Liquid Photopolymer Enables Fast Turnarounds Customers Seek

Ask any box printer what they want and you quickly find that shorter turnaround times and reliable ink transfer often rise to the top of their wish lists. Other top “wants” include lower material costs, faster print speed, and improved press maintenance.

Turnaround and ink transfer are two elements that come with almost every job. Fortunately, there are ways of taking charge of these concerns.

Wanted When?

Not long ago, a turnaround time of three to five days was perfectly acceptable. Nowadays, turnaround times of just one or two days have become the norm. Blame it on the internet. This is part of a shift in expectations that spans social and business interactions alike: Immediate—if not instant—gratification has become the norm and all types of businesses face the same challenge. Box printing is no different.

One way many box printers and trade shops can address this is with liquid photopolymer printing plates (LP). Although not the best match for every application, liquid plates can be produced in about one-third of the time required for sheet plates, helping trade shops deliver plates faster and box makers get jobs on press sooner. With the advent of the liquid island plate, the overall weight is lower too, helping reduce shipping costs and making plates easier for press operators to handle.

These factors combine to make LP a more practical, efficient, and economical choice for plates intended for putting copy and images on corrugated containers. LP allows more plates to be produced faster, making it a compelling alternative to sheet plates.

Knowing the details of a given job (including the press it will be run on) is critical. As I’ll get to in a moment, with the advanced technology of some new high-speed box-making presses, and where digitized graphics are demanded, thinner LP plates are less appealing. Be sure to learn all the details of a job before choosing the type of plate being utilized.


Cardboard’s Changed

Back in the day—15 or so years ago—corrugated top sheets offered up a consistent surface that made printing easy. Today, not so much, and there are ink transfer problems to prove it. Blame it on all the “post-consumer waste” that’s recycled into just about every paper product imaginable.

Running corrugated board, or top sheet, through a flexo press is likely to highlight ink transfer problems—notably text and graphics not being laid down evenly. No, it’s not necessarily your anilox rolls or impression cylinders—it’s the irregular surface of the recycled substrates you are more or less mandated to buy because it’s so much less expensive than nice, new, fluted stock.

Moreover, the options can be limited because the recycled stock is what your customer specified. She/he probably doesn’t know or have the time to consider that ink transfer is challenging for you and your pressman and takes more effort to use. The customer wants printed boxes shipped tomorrow! No problem, right?

Well, maybe not, if you’re using LP plates. LP plates can provide a lower durometer, which lets them be more tolerant of the surface irregularities typical in recycled board. This lower durometer allows the ink to better penetrate the variable surfaces of recycled stocks more effectively—which means more productivity and the ability to meet or beat deadlines with less stress and frustration.

“Although not the best match for every application, liquid plates can be produced in about one-third of the time required for sheet plates, helping trade shops deliver plates faster and box makers get jobs on press sooner.”

Care & Handling

One of the big advantages of LP is that it is a relatively environmentally conscious technology. LP plates are produced with water-based chemistry and cleaned up with soap and water. One added benefit is that the waste byproducts are compatible with most municipal sewage services. The environmentally conscious effluent can provide a big bonus in cities and towns that have restrictions on the disposal of chemicals or solvents associated with printing, such as those used in imaging sheet plates.

Adding LP to your repertoire brings more capabilities to your shop and enables some of the faster turnarounds customers are seeking. The equipment used is quite robust. Once mastered, it typically delivers predictable quality plates for many years.

Two limitations with LP, at least for some applications, are linescreen and plate thickness. Linescreens of up to 100 LPI are possible, but many shops consider 85 LPI as the practical limit for most applications. This is perfectly acceptable for many box-printing applications, as is the plate thickness of 0.125-in. to 0.250-in. However, when higher linescreens are required, a process called “capping” can be implemented, which allows a thin layer of exposed polymer with a harder durometer to be incorporated during the plate making process. This cannot be done with sheet plates.

Another challenge for LP plates is light and storage. Because the plates are “set” using UV light, additional exposure to UV light is not a good thing. This means sunlight and even overhead lights in your warehouse can put out too much UV light. Excess UV exposure can induce brittleness in the photopolymer and make the plate less effective or even unusable.

Be sure to protect LP plates from UV light sources, even in storage, to help ensure they will be ready for the next run of boxes. To work with confidence, check the amount of UV light your incandescent and fluorescent bulbs emit. Incandescent bulbs are usually not an issue, but fluorescent tubes can be, so ask your LP material provider about your plate materials’ tolerance for additional UV exposure and obtain different fluorescent bulbs if necessary.

Press Maintenance

Finally, another concern box makers mention is the increased need for press maintenance. If the bulk of your box production is light brown containers with a bar code and the words “This End Up,” then having clean anilox rolls is maybe not a top item on your to-do list. But, if your production makes up some of the growing number of cardboard boxes with a white or light-colored top sheet and 4-, 5- or 6-color graphics, then press and anilox roll cleanliness is a little more critical.

An increasing number of box printers are paying closer attention to roll condition and overall press cleanliness than they once did. Why? So they can deliver the print quality customers require. Roll condition and press cleanliness mean regular cleaning of anilox rolls, replacing doctor blades and end seals, and always using the best plates for the job—which may be LP.

Integrating such best practices is new territory for some trade shops and box printers. Today it’s part and parcel of an evolving print production environment, particularly in plants that are expanding from basic blow-and-go printing to containers that become part of point-of-purchase displays on retail floors.

LP is more than an alternative to sheet plates. It is a way to increase the performance of your operation and add value to your offerings. Forward-looking trade shops and box printers are adopting LP plates as valuable tools that help them make their business smarter, more proactive, and more competitive.

This article was originally published in the October 2019 issue of FLEXO Magazine.