JPH0564678B2 - - Google Patents

Description

[Detailed description of the invention]

(1) Technical Field The present invention relates to a liquid crystal composition used in a thermal writing liquid crystal element that utilizes the thermo-optic effect of liquid crystal. (2) Conventional technology and its problems Cholesteric liquid crystal exhibiting a transparent liquid crystal structure,
Alternatively, when a thin layer of smectic liquid crystal is partially heated and rapidly cooled, that area transforms into an opaque liquid crystal structure that generally scatters light, a phenomenon known as the thermo-optic effect of liquid crystals. In addition, several liquid crystal devices have been proposed that take advantage of this phenomenon and write information by applying a temperature change to a portion of the liquid crystal cell to make that portion opaque. For example, a direct-view display element in which an image is written and the image is viewed directly, a light valve element used for a projection display in which the written image is projected and viewed, and the written information is read electrically or optically. type of recording element, etc. There are also methods for writing information, such as irradiating laser light and causing a temperature rise in the irradiated area,
Several methods are known, such as a method that uses Joule heat generation in a resistor to raise the temperature. For the sake of simplicity, we will explain below the details of a liquid crystal light valve element used in a projection display device in which an image is written by irradiating a liquid crystal cell with a laser beam, and the written image is enlarged and projected using a separate optical system. This will be explained using a case as an example. Our company uses a general formula for thermal writing liquid crystal light valves. A so-called Schiff base-based liquid crystal material was used. This is because no liquid crystal material other than Schiff base-based materials has been found that exhibits a smectic phase at the operating temperature of the liquid crystal light valve, that is, around room temperature, and has an appropriate phase transition temperature. Here, the appropriate phase transition temperature refers to the temperature Tc at which the liquid crystal transitions to an isotropic liquid phase; if Tc is too high, the temperature rise required for writing will be large, which is disadvantageous in terms of power consumption and writing speed. occurs, and if Tc is too low, the liquid crystal temperature in a steady state after writing is close to the phase transition temperature Tc, resulting in a decrease in the degree of orientation order of liquid crystal molecules, resulting in the disadvantage of a decrease in contrast. Regarding Schiff base-based liquid crystal materials, Taylor et al. of Bell Laboratories reported in the Journal of Applied Physics.
This is reported in Volume 45, Issue 10. However, it is widely known that Schiff base-based liquid crystal materials are prone to hydrolysis, and therefore thermal writing liquid crystal devices using this type of liquid crystal material have a short lifespan and lack reliability, especially in terms of moisture resistance. ing. Therefore, subsequent attempts were made to improve liquid crystal materials, and chemically stable general formula

A biphenyl-based liquid crystal material represented by the formula: (R is an alkyl group or an alkoxy group) was created. International Business Machines' Duy is

In the structure of [Formula], R is C ₈ H ₁₇ , C ₉ H ₁₀ , C ₁₀ H ₂₁ , C ₁₁ H ₂₃ , C ₆ H ₁₇ O,
A report was published in "The _Physics and Chemistry" published by Plenum Publishers that a three-component liquid crystal mixture selected from the group of _C9H19O liquid crystal materials is optimal for use in thermal writing liquid crystal light valves.・
Of Liquid Crystal Devices”
It is presented on pages 219 to 239. In addition, Thomson SA's Dupore is anal and
On pages 131 to 138 of Volume 3 of De Huisique (published in 1978),

In the structure of [Formula], R is C ₈ H ₁₇ , C ₉ H ₁₉ , C ₃ H ₇ O, C ₈ H ₁₇ O,
A mixed liquid crystal consisting of components selected from a group of liquid crystal substances C ₈ H ₁₇ COO, C ₉ H ₁₉ COO is compared, and R is C ₈ H ₁₇ , C ₉ H ₁₉ , C ₉ H ₁₉ COO. It has been reported that a three-component mixed liquid crystal is optimal for use in thermal writing liquid crystal light valves. In this way, improvements have been made in liquid crystal materials, and the shortcomings such as short lifespan and low reliability, which were the case with Schipf's base-based liquid crystals, have been overcome. However, all of the known mixed liquid crystals as described above are unsatisfactory, particularly in terms of liquid crystal phase temperature range. For example, as recommended by Dewey mentioned above,

[Formula] and

Even in the mixed liquid crystal with [Formula], the crystal-liquid crystal transition temperature Tm is approximately 120℃, and the above-mentioned

