JP2010286520A - Display and designing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display which is less apt to cause a multiple images, and to provide a designing method for the device. <P>SOLUTION: In the display, the width W of a double image generated by emitting two video light beams from a surface of a light diffusion layer in the same direction is defined by the expression: W=L*cosäasin(n<SB>H</SB>*sinθ<SB>d-in</SB>)}*ätanθ<SB>d-in</SB>+tan(θ<SB>d-in</SB>-α)}<250 μm, if the distance between the base of the light diffusion layer and a pixel surface is L; the refractive index of a first refraction part constituting the light diffusion layer is n<SB>H</SB>; the internal advancing angle of the video light beam emitted from the pixel surface, relative to a normal on the base of the light diffusion layer, is θ<SB>d-in</SB>; and the vertex angle of the wedge part of a second refraction part is α. Thus, the display which is improved in visibility by suppressing the occurrence of double image is provided. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a display device having a light diffusion layer and a design method thereof.

  As a method for improving the viewing angle in a display device, a method using a light diffusion layer is known. For example, if a light diffusion layer (for example, using TIR (Total Internal Reflection)) composed of a plurality of substances having a difference in refractive index is provided on the surface of the display panel on the viewer side, total reflection or By utilizing characteristics such as diffuse reflection, the image light emitted from the display panel surface can be diffused over a wide range. For this reason, the viewing angle characteristics of the display device can be improved on the viewer side.

  Also, a viewing angle control sheet using reflection characteristics and a display device using the same are known (for example, Patent Document 1).

JP 2006-343711 A

  As described above, when a light diffusion layer using TIR is provided on the viewer side of the display panel, viewing angle characteristics can be improved. However, on the other hand, a problem arises in that multiple images are generated when a plurality of video lights having different light paths are emitted in the same direction.

  An example of multiple images will be shown using FIG. Note that FIG. 16 shows an example of a double image generated by two video lights and viewed from an oblique direction.

  When the image light emitted from the pixel surface 99 passes through the light diffusion layer (TIR) existing at a distance L and is emitted to the outside, there are roughly two different paths.

  One is light that is not incident on the low-refractive portion 91 made of a material having a low refractive index but is transmitted only through the high-refractive portion 93 made of a material having a high refractive index and is emitted from the light diffusion layer surface 95. 90 (referred to as direct light). The other is light 92 (assumed to be low-reflected light) emitted from the light diffusion layer surface 95 after being totally reflected once by the low refraction part 91.

  The direct light 90 and the low reflection light 92 are emitted at the same angle on the light diffusion layer surface 95, whereby a double image (double image having a width W) is generated.

  When such a double image is remarkably generated, a problem arises in a display device that requires high display accuracy in all directions of the viewing angle, such as a medical display.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a display device that hardly generates multiple images and a design method thereof.

In order to achieve the above object, in a display device design method disclosed below, the display device includes a backlight and a plurality of pixels that emit video light toward the light diffusion layer with light from the backlight directed toward the light diffusion layer. At least a pixel surface having the pixel surface and a transparent member pasted through the transparent surface, wherein the light diffusion layer has a vertical angle in a cross section of the first refracting portion and the light diffusion layer. A wedge-shaped second refracting portion having a distance L between the bottom surface passing through the apex of the apex angle in the second refracting portion of the light diffusing layer and the pixel surface, and a first refracting that constitutes the light diffusing layer. N _H , the internal advancing angle of the image light emitted from the pixel surface with respect to the normal at the bottom surface of the light diffusion layer is θ _d-in , and the apex angle at the second refracting portion is α. When two image lights are identical from the surface of the light diffusion layer The width W of the double image generated by being emitted in the direction is defined by the following equation:
W = L * cos {asin (n _H * sinθ _d-in )} * {tan θ _d-in + tan (θ _d-in −α)}
The values of L, n _H , θ _d-in, and α are determined using the above formula.

  When designing a display device with improved viewing angle characteristics, the value of the double image width that can occur can be calculated by the display device design method.

  As described above, the display device design method of the present invention has an effect that a display device that hardly generates multiple images can be designed.

