GB1571439A - Benzene-azo-naphthalene pigments and electrographic developers containing them - Google Patents

Description

(54) BENZENE-AZO-NAPHTHALENE PIGMENTS AND ELECTROGRAPHIC DEVELOPERS CONTAINING THEM (71) We, EASTMAN KODAK COMPANY, a Company organized under the Laws of the State of New Jersey, United States of America of 343 State Street, Rochester, New York 14650, United States of America do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to azo pigments and their use in electrography, particularly electrographic liquid developers.

Known electrographic liquid developers containing pigments have generally suffered from the poor dispersion stability and/or poor light stability of the developed image. Prior art processes which use carbon as the pigment in electrographic liquid developers have generally suffered from such problems as batch-to-batch nonuniformity and yield poor continuous tone images on some substrates. Thus, there is a continuing need for pigments in electrographic liquid developers to provide such developers with improved dispersion stability and to provide developed images having improved stability to light. In particular, there is a need to provide a pigment having the desirable neutral density colour characteristics of carbon without the problems associated therewith.

The azo dyes of the present invention can be used to make electrographic liquid developers which have good dispersion stability, which yield good light stability of developed images, and which can provide good continuous tone images.

Electrographic liquid developers made using the azo dyes of the present invention further provide high-quality developed images having low contrast and high resolution.

According to the present invention there is provided an azo pigment of the general formula:

wherein R' is -H, -COOM, -CONH2, SO2NH2 or -SO3M where M is an alkali metal or ammonium cation, R2 is substituted or unsubstituted lower alkoxy -OCH2CONH2 or -N(R0)R7 group where RC and R7 are substituted or unsubstituted lower alkyl groups, R8 is hydrogen or halogen or a substituted or unsubstituted lower alkyl or lower alkoxy group or a nitro group.

R4 is hydrogen or

m is 0 or 1, n-is 1 when m = 0, and 1 or 2 when m = 1 (according to the charge on J), Q is -OH when m = 0 or --0- when m = 1, and J is an ammonium or metal cation.

The word "lower" used to describe alkyl and alkoxy groups means that they may contain 1--4 carbon atoms in their unsubstituted condition. The substituted groups may, for example, contain one or more -OH or -SO3M groups or halogen atoms wherein M is as defined above.

Examples of alkoxy groups R2 are methoxy, ethoxy and n-butoxy.

Examples of substituted alkyl groups R6 and R7 are -C2H4OH and -C2H4SO3M where M is as defined above.

The cation J may be NH+4 or Na+ or a cation of Ba, Ca, Cd, Cr, Mg, Mn, Sn, Sr or Zn.

A preferred group of pigments of the present invention comprise those of the general formula:

wherein R' is hydrogen or a -SO2NH2, -SONa or -SO3NH4 group, R2 is a lower alkoxy or -OCH2CONH2 group, and R3 is hydrogen or -NO2.

The present invention also provides an electrographic liquid developer comprising a liquid carrier and toner particles comprising a pigment according to the present invention.

Certain of the above pigments exhibit a particularly useful spectral response.

These dyes absorb radiation relatively uniformly in the range of from 400 nm. to 700 nm. and therefore exhibit a neutral density coloration which is similar to carbon black. The pigments exhibiting this neutral density coloration are the naphthalenediol disazo dyes of Formula I wherein R4 is an arylazo group and R2 is -OCH2CONH2 or an alkoxy group having from 1--4 carbon atoms.

A preferred embodiment of the present invention provides liquid developers having toner particles comprising these neutral density dyes. Such developers do not require colour balancing with multiple dyes to provide the required neutral density images.

The accompanying drawing illustrates a spectral response curve of such preferred pigments of this invention that exhibit this substantially neutral density coloration.

Carrier liquids which may be used to form the present liquid developers may be selected from a wide variety of materials. Preferably, the liquid has a low dielectric constant and a very high electrical resistance such that it will not disturb or destroy the electrostatic latent image. The preferred carrier liquids have a dielectric constant of less than 3, and a volume resistivity greater than 10'0 ohm-cm.

