PLEOCHROIC ANTHRAQUINONE DYES

Abstract: An anthraquinone compound of the formula: wherein: P & Q are H or CH₂R¹; Y & Z are OH, NHT, NO₂ or SR² X is NHT, NO₂ or SR³ R & R¹ are independently C₁₋₂₀-alkyl; R² & R³ are independently alkyl, aryl or cycloalkyl; and T is H or C₁₋₄-alkyl; provided that, when Y is OH Z is NHT, NO₂ or SR², Q is CH₂R¹ and P is H; when Z is OH Y is NHT, NO₂ or SR², P is CH₂R¹ and Q is H; and at least one of X, Y and Z is SR² or SR³. The anthraquinone is pleochroic and suitable for the coloration of liquid crystals for use in electronic displays.

Description: This invention relates to anthraquinone compounds and methods for their preparation. According to the present invention there is provided an anthraquinone compound according to the formula: EMI1.1 wherein: P & Q are H or CH2R1; Y & Z are OH, NHT, NO2 or SRê X is NHT, N02 or SR R & R 1 are independently C1 20-alkyl; R2 & R are independently alkyl, aryl or cycloalkyl; and T is R or C1-4-alkyl; provided that, when Y is OH Z is NHT, N02 or SR2, Q is CH2R1 and P is H; when Z is OH Y is NHT, NO2 or SRê, P is CH2R1 and Q is H; and at least one of X, Y and Z is SRê or SR . The alkyl groups represented by R and R1 preferably contain from 3 to 12 and more preferably from 4 to 7 carbon atoms. They are preferably straight chain alkyl groups. It is further preferred that R and R1 are identical. The alkyl groups represented by Rê and R preferably contain up to 20 carbon atoms and more preferably are C1-10-alkyl groups. The cycloalkyl groups represented by these symbols preferably contain from 4 to 8 carbon atoms and more preferably cyclohexyl. The aryl groups represented by Rê and R preferably contain up to 15 carbon atoms and are more preferably mono- or bi-carbocyclic aryl groups such as naphthyl or, more especially, phenyl. The groups represented by Rê and R3 may be substituted or unsubstituted. Preferred substituents for the alkyl groups are C1 4-alkoxy, halogeno or aryl containing up to 15 carbon atoms, more preferably moncyclic aryl, such as phenyl. Preferred substituents for the aryl and cycloalkyl groups are C1-4-alkyl, C4 8-cycloalkyl, preferably cyclohexyl, and aryl containing up to 15 carbon atoms, more preferably monocyclic aryl, such phenyl. Preferred classes of dye with the scope of Formula I are those in which: Z = OH and Y = SRê # X = SR ; Y = OH and Z = SRê # X = SR ; Z = OH and Y = SRê = X = SR ; Y = OH and Z = SRê = X = SR ; Z = OH, Y = KH2 and X = SR3; Y = OH, Z = NH2 and X = SR and Y = OH, Z = NO2 and X = SR One preferred class of dyes within the cope of the present invention as defined in Formula I has the general formula: EMI2.1 wherein:P & Q are H or CH2R1; Y & Z are OH orSR provided that when Z is OH Y is SR , Q is CH2R1 and P is H; and when Y is OH Z is SR , Q is H and P is CH2R1; R & R1 are C1-20-alkyl; and Rê & R3 are as hereinbefore defined. Within the class of dyes represented by Formulae I and II it is preferred that R and R1 are identical and that they represent C 3-12-alkyl which may be branched or straight chain. It is also preferred that R2 and R3 are different. An especially r eferred dye from this class having particularly good solubility and a high order parameter is 1,8-d ihydroxy-2, 7-d i-n-heptyl-4-phenylthi o- 5-(4-t-butylphenylthio)anthraquinone. Other useful dyes of this class include 1, 8-dihydroxy-2, 7-di-n-pentyl-4- (t-butylphenylthio) -5-phenylthioanthraquinone, 1,8-dihydroxy-2,7-di-n-dodecyl-4-phenyl thio-5-(4-t-butylphenylthio)anthraquinone and 1,5-dihydroxy-2,6-di (2,4,4-trimethyl-n-butyl)-4-phenylthio-8-(4-t-butylphenylthio) anthraquitone. The compounds of Formula I, and especially the aforementioned preferred