The Versatility of Flexo
Flexography is without doubt the most versatile of all the print processes. No other process can print on such a wide range of flexible materials, label stock, corrugated substrate, rigid plastics, envelopes, tissue paper and newsprint and produce an excellent result in all cases. No other process has been able to utilise a variety of machine formats to produce these results. Why have companies made this their process of choice and why does it continue to be the fastest growing of all the print processes.
Above are pictures of winning prints from recent EFTA Print Awards. Shown is the Best in Show Entry of 2009 a flexible packing entry printed on polyethylene, a corrugated box and a label printed on high quality paper using UV Inks. This demonstrates the versatility of the process and the quality that is regularly being achieved by the industry.
To understand how flexo has developed it is worth examining the history of the process as this will give us clues as to why flexo has developed into the most versatile of all the print processes.
Aniline printing - as flexography was first known evolved out of rotary letterpress and its name was taken from the aniline dyes in the inks that were used. Early forms of aniline presses were in use in Europe as far back as 1860 and historians can trace the first modern style of aniline press to 1890 when Bibby Baron and Sons of Liverpool built what resembled a central impression press, with printing units around a drum.
The first patent for a flexographic type printing press was issued in 1908 to C A Holweg. The press was a stack type press used in line with a bag making machine. Since the dyestuff dried so quickly it was possible to produce bags in a continuous operation after printing.
In the late 1880’s Francis Hooper designed and built a press for stamping ink identification marks onto the wooden planks of shipping crates using metal type known as “printing dies” and around the turn of the century George W Swift Company developed aniline presses that could print onto fibreboard. This was the start of printing in the corrugated industry and presses soon appeared that could die cut after printing and add slots and creases to the corrugated box. The early corrugated printers saw the need for a flexible displaceable plates that would not crush the fluted materials. It is said that that one of the first people to use rubber printing plates for use with aniline inks was a KH Mathews of Pittsburg who in 1910 used them to print bags and packaging items.
So even by the early 20th century early forms of flexography, as we now know it, were being used to print on a variety of substrates in a variety of methods.
A recognisable form of the modern CI (Central Impression) press was not developed until the 1940’s. This challenged the stack type presses that had been in operation until then. The CI press allowed for greater control over extensible materials and came at an opportune moment with the development of polyethylene in the 1950’s which required improved printing techniques to handle this more difficult substrate.
At the same time a mechanically engraved chrome plated ink metering roll was being developed and the name anilox roller came into being with the name derived from the aniline industry. Its introduction was a milestone in the development of an accurate inking system.
In the early 1950’s a campaign to change the name “aniline printing” was launched in the USA and over 200 submissions for an alternative name were received. The name flexographic printing was the favourite and the industry embraced this name change. Aniline printing was consigned to history.
The development of phenolic-resin moulding boards for rubber plate making via zinc engraving was another breakthrough in the 1950’s. Using this technique finer more accurate print could be produced. The quality of flexo really increased in the 1970’s with the introduction of photopolymer plates which began to replace the moulded rubber previously used. Modern mounting tapes with cushioning characteristics were introduced in the 1970’s again designed to improve print quality. Coupled with this, improvements in ink technology with the development of polyamide resins further improved the quality of what could be produced.
Since the 1980’s developments have moved quickly with flexo particularly the digital revolution which has impacted on all areas of the flexo process from the initial design to production and printing. The key reasons for the success of flexo can be summarised as follows
- The ability to print on a wide range of substrates including very thin extensible materials through to corrugated board
- Reduced turnaround time for print orders because of less handling and in line finishing capabilities
- Good ink opacity and film thickness with fast drying low viscosity inks
- Excellent solid ink coverage for outstanding graphics
- Very fast press speeds for economy and productivity
- Ability to print very high quality half tones with digitally produced plates
Current estimates indicate that c 40% of all packaging printed globally is through the flexo process with annual growth c 5%. This varies enormously across countries with 70% of all US flexible packaging produced via flexo but only 2-3% in Japan where gravure is the process of choice.