They should preferably be stable under a variety of conditions. Examples of such carrier liquids include halogenated hydrocarbon solvents, for example, fluorinated lower alkanes, such as trichloromonofluoromethane or trichlorotrifluoroethane, having a typical boiling range of from 2"C. to 550C. Other hydrocarbon solvents are useful, such as isoparaffinic hydrocarbons having a boiling range of from 1450C. to 1850C., such as Isopar G (trademark of Humble Oil & Refining Co.) or cyclohydrocarbons having a major aromatic component and also having a boiling range of from 145"C. to 185"C., such as Solvesso 100 (trademark of Humble Oil & BR< Refining Co.). Additional useful carrier liquids include polysiloxanes, odourless mineral spirits, octane and cyclohexane.

The toner particles for the developers of this invention may be provided simply by grinding the pigments to the appropriate size and then dispersing the pigment powder in a carrier liquid without the addition of a resinous binder and/or charge control agent. However, a developer which does not contain a binder material would produce developed images which are rot easily fixable. Accordingly, it would normally be necessary, for example, to overcoat such images by spraying with a lacquer composition in order to hold the pigment particles in place.

The azo pigments of this invention may be prepared by methods in themselves known, for example by coupling diazonium salts with 2,3-naphthalenediol derivatives according to the following reaction:

wherein X is an anion, q is 1 or 2, and the R's have the meanings given for formula I. When the diazonium salt is complexed with a heavy metal cation the dye salt structure of Formula I when m = 1 is obtained. Various heavy metal cations may be used to obtain the dye salt, preferably the cations of Zn, Cd and Sn.

Pigments that are particularly useful in the practice of this invention include those listed in Table I below: TABLE I 1. zinc di - 1 - [p - (N - ethyl - N - 2 - hydroxyethylamino)phenylazo] - 2 - hydroxy 3 - naphthoxide; 2. 1 - [p - (N- ethyl -N- 2 - hydroxyethylamino)phenylazo] - 2,3 - naphthalenediol; 3. 1,4 - bisfp - (N - ethyl - N - 2 - hydroxyethylamino)phenylazo] - 2,3 - naph thalenediol; 4. 1,4 - bis[4 - (N - ethyl - N - 2 - hydroxyethylamino)phenylazoi - 2,3 - dihydroxy 7 - naphthalenesulfonic acid ammonium salt; ; 5. 14 - bis[4 - (N- ethyl - N - 2 - sulphoethylamino) - 2 - methylphenylazol - 2,3 naphthalenediol disodium salt; 6. 2,3 - dihydroxy - 1,4 - bis[4 - (N - ethyl - N - 2 - sulphoethylamino) - 2 - methyl phenylazo] - 7 - naphthalenesulphonamide disodium salt; 7. 1,4 - bis(p - anisylazo) - 2,3 - naphthalenediol; 8. 1,4 - bis(o - anisylazo) - 2,3 - naphthalenediol; 9. 1,4 - bis(p - ethoxyphenylazo) - 2,3 - naphthalenediol; 10. 1,4 - bis(4 - n - propoxyphenylazo)- 2,3 - naphthalenediol; 11. 1,4 - bis(p - anisylazo) - 2,3 - dihydroxynaphthalenesulphonic acid sodium salt; 12. 1;4 - bis(o - anisylazo) - 2,3 - dihydroxynaphthalene - 6 - sulphonic acid sodium salt; 13. 1,4 - bis(4 - anisylazo) - 2,3 - dihydroxy - 6 - naphthalene - 6 - sulphonamide; 14. 1,4 - bis(4 - carbamoylmethoxyphenylazo) - 2,3 - naphthalenediol; 15. 1,4 - bis(2 - nitro - 4 - anisylazo) - 2,3 - naphthalenediol; and 16. 1,4 - bis(5 - nitro - 2 - anisylazo) - 2,3 - naphthalenediol.

