GB2385331A - Surface modified carbon black pigment prepared by reacting carbon black with an active methylene compound, a source of formaldehyde & an acidic catalyst - Google Patents

Abstract

A process for preparing a surface modified carbon black pigment having an organic group attached to the carbon black comprising the step of reacting: <SL> <LI>A) at least one active methylene or active methine compound; <LI>B) a carbon black; and <LI>C) a source of formaldehyde; </SL> in the presence of an acidic catalyst. The active methylene compound may be a cyclic compound having a ketomethylene group in a carbocyclic or heterocyclic ring. The source of formaldehyde may be paraformaldehyde. The acidic catalyst may be (95-98%) concentrated sulphuric acid oleum or polyphosphoric acid, used as a reaction medium. Such modified pigments may be used as a component of a recording liquid, for example an ink for use in an inkjet printer.

Description

1 238533 1

Modified Carbon Black FIELD OF THE INVENTION

This invention relates to a process for the preparation of surface modified carbon black pigments, to new carbon black products and to the use thereof. It particularly relates to the 5 use thereof in inks for ink jet printing.

BACKGROUND OF THE INVENTION

Carbon black pigments, for example furnace black, lamp black, acetylene black, and channel black and the like are well known under the designation C.I. Pigment Black 7 and are of wide commercial use. Carbon black is generally produced by partial combustion or 10 pyrolysis of organic (i.e. carbon containing) fuels. The pigment substantially consists of particles of elementary carbon together with other materials dependent on the exact method of manufacture. Carbon black is relatively inexpensive and has many desirable properties such as excellent lightfastness, high opacity, a good black colour, and resistance to acids, alkalis, soaps, and solvents.

15 In recent years, there has been increased interest in the use of carbon black pigments in inks for ink jet printers. In an ink jet printer, droplets of a recording fluid, the ink, are formed by forcing the fluid through a tiny nozzle (or a series of nozzles) under computer control and applied to the recording material such as paper or transparent film. There are several kinds of ink jet printers, for example thermal and piezo drop on demand printers and continuous 20 ink jet printers. In a thermal printer, the droplets are ejected on demand from tiny ink reservoirs by heating to form bubbles as the print head scans the recording material. In a piezo drop on demand printer the droplets are expelled by flexure of a piezoelectric element controlled by the computer. In the continuous printing method, the droplets may be electrostatically charged and attracted to an oppositely charged platen behind the recording 25 material, the trajectories of the droplets can be controlled by means of electrically controlled deflection plates to hit the desired spot on the paper, and unused droplets may be deflected away from the paper into a reservoir for recycling.

! 2 It is common to formulate black pigmented inks for the ink jet process as dispersions comprising finely divided particles of carbon black stabilised by one or more stabiliser or dispersant in a suitable liquid carrier vehicle. Typically the carrier vehicle comprises a predominantly aqueous solvent, that is to say water together optionally with at least one 5 water soluble organic cosolvent and other additives. The dispersant serves to facilitate the wetting and de-aggregation of the raw pigment, to maintain colloidal particle stability, and to retard particle re-agglomeration and settling out during use. Several dispersants suitable for use in aqueous ink jet inks are known in the art, but there are limitations to the use of such dispersants in that they can affect the desired properties of the ink such as the 10 viscosity and surface tension, and can also give rise to the generation of foam either when the ink is prepared or in use.

Over the years, much effort has been expended in attempts to obviate the use of dispersants by modifying the surface chemistry of carbon black to provide stable pigments, sometimes called self-dispersing carbon black. For instance, it is well known that a carbon black 15 surface can be oxidised with a variety of treating agents such as, for example, sodium hypochlorite as disclosed in United States Patent 2,439,442. European Patent Applications 0 802 247 A and 1 035 178 A disclose aqueous ink jet inks comprising such oxidised products. Sulphonation of a carbon black surface using sulphuric or chlorosulphonic acid is also known. These methods provide hydrophilic modification of the carbon black surface.

