JP4565570B2 - Light guide plate for surface light source and surface light source device using the same - Google Patents

Description

  The present invention relates to a light source plate for a surface light source and a surface light source device using the same, and more particularly to a light source plate for a surface light source for a backlight in, for example, a transmissive liquid crystal display device.

For example, in order to uniformly illuminate a transmissive liquid crystal display device from the back, a light guide plate in which a scattering source composed of a fine V-shaped reflection surface is arranged on the back, and a plurality of point light sources such as LEDs are arranged on one side thereof In addition, a light source plate for surface light source in which one point light source is arranged at the corner is known (Patent Document 1).
JP 2001-243822 A Republished patent WO2002 / 008662 Utility Model Registration No. 2507092

  However, when arranging a plurality of point light sources along one side, the shape of the scattering source in the direction along the one side has not been devised, and in the case where the point light source is arranged at the corner, more In order to make it bright, when a plurality of point light sources are arranged, it has not been studied how to make the shape of the scattering source. For this reason, when a backlight for a liquid crystal display device is configured using a point light source array such as an LED, it has been difficult to obtain bright and uniform illumination.

  The present invention has been made in view of such problems of the prior art, and its object is to provide a bright surface with uniform in-plane brightness and no variation when a point light source array such as an LED is used as a light source. It is providing the light-guide plate for light sources, and a surface light source device using the same.

The light source plate for a surface light source of the present invention that achieves the above object is a transparent plate-like body, and the end surface where the light from the point light source array arranged facing the one end surface around the surface faces the point light source array The light incident on the transparent plate-like body and guided by internal reflection is scattered by the scattering source disposed at least on the surface of the transparent plate-like body and scattered on the surface side of the transparent plate-like body, In a light source plate for a surface light source used as a planar light source,
A linear protrusion having a Λ-shaped cross-section extending along the end face on at least the surface of the transparent plate-like body and having a height distributed in a direction perpendicular to the end face, or aligned at regular intervals along the end face And a scattering source composed of a row of minute dot-like projections whose height is distributed in a direction perpendicular to the end face is disposed, and light scattered on the surface side of the transparent plate-like body is disposed. In the vicinity of the end surface, the height distribution in the direction along the end surface of the linear protrusions having the Λ-shaped cross section or the row of minute point-like protrusions is set so that the luminance is substantially uniform in the plane. Corresponding to the point light source in the light source array, the height is minimized at the position where the luminance is maximized, and the wave shape changes so that the height is maximized at the position where the luminance between the point light source and the point light source is minimized. In the position where the luminance between the point light source and the point light source is minimum, the direction orthogonal to the end face The scattering coefficient distribution once decreases and then increases as the process proceeds to, and the scattering coefficient distribution increases as the process proceeds in a direction perpendicular to the end face at the position where the luminance is maximum corresponding to the point light source. As described above, at least one of the height of the line projections of the Λ-shaped cross section or the row of the minute dot projections or the pitch in the direction orthogonal to the end face is changed. .

  In this case, the height distribution in the direction along the end face of the line-shaped protrusions or the array of minute point-like protrusions at the position away from the end face is a local scattering coefficient distribution. It is desirable to vary to compensate for uniformity.

  Moreover, the scattering source which consists of the line | wire process of the said (LA) -shaped cross section or the row | line | column of the said fine dot-like projection can also be arrange | positioned on both surfaces of the surface and back surface of the said transparent plate-shaped object.

  According to the present invention, the surface light source plate described above and a surface-side light guide plate side or the surface light source plate opposite to the surface light source plate is disposed on the scattered light exit side. And a surface light source device provided with a prism sheet provided on the surface.

  According to the present invention, when a point light source array is used as a light source, it is possible to obtain a bright surface light source light guide plate having uniform in-plane luminance and no variation, and a surface light source device using the same, and a transmissive liquid crystal display Even when used for a backlight of an apparatus, a bright surface light source light guide plate with uniform brightness in the display surface and no variation can be provided.

  Below, the principle of the light source plate for surface light sources of this invention and the Example of the light source plate for surface light sources obtained based on the principle are demonstrated.

  First, the design principle of the light source plate for surface light source of the present invention will be described.

