JPH03233553A - Projection type liquid crystal display device - Google Patents

Abstract

PURPOSE:To attain a sharp color display by making light which is subjected to ternary partite incident on a phase shift type liquid crystal panels which are equipped with red, green, and blue filters by using plural mirrors and obtaining a red, green, or blue light image. CONSTITUTION:The white light from a light source 1 is collimated by a condenser lens 9 into parallel light, which is subjected to ternary partite by a half-mirror 12 and they are made incident on the phase shift type liquid crystal panel 14 equipped with the red filter 13, the phase shift type liquid crystal panel 18 equipped with the green filter 15, and the phase shift type liquid crystal panel 18 equipped with the blue filter 17, thereby forming the red, green, and blue light images. When a liquid crystal display element which constitutes a panel is in a translucent state, the light which is made incident on the panel is nearly transmitted, and consequently light red, green, and blue, and their mixed colors are displayed. When the liquid crystal display element is in a scattering state, the wavelength of the incident light is scattered most efficiently to obtain excellent black. Consequently, a sharp and light projection image is obtained at low cost.

Description

[Detailed Description of the Invention] [Summary] Regarding a projection type color liquid crystal display device, for the purpose of displaying clear color, light (2) from a light source (1) is converted into parallel light by a condensing lens (9). After that, the divided light (2) is divided into three by a half mirror (02), and the divided light (2) is passed through a plurality of mirrors (4) to form a phase change type light filter equipped with a red filter surface, a green filter (05), or a blue filter (17). A means for obtaining red, green, and blue light images by entering the liquid crystal panels 04), 06), and 01, and a means for transmitting or reflecting the three types of light images by a dichroic prism (6) to combine them; A phase change type liquid crystal panel 04 having a means for enlarging and projecting an image onto a screen (8) using a lens (7), and equipped with the red filter θ3), the green filter solid state, or the blue filter θη described above.
), (lω, 08) are the filters 03), 0ω, (1
The projection type liquid crystal display device is characterized in that the maximum scattering wavelength of the liquid crystal matches the maximum transmission wavelength of 7).

[Industrial application field]

The present invention relates to a projection type liquid crystal display device capable of displaying bright (clear) colors.

With the progress of OA (Office Automation), there are increasing opportunities to provide explanations while displaying images projected on screens at lecture halls, conferences, and the like.

Conventionally, overboard projectors and slide projectors have been used for such applications.

However, demand for display devices that input information in the form of signals to a liquid crystal display element, rewrite the content at will, and display it on a screen is increasing, rather than a projection device that periodically changes information and displays it on a screen. ing.

[Prior Art] As a projection type display device that inputs information in the form of a signal,
Video projectors have been used in the past, but there is a problem in that the screen is dark because the light emitted by a cathode ray tube (CRT) is magnified and projected.

In contrast, in recent years, display devices have been realized that use a liquid crystal panel as a light shutter and perform projection display by 0N10FF of light from a projection light source.

Figure 2: Scale display device (Society for I)
nformation Display: S10
86 DIGEST, p375-378.1986), the light 2 from the light source 1 is divided into three lights of red (R), green (G) and blue (B) by the dichroic mirror 3, and the light is directly or A mirror 4 is used to make each light incident on a liquid crystal panel 5 consisting of a liquid crystal display element driven by a thin film transistor (TPT).

Next, each of the incident R, G, and B lights passes through the liquid crystal panel 5 to become an optical image, and the optical image of each color is transmitted or reflected by the dichroic prism 6 and enters the lens 7, and the optical image is The image is enlarged and projected onto the screen 8 by this lens 7.

However, since this method can use a powerful halogen lamp as the projection light source 1, it is possible to obtain a brighter screen than a video projector. Therefore, more than 50% of the incident light is absorbed by the liquid crystal panel 5, and therefore the brightness of the screen is not sufficient.

Furthermore, if the brightness of the projection light source is increased in order to brighten the screen, the temperature of the liquid crystal panel 5 will increase significantly due to light absorption, and the drive characteristics of the liquid crystal will change, making it impossible to display.

Note that in this method, the liquid crystal panel 5 uses a TPT type liquid crystal display element in order to obtain sufficient display capacity;
In this type of liquid crystal display element, it is necessary that all the TPTs provided for each pixel be formed without defects, and there is a problem that the yield is low and the manufacturing cost is high.

[Problem to be solved by the invention]

Conventional projection type color liquid crystal display devices have problems in that the projection screen is dark and the manufacturing cost is high, so that they have not been put into practical use.

Therefore, the challenge is to solve this problem.

