JPH0564998B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a liquid crystal composition for use in a thermal writing liquid crystal element that utilizes the thermo-optic effect of liquid crystal. [Prior art] 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. Direct-view display elements that write images once cooled and are viewed directly; light valve elements that are used for projection-type displays that project written images for viewing; written information is transmitted electrically and optically. It is a recording element etc. in a readable format. In addition, there are several known methods for writing information, such as irradiating a laser beam to cause a temperature rise in the irradiated area, and using Joule heat generation in a resistor to cause a temperature rise. It is being 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 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. In addition, 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 orientational order of liquid crystal molecules, resulting in a 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.
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 formulas such as

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 ₁₉ , C ₁₀ H ₂₁ , C ₁₁ H ₂₃ , C ₈ H ₁₇ O,
A report was published in ``The Physics and Chemistry'' published by Plenal Publishers that a three-component liquid crystal mixture selected from the group of C ₉ H ₁₉ O liquid crystal materials is optimal for use in thermal writing liquid crystal light valves.・
Of Liquid Crystal Devices”
Published on pages 219 to 239. In addition, Thomson SA's Dubois offers 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. [Problems to be Solved by the Invention] In this way, improvements have been made in liquid crystal materials, and the shortcomings such as short life and low reliability of early Schipf base 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,
Recommended by Duy, mentioned above.

[Formula] and

The crystal-liquid crystal transition temperature Tm is approximately 12°C even in the mixed liquid crystal with [Formula], and the above-mentioned Even in a mixed liquid crystal consisting of three components, Tm is 8°C.
It is. Liquid crystal light valves using such mixed liquid crystals do not contain the liquid crystal composition during operation or storage.
Below Tm, that is, below about 10 degrees Celsius, the liquid crystal composition crystallizes and becomes inoperable, and even after the temperature recovers, crystallization causes defects in the alignment of liquid crystal molecules, reducing display image quality. This inconvenience arises. 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. An object of the present invention is to provide a liquid crystal composition for a thermal writing liquid crystal element having excellent performance. [Means for solving the problems] That is, the present invention has the general formula: ( _R1 represents a straight chain alkyl group having 8 to 12 carbon atoms); and at least one compound represented by the general formula: ( _R2 represents a linear alkoxy group having 8 to 10 carbon atoms); and at least one compound represented by the general formula: (R ₃ represents a straight-chain alkyl group or a straight-chain alkoxy group having 8 to 12 carbon atoms) and at least one of the compounds shown in Table 7. This is a liquid crystal composition for writing liquid crystal elements. The liquid crystal composition for a thermal writing liquid crystal element of the present invention is used in a thermal writing liquid crystal element in which information is written by partially applying heat to the liquid crystal composition. In addition, the liquid crystal composition of the present invention includes a mixed liquid crystal consisting only of the compositions represented by the above-mentioned general formulas (), (), and (), as well as a mixed liquid crystal containing these as main components, and liquid crystal compositions having other structures. There is no problem even if it contains a small amount of. Examples of liquid crystal compositions having other structures include compositions represented by the following chemical formula. Here, R represents an alkyl group or alkoxy. [Function] By adopting the above-mentioned composition, the mixed liquid crystal 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 can be used as a thermal writing liquid crystal. When used in devices, it has the advantage that written information can be erased with a low voltage. [Examples] The present invention will be described in detail below with reference to Examples. Figure 1 is a chemical formula (hereinafter referred to as 8BP), (hereinafter referred to as 10BP), (hereinafter referred to as 10BP), (hereinafter referred to as 8BTPE), (hereinafter referred to as 10BTPE) mixed liquid crystal (hereinafter referred to as NSP43B) in a weight ratio of 37.0:19.9:7.1:18.0:18.0 with 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 10X) 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 the figure, the mixed liquid crystal containing 10X not only has an advantageous increase in Tc, but also has the favorable characteristic that the nematic liquid crystal phase does not spread significantly. Furthermore, Tm is sufficiently low at 0° C. or less for mixed liquid crystals in which the mixing ratio of 10X is about 20% by weight or less. Thus, the mixed liquid crystal containing preferably about 20 weight percent or less of 10X has an extremely wide smectic liquidus temperature range and a sufficiently low Tm. For example, 9 weight percent 10X and 91 weight percent NSP43B
A mixed liquid crystal (hereinafter referred to as NSP40F) consisting of
Tm is extremely low at -25.3℃, and liquid crystal light valves using NSP40F do not cause any problems even at storage temperatures of -10℃. NSP40F has a Tc of 63.2°C and a nematic phase temperature range of 6.1°C, making it suitable for writing when used in liquid crystal light valves. In other words, as an example, the increase was written by irradiating a liquid crystal light valve using NSP40F with an argon laser beam of 300 mW for 10 μsec per point.
Gain 6.4 using xenon lamp with 1KW light intensity
When projected onto a screen, the brightness is 100ft.
A contrast of 10:1 was obtained at t-L, and the image could be erased by applying a voltage of 90V. This is a contrast of 7:1 under the same writing conditions for a liquid crystal light valve using a conventional liquid crystal composition.
1, which is an excellent display performance compared to an erase voltage of 100V. It should be noted that the same excellent performance as NSP40F was observed not only in NSP40F but also in many mixed liquid crystals with different mixing ratios of 10X and NSP43B. Also, chemical formula instead of 10X (n = 8, 9, 11, 12, hereinafter referred to as 8X, 9X, 11X, 12X), or two or three substances selected from these 8X, 9X, 11X, 12X A similar effect was observed when the substances were used together. Also 8BP, 10BP, 10BP and formula instead of NSP43B (hereinafter referred to as 12OBP), 8BTPE, 10BTPE and the chemical formula A similar effect was observed when a mixed liquid crystal consisting of at least one of the substances represented by was used. Examples of these effective mixed liquid phases and their Tc are
Shown in the table. The Tm of all these mixed liquid crystals is −10
below ℃. Note that ( ) in Table 1 is a mole percentage indicating the mixing ratio.

【table】

【table】

[Table] In this example, the above general formula (), general formula ()
Although examples of mixed liquid crystals consisting only of substances represented by the general formula (2) and (2) have been described, excellent performance has also been observed in cases where other liquid crystal substances are added to these liquid crystals. Furthermore, in the above example, 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 explained by taking examples, the present invention may be applied to thermal writing by other means,
The liquid crystal composition of the present invention also has excellent performance when used as a direct-view display element, a memory element, or other elements. [Effects of the Invention] As explained above, according to the present invention, a liquid crystal composition for a thermally written liquid crystal element can be obtained which has a wide liquid crystal phase temperature range, requires only a low applied voltage, and has excellent performance.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the mixing ratio of mixed liquid crystals and phase transition temperature according to an embodiment of the present invention.

Claims (1)

[Claims] 1. General formula: (R ₁ represents a straight chain alkyl group having 8 to 12 carbon atoms); and at least one compound represented by the general formula: ( _R2 represents a linear alkoxy group having 8 to 10 carbon atoms); and at least one compound represented by the general formula: (R ₃ represents a linear alkyl group or a linear alkoxy group having 8 to 12 carbon atoms) as a main component. Liquid crystal composition for devices.