For simplicity, it is assumed that the light source 10 is disposed facing one end surface 15 of the light guide plate 1 having a rectangular outer shape as shown in FIG. The light source 10 may be a linear light source arranged parallel to the end face 15, or a point light source array made up of point light sources 10 ₁ to 10 _s such as LEDs may be used. Such an incident light amount distribution on the end face 15 from the light source 10 is defined as I ₀ . FIG. 1 schematically shows that the incident light amount distribution I _{0 on} the end face 15 is distributed depending on the emitted light amount distribution of the light source 10. The incident light amount distribution I _{0 on the} end face 15 may be obtained by calculating the incident light amount from the light source 10 or measured (step ST1 in FIG. 2).

Then, the end surface 15 of the light guide plate 1 is equally divided into N small surfaces in the direction along the light source 10, and the amount of incident light on the _nth minute surface 15 _n is set to I _0n (step ST2).

Considering a light beam starting from the incident surface 15 _n and radiating into Δθ in the angle θ direction in the polar coordinate system as shown in FIG. 1, M minute regions 2 ₁ divided by a minute length Δr in the radial direction. ,..., 2 _m ,... 2 _M are considered (step ST3).

The amount of light I _0n incident on the minute region 2 ₁ at M = 1 and the amount of light I _1n emitted from the region are represented by K (r, θ) as the scattering coefficient in the region.
I _1n = I _0n · Θ (θ) · exp {−K (r, θ) · Δr} (1)
It becomes. Here, Θ (θ) is an angular distribution function of light from the incident surface 15 _n .

Similarly, for each area 2 _m in the radial direction,
I _2n = I _1n · exp {−K (r, θ) · Δr}
・ ・ ・ ・ ・ ・
I _mn = I _m−1n · exp {−K (r, θ) · Δr} (2)
It becomes. The recurrence formulas (1) and (2) are calculated sequentially in the range of θ _max to θ _min . Here, θ _max and θ _min are the maximum and minimum angles determined by the angular distribution Θ (θ) of light from the incident surface 15 _n (step ST4).

The above calculation is repeated for all the minute surfaces 15 ₁ to 15 _N of the end surface 15.

  For each position in the surface of the light guide plate 1, the result of superimposing all the differences between the incident light amount and the emitted light amount of each minute region obtained by the above calculation is the scattered light intensity D (x, y from the light guide plate 1. (Step ST5). Here, the coordinates (x, y) are in-plane coordinates of the light guide plate 1.

From the scattered light intensity distribution D (x, y) thus obtained, in-plane variation (D _max −D _min ) / D _max and scattering efficiency 求 め D (x, y) dxdy / ΣI _0n are obtained. It is determined whether or not the above condition is satisfied (step ST6). Here, D _max is the maximum value of the intensity of scattered light in the plane of the light guide plate 1, and D _min is the minimum value.

(D _max −D _min ) / D _max ≦ δ (3)
∬D (x, y) dxdy / ΣI _0n ≧ E ₀ (4)
Here, for example, δ is set to 0.15 (15%), preferably 0.10 (0.10%), and E ₀ is set to 0.7 (70%), preferably 0.9 (90%). Is set.

An error ΔD (x, y) at each point (x, y) from the scattered light intensity distribution D (x, y) thus obtained and the desired scattered light intensity distribution D ₀ (x, y).
D (x, y) −D ₀ (x, y) = ΔD (x, y) (5)
(Step ST7), and the error ΔD (x, y) is converted into a polar coordinate system ΔD (r, θ) (step ST8), which is converted from the scattering coefficient K (r, θ) of each point to K (r, θ) −ΔD (r, θ) is subtracted and K (r, θ) ← K (r, θ) −ΔD (r, θ) (6)
And a new scattering coefficient K (r, θ) (step ST9), and the above calculation is repeated again to obtain the optimum K (r, θ).

  The optimum K (r, θ) obtained by the above procedure is converted into orthogonal coordinates within the surface of the light guide plate 1 to obtain K (x, y) (step ST10).

The scattering coefficient K (x, y) is such that the thickness of the light guide plate 1 is T (x, y), the height of the scatterer disposed on the surface thereof is H (x, y), and the density of the scatterer. If P (x, y),
K (x, y) = C.H (x, y) .P (x, y) / T (x, y) (7)
(Step ST11). Here, C is a coefficient representing the scattering efficiency depending on the shape of the scatterer.