Generally it is desirable to include a resinous material in the toner particle to facilitate fixing of the particle on the substrate. Such resins may be selected from a wide variety of substances. The following are examples of resins which may be used: rosins, including hydrogenated rosins and esters of hydrogenated rosins; alkyl methacrylate copolymers having from 2-5 carbon atoms in each alkyl moiety, e.g.

isobutyl methacrylate and normal butyl methacrylate copolymers; phenolic resins including modified phenolic resins such as phenol formaldehyde resins; pentaerythritol phthalate; coumaroneindene resins; ester gum resins; vegetable oil polyamides; alkyd resins, including modified alkyds such as soya oil-modified and linseed oil-modified alkyds, phthalic, maleic and styrenated alkyls and compatible mixtures thereof.

In addition, the electrostatic charge polarity of the toner particles of the present invention may be enhanced or altered by the addition of charge control agents if so desired. A variety of materials may be used as charge control agents.

Illustrative of such agents are the polyoxyethylated alkyl surfactants such as polyoxyethylated alkylamine, polyoxyethylene palmitate and polyoxyethylene stearate. Other useful materials are magnesium and heavier metal soaps of fatty and aromatic acids as described in U.S. Patent 3,417,019. Useful metal soaps include cobalt naphthenate, magnesium naphthenate and manganese naphthenate, zinc resinate, calcium naphthenate, zinc linoleate, aluminium resinate, isopropyltitanium stearate, aluminium stearate and others, many of which are also described in U.S. Patent 3,259,581. Typically, the amount of such materials used is less than 2% by weight based on the weight of liquid developer. In certain instances, the resinous binder per se can function as the charge control agent, as can the pigment.

Developers may be prepared by grinding, for example by ball-milling, one of the pigments with a polymer solution to make a concentrate and diluting this concentrate with an insulating carrier liquid. The resultant working strength developer is in the form of a carrier liquid having dispersed therein toner particles.

Typical developer compositions comprising the pigments of this invention will contain the pigments in a concentration of from 0.01 to 1.0 gram per litre. When a resin binder is used, the pigment-to-binder weight ratio can vary from 1:20 to 2:1.

The invention is illustrated by the Examples which follow. Examples 1-19 described the preparation of the pigments of the invention or intermediates thereof. All percentages and ratios given are by weight.

Example 1.

Preparation of zinc di-l-[p-(N-ethyl-N-2-hydroxyethylamino)phenylazo]-2-hydroxy 3-naphthoxide

To a solution of 25.0 g. (0.0845 mole) of p-(N-ethyl-N-2-hydroxyethylamino)benzenediazonium zinc chloride double salt and 11.0 g. (0.0688 mole) of 2,3naphthalenediol in 200 ml. of distilled water was added excess 28% aqueous ammonia. After I hr., the solid was collected, slurried in 200 ml. of acetone and dried to give 9.2 g. of green product. Recrystallization by boiling in 300 ml. of pyridine, filtration, concentration of the filtrate to 50 ml. and cooling overnight to room temperature gave 3.4 g. Recrystallization from 250 ml. of pyridine concentrated to 30 ml. gave 2.8 g. (5.3%) of green crystals whose maximum wavelength of absorption and extinction coefficient was determined in dimethyl formamide (DMF).

1DMF (log E) 523 nm. (4.67).

max Anal. calc'd. for C40H40N"O ,Zn: C, 62.6; H, 5.23; N, 11.0; Zn, 8.56 Found: C,62.6;H,5.1; N,ll.5;Zn, 7.9 Example 2.

Preparation of 1 - [p-(N-ethyl-N-2-hydroxyethylamino)phenylazo] -2,3-naphthalene- diol

To a stirred solution of 27.8 g. (0.100 mole) of N-ethyl-N-2-hydroxyethyl-pphenylenediamine bisulphate (PDA) 34 ml. (0.40 mole) of concentrated hydrochloric acid and 200 ml. of distilled water was added dropwise with stirring at 010 C. a solution of 6.9 g. (0.10 mole) of sodium nitrite in 35 ml. of water. The resulting green solution was added dropwise with stirring at 0--100C. to a solution of 15.9 g. (0.0944 mole) of 2,3-naphthalenediol, 60.8 g. (1.00 mole) of aqueous 28% ammonia and 400 ml. of ethyl alcohol. The mixture was stirred for 1 hr. after completion of the addition. The solid was collected, washed with water and dissolved in 450 ml. of boiling 2-butanone.The filtered solution was. cooled overnight to room temperature, filtered from 1.0 g. of dark green solid, m.p. 2200 C.

dec., concentrated to 200 ml. and cooled overnight in the refrigerator. The solid was collected, washed with ice-cold 2-butanone and dried to give 10.0 g., m.p.

