JPH03150533A - Projection type color liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain the green projection type color display element which is fast in response because original liquid crystal is low in viscosity by mixing yellow dichroic pigment with phase shift type liquid crystal where blue light is transmitted selectively and setting the hue to green. CONSTITUTION:When a green color display is made by using the phase shift type liquid crystal, cell thickness is reduced so as to adapt a driving voltage to a C-MOS IC and then refractive index anisotropy needs to be increased. Consequently, the viscosity of the liquid crystal is increased and the response becomes fast. For the purpose, the yellow dichroic pigment is mixed with blue display liquid crystal which may be small in refractive index anisotropy and cell thickness and the hue is varied from blue to green. Consequently, the refractive index anisotropy of the blue display liquid crystal is small, so the viscosity is small, so the green projection type color liquid crystal display element which is fast in response speed is obtained.

Description

[Detailed Description of the Invention] [Summary] With regard to liquid crystal display elements that perform color projection display, the purpose of the present invention is to provide a green display with quick response, and by utilizing the optical wavelength selectivity of nematic-cholesteric phase transition type liquid crystal, a white A projection type color liquid crystal display, characterized in that a display element displays a blue image on a screen by irradiating light from a light source onto a liquid crystal cell, and is characterized in that a yellow dichroic dye is mixed with the liquid crystal to produce a green display. Configure the element.

[Industrial Field of Application] The present invention relates to a projection type color liquid crystal display device that provides a green display with quick response.

With the progress of OA (Office Automation), opportunities to provide explanations while using projection-type displays at lecture halls, conferences, etc. are increasing.

Traditionally, over-the-air projectors and slide projectors have been used for such purposes.

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.

[Conventional technology]

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

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

Figure 2 shows the display principle of a nematic cholesteric phase change liquid crystal. scattering transmittance).

In other words, when a liquid crystal composition consisting of a nematic liquid crystal and a cholesteric liquid crystal is mixed, when no voltage is applied or when the applied voltage is low, the liquid crystal assumes a cholesteric phase with a spiral molecular arrangement, and light is scattered and collected for projection. Since the light is scattered outside the 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 is scattered and directly enters the condenser lens, resulting in a bright area on the screen.

And 1. As shown in the figure, the phase transition between the cholesteric phase and the nematic phase draws a hysteresis curve with respect to the applied voltage.

A necessary condition for such a phase change type liquid crystal display element is that the voltage width (hysteresis width) of the rising curve 1 and falling curve 2 of the hysteresis loop is sufficiently wide.

Here, the hysteresis width is the difference between the applied voltage value (VD!) at which the transmittance is 90% on the falling curve 2 and the applied voltage value (V, 2°) at which the transmittance is 20% on the rising curve 1. The intermediate voltage value is the drive voltage (
V, ).

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

As you can see, the inventors believe that scattering in the cholesteric phase in a bistable state is caused by the helical structure of the liquid crystal, but that a refractive index modulation occurs in response to the helical pitch, and this causes light to be diffracted. I paid attention.

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

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 helical axis is not constant, the light is scattered on wide concentric circles.

At the knee, the scattering efficiency η,18 is approximated by the following equation under the condition of Bragg angle incidence.

ηmax = sin2 (kgΔ,,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.

The projection type color display method proposed by the inventor uses the wavelength dependence of light transmittance to produce color display on the image on the screen, and uses the refractive index difference. As the orientation and cell thickness increase, the display color becomes red →
It is clear that the color changes from purple to blue to green.

[Problem H to be Solved by the Invention] The projection type color display method proposed by the inventors utilizes the diffraction scattering of liquid crystal, and has been successful in displaying green color.

However, when performing green color display using such a method, it is necessary to increase the refractive index anisotropy and the cell thickness.

However, increasing the refractive index anisotropy generally increases the viscosity of the liquid crystal, and increasing the cell thickness increases the driving voltage in proportion to the cell thickness, so there is a problem that it cannot be driven with an inexpensive C-MOS IC. There is.

[Means to solve the problem]

The above problem is solved by using the light wavelength selectivity of nematic cholesteric phase transition type liquid crystal to irradiate a liquid crystal cell with light from a white light source to display a blue image on the screen. This problem can be solved by configuring a projection type color liquid crystal display element that is characterized by a mixture of dichroic dyes and performing green display.

