Aqueous pigmented inks for ink jet printers

Abstract: A pigmented ink for ink jet printers which comprises an aqueous carrier medium, pigment particles dispersed in an AB or BAB block copolymer having a hydrophilic segment and a segment that links to the pigment, and an effective amount of a surfactant sufficient to decrease the drying time of the ink. The A block and the B block(s) have molecular weights of at least 300. These inks give images having good print quality, water and smear resistance, lightfastness, and storage stability.

Description: FIELD OF THE INVENTION This invention relates to aqueous pigmented inks for ink jet printers, and, more particularly, to aqueous pigmented inks wherein the pigment dispersant is an acrylic block polymer. BACKGROUND OF THE INVENTION Ink jet printing is a non-impact method for recording information in response to an electronic signal, such as that generated by a computer. In the printer the electronic signal produces droplets of ink that are deposited on a substrate such as paper. Ink jet printers have found broad commercial acceptance due to their rapid printing speeds, relatively quiet operation, graphic capability and low cost. The printed image produced by an ink jet printer, as in most printing processes, consists of discrete dots. While satisfactory for many applications, conventional dye based inks are not well suited for recording high quality images since the dye tends to wick in the paper fibers, causing the dots to have a feathered edge. Thus, the dots do not have the sharp boundaries needed to produce a high resolution image unless special paper is used. Also, the dyes tend to smear after the printing operation due to their high water solubility. Limitations of dye based inks are particularly apparent when it is desired to record a high quality, multicolored image. Color selection is limited in that many of the readily available dyes lack color fastness (i.e., the dye tends to fade upon exposure to ultraviolet light) or do not have enough solubility to give the desired chroma. Moreover, the tendency of the printed dots to wick, or bleed together, is an aggravated problem because the printing of a high quality image depends on the formation of small, sharply defined dots of each printing color. While some of the problems associated with dye based inks may be overcome or alleviated to some extent by using special substrates, such as coated paper, there is a need for improved inks for ink jet printing. Water-based pigment dispersions are well known in the art, and have been used commercially for applying films, such as paints, to various substrates. The pigment dispersion is generally stabilized by either a non-ionic or ionic technique. When using the non-ionic technique, the pigment particles are stabilized by a polymer that has a water-soluble, hydrophilic section that extends into the water and provides entropic or steric stabilization. Representative polymers useful for this purpose include polyvinyl alcohol, cellulosics, ethylene oxide modified phenols, and ethylene oxide/propylene oxide polymers. While the non-ionic technique is not sensitive to pH changes or ionic contamination, it has a major disadvantage for many applications in that the final product is water sensitive. Thus, if used in ink applications or the like, the pigment will tend to smear upon exposure to moisture. In the ionic technique, the pigment particles are stabilized by a polymer of an ion containing monomer, such as neutralized acrylic, maleic, or vinyl sulfonic acid. The polymer provides stabilization through a charged double layer mechanism whereby ionic repulsion hinders the particles from flocculating. Since the neutralizing component tends to evaporate after application, the polymer then has reduced water solubility and the final product is not water sensitive. U.S. Patent 4,597,794 to Canon proposes an aqueous ink dispersion for ink jet printers in which pigment is contained in a polymer having ionic hydrophilic segments and aromatic hydrophobic segments that adhere to the pigment surface. While the random polymer dispersants proposed therein offer improved stability for the dispersed pigment, further improvements are desired to meet the demanding needs of commercial ink jet printers. SUMMARY OF THE INVENTION The present invention provides a thermal ink jet pigmented ink comprising an aqueous carrier medium and particles of pigment stabilized by an AB or BAB block copolymer comprising an A block which is a hydrophobic homopolymer or copolymer segment which serves to link with the pigment, and a B block which is a hydrophilic polymer segment or salt thereof which serves to disperse the pigment in the aqueous medium, and the ink contains an effective amount of a surfactant sufficient to decrease the drying time of the ink, wherein the AB or BAB block copolymer is selected from AB or BAB block copolymers wherein: (a) the A segment is a hydrophobic homopolymer or copolymer of an acrylic monomer having the formula CH 2 =C(X) (Y) wherein X is H or CH 3 ; and Y is C(O)OR 1 , C(O)NR 2 R 3 , or CN, wherein R 1 is an alkyl, aryl, or alkylaryl group having 1 to 20 carbon atoms, and R 2 and R 3 are hydrogen or an alkyl, aryl, or alkylaryl group having 1 to 9 carbon atoms; said A segment having an average molecular weight of at least approximately 300 and being water insoluble; and (b) the B segment is a hydrophilic polymer, or salt thereof, of (1) an acrylic monomer having the formula CH 2 =C(X) (Y 1 ), wherein X is H or CH 3 ; and Y 1 is C(O)OH, C(O)NR 2 R 3 , C(O)OR 4 NR 2 R 3 or C(O)OR 5 ; wherein R 2 and R 3 are hydrogen or an alkyl, aryl, or alkylaryl group having 1 to 9 carbon atoms; R 4 is an alkyl diradical having 1 to 5 carbon atoms; and R 5 is an alkyl diradical having 1 to 20 carbon atoms and optionally containing one or more hydroxyl or ether groups; or (2) a copolymer of the acrylic monomer of (1) with an acrylic monomer having the formula CH 2 =C(X) (Y) where X and Y are the substituent groups defined for said A segment; said B segment having an average molecular weight of at least approximately 300 and being water soluble, with the proviso that said B segment(s) constitute 10 to 90% of said block copolymer by weight. Preferred A segments are polymers and copolymers methyl methacrylate, butyl methacrylate, or 2-ethylhexyl methacrylate. Polymers or copolymers of methacrylic acid or dialkylaminoethyl methacrylate, where alkyl is methyl through butyl, are preferred as the B segments. The B block preferably comprises 25 to 65%, by weight of the entire polymer. The pigmented inks generally will contain 0,1 to 10% pigment, by weight, but may contain higher amounts, such as 30%, depending on the selected pigment and block polymer, and the ink jet printer. The inks are extremely stable, have low viscosity, exhibit excellent print quality, have long crusting time, and provide excellent smear resistance after drying. They may be used with a variety of ink jet printers, and are particularly adapted for use in thermal ink jet printers. DETAILED DESCRIPTION OF THE INVENTION The present invention provides inks having a combination of properties particularly suited for use in ink jet printers in general, and thermal ink jet printers in particular. The inks are aqueous dispersions of pigment particles, stabilized by polymers, that are stable over long periods, both in storage and in the printer. The inks may be adapted to the requirements of a particular ink jet printer to provide a balance of light stability, smear resistance, viscosity, surface tension, high optical density, and crust resistance. Resulting printed images are of high quality in that the individual dots are round with sharp edges, and there is little bleeding, feathering, or strike through. ACRYLIC BLOCK COPOLYMER The polymer is an AB or BAB block copolymer wherein the A block is hydrophobic and serves to link with the pigment, and the B block is hydrophilic and serves to disperse the pigment in the aqueous medium. Selection of the polymer for a specific application will depend on the selected pigment and aqueous medium. The polymer is an AB or BAB block copolymer as defined above. The A block is a polymer or copolymer prepared from at least one acrylic monomer having the formula set forth above. The R 1 , R 2 and R 3 groups optionally may contain hydroxy, ether, OSi(CH 3 ) 3 groups, and similar substituent groups. Representative monomers that may be selected include, but are not limited to, the following: methyl methacrylate (MMA), ethyl methacrylate (EMA), propyl methacrylate, n-butyl methacrylate (BMA or NBMA), hexyl methacrylate, 2-ethylhexyl methacrylate (EHMA), octyl methacrylate, lauryl methacrylate (LMA), stearyl methacrylate, phenyl methacrylate, hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2- ethoxyethyl methacrylate, methacrylonitrile, 2-trimethylsiloxyethyl methacrylate, glycidyl methacrylate(GMA), p-tolyl methacrylate, sorbyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, lauryl acrylate, stearyl acrylate, phenyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate acrylonitrile, 2-trimethylsiloxyethyl acrylate, glycidyl acrylate, p-tolyl acrylate, and sorbyl acrylate. Preferred A blocks are homopolymers and copolymers prepared from methyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, or copolymers of methyl methacrylate with butyl methacrylate. The A block also may contain a hydrophilic monomer such as CH 2 =C(X) (Y)', wherein X is H or CH 3 and Y' is C(O) OH, C(O)NR 2 R 3 , C(O)OR 4 NR 2 R 3 , C(O)OR 5 , or their salts, wherein R 2 and R 3 may be H or C1 to C9 alkyl, aryl, or alkylaryl, R 4 is a C1 to C5 alkyl diradical, and R 5 is a C1 to C20 alkyl diradical which may contain hydroxy or ether groups, to provide some changes in solubility. However, there should not be enough hydrophilic monomer present in the A block to render it, or its salt, completely water soluble. The B block is a polymer prepared from at least one acrylic monomer having the formula provided above. Representative monomers include methacrylic acid (MAA), acrylic acid, dimethylaminoethyl methacrylate (DMAEMA), diethylaminoethyl methacrylate, t-butylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide, methacrylamide, acrylamide, and dimethylacrylamide. Homopolymers or copolymers of methacrylic acid or dimethylaminoethyl methacrylate are preferred. The acid containing polymer may be made directly or may be made from a blocked monomer with the blocking group being removed after polymerization. Examples of blocked monomers that generate acrylic or methacrylic acid after removal of the blocking group include: trimethylsilyl methacrylate (TMS-MAA), trimethylsilyl acrylate, 1-butoxyethyl methacrylate, 1-ethoxyethyl methacrylate, 1-butoxyethyl acrylate, 1-ethoxyethyl acrylate, 2-tetrahydropyranyl acrylate, and 2-tetrahydropyranyl methacrylate. The B block may be a copolymer of an acid or amino containing monomer with other monomers, such as those used in the A block. The acid or amino monomer may be used in a range of 10 to 100%, preferable in a range of 20 to 60%, of the B block composition. The B block(s) generally will constitute 10 to 90%, preferably 25 to 65%, of the entire block polymer by weight. Block copolymers that are selected in practicing the invention have a number average molecular weight below 20,000, preferably below 15,000, and typically in the range of 1,000 to 3,000. Preferred block copolymers have number average molecular weights in the range of 500 to 1500 for each A and B block. Representative AB and BAB block polymers that may be selected include the following, wherein the values recited represent the degree of polymerization of each monomer. A double slash indicates a separation between blocks and a single slash indicates a random copolymer. For example, MMA//MMA/MMA 10//5/7.5 is an AB block polymer with an A block of MMA that is 10 monomer units long - molecular weight of 1000 - and a B block that is a copolymer of MMA and MAA with 5 monomer units of MMA and 7.5 units of MAA; molecular weight of the B block is 1145. AB BLOCK POLYMER MOL. WEIGHT EHMA//EHMA/MAA 3//3/5 1618 5//2.5/2.5 1700 5//5/10 2840 20//10/10 6800 15//11/22 7040 EHMA//LMA/MAA 10//10/12 5552 EHMA//MMA/EHMA/MAA 10//5/5/12 4502 EHMA//MMA/MAA 5//5/10 2350 5//10/10 2850 EHMA//MAA 15//5 3400 BMA//BMA/MAA MOL. WEIGHT 5//2.5/2.5 1280 10//5/10 3000 20//10/20 6000 15//7.5/3 3450 5//5/10 2300 5//10/5 2560 AB BLOCK POLYMER BMA//MMA/MAA 15//15/5 4060 15//7.5/3 3140 10//5/10 2780 MMA//MMA//MAA 10//5/10 10//5/10 2360 2360 10//5/5 1930 10//5/7.5 2150 20//5/7.5 3150 15/7.5/3 2770 MMA//EHMA/MAA 5//5/10 2350 10//5/10 2850 BMA/MMA//BMA/MAA 5/5//5/10 2780 BMA//HEMA/MAA 15//7.5/3 3360 7-5//7.5/3 2300 15//7.5/7.5 3750 BMA//BMA/DMAEMA MOL. WEIGHT 10//5/10 3700 BMA//BMA/DMAEMA/MAA 10//5/5/5 2635 BAB BLOCK POLYMER BMA/MAA//BMA//BMA/MAA 5/10//10//5/10 4560 MMA/MAA //MMA //MMA/MAA 5/7.5//10//5/7.5 3290 Preferred block polymers are methyl methacrylate//methyl methacrylate/methacrylic acid (10//5/7.5), 2-ethylhexyl methacrylate//2-ethylhexyl methacrylate/methacrylic acid (5//5/10), n-butyl methacrylate//n-butyl methacrylate/methacrylic acid (10//5/10), ethylhexyl methacrylate//methyl methacrylate/methacrylic acid (5//10/10), n-butylmethacrylate//2-hydroxyethyl methacrylate/methacrylic acid (5//10/10), n-butylmethacrylate//2-hydroxyethyl methacrylate/methacrylic acid (15//7.5/3), methyl methacrylate//ethylhexyl methacrylate/methacrylic acid (5//5/10), and butyl methacrylate//butyl methacrylate/dimethylaminoethyl methacrylate (10//5/10). To solubilize the B block into the aqueous medium, it may be necessary to make salts of either the acid or amino groups contained in the B block. Salts of the acid monomers can be made with the counter component being selected from organic bases such as mono-, di, tri-methylamine, morpholine, n-methyl morpholine; alcohol amines such as dimethylethanolamine (DMEA), methyldiethanolamine, mono-, di, and tri-ethanolamine; pyridine; ammonium hydroxide; tetra-alkylammonium salts such as tetramethylammonium hydroxide, tetraethylammonium hydroxide; alkali metals such as lithium, sodium and potassium. Preferred neutralizing agents include dimethylethanolamine and sodium and potassium hydroxides, with potassium hydroxide being particularly preferred for inks to be used in thermal ink jet printers. Salts of the amino monomers can be made with the counter component being selected from organic acids such as acetic acid, formic acid, oxalic acid, dimethylol propionic acid, halogens such as chloride, fluoride, and bromide, and inorganic acids, such as sulfuric acid, and nitric acid, and the like. It is also possible to convert the amino group into a tetra-alkyl ammonium salt. Acetic and formic acid are preferred neutralizing agents. Amphoteric polymers, that is polymer that contains both an acid group and an amino group, may be used as is or can be neutralized with either addition of acid or base. The AB and BAB polymers can be advantageously produced by stepwise polymerization process such as anionic or group transfer polymerization as described in Webster, U.S. Patent 4,508,880. Polymers so produced have precisely controlled molecular weight, block sizes and very narrow molecular weight distributions. The polymer typically has a dispersity less than 2, generally in the range of 1.0 to 1.4. Dispersity is the polymer weight average molecular weight divided by its number average molecular weight. Number average molecular weight can be determined by gel permeation chromatography (GPC). The AB or BAB block polymers may also be formed by free radical polymerization wherein the initiation unit is comprised of two different moieties which initiate polymerization at two distinctly different temperatures. However, this method may cause contamination of the block copolymers with homopolymer and coupled products. The AB block polymers also may be prepared using conventional anionic polymerization techniques, in which a first block of the copolymer is formed, and upon completion of the first block, a second monomer stream is started to form a subsequent block of the polymer. A low reaction temperature (e.g., 0 to -70°C) is maintained in this case to minimize side reactions and form blocks of the desired molecular weights. With many of these techniques, and especially with the group transfer polymerization process, the initiator may be non-functional, may contain an acid group (used as is or in a blocked form) or may contain an amino group. Either the hydrophobic A block or the hydrophilic B block may be made first. The BAB block polymers also may be prepared by anionic polymerization or group transfer polymerization techniques by first polymerizing one of the B Blocks, then polymerizing the hydrophobic A block, and then polymerizing the second B Block. PIGMENTS A wide variety of organic and inorganic pigments, alone or in combination, may be selected to make the ink. The term "pigment" as used herein means an insoluble colorant. The pigment particles are sufficiently small to permit free flow of the ink through the ink jet printing device, especially at the ejecting nozzles that usually have a diameter ranging from 10 µm to 50 µm The particle size also has an influence on the pigment dispersion stability, which is critical throughout the life of the ink. Brownian motion of minute particles will help prevent the particles from flocculation. It is also desirable to use small particles for maximum color strength and gloss. The range of useful particle size is 0.005 µm to 15 µm. Preferably, the pigment particle size should range from 0.005 to 5 µm and, most preferably, from 0.005 to 1 µm. The selected pigment may be used in dry or wet form. For example, pigments are usually manufactured in aqueous media and the resulting pigment is obtained as water wet presscake. In presscake form, the pigment is not agglomerated to the extent that it is in dry form. Thus, pigments in water wet presscake form do not require as much deflocculation in the process of preparing the inks as dry pigments. Representative commercial dry pigments that may be selected to advantage are: Pigment Brand Name Manufacturer Colour Index Pigment Permanent Yellow DHG Hoechst Yellow 12 Permanent Yellow GR Hoechst Yellow 13 Permanent Yellow G Hoechst Yellow 14 Permanent Yellow NCG-71 Hoechst Yellow 16 Permanent Yellow GG Hoechst Yellow 17 Hansa Yellow RA Hoechst Yellow 73 Hansa Brilliant Yellow 5GX-02 Hoechst Yellow 74 Dalamar® Yellow YT-858-D Heubach Yellow 74 Hansa Yellow X Hoechst Yellow 75 Novoperm® Yellow HR Hoechst Yellow 83 Chromophtal® Yellow 3G Ciba-Geigy Yellow 93 Chromophtal® Yellow GR Ciba-Geigy Yellow 95 Novoperm® Yellow FGL Hoechst Yellow 97 Hansa Brilliant Yellow 10GX Hoechst Yellow 98 Permanent Yellow G3R-01 Hoechst Yellow 114 Chromophtal® Yellow 8G Ciba-Geigy Yellow 128 Irgazin® Yellow 5GT Ciba-Geigy Yellow 129 Hostaperm® Yellow H4G Hoechst Yellow 151 Hostaperm® Yellow H3G Hoechst Yellow 154 L74-1357 Yellow Sun Chem. L75-1331 Yellow Sun Chem. L75-2377 Yellow Sun Chem. Hostaperm® Orange GR Hoechst Orange 43 Paliogen® Orange BASF Orange 51 lrgalte® Rubine 4BL Ciba-Geigy Red 57:1 Quindo® Magenta Mobay Red 122 lndofast® Brilliant Scarlet Mobay Red 123 Hostaperm® Scarlet GO Hoechst Red 168 Permanent Rubine F6B Hoechst Red 184 Monastral® Magenta Ciba-Geiby Red 202 Monastral® Scarlet Ciba-Geiby Red 207 Heliogen® Blue L 6901F BASF Blue 15:2 Heliogen® Blue NBD 7010 BASF Heliogen® Blue K 7090 BASF Blue 15:3 Heliogen® Blue L 7101F BASF Blue 15:4 Paliogen® Blue L 6470 BASF Blue 60 Heucophthal® Blue G, XBT-583D Heubach Blue 15:3 Heliogen® Green K 8683 BASF Green 7 Heliogen® Green L 9140 BASF Green 36 Monastral® Violet R Ciba-Geigy Violet 19 Monastral® Red B Ciba-Geigy Violet 19 Quindo® Red R6700 Mobay Quindo® Red R6713 Mobay lndofast® Violet Mobay Violet 23 Monastral® Violet Maroon B Ciba-Geigy Violet 42 Raven® 1170 Col. Chem. Black 7 Pigment Brand Name Manufacturer Colour Index Pigment Special Black 4A Degussa Black 7 Sterling® NS Black Cabot Black 7 Sterling® NSX 76 Cabot Black 7 Tipure® R-101 Du Pont Mogul L Cabot Black 7 BK 8200 Paul Uhlich Black 7 Representative commercial pigments that can be used in the form of a water wet presscake include: Heucophthal® Blue BT-585-P, Toluidine Red Y (C.I. Pigment Red 3), Quindo® Magenta (Pigment Red 122), Magenta RV-6831 presscake (Mobay Chemical, Harmon Division, Haledon, NJ), Sunfast® Magenta 122 (Sun Chemical Corp., Cincinnati, OH), Indo® Brilliant Scarlet (Pigment Red 123, C.I. No. 71145), Toluidine Red B (C.I. Pigment Red 3), Watchung® Red B (C.I. Pigment Red 48), Permanent Rubine F6B13-1731 (Pigment Red 184), Hansa® Yellow (Pigment Yellow 98), Daiamar® Yellow YT-839-P (Pigment Yellow 74, C.I. No. 11741, Sunbrite® Yellow 17 (Sun Chemical Corp, Cincinnati, OH), Toluidine Yellow G (C. I. Pigment Yellow 1), Pigment Scarlet (C.I. Pigment Red 60) and Auric Brown (C. I. Pigment Brown 6). Black pigments, such as carbon black, generally are not available in the form of aqueous presscakes. Fine particles of metal or metal oxides also may be used to practice the invention. For example, metal and metal oxides are suitable for the preparation of magnetic ink jet inks. Fine particle size oxides, such as silica, alumina, titania, and the like, also may be selected. Furthermore, finely divided metal particles, such as copper, iron, steel, aluminum and alloys, may be selected for appropriate applications. AQUEOUS CARRIER MEDIUM The aqueous carrier medium is water or a mixture of water and at least one water soluble organic solvent. Selection of a suitable mixture depends on requirements of the specific application, such as desired surface tension and viscosity, the selected pigment, drying time of the pigmented ink jet ink, and the type of paper onto which the ink will be printed. Representative examples of water-soluble organic solvents that may be selected include (1) alcohols, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, see-butyl alcohol, t-butyl alcohol, iso-butyl alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol; (2) ketones or ketoalcohols such as acetone, methyl ethyl ketone and diacetone alcohol; (3) ethers, such as tetrahydrofuran and dioxane; (4) esters, such as ethyl acetate, ethyl lactate, ethylene carbonate and propylene carbonate; (5) polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, 2-methyl-2, 4-pentanediol 1,2,6- hexanetriol and thiodiglycol; (6) lower alkyl mono- or di-ethers derived from alkylene glycols, such as ethylene glycol mono-methyl (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 di-methyl (or -ethyl) ether; (7) nitrogen containing cyclic compounds, such as pyrrolidone, N-methyl-2-pyrrolidone, and 1,3-dimethyl-2- imidazolidinone; and (8) sulfur-containing compounds such as dimethyl sulfoxide and tetramethylene sulfone. A mixture of water and a polyhydric alcohol, such as, diethylene glycol, is preferred as the aqueous carrier medium. In the case of a mixture of water and diethylene glycol, the aqueous carrier medium usually contains from about 30% water/70% diethylene glycol to about 95% water/5% diethylene glycol. The preferred ratios are approximately 60% water/40% diethylene glycol to about 95% water/5% diethylene glycol. Percentages are based on the total weight of the aqueous carrier medium. SURFACTANTS Surfactants may be added to the ink jet inks of the invention to improve their drying characteristics. Useful surfactants may be selected from McCutcheon's Emulsifiers and Detergents, published by Manufacturing Confectioners Publishing Company, Glen Rock, NJ. The choice of surfactant is highly dependent on the type of paper to be printed. It is expected that one skilled in the art can select the appropriate surfactant for the specific paper to be used in printing. For example, the following surfactants were found to be useful in printing on Gilbert Bond paper (25% cotton) designated style 1057 manufactured by Mead Company, Dayton, Ohio. Supplier and Tradename Description Air Products Surfynol® 465H Ethoxylated Tetramethyl Decynediol Surfynol® CT-136 Acethylenicdiol, Anionic Surfactant Blend Surfynol® GA Acetylenic Diol Blend Surfynol® TG Acetylenic Diol Blend in Ethylene Glycol Cyanamid Aerosol® OT Dioctyl Ester of Sodium Sulfosuccinic Acid Aerosol@ MA-80 Dihexyl Ester of Sodium Sulfosuccinic Acid Aerosol@ MA-80/ Aerosol OT 2/1 Du Pont Duponol® RA Fortified Sodium Ether-Alcohol Sulfate Merpol® A Ethylene Oxide, Ester Condensate Merpol® LF-H Polyether Merpol® SE Alcohol Ethoxylate Merpol® SH Ethylene Oxide Condensate Zelec® NK Alcohol Phosphate Composition Fisher Scientific Polyethylene Glycol 3350 Polyethylene Glycol 400 Polyethylene Glycol 600 ICI Renex® 30 Polyoxyethylene C(12) Tridecyl Ether Synthrapol® KB Polyoxyethylene Alkyl Alcohol Rohm & Haas Triton® CF 10 Alkylaryl Polyether Triton® CF 21 Alkylaryl Polyether Triton@ N-111 Nonylphenoxy Polyethoxy Ethanol Triton® X-100 Octylphenoxy Polyethoxy Ethanol Triton® X-102 Octylphenoxy Polyethoxy Ethanol Triton® X-114 Octylphenoxy Polyethoxy Ethanol Union Carbide Silwet® L-7600 Polyalkyleneoxide Modified Polydimethylsiloxane Silwet® L-7607 Polyalkyleneoxide Modified Polydimethylsiloxane Silwet® L-77 Polyalkyleneoxide Modified Polydimethylsiloxane UCON® ML1281 Polyalkylene Glycol W. R. Grace Hampshire Div., Lauryoyl Hamposyl® Lida Iminodiacetic Acid The printing speed of ink jet printers is currently limited by the relatively slow rate at which ink penetrates the paper substrate. The addition of surfactants to ink jet inks permits the ink to wet rapidly into a variety of papers without introducing potentially toxic and destabilizing additives. The drying time is reduced from about 70 seconds required for non-surfactant containing inks to as little as 5 seconds for inks containing surfactants. Moreover, the addition of surfactants permits the preparation of inks suitable for high speed printing without the necessity for the addition of relatively large quantities of solvent (15% versus 2% for surfactant containing inks) which may injure the ink stability, materials of construction of the ink cartridge, or possibly introduce toxicity or flammability. Since a surfactant increases the speed of drying of the ink, smearing of the printed image on the paper is also prevented. The surfactant selected for the ink composition needs to be compatible with the other components, particularly the polymer and surfactant have to be of the same type, i.e., anionic or cationic. Non-ionic surfactants can be used with either type of polymer. A concentration of surfactant of from 0.1% to 10% of the total ink composition is effective with 0.5% to 3% being preferred. Preferred surfactants are Silwet® L-77, Synthrapol® KB, Triton® X-100, Aerosol® MA and Aerosol® OT or mixtures thereof, which are anionic wetting agents except for Triton® X-100 which is non-ionic. With the polymers used in the compositions exemplified being anionic, anionic or non-ionic surfactants were used in the compositions. However, cationic surfactants can be used with ink compositions including cationic or non-ionic polymers. Amphoteric surfactants have also been found to be useful. INK PREPARATION The ink is prepared by premixing the selected pigment(s) and acrylic block copolymer in water, a water soluble solvent, or the aqueous carrier medium, and then deflocculating the pigment. Optionally, a dispersant compound may be present. An ionic/nonionic surfactants, such as Daniel's Disperse-Ayd W-22, and W-28 and/or a polymeric pigment dispersant, such as, Tamol SN manufactured by Rohm and Haas and SMA 1000 resin manufactured by Sartomer Co., may be used for this purpose. The deflocculating (i.e., dispersing) step may be accomplished in a horizontal mini mill, a ball mill, an attritor, or by passing the mixture through a plurality of nozzles within a liquid jet interaction chamber at a liquid pressure of at least 68.9 bar (1000psi) to produce a uniform dispersion of the pigment particles in the aqueous carrier medium. It generally is desirable to make the pigmented ink jet ink in concentrated form, which is subsequently diluted to the appropriate concentration for use in the ink jet printing system. This technique permits preparation of a greater quantity of pigmented ink from the equipment. If the pigment dispersion was made in a solvent, it is diluted with water and optionally other solvents to the appropriate concentration. If it was made in water, it is diluted with either additional water or water soluble solvents to make a pigment dispersion of the desired concentration. By dilution, the ink is adjusted to the desired viscosity, color, hue, saturation density, and print area coverage for the particular application. In the case of organic pigments, the ink may contain up to approximately 30% pigment by weight, but will generally be in the range of 0,1 to 10%, preferably 0,1 to 5%, by weight of the total ink composition for most thermal ink jet printing applications. If an inorganic pigment is selected, the ink will tend to contain higher weight percentages of pigment than with comparable inks employing organic pigment, and may be as high as 75% in some cases, since inorganic pigments generally have higher specific gravities than organic pigments. The acrylic block polymer is present in the range of 0.1 to 20% by weight of the total ink composition, preferably in the range of 0.1% to 5%. If the amount of polymer becomes too high, the ink color density will become unacceptably low and it will become difficult to maintain desired ink viscosity. Dispersion stability of the pigment particles is adversely affected if insufficient acrylic block copolymer is present. The amount of aqueous carrier medium is in the range of 70 to 99.8%, preferably 90 to 99.8%, based on total weight of the ink when an organic pigment is selected and 25 to 99.8%, preferably 70 to 99.8% when an inorganic pigment is selected. Other additives, such as biocides, humectants, chelating agents, and viscosity modifiers may be added to the ink for conventional purposes. The choice of additive or combination of additives will be governed by the surface behavior of the additive(s) selected. Optionally, other acrylic and non-acrylic polymers, may be added to improve properties such as water fastness and smear resistance. These may be solvent based, emulsions, or water soluble polymers. Jet velocity, separation length of the droplets, drop size and stream stability are greatly affected by the surface tension and the viscosity of the ink. Pigmented ink jet inks suitable for use with ink jet printing systems should have a surface tension in the range of 0.02 to 0.07 N/m (20 dyne/cm to 70 dyne/cm) and, more preferably, in the range of 0.03 to 0.07 N/m (30 dyne/cm to 70 dyne/cm) Acceptable viscosities are no greater than 20 cP, and preferably in the range of 1.0mPa·s (cP) to 10.0 mPa·s (cP). The ink has physical properties compatible with a wide range of ejecting conditions, i.e., driving voltage and pulse width for thermal ink jet printing devices, driving frequency of the piezo element for either a drop-on-demand device or a continuous device, and the shape and size of the nozzle. The ink has excellent storage stability for a long period and does not clog in an ink jet apparatus. Fixing of the ink on the image recording material, such as, paper, fabric, film, etc., can be carried out speedily and surely with the printing dot being smooth at the border thereof and with spreading of the ink being slight. The printed ink images have clear color tones, high density, excellent water resistance and light fastness. Further the ink does not corrode parts of the ink jet printing device it comes in contact with, and it is essentially odorless, non-toxic and inflammable. This invention now will be further illustrated, but not limited, by the examples. A block polymer was prepared using the following procedure: PREPARATION 1: A BMA//MAA 10//10, Acid Initiator, Acid Block First polymer was prepared using the following procedure: A 12-liter flask was equipped with a mechanical stirrer, thermometer, N 2 inlet, drying tube outlet, and addition funnels. Tetrahydrofuran THF, 3750 g, and p-xylene, 5.0 g, was charged to the flask. The catalyst tetrabutyl ammonium m-chlorobenzoate, 3 ml of a 1.0 M solution in acetonitrile, was then added. Initiator, 1,1-bis(trimethylsiloxy)-2-methyl propene, 290.0 g (1.25 M) was injected. Feed I [tetrabutyl ammonium m- chlorobenzoate, 3 ml of a 1.0 M solution in acetonitrile] was started and added over 150 minutes. Feed II [trimethylsilyl methacrylate, 1975.0 g (12.5M)] was started at 0.0 minutes and added over 50 minutes. Eighty minutes after Feed II was completed (over 99 % of the monomers had reacted), Feed III [butyl methacrylate, 1770.0 g (12.5 M) was started and added over 30 minutes. At 180 minutes, 780 g of methanol was added to the above solution. It was refluxed for 120 minutes. Then 5133 g of solvent was stripped out while 2350 g of i- propanol were added. This made a BMA//MAA 10//10 polymer at 50 % solids. The above block polymer was neutralized using the following procedure: Procedure A: N,N-Dimethylethanolamine The BMA//MAA block polymer prepared above was neutralized (100 %) by adding the amine to the block copolymer solution and mixing until a homogeneous solution was obtained, usually 2-3 hours. After neutralization, the material was reduced to approximately 25% solids with deionized water. INGREDIENT AMOUNT (g) BLOCK POLYMER 102.5 N,N DIMETHYLETHANOLAMINE 21. DEIONIZED WATER 102.5 TOTAL 223.7 WT.% SOLIDS: 25 pH: 8.4 Procedure B: Potassium Hydroxide The BMA//MAA block polymer prepared above was neutralized (100%) by adding 15% aqueous potassium hydroxide solution to the block copolymer solution and mixing until a homogeneous solution was obtained. After neutralization, the material was reduced to approximately 25% solids with deionized water. INGREDIENT AMOUNT (g) BLOCK POLYMER 102.5 POTASSIUM HYDROXIDE (15% SOLUTION IN DEIONIZED WATER) 88.9 DEIONIZED WATER 32.3 TOTAL 223.7 WT.