It is a side view which shows schematic structure of a liquid crystal display device. It is a schematic diagram which shows the case where a double image generate | occur | produces in a liquid crystal display device. It is a side view which shows the structure of a light-diffusion layer. 6 is a graph showing an example of a relationship between an internal advance angle θd-in and a double image width W. 5 is a graph showing an example of a relationship between an emission angle θd-out and a double image width W. 6 is a graph showing an example of a relationship between an internal advance angle θd-in and a double image width W. It is a schematic diagram which shows the case where a double image generate | occur | produces in a liquid crystal display device. 6 is a graph showing an example of a relationship between an internal advance angle θd-in and a double image width W. 6 is a graph showing an example of a relationship between a distance L and a double image width W. 6 is a graph showing an example of a relationship between an internal advance angle θd-in and a double image width W. 5 is a graph showing an example of a relationship between an aperture ratio apa and a double image width W. 6 is a graph showing an example of a relationship between an internal advance angle θd-in and a double image width W. 3 is a graph showing an example of a relationship between an apex angle α and a double image width W. 6 is a graph showing an example of a relationship between an internal advance angle θd-in and a double image width W. It is a schematic diagram which shows the case where a double image generate | occur | produces in a liquid crystal display device. 6 is a graph showing an example of a relationship between an internal advance angle θd-in and a double image width W. 6 is a graph showing an example of a relationship between a distance L and a double image width W. 6 is a graph showing an example of a relationship between an internal advance angle θd-in and a double image width W. Is a graph showing an example of the relationship between the refractive index n _H and a double image width W of the high bending resin. 6 is a graph showing an example of a relationship between an internal advance angle θd-in and a double image width W. 3 is a graph showing an example of a relationship between an apex angle α and a double image width W. 6 is a graph showing an example of a relationship between an internal advance angle θd-in and a double image width W. It is a schematic diagram which shows the case where a double image generate | occur | produces in a liquid crystal display device. 6 is a graph showing an example of a relationship between an internal advance angle θd-in and a double image width W. It is a graph which shows an example of the relationship between the largest output angle (theta) bl, max of a backlight, and the largest double image width Wmax. 6 is a graph showing an example of a relationship between an internal advance angle θd-in and a double image width W. It is a graph which shows an example of the relationship between the backlight emission angle θbl and the relative luminance. It is a schematic diagram which shows the case where a double image generate | occur | produces in a liquid crystal display device.

(1) In the display device design method according to an embodiment of the present invention, the display device includes a backlight and a plurality of pixels that emit video light toward the light diffusion layer with light from the backlight directed to the light diffusion layer. At least a pixel surface and the light diffusion layer pasted through the pixel surface and a transparent member, and the light diffusion layer has an apex angle in a cross section of the first refracting portion and the light diffusion layer. A second refracting portion having a wedge shape, wherein the distance between the bottom surface passing through the apex of the apex angle in the second refracting portion of the light diffusing layer and the pixel surface is L, and the first refracting portion constituting the light diffusing layer is When the refractive index is n _H , the internal traveling angle of the image light emitted from the pixel surface with respect to the normal line at the bottom surface of the light diffusion layer is θ _d-in , and the apex angle at the second refracting portion is α, Two video lights are emitted in the same direction from the surface of the light diffusion layer. The width W of the double image generated by is defined by the following equation:
W = L * cos {asin (n _H * sinθ _d-in )} * {tan θ _d-in + tan (θ _d-in −α)}
The values of L, n _H , θ _d-in, and α are determined using the above formula.

Thereby, when designing a display device with improved viewing angle characteristics, it is possible to calculate the value of the double image width that can occur. For example, an optimal display device can be designed while changing each parameter value (L, n _H , θ _d-in , α) of the display device to be designed.

(2) In the display device design method, the values of L, n _H , θ _d-in, and α are determined so that the width W of the double image is 250 μm or less. May be.

  Thereby, the double image which can be generated can be suppressed to such an extent that it cannot be visually recognized.

(3) In the design method of the display device, when the aperture ratio of the first refracting portion relative to the second refracting portion on the surface of the light diffusion layer is apa, the θ _d-in is determined within the following range. May be.
0 ≦ θ _d-in ≦ atan {(1 + apa) / (1-apa) * tan (α / 2)}
Accordingly, it is possible to design a display device with improved viewing angle characteristics while defining the width value of the double image that can be generated with a small number of parameters.

(4) In the design method of the display device, the θ _d-in may be determined within the following range.
0 ≦ θ _d-in ≦ 90−asin (n _L / n _H ) + α / 2
Accordingly, it is possible to design a display device with improved viewing angle characteristics while defining the width value of the double image that can be generated with a small number of parameters.

(5) In the display device design method, when the maximum light emission angle from the backlight is θbl, max, the θ _d-in may be determined within the following range.
0 ≦ θ _d-in ≦ asin (sin θbl, max / n _H )
(6) In the display device according to an embodiment of the present invention, the display device includes a backlight, and a pixel surface having a plurality of pixels that emit light from the backlight toward the light diffusion layer. And at least the light diffusing layer pasted through the pixel surface and a transparent member, the light diffusing layer having a wedge shape having an apex angle in a cross section of the first refracting portion and the light diffusing layer. A second refracting portion, the distance between the bottom surface passing through the apex of the apex angle in the second refracting portion of the light diffusing layer and the pixel surface is L, and the refractive index of the first refracting portion constituting the light diffusing layer is n _H , where θ _d-in is the internal advancing angle of the image light emitted from the pixel surface with respect to the normal line at the bottom surface of the light diffusion layer, and α is the apex angle in the second refracting portion. By emitting two image lights in the same direction from the surface of the layer The width W of the generated double image satisfies the following expression.

W = L * cos {asin (n _H * sinθ _d-in )} * {tan θ _d-in + tan (θ _d-in −α)} <250 μm
As a result, the width of the double image that can occur in all directions can be suppressed within a range in which it is difficult for humans to discriminate, and visibility can be prevented from being lowered while improving the viewing angle characteristics.

  Hereinafter, preferred embodiments of a display device of the present invention will be described with reference to the drawings. In the following description, the case where the present invention is applied to a display device having a liquid crystal panel will be described as an example. The present invention can also be applied to other display devices having a pixel surface such as an organic EL and a PDP.

