GB1577902A

GB1577902A - Ink composition

Info

Publication number: GB1577902A
Application number: GB44401/77A
Authority: GB
Original assignee: Whittaker Corp
Current assignee: Whittaker Corp
Priority date: 1976-10-26
Filing date: 1977-10-25
Publication date: 1980-10-29
Also published as: DE2747630A1; BR7707066A; ES463421A1; CS195341B2; NL7711755A; SE7711941L; NO773612L; GR65960B; JPS5355214A; BE859820A; IL52911A0; DK472877A; ZA775618B; IT1089477B; FR2369327A1; AU2989377A

Description

(54) AN INK COMPOSITION (71)We, WHITTAKER CORPORA TION, a corporation organised and existing under the laws of the State of California, United States of America, of 10880 Wilshire Boulevard, Los Angeles, California 90024, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to ink compositions characterized by fluorescent properties in ultraviolet light.More specifically, this invention relates to ink compositions, which are generally colourless in ordinary light and fluorescent in ultraviolet light so as to render them particularly suitable as a means for making various materials whereby the marking is normally invisible but easily detectable when subjected to ultraviolet illumination, for use in a printing apparatus operating on the so-called "ink jet printing" principle. Ink jet printing is a recent development in the art of applying identifying and decorative indicia to a base. In general terms, a fluid ink is forced, under pressure, through a very small orifice in an orifice block which contains a piezoelectric crystal vibrating at high frequency (50 - 100,000 vibrations per second) causing the ink passing through the orifice to be broken into minute droplets equal in number to the crystal vibrations.The minute droplets are passed through a charging area where individual droplets receive an electrical charge in response to a video signal, the amplitude of the charge being dependent on the amplitude of the video signal. The droplets then pass through an electrical field of fixed intensity, causing a varied deflection of the individual droplets dependent on the intensity of the charge associated therewith, after which the deflected drops are allowed to infringe on the base medium which is to receive the decorative or informative printed indicia. Apparatus suitable for carrying out the ink jet printing process is described in detail in U.S. Patent Specifications 3,465,350 and 3,465,351, issued September 2, 1969, and it is in connection with an apparatus and process such as are described in the aforementioned U.S.Patent Specifications that the ink composition of the present invention is designed to function.

In order to operate satisfactorily in an ink jet printing system, an ink composition must display a consistent break-up length, drop velocity and drop charge under set machineoperating conditions. To achieve these ends, the ink composition must meet strict requirements with regard to viscosity and resistivity, solubility and compatibility of components, stability and anti-skinning properties and must readily re-dissolve in a suitable solvent for rapid clean-up of the machine components with a minimum of effort.

It has been determined that the workable range of viscosity of an ink which is to be used in a jet printing apparatus in which the nozzle orifice is 0.003 inch in diameter, must be no more than about 16 cps. at 680F., with about 1.90 - 2.0 being the most desirable viscosity level for superior performance.

The viscosity may be somewhat higher than the above values if the orifice diameter is increased but in any case an ink composition of less than 20 cps., and preferably less than about 16 cps, at 68"F., is highly desirable.

Resistivity may range from less than 10 ohm-cm. to about 2000 ohm-cm., the most desirable value being between about 150 and 300 ohm-cm. Resistivity in excess of about 1000 ohm-cm. creates problems in obtaining the proper charge on the droplets and therefore the deflectability of the droplets in an electric field is erratically impaired.

The orifice through which the ink composition must pass is normally in the range of 0.002 inch to 0.005 inch in diameter. In order to prevent plugging of this orifice, it is highly desirable that all components of the ink be in solution in the carrier medium rather than in a colloidal or other suspended state. In any case, the complete ink composition must advantageously pass at least a 2 micron filter in order to be satisfactory for use. Further, the ink composition components must generally not sludge out or otherwise deposit in any of the transporting lines, the supply tank, the orifice or any other portion of the ink supply system, even though the solvent medium of the ink composition is subject to a certain amount of evaportion in the ink return system and the supply tank.In other words, the solvent medium must in general have a reserve solubility for the solute components of the ink composition in order to pevent any undesired precipitation which could clog or plug the minute jet orifice. The ink must in general also possess anti-skinning properties to prevent skinning over of the orifice or the tank during periods of shut-down. Any skin formed in such circumstances could then break up into small particles which could plug the orifice.

