Phase change inks

0001Disclosed herein are phase change inks. More specifically, disclosed herein are phase change inks containing an ink carrier, a pigment colorant, and a polyalkylene succinimide. One embodiment is directed to an ink composition comprising (a) an ink carrier which comprises a monoamide, or a tetra-amide, or a mixture thereof; (b) a polyalkylene succinimide; and (c) pigment particles. Another embodiment is directed to an ink composition comprising (a) an ink carrier, (b) a polyalkylene succinimide, and (c) pigment particles, said Ink having a conductivity greater than 1×10^-8 Siemens per centimeter. Yet another embodiment is directed to an Ink set comprising (1) a first Ink comprising (a) an ink carrier, (b) a polyalkylene succinimide, and (c) pigment particles, and (2) a second Ink comprising a dye colorant and a second Ink carrier, wherein the first ink carrier contains substantially the same components as the second Ink carrier.

0002<patcit id="pcit0001" dnum="US20020062763A"><text>US 2002/0062763</text></patcit> relates to the use of copper phthalocyanine compositions in electrophotographic toners, developers, powder coating materials and inkjet inks.

0003<patcit id="pcit0002" dnum="US6251553A"><text>US-A-6,251,553</text></patcit> discloses mixed-crystal pigments of the quinacridone series as colorants in electrophotographic toners and developers, powder coating materials, inkjet inks, electret fibers, and filters.

0004<patcit id="pcit0003" dnum="US5935755A"><text>US-A-5,935,755</text></patcit> discloses a process for indentifying documents by detection with Raman spectroscopy, comprising the application to a recording sheet of a marking material comprising a Raman-detectable component which, when irradiated with monochromatic radiation, exhibits a detectable Raman spectrum, thereby forming a mark on the recording sheet; further the irradiation of the mark on the recording sheet with monochromatic radiation; and the measurement of the Raman spectrum of radiation scattered from the mark when the mark is irradiated with monochromatic radiation.

0005<patcit id="pcit0004" dnum="US644018A"><text>US-A-6,44,018</text></patcit> relates to a phase change ink carrier composition comprising at least one anhydride/amino alcohol inclusive reaction product, wherein said at least one anhydride/amino alcohol inclusive reaction product is an ester or an amide, but not an ester-amide.

0006<patcit id="pcit0005" dnum="US5902841A"><text>U.S. Patent 5,902,841</text></patcit> discloses a phase change ink composition wherein the ink composition utilizes colorant in combination with a selected phase change ink carrier composition containing at least one hydroxy-functional fatty amide compound.

0007While known compositions and processes are suitable for their intended purposes, a need remains for improved phase change inks. In addition, a need remains for phase change inks having pigment colorants. Further, a need remains for phase change inks having pigment colorants wherein the pigment particles are stable and uniformly dispersed within the ink formulation. Additionally, a need remains for ink sets of different colored inks wherein some inks have pigment colorants and some inks have dye colorants, and wherein the other ink components remain the same for both the pigment-based inks and the dye-based inks. There is also a need for phase change inks containing pigment colorants that have increased stability and lightfastness at elevated temperatures, thereby enabling improved fade resistance upon exposure to heat and/or light. In addition, there is a need for phase change inks containing pigment colorants that exhibit reduced diffusion of the colorant from the ink to paper, thereby enabling reduced showthrough. Further, there is a need for phase change inks containing pigment colorants that exhibit reduced diffusion of colorants from image areas of one color to image areas of another color, thereby enabling improved image quality. Additionally, there is a need for phase change Inks containing pigment colorants wherein the pigment colorants exhibit reduced agglomeration and settling in the ink when the ink is exposed to prolonged and/or excessive heating conditions, such as the temperatures (typically at load 110°C, and frequently at least 135°C) and time periods (typically at least a day, and frequently at least a week) to which phase change inks are exposed In phase change ink jet printers. A need also remains for phase change Inks containing pigment colorants that exhibit reduced clogging of jets In the printhead and reduced printhead failure that might be caused by agglomeration of the pigment colorant In the Ink.

0008The present invention provides: <ul id="ul0001" list-style="none" compact="compact"><li>An ink composition comprising (a) an ink carrier which comprises a monoamide, or a tetra-amide, or a mixture thereof; (b) a polyalkylene succinimide; and (c) pigment particles.</li><li>An ink set comprising (1) a first ink comprising (a) an ink carrier, (b) a polyalkylene succinimide, and (c) pigment particles, and (2) a second ink comprising a dye colorant and a second ink carrier, wherein the first ink carrier contains substantially the same components as the second ink carrier, wherein the first ink is the above ink.</li></ul>

0009Preferred embodiments are set forth in the subclaims.

0010The inks comprise an ink carrier, a polyalkylene succinimide, and pigment particles.

0011Examples of suitable ink carrier materials include fatty amides, such as monoamides, or tetra-amides, or mixtures thereof. Suitable monoamides include both solid and liquid monoamides, provided that the ink containing the mixture of all ingredients is solid at room temperature. In one embodiment, the monoamide has a melting point of at least 50°C, although the melting point can be below this temperature. In another embodiment, the monoamide has a melting point of no more than 100°C, although the melting point can be above this temperature. Some examples of suitable monoamides include primary monoamides and secondary monoamides. Stearamide, behenamide, oleamide, technical grade oleamide, and erucamide are some examples of suitable primary amides. Behenyl behenamide, stearyl stearamide, stearyl erucamide, erucyl erucamide, oleyl palmitamide, and erucyl stearamide are some examples of suitable secondary amides. In one embodiment, the monoamide is of the formula <chemistry id="chem0001" num="0001"><img file="EP1535973B1_D0001.tif" /></chemistry> wherein x is an integer of from 5 to 21, y is an integer of from 11 to 43, a is an integer of from 6 to 22, and b is an integer of from 13 to 45. Mixtures of two or more monoamides can also be present in the ink.

0012The monoamide is present in the ink carrier in any desired or effective amount, in one embodiment at least 8 percent by weight, in another embodiment at least 10 percent by weight, and in yet another embodiment at least 12 percent by weight, and in one embodiment no more than 70 percent by weight, in another embodiment no more than 60 percent by weight, in yet another embodiment no more than 50 percent by weight, in still another embodiment no more than 32 percent by weight, in another embodiment no more than 28 percent by weight, and in yet another embodiment no more than 25 percent by weight, although the amount can be outside of these ranges.