classes, are useful for the colouration of liquid crystal for use in electronic displays They have bluish reds shades and generally exhibit high order parameters and/or high solubilities in liquid crystal materials. Examples of some compounds having particularly useful propertics are those of Formula I in which: P = CH2R1, R = R1 = n-hexyl, Q = H, Z = OH, Y = phenylthio and X = 4-t-butylphenylthio; P = CH2R1, R = R1 = n-butyl, Q = H, Z = OH, Y = phenylthio and X = 4-t-butylphenylthio; 1 R = R1 P = CH2R , R = R = 4-trimethyl-2-methyl-n-butyl, Q = H, Z = OH and Y = X = phenylthio; P = CH2R1, R= R1 = n-hexyl, Q = H, Z = OH & Y = X = phenylthio Q = CH2r1, R = R = 5-trimethyl-3-methyl-n-pentyl, P = H, Y = OH and Z = X = phenylthio; Q = CH2R1, R = R1 = 5,5,5.trimethyl-3-methyl-n-pentyl, P = H, Y = OH, Z = phenylthio and X = NO2; P = CH2R1, R = R1 = 5,5,5-trimethyl-3-methyl-n-pentyl, Q = H, Z = OH, Y = phenylthio and X = NO2; P = CH2R1, R = R1 = 5,5,5-trimethyl-3-methyl-n-pentyl, Q = H, Z = OH, y = phenylthio and X = NH2; Q = CH2R1, R = R1 = 5,5,5-trimethyl-3-methyl-n-pentyl, P = H, Y = OH, Z = phenylthio and X = NH2; The dyes of Formula I may be prepared by the substitution of at least one of the nitro groups in a compound of the formula: : EMI4.1 wherein: P & Q are H or CH2R1; Z1 & Y1 are OH or NO2 provided that when Z1 is OH Y1 is NO2, P is CH2R1 and Q is H; and when Y1 is OH Z1 is NO2, P is H and Q is CH2R1; and R & R1 are C1-20-alkyl, with at least one substituted thio group, -SR2 and/or -SR and, wh only a single nitro group is replaced, optionally followed by the reduction of the other nitro group to an amino group. This amino group may then be alkylated in a conventional manner. A process for the preparation of the preferred dyes of Formula II has two stages, the first comprising the reaction of a mercaptan, R1SH, with the compound of Formula III, in pyridine at a temperature around or below 300 C, preferably below 35 C, to give an intermediate compound of the formula: EMI5.1 wherein: P & Q are H or CH2R1; yl & z1 are OH orNO2 provided that when Z1 is OH Y1 is N02, P is C112R1 and Q is H; and when Y1 is OH Z1 is NO2, P is H and Q is CH2R1; R & R1 are C1 alkyl and R2 is as hereinbefore defined, and the second comprising the reaction of the intermediate compound of Formula IQ with a second mercaptan, R3SH, at a higher temperature. The second stagc, the reaction with the second mercaptan, is preferably performed in a polar solvent, more preferably a hydroxylic solvent such as an alkanol, e.g. isopropanol, and is also preferably performed at the reflux temperature of the solvent. The starting material for this process may be prepared by the reaction of quinizarin or anthrarufin with one or more aldehydes of the formula RCHO and R1CHO in the presence of pyridine to give a 2,7-dialkylquinizarin or a 2,6-dialkylanthrarufin and nitrating this to give a 2,7-dialkyl-4,5-dinitroquinizarin or a 2,6-dialkyl-4,8-dinitroanthrarufin of Formula III. The intermediate compounds of Formula IV and the reduction products thereof, wherein the N02 group is converted into an NHT group, also fall within the scope of Formula I and form another preferred feature of the present invention some of these dyes have particularly good solubilities and/or order parameters in liquid crystal materials. The reduction products derived from the compounds of Formula IV wherein V1 or z1 is NO2 may be prepared from the compounds of Formula 1V by reduction of the NO2 group with a mixture of sodium sulphide and sulphur in an aqueous medium, optionally followed by methylation of the NH2 group. Preferred compounds within this class are those of Formula I in which Z is OH and Y is NH2 and X is SR2 and those in which Y is OH, Z is NH2 and X is SR2. Examples of such compounds are 1,8-dihydroxy2,7-di(3,5,5,5-tetramethyl-n-pentyl)-4-phenylthio-5-amino-anthraquinone, 1,5-dihydroxy-4-phenylthio-8-amino-2,6-di-(3,5,5,5-tetramethyl n-pentyl)anthraquinone and 1, 5-dihydroxy-4-phenylthio-8-nitro 2,6-di(2,4,4-tri- methyl-n-butyl)anthraquinone. The invention is further illustrated by the following Examples in which all parts and percentages are by weight unless otherwise indicated and the letters "AQ" are used to represent anthraquinone. Example 1 (a) Preparation of 1,5-dihydroxy-2,6-dinonyl-4-phenylthio- 8-nitroanthraquinone A mixture of 1.1 ml (0.01 moles) of thiophenol and 5.8g of 1,5-dihydroxy-2,6-dinonyl-4,8-dinitro-AQ (0.01 moles) in 50 ml pyridine was stirred for 30 minutes at room temperature andthen drowned out into 100 ml water. Concentrated HC1 (75 ml) was added and the precipitated solid was filtered, washed with water and dried to yield 6g of crude material. A portion of this (3g) was recrystallised from 100-120 petroleum ether to yield 1.3g of the intermediate 1,5-dihydroxy-2,6-dinonyl-4-phenylthio-8-nitro-AQ (structure confirmed by mass spectrometry). (b) Preparation of 1, 5-dihydroxy-2, 6-dinonyl-4-phenylthio- 5-(t-butylphenylthio)anthraquinone A mixture of 0.65g of the above intermediate and 0.2g of 4-t-butylphenylthiol in 10 ml pyridine was stirred at 90-50C for 16hours and then drowned out into 50 ml of dilute HC1. The precipitated solid was filtered, washed successively with water and methanol and dried. It was then recrystallised from 40-60 petroleum ether to yield O.1g of product consisting mainly of 1,5-dibydroxy-2,6-dinonyl (4-t-butylphenylthio)-8-phenylthio-AQ (structure confirmed by mass spectrometry). (c) Preparation of 1,5-dihydroxy-2,6-dinonyl-4-phenylthio- 8-aminoanthraouinonc: A solution of 10g of Na2S*91120 and 2g of sulphur in 20ml of water was added to 3.0g of the product of Example 23(a) in 1OOml ofwater and 50m1 of pyridine and heated to 90 C. After 1 hour at 900C the pyridine was evaporated and the remainder cooled to 6O0C. The oil which separated was extracted into 100-120 petroleum ether and the water removed (by Dean & Stark). The solution was purified by passage through a silica gel column and a small quantity of HC1 added to precipitate a solid. The solid (1.2g) was dried at 70 C and the structure confirmed by mass spectral and l R analysis. (d) Preparation of 1,5-dihydroxy-2,6-dinonyl-4,8-diphenylthio-AQ The procedure of Example 1(b) was repeated using the equivalent amount of thiophenol in place of the 4-t-butylphenyl- thiol. Example 2 (a) Preparation of 1,8-dihydroxy-2,6-dinonyl-4-phenyltllio-5-nitro-AQ The procedure, of Example 1(a) was repreated using 5.8g of 1,S-dihydroxy-2,7-dinonyl-4,8-dinitro-AQ (0.01 moles) in place of the 5.8g of 1,5-dihydroxy-2,6-dinonyl-4,8-dinitro-AQ. (b) Preparation of 1 , 8-dihydroxy-2, 7-dinoyl-4-phenylthio-5-amino-AQ The procedure of Example 1(c) was repeated using 3.0g of 1,8-dihydroxy-2,6-dinonyl-4-phenylthio-5-nitro-AQ from Example 2(a) in place of the product of Example l(c). (c) Preparation of 1,8-dihydroxy-2,7-dinoyl-4,5-diphenylthio-AQ The procedure of Example 1(d) was repeated using the equivalent amount of 1,8-dihydroxy-2,7-dinoyl-4-phenylthio-5-nitro-AQ in place of the 1,5-dihydroxy-2,6-dinonyl-4-phenylthio-8-nitro-AQ. The 1,5-dihydroxy-2,6-dinonyl-4,8-dinitro-AQ and the 1,8-dihydroxy-2,7-dinoyl-4,5-dinitro-AQ were made according to the method described in UK Patent Specification No. 2038809A by reacting 1,5-dihydrox.y-AQ and 1,8-ditydroxy-AQ, respectively, with nonanal and nitrating the di-nonyl derivatives. The alkyl radical