[1. First Embodiment]
[1-1. Configuration of liquid crystal display device]
FIG. 1 is a side view showing a schematic configuration of a liquid crystal display device 1 according to the present invention. The liquid crystal display device 1 includes a backlight 14, a back polarizing plate 13, a liquid crystal panel 12, a front polarizing plate 11, and a light diffusion layer 10 in order from the lower side of FIG. 1. The liquid crystal panel 12 includes a glass substrate, a transparent electrode, an alignment film, a liquid crystal layer, a color filter, and the like.

  A front polarizing plate 11 is provided on the upper surface of the liquid crystal panel 12, and a rear polarizing plate 13 is provided on the lower surface. A light diffusion layer 10 is provided on the upper surface of the front polarizing plate 11. The front polarizing plate 11 and the light diffusion layer 10 are bonded via an adhesive layer (not shown).

[1-2. Definition of double image]
FIG. 2 is a schematic diagram illustrating a case where a double image of image light is generated in the liquid crystal display device 1 of FIG. FIG. 3 is a cross-sectional view in the vertical direction of the surface of the light diffusion layer 10.

  As shown in FIG. 3, the light diffusion layer 10 includes a base film 31 and a resin portion 33, and the resin portion 33 includes a resin having a high refractive index (referred to as a highly bent resin 93) and a resin having a low refractive index ( It is comprised from the low refractory tree 91). This low refractory tree 91 can be approximated to an isosceles triangle shape (wedge shape) with an apex angle α, and a plurality of low refractory trees 91 are arranged at predetermined intervals. In addition, the low refractory trees 91 are arranged in stripes in the light diffusion layer 10. Moreover, you may arrange the low refractory tree 91 as a cone shape.

The refractive index of the high bending resin 93 is n _H , the refractive index of the low bending resin 91 is n _L , and the ratio of the high bending resin 93 to the low bending resin 91 in the surface 35 of the opening of the light diffusion layer 10. The aperture ratio is apa, the apex angle of the wedge portion of the low-fat resin 91 is α, and the pitch between the low-fat trees 91 is p.

In this case, the light diffusion characteristics of the liquid crystal display device 1 can be defined using parameters such as n _H , n _L , apa, and α. It should be noted that the pitch p indicating the distance between the low-friction resin trees has little influence on the light diffusion characteristics when the low-friction resin trees 91 having the same shape are used. Do not consider.

  As shown in FIG. 2, a double image (hereinafter referred to as a double image) that can be viewed at an oblique viewing angle is emitted from the backlight surface 21, and the two image lights that have passed through the same pixel are applied to the low bending resin 91. The light 90 (hereinafter referred to as direct light) that passes through the high-flex resin 93 without being incident and the light 92 that is totally reflected once by the low-flex resin (hereinafter referred to as low-reflected light) are different paths. And is emitted from the surface 23 of the light diffusion layer 10 at the same angle (θd−out = θr−out).

  Depending on the possible range of the internal traveling angles θd-in and θr-in of the light, the double image width W becomes large, and the double image becomes more visible. Further, the double image width W increases in proportion to the distance L between the bottom surface 97 of the light diffusion layer 10 and the pixel surface 99, and the double image is easily visually recognized.

  The direct light 90 and the low-reflected light 92, which are light that travels in two different paths after passing through the same pixel, enter the bottom surface 97 of the light diffusion layer 10 with a distance D as the direct light. When the distance between the positions where the light 90 and the low-reflected reflected light 92 are emitted from the surface 95 of the light diffusion layer 10 is D ′, the double image width W can be expressed by the following equation.

W = D '* cosθd-out (= D' * cosθr-out)
Here, the distance D of each position where the direct light 90 and the low-reflected reflected light 92 are incident on the bottom surface 97 of the light diffusion layer 10, and the distance D ′ of each position where the light is emitted from the surface 95 of the light diffusion layer 10. Are substantially equal, the double image width W can be approximated by the following equation.

W = D * cosθd-out (= D * cosθr-out)
Further, the distance D includes the internal traveling angle θd-in of the straight through light 90, the internal traveling angle θr-in of the low-reflected reflected light, and the bottom surface 97 of the light diffusion layer 10 (the apex angle α in the wedge portion of the low-reflecting tree 91). Using the distance L from the pixel surface to the bottom surface passing through the apex of the pixel surface, the following expression is used.

D = L * (tanθd-in + tanθr-in)
Strictly speaking, the light traveling angle in the highly flexible resin 93 constituting the light diffusing layer 10 and the light traveling angle in the glass are different depending on the difference in the refractive index of the material. Can be approximated using only the internal traveling angle θd-in of the straight through light 90 and the internal traveling angle θr-in of the low-reflected reflected light 92. Therefore, the double image width W is expressed by the following equation.

W = L * cosθd-out * (tanθd-in + tanθr-in)
Further, the exit angle θd-out of the direct-through light 90 from the surface of the light diffusion layer 10 and the internal advance angle θr-in of the low-reflected reflected light 92 are respectively determined using the internal advance angle θd-in of the direct-through light 90. Is replaced by

θd-out = asin (n _H * sinθd-in), θr-in = θd-in-α
For this reason, the double image width W is expressed by the following equation (1).

W = L * cos {asin ( n H * sinθd-in)} * {tanθd-in + tan (θd-in-α)] ... (1)
[1-3. Double image visibility]
Here, a condition for preventing the double image from being recognized is considered. Human visual acuity can be measured as the resolution, that is, the ability to distinguish two adjacent points as separate points, and the Landolt ring is used at that time. The visual acuity is represented by the reciprocal of the minimum recognizable visual angle, and the visual acuity that can confirm the visual angle of 1 minute (1 minute is an angle of 1/60 of 1 degree) is defined as visual acuity 1.0. If the minimum viewing angle that can be confirmed is 2 minutes, the visual acuity is 0.5.

  The distance of a general visual acuity test is 5 m from the visual acuity test table, but it is a distance of 1.5 mm that can be recognized as separate points or lines in the Landolt ring corresponding to visual acuity 1.0. That is, the viewing angle from a distance of 5 mm, which is 1.5 mm, is 1 minute. For example, in the case of a visual acuity of 1.0 (1.0 minute when expressed in terms of viewing angle) based on the Landolt ring, when the observer is 50 cm away from the display surface of the liquid crystal display device 1, identification of about 150 μm is possible.

  Therefore, when the double image width W can be made smaller than 150 μm, it is possible to effectively prevent multiple images from being visually recognized. That is, in order not to recognize the double image, it is only necessary to set each parameter so that Wmax satisfies the following expression as the maximum double image width that can be generated.

Wmax <150μm
Ideally, the numerical value is 150 μm, but as a result of the subjective evaluation, the allowable value may be “Wmax <250 μm”.

[1-4. Specific example of double image]
For example, when the refractive index n _H of the highly flexible resin is 1.58, the apex angle α is 18 °, and the distance L from the bottom surface of the light diffusion layer to the pixel surface is 1000 μm, the internal propagation of the direct light 90 is obtained from the above equation (1). The relationship between the angle θd-in and the double image width W is as shown in FIG. 4A.

  Referring to FIG. 4A, when the internal traveling angle θd-in of the direct light 90 is smaller than 9 °, the direct light 90 and the low-reflected light 92 are not emitted from the light diffusion layer surface 95 at the same angle. Therefore, a double image does not occur.

  However, when the internal traveling angle θd-in of the direct light 90 is in the range of 9 ° to 39.3 °, a double image is generated, and the double image width W changes depending on the angle. In particular, a double image width W is not less than the allowable value of 250 μm at 16.8 ° to 38.2 °, so a double image is recognized, and at 30.3 °, the double image width W is maximum at 485 μm.

Note that the maximum double image width W is that θd-in satisfying dW / dθd-in = 0, where dW / dθd-in is a derivative such as Equation (1) representing the double image width W. This is the case.

  In the range where the internal traveling angle θd-in of the direct light is larger than 39.3 °, the traveling light is totally reflected by the light diffusion layer back surface 97 and is not emitted to the outside from the light diffusion layer surface 95. No image is generated.

  FIG. 4B is a graph showing the double image width W, where the horizontal axis is the exit angle θd-out (or θr-out) of the straight-through light 90 (or low-reflected reflected light 92) on the light diffusion layer surface 95. is there. In this case, a double image is visually recognized in the range of the oblique viewing angle 27.2 ° to 77.7 ° in the light diffusion direction of the light diffusion layer 10. In particular, the double image becomes most prominent near an oblique viewing angle of 52.9 °.

  In order to prevent the double image from being recognized in all directions, the maximum double image width Wmax needs to be Wmax <250 μm. For this purpose, the distance L from the bottom surface of the light diffusion layer to the pixel surface is reduced, and the double image width W is reduced as a whole (image in the direction A in FIG. 5), or parameter setting of the surface diffusion layer is performed. Therefore, it is necessary to limit the range that the internal traveling angle θd-in of direct light can take (image in the B direction in FIG. 5). Specifically, the following may be performed.

  (A) When the characteristics of the backlight are not taken into consideration, the maximum internal traveling angle θd-in, max of direct light is determined by the aperture ratio apa and the apex angle α of the light diffusion layer. Therefore, the double image width W can be reduced by optimizing the aperture ratio apa, apex angle α, and distance L of the light diffusion layer.

(B) Further, when the characteristics of the backlight are not taken into consideration, the maximum internal traveling angle θr-in, max of the low-reflected reflected light is determined by the resin refractive indexes n _H and n _L and the apex angle α of the light diffusion layer 10. The As a result, the maximum internal traveling angle θd-in, max of straight-through light under the condition that a double image is generated is also determined. Therefore, the double image width W can be reduced by optimizing the refractive indexes n _H , n _L , apex angle α, and distance L.

  (C) Further, when the maximum emission angle θbl, max of the backlight is reduced (the degree of condensing is increased), the maximum internal traveling angle θd-in, max of direct light is also reduced at the same time. Therefore, the double image width W can also be reduced by optimizing the maximum emission angle θbl, max of the backlight.

Thus, when designing a display device with improved viewing angle characteristics, a double image is obtained while changing each parameter value (L, n _H , θ _d-in , α, etc.) of the display device to be designed. An optimum display device with a reduced width W can be designed.