0013Suitable tetra-amides include both solid and liquid tetra-amides, provided that the ink containing the mixture of all ingredients is solid at room temperature. One class of suitable tetra-amides is that encompassed by the formula <chemistry id="chem0002" num="0002"><img file="EP1535973B1_D0002.tif" /></chemistry> wherein R_a, R_b, R_c, and R_d each, independently of the others, is (a) a hydrogen atom, (b) an alkyl group (including linear, branched, saturated, unsaturated, cyclic, substituted, and unsubstituted alkyl groups, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in the alkyl group), in one embodiment with at least 1 carbon atom, in another embodiment with at least 2 carbon atoms, in yet another embodiment with at least 4 carbon atoms, and in still another embodiment with at least 8 carbon atoms, and in one embodiment with no more than 100 carbon atoms, and in another embodiment with no more than 50 carbon atoms, although the number of carbon atoms can be outside of these ranges, (c) an aryl group (including unsubstituted and substituted aryl groups, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in the aryl group), in one embodiment with at least 5 carbon atoms, and in another embodiment with at least 6 carbon atoms, and in one embodiment with no more than 100 carbon atoms, and in another embodiment with no more than 50 carbon atoms, although the number of carbon atoms can be outside of these ranges, (d) an arylalkyl group (including unsubstituted and substituted arylalkyl groups, wherein the alkyl portion of the arylalkyl group can be linear, branched, saturated, unsaturated, and/or cyclic, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus either may or may not be present in either or both of the alkyl portion and the aryl portion of the arylalkyl group), in one embodiment with at least 6 carbon atoms, and in another embodiment with at least 7 carbon atoms, and in one embodiment with no more than 100 carbon atoms, and in another embodiment with no more than 50 carbon atoms, although the number of carbon atoms can be outside of these ranges, such as benzyl, or (e) an alkylaryl group (including unsubstituted and substituted alkylaryl groups, wherein the alkyl portion of the alkylaryl group can be linear, branched, saturated, unsaturated, and/or cyclic, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in either or both of the alkyl portion and the aryl portion of the alkylaryl group), in one embodiment with at least 6 carbon atoms, and in another embodiment with at least 7 carbon atoms, and in one embodiment with no more than 100 carbon atoms, and in another embodiment with no more than 50 carbon atoms, although the number of carbon atoms can be outside of these ranges, such as tolyl wherein R₂, R₃, and R₄ each, independently of the others, are (a) an alkylene group (including linear, branched, saturated, unsaturated, cyclic, substituted, and unsubstituted alkylene groups, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in the alkylene group), in one embodiment with at least 1 carbon atom, in another embodiment with at least 2 carbon atoms, in yet another embodiment with at least 4 carbon atoms, and in still another embodiment with at least 8 carbon atoms, and in one embodiment with no more than 100 carbon atoms, in another embodiment with no more than 50 carbon atoms, and in yet another embodiment with no more than 12 carbon atoms, although the number of carbon atoms can be outside of these ranges, (b) an arylene group (including unsubstituted and substituted arylene groups, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in the arylene group), in one embodiment with at least 5 carbon atoms, and in another embodiment with at least 6 carbon atoms, and in one embodiment with no more than 100 carbon atoms, in another embodiment with no more than 50 carbon atoms, and in yet another embodiment with no more than 12 carbon atoms, although the number of carbon atoms can be outside of these ranges, (c) an arylalkylene group (including unsubstituted and substituted arylalkylene groups, wherein the alkyl portion of the arylalkylene group can be linear, branched, saturated, unsaturated, and/or cyclic, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in either or both of the alkyl portion and the aryl portion of the arylalkylene group), in one embodiment with at least 6 carbon atoms, and in another embodiment with at least 7 carbon atoms, and in one embodiment with no more than 100 carbon atoms, in another embodiment with no more than 50 carbon atoms, and in yet another embodiment with no more than 12 carbon atoms, although the number of carbon atoms can be outside of these ranges, or (d) an alkylarylene group (including unsubstituted and substituted alkylarylene groups, wherein the alkyl portion of the alkylarylene group can be linear, branched, saturated, unsaturated, and/or cyclic, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in either or both of the alkyl portion and the aryl portion of the alkylarylene group), in one embodiment with at least 6 carbon atoms, and in another embodiment with at least 7 carbon atoms, and in one embodiment with no more than 100 carbon atoms, in another embodiment with no more than 50 carbon atoms, and in yet another embodiment with no more than 12 carbon atoms, although the number of carbon atoms can be outside of these ranges, and wherein R₁ and R₅ each, independently of the other, is (a) an alkyl group (including linear, branched, saturated, unsaturated, cyclic, substituted, and unsubstituted alkyl groups, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in the alkyl group), in one embodiment with at least 1 carbon atom, in another embodiment with at least 2 carbon atoms, in yet another embodiment with at least 4 carbon atoms, in still another embodiment with at least 8 carbon atoms, in another embodiment with at least 12 carbon atoms, in yet another embodiment with at least 18 carbon atoms, in still another embodiment with at least 37 carbon atoms, in another embodiment with at least 40 carbon atoms, and in yet another embodiment with at least 48 carbon atoms, and in one embodiment with no more than 100 carbon atoms, and in another embodiment with no more than 50 carbon atoms, although the number of carbon atoms can be outside of these ranges, (b) an aryl group (including unsubstituted and substituted aryl groups, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in the aryl group), in one embodiment with at least 5 carbon atoms, in another embodiment with at least 6 carbon atoms, in another embodiment with at least 12 carbon atoms, in yet another embodiment with at least 18 carbon atoms, in still another embodiment with at least 37 carbon atoms, in another embodiment with at least 40 carbon atoms, and in yet another embodiment with at least 48 carbon atoms, and in one embodiment with no more than 100 carbon atoms, and in another embodiment with no more than 50 carbon atoms, although the number of carbon atoms can be outside of these ranges, (c) an arylalkyl group (including unsubstituted and substituted arylalkyl groups, wherein the alkyl portion of the arylalkyl group can be linear, branched, saturated, unsaturated, and/or cyclic, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in either or both of the alkyl portion and the aryl portion of the arylalkyl group), in one embodiment with at least about 6 carbon atoms, in another embodiment with at least 7 carbon atoms, in another embodiment with at least 12 carbon atoms, in yet another embodiment with at least 18 carbon atoms, in still another embodiment with at least 37 carbon atoms, in another embodiment with at least 40 carbon atoms, and in yet another embodiment with at least 48 carbon atoms, and in one embodiment with no more than 100 carbon atoms, and in another embodiment with no more than 50 carbon atoms, although the number of carbon atoms can be outside of these ranges, such as benzyl, or (d) an alkylaryl group (including unsubstituted and substituted alkylaryl groups, wherein the alkyl portion of the alkylaryl group can be linear, branched, saturated, unsaturated, and/or cyclic, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in either or both of the alkyl portion and the aryl portion of the alkylaryl group), in one embodiment with at least 6 carbon atoms, in another embodiment with at least 7 carbon atoms, in another embodiment with at least 12 carbon atoms, in yet another embodiment with at least 18 carbon atoms, in still another embodiment with at least 37 carbon atoms, in another embodiment with at least 40 carbon atoms, and in yet another embodiment with at least 48 carbon atoms, and in one embodiment with no more than 100 carbon atoms, and in another embodiment with no more than 50 carbon atoms, although the number of carbon atoms can be outside of these ranges, such as tolyl, wherein the substituents on the substituted alkyl, aryl, arylalkyl, alkylaryl, alkylene, arylene, arylalkylene, and alkylarylene groups can be (but are not limited to) hydroxy groups, halogen atoms, amine groups, imine groups, ammonium groups, cyano groups, pyridine groups, pyridinium groups, ether groups, aldehyde groups, ketone groups, ester groups; amide groups, carbonyl groups, thiocarbonyl groups, sulfate groups, sulfonate groups, sulfide groups, sulfoxide groups, phosphine groups, phosphonium groups, phosphate groups, nitrile groups, mercapto groups, nitro groups, nitroso groups, sulfone groups, acyl groups, acid anhydride groups, azide groups, azo groups, cyanato groups, isocyanato groups, thiocyanato groups, isothiocyanato groups, carboxylic acid groups, mixtures thereof, wherein two or more substituents can be joined together to form a ring. In one embodiment, one or both of R₁ and R₅ are alkyl groups with 18 carbon atoms. In another embodiment, one or both of R₁ and R₅ are alkyl groups with at least 37 carbon atoms. In yet another embodiment, one or both of R₁ and R₅ are alkyl groups with 48 carbon atoms. In still another embodiment, R₁ and R₅ are both -(CH₂)₁₆CH₃, R₂ and R₄ are each -CH₂CH₂-, and R₃ is a branched unsubstituted alkyl group having 34 carbon atoms. In another embodiment, R₁ and R₅ are both -(CH₂)_nCH₃ wherein n is 47 or 48, R₂ and R₄ are each -CH₂CH₂-, and R₃ is a branched unsubstituted alkyl group having 34 carbon atoms.

0014Tetra-amides can be prepared as disclosed in, for example, <patcit id="pcit0006" dnum="US6174937B"><text>U.S. Patent 6,174,937</text></patcit>. One example of a suitable tetra-amide is a tetra-amide resin obtained from the reaction of one equivalent of a C-36 dimer acid obtained from Uniqema, New Castle, DE with two equivalents of ethylene diamine and UNICID® 700 (obtained from Baker Petrolite, Tulsa, OK, a long chain hydrocarbon having a terminal carboxylic acid group), prepared as described in Example 1 of <patcit id="pcit0007" dnum="US6174937B"><text>U.S. Patent 6,174,937</text></patcit>.