in the nonanal used in Examples 1 and 2 had the formula: -CH2#CH2#CH(CH3)#CH2#CH(CH3)3 Example 3 (a) Preparation of 1,8-dihydroxy-2,7-didocyl-4-phenylthio- 5-nitroanthraquinone A mixture of 6.6g of 1,8-dihydroxy-2,7-didodecyl-4,5-dinitro-AQ, 1.1g of thiophenol and 100ml pyridine were stirredmixed at ambient temperature for 2 hours and then drowned out into 200ml water. The precipitated solid was filtered, washed successively with water and methanol and dried to yield 4.5g of crk e material. After recrystallisation from 100-120 petroleum ether the product was 1,8-dihydroxy-2,7-didodecyl-4-phenylthio- 5-nitro-AQ (4.15g: structure confired by mass spectrometry). (b) Preparation of 1,8-dihydroxy-2,7-didocyl-4-phenylthio 5-(4-t-butylphenylthio)anthraquinone A portion of this intermediate (3.7g) was added to a solution of 0.83g of 4-t-butylphenylthiol and 0.3g ROH in 50ml iso-propanol at 650C. After heating the mixture at the reflux (830C) for 3 hours it was cooled to ambient temperature, filtered, washed successively with isopropanol and methanol, dried and recrystallised from 100-120 petroleum ether. The product (2.i5g) was essentially 1,8-dihydroxy2,7-didodecyl-4-phenylthio-5-(4-t-butylphenylthio)AQ. The 1,8-dihydroxy-2,7-didodecyl-4,5-dinitro-AQ was made according to the method described in UK Patent Specification No. 2038809A by reacting 1,8-dihydroxy-AQ with n-dodecanal and nitrating the di-n-dodecyl derivative. Example 4 (a) Preparation of -2,7-Di-n-pentylchrysazin Chrysazin (120g) was stirred into a solution of 120g of sodium hydroxide in a mixture of water (1500 ml) and pyridine (220 ml) at 550C. Sodium hydrosulphite (200g) was added to the mixture which was stirred under N2 for 30 minutes before addition of a further 100g of sodium hydrosulphite. The reaction mixture was heated to 80 C, over 30 minutes during which period was added, dropwise, n-pentanal (142g) and the mixture stirred for 2 hours at 80 C still under N2. It was then cooled to room temperature, poured into an acidified ice/water mixture (ice/water. 4 litres and 35% liCl: 700 ml), in which it was stirred for 2 hours, filtered and the filter cake washed with water. The tarry cake was slurried in 40u ml of ethyl acetate, filtered, wasted with methanol and Dulled until damp-dry. This paste was recrystallised from ethyl acetate to give 83g of dry product (yield 45%) melting at 127 C. Elemental analysis gave C = 76.1% (75.8%) and H = 7.5% (7.4%). (b) Preparation of 2,7-b-n-pentyl-4 ,5-dinitrochrysazin 2,7-Dipentylchrysazin (56g) fijrn Example 4(a) was stirred in 800 ml of 98% sulphuric acid at room temperature for 30 minutes andthcn cooled to O C. To the cooled mixture was added, dropwise over a period of 30 minutes while maintaining the temperature < 100C, 160 ml of of an anhydrous nitration acid, comprising 33X nitric acid and 67% suiphuric acid, and the mixture stirred for 2 hours at < 1(i'C. The mixture was then poured into 4 litres of ice/water, stirred at rooni temperature for 30 minutes , filtered, washed acid-free and dried to give 50.5g (yield 73%) of dry product melting at 1400C. Elemental analysis gave C = 58.8% (61.3%), H = 5.4% (5.5%) and N. 5.5% (6.0X) (c) Preparation of 2,7-Di-n-pentyl-4-phenylthio-5-nitrochrysazin To a mixture of 9.4g of 2,7-di-n-pentyl-4,5-dinitro- chrysazin from Example 4(b) in 200ml of pyridine at 20 C there was added a solution of 2.2ml of thiophenol in 50ml of pyridine. The colour of the mixture gradually changed from orange-brownbto red and after 2 hours at 200C was drowned into water, filtered, washed successively with water and methanol and dried to yield 9.5g of product (88% theory). The structure was confirmed by mass