In order to facilitate clean-up of the apparatus after use, the ink composition components should be readily soluble in a common solvent medium. This will prevent any gradual build-up of ink residues in the system which could result in malfunction.

It is a particular objective of this invention to provide ink compositions for paper, paperboard and metal non-coated, clear coated or decorated substrates which are not heavily lubricated or waxed and which require little or no heat or water resistance, or which require heat resistance up to 1800F.

and water resistance, and for metal, noncoated, clear coated or decorated substrates which are heavily lubricated and waxed and require heat resistance up to 4000F. and excellent water resistance.

In cases where paper, paperboard and metal substrates are concerned requiring heat resistance up to 18() F. a binderless ink system is operable.

In all cases the inks are essentially free from visual colourants.

It is a further object of this invention to provide inks for use in the ink jet printing of indicia or substrates which combine properties necessary for satisfactory operation of the ink in the printing apparatus and which fluoresce when dry, with very short luminescence lifetimes, when exposed to ultraviolet radiation. The ink compositions of the invention include both solvent type ink compositions in which a pigment is dissolved in a solvent and disperse-type ink composition, in which a pigment is dispersed in a vehicle in which it is insoluble.

According to the present invention there is provided an ink composition suitable for use in jet printing comprising: from 0.5 to 20 weight percent of (a) at least one normally colourless compound which fluoresces in ultraviolet light; from 0 to 30 weight percent of (b) at least one solvent modifier chosen from ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether and propylene glycol monoethyl ether; from 0 to 2 weight percent of electrolyte (c); 0 to 20 weight percent of resin (d); and (e) a blend of water and lower aliphatic monohydric alcohol(s) of no more than three carbon atoms, in a water to total alcohol ratio by weight of 1: 5 to 1: 60, the proportions of the components being such that the ink composition has: (i) a surface tension at 680F of 22 to 40 dyne/cm; (ii) a viscosity at 68"F of 1.5 to 16 cps.; (iii) a pH of 2.5 to 9.5, and (iv) resistivity of less than 2000 ohm cm.

The ink composition may include from 0.5 to 10, preferably 0.5 to 5 weight percent of Component (a). The resistivity of the ink composition is preferably from 10 to 2000 ohm cm. Preferably the water to total alcohol content of Component (e) is 1:10 to 1: 30. Component (d) is an amount of 1 to 12 weight percent may be included. Component (d) may comprise shellac. An especially suitable ink composition is one having a viscosity at 68"F of from 1.75 to 3 cps.

In one preferred embodiment of ink composition Component (e) has as its alcoholic content a mixture of ethyl alcohol and propyl alcohols, and the viscosity of the ink composition has a viscosity of from 3 to 5 cps. at 68"F. In another preferred embodiment of ink composition Component (e) has as its alcoholic content a mixture of methyl and ethyl alcohols, and the ink composition has a viscosity of from 1.90 to 3 cps. at 68"F.

Ink compositions whose dyes or pigments have luminescent lifetimes which are short enough can be used to trigger switching devices and phosphorescent compounds with lifetimes of greater than 1/900th of a second are theoretically unusable. In practice, emission lifetimes much shorter than this are preferred. Simple fluorescence lifetimes are of the order of l0-') to 10- 12 seconds. Phosphorescence lifetimes may be as high as hours or more.

Red ink compositions which fluoresce in a 500 to 700 nm. region are less acceptable than blue or green ink compositions to which most persons are accustomed. Blue or green ink compositions which fluoresce suf ficiently in the 500 to 700 nm. region are desirable for aestgetic as well as practical reasons.

Preferably the ink compositions are yellow or green ink compositions which fluoresce upon excitation with near (365 nm.) ultraviolet or middle (254 nm) ultraviolet radiation, and which emit their light, with very short luminescence lifetimes, in a 500 to 700 nm. region. These ink compositions are organic in nature, also an advantage, in that they do not have the abrasive wearing quality of many inks based on abrasive, inorganic pigments.

