CA1192038A - Jet printing ink - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Disclosure utility of modified cationic dyestuffs as ink jet printing fluids. Conductivity can be adjusted to 500 micromhos/cm with specific organic acids.

Description

JET PRINTING INI<
Bacl<ground of the Invention Field of the I nvention The invention relates to ink and particularly an aqueous jet 5 printing ink for printing with an ink jet printing system.

Description of the Prior Art The principle underlying jet printing wi-th ink is based on driving ink through a fine nozzle of metal or glass, so -that uni-form 10 ink droplets are ejec-ted from the nozzle tip. These ink droplets are electros-tatically deflected with a deflecting electrode, arranged in front of -the nozzle, so that symbols are recorded in accordance wi-th a preliminarily determined matrix~ In this printing process -the ink in the nozzle is divided in fine ink droplets and -the direction o-f 15 the ink jet is controlled by deflecting plates or through nozzle movement. This prin-ting process is highly dependent on the properties of -the ink. The ink mus-t be capable of forming stable ink droplets which, under pressure and under an elec-trical field, have a high deflection sensitivity. Further, the ink mus-t readily 20 emerge from the nozzle. In addition, clogging of -the nozzle by drying ink must be prevented.
Continuous drop printers using a binary array of je-ts are of greatest in-terest a-t present because they are capable o-f operating at higher speeds than other -types. Illustra-tive apparatus is 25 disclosed in Brady et al, U.5. Patent No. 3,~05,273. See a~

'IReliable Pr inLir)g lJsing a Binary Ink ~ei Am-ay", Chas. L. Cha IndusLrial Research ~ Devel_pment, April 19~30, pp. 131-134. In conlinuous jeL printing, a liquid ir-l< is forced -through a very small cliameLer orifice, normally in the range of one Lo -five lhousandtils of 5 an inch, to form a stream of uniformly-sized, spaced spherical droplets. ~I~he droplets are formed at the rate oF abou-t 50,000 per second through each of 500 or more orifices in a mani-fold assembly.
The stream of drople-ts is then directed, usually by elec-trical means which selec-tively charge the drops, onto the sur-face of a -fas-t 10 moving web, such as paper, where the stream -forms prin-ted characters or other images in response an electronic character generator which controls the electrical charging and directing means. O-ther ink jet recording sys-tems are described in the "Des-cription of the Prior Art" in U~S. Patent 4,295,8.,9 published 15 October 20, 19.,1.
Tne ink used in jet prin-ting, regardless of type, must possess a unique combination of proper-ties. The ink mus-t be electrically conductive for proper drop charging . I t must have a workable viscosity in the range of about 1 to 10 cen-tipose (cps) a-t 25C and 20 must be free of all bu-t the smallest particulate ma-tter -to preven-t plugging of the orifices. For optimum perfor-mance, the ink should be stable over long periods of -time, compatible with the materials with which it comes in contact, -free of living organisms, and, a-f-ter printing, smear resistan-t, -fast drying, and wa-ter insoluble when 25 dry.

Ink jet printing appears to be an importanl new technology that is capable ol hicJh speecl"nulti-colored, registered non-con-tact printin~ on almost any surrace. The potential applications o-F jet printing range fr orm low resolu~ion needs, sucrl as the decora-ting oF
soft or tissue yrade paper to the hiyh resolution req~lirements of facsimile reproduction. i-leretofore colorants for jet prin-ting inks have consisted of either anionic dyestuffs, pigments or solven-t dyes. A resinous binder is incorpora-ted into the ink to cause it to be retained by the substrate on which it is printed and to improve 10 i-ts bleed fastness. The conductivity level oF such jet printing fluids is normally adjusted by the use of ioni~able salts such as:
sodium sulfate, sodium nitrate, sodium or potassium thiocyanate, sodium acetate, sodium proprionate, sodium chloride and ammonium formate The pH of these fluids is normally adjusted above 7.5.
15 The following U.S. patents disclose representative examples o-f the a-foredescribed printing fluids: 4,299,630, 4,256,493, 4,239,544, 4,168,254, 4,155,768 and 3,903,034.
Insofar as the present inventor is aware, all printing fluids heretofore used have been al kaline or adjusted -toward a neu-tral or 20 alkaline pi-l. The reason generally expressed is for the purpose o-F
maintaining the s-tabiii-ty of the printing Fluid. Conventional wisdom has also held that acidic fluids would cause excessive corrosion o-f the jet printing apparatus.
Summary of the I nven-tion The present inventor has discovered that modi-fied cationic dyestuffs (as hereinafter de-fined) are use-ful as jet prin-ting -fluids.

