WO2003011990A2 - Liquid pigment ink with stable viscosity for ink-jet printing - Google Patents

Abstract

The invention concerns a liquid pigment ink for ink-jet printing having a time-stable viscosity not higher than about 20 mPa's at 25 °C, consisting of a pigment suspended in a vehicle UV-curable in the presence of a photoinitiator, said vehicle comprising at least a glycidylether and/or a diglycidylether and at least two different (meth)acrylates, and optionally a vinyl ether and/or a divinyl ether. Preferably, it does not contain either volatile solvent or water.

Description

 Liquid pigment ink with stable viscosity for inkjet printing

The present invention relates to the field of liquid pigment inks, in particular those intended for ink jet printing.

Such inks are made up of a pigment, black or colored, which is suspended in a vehicle (or binder). This vehicle generally comprises at least one oxidizable or crosslinkable compound, that is to say capable of polymerizing by solidifying, by exposure to air or to ultraviolet radiation, and a volatile, organic or aqueous solvent. The role of the solvent is to give the ink composition the fluidity or viscosity necessary to be easily "ejected" from the nozzle of the print head, and also to prevent, during stops, that the ink does not take up en masse by clogging the channels of the nozzle.

After printing, that is to say the deposition of the ink on the surface of a support, the solvent must be removed by evaporation and / or penetration into said support if the latter is more or less porous. This drying must be rapid, which implies either the presence of a small amount of solvent in the ink composition, or a high volatility of the latter.

However, the presence of volatile organic solvents poses problems of environmental pollution and toxicity.

This is why ink compositions for inkjet printing in which the volatile solvent has been partly replaced by water have been recently developed. Japanese patent JP07041712 describes an ink preparation of this type, prepared by dispersion in water of a UV crosslinkable compound, such as a (meth) acrylic monomer.

However, such inks have the disadvantage of containing a large amount of water which must then also be evaporated, which poses significant difficulties, because of the latent heat of high vaporization of the water. All the difficulties mentioned above are further accentuated in cases where the printing surface is large (for example if the surface reaches several square meters).

The object of the present invention is therefore to overcome all of these drawbacks by proposing an ink having the necessary fluidity at the time of ejection of the print head and not likely to clog the channels of the ejection nozzle during interruptions or prolonged stops. The composition of this ink must contain the smallest possible amount (less than about 5%), of solvent to be evaporated (neither volatile organic, nor aqueous) or even none, and be compatible with current technologies of jet printing. ink, for operation at room temperature, in particular in cases where it is not planned, nor possible, to heat the print head itself.

After manufacturing, the ink is often stored for several weeks or even months before use. It is therefore common to note a considerable increase in the viscosity of the ink which can be multiplied by 3, 4 or 10 and even go as far as solidification of the ink, which is then unusable.

Another object of the present invention is to provide an ink stable over time, mainly during storage, the dispersion remaining perfectly homogeneous, without any sedimentation of the pigment particles, or polymerization, that is to say without significant increase in viscosity (i.e. an increase in the order of

10-15% maximum over a temperature range from 5 to 45 ° C approximately).

These objects are achieved by the liquid pigment ink, preferably without volatile organic solvent or water, according to the present invention having a viscosity less than or equal to about 20 mPa.s at 25 ° C stable over time, consisting of a pigment suspended in a vehicle crosslinkable by ultraviolet light in the presence of a photoinitiator, said vehicle comprising at least one glycidylether and / or diglycidylether and at least two different (meth) acrylates.

Thus, thanks to the composition of liquid pigment ink according to the present invention, the polymerization of the monomers or oligomers constituting the vehicle does not take place in the narrow channels of the ink ejection nozzle, crosslinking does not occur. only after printing, when they are actually exposed to ultraviolet radiation.

If no solvent is present, there is no drying step, nor environmental problems. Here the (di) glycidyl ether acts as a reactive diluent, that is to say that it participates in the polymerization reaction of said ink vehicle. Low viscosity, it lowers the general viscosity of the ink. In addition, (di) glycidyl ethers have a good solvent power for the resin (generally vinyl) coating the pigment.

