JPH0197092A - Projection liquid crystal display device - Google Patents

Abstract

PURPOSE:To optimize the characteristics of transmission factors of RGB by altering the crossing angles of deflection axes of polarizers and analyzers in each RGB of TN type liquid crystal panels in a projection liquid crystal display device having an optical system where three color lights of R, G and B are transmitted through three TN type liquid crystal panels and the images of the TN type liquid crystal panels are image-formed on a same screen. CONSTITUTION:It is assumed that a case for shifting the deflection axes in the direction where rotatory polarization angles of linear deflection is reduced to be positive, the crossing angle thetaR of the deflection axis of the liquid crystal panel for R light beams to 0--20 deg., and the crossing angle thetaB of the deflection axis in the liquid crystal panel for B light beams to 0-+20 deg.. The crossing angle thetaG of the deflection axis in the liquid crystal panel for G light beams is assumed to be thetaG=0 or thetaR<thetaG<thetaB. The totally equal liquid crystal panels can be used for the liquid crystal panels for R, G and B except for the arrangement angles of deflecting plates according to said means and constitution. A multiple number of liquid crystal panels of same specification are manufactured and a system can be constituted by using the liquid crystal panels of mean performance. Since three liquid crystal panels for R, G and B have same gap lengths, the responsibility of liquid crystal are the same.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a projection type liquid crystal display device for full-color display, and particularly to the structure of a TN type liquid crystal panel used therein.

Conventional technology As a liquid crystal display panel capable of displaying full-color images, a liquid crystal panel has been put into practical use that uses a TN-type liquid crystal panel with a large number of pixels arranged in a matrix as an optical shutter, and a three-color filter of RGB arranged for each pixel. There is. In order to display a full-color TV image comparable to that of a CRT, it is necessary to control the on and off of the optical shutter with a J100'% duty using the image signal line and scanning line, so a thin film transistor or diode for switching is required for each pixel. An active matrix type liquid crystal display panel with built-in is advantageous. However, since these active matrix liquid crystal display panels are manufactured using a so-called semiconductor process using film formation and photofabrication, it is generally difficult to increase their size. On the other hand, in a projection type liquid crystal display device that projects this onto a screen as a light pulp, this increase in size can be easily realized.

When RGE three-color light is transmitted through three TN-type liquid crystal panels and the images of these TN-type liquid crystal panels are formed on the same screen, the polarization state of the output light changes depending on the wavelength of the incident light on the TN-type liquid crystal panel. Therefore, it is necessary to use a TN type liquid crystal panel with an optimal optical design for each of these RGB colors. The transmittance characteristics of the normally black TN cell are Gooch.

Tarry published the document J, Phys, D8, 1575 (1
975), the transmittance T in the case of a 9007N cell can be expressed as T=s'+n2-(1+u)/(1+u). Here, the parameter U is defined as u=2Δnd/λ, where Δn is the refractive index anisotropy of the liquid crystal, d is the gap length of the liquid crystal layer, and λ is the wavelength. The minimum value of the transmittance T varies depending on the wavelength, and the center wavelength of each RGB is 450n.
The calculated value of the transmittance T for the gap length d when m, 545 nm, and 610 nm and Δn = 0.098 is the second
It is shown in the figure. Curve 1 in FIG. 2 shows the transmittance when R light is transmitted, and the transmittance takes a minimum value at a gap length of 5.4 μm. Similarly, curves 2 and 3 are for G light.

It shows the transmittance of B light, and the gear lug length is 4.8 μm.

The minimum value of transmittance is taken at 4.0 μm. Therefore RGB
When using the same liquid crystals with the same Δn value as liquid crystal panels for use with other devices, transmittance characteristics can be optimized by adjusting the gap length of each liquid crystal panel to the above value. Also, Δ for each RGB! It is possible to optimize the transmittance characteristics by using liquid crystals with different values, but the practical characteristics required for liquid crystal materials, such as viscosity related to response, and dielectric constant difference related to voltage-transmittance characteristics, are considered. It is difficult and impractical to optimize the above-mentioned properties while also satisfying the ditropic elastic modulus and the like.

Problems to be Solved by the Invention The conventional method of optimizing the transmittance characteristics by changing the gap length of the liquid crystal panel for each RGB cannot realize an image display device with high contrast and good color reproducibility. requires a liquid crystal display panel with a highly accurate gap length of submicrons, and constructing liquid crystal panels with different gap lengths for each RGB is disadvantageous in terms of manufacturing technology and manufacturing control.