【formula】

【formula】

Even in the mixed liquid crystal consisting of the three components of [Formula], Tm is 8°C.
A liquid crystal light valve using such a mixed liquid crystal has a temperature below the Tm of the liquid crystal composition during operation or storage.
In other words, when the temperature drops below about 10 degrees Celsius, the liquid crystal composition crystallizes and becomes inoperable, and even after the temperature recovers, defects occur in the alignment of liquid crystal molecules due to the history of crystallization, resulting in the inconvenience of deteriorating the display image quality. arise. It is practically inconvenient that the lower limit of storage temperature is limited to about 10°C, and it is well known that about -10°C is required. The reality is that a satisfactory liquid crystal light valve cannot be obtained by using existing mixed liquid crystals. However, the inventors of the present invention have investigated in detail the relationship between the transition temperature of liquid crystal compositions and display performance, and have conducted experimental studies on a number of liquid crystal compositions. The present invention was achieved by discovering a liquid crystal composition that can realize a high-performance device. (3) Object of the invention An object of the invention is to provide a liquid crystal composition for a thermal writing liquid crystal element having excellent performance. (4) Structure of the Invention The liquid crystal composition for a thermal writing liquid crystal element of the present invention is used for a thermal writing liquid crystal element in which information is written by partially applying heat to a liquid crystal material. , as the main component, (a) chemical formula Liquid crystal compound (b) chemical formula represented by Liquid crystal compound (c) represented by chemical formula Liquid crystal compound represented by and chemical formula One or both of the liquid crystal compounds represented by (d) chemical formula Liquid crystal compound represented by and chemical formula It is characterized by containing one or both of the following liquid crystal compounds. (5) Examples The present invention will be described in detail below with reference to Examples. Figure 1 is a chemical formula Substance represented by (hereinafter referred to as 8BP) and chemical formula Substance represented by (hereinafter referred to as 10BP) and chemical formula A mixed liquid crystal (hereinafter referred to as NSPB) made by mixing the substance represented by (hereinafter referred to as 10OBP) in a ratio of 59.1:32.1:8.8 by weight, and then the chemical formula FIG. 2 is a diagram showing the results of measuring the phase transition temperature of mixed liquid crystals prepared by mixing substances represented by (hereinafter referred to as 9EBP) in various proportions. In Figure 1, I, N,
S and C indicate regions where an isotropic liquid crystal phase, a nematic liquid crystal phase, a smectic liquid crystal phase, and a solid phase appear, respectively. As is clear from FIG. 1, the mixed liquid crystal containing 9EBP not only has an advantageous increase in Tc, but also has the favorable characteristic that the nematic liquid crystal phase does not spread. Furthermore, Tm is 9EBP
In a mixed liquid crystal with a mixing ratio of about 45% by weight or less, the temperature is sufficiently low as 0°C or less. Thus, preferably about 45% by weight or less
The mixed liquid crystal containing 9EBP has an extremely wide smectic liquid crystal phase temperature range and a sufficiently low Tm. For example, a mixed liquid crystal consisting of 25% by weight of 9EBP and 75% by weight of NSPB (hereinafter
NSPZ) has an extremely low Tm of -25°C.
Liquid crystal light valves using NSPZ are stored at -10
There is no problem even at ℃. Also, the Tc of NSPZ is
The nematic phase temperature range is 55℃ and 3.5℃, both of which are optimal for writing when used in liquid crystal light valves. That is, as an example, NSPZ
When an image written by irradiating a liquid crystal light valve with an output power of 300 mW for 1 μs per point with an argon laser beam of 300 mW was projected onto a screen with a gain of 6.4 using a xenon lamp with a light power of 1 kW, the brightness was A contrast of 9:1 was obtained at 100 ft-L. This is an excellent display performance compared to a conventional liquid crystal light valve using a liquid crystal material, which has a contrast of 7:1 under the same writing conditions.
In addition, it is not limited to NSPZ, but 9EBP and
Extremely excellent performance similar to that of NSPZ was observed in a number of mixed liquid crystals with different mixing ratios of NSPB. Figure 2 shows 8BP, 10BP,
12OBP eutectic mixture “NSPC”, 8BP, 10OBP,
Eutectic mixture of 12OBP “NSPD”, 8BP, 10BP,
Tm of eutectic mixture "NSPE" of 10OB, 12OBP,
It is a figure showing Tc. As shown in Figure 2, “NSPB”
"NSPC" and "NSPE" have a lower Tm of 0℃ or less compared to "NSPD", and the Tm is also in the range of 45 to 48℃.
It is a mixed smectic liquid crystal with a wide temperature range.
All eutectic mixtures that do not contain 8BP have a Tm of 10
The temperature was high, exceeding ℃, which was inconvenient. in this way,
A mixed liquid crystal containing 8BP, 10BP, and one or both of 10OBP and 12OBP has a wide smectic phase temperature range and a low Tm. Furthermore, as shown in FIG. 1, the phase transition temperature shows a favorable change by mixing 9EBP. The example in Figure 1 is an example of a mixed liquid crystal of "9EBP" and "NSPB", but the same phase diagram as in Figure 1 can also be obtained for a mixed liquid crystal of "9EBP" and "NSPC" or "NSPE". is,
Chemical formula instead of "9EBP" Even if we use the substance "8EBP" represented by
The results were similar even when both "9EBP" and "8EBP" were used. In the above, we will take as an example the case where the liquid crystal light valve is used in a projection type display device in which an image is written by irradiating the liquid crystal cell with a laser beam, and the written image is enlarged and projected using a separate optical system for viewing. Although the invention has been described, it goes without saying that the liquid crystal composition of the present invention has excellent performance when thermally written by other means or when used as a direct-view display element, a memory element, or other elements. (6) Effects of the Invention As explained above, according to the present invention, a liquid crystal composition for a thermal writing liquid crystal element having a wide liquid crystal phase temperature range and excellent performance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the mixing ratio of mixed liquid crystals and the phase transition temperature for explaining the present invention,
I, N, S, and C in the figure are isotropic liquid phases, respectively.
It shows the regions where nematic liquid crystal phase, smectic liquid crystal phase, and solid phase appear. FIG. 2 is a diagram showing the liquid crystal-isotropic liquid phase transition temperature Tc and the crystal-liquid crystal phase transition temperature Tm of the mixed liquid crystal.

Claims (1)

[Claims] 1. As a main component: (a) a chemical formula; Liquid crystal compound (b) chemical formula represented by Liquid crystal compound (c) represented by chemical formula Liquid crystal compound represented by and chemical formula One or both of the liquid crystal compounds represented by (d) chemical formula Liquid crystal compound represented by and chemical formula A liquid crystal composition for a thermal writing liquid crystal element, characterized in that it contains one or both of the following liquid crystal compounds: