Taking the test
- Improved printability with new Swedish research
Print quality is a key factor in producing competitive packaging. Good print quality not only makes the package more aesthetically pleasing, but it also contributes to the efficiency of the print process.
But how is it measured? Sofia Thorman, a PhD student from Vipp industrial graduate school at Karlstad University, has developed a new testing method that can be used to verify the print quality of board material.
Packaging is an important part of a product. It protects and preserves its contents, provides information and, ideally, invites potential buyers to make a purchase. If the board material offers satisfactory print quality, a greater proportion of the board that is manufactured and transported to printers will be used, thereby generating less waste.
Sofia Thorman recently completed her licentiate thesis from Vipp industrial graduate school at Karlstad University, marking the halfway point to her phd. She has done research at Innventia, a leading Stockholm-based research institute that works with innovations based on forest raw materials, to develop a new method for testing how evenly board absorbs liquid.
“We’ve believed for some time that the absorbency of the board affects its printability, but there’s never been a way of actually measuring it before,” she explains.
Innventia is a world-leading research institute that works with innovations based on forest raw materials. The majority of its operations are carried out in project form via research programmes involving multiple partners or in development projects with individual customer companies. Innventia also carries out a large number of direct commissions in the form of analyses, testing and demonstrations in its lab and pilots.
Thorman’s research studied coated board material used for high volume flexo printed packaging such as milk and juice cartons, and catering utensils. The results suggest that an uneven absorption of printing ink can lead to printed images and text looking mottled or uneven.
When board is produced, its properties are checked according to a variety of criteria. For example, surface smoothness is known to be a property that impacts printability, but even though an even surface generally supports better printing results, it is not unheard of for problems to arise even when the board is smooth. According to Thorman, quality control for printability would be more reliable if it also included a test to measure the ability of the board to absorb ink.
Thorman’s method involves spreading a thin layer of dyed liquid on a piece of board and allowing it to absorb for less than two-tenths of a second. The liquid is then removed, revealing a piece of board that has either been evenly stained or contains uneven spots of colour. If the dye is blotchy, it means the material does not absorb printing ink evenly.
“Carrying out this test on newly developed materials, or before a major print run, would allow the manufacturer to make improvements to the material before printing, thus eliminating the risk of the board being wasted due to a failed print run,” Thorman says. She believes this new method could lead to the development of better-quality board materials in the long run. “If you can measure a feature, you can also learn from it and use it to make improvements,” she says.
Read more: Flexography
“The method looks promising in the studies we’ve done so far,” Thorman says. “I look forward to carrying out trials on a larger scale, in order to confirm that the technique can provide valuable information for board manufacturers.”
So far, most of Thorman’s research has examined flexographic print quality for coated board material used for liquid packaging. While some absorption tests have been carried out on high-quality board types, such as folding box board and solid bleached board, which are usually printed in offset presses, it is not yet clear if similar test methods can be developed for board of this kind.
So how can manufacturers measure absorption? “Innventia can carry out absorption tests on behalf of board manufacturers,” Thorman says. “Alternatively, we can help manufacturers to set up the test in-house.”
- All paperboard from Iggesund is supplied with ink absorptio values. Measurements are carried out by applying ink to the print surface for two minutes, then measuring the brightness of the untreated paperboard and comparing it to the brightness of the ink setting on the paperboard being tested.
- One advantage of the method developed by Sofia Thorman is that it is closer to reality, as the short exposure time is more like real-life production conditions. However, this method does not really measure absorption, but rather the printed medium’s tendency to become mottled or uneven in the printing process – an area where there are no standardised measurement methods.
- Whether measuring mottling or ink absorption, these would be methods that manufacturers could use to assure and develop the level of quality, rather than something that individual printers or converters would need to use.
TEXT CARI SIMMONS PHOTO GUSTAV HUGOSSON