Ink compositions

Abstract: An improved ink composition comprised of a major amount of water; an organic solvent selected from the group tetramethylene sulfone; 1,1,3,3-tetramethyl urea; and/or 3-­ methyl sulfolane; which solvent has permanently dissolved therein spirit-soluble dyes, such as black, yellow, cyan, magenta, or brown, or mixtures thereof.

Description: The present invention is generally directed to ink compositions, and more specifically the present invention is directed to specific compositions useful in ink jet printing systems. Accordingly, in one embodiment of the present invention there are provided aqueous ink compositions comprised of certain dyes with solubility in the solvent selected, and substantial insolubility in water. Therefore, in one preferred embodiment of the present invention the ink compositions are comprised of water, specific organic solvents inclusive of Sulfolane®, and spirit solvent dyes with solubility in the aforementioned solvents and substantial insolubility in water. The ink compositions of the present invention, in addition to possessing the improved characteristics indicated hereinafter, such as excellent waterfastness, are useful in various imaging and printing processes inclusive of thermal ink jet or bubble jet wherein the ink is heated to its boiling temperature enabling the injection of a bubble, reference US-A-4,243,994; 4,325,735, and 4,396,429, and GB-A-2,007,162 and 2,060,499. Compositions which are useful in ink jet printing systems are well known, and generally contain water-soluble dyes. There is thus disclosed, for example in US-A-3,846,141, an ink composition useful in jet printing comprised of an aqueous solution of a water-soluble dye; and a humectant material formed of a mixture of a lower alkoxy triglycol, and at least one other compound consisting of a polyethylene glycol, a lower alkyl ether of diethylene glycol, or glycerol. The humectant system disclosed in this patent substantially prevents or minimizes tip drying of the printing ink in the orifice or nozzle during down-time of the printer, such as when the printer is rendered inoperative. As further disclosed in this patent, the basic imaging technique in jet printing involves the use of one or more ink jet assemblies connected to a pressurized source of ink. Each individual ink jet includes a very small orifice, usually of a diameter of 60 µm, which is energized by magneto-restrictive piezo-electric means for the purpose of emitting a continuous stream of uniform droplets of ink at a rate of 33 to 75 kilohertz. This stream of droplets is desirably directed onto the surface of a moving web of, for example, paper; and is controlled to form printed characters in response to video signals derived from an electronic character generator and in response to an electrostatic deflection system. Furthermore, there are illustrated in US-A-4,295,889 recording liquid ink compositions and more specifically liquid compositions for use in a recording system, wherein the liquid recording component is jetted from a small orifice in a form of a droplet. According to the disclosure of this patent, the recording liquid composition comprises a compound of the general formula (A) as illustrated in column 3, beginning at line 30; or compound of the general formula (B), reference column 3, beginning at line 47, which components are referred to as dye compounds, see column 4, line 28. Examples of numerous dyes are provided beginning at column 4, line 51, and continuing on to column 42, for example. In column 43, beginning at line 29, of the '889 patent, there are disclosed examples of water-soluble organic solvents useful as a carrier component together with water, which solvents include alkylene glycols containing 2 to 6 carbon atoms in the alkylene moiety; and moreover, it is stated in column 44, beginning at line 8, that the properties of the liquid developer may be further improved by adding additives including nitrogen-containing compounds such as 1,3-dimethyl-2-imidazolidinone, see column 44, line 22. Other patents containing similar teachings include US-A-4,325,735; 4,395,287; 4,395,288; and 4,396,429. There is no disclosure in these references, however, with respect to ink compositions containing spirit-soluble dyes with, for example, higher solubility in certain non-volatile organic solvents than in water, thereby avoiding ink clogging caused primarily because of water evaporation Thus, with the inks of the present invention, ink jet clogging is avoided and other advantages are achievable especially because, for example, of the intrinsic low water solubility or insolubility of the spirit-soluble dyes which enables, for example, improved waterfastness characteristics as compared to inks wherein typical water-soluble acid dyes and direct dyes are selected. Furthermore, the ink composition of the present invention, with the spirit-soluble dyes, permit the presence of greater quantities of the organic phase solvent in the aforementioned inks, for example up to 80 percent, thereby rendering these