20 United States Patent 3,043,708 describes modified carbon blacks having hydrocarbon groups chemically attached to the surface of the carbon black prepared by reacting carbon black with an alkylating agent in the presence of a Friedel-Crafts type reaction catalyst. The hydrocarbon groups which reportedly can attach to the surface of the carbon black include aliphatic and aromatic groups. These hydrophobically modified products are disclosed as 25 useful in rubbers and the like but not in aqueous systems.

United States Patent 5,851,280 provides a processes for preparing a modified carbon black product involving the reaction of at least one diazonium salt with a carbon black in a protic reaction medium, and United States Patents 5,803,959 and 5,885,335 disclose modified carbon black products and inks, including aqueous inks, comprising these products.

Despite the technology discussed above, there remains a need to modify the surface chemistry of carbon black and impart desired properties to the carbon black suitable for use in ink jet inks.

5 SUMMARY OF THE INVENTION

Accordingly, the present invention provides a process for preparing a surface modified carbon black pigment having an organic group attached to the carbon black comprising the step of reacting: A) at least one active methylene compound, 10 B) a carbon black; and C) a source of formaldehyde; in the presence of an acidic catalyst.

Any carbon black may be used in the processes of this invention, for example, furnace black, lamp black, gas black, thermal black, acetylene black, and channel black. Further, 15 the carbon black may be basic, neutral, or acidic. Furthermore the carbon black may be used in fluffy or pelleted form. Gas black or furnace black of small particle size is preferred. Any source of formaldehyde may be used in the process of the invention, but the preferable source of formaldehyde is paraformaldehyde.

20 By active methylene compound is meant an organic compound possessing a reactive methylene or methine position which is capable of reaction with electrophilic reagents.

Such compounds are well known as coupler intermediates in dye synthesis, for example as colour couplers in the synthesis of azo dyes, azomethine dyes, merocyanine dyes, oxonol dyes, and in colour photography and include in particular compounds having a 25 ketomethylene group. Almost any organic compound possessing such a reactive position may be used in the process of the invention, but suitable compounds include in particular heterocyclic compounds having an active methylene position in the ring, such as for example pyrazolone compounds and derivatives, pyridone compounds and derivatives,

(thio)barbiturate compounds and derivatives, (thio)hydantoin compounds and derivatives, isoxazolidone compounds and derivatives, (thio)indoxyl compounds and derivatives, coumaranone compounds and derivatives, oxindole compounds and derivatives, pyrimidazolone compounds and derivatives, glutaconimide compounds and derivatives, 5 homophthalimide compounds and derivatives, and the like. These compounds are known or can be prepared by methods well known in the art.

The active methylene compound may be a substituted compound wherein the substituents may be any functional group compatible with the conditions of the reaction. Suitable functional groups for the preferred heterocyclic compounds include, but are not limited to, 10 R. OR, carboxylic acids or salts thereof, halogen, CN, NRR', sulphonic acids or salts thereof, NR(COR'), CONRR', or SO2NRR', wherein the groups R and R', which can be the same or different, are independently hydrogen, branched or unbranched Cal - C20 substituted or unsubstituted, saturated or unsaturated hydrocarbon, e.g., alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, substituted or unsubstituted aryl, substituted or unsubstituted 15 heteroaryl, substituted or unsubstituted alkylaryl, or substituted or unsubstituted arylalkyl, or the groups R and R' may be combined to form a ring system.

Preferred substituents include in particular groups comprising an ionic or an ionisable group as a functional group. An ionisable group is one which is capable of forming an ionic group in the medium of use. The ionic group may be an anionic group or a cationic group 20 and the ionisable group may form an anion or a cation. Suitable groups include salt forming groups such as sulphonic acids, carboxylic acids, phosphoric acids, and basic nitrogen containing groups.

