(May 20, 2008) Until now, flexible package manufacturing has been predominantly restricted to two processes: flexo and gravure printing.  However, new possibilities offered by infinitely variable size web offset printing technology – such as the Muller Martini Alprinta-V press – have developed into a viable alternative for manufacturers.  At drupa 2008 (exhibit 14B38), Muller Martini will be demonstrating web offset printing with flexo varnishing on OPP film on an Alprinta 52V.

Considerable numbers of machine installations 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, which has been the case in narrow web and label printing for quite some time?

Today’s marketplace: The benefits of established processes are disappearing
The declared goal of package manufacturers is that it must be possible to produce flexible packaging in a wide range of print lengths at a reasonable cost.  Which explains why until recently flexo and gravure printing processes have dominated this area. And now, the realization of infinitely variable size lengths is a standard feature with package printing machines.

Indeed, 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 sums for an 8-color machine and have prevented the growth of offset printing in the flexible packaging segment. As a result, expensive offset solutions have only prevailed where 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 cost associated with printing a wide range of sizes has become a thing of the past for web offset printing. Muller Martini, for instance, offers the Alprinta-V, an infinitely variable size web offset press for the cost-efficient printing of labels and flexible packaging. The print length on the Alprinta-V 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.

The fact is, infinitely variable size web offset printing meets the key requirements for package printing...very low cost printing methods, rapid production, a high level of standardization, the avoidance of high levels of VOCs (Volatile Organic Compounds) and short machine make-ready times.

Possibilities and limitations
The following is intended as a comparison of the possibilities and limitations offered by the traditional methods of printing packaging and web offset printing.
 
Flexo package printing
Flexo methods for printing can be categorized into:
a) Central cylinder presses: These are ideally suited for processing a wide range of materials (flexible packaging, labels, corrugated cardboard liners). Central cylinder presses are configured for medium to large runs and deliver overall excellent print quality, including registration that other production methods cannot match. 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 are cost-intensive.

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

c) Narrow web presses in-line: Typically, these have a working width from 10” (250 mm) to approximately 20” (510 mm) and deliver production speeds of 200 to 500 fpm (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 in-line 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 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 costly: it takes a long time to set up the machine and the peripherals are expensive.

Sheet-fed offset printing
Where print quality and standardization are concerned, sheet-fed offset presses have been able to set new trends. 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 because 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 roll-fed products. The sheet substrates are printed with coldset and UV inks and UV-coating is also used. There is limited opportunity for in-line 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 job changes. The very fast and easy production associated with variable size web offset printing enables turnaround times that are not currently available with flexo and gravure printing. Make-readies are short, thanks in part to the uncomplicated size change. Neither assembly nor disassembly of the printing plate (flexo) nor a handling system or storage for heavy cylinders (gravure) are required.

Once the image has been output to the offset printing plates, the plates are immediately available for the production process. 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 (i.e., 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. Furthermore, a large storage space is not required for cylinders as well as for size parts or printing plates. There’s also no need to budget time for the mounting of printing plates.

With today’s technology, web offset ensures excellent printing quality using fewer printing towers. Short web lengths in the press help to keep waste rates low. And with the option of integrating different in-line modules for finishing, the presses can be configured for specific customer requirements.

Limitations
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. Setting 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 machines, 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. In addition, since the ITX scandal, the term “UV” may have negative associations with some customers.

Conclusion
As a way of offering packaging printers a larger range of different solutions in the increasingly complex world of package manufacturing, and also to expand their own product offering, variable size offset printing can provide many benefits.

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 applicable 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.”

Web offset has become a valuable supplement to established package manufacturing processes, particularly for small and medium print runs where plate costs and turnaround times play a key role today. A large number of alternative solutions are opening up for packaging printers which will allow 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.