inks substantially more compatible with typical transparency materials. Also, there is disclosed in US-A-4,279,653 ink jet compositions containing water-soluble wetting agents, a water-soluble dye and an oxygen absorber. Similarly, US-A-4,196,007 describes an ink jet printing composition containing an aqueous solution of a water-soluble dye and a humectant consisting of at least one water-soluble unsaturated compound. Further, there is disclosed in US-A-4,267,088 coatings particularly useful as marking inks wherein there is selected an epichlorohydron - modified polyethylenimine, and an ethylene oxide modified polyethylenimine in an aqueous solution. Other patents of interest are U.S-A-4,101,329; 4,290,072; 4,383,859; 4,235,773; 4,279,814; 4,443,371; 4,286,989; 4,299,630; 4,167,393; 3,864,296; 4,238,234; 3,234,025; 4,520,143; 3,920,855; and 4,182,612. Additionally, there is disclosed in US-A-4,197,135 ink compositions with improved waterfastness comprised of at least one water-soluble dye, and a polyamine with 7 or more nitrogen atoms per molecule. Specifically, there is illustrated in this patent an ink composition comprising an aqueous solution of at least one water-soluble dye, and about 0.5 percent to about 10 percent by weight concentration of a polyamine having 7 or more nitrogen atoms per molecule; and wherein the composition has a pH of 8 or above. In column 1, beginning at line 61, of this patent it is indicated that the preferred polyamines have the hydrogen of the primary amine group replaced with either a methyl or a hydroxyethyl group. Examples of fully-substituted polyamines selected are outlined in column 2, beginning at line 40, of the '135 patent. Further, there is disclosed in US-A-4,659,382 ink compositions comprised of hydroxylated polyethylenimines, dyes and water. More specifically, there are described in this patent inks with a major amount of water, a hydroxyethylated polyethylenimine polymer, and a dye component wherein the polymer has incorporated therein from 65 to 80 percent by weight of hydroxyethyl groups. Additionally, illustrated in U.S. 4,664,708 are ink compositions comprised of water and a polymeric dye comprised of water-soluble polymers with highly-stable chromophores covalently bonded thereto. Specifically, there are described in this patent inks with a major amount of water, and a polymeric dye comprised of the reaction product of a water-soluble polymer with a reactive dye. DE-A-3 410 855 discloses an ink comprising a dye dissolved in a liquid medium comprising: polyethylene glycol or polyethylene glycol monomethyl ether; diethylene glycol or sulfolane; N-methyl-2-pyrrolidone, and water. Similar inks are disclosed in Patent Abstracts of Japan, vol 5, No. 160, 6 Oct 1981; vol 5, No. 160, 15 Oct 1981; vol 9, No. 278, 6 Nov 1985, and vol 11, No. 63, 26 Feb 1987. All of these disclosures fall short of disclosing the specific solvents on which this invention is based, and of specifying that the dye is soluble only in the solvent, and virtually not in the water. Although many of the above compositions are suitable for their intended purposes, there continues to be a need for other ink compositions. Specifically, there is a need for ink jet compositions with excellent waterfastness characteristics, and wherein, for example, the dyes selected are retained in solution rather than forming as precipitates, and thereby causing clogging of the ink jet nozzles. Additionally, there is a need for ink compositions with excellent color intensities, and wherein, for example, the amount of dyes selected can be decreased. For example, only about 1 percent of dye is needed with the inks of the present invention in some situations, as compared with about 3 to 5 percent with the direct dyes of the prior art. Furthermore, there is a need for ink compositions wherein the waterfastness is greater than about 80 percent. Also, the inks of the present invention possess other desirable characteristics, including acceptable viscosity parameters, suitable surface tension values, excellent color intensity, especially with respect to the black inks; and these inks enable the retention of the dye molecules therein, thereby preventing precipitation and undesirable clogging of the ink jet nozzles. Other important characteristics associated with the inks of the present invention include the enablement of permanent transparency formation, and the continued solubility of the inks, including solubility subsequent to evaporation of the water contained therein. It is an object of the present invention to provide ink compositions overcoming the above problems. Accordingly the present invention provides ink compositions for jet printing, which are as claimed in the appended claims. Thus, the ink compositions of the present invention are comprised of water present in an amount of 10 to 90 percent of a mixture of water with an organic solvent consisting of tetramethylene sulfone; 1,1,3,3-tetramethyl urea; 3-methyl sulfolane, or mixtures thereof, with the optional addition of N-methyl pyrrolidone. The organic solvent has permanently dissolved therein a spirit-soluble dye coloured black, yellow, cyan, magenta or brown, the dye being substantially insoluble in water. In an embodiment of the present invention the ink composition is comprised of water mixed with from 10 to 90 percent by weight of the mixture of the organic solvent tetramethylene sulfone, (commercially available as Sulfolane®); and from 0.5 to 5 percent by weight of the mixture of a spirit-soluble dye coloured black, cyan, magenta, brown, or yellow components; wherein the dye is substantially soluble in the Sulfolane®, and substantially insoluble in water. Additionally, the inks of the present invention can be comprised of from 10 to 90 percent by weight of water, from 90 to 10 percent by weight of at least one of the specified organic solvents, and from 0.5 to 5 percent by weight of the water/solvent mixture of a spirit-soluble dye. A specific preferred ink composition of the present invention is comprised of a mixture of 60 percent by weight of water with 40 percent by weight of the organic solvent tetramethylene sulfone and, as an added component, from 0.5 to 5 percent by weight of the mixture of a spirit-soluble dye. When mixtures of solvents are selected, generally there can be utilized mixtures of the Sulfolanes® as specified, or mixtures of Sulfolanes® with N-methyl pyrrolidone. Mixtures of solvents include effective amounts of components, for example there can be selected from 20 to 30 percent by weight of a first solvent; and from 10 to 15 percent by weight of a second or third solvent. The specified solvents selected for the inks of the present invention have important characteristics, such as complete compatibility with water; desirable vapor pressures, that is for example, less than 0.1 millimeter of mercury (Hg); low toxicity properties; desirable intrinsic viscosities, for example, less than about 10 centipoise; high surface tension values exceeding, for example, 30 dynes/centimeter, and high solubility for the substantially-complete dissolution of the dye components. The organic solvents are usually present in an amount of from 10 to 90 percent by weight. A particularly preferred solvent, since it possesses many desirable properties inclusive of substantially no toxicity characteristics, is tetramethylene sulfone. There is generally incorporated into the ink compositions of the present invention dyes that are substantially or completely-soluble in the organic solvent, and substantially insoluble in water. Thus, for example, the spirit-soluble dyes have a solubility in the organic solvent of at least 2 grams per 100 milliliters. In contrast, the solubility of the dyes selected for the inks of the present invention in water is minimal, and at the most about 1 gram per 100 milliliters. In most situations, the dyes for the inks of the present invention have no solubility in water. Accordingly, specific spirit-soluble dyes for incorporation into the ink compositions of the present invention are Orasol Black RL or Intraplast Black RL/Solvent Black 29, Lapranol Black BR, Savinyl Black RLS, Orasol Black RLP, and Neozapon Black; solvent yellow dyes inclusive of Savinyl Yellow 2 RLS, Savinyl Yellow RLSN, Intraplast Yellow 2GLN, Neozapon Yellow 081, Neozapon Yellow 141, Levaderm Lemon Yellow, Zapon Fast Yellow CGR, Aizen Fast Yellow CGNH, Zapon Yellow 100, Zapon Yellow 157, and Savinyl Yellow RLS; magenta dyes such as Neozapon Red 492, Direct Brilliant Pink B, Savinyl Pink 6 BLS, Savinyl Red 3 BLS, Orasol Red 2 BL, Intraplast Red G (Orasol Red), Savinyl Red BLSN, Savinyl Scarlet RLS, Savinyl Fire Red 3GLS, and Zapon Red 335; cyan dyes Orasol Blue 2 GLN, Neozapon Blue 807, Savinyl Blue RLS, Savinyl Blue GLS, Orasol Blue GN, and Losol Blue; brown dyes inclusive of Zapon Brown 187 and Savinyl Brown GLS. Examples of preferred dyes are Orasol Black RL, Savinyl Black RLS, Direct Brilliant Pink B, Savinyl Yellow RLS, Intraplast Yellow 2GLN (Solvent Yellow 88), and Orasol Blue GN. The aforementioned dyes are added to the ink compositions in effective amounts. Thus, for example, from 0.5 to 5 percent by weight of the water/solvent mixture, and preferably from 1 to 2 percent by weight of the dye component is selected. Other amounts of dye components can be utilized depending on the color intensity desired, for example, dye availability, cost, toxic characteristics thereof, and solubility in the organic solvent selected. The ink compositions of the present invention therein include therein water, preferably distilled water, generally in an amount of from 10 to 90 percent by weight of the water/solvent mixture, and preferably in an amount of from 30 to 60 percent by weight. Another preferred ink composition of the present invention is comprised of from 60 to 70 percent by weight of water, mixed with from 30 to 40 percent by weight of the Sulfolane® solvent, which composition has added thereto from 0.5 to 5 percent by weight of the mixture of a spirit-soluble dye. Moreover, with respect to the aforementioned ink compositions, there