JP4499540B2 - Surface light source device, transmissive display device - Google Patents

Description

The present invention relates to a liquid crystal display device the surface light source device that is used to illuminate the like, and to a transmissive type display device using the Re it.

Various surface light source devices have been proposed and put into practical use as surface light sources for illuminating a transmissive liquid crystal display (LCD panel) or the like from the back. The surface light source device mainly includes an edge light type and a direct type by converting a light source that is not a surface light source into a surface light source.
For example, in the direct type, light is introduced using a cold cathode tube (light emitting tube) in parallel from the back, and the distance between the cold cathode tube and a transmissive display unit such as an LCD panel is appropriately increased, In the meantime, a diffusion plate was used, and a plurality of sheets for converging light were used.
In such a conventional method, the convergence characteristics are insufficient for the large number of optical sheets required, and the LCD panel is improved to compensate for this, and the image quality is also improved even for incident light from an oblique direction. It was set as the structure which does not drop.

However, this method has a problem in that the light use efficiency is reduced and the configuration of the LCD panel is complicated, resulting in an increase in cost.
In particular, in the direct type, the light depends on whether it is a part close to the cold cathode tube (a position close to the cold cathode tube or a position close to a gap part of the cold cathode tubes arranged in parallel). Unevenness is likely to occur in intensity (luminance). In order to suppress this, if the distance between the cold cathode tube and the LDC is made large, there is a problem that the thickness of the display becomes thick. In addition, when the diffusion is increased or the transmission amount is limited in order to suppress unevenness, there is a problem that the amount of light used is reduced.

For example, in the surface light source devices described in Patent Documents 1 and 2, uniformity is maintained by providing a light-shielding portion (lighting curtain, light-shielding dot layer). In this method, the amount of light used is as described above. Decreased.
Also, a method using a sheet provided with lenticular lenses on both sides is reported, for example, in Patent Document 3, but this is a configuration for performing diffusion control in two directions and has no function of converging light. Therefore, there is a problem in that unevenness of brightness occurs depending on the position where the screen is observed because the optical axis varies depending on the location of the LCD depending on the positional relationship with the cold cathode tube.
JP 05-119703 A JP 11-242219 A Japanese Patent Laid-Open No. 06-347613

An object of the present invention, can be Ru surface light source device performing the unevenness without uniform illumination regardless of the position to observe the screen is to provide a transmission type display device.

The present invention solves the above problems by the following means. In order to facilitate understanding, description will be made with reference numerals corresponding to the embodiments of the present invention, but the present invention is not limited to this.
The first aspect of the present invention is a direct-type surface light source device that illuminates the transmissive display unit from the back, and uniformly diffuses the light emitted from the light source unit in which a plurality of light sources are arranged and the light source (13). The uniformizing sheet (14) is a part of a substantially elliptic cylinder whose major axis continues perpendicular to the sheet surface, or the major axis is orthogonal to the sheet surface. A unit lens set (141), which is a set of n types of unit lenses (141a, 141b) that is a part of a substantially spheroid, is repeatedly arranged, and the lens surface of the nth unit lens in the unit lens set The major radius of the substantially oval shape that forms the lens is An, the minor radius is Bn, and the area ratio of the n-th unit lens in the unit lens assembly occupying the sheet surface when viewed from the sheet normal direction is Rn. Sometimes 2.0 ≦ Σ (Rn × An / Bn) satisfy the relation of ≦ 2.8, wherein the light source is a light-emitting tube arranged at equal intervals L, and the distance between the center and the uniform entrance surface of the sheet of the arc tube D The surface light source device (12, 13, 14, 15, 16) is characterized by satisfying a relationship of 2.5 ≦ Σ (Rn × An / Bn) × 2D / L ≦ 3. .

According to a second aspect of the present invention, in the surface light source device according to the first aspect , the unit lens assembly (141) includes two types of unit lenses (141a, 141b) having different heights, and the two types of unit lenses. Where the height of the unit lens (141b) having a high height is H, the width of the unit lens having a high height is W, and the refractive index of the unit lens is N, arcsin (1 / N) <arctan It is a surface light source device ( 12, 13, 14 , 15, 16 ) characterized by satisfying (1 / ((2H / W) -0.1)).
The invention according to claim 3, in the surface light source device according to claim 1 or claim 2, between the unit lenses (141a, 141b) is flat shape (141c), a concave shape, either fine irregularities Is a surface light source device ( 12, 13, 14 , 15, 16 ).