[Means to solve the problem]

The above-mentioned problem is to convert the light from the light source into parallel light using a condensing lens, and then divide it into three parts using a half mirror, and to convert the divided light into three parts using multiple mirrors with a red filter, a green filter, or a blue filter. A means for obtaining red, green, and blue light images by entering a liquid crystal panel, and after combining these three types of light images by transmitting or reflecting them through a dichroic prism, this light image is enlarged and projected onto a screen using a lens. A phase change type liquid crystal panel having the above-mentioned red filter, green filter, or blue filter as described above matches the maximum transmission wavelength of the filter with the maximum scattering wavelength of the liquid crystal to constitute a projection type liquid crystal display device. This can be solved by

[Effect]

The inventors have been researching nematic-cholesteric phase transition type liquid crystal displays for some time, and found that light transmittance becomes wavelength-dependent due to diffraction and scattering caused by the helical structure of the cholesteric phase in the scattering state of liquid crystals. We are proposing a projection color display method that utilizes this phenomenon.

(Japanese Unexamined Patent Publication No. 63-49736. Published on March 21, 1986) The outline is as follows.

Figure 6 shows the display principle of a nematic-cholesteric phase change liquid crystal. transmittance).

In other words, when no voltage is applied to a liquid crystal composition consisting of a mixture of nematic liquid crystal and cholesteric liquid crystal, or when the applied voltage is low, the liquid crystal assumes a cholesteric phase with a spiral molecular arrangement, and light is scattered and used for projection. Since the light is scattered outside the condensing lens, the light transmittance is low, resulting in a dark area on the screen.

Furthermore, when the voltage is high, the liquid crystal becomes a nematic phase in which molecules are aligned in the direction of the electric field, and the light enters the condenser lens without being scattered, resulting in a bright area on the screen.

The phase transition between the cholesteric phase and the nematic phase draws a hysteresis curve with respect to the applied voltage, as shown in the figure.

A necessary condition for such a phase change type liquid crystal display element is that the voltage width (hysteresis width) of the rising curve 10 and falling curve 11 of the hysteresis loop is sufficiently wide.

Here, the hysteresis width is determined by the applied voltage value (Vt+q.) at which the transmittance is 90% in the falling curve 11 and the applied voltage value (VL12) at which the transmittance is 20% in the rising curve 10.
The voltage value in between is defined as the difference between VO and VO.

This indicates that optically different bistable states can be achieved with the same driving voltage (Vo), and this phenomenon is utilized to perform large-capacity displays.

Here, the inventors believe that scattering in the cholesteric phase in a bistable state is caused by the helical structure of the liquid crystal, but refractive index modulation occurs in response to the helical pitch, which causes light to be diffracted. We focused on the fact that

In other words, since liquid crystal molecules have an elongated structure and have anisotropy in refractive index, the refractive index is different where the liquid crystal molecules are aligned perpendicularly to the substrate and where they are aligned horizontally. There is.

Therefore, there is a refractive index modulation corresponding to the helical pitch, and a volume phase type diffraction grating is formed.

However, since there is some variation in the helical pitch and the direction of the pongee is not constant, the light is scattered on wide concentric circles.

Here, the scattering efficiency η□ is approximated by the following equation under the condition of Bragg angle incidence.

77 +nax = 5in2(1(πΔ, d/λ”
) ・(1) However, Δ, ... Refractive index anisotropy d ... Cell thickness λ ... Light wavelength As can be seen from equation (1), light transmittance (non-scattering transmittance)
has wavelength and cell thickness dependence, and experimentally the light transmittance changes periodically in the range of about 40% to about 2% in proportion to the increase in cell thickness, and the repetition period changes depending on the measurement wavelength. do.

This shows that the wavelength of light most scattered by the liquid crystal panel can be changed by changing the cell thickness and the value of refractive index anisotropy.

The inventors have confirmed through experiments that as the cell thickness and refractive index anisotropy increase, the wavelength of the most scattered light shifts to the longer wavelength side.

It has also been found that by increasing the helical pitch, the wavelength of the scattered light shifts to the longer wavelength side.

As described above, by changing the helical pitch, refractive index anisotropy, cell thickness, etc. of the nematic-cholesteric phase transition type liquid crystal, the wavelength of light that is most scattered by the panel can be changed.

Therefore, by matching the wavelength of the light that is most scattered to the wavelength of the light incident on the panel, scattering in the cholesteric state can be efficiently performed, and therefore a good dark state can be obtained.

As shown in FIG. 1, the projection type liquid crystal display device according to the present invention converts white light 2 from a light source 1 into parallel light using a condensing lens 9, and then divides it into three parts using a half mirror 12. A phase change type liquid crystal panel 14 , which is reflected by a red filter 13 . A phase change type liquid crystal panel 16 equipped with a green filter 15. Phase change type liquid crystal panel 1 equipped with blue filter 17
8 to create red, green, and blue light images, respectively.

Next, these optical images are passed through or reflected by a dichroic ink prism 6 and combined as in the conventional manner, and then enlarged and projected onto a screen 8 using a lens 7.

