CH642675A5 - Nematic liquid-crystal mixtures - Google Patents

Description

The present invention relates to nematic liquid crystal mixtures and compounds. They can be used in liquid crystal display units.

With the increasing spread of display devices based on the electro-optical effects of nematic liquid crystals, the type of control changed more and more from conventional, static control to multiplex control.

The present invention provides colorless, semi-stable nematic liquid crystal mixtures and compounds with positive dielectric anisotropy and low viscosity, which are suitable for multiplex control.

The present invention relates to nematic liquid-crystal mixtures comprising a) at least one compound of the formula (I)

where X3 and Y are as defined above and X5 is alkyl, alkoxy or acyloxy.

In order to use nematic liquid crystal materials in liquid crystal display devices, it is not sufficient if the compounds have a wide temperature range for the liquid crystal phase and are stable, but they must have other special properties. The response time must be short, the viewing angle of the display device must be large, and the changes in properties with temperature must be small, etc. All of these properties must be present in the mixtures and compounds mentioned in order to enable uncomplicated production of the display units . 40 The use of these display units in a wide variety of devices, such as electronic computers etc., necessitates multiplex control.

In conventional liquid crystal display devices, static control has hitherto been customary, in which all Zif-45 remote from the display unit are controlled simultaneously, due to the long response time and the change in properties with temperature.

The present invention now describes new nematic liquid crystal mixtures for multiplex control of such multi-digit display units, which control can be carried out with low voltages. The main components of these mixtures contain compounds of the formulas I-V, nematic liquid crystal compounds with cyclohexane ring and nematic liquid crystal compounds of the 55 cyano-biphenyl type.

When these nematic liquid crystal mixtures are used in display units, taking advantage of the field effect by applying a voltage to the liquid crystal cell, multi-digit liquid crystal display units for multi-6o plex control with excellent properties are obtained. In addition to these field effect display units, in which an electric field is applied to the crystal cell, the existing nematic liquid crystal mixtures can also be used in display units using the “guest 65 host” effect using pleochroic dyes.

642 675

The following tables show examples of liquid crystal compounds I-V of the present invention.

Compound I, II or III A (° C) B (° C)

Compound IV

C5Hll - @ ^ ©> -CN

A (° C) B (° C) 23 35

C3H7 "(®-COO- (0) -OC2H5

47

79

C6H13 "©> - <0> -CN

13

27th

C3H7H®-COO "<0> -OC4H9

42

72

, .C7H15- ©> -®-CN

29

42

C3H7- (E> -COO- <0 ^ OC5H11

39

69

c5Hir0-®- ©> -CN

48

67

C4H9 "(D" COO "C ^" OCH3

41

58

1! C6Hi3- ° - € M2> -cN

58

76

C4H9 "®" COO "<0)" OC2H5

36

76

mC7H15- ° "<0> '0-CN

54

75

C4H9_ {Ì) -COO- <© -OC3H7

33

60

CH3 "© -c ° 0- <g> -cN

120

-

C4H9 "<S) -COO- <0> -OC5H11

30th

66

,, C2H5- © -CO ° - © -èN

72

43

C4H9 "(H) -C00-O> -0C6H13

25th

70

C3H7- <0> -COO- © -CN

98

54

C5Hll- <®> -COO- © -OC5Hll

28

70

"C4h9 - ^ - COO - ^ - CN

67

42

c4H9-0-C ° O- <g> -CN

54

68

C5H11 "0>" COO "<0> _CN

61

56

C5Hll "(E)" COO "<0>" CN

25th

50

35 In the tables above, column A denotes the melting point and column B the clear point.

C5H11- © -C00-Ö> ~ C2H5

42

30th

The nematic liquid crystal compounds are produced by the following reactions:

40

.—. soci2 .—,

I, H and i ": CnH2n + 1- (H) -COOH> CnH2n ^ A ^)" 0001

CnH2n + l- (D-C0C: L

HO-0-OCmH2m + 1 (or HO-0-CN)

2m + l

CnH2n + l-®-C00-O-0CmH; (or CnIi2n + l- (E> -COO- | 0> -CN)

IV: CnH2n + l- <0> ^ 0> -Br g =

CuCN

Methyl 2-pyrrölidone

CnH2n + l »-CN

642675

V: C H

n 2n + l c Ho n 2n + l

-Q - Q-

SOCI.

