JP3699145B2 - Lens sheet and backlight - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a lens sheet and a backlight used in a liquid crystal display device and the like, and more specifically, a lens sheet that can improve the front luminance of the backlight by optical means, and such a lens. The present invention relates to a backlight using a sheet.
[0002]
[Prior art]
In recent years, battery-powered products such as portable notebook PCs equipped with color liquid crystal display devices, portable liquid crystal TVs using color liquid crystal panels, and video-integrated liquid crystal TVs, the power consumption of the liquid crystal display devices increases the battery drive time. Has become an obstacle. In particular, the percentage of power consumption of the backlight used in liquid crystal display devices is large, and keeping this power consumption as low as possible is considered an important issue in extending battery operating time and increasing the practical value of the above products. ing.
[0003]
However, reducing the backlight brightness by reducing the power consumption of the backlight is not preferable because the liquid crystal display is difficult to see. Therefore, in order to reduce power consumption without sacrificing the luminance of the backlight, it is desired to improve the optical efficiency of the backlight. As means for realizing this, as shown in FIG. 8, a backlight 3 is proposed in which a prism sheet 1 in which a prism row 2 is formed on one side is placed on the exit surface side of a light guide 7. The increase in front luminance by the prism sheet 1 is caused by the following mechanism.
[0004]
In such a backlight 3, the light emitted from the light guide 7 enters the prism sheet 1, a part of the incident light is refracted and transmitted by the prism sheet 1, and the rest is reflected back to the light guide 7. It is. For example, the edge light type backlight 3 as shown in FIG. 8 generally has a directivity characteristic in which the front luminance is relatively low and the luminance viewed from an oblique direction is high. The directivity is improved so that the brightness in front increases by refracting. The reflected light from the prism sheet 1 is diffused and reflected by the diffusion sheet 4 placed on the light exit surface of the light guide 7, and the brightness of the light exit surface can be increased. Will be increased.
[0005]
[Problems to be solved by the invention]
FIG. 9 shows a cross section of such a prism row 2 of the prism sheet 1. A light ray incident on the prism sheet 1 is directly transmitted through the prism slope according to the incident angle, and one of the components a. After being reflected once by the prism slope, it is divided into a component b that is reflected again by the other prism slope and returns to the incident side, and a component c that is once reflected by one prism slope and then transmitted through the other prism slope and emitted. In this case, depending on the selection of the prism apex angle, there may be a component that causes multiple reflection, but the ratio is usually small. Among them, the component a is a light beam that is emitted in the front direction, that is, the observation direction and is actually used. The component b is an effective light ray that is diffusely reflected by the diffusion sheet 4 on the exit surface of the light guide 7 and increases the brightness of the exit surface. On the other hand, the component c is a light beam that is emitted at a wide angle outside the effective viewing angle of the liquid crystal display device, and is a light beam that does not contribute to an increase in front luminance.
[0006]
As a result, the light emitted from the prism sheet 1 has a viewing angle of about ± 40 ° from the front (vertical angle 90 ° to 100 °, refractive index about 1.5 to 1.59) in the direction perpendicular to the ridge line of the prism row 2. In the case of). When the viewing angle is larger than this, the luminance rapidly decreases, and once it becomes almost zero, the luminance increases again at a larger viewing angle. Therefore, as a result, the emission range of the emitted light is narrowed to increase the luminance.
[0007]
However, in recent years, the directional characteristics of liquid crystal panels have been improved, and those having a sufficiently practical contrast have been developed even in a narrow directional characteristic even at a viewing angle of ± 40 ° or more. The backlight 3 having a directivity characteristic in which the luminance rapidly decreases in a range of corners or more is not preferable, and a backlight having a wide directivity characteristic to some extent is desired, with a decrease in luminance accompanying an increase in viewing angle. .
The present invention has a directivity characteristic that maximizes the luminance in the front direction, has a luminance distribution that gradually decreases as the angle increases above a predetermined viewing angle, and has the front luminance as described above. An object of the present invention is to provide a lens sheet and a backlight that suppresses the generation of the component c that is not involved in the increase in brightness and has a highly efficient luminance increasing effect.