But why has flexo become the process of choice of so many companies particularly in packaging industry. If we examine each of the major sectors briefly we can summarise as follows
Flexible Packaging
The advent of gearless servo driven presses, with sleeve systems and the development of higher volume anilox rollers, improved inks and digital plates have all contributed to flexo being recognised as a truly viable but extremely cost effective method of meeting the demands of the marketplace which require the ability to respond to speed of design change. The quality of flexo printing means that the process has grown market share to the detriment of the gravure process.
Labels
It is in this area that flexo has seen its greatest growth in the past 5 years with over 90% of new machine installations in Europe are believed to be flexo machines. The improvements in quality that can be seen by using UV inks have contributed to this growth. Many of these machines are being used to print narrow web flexible packaging which will ultimately be converted in sachets or be used as shrink sleeves.
Corrugated Post Print
Flexography has long been the process of choice for Corrugated post print but was traditionally seen as a crude “rubber stamp process” with high quality corrugated print being achieved using the litho lamination process or pre print technology both requiring additional operations. Demands from end users for higher quality complex graphics as a norm, coupled with shorter lead times, run lengths and quicker turnaround times means that the industry has responded by investing in 4, 5 and 6 colour machines utilising the technology developments that have taken place within the industry. The greatest improvements in quality over the last 4 years have been seen in corrugated post print and these improvements coupled with changes in demand patterns has reduced the demand for preprint.
Cartons
In the UK this market sector has been slower to adopt flexo technology than other areas of the packaging industry. However amongst those who have made the leap, cost savings by having a one pass operation have clearly been identified as a major advantage of the process and from samples of work seen the flexo can clearly compete head to head with offset litho from a quality perspective. Perhaps the only major cost disadvantage is the cost of flexo plates compared to litho plates but depending on work mix and housekeeping practices these disadvantages can be outweighed by savings in other areas.
Newspapers
The UK houses 2 of the largest flexo plants in the world at Harmsworth Quays and Didcot printing the Daily Mail, Metro and the Evening Standard. These are the only newspapers printed using flexography in the UK although there are more than 40 such installations in the USA. The decision to move to flexo printing was made in the late 1980’s with further investment in the 1990’s and 2000’s. The major reasons cited for the use of flexo have been the improvements in colour, the simplicity of the process compared to web offset and the newspaper has the major advantage of no ink rub. The ability to train personnel in house has also been included as a reason for the decision to make this investment.
Where to next
In recognising the ability of the flexo process it is should be to noted that flexo stations are already installed on conventional offset litho presses to lay down varnishes and are now being installed to apply special inks as the offset process is not capable of producing for example, a good metallic finish. A number of gravure presses also have flexo units installed on them. So alternative less versatile processes recognise that flexo can offer features they cannot.
From an ink perspective modern pigment dispersion techniques ensure there is no difference in ink quality between flexo and gravure. Colour bases can now be produced with maximum strength and consistency, thus allowing required colour to be printed using lower ink film weights which contribute to better cleaner prints and improved press speeds. Indeed for consistent colour on press it could be argued that flexo is more consistent now than gravure on long runs. e.g. when producing 1 million metres a gravure cylinder will wear and require colour adjustment to compensate whereas a ceramic anilox roller will not.
Modern flexo presses are extremely productive and are able to run in excess 600 metres per minute on film and 800 metres per minute on paper.
From a plate perspective developments in digital plates have allowed finer half tones and highlight areas to be printed . However it is critical that these plates are manufactured effectively and consistently to allow the best possible quality. Paying attention to detail and controlling plate making is critical.
Equally important to delivering consistent quality is the care of anilox rollers which are crucial to maintaining consistency.
Indeed one of the few criticisms of the flexo process is that it is not always as consistent as it should be. Good housekeeping, paying attention to detail measuring and controlling all aspects the process is increasingly important to ensure consistency. This is true not only for printers but for trade shops as well. Printers themselves need to adopt more sophisticated approaches to measuring colour to ensure consistency and it is essential that personnel are trained in the underlying technology of the process and are not just button pushers. With the increasing use of flexo it is important that designers understand the principles of design for flexo which are different than offset design principles.