Most conventional fluid fluorescent printing ink compositions include three basic components. The first is a fluorescent colourant for providing visibility of the printed indicia in contrast to the substrate surface.

The fluorescent colourant may be either a dye which is soluble in the ink solvent medium, or a pigment which is suspended in the solvent medium. The second component is a resin or binder which remains on the substrate surface after printing and serves to adhere and bind the dye or pigment in position on the substrate surface. The third major component is the solvent which provides fluidity to the ink and carries in solution or suspension the resin and colourant. In addition to these three components which are found in nearly all fluid printing ink compositions, various other ingredients may be utilized, including drying, dispersing and wetting agents, plasticizers, diluents and the like.Ink jet printing ink compositions, in addition to the three basic components above mentioned, may also desirably contain a fourth, optional component made appropriate to the ink composition by the nature of the apparatus and process of ink jet printing. This is an electrolyte, which is desirably added so that the ink droplets may be given a strong, reproducibly variable electric charge which in turn enables a controlled, reproducible deflection of the droplets by application of an electrical field to the droplet stream.

Printing processes other than ink jet printing do not require inks with electrical properties capable of achieving these ends.

The properties of the solvent and the characteristics which are imparted to the ink by the solvent are of paramount importance in the present invention. It has been previously pointed out that the overall ink composition must be of very low viscosity.

Satisfactory results are readily obtainable with inks having a viscosity as high as 16 cps.

at 68"F., and it is possible to operate with limitations with ink having a viscosity approaching 20 cps., although the jet printing process becomes increasingly difficult to control as the ink viscosity increases with the consequence that an ink viscosity greater than 16 cps at 680F is not practicable for jet printing. A viscosity of about 1.90 cps. is considered most desirable. Since the resinous component tends to increase the viscosity of the solvent medium, it is therefore necessary to have the solvent display a very ]ow viscosity to prevent an undesirable viscosity build-up as a result of compounding. Few solvents are capable of meeting the stringent viscosity requiremets as well as the other functional requirements of the ink jet printing inks illustrative of this invention.

Only the aliphatic monhydric alcohols of low molecular weight, comprising methyl, ethyl, n-propyl and isopropyl alcohols, either individually or in blends thereof, exhibit the proper combination of low viscosity, solubility for basic dyes and for eletrolytes, water-miscibility and surface tension characteristics required. Hereinafter, the term "lower aliphatic monhydric alcohols" will be used to refer to the four alcohols mentioned above.

Ink compositions having the lowest viscosity are those wherein the alcoholic solvent component is methyl alcohol or a blend of methyl and ethyl alcohols. The substitution of one of the propyl aocohols for methyl alcohol in a given ink composition will result in an ink of somewhat higher viscosity, as will be illustrated by examples hereinafter. Optimum performance is obtained in jet printing apparatus having a nozzle orifice diameter of 0.003 inch, as is common in the industry, with inks having a viscosity between about 1.5 and 13 cps. at 68"F., viscosities in this range being obtained with methyl alcohol or a blend of methyl and ethyl alcohol as the organic solvent. Comparable ink compositions made with a propyl alcohol solvent will have viscosities in the range of 3 - 5 cps. or more.

The standard ink jet printing apparatus with nozzle orifices of 0.003 inch will operate satisfactorily with ink compositions of up to about 5 cps. or slightly above, whereas ink compositions of higher viscosity (up to about 8 to 10 cps.) may also be considered acceptable, but require larger nozzle orifices, higher driving pressures and substantial alterations in the electrical system and geometry of the printing apparatus. It is, therefore, practically and economically necessary that inks of no more than 16 cps be employed. It is to be noted that the viscosity of the ink compositions is not governed by the solvent viscosity alone, but is also affected by the concentrations of the other ink components as well, including particularly the resinous component, water, and optional modifying additives as will be discussed in greater detail hereinafter.