[0008]
[Means for Solving the Problems]
In view of such a situation, the inventors of the present invention have reached the present invention as a result of intensive studies on the lens shape of the lens sheet.
That is, the lens sheet of the present invention is formed on at least one surface with a large number of shape units in which two convex curved column surfaces whose buses are parallel to each other are coupled symmetrically in a direction perpendicular to the bus. The tangent surfaces of the two convex curved column surfaces in the joint portion intersect each other at an angle smaller than 180 °. Further, the backlight of the present invention is a shape unit in which two convex curved column surfaces whose buses are parallel to each other are symmetrically coupled to the light exit surface side of the light guide through a diffusion layer having a diffuse reflection function. However, a lens sheet is formed in which a large number of lenses are arranged on at least one surface in a direction perpendicular to the generatrix and the contact surfaces of the two convex curved column surfaces at the joint intersect each other at an angle smaller than 180 °. It is characterized by having placed.
[0009]
In the lens sheet of the present invention, as shown in FIG. 3, the lens unit having a shape in which two convex curved column surfaces 10 and 10 ′ whose buses are parallel to each other are coupled symmetrically is arranged in a direction perpendicular to the bus. It is formed in a large number, and has a shape in which the contact surfaces of the two convex curved column surfaces 10 and 10 ′ with respect to the respective convex curved column surfaces intersect at an angle smaller than 180 °. It is what you have. In the lens sheet 9 having such a lens unit, among the light rays incident on the lens sheet 9, most of the light rays reflected by the one convex curved column surface 10 are the other convex curved column surface. Light rays that are totally reflected at 10 ′, return to the incident surface side, are reflected by one slope, and are emitted from the other slope at a wide angle and are not involved in an increase in front luminance can be reduced.
[0010]
Further, in the lens sheet 9 of the present invention, the shape of the two convex curved column surfaces 10 and 10 ′ constituting the lens unit is reflected by one convex curved column surface 10 of the light rays incident on the lens sheet 9. In such a shape, the light beam is totally reflected in the incident direction on the other convex curved column surface 10 ', so that only the light beam that is directly transmitted and the light beam that is reflected and returned are present and reflected on one slope. This is preferable because there is no light beam emitted later from the other slope at a wide angle. The light beam that is totally reflected by the other convex curved surface 10 ′ and returned to the incident surface side is diffusely reflected by the diffusing surface provided on the light emitting surface of the light guide and is effective in increasing the luminance of the light emitting surface. Light.
Furthermore, in the present invention, the slope shape of the lens sheet 9 is a curved surface, so that the brightness does not drop suddenly when the angle exceeds a specific viewing angle as in the conventional prism sheet, and is typical. In the example, the brightness gradually decreases from 30 ° to 35 °, and shows a gentle decrease such that it becomes zero at 70 ° to 80 °.
[0011]
Next, a preferred embodiment of the present invention will be specifically described with reference to FIGS. FIG. 3 is an xz cross-sectional view of the lens sheet 9 according to a preferred embodiment of the present invention, and represents optical path tracking in the most characteristic case where φ = θc and p = T in the expressions (1) to (3). It is. In order not to generate a light beam emitted at a wide angle not related to the increase in front luminance as described above, the light beam reflected by one convex curved column surface 10 reaches the other convex curved column surface 10 ′. In addition, it is only necessary to always enter the convex curved column surface 10 ′ at an incident angle equal to or greater than the total reflection angle. That is, when the refractive index of the lens unit is n, the light beam reflected by one convex curved cylinder surface 10 is projected at an angle equal to or greater than the total reflection angle θc represented by θc = sin ⁻¹ (1 / n). When the curved curved surface 10 ′ is incident, it is totally reflected by the convex curved cylindrical surface 10 ′ and returns to the incident surface side like the light beams indicated by B to D.
