Abstract:
Compounds of the general formula C m  H 2m+2 , wherein m signifies 10 to 35, are added to liquid crystalline nematic substances to shorten the switching time of the substances when used in opto-electronic components.

Description:
This application is a continuation of application Ser. No. 810,467, filed Dec. 18, 1985, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
     The invention relates to switching-time-shortening dopants for nematic mixtures, which can be utilized in opto-electronic components (displays) for the electronically controlled modulation of transmitted or reflected light, as well as for the rendition of numbers, symbols and images. 
     Nematic crystalline liquids can be used in opto-electronic components (displays) G. Meiner, E. Sackmann, J. G. Grabmaier: Applications of Liquid Crystals, Berlin, New York, London 1975. 
     In order to be suitable for displays, liquid crystals have to fulfill a multitude of requirements, among which there are also included very short switching times which, among other, can also be attained by low viscosities. As viscosity-reducing admixtures dialkylbiphenyl derivatives have become known up to now. J. Krause, R. Steinstraesser, L. Pohl, F. del Pino, G. Weber, DE-OS No. 2,548,360. The disadvantages in the utilization of the biphenyl derivatives are the lowering of the clarification points which have to be increased again by adding other substances. Furthermore, the admixture of approximately 25 weight parts of biphenyl derivatives is required in order to reduce the viscosity by one half, whereby the clarification point is lowered by almost 20° C. 
     The object of the invention is to provide liquid crystalline mixtures of short switching times for opto-electronic components. 
     The object of the invention are substances which reduce the rotational viscosity of nematic crystalline liquids and thus lead to fast switching times and which, furthermore, excell in a high effectiveness and are simple to produce. 
     SUMMARY OF THE INVENTION 
     It has been found that by the admixture of 0.5 to 30% of one or several compounds of the general formula 
     
         C.sub.m H.sub.2m+2                                         (I) 
    
     wherein m=10 to 35, the electro-optical switching time of liquid crystalline nematic substances is considerably reduced. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereonafter, the invention will be explained in greater detail by means of examples. 
     EXAMPLE 1 
     The subsequently mentioned mixtures are used in an opto-electronic cell of the Schadt-Helfrich type (twisted nematic structure, TNP cell). The cell consists of two glass plates which, by means of distance spacers, are fixed at a distance of 7 to 25 μm and which are provided on the inside with stannic dioxide. Furthermore, the inside is pre-treated according to conventional methods such that the liquid crystal located between the plates orients itself parallel to the plates, the preferred direction on the two plates, however, including an angle of 90°, so that a twisted nematic structure results, which is arranged between the crossed or parallel polarizers. 
     By turning the electrical field on and off, strong changes of the light-transmitting capability of the cell are attained. 
     Into the Schadt-Helfrich cell mixtures of the following compositions are introduced: 
     Basic component: 
     4-n-pentyl-cyclohexanecarboxylic acid-4&#39;-cyanophenylester 
     Dopant: 
     n-eicosane (n-C 20  H 42 ) 
     The characteristics of mixtures of the basic component with the dopant are summarized in the following table (test frequency 500 Hz, test temperature 42.5° C., thickness of layer 10 μm). 
     The symbols in the tables have the following meanings: 
     U o  --voltage for an intensity change of 10% 
     t E50  --time from applying the electrical field until an intensity change of 50% is attained 
     t A50  --time from turning off the electrical field until an intensity change of 50% is attained 
     γ--rotational viscosity 
     υNI--clarification temperature 
     υKN--transformation temperature, crystalline-nematic 
     ΔE E  --activation energy for the switching-on times 
     
         ______________________________________mol % Dopant       0       2          8     10______________________________________U.sub.o /V  1.10    1.12       1.17  1.18t.sub.E50 (U = 2U.sub.o)/ms       169     122        69    43t.sub.E50 (U = 5V)/ms       26      19         12    9t.sub.A50 /ms       75      47         19    11γ/cP  82      41         15    11νNI/°C.       79      75-76      65-68 61-65νKN/°C.       47      46.5       46    45.5______________________________________ 
    
     The electro-optical Schadt-Helfrich type cell (TNP-cell) described in Example 1 is operated in the further Examples 2 to 7 with basic substance mixtures, to each of which 4% of a compound in the general formula (I) has been added. (Measurement of the switching times at twice the threshold voltage U o ) 
     In the examples 2-6 the basic substance mixture A consists of 
     
         ______________________________________Mol %______________________________________21.2   ##STR1##28.2   ##STR2##21.2   ##STR3##8.1   ##STR4##3.7   ##STR5##12.0   ##STR6##5.6   ##STR7##______________________________________ 
    
     EXAMPLE 2 
     
         ______________________________________              Mixture A + 4 weight %              C.sub.24 H.sub.50Mixture A          ν.sub.NI = 44° C., ΔE.sub.E =ν.sub.NI = 46° C., ΔE.sub.E = 2.29 kJMol.sup.-1              27.7 kJMol.sup.-1ν/°C. U.sub.o /V         t.sub.E50 /ms                  t.sub.A50 /ms                        U.sub.o /V                               t.sub.E50 /ms                                     t.sub.A50 /ms______________________________________20    1.34    156      68    1.24   127   5125    1.23    133      50    1.11   86    4430    1.17    106      41    1.01   79    3535    1.06    90       36    0.93   55    3040    0.98    80       32    0.87   48    2745    0.93    72       31    0.80   45    2450    0.88    67       30    0.75   41    22______________________________________Mixture A + 4 weight % C.sub.20 H.sub.42ν.sub.NI = 44° C.; ΔE.sub.E = 10.7 kJmol.sup.-1ν/°C.    U.sub.o /V    t.sub.E50 /ms                          t.sub.A50 /ms______________________________________20       1.34          142     5025       1.19          121     4430       1.05          114     4235       0.95          103     3840       0.85          100     3545       0.77           96     3250       0.69           92     29______________________________________ 
    
