Patent ID: 12197075

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, the present invention will be described in detail by an embodiment.

First Embodiment

FIG.1is a plan view of a liquid crystal display device. The liquid crystal display device includes a liquid crystal display panel and a backlight, and inFIG.1, the liquid crystal display panel is seen. InFIG.1, in the liquid crystal display panel, a TFT substrate100formed with a pixel electrode, a video signal line, a scan line, a TFT (Thin Film Transistor) and the like, and an opposing substrate200formed with a black matrix, a color filter and the like are bonded via a seal material150in its periphery, and a liquid crystal is sealed in its interior.

InFIG.1, a display region is formed in the portion in which the opposing substrate200and the TFT substrate100are overlapped. In the display region, scan lines101extend in the horizontal direction, and are arrayed in the vertical direction. In addition, video signal lines102extend in the vertical direction, and are arrayed in the horizontal direction. Pixels103are formed in the regions surrounded by the scan lines101and the video signal lines102. The pixels103are formed in the display region in a matrix.

The TFT substrate100is formed to be larger than the opposing substrate200, and the portion in which the TFT substrate100is not overlapped with the opposing substrate200is a terminal region. A driver IC160that connects the video signal lines102and the scan lines101is disposed in the terminal region. To supply a signal and a power supply from the outside, a flexible wiring substrate is connected to the terminal region, which is omitted inFIG.1.

FIG.2is a cross-sectional view taken along line A-A ofFIG.1, and is a cross-sectional view of the liquid crystal display device. InFIG.2, the backlight is disposed on the back surface of a liquid crystal display panel300including the TFT substrate100and the opposing substrate200. The backlight is of a direct under type, and a plurality of LEDs20are used as light sources. InFIG.2, a housing that accommodates the entire liquid crystal display device is omitted.

The backlight includes a reflection sheet10, the plurality of LEDs20configuring the light sources, a diffusion plate30, a diffusion sheet40, a prism sheet50, and a diffusion sheet60in that order from the lower side. Note that the structure of the backlight illustrated inFIG.2is an example, any one of the optical components may also be omitted, and a different optical sheet may also be added.

InFIG.2, the reflection sheet10reflects a light that goes downward from the LED20, to the direction of the liquid crystal display panel300. Since the LED20is a point light source, the diffusion plate30is used in order to prevent the individual point light sources from being visibly recognized on the screen. Since the diffusion plate30has a role of placing thereon other optical components, the diffusion plate30is formed to be thick and to be, for example, approximately 1.5 mm. To prevent the warp of the diffusion plate30, a spacer may also be disposed between the diffusion plate30and the reflection sheet10. It should be noted that although inFIG.2, the diffusion plate30is used as an example, the diffusion plate30is not necessarily required to be a plate, and may be replaced by a diffusion sheet. In this case, its thickness may be reduced.

InFIG.2, the diffusion sheet40is disposed on the diffusion plate30, and further diffuses the light that has not been able to be completely diffused by the diffusion plate30. To control the light that attempts to be spread in the horizontal direction, the prism sheet50is disposed on the diffusion sheet40. The prism sheet50ofFIG.2is a so-called reverse prism sheet in which a prism array is formed on its lower surface. As described later, the prism sheet50is made to have a special structure, so that the present invention obtains the necessary light distribution characteristic of the backlight. InFIG.2, on the prism sheet50, the diffusion sheet60is disposed. This is for reducing moiré due to the interference between the components on the backlight side and the video signal lines102, the scan lines101, the black matrix, and the like that are formed on the liquid crystal display panel.

FIG.3is a perspective view of the front half portion of an automobile, seen from above. InFIG.3, a light560is disposed in front of a hood, a windshield510is formed obliquely upward from the hood, and a roof is present thereon. A dashboard550is present inside the windshield510, and a liquid crystal display device600is disposed on the dashboard550. InFIG.3, a sideview mirror530is mounted on a door, and a driver700visibly recognizes the sideview mirror530through a door glass520.

However, when as indicated by the arrow ofFIG.3, the outgoing light from the liquid crystal display device600is projected onto and reflected on the door glass520and goes toward the driver700, the driver700can see the screen of the display device but cannot see the sideview mirror530, which is dangerous. The present invention solves such the problem.

FIGS.4A and4Billustrate a distributed light distribution when a typical reverse prism sheet is used.FIG.4Ais a cross-sectional view of the reverse prism sheet.FIG.4Bis a graph illustrating the distributed light distribution of the backlight when the reverse prism sheet ofFIG.4Ais used. InFIG.4B, the horizontal axis indicates the zenith angle (degrees) θ, and the vertical axis indicates the luminance normalized with a maximum value as 1. The luminance distribution ofFIG.4Bis a substantially normal distribution. InFIG.4B, the range indicated by two straight dotted arrows is an FWHM (Full Width Half Maximum).

However, with the distributed light distribution as illustrated inFIG.4B, for example, the distributed light on the right side goes toward the door glass, is reflected on the door glass, and goes to the driver, thereby inhibiting the driver from seeing the sideview mirror. Accordingly, in the present invention, for example, the distributed light distribution on the right side is reduced, and as a result, for example, the distributed light distribution as illustrated inFIG.5is provided.

InFIG.5, the horizontal axis indicates the zenith angle, and the vertical axis indicates the brightness. InFIG.5, the distribution on the right side to the door glass side is narrow, and the distribution on the left side to the driver side is wide. Therefore, the light that goes from the display device toward the door glass side is reduced, and the reflection light that is reflected on the door glass to go toward the driver is also reduced. Therefore, the driver is not inhibited from seeing the sideview mirror.

FIGS.6A,7A, and8Aare cross-sectional views explaining the prism sheet structures according to the present invention that enable the backlight having the distributed light distribution as illustrated inFIG.5.FIG.6Ais a cross-sectional view of the typical reverse prism sheet. As illustrated inFIG.6A, the light that is indicated by the arrow and is incident with an angle with respect to the normal line direction of the reverse prism sheet is refracted by the reverse prism sheet, and exits to the normal line direction.

FIG.6Bis a graph illustrating an example of the distributed light distribution corresponding to this. InFIG.6B, the horizontal axis indicates the zenith angle (degrees), the vertical axis indicates the normalized brightness with the maximum value of the brightness as 100, and the unit is a. u. (arbitrary unit). As illustrated inFIG.6B, the distributed light distribution of the light by the reverse prism sheet is a substantially normal distribution.

FIG.7Ais a cross-sectional view illustrating a state where an anisotropic prism array is formed on the upper side surface of the prism sheet. As illustrated inFIG.7A, the light that is indicated by the arrow and is incident along the normal line direction of the prism sheet is refracted to the left direction by the anisotropic prism sheet.

FIG.7Bis a graph illustrating an example of a distributed light distribution corresponding to the prism sheet ofFIG.7A. InFIG.7B, the peak of the distributed light distribution is not present in the portion in which the zenith angle on the horizontal axis is zero, but is present, for example, at around 25 degrees. That is, the light that is incident to the normal line direction of the prism sheet is refracted by approximately 25 degrees by the anisotropic prism sheet, and exits from the prism sheet.

FIGS.8A and8Bare a cross-sectional view of the prism sheet according to the present invention having both of the characteristic ofFIG.6Aand the characteristic ofFIG.7Aand a graph illustrating its function.FIG.8Ais a cross-sectional view of the prism sheet of the present invention. InFIG.8A, the same reverse prism array asFIG.6Ais formed on the lower side of the prism sheet. On the other hand, the anisotropic prism array as illustrated inFIG.7Ais formed on the upper surface of the prism sheet ofFIG.8A. However, inFIG.8A, the anisotropic prism array ofFIG.7Ais not formed as-is.

As illustrated inFIG.8A, the anisotropic prism array is formed in, for example, one half region on the upper side of the prism sheet, and the other half region is flat. Therefore, half of the lights exiting from the prism sheet ofFIG.8Aand receiving the function of the prism array ofFIG.6Aexit, and the other half receiving the functions of the prism array ofFIG.6Aand the prism array ofFIG.7Aexit.

FIG.8Bis a graph illustrating the distributed light distribution of the light corresponding to the prism sheet ofFIG.8A. InFIG.8B, the horizontal axis indicates the zenith angle, the vertical axis indicates the brightness, and on the vertical axis, the maximum value is 50 in order thatFIG.8Bcan be compared withFIGS.6B and7B. InFIG.8B, the distributed light distribution as the entire prism sheet is as indicated by the solid line. This distributed light distribution has a form that combines the distributed light distribution that is indicated by the dotted line A and receives the influence of only the reverse prism array and the distributed light distribution that is indicated by the dotted line B and receives the influence of both of the reverse prism array and the anisotropic prism array.

It should be noted that since the area in which the anisotropic prism array is formed corresponds to the half of the area in which the reverse prism array is formed, the dotted line A and the dotted line B have the same peak. By the way, inFIG.8A, the area in which the anisotropic prism array is formed is half the area in which the reverse prism array is formed, but the term “half” is an example, and how much of the area is appropriate will be described later.

FIGS.9and10A to13Care drawings explaining the structures and functions of the prism sheet according to the present invention.FIG.9is a cross-sectional view of the prism sheet for defining the parameters illustrated inFIGS.10A to13C. InFIG.9, the pitch of the reverse prism array in which the apex angle θ3is, for example, 63 degrees is L1. It should be noted that the L1may be restated as the length of the base of the reverse prism. The length of the base of the anisotropic prism array that is formed on the surface on the upper side of the prism sheet is L2, and the pitch of the anisotropic prism array is the L1that is the same as the pitch of the reverse prism array. The first base angle of the anisotropic prism is θ1(hereinafter, simply referred to as a first angle), and the second base angle is θ2(hereinafter, simply referred to as a second angle). InFIGS.10A to13C, the characteristic of the prism sheet according to the present invention is evaluated by using the first angle θ1, the second angle θ2, and the L2/L1of the anisotropic prism as the parameters.

FIGS.10A to10Eare graphs illustrating luminance distributions when the first angle θ1of the anisotropic prism is fixed to 70 degrees, the L2/L1of the anisotropic prism is fixed to 0.5, and the second angle θ2of the anisotropic prism is changed from 10 degrees to 50 degrees. InFIG.10A, the horizontal axis indicates the zenith angle (degrees), and the vertical axis indicates the luminance (a.u. (arbitrary unit)). InFIG.10A, the solid line indicates the distributed light distribution of the light exiting from the anisotropic prism array, and the dotted line indicates the distributed light distribution of the light passing through only the reverse prism. Then, the alternate long and short dash line indicates the distributed light distribution of the entire prism sheet. It should be noted that the straight dotted arrows inFIG.10Aindicate the FWHM, which becomes the reference of the magnitude of the dispersion of the outgoing light of the entire prism sheet. The description of the drawings described above is the same up toFIG.13C.

InFIG.10A, in the light exiting from the anisotropic prism array, the peak is shifted to the minus side in the zenith angle, that is, shifted to the left side of the drawing. Therefore, also in the synthetic light distribution indicated by the alternate long and short dash line, the peak is shifted to the left side. In addition, the FWHM is also shifted to the minus side in the zenith angle. However, the peak of brightness that is caused in the normal line direction of the prism sheet is reduced to be 94%.

FIG.10Billustrates the luminance distribution when the first angle θ1of the anisotropic prism is fixed to 70 degrees, the L2/L1of the anisotropic prism is fixed to 0.5, and the second angle θ2of the anisotropic prism is 20 degrees. InFIG.10B, the effect of the anisotropic prism is greater than the case ofFIG.10A, and therefore, the luminance distribution by the anisotropic prism indicated by the solid line is further shifted to the minus side in the zenith angle.

As a result, the entire brightness distribution indicated by the alternate long and short dash line is also shifted to the minus side in the zenith angle. The FWHM is also shifted to the left side, and is from 10 degrees to −20 degrees. The peak of the brightness is reduced to be 0.86.

FIG.10Cillustrates the luminance distribution when the first angle θ1of the anisotropic prism is fixed to 70 degrees, the L2/L1of the anisotropic prism is fixed to 0.5, and the second angle θ2of the anisotropic prism is 30 degrees. InFIG.10C, the effect of the anisotropic prism is further greater than the case ofFIG.10B, and therefore, the luminance distribution by the anisotropic prism indicated by the solid line is further shifted to the minus side in the zenith angle.

As a result, the entire luminance distribution indicated by the alternate long and short dash line is also shifted to the minus side in the zenith angle. The FWHM is also shifted to the left side, and is from 10 degrees to −25 degrees. The peak of the brightness is reduced to be 0.72.

FIG.10Dillustrates the luminance distribution of the anisotropic prism when the first angle θ1of the anisotropic prism is fixed to 70 degrees, the L2/L1of the anisotropic prism is fixed to 0.5, and the second angle θ2of the anisotropic prism is 40 degrees. InFIG.10D, the effect of the anisotropic prism is further greater than the case ofFIG.10C, and therefore, the luminance distribution by the anisotropic prism indicated by the solid line is further shifted to the minus side in the zenith angle.

InFIG.10D, in the luminance distribution by the anisotropic prism indicated by the solid line, the first peak is present at around −20 degrees in the zenith angle, and further, the second peak is present at around 60 degrees. This represents that the light incident onto the anisotropic prism array is totally reflected without being partly refracted on the prism surface. The totally reflected light is not to be controlled, which is not preferable. The FWHM inFIG.10Dis from 11 degrees to −24 degrees, and the peak of brightness is 0.62.

FIG.10Eillustrates the luminance distribution when the first angle θ1of the anisotropic prism is fixed to 70 degrees, the L2/L1of the anisotropic prism is fixed to 0.5, and the second angle θ2of the anisotropic prism is 50 degrees. InFIG.10E, in the luminance distribution by the anisotropic prism indicated by the solid line, the large peak is present in the portion exceeding-80 degrees. This represents that a further larger amount of the light incident onto the anisotropic prism array is totally reflected without being refracted on the prism surface. The totally reflected light is not to be controlled, which is not preferable. The FWHM inFIG.10Eis from 12 degrees to −15 degrees, and the peak of brightness is 0.61. However, since the totally reflected light is present, the use ofFIGS.10D and10Ecannot be simply compared with the use ofFIGS.10A to10C.

When the above results are compared, when the first angle θ1of the anisotropic prism is fixed to 70 degrees and the L2/L1of the anisotropic prism is fixed to 0.5, it is possible to evaluate that the second angle θ2of the anisotropic prism is suitably 20 to 30 degrees.

FIGS.11A to11Care graphs illustrating luminance distributions when the first angle θ1of the anisotropic prism is fixed to 70 degrees, the second angle θ2of the anisotropic prism is fixed to 30 degrees, and the L2/L1of the anisotropic prism is changed from 0.5 to 0.7. The horizontal axis, the vertical axis, and the like of each of the graphs are as described inFIG.10A.

FIG.11Aillustrates the case where the L2/L1is 0.5. InFIG.11A, in the light exiting from the anisotropic prism array indicated by the solid line, the peak is shifted to the minus side in the zenith angle, that is, to the left side of the drawing. Therefore, also in the synthetic light distribution indicated by the alternate long and short dash line, the peak is shifted to the left side. In addition, the FWHM is also shifted to the minus side in the zenith angle, and is 10 degrees to −25 degrees in the zenith angle. The peak of the synthetic brightness indicated by the alternate long and short dash line is 0.72.

FIG.11Billustrates the case where the L2/L1is 0.6. InFIG.11B, in the light exiting from the anisotropic prism array indicated by the solid line, the peak is shifted to the minus side in the zenith angle, that is, to the left side of the drawing. Therefore, also in the synthetic light distribution indicated by the alternate long and short dash line, the peak is shifted to the left side. In addition, the FWHM is also shifted to the minus side in the zenith angle, and is 11 degrees to −28 degrees in the zenith angle. The peak of the synthetic brightness indicated by the alternate long and short dash line is 0.70.

FIG.11Cillustrates the case where the L2/L1is 0.7. InFIG.11C, in the light exiting from the anisotropic prism array indicated by the solid line, the peak is shifted to the minus side in the zenith angle, that is, to the left side of the drawing. Therefore, also in the synthetic light distribution indicated by the alternate long and short dash line, the peak is shifted to the left side. In addition, the FWHM is also shifted to the minus side in the zenith angle, and is 11 degrees to −30 degrees in the zenith angle. The peak of the synthetic brightness indicated by the alternate long and short dash line is 0.60.

As illustrated inFIGS.11A to11C, when the first angle θ1of the anisotropic prism is fixed to 70 degrees, the second angle θ2of the anisotropic prism is fixed to 30 degrees, and the L2/L1of the anisotropic prism is changed from 0.5 to 0.7, the characteristic of the prism sheet causes no significant change. Therefore, the L2/L1should be set so as to correspond to the designing specifications.

FIGS.12A to12Care graphs illustrating brightness distributions when the second angle θ2of the anisotropic prism is fixed to 20 degrees, the L2/L1of the anisotropic prism is fixed to 0.5, and the first angle θ1of the anisotropic prism is changed from 70 degrees to 90 degrees. The horizontal axis, the vertical axis, and the like of each of the graphs are as described inFIG.10A.

FIG.12Aillustrates the case where the first angle θ1is 70 degrees. InFIG.12A, in the light exiting from the anisotropic prism array indicated by the solid line, the peak is shifted to the minus side in the zenith angle, that is, to the left side of the drawing. Therefore, also in the synthetic light distribution indicated by the alternate long and short dash line, the peak is shifted to the left side. In addition, the FWHM is also shifted to the minus side in the zenith angle, and is 10 degrees to −20 degrees in the zenith angle. The peak of the synthetic brightness indicated by the alternate long and short dash line is 0.86.

FIG.12Billustrates the case where the first angle θ1is 80 degrees. InFIG.12B, in the light exiting from the anisotropic prism array indicated by the solid line, the peak is shifted to the minus side in the zenith angle, that is, to the left side of the drawing. Therefore, also in the synthetic light distribution indicated by the alternate long and short dash line, the peak is shifted to the left side. In addition, the FWHM is also shifted to the minus side in the zenith angle, and is 10 degrees to −20 degrees in the zenith angle. The peak of the synthetic brightness indicated by the alternate long and short dash line is 0.88.

FIG.12Cillustrates the case where the first angle θ1is 90 degrees. InFIG.12C, in the light exiting from the anisotropic prism array indicated by the solid line, the peak is shifted to the minus side in the zenith angle, that is, to the left side of the drawing. Therefore, also in the synthetic light distribution indicated by the alternate long and short dash line, the peak is shifted to the left side. In addition, the FWHM is also shifted to the minus side in the zenith angle, and is 10 degrees to −20 degrees in the zenith angle. The peak of the synthetic brightness indicated by the alternate long and short dash line is 0.91.

WhenFIGS.12A and12Care compared with one another, the FWHM is almost the same, but the peak value of the synthetic brightness is further larger when the first angle θ1is 80 degrees and 90 degrees. Therefore, when the second angle θ2of the anisotropic prism is fixed to 20 degrees and the L2/L1of the anisotropic prism is fixed to 0.5, when other conditions are allowed, the first angle θ1of the anisotropic prism is preferably set to 80 degrees to 90 degrees.

FIGS.13A to13Care graphs illustrating luminance distributions when the second angle θ2of the anisotropic prism is fixed to 30 degrees, the L2/L1of the anisotropic prism is fixed to 0.5, and the first angle θ1of the anisotropic prism is changed from 70 degrees to 90 degrees. The horizontal axis, the vertical axis, and the like of each of the graphs are as described inFIG.10A.

FIG.13Aillustrates the case where the first angle θ1is 70 degrees. InFIG.13A, in the light exiting from the anisotropic prism array indicated by the solid line, the peak is shifted to the minus side in the zenith angle, that is, to the left side of the drawing. Therefore, also in the synthetic light distribution indicated by the alternate long and short dash line, the peak is shifted to the left side. In addition, the FWHM is also shifted to the minus side in the zenith angle, and is 10 degrees to −25 degrees in the zenith angle. The peak of the synthetic brightness indicated by the alternate long and short dash line is 0.72.

FIG.13Billustrates the case where the first angle θ1is 80 degrees. InFIG.13B, in the light exiting from the anisotropic prism array indicated by the solid line, the peak is shifted to the minus side in the zenith angle, that is, to the left side of the drawing. Therefore, also in the synthetic light distribution indicated by the alternate long and short dash line, the peak is shifted to the left side. In addition, the FWHM is also shifted to the minus side in the zenith angle, and is 11 degrees to −25 degrees in the zenith angle. The peak of the synthetic brightness indicated by the alternate long and short dash line is 0.76.

FIG.13Cillustrates the case where the first angle θ1is 90 degrees. InFIG.13C, in the light exiting from the anisotropic prism array indicated by the solid line, the peak is shifted to the minus side in the zenith angle, that is, to the left side of the drawing. Therefore, also in the synthetic light distribution indicated by the alternate long and short dash line, the peak is shifted to the left side. In addition, the FWHM is also shifted to the minus side in the zenith angle, and is 11 degrees to −25 degrees in the zenith angle. The peak of the synthetic brightness indicated by the alternate long and short dash line is 0.79.

WhenFIGS.13A and13Care compared with one another, the FWHM is almost the same, but the peak value of the synthetic brightness is further larger when the first angle θ1is 80 degrees and 90 degrees. Therefore, when the second angle θ2of the anisotropic prism is fixed to 30 degrees and the L2/L1of the anisotropic prism is fixed to 0.5, when other conditions are allowed, the first angle θ1of the anisotropic prism is preferably set to 80 degrees to 90 degrees.

FIGS.14A and14Billustrate the preferable range of the shape of the prism sheet, in particular, the anisotropic prism, from the results illustrated inFIGS.10A to13C. InFIG.14A, the table describes the preferable range of the first angle θ1, the second angle θ2, and the L2/L1. That is, in the preferable range, the first angle θ1of the anisotropic prism is 80 degrees to 90 degrees, the second angle of the anisotropic prism is 20 degrees to 30 degrees, and the L2/L1of the anisotropic prism is 0.5 to 0.7.

Each of the parameters is as described inFIG.9, and is also described in the cross-sectional view ofFIG.14B. In this drawing, the L1can be referred to as the length of the base of the reverse prism, and the L2can be referred to as the length of the base of the anisotropic prism.

FIG.15is a cross-sectional view illustrating an example of the prism sheet when the anisotropic prism array as illustrated inFIGS.14A and14Bis used. The unit of the numerical value ofFIG.15is μm. InFIG.15, the pitch of the reverse prism array is 50 μm, and the apex angle of the reverse prism is 63 degrees. On the other hand, the length of the base of the anisotropic prism formed on the surface on the upper side is 25 μm, the first angle of the anisotropic prism is 80 degrees, and the second angle of the anisotropic prism is 30 degrees. The height of the anisotropic prism is 13 μm, and this is a value determined by the first angle θ1, the second angle θ2, and the length L2of the base. The thickness of the entire prism sheet also including the prism is 179 μm, and the thickness of the substrate portion except for the prism portion is 125 μm.

As described above, when the liquid crystal display device using the backlight having the prism sheet as described inFIGS.9to15is used, the light from the display device can be set so as to be directed to the necessary direction and not to be directed to the direction in which the light is not desired to be distributed.