Especially suitable active methylene heterocyclic compounds include pyrazolone compounds of the general structure I 25 R; I-\ R N7o I Rl

s wherein the groups R. and R2 which can be the same or different, are independently hydrogen, branched or unbranched Cal - C20 substituted or unsubstituted, saturated or unsaturated hydrocarbon, e.g., alkyl, alkenyl, alkynyl, cycloaLkyl, cycloalkenyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted 5 alkylaryl, or substituted or unsubstituted arylalkyl; and the group R3 is hydrogen, aliphatic which may be substituted, aryl which may be substituted, heterocyclyl which may be substituted, or a group NO2, COOR, OR, NRR', CONRR', NRCOR', or NRSO2R' wherein R and R' are as defined above; or wherein two or more of the groups R. R', R., R2, and R3 are combined to form a ring system or systems. By aliphatic is meant a straight chain, 10 branched chain, or cyclic aliphatic group having up to 20 carbon atoms.

It is to be understood that pyrazolones of fonnula I wherein the group R2 is hydrogen are potentially tautomeric and may exist as other tautomers such as the corresponding 2-pyrazolin-5-ones. Preferably the group R is a substituted aryl group and the group R2 is hydrogen, and therefore particularly preferred pyrazolones are compounds of general 15 formula II R3 N R8,,R6

20 11

R7\R5 II

R4 25 wherein the group R3 has the meaning defined above and the groups R4, R5, R6, R7, and R8 are each independently H. R. halogen, NO2, phosphoric acids or salts thereof, sulphonic acid or salt thereof, or a group COOR, OR, NRR', CONRR', NRCOR', NRSO2R', or SO2NRR' wherein R and R' have the meanings assigned above.

Further especially suitable active methylene heterocyclic compounds include 30 hydroxypyridone compounds of the general structure III

x HoJ:No III 5 wherein the group R has the meaning assigned above and the groups X and Y are each independently H. R. CN, NO2, COOR, OR, NRR', CONRR', NRCOR', NRSO2R', or SO2NRR' wherein R and R' have the meanings assigned above Further especially suitable active methylene heterocyclic compounds include barbiturate compounds of the general structure IV o 10 AN O'lNO IV R Wherein the groups R and R' have the meanings assigned above.

It is to be understood that active methylene compounds in general, and the preferred 15 heterocyclic compounds of formula I, II, III, and IV in particular, are potentially tautomeric, and that all relevant tautomers of such compounds are of use in this invention.

The process of the invention may be carried out under a wide variety of conditions and in general is not limited by any particular condition. The process of the invention may be carried out in any reaction medium which allows the reaction between the active methylene 20 compound, source of formaldehyde, and the carbon black to proceed. Preferably, the reaction medium comprises the acidic catalyst and is a dehydrating acidic solvent such as concentrated (9S - 98%) sulphuric acid, oleum, or polyphosphoric acid and most preferably the reaction medium comprises approximately 95 96% concentrated sulphuric acid. The conditions for the reaction may vary, primarily depending on the reactivity of the 25 heterocyclic compound and the desired degree of reaction of the carbon black, but reaction

temperatures in 96% sulphuric acid typically range from about 50 C to about 110 C and reaction times may be in the range from 1 - 10 hours.

The carbon black product from the reaction may be isolated by means known in the art.

Further, the resultant carbon black product can be treated to remove impurities by known 5 techniques, if desired. For instance, isolation of the products may generally be achieved by drowning out of the acid solution into ice or a convenient solvent, filtration, and washing free from acid. If desired, the product may be further purified of soluble impurities by dialysis. Furthermore, the process of the invention may also produce organic by-products, and these may be removed, for example, by extraction with suitable organic solvents. Other 10 suitable methods may be used as known to those of skill in the art. The products may be characterized by, for example, elemental analysis or other methods known in the art.

Additionally, the carbon black product may be dried by techniques used for conventional carbon blacks, for example by drying in ovens and rotary kilns.

As a consequence of the tautomeric nature of many active methylene organic compounds 15 the position of attachment to the pigment surface is not defined. Without wishing to be constrained by any particular theory, with the preferred heterocyclic active methylene compounds it is believed that reaction occurs with the formaldehyde at the active position to provide a modified carbon black product which may be represented by the general formula V 20 PB - [CH2Het]n V wherein PB represents the carbon black particle, Het represents the radical of the heterocyclic ring, and n represents a degree of substitution on the surface. The number n of formula V may vary over wide limits and may primarily be determined by the stoichiometry and conditions of the reaction. However as the steric hindrance of the 25 heterocyclic group increases, the maximum possible number of organic groups attached to the carbon black from the reaction may be diminished.