Il SllCh d~estul~`s as comrllerciall~ available do not have the appropriate conduclivi~ for use in jet printing apparatus, their condue~ivi~y can be suitably acljusted in accordance ~vith the ~eachings of the preselll invenlion T le modiFied calionic dyestuffs wllich can be used in accordance ~vith the presenL invention are chromophoric systems generally called basic or direct dyes w hose cationic character is derived from cationic amino groups introduced into -the desired dyestut`f and the non-chromophoric portion of which has been "modified" to improve bleedfastness and fade resistance under e~posure to actinic li~ht Illustrative e~<amples of modified cationic dyestuffs include dimeric bismethine dyes of pyridine series as dis-closed in British Patent 2,011,457, bisquaternary basic dyes as disclosed in British Patent 2 026,522 and in U S Pa-tent 4,280,964, 15 imida~Qlyl methylene group containing dyes as disclosed in DE3006-013, cationic bis-styryl dyestuff compounds as disclosed in European Patent Application Publication 0027611, direct blue dyes as dis-closed in U S Patent '1,314,816, monoazo compounds as disclosed in U S Patent 4,314,817 and disazo and trisazo compounds as disclosed 20 in U S Patents 4 213,897 and 4,235 773 Par~icularly preferred by the present inventor are the modified cationic dyestuffs whose cationic character is derived from a difunctional cationic group which may be introduced singly or plurally into the desired dyes-tuf-f either directly or indirectly and whose structural formula corresponds to her~
\ + 1I R = lo~i mo:L~c~ r ~eight alkyl 1~ - N --- (c`ll~ " R'= color ~ro(l~lcin~ moicty 1~' C] R"= }l or ac~l n is ~ sm~LI number~
typically 1 to 8 E~amples oF suitable chromopl)oric syslems are methine, azomethine, nydrazone, azine, oxazine, thiazine, diazine, xanthene, acridine, polyarylmeLharle .
Especially preferred For use in the present invention is an aqueous inlc composition for jet printing which contains an aldehyde selected from the group consisting of formaldehyde, glyoxal and gluturaldehyde and a water soluble, modified cationic dyestu-ff of the foregoing particularly pre-ferred type, which has a functional group capable of reacting with the aldehyde. Said combination is disclosed and claimed as a printing fluid in U.S. Patent 4,221,562 Aqueous printing fiuids comprising a water soluble, modified cationic dyestuff are characterized in being acidic, typically having a pH of about 2. Frequently such fluids have a conductivity suitable for use in jet printing. The presen-t inventor has -found that ~vhen such fluids are not suitable For use in je-t printing because oF a lack of sufficient conductivity, the ionizable salts normally employed for conductivity control in alkaline jet printing Fluicis do not Function satisfactorily with said acidic prin-ting Fluids.
In accordance ~vith the present inven-tion, when an organic acid taken From the group consisting of maleic acid, methane sulfonic f 3~

