Alprinta 74V for printing flexible packaging and labels.

A considerable number of machine installations undertaken mainly in Europe in recent months have shown that for many companies, infinitely variable size web offset printing with UV or EB curing has become more than just an alternative solution in the manufacture of flexible packaging. Does this represent the rise of a serious competitor to the established flexo and gravure printing methods, such as has already been observable in narrow web and label printing for quite some time? A comparison of the processes would in any case be interesting.

The status quo: The benefits of established processes are disappearing
The manufacturers’ declared goal is that it must be possible to produce flexible packaging in a wide range of print lengths at a reasonable cost. This is why up to now the established processes, flexo and gravure printing, have dominated this area. The positive drive and therefore also the realization of infinitely variable size lengths are now standard features with package printing machines.

Web offset machines have been missing this cost-efficient size range.The costs for a size set in the form of conventional printing inserts have amounted rapidly to six-figure euro sums for an 8-color machine and prevented the establishment of more offset printing in the flexible packaging segment.These expensive offset solutions have thus only prevailed where merely a small number of different size dimensions has been required.For example:as early as the 1980s, Tetra Pak started to print certain packaging for liquid foodstuffs using web offset.

However, the high costs associated with a wide range of sizes are now a thing of the past for web offset printing. Muller Martini, for example, offers the Alprinta V, an infinitely variable size web offset press for printing labels and flexible packaging which no longer has this disadvantage. The print length is changed as required by replacing the actual size parts: the plate cylinder and the blanket cylinder. This is a quick procedure accomplished without the use of tools.

Infinitely variable size web offset printing does now indeed meet the requirements for printing packaging. These include very low cost printing methods, their rapid manufacture, a high level of standardization, avoiding high levels of VOCs (Volatile organic compounds) and short machine make-ready times.

Possibilities and limitations of the processes
The following is intended as comparison of the possibilities offered by the traditional methods of printing packaging and web offset printing and their limitations.

Flexo package printing
Flexo methods for printing can be categorized into

a) Central cylinder presses: These are ideally suited to processing a wide range of materials (flexible packaging, labels, corrugated cardboard liners) They are configured for medium to large runs and deliver overall excellent print quality. Other production methods cannot compete with the excellent registration during the print run. The use of solvent-based inks is resulting in the steadily rising cost of complying with environmental requirements and safety regulations that are becoming increasingly more stringent. Set-up times for a central cylinder machine are medium to short. Compared to web offset, the printing method costs are high and peripherals cost-intensive.

b) Flexo presses in-line: These are used mainly for manufacturing folding box packaging for products such as cigarettes, cornflakes and containers for liquids (for example, SIG Kombiblock). Equipped with inline units for die cutting and laminating, for example, and a fully automatic delivery system, they are configured for large to very large runs. Both solvent-free inks and UV inks are used in the category.

c) Narrow web presses in-line: Typically, these have a working width from 250 mm to approximately 510 mm and deliver production speeds of 60 to 150 m/min. They are hybrid machines which in some cases combine up to four printing processes and have a wide range of inline stations for finishing. UV inks are used on these machines to print self-adhesive labels, shrink sleeves and many specialized products in small to medium runs.

Gravure package printing
Gravure presses are mainly used for manufacturing flexible packaging and cigarette packets. They deliver high print quality and very good, but expensive reproduction. Advantages over the other methods include a wide range of materials and easy machine operation (direct print method). On the other hand, the print methods are expensive, it takes a long time to set up the machine and the peripherals are cost-intensive.

Sheet-fed offset printing
Where print quality and standardization are concerned, sheet-fed offset presses have also been able to set new trends for the other methods. In the packaging segment, sheet-fed offset is used mainly for labels (wet labels, pre-cut wrap-around labels) and folding boxes. There are only limited possibilities for film printing as sheet fed offset presses cannot work with material thinner than 50 µm. These machines have a certain amount of “size variability” with sheets in different sizes, but there is no option for producing reel-applied products. The sheet substrates are printed with coldset and UV inks and UV-coating is also used. There is limited opportunity for inline production.

Web offset printing
Printing with the infinitely variable size web offset method (e.g. the Alprinta V) has cost benefits compared to flexo and gravure printing. This is a positive point when there are frequent changes of motif and jobs that are unlikely to be repeated. The very fast and easy production of the printing methods permits response times that are not currently available with flexo and gravure printing.Make-ready times are short thanks in part to the uncomplicated size change.Neither assembly nor disassembly of the printing plate (flexo) nor a handling system nor storage for heavy cylinders (gravure) are required.

Once the image has been output to the offset printing plates, they are immediately available for the production process. The set-up times are very short, providing flexibility in job processing and ensuring high productivity. The use of UV or electron beam cured inks means that there is no cost involved in complying with extensive environmental requirements (purifying exhaust air or explosion protection). There is no waste ink, nor is there any need to provide large amounts of storage space for ink. Nor is a large storage space required for cylinders, size parts or printing plates. There is no need to budget time for the mounting of printing plates (flexo printing).

Nowadays, web offset guarantees excellent printing quality using fewer printing towers. Short web lengths in the press help to keep wastage rates low. With the option of integrating different inline modules for finishing, the presses can be configured for specific customer requirements.

Limitations of the process
Infinitely variable size web offset printing for the production of flexible packaging is a new process which does not offer off-the-rack solutions. It changes more than the previous workflow. Drawing up the correct machine specifications requires a great deal of communication between all those involved, as there is not yet a large base of user knowledge. In most cases, another printing process in addition to offset is used in line for opaque white, varnishing and decorative inks. For those who use it, this makes web offset a more ambitious undertaking. There are also system-related limitations regarding the substrates that can be printed on. The tendency of certain materials to stretch requires special knowledge of the process.

The acquisition of new types of machine, size parts and if necessary the development of a dedicated pre-press process, combined with UV or EB cured ink systems, are new territory for many printers. Furthermore, the term “UV” has negative associations since the ITX scandal; end customers sometimes respond with an “emotional shutdown”.

Muller Martini product and marketing manager, Bernd Schopferer.

Conclusion
In order to offer the packaging printer the largest possible range of different solutions in the increasingly complex manufacture of packaging, or also to expand their own product palette, it will in future be possible for them to have the printing process in question in house and to benefit from its strengths.

Variable size offset printing is an up-and-coming process with rapidly developing technology that will increase its share in the flexible packaging market. The producers of printing inks are playing a key role in this process and have recently made great strides in developing appropriate UV and EB inking systems. Today, the web offset method is used to print on substrates that even two years ago were considered “non-processable”.

In competition with the established processes, web offset has become a useful supplement, particularly for the range of small and medium print runs, where printing plate costs and response times play a key role today. A large number of alternative solutions are opening up for packaging printers which will permit them to expand their product range. As a result, not only flexo, gravure and web offset printing but also digital printing will be found increasingly under one roof and will complement each other.

Bernd Schopferer (Product and Marketing Manager, Muller Martini Presses GmbH)