For example, the gap in the liquid crystal layer of a liquid crystal panel is maintained using glass fibers or beads as spacers, but this gap distance depends on the diameter, material, and dispersion density of these Nupaca materials. It is not easy to achieve the required gap length of submicron diameter because of the warping, pressing force and temperature conditions for correcting the warping and sealing. Furthermore, if the gap length of the TN type liquid crystal panel is different, not only the optical characteristics but also the response characteristics and voltage-i pass rate characteristics will change, which is disadvantageous.

Means for Solving the Problems In order to solve the above problems, the present invention transmits RGB three-color light through three TN-type liquid crystal panels and forms images on the TN-type liquid crystal panels on the same screen. A projection type liquid crystal display device having an optical system, which is characterized by optimizing the transmittance characteristics for each RGB by changing the intersection angle of the polarization axes of the polarizer of the TN type liquid crystal panel and the analyzer for each RGB. That is.

In particular, a normally black display format in which the alignment directions of the TN type liquid crystal panel are approximately orthogonal, and the polarizer and analyzer are arranged in a direction close to parallel Nicols so that the transmission axis or absorption axis of the polarizer and analyzer approximately coincide with one of the alignment directions. The intersection angle θR of the polarization axis of the liquid crystal panel for R light is 0--200, B
The intersection angle θB of the polarization axis of the liquid crystal panel for light is 0 to +20°,
It is convenient to set the intersection angle θG of the polarization axes of the liquid crystal panel for G light to θG=o or aR x θG x θB.

Effects According to the means and structure of the present invention, the liquid crystal panels for RGB can use exactly the same liquid crystal panels except for the arrangement angle of the polarizing plates, so the structure is simple and advantageous in manufacturing the liquid crystal panel. It is possible to manufacture a large number of liquid crystal panels with the same specifications and configure a system using liquid crystal panels with uniform performance. Furthermore, since the three liquid crystal panels for RGB have the same gap length, the response characteristics of the liquid crystals are also the same, and the voltage-transmittance characteristics are also similar.

The present invention focuses on the fact that the above advantages can be obtained with a simple configuration of a three-panel projection liquid crystal display device by simply adjusting the arrangement angle of the polarization axis of the liquid crystal panel, and the transmittance characteristics of the liquid crystal panel are as follows. can be optimized.

1, Appl, Phys, 48. (4), P1427
(1977), the incident linearly polarized light is 900TN.
The following conditional expression is theoretically derived as a condition for transmitting through the cell and emitting as linearly polarized light.

(1+u2)T Here, the parameter U is defined as u = 2Δnd/λ as above, and α represents the angle of the polarization axis with respect to the orientation direction, and the rotation of the linearly polarized light of the TN cell with respect to the orientation direction on the incident side. The angle is defined as positive when the polarization axis on the input side is shifted in the direction and the polarization axis is shifted in the direction in which the angle of rotation of linearly polarized light decreases on the output side.The above condition for the output light to be linearly polarized is This is a case where the intersection angle between the polarization axis on the side and the polarization axis on the emission side is 2a.

Figure 2a shows the relationship between the angle α of the polarization axis and the gap length d that satisfies this conditional expression for the case of Δn = 0.098, with each center wavelength of RGB, 450 am, 546 am,
This is calculated for 610am.

Curves 4 and 5.6 represent the relationship between the angle a of the RGB polarization axes and the gap d, respectively. When α=0, the above Goo
This corresponds to the optimum gap calculated from the formula of ch and Tarry. This relationship is illustrated in FIG. 2A and FIG. 2S in relation to each other. Assuming that the polarizing plate of the TN cell for G light is parallel Nicol, that is, αG = O, the optimum gear length is 4.8 μm. Gap length is 4.8μm
The optimal angle αB of the polarization axis of the TN cell for B light when
It is. Similarly, the optimum angle aR of the polarization axis of the TN cell for R light is indicated by point 8 in the figure, and is α8m 40'. In this way, by using liquid crystal panels with the same gap and changing the angles of the polarization axes, an optimal configuration can be achieved for each RGB. Moreover, in the 4th case that satisfies this theoretical formula, the transmittance of the liquid crystal panel in the black state when not lit is RG.
Both B are theoretically zero, and an excellent black level, which is important for TV image grade display, is achieved, and color reproducibility is also high. Furthermore, the transmittance in the white state when the light is turned on is for B light and R
For light, the polarization axis is different from parallel Nicols, so it is slightly lower, but the intersection angle of the polarization axes for B light is θB = 2αB =
+13.2° For R light aR= 2 aR= -aO6
and the decrease in transmittance is 5.2% and 1.9%, respectively.
Therefore, there is no problem in practical use, and there is little decrease in contrast. The reason why the intersecting angle of the polarization axes is limited to 20° or less is because if the intersecting angle is larger than this, the transmittance during lighting will decrease by more than ten percent, which will cause problems.