Invention 請 Motomeko 4, in the surface light source device according to any one of claims 1 to 3, wherein arranged on the exit side of the equalizing seat (14), the fine irregularities on at least one side It is a surface light source device (12, 13, 14, 15, 16) characterized by having a diffusion sheet (16) having

The invention of claim 5 includes a transmissive display unit (11) and the surface light source device (12, 13, 14, 15, 16) according to any one of claims 1 to 4. It is a transmissive display device.

According to the present invention, the following effects can be obtained.
(1) Since the relationship of 2.0 ≦ Σ (Rn × An / Bn) ≦ 2.8 is satisfied, the convergence of the emitted light is good, and even when viewed from an oblique direction while ensuring sufficient front luminance, It is possible to emit uniform illumination light.

(2) Since arcsin (1 / N) <arctan (1 / ((2H / W) −0.1)) is satisfied, it is possible to prevent emission in a direction with a large emission angle and to observe from an oblique direction. Even if it exists, tube utilization does not arise and the utilization efficiency of light can be improved.

(3) Since any one of a flat shape, a concave shape, and a fine concavo-convex shape is formed between the unit lenses, a part of light incident at an incident angle close to the normal direction is in the normal direction. The light can be emitted at a close emission angle, an extreme decrease in luminance at a position close to the light source can be suppressed, and uniformity can be improved. Moreover, the light which goes to the diagonal direction from these flat shape, concave shape, and fine uneven | corrugated shape can inject into an adjacent unit lens, and can improve the convergence property of light.

(4) Since 2.5 ≦ Σ (Rn × An / Bn) × 2D / L ≦ 3 is satisfied, it is possible to emit illumination light without uneven brightness even when the interval between arc tubes is wide. Can do.

(5) Since the diffusion sheet having the fine unevenness shape is provided on at least one surface, the diffusion effect by the homogenization sheet can be assisted and a surface light source with higher uniformity can be obtained.

  The objective of uniform illumination without unevenness was realized without increasing the number of optical sheets.

FIG. 1 is a diagram showing an embodiment of a transmissive display device according to the present invention.
In addition, each figure shown below including FIG. 1 is the figure shown typically, and the magnitude | size and shape of each part are exaggerated suitably for easy understanding.
The transmissive display device 10 in this embodiment includes an LCD panel 11, a reflecting plate 12, an arc tube 13, a uniformizing sheet 14, a reflective polarizing sheet 15, a diffusion sheet 16, and the like, and an image formed on the LCD panel 11. This is a transmissive liquid crystal display device that illuminates information from the back by a surface light source device that includes a reflecting plate 12, an arc tube 13, a uniformizing sheet 14, a reflective polarizing sheet 15, and a diffusing sheet 16.

  The LCD panel 11 is a light valve formed by a so-called transmissive liquid crystal display element, and can display a 30-inch size and 800 × 600 dots. The direction along the longitudinal direction of the arc tube 13 is used as the horizontal direction, and the direction in which the arc tubes 13 are arranged is used as the vertical direction.

The arc tube 13 is a cold cathode tube of a line light source that forms a light source part of a backlight. In this embodiment, six are arranged in parallel at equal intervals of approximately 80 mm. Further, the distance between the arc tube 13 and the homogenizing sheet 14 described later is 50 mm.
A reflector 12 is provided on the back surface of the arc tube 13, and the design allows the incident light illuminance to each part of the screen to be made uniform.
The reflective polarizing sheet 15 is a sheet that is disposed between the LCD panel 11 and the homogenizing sheet 14 and increases the luminance without narrowing the viewing angle. In this embodiment, DBEF (manufactured by Sumitomo 3M Limited) is used.

The diffusion sheet 16 is a sheet that is provided on the emission side from the homogenization sheet 14 and assists the diffusion function of the homogenization sheet 14. In this embodiment, the diffusion sheet 16 is disposed between the homogenizing sheet 14 and the reflective polarizing sheet 15. The diffusion sheet 16 is also called a bead diffusion plate and contains almost no diffusing agent inside. The diffusion bead is dispersed on the surface to form a fine uneven shape on the surface, and according to the curvature of the diffusion bead. Diffuses outgoing light. Therefore, the diffusion sheet 16 can adjust the diffusion degree by the diffusion beads. The haze value of the diffusion sheet 16 in this example is 83.6%.
A uniformizing sheet 14 is provided between the arc tube 13 and the diffusion sheet 16.