[Effect]

As mentioned above, when performing green color display using the phase change type liquid crystal according to the present invention, the drive voltage is changed to C-MOS I
If the cell thickness is suppressed in order to comply with C, the refractive index anisotropy must be made thicker, which raises the problem of increasing the viscosity of the liquid crystal and slowing down the response.

Therefore, the present invention changes the hue from blue to green by mixing a yellow dichroic dye into a blue display liquid crystal that requires small refractive index anisotropy and cell thickness. Since the refractive index anisotropy is small, the viscosity is low, and therefore a green projection type color liquid crystal display element with a fast response speed can be obtained.

Note that a dichroic dye is a dye that is transparent when irradiated with light in the long axis direction, but has a directional property of being colored when irradiated with light in the short axis direction.

〔Example〕

As a phase change type liquid crystal, 10 chiral nematic ink liquid crystals having two chiral centers are added to the nematic liquid crystals shown in Table 1.
It was formed by mixing % by weight.

Table 1 Here, no.

Nos. 1 to 4 are all ethane-based liquid crystals, with a mixing ratio of 20:20:10:10 by weight, and the remaining 40% is other-based liquid crystals.

Then, by changing the composition of other liquid crystals, the refractive index anisotropy of the nematic liquid crystal for blue display was set to 0.203 at 25°C, and the refractive index anisotropy of the nematic liquid crystal for green display was set to 25°.
It was adjusted to 0.253 with C.

In addition, the viscosity is 25°C and the blue display liquid crystal is 20°C.
．． 8 cps, and 65 cps for green display.

Next, azo (^2oNM), which has a yellow color tone, is added to the blue display liquid crystal.
Conductive dichroic dye (product name 5l-209, Mitsui Toatsu Chemical ■)
2% by weight was mixed.

And this liquid crystal has a pixel size of 3501ttn x
1 with 640 x 400 pixels at 330 μm
It was sealed in a 2-inch liquid crystal display element.

In addition, for comparison, a display element was formed using a green display liquid crystal in which no dichroic dye was mixed.

Then, the half change in light transmission when the phase change liquid crystal changes from the nematic phase to the cholesteric phase is recorded on a storage scope (product name 034020. Golf, Company D), and the time required for the phase transition from the nematic phase to the cholesteric phase is recorded. The response time was measured.

The obtained values are 2.4ms for a blue display liquid crystal mixed with a yellow dichroic dye, and 6.6ms for a green display liquid crystal.
It was s.

Next, this display element was mounted on a projection type display device, and the transmission spectrum of the display color in each display element was measured at room temperature while changing the applied voltage as shown in JIS Z 8721.
The saturation equivalent C95 hue equivalent H° and lightness equivalent L* of the a"b" display system were determined.

Furthermore, as a result of setting the writing time to be the response time for phase change type liquid crystal to change from the nematic phase to the cholesteric phase plus 0.5 ms, the liquid crystal for blue display mixed with yellow dichroic dye is 3Ills. / line, and 7 fas/line with green display liquid crystal.

Figure 1 shows hue equivalent H0, saturation equivalent C'', and lightness equivalent L for an element in which a dichroic dye is enclosed in a blue display liquid crystal (displayed by a solid line) and an element in which a green display liquid crystal is enclosed (indicated by a broken line).
1 shows the dependence on the applied voltage.From this figure, it can be seen that the hues are all green, and the saturation and brightness are somewhat inferior to the green display liquid crystal.

However, as mentioned earlier, the response time is more than twice as fast, which more than makes up for the weaknesses in saturation and brightness.

〔Effect of the invention〕

In the present invention, the hue is made green by mixing a yellow dichroic dye into a phase change liquid crystal that is configured to selectively transmit blue light, and because the viscosity of the original liquid crystal is low, , it is possible to realize a green projection type color display element with quick response.

[Brief explanation of the drawing]

FIG. 1 shows the display characteristics of the display element of the example, and FIG. 2 shows the display principle of the phase change type liquid crystal.

Claims (1)

[Claims] Utilizing the light wavelength selectivity of nematic-cholesteric phase transition type liquid crystal, the liquid crystal cell is irradiated with light from a white light source,
A projection type color liquid crystal display element for displaying a blue image on a screen, characterized in that a yellow dichroic dye is mixed with the liquid crystal to display a green image.