Incremental printing of symbolic information – Ink jet – Medium and processing means
Patent
1998-07-15
2000-11-14
Royer, William J.
Incremental printing of symbolic information
Ink jet
Medium and processing means
B41J 201
Patent
active
061459798
DESCRIPTION:
BRIEF SUMMARY
This invention is concerned with improvements in and relating to printing apparatus and processes, more especially ink jet printing processes and, particularly, such processes employing radiation-curable inks such as UV-curable inks.
Ink jet printing processes are well known and well established (see, for example "Output Hardcopy Devices", Durbeck R. C. and Sherr S., Eds Academic Press Inc., 1908, at pages 311-370). The rise of radiation-curable, especially V-curable, inks in such a process would appear highly desirable since, after appropriate curing, radiation curable inks afford a tough, durable image upon the substrate to which they are applied. This makes the process especially applicable to printing on plastics packaging where high durability is required. Therefore, it can be applied not only to conventional cellulosic substrates such as paper and board, but also to synthetic polymcric substrates.
We have found that problems can be encountered in printing a radiation-curable ink upon a substrate by an ink jet printing process and subsequently curing the substrate, bearing the uncured printed image, by exposing it to radiation in a conventional manner. Thus in accordance with usual procedures, substrates bearing uncured radiation-curable images are cured by passing them under one or more radiation sources (e.g. mercury vapour lamps in the case of UV-radiation) at a relatively high linear speed. Since ink jet printing is relatively slow, as compared with some other printing methods, the fist printed portion of a substrate may well bear an uncured image for a markedly longer period of time than the last printed portion of that substrate, before curing of the printed image. We have found that this can give rise to problems and undesirable results due, for example, to differential absorption of the ink into a porous substrate, such as a cellulosic web, or spreading or mixing of colours before curing.
In accordance with a first aspect of the present invention, there is provided a process for forming an image upon a moving substrate, the process comprising the steps of ink jet printing a radiation-curable ink onto the substrate with a print head and subsequently curing the printed image by exposure to appropriate radiation, in which the process time period between printing and curing is substantially the same for all portions of the substrate.
In accordance with a second aspect of the present invention, there is provided, an ink jet printing apparatus for printing onto a substrate with a radiation-curable ink, the apparatus comprising a print head for directing the ink onto the substrate and curing means for curing a printed image by exposure to appropriate radiation the curing means being adapted to cause the time period between printing and curing to be substantially the same for all portions of the substrate.
The process and apparatus of the present invention are particularly suitable for use in combination with a drop on demand process but, of course, may also be used in combination with other ink jet printing processes, either continuous or intermittent. In the following description, reference will be made only to UV-curable inks but it is to be understood that, where the context permits, reference to other forms of radiation-curable inks is intended.
In accordance with one particular embodiment of the invention, appropriate curing means is arranged in combination with the print head of the ink jet apparatus, travelling therewith so that images printed upon the surface of the substrate are exposed to curing radiation very shortly after having been printed upon the substrate. In such an arrangement it is very difficult with presently available UV sources, to provide a small enough radiation source connected to and travelling with the print head. In accordance with a particular embodiment of the present invention, a static fixed radiation source is employed and the curing UV radiation is supplied from that source to an irradiation head, of appropriate dimensions, connected with the radiation source by me
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International Search Report.
Caiger Nigel Antony
Cockett Michael Anthony
Coates Brothers PLC
Royer William J.
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