COOH

C H, n 2n + l

-COC1

COC1

HO- <C)) - CN

"CnH2" + l- € H0 ° - <0> -CN

The following table shows examples of the new liquid crystal mixtures according to the invention.

mixture

CSH11

coo- «» -ocjh, x

C5H11

<E> -

° 4H9 "{D" COO "0>" OC «H

C6H13 "€ M3> -CN

-eoo ~ ö -cn c4h9-®-coo - @ - ° C2h

CS8ll- ° - © -0> -CN

13

C5H11

-cn

C5HXl- (D-COO- © -C2H!

C6H13

C5H11

<H) -

-CN COO-dFh-CN

CH3 ° - © -CO ° -0> -C3B7

CSH11 "0H0) -0> -CN

C3H7 "(Ë) -COOH0> -OC2H" = 4-9 * 0 -eoo

- ° C2H

C5HXl-0> - © -CN ch3-o - ^ - coo-0-c5h11

C3 H? - ^ P) -COO - ^> - CN

C4H9 "0" COO "© 'CN

Weight ratio%

45 55

35

50

15

40

45

15

10th

35

30th

10th

15

15 20

50

15 8

12

A B ti V.K ° C ° C 25 "C volt

-1 51

-10 55

-3 78

60

-8 58

32

28

30th

35

32

Table (continued)

mixture

Weight ratio%

C5Hir ©> -0-CN

45

C5Hll- ° - © -ö> -CN

20th

15

C4H9 "(®)" COO "©" "OCH3

18th

C6H13- ° -0> ^ 0> -CN.

34

C5Hll-0-O "CN

36

C5Hll- © - © - <0, -CN

12

C4B9 "®" C00 "O" 0C2H5

50

C2H5 "©" COO "0>" CN

15

C5Hll-0-CO ° -0-CN

35

C4H9-0-CO ° - © - ° C6H13

.50

C4B9 "(D" COO ~ @ "CN

30th

C3H7- <oil ~ COO ~ ö, ~ CN

5

C3 H? - ^ H ^ -COO - ^^ - CN

15

C3H7-®-CO ° - © - ° C5Hll

45

CH3 ° - © -COO- © -C3H7

20th

C4H9- © "COO" © "CN

15

C2H5 "©" COO "0" CN

10th

C5H1I "© - <O) -0-CN

10th

C4H9 "0" COOH © "OC3H7

35

C4H9-0-COO "O> - ° C5Hll

35

5

642 675 6

Table (continued)

Mixture Weight A B rill Vth -

relationship

% ° C ° C 25 ° C volts

C5Hll "©" 000 "0>" CN 10

C5Hll "®" C00 "@" CH 15

C5Hll "^) ~ C00 ~ ^^ ~ CN 30

C3H7 "®'COO" 0> "OC4H9 20

C5H11 ~ C ^ ~ C ^ ~ CN 30 -3 60 35 1.1

c2h5 - <()) - coo - <()) - cn 10

C5H11 -0-eoo -CK «.

10th

In the table above, r | (25 ° C) represents the viscosity of the cyanobiphenyl liquid crystal in a mixture.

Mixture at 25 ° C. The threshold voltage Vth is detected because the double refractive ratio in the Cy-

speaks the voltage, corresponding to 10% saturation contrast 30 clohexyl ester compounds is relatively small. Furthermore,

at the display device. An insulating spacer changes the properties due to the temperature at approx. 10 | i thickness between electrodes consisting of liquid crystal compounds present is relatively small, since they are two transparent conductive films, the liquid crystal a wide temperature range for the liquid crystal phase between the located two electrodes. Using the present nematic, thereby obtaining a display device. 35 liquid crystal mixtures in display units all speak

Each compound is mixed, heated and enough of these points are stirred for multiplex control until an isotropic liquid is obtained, the multi-digit units.