159"C. Recrystallization from 200 ml. of 2-butanone gave 5.0 g. (14%), m.p.

167--1700C., ADMF (log E) 512 nm. (4.42), 590 nm. (4.27).

max Anal. calc'd. for C20H2,N303: C, 68.5; H, 5.98; N, 12.0 Found: C, 68.0; H, 6.0; N, 11.8 Example 3.

Preparation of 1,4-bis[p-(N-ethyl-N-2-hydroxyethylamino)phenylazo]-2,3-naphtha- lenediol

A solution of 0.200 mole of p-(N-ethyl-N-2-hydroxyethylamino)benzene- diazonium chloride (made as in the preceding procedure using twice the amount of PDA, sodium nitrite, hydrochloric acid and water) was added dropwise with stirring at 0--5"C. to a solution of 15.9 g. (0.0994 mole) of 2,3-naphthalenediol, 400 ml. of pyridine and 150 ml. of aqueous 28% ammonia. The mixture was stirred for 1-1/2 hr. after completion of the addition. The solid was collected,. washed with methanol and then water and dried in vacuum at 450C. to give 42.3 g. of green product, m.p. 240"C. Recrystallization from 400 ml. of pyridine gave 33.2 g.

(61.6%) of green crystals, m.p. 2470C. (dec.), ADMF (log E) 614 urn. (4.82), 657 nm. (4.87).

Anal. calc'd. for C30H34N8O4: C, 66.6; H, 6.28; N, 15.5 Found: C, 66.2; H, 6.3; N, 15.3 Example 4.

Preparation of 1,4 - bis[4 - (N - ethyl - N- 2 - hydroxyethylamino)phenylazo] - 2,3 dihydroxy - 7 - naphthalenesulphonic acid ammonium salt

A solution of 34.5 g. (0.100 mole) of 2,3-diacetoxy-7-naphthalenesulphonic acid sodium salt (see Example 5), 40.0 g. (1.00 mole) of sodium hydroxide and 700 ml. of water was stirred for 2 hr. at 25--300C., cooled and treated dropwise at 5--10"C. with a solution of 0.200 mole of p-(N-ethyl-N-2-hydroxyethylamino)benzenediazonium chloride made as in the preceding procedure. The mixture was stirred overnight. The solid was collected, pressed as dry as possible, dissolved in 1 1. of water and treated dropwise with a hot solution of 28.7 g. (0.100 mole) of 1,2,3triphenylguanidine, 250 ml. of ethyl alcohol, 15 ml. of glacial acetic acid and 15 ml.

of water. After 1 hr., the solid was collected, washed with water and vacuum-dried at 35"C. to give 71.8 g. of a mixture of blue and violet dyes. It was stirred for 1 hr. in 760 ml. of methanol, collected, washed with 500 ml. of methanol and dried to give 25.1 g., m.p. 238--239"C. (Thin-layer chromatography of this material showed only the blue component). Stirring this material for 1 hr. at reflux with a solution of 2.5 g. (0.032 mole) of ammonium acetate in 350 ml. of ethyl alcohol, collection (without cooling) of the solid, washing with ethyl alcohol and vacuum-drying at 45"C. gave 20.5 g. (32.1 ó) of blue powder.

Anal. Calc'd. for C30H3,N7O,S: C, 56.4; H, 5.78; N, 15.3; S, 5.00 Found: C, 58.8; H, 5.6; N, 13.2; S, 4.4 Example 5.

Preparation of 2,3-diacetoxy-7-naphthalene sulphonic acid sodium salt A mixture of 72.3 g. (0.276 mole) of 2,3-dihydroxy-7-naphthalenesulphonic acid sodium salt, 360 ml. of acetic anhydride and 5 drops of concentrated sulphuric acid was stirred 8 hr. on a steam bath and cooled overnight to room temperature.