spectrometry and elemental analysis, C = 67.5 (67.5) H = 5.8 (5.8) S - 6.7 (6.0) and N = 3.0 (2.7). This product had a molar extinction coefficient of 12,541 at 540 nm in chloroform. (d) Preparation of 2,7-di-n-pentyl-4-phenylthio-5-(4-t-butyl phenyltillo) chrysain To a mixture of 1.7ml of 4-t-butylphenylmercaptan and 0.4g of KOH in 50ml of isopropanol at 600C was added 3.7g of the product of Example 4(c) and the temperature raised to 80 C for 1.5 hour. It was then cooled to room temperature, filtered, washed successively with isopropanol and methanol and dried to give 3.5g of product. After recrystallisation from petroleum ether, the structure was confirmed by mass spectrometry and elemental analysis, C = 73.0 (73.6) H = 6.5 (6.8) S = 9.1 (9.8). This product had a molar extinction coefficient of 19,183 at 592nm in chloroform. (e) Preparation of 2,7-di-n-pentyl-4,5-diphenylthiochrysazin The procedure of Example 4(d) was repeated using the equivalent amount of thiophnol in place of the 4-t-butylphenyl- mercaptan. Example 5 (a) Preparation of 2,7-Di-n-heptyl-chrysazill The process of Example 4(a) was repeated except for the replacement of the 142g of of n-pentanal with 371g of n-heptanal. The quantity of dry product was 103g (yield 47.6%) which melted at 116-118 C. Elemental analysis gave C = 76 (75.8%) and H = 7.5t (7.4%). (b) Preparation of 2,7-Di-n-heptyl-4,5-dinitrochrysazin The process of Example 4(b) was repeated using 8.2g o 2,7-di-n-heptylchrysazin in place of the 56g of 2,7-di-n-pentylchrysazin and increasing the quantity of the other ingredients by 25X. The quantity of dry product was 50.5g (yield 69.1%) melting at 1400C. Elemental analysis gave C = 58.8% (61.3Z), H = 5.4% (5.5%) and N = 5.5Z (6.0%). (c) Preparation of 2,7-Di-n-heptyl-4-phenylthio-5-nitrochrysazin The process of Example 4(c) was repeated using 9.6g of 2,7-n-heptyl-4,5-dinitrochrsazin in place of the 9.4g of 2,7-di-n-pentyl-4,5-dinitrochrysazin. The structure was confirmed by mass spectrometry. This product had a molar extinction coefficient of 12,095 at 540nm in chloroform. (d) Preparation of 2,7-Di-n-heptyl-4-phenylthio-5-(4-t-butyl- phenylthio)chrysazin The process of Example 4(d) was repeated using 3.8 g of 2,7-di-n-heptyl-4-phenylthio-5-nitrochrysazin in place of the 3.7g of 2,7-di-n-pentyl-4-phenylthio-5-nitrochrysazin. After recrystallization from petroleum ether, the structure was confirmed by mass spectrometry. This product had a molar extinction coefficient of 19,650 at 592nm in chloroform. (e) Preparation of 2,7-Di-n-heptyl-4 ,5-diphenylthiochrysazin The procedure of Example 5(d) was repeated using the equivalent amount of thiophenol in place of the 4-t-butylphenyl- thiol. Example 6 A black mixture dye was made by mixing together 8 parts of 2,7-di-n-pentyl-4,5-diaminochrysazin (blue) which is the product of Example l(c) of our co-pending UIs Patent Application No 8308132 15 parts of 2, 7-di-n-heptyl-4-phenylthio-5- (4-t-butyl- phenylthio)chrysazin (violet), which is the product of Example 5(d) above and 20 parts of 1-phenylthio-5-(4-t-butyl-phenylthio)- anthraquinone (yellow) which is the product of Example 11 in UR Patent Specification No 2094822A. Example 7 Another black mixture dye was prepared from the same dyes as the mixture of Example 6, by mixing 12 parts of the blue dye, 20 parts of of the violet dye and 30 parts of the yellowdye. Example 8 A black mixture was made by mixing together 10 parts of the blue dye used in Example 6, 10 parts of the violet dye used in Example 6, 20 parts of the yellow dye used in Example 6, 30 parts of 1 5-di(4-t-butylphenylthio)-4-phenylthioanthraquinone (orange) which is the product of Example 22 in UK