Embodiment FIG. 1 shows an embodiment corresponding to the structure of claim 3 as a first embodiment of the present invention. This configuration is an example of arranging the polarization axes according to the theory described above.
The angle Ω between the alignment direction 11 (indicated by a dotted arrow) on the incident light side of the TN cell 10 and the alignment direction 12 on the output side is Ω=90.
This is a TN cell in which the rotating direction of the angle is clockwise, and the three TN cells for RGB light have the same gear length d of their liquid crystal layers, and the gap length is optimized for G light. Namely, the aforementioned Gooch and Torry.

In the formula, the conditions for the first peak where the transmittance at the time of non-lighting is zero are as follows. The wavelength λ is 0.545 pm of G light, Δn=0.
098, the above equation becomes d=48 μm.

The polarization axis of the TN cell for G light is in the same direction as the alignment direction on the input side, and the polarization axis on the output side is parallel, so-called t.
aoo Forms a parallel Nicol normally black display type cell of the TN cell. On the other hand, in the TN cell for R light, the angle of the polarization axis is set in the direction 13, which is changed by aR from the orientation direction 11 on the input side, and the polarization axis on the output side is perpendicular to the orientation direction on the input side. From the azimuth, the direction is 14, which is shifted by Zu in the opposite direction to the incident side.

In order to make the transmittance of the TN cell for R light zero when it is not lit, from the above-mentioned formula of Gosc i ansk i, d =
4.8 μm.

If λ=o, e1o, Δn=0.098, αpt
= 4.00. Here, the sign of the angle is positive when the polarizing plate is shifted in the direction in which the angle of rotation of linearly polarized light decreases. Since it is emitted as linearly polarized light at an angle rotated by .0', by aligning the polarization axis on the emitting side in a direction perpendicular to this, the transmittance when the light is not turned on can be made zero.Similarly, for B light Even for d = 4.
8 pm, λ=0.450 μm.

When optimizing the polarizing plate angle by setting Δn=o・098, α
B = +6.6°, and in the case of B light shown in the figure, the polarization axis 15 on the incident side is set in the opposite direction to the case of R light, and the polarization axis 16 on the output side is set by α8 with respect to the orientation 11. It is only necessary to shift it by α3 from the direction perpendicular to the orientation direction of . Note that illustration of the projection optical system is omitted in the figure.

The R of the TN cell with the polarizer arrangement direction optimized in this way
FIG. 3 shows the theoretical values of the transmittance characteristics with respect to the gap length for each GB. Curves 21, 22, and 23 are R light and G light, respectively.
The transmittance of the TN cell for light and B light is shown. Here, at a constant gap length (4.8 μm), the transmittance of both RGB light becomes zero, and the black level when the light is not turned on is optimized. As a demonstration experiment, Δn = 0.098, d = 4.
When we created an 8pm TN cell and used an RGB dielectric multilayer interference filter to find the optimal placement angle of the polarizer when the lights were not on, we found that for the R light panel, the polarizer intersection angle was 18°. .

For the B-light panel, when the polarizer intersection angle was +13°, the panel brightness when not lit was at its minimum, showing good agreement with the theoretically calculated value. Further, in the above explanation, Δn was treated as a constant, but it has slight wavelength dependence and relatively large temperature dependence, and accuracy can be improved by performing calculations that take these into account. Furthermore, as shown in FIG. 3, the transmittance of the actually produced panel did not reach zero at its optimum point, but there was some residual transmittance. Furthermore, RGB
When using the above-mentioned dielectric multilayer interference filter as a filter, the width of the filter characteristic in the wavelength range is relatively narrow, so the theoretical calculation formula with a fixed number length as described above agrees well with the experimental facts. However, with emphasis on the amount of transmitted light, each R
When using a filter in which the GH has a wavelength width, the experimental value of the polarizing plate intersection angle that minimizes the transmittance deviates from the above calculated value. However, this deviation is within the wavelength width.

The main cause is thought to be the optical rotary dispersion phenomenon of the light source, and it can be analyzed by integrating the transmittance of the TN cell over the wavelength width of the light source and filter, taking into account the polarizing plate intersection angle.
The accuracy of design calculation values can be further improved. Such deviations of the residual component of transmittance and the polarizing plate intersection angle from the theoretical values were particularly noticeable in panels for B light. One reason for this is that in the B-light panel, the above-mentioned optical rotational dispersion phenomenon is particularly large in the narrow gap region, and it is also thought to be influenced by the Britepult angle of liquid crystal alignment. Furthermore, when we fabricated a liquid crystal panel for B light with d = 4.0 μm by optimizing the gap length as before, due to the narrow gap, the uniformity of the gap within the panel was noticeable and there was significant residual transmission. The contrast was poor. From this point of view, the present patent is advantageous in that it is possible to optimize the transmittance characteristics for B light by using a liquid crystal panel with a relatively large gap.

Since RGB panels have the same gap, their response characteristics are almost the same, and the voltage-transmittance characteristics when voltage is applied are also R.
There was no difference in GB that would pose a practical problem.

FIG. 4 shows another embodiment of the present invention, in which a corresponds to the structure of claim 3, as in the first embodiment, and b and C correspond to the structure of claim 4. An example is shown below. In the above demonstration experiment, we maintained the polarizing plate intersection angle θ and changed the polarizing plate intersection angle by fixing the polarization axis on the incident side or the output side in a fixed direction instead of distributing the angle in both directions as shown in Figures 4 and 4. It has become clear that the same effect as in FIG. 4a can be obtained.

The panels for G light all have a gap length optimized with parallel Nicols, and the panels for B light and R light have the same gap length and the intersection angles of the polarization axes are optimized. Orientation direction example Oc) on the incident side and orientation direction 32 (Oc) on the output side
y) intersect at an intersection angle Ω close to 90', and have a molecular axis director oriented in the direction of the arrow, forming a clockwise TN cell.

Note that all the figures here are viewed from the emission side.

In the panel for B light shown in Fig. 4a, the polarization axis 33 (P
i) is arranged in a direction with an angle of IZB in the optical rotation direction with respect to the orientation direction 31(x) on the incident side, and the linearly polarized light incident in this direction rotates clockwise by π-2αB and then The light is emitted as linearly polarized light in the rotation direction (Po') of 34. If the polarization axis on the output side is aligned with the direction 36 (Po) perpendicular to this, the transmittance during non-lighting will be minimized. Therefore, the intersection angle θB between the polarization axis on the input side and the polarization axis on the output side is θB =
2 (IB.

The same is true for the panel for R light, but while the angle of rotation for B light (the angle formed by Pi and Po) is an acute angle, for R light it is an obtuse angle, and the arrangement of the polarization axes on the incident side and output side The relationship is mutually inverse.

FIGS. 4A and 4C show the case where the polarization axis on the incident side is made to coincide with the orientation direction, and the case where the polarization axis on the output side is made to coincide with the orientation direction, respectively. In this case as well, the transmittance can be optimized by appropriately selecting the intersection angle of the polarizing plates, similar to the case of the configuration shown in FIG. 4(d). In the first approximation, from the aforementioned Goscianski equation, the polarizing plate intersection angle θ is θ=2α
It can be found by In such a configuration, since one polarization axis is common to each RGB panel, the configuration is simple and it is also advantageous in manufacturing a projection type liquid crystal display device.

For example, a polarizing plate is attached directly to the liquid crystal panel as the polarizing axis on the common side, and a polarizing plate on the side for adjusting the intersection angle is placed on the opposite side.

An example of a configuration in which the angle of the polarization axis on the incident side is the same as shown in Figure 4 is used when illumination light is transmitted through a polarization beam splitter, and the resulting linearly polarized light is split into RGB light and incident on a liquid crystal panel. It's advantageous.

That is, in this case, it is difficult to select the direction of the polarization axis on the incident side in an arbitrary direction, so it is convenient if the polarization axis on the incident side is common.

An example of a configuration in which the angle of the polarization axes on the output side is the same as shown in Figure 4C is to place a polarizing plate with an angle adjustment mechanism on the input side away from the liquid crystal panel, and on the output side, place the polarizing plate directly on the liquid crystal panel. This is advantageous when the structure is pasted. In this case, the polarizing plate on the incident side in particular absorbs the radiant heat from the light source and generates heat, but this arrangement prevents this heat from being transmitted to the liquid crystal panel, thereby reducing the liquid crystal panel temperature. increase can be reduced.