acid and ethane sulf`onic acid is addecl to Ihe printing fluid the combina~ion functions well in jet printiny appara-tus The operability ol` these lhree organic acids is especially surprising in as much as hydroxyclcetic acid, acetic acid and lactic acid, other common stabilizing acids for dyestuFfs, were Found not to improve -the conductivity oF the printing fluid ~leptanoic acid, propyl, isopropyl, butyl and naphthal sulfonic acids, benzene disul-Fonic acid and benzene phosphonic acid were Found to be incompatible with the printing fluid in that they caused instabili-ty, formed precipi-tates or adversly aFfected viscosity While some suitable cationic dyes are prepared and sold as methane sulFonic acid addition salts, see for example U S Patent 4,081,239, methane sulfonic acid is added in such case for the purpose o-F providing storage stability to the dye See especially Col 6, lines 8-18 oF said patent 4,081,239 To applicant s knowledge there is no teaching in the prior art nor in U S Patent 4,081,239 in particular tha-t methane sulfonic acid will impar-t suitable conduc-tivity to such a dyestuff so as to make it suitable for use in jet printing While llwang in U S Patent 4,299,630, teaches that in order to perform successfully in a jet printing system, a prin-tiny fluid mus-t have a resistivity oF less than 1,000 ohms-cm (a conductivity greater -than 1000 micrornhos/cm) and preferably less than 500 ohms-cm (a con-ductivity grea-ter than 2000 micromhos/cm), -the present inven-tor has found, using -the same type of apparatus, tha-t a conduc-tivity of 500 micromhos/cm (resistivity of 2000 ohms-cm) is sufficient -to provide satlsEactory images wlth the printlng fluids of the present invention. The present lnventor considers conductivity (mlcromhos/cm) to be a more relevant measure of operability than resistivi-ty because in binary ~et printing the droplets are preferentially charged. In accordance with the present invention, iE -the modified cationic dyestuff as commercially available does not have a conductivity of 500 micromhos/cm, it is possible to raise the conduc-tivity of the printing fluid to at least 500 micromhos/
cm with a small amount (1% or less) of an acid taken from the group consisting of maleic acid, methane sulfonic acid and ethane sulfonic acid.
An aspect of the invention is as follows:
In a method of ink jet printing, the improve-ment which comprises printing with an aqueous ink composition comprising a water soluble, modified cationic dyestuff, said composition being acidic and having a conductivity of at least 500 micromhos/cm.
DESCRIPTION OF THE PREFERRED EMBODIMENT
I-t is well-known that jet printing inks shoull contain a humectant in order to minimize undesired drying of the ink within the print head. It is common to run a flush fluid through the print head prior to start up and to flush the print head after shutdown.
Ordinarily, the ink is not permi-tted -to stand for a long period of time in the print head, and this reduces the problem of ink drying. To further reduce the problem, -the addition of a humectant such as propylene glycol added in an amount as small as 1.0 weight `L d 3~
-7a-percent produces satisfactory resul-ts. O-ther humectants, such as those disclosed in Zabiak, U.S.
Pa-ten-t No~ 3,705,043, as well as other humectan-ts known in the art may also be added. As wi]l be apprecia-ted by one o-E ordinary skill in the art, the composition may fur-ther include a corrosion inhibitor. See Ashley et al, "Development and Characterization oE Ink for an Elec-trosta-tlc Ink Jet Printer." IBM J. RES. DEV.
(January 1977) The ink composition of the present invention can be prepared by thorollghly ImiXin9 the comporlents to insur-e uniforrn rnixiny and complele dissolutiorl of lhe wclter-soluble clye, and then Filtering the resulting composition to remove particulate contamination. As will be apparent to those sl<illecl in the art, -filtration of the composition after mi~ing the components is highly desirable in order to remove from the inl< composition particulate mat-ter, such as contamination or undissolved dye, which migh-t otherwise serve to clog or obs-truct the jet of a jet printer during use. I t is 10 -frequen-tly pre-ferred to filter the composition of the inven-tion -to remove particulate ma-tter having a diameter greater than 2 microns, and preferably 1 micron, to insure that obstruction of -the oriface of the je-t printer will be avoided.
The inven-tion is described in further de-tail in the -following 15 examples. While there are disclosed below but a limited number of embodiments o-f the invention herein presen-ted, it is possible -to produce still other embodiments wi-thout departing from -the inventive concepts herein disclosed. Various other modi-fica-tions will be readily apparent to those skilled in the art.
The following novel composi-tions are expressed in percent by weight of the fluid. When "water" is indica-ted, deionized distilled water was used. The percent of dyestuf-f refers -to the cdyestuff material as supplied by the manu-facturer, as it is not possible, through means available to -the present inventor, to de-termine -the 25 por-tion o-f active dyestu-ff in the commercial preparation. Commer-cially available dyestuffs are generally proprie-tary or tracle secre-t 3~3 form-llatiol1s ar-d it i5 usucllly impossible Lo ascerLain the composi-tion of tl1e clyec.turl` e~cept under an obligation of conFidentiality.
All ol the for muldtioos given in ~he followirlg examples were tested in a contirIuous jet ir-l< jet pr ir1ter having a binary ink jet array.
They all exhibited t le proper cond-lctivity at least 500 micromhos/cm, and in general, greater than 5000 micromhos/crn --and produced excel-lent irnages in such a continuous jet ink jet printer. Examples I
and 5-9 as actually ~ested included a small amount, less than 0.5%, of a corrosion inhibitor. This component was added as a precaution but subsequently its absence has not been shown to be deieterious to the apparatus. Since the amount employed was so small and because the use of a corrosion inhibitor is considered optional in -the prac-tice oF the present invention it is not shown in -the formulations below .
"Aquonium" dyes are commercially available from -the Hil-ton Davis division of Sterling Drug, Inc. owner of -the registered trade-mark "Aquonium". In the examples which follow, each dye is referred to by the manuFacturer's current designation -to the trade. While -their exact composi-tion is no-t known to the presen-t inven-tor, i-t is believed that they are -the subject of one or more o-F -the Following U.S. Patents: 3,709,903, 3,784,599, 3,935,182, 3,996,282, 4,065,500, 4,081,239, ~1,103,092 and 4, I 43,03'1.