  As described above, in the description of the present embodiment, the example in which the cross-sectional shape of the second refracting portion is an isosceles triangle has been described, but in the present invention, the cross-sectional shape of the second refracting portion is not limited thereto. Absent. For example, other shapes may be used as long as a reflective surface is provided.

[2. Second Embodiment]
As described above, (a) when the characteristics of the backlight are not taken into consideration, the maximum internal traveling angle θd-in, max of direct light is determined by the aperture ratio apa and the apex angle α of the light diffusion layer. In the present embodiment, an example in which the double image width W is reduced by optimizing the aperture ratio apa, the apex angle α, and the distance L of the light diffusion layer will be described.

[2-1. Parameter optimization]
As shown in FIG. 6, when the characteristics of the backlight are not taken into consideration, the internal traveling angle θd-in of the direct light 90 is adjacent from the apex point 91 a (the tip of the wedge portion) of the low-fat resin 91. The maximum internal traveling angle θd-in, max of the straight light 90 is expressed by the following equation using the aperture ratio apa and the apex angle α. .

θd-in, max = atan {(1 + apa) / (1-apa) * tan (α / 2)}
here,
A = atan {(1 + apa) / (1-apa) * tan (α / 2)}
Then, a possible range of the internal traveling angle θd-in of direct light is expressed by the following equation.

0 ≦ θd-in ≦ A (2)
Further, the maximum external emission angle θd-out, max of the direct light 90 is expressed by the following equation.

θd-out, max = asin (n _H * sin A)
Therefore, the range that the external exit angle θd-out of the direct light 90 can take is as follows.

0 ≦ θd-out ≦ asin (n _H * sin A)
When the low-bend reflected light 92 is emitted outside at the same angle as the direct-through light 90 (θd-out = θr-out), a double image is generated. In this case, the internal traveling angle θr-in of the low-bend reflected light 92 is expressed by the following equation.

θr-in = θd-in-α
Here, the double image width W is expressed by the following equation.

W = L * cos {asin (n _H * sin θd-in)} * {tan θd-in + tan (θd-in−α)}
In order to prevent double images in all directions from being seen,
In the range of 0 ≦ θd-in ≦ A, it is necessary that the maximum double image width Wmax does not exceed the allowable value of 250 μm. In other words, in order to prevent the double image from being recognized,
0 ≦ θ ≦ atan {(1 + apa) / (1-apa) * tan (α / 2)}
In the range of θ, each parameter may be set so as to satisfy the following equation.

L * cos {asin (n _H * sin θ)} * {tan θ + tan (θ−α)} <250 μm
[2-2. Effect verification]

As shown in Table 1, as an example, consider a case (base) where n _H = 1.58, α = 18 °, apa = 50%, and L = 1000 μm. The range that the internal traveling angle θd-in of the direct light 90 can take is given by the above equation (2).
0 ° ≦ θd-in ≦ 25.4 °, and the double image width W in this range is as shown in FIG.

  As shown in FIG. 7, when the internal traveling angle θd-in of the direct light 90 is smaller than 9 °, the direct light 90 and the low-reflected light 92 are emitted from the light diffusion layer surface 95 at the same angle. There is no double image.

  A double image is generated in the range of 9 ° to 25.4 °, and the double image width W changes depending on the angle. In particular, the double image width W is not less than the allowable value of 250 μm at 16.8 ° to 25.4 °, so that a double image is recognized. At 25.4 °, the double image width W is 445 μm at the maximum.

The internal advancing angle θd-in of the direct light 90 cannot be in a range larger than 25.4 ° due to limitations due to the aperture ratio apa and the apex angle α. That is, in the above condition, the range in which the double amplification W is an allowable value of 250 μm or more.
16.8 ° ≦ θd-in ≦ 25.4 ° exists, and the corresponding orientation
If 27.2 ° ≦ θd-out ≦ 42.7 °, a double image is recognized.

  Consider a case where by changing only one parameter, Wmax <250 μm so that a double image is not recognized.

[2-2-1. When changing L]
As shown in FIG. 8A, when the distance L is changed small, a double image is not recognized when the value of L is 560 μm or less (for example, the base film thickness of the light diffusion layer 10 is 70 μm, the surface polarizing plate thickness is 140 μm, In the case of Table 1 (i) where the surface side glass thickness is 350 μm).

  FIG. 8B shows a change in the double amplification W when the distance L is 560 μm. In this case, a double image is generated in the range of 9 ° ≦ θd-in ≦ 25.4 °, but at θd-in = 25.4 ° where the double image width W is maximum, the double image width W is smaller than the allowable value of 250 μm. Therefore, the double image is not recognized.

[2-2-2. When changing apa]
When the aperture ratio apa is reduced, a double image is not recognized at 31% or less as shown in FIG. 8C. FIG. 8D shows a change in double amplification W when the aperture ratio apa is 31%. In this case, a double image is generated when 9 ° ≦ θd-in ≦ 16.7 °. However, even when θd-in = 16.7 ° at which the double image width W is maximum, the double image width W is smaller than the allowable value of 250 μm. Double images are not recognized.