Mixture is produced. As phase transition temperature A In conventional mixtures, only two to three and B can be used at those temperatures at which points are controlled multiplex. When using the nematic liquid crystal mixtures present in the field during the temperature increase,

follow, after the mixture in the fekt display units has sufficient time, four or more digits can be

Cryostat stored from approx. - 40 ° C until solidification can be controlled plex.

had been. The viscosity is measured in a Rota- For liquid crystal mixtures with positive dielectric viscometer from Tokyo Keiki Kabushiki Kaisha. Anisotropy, such as that for nematic liquid crystals in helix. As can be seen in the tables above, the structure in display units and in liquid-crystal display-matical liquid crystal mixture of the present invention contains units using the “guest host effect” ver-cyclohexyl ester group. Compounds I and III and cyano-, it is necessary that external factors, such as ester group compounds V as main components. It is colorless water, air, light, heat etc. no negative influence and its viscosity is low. Furthermore, the fact that the nematic state can be controlled over a wide mix at low voltages and its temperature range in which the display units used make it particularly suitable for multiplexing is retained. To control such liquid crystal mixtures in multi-digit display devices. In particular, usually several liquid crystal properties, such as low viscosity and driving compounds having a suitable chemical structure, are mixed with low voltage as obtained by mixing the liquid crystal mixtures as used today with the cyanoester group compound 55, are usually those that were previously not known as the main compound. nente an azoxy liquid crystal of the formula

Furthermore, the mixture has the properties that the / ^ \ / ~~ \

Viscosity is low and the temperature range of nemati- R-flTjly-N = N- «~ j ^ -R '

see liquid crystal phase is large. The low viscosity - * —v—

has two main causes: The first 60 O

is that the ester-type liquid crystal containing Cy-, in which R and R 'represent alkyl or alkoxy, or clohexane ring itself has a remarkably lower viscosity Formula benzene ring. The other reason is that the low viscosity is maintained when the cyanobiphenyl-type liquid 65-n-sig crystal is mixed. It is also possible to circumvent the usual disadvantage of cyanobiphenyl liquid crystals, which is in a small viewing angle, in that R is alkyl or alkoxy etc.

642 675

Liquid crystal mixtures with azoxy liquid crystal as the main component have good properties. However, it is necessary to use a yellow filter to prevent the liquid crystal from decomposing because its absorption occurs in the visible range. Such liquid crystal display units are therefore colored yellow, which is undesirable in many cases.

On the other hand, liquid crystal mixtures with biphenyl liquid crystals as main components are stable against a wide variety of external factors and do not require an upstream yellow filter when used in display units. In these display units, however, there is the disadvantage that with multiplex control taking into account the change in temperature and the change in the viewing angle, the area becomes very small and is only approximately half as large as in liquid crystal mixtures based on azoxy liquid crystals as the main component. Although the working range can be expanded by approx. 10-20% by further addition to the mixture, the viscosity of the mixture is increased and the low-temperature properties become poor.

The present invention therefore furthermore relates to colorless liquid-crystal mixtures with good control properties, which are stable to a wide variety of external factors and which have a large nematic temperature range.

Such a liquid crystal mixture according to the present invention. e.g. obtained by mixing the following seven compounds in the proportions indicated.

4- (n-ethyl) -cyclohexylcarbon-

4'-cyanophenyl acid

4- (n-propyl) -cyclohexylcarbon-

4'-cyanophenyl acid

4- (n-pentyl) cyclohexylcarbon-

4'-cyanophenyl acid

4- (n-propyl) -cyclohexylcarbon-

4'-ethoxyphenyl acid

4- (n-butyl) cyclohexylcarbon-

4'-ethoxyphenyl acid

4- (n-pentyl) -cyclohexycarbon-

acid 4'-methoxyphenyl ester

4- (n-hexyl) -cyclohexylcarbon-

acid 4'-methoxyphenyl ester

0.85 g

(16.7%)

0.55 g

(10.8%)

0.68 g

(13.4%)

0.50 g

(9.8%)

0.98 g

(19.3%)

1.03 g

(20.3%)

0.49 g

(9.7%)

Vqn * voltage at 10% transmission when viewing the TN cell at an angle of 10 ° and applying the ON waveform at 0 ° C,

V0FF: voltage at 90% transmission when viewing the TN cell at an angle of 40 ° and applying the OFF waveform at 40 ° C.