FIG. 2 is a perspective view showing the homogenizing sheet 14.
The homogenizing sheet 14 is a sheet that diffuses and homogenizes the light emitted from the arc tube 13, and a lenticular lens shape composed of two types of unit lenses is formed on the emitting side in order to emit light uniformly. ing.
FIG. 3 is an enlarged view of the DD cross section in FIG.
The uniformizing sheet 14 is arranged with a large number of unit lens sets 141 in which two types of unit lenses 141a and 141b are regularly arranged in parallel on the emission side. Note that the direction in which the unit lenses are aligned is the same as the direction in which the arc tubes 13 are aligned (see FIG. 1).

The two types of unit lenses 141 a and 141 b formed on the exit side of the homogenizing sheet 14 in the present embodiment have a shape of a part of a continuous elliptic cylinder whose major axis is orthogonal to the sheet surface of the homogenizing sheet 14. Yes, forming a lenticular lens shape.
In the cross section shown in FIG. 3, the unit lens 141a is an ellipse having a long radius of 400 μm and a short radius of 120 μm, and the height protruding from the light output side (height from the flat portion 141c) is 96 μm. The width of the portion is 156 μm.
In the cross section shown in FIG. 3, the unit lens 141b is an ellipse having a major radius of 480 μm and a minor radius of 240 μm. The unit lens 141b projects to the light output side (height from the flat portion 141c) and projects 156 μm. The width of the portion is 356 μm.

The unit lens 141a and the unit lens 141b have a long axis interval of 259 μm and the long axis is orthogonal to the sheet surface of the uniformized sheet 14, and this combination is regarded as one unit lens set, and the pitch is 518 μm. Are arranged side by side in parallel. A flat portion 141c is provided between the unit lens 141a and the unit lens 141b, and the width of the flat portion 141c is approximately 3 μm.
Moreover, the thickness of the homogenization sheet | seat 14 is 2 mm, and is formed with MS resin (acryl styrene copolymer) of refractive index N = 1.55.

FIG. 4 is a diagram showing a typical trajectory of light incident on the uniformizing sheet 14.
As apparent from FIG. 4, most of the light rays incident on the uniformizing sheet 14 at a small incident angle are returned to the light source side, and light rays incident at a large incident angle are not returned to the light source side. Can be emitted. Since the homogenizing sheet 14 has such an action, the illumination light emitted by the arc tube 13 passing through the homogenizing sheet 14 has a small incident angle at a position close to the arc tube 13, and thus the arc tube 13. The ratio of returning to the side increases, and the ratio of emission increases with increasing distance from the arc tube 13 (approaching the gap between the arc tubes 13 in parallel). Therefore, the illumination light emitted from the homogenizing sheet 14 is made uniform.

As described above, since the height H of the higher unit lens 141b is 156 μm and its width W is 356 μm, these values satisfy the following formula (1). ing.
arcsin (1 / N) <arctan (1 / ((2H / W) −0.1)) (1)
This expression (1) is an expression for determining whether or not the light totally reflected at the position of 10% of the height from the end of the lens valley is totally reflected at the top of the lens.

FIG. 5 is a view showing how the light travels in the uniformizing sheet 14 in the present embodiment compared to the comparative example. FIG. 5A shows the case of the present embodiment, and FIG. 5B shows the case of a uniformized sheet having only a shape that does not satisfy the above formula (1) as a comparative example.
Light reaches the top of the lens from various directions, but in the valley between the unit lenses of the unit lens assembly 141, when light coming from a certain direction is totally reflected and emitted from the top, it proceeds in an oblique direction. (See the light beam L4 in FIG. 5 (b)), so that it appears uneven when observed from an oblique direction. By satisfying the expression (1), it is possible to emit light with a small emission angle like the light beam L1 in FIG. 5A, and to prevent the above-described unevenness from being observed when observed from an oblique direction. In addition, the light utilization efficiency can be increased.

  Here, the long / short ratio A / B, which is a ratio when the major radius of the ellipse is A and the minor radius is B, is 2.0 ≦ A / B ≦ 2. It is desirable to satisfy 8. When A / B is smaller than 2.0, the convergence of the emitted light is deteriorated, and the front luminance is excessively lowered. On the other hand, if A / B is larger than 2.8, the convergence is improved, but the amount of light emitted from the opposite inclined surface after total reflection once by the unit lens increases, and unevenness can be seen from an oblique direction. Become.