An advantage of the carbon black products having an attached organic group substituted with an ionic or an ionisable group is that the carbon black product may have increased

water dispersibility relative to the corresponding untreated carbon black. In general, but without limiting the invention, it can be noted that the water dispersibility of a carbon black product increases as the number of ionisable functional groups modifying the surface increases. Thus, increasing the number of ionisable groups associated with the carbon black 5 product should increase its water dispersibility and permits control of the water dispersibility to a desired level. In addition, the dispersibility of a pigment containing a basic functional group such as an amine may generally be increased by lowering the pH of the aqueous medium and the dispersibility of a pigment containing an acidic functional group such as a carboxylic or sulphonic acid or salt may generally be increased by raising 10 the pH of the aqueous medium.

If basic nitrogen substituents are present or if the active methylene organic component is sufficiently basic then the product from the reaction in the preferred sulphuric acid reaction medium may frequently be isolated in the form of an addition compound with sulphuric acid, that is to say a sulphate or bisulphate salt. After isolation of the product, this sulphuric 15 acid may be neutralised and salt formation of any sulphonic acid or carboxylic acid substituent groups may be achieved if desired by treating an aqueous slurry of the product with a suitable base or salt, such as ammonium hydroxide or sodium hydroxide.

When concentrated sulphuric acid or oleum is used as the reaction medium, or if the temperature is excessive, it is possible for sulphonic acid groups to be incorporated to a 20 small extent as additional surface modifying substituents on the carbon black. This small degree of additional substitution may be advantageous.

The modified carbon black products prepared according to a process of the invention may be used in the same applications as conventional carbon blacks, but the pigments prepared according to the invention may provide advantageous properties not associated with 25 conventional carbon blacks. The groups attached to the carbon black can be used to modify and improve the properties of a given carbon black for a particular use. Such uses include, but are not limited to, plastic compositions, aqueous inks, aqueous coatings, rubber compositions, paper compositions, and textile compositions. The modified carbon black products are especially useful in aqueous ink formulations.

Therefore the present invention also provides recording liquids, for example inks, comprising the surface modified carbon black pigments prepared according to the process of the invention. These recording liquids are suitable in particular for use in aqueous ink jet inks such as are generally used in office or home printers but may also be used in 5 conventional printing processes, for example as flexographic ink compositions. According to this aspect of the present invention there is provided a recording liquid comprising essentially: a) an aqueous carrier medium; and b) at least one carbon black pigment prepared from the reaction of at least one active 10 methylene organic compound having a reactive position; a carbon black; and a source of formaldehyde; in the presence of an acidic catalyst as hereinbefore described.

The aqueous carrier medium is water or a mixture of water and at least one water soluble organic cosolvent. Deionised water is commonly used. The water soluble organic cosolvent may be any organic solvent which has sufficient solubility in water. Representative 15 examples of watersoluble organic solvents that may be selected include: (1) alcohols, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, nbutyl alcohol, sec-butyl alcohol, t-butyl alcohol, iso-butyl alcohol, neopentyl alcohol, benzyl alcohol, firfiaryl alcohol, and tetrahydrofirfuryl alcohol: (2) ketones or ketoalcohols such as acetone, methyl ethyl ketone and diacetone alcohol; 20 (3) ethers, such as tetrahydrofuran and dioxane; (4) esters, such as ethyl lactate; (5) polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, glycerol, 2-methyl-2,4-pentanediol, 1,5pentanediol, 1,2-hexanediol, and 1,2,6-hexanetriol; 25 (6) lower alkyl mono-or all-ethers derived from alkylene glycols, such as ethylene glycol monomethyl (or -ethyl) ether, diethylene glycol mono-methyl (or -ethyl) ether, propylene glycol mono-methyl (or -ethyl) ether, triethylene glycol mono-methyl (or -ethyl) ether and diethylene glycol all-methyl (or -ethyl) ether; (7) sulphur-containing compounds such as tetramethylene sulphone, dimethyl sulphoxide, 30 and thiodiglycol; and

(8) nitrogen containing organic compounds such as urea, N,N-dimethyl imidazolidinone, pyrrolidone and N-methyl-2-pyrrolidone.

