With soft fading vignettes staying on top of flexo print quality Asahi Photoproducts,
Successful with higher quality development in the prepress segment during the past five years has mostly concentrated on screening techniques or advantageous cell
structures in the solid areas of the image carrier. Several techniques are making use of the photopolymer oxygen inhibition effect, which speeds up the free-radical crosslinking process of a photopolymer plate by use of high UV-A energy density. This ensures that the crosslinking of the photopolymer is finished before the oxygen molecules inhibit the curing process. Another technique is the reduction of oxygen before the cross linking process which is initiated by UV-A light such as with a gas or physical oxygen barrier (film layer). Both techniques use the same principle.
The trend to improve quality in various areas has taken place both up and down stream from the image carrier inside the flexographic printing segment. Some of the significant developments are new ink formulations which are leading to improved drying, better ink lay down, and higher ink densities.
Predominantly due to a wide color space with vibrant color reproduction and soft tonal shades fading out to zero, the gravure printing process, so far, has been the printing technology of choice for brands and retailers, to ensure a high level of brand recognition. It is vital to use a process with constant repeatability of printing quality during the
A massive effort, during the last couple of years, from prepress suppliers to the flexographic industry has lifted quality in flexographic printing to draw level with gravure. Particularly the areas with smooth vignettes running out without any hard printing edge.
Anilox manufacturers have introduced highend anilox rolls with new cell structures, high
screen rulings and low cell volumes. This has led to the printing of lower ink film thicknesses giving more contrast and better definition of the printed character on the substrate.
The flexographic industry has benefited from these new developments carried out by industry pioneers. Brand owners and retailers have started to recognize the improving capability of the flexographic printing process and have started to shift printing jobs to
flexo, which have previously been produced using another printing technology.
Most of the developments in prepress have been related to technique and system solutions and it has been found that there is still some room for development of materials
giving a product solution rather than a system solution. In this way the industry can gain the most, as product solutions can generally be integrated into existing processes
without the need for additional investment for the repro-house or printer.
Over the years Asahi Photoproducts has looked for constant improvement with photopolymer plates and equipment. The recently launched TOP flexo plate is the result of a newly engineered photopolymer plate chemistry, which is dedicated to support the premium flexographic segment by enabling the transfer of jobs from other printing technologies to flexography.
The market demand by brand owners and retailers for a constant print quality over the production run with fine smooth tonal gradation fading to zero has been of particular focus as has the enlargement of the color gamut.
In recent years, the introduction of HD television technology has stimulated consumer awareness so that they demand more brilliant and vivid colors on packaging. Consumer behavior has influenced the expectation of the color gamut extension in the packaging industry. But how can the gamut expand and what are the tools for color gamut extension?
There is a myth in our industry that higher print density means a wider color gamut. Several technical articles have been published to illustrate that there is an optimum
density a printer should use for achieving a wide color gamut.
Normally the optimum density point is reached when the plotted L*a*b values versus the plotted density values are reading the backwards trend. This optimum density point is often lower than the density, which can be reached with several of the today’s available
“density boosting” technologies. Too high optical density will lead to a reduction in color space and a reduction in printed contrast. It is the homogeneous laydown of the ink film, which is more important than the density. Several screening sets are available from industry vendors, which means that the customer today has a choice and can actually use a set, which gives the optimum homogeneous ink distribution. However, by looking at the opposite end of the density scale +L*, at the very low density highlight dots, it can be seen that there is more room for an increase of the total color gamut. Highlight dot reduction gives the flexographic printing process a more significant gamut enlargement. Hence, a total color gamut enhancement is created by means of color combinations of
dots rather than a global density boost. This increase of the color space by using the new TOP plate is made possible because of the newly engineered Asahi polymer chemistry, which is based on its “pinning technology”.
The pinning technology makes use of the plate surface tension. This is described as the internal pressure that restrains a liquid from flowing. Polar liquids such as water have a
high surface tension, non-polar liquids for example litho printing ink, have a low surface tension. When a drop of liquid is placed on a solid plate surface, the relationship between the surface energy and the surface tension of the liquid determines whether the droplet will spread across the surface or form globules. If the liquid is placed on a surface of lower surface energy than itself, it will form into globules and fail to wet the surface. Conversely, if the liquid has a lower surface energy than the solid surface, the liquid will spread across and wet the surface. If a liquid wets a surface, it is said to have a low contact angle; if it forms globules, it is said to have a high contact angle. The contact line where the liquid surface meets the solid surface is called the pinning point. The higher
the position of the pinning point on a flexographic relief printing plate, the lower the plate wettability, but the higher the wettability of the printed substrate, hence an improved ink transfer from plate to print.
Plates with a high point of ink pinning show a good transfer of ink to the subsequent substrate. It is inevitable, that the surface energy through the process from anilox to
substrate must increase in sequence. Whereas there are differences between the plate pinning point from ink system to ink system, the general higher pinning point facilitates the reduction of printing pressure during the production run for all ink systems used. Hence a longer plate life time can be achieved.
Customer production print runs with TOP have also shown that the pinning technology can reduce the ink filling-in in the midtone area over the printing run leading to
fewer cleaning intervals of TOP and press stop downtimes for the printer. This feature is in concert with the demand from brands and retailers to achieve a production run without
a loss in quality from start to finish.
In summary, The quality increase within the flexographic industry as a whole has enabled brands and retailers to move gravure jobs to flexo. Further material developments such as Asahi Photoproducts’ pinning technology set out to push back
print quality boundaries. Developments by the product rather than the system support a fast integration into existing production lines without the need of additional customer investments. The TOP plate is compatible with a variety of new technologies from other vendors which can be utilized, such as the high definition microcell screening solutions to improve ink homogeneity. System compatibility rather than system solutions is of importance for easy customer implementation. At the same time TOP reduces the highlight dot gain due to its pinning technology leading to smooth and soft vignettes fading out to zero with a wider total color gamut. Print production with low pressure set-up is ensuring a constant quality level from start to finish.
TOP is Asahi Photoproducts’ new solvent washable plate development for the flexible packaging segment with solvent- and waterbased inks on filmic substrates to
facilitate premium quality in flexographic printing.