Thanks to their lightweight nature, folding cartons are witnessing an increased customer demand globally. This means quality assurance is not only important for the physical carton, but also for the final package print.
To address this growth and meet demand, printers are looking at multi-site printing operations. In such a multi-site operation, a critical challenge comes into play: print consistency.
Ready to set about tackling the issue and gaining control? Let’s examine the criteria to ensure a uniform print, as well as the variables in the print package allowing a printer to gain this consistency. Outlined here are key areas to watch for to ensure you are on the right track for folding cartons.
Design Considerations
Consistency is the key word here, meaning work closely with your designers and suppliers to develop good, repeatable artwork that can be printed to your specifications.
Some things to consider with artwork for folding cartons include:
- Keep ink coverage to a minimum to keep screens open and print clean
- Watch for moiré in screening more than CMYK. Some designs tend to have many colors that overlap screens and won’t be visible until print reproduction
- Review all components within the artwork to ensure they meet the specifications set by the printer (minimum dots, blends, images, text, bar codes, etc.)
- Combo plates (images with large solids with minimum dots all on same plate) can be difficult to reproduce and special screening may need to be applied to the flexo plate
- FTA’s Flexographic Image Reproduction Specifications & Tolerances (FIRST) 6.0 has a very comprehensive and detailed Design Guide you can download for free and use to follow for artwork elements
Screening
Screening of the plate image has drastically changed over the years and there are now many different options. Currently:
- The most widely used screening in folding carton is circular, in which the dots maintain a round/circular shape in the entire halftone
- Most folding carton printers are running between 120 lpi and 150 lpi for solid bleached sulfate (SBS) board
- Hybrid screening is also a common way to keep the highlight dots from having a harsh tone break when transitioning off to zero (white)
- In the last few years, companies have been testing and using flat top dot technology, along with screening modifications to the surface of the plate, to create improved surface ink transfer to the paper. This has been widely used in flexible packaging with film substrates, but not as widely used in printing on paper substrates
- Surface screening utilizes higher-resolution images (HD imaging at greater than 4,000 ppi) to create the patterns on the surface of the plate. You will need to test and validate surface modification techniques based on your anilox and ink system
“Measuring is key! Have a system in place to manage and monitor print density, dot gain, ink pH and ink viscosity.”
Plate Materials
Selecting the best possible plate for paper substrates is a never-ending discussion between printers. It’s important to understand that paper materials have a variety of ink absorption, coatings and textures. It is critical to monitor substrates throughout the pressrun. Pay close attention to the amount of ink carried to the plate and the amount of latitude you have when impressing the plate to the substrate.
For folding carton paper substrates:
- There is a decent amount of absorption needed for the paper stock to impress a good, solid image
- A medium durometer (58-65 Shore A) plate works very well
- Plate thickness will generally be determined by initial plate undercut of cylinder/sleeve. The most common plate thicknesses in the folding carton segment are between 0.045-in. and 0.067-in.
- Photopolymer plate relief specifications will vary based on substrate, plate thickness and type of material
- FIRST recommends a relief thickness between 0.018-in. and 0.022-in. for folding carton printing on SBS
- It is important to work closely with your plate manufacturers for the tolerances recommended and use what works best in your environment for the specific type of plate
- Newer plate materials with flat top dot technology are now in use to get a more even surface area, to increase ink density and to improve ink transfer. This is being driven primarily by increased press speeds and demand for higher linescreen graphics