Ink compositions and process for ink jet printing

Claim 2

The preferred initiator is bis-[4-(diphenylsulfonio) phenyl] sulfide bis-hexafluorophosphate (BDS), manufactured by ourselves, and is solvated to a 33% by weight solution in propylene carbonate. However, triphenylsulfonium hexafluorophosphate (TPS) also rapidly cures the resin.

Claim 3

It is believed that conventional electrolytes, generally necessary in conventional jet ink formulations to achieve the proper resistivity of less than 4000 ohm-cm., preferably less than 3000 ohm.-cm., interfere with the photoinitiating reaction, probably by neutralizing the Lewis acid. However, the aforesaid BDS and TPS initiators, and most likely other complex salt initiators, when provided in excess of the amount required to trigger the curing reaction, do provide the specified resistivity. Hence, while only 0.3 to 3.0% initiator by weight would generally be considered appropriate to start polymerization, we prefer to add between 3 to 12% initiator by weight. Percentages referred to in the preceding sentence are on an inert free basis. That is, solvents such as propylene carbonate for BDS initiator, and other inert materials that may be in the initiator formulation as obtained from the source of supply are not included in said percentage ranges.

Claim 4

Colorants

Claim 5

Colorants used herein are either dyes or pigments. Pigments are defined as any substance, usually a dry powder insoluble in water or organic solvent, that has a positive colorant value and imparts color to another substance, e.g., metallic oxides for instance of titanium. Because pigments are insoluble in ink compositions, they are included as fine powders, typically below 5 microns, yet they still tend to plug the fine jet nozzles. For this reason, dyes soluble in the solvent system are the preferred colorants. However, most dyes, which contain active organometallic complexes, have been found to affect the cure mechanism, especially those dyes with sulfur and sodium groups. We have found that certain azo/metal complex dyes do not adversely affect the initiator for example. Spirit Soluble Fast Violet RR, manufactured by BASF-Wyandotte and Orasol Black RL by Ciba-Geigy, Inc.

Claim 6

Solvent System

Claim 7

The organic solvent serves to reduce the viscosity of the ink composition to values suitable for use in jet printing equipment. The solvent blend used should be adapted to dissolve the resins as well as the dyes, and preferably will be sufficiently polar to form the more stable Lewis acid hydrolysis product, although small amounts of water may be added or may be provided from the environment to do so. The solvent system should be suitable for substantially complete dissolution of the other ink constituents, and evaporate substantially from the droplets of ink leaving the jet printing nozzle. The solvent can be a blend of one or more solvents selected from alkyl ketones of from 2 to 5 carbon atoms, aromatic hydrocarbons of benzene, toluene and xylene, ethylene glycol ethers of 3 or 4 carbon atoms, acetates of from 2 to 4 carbon atoms and aliphatic alcohols of 1 to 5 carbon atoms. Preferably, one solvent should be included to readily solubilize the dye, if used, for example the aliphatic alcohol of from 1 to 5 carbon atoms. The solvent blend is formulated for adjustment of ink properties such as the velocity of sound, its wetting ability and its viscosity. Propylene carbonate, used to solvate BDS initiator, has also been found to be a proper component of the solvent system .

Claim 8

Miscellaneous Components:

Claim 9

In addition to the aforesaid resin, initiator, colorant and solvent constituents, the ink composition may contain small amounts of other additives such as optical brighteners, e.g., HM-35 from Day-GLO Corporation, surfactants, e.g., FC 430 from 3M Corporation, which is a fluorinated alkyl ester surfactant, and coupling agents, e.g., L720 which is an organosilane available . from Dow Chemical Company.

Claim 10

Composition of the Jet Inks

Claim 11

The inks disclosed herein contain 10 to 70% by weight of one or more of the epoxy resins hereinbefore referred to as the essential prepolymers, preferably 25 to 60% by weight of the said resins. Preferably, a blend of epoxy resins comprising DGEBA resins and one or more of the other essential epoxy resins hereinbefore named (that is, not including the reactive diluents or the high molecular weight reactive resins used to enhance adhesion) are used in the weight ratio of between 1:4 to 4:1, most preferably 1:2 to 2:1. Novolac resins are advantageously included in the preferred resin blends to promote crosslinking having highly branched structures. Substantial branching, sufficient to obtain improved adhesion of the cured indicia on the substrate surface,_is obtained with a ratio of between about 0.1 to 0.5 parts novolac resin per part of non-novolac resin. Hence, excellent jet ink compositions are obtained, based on the most preferred blends mentioned above, with the essential epoxy resins within the following ratios:

Claim 12

Depending upon the selection of essential resins and the solvent system, up to 40% by weight of the ink may contain reactive diluents, although generally the amount of reactive diluent, if used, would be less than 15% by weight of the ink. The reactive diluent is especially useful where high concentrations, over 35% by weight of the ink, of high viscosity or solid DGEBA or novolac resins are included in the ink concentration. The diluents serve to reduce viscosity of such formulations without providing substantial amounts of solvent that otherwise flash evaporate. While the diluent does not enhance adhesion and rub resistance to the cured indicia, its use in combination with the essential resins and in proper amounts does not deleteriously affect indicia properties.