In the present embodiment, the unit lenses 141a and 141b are a combination of unit lenses formed in different elliptical shapes. In this case, how to set the above-described long / short ratio will be described. Since a large number of unit lenses are arranged at a very fine pitch, even if a part of the unit lenses does not satisfy the above-mentioned ratio (2.0 ≦ A / B ≦ 2.8), the entire length is short. The ratio (2.0 ≦ A / B ≦ 2.8) may be satisfied. In other words, the major ellipse forming the lens surface of the n-th unit lens among the unit lenses is viewed from the normal direction of the sheet of the n-th unit lens in the unit lens set with An as the major radius and Bn as the minor radius. Sometimes (when the projected unit lens shape) occupies the area ratio on the sheet surface as Rn,
2.0 ≦ Σ (Rn × An / Bn) ≦ 2.8 (2)
If you satisfy the relationship.
When the unit lens has a lenticular lens shape, the area ratio Rn is not equivalent to the ratio occupied by the width of the unit lens, but a lens array in which the unit lens is a part of a spheroid (so-called “so-called”). In consideration of the case of the eyelet lens, it is necessary to set the area ratio.

In the above formula (2), the upper limit value 2.8 and the lower limit value 2.0 are experimentally created by actually changing the shape of the unit lens to create a plurality of uniform sheets having different values of Σ (Rn × An / Bn). Asked for.
Specifically, five types of uniformized sheets of Σ (Rn × An / Bn) = 1, 1.5, 2, 2.5, and 3 are created, and luminance unevenness and unevenness when viewed obliquely (oblique) Unevenness), and the front luminance was evaluated. The results are shown in Table 1.

From the results shown in Table 1, Equation (2) was used as a condition as a range that can satisfy any of luminance unevenness, oblique unevenness, and front luminance.
In the unit lens 141a of the uniformizing sheet 14 in the present embodiment, A141a = 400 μm and B141a = 120 μm. The width of the protruding portion of the unit lens 141a is approximately 156 μm, and the width per unit lens group is 518 μm. Here, since the unit lens 141a is a lenticular lens, the area ratio Rn is equivalent as a ratio occupied by the width of the unit lens 1412a, and therefore R141a = 156 / 518≈0.3.
In the unit lens 141b, A141b = 480 μm and B141b = 240 μm. Further, the width of the protruding portion of the unit lens 141b is approximately 356 μm, and the width per unit lens group is 518 μm. Therefore, as in the case of the unit lens 141a, R141b = 356 / 518≈0. .69. Therefore, the value of Σ (Rn × An / Bn) of formula (2) is as follows.
Σ (Rn × An / Bn) = 0.3 × 400/120 + 0.69 × 480/240 = 2.38
Therefore, the homogenization sheet 14 in the present example satisfies Expression (2).

In the above formula (2), if the value of Σ (Rn × An / Bn) is too large, the luminance of the portion corresponding to the vicinity of the middle between the arc tube and the arc tube increases, and the value of Σ (Rn × An / Bn) If the value is too small, the luminance directly above the arc tube is increased, and thus the value range of Σ (Rn × An / Bn) is defined.
However, even if the expression (2) is satisfied, luminance unevenness occurs when the interval between the arc tubes is widened. Therefore, in the case where the interval between the arc tubes is wide and luminance unevenness occurs, the luminance uniformity can be maintained by further satisfying the following expression (3).
2.5 ≦ Σ (Rn × An / Bn) × 2D / L ≦ 3 (3)
Here, L represents the interval between the arc tubes, and D represents the distance between the center of the arc tube and the incident surface of the homogenizing sheet.
Further, 2D / L smaller than 1 is preferable in order to obtain a surface light source device that is thin and has high efficiency. This is because if 2D / L is greater than 1, the thickness of the surface light source device is increased.

  In the above formula (3), the upper limit value 3.0 and the lower limit value 2.5 are obtained by actually changing the shape of the unit lens to obtain a plurality of uniformized sheets having different values of Σ (Rn × An / Bn) × 2D / L. Created and determined experimentally. Specifically, five types of uniformized sheets of Σ (Rn × An / Bn) × 2D / L = 2, 2.5, 2.8, 3, 3.5 are created, luminance unevenness, oblique unevenness, The front brightness was evaluated. The results are shown in Table 2.