0015The tetra-amide is present in the ink carrier in any desired or effective amount, in one embodiment at least 10 percent by weight, in another embodiment at least 13 percent by weight, and in yet another embodiment at least 16 percent by weight, and in one embodiment no more than 32 percent by weight, in another embodiment no more than 27 percent by weight, and in yet another embodiment no more than 22 percent by weight, although the amount can be outside of these ranges.

0016Further information on fatty amide carrier materials is disclosed in, for example, <patcit id="pcit0008" dnum="US4889560A"><text>U.S. Patent 4,889,560</text></patcit>, <patcit id="pcit0009" dnum="US4889761A"><text>U.S. Patent 4,889,761</text></patcit>, <patcit id="pcit0010" dnum="US5194638A"><text>U.S. Patent 5,194,638</text></patcit>, <patcit id="pcit0011" dnum="US4830671A"><text>U.S. Patent 4,830,671</text></patcit>, <patcit id="pcit0012" dnum="US6174937B"><text>U.S. Patent 6,174,937</text></patcit>, <patcit id="pcit0013" dnum="US5372852A"><text>U.S. Patent 5,372,852</text></patcit>, <patcit id="pcit0014" dnum="US5597856A"><text>U.S. Patent 5,597,856</text></patcit>, <patcit id="pcit0015" dnum="US6174937B"><text>U.S. Patent 6,174,937</text></patcit>, and <patcit id="pcit0016" dnum="GB2238792A"><text>British Patent GB 2 238 792</text></patcit>.

0017Also suitable as components in the phase change ink carrier are isocyanate-derived resins and waxes, such as urethane isocyanate-derived materials, urea isocyanate-derived materials, urethane/urea isocyanate-derived materials, mixtures thereof, and the like. One example of a suitable isocyanate-derived material is a urethane resin derived from the reaction of two equivalents of hydroabietyl alcohol and one equivalent of isophorone diisocyanate. Materials of this kind can be prepared as described in Example 1 of <patcit id="pcit0017" dnum="US5782966A"><text>U.S. Patent 5,782,966</text></patcit>. Another example of a suitable isocyanate-derived material is a material that is the adduct of three equivalents of stearyl isocyanate and a glycerol propoxylate. Materials of this kind can be prepared as described in Example 4 of <patcit id="pcit0018" dnum="US6309453B"><text>U.S. Patent 6,309,453</text></patcit>. Yet another example of a suitable isocyanate-derived material is a material that is the product of the reaction of 1.5 parts hydroabietyl alcohol, 0.5 part octadecyl amine, and 1 part isophorone diisocyanate. Materials of this kind can be prepared as described in Example 2 of Copending application <patcit id="pcit0019" dnum="US08672816B"><text>U.S. Serial No. 08/672,816</text></patcit>. Further information on isocyanate-derived carrier materials is disclosed in <patcit id="pcit0020" dnum="US5750604A"><text>U.S. Patent 5,750,604</text></patcit>, <patcit id="pcit0021" dnum="US5780528A"><text>U.S. Patent 5,780,528</text></patcit>, <patcit id="pcit0022" dnum="US5782966A"><text>U.S. Patent 5,782,966</text></patcit>, <patcit id="pcit0023" dnum="US5783658A"><text>U.S. Patent 5,783,658</text></patcit>, <patcit id="pcit0024" dnum="US5827918A"><text>U.S. Patent 5,827,918</text></patcit>, <patcit id="pcit0025" dnum="US5830942A"><text>U.S. Patent 5,830,942</text></patcit>, <patcit id="pcit0026" dnum="US5919839A"><text>U.S. Patent 5,919,839</text></patcit>, <patcit id="pcit0027" dnum="US6255432B"><text>U.S. Patent 6,255,432</text></patcit>, <patcit id="pcit0028" dnum="US6309453B"><text>U.S. Patent 6,309,453</text></patcit>, <patcit id="pcit0029" dnum="GB2294939A"><text>British Patent GB 2 294 939</text></patcit>, <patcit id="pcit0030" dnum="GB2305928A"><text>British Patent GB 2 305 928</text></patcit>, <patcit id="pcit0031" dnum="GB2305670A"><text>British Patent GB 2 305 670</text></patcit>, <patcit id="pcit0032" dnum="GB2290793A"><text>British Patent GB 2 290 793</text></patcit>, <patcit id="pcit0033" dnum="WO9414902A"><text>PCT Publication WO 94/14902</text></patcit>, <patcit id="pcit0034" dnum="WO9712003A"><text>PCT Publication WO 97/12003</text></patcit>, <patcit id="pcit0035" dnum="WO9713816A"><text>PCT Publication WO 97/13816</text></patcit>, <patcit id="pcit0036" dnum="WO9614364A"><text>PCT Publication WO 96/14364</text></patcit>, <patcit id="pcit0037" dnum="WO9733943A"><text>PCT Publication WO 97/33943</text></patcit>, and <patcit id="pcit0038" dnum="WO9504760A"><text>PCT Publication WO 95/04760</text></patcit>.

0018Additional suitable phase change ink carrier materials include paraffins, microcrystalline waxes, polyethylene waxes, ester waxes, amide waxes, fatty acids, fatty alcohols, fatty amides and other waxy materials, sulfonamide materials, resinous materials made from different natural sources and many synthetic resins, oligomers, polymers and copolymers, such as ethylene/vinyl acetate copolymers, ethylene/acrylic acid copolymers, ethylene/vinyl acetate/acrylic acid copolymers, copolymers of acrylic acid with polyamides, ionomers, as well as mixtures thereof. One or more of these materials can also be employed in a mixture with a fatty amide material and/or an isocyanate-derived material.

0019In one embodiment, the phase change ink carrier comprises (a) a polyethylene wax, present in the carrier in an amount in one embodiment of at least 25 percent by weight, in another embodiment of at least 30 percent by weight, and in yet another embodiment of at least 37 percent by weight, and in one embodiment of no more than 60 percent by weight, in another embodiment of no more than 53 percent by weight, and in yet another embodiment of no more than 48 percent by weight, although the amount can be outside of these ranges; (b) a stearyl stearamide wax, present in the carrier in an amount in one embodiment of at least 8 percent by weight, in another embodiment of at least 10 percent by weight, and in yet another embodiment of at least 12 percent by weight, and in one embodiment of no more than 32 percent by weight, in another embodiment of no more than 28 percent by weight, and in yet another embodiment of no more than 25 percent by weight, although the amount can be outside of these ranges; (c) a dimer acid based tetra-amide that is the reaction product of dimer acid, ethylene diamine, and a long chain hydrocarbon having greater than thirty six carbon atoms and having a terminal carboxylic acid group, present in the carrier in an amount in one embodiment of at least 10 percent by weight, in another embodiment of at least 13 percent by weight, and in yet another embodiment of at least 16 percent by weight, and in one embodiment of no more than 32 percent by weight, in another embodiment of no more than 27 percent by weight, and in yet another embodiment of no more than 22 percent by weight, although the amount can be outside of these ranges; (d) a urethane resin derived from the reaction of two equivalents of hydroabietyl alcohol and one equivalent of isophorone diisocyanate, present in the carrier in an amount in one embodiment of at least 6 percent by weight, in another embodiment of at least 8 percent by weight, and in yet another embodiment of at least 10 percent by weight, and in one embodiment of no more than 16 percent by weight, in another embodiment of no more than 14 percent by weight, and in yet another embodiment of no more than 12 percent by weight, although the amount can be outside of these ranges; (e) a urethane resin that is the adduct of three equivalents of stearyl isocyanate and a glycerol-based alcohol, present in the carrier in an amount in one embodiment of at least 2 percent by weight, in another embodiment of at least 3 percent by weight, and in yet another embodiment of at least 4.5 percent by weight, and in one embodiment of no more than 13 percent by weight, in another embodiment of no more than 10 percent by weight, and in yet another embodiment of no more than 7.5 percent by weight, although the amount can be outside of these ranges; and (f) an antioxidant, present in the carrier in an amount in one embodiment of at least 0.01 percent by weight, in another embodiment of at least 0.05 percent by weight, and in yet another embodiment of at least 0.1 percent by weight, and in one embodiment of no more than 1 percent by weight, in another embodiment of no more than 0.5 percent by weight, and in yet another embodiment of no more than 0.3 percent by weight, although the amount can be outside of these ranges.

0020The ink carrier is present in the phase change ink in any desired or effective amount, in one embodiment of at least 0.1 percent by weight of the ink, in another embodiment of at least 50 percent by weight of the ink, and in yet another embodiment of at least 90 percent by weight of the ink, and in one embodiment of no more than 99 percent by weight of the ink, in another embodiment of no more than 98 percent by weight of the ink, and in yet another embodiment of no more than 95 percent by weight of the ink, although the amount can be outside of these ranges.

0021The inks also contain a polyalkylene succinimide. Suitable polyalkylene succinimides include (but are not limited to) those of the general formula <chemistry id="chem0003" num="0003"><img file="EP1535973B1_D0003.tif" /></chemistry> wherein x is an integer representing the number of repeat succinimide units, and is in one embodiment from 1 to 3, y is an integer representing the number of repeat alkylene units, and is in one embodiment from 1 to 3, n is an integer, in one embodiment at least 2, in another embodiment at least 10, and in yet another embodiment at least 50, and in one embodiment no more than 500, in another embodiment no more than 300, and in yet another embodiment no more than 100, although the values of x, y, and n can be outside of these ranges, R₁ is an alkyl group (including linear, branched, cyclic, saturated, unsaturated, substituted, and unsubstituted alkyl groups, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in the alkyl group), in one embodiment with at least 1 carbon atom, in another embodiment with at least 10 carbon atoms, and in yet another embodiment with at least 30 carbon atoms, and in one embodiment with no more than 100 carbon atoms, in another embodiment with no more than 50 carbon atoms, and in yet another embodiment with no more than 40 carbon atoms, although the number of carbon atoms can be outside of these ranges, an aryl group (including substituted and unsubstituted aryl groups, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in the aryl group), in one embodiment with at least 4 carbon atoms, in another embodiment with at least 5 carbon atoms, and in yet another embodiment with at least 6 carbon atoms, and in one embodiment with no more than 100 carbon atoms, in another embodiment with no more than 50 carbon atoms, and in yet another embodiment with no more than 40 carbon atoms, although the number of carbon atoms can be outside of these ranges, an arylalkyl group (including substituted and unsubstituted arylalkyl groups, and wherein the alkyl portion thereof can be linear, branched, cyclic, saturated, or unsaturated, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in either or both of the aryl portion and the alkyl portion of the arylalkyl group), in one embodiment with at least 5 carbon atoms, in another embodiment with at least 6 carbon atoms, and in yet another embodiment with at least 7 carbon atoms, and in one embodiment with no more than 100 carbon atoms, in another embodiment with no more than 50 carbon atoms, and in yet another embodiment with no more than 40 carbon atoms, although the number of carbon atoms can be outside of these ranges, such as benzyl, or an alkylaryl group (including substituted and unsubstituted alkylaryl groups, and wherein the alkyl portion thereof can be linear, branched, cyclic, saturated, or unsaturated, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in either or both of the aryl portion and the alkyl portion of the alkylaryl group), in one embodiment with at least 5 carbon atoms, in another embodiment with at least 6 carbon atoms, and in yet another embodiment with at least 7 carbon atoms, and in one embodiment with no more than 100 carbon atoms, in another embodiment with no more than 50 carbon atoms, and in yet another embodiment with no more than 40 carbon atoms, although the number of carbon atoms can be outside of these ranges, such as tolyl, and R₂ R₃, R₄, and R₅ each, independently of the others, is a hydrogen atom or an alkyl group (including linear, branched, cyclic, saturated, unsaturated, substituted, and unsubstituted alkyl groups, and wherein hetero atoms, such as oxygen, nitrogen, sulfur, silicon, phosphorus, either may or may not be present in the alkyl group), in one embodiment with at least 1 carbon atom, and in one embodiment with no more than 30 carbon atoms, in another embodiment with no more than 20 carbon atoms, in yet another embodiment with no more than 10 carbon atoms, and in still another embodiment with no more than 5 carbon atoms, although the number of carbon atoms can be outside of these ranges, and wherein the substituents on the substituted alkyl, aryl, arylalkyl, and alkylaryl groups can be (but are not limited to) hydroxy groups, halogen atoms, amine groups, imine groups, ammonium groups, cyano groups, pyridine groups, pyridinium groups, ether groups, aldehyde groups, ketone groups, ester groups, amide groups, carbonyl groups, thiocarbonyl groups, sulfate groups, sulfonate groups, sulfonic acid groups, sulfide groups, sulfoxide groups, phosphine groups, phosphonium groups, phosphate groups, nitrile groups, mercapto groups, nitro groups, nitroso groups, sulfone groups, acyl groups, acid anhydride groups, azide groups, azo groups, cyanato groups, isocyanato groups, thiocyanato groups, isothiocyanato groups, carboxylate groups, carboxylic acid groups, urethane groups, urea groups, mixtures thereof, wherein two or more substituents can be joined together to form a ring. In one embodiment, R₂, R₃, and R₄ are hydrogen atoms and R₅ is an alkyl group. In another embodiment, R₂ and R₃ are hydrogen atoms and R₄ and R₅ are methyl groups. Examples of suitable polyalkylene succinimides include polyisobutylene succinimide and the like. Examples of commercially available polyalkylene succinimides include the Chevron Oronite OLOA 11000, OLOA 11001, OLOA 11002, OLOA 11005, OLOA 371, OLOA 375, OLOA 411, OLOA 4500, OLOA 4600, OLOA 8800, OLOA 8900, OLOA 9000, OLOA 9100, OLOA 9200, available from Chevron Oronite Company LLC, Houston, TX, as well as mixtures thereof. Examples of suitable polyalkylene succinimides and their precursors and methods of making them are also disclosed in, for example, <patcit id="pcit0039" dnum="US3172892A"><text>U.S. Patent 3,172,892</text></patcit>, <patcit id="pcit0040" dnum="US3202678A"><text>U.S. Patent 3,202,678</text></patcit>, <patcit id="pcit0041" dnum="US3280034A"><text>U.S. Patent 3,280,034</text></patcit>, <patcit id="pcit0042" dnum="US3442808A"><text>U.S. Patent 3,442,808</text></patcit>; <patcit id="pcit0043" dnum="US3361673A"><text>U.S. Patent 3,361,673</text></patcit>, <patcit id="pcit0044" dnum="US3172892A"><text>U.S. Patent 3,172,892</text></patcit>, <patcit id="pcit0045" dnum="US3912764A"><text>U.S. Patent 3,912,764</text></patcit>, <patcit id="pcit0046" dnum="US5286799A"><text>U.S. Patent 5,286,799</text></patcit>, <patcit id="pcit0047" dnum="US5319030A"><text>U.S. Patent 5,319,030</text></patcit>, <patcit id="pcit0048" dnum="US3219666A"><text>U.S. Patent 3,219,666</text></patcit>, <patcit id="pcit0049" dnum="US3381022A"><text>U.S. Patent 3,381,022</text></patcit>, <patcit id="pcit0050" dnum="US4234435A"><text>U.S. Patent 4,234,435</text></patcit>, and <patcit id="pcit0051" dnum="EP0776963A"><text>European Patent Publication 0 776 963</text></patcit>.

