Lawrence Wild, of Edlon Machinery, looks at EB curing of flexo inks, solventless adhesives and overprint varnishes
Smaller, lower cost, energy efficient, low voltage, electron beam (EZCure 2) EB equipment from Energy Sciences, of Boston, Massachusetts, has been developed to meet the broader needs of packaging film converters.
The cost effective and environmentally friendly EB process could be the future curing/drying method of choice given certain restrictions and problems which face the converter today, particularly in the field of solventless laminating adhesives and solvent based adhesives and lacquers. The application of the technology to date has been, for example, in the folding carton and liquid packaging markets, to cure high gloss abrasion resistant lacquers, over conventional printing inks.
Electron beam chemistry is 100 per cent solids, not unlike UV, but does not require the photo-initiator catalyst of UV whose presence has restricted its growth in food packaging because of regulatory concerns and odour. EB cures at ambient temperatures.
However, EB processing still remained as a niche application and was restricted to a few, very large converters. The introduction of the low voltage EZCure 1 EB units, opened up doors to converters who wanted the benefits of EB processing, but could not use them because of size and cost limitations of machines.
To penetrate this market further, giving converters the opportunity to use the EB equipment to cure high gloss type coatings andor laminating adhesives combining thin gauge films at reasonable speeds, it was necessary to develop a smaller and less expensive derivative of the EZCure 1 system.
One of the key restrictions was size, specifically the in-line space required at the end of a printing line or on the top of a solventless laminator. A 50 per cent reduction in the in-line space requirement of the EZCure 2 makes it more adaptable. In addition it requires almost 40 per cent less power to operate, thus reducing costs. The EB unit is slaved to the press or laminator speed automatically, so saleable product is made during acceleration and deceleration of the host machine. The development addresses the capital cost issue as well. For a typical 1,350mm wide EB unit, a price reduction of about 15 per cent is observed.
The major potential market is flexible packaging, with EB coatings replacing laminations or other coatings, EB curable laminating adhesives replacing con-ventional laminating adhesives and with work underway for the curing of wet-on-wet flexo inks on CI presses.
One example in the food packaging market is the typical reverse printed PP adhesive laminated to another PP film, possibly metallized. Coldseal is then pattern coated to the back of the laminate.
Move to mono-web
Both material and process cost savings have allowed a move towards a mono-web, thicker gauge OPP film which is then surface printed with an EB overprint varnish applied on top of the inks. A coldseal adhesive is then applied on the back. The EB coating is designed to provide scratch and scuff resistance. In addition it provides very high gloss and low COF.
The maximum coat weight of the EB coating is around 5g/m2. If the maximum speed requirement is about 260mmin and dose to cure is less than 3 Mrads then the choice of the EB unit should be EZCure 2. If 300+mmin is required the choice should be EZCure 1.
Conventional time cured isocyanate based systems (water based emulsions, solvent or solventless) are used for packaging laminations. Instantaneous cured EB laminating adhesives have a distinct advantage over these time cured systems allowing in line processing and slitting, as well as less labour and warehousing
Pioneered by Sun Chemical, the revolutionary process of EB curable flexo inks permits wet-on-wet printing of flexo printing inks, without intercolour dryers, curing after the CI group by a single electron beam unit such as EZCure 1.
It is possible to laminate using EB adhesives following printing with EB flexo inks, then adding the top film, nipping and then EB curing in line (see picture).
Only a few years ago EB use was just a dream due to the oversize and prohibitive cost of the traditional EB equipment. Today many major ink, lacquer and adhesive formulators are working on future generation EB products.
| Edlon Machinery
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