Another liquid crystal mixture was obtained by mixing the following seven compounds:

io 4- (n-propyl) -cyclohexylcarbonate-4'-cyanophenyl ester 4- (n-pentyl) -cyclohexylcarbonate-4'-cyanophenyl ester 4- (n-propyl) -cyclohexylcarbonate-4'-ethoxyphenyl ester 4- (4-n-Butyl) -cyclohexylcarbonate-4'-ethoxyphenyl 4- (n-pentyl) -cyclohexylcarbonate-4'-methoxyphenyl ester 4- (n-Hexyl) -cyclohexylcarbonate 4'-methoxyphenyl 4-n -HeptyI- (4'-cyanobiphenylyl-4) cyclohexane

The clear point of this liquid crystal mixture was 25 64.5 ° C and the characteristics in a TN cell with a helix angle of 90 ° were as follows:

With static control, the voltage was 90 V at 90% transmission and 2.6 V at 10% transmission at 20 ° C. The response time when controlled with 4 V was TR 30 = 280 m-sec. or TD = 166 m-sec at 0 ° C, and TR = 78 m-sec. or TD = 59 m-sec at 20 ° C.

With multiplex control, the range M was 10-11%.

Table 1 shows the properties of the two last-mentioned liquid crystal mixtures in comparison with other liquid crystal mixtures.

0.55 g

(10.8%)

0.68 g

(13.4%)

0.50 g

(9.8%)

0.98 g

(19.3%)

1.03 g

(20.3%)

0.49 g

(9.7%)

0.85 g

(13.4%)

Table 1

40 liquid crystal

Static response time (m-sec) range

0 ° C 20 ° C%

Increase waste increase waste

Mixture 1

162

132

49

.53

10-11

Mixture 2

280

166

78

59

10-11

45 azoxy

280

250

82

72

12-13

Biphenyl

330

210

78

62

7- 8

The clear point of this liquid crystal mixture was 60.5 ° C. The properties when used in a nematic cell (TN cell) with a helix angle of 90 ° were as follows:

With static control and 20 ° C, the threshold voltage (voltage with 90% transmission) was 1.8 V and the saturation voltage (voltage with 10% transmission) was 2.5 V. With control with 4 V, the rise time TR was 160 m-sec, the fall time TD 130 m-sec at 0 ° C, and TR = 49 m-sec and TD = 53 m-sec at 20 ° C. (The measured frequency was 32 Hz and an average of five display units was used. These conditions were the same in the subsequent measurements).

With multiplex control and taking into account temperature changes and changes in the viewing angle, the range was 10-11%. This area M was defined as follows:

M =

VofF-VQN

OFF

+ V,

As can be seen in Table 1, the liquid crystal mixtures of the present invention have both a short response time and a wide range in comparison with conventional liquid crystal mixtures. In particular, the short rise times indicate the low viscosity of the cyclohexyl ester compounds. The viscosity is in the range of 40-50 C.P. at 20 ° C.

55 With conventional liquid crystal mixtures, those with a wide range have a high viscosity and therefore a slow response time. These connections include e.g. the liquid crystals of the ester type, containing compounds of the formula as the main component

60

eoo - © -H '

ON

wherein R and R 'represent alkyl or alkoxy. On the other hand, biphenyl type liquid crystal mixtures have a low range M instead of short response times. None of the conventional liquid crystal mixtures * has both a wide range M and short response times, in Ge

642675

in contrast to the present mixtures, which combine both advantages.

In addition to the latter two liquid crystal mixtures of the present invention, a large number of other combinations are possible. When using cyclohexyl ester liquid crystal compounds, liquid crystal mixtures with low viscosity, short response time and high range M are obtained. These mixtures are well suited for colorless liquid crystal display units with multiplex control as well as with static control.

Furthermore, liquid crystal mixtures can be obtained by mixing cyclohexyl ester compounds with azoxy compounds. Such liquid crystal mixtures have shorter response times and a larger range M than the conventional azoxy liquid crystals.

Finally, new compounds are used in liquid crystal mixtures in the present invention.

Xf- (ä) -

cooh + soci.

VI

The compounds mentioned are 4- (n-alkyl) -cyclohe-xylcarboxylic acid 4'-cyanophenyl esters of the formula

■ XrGD-coo - ^ -

• cn in which X] represents n-alkyl with 1-6 C atoms.

The compounds are obtained as follows: The 4- (n-alkyl) -cyclohexylcarboxylic acid VI is reacted with thionyl chloride, 4- (n-alkyl) -cyclohexylcarboxylic acid chloride VII being obtained. This is then reacted with p-cyanophenyl in an organic solvent, such as ethyl ether, chloroform, etc., in the presence of triethylamine as a catalyst.

This two-step synthesis is represented by the following reaction scheme:

X-0-

coc1

VII

X, - (h) -COC1 + HO-0-CN

h> -coo- <q; -cn (i)

The process will now be described in more detail below:

First, the starting product VI e.g. prepared by reducing the 4- (n-alkyl) carboxylic acid in an autoclave at elevated temperature and pressure. In this way 4- (n-alkyl) -cyclohexylcarboxylic acid VI is obtained.

The compound (I) is obtained as follows:

First, an excess of thionyl chloride (SOCl2) is added to the compound VI and the reaction is carried out by refluxing, the 4- (n-alkyl) cyclohexylcarboxylic acid being

re-chloride VII of the formula Xi

{H)"

C0C1 is obtained by removing the excess thionyl chloride by distillation. The acid chloride is then slowly added to a solution of p-cyanophenol in anhydrous ethyl ether, and then triethylamine is added, the reaction vessel being kept in an ice / water bath, and the reaction is completed by refluxing after the addition has ended. In a third step, the ethyl ether is finally distilled off and the residue is recrystallized from ethanol and n-hexane. In this way, the compound (I) was obtained in a yield of 20-50%.

Reference example 1

Preparation of 4'-cy-anophenyl 4- (n-hexyl) -cyclohexylcarboxylic acid.

10.6 g of 4- (n-hexyl) -cyclohexylcarboxylic acid, produced by reducing the 4- (n-hexyl) -carboxylic acid, were mixed with 12 g of thionyl chloride in a reaction vessel of 100 ml and then refluxed until no more gas formation occurred . After about 1 h, the excess thionyl chloride was distilled off and the pressure in the reaction vessel was reduced. The 4- (n-hexyl) -cyclohexylcarboxylic acid chloride obtained was reduced

3o tem pressure distilled (0.1 mm Hg, 103-106 ° C), 9.3 g were obtained.

5 g of p-cyanophenyl were then dissolved in 80 ml of anhydrous ethyl ether in an egg-shaped reaction vessel of 200 ml, 10 g of triethylamine were added and the whole was cooled in ice. A solution of 4- (n-hexyl) -cyclohexylcarboxylic acid chloride in 20 ml of ethyl ether was slowly added to this solution. As the reaction proceeded, the hydrochloride of triethylamine was formed. After the two solutions had been mixed, the mixture was refluxed for about 1 hour to complete the reaction. After cooling, the salt was hydrolyzed and the ethyl ether solution was washed three times with 5N hydrochloric acid, three times with 10% aqueous sodium hydroxide solution and three times with water and then dried over anhydrous sodium sul-45 fat. After filtering off the sodium sulfate, the ethyl ether was distilled off. The residue was then repeatedly recrystallized from ethanol and n-hexane, 4 g of colorless acicular crystals being obtained. The yield was 27%.

The 4- (n-hexyl) -cyclohexylcarboxylic acid 4'-cyanophenyl ester obtained in this way had a melting point of 49 ° C. and a clear point of 71 ° C. Fig. 1 shows the IR absorption spectrum thereof. The enthalpy of fusion AH obtained by D.T.A. was 11.3 Kcal.

55

Reference Examples 2-6

Reference example 1 was repeated, but instead of the 4- (n-hexyl) -cyclohexylcarboxylic acid, the corresponding 4- (n-alkyl) -cyclohexylcarboxylic acids were used. This gave compounds in which R in the formula IC5H! i, C4H9, C3H7, C2H5 and CH3 respectively.

Table 2 below describes the compounds VII obtained from reference examples 2-6 together with those of the compound from reference example 1. 65 Table 3 shows the results for the compounds (I). Fig. 2-6 are the IR absorption spectra of the compound

(I)

9

642 675

Table 2 Example X1

proportion of compound VI used

Compound VII

Off off pressure boiling point booty booty%

mmHg ° C

1

c6h13

10.6

9.3

80.6

0.1

103-106

2nd

c5h "

9.9

9.0

83.0

0.5

82-86

3rd

c4h9

9.2

7.6

75.1

1

86-89

4th

c3h7

8.5

7.5

79.6

1

57-59

5.

c2h5

7.8

7.6

87.1

0.5

49-58

6

ch3

7.1

6.8

84.8

88

125-128

Table 3

example

X1

used

Compound (I)

Proportion of ver

Out

Out

Melting N-I

Ah

IR absorber

binding VII

loot loot point

Point

tion

g g

%

° c

° c

Kcal spectrum

1

c6hi3

6.9

2.5

26.6

49

71

11.3

Fig. 1

2nd

c5h "

6.5

4.1

45.6

46.5

77.5

8.5

Fig. 2

3rd

c4h9

6.1

3.4

39.7

43

66.5

7.7

Fig. 3

4th

c3h7

5.7

2.7

32.6

54

68.5

8.09

. Fig. 4

5

c2h5

5.2

3.2

41.5

46

31 *

5.02

Fig. 5

6

ch3

4.8

4.0

54.8

63 **

-

9.0

Fig. 6

* monotropic

** no nematic phase

Example 8 35 point was 60.5 ° C, the threshold voltage at a temperature

0.50 g 4- (n-propyl) -cyclohexylcarboxylic acid-4'-ethoxy-temperature of 20 ° C was 1.8 V and the saturation voltage nyl ester, 0.98 g 4- (n-butyl) -cyclohexylcarboxylic acid-4 ' -ethoxy- 2.5 V.

phenyl ester, 1.03 g 4- (n-pentyl) cyclohexylcarboxylic acid 4'-methoxyphenyl ester and 0.49 g 4- (n'hexyl) cyclohexylcar-

4'-boxy-methoxyphenyl esters were mixed with 0.68 g of 4 <> Brief description of the figures:

4- (n-Pentyl) -cyclohexylcarboxylic acid 4'-cyanophenyl ester, Fig. 1-6 show IR absorption spectra of compounds

0.55 g of 4- (n-propyl) cyclohexylcarboxylic acid 4'-cyanophenyl gene of the formula (I).

esters and 0.85 g of 4- (n-ethyl) -cyclohexylcarboxylic acid-4'-cyano- The spectra in FIGS. 1, 2, 3, 4, 5 and 6 correspond to ver-phenyl esters from Examples 2, 4 and 5 mixed , a bond meaning R of C6Hi3, C5HU, C4H9,

Liquid crystal mixture was obtained. The measured N-I- «C3H7, C2H5 or CH3.

C.

3 sheets of drawings

Claims (7)

642 675 PATENT CLAIMS 1. Nematic liquid crystal mixture containing at least one compound of the formula I xf <ï> COQ- ^ O ^ -CN (I) xKE> - eoo - ^ 0} cN wherein Xj is n-alkyl having 1-6 C atoms, or b) at least the two compounds (III) and (IV) (I) wherein X] represents n-alkyl with 1-6 C atoms. 2. Nematic liquid crystal mixture according to claim 1, comprising, in addition to the compound of formula I, the compound of formula II X 10th r © - eoo X KD "eoo CN (III) (IV) (II) 15 wherein X2 and R3 represent n-alkyl with 1-6 C atoms. 3. Nematic liquid crystal mixture according to claim 2, comprising at least one further liquid crystal compound. 4. Nematic liquid crystal mixture containing at least the two compounds of the formula III and IV wherein X3 and X4 represent alkyl, alkoxy or acyloxy and Y cyano, alkyl or alkoxy, or c) at least the two compounds (III) and (V) 20 ' 3 <Z> C0 ° ^ 25th 3 ~~ (Z) "coo ^ O> -y eoo (in) (V) (in) X CN (IV) wherein X3, X4 represent alkyl, alkoxy or acyloxy and Y cyano, alkyl or alkoxy. 5. Nematic liquid crystal mixture according to claim 4, wherein X3 is butyl, Y is hexyloxy and X4 is hexyl. 6. Nematic liquid crystal mixture containing at least the two compounds of the formula III, in which X3 and Y have the meaning given in claim 4, and of the formula V X r @ - eoo CN (V) wherein X5 is alkyl, alkoxy or acyloxy. 7. Nematic liquid crystal mixture according to claim 6, wherein X3 is butyl, Y is ethoxy and X5 is ethyl.