Fixation of reactive dyes to paper by ink-jet printing

Abstract: The water-fastness and smear resistance of prints from inks in which a reactive moiety ies attached to a chromo­ phore are improved if the prints are treated with a strong base solution. Preferably, the paper is first treated with the base solution and then printed with the ink.

Description: TECHNICAL FIELD This invention is concerned with the use of reactive dyes in ink-jet printing. More particularly, it involves the fixation of such dyes to paper. BACKGROUND ART Ink-jet printers generally use inks that contain water-soluble dyes. Such dyes are often not very smear resistant or water resistant when printed on paper. The use of colored inks in ink-jet printing is known; for example, U.S. Patent No. 4,382,262 and U.S. Patent No. 4,360548 disclose such systems. These patents, however, do not disclose or suggest forming smear-resistant inks on a substrate, such as paper. Hackleman and Pawlowski addressed this problem in U.S. Patent 4,694,302. In their method, a polymer is formed on the substrate from two reactive components; one component may be in the ink and the other may be in the substrate or it may be applied from a second reservoir. The resultant polymer binds the dye. In one example, sebacyl chloride was include in the ink; when it was deposited on a cellulose-containing substrate, it formed a cellulosic polymer. In another example, the ink contained carboxymethyl cellulose, and a second solution contained 2% AlCl₃. When these solutions were deposited on a substrate, they reacted to form an insoluble salt of the carboxymethyl cellulose polymer. A method for determining the degree of reactive dye bonding to cellulose is summarized in Dialogue abstract 268024 50-08024. Dyed chromatographic paper is boiled for 5 minutes in distilled water followed by colorimetric determination of the desorbed dye. The summary also notes that the test can be used for the determination of the effects of alkali concentration on the bonding degree. US-A-3951588 describes a process for the printing of cellulose textile materials comprising the steps of: impregnating the materials with an aqueous liquor or printing paste containing at least one cellulose fiber-reactive dyestuff, drying the impregnated materials, followed by fixing the dyestuffs by treatment in a salt-free single-phase bath containing at least one alcohol and alkali and optionally water. Finally, a finishing step is carried out which includes removing the fixing liquor and rinsing the material. GB-A-2184742 describes an ink for ink-jet printing comprising a reactive dye that reacts with the fibers of the printing substrate e.g. cellulose fibers, water and an organic solvent that does not react with the reactive dye. Suitable reactive dyes include monochlorotriazine, dichlorotriazine and vinylsulfone dyes. The dye can be fixed by alkali treatment US-A-4512807 also describes ink-jet printer ink compositions optionally containing reactive dyes. The compositions are aqueous solutions, preferably also comprising 2-pyrrolidone as a wetting agent. Patent Abstracts of Japan, vol. 9, no. 139, (M-387), [1862], 14th June 1985 and JP-A-60019583 describes a method of ink-jet printing using ink compositions containing a reactive dye, such as a monochlorotriazine or dichlorotriazine dye. The ink compositions contain, by weight, 0.1-20% of the dye, 20-70% water and 10-70% of one or more water-miscible organic solvents. This ink composition is printed onto a printing substrate. The reactive dye is fixed by also printing on the substrate with an aqueous alkali solution, the printing with alkali being carried out simultaneously with, or before or after, the step of printing with the ink composition. The present invention provides a process of ink-jet printing reactive dyes on a medium comprising: (a) printing said medium with an ink-jet ink comprising, by weight: (1) 1 to 10% of a reactive dye having a reactive moiety, (2) 5 to 15% of an organic solvent selected from the group consisting of 2-pyrrolidone, N-methyl pyrrolidone, and glycols, and (3) 75 to 94% water, said ink having a pH adjusted to 5 to 9; and (b) treating said medium with a basic alcoholic solution, in which the solvent comprises from 90% to 100% by weight of an alcohol having from 1 to 6 carbon atoms, said alcoholic solution having a pH from 10 to 13. The pH of the inks is kept from about 5 to about 9 because of stability considerations. The optimal pH is dependent upon the particular class of reactive moiety in the dye. The more reactive dyes, such as dichlorotriazinyl dyes require milder conditions. A buffer is used to keep the pH constant so that the reactive dye will not degrade under too acidic or too basic conditions. Buffers which have a buffering capacity in the pH range indicated may employed. If the pH strays beyond this range, it will accelerate the decomposition of the reactive dye; the degree is dependent on the reactivity of the dye. Preferred ink compositions of this invention correspond to the following formulation, by weight: reactive dye about 2 to 4% 2-pyrrolidone about 8 to 12% water about 84 to 90% pH adjusted to about 5 to 8. In general, the pH of the inks should be fairly neutral, since reactive dyes tend to react with a wide range of materials, including the hydroxyl ion in water. On the other hand, if the ink is too acidic, it is likely to cleave the reactive moiety from the dye molecule. The inks of this invention generally will contain a biocide. If crusting is a problem, then a humectant can be added. After solubilization, the ink is printed on paper from an ink-jet cartridge with a thermal ink-jet printer. A second ink-jet cartridge containing a strong base solution, with or without alcohol, is used to fix the ink to the paper. The pH of the base solution is from 10 to 13, and the base may be compounds such as NaOH, KOH, LiOH, or amines. Preferably, the base solution will be applied first, followed by printing with the ink solution. The base breaks up hydrogen bonding in the paper. It causes the paper to swell which helps absorption of the dye. After abstraction of the proton by the base, the cellulosic fiber becomes nucleophilic and is capable of attacking the reactive group of the dye and form a covalent bond. For example, if the paper has been treated with NaOH solution and then printed with a chlorotriazine dye, sodium chloride splits off and leaves the rest of the dye bonded to the cellulose. The base solution includes from 90% to 100% by weight of an alcohol corresponding to the formula ROH, wherein R is an alkyl radical which has from 1 to 6 carbon atoms, so that the print will dry faster and the amount of wrinkling of the paper is reduced. Typical alcohols are methyl, ethyl, isopropyl, and n-butyl alcohol. The best method to apply the base and the ink is by dot-on-dot printing. In this method, one applies a dot of base followed by a dot of ink. This ensures that full coverage of base will bind the dye to the paper and minimize print quality defects. The base may be applied after the ink has been laid down without significantly reducing the quality of the print or its fastness, but the result appears to be not quite in the same par as that obtained with printing after the base has been laid down. In either event, the printed paper is allowed to dry. The invention is particularly useful for printing pure cellulosic papers, such as chromatography paper, or papers which contain cotton content, such as 50% or 25% cotton bond. The degree of water-fastness can be determined by submerging a sample in water for five minutes and determining the amount of ink which is transferred to the white portion of the paper. Smear resistance is determined by measuring the amount of dye transferred across the white portion of the paper using a conventional highlighter pen. Optical density is measured, using a densitometer. The present invention provides prints that have high smear resistance and water fastness. As indicated in the following tables, zero smear resistance is obtained as well as low ΔL values. L is a measure of the darkness of the sample; the higher the L value, the lighter the print. A smaller ΔL value after washing between two samples with similar initial L values indicates less dye transferred or lost. In the claimed process, the dye is bonded to the paper by the base. This is indicated by the following: 1. The hydrolyzed dye does not show the same behavior as the unhydrolyzed dye. 2. The reactive site on the dye is disabled. 3. Water-fast tests done at 100°C for 10 minutes instead of the normal five minute test at room temperature show only a one unit increase in ΔL. 4. Water based dyestuffs which do not contain reactive moieties show no improvement when used with the base treatment, and solvent induced effects, for example, the effect of a solvent such as 2-pyrrolidone, does not help much in aiding water-fastness when reactive dyes are present in the ink. 5. Drytime is less than 10 seconds with the base treatment, and this is considerably less than drytime without the base treatment. When a two-pen design is used, the stability of the ink formulation is increased, because the pH of the ink formulation can be set near neutral where stability of the reactive dye is greatest. The invention also permits the use of other curing agents that are suitable for fixation and can possibly be included in the pen. Curing agents may be amines such as ammonia (from about 0.1 to about 0.5M), propylamine, or ethylamine; about 0.1 to about 1M sodium methoxide or sodium