Most wide web flexographic printers in North America predominantly use solvent-based inks for printing on flexible packaging materials. Why? Primarily because solvent-based inks dry fast, allowing for faster press speeds than their water-based and UV energy-curable ink counterparts. Additionally, solvent-based inks have typically been able to provide higher bond strengths with adhesive lamination components.
Although these factors are still true, water-based and UV energy-curable inks have come a long way in narrowing the gap. There used to be other factors where solvent-based inks had certain advantages over water and UV inks, such as adhesion, wetting and durability; however, most of these advantages have now been overcome with advancements in ink, plate, anilox roller and press equipment technologies.
Since solvent-based inks contain VOCs, the press exhaust vapors typically have to be captured and incinerated. Solvents are needed for press maintenance and for cleaning up on press. Solvent-based inks are flammable, so they require special handling, storage and disposal.
Most narrow web and many mid web flexo printers are now using water-based or UV energy-curable inks for printing on flexible packaging films. Why? For one, many of the pressruns are shorter, so excessive speeds are not a factor. Fast cleanup and ease of use are also benefits that water- and UV-based inks can make job changeovers quick and easy. Due to technological advancements, press speeds have also dramatically increased. Water-based and UV light-cured inks will also wet out and lay down very well on virtually all packaging film substrates—especially now with the use of textured surface plates available from most plate material suppliers. Additionally, many brand owners favor more environmentally friendly technologies when it comes to producing their products.
Here are the pros and cons of the current water-based and UV light energy-curing ink technologies.
Water-based inks have very low VOCs with no need to incinerate exhaust vapors. They are non-flammable, with no special handling or storage requirements. Water-based inks are more stable on press than solvent-based inks. The volatile components evaporate slower, so water-based inks require less maintenance when running. Cleanup is easy with soap and water. Press waste is non-hazardous.
New hybrid water-based ink formulations are allowing higher than ever adhesive bond strengths with current lamination technologies. Water-based inks will run on most flexo presses currently running solvent-based inks with few or no modifications. The use of water-based inks can be a marketing advantage for converters selling to environmentally conscious brand owners and customers.
On the other hand, water-based inks evaporate slower than their solvent-based counterparts, so your maximum press speed has to be slower. Water-based inks are not as durable as solvent-based or UV light energy-curable varieties. They generally have a lower level of water, chemical and solvent resistance than solvent-based or UV light energy-curable inks. However, water-based inks can be catalyzed when running to provide a high level of product resistance.
Also, water-based inks have a higher surface tension than solvent-based, so wetting and adhesion on some substrates can be challenging. In adhesive lamination applications, achievable bond strength with water-based inks is typically lower than with solvent-based, so testing and qualifying is needed to determine feasibility.
Typical products printed with water-based inks include:
- Most surface and reverse printed flexible packaging materials
- Pressure-sensitive (PS) labels
- Food and snack bags, wrappers and pouches
- Foil and film lidding materials
- In-mold labels
- Folding cartons
- Corrugated containers
- Envelopes, tags and forms
- Most paper and paperboard substrates
There are a few other considerations when it comes to water-based inks:
- High-strength, water-based inks running spot colors on 2.5 bcm anilox rollers and process colors on 1.2 bcm anilox rollers allow for much faster press speeds and a smoother ink laydown
- Enhanced ink drying systems that utilize high-velocity impinged air will maximize water-based ink drying
- Textured surface plates provide ink wetting and laydown similar to solvent-based inks
- Soap and water is used for cleaning up water-based inks
- Water-based inks typically need 24 hours to cure for full adhesion and for full durability properties to develop
- Ink cure can be accelerated on press by applying heat or by placing prints in an oven