0022The polyalkylene succinimide is present in the ink in any desired or effective amount, in one embodiment at least 1×10^-7 percent by weight of the ink, in another embodiment at least 1×10^-5 percent by weight of the ink, in yet another embodiment at least 0.001 percent by weight of the ink, in still another embodiment at least 0.005 percent by weight of the ink, and in another embodiment at least 0.01 percent by weight of the ink, and in one embodiment no more than 40 percent by weight of the ink, in another embodiment no more than 30 percent by weight of the ink, in yet another embodiment no more than 20 percent by weight of the ink, and in still another embodiment no more than 10 percent by weight of the ink, although the amount can be outside of these ranges. The effective amount of polyalkylene succinimide in the ink can vary depending on the physical and chemical characteristics of the pigment particles, such as aggregate size, surface area, density of functional groups on the particle surfaces, quality of the interaction between the pigment particles and the ink carrier or components thereof, and many other such considerations.

0023The inks also contain a pigment colorant. The pigment particles can be of any desired color, including (but not limited to) black, cyan, magenta, yellow, red, blue, green, brown, gold, gray, purple, orange, pink, as well as mixtures thereof. Examples of suitable pigments include SPECIAL BLACK 100, SPECIAL BLACK 250, SPECIAL BLACK 350, FW1, FW2 FW200, FW18, SPECIAL BLACK 4, NIPEX 150, NIPEX 160, NIPEX 180, SPECIAL BLACK 5, SPECIAL BLACK 6, PRINTEX 80, PRINTEX 90, PRINTEX 140, PRINTEX 150T, PRINTEX 200, PRINTEX U, and PRINTEX V, all available from Degussa, MOGUL L, REGAL 400R, REGAL 330, and MONARCH 900, available from Cabot Chemical Co., MA77, MA7, MA8, MA11, MA100, MA100R, MA100S, MA230, MA220, MA200RB, MA14, #2700B, #2650, #2600, #2450B, #2400B, #2350, #2300, #2200B, #1000, #970, #3030B, and #3230B, all available from Mitsubishi, RAVEN 2500 ULTRA, Carbon Black 5250, and Carbon Black 5750 available from Columbia Chemical Co..

0024The pigment is present in the phase change ink in any desired or effective amount to obtain the desired color or hue, in one embodiment at least 0.1 percent by weight of the ink, in another embodiment at least 0.2 percent by weight of the ink, and in yet another embodiment at least 0.5 percent by weight of the ink, and in one embodiment no more than 50 percent by weight of the ink, in another embodiment no more than 20 percent by weight of the ink, and in yet another embodiment no more than 10 percent by weight of the ink, although the amount can be outside of these ranges.

0025If so desired, dyes can also optionally be included in the inks as auxiliary colorants.

0026The inks can also optionally contain an antioxidant. The optional antioxidants of the ink compositions protect the images from oxidation and also protect the ink components from oxidation during the heating portion of the ink preparation process. When present, the optional antioxidant is present in the ink in any desired or effective amount, in one embodiment of at least 0.01 percent by weight of the ink, in another embodiment of at least 0.1 percent by weight of the ink, and in yet another embodiment of at least 1 percent by weight of the ink, and in one embodiment of no more than 20 percent by weight of the ink, in another embodiment of no more than 5 percent by weight of the ink, and in yet another embodiment of no more than 3 percent by weight of the ink, although the amount can be outside of these ranges.

0027The inks in one embodiment have conductivity values of in one embodiment greater than 1×10^-8 Siemens per centimeter, in another embodiment greater than 1.5×10^-8 Siemens per centimeter, in yet another embodiment greater than 2×10^-8 Siemens per centimeter, in still another embodiment greater than 3×10^-8 Siemens per centimeter, in another embodiment greater than 4×10^-8 Siemens per centimeter, in yet another embodiment greater than 5×10^-8 Siemens per centimeter, and in still another embodiment greater than 3.5×10⁺³ Siemens per centimeter, although the conductivity can be outside of these ranges. Inks within these conductivity ranges are particularly useful in phase change ink printers wherein the ink level remaining in the machine is detecting by measuring the conductivity of the ink.

0028In embodiments wherein it is desired to increase the conductivity of the ink, conductivity agents can be included in the ink if so desired. Any desired or effective conductivity enhancing agent can be employed. Examples of suitable conductivity enhancing agents include complexes of dianilines, said dianilines being complexed with, for example, conductivity inducing phosphorous compounds such as phosphorus-containing acid compounds. The conductivity enhancing agent, when present, is present in the ink in any desired or effective amount, in one embodiment at least 0.25 percent by weight of the ink, in another embodiment at least 0.5 percent by weight of the ink, in yet another embodiment at least 2 percent by weight of the ink, in still another embodiment at least 8 percent by weight of the ink, and in another embodiment at least 13 percent by weight, and in one embodiment no more than 50 percent by weight of the ink, in another embodiment no more than 45 percent by weight of the ink, in yet another embodiment no more than 35 percent by weight of the ink, in still another embodiment no more than 25 percent by weight of the ink, and in another embodiment no more than 20 percent by weight of the ink, although the amount can be outside of these ranges.

0029Dyes used in the ink as auxiliary colorants can also be used to increase the conductivity of the ink.

0030Also disclosed herein is an ink set comprising (1) a first ink comprising (a) an ink carrier, (b) a polyalkylene succinimide, and (c) pigment particles, and (2) a second ink comprising a dye colorant and a second ink carrier, wherein the first ink carrier contains substantially the same components as the second ink carrier. By "wherein the first ink carrier contains substantially the same components as the second ink carrier" is meant that the two carriers contain substantially the same components, although the amounts of the components in each carrier can differ. By "substantially the same components" is meant that the ink ingredients are of the same composition in the first and second ink carriers, except that the second ink need not contain any polyalkylene succinimide.

0031Suitable dyes for the second ink include those disclosed hereinabove as being suitable as auxiliary colorants.

0032The ink compositions in one embodiment have melting points no lower than 50°C, in another embodiment no lower than 70°C, and in yet another embodiment no lower than 80°C, and in one embodiment have melting points no higher than 160°C, in another embodiment no higher than 140°C, and in yet another embodiment no higher than 100°C, although the melting point can be outside of these ranges.

0033The ink compositions generally have melt viscosities at the jetting temperature (in one embodiment no lower than 75°C, in another embodiment no lower than 100°C, and in yet another embodiment no lower than 120°C, and in one embodiment no higher than 180°C, in another embodiment no higher than 150°C, and in yet another embodiment no higher than 130°C, although the jetting temperature can be outside of these ranges) in one embodiment of no more than 30 centipoise, in another embodiment no more than 20 centipoise, and in yet another embodiment no more than 15 centipoise, and in one embodiment of no less than 2 centipoise, in another embodiment no less than 5 centipoise, and in yet another embodiment no less than 7 centipoise, although the melt viscosity can be outside of these ranges.

0034The inks can be employed in apparatus for direct printing ink jet processes and in indirect (offset) printing ink jet applications. Another embodiment is directed to a process which comprises incorporating an ink of the present invention into an ink jet printing apparatus, melting the ink, and causing droplets of the melted ink to be ejected in an imagewise pattern onto a recording substrate. A direct printing process is also disclosed in, <patcit id="pcit0052" dnum="US5195430A"><text>U.S. Patent 5,195,430</text></patcit>. Yet another embodiment is directed to a process which comprises incorporating an ink of the present invention into an ink jet printing apparatus, melting the ink, causing droplets of the melted ink to be ejected in an imagewise pattern onto an intermediate transfer member, and transferring the ink in the imagewise pattern from the intermediate transfer member to a final recording substrate. In one embodiment, the intermediate transfer member is heated to a temperature above that of the final recording sheet and below that of the melted ink in the printing apparatus. An offset or indirect printing process is also disclosed in, for example, <patcit id="pcit0053" dnum="US5389958A"><text>U.S. Patent 5,389,958</text></patcit>. In one embodiment, the printing apparatus employs a piezoelectric printing process wherein droplets of the ink are caused to be ejected in imagewise pattern by oscillations of piezoelectric vibrating elements. The inks can also be employed in other hot melt printing processes, such as hot melt acoustic ink jet printing, hot melt thermal ink jet printing, hot melt continuous stream or deflection ink jet printing, or the like. Phase change inks can also be used in printing processes other than hot melt ink jet printing processes, such as hot melt gravure printing, hot melt medical imaging printing.