The propensity for the solvent to wet the substrate, as measured by the property of surface tension of the solvent and of the ink composition incorporating it, is of great importance and must be carefully controlled. Water, for example, will not properly wet a metallic aluminium substrate such as an aluminium can because of its undesirably high surface tension (72 dyne/cm. at standard temprature), and ink compositions having a water base are not satisfactory for use in metal can printing, although such inks have been employed in jet printing of paperboard, for example, since paperboard surfaces are readily wet by water.On the other hand, methyl, ethyl, propyl and isopropyl alcohols, which have surface tensions of 22, 23, 24 and 22 dyne/cm., respectively, at standard temperature, wet aluminium so readily that the metal surface is flooded by the solvent, which spreads out and merges with other droplets to obscure the limits of any indicia printed by use of these solvents.

The ink compositions of the present invention, when intended for use on an aluminium surface, are compounded to have surface tensions at 68 F., of between 28 and 40 dyne/cm. For use on other metal surfaces, such as steel and tinplate, and on organic coating surfaces such as those commonly used in steel can manufacture, surface tension values of the printing inks between 22 and 35 dyne/cm. are necessary, the lower portion of this range being generally preferred.

In order to be effective in the formulation of a jet printing ink composition for metal cans, the solvent medium must readily dissolve sufficient amounts of the resin component, the dye and any desirable optional components such as an electrolyte to achieve the desired level of adhesiveness, conductivity and visual impact of the ink composition. Further, since some degree of evaportion of solvent will occur in the ink supply and ink return systems, thereby increasing the solids concentration of the composition in these areas, the solvent must have a reserve solvent power sufficient to prevent precipitation in this situation.

Although evaporation of the solvent from the ink supply and return systems is generally undesirable, it is important that the solvent evaporate relatively rapidly from the printed image area in order to leave the printed indicia smearproof and moistureproof fairly promptly after the printing operation is carried out. The solvent must achieve a satisfactory balance in evaporative properties between these opposed objectives.

A resin componcnt of a jet printing ink may be necessary for printing on metal and must also meet a variety of requirements.

Of primary importance is the ability of the resin to adhere strongly to the metal surface on which the ink is printed and to maintain this strong adhesion under widely varying conditions of humidity and tenmperature.

When the ink composition is applied to the metal surface, it must "set" or adhere quickly and strongly to the metal, even in the presence of some moisture, and must exhibit a high degree of moistureproofness, not only to maintain adhesion to the metal but also to protect the dye, which may be water-sensitive, from the effects of moisture which may make the dye bleed into surrounding areas.

The resin component for printing on metal must also be very readily soluble in the solvent medium to form a stable, low viscosity solution so that effective amounts can be dissolved in the solvent without unduly increasing the viscosity of the composition. Similarly, the electrolytic component used in the preferred embodiments of the invention must also be effective at concentrations well below its solubility limit in order to achieve the desired drop deflection characteristics without danger of precipitation and plugging of the system.

As previously mentioned, the ink compositions of this invention contain at least one normally colourless compound (a) which fluoresces in ultraviolet light, a solvent blend (e), and optionally an electrolyte (c) in an amount effective to achieve desired drop deflection characteristics, all of which must be in carefully balanced proportion to achieve successful operation of the ink composition in a jet printing apparatus. A resinous component may be necessary for printing on metal.

The Solvent Blend (e) - Although or'minor amounts of other solvents may be included in the overall ink composition for specific purposes, the primary solvent blend is a mixture of one or more of the lower aliphatic alcohols previously mentioned and water. For printing on the surface of aluminium metal, the weight ratio of water to the total alcoholic component should desirably be in a range 1 10 to 1: 30 since this ratio yields inks having surface tensions of about 30 - 35 dyne/cm. If the solvent blend contains a higher than desired concentration of water, the resulting ink composition will tend to bead up on the metal surface, whereas a particularly high concentration of the alcohol causes the ink to spread unduly on the metal surface with resultant smearing or diffusion of the printed indicia. Since the wetting characteristics of steel and tin plated steel vary somewhat from those of aluminium, when these metals are the substrate on which the printing is to be applied, the solvent ratio must be adjusted somewhat, a suitable water-to-total alcohol ratio by weight being from 1 to 10 to 1 to 30, yielding ink compositions in the desired surface tension range of 22 - 30 dyne/cm.