Patent Specification No 2094822A and 10 parts of the partially methylated derivative of the blue dye used in Example 6 above blue green). which is the product of Example 5(a) of our co-pending UK Patent Application No 8308132. This black mixture exhibits an excellent flat absorbance of 0.8 in the liquid crystal material, E43 in a 12 x 106m cell, over the range 450 nm to 650 nm. The compounds described in the Examples have the properties identified in Table I as solutions in the liquid crystal medium, E43, at 200C, unless otherwise stated. Eb3 contains the compounds: EMI12.1 and is available from BDH Chemicals Limited of Broom Road, Poole, Dorset, England. Table 1 Example Solubility max Order (%) (nm) Parameter l(a) 2.8 0.72 l(b) 4.6 580/542 0.79 l(c) 5.8 565/610 0.73 1(d) 2.0 580/542 0.73 2(a) 1.5 0.77 2(b) 6.2 565/610 0.74 2(c) 3.0 580/542 0.72 3(b) 3.6 580/542 0.83 4(c) 0.5 0.73 4(d) 2.5 5801542 0.77 4(e) 1.0 . 580/542 0.77 5(c) 0.8 0.73 5(d) 7.2 580/542 0.78 5(e) 1.8 580/542 0.78

Claims: CLAIMS 1. An anthraquinone compound of the formula: EMI14.1 wherein: P & Q are H or CH2R ;. Y & Z are OH, NHT, NO2 or SRê X is NHT, NO2 or SR R & R1 are independently C1-20-alkyl; Rê & R are independently alkyl, aryl or cycloalkyl; and T is H or C1 1-4-alkyl; provided that, when Y is OH Z is NHT, N02 or SR2, Q is CH2R and P is H; when Z is OH Y is NHT, NO2 or SRê, P is CH2R1 and Q is B; and at least one of X, Y and Z is SRê or SR 2. An anthraquinone compound of the formula: EMI14.2 wherein: P & Q are H or CH2R1; Y & Z are ON or SR provided that when Z is 011 Y is SR3, Q is CH2R1 and P is H; and when Y is OH Z is SR , Q is H and P is CH2R1 R & R1 are C 1-20-alkyl; and 2' R2 & R3 are independently alkyl, aryl or cycloalkyl. 3. An anthraquinone compound according to Claim 1 or Claim 2 wherein R2 and R3 are different. 4. An anthraquinone compound according to any one of Claims 1 to 3 wherein Rê and R are selected from phenyl and substitued phenyl. 5. An anthraquinone compound according to Claim 4 wherein the substituted plienyl is Cl 4-alkylphenyl. 6. An anthraquinone compound of the formula: EMI15.1 wherein: P & Q are H or CH2R1; Y1 & Z1 are OH or NO2 provided that when Z1 is OH Y1 is NO2, P is CH2R1 and Q is H; and when yl is OH Z1 is NO2, P is H and Q is CH R1; R & R1 are C1-20-alkyl; and Rê is alkyl, aryl or cycloalkyl. 7. An anthraquinone compound according to any one of Claims 1 to 6 wherein R and R1 are thc same and C3 12-alkyl. 8. The anthraquinone compound 1,8-dihydroxy-2,7-di-n-heptyl- 4-phenylthio-5(4-t-butylphenylthio)anthraquinone. 9. A process for the preparation of an anthraquinone compound according to any one of Claims 1 to 8 which comprises the substitution of at least one of the nitro groups in a compound of the formula: EMI16.1 wherein: P & Q are 11 or CH2R1; Z1 & Y1 are OH or NO2 provided that when Z1 is OH Y1 is NO2, P is CH2R1 and Q is H; and when Y1 is OH Z1 is NO2, P is H and Q is CH2R1; and R & R1 are C1-20-alkyl, with at least one substituted thio group, -SR and/or -SR , wherein R and R3 are as defined in Claim 1. 10. A process for the preparation of a compound according to Claim 6 which comprises the reaction of a compound of Formula III as defined in Claim 9 with a mercaptan, R1SH in pyridine at a temperature around or below 30 C. 11. A process for the preparation of a compound according to any one of Claims 1 to 5 which comprises the reaction of a compound of formula IV as defined in Claim 6 with a mercaptan, R SH, at a temperature above 35 C.

Inventors: NEWTON, DAVID FRANCIS, THOMPSON, DAVID JOHN
Applicants: IMPERIAL CHEMICAL INDUSTRIES PLC
Application year: 1983
Main classification: C09B1
IPC codes: C09K19, C09B1