ethoxide; sodium bicarbonate or sodium hydroxide. In addition, a two-pen design provides greater versatility in printing; the ink and the alkali may be incorporated into a single compartmentalized unit or two separate units may be used. EXAMPLES Example 1 Ink formulations containing 2% (A), and 4% (B) Procion® MX-CWA (a dichloro-s-triazinylamino dye), and 10% 2-pyrrolidone in water were printed on 100% cellulosic paper from a ink-jet printer. Papers had first been treated in the same alphanumeric pattern with 0.1M NaOH and 0.5M NaOH solutions, respectively. Formulation Treatment L ΔL A1 (pHi=9.7) untreated 58 22 A1 0.1M NaOH 58 5.3 A1 0.1M NaOH (boiled) 58 7.4 (boiled)=10 min. in distilled water A1 0.5M NaOH 56 6.4 A2 (pHi=9.8) untreated 58 20.7 A2 0.1M NaOH 57 6.7 A2 0.5M NaOH 56 6.2 A3 (pHi=6-7) untreated 59 21.3 A3 0.1M NaOH 54 7.7 A3 0.5M NaOH 56 4.6 A4 (pHi=6.9) untreated 57 25.1 A4 0.1M NaOH/MeOH 57 4.0 A4 0.5M NaOH/MeOH 57 4.5 B (pHi=7.1) untreated 49 28.1 BP 0.1M NaOH/MeOH 49 4.3 BP 0.5M NaOH/MeOH 49 4.6 pHi is initial pH; MeOH is 100% methyl alcohol. Example 2 Formulations A3, A4, and B were printed on 50% cotton bond paper. Specimens were treated as indicated below, and water-fastness tested with the following results: Formulation Treatment L ΔL A3 untreated 49 24.5 A3 0.1M NaOH 54 9.3 A3 0.5M NaOH 57 5.9 A4 untreated 49 26.2 A4 0.1M NaOH/MeOH 59 6.2 A4 0.5M NaOH/MeOH 58 4.7 B untreated 40 34.5 BP 0.1M NaOH/MeOH 52 12.3 BP 0.5M NaOH/MeOH 52 4.9 Example 3 Formulation A5, which duplicated formulation A4, was printed on 25% cotton bond paper; the paper had been treated as indicated below. The specimens were tested for water-fastness. Formulation Treatment L ΔL A5 untreated 47 22.2 A5 0.1M NaOH/MeOH 61 4.4 A5 0.5M NaOH/MeOH 60 3.6 Example 4 4% Procion® Red MX-58 (a dichloro-s-triazinylamino dye) and 10% 2-pyrrolidone were dissolved water and the pH adjusted to 7.4 with aqueous NaOH. Specimens of paper were printed with the formulation after pretreatment with 0.5M NaOH/100% MeOH. The specimens were then tested as indicated. Paper Dye Transfer (mOD) Smear Resistance 2-pass (mOD) Cellulose Gilbert Gilbert Gilbert L ΔL L ΔL OD Dye 55.3 4.1 57.8 4.4 0.63 30 0 When the paper was printed first and then the base was applied, the results were as follows: xx xx 52.0 5.6 0.76 111 22.4 Untreated paper gave the following results: xx xx xx xx 0.76 351 140 Example 5 4% Procion® Red MX-8B, 10% 2-pyrrolidone, in water with pH adjusted to 6.7 gave the following results on Gilbert Bond: Example 6 1% Cibacron® Black (a monochloro-s-triazinylamino dye) and 10% 2-pyrrolidone water dissolved in water and the pH adjusted to 6.91. When printed on Gilbert Bond that had first been treated with 0.5M NaOH/100% MeOH, a two pass smear resistance test gave an mOD (millioptical) density as measured by densitometer of 16.2 on 50% cotton bond. INDUSTRIAL APPLICABILITY The present invention is useful in printing reactive dyes from ink-jet printers. It is particularly useful in printing papers containing cellulosic fibers.

Claims: A process of ink-jet printing reactive dyes on a medium comprising: (a) printing said medium with an ink-jet ink comprising, by weight: (1) 1 to 10% of a reactive dye having a reactive moiety, (2) 5 to 15% of an organic solvent selected from the group consisting of 2-pyrrolidone, N-methyl pyrrolidone, and glycols, and (3) 75 to 94% water, said ink having a pH adjusted to 5 to 9; and (b) treating said medium with a basic alcoholic solution, in which the solvent comprises from 90% to 100% by weight of an alcohol having from 1 to 6 carbon atoms, said alcoholic solution having a pH from 10 to 13. The process of claim 1 wherein the medium is first printed and then treated. The process of claim 1 wherein the medium is first treated and then printed. The process of claim 1 wherein the reactive dye has a monochlorotriazine group as the reactive moiety. The process of claim 1 wherein the reactive dye has a dichlorotriazine group as the reactive moiety. The process of claim 1 wherein the reactive dye has a vinyl sulphone group as the reactive moiety. The process of any preceding claim wherein the medium is a cellulosic material. The process of claim 7 wherein the medium is a cellulosic paper. The process of any preceding claim wherein the basic solution is 0.05M to 1M NaOH. The process of any preceding claim wherein the alcohol is methyl, ethyl, propyl, or isopropyl alcohol. The process of claim 10 wherein the alcohol is methyl alcohol. The process of claim 1 wherein said ink has the formulation reactive dye 2 to 4% 2-pyrrolidone 8 to 12% water 84 to 90% pH 5 to 8.

Inventors: ADAMIC RAYMOND J, ADAMIC, RAYMOND J.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1990
Main classification: B41M7
IPC codes: C09D11, B41M5, B41M7, B41J2