of grooves corresponding to the cylindrical lens 31 may be used. In this case, the groove of the lithographic plate is filled with a thermoplastic resin, an ionizing radiation curable resin, or the like, and a substrate to be the base material portion 32 is laid thereon. The thermoplastic resin or ionizing radiation curable resin is cured to form the cylindrical lens 31, and the optical lens sheet 3 is manufactured. The ionizing radiation curable resin is a resin that is cured by ionizing radiation such as ultraviolet rays or electron beams.

  The optical lens sheet 40 shown in FIG. 23 can also be manufactured by the same method as the optical lens sheet 3. That is, the interval 2L and the height H are determined, and the angle θ1 is determined based on the determined interval 2L, the height H, and Equation (1). After determining the angle θ1, the lens shape of the cylindrical lens 41 is determined so that the curvature of the transverse shape (curve) of the convex surface 410 of the cylindrical lens 41 gradually decreases from the lens center LC toward the lens edge LE.

  The above-described optical lens sheets 3 and 40 can be manufactured by the above manufacturing method.

  In general, the interval 2L and the height H are set so that the incident angle θa of the light ray 7a incident on the intermediate point P is 15 ° to 50 °. However, the optical lens sheet according to the present embodiment. Then, even if the incident angle θa exceeds the above range, the above-described effects can be obtained.

  The interval 2L between the cold cathode tubes 1 is preferably 10 μm to 500 μm. If the thickness is less than 10 μm, it is difficult to form a cylindrical lens. If the thickness exceeds 500 μm, the effect of uniforming the luminance distribution is reduced. However, the effect of the present invention can be obtained to some extent even outside the above range.

In the present embodiment, in FIG. 1 and FIG. 2, the plurality of cold cathode tubes 1 are arranged in the vertical direction (y direction in FIG. 1) in front of the rear surface of the housing 4. You may arrange in parallel in the left-right direction (x direction in FIG. 1).
Further, the cylindrical lens 31 on the optical lens sheet 3 in the present embodiment may have its lens edge LE in contact with the lens edge LE of another adjacent cylindrical lens 13, or the lens edges LE may not contact each other. A predetermined interval may be provided. The same applies to the optical lens sheet 40.

  While the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

1 is a perspective view of a display device including a direct type backlight device according to an embodiment of the present invention. It is sectional drawing in line segment II-II in FIG. It is a cross-sectional view of the cylindrical lens which comprises the optical lens sheet | seat in FIG. It is sectional drawing of the direct type backlight apparatus which does not use a diffuser plate and an optical lens sheet. FIG. 5 is a luminance distribution diagram of the direct type backlight device shown in FIG. 4. It is a perspective view of a prism sheet. FIG. 7 is a cross-sectional view of a direct type backlight device including the prism sheet shown in FIG. 6. FIG. 8 is a luminance distribution diagram of the direct type backlight device shown in FIG. 7. FIG. 8 is a diagram for explaining a locus of light rays emitted from a line light source in the direct type backlight device shown in FIG. 7. It is a schematic diagram which shows the locus | trajectory until the light beam shown in FIG. 9 permeate | transmits a prism sheet, and is radiate | emitted outside. FIG. 11 is another schematic diagram different from FIG. 10, showing a trajectory until the light beam shown in FIG. 9 passes through the prism sheet and is emitted to the outside. FIG. 12 is another schematic diagram different from FIGS. 10 and 11, showing a trajectory until the light beam shown in FIG. 9 is transmitted through the prism sheet and emitted to the outside. FIG. 13 is another schematic diagram different from FIGS. 10 to 12, showing a trajectory until the light beam shown in FIG. 9 passes through the prism sheet and is emitted to the outside. It is a perspective view of a lenticular lens sheet. FIG. 15 is a luminance distribution diagram of a direct type backlight device including the lenticular lens sheet illustrated in FIG. 14. It is a schematic diagram which shows the locus | trajectory of the light ray which permeate | transmits the lenticular lens sheet | seat shown in FIG. It is a schematic diagram for demonstrating the conditions for the light ray inject | poured into the optical lens sheet | seat in this Embodiment to be radiate | emitted to the front in the lens edge vicinity. It is a schematic diagram which shows the locus | trajectory until the light ray from a linear light source permeate | transmits the optical lens sheet by this Embodiment, and is radiate | emitted outside. FIG. 19 is another schematic diagram different from FIG. 18 showing a trajectory until a light beam from the line light source passes through the optical lens sheet according to the present embodiment and is emitted to the outside. FIG. 20 is another schematic diagram different from FIGS. 18 and 19, showing a trajectory until a light beam from the line light source passes through the optical lens sheet according to the present embodiment and is emitted to the outside. It is another schematic diagram different from FIGS. 18-20 which shows the locus | trajectory until the light ray from a line light source permeate | transmits the optical lens sheet by this Embodiment, and is radiate | emitted outside. It is a luminance distribution figure of the direct type backlight apparatus by this Embodiment. It is sectional drawing of the optical lens sheet of another lens shape different from FIG. It is a schematic diagram for demonstrating the lens shape of the optical lens sheet | seat shown in FIG. It is sectional drawing of the conventional direct type | mold backlight apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cold cathode tube 3, 40 Optical lens sheet 10 Backlight apparatus 31, 41 Cylindrical lens 32, 42 Base part 310 Surface 320 Plane 410 Convex surface 410a Curve 411 Plane LE Lens edge LC Lens center

Claims (6)

A plurality of line light sources arranged in parallel with each other;
An optical lens comprising: a base part disposed at a predetermined distance from the plurality of line light sources; and a plurality of cylindrical lenses formed on the base part and arranged in parallel in the direction in which the plurality of line light sources are arranged. With seats,
The cylindrical lens has a polygonal cross-sectional shape, and in the cross-sectional shape, a difference in inclination angle between each of adjacent sides and a virtual line segment connecting the lens edges of the cylindrical lens is determined from the lens center. Gradually getting smaller towards the edge,
The interval between the two line light sources arranged in parallel with each other is 2L, and the height from the central axis of the line light source to the lower surface of the optical lens sheet is H,
The direct-type backlight device characterized in that, among the cross-sectional shapes, the inclination angle θ1 of the side including the lens edge satisfies the formula (1).
1.6 × arctan (L / H)>θ1> 1.2 × arctan (L / H) (1) A plurality of line light sources arranged in parallel with each other;
An optical lens comprising: a base part disposed at a predetermined distance from the plurality of line light sources; and a plurality of cylindrical lenses formed on the base part and arranged in parallel in the direction in which the plurality of line light sources are arranged. With seats,
The cylindrical lens has a convex cross-sectional shape that is a curve, and the curvature of the curve gradually decreases from the center of the lens toward the lens edge.
The interval between the two line light sources arranged in parallel with each other is 2L, and the height from the central axis of the line light source to the lower surface of the optical lens sheet is H,
The direct-type backlight device characterized in that, at the lens edge of the cylindrical lens, an angle θ1 formed by the plane of the cylindrical lens and the convex surface satisfies Expression (1).
1.6 × arctan (L / H)>θ1> 1.2 × arctan (L / H) (1) The direct type backlight device according to claim 1 or 2,
The direct-type backlight device according to claim 1, wherein the base material portion is light-transmissive and has a plate shape. An optical lens sheet used in a direct type backlight device having a plurality of line light sources arranged in parallel with each other,
A base material portion disposed at a predetermined distance from the plurality of line light sources;
A plurality of cylindrical lenses formed on the base material portion and arranged in the same direction as the arrangement direction of the plurality of line light sources;
A cross-sectional shape of the cylindrical lens is a polygon, and in the cross-sectional shape, a difference in inclination angle between each of adjacent sides and a virtual line segment connecting the lens edges of the cylindrical lens is from the center of the lens. It becomes gradually smaller toward the lens edge,
The interval between the two line light sources arranged in parallel with each other is 2L, and the height from the central axis of the line light source to the lower surface of the optical lens sheet is H,
Of the cross-sectional shape, the inclination angle θ1 of the side including the lens edge satisfies the formula (1).
1.6 × arctan (L / H)>θ1> 1.2 × arctan (L / H) (1) An optical lens sheet used in a direct type backlight device having a plurality of line light sources arranged in parallel with each other,
A base material portion disposed at a predetermined distance from the plurality of line light sources;
A plurality of cylindrical lenses formed on the base portion and arranged in the same direction as the parallel direction of the plurality of line light sources,
The cylindrical lens has a convex cross-sectional shape that is a curve, and the curvature of the curve gradually decreases from the center of the lens toward the lens edge.
The interval between the two line light sources arranged in parallel with each other is 2L, and the height from the central axis of the line light source to the lower surface of the optical lens sheet is H,
An optical lens sheet, wherein an angle θ1 formed by a plane of the cylindrical lens and the convex surface at the lens edge of the cylindrical lens satisfies the formula (1).
1.6 × arctan (L / H)>θ1> 1.2 × arctan (L / H) (1) The optical lens sheet according to claim 4 or 5, wherein
The said base-material part has a light transmittance, and is a plate shape, The optical lens sheet characterized by the above-mentioned.

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