[0012]
When viewed from each point of the convex curved column surface 10 on the right slope in FIG. 3, the light ray incident on the convex curved column surface 10 ′ of the left slope at the smallest incident angle is reflected light from the point P. If the angle between the straight line connecting each point of the convex curved cylinder surface 10 ′ from the point P and the normal of the tangent surface at each point of the convex curved cylinder surface 10 ′ is selected to be equal to the total reflection angle θc, All the reflected light from other points of the convex curved column surface 10 is totally reflected by the convex curved column surface 10 '. That is, when the O point corresponding to the valley of the convex curved column surface 10 ′ is taken as the origin (0, 0), the coordinates of the P point are (T, 0), and the convex curved column surface 10 ′ has x = 0. When the condition of the following expression (4) is satisfied sometimes, and the condition of the following expression (5) is satisfied when 0 <x <T / 2, all the reflected light from the convex curved column surface 10 is convex. It will be totally reflected at the curved surface 10 '.
[0013]
[Expression 4]
z = 0 (x = 0) (4)
[0014]
[Equation 5]
dz / dx = {ztanθc + (xT)} / {(xT) tanθc-z} (0 <x <T / 2) (5)
Similarly, the convex curved column surface 10 on the right slope satisfies the condition of the following expression (6) when x = T, and the following expression (7) when T / 2 <x <T. Is satisfied, all the reflected light from the convex curved column surface 10 ′ is totally reflected by the convex curved column surface 10.
[0015]
[Formula 6]
z = 0 (x = T) (6)
[0016]
[Expression 7]
-dz / dx = {ztanθc-x} / {-xtanθc-z} (T / 2 <x <T) (7)
Although the case where φ = θc and p = T has been described above, the directivity characteristics of the lens sheet 9 can be changed by adjusting the values of φ and p. For example, when φ> θc or p <T, the slope of the slope of the lens unit is uniformly loosened, and the effective viewing angle can be made wider, particularly effective when a wide viewing angle is required. It becomes. In this case, light rays emitted at a wide angle are not generated, but the increase rate of the front luminance tends to be lower than that in the case of φ = θc and p = T by widening the viewing angle. If the increase rate of the front luminance is too low, the merit of using the lens sheet 9 becomes thin. Therefore, it is preferable that φ is at most about 1.2θc and p is at most about 0.8T.
[0017]
On the other hand, in the case of φ <θc or p> T, the viewing angle is narrowed, but the rate of increase in the front luminance can be increased, and a high front luminance is required even if the viewing angle is somewhat sacrificed. Effective. In this case, some light rays are emitted at a wide angle. However, if the decrease in φ or the increase in p is slight, practically no light rays are emitted at a wide angle, and this is not a problem. That is, FIG. 4 shows optical path tracking when p is slightly larger than T, but after reflection at one convex curved column surface 10, the other convex curved column surface 10 ′ has a wide angle. The emitted light C reaches the adjacent lens unit and returns to the lens sheet 9 again, and as a result, almost no light emitted at a wide angle is generated. If p is further increased, a light beam that is emitted at a substantially wide angle is generated. However, if the ratio is small, there is no practical problem. The same applies to φ, and even if φ is reduced to such an extent that the proportion of light rays emitted at a wide angle becomes small, it does not cause a large problem in practice. However, if p is made too large or φ is made too small, the proportion of light rays emitted at a wide angle increases, leading to a decrease in front luminance. Therefore, it is preferable that φ is at most about 0.8θc and p is at most about 1.5T.
[0018]
Therefore, in the lens sheet 9 of the present invention, the shape of the convex curved cylindrical surface constituting the lens unit satisfies the condition of the following formula (1) when x = 0 or x = T, and 0 <x < Preferably, the shape satisfies the condition of the following expression (2) when T / 2, and satisfies the condition of the following expression (3) when T / 2 <x <T. In this case, φ is in the range of 0.8θc to 1.2θc, and p is in the range of 0.8T to 1.5T.