  The flow of the above processing is illustrated in the flowchart of FIG.

  Here, in the present invention, the scatterer 20 provided on the surface of the light guide plate 1 extends in the Y-axis direction along the end surface 15 on the surface 11 of the light guide plate 1 as shown in FIG. The linear protrusions 21 having a Λ-shaped cross section distributed in the X-axis direction orthogonal to the surface are provided on the surface 11 of the light guide plate 1 so as to be aligned at regular intervals in the Y-axis direction, as shown in FIG. A row 22 of minute point-like projections distributed in the X-axis direction is assumed.

Then, as shown in FIG. 4, a unit cell 2 ′ at an arbitrary position of the light guide plate 1 having a length in the X-axis direction and a length in the Y-axis direction orthogonal to the X-axis direction is assumed, and the unit cell 2 The repeat dimension (pitch) in the X-axis direction of the scatterer 20 at ′ is p _x (x, y), the repeat dimension (pitch) in the Y-axis direction is p _y (x, y), and the scatterer 20 in the Y-axis direction is When the width is W (x, y) and the thickness of the unit cell 2 ′ is T (x, y), the equation (7) is
K (x, y) = C.H (x, y) .W (x, y)
/ {T (x, y) · p x (x, y) · p y (x, y)}
... (8)
It becomes.

Therefore, to determine the scattering coefficient K (x, y), H (x, y), W (x, y), T (x, y), p _x (x, y), p _y (x, y) Any of y) may be changed.

  From the above formula (8), the light guide plate 1 that gives the desired scattered light intensity distribution D (x, y) (= constant value) is obtained.

  In the case where the scatterers 20 are linear protrusions 21 having a Λ-shaped cross section extending in the Y-axis direction and distributed in the X-axis direction as shown in FIG. (8) It is written as'.

F (x, y)
= C ′ · H (x, y) / T (x, y) · p _x (x, y) (8) ′
Next, examples of the light source plate for surface light source of the present invention obtained based on the above principle will be described.

FIG. 5 is a diagram showing the light intensity distribution on the end face 15 facing the array of LEDs 10 ₁ to 10 _s of the light source of the light guide plate 1. In this embodiment, as the light source 10, one in which six LEDs 10 ₁ to 10 _s are arranged at intervals of 12 mm is used. The light guide plate 1 has a length of 74 mm in the Y-axis direction of the side of the incident end, a length in the X-axis direction orthogonal to the end surface 15 of 50 mm, and a thickness of 0.7 mm.

  FIG. 6 is a diagram showing the scattering coefficient distribution K (x, y) of the surface 11 of the light guide plate 1 calculated as described above. FIG. 7 is a view showing the height distribution H (x, y) of the linear protrusion 21 having a Λ-shaped cross section disposed on the surface 11 of the light guide plate 1 for obtaining the scattering coefficient distribution as shown in FIG. It is. However, the pitch in the X-axis direction orthogonal to the end surface 15 of the linear protrusion 21 is 200 μm, and the linear protrusions 21 are provided so as to extend in the Y-axis direction parallel to each other. FIG. 8 is a diagram showing the height distribution of the linear protrusion 21 in the Y-axis direction. In FIG. 8, the incident end (X = 0 mm), 1/4 position (X = 12.5 mm), 1/2 position (X = 25 mm), 3/4 position (X = 37.5 mm), opposite The height distribution in the Y-axis direction of the linear protrusion 21 at the end (50 mm) is shown. FIG. 9 is a diagram showing the height distribution of the linear protrusions 21 in the X-axis direction. In FIG. 9, the height distribution in the X-axis direction at the position where the luminance corresponding to the point light source (LED) is maximized near the center of the end face 15 and the luminance between the point light source (LED) and the point light source (LED) is minimum. And the height distribution in the X-axis direction of the position to become. The in-plane luminance distribution of the light guide plate 1 is as shown in FIG. 10, and it is understood that the in-plane luminance distribution is substantially uniform and uniform, and a bright and highly efficient light source plate for a surface light source can be obtained.