The solid was collected, washed with acetic anhydride, pressed as dry as possible, dissolved in 400 ml. of water, mixed with 500 ml. of 20% sodium chloride solution and allowed to stand overnight. The solid was collected, washed with 20% sodium chloride and dried to give 69.9 g. (73.1%) of colourless crystals, m.p. 270--300"C.

(dec).

Anal. Calc'd. for C,4H"NaO7S: C, 48.6; H, 3.18; Na, 6.65; S, 9.25 Found: C,45.7;H,3.3; Na,6.4; S,8.7 Example 6.

Preparation of 2,3-diacetoxy-7-naphthalenesulphonyl chloride A mixture of 14.4 g. (0.0416 mole) of 2,3-diacetoxy-7-naphthalenesulphonic acid sodium salt, 150 ml. of thionyl chloride and 1 ml. of dimethyl formamide (DMF) was stirred 1 hr. at room temperature and 1 hr. at reflux, cooled to room temperature and poured into I litre of petroleum ether The solid was collected, washed with petroleum ether and dried to give 11.3 g (79.9%) of cream-coloured product, m.p. 158--1670C.

Anal. Calc'd. for C,4H1,CIO"S: C, 49.0; H, 3.21; Cl, 10.4; S, 9.33 Found: C, 48.3; H, 3.4; Cl, 9.8; S, 10.1 Example 7.

Preparation of 2,3-dihydroxy-7-naphthalene-sulphonamide A solution of 20.0 g. (0.0583 mole) of 2,3-diacetoxy-7-naphthalenesulphonyl chloride in 300 ml. of tetrahydrofuran was treated with 8.7 ml. (0.13 mole) of aqueous 28% ammonia. The solid (9.9 g., infrared spectrum identical with that of 6,7-diacetoxy-2-naphthalenesulphonic acid sodium salt) was removed by filtration and the filtrate evaporated to dryness. The residue was dissolved in 150 ml. of ethyl acetate. The residue from evaporation of the dried (anhydrous sodium sulphate) solution was slurried with four 100-ml. portions of ether and then dissolved in 150 ml. of denatured ethyl alcohol. The solution was saturated with hydrogen chloride, allowed to stand overnight, and then concentrated at the water pump to give 9.7 g.

of colourless residue. Recrystallization from 50 ml. of water gave 5.1 g. (37%) of pale violet solid, m.p. 218--2280C.

Anal. Calc'd. for C10H9NO4S: C, 50.2; H, 3.77; N, 5.85; S, 13.4 Found: C,50.2;H,4.1; N,5.3; S, 13.0 Example 8.

Preparation of 1,4 - bis[4 - (N - ethyl -N - 2 - sulphoethylamino) - 2 - methylphenyl azo] - 2,3 - naphthalenediol disodium salt

A solution of 6.4 g. (0.093 mole) of sodium nitrite in 15 ml. of water was added dropwise with stirring at 0--5 O C. to a solution of 24 g. (0.093 mole) of 4-(N-ethyl-N- 2-sulphoethylamino)-o-toluidine, 27 ml. (0.32 mole) of concentrated hydrochloric acid and 100 ml. of water. The resulting dark solution was added dropwise with stirring at 0--50C. to a solution of 7.5 g. (0.047 mole) of 2,3-naphthalenediol 20 g. (0.50 mole) of sodium hydroxide and 500 ml. of water. The mixture was stirred overnight and filtered from a small amount of solid.The filtrate was diluted to 800 ml. with water and treated dropwise with stirring with a hot solution of 15 g. (0.052 mole) of 1,2,3-triphenylguanidine, 250 ml. of denatured ethyl alcohol, 10 ml. of glacial acetic acid and 10 ml. of water. The solid was collected and shown by thin layer chromatography (TLC) to be a mixture of blue and violet dyes. The filtrate was treated with a second portion of 1,2,3-triphenylguanidine acetate made as described above. The 8.9 g. of gummy solid which resulted was stirred at reflux for 1 hr. with a solution of 2.0 g. (0.024 mole) of sodium acetate in 250 ml. of ethyl alcohol. The solid was collected washed with ethyl alcohol and dried at 600C. to give 6.4 g. (18%) of black powder. TLC showed a trace of violet contaminant.