0035The pigment-containing inks disclosed herein can be made by any desired or effective process. Following is one example of a suitable process employing extrusion and high shear mixing. The inks herein are not limited to inks prepared by this process.

0036The inks are prepared by first admixing in an extruder the pigment particles with one of the ink carrier ingredients, which acts as a pigment dispersant, to prepare a pigment dispersion, wherein the extruder is maintained at a temperature that is at or above about the peak crystallization temperature of the dispersant and below about the peak melting temperature of the dispersant, followed by admixing the pigment dispersion with the additional ink carrier ingredients and any desired additional optional ingredients and subjecting the resulting mixture to high shear agitation to prepare the ink.

0037The pigment dispersion is prepared by admixing the pigment particles with one or more of the ink carrier ingredients having polar groups thereon. By "polar" is meant that the selected ink carrier ingredient has one or more functional groups thereon with a polarity higher than that of an unsubstituted hydrocarbon molecule (aliphatic, aromatic, or one having both aliphatic and aromatic portions), such as amide groups, ester groups, hydroxy groups, amine groups, carbonyl groups, carboxylic acid groups, urea groups, urethane groups, or the like, whereas a nonpolar ingredient would be an ink ingredient without any such functional groups thereon. For example, when the ink carrier contains a tetra-amide, the tetra-amide is a highly effective pigment dispersant. The ink carrier ingredient or mixture of ingredients with which the pigment is admixed is hereinafter referred to as the "dispersant".

0038The dispersant in one specific embodiment is reduced to powder form before admixing it with the pigment. While not required, reducing the dispersant to powder form renders the subsequent mixing easier to process, since a mixed homogenous powder mixture, when melted, places the pigment particles and the dispersant in close contact with each other. The dispersant in this embodiment can be reduced to powder of any desired or effective particle size, in one embodiment at least 300 microns average particle diameter, in another embodiment at least 425 microns average particle diameter, and in yet another embodiment at least 600 microns average particle diameter, and in one embodiment no more than 850 microns average particle diameter, as measured by sieving, although the dispersant particle size can be outside of these ranges.

0039The pigment and the dispersant are admixed in any desired or effective relative amounts, in one embodiment at least 0.1 parts by weight dispersant per every 1 part by weight pigment, in another embodiment at least 0.5 parts by weight dispersant per every 1 part by weight pigment, and in yet another embodiment at least 3 parts by weight dispersant per every 1 part by weight pigment, and in one embodiment no more than 20 parts by weight dispersant per every 1 part by weight pigment, in another embodiment no more than 10 parts by weight dispersant per every 1 part by weight pigment, and in yet another embodiment no more than 6 parts by weight dispersant per every 1 part by weight pigment, although the relative amounts can be outside of these ranges.

0040The relative amounts of pigment and dispersant can also, if desired, be selected so that at the extruder temperature the pigment/dispersant mixture has a viscosity sufficiently low to enable mixing in the extruder and also sufficiently high to enable a desirable degree of shear to be generated within the extruder. This viscosity value can be any desired or effective value, in one embodiment at least 50 centipoise, in another embodiment at least 100 centipoise, and in yet another embodiment at least 200 centipoise, and in one embodiment no more than 10,000 centipoise, in another embodiment no more than 1,000 centipoise, and in yet another embodiment no more than 600 centipoise, although the viscosity value of the mixture during the extrusion process can be outside of these ranges.

0041The pigment and the dispersant are then heated and admixed in an extruder. In embodiments wherein the dispersant is powderized prior to admixing with the pigment, the pigment particles and the dispersant particles can be mixed thoroughly before introducing them into the extruder. Any desired or effective extruder can be employed, including single screw extruders, twin screw extruders, including corotating twin screw extruders (wherein both screws rotate in the same direction), counterrotating twin screw extruders (wherein the screws rotate in opposite directions), and the like. Examples of suitable extruders include a fully intermeshing counter-rotating twin-screw DAVO extruder, Type VB.22.01, available from Reifenhäuser GmbH &amp; Co., Troisdorf, Germany, which has a screw diameter of 22 millimeters and a length-to-diameter (L/D) ratio of 23.2, a fully intermeshing co-rotating ZSK-30 twin screw extruder, available from Werner &amp; Pfleiderer Corporation, Ramsey, NJ, which has a screw diameter of 30.7 millimeters and a length-to-diameter (L/D) ratio in this example of 37.2. Examples of extruders are also disclosed in, for example, <patcit id="pcit0054" dnum="US4894308A"><text>U.S. Patent 4,894,308</text></patcit>, <patcit id="pcit0055" dnum="US4649005A"><text>U.S. Patent 4,649,005</text></patcit>, <patcit id="pcit0056" dnum="US4110844A"><text>U.S. Patent 4,110,844</text></patcit>, and <patcit id="pcit0057" dnum="US4894308A"><text>U.S. Patent 4,894,308</text></patcit>. Rotation speeds for counter-rotating extruders are in one embodiment at least 40 rpm, and in one embodiment no more than 100 rpm, although the rotation speed can be outside of these ranges. Rotation speeds for co-rotating extruders are in one embodiment at least 50 rpm, and in one embodiment no more than 500 rpm, although the rotation speed can be outside of these ranges.

0042The pigment and the dispersant are admixed in the extruder at a temperature that is at or above about the peak crystallization temperature of the dispersant and below about the peak melting temperature of the dispersant. The crystallization point of the dispersant is measured by differential scanning calorimetry (DSC). The molten material is allowed to cool in the DSC. A curve is plotted measuring heat flow (Watts per gram; y-axis) as a function of temperature (°C; x-axis). The range between the onset of crystallization and the completion of crystallization, measured as the heat absorbed by the instrument, can be sharp or broad, depending on the crystalline or amorphous characteristics of the material. The peak of this curve is considered the peak crystallization point. For example, a material may exhibit a cooling transition range of from 93°C to 46°C, with the maximum crystallization transition peak at 85°C. Similarly, the melting point of the dispersant is measured by DSC by heating the solid material in the DSC and plotting a curve measuring heat flow as a function of temperature. Again, the range between the onset of melting and the completion of melting can be sharp or broad, depending on the crystalline or amorphous characteristics of the material. The peak of this curve is considered the peak melting point. For example, for the material having a cooling transition range of from 93°C to 46°C, with the maximum cooling transition peak at 85°C, the melting transition may be from 52°C to 124°C, with the maximum melting transition peak at 115°C. The peak crystallization temperature is below the peak melting temperature. Accordingly, for the inks disclosed herein, if the temperature selected for the extruder is based on the peak crystallization temperature of the dispersant, when the dispersant has a peak crystallization temperature of 85°C and a peak melting temperature of 115°C, the extruder is maintained within a temperature range of from 85°C to 115°C.

0043In one embodiment, the extruder is also maintained within a temperature range of from about the peak crystallization temperature to 30 percent above the peak crystallization temperature. For instance, taking again the example of a dispersant with a peak crystallization temperature of 85°C, the extruder is maintained within a temperature range of from 85°C to 111°C. In another embodiment, the extruder is maintained within a temperature range of from about the peak crystallization temperature to 20 percent above the peak crystallization temperature, and in yet another embodiment, the extruder is maintained within a temperature range of from about the peak crystallization temperature to 10 percent above the peak crystallization temperature, although the temperature is not limited to these ranges.

0044In another specific embodiment, the extruder is also maintained within a temperature range of 10 percent or more below the peak melting temperature. For instance, taking again the example of a dispersant with a peak melting temperature of 115°C, the extruder is maintained within a temperature range of 104°C or lower. In another embodiment, the extruder is maintained within a temperature range of 15 percent or more below the peak melting temperature, and in yet another embodiment, the extruder is maintained within a temperature range of 20 percent or more below the peak melting temperature, although the temperature is not limited to these ranges. While not being limited to any particular theory, it is believed that by maintaining the temperature in the extruder within this range, the viscosity of the mixture can be maintained at a value sufficiently low to enable mixing of the ingredients and sufficiently high to enable mixing the ingredients under effectively high shear.