Claim 13

The initiator comprises 1 and 12% of the ink on a weight basis, said percentage range being on a solvent and/or inert free basis.

Claim 14

Typically, the colorant comprises less than 2% by weight of the ink, preferably less than 1.0% by weight.

Claim 15

The solvent blend comprises the remainder of the ink composition, the solvent percentage including the solvent, if any, for the photoinitiator. Hence, the solvent can comprise/between about 10 to about 85% of the ink by weight although typically the solvent represents about 25 to about 60% of the ink by weight. Low solvent concentrations, i.e., solvent weight percents between about 10 to 25% usually indicate that a reactive diluent has been included in the ink composition. High solvent concentrations, above 60%, are typically employed when a reactive diluent is not included and high viscosity DGEBA and novolac resins are used. Preferably, the solvent blend comprises methanol and methyl ethyl ketone in the weight ratios of 1:4 to 4:1, preferably between 1:2 to 2:1. Up to 20% isopropanol may advantageously be included in the above solvent blend to enhance the wetting properties of the ink on the substrate, the isopropanol evaporating more slowly from the ink droplets leaving the printer. Methanol is also a preferred solvent because we have found it acts as a chain terminator, thereby preventing reaction until use, thus providing excellent ink stability. When the ink is used, the methanol evaporates rapidly from the system permitting reaction to occur.

Claim 16

The jet printing process employing inks as described above will now be described by way of example.

Claim 17

A continuous stream of ink is transferred from a pressurized supply reservoir for discharge as droplets from a printing nozzle at ambient conditions. The pressure in the reservoir is sufficient to overcome transfer line and nozzle pressure drops, the pressure being about 10 to 50 psia (0.69 to 3.45 bar). The disposition of the droplets exiting the nozzle is dependent on whether a coded message is to be printed on a substrate. Assuming that the coded message is not to be printed, the droplets are recaptured proximate to the nozzle and cycled back to a return tank. Because the nozzle always discharges to atmosphere, it is necessary that the return tank be under vacuum, the return tank pressure being about 4-6 psia (0.28 to 0.41 bar).

Claim 18

When an article to be encoded passes beneath the printer nozzle, a portion of the droplet stream is deflected by a pre-set series of electric signals thereby causing the coded message to be printed. The bulk of the droplets, however, continue to be recaptured for transfer to the return tank. This system is used because the actual amount of ink necessary for printing the coded messages is substantially smaller than the volumetric flow rate through the printing equipment required for meaningful control. Droplets applied to the substrate are exposed to ultra-violet light, and the reaction begins, residual solvent simultaneously evaporating from the droplets, the drier and cured indicia adhering strongly to the substrate and resistent to fading, rubbing and smearing. Make-up Solution

Claim 19

Because of the flash vaporization which occurs at the nozzle, and the reduction in pressure in the return tank, the composition of the ink in the return tank is different than the ink in the supply reservoir. For this reason it is necessary to reconstitute the former for eventual re-use by the addition of make-up solution. - The make-up formulation is a function of the rate of loss of the ink constituents, and consists essentially of the volatile solvent species, but may also include non-solvent constituents. In general, the make-up formulation is added intermittently. The return tank can be mounted on a weigh scale, or its volume measured, and as evaporation occurs, an automatic valve actuated to transfer make-up solution to the supply reservoir. Alternately, a property of the ink could be monitored, e.g., specific gravity, to actuate the transfer. Because the rate of loss is dependent upon the actual ink composition and operating conditions, the make-up solution composition should be determined a priori by a trial and error procedure.

Claim 20

The examples below further illustrate the present invention:

Claim 21

Example 1

Claim 22

Solvent System

Claim 23

Other Components

Claim 24

The monoglycidyl ether is a reactive diluent. Although run successfully on aluminium foil, several drawbacks were noted. Not all of the dye dissolved, and curing of the resin took longer than expected. It appeared that the presence of the electrolyte, normally included in jet ink compositions, interfered with formation of the Lewis acid, and prevented rapid curing. The high percentage of methyl Cellosolve also affected drying time in that this solvent tended to remain with the resin rather than be subject to flash evaporation. Finally, the solvent system was not formulated for complete dissolution of the dye. In Example 1 as well as in the other examples below, the amount designated for the initiator includes the solvent and/or inert material therefor.