In this way, a color filter is used to separate the light from the light source into the three primary colors of red, green, and blue and input it to the liquid crystal panel. , most of the light incident on the panel is transmitted,
Hence the bright red color.

It can display green, blue and mixed colors.

Furthermore, when the liquid crystal display element is in a scattering state (the liquid crystal is in a cholesteric phase), the liquid crystal panel is configured so that the wavelength of the incident light is most efficiently scattered, so that a good black color can be obtained.

〔Example〕

A projection type liquid crystal display device having the configuration shown in FIG. 1 was manufactured as a prototype.

Figure 3 shows the transmission spectra of the color filters used.The red filter 03) transmits wavelengths of 600 nm or more, the green filter transmits wavelengths around 540 nm, and the blue filter transmits wavelengths around 480 nm. are doing.

Next, a phase change liquid crystal was prepared by mixing 10% by weight of chiral nematic liquid crystal with the ethane liquid crystal shown in Table 1.

No, the mixing ratio of 1 to 4 is 20 by weight:
The ratio is 20:10:10, and the remaining 40% by weight is other types of liquid crystal.

Table 1 Then, by changing the refractive index anisotropy of the liquid crystal by changing the composition of the liquid crystal of another type, and by changing the panel thickness, the wavelength of light that is most scattered by the phase change type liquid crystal can be changed to the phase change type equipped with a red filter. The wavelength was adjusted to 600 nm for the liquid crystal panel 14, 540 nm for the panel 16 equipped with a green filter, and 480 nm for the panel 18 equipped with a blue filter.

FIG. 4 shows the transmission spectrum of each panel thus prepared in a scattering state, and the light transmittance is at a minimum at the target wavelength.

Next, the maximum transmission wavelength of each filter and the maximum scattering wavelength of each liquid crystal panel are matched, the liquid crystal is phase-transformed into a transmission state and a scattering state, and the transmission spectrum of the projected image in each combination is measured using a spectrophotometer (product name: MCPD-100). (manufactured by Otsuka Electronics Co., Ltd.).

FIG. 5 shows the transmission spectra when each panel is in the transmission state and the scattering state, and also shows the transmission spectrum of only the color filter for reference.

From the figure, when the maximum transmission wavelength of the filter and the maximum scattering wavelength of the liquid crystal are combined, that is, when they are combined as shown in Figure 1, and the phase change type liquid crystal is in a transparent state, the spectrum of the projected image is the same as that of the color filter. The spectrum is faithfully reproduced with high transmittance, and the displayed colors are bright and vivid.

On the other hand, when the liquid crystal is in a scattering state, the spectrum of the projected image becomes flat, the transmittance is low, and it can be seen that good black display is achieved.

As described above, the liquid crystal display device according to the present invention matches the maximum transmission wavelength of the filter and the maximum scattering wavelength of the liquid crystal, and by each combination, it is possible to display bright and vivid display colors and good black. By mixing, a bright and vivid multi-color display can be created.

〔Effect of the invention〕

By implementing the present invention, it is possible to realize a much lower cost than a conventional TPT type liquid crystal display device, and also to obtain a clear and bright projected image.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a projection type liquid crystal display device according to the present invention, Fig. 2 is a block diagram of a conventional projection type liquid crystal display device, Fig. 3 is a transmission spectrum of a color filter, and Fig. 4 is a block diagram of each prototype liquid crystal display device. The transmission spectrum of the panel in the scattering state; FIG. 5 is the transmission spectrum when each liquid crystal panel is in the transmission and scattering state; FIG. 6 is the display principle diagram of the phase change type liquid crystal. In the figure, 1 is a light source, 2 is a light, 4 is a mirror 6 is a dichroic prism, 7 is a lens, 8 is a screen, 9 is a condenser lens, 12 is a half mirror, 13 is a red filter, 14, 16, and 18 are phase transitions 15 is a green filter, and 17 is a blue filter.

Claims (2)

[Claims] (1) A means for collimating the light (2) from the light source (1) with a condensing lens (9) and dividing it into three parts with a half mirror (12); a phase change type liquid crystal panel (14) equipped with a red filter (13), a green filter (15) or a blue filter (17) by a mirror (4);
(16) and (18) to obtain red, green, and blue light images, and after combining the three types of light images by transmitting or reflecting them through a dichroic prism (6), the light image is A projection type liquid crystal display device characterized by having means for enlarging and projecting onto a screen (8) using a lens (7). (2) The phase change type liquid crystal panel (14), (16), (18) equipped with the red filter (13), the green filter (15), or the blue filter (17) described in the previous section is the filter (13), 2. The projection type liquid crystal display device according to claim 1, wherein the maximum scattering wavelength of the liquid crystal matches the maximum transmission wavelength of (15) and (17).