Preferably the aqueous carrier medium is a mixture of water and at least one water soluble organic cosolvent. Selection of a suitable mixture of water and water soluble organic 5 cosolvent depends on the requirements of the specific application, such as the printer in use, the desired surface tension and viscosity, the type of substrate onto which the ink will be printed, and the drying time of the pigmented ink jet ink. A mixture of water and at least one water soluble organic solvent having at least two hydroxyl groups is preferred.

Therefore preferred organic cosolvents include for example diethylene glycol, triethylene 10 glycol, polyethylene glycol, thiodiglycol, glycerol, 1,2-hexanediol, 1,5-pentanediol, and mixtures comprising these solvents. The aqueous ink composition may contain up to 50% of the organic cosolvent or mixture of organic cosolvents. Preferably the ink comprises up to 10% of each organic cosolvent, and most preferably between about 5% and about 10% of each of a mixture of at least two organic cosolvents.

15 The ink compositions of this aspect of the invention preferably contain from 0 5% to 20%, more preferably from 0 5% to 10%, and especially from 1% to 5%, by weight of the surface modified carbon black pigment based on the total weight of the ink.

The inks of the invention may also comprise other components which are advantageously added to aqueous ink jet inks, such as surfactants, viscosity modifiers, pH buffers, and 20 biocides. In addition, sequestering agents such as EDTA may also be included to eliminate deleterious effects of heavy metal impurities and optionally further additives, for example for adjusting the electrical conductivity, specific heat or coefficient of thermal expansion, may also be present. The pH of the ink may be controlled by appropriate addition of acid or base, for example to the final ink as required. The pH of the ink may be between about 5 25 and about 10, preferably between about 7 and about 8 5.

Further, the inks of the invention may also comprise a water soluble binder resin in amounts that do not compromise the purpose of the invention. The water soluble resin is preferably an acrylic polymer having an average molecular weight of between about 2000 and about 20000, an acid number of between about 150 and about 250, and a glass

transition temperature between about 70 and about 100 . Such acrylate polymers are well known. The carbon black products of the invention, either as predispersion or as a solid, can be incorporated into the aqueous ink formulation using standard techniques. Use of a readily 5 dispersible carbon black product of the invention provides a significant advantage and cost saving by reducing or eliminating the milling steps generally used with other conventional carbon blacks.

According to a further aspect of the present invention there is provided a process for printing a substrate with an ink composition using an ink jet printer, characterized in that 10 the ink composition comprises at least one modified carbon black pigment prepared according to the process of the invention. The inks of the invention may be used with a variety of ink jet printers such as continuous, piezoelectric drop-on-demand and thermal or bubble jet drop-on-demand printers, and are particularly adapted for use in piezoelectric and thermal drop on demand printers. The printer may be a desk top printer or a wide 15 format ink jet printer.

The following examples are intended to illustrate, not limit, the claimed invention.

Example 1

A commercial Carbon Black pigment [Black S170] (3 0g) was stirred in concentrated sulphuric acid (50g) at ca 80 (oil bath temperature), to which was added a solution of 20 1-(4-sulphophenyl)-3-methyl-5-pyrazolone (2 54g, 10 mnol) in concentrated sulphuric acid (50g). Paraformaldehyde (0 3g; 10 mmol) was then added to this mixture and heating was continued for a further 21/2 hours. The reaction mixture was poured into ice (130g), filtered, washed (water; methanol; acetone) and dried in vacuo to give a black solid 3 18g. This material was then heated under reflux in methanol (120 ml) for 7h, allowed to 25 cool to room temperature, filtered, washed (water; methanol, acetone) and dried in vacuo i over phosphorus pentoxide to provide the inventive modified pigment as a black solid, yield 2 63g, Found by microanalysis: C = 90 1%, H = 0 2%, N = 1 2%. For comparison, ' the unmodified starting black had C = 92 20%, H = 0 46%, N = 0 70% ' i L

Dispersion test:- The dispersibility of the modified pigment was tested by treatment of a 5% suspension in water with a Silverson mixer for 20 minutes. The product was found to give an acceptable dispersion which did not settle out on standing overnight at room temperature; The pH was measured at 2 6.