A typical jet printing ink -Formulation oF this inven-tion For a je-t prin-ting application is as follows:

-1n-CaLionic dyestuFI` - Aquonium turquoise 20-4471 4.00 BleedlasL reack~nL - glutaraldehyde 0.33 Con~ucLiviLy additive - methane sulFonic acid 0.49 S HumecLanL - propylene glycol 10.00 ~Vater 85. 18 'I 00 . 00 The physical properties oF the above Fluid are:
p~l 1.98 10 Viscosi-ty 3 2 cps Conductivi-ty 11, 000 micromhos/cm Resistivity 91 ohms-cm Surface tension 51.7 dynesJcm Specific Gravity 1.010 15 The Following Table I depicts the e-f-fect on conductivity of variation of the concentration of methane sulfonic acid in the jet printing ink formulation o-f Example 1. When added a-t concen-tra-tions oF from 0.3% to 2.0% by weight of the fluid, the acid imparts a conductivity r ange of from 6300 -to 31000 micromhos/cm. In Tables 20 I thro-,gh IV, "C" refers to conduc-tivity, expressed in micrornhos/cm and "R" refers to resis-tivity expressed in ohms-cm.

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Methane sulfonic acid, when used to control conductivity, imparts a conducivity range from 3000 micromhos/cm to 70,000 micromhos/cm when added to a 4% solution of other cationic dyestuffs (similar to the formulation of Example 1 but without a dialdehyde) at concen-trations of 0.2% to 4.0% by weight of the fluid, as described in greater detail in the following Table 11.

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Lxam~le 2 ~\notiler ty~)icaL jet ~rinting ink :Eormulati.oll of this invelltion Eor a Jet l)rinLing a})l)1icat:ion is as follows:
CaLiorlic dyesLIlrf - Aqllor~ m tur~loisc 20-2358 4.0%
Bleedlast rcacLant - g:lyoxoL 0.4%
Con(lucLiviLy ad(lit-ive - ma:leic acid 1.0%
Water 94.6%
Tlle eEfects of maleic acid on conductivity and resistivity with Aquonium turquoise 20-2358 and two other cationic dyestuffs are sho~n :in Table III.

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Another typical jet printing ink formulation of this invention For a jet printing application is as follows:
Ca-tionic dyes-tuff - Aquonium yellow 20-4459 4.0%
Bleedfast reac-tant - glyoxal 0.4~, Conductivity additive - ethane sulfonic acid 0. 3%
Wa te r 95.3%
The effects of ethane sulfonic acid on conductivity and resis-tivity wi-th Aquonium yellow 20-4459 are shown in Table IV.

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ln l~le e~:anlples which follow, no cond-lcLivity additive was required to produce excellent imacJincJ on a jet printer. The images, lil<e those of the preceding examples, were waler fast.

Another jet prinLing inl< formulaLion representative of -this invenLion and capable of proclucing a green color on paper is as ~ollows:

2.00o Aquonium yellow 20-4459 1.50% BASF CatioFas-t turquoise 101.00% Aquoni-lm scarlet 20-4477 0.50% Gluteraldehyde 10.00% Ethylene glycol 85.00% Distilled Water Physical Properties 15pH - 3.55 Conductivity - 700 micromhos/cm Viscosity - 4.0 cps Specific Gravity - 1.009 The BASF Catiofast turquoise is a modiFied ca-tionic dyes-tuF-F. I-t 20 is believed to be an imidazolyl methylene group con-taining dye dis-closed in German Patent Publication DE3006-013.