[2-2-3. When changing α]
When the apex angle α is reduced, a double image is not recognized at 7.5 ° or less as shown in FIG. 8E. FIG. 8F shows a change in the double amplification W when the apex angle α is 7.5 °.
A double image is generated when 3.8 ° ≦ θd-in ≦ 11.1 °, but even when θd-in = 11.1 ° at which the double image width W is maximum, the double image is smaller than the allowable value of 250 μm. Not recognized.

[2-2-4. Summary]
The above is a specific example, and each parameter may be set so that Wmax <250 μm. Further, considering the case where the maximum double image width Wmax <250 μm and the double image is not recognized by changing a plurality of parameters simultaneously, the results are as shown in Tables 1 (iv) to (vii). In actual design, it may be difficult to change the parameter value by one, or even if the parameter value can be changed, the optical characteristics may be changed greatly. It is preferable to change at the same time in a balanced manner.

[3. Third Embodiment]
As described above, (b) when the characteristics of the backlight are not taken into consideration, the maximum internal traveling angle θr-in, max of the low-reflected reflected light 92 is the resin refractive index n _H , n _L and apex angle α of the light diffusion layer 10. Determined by As a result, the maximum internal traveling angle θd-in, max of the direct light 90 under the condition that a double image is generated is also determined. In the present embodiment, an example in which the double image width W is reduced by optimizing the refractive indexes n _H , n _L , the apex angle α, and the distance L will be described.

[3-1. Parameter optimization]
Consider a case where the internal advancing angle θr-in of low-bend reflected light is reduced to reduce double images. As shown in FIG. 9, when the characteristics of the backlight are not taken into account, the internal advancing angle θr-in of the low bending reflection light is the total reflection critical angle between the low bending resin 91 and the high bending resin 93 and The maximum internal traveling angle θr-in, max of the low-reflected reflected light 92 is maximum under the incident condition, and a double image is generated when the resin refractive index nH and nL θr-in = θd-in-α. The maximum internal traveling angle θd-in, max of straight-through light under the condition where multiple images are generated is expressed by the following equation.

θd-in, max = 90−asin (n _L / n _H ) + α / 2
here,
B = 90−asin (n _L / n _H ) + α / 2
Then, a possible range of the internal traveling angle θd-in of the direct light is expressed by the following equation. 0 ≦ θd-in ≦ B (3) Further, the maximum external emission angle θd-out, max of direct light is expressed by the following equation.

θd-out, max = asin (n _H * sin B)
The range that the external exit angle θd-out of the direct light 90 can take is expressed by the following equation.

0 ≦ θd-out ≦ asin (n _H * sinB)
When low-bend reflected light is emitted outside at the same angle as the direct-through light 90 (θd-out = θr-out), a double image is generated. In this case, since the internal traveling angle θr-in of the low-reflected reflected light is θr-in = θd-in-α, the double image width W is expressed by the following equation.

W = L * cos {asin (n _H * sin θd-in)} * {tan θd-in + tan (θd-in−α)}
In order to avoid recognizing double images in all directions,
It is necessary to prevent the maximum double image width Wmax in the range of 0 ≦ θd-in ≦ A from exceeding the allowable value of 250 μm. In other words, in order not to recognize the double image,
In the range of 0 ≦ θ ≦ 90−asin (n _L / n _H ) + α / 2,
L * cos {asin (n _H * sinθ)} * {tan θ + tan (θ−α)} <250 μm
Each parameter may be set so that

  [3-2. Effect verification]

As shown in Table 2, as an example, consider a case (base) where n _H = 1.55, n _L = 1.49, α = 22 °, and L = 1000 μm. The possible range of the internal traveling angle θd-in of the direct light 90 is given by the above equation (3).
0 ° ≦ θd-in ≦ 26.9 °, and the double image width W in this range is as shown in FIG.

  As shown in FIG. 10, when the internal traveling angle θd-in of the direct light 90 is smaller than 11 °, the direct light 90 and the low-reflected light 92 are emitted from the light diffusion layer surface 95 at the same angle. There is no double image.

Further, a double image is generated in the range of 11 ° to 26.9 °, and the double image width W changes depending on the angle. In particular, from 18.9 ° to 26.9 °, the double image width W is an allowable value of 250 μm or more, so a double image is recognized, and at 26.9 °, the double image width W is 423 μm at the maximum. The internal advancing angle θd-in of the direct light cannot be in a range larger than 26.9 ° due to restrictions by the resin refractive indexes n _H and n _L and the apex angle α. That is, in the above conditions, the range in which the double image width W is an allowable value of 250 μm or more.
18.9 ° ≦ θd-in ≦ 26.9 ° exists and the corresponding orientation
When 30.1 ° ≦ θd-out ≦ 44.5 °, a double image is recognized.

  Consider a case in which only one parameter is changed so that Wmax <250 μm and a double image is not recognized.

[3-2-1. When changing L]
As shown in FIG. 11A, when the distance L is changed small, a double image is not recognized when the value of L is 590 μm or less (for example, the base film thickness of the light diffusion layer 10 is 80 μm, the surface polarizing plate thickness is 150 μm, Table 2 (i) where the surface side glass thickness is 360 μm).