0045Subsequent to mixing the pigment and dispersant in the extruder, the resulting pigment dispersion generally (although not necessarily) is recovered from the extruder as a solid: Thereafter, the pigment dispersion is remelted (if recovered in solid form) or maintained in the molten state (if recovered in the liquid form). In one embodiment, the molten pigment dispersion is admixed with the other ingredients followed by subjecting the resulting molten ink composition to high shear mixing. In another embodiment, prior to addition of the other ink ingredients, the molten pigment dispersion is subjected to high shear mixing. In the embodiment wherein prior to addition of the other ink ingredients, the molten pigment dispersion is subjected to high shear mixing, prior to high shear mixing, additional dispersant (which is one or a mixture of two or more ink carrier ingredients having polar groups thereon) and, optionally, the polyalkylene succinimide can be added to the pigment dispersion. The relative amounts of additional ingredients are selected so that the mixture has a viscosity sufficiently low to enable high shear mixing and also sufficiently high to enable a desirable degree of shear to be generated with the high shear mixer. This viscosity value can be any desired or effective value, in one embodiment at least 200 centipoise, in another embodiment at least 300 centipoise, and in yet another embodiment at least 400 centipoise, and in one embodiment no more than 10,000 centipoise, in another embodiment no more than 5,000 centipoise, and in yet another embodiment no more than 1,000 centipoise, although the viscosity value can be outside of these ranges.

0046In this specific embodiment, the pigment dispersion (including additional dispersant and polyalkylene succinimide if so desired) is then subjected to high shear mixing. Subsequent to high shear mixing of the pigment dispersion, any additional ink ingredients not present in the pigment dispersion can be added either while high shear mixing is continued or during a pause in the mixing followed by reinitiation of high shear mixing after these additional ingredients have been added, including ink ingredients having no polar groups, such as hydrocarbons. Additional amounts of ink ingredients that are already present in the pigment dispersion can also be added at this time.

0047In embodiments wherein the molten pigment dispersion is admixed with the other ingredients without initial high shear mixing of the pigment dispersion, followed by subjecting the resulting molten ink composition to high shear mixing, some or all of the additional ink ingredients can be added to the molten pigment dispersion, followed by initiation of high shear mixing. For example, high shear mixing can be initiated after one or more additional ingredients have been added, with the high shear mixing continuing during addition of even more additional ingredients, or all of the additional ingredients can be added followed by high shear mixing.

0048The polyalkylene succinimide can be added at any point in the process prior to final high shear mixing of the ink ingredients, including prior to extrusion, subsequent to extrusion but prior to high shear mixing of the pigment dispersion, or subsequent to high shear mixing of the pigment dispersion and prior to or during high shear mixing of the remaining ink ingredients.

0049High shear conditions can be imposed upon the ink components by any desired or effective method, such as by use of a media mill, such as a Buhler media mill, an attritor, such as a Dispermat attritor, a microfluidizer, an impact homogenizer at high pressure (for example, 10,000 psi in a confined chamber), including homogenizers made by Brinkman/KINEMATICA of Westbury, NY, such as the models PT 1200C, PT 1200CL, PT 10/35, PT2100, PT 1300D, PT 3100, PT 6100, and PT 1200B, a rotor/stator type high shear mixer operating with a tip speed in one embodiment of at least 7 meters per second, and in another embodiment of at least 12 meters per second, and in one embodiment of no more than 30 meters per second, and in another embodiment of no more than 25 meters per second, although the tip speed can be outside of these ranges, and in one embodiment at least 1,000 rpm, in another embodiment at least 5,000 rpm, and in yet another embodiment at least 7,500 rpm, and in one embodiment no more than 20,000 rpm, in another embodiment no more than 15,000 rpm, and in yet another embodiment no more than 12,500 rpm, although the rate can be outside of these ranges, such as those commercially available from IKA, Wilmington, NC, such as the IKA Model UTC 65 (having a 65 millimeter rotor) and the IKA Model UTC T 115 KT (having a 115 millimeter rotor, a 7.5 HP motor, and a tip speed of 18 m/s at 60 Hz), and those commercially available from Quadro, such as the Quadro Model Y2 (having a 115 millimeter rotor, a 3 HO motor, and a tip speed of 19 m/s).

0050In one embodiment, the shear rate to which the ink ingredients are subjected is in one embodiment at least 5,000 s^-1, and in another embodiment is no more than 15,000 s^-1, although the shear rate can be outside of these ranges. Shear rate (s^-1) is defined as the relative velocity between two surfaces (meters per second) divided by the gap distance between them (meters). For example, if a rotor/stator type high shear mixer is used with a tip speed of from 10 to 30 meters per second and the gap between the rotor and stator is 2 millimeters (0.002 meters), the shear rate is from 5,000 to 15,000 s^-1. In one specific embodiment, the shear stress to which the ink ingredients are subjected is at least 50 kilograms per meter, and in another embodiment is no more than 150 kilograms per meter, although the shear stress can be outside of these ranges. Shear stress is defined as the product of the shear rate and the viscosity; for example, if the viscosity of the ink ingredients at a given temperature (for example, 140°C) is 10 centipoise (0.01 kilograms per meter-second), the shear stress for a shear rate of from 5,000 to 15,000 s^-1 will be from 50 to 150 kilograms per meter.

0051The ink ingredients are subjected to high shear at a temperature at which the mixture of ingredients is molten, in one embodiment at least 110°C, in another embodiment at least 120°C, and in yet another embodiment at least 130°C, and in one embodiment no more than 160°C, in another embodiment no more than 140°C, and in yet another embodiment no more than 135°C, although the temperature can be outside of these ranges.

0052The ink ingredients are subjected to high shear for any desired or effective period of time, and will depend on the amount of material being sheared and the size of the mixer. For example, a 2.5 kilogram batch may be sheared for from 3 to 12 minutes, and an 18 kilogram batch may be sheared for from 60 to 90 minutes.

0053Subsequent to addition of all of the ink ingredients, high shear mixing is maintained for an additional effective period, in one embodiment at least 9 minutes, in another embodiment at least 12 minutes, and in yet another embodiment at least 90 minutes, although the period of time can be outside of these ranges.

0054Thereafter, the mixture can, if desired, optionally be filtered. In one embodiment, the ink is filtered through one or more filters of sequentially smaller particle size to filter out undesirably large particles. In this specific embodiment, the ink has pigment particle sizes in one embodiment no larger than 2 microns, in another embodiment no larger than 1 micron, in yet another embodiment no larger than 0.45 micron, and in still another embodiment no more than 0.2 micron, although the pigment particle size can be outside of these ranges.

PREPARATION OF PIGMENT DISPERSION A

0055Into a DAVO counter-rotating twin screw extruder (Model VS 104, obtained from Deutsche Apparate-Vertrieborganisation GmbH &amp; Co, Troisdorf, Germany) were added 239.7 grams of Special Black 4 carbon black (obtained from Degussa Canada, Burlington, Ontario) and 750.72 grams of a tetra-amide resin obtained from the reaction of one equivalent of a C-36 dimer acid obtained from Uniqema, New Castle, DE with two equivalents of ethylene diamine and UNICID® 700 (obtained from Baker Petrolite, Tulsa, OK, a long chain hydrocarbon having a terminal carboxylic acid group), prepared as described in Example 1 of <patcit id="pcit0058" dnum="US6174937B"><text>U.S. Patent 6,174,937</text></patcit>. The tetra-amide, originally in the form of chips or chunks, was processed through a Fitz Mill to reduce it to powder form. The carbon black and the tetra-amide powder were then mixed in a LiffleFord M5 Blender for 30 minutes at room temperature at 140 rpm before being added to the extruder. The mixed carbon black and tetra-amide powder were then processed through the extruder output at 1 pound per hour, with the process temperature at 90°C, the screw rotation at 50 rpm, and the residence time around 1 to 2 minutes.