Anal. Calc'd. for C32H36N6Na2O S C, 51.8; H, 4.85; N, 11.3; Na, 6.20; S, 8.62 Found C, 49.3; H, 4.8; N, 12.0; Na, 7.9; S, 8.0 Example 9.

Preparation of 2,3 - dihydroxy - 1,4 - bis[4 - (N - ethyl - N - 2 - sulphbethylamino)- 2 - methylphenylazo] - 7 - naphthalenesulphonamide disodium salt

A solution of 0.042 mole of diazonium salt made as in the preceding procedure from 10.8 g. of 4-(N-ethyl-N-2-sulphoethylamino)-o-toluidine, 10.5 ml. of concentrated hydrochloric acid, 2.9 g. of sodium nitrite and 35 ml. of water was added dropwise with stirring at 0--50C. to a solution of 5.0 g. (0.021 mole) of 2,3 dihydroxy-7-naphthalenesulphonamide in 150 ml. of 2N sodium hydroxide.The mixture was stirred overnight and then treated dropwise with a hot solution of 12.1 g. (0.0420 mole) of 1,2,3-triphenylguanidine, 100 ml. of ethyl alcohol, 10 ml. of acetic acid and 10 ml. of water, acidified to pH 4 with acetic acid and allowed to stand overnight. The solid was collected, washed with 300 ml. of water and vacuum-dried at 400C. The 16.1 g. of blue product was stirred at reflux for 1 hr.

with a solution of 3.5 g. (0.043 mole) of sodium acetate in 350 ml. of ethyl alcohol.

The solid was collected, washed with ethyl alcohol and vacuum-dried at 400 C. to give 6.9 g. (42%).

Example 10.

Preparation of 1,4-bis(p-anisylazo)-2,3-naphthalenediol To a stirred solution of 24.6 g. (0.200 mole) ofp-anisidine, 50 ml. (0.60 mole) of concentrated hydrochloric acid and 100 ml. of water was added dropwise at 0--50C. a solution of 13.8 g. (0.200 mole) of sodium nitrite in 30 ml. of water. The diazonium salt solution was stirred for 10 min. after the final addition, then was added dropwise to a solution of 15.9 g. (0.0944 mole) of 2,3-naphthalenediol, 110 ml. of 28% aqueous ammonia and 350 ml. of pyridine at 5--100C. The mixture was stirred for 1.5 hrs. after completion of the addition. The solid was collected, washed with methanol and then water, and dried to give 26.7 g. of crude product, m.p.

245--251"C. Recrystallization from pyridine gave 20.7 g. (48.5%) of dark solid, m.p. 258-2600C.

Examples 11-19.

Dyes 8-16 of Table I herein were prepared by a procedure similar to that described in Example 10. Table II below lists the melting points and structures of the dyes with reference to formula II.

TABLE II Substituents (See Formula II) Example Dye Melting No. No. R' R2- R3 Point C.

11 8 H o-CH3O- H 271-273 12 9 H p-C2H5O- H 255-257 13 10 H pHt-C3H7O- H 242-244 14 11 6-SO3Na p-CH3O- H > 385 15 12 6-SO3Na o-CH3O- H > 385 16 13 6-SO2NH2 4OCH3 H 258-260 17 14 H 4-OCH2CONH2 H 301-303 18 15 H 4-OCH3 2-NO2 308-312 19 16 H 2-OCH3 5-NO2 331-333 The materials defined below are used in the Examples which follow: Isopar-G: a liquid mixture of aliphatic hydrocarbons obtained from Humble Oil & Refining Co.

Beckosol7: a soya-modified alkyd resin containing 42% phthalic anhydride and 41% soya fatty acids from Reichold Chemical Co. "Beckosol" is a trade mark.

Solvesso 100: a hydrocarbon solvent consisting of alkylbenzenes from Esso Standard Oil Co.

