Gravure breaks out of the cell

Gravure remains the best quality printing process. And it's a quality that remains unchanged even after millions of metres of substrate have been printed.

So believes DCM's sales manager Gerard Lansade. “But it's a printing technique that is going through a time of change,” he asserts. “Competition from the improved flexo and litho industries has meant that the majority of the present gravure print machines in the UK, for example, are the incorrect design to give quality and cost effectiveness.

“The quality of print and inks from gravure is still in demand from a number of market sectors, including the food packaging industry. However, the calculation of costs, which includes the man hours for machine clean-up and change-over, coupled with origination costs for each print unit, means that when a direct comparison is made, the buyer is moving his purchasing to flexo.”

The Nanterre, France, based company believes that large volumes of gravure are still being used, but more and more is being sourced from outside the UK, due mainly to the cost of labour. “There is a lack of gravure presses in the UK of a design that will enable quick change of print units, reduced change-over times and reduced material waste on re-start,” he says.

His company is offering its new BIVA narrow web rotogravure printing press designed for the short run market. “Installations have shown that operating speeds of 400m/min can be achieved and the change time per unit can be as low as five minutes/print unit. And the restart material loss and back into registered print is down to 10m.”

The machine is supplied in web widths of 580, 680 and 820mm. Key design features include electronic direct drive on each print unit (shaftless drive), quick change of the print and impression rollers, sleeve design for both impression and print cylinder with cantilevered shafts for side removal from the machine, quick access to each drying module and small size print cylinders for short runs. A trolley is not needed for parts or cylinder removal and all inking parts may be handled by one operator, says DCM. A low investment cost is claimed for both press and spare inking parts.

Change-over and wash-down can be done on the fly and water based or solvent inks can be handled by hot air dryers on each unit. In line registered coldseal, hotmelt, and solventless or solvent based lamination can be accommodated. “Sleeve cylinders are being sourced at ever lowering prices as the competition for supply increases,” added Gerard Lansade.

When it comes to innovation in the process the cylinder engraving technology specialists can usually be relied upon to make the first move.

The first presentation of direct laser engraving for copper cylinders offered over 200 visitors an in-depth look at the world's most modern cylinder production system at 4 Packaging, in Dissen, Germany, at the end of June.

The centrepiece of direct laser engraving is the Hell Gravure Systems Cellaxy output device. The Cellaxy is fitted with a high power multi kilowatt laser with a resolution of 2,540dpi (1,000 l/cm) that lasers cells directly into the copper surface. The electroplating process for producing the engraving cylinder surface remains unchanged.

The laser is in continuous operation and is controlled with a 3D-Rip. Thus the writing principle is similar to that of an offset platesetter, with each cell being formed from a matrix of 16 x 16 laser dots, for example.

However, in contrast to offset, the laser can vary the intensity, and therefore the depth, of each individual laser dot. This enables the engraving screen to be adjusted in terms of screen resolution, dot shape, depth, and cell-to-wall ratio. In the future, this property will allow a printing form to be adapted to the specific printing conditions, says Hell.

As the Cellaxy always employs a write resolution of 2,540 dpi, extremely high contour definition is produced, explains the company. This is claimed to make it ideal for applications in the cigarette, labelling and pharmaceuticals sectors.

At 4 Packaging, the Cellaxy is initially used for engraving full tone cylinders in the cigarette sector, where requirements are high print densities and ultra fine text and graphics. Hell and 4 Packaging are now beta testing to gather practical experience in using the new technology.

The Cellaxy is expected to be available from the middle of 2007 onwards.

Another recent innovation comes from Dalim Software and Hell Gravure Systems. A joint technical venture between the two companies has resulted in what is claimed to be a revolutionary interface - including the first automatic cylinder imposition tool.

The HELiOFLOW system is claimed to afford operators a considerably greater level of production automation using an advanced, high performance automated imposition engine built from the ground up for the exacting and precise demands of the gravure printing industry, says Dalim. It interfaces with the Hell FormManager system, as well as with third party MIS systems and production databases, whether JDF enabled or otherwise - and, by using the DALiM TWiST premedia engine, automatically creates a cylinder imposition without any manual intervention.

Operators, on a web browser, can also receive a complete view of the imposition before engraving a cylinder. “Thus they can administer, edit, manage, and approve the imposition process on the fly, anywhere in the world, 24/7, reducing errors and speeding turnaround time,” claims the company.

On the makeready front, the installation of a patented single-head register mark scanning system on a Komori Chambon gravure press results in shorter make ready times.

Nampak Gravure Western Cape, in Cape Town, retrofitted its nine colour Komori Chambon gravure press with a fully automatic eltromat dgc_650 register control system. The installation of the digital multiple processor based system is said to offer short makeready times and other matching benefits increasing productivity of presses to an upper level.

Nampak Gravure plant engineer Greg Evershed commented: “Originally our Komori Chambon press had six printing units. In 2003 we added another three units to meet market needs and high level customer requirements. At the same time we decided to replace the register control to reach considerable savings of set-up time, waste and production costs.”