can be selected mixtures of solvents including, for example, from 10 to 15 percent by weight of N-methyl pyrrolidone, and 25 percent by weight of Sulfolanes®, which inks include therein, when 10 percent by weight of the pyrrolidone is present, 65 percent by weight of water. With the ink compositions of the present invention, the dye is permanently retained in the ink mixture, therefore, no precipitates of the dye result, thereby substantially eliminating any of the problems associated with the undesirable clogging of the ink jets. Additionally, many compositions of the present invention possess other important properties, including a waterfastness of from 80 to 95 percent, a pH of from 4 to 7, a surface tension of from 30 to 60 dynes/cm, and a viscosity of from 3 to 5 centipoise. Images with acceptable color intensity and superior resolution result when these inks are incorporated into ink jet marking processes. Additive components, in amounts of from 5 to 15 percent by weight of the water/solvent mixture, may be included in the ink compositions of the present invention, such as surfactants, such as polyethoxy alcohol, biocides, chelating agents, such as the sodium salts of ethylene diamine tetra acetic acid, and buffer solutions. Specifically, thus for example, there can be selected as surfactants polyethylene derivatives of long chain alkyl amines, alcohols, alkylphenols, and fatty acid esters. Examples of biocides are Dowcide, and buffer solution examples include ammonium acetate/aluminum hydroxide and the like. With the inks of the present invention, it is preferred that no surfactants or chelating agents be incorporated therein. Formulation of the ink compositions described herein is accomplished by the simple admixing of the components, including water, the organic solvent, and the dye components. In one specific embodiment of the present invention, the ink compositions are prepared by, for example, dissolving a sufficient amount of dye in a substantially saturated solution of organic solvent. Thereafter, the solution is mixed at room temperature, followed by filtration, for example, utilizing a three µm filter for the purpose of removing insoluble impurities and any undissolved dye material. Subsequently, the final ink composition is formulated by simply adding an appropriate amount of distilled water and pure solvent, such as Sulfolane®, resulting in an ink that preferably has contained therein 2 percent by weight of dye and 98 percent by weight of a 40:60 mixture of solvent: water. Other similar methods of preparation can be selected, including specifically the admixing of water with the solvent, followed by the addition of the spirit-soluble dye, and the admixing of water with solvent mixtures, followed by the addition of a spirit-soluble dye. There can be selected water-soluble dyes which have been converted to spirit-soluble dyes, reference the magenta dye illustrated in working Example II. Additionally, the present invention enables the production of transparencies comprised of a support substrate of, for example, polysulfones containing thereover as a coating the ink compositions illustrated herein. The supporting substrate thickness of the transparency depends on a number of factors including the components selected. Generally, however, this substrate is of a thickness of from 75 to 125 µm. The following examples are specific embodiments of the present invention. Parts and percentages are by weight unless otherwise indicated. EXAMPLE I There was prepared a black ink composition by the following procedure. In a 100 milliliter flask, 4 grams of the black dye Orasol Black RLP were mixed for about 4 hours with 30 grams of the organic solvent tetramethylene sulfone, available as Sulfolane® from Phillips Petroleum. Thereafter, the resulting solution was filtered through a 3 µm filter to remove a very slight amount of residue, and the filtrate obtained was then diluted with an additional 47 grams of Sulfolane®, 118 grams of water, and 20 grams of N-methyl pyrrolidone. There resulted a final ink composition containing 2 percent of Orasol Black RLP dye, 35 percent of Sulfolane®, 10 percent of N-methyl pyrrolidone, and 53 percent of water. This ink had a waterfastness of 95 percent on silica-coated Diablo paper as determined by measuring the optical densities prior to, and subsequent to, immersing the ink as a coating on paper in water for 10 minutes with stirring. The waterfastness value is the ratio of the optical density after immersing in water, and before immersing in water. Additionally, this ink had the following characteristics: Surface Tension 48 dynes/centimeter Viscosity 3.5 centipoise Frequency Response 5 kilohertz Latency Time 600 seconds Heater Life greater than 10⁷ drops Frequency response refers to the rate at which the ink composition drops can be emitted from an ink jet nozzle, while latency time refers to the time a given ink jet concentration remains inoperative (quiescent state) at a relatively low relative humidity of about 10 percent. Heater life refers to the