[0019]
[Equation 8]
z = 0 (x = 0, x = T) (1)
[0020]
[Equation 9]
dz / dx = {ztanφ + (xp)} / {(xp) tanφ-z} (0 <x <T / 2) (2)
[0021]
[Expression 10]
-dz / dx = {ztanφ + (Txp)} / {(Txp) tanφ-z} (T / 2 <x <0) (3)
As shown in FIG. 1, the lens sheet 9 of the present invention is formed by arranging a large number of lens units 8 having the above shapes in parallel to at least one surface. Usually, the thickness of the lens sheet 9 is preferably about 0.1 mm to 3 mm, and the pitch T of the lens unit 8 is preferably about 30 μm to 0.5 mm.
Such a lens sheet 9 is placed on the exit surface side of the light guide 7 instead of the prism sheet 1 shown in FIG. 8, and constitutes the backlight 3 of the present invention. Further, as shown in FIG. 2, the effect of increasing the front luminance of the backlight 3 can be further improved by using the lens sheet 9 of the present invention by stacking a plurality of the lens sheets 8 with the lens units 8 orthogonal to each other. it can.
[0022]
In the backlight of the present invention, the exit surface of the light guide is used as a diffusion surface, or a diffusion sheet is placed on the exit surface and a lens sheet is placed thereon. This is because, by providing a diffusion surface having a diffuse reflection function on the incident surface side of the lens sheet, it is reflected on one convex curved column surface constituting the lens unit of the lens sheet and then on the other convex curved column surface. This is because the light beam that has been totally reflected and returned to the incident surface side is diffusely reflected by the diffusing surface or the diffusing sheet and becomes an effective light beam that is incident on the lens sheet again and increases the luminance of the emitting surface. In addition, a reflective layer is usually formed on the surface opposite to the light exit surface of the light guide by a reflective sheet or the like, and such a reflective layer forms one convex curve that constitutes a lens unit of the lens sheet. Of the light rays that have been reflected by the column surface and then totally reflected by the other convex curved column surface and returned to the incident surface side, the light rays that have passed through the diffusion surface or diffusion sheet and entered the light guide are reflected by the reflective layer. The light is incident on the lens sheet again, and becomes an effective light beam that increases the luminance of the exit surface.
[0023]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
[0024]
Example 1
With respect to each lens sheet made of polycarbonate having a refractive index of 1.59 and polymethyl methacrylate having a refractive index of 1.49, a lens when φ = θc and p = T based on the equations (4) to (6) The shape of the unit was determined, and the cross-sectional shape is shown by a solid line and a dotted line in FIG. Based on this cross-sectional shape, a mold having a lens pattern similar to the cross-sectional shape shown in FIG. Using this mold, a lens pattern was transferred to a polycarbonate plate (refractive index = 1.59) having a thickness of 0.5 mm by hot pressing to obtain a lens sheet. Next, the diffusion sheet was placed on the exit surface of the edge light type light guide, and the obtained lens sheet was placed to constitute a backlight. For this backlight, the angular distribution of luminance was measured, and the result is shown by a solid line in FIG. At this time, the increase rate of the front luminance was 1.4 times. Note that the angular distribution of luminance indicated by the dotted line in FIG. 6 is measured for a backlight that does not use a lens sheet.
[0025]
Comparative Example 1
A mold having a lens pattern in which prisms with apex angles of 90 ° were arranged at a pitch of 50 μm was manufactured. Using this mold, a lens pattern was transferred to a polycarbonate plate (refractive index: 1.59) having a thickness of 0.5 mm by hot pressing to obtain a prism sheet. The obtained prism sheet was placed on the exit surface of the edge light type light guide, and then the obtained lens sheet was placed to constitute a backlight. For this backlight, the angular distribution of luminance was measured, and the result is shown by a solid line in FIG. The increase rate of the front luminance at this time was 1.55 times. Note that the angular distribution of luminance indicated by a dotted line in FIG. 7 is measured for a backlight that does not use a lens sheet.