  As is apparent from FIGS. 6 to 10, in the configuration of this embodiment, when the point light source array 10 is disposed in the vicinity of the incident end 15, the height in the Y-axis direction along the end surface 15 of the linear protrusion 21 is increased. In the vicinity of the incident end, the height distribution is minimum at the position where the luminance is maximum corresponding to the point light source in the light source array, and is high at the position where the luminance between the point light source is minimum. It changes in a wave shape so that the length is maximum.

  The height of the linear protrusion 21 increases from the incident end 15 in the X-axis direction orthogonal to the incident end 15 at a position where the luminance is maximum corresponding to the point light source, and the point light source and the point light source At a position where the brightness becomes minimum in the meantime, it temporarily decreases and then increases, and thereafter increases in the same manner as the position where the brightness becomes maximum corresponding to the point light source.

  Further, the height distribution in the Y-axis direction at a position away from the incident end 15 slightly varies in order to correct local scattering coefficient nonuniformity.

However, from the relationship of Expression (8) ′, the height H (x, y ₀ ) in the X-axis direction is inversely proportional to the pitch p _x (x, y ₀ ) in the X-axis direction. The pitch in the X-axis direction is not fixed to 200 μm, and the height in the X-axis direction at the position where the luminance between the point light sources becomes the minimum is set to 10 μm at any position in the X-axis direction (see FIG. The height of the curve at the entrance end, the curve at the 1/4 position, the curve at the 1/2 position, the curve at the 3/4 position, and the curve at the opposite end at the peak position of the curve at the 8 entrance end. In the above embodiment, as shown in FIG. 11, the pitch in the X-axis direction orthogonal to the end face 15 of the linear protrusion 21 is as follows: As it advances in the X-axis direction, it once increases and then decreases. Even in such a case, the height distribution in the Y-axis direction along the end face 15 of the linear protrusion 21 has a minimum height at a position where the luminance is maximum corresponding to the point light source in the light source array in the vicinity of the incident end. And changes in a wave shape so that the height is maximized at the position where the luminance between the point light source and the point light source is minimized. 8 and 11, the height of the linear protrusion 21 increases for a certain distance at the position where the luminance is maximum corresponding to the point light source as it proceeds from the incident end 15 in the X-axis direction. Are substantially the same, and naturally remain constant (10 μm) at the position where the luminance between the point light sources is minimum.

  Further, from the above consideration, the position in the Y-axis direction where the height of the linear protrusion 21 is set constant at any position in the X-axis direction is set to a position where the luminance is maximized corresponding to the point light source (FIG. 8). The height of the curve at the incident end, the curve at the 1/4 position, the curve at the 1/2 position, the curve at the 3/4 position, and the curve at the opposite end at the valley position of the curve at the incident end of The pitch in the X-axis direction perpendicular to the end face 15 of the linear protrusion 21 decreases as the X-axis direction advances. Even in such a case, the height distribution in the Y-axis direction along the end face 15 of the linear protrusion 21 has a minimum height at a position where the luminance is maximum corresponding to the point light source in the light source array in the vicinity of the incident end. And changes in a wave shape so that the height is maximized at the position where the luminance between the point light source and the point light source is minimized. And as it advances from the incident end 15 in the X-axis direction, the height of the linear protrusion 21 naturally remains constant at the position where the luminance is maximum corresponding to the point light source, and between the point light source and the point light source. At the position where the brightness is minimized, the brightness decreases for a certain distance and then becomes substantially the same.

  As described above, the height distribution in the Y-axis direction along the end surface 15 of the linear protrusion 21 is minimum at the position where the luminance is maximum corresponding to the point light source in the light source array in the vicinity of the incident end 15. At the position where the luminance between the point light source and the point light source is minimized and changes in a wave shape so that the height is maximized. The scattering coefficient distribution once decreases and then increases as it proceeds in the orthogonal X-axis direction, and also proceeds in the X-axis direction orthogonal to the end face 15 at a position where the luminance is maximum corresponding to the point light source. Accordingly, at least one of the height of the linear protrusions 21 or the pitch of the linear protrusions 21 changes so that the scattering coefficient distribution increases (FIG. 6). The height distribution in the Y-axis direction at a position away from the incident end 15 slightly fluctuates in order to correct the local nonuniformity of the scattering coefficient distribution.