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EXAlvlPLE 5 Ano~her jeL printinq ink formulation representative oF this invenLion and capable of proclucina an orancge color on paper is as f`ol lo~vs:
1 . 30% Sandoz red t<2B
0 . 40O Glyoxal 10~00o ELhyler)e glycol 88 . 30% Water ~s i c a l P ro~_ pH - 6.2 Conductivi ty - 1000 micromhos/cm Sandoz recl K2B is a modified cationic dyes-tu-FF believed to be dis-closed in U.S. Patent No. 4,213,897.

Another jet printing ink formulation representative o-f -this invention and capable of producing an orange color on paper is as fol lows:
2 . 00% Aquonium yellow 20-4459 0. 80% Sandoz red K2B
I . 20% Glyoxal 10.00~, Ethylene glycol 86 . 00 Wa ter 3~

Physic a l Properties , _ p~ I . 26 Conductivity - 900 micromhos/cm ViscosiLy - 3.5 cps Surface Tension - 48.6 dynes/cm Specific Gravily - 1.02"

Another jet prin-ting ink formul3tion represen-tative o-F this invention and capable of producing a brown color on paper is as 10 Fol lows:
3.00% Aquonium yellow 20-4459 1.10% Sando~ red K2B
0.40% BASF Catiofast turquoise 1 . 20% Glyoxal 15 10.00% Ethylene glycol 84. 30% Water Physical Properties pH - 3.81 Conduc-tivity - 1200 micromhos/cm Viscosity - 4.0 cps Sur-Face Tension - 50. 6 dynes/cm Specific Gravity - 1.108 E><AMPLE 8 Another jet printing ink formulation represen-tative o-F -this 25 invention and capable oF producing a bleedfas-t yellow color on paper is as follows:

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12 00-" Mobay Astra yel low KS -ZG
1 20o Glyo~<al 10 00- Ethylene ~Iycol 76.80~-o Wa Ler _~ysical Properties p~l ~ 2.61 Conduc~ivity - 5800 micromhos/cm Viscosity - 3.8 cps Surface Tension - 44 8 dynes/cm Speci-Fic Gravity - 1.028 Astra yellow KS-26 is available from Mobay Chemical Corporation, Pittsburgh PA This Mobay dyes-tu-Ff is a modi-Fied ca-tionic dyes-tuFF
whose specific composition is unknown Ano-ther jet printing ink Formulation representative oF this inven-tion and capable oF producing a bleedfas-t red color on paper is as -Follows 8.00% Mobay Pon-tamine red KS-4BE
1 20~o G l yox a l 10 00% Ethylene glycol 80.80~ ~ater Phvslcal ProE~e-ties p~1 - 1.97 Conciuclivity - 5200 micromhos/cm Viscosily - 3.5 cps Surface Tension - 35. ~ dynes/cm Speci fic Gravi ty - 1 . 031 The specific composition oF this modified cationic dyes-tuff from Mobay Chemical Corporation is unknown.
Al though the invention has been described wi-th reference to 10 preferred embodiments thereof, it is to be understood -tha-t various chanc~3es may be resorted -to by one skilled in the art wi-thou-t departing from the spiri-t and scope of the inven-tion as defined by the appended claims .

Claims (6)

WHAT IS CLAIMED IS:

1. In a method of ink jet printing, the improvement which comprises printing with an aqueous ink composition comprising a water soluble, modified cationic dyestuff, said composition being acidic and having a conductivity of at least 500 micromhos/cm.

2. The method of Claim 1 wherein the ink composition contain; an organic acid taken from the group consisting of maleic acid, methane sulfonic acid and ethane sulfonic acid.

3. The method of Claim 2 wherein the conductivity is at least 5000 micromhos/cm.

4. The method of Claim 2 wherein the organic acid comprises from 0.2% to 4.0% by weight of the fluid.

5. The method of Claim 1 wherein the ink composition contains an aldehyde selected from the group consisting of formaldehyde, glyoxal and glutaraldehyde, and a water-soluble, modified cationic dyestuff having a functional group capable of reacting with the aldehyde.

6. The method of Claim 5 wherein the ink composition contains an organic acid taken from the group consisting of maleic acid, methane sulfonic acid and ethane sulfonic acid.