In addition to methanol and water, the solvent blend in the preferred ink compositions often contains some ethanol, used as the primary solvent for the resinous component. As previously stated, ethyl alcohol and the propyl alcohols have higher viscosities than methyl alcohol and the viscosity of a particular ink composition will, of course, vary substantially depending on which of these alcohols are incorporated and in what proportions. The choice of the alcoholic component will depend on the specific characteristics desired in the final ink composition. If rapid drying and/or very low viscosity are required, the alcoholic component will necessarily be primarily methyl alcohol. If slower drying and a somewhat higher viscosity may be tolerated in a given situation, part or all of the methyl aocohol may be replaced with ethyl, n-propyl or isopropyl alcohol.Compositions employing these less volatile alcohols require less make-up solvent addition and are less subject to line plugging problems associated with rapid evaporation of the ink solvents.

In general, ink compositions of very low viscosity, particularly below 3 cps. at 68"F., are preferred, although inks of 5 cps. at 68"F. may be used very satisfactorily and, in extreme cases in which high driving pressure and relatively large nozzle orifice size (0.005 inches, for example) are employed, inks approaching a viscosity of 8 - 10 cps. at 680F may be used.

In each ink composition, the particular alcoholic component used must be in balanced porportion to the amount of water present in the ink composition, the proportions being within the limits previously set forth for satisfactory operation.

A small amount of ammonia or similar alkalizing agent, in the form of a concentrated aqueous solution, may be added to the ink composition to maintain the system in a preferred pH range of 8.0 to 9.5. A preferred pH range of 8.6 to 8.8 is generally maintained by adition of about 1% by weight of concentrated ammonia solution (26 Baumé) to the ink, but it is to be understood that the amount of this component or an equivalent substitute which is added may be varied in accordance with the pH requirements set forth above.

Control of the pH of the ink composition is important to the success of the ink composition in jet printing operations.

Alkalinity in excess of that indicated by the stated pH range results in slow drying of the ink composition on a printed surface and relatively poor adhesion, whereas a pH below the acceptable range may seriously affect the stability of composition, causing sludging in the system and plugging of the printing jet orifices.

If the desired dye or pigment has a relatively limited solubility in the solvent media hereinbefore described, the composition may be modified by the inclusion of a moderate amount of a solvent modifier(b) in which the dye or pgiment has a high solubility, which has a low surface tension and low viscosity, which is completely miscible with water and which has a suitable evaporation rate. Certain of the relatively low molecular weight glycol ethers, including ethylene glycol monomethyl ether (commonly known as "Methyl Cellosolve"), ethylene glycol monoethyl ether (commonly known as "Cellosolve"), propylene glycol monomethyl ether and propylene glycol monoethyl ether, have proven to be eminently satisfactory in this regard and may be added to the ink composition in amounts of up to about 30% by weight, as required to stabilize the cokouring agent in solution.

Amounts of the listed glycol ethers in excess of 30% by weight of the composition must be avoided if the ink is to wet the surface of the metal printing substrate satisfactorily "Cellosolve" is Trade Mark.

The Resin Component (d).

The preferred resin component is dewaxed and bleached shellac, or its equivalent, although any comparable resin having the requisite properties of solubility in the solvent medium and ability to anchor the colour component on the metal surface could be satisfactorily utilized in the ink composition. In general, a high concentration of resin is desired in order to anchor the dye or pigment most firmly on the printed surface. The resin concentration, however, is limited by the increase in viscosity which results as the amount of resin in the composition increases.

Further, as the concentration of shellactype resin increases, interaction between the resin and the colouring component may occur with resultant scumming or sludging of the ink composition. This penomenon is particularly evident in those compositions which include substantial amounts of water.

The problem cannot be overcome by elimination of the aqueous component, however, because some water is necesary in order to maintain the surface tension of the ink within the operative range to achieve proper wetting of the substrate. If the alcoholic component is primarily methyl alcohol, the ink may contain from 1% to 17% shellac, which provides effective pigment anchoring capacity within the preferred operative range of 1.75 - 5 cps. in overall ink viscosity heretofore mentioned in connection with nozzle orifices of about 0.003 inch in diameter. Somewhat higher shellac contents may be tolerated if the orifice size is increased proportionately as the viscosity increases due to the higher resin content.

Thus, with orifices of about 0.005 inch in diameter, the shellac content may be as high as about 25% by weight, it being understood that, in inks of the higher shellac contents, the amount of water and of the higher alcohols will be maintained at a minimum compatible with the requirements of substrate wettability, drying speed and sludge prevention previously mentioned.

It has previously been noted that the use of ethyl and propyl alcohols results in inks of higher viscosity than is obtained when methyl alcohol is the primary alcoholic solvent. Since an increase in the resinous component also tends to increase the viscosity, it will be apparent that, in order to maintain a desired viscosity level, less shellac will be utilized with propyl alcohol than with methyl alcohol as the solvent.

The Elect olyte Component (c) In order that the droplets of ink composition ejected from the nozzles may receive and hold the proper electrical charge, the ink composition must have a specific resistivity within a range from somewhat below 10 ohm cm. to 2000 ohm cm., the preferred operative range being between 150 and 300 ohm cm. It has been found that some of the ink compositions of this invention will naturally have a resistivity within the operable range without the necessity of adding an electrolytic component specifically for the purpose of adjusting the resistivity of the ink.In general, however, it has been found that optimum results are obtained if there is added to the ink an optional component which comprises a salt or mixture of salts which is soluble in the ink medium and which has no deleterious effects on the printing apparatus or on the printed substrate. Particularly satisfactory for this use are dimethylamine hydrochloride and lithium chloride, although other alkali metal chlorides, nitrates, sulphates and similarly soluble salts may also be used. Dimethylamine hydrochloride, which has a high solubility in the solvent media hereinbefore described, is of particular utility because of this property.

The electrolyte component (c) may be added in an amount which will be effective in lowering the resistivity of a given ink to the desired level. The effective amount of electrolyte will vary from zero to 2% depending on the original resistivity of the ink and on the resistivitv desired. Amounts of the preferred electrolytes, dimethylamine hydrochloride and lithium chloride. in excess of 1.5cm are generally considered unnecessary and are therefore economically undesirable. Higher salt concentrations result in ink compositions of progressively lower resistivity. Although ink compositions of very low specific resistivity are quite operable in the process of jet printing, resistivity values of less than 100 ohms cms.

present no particular advantage over those ink compositions having a resistivity between 100 and 300 ohms cms., the latter range of values being considered optimum.

The alkali metal salts previously mentioned may also be used in concentrations up to about 2.0%, higher concentrations being both unnecessary and difficult to maintain because of the limited solubility of these materials in the solvent media used in the ink compositions of this invention. Because of their greater solubility in the alcoholwater solvent system, the preferred salts are dimenthylamine hydrochloride and lithium chloride, used either alone or in combination, in a total salt concentration of about 1.5% by weight of the ink composition.

The Colouring Component (a) The ink compositions of this invention may be prepared by dissolving a quantity of dye-former in a lower alkyl carboxylic acid.

The dye-former will be a normally colourless compound which fluoresces in ultraviolet light. A quantity sufficient to give an intense enough blue or green, but less than the solubility of the dye-former in acetic acid, may be used. For example, 0.263 g. of dye-former per cc. of acetic acid has been found to be a convenient amount, fulfilling the above requirements for many dye precursors. More or less acid may be added where convenient. A quantity of a polymer solution is now added in a solvent system chosen for compatibility with all components and proper drying rate.

The following example is illustrative of ink compositions embodying this invention which are effective in jet printing operations: Example To a mixture of 53 gm. of methanol, 22 gm of water, 1 gm. of 26 Baumé ammonium hydroxide and 1.0 gm of lithium chloride was added 16 gm. of dye dissolved in 170 gm. of methanol together with a solution of 15 gm. of shellac in 105 gm. of ethanol. The dye is a normally colourless compound which fluoresces in ultraviolet light.

The resulting ink composition had a viscosity of 2.36 cps. at 68"F., a resistivity of 149 ohm cm., a pH of 8.6 and a surface tension of 31 - 32 dyne cm. at 68"F.