PREPARATION OF PIGMENT DISPERSION B

0056The process used to prepare Pigment Dispersion A was repeated except that Nipex 150 carbon black (obtained from Degussa) was used instead of Special Black 4 carbon black.

EXAMPLE I (COMPARATIVE)

0057310.8 Grams of Pigment Dispersion A were melted in a 2 liter beaker (Beaker 1).

0058In a 1 liter beaker (Beaker 2) were melted 571.89 grams of stearyl stearamide (KEMAMIDE S-180, obtained from Witco, Humko Chemical Division, Memphis, TN) and 1.8 grams of NAUGARD N445 antioxidant (obtained from Uniroyal Chemical Co., Middlebury, CT).

0059In a 2 liter beaker (Beaker 3) were melted 777.4 grams of polyethylene wax (POLYWAX 655, obtained from Baker Petrolite, Lakewood, OH, of the formula CH₃(CH₂)₅₀CH₃)), 218.63 grams of a urethane resin obtained from the reaction of two equivalents of ABITOL® E hydroabietyl alcohol (obtained from Hercules Inc., Wilmington, DE) and one equivalent of isophorone diisocyanate, prepared as described in Example 1 of <patcit id="pcit0059" dnum="US5782966A"><text>U.S. Patent 5,782,966</text></patcit>, 92.77 grams of a urethane resin that was the adduct of three equivalents of stearyl isocyanate and a glycerol-based alcohol, prepared as described in Example 4 of <patcit id="pcit0060" dnum="US6309453B"><text>U.S. Patent 6,309,453</text></patcit>, and 1.8 grams of NAUGARD N445 antioxidant.

0060Beakers 1, 2, and 3 were kept in an oven at 135°C for about one hour.

0061Thereafter, the pigment dispersion in Beaker 1 was stirred with a mechanical stirrer for 15 minutes, followed by adding the contents of Beaker 2 to Beaker 1 and continuing stirring for an additional 15 minutes. The resulting dispersion was subjected to high shear mixing for 9 minutes at 135°C at 10,000 rpm with an IKA ULTRA TURAX T50 homogenizer. Thereafter, the homogenized dispersion was transferred to a 4 liter flask, followed by adding to the 4 liter flask the contents of Beaker 3 and subjecting the resulting dispersion to high shear mixing for 9 minutes at 135°C at 8,000 rpm with an IKA ULTRA TURAX T50 homogenizer. The resulting ink composition was then filtered through a series of glass fiber filter cartridges from 10 micron down to 0.45 micron to remove from the ink any large particles.

EXAMPLE II

0062The process of Example I was repeated except that Beaker 1 contained, in addition to 310.8 grams of Pigment Dispersion A, 14.6 grams of Oronite OLOA 11000 (polyisobutylene succinimide, obtained from Chevron, Belle Chasse, LA).

EXAMPLE III

0063380.07 Grams of Pigment Dispersion B and 11.25 grams of Oronite OLOA 11000 (polyisobutylene succinimide) were melted in a 2 liter beaker (Beaker 1).

0064In a 1 liter beaker (Beaker 2) were melted 648.00 grams of stearyl stearamide (KEMAMIDE S-180, obtained from Witco) and 2.25 grams of NAUGARD N445 antioxidant.

0065In a 2 liter beaker (Beaker 3) were melted 961.2 grams of polyethylene wax (POLYWAX 655), 270.32 grams of a urethane resin obtained from the reaction of two equivalents of ABITOL® E hydroabietyl alcohol (obtained from Hercules Inc.) and one equivalent of isophorone diisocyanate, prepared as described in Example 1 of <patcit id="pcit0061" dnum="US5782966A"><text>U.S. Patent 5,782,966</text></patcit>, 114.7 grams of a urethane resin that was the adduct of three equivalents of stearyl isocyanate and a glycerol-based alcohol, prepared as described in Example 4 of <patcit id="pcit0062" dnum="US6309453B"><text>U.S. Patent 6,309,453</text></patcit>, and 2.25 grams of NAUGARD N445 antioxidant.

0066Beakers 1, 2, and 3 were kept in an oven at 135°C for about one hour.

0067Thereafter, the pigment dispersion in Beaker 1 was stirred with a mechanical stirrer for 15 minutes, followed by adding the contents of Beaker 2 to Beaker 1 and continuing stirring for an additional 15 minutes. The resulting dispersion was subjected to high shear mixing for 9 minutes at 135°C at 10,000 rpm with an IKA ULTRA TURAX T50 homogenizer. Thereafter, the homogenized dispersion was transferred to a 4 liter flask, followed by adding to the 4 liter flask the contents of Beaker 3 and subjecting the resulting dispersion to high shear mixing for 9 minutes at 135°C at 8,000 rpm with an IKA ULTRA TURAX T50 homogenizer. The resulting ink composition was then filtered through a series of glass fiber filter cartridges from 10 micron down to 0.45 micron to remove from the ink any large particles.

EXAMPLE IV

0068The process of Example III was repeated except that Beaker 1 contained 45 grams of Oronite OLOA 11000 instead of 11.25 grams, and except that the high shear mixing at 10,000 rpm and the high shear mixing at 8,000 rpm were each carried out for 11 minutes instead of 9 minutes.

HEAT STABILITY TESTING OF INKS

0069The inks of Examples I through IV were each tested for heat stability as follows. Two 100 gram samples of the ink were taken. One sample of the fresh ink was held in an oven at 135°C for 1 hour. The second sample was aged in an oven at 135°C for 1 week. The times for 100 gram samples of the fresh and aged inks to filter through a 0.45 micron glass fiber filter under a constant pressure of 15 psi were then measured. The heat stability of the ink was determined by comparing the time for the aged ink to filter through the 0.45 micron filter (T₇) to the time for the fresh ink to filter through the 0.45 micron filter (T₀). The heat stability factor, T₇/T₀, is most desirably about 1 or below. <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="4"><colspec colnum="1" colname="col1" colwidth="23mm" /><colspec colnum="2" colname="col2" colwidth="22mm" /><colspec colnum="3" colname="col3" colwidth="22mm" /><colspec colnum="4" colname="col4" colwidth="13mm" /><thead><row><entry align="center" valign="top">Ink Example</entry><entry align="center" valign="top">T₀ (minutes)</entry><entry align="center" valign="top">T₇ (minutes)</entry><entry align="center" valign="top">T₇/T₀</entry></row></thead><tbody><row><entry align="center">I</entry><entry align="center">30</entry><entry align="center">120</entry><entry align="char" char="." charoff="30">4.0</entry></row><row><entry align="center">II</entry><entry align="center">12.75</entry><entry align="center">8.0</entry><entry align="char" char="." charoff="30">0.6</entry></row><row><entry align="center">III</entry><entry align="center">15.5</entry><entry align="center">120</entry><entry align="char" char="." charoff="30">7.7</entry></row><row><entry align="center">IV</entry><entry align="center">4</entry><entry align="center">4.5</entry><entry align="char" char="." charoff="30">1.1</entry></row></tbody></tgroup></table></tables>

0070The aged ink of Example I, containing no polyisobutylene succinimide, could not be filtered through the 0.45 micron filter within 120 minutes, and the stability factor was 4.

0071The aged ink of Example II had an excellent stability factor of 0.6. When incorporated into a XEROX® PHASER 850 phase change ink jet printer, this ink demonstrated excellent print quality with no jetting problems. This ink contained an amount of the polyalkylene succinimide for the specific pigment in the ink sufficient to enable desirable interaction with the selected pigment.

0072The aged ink of Example III, containing polyisobutylene succinimide in an amount of the polyalkylene succinimide for the specific pigment in the ink insufficient to enable desirable interaction with the selected pigment, could not be filtered through the 0.45 micron filter within 120 minutes, and the stability factor was 7.7.

0073The aged ink of Example IV had an excellent stability factor of 1.1. When incorporated into a XEROX® PHASER 850 phase change ink jet printer, this ink demonstrated excellent print quality with no jetting problems. This ink contained an amount of the polyalkylene succinimide for the specific pigment in the ink sufficient to enable desirable interaction with the selected pigment.