The possible presence of a (di) vinyl ether in the composition according to the invention also makes it possible to lower the viscosity of the ink. Like (di) glycidyl ether, (di) vinyl ether has good diluting power, as well as good reactivity during polymerization, which must be almost instantaneous at the outlet of the ejection nozzle.

(Meth) acrylates, and in particular Poligomer acrylate are very reactive resins.

The mixture of these three (or four) constituents makes it possible to reconcile a low viscosity of the ink with the need for high reactivity, this last criterion being notably characterized by a very short "drying" (or rather polymerization) time.

In addition, such inks have a high resistance to friction, that is to say that they resist the passage for example of a finger or a nail on their surface. Advantageously, the ink contains from 2 to 42% by weight of

(di) glycidylether (preferably from 2 to 25%), and possibly up to approximately 29% by weight of (di) vinyl ether.

The (di) glycidyl ether is advantageously chosen from a C ₁₅ to C ₁₅ aliphatic or aromatic monofunctional glycidyl ether, a C ₄ to C ₁₅ aliphatic or cycloahphatic (di) glycidyl ether, the preferred (di) glycidyl ethers being chosen from phenyl glycidylether, o-cresyl glycidylether, ethylene glycol diglycidylether, 1,4-butane diglycidylether, 1,6-hexane diglycidylether, neopentylglycol diglycidylether, polypropylene glycol diglycidylether, polytetrahydrofuran diglycidylether, cyclohexane dimethanol diglycidyl diglycidylether 2-ethylhexyl glycidylether, a C _12-15 alkyl glycidylether, or a mixture thereof.

The (di) vinyl ether can be chosen from diethylene glycol divinyl ether, triethylene glycol divinyl ether, dodecyl vinyl ether, 1,4-cyclohexane dimethanol divinyl ether, hydroxy butyl vinyl ether, or a mixture of these. One of the (meth) acrylates can advantageously be a difunctional di (meth) acrylate monomer, in a proportion of approximately 10 to 50% by weight of the ink.

The di (meth) acrylate is advantageously chosen from dipropylene glycol diacrylate, hexanediol diacrylate, Phexanediol dimethacrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, butanediol diacrylate, polyethylene glycol diacrylene diethylacrylate diacrylate of these.

The second (meth) acrylate is for example a polyfunctional acrylate oligomer in a proportion of approximately 5 to 25% by weight of the ink. Preferably, this acrylate oligomer is an oligomer of urethane (meth) acrylate, of amine-acrylate, of aliphatic acrylate, of epoxyacrylate, of a polyether acrylate, of a polyester acrylate, or of a mixture of these.

The pigment is generally present in the form of a pigment preparation, for example comprising a “covering” based on vinyl resin, and represents approximately from 2 to 10% by weight of the ink. To initiate the polymerization reaction of the constituents of the ink vehicle, the latter advantageously contains from 1 to 15% by weight approximately of photoinitiator, preferably from 4 to 10% by weight.

Preferably, the ink according to the invention contains a mixture of photoinitiators and photoactivators comprising derivatives of benzophenone, thioxanthone and / or amino-benzoic acid.

The thioxanthone derivative can for example be chosen from isopropylthioxanthone, 1-chloro-4-propoxythioxanthone, 2-chlorothioxanthone and 2,4-diethylthioxanthone, and the aminobenzoic acid derivative chosen from ethyl- 4 dimethylaminobenzoate, 2-butoxyethyl-4-dimethylaminobenzoate, 2-dimethylaminoethylbenzoate or 2-ethylhexyl-4-dimethylaminobenzoate.

In addition to the majority constituents of the vehicle or binder described above, the ink can also contain up to 5% of dispersing agent and / or synergistic agent and / or viscosity stabilizing agent.

The ink according to the invention can also contain up to 0.5% of surfactant, preferably up to 0.1% by weight. The liquid pigment ink according to the invention can be used for printing by ink jet, in particular by piezoelectric or thermal techniques.

EXAMPLES:

The inks tested are prepared according to a general procedure described below:

Firstly, the pigment preparation is dispersed in the acrylate oligomer and / or in one or more difunctional monomer (s), in the presence of any dispersing additives. This dispersion can take place in a grinder, in a reactor or a stirrer at a temperature below 70 ° C, for several hours, with stirring.