The ink composition was used in the ink jet printing of indicia on the ends of aluminium cans containing beer and on tin-free steel cans. The printed indicia dried very quickly to form images displaying excellent adhesion to the substrate, high resistance to abrasion and excellent resistance to water. The images bled slightly when subjected to steam pasteurization.

Substitution of an equal amount of dimethylamine hydrochloride for the lithium chloride gave equivalent results, the minute droplets of ink composition projected from the jet nozzles in each case readily accepting a satisfactory charge to undergo the desired degree of deflection in the electric field responsible for positioning the droplets on the substrate. Similar results may be obtained if other basic dye (a) is substituted in the above composition.

WHAT WE CLAIM IS 1. An ink composition suitable for use in jet printing comprising: from 0.5 to 20 weight percent of (a) at least one normally colourless compound which fluoresces in ultraviolet light; from 0 to 30 weight percent of (b) at least one solvent modifier chosen from ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether and propylene glycol monoethyl ether; from 0 to 2 weight percent of electrolyte (c); 0 to 20 weight percent of resin (d); and (e) a blend of water and lower aliphatic monohydric alcohol(s) of no more than three carbon atoms, in a water to total alcohol ratio by weight of 1: 5 to 1:60, the proportions of the components being such that the ink composition has: (i) a surface tension at 680F of 22 to 40 dyne/cm; (ii) a viscosity at 680F of 1.5 to 16 cps.; (iii) a pH of 2.5 to 9.5, and (iv) a resistivity of less than 2000 ohm cm.

2. An ink composition according to Claim 1, which includes from 0.5 to 10 weight percent of Component (a).

3. An ink composition according to Claim 2, which includes from 0.5 to 5 weight percent of Component (a).

4. An ink composition according to any preceding claim, wherein the resistivity of the composition is from 10 to 2000 ohm cm.

5. An ink composition according to any preceding claim, wherein the water to total alcohol content of Component (e) is 1:10 to 1: 30.

6. An ink composition according to any preceding claim. which includes 1 to 12 weight percent of Component (d).

7. An ink composition according to any preceding claim, wherein Component (d) is present and comprises shellac.

8. An ink composition according to any preceding claim, wherein the viscosity of the ink composition at 68"F is from 1.75 to 3 cps.

9. An ink composition according to Claim 1, wherein Component (e) has as its alcoholic content a mixture of ethyl and propyl alcohols, and the viscosity of the ink composition has a viscosity of from 3 to 5 cps. at 68"F.

10. An ink composition according to Claim 1, wherein Component (e) has as its alcoholic content a mixture of methyl and ethyl alcohols, and the ink composition has a viscosity of from 1.90 to 3 cps. at 68"F.

11. An ink composition according to Claim 1 substantially as herein described and exemplified.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. when subjected to steam pasteurization. Substitution of an equal amount of dimethylamine hydrochloride for the lithium chloride gave equivalent results, the minute droplets of ink composition projected from the jet nozzles in each case readily accepting a satisfactory charge to undergo the desired degree of deflection in the electric field responsible for positioning the droplets on the substrate. Similar results may be obtained if other basic dye (a) is substituted in the above composition. WHAT WE CLAIM IS

1. An ink composition suitable for use in jet printing comprising: from 0.5 to 20 weight percent of (a) at least one normally colourless compound which fluoresces in ultraviolet light; from 0 to 30 weight percent of (b) at least one solvent modifier chosen from ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether and propylene glycol monoethyl ether; from 0 to 2 weight percent of electrolyte (c); 0 to 20 weight percent of resin (d); and (e) a blend of water and lower aliphatic monohydric alcohol(s) of no more than three carbon atoms, in a water to total alcohol ratio by weight of 1: 5 to 1:60, the proportions of the components being such that the ink composition has: (i) a surface tension at 680F of 22 to 40 dyne/cm; (ii) a viscosity at 680F of 1.5 to 16 cps.; (iii) a pH of 2.5 to 9.5, and (iv) a resistivity of less than 2000 ohm cm.