  FIG. 11B shows a change in the double image width W when the distance L is 590 μm. In this case, a double image is generated at 11 ° ≦ θd-in ≦ 26.9 °, but even when θd-in = 26.9 ° at which the double image width W is maximum, the double image width W is smaller than the allowable value of 250 μm. Double images are not recognized.

[3-2-2. If you want to change the n _H]
When the refractive index n _H of the highly flexible resin is reduced, a double image is not recognized at 1.504 or less as shown in FIG. 11C. FIG. 11D shows the change in the double image width W when the refractive index n _H of the highly flexible resin is 1.504. In this case, a double image is generated when 11 ° ≦ θd-in ≦ 18.8 °. However, even when θd-in = 18.8 ° at which the double image width W is maximum, the double image width W is smaller than the allowable value of 250 μm. Double images are not recognized.

[3-2-3. When changing α]
When the apex angle α is reduced, a double image is not recognized at 44 ° or more as shown in FIG. 11E. FIG. 11F shows a change in the double image width W when the apex angle α is 44 °.

in this case,
A double image is generated at 22.0 ° ≦ θd-in ≦ 38.0 °, but the double image width W is smaller than the allowable value of 250 μm even at θd-in = 34.4 ° where the double image width W is maximum. Is not recognized.

[3-2-4. Summary]
The above is a specific example, and each parameter may be set so that Wmax <250 μm. Considering the case where the maximum double image width Wmax <250 μm is set so that the double image is not recognized by simultaneously changing a plurality of parameters, the results are as shown in Tables 2 (iv) to (vii). In actual design, it may be difficult to change the parameter value by one, or even if the parameter value can be changed, the optical characteristics may be changed greatly. It is preferable to change at the same time in a balanced manner.

[4. Fourth Embodiment]
As described above, when the maximum emission angle θbl, max of the backlight is reduced (the degree of light collection is increased), the maximum internal traveling angle θd-in, max of direct light is also reduced at the same time. Therefore, the double image width W can also be reduced by optimizing the maximum emission angle θbl, max of the backlight. In the present embodiment, an example will be described in which the internal advancing angle θd-in of straight-through light is reduced by adjusting the condensing degree of the backlight, thereby reducing the double image at an oblique viewing angle.

[4-1. Parameter optimization]
As shown in FIG. 12, when the characteristics of the light diffusion layer 10 are not taken into consideration, if the maximum emission angle of the backlight is θbl, max, the internal traveling angle θd-in of the direct light 90 is the maximum emission angle of the backlight. The maximum internal traveling angle θd-in, max of direct light is expressed by the following equation using the maximum emission angle θbl, max of the backlight and the refractive index n _H of the highly flexible resin 93.

θd-in, max = asin (sin θbl, max / n _H )
here,
Assuming that C = asin (sin θbl, max / n _H ), a possible range of the internal traveling angle θd-in of the direct light 90 is expressed by the following equation.

0 ≦ θd-in ≦ C (4)
Further, the maximum external emission angle θd-out, max of the direct light 90 is expressed by the following equation.

θd-out, max = asin (n _H * sin C)
The range that the external exit angle θd-out of direct light can take is expressed by the following equation.
0 ≦ θd-out ≦ asin (n _H * sinC)
When the low-bend reflected light 92 is emitted outside at the same angle as the direct-through light 90 (θd−out = θr−out), a double image is generated.

In this case, the internal advancing angle θr-in of the low bending reflection light 92 is
Since θr-in = θd-in-α, the double image width W is expressed by the following equation.

W = L * cos {asin (n _H * sin θd-in)} * {tan θd-in + tan (θd-in−α)}
In order to prevent double images in all directions from being seen,
In the range of 0 ≦ θd-in ≦ C, it is necessary that the maximum double image width Wmax does not exceed the allowable value of 250 μm. In other words, in order to prevent the double image from being recognized, each parameter may be set so as to satisfy the following expression in the range of 0 ≦ θ ≦ asin (sin θbl, max / n _H ).

L * cos {asin (n _H * sin θ)} * {tan θ + tan (θ−α)} <250 μm
[4-2. Effect verification]
As an example, consider a case where n _H = 1.58, α = 18 °, L = 800 μm, θbl, max = 60 °. The possible range of the internal traveling angle θd-in of the direct light 90 is given by the above equation (4).
0 ° ≦ θd-in ≦ 33.2 °, and the double image width W in this range is as shown in FIG.

  As shown in FIG. 13, when the internal traveling angle θd-in of the direct light 90 is smaller than 9 °, the direct light 90 and the low-reflected light 92 are emitted from the light diffusion layer surface 95 at the same angle. Because there is no double image.

A double image is generated in the range of 9 ° to 33.4 °, and the double image width W changes depending on the angle. In particular, the double image width W is not less than the allowable value of 250 μm at 19.0 ° to 33.4 °, so that a double image is recognized. At 30.3 °, the double image width W is maximum at 388 μm. The internal traveling angle θd-in of the direct light 90 is limited by the resin refractive index n _H and the maximum emission angle θbl, max of the backlight, and cannot be in a range larger than 33.4 °. In other words, under the above conditions, the double amplification W is within the allowable range of 250 μm or more.
19.0 ° ≦ θd-in ≦ 33.4 ° exists, and the corresponding orientation
When 31.0 ° ≦ θd-out ≦ 60.0 °, a double image is recognized.

  Consider a case in which Wmax <250 μm and the double image is not recognized by changing the maximum emission angle θbl, max of the backlight.

  When the maximum emission angle θbl, max of the backlight is reduced, a double image is not recognized at 31.0 ° or less as shown in FIG. 14A.

  FIG. 14B shows a change in the double amplification W when the maximum emission angle θbl, max of the backlight is 31.0 °. In this case, a double image is generated at 9.0 ° ≦ θd-in ≦ 19.0 °, but the double image width W is smaller than the allowable value of 250 μm even at θd-in = 19.0 ° at which the double image width W is maximum. Double images are not recognized. FIG. 15 shows an example of emission characteristics of a backlight having a maximum emission angle θbl, max of 31.0 °. Such emission characteristics of the backlight can be obtained by providing the backlight itself with a condensing function, using an optical sheet, or combining them.

  The above is a specific example, and each parameter may be set so that Wmax <250 μm. It is also possible to prevent a double image from being recognized by simultaneously changing a plurality of parameters so that the maximum double image width Wmax <250 μm. In actual design, it may be difficult to change the parameter value by one, or even if the parameter value can be changed, the optical characteristics may be changed greatly. It is preferable to change at the same time in a balanced manner.

  The present invention is useful for a display device including a light diffusion layer and a design method thereof.

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 10 Light-diffusion layer 11 Front polarizing plate 12 Liquid crystal panel 13 Back polarizing plate 14 Backlight

Claims (9)

A method for designing a display device including a light diffusion layer,
The display device includes a backlight, a pixel surface having a plurality of pixels that emit light from the backlight toward the light diffusion layer, and the pixel surface and the transparent member. A light diffusion layer, at least,
The light diffusing layer has a first refracting portion and a wedge-shaped second refracting portion having an apex angle in a cross section of the light diffusing layer,
The distance between the bottom surface passing through the vertex of the apex angle in the second refracting portion of the light diffusion layer and the pixel surface is L,
The refractive index of the first refractive part constituting the light diffusion layer is n _H ,
Θ _d-in is the internal advancing angle of the image light emitted from the pixel surface with respect to the normal at the bottom surface of the light diffusion layer.
When the apex angle in the second refracting portion is α,
The width W of the double image generated when two image lights are emitted in the same direction from the surface of the light diffusion layer is defined by the following equation:
W = L * cos {asin (n _H * sinθ _d-in )} * {tan θ _d-in + tan (θ _d-in −α)}
A method for designing a display device, wherein the values of L, n _H , θ _d-in, and α are determined using the above formula. The display device design method according to claim 1, wherein the values of L, n _H , θ _d-in, and α are determined so that a value of the width W of the double image is 250 μm or less. When the aperture ratio of the first refractive part relative to the second refractive part on the surface of the light diffusion layer is apa,
The method of designing a display device according to claim 1, wherein the θ _d-in is determined within the following range.
0 ≦ θ _d-in ≦ atan {(1 + apa) / (1-apa) * tan (α / 2)} The method of designing a display device according to claim 1, wherein the θ _d-in is determined within the following range.
0 ≦ θ _d-in ≦ 90−asin (n _L / n _H ) + α / 2 When the maximum emission angle of light from the backlight is θbl, max,
The method of designing a display device according to claim 1, wherein the θ _d-in is determined within the following range.
0 ≦ θ _d-in ≦ asin (sin θbl, max / n _H ) A display device comprising a light diffusion layer,
The display device includes a backlight, a pixel surface having a plurality of pixels that emit light from the backlight toward the light diffusion layer, and the pixel surface and the transparent member. A light diffusion layer, at least,
The light diffusing layer has a first refracting portion and a wedge-shaped second refracting portion having an apex angle in a cross section of the light diffusing layer,
The distance between the bottom surface passing through the vertex of the apex angle in the second refracting portion of the light diffusion layer and the pixel surface is L,
The refractive index of the first refractive part constituting the light diffusion layer is n _H ,
Θ _d-in is an internal advancing angle of image light emitted from the pixel surface with respect to a normal line on the bottom surface of the light diffusion layer,
When the apex angle in the second refracting portion is α,
A display device, wherein a width W of a double image generated when two image lights are emitted in the same direction from the surface of the light diffusion layer satisfies the following expression.
W = L * cos {asin (n _H * sinθ _d-in )} * {tan θ _d-in + tan (θ _d-in −α)} <250 μm When the aperture ratio of the first refractive part relative to the second refractive part on the surface of the light diffusion layer is apa,
The display device according to claim 5, wherein the θ _d-in is determined within the following range.
0 ≦ θ _d-in ≦ atan {(1 + apa) / (1-apa) * tan (α / 2)} The display device according to claim 5, wherein the θ _d-in is determined within the following range.
0 ≦ θ _d-in ≦ 90−asin (n _L / n _H ) + α / 2 When the maximum emission angle of light from the backlight is θbl, max,
The display device according to claim 5, wherein the θ _d-in is determined within the following range.
0 ≦ θ _d-in ≦ asin (sin θbl, max / n _H )

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