Claim 25

Example 2

Claim 26

The ink cured more easily than the jet ink of Example 1, and provided slightly better adhesion to the substrate. Varcum 27-109 is not considered an essential prepolymer, but was included for improved adhesion.

Claim 27

Example 3

Claim 28

The dye dissolved more readily in the above solvent system, while the presence of the novolac resin provided branching of the crosslinked epoxy resins. As a result, better solvent resistance of the cured indicia was noted.

Claim 29

Example 4

Claim 30

Methyl Cellosolve was eliminated from the solvent system and was found not to be essential for solubilizing the epoxy resins. Surprisingly, about 4.5% water by weight did not cause instability of the ink or prevent cure.

Claim 31

Example 5

Claim 32

Viscosity of the above ink composition was about 5 mPa.s and the velocity of sound was about 1,400 meters per second, each property being measured at about 25°C.

Claim 33

Example 6

Claim 34

EXAMPLE 7

Claim 35

Example 8

Claim 36

Example 9

Claim 37

Pentalyn 255 is a rosin binding agent to provide better adhesion of the indicia to the substrate. The properties of the ink were:

Claim 38

A jet ink composition for producing visible indicia on a substrate, the ink composition being formulated from a polymerizable epoxy resin, a colorant and a solvent, characterised in that the ink composition has at 25°C a viscosity of 1.5 and 25 mPa.s, a resistivity of less than 4000 ohm-cm., and a velocity of sound between 800 and 2,500 meters per second, and the ink composition comprising (A) 10 to 70% by weight of an epoxy resin selected from (i) diglycidyl ethers of bisphenol A, said resin being predominately the monomer thereof, (ii) polyepoxidized phenol or cresol novolacs, (iii) diepoxide ethers or esters having two epoxy cycloalkyl groups, (iv) polyglycidyl ethers of polyhydric alcohols, and (v) combinations thereof, the said epoxy resins being liquid at room temperature or having a Durran melting point of less than 100°C., and having an epoxy equivalent weight of less than 300; (B) 1 to 12% by weight of a photoinitiator, capable of rapidly polymerizing the epoxy resins which provides a Lewis acid effective to initiate said polymerization reaction upon exposure to a source of radiation such as ultra-violet light; (C) less than 2% by weight of a colorant that does not adversely affect cure of the epoxy resins; and (D) a solvent blend containing solvents selected from aliphatic alcohols having one to five carbon atoms, alkyl ketones having two to five carbon atoms, aromatic hydrocarbons of benzene, toluene and xylene, propylene carbonate, ethylene glycol ethers having three or four carbon atoms, alkyl acetates having two to four carbon atoms, and combinations of these solvents, the solvent blend being volatile at ambient conditions.

Claim 39

The composition according to claim 1, characterised in that the epoxy resin is selected from resins including liquid diglycidyl ether of bisphenol A having a viscosity of between 5000 to 35000 mPa.s at 25°C.has an epoxy equivalent weight of between 170 and 230, phenol or cresol novolac is selected from novolacs having a viscosity of between 1400 to 70000 mPa.s at 52°C, and an epoxy equivalent weight of between 170 to 235, the diepoxide resin is selected from 3,4-epoxycyolohexylmethyl-3,4-epoxycyclohexane carboxylate, bis (3,4-epoxy-6-methylcyclohexylmethyl) adipate, and bis (2,3-epoxycyclopentyl) ether, and the polyglycidyl ether is selected from 1,4-bis (2,3-epoxypropoxy) butane, bis [2-(2,3-epoxyproxy) ethyl] ether, and 1,2,3-tris (2,3-epoxypropoxy)propane.

Claim 40

The composition according to claim 1 or claim 2, characterised in that the epoxy resin is a blend of diglycidyl ether of bisphenol A and one or more other resins in the weight ratio of 1:4 to 4:1.

Claim 41

The composition according to any of claims 1 to 3, characterised in that the resin blend contains 0.1 to 0.5 parts novolac epoxy resin per part of non-novolac epoxy resins.

Claim 42

The composition according to any of claims 1 to 4, characterised in that the colorant is a pigment having a particle size of less than 5 microns, or an azo/metal complex dye.

Claim 43

The composition according to claim 5, characterised in that the colorant is selected from Spirit Soluble Fast Violet RR and Orasol Black RL dyes.

Claim 44

The composition according to any of claims 1 to 6, characterised in that the solvent system comprises methanol and methyl ethyl ketone in a weight ration of 1:4 to 4:1.

Claim 45

The composition according to claim 7, characterised by the solvent system containing up to 20% isopropanol by weight.

Claim 46

The composition according to any of claims 1 to 8 characterised in that the epoxy resin constitutes 25 to 50% of the ink by weight.