Then this mother ink is diluted successively with the other constituents, or after a premix of the latter.

Photoinitiators / photoactivators, and any other additives are added in the terminal phase. These inks are spread, with a thickness of a few μm, on a support placed on a moving carpet at a speed of 15 m / min. and pass through an oven where they polymerize, under the action of an ultraviolet lamp.

The tests carried out on the inks carried out relate to:

- viscosity, measured using a capillary viscometer; - reactivity, checked if the ink is dry after passing through the oven under ultraviolet rays;

- resistance to friction and scratching, tested by rubbing with a finger or a nail.

EXAMPLE 1: Addition of several types of acrylates.

Two pigment inks (a) and (b) containing the following constituents were prepared (% by weight): (a) (b) nbutylglycidylether 24.9 24.9

12 10 acrylate oligomer

Octyldecylacrylate 15.1 17.1

Trimethylol propane ethoxytriacrylate / 10

Dipropylene glycol diacrylate 35 25

Mixture of photoinitiators / photoactivators 9 9

Pigment preparation (Black) 4 4

TOTAL 100 100

Viscosity (mPa.s) 11.5 12 at 19.4 ° C at 20 ° C

These two inks, containing several acrylates of different types (including a triacrylate for ink b)) exhibit very good polymerization (reactivity of the constituents) since they are dry right out of the oven. They also have excellent resistance to friction.

EXAMPLE 2:

Different inks (c) to (f) having various proportions of majority constituents of the vehicle were prepared according to the general procedure indicated above. These inks have the following compositions (% by weight):

All these inks (c) to (j) have viscosities less than or equal to 20 mPa.s at 20 ° C, and show great reactivity (polymerization).

However the inks (d) and (e) indicate the upper limits respectively of the constituents glycidylether and divinylether. Indeed, the friction resistance of the ink (d) is poor, and the appearance of the ink (e) does not comply with the desired requirements, that is to say that the ink does not is not homogeneous when spread on a vinyl type support (plastic cards, posters ...).

In separate tests, it has also been found that for the constituent diacrylate, hexanedioldiacrylate and tripropylene glycoldiacrylate exhibit as good results as dipropylene glycol diacrylate. EXAMPLE 3:

According to the same procedure, the pigment ink (magenta in color) was prepared with the following constituents (% by weight): nubutylglycidylether 24.85

Amino acrylate oligomer 10

Octyldecylacrylate 15.1

Trimethylol propane ethoxy triacrylate 12

Dipropylene glycoldiacrylate 25

Mixture of photoinitiators / photoactivators 9

Surfactant 0.05

Pigment preparation (Magenta) 4

TOTAL 100

This ink has a viscosity of 11 mPa.s at 21.7 ° C.

EXAMPLE 4:

Inks of different colors:

Toutes les encres polymérisent très bien (sont sèches à la sortie du four). La présence de divinyléther dans l'encre (1), en remplacement de l' octyldécylacrylate (encre k), permet de renforcer la résistance au frottement après l'impression.

All inks polymerize very well (are dry when removed from the oven). The presence of divinyl ether in the ink (1), replacing the octyldecylacrylate (ink k), makes it possible to reinforce the resistance to friction after printing.

EXAMPLE 5:

Stability of the viscosity of the ink over time.

Two inks according to the invention, of different colors, of composition identical to that of the ink (1) of Example 4 were placed in opaque polyethylene bottles (in particular ultraviolet) and kept at a temperature of 45 ° C for several months. This is to "exaggerate" the storage conditions, which are generally recommended between 15 and 25 ° C. In fact, at a temperature above 20 or 25 ° C, the phenomena of solidification and polymerization induced by ultraviolet are accelerated.

The results of the viscosity measurements at 0, 1, 3 and 6 months are as follows:

Magenta ink Black ink at t ^≈ O 14.7 mPa.s at T = 25 ° C 15, l mPa.s at T = 25 ° C after 1 month at 45 ° C 15.6 15.4 after 3 months at 45 ° C 15.1 14.8 after 6 months at 45 ° C 15.1 14.1

No solidification or polymerization phenomenon was observed, the viscosity remained completely constant for 6 months.