     EXAMPLE 3 
     
         ______________________________________Mixture A + 10 mol % ##STR8##                     (B)Mixture A and 10 mol % Bυ.sub.NI = 56° C.: ΔE.sub.E = 10.4 kJmol.sup.-1υ/°C.    U.sub.o /V   t.sub.E50 /ms                         t.sub.A50 /ms______________________________________20       1.30         140     5925       1.22         130     4230       1.15         107     3435       1.09         98      3140       1.05         89      2845       0.97         82      2650       0.92         74      25______________________________________Mixture A + 10 mol % B + 4 weight % C.sub.24 H.sub.50υ.sub.NI = 47° C.: ΔE.sub.E = 9.4 kJmol.sup.-1υ/°C.    U.sub.o /V   t.sub.E50 /ms                         t.sub.A50 /ms______________________________________20       1.23         118     4325       1.17         110     3630       1.04         103     3135       0.98         97      2740       0.94         92      2445       0.89         87      2150       0.85         85      18______________________________________ 
    
     EXAMPLE 4 
     
         ______________________________________Mixture A + 10 mol % B + 10 mol % C ##STR9##                     (C)              Mixture A + 10 mol % B +              10 mol % C + 4 weight %Mixture A + 10 mol % B +              C.sub.24 H.sub.5010 mol % C         υ.sub.NI = 60° C.: ΔE.sub.E =              7.2υ.sub.NI = 67° C.: ΔE.sub.E = 10.0              kJmol.sup.-1υ/°C. U.sub.o /V         t.sub.E50 /ms                 t.sub.A50 /ms                        U.sub.o /V                              t.sub.E50 /ms                                     t.sub.A50 /ms______________________________________20    2.01    168     116    2.14  165    12225    1.65    162     98     1.73  160    9730    1.52    155     86     1.49  151    7735    1.43    146     75     1.33  142    6540    1.33    138     67     1.20  135    5545    1.23    130     61     1.09  125    4650    1.16    122     55     0.98  100    38______________________________________ 
    
     EXAMPLE 5 
     
         ______________________________________Mixture A + 10 mol % B + 10 mol % D ##STR10##                    (D)              Mixture A + 10 mol % B +              10 mol % D + 4 weight %Mixture A + 10 mol % B +              C.sub.24 H.sub.5010 mol % D         υ.sub.NI = 65° C.; ΔE.sub.E =              16.6υ.sub.NI = 74° C.: ΔE.sub.E = 19.4              kJmol.sup.-1υ/°C. U.sub.o /V          t.sub.E50 /ms                  t.sub.A50 /ms                         U.sub.o /V                               t.sub.E50 /ms                                     t.sub.A50 /ms______________________________________25                            1.68  99    5030    1.60     115     64     1.50  83    3835    1.49     101     51     1.40  72    3040    1.42     90      41     1.32  66    2445    1.35     86      33     1.25  60    2150    1.29     71      28     1.18  55    20______________________________________ 
    
     EXAMPLE 6 
     
         ______________________________________Mixture A + 10 mol % B + 10 mol % C + 10 mol % D              Mixture A + 10 mol % B +              C + 10 mol % D + 4Mixture A + 10 mol % B +              weight % C.sub.24 H.sub.5010 mol % C + 10 mol % D              ν.sub.NI = 65° C.; ΔE.sub.E =ν.sub.NI = 77° C.; ΔE.sub.E = 12.5 kJmol.sup.-1              10.8 kJmol.sup.-1ν/°C. U.sub.o /V         t.sub.E50 /ms                  t.sub.A50 /ms                        U.sub.o /V                               t.sub.E50 /ms                                     t.sub.A50 /ms______________________________________20    2.27    125      80    1.78   72    4325    1.99    116      69    1.63   64    3730    1.78    108      59    1.50   59    3235    1.58    101      51    1.38   55    2840    1.46     94      42    1.27   52    2645    1.36     87      36    1.20   48    2350    1.28     82      31    1.12   46    21______________________________________ 
    
     EXAMPLE 7 
     In example 7 the basic substance mixture consists of a biphenyl mixture E 5 (BDH) 
     
         ______________________________________              Mixture E 5 + 4 weight %              C.sub.20 H.sub.42Mixture E 5        ν.sub.NI = 48° C.; ΔE.sub.E =ν.sub.NI = 50° C.; ΔE.sub.E = 38.1 kJmol.sup.-1              26.1 kJmol.sup.-1ν/°C. U.sub.o /V         t.sub.E50 /ms                  t.sub.A50 /ms                        U.sub.o /V                               t.sub.E50 /ms                                     t.sub.A50 /ms______________________________________20    1.63    250      126   1.44   200   8825    1.46    206      92    1.38   170   7530    1.30    167      73    1.34   150   6735    1.18    136      55    1.30   136   6140    1.07     99      48    1.26   126   5545    0.98     80      45    1.21   117   4950    0.90     62      41    1.17   105   45______________________________________Mixture E 5 + 4 weight % C.sub.24 H.sub.50ν.sub.NI = 49° C.; ΔE.sub.E = 23.8 kJmol.sup.-1ν/°C.    U.sub.o /V    t.sub.E50 /ms                          t.sub.A50 /ms______________________________________20       1.57          145     5425       1.40          100     4730       1.29          75      3635       1.23          66      3340       1.17          59      3045       1.12          55      2750       1.07          52      26______________________________________