  FIG. 12 schematically shows a part of the linear protrusion 21 having a Λ-shaped cross section provided on the surface 11 of the light source plate 1 for a surface light source of the present invention configured as described above. As described above, each linear protrusion 21 is provided so that its height varies in order to correct the unevenness of the local scattering coefficient distribution in the Y-axis direction.

  By the way, in the above embodiment, the line projections 21 or the row 22 of dot projections having the above height distribution are provided only on the surface 11 of the light source plate 1 for surface light source. The back surface 12 of the optical plate 1 is also provided with the same linear projections 21 or rows of dotted projections 22 provided on the front surface, so that both the front side and the back side of the light source plate 1 for surface light source are uniform and bright. A light guide plate for a surface light source that can be obtained is obtained. However, in this case, since the light guided to the back surface side is scattered similarly to the front surface side, the linear protrusions 21 or the row 22 of dot protrusions on the front surface and the back surface are orthogonal to the end surface 15 in FIG. The increase tendency of the curve of the height distribution in the X axis direction becomes larger, and the decrease tendency of the curve of the pitch in the X axis direction orthogonal to the end face 15 in FIG. 11 becomes larger, but the overall distribution shape is the same. It is.

Next, FIG. 13 shows a configuration example of a surface light source device using the above-described light source plate for surface light source of the present invention. FIGS. 13A to 13C are cross-sectional views of the main part taken in the X-axis direction orthogonal to the end face 15 facing the point light source array 10 of the light source, and one point in the point light source array 10. A light source (LED) is indicated by reference numeral 10 _t . The examples of FIGS. 13A and 13B are examples in which the linear protrusions 21 according to the present invention are disposed only on the surface 11 of the light source plate 1 for surface light source, and the example of FIG. This is an example in which the linear protrusions 21 according to the present invention are arranged on both the front surface 11 and the back surface 12 of the light guide plate 1.

  13 (a) has a sawtooth cross section on the scattered light exit side (surface 11 side) of the light source plate 1 for surface light source provided with linear protrusions 21 whose heights are distributed on the surface 11 according to the present invention. A prism sheet 31 provided with a fine prism on the surface of the surface light source light guide plate 1 side is disposed, and a diffusion plate 35 is disposed on the exit side thereof. Here, the prism sheet 31 is a prism sheet proposed in Patent Document 2, for example, and focuses light scattered outwardly from the surface 11 of the surface light source light guide plate 1 in the front direction. In this configuration, the diffusion plate 35 may be omitted.

  The configuration of FIG. 13B is a diffusion plate on the scattered light exit side (surface 11 side) of the light source plate 1 for surface light source provided with linear protrusions 21 whose height is distributed on the surface 11 according to the present invention. 35 is disposed, and a prism sheet 32 provided with a fine prism having a sawtooth cross section on the surface opposite to the light source plate 1 for surface light source is disposed on the exit side. Here, the prism sheet 32 is a prism sheet proposed in Patent Document 3, for example, and converges the light scattered from the surface 11 of the surface light source light guide plate 1 and passed through the diffusion plate 35 in the front direction. .

  In the configuration of FIG. 13C, linear protrusions 21 whose heights are distributed according to the present invention are provided on both the front surface 11 and the back surface 12 of the light source plate 1 for surface light source, and the front surface 11 side and the back surface 12 side. Similarly to the case of FIG. 13A, a prism sheet 31 in which a fine prism having a sawtooth cross section is provided on the surface of the surface light source light guide plate 1 side is arranged, and on the emission side of each prism sheet 31. This is an example in which a diffusing plate 35 is arranged and two transmissive liquid crystal display devices and the like are illuminated by a single surface light source light guide plate 1. Also in this case, the diffusion plate 35 may be omitted. Note that the diffusion plate 35 and the prism sheet 32 may be disposed on both the front surface 11 side and the back surface 12 side, as in the case of FIG.

  As described above, the light source plate for surface light source and the surface light source device using the same according to the present invention have been described based on the design principle and the embodiments, but the present invention is not limited to these embodiments and can be variously modified. . Note that the linear protrusion 21 having a Λ-shaped cross section may be an isosceles triangle or may be an unequal triangle as shown in FIGS.

It is a figure for demonstrating the design principle of the light-guide plate for surface light sources of this invention. It is a flowchart for obtaining the light-guide plate for surface light sources of this invention. It is a perspective view for demonstrating the structure of a scatterer. It is a figure for demonstrating the repetition dimension of the scatterer in a unit cell, and the width | variety of a scatterer. It is a figure which shows the light intensity distribution in the end surface of the light-guide plate for surface light sources in one Example of this invention. It is a figure which shows the scattering coefficient distribution of the surface of the light-guide plate for surface light sources of one Example of this invention. It is a figure which shows the height distribution of the linear protrusion arrange | positioned on the light-guide plate surface for obtaining scattering coefficient distribution like FIG. It is a figure which shows the height distribution of the Y-axis direction of the linear protrusion of FIG. It is a figure which shows the height distribution of the X-axis direction of the linear protrusion of FIG. It is a figure which shows the luminance distribution in the surface of the light-guide plate for surface light sources of one Example of this invention. It is a figure which shows the change of the pitch of the X-axis direction in the example which changes the pitch of the X-axis direction of a linear protrusion. It is a figure which shows typically a part of linear protrusion of the cross-sectional (LA) shape provided in the surface of the light-guide plate for surface light sources of this invention. It is a figure which shows the structural example of the surface light source device using the light-guide plate for surface light sources of this invention.

Explanation of symbols

1 ... surface light source for the light guide plate 2 _1, 2 _m, 2 _M ... minute regions 2 '... unit cell 10 ... light source 10 ₁ to 10 _s, 10 _t ... point light source (LED)
11 ... end surface of the rear surface 15 ... light guide plate surface 12 ... light guide plate of the light guide plate 15 _1, 15 _n, 15 _N ... microfacets (incident surface)
20 ... scatterer 21 ... linear projection 22 ... array of point projections 31 ... prism sheet 32 ... prism sheet 35 ... diffusion plate

Claims (4)

Light from a point light source array, which is a transparent plate-like body facing one end surface around the transparent plate-like body, enters the transparent plate-like body from the end surface facing the point light source array, and is guided by internal reflection. In the light source plate for a surface light source used as a planar light source, the scattered light is scattered by the scattering source disposed on at least the surface of the transparent plate and scattered on the surface side of the transparent plate.
A linear protrusion having a Λ-shaped cross-section extending along the end face on at least the surface of the transparent plate-like body and having a height distributed in a direction perpendicular to the end face, or aligned at regular intervals along the end face And a scattering source composed of a row of minute dot-like projections whose height is distributed in a direction perpendicular to the end face is disposed, and light scattered on the surface side of the transparent plate-like body is disposed. In the vicinity of the end surface, the height distribution in the direction along the end surface of the linear protrusions having the Λ-shaped cross section or the row of minute point-like protrusions is set so that the luminance is substantially uniform in the plane. Corresponding to the point light source in the light source array, the height is minimized at the position where the luminance is maximized, and the wave shape changes so that the height is maximized at the position where the luminance between the point light source and the point light source is minimized. In the position where the luminance between the point light source and the point light source is minimum, the direction orthogonal to the end face The scattering coefficient distribution once decreases and then increases as the process proceeds to, and the scattering coefficient distribution increases as the process proceeds in a direction perpendicular to the end face at the position where the luminance is maximum corresponding to the point light source. As described above, for a surface light source, at least one of a height of a line protrusion of the Λ-shaped cross section or a row of the minute dot protrusions or a pitch in a direction orthogonal to the end face is changed. Light guide plate. The height distribution in the direction along the end face of the line-shaped protrusions of the Λ-shaped cross section or the row of minute dot-like protrusions at a position away from the end face corrects the local nonuniformity of the scattering coefficient distribution. The light guide plate for a surface light source according to claim 1, wherein the light guide plate fluctuates in order to achieve. 3. A scattering source comprising linear projections having a Λ-shaped section or rows of minute dot-like projections is disposed on both the front and back surfaces of the transparent plate-like body. The light guide plate for surface light sources of description. The surface light source light guide plate according to any one of claims 1 to 3 and a fine prism having a sawtooth cross-section disposed on the scattered light emission side thereof are arranged on the surface light source light guide plate side or the surface light source guide. A surface light source device, comprising: a prism sheet provided on a surface opposite to the light plate.

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