Claims

1. Liquid pigment ink for inkjet printing having a viscosity less than or equal to about 20 mPa.s at 25 ° C stable over time, consisting of a pigment suspended in a vehicle crosslinkable by ultraviolet in the presence of a photoinitiator, said vehicle comprising at least one glycidylether and / or diglycidylether and at least two (meth) acrylates. 2. Ink according to claim 1, characterized in that it does not contain a volatile solvent, or water. 3. Ink according to one of claims 1 or 2, characterized in that the vehicle comprises a vinyl ether and / or a divinyl ether. 4. Ink according to one of claims 1 to 3, characterized in that it contains from 2 to 42% approximately by weight of (di) glycidylether. 5. Ink according to one of claims 3 or 4, characterized in that it contains up to approximately 29% by weight of (di) vinyl ether. 6. Ink according to one of claims 1 to 5, characterized in that it contains from 5 to 25% approximately by weight of a monofunctional acrylate oligomer and from 10 to 50% approximately by weight of a di (meth ) difunctional acrylate. 7. Ink according to any one of the preceding claims, characterized in that the pigment is present in the form of a pigment preparation, representing approximately from 2 to 10% by weight of the ink. 8. Ink according to claim 7, characterized in that the pigment preparation comprises a vinyl resin. 9. Ink according to any one of the preceding claims, characterized in that it contains from 1 to 15% by weight of photoinitiator, preferably from 4 to 10% by weight. 10. Ink according to claim 9, characterized in that it contains a mixture of photoimators and photoactivators comprising derivatives of benzophenone, thioxanthone and / or amino-benzoic acid. 11. Ink according to claim 10, characterized in that the thioxanthone derivative is chosen from isopropylthioxanthone, l-chloro-4-propoxythioxanthone, 2-chlorothioxanthone and 2,4-diethylthioxanthone, and the derivative of l amino-benzoic acid is chosen from 4-ethyl dimethylaminobenzoate, 2-butoxyethyl-4-dimethylaminobenzoate, 2-dimethylaminoethylbenzoate or 2-ethylhexyl-4-dimethylaminobenzoate. 12. Ink according to any one of the preceding claims, characterized in that the (di) glycidyl ether is selected from monofunctional aliphatic glycidyl ether, C ₄ -C ₁₅ aromatic or a (di) glycidyl ether difunctional aliphatic C to C ₁₅ or cycloahphatic, or a mixture thereof. 13. Ink according to any one of the preceding claims, characterized in that the glycidylether or diglycidylether are chosen from: phenyl glycidylether, o-cresyl glycidylether, ethylene glycol diglycidylether, 1,4-butane diglycidylether, 1,6-hexane diglycidylether, neopentylglycol diglycidylether, polypropylene glycol diglycidylether, polytetrahydrofuran diglycidylether, cyclohexane dimethanol diglycidylether, nbutyl glycidylether, 2-ethylhexyl glycidylether, a glycidylether of C _12-1 them. 14. Ink according to any one of claims 3 to 13, characterized in that the (di) vinyl ether is chosen from diethylene glycol divinyl ether, triethylene glycol divinyl ether, dodecyl vinyl ether, 1,4-cyclohexane dimethanol divinyl ether, l 'hydroxy butyl vinyl ether, or a mixture thereof. 15. Ink according to any one of the preceding claims, characterized in that the di (meth) acrylate is chosen from dipropylene glycol diacrylate, hexanediol diacrylate, hexanediol dimethacrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, butanediol diacrylate, polyethylene glycol diacrylate, triethylene glycol dimethacrylate, or a mixture thereof. 16. Ink according to one of claims 6 to 15, characterized in that the acrylate oligomer is an urethane (meth) acrylate, amine-acrylate, aliphatic acrylate, epoxyacrylate, polyether acrylate oligomer. , polyester acrylate, or a mixture thereof. 17. Ink according to any one of the preceding claims, characterized in that it contains up to 0.5% of surfactant, preferably up to 0.1% by weight. 18. Ink according to any one of the preceding claims, characterized in that it contains up to 5% of dispersing agent and / or synergistic agent and / or viscosity stabilizing agent.