Claim 47

The composition according to any of claims 1 to 9, characterised in that its viscosity is 1.5 to 18 mPa.s, its resistivity is 500 to 2500 ohm-cm., and the velocity of sound therein is 1,150 to 1,750 mps, all measured at 25°C.

Claim 48

The composition according to any of claims 1 to 10, characterised in that the photoinitiator is an onium salt selected from aromatic diazonium salts of complex halogen halides, diaryliodonium salts, and aromatic onium salts of Group Va and VIa elements of the Periodic classification of the elements.

Claim 49

The composition according to claim 11, characterised in that the photoinitiator is a bis-[4-(diphenylsulfio)phenyl] sulfide bis-M.X6 aromatic onium salt of Group Va, where M is selected from the group consisting of phosphorous, antimony and arsenic, and X is a halide, the photoinitiator being solvated in a 33% solution by weight of propylene carbonate.

Claim 50

The composition according to any of claims 1 to 12, characterised by having a tack free time less than 30 seconds and preferably less than 5 seconds.

Claim 51

The composition according to any of claims 1 to 13, further characterised by comprising up to 40% by weight of a reactive diluent epoxy resin.

Claim 52

The composition according to any of claims 1 to 14, characterised by further comprising up to 15% by weight of a binding agent resin.

Claim 53

A process of jet printing for producing visible coded messages on glass, metal or polymeric substrates, characterised by (1) forming a jet ink composition having (at 25°C) a viscosity of 1.5 to 25 mPa.s, a resistivity of less than 4000 ohm-cm., and a velocity of sound therein of 800 to 2,500 meters per second, the ink composition being formed from (A) 10 to 70% by weight of an epoxy resin selected from (i) diglycidyl ethers of bisphenol A, said resin being predominately the monomer thereof, (ii) polyepoxidized phenol or cresol novolacs, (iii) diepoxide ethers or ester having two epoxy cycloalkyl groups, (iv) polyglycidyl ethers of polyhydric alcohols, and (v) combinations thereof, the epoxy resins being liquid at room temperature or having a Durran melting point of less than 100°C. and having an epoxy equivalent weight of less than 300; (B) 1 to 12% by weight of a photoinitiator capable of rapidly polymerizing the epoxy resins and of the type that provides a Lewis acid effective to initiate said polymerization reaction upon exposure to a source of radiation such as ultra-violet light; (C) less than 2% by weight of a colorant that does not adversely affect cure of the resins, and (D) a solvent blend containing solvents selected from aliphatic alcohols of one to five carbon atoms, alkyl ketones of two to five carbon atoms, aromatic hydrocarbons of benzene, toluene and xylene, propylene carbonate, ethylene glycol ethers of three or four carbon atoms, alkyl acetates of two to four carbon atoms, and combinations of same, said solvent being volatile at ambient conditions; (2) discharging the ink composition as a stream of electrically deflectable droplets through a nozzle; (3) passing a substrate beneath the nozzle, (4) deflecting the droplets onto the substrate in response to pre-set electric signal to form the coded message, and (5) contemporaneously exposing the deflected ink composition to a source of the said radiation, whereby its photoinitiator releases sufficient amounts of the Lewis acid to effect rapid and substantial polymerization of the epoxy resin constituents.

Claim 54

A process according to claim 16, characterised in that the ink employed comprises 25 to 50% by weight of an epoxy resin blend comprising, by weight percent of said blend, 20 to 80% of a diglycidyl ether of bisphenol A, said resin being predominantly the monomer thereof and having a viscosity of between 5000 to 350O0 mPa.s at 25 0 C. and has an epoxy equivalent weight of between 170 and 230, 0 to 25% of a polyepoxidized phenol or cresol novolacs having a viscosity of between 1,400 to 70,000 mPa.s at 52°C, and an epoxy equivalent weight of between 170 to 235, and 20 to 80% of a diepoxide ether or ester having two epoxy cycloalkyl groups.

Claim 55

A process according to claim 16 or claim 17, characterised in that the ink employed contains an onium salt photoinitiator selected from aromatic diazonium salts of complex halogen halides, diaryliodonium salts and aromatic onium salts of Group Va and VIa elements.

Claim 56

A process according to claim 18, characterised in that the photoinitiator is a bis-[4-(diphenylsulfio) phenyl] sulfide bis-M.X6 aromatic onium salt of a Group Va element, where M is selected from the group consisting of phosphorous, antimony and arsenic, and X is a halide, the photoinitiator being solvated in a 33% solution by Weight of propylene carbonate.

Claim 57

A process according to claim 16, 17 or 18, characterised in that the ink employed has a colorant selected from Spirit Soluble Fast Violet RR and Orasol Black RL dyes.

Claim 58

A process according to any of claims 16 to 20, characterised in that the ink is discharged continuously from a supply reservoir and through the nozzle at ambient conditions, ink not deflected onto the substrate being captured for reuse.