VT: vinyl toluene LM: lauryl methacrylate LiM: lithium methacrylate MA: methacrylic acid EA: ethyl acrylate EM: ethyl methacrylate LiSEM: lithium sulphoethyl methacrylate t-BuS: tertiary butyl styrene VT/LM/LiM/MA: a copolymer of 56% VT, 40% LM, 3.6% LiM and 0.4% MA solids by weight EA/EM/LM/LiSEM: a copolymer of 46% EA, 26% EM, 16% LM and 12% LiSEM solids by weight t-BuS/LM/LiM/MA: a copolymer of 56% t-BuS, 40% LM, 3.6% LiM and 0.4% MA solids by weight Example 20.

To 13.5 ml. VT/LM/LiM/MA solution (7% Solvesso 100 solution) was added 0.7 g. of pigment of Example 9. The mixture was ball-milled for a week. To 3.5 g. of the concentrate was added 0.7 g. EA/EM/LM/LiSEM solution (14% Solvesso 100 solution). The mixture was then dispersed in 500 ml. Isopar-G by ultrasonic means.

The resulting developer, when utilized to develop electrostatic charge pattern, yielded good-quality, high-resolution images. Duplicates of such images obtained on diazo vesicular materials exhibited low contrast and excellent continuous tone.

Example 21.

With 15.6 ml. VT/LM/LiM/MA solution (7% solution as above) was mixed 0.8 g. of pigment of Example 8. The mixture was then treated as in Example 20. The quality of the first- and second-generation images was similar to the quality of images of Example 20.

Example 22.

To 15.6 ml. VT/LM/LiM/MA solution (7% Solvesso 100 solution) was added 0.8 g. of pigment of Example 4. The mixture was treated as in Example 20. The developed images were of good quality and exhibited high resolution. The secondgeneration images also show good continuous tone.

Example 23.

With 30 ml. VT/LM/LiM/MA (7% Solvesso 100 solution), 2.0 g. of the pigment of Example 3 were mixed and ball-milled for 10 days. A developer was then prepared by adding to 2.98 g. of the pigment concentrate 0.7 g. binder solution EA/EM/LM/LiSEM (14% Solvesso 100 solution) and dispersing the mixture in 500 ml. of Isopar-G by ultrasonic means. The developer was made up of particles less than 1y in size and yielded high-quality images. The second-generation images exhibited the same characteristics as in Example 20.

Example 24.

To 30 ml. VT/LM/LiM/MA 7% solution, 2.0 g. of the pigment of Example 3 were added and ball-milled for 15 days. A developer was then prepared by adding 0.7 g. Beckosol-7 (14% Solvesso 100 solution) and 0.15 g. cobalt naphthenate to 2.98 g. pigment concentrate and dispersing the mixture in 500 ml. Isopar-G by ultrasonic means. Images from such a developer exhibited high resolution, high density and very high quality. Continuous tone and low contrast were again the properties of the second-generation images.

Example 25.

A concentrated liquid toner was prepared by ball-milling 3.0 g. of the pigment of Example 10 in a 7% Solvesso 100 solution of 3.9 g. of VT/LM/LiM/MA (1.0 to 1.3 pigment-to-polymer ratio). A liquid toner was then obtained by adding to an aliquot of the concentrate to yield 0.35 g./l. pigment content the EA/EM/LM/LiSEM binder solution such to obtain 1/1.3/0.5 pigment-to-stabilizerto-binder ratio, and diluting the mixture to 1 litre with Isopar-G under ultrasonic shear.

The resultant developer had particle size < 2W was positively charged and, when used in the conventional electrophotographic process, provided excellent, neutral-toned images.

Example 26.

From the concentrate described in Example 25, another liquid toner was obtained by replacing the EA/EM/LM/LiSEM binder with chlorinated polyethylene solution at 1/1.3/0.5 pigment-to-stabilizer-to-binder ratio. The final developer was negatively charged, well-dispersed and yielded excellent, neutral images.

Example 27.

A concentrated liquid toner using the pigment of Example 11 was prepared by ball-milling 3.0 g. of the pigment as in Example 25. A diluted developer at 0.35 g./l.

pigment content was obtained as in Example 25. Excellent-quality electrophotographic images were obtained.

Example 28.

A concentrated liquid toner was prepared by ball-milling 3.0 g. of the pigment of Example 14 in a 7% Solvesso 100 solution of 3.0 g. of VT/LM/LiM/MA at 1.0 to 1.0 pigment-to-polymer ratio. A working developer was then obtained as in Example 25. The electrophographic images obtained were also of excellent quality.

WHAT WE CLAIM IS: 1. An azo pigment of the general formula:

wherein R' is -H, -COOH, -CONH2, SO2NH2 or -SO3M where M is an alkali metal or ammonium cation, R2 is a substituted or unsubstituted lower alkoxy, -OCH2CONH2 or -N(R6)R7 group where R6 and R7 are substituted or unsubstituted lower alkyl groups, R3 is hydrogen or halogen or a substituted or unsubstituted lower alkyl or lower alkoxy group or a nitro group, R4 is hydrogen or

m is 0 or 1, n is 1 when m = 0, and 1 or 2 when m = 1 (according to the charge on J), Q is -OH when m = 0 or -0- when m = 1, and J is an ammonium or metal cation.

2. An azo pigment as claimed in Claim 1 which has the general formula:

wherein R' is hydrogen or a -SO2NlI2, -SO3Na or --SO,NH, group, R2 is a lower alkoxy or -OCH2CONH2 group, and R3 is hydrogen or -NO2.

3. An azo pigment as claimed in Claim 2 in which R2 is a methoxy or -OCH2CONH2 group.

4. An azo pigment as claimed in Claim 1 in which J is an ammonium, sodium, zinc, cadmium or tin cation.

5. The azo pigments listed in Table I hereinbefore.

6. An azo pigment substantially as described herein and with reference to Examples l4, 8-10 and 11-19.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. Example 27. A concentrated liquid toner using the pigment of Example 11 was prepared by ball-milling 3.0 g. of the pigment as in Example 25. A diluted developer at 0.35 g./l. pigment content was obtained as in Example 25. Excellent-quality electrophotographic images were obtained. Example 28. A concentrated liquid toner was prepared by ball-milling 3.0 g. of the pigment of Example 14 in a 7% Solvesso 100 solution of 3.0 g. of VT/LM/LiM/MA at 1.0 to 1.0 pigment-to-polymer ratio. A working developer was then obtained as in Example 25. The electrophographic images obtained were also of excellent quality. WHAT WE CLAIM IS:

1. An azo pigment of the general formula:

wherein R' is -H, -COOH, -CONH2, SO2NH2 or -SO3M where M is an alkali metal or ammonium cation, R2 is a substituted or unsubstituted lower alkoxy, -OCH2CONH2 or -N(R6)R7 group where R6 and R7 are substituted or unsubstituted lower alkyl groups, R3 is hydrogen or halogen or a substituted or unsubstituted lower alkyl or lower alkoxy group or a nitro group, R4 is hydrogen or

m is 0 or 1, n is 1 when m = 0, and 1 or 2 when m = 1 (according to the charge on J), Q is -OH when m = 0 or -0- when m = 1, and J is an ammonium or metal cation.

2. An azo pigment as claimed in Claim 1 which has the general formula:

wherein R' is hydrogen or a -SO2NlI2, -SO3Na or --SO,NH, group, R2 is a lower alkoxy or -OCH2CONH2 group, and R3 is hydrogen or -NO2.

3. An azo pigment as claimed in Claim 2 in which R2 is a methoxy or -OCH2CONH2 group.

4. An azo pigment as claimed in Claim 1 in which J is an ammonium, sodium, zinc, cadmium or tin cation.

5. The azo pigments listed in Table I hereinbefore.

6. An azo pigment substantially as described herein and with reference to Examples l4, 8-10 and 11-19.

7. An electrographic liquid developer comprising a liquid carrier and toner

particles comprising a pigment according to any of Claims 15.

8. An electrographic developer as claimed in Claim 7 in which the liquid carrier has a dielectric constant of less than 3 and a volume resistivity greater than 10'0 ohm-cm.

9. An electrographic developer as claimed in Claim 7 or 8 in which the toner particles comprises a resinous material.

10. An electrographic developer as claimed in any of Claims 7-9 which comprises a charge control agent.

11. An electrographic liquid developer according to Claim 7 substantially as described herein and with reference to Examples 2028.