Although not shown, there is no problem in practice even if the polarization axis does not exactly match the orientation direction as long as the relative angle is constant within a range of several degrees. In addition, the twist angle Ω is also 90° in order to prevent the domain from rotating in the opposite direction of the liquid crystal (reverse domain).
Although a configuration in which the twist angle is several degrees smaller than 0° is often used, in the demonstration experiment, a twist angle of 88° was selected for this purpose.

Fig. 6 shows still another embodiment, and Fig. 4 a'-c
is a case of so-called transmission axis alignment, in which the orientation direction on the incident side is aligned with the polarization axis (transmission axis) of the polarizing plate. The figure shows a case of so-called absorption axis alignment, in which the two directions are aligned. In this case as well, similar effects can be obtained with the arrangement according to FIGS. 4a-C.

FIG. 6 further shows that, whereas in the previous embodiments, the G light panel was selected as the best gap and panels with the same gap length were used for R and B, the G light wavelength was shifted from the G light wavelength. This example shows the case of using a TN cell that has the best gap at wavelength (in this example, the best gap is at a wavelength slightly shorter than the G light wavelength). Adjust the polarizing plate intersection angle for the G light panel as well. By doing so, it is possible to optimize the transmittance characteristics when the light is not lit.

Furthermore, in the above embodiments, the case where the gap is the same for both the RGB panels has been described. In this case, the advantage of the simple configuration of the present invention is maximized, but the system can be configured as a compromise with the conventional optimization method of changing the gap length or changing the refractive index anisotropy. Good too.

As described in detail, according to the present invention, R can be achieved with a relatively simple configuration.
It is possible to optimize the transmittance characteristics for each GB, and in other words, it is possible to provide a projection type liquid crystal display device with excellent black level, color characteristics, contrast, and color reproducibility, which are important for full-color TV image quality. , is of great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the arrangement of polarization axes of a liquid crystal panel according to a first embodiment of the present invention, FIG. is Figure 2a
FIG. 3 is a graph showing the relationship between the gap length and transmittance of a conventional liquid crystal panel in comparison with FIG.
FIG. 4 is a plan view showing the arrangement relationship between the orientation direction and the polarization axis in the case of the first embodiment of the present invention; FIGS. FIG. 6 is a plan view showing the arrangement relationship between the orientation direction and the polarization axis, showing another embodiment of the present invention. 1o...TN cell, 11.12...Orientation direction, 13.14...Polarization axis (for R light), 1
5.16...Polarization axis (for B light), 31...
...Alignment direction on the incident side, 32...Alignment direction on the output side, 33...Polarization axis on the incident side, 34...
...Emission direction of linearly polarized light, 35...Polarization axis on the emission side. Name of agent: Patent attorney Toshio Nakao and 1 other person
Figure 2 (
a) (b) 4v knob length Fig. 3 Gap length <b) Fig. 5 Fig. 6

Claims (4)

[Claims] (1) A projection type liquid crystal display device that has an optical system that transmits RGB three-color light through three TN-type liquid crystal panels and forms images of the TN-type liquid crystal panels on the same screen, A projection type liquid crystal display device characterized in that transmittance characteristics for each RGB are optimized by changing the intersection angle of the polarization axes of a polarizer and an analyzer of a TN type liquid crystal panel. (2) Normally black display in which the orientation directions of the TN-type liquid crystal panels are approximately orthogonal, and the polarizer and analyzer are arranged in a direction close to parallel Nicols so that the transmission or absorption axes of the polarizer and analyzer approximately coincide with one orientation direction. In the format, the case where the polarization axis is shifted in the direction in which the angle of rotation of linearly polarized light decreases is considered positive, and the intersection angle θ_R of the polarization axis of the liquid crystal panel for R light is 0 to -20°,
The intersection angle θ_B of the polarization axis of the liquid crystal panel for B light is 0 to +20.
゜, the intersection angle θ_G of the polarization axis of the liquid crystal panel for G light is θ_G
2. The projection type liquid crystal display device according to claim 1, wherein θ_R<θ_G<θ_B. (3) The angle α_R between the transmission axis or absorption axis of the analyzer of the liquid crystal panel for R light and the alignment direction on the incident side is 0 to -10.
degree, the angle of intersection θ_R of the polarization axes is θ_R=2α_R, the angle α_B for B light is 0 to +10 degrees, and the angle of intersection θ_B of the polarization axes is θ_B=2α_B. Projection type liquid crystal display device. (4) Projection according to claim 2, characterized in that the angle of the polarization axis of either the incident side or the output side with respect to the liquid crystal panel is the same for RGB, and the angle of the other polarization axis is changed. type liquid crystal display device.