[0026]
As apparent from the comparison between FIG. 6 and FIG. 7, the lens sheet of the present invention has a slightly lower front luminance than the conventional prism sheet, but increases the viewing angle like the conventional prism sheet. Accordingly, the directivity characteristic that the luminance gradually decreases as the viewing angle increases without causing a sharp decrease in luminance is exhibited. As a result, the full width at half maximum is increased by about 20 °, and the directional characteristics do not impair the performance of the liquid crystal panel having a wide viewing angle. Further, unlike the conventional prism sheet shown in FIG. 7, there is no increase in luminance in a wide angle region of 50 ° or more, and generation of light rays emitted at a wide angle that does not contribute to the increase in front luminance is suppressed. Is.
[0027]
Example 2
As shown in FIG. 2, two polycarbonate lens sheets obtained in Example 1 were used, and their lens units were orthogonally stacked to form a backlight in the same manner as in Example 1. When the front luminance and the angular distribution of the luminance were measured for this backlight, the increase rate of the front luminance was 1.7 times and the half value width (viewing angle) of the luminance was ± 35 °.
[0028]
【The invention's effect】
In the lens sheet of the present invention, the shape of each lens unit is such that two convex curved column surfaces whose generating lines are parallel to each other are coupled symmetrically, and the tangent surfaces of both of the two convex curved column surfaces at the coupling portion are By having a shape that intersects at an angle smaller than 180 °, the directivity of the lens sheet is improved, and the directivity that can be used for a wide viewing angle liquid crystal panel is obtained without impairing the effect of improving the front luminance. Made it possible to provide a backlight.
[Brief description of the drawings]
FIG. 1 is a perspective view of an embodiment of a lens sheet of the present invention.
FIG. 2 is a perspective view of an embodiment of a backlight using the lens sheet of the present invention.
FIG. 3 is a cross-sectional view illustrating the operation of the lens sheet of the present invention.
FIG. 4 is a cross-sectional view illustrating the operation of the lens sheet of the present invention.
FIG. 5 is a design example of a lens unit formed on one side of the lens sheet of the present invention.
FIG. 6 is a diagram showing an angular change in luminance of a backlight using the lens sheet of the example.
FIG. 7 is a diagram showing an angular change in luminance of a backlight using a conventional prism sheet of a comparative example.
FIG. 8 is a perspective view showing a form in which a conventional prism sheet or a lens sheet of the present invention is used.
FIG. 9 is a cross-sectional view illustrating the operation of a conventional prism sheet.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Prism sheet 2 ... Prism row | line | column 3 ... Backlight 4 ... Diffusion film 5 ... Cold cathode tube 6 ... Reflective film 7 ... Light guide 8 ... Lens sheet Surface forming unit 9 ... convex curved column surface 11 of lens sheet 10, 10 '... of one embodiment according to the present invention ... coupling portion

Claims (4)

On at least one surface, a plurality of shape units in which two convex curved cylindrical surfaces whose buses are parallel to each other are connected symmetrically are formed side by side in a direction perpendicular to the bus, and two convex shapes at the connecting portion are formed. A lens sheet characterized in that both contact surfaces of the curved column surface intersect at an angle smaller than 180 °. The convex curved column surface is shaped such that the light beam reflected by one convex curved column surface among the light beams incident on the lens sheet is totally reflected in the incident direction by the other convex curved column surface. The lens sheet according to claim 1. When the z-axis is parallel to the normal of the lens sheet, the y-axis is parallel to the generatrix of the convex curved cylindrical surface, and the x-axis is in the column direction of the shape unit, the shape unit is expressed by the following formulas (1) to (3 2. The lens sheet according to claim 1, wherein the lens sheet has a shape satisfying

In the formulas (1) to ( 3 ), φ = 0.8θc to 1.2θc (where θc = sin ⁻¹ (1 / n), n represents the refractive index of the forming unit), p = 0.8T to 1.5T , T represents the width of the forming unit. A shape unit in which two convex curved cylindrical surfaces whose buses are parallel to each other are connected to the light-emitting body side through a diffusion layer having a diffuse reflection function is symmetrically connected to at least one surface. And a lens sheet which is formed in a line in a direction perpendicular to each other and in which the contact surfaces of both convex curved column surfaces of the connecting portion intersect at an angle smaller than 180 ° is mounted. .

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