From the results shown in Table 2, Equation (3) was used as a condition as a range that can satisfy any of luminance unevenness, oblique unevenness, and front luminance.
In this embodiment, L = 80 mm, D = 50 mm, and Σ (Rn × An / Bn) = 2.38 from the previous calculation, so Σ (Rn × An / Bn) × 2D in equation (3). When / L is obtained, the following expression (3) is satisfied.
Σ (Rn × An / Bn) × 2D / L = 2.38 × 2 × 50/80 = 2.975
According to the present embodiment, since the dimensional relationship between the lens shape of the homogenizing sheet and the arc tube is defined, high luminance illumination can be obtained without luminance unevenness. In addition, it is not necessary to make a large number of prototypes by trial and error in the shape of the homogenizing sheet, and as a result, the homogenizing sheet, the surface light source device, and the transmissive display device can be provided at low cost.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the equivalent scope of the present invention.
(1) In the present embodiment, the example in which the homogenization sheet has a shape close to the lenticular lens shape on the surface on the emission side is shown, but the present invention is not limited to this. A so-called lens array shape arranged in a dimensional direction (an eye lens shape) may be used.

(2) In the present embodiment, the incident side of the homogenizing sheet 14 is a flat surface. However, the present invention is not limited to this. For example, in order to give a further light diffusing action, a fine uneven shape is formed by embossing or the like. May be formed.

(3) In this embodiment, the surface light source device and the transmissive display device are shown by combining the homogenizing sheet 14, the diffusion sheet 16, and the reflective polarizing sheet 15. However, the present invention is not limited to this. The diffusion sheet 16 may be omitted, or a surface light source device and a transmissive display device may be formed by combining various optical sheets other than these and the uniformizing sheet 14.

(4) In the present embodiment, the homogenization sheet 14 is an example in which two types of unit lenses 141a and 141b having different heights are arranged side by side. Different unit lenses may be arranged side by side, or more unit lenses having different heights may be arranged side by side.

(5) In the present embodiment, an example in which the flat portion 141c is provided between the unit lenses 141a and 141b has been shown. However, the present invention is not limited thereto, and for example, a concave shape or a fine uneven shape is formed, and the light The uniformity and convergence of the image may be improved.

It is a figure which shows the Example of the transmissive display apparatus by this invention. FIG. 3 is a perspective view showing a uniform sheet 14. It is the figure which expanded and showed DD cross section in FIG. FIG. 6 is a diagram showing a typical trajectory of light incident on the homogenizing sheet 14. It is the figure which showed how the light progressed in the uniformization sheet | seat 14 in a present Example compared with a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transmission type display apparatus 11 LCD panel 12 Reflector 13 Light emitting tube 14 Uniform sheet 141a, 141b Unit lens 15 Reflective polarizing sheet 16 Diffusion sheet

Claims (5)

A direct-type surface light source device that illuminates a transmissive display unit from the back,
A light source section in which a plurality of light sources are arranged;
And a uniformizing sheet that diffuses and uniformizes the light emitted from the light source ,
The homogenizing sheet is
It is a set of n types of unit lenses whose major axis is a part of a substantially elliptic cylinder that is continuous perpendicular to the sheet surface, or a part of a substantially spheroid whose major axis is perpendicular to the sheet surface. Unit lens set is repeatedly arranged,
The major ellipse forming the lens surface of the nth unit lens in the unit lens group has a major radius An and a minor radius Bn, as viewed from the normal direction of the nth unit lens in the unit lens group. When the area ratio on the sheet surface is Rn,
2.0 ≦ Σ (Rn × An / Bn) ≦ 2.8
Satisfied with the relationship
The light sources are arc tubes arranged at equal intervals at intervals L,
When the distance between the center of the arc tube and the incident surface of the homogenizing sheet is D,
2.5 ≦ Σ (Rn × An / Bn) × 2D / L ≦ 3
Satisfying the relationship
A surface light source device. The surface light source device according to claim 1,
The unit lens assembly is composed of two types of unit lenses having different heights,
Of the two types of unit lenses, when the height of the unit lens having a high height is H, the width of the unit lens having a high height is W, and the refractive index of the unit lens is N,
arcsin (1 / N) <arctan (1 / ((2H / W) −0.1))
Be satisfied,
A surface light source device . In the surface light source device according to claim 1 or 2,
Between the unit lenses, either a flat shape, a concave shape, or a fine uneven shape is formed,
A surface light source device . In the surface light source device according to any one of claims 1 to 3 ,
Having a diffusion sheet disposed on the exit side of the homogenizing sheet and having a fine irregular shape on at least one surface;
A surface light source device. A transmissive display;
A surface light source device according to any one of claims 1 to 4 ,
A transmissive display device.

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