JPS6353238B2 - - 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. It is a memory element of the format, 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. Initially, a general formula was used for thermal writing liquid crystal light valves. A composition comprising a so-called Schiff base-based liquid crystal compound represented by the following was used. This is because no liquid crystal composition other than Schiff base-based compositions 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. Such Schiff base-based liquid crystal compositions are reported by Taylor et al. of Bell Laboratories in Volume 45, No. 10 of the Journal of Abrid Physics. However, Schiff base-based liquid crystal compounds tend to undergo hydrolysis;
Therefore, it is widely known that thermal writing liquid crystal devices using this type of liquid crystal composition have short lifespans and lack reliability, especially in terms of moisture resistance. Therefore, subsequent attempts were made to improve liquid crystal compounds, and chemically stable general formula

A biphenyl liquid crystal compound 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 ₁₉ , C ₁₀ H ₂₁ , C ₁₁ H ₂₃ , C ₈ H ₁₇ O,
Plenum Publishing Co. _, Ltd.'s ` <sub>`</sub> The Physics and Published on pages 219 to 239 of ``Chemistry of Liquid Crystal Devices''. In addition, Thomson SA's Dubois is the third volume of Anal de Fuisique (published in 1978, No. 131).
From page 138,

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, C ₈ H ₁₇ COO,
By comparing liquid crystal compositions consisting of components selected from a group of liquid crystal compounds that are C ₉ H ₁₉ COO, it was determined that R is
It has been reported that a three-component liquid crystal composition consisting of C ₈ H ₁₇ , C ₉ H ₁₉ , and C ₉ H ₁₉ COO is optimal for use in thermal writing liquid crystal light valves. In this way, improvements have been made in liquid crystal compounds, and the shortcomings such as short life and low reliability of early Schipf base liquid crystals have been overcome. However, all of the known liquid crystal materials mentioned 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 liquid crystal composition with [formula], the crystal-liquid crystal transition temperature Tm is about 12℃, and the above-mentioned

【formula】

【formula】

The Tm of the liquid crystal composition consisting of the three components of the formula is also 8°C. A liquid crystal light valve using such a liquid crystal composition has a Tm of the liquid crystal composition during operation or storage.
In other words, when the temperature drops below about 10℃, 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, degrading the display image quality. This will cause inconvenience. 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 liquid crystal compositions. 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 numerous liquid crystal materials. The present invention was achieved by discovering a liquid crystal composition that realizes the device described above. (3) Object of the invention An object of the invention is to provide a liquid crystal composition for a calorific liquid crystal element having excellent performance. (4) Means for solving the problems The liquid crystal composition for thermal writing liquid crystal elements of the present invention is used in thermal writing liquid crystal elements in which information is written by partially applying heat to a liquid crystal material. chemical formula

[Formula] (R ₁ is a linear alkoxy group with n ₁ = 8, 9, or 10 carbon atoms) One or more substances and the chemical formula

[Formula] (R ₂ is a straight-chain alkyl group with n ₂ = 8 or 9 carbon atoms) as a main component, and in addition to the above main components, the chemical formula

[Formula] (R ₃ is a linear alkyl group or a linear alkoxy group with carbon number n ₃ = 8, 9, 10, 11, 12) containing one or more substances as a main component. It is distinctive in that it is By adopting the above-mentioned composition, the liquid crystal composition of the present invention has an extremely wide smectic liquid crystal phase temperature range, and since the main component liquid crystal has large dielectric anisotropy, it is suitable for thermal writing liquid crystal elements. When used, it has the advantage that written information can be erased with a low voltage. (5) Examples The present invention will be described in detail below with reference to Examples. The diagram is a chemical formula Substance represented by (hereinafter referred to as OBTPE) and chemical formula

A liquid crystal composition (hereinafter referred to as NSPX) prepared by mixing the substance represented by [Formula] (hereinafter referred to as 9EBP) in equal weight ratios.
, the chemical formula

[Formula] (hereinafter referred to as 8BP),

[Formula] (hereinafter referred to as 10BP ),

[Formula] (hereinafter referred to as 10OBP),

Created by mixing four substances represented by the formula (hereinafter referred to as 12OBP) in various proportions with a liquid crystal composition (hereinafter referred to as NSP36A), which is a mixture of 4 types of substances represented by the formula (hereinafter referred to as 12OBP) at a weight ratio of 58.6:31.4:8.2:1.8. FIG. 3 is a diagram showing the results of measuring the phase transition temperature of a mixed liquid crystal. In the figure, 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 the figure, the liquid crystal composition containing NSPX is
Not only is Tc increased, which is advantageous, but also the nematic liquid crystal phase does not spread, which is a desirable feature. Furthermore, Tm has a mixing ratio of NSPX of 75
In a liquid crystal composition of about weight percent or less, the temperature is sufficiently low as 0° C. or less. In this way, preferably
A liquid crystal composition containing about 75 weight percent or less of NSPX has an extremely wide smectic liquid crystal phase temperature range and a sufficiently low Tm. For example, 45 weight percent NSPX and 55 weight percent NSPX
The Tm of the liquid crystal composition consisting of NSP36A (hereinafter referred to as NSP37B) is extremely low at -32.7°C.
Liquid crystal light valves using this method do not cause any problems even at storage temperatures of -10°C. Also, the Tc of NSP37B is
57.3℃, nematic phase temperature range is 3.2℃,
Both are ideal for writing when used in liquid crystal light valves. That is, as an example
When an image written on a liquid crystal light valve using NSP37B by irradiating an argon laser beam with an output light intensity of 300 mW for 1 μs per point was projected onto a screen with a gain of 6.4 using a xenon lamp with a light intensity of 1 kW. A contrast of 10:1 was obtained at a brightness of 100 ft-L. Also, erasing this image is at 90V.
This could be done by applying a voltage of This is superior display performance compared to a liquid crystal light valve using a conventional liquid crystal composition, which has a contrast of 7:1 under the same writing conditions and an erase voltage of 100V. In addition, it is not limited to NSP37B,
Extremely excellent performance similar to that of NSP37B was observed in many liquid crystal compositions with different mixing ratios of NSPX and NSP36A. Also instead of OBTPE the chemical formula (hereinafter referred to as NBTPE), or When a substance represented by (hereinafter referred to as DBTPE) is used, or the chemical formula is used instead of 9EBP

When using the substance represented by [Formula] (hereinafter referred to as 8EBP),
Furthermore, similar effects were observed when one or more of three substances selected from OBTPE, NBTPE, and DBTPE were used in combination with one or both of 8EBP and 9EBP. Also, instead of NSP36A, 8BP, 10BP, 10OBP, 12OBP and chemical formula

[Formula] CN,

【formula】

【formula】

【formula】

【formula】

A similar effect was observed when a liquid crystal composition consisting of a substance selected from among the substances represented by the formula or a plurality of substances selected from them was used. Examples of these effective liquid crystal compositions and their Tc are shown in the table.
All of these liquid crystal compositions have a Tm of -10°C or lower. In the table, the numbers in parentheses are mole percentages indicating the mixing ratio.

[Table] In addition, the chemical formula

Substances and chemical formulas represented by [formula]

Represented by [formula] substances and chemical formulas

Although we have described an example of a liquid crystal composition consisting only of the substance represented by the formula, it is sufficient to use a liquid crystal composition containing these substances as the main components, and there is no problem even if it contains a small amount of liquid crystal compounds with other structures. Needless to say. Examples of liquid crystal compounds having other structures include substances represented by the following chemical formulas. Here, R represents an alkyl group or an alkoxy group. The above example uses a liquid crystal light valve for 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 present invention has been described, it goes without saying that the liquid crystal composition of the present invention has excellent performance when thermal writing is performed by other means or when used as a direct-view display element, a memory element, or other elements. In addition, the general formula

The effect of containing the compound represented by [Formula] is, for example,
To explain a specific example where R ₂ has 9 carbon atoms, as shown in the drawing, the smectic phase temperature range is the widest, but NSPX containing the above compound has a carbon number of 40~
This is the case where the content is 50%, and the Tc at that time is approximately 60
It is ℃. However, in a composition that does not contain the above compound, the compound OBTPE is added to 30% of the composition.
%, the smectic phase temperature range is widest, and Tc in that case is about 50°C.
In practice, it is desirable to have a wide smectic phase temperature range, and as mentioned above, the optimal value for Tc varies depending on the device specifications, but in general, the higher the Tc, the higher the upper limit of the device's operable temperature. be. The effect of containing the above-mentioned compound in this manner is particularly effective in raising the upper limit of the operable temperature of the element and widening the temperature range. (6) Effects of the Invention As explained above, according to the present invention, it is possible to obtain a liquid crystal composition for a thermal writing liquid crystal element that has a wide liquid crystal phase temperature range, requires only a low applied voltage, and has excellent performance.

[Brief explanation of the drawing]

The figure is a diagram showing the relationship between the mixing ratio of the liquid crystal composition and the phase transition temperature for explaining the present invention, and I, N, S, and C in the figure are an isotropic liquid crystal phase and a nematic liquid crystal phase, respectively. , indicates the region where the smectic liquid crystal phase and solid phase appear.

Claims (1)

[Scope of Claims] 1 Containing 40 to 70 weight percent of one or more substances represented by the chemical formula [Formula] (R ₁ is a linear alkoxy group with n ₁ = 8, 9, or 10 carbon atoms); A substance represented by the chemical formula [Formula] (R ₂ is a straight chain alkyl group with n ₂ = 9 carbon atoms) is
71% by weight or less, and contains 75% by weight or less of the above two substances in total, and in addition to the above components, a compound with the chemical formula [Formula] (R ₃ is a straight chain carbon number n ₃ = 8, 10, 25 to 91 in total of one or more substances represented by (alkyl group), or one or more substances represented by chemical formula [formula] and chemical formula [formula]
A liquid crystal composition for a thermal writing liquid crystal element, characterized in that it contains % by weight.