5 As a control, the dispersion test was repeated with an unmodified pigment. The attempted dispersion severely thickened within 2 minutes; The pH was measured at 4 0.

The dispersion test was repeated with the inventive modified carbon black pigment at 1% loading. The product gave an acceptable dispersion which did not settle out on standing overnight at room temperature; The pH was measured at 3 5.

Examule 2 A sample of the same commercial Carbon Black pigment as in Example 1 (3 fig) was stirred in warm concentrated sulphuric acid (50g) and a solution of 1-(4-sulphophenyl)-5-pyrazolone-3-carboxylic acid (5 68g; 20 mmol) in concentrated 15 sulphuric acid (60g) was added. This stirred mixture was heated at ca 90 (oil bath temperature) and paraformaldehyde (0 6g; 20 mmol) was then added. The reaction was heated for a further 31/z hours. The reaction was poured onto ice (lSOg), filtered and dried in air to give a black solid 6 6g. This material was heated under reflux in methylated spirit (180ml) for 3h, filtered, washed (spirit; acetone) and dried in vacua over phosphorus 20 pentoxide to provide the modified pigment as a black solid, yield 2 gig; Found: C = 877%,H=09%,N=1 2%.

Dispersion test:- The dispersibility of the modified pigment was tested by treatment of a 5% suspension as in Example 1. The pigment dispersed successfully and did not settle out on standing overnight at room temperature. The pH was measured at 1 7.

25 Print test:- An ink was prepared using the modified pigment using the following formulation. l

Component Quantity weight % Modified pigment 3 Polyethylene glycol mw 300 10 Diethylene glycol 10 Dioctyl sulphosuccinate 0 2 Deionised water to 100 The pH was adjusted to 8 5 by addition of ammonia. The mixture was treated with a Silverson mixer for 20 minutes at medium speed and filtered through an 8,um membrane filter. Examination with a microscope showed a good dispersion. The ink was then loaded 5 into an 51626a cartridge and a 100% density test page printed using a Hewlett-Packard Deskjet 420 printer using "best quality" settings. The ink printed successfully to give an excellent dense black print.

Example 3

A solution of barbituric acid (2 56g; 20 mmol) in concentrated sulphuric acid (60 ml) was 10 added to a warm, stirred mixture of the same commercial Carbon Black pigment as in Example 1 (3 fig) in concentrated sulphuric acid (60 ml). Paraformaldehyde (0 6g; 20 mmol) was added and the mixture heated at ca 100 (oil bath temperature) for 3h. The reaction was cooled to room temperature and poured onto ice (200g), filtered, washed (water; methanol; acetone) and dried in air. This black solid was then heated under reflex 15 in methanol (150 ml) for 3h, filtered whilst hot, washed (methanol; acetone) and dried in vacuo over phosphorus pentoxide to give a black solid, yield 3 leg; Found: C = 88 9%, H =05%,N= 1 7%.

Dispersion Test:- The dispersibility of the modified pigment was tested by adding a sample of the modified carbon black (l Og) to water (20 ml) and stirring with a small Silverson 20 mixer for 20 min at maximum rpm. The dispersion was successful, but thickened significantly at ca 10 min. Example 4

A warm solution of citrazinic acid (3 1g; 20 mrnol) in concentrated sulphuric acid (50 ml) was added to a warm, stirred mixture of the same commercial Carbon Black pigment as in

Example 1 (3 0g) in concentrated sulphuric acid (50 ml). Paraformaldehyde (0 6g; 20 mmol) was then added and the reaction mixture heated at ca 100 (oil bath temperature) for 4h. The reaction was cooled to room temperature and poured onto ice (200g), filtered, washed (water; methanol; acetone) and dried in air. This material was then heated under 5 reflux in methanol (160 ml) for 3h, filtered whilst hot, washed (methanol; acetone) and dried in vacuo over phosphorus pentoxide to afford a black solid, yield 3 3g; Found: C = 83 48 %, H = 0 81%, N = 1 58%.

Dispersion Test:- The dispersibility of the modified pigment was tested by adding a sample 10 of the modified carbon black (l Og) to water (20 ml) and stirring with a small Silverson mixer for 20 min at maximum rpm. The dispersion remained fluid and microscopic examination indicated a successful dispersion.

Example 5 - conko1 As a condole a sample of the same commercial Carbon Black pigment as in Example 1 was 15 heated in concentrated sulphuric acid at ca 100 (oil bath temperature) for 4h, in the absence of any organic compound and of paraformaldehyde. The product was isolated as in Example 4 and subjected to the same dispersion test as in Example 1. The product failed to disperse, showing that the dispersibility of the inventiveproducts is due to the reaction with the organic component and paraformaldehyde.

Claims (9)

1. A process for preparing a surface modified carbon black pigment having an organic group attached to the carbon black comprising the step of reacting: A) at least one active methylene compound, 5 B) a carbon black, and C) a source of formaldehyde; in the presence of an acidic catalyst.

2. A process according to claim 1 wherein the active methylene compound is a heterocyclic compound having a ketomethylene group in the heterocyclic ring.

10

3. A process according to either of claims 1 or 2 wherein the active methylene compound is selected from pyrazolone compounds and derivatives, pyridone compounds and derivatives, (thio)barbiturate compounds and derivatives, (thio)hydantoin compounds and derivatives, isoxazolidone compounds and derivatives, 1,3-indanedione compounds and derivatives, (thio)indoxyl compounds 15 and derivatives, coumaranone compounds and derivatives, oxindole compounds and derivatives, pyrimidazolone compounds and derivatives, glutaconimide compounds and derivatives, and homophthalimide compounds and derivatives.

4. A process according to claim 3 wherein the active methylene compound is a pyrazolone of general formula II R3 Nemo R8'R6 25 R7R5 II

wherein the group R3 is hydrogen, aliphatic which may be substituted, aryl which 30 may be substituted, heterocyclyl which may be substituted, or a group NO2, COOR, OR, NRR', CONRR', NRCOR', or NRSO2R' wherein R and R' which can be the same or different, are independently hydrogen, branched or unbranched C, - C20

r substituted or unsubstituted, saturated or unsaturated hydrocarbon, e.g. , alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted alkylaryl, or substituted or unsubstituted arylalkyl; the groups R4, R5, Ret, R., and R8 are each 5 independently H. R. halogen, NO2, phosphoric acids or salts thereof, sulphonic acid or salt thereof, or a group COOR, OR, NRR', CONRR', NRCOR', NRSO2R', or SO2NRR' wherein R and R' are as defined above; or wherein two or more of the groups R. R', R., R2, and R3 are combined to form a ring system or systems.

5. A process according to any of claims 1 - 4 wherein the active methylene compound 10 is substituted by an ionic group or an ionisable group as a functional group.

6. A process according to any of clains 1 - 5 wherein the acidic catalyst comprises approximately 95 - 96% concentrated sulphuric acid as reaction medium.

7. A process according to any of claims 1 - 6 wherein the source of formaldehyde is paraformaldehyde. 15

8. A recording liquid comprising: a) an aqueous carrier mediun; and b) at least one carbon black pigment prepared from the reaction of at least one active methylene compound having a reactive position; a carbon black; and a source of formaldehyde; in the presence of an acidic catalyst.

20

9. A process for printing a substrate with an ink composition using an ink jet printer, characterised in that the ink composition comprises at least one modified carbon black pigment prepared according to the process of claim 1.