Printing Ink

Abstract

This invention relates to a radiation-curable ink-jet ink having a viscosity of 30 mPas or less at 25° C., the ink comprising: at least two monofunctional (meth)acrylate monomers which comprise a cyclic monofunctional (meth)acrylate monomer and 2-(2-ethoxyethoxy)ethyl acrylate; a monofunctional monomer selected from an N-vinyl amide, and N-acryloyl amine or a mixture thereof; a multifunctional (meth)acrylate monomer; a polymerisable (meth)acrylate oligomer; a radical photoinitiator; and a colouring agent. The ink is preferably used in reel-to-reel printing and in printing where the substrates are stacked.

Description

FIELD OF INVENTION[0001]This invention relates to a printing ink and in particular to inks for use in applications where blocking is an issue, such as reel-to-reel ink-jet printing.BACKGROUND OF THE INVENTION[0002]In ink-jet printing, minute droplets of black, white or coloured ink are ejected in a controlled manner from one or more reservoirs or printing heads through narrow nozzles on to a substrate which is moving relative to the reservoirs. The ejected ink forms an image on the substrate. For high-speed printing, the inks must flow rapidly from the printing heads and, to ensure that this happens, they must have in use a low viscosity, typically no more than 100 mPas (cP) at 25° C. although in most applications the viscosity should be no more than 50 mPas, and often no more than 30 mPas. Typically, when ejected through the nozzles, the ink has a viscosity of less than 25 mPas, preferably 10-12 mPas and ideally 10.5 mPas at the jetting temperature which is often elevated to about ...

AI Technical Summary

Benefits of technology

The invention provides a special ink that can be used in ink-jet printing. This ink has many components that work together to make it suitable for printing. These components include certain chemicals that are mixed together to create the ink, which has a specific viscosity. The invention allows for the careful selection of these components to create a high-quality ink that can produce clear and accurate prints.

Problems solved by technology

In those systems, great effort must be made to ensure the inks do not dry in the head due to water evaporation.

Unfortunately, ink-jet inks that include a large proportion of water or solvent cannot be handled after printing until the inks have dried, either by evaporation of the solvent or its absorption into the substrate.

This drying process is often slow and in many cases (for example, when printing on to a heat-sensitive substrate such as paper) cannot be accelerated.

In addition, low-power pinning lamps are used between each printhead colour application (inter-colour pinning) since low power is needed to achieve dot gain requirements.

This places further demands on the nature of the radiation-curable components as high pigment loading and high film weights both work against absorption of the radiation by the components of the ink.

The accumulation of layer upon layer of printed substrate causes significant temperatures and pressures to develop in the receiving reel and, as a result, the ink has a tendency to cause blocking, i.e. the ink has a tendency to cling to the unprinted side of the substrate 2 as the receiving reel 12 is unwound.

It has also been found that the same problem occurs in automated and semi-automated printing processes using a flat-bed ink-jet printer where the substrate is loaded into the printer and the printer then prints and stacks the printed substrates upon one another.

With automated processes, a significant pressure may build up under the weight of the printed substrates.

Typical substrates are polyolefins, such as polypropylene and polyethylene, both with and without a topcoat which represent a further challenge for the ink formulator.

Against this background, the ink-jet ink must also satisfy the requirement of low viscosity which, as described above, is a general requirement for ink-jet inks Achieving a low viscosity can be a particular challenge at high pigment loadings.

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