% SOLIDS: 25 pH: 8.0 Example 1 (Black) Black inks were prepared from a concentrated dispersion of Carbon Black FW-200 pigment, (Degussa Corp., Allendale, NJ) in water using a block copolymer dispersant. The concentrated Carbon Black FW-200 pigment dispersion in water which contained 14% carbon black solids and 9.3% solids of a dispersant BMA//MAA (10//10) copolymer neutralized with potassium hydroxide to a pH = 8.0 was prepared by adding the following ingredients in turn to a beaker having magnetic bar stirring: INGREDIENT AMOUNT (g) (parts by weight) Carbon Black FW-200 pigment (Degussa Corp., Allendale, NJ) 14.0 Polymer obtained in Preparation 1 (25% solution, neutralized by Procedure A) 9.3 Deionized water 76.7 Stirring was continued for 10-15 minutes until no lumps or dry clumps of pigment were visible. The mixture was added to a mini motormill 100 (Eiger Machinery Inc., Bensenville, IL 60106). Milling was carried out at 4500 r.p.m. After 5 minutes the pH was adjusted to 7.5-8.5 with potassium hydroxide. Milling was continued for 55 minutes at which time the particle size was 167 nm as determined on a Brookhaven Bl-90 Particle Sizer (Brookhaven Instrument Corp., Holtsville, NY 11742). The dispersion was filtered through a 3M 114A Liquid Filter Bag (3M St. Paul, MN 55144) under vacuum. Black inks were prepared from the Carbon Black FW- 200 pigment dispersion prepared above by mixing the following ingredients and agitating for a 30 minute period. INGREDIENT AMOUNT (g) (parts by weight) Sample # 1 (Ctrl) 2 3 4 Water 160 160 163 163 Diethylene glycol 17.4 17.4 17. 17.0 Triton® CF-21, (Rohm & Haas, Philadelphia, PA) - 5.0 - - Aerosol® MA-80 (American Cyanamid, Linden, NJ) - - 5.0 2.5 Aerosol® OT (75%) (American Cyanamid, Linden, NJ) - - 2.5 1.25 Carbon Black FW-200 dispersion 71.4 71.4 71.4 71.4 The inks were evaluated in a Hewlett-Packard Deskjet (Hewlett Packard, Palo Alto, CA) on Gilbert Bond Paper (25% cotton) designated style 1057, (Mead Company, Dayton, OH). Results are shown in Table 1 below. Sample No. Drying Time (seconds) 1 (Control) Over 170 2 75 3 Less than 5.0 4 = 10 The wetting agent containing inks printed well and dried to the touch very rapidly when compared to the inks that did not contain the wetting agents. Example 2 Cyan inks were prepared from a concentrated dispersion of Heucophthal Blue GBT-583 (Cookson Pigments, Wayne, NJ) in water using a block copolymer dispersant. The concentrated Cyan pigment dispersion in water which contained 15% Cyan pigment solids and a dispersant BMA//MAA 10//10 copolymer neutralized with potassium hydroxide to a pH = 8.0 was prepared by adding the following ingredients in turn to a beaker having a magnetic stirring bar: INGREDIENT AMOUNT (g) (parts by weight) Heucophthal Blue GBT-583 15 Polymer obtained in Preparation 1 (25% solution neutralized by Procedure b) 15 Deionized Water 70 Stirring was continued for 10-15 minutes until no lumps or dry clumps of pigment were visible. The mixture was added to a mini motormill 100 (Eiger Machinery Inc., Bensenville, IL 60106). Milling was carried out at 4500 r.p.m. After 5 minutes the pH was adjusted to 7.5-8.5 with potassium hydroxide. Milling was continued for 55 minutes at which time the particle size was 100 nm as determined on a Brookhaven Bl-90 Particle Sizer (Brookhaven Instrument Corp., Holtsville, NY 11742). The dispersion was filtered through a 3M 114A Liquid Filter Bag (3M St. Paul, MN 55144) under vacuum. A cyan ink was prepared from the Cyan pigment dispersion prepared above by mixing the following ingredients and agitating over a 30 minute period: INGREDIENT AMOUNT (g) (parts by weight) Cyan pigment dispersion 66.7 Diethylene glycol 23.5 Water 137.3 Triton® X-100 1.5 g The wetting agent containing ink printed well and dried to the touch very rapidly when compared to the ink that did not contain the wetting agent.

Claims: A thermal ink jet pigmented ink comprising an aqueous carrier medium and particles of pigment stabilized by an AB or BAB block copolymer comprising an A block which is a hydrophobic homopolymer or copolymer segment which serves to link with the pigment, and a B block which is a hydrophilic polymer segment or salt thereof which serves to disperse the pigment in the aqueous medium, and the ink contains an effective amount of a surfactant sufficient to decrease the drying time of the ink, wherein the AB or BAB block copolymer is selected from AB or BAB block copolymers wherein: (a) the A segment is a hydrophobic homopolymer or copolymer of an acrylic monomer having the formula CH 2 =C(X) (Y) wherein X is H or CH 3 ; and Y is C(O)OR 1 , C(O)NR 2 R 3 , or CN, wherein R 1 is an alkyl, aryl, or alkylaryl group having 1 to 20 carbon atoms, and R 2 and R 3 are hydrogen or an alkyl, aryl, or alkylaryl group having 1 to 9 carbon atoms; said A segment having an average molecular weight of at least 300 and being water insoluble; and (b) the B segment is a hydrophilic polymer, or salt thereof, of (1) an acrylic monomer having the formula CH 2 =C (X) (Y 1 ), wherein X is H or CH 3 ; and Y 1 is C(O)OH, C(O)NR 2 R 3 , C(O)OR 4 NR 2 R 3 or C(O)OR 5 ; wherein R 2 and R 3 are hydrogen or an alkyl, aryl, or alkylaryl group having 1 to 9 carbon atoms; R 4 is an alkyl diradical having 1 to 5 carbon atoms; and R 5 is an alkyl diradical having 1 to 20 carbon atoms and optionally containing one or more hydroxyl or ether groups; or (2) a copolymer of the acrylic monomer of (1) with an acrylic monomer having the formula CH 2 =C(X) (Y) where X and Y are the substituent groups defined for said A segment; said B segment having an average molecular weight of at least 300 and being water soluble, with the proviso that said B segment (s) constitute 10 to 90% of said block copolymer, by weight. The thermal ink jet pigmented ink of claim 1 wherein the surfactant is anionic or non-ionic. The thermal ink jet pigmented ink of claim 1 wherein the surfactant is present in an amount of from 0.1% to 10% of the total ink composition. The thermal ink jet pigmented ink of claim 1 wherein the surfactant is polyalkyleneoxide modified polydimethylsiloxane, polyethylene oxide, octylphenoxy polyethoxy ethanol, dioctyl ester of sodium sulfosuccinic acid, dihexyl ester of sodium sulfosuccinic acid, or mixtures thereof. The thermal ink jet pigmented ink of claim 1 wherein the A segment of said block copolymer is a homopolymer or copolymer prepared from at least one monomer selected from the group consisting of methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, lauryl methacrylate, stearyl methacrylate, phenyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, 2-ethoxyethyl methacrylate, methacrylonitrile, 2-trimethylsiloxyethyl methacrylate, glycidyl methacrylate, p-tolyl methacrylate, sorbyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, lauryl acrylate, stearyl acrylate, phenyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate acrylonitrile, 2-trimethylsiloxyethyl acrylate, glycidyl acrylate, p-tolyl acrylate, and sorbyl acrylate. The thermal ink jet pigmented ink of claim 5 wherein the A segment of said block copolymer is a polymer of methyl methacrylate, n-butyl methacrylate, or 2-ethylhexyl methacrylate. The thermal ink jet pigmented ink of claim 6 wherein the A segment is a copolymer of methyl methacrylate and n-butyl methacrylate. The thermal ink jet pigmented ink of claim 1 or 6 wherein the B segment of said block copolymer is a homopolymer or copolymer prepared from at least one monomer selected from the group consisting of methacrylic acid, acrylic acid, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, t-butylaminoethyl methacrylate, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide, methacrylamide, acrylamide, and dimethylacrylamide. The thermal ink jet pigmented ink of claim 1 or 6 wherein the B segment of said block copolymer is a polymer of methacrylic acid or dimethylaminoethyl methacrylate. The thermal ink jet pigmented ink of claim 1 wherein said ink contains 0.1 to 10% pigment, 0.1 to 20% block copolymer, and 70 to 99.8% aqueous carrier medium. The thermal ink jet pigmented ink of claim 10 wherein said in contains 0.1 to 5% pigment, 0.1 to 5% block copolymer, and 90 to 99.8% aqueous carrier medium. The thermal ink jet pigmented ink of claim 10 wherein the A segment of said block copolymer is a polymer of methyl methacrylate, butyl methacrylate, or 2-ethylhexyl methacrylate and the B segment is a polymer of methacrylic acid or dimethylaminoethyl methacrylate. The thermal ink jet pigmented ink of claim 1 or 10 wherein de B segment(s) constitute approximately 25 to 65%, by weight, of said block copolymer. The thermal ink jet pigmented ink of claim 1 or 10 wherein the A segment monomer is methyl methacrylate and the B segment is a copolymer of methyl methacrylate and methacrylic acid. The thermal ink jet pigmented ink of claim 1 or 10 wherein the A segment monomer is 2-ethylhexyl methacrylate and the B segment is a copolymer of 2-ethylhexyl methacrylate and methacrylic acid. The thermal ink jet pigmented ink of claim 1 or 10 wherein the A segment monomer is n-butyl methacrylate and the B segment is a copolymer of n-butyl methacrylate and methacrylic acid. The thermal ink jet pigmented ink of claim 1 or 10 wherein the A segment monomer is ethylhexyl methacrylate and the B segment is a copolymer of methyl methacrylate and methacrylic acid. The thermal ink jet pigmented ink of claim 1 or 10 wherein the A segment monomer is n-butyl methacrylate and the B segment is a copolymer of 2-hydroxyethyl methacrylate and methacrylic acid. The thermal ink jet pigmented ink of claim 1 or 10 wherein the A segment monomer is methyl methacrylate and the B segment is a copolymer of ethylhexyl methacrylate and methacrylic acid. The thermal ink jet pigmented ink of claim 1 or 10 wherein the A segment monomer is butyl methacrylate and the B segment is a copolymer of butyl methacrylate and dimethylaminoethyl methacrylate. The thermal ink jet pigmented ink of claim 1 wherein the aqueous carrier medium is a mixture of water and a polyhydric alcohol. The thermal ink jet pigmented ink of claim 1 wherein the pigment particles have a size of 0.01 to 5µm. The thermal ink jet pigmented ink of claim 1 wherein the surface tension is in the range of 0.30 to 0.70 mN/cm (30 to 70 dyne/cm) and the viscosity is in the range of approximately 1.0 to 10.0 mPa·s (cP). The thermal ink jet pigmented ink of claim 1 wherein the neutralizing agent for the B segment is selected from the group consisting of organic bases, alkanolamines, alkali metal hydroxides, and mixtures thereof. The thermal ink jet pigmented ink of claim 1 or 10 wherein the A segment monomer is n-butyl methacrylate and the B segment is a copolymer of methyl methacrylate and methacrylic acid.

Inventors: HOCHBERG JEROME, MA SHEAU-HWA, MATRICK HOWARD, SHEPARD MICHELE ELISE, SHOR ARTHUR CHARLES, SPINELLI HARRY JOSEPH, HOCHBERG, JEROME, MA, SHEAU-HWA, MATRICK, HOWARD, SHEPARD, MICHELE ELISE, SHOR, ARTHUR CHARLES, SPINELLI, HARRY JOSEPH
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1992
Main classification: C09D11
IPC codes: C09D11