Other advantages were pricing and an excellent back-up service from eltromat and its South African representative, Printing Products, he added.

“The system provides several kinds of presetting and a high tech single head measurement. This patented measurement for register marks ensures simple handling for fixed selection of sequential or key colour control providing a combination of both types of control procedures automatically.”

“Gravure printing is undoubtedly the printing process that achieves the best quality, says Saueressig, but due to the initial comparatively high purchasing costs of steel base cylinders and the logistics, it cannot always stand up to the price pressure exerted by flexo and offset. The company's sleeve technology, expander core shafts and Gelenium sleeves have been developed to meet this problem. Replacing the expensive steel bases previously required for each single printing cylinder with aluminium and multilayer sleeves on standardized core shafts contributes to this improvement in the economics. The robust base body of the sleeve is manufactured from aluminium, providing a high resistance to environmental influences as well as solvents and inks, it is claimed.

The Expander Core Shaft ECS (Easy Change System) is designed to mount the Gelenium sleeves on the press. It comprises a high precision steel body with a precisely ground functional layer. The connecting fit between the sleeves and ECS is achieved by friction force, which is provided through hydraulic pressure. The construction is based on a conical principle permitting a simple joining and fitting operation. It contains a built-in deflection compensation for homogeneous print densities across the full print width.

Presses with integrated sleeve change systems are suited to the system. Examples are the Heliostar GS from Windmöller & Hölscher and Uteco's Q-Press.

Proofing

“It is common to hear complaints from gravure cylinder engravers relating to their conventional cylinder proofing presses,” reports Peter Hughes, of Ameco Raster UK. “Gravure proofing has generally lagged behind developments made in other sectors of gravure pre-print over the last two decades, specifically in the areas of standardization and efficiency.”

He continues: “The use of the alternative technology of digital printing, which apart from having advantages in its own right for some applications, for other users has simply become a way of circumventing the failure of conventional proofing to improve its performance.

“However, one crucial aspect of conventional proofing that cannot be fulfilled by digital technology is the quality control of cylinder engraving.” He maintains that this is of at least equal importance to many engravers as the production of a representative proof to present to the end customer. “Digital proofing also has severe limitations in reproducing special colours, especially in the flexible packaging and decorative printing sectors,” he adds.

He argues that conventional proofing for gravure engraved cylinders is ideal, as it meets all the technical requirements demanded by the engraver/printer, in that it uses the same inks, ink doctoring, print pressure and substrates as used on the main press for the print run and therefore can meet all requirements for colour variations and produces a proof totally representative of the finished job. It uses the final product (the engraved cylinder itself) to produce the proof and therefore acts also as the quality control for the engraving.

“So what's the problem?” he asks. “Conventional proofing is costly, labour intensive, time consuming and the design construction of the proof presses cannot be totally in accordance with the construction of the main presses for all sorts of practical reasons.

However, over the last few years significant strides have been made to resolve some of these limitations.

“In terms of standardization there are two distinct aspects: the proof press settings and the mechanical configuration of the proofing presses. Press settings on modern gravure proofers can be standardized using fully automated systems (APS) or CPS - Calculated Press Setting - systems which can be either off-line or built into the press. CPS differs from APS, in that the system calculates and digitally displays all the settings for the operator to then make manually.

“When an engraver has more than one type of proof press, for example Ameco, Heaford, GMS or Timmins, a standard machine configuration for all of the proof presses handling a particular range of cylinder sizes is achieved by checking (and modifying where necessary) all the mechanical factors which influence print quality. These include doctor blade distance from surface of proofing drum, distance of centre line of doctor blade angle pivot point from edge of doctor blade, and calibration of pneumatic air pressure to unit length of doctor blade in contact with the engraved cylinder surface.

“Also of importance are the setting of zero reference points for the doctor blade position in relation to the minimum and maximum cylinder circumferences and replacing graduated mechanical scales with calibrated LED readouts to interface with the CPS readouts. Calibration of hydraulically applied proofing pressure from atmospheres (bar) to Kps of printing pressure per unit length of engraved cylinder is also required. Also to be taken into consideration are the value of the camber on the surface of the proofing drum, tension and hardness of the rubber proofing blanket and print speed control. Without bringing these parameters into line, the same set of cylinders proofed on different presses will generally give two different results.”

Using PLC controls, servo drives and proportional hydraulic valves, proof presses can now be programmed for automatic setting. Says Peter Hughes: “This has a number of distinct advantages over conventional controls in that it offers the potential to interface into automatic cylinder preparation lines such as those supplied by Hell-KasperWalter-Bauer, Daetwyler and Acigraf. Secondly, the machine setting times are greatly reduced, improving productivity, and thirdly, the accuracy of settings are not dependent upon the skills or experience of the individual press operator.”

Automatic settings include: support positioning to accommodate the particular length of the engraved cylinