JP2008281749A - Liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance luminance of a liquid crystal display without increasing power consumption by specifying a positional relation between a prism sheet and a polarizing plate in the liquid crystal display. <P>SOLUTION: In the liquid crystal display in which a light condensing prism sheet including one or two or more prism sheets whose prism axes are orthogonal to each other is disposed between a backlight and the polarizing plate on the backlight side of the liquid crystal display, the light condensing prism sheet adjacent to the polarizing plate is disposed so that the prism axis thereof is orthogonal to the transmission axis of the polarizing plate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device including a condensing prism disposed adjacent to a polarizing plate.

  Liquid crystal display devices, in particular, active matrix liquid crystal display devices have high display quality, can be reduced in size and weight, and have low power consumption. Therefore, by incorporating them into products such as mobile phones, video cameras, and car navigation systems, It has been applied in many fields.

  However, in an active matrix liquid crystal display device, particularly a color liquid crystal display device, the panel transmittance is low, and thus a high-luminance backlight is required. In general, power consumption may be increased in order to increase the luminance of the backlight. However, low power consumption cannot be realized, and adverse effects on the liquid crystal display device due to heat generation of the backlight cannot be ignored.

  Therefore, the use of a condensing prism sheet has been proposed as a method for effectively using the light diffusion of the backlight without increasing the power consumption to increase the concentration of light within the viewing angle and substantially increase the luminance. ing.

  For example, Patent Document 1 below proposes that a high luminance is obtained by forming a large number of lens units on the surface of a rectangular transparent substrate and disposing the lens unit on the transparent substrate.

In addition, in order to use the diffused light in the direction perpendicular to the prism on the lens film surface, it has also been proposed to overlap at least two lens films so that the prism arrangement direction on the lens film surface is orthogonal. FIG. 4 shows an arrangement relationship in the case where the two lens films are arranged such that the prism array directions on the lens film surface are orthogonal to each other. A condensing prism sheet 42 is disposed on the backlight 41, a condensing prism sheet 43 having a prism axis 46 orthogonal to the prism axis 45 of the condensing prism sheet 42 is disposed thereon, and a polarizing plate 44 is further disposed thereon. Are closely attached. At this time, the relationship between the transmission axis of the polarizing plate 44 and the prism axis 46 of the condensing prism sheet 43 is not clear, and does not help to maximize the improvement in luminance as will be described later.
Japanese Patent Laid-Open No. 2-17

  In the use of the conventional prism sheet as described above, the prism axis of the condensing prism sheet is determined regardless of the transmission axis of the polarizing plate, and the light emitted from the backlight is absorbed by the polarizing plate. There was a problem of high power consumption.

  An object of the present invention is to substantially improve luminance by using a condensing prism sheet without increasing power consumption.

  The present invention provides a liquid crystal display device in which a condensing prism sheet composed of one or more prism sheets is disposed between a backlight and a polarizing plate on the backlight side of the liquid crystal display device. By arranging the prism axes of the prism sheet so as to be orthogonal to each other, light emitted from the backlight is transmitted without being absorbed by the polarizing plate, and is further collected by the condensing prism sheet.

  The present invention is also a backlight module including a backlight and a light guide plate for introducing light from the backlight into the display device, and a diffusion sheet is sequentially formed on a surface of the light guide plate on the display device side. The first prism sheet, the second prism sheet, and the polarizing plate attached to the glass are laminated, and the prism axis of the second prism sheet and the transmission axis of the polarizing plate are arranged to be orthogonal to each other. A backlight module is provided.

  The present invention further relates to an electronic device having the above backlight module, which is a mobile phone, a personal digital assistant (PDA), a notebook personal computer, a car navigation (TV), a digital still camera (DSC), and a liquid crystal timepiece device. An electronic device selected from the group consisting of:

  The condensing prism sheet is generally an isosceles triangle having an apex angle of 90 °, and the shape is formed in the prism axis direction.

  The prism sheet used in the present invention may be a generally available prism sheet (for example, Sumitomo 3M BEF, Mitsubishi Rayon Diamond Art, etc.).

  As the polarizing plate used in the present invention, a generally available polarizing plate can be used, and for example, an iodine-based polarizing plate can be used.

FIG. 1 shows the relationship between the prism axis of the prism sheet 1 and the transmission axis of the polarizing plate 2 when one prism sheet is used. When the prism axis of the prism sheet 1 is Θ ₁ and the angle of the transmission axis of the polarizing plate 2 is Θ _PL , Θ _PL −Θ ₁ is from the backlight in each case of 90 °, −45 °, 0 °, + 45 °. For each of these rays, a simulation was performed using ray tracing software.

As a result of the simulation, the brightness index of each case when theta _PL - [theta] ₁ is the luminance when the 90 ° and 100 shown in Table 1. As can be seen from Table _1, Θ _PL -Θ 1 revealed that the luminance is maximized when the 90 °.

Similarly, FIG. 2 shows the relationship between the prism axes of the prism sheets 22 and 23 and the transmission axis of the polarizing plate 24 when two prism sheets are used. When the prism axes of the two prism sheets 22 and 23 are Θ ₁ and Θ ₂ from the backlight side, respectively, and the angle of the transmission axis of the polarizing plate 24 is Θ _PL , Θ _PL −Θ ₂ is 90 ° and −45 °. Each ray from the backlight in each case of 0 °, + 45 ° was simulated using ray tracing software.

As a result of the simulation, the brightness index of each case when theta _PL - [theta] ₂ has a luminance when the 90 ° and 100 shown in Table 2. As can be seen from Table _2, Θ _PL -Θ 2 revealed that the luminance is maximized when the 90 °.

  According to the present invention, a liquid crystal display device with low power consumption and substantially high luminance can be provided.

  Next, the converging prism sheet and the polarizing plate were actually arranged as in the present invention, and the luminance was measured to confirm that the simulation result was correct. The following examples are illustrative and the present invention is not limited to these.

The effect of the present invention was confirmed by measuring the luminance when the angle between the transmission axis of the polarizing plate and the prism axis of the condensing prism sheet was changed using an apparatus as shown in FIG. As a backlight, the LED 37 is disposed beside a light guide plate 31 having a screen size of 7 inches made of a transparent acrylic plate, and a diffusion sheet 32 is disposed on the front surface of the light guide plate 31. On the front surface of the diffusion sheet 32, a prism sheet (BEFIII90 / 50-T, manufactured by 3M Company) 33 having a prism axis of 13 °, a prism sheet (BEFIII90 / 50-T, manufactured by 3M Company) 34 having a prism shaft of 103 °, The polarizing plate 35 attached to the glass is laminated, and the luminance is measured by changing the angle formed by the transmission axis of the polarizing plate 35 and the prism axis of the condensing prism sheet 34 by rotating the polarizing plate 35 attached to the glass. did. The luminance was measured by placing a luminance meter (BM-5A manufactured by Topcon Corporation) at the center position of the backlight 50 cm away from the polarizing plate surface and setting the aperture size to 0.2 °. Each luminance (cd /) when the transmission axis of the polarizing plate 35 with respect to the prism sheet (BEFIII90 / 50-T, 3M) 34 having a prism axis of 103 ° is −45 °, 0 °, + 45 °, and + 90 °. The results of measuring m ² ) are shown in Table 3.

  As shown in Table 3, it was confirmed that the luminance was maximized when the angle formed by the transmission axis of the polarizing plate 35 and the prism axis of the condensing prism sheet 34 was 90 °, and the simulation shown in Table 2 It was verified that the results were the same in the actual measurement results.

  The structure of the embodiment of the backlight module of the present invention is schematically shown in FIG. Referring to FIG. 3, the backlight module includes a backlight LED 37 and a light guide plate 31 having a screen size of 7 inches made of a transparent acrylic plate. A diffusion sheet 32 is disposed on the front surface of the light guide plate 31. Yes. On the front surface of the diffusion sheet 32, a prism sheet (BEFIII90 / 50-T, manufactured by 3M Company) 33 having a prism axis of 13 °, a prism sheet (BEFIII90 / 50-T, manufactured by 3M Company) 34 having a prism shaft of 103 °, A polarizing plate 35 attached to glass is laminated.

The arrangement | positioning relationship of a prism sheet and a polarizing plate is shown. The arrangement | positioning relationship of the prism sheet and polarizing plate in the case of using two prism sheets is shown. The brightness | luminance measuring method and the backlight module in the Example of this invention are shown typically. The arrangement | positioning of the conventional prism sheet is shown.

Explanation of symbols

1 Prism sheet (prism axis Θ ₁ )
2 Polarizing plate (Transmission axis Θ _PL )
21 Diffusion sheet 22 Prism sheet (prism axis Θ ₁ )
23 Prism sheet (prism axis Θ ₂ )
24 Polarizing plate (Transmission axis Θ _PL )
31 Light guide plate 32 Diffusion sheet 33 Prism sheet (prism axis 13 °)
34 Prism sheet (prism axis 103 °)
35 Polarizing plate 36 Luminance meter (BM-5A manufactured by Topcon)
40 liquid crystal display element 41 backlight 42 prism sheet 43 prism sheet 44 polarizing plate 45 prism axis 46 of prism sheet 42 prism axis of prism sheet 43

Claims (7)

In a liquid crystal display device in which a condensing prism sheet including one or more prism sheets is disposed between a backlight and a polarizing plate on the backlight side of the liquid crystal display device, the prism of the condensing prism sheet adjacent to the polarizing plate A liquid crystal display device, characterized in that an axis is arranged so as to be orthogonal to a transmission axis of the polarizing plate. The liquid crystal display device according to claim 1, wherein the condensing prism sheet is composed of one prism sheet. The liquid crystal display device according to claim 1, wherein the condensing prism sheet includes two prism sheets whose prism axes are orthogonal to each other. The liquid crystal display device according to claim 1, wherein a non-absorbing polarizing plate is integrated with the polarizing plate. The liquid crystal display device according to claim 4, wherein a transmission axis of the non-absorbing polarizing plate and a prism axis of a prism sheet adjacent to the polarizing plate of the condensing prism sheet are arranged orthogonal to each other. A backlight module including a backlight and a light guide plate for introducing light from the backlight into the display device, wherein a surface of the light guide plate on the display device side is in turn a diffusion sheet and a first prism sheet The second prism sheet and a polarizing plate attached to glass are laminated, and the prism axis of the second prism sheet and the transmission axis of the polarizing plate are arranged to be orthogonal to each other. Backlight module. An electronic device having the backlight module according to claim 6, comprising a mobile phone, a personal digital assistant (PDA), a notebook personal computer, a car navigation (TV), a digital still camera (DSC), and a liquid crystal clock device. An electronic device selected from the group.

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