number of drops that can be generated without burnout or loss of drop characteristics. EXAMPLE II There was prepared a magenta ink composition by the following procedure. In a 250 mil flask, 21 grams of the magenta dye Direct Brilliant Pink B (C.I. Direct Red No. 9) were mixed with 21 grams of diphenyl guanidinium sulfate and 161 grams of the organic solvent tetramethylene sulfone, available as Sulfolane®. Thereafter, the resulting solution was heated to 60°C with stirring for four hours, which substantially dissolved the original magenta chromophoric material, and precipitated a quantity of crystalline white salt consisting essentially of sodium sulfate. The resultant solution was filtered through a 3 µm filter to separate the white precipitate from the filtrate. The nominal composition of the filtrate was 11.4 percent Direct Red No. 9 and 88.6 percent Sulfolane®. To 10 grams of the filtrate were added 3 grams of N-methyl pyrrolidone, 12 grams of additional Sulfolane®, and 13.9 grams of water to provide a final ink composition of 3.8 percent of the diphenyl guanidinium salt of Direct Red No. 9 dye; 10.0 percent N-methyl pyrrolidone, 40.0 percent Sulfolane®, and 46.2 percent water. This ink possessed a high surface tension of 52 dynes/centimeter and a viscosity of 2.5 centipoise. Heater deposits were negligible at least up to 10⁷ pulses, and latency was about 800 seconds at room temperature and 10 percent relative humidity. A waterfastness of 80 percent was achieved on Diablo silica paper several days after printing. EXAMPLE III Two grams of the commercial dye Aizen Spilon Yellow CGNH, a spirit-soluble solvent dye essentially insoluble in water, available from Hodogaya Chemical Company, Ltd., were mixed with 18 grams of the Sulfolane® solvent in a 100 milliliter flask, heated to 38°C for 10 minutes, then filtered through a 31 µm filter. The resulting filtrate, 17.9 grams, was then mixed with 0.9 gram of Sulfolane®, 21.5 grams of water, and 4.5 grams of N-methyl pyrrolidone, yielding a final ink composition comprised of 4 weight percent of Aizen Spilon Yellow CGNH dye, 10 weight percent of N-methyl pyrrolidone, 38 weight percent of Sulfolane®, and 48 percent of water. This ink yielded a bright process yellow color with a reflection density in excess of 1.2 when printed in a modified Diablo printer breadboard on Diablo silica-coated paper. Furthermore, this ink had characteristics similar to the ink composition of Example I. Further, with the ink of this Example, as well as Example I, no clogging of the ink jets occurred, and moreover no image defects were observed. EXAMPLE IV An ink composition was prepared that was particularly useful in thermal ink jet processes as illustrated hereinbefore as follows. Two grams of the spirit-soluble cyan dye Orasol Blue GN (C.I. 67) (Ciba-Geigy) was stirred with 25.4 grams of Sulfolane® for six hours. The resultant solution was then diluted with 39 grams of water, stirred for one hour then filtered through a 3 µm filter. Subsequently, the resultant concentrated ink was diluted with the appropriate amount of a 40/60 solvent mix of Sulfolane® and water, yielding an ink containing 1.5 percent of Orasol Blue GN, 40 percent of Sulfolane®, and 58.5 percent of water. This ink possessed properties similar to the ink of Example I. A solid area density of 1.30 was achieved on Diablo silica-coated paper, and insignificant heater deposits were found after 2 x 10⁷ drops with the above prepared ink. Other important properties for this ink include a relatively high surface tension, 48 dynes/centimeter; a low viscosity, 2.5 centipoise; 84 percent waterfastness; and a non-mutagenic Ames test response.

Claims: An ink composition comprising a mixture of 10 to 90 percent by weight of water with from 90 to 10 percent by weight of an organic solvent, the organic solvent consisting of at least one of tetramethylene sulfone, 1,1,3,3-tetramethyl urea and 3-methyl sulfolane, with or without N-methyl pyrrolidone, the solvent having permanently dissolved therein a dye in an amount of from 0.5 to 5 percent by weight of the mixture, and the dye being substantially insoluble in water. An ink composition as claimed in claim 1, wherein the amount of water is from 20 to 80 percent by weight of said mixture. An ink composition as claimed in claim 1 or claim 2, wherein the dye is Orasol Black RL, Intraplast Black RL/Solvent Black 29, Savinyl Black RLS, Savinyl Yellow 2 RLS, Savinyl Yellow RLSN, Savinyl Yellow RLS, Intraplast Yellow 2 GLN, Neozapon Yellow 081, Neozapon Yellow 141, Zapon Yellow 100, Zapon Yellow 157, Neozapon Red 492, Direct Brilliant Pink B, Savinyl Pink 6 BLS, Savinyl Red 3 BLS, Orasol Red 2 BL, Intraplast Red G, Savinyl Red BLSN, Savinyl Scarlet RLS, Savinyl Fire Red 3GLS, Zapon Red 335, Orasol Blue 2 GLN, Neozapon Blue 807, Savinyl Blue RLS, Savinyl Blue GLS, Losol Blue, Zapon Brown 187, Savinyl Brown GLS or mixtures thereof.

Inventors: SCHWARZ WILLIAM M, SCHWARZ, WILLIAM M.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1988
Main classification: C09D11
IPC codes: C09D11