Method for printing a substrate with radiation curable ink, and an ink suitable for application in the said method

Abstract

A method for printing a substrate with radiation curable ink supported on a substrate which includes the steps of providing an inkjet print head at an operating temperature, jetting droplets of the curable ink from the inkjet print head onto the substrate, controlling the interaction between the ink and the substrate, and then curing the ink received on the substrate by directing radiation toward the substrate, wherein the controlling of the interaction is provided for by applying an ink comprising a carrier composition and an agent that is able to reversibly gel the carrier composition, which agent is soluble in the carrier composition at the operating temperature of the inkjet print head and gels the ink when it is received on the substrate. Also provided is an ink for enabling the use of the method and a printer adapted for applying the method.

Description

[0001] This application claims priority benefit of European Patent Application No. 05107997.8 filed Sep. 1, 2005, which is hereby incorporated by reference. BACKGROUND OF THE INVENTION [0002] The present invention pertains to a method for printing a substrate with radiation curable ink which comprises providing the substrate on a support, providing an inkjet print head at an operating temperature, jetting droplets of the curable ink from the inkjet print head onto the substrate, controlling the interaction between the ink and the substrate, and then curing the ink received on the substrate by directing radiation toward the substrate. The present invention also pertains to an ink suitable for application in the present method and a printer for applying the method. [0003] Such a method is known from European patent EP 1 349 733, issued Nov. 10, 2004 as well as from U.S. Pat. No. 6,145,979 issued Nov. 14, 2000. Radiation curable inks have become widely considered in recent years as the...

AI Technical Summary

Benefits of technology

[0014] In still a further embodiment, the ink received on the substrate is subjected to a physical treatment before it is cured. In this embodiment the ink is physically treated between the moment of impact on the substrate and curing by the influence of radiation. This provides for an opportunity to fine tune the spread of the ink before it is actually cured. Different levels of spread are, for example, needed depending on the use of the printed image. This embodiment enables the influence of the dot gain without the need of changing the amount or type of gelling agent in the ink. Preferably, the physical treatment comprises the transfer of heat and/or the application of pressure. It appears that the use of heat, or pressure or both (for example by using a fuser roller well known in the art of printing) adequately enables the fine-tuning of the dot gain.

[0015] In yet a further embodiment, the print head is scanned over the substrate on a scanning carriage, and the ink of a predetermined area of the substrate is not cured until the scanning of the said area of the substrate is completed. The use of a gelling agent enables the complete printing of an area of the substrate with the ink, without the need of intermediate curing. This has a very important advantage. In the prior art namely, intermediate curing between different print stages is often applied to avoid that the ink spreads too much over and in the substrate. This means, however, that some ink droplets are jetted on already cured ink droplets, whereas others are jetted on not yet cured ink droplets. This gives rise to local differences in the appearance of the printed image, i.e., caused by different degrees of coalescence of the droplets, which is very disturbing when high quality images are desired. In the present embodiment, the interaction between printed (but not yet cured) ink droplets is consistent over the whole substrate since newly jetted ink droplets are always neighbored by the same type of gelled but uncured ink droplets. This greatly improves the print quality that can be achieved by jetting radiation curable inks. In a preferred embodiment the radiation is sent from a source that is mounted separately from the print head. This avoids the need of scanning the radiation source together with the print head.

[0016] The present invention also pertains to a radiation curable ink comprising a carrier composition and an agent that is able to thermally reversible gel the carrier composition, which agent is soluble in the carrier composition at first temperature and gels the carrier composition when it is cooled to a second temperature below the first temperature. Typical gelling agents are high-molecular elongated molecules which form an elastic network in a carrier composition, the interstices of the network being filled with the carrier composition which can be in a liquid or a solid state. If the carrier composition in the interstices is in a liquid state, a gel arises which has some fluid-like properties, such as the property that molecules can diffuse relatively easily into the continuous liquid matrix and some solid-like properties such as the property that the gel can withstand a certain shear stress without deformation occurring, before the gel starts to flow like a liquid. When the liquid in the interstices of the network solidifies or cures, the gel passes over to the solid state.

[0017] In an embodimen

Problems solved by technology

In general, if the gelling agent forms a second phase in the ink at the operating temperature, this gives rise to unstable and unpredictable processes when printing the ink from an inkjet print head, which typically has multiple miniaturized ink chambers for jetting the ink droplets.

In particular, if the gelling agent consists of insoluble particles, there is a tendency of these particles

Images