Focus on flexo

10 August 2015



Focus on flexo


Focus on flexo

Focused mainly on package and label printing segments, flexo has been the least affected of all traditional printing processes by the rise of digital and by the downturn in graphic printing markets in the west, as well as some transitional and even emerging economies in some instances. With corrugated packaging generally growing in line with the global economy, and flexible packaging taking share from other pack types, flexo has performed creditably and there are growth opportunities on offer around the world going forward. Only in labels is digital beginning to make real inroads into flexo, although in the longer term the trend towards shorter run lengths could have an impact in areas such as cartons and flexibles, albeit mainly in niche fields at the margins.

Flexographic printing is continuing to improve as a result of various developments; these include advancements in plate technology and exposure methods, improved methods for mounting plates, print unit and press design, anilox rollers, inks and curing/drying systems. Up to 2019, there will be continuing improvements in the process as suppliers continue to innovate to win a greater share of a market that has growth prospects. Whether an individual flexographic printing concern will flourish or not in the new environment will depend to a large extent on its technological investment decisions and how it adapts to changes in technology. With this in mind, Smithers Pira has identified a number of practices that are designed to take advantage of these changes in the future.

Optimise prepress workflow to boost quality and turnaround
The greatest changes in flexo printing have been in prepress, where plate technology has developed with enhanced imaging as flexo computer to plate (CtP) exposure has improved the reproduction quality with a greater dynamic range and more detail, particularly in highlights. Another change is that an increased number of converters and printers are taking CtP in-house to offer improved service to customers. There are also improvements in ink: in solvent, water-based and radiation curing, inkmakers are increasing pigment loadings and offering speciality inks and coatings. Anilox rollers have improved in consistency, resolution and in terms of using lighter weight cylinders, with quick-change chambered doctor blade ink units more widely used. New flexo presses are more sophisticated, with servo motors largely replacing single-drive shafts and allowing more automation. Cameras and colour monitoring also provide closed-loop feedback to maintain consistency.
The most important trend at this time on the evolution of flexo is the continuing development of the prepress, or pre-production, stage. Quality is improving, while the time and cost of approving artwork and producing plates are being reduced.

Improved plate materials and imaging
More flexo printers are taking control of prepress, including in-house CtP, as they establish recognised specifications and quality monitoring, as well as improve the performance and productivity of the process. There have been developments in flexo platemaking that have vastly improved quality, allowing valid comparisons with offset and gravure. Flexo CtP is now common, with laser ablation masks and direct exposure systems allowing fine details and text to be reproduced. In addition, there have been developments in screening to improve highlight and shadow details.
The Esko HD Flexo system boosted the plate production, and improved ink transfer and lay; other suppliers are joining Kodak, Fujifilm, Screen and Xeikon in offering high-quality flexo imaging. There are many developments in plate technology - for example Asahi's ink pinning system on harder water-wash plates that reduces ink spread, which produces crisper dots and reduces ink build-up on the shoulder of dots.

Anilox technology
Anilox rollers have changed significantly in recent years and are a major contributor to improvements across the process in terms of quality and consistency. The anilox roller and doctor blade act as the ink metering mechanism, transferring a consistent volume of ink from the ink pan to the plate surface. Replacing mechanical engraving of copper (chrome plated) and steel rollers with laser-engraved ceramic surfaces transformed the consistency of flexo printing by stabilising the ink supply. Surface materials and engraving continue to improve, with higher cell counts enabling finer detail on the plate. Higher cell volumes and cell configurations are helping to transfer more ink to the plate, while chambered doctor blade ink systems are becoming more widespread.
With the latest generation of digitally imaged flexo plates printing well at 175lpi and 200lpi screens, there will be dots below 10µ in highlights. This can be a challenge for anilox rollers, as the cell opening should be narrower than the diameter of the smallest plate dot to avoid dot dipping. A cell ruling of 2,540lpi has individual cells 10µ across, including the cell wall of 2-3µ, just enough to prevent the 10µ dot on the plate dipping into the cell and spreading the ink while wearing the plate.
The higher the anilox line screen, the thinner and more delicate the cell walls will be. This results in lower resistance to wear, and consequently improve the durability of the roller surface and determine the optimal cell pattern for particular applications.
The coating is a crucial stage in anilox manufacturing; it is important to achieve a consistent coating with no holes (voids) that would not take engraving. This is referred to as 'porosity', with a maximum of no more than 0.5-1.0%. Consistent coating allows the laser to create strong cell walls; substandard coating may lead to the cell breaking down, and allow ink and chemicals to penetrate to the bond layer - this can result in the surface coming away from the roller.
Manufacturers compete on quality, offering measurement and verification of aniloxes before they are despatched. The consistency of cell volumes can be improved through the use of scanning interferometry measurement, using a series of reflective lightwaves on a sub-micron level to capture cross sections of the engravings and composing a 3D image of the cell, resulting in a true volumetric measurement. It is the most accurate way of measuring the cell volume, and improving coating and engraving, which will lead to more consistent ink feeding and more stable colours.
Anilox rollers need to be cleaned regularly and properly to avoid build-up of dried ink reducing the cell volume and plugging. There is simple, non-abrasive on-press cleaning, and thorough off-line cleaning using brushes, speciality chemicals, baking soda or poly-bead blasting and ultrasonic treatment. This creates cavitation effects, with tiny bubbles generated in cells to dislodge dried ink and debris physically.
As with plate cylinders, there is a trend towards using lightweight sleeves to replace heavier, more expensive cylinders with shafts. There are aluminium, composite and stainless steel versions that are designed for easier handling and smoother changeovers to help reduce downtime.

Growing use of process colour to replace multiple spot colours
Many converters are changing from multiple spot colour printing to using process colours to match the required brand colours. This minimises press downtime by reducing the number of ink changes, boosting press uptime and minimising waste.
Innovations to improve wet-on-wet trapping by incorporating solvents are being developed. This is a result of process printing to recognised standards becoming more widely accepted. In radiation curing, the use of wetflex technology (using a hybrid UV or EB formulation incorporating a solvent that evaporates, to aid wet-on-wet trapping) has been in operation for several years. This is improving the achievable process colour quality, while the prepress stage now has many tools allowing spot to process colour conversion to give good colour matching. Standardised printing conditions have developed, allowing brands more predictability when using converters in several locations. The objective of the standards is to help reduce cycle time and minimise rework through improved process control.
In Europe, the ISO 12647:2012 part six standard covers the requirements for the exchange of data and information necessary for the definition of the aims for four-colour flexographic printing of packaging and publication materials, including newsprint. One of the published objectives of this and other specifications is to improve flexo quality to equal or exceed offset litho and gravure.

Better press control
Modern flexo presses are capable of fast changeovers with waste measured in metres per colour printed. Italian narrow web press manufacturer Nuova Gidue is refining its 'Digital Flexo', using high levels of control to automate press set-up. It employs eight servo motors on each print unit with a high-definition camera reading register and pressure marks for fully automated adjustments. The system also increases consistency during the run by controlling the pressure on each unit. In the Digital Flexo 4 system, the camera compares the printed result with the original artwork file to maintain consistency and identify defects. This feature is also offered by Comexi, with the CingularReal solution for automated pressure and register. The solution works by comparing the printed image with a digital master file. When carrying out the register adjustment the image is processed digitally and compared with a PDF file using real-time image processing algorithm.


The focus of these developments is to help flexo to compete with digital technology, particularly for short runs where digital is taking share. High-quality print, increased efficiency, higher productivity and improved sustainability are the desired results to boost the competitive position of flexography.


This article is from the wider white paper by Smithers Pira on flexo; more details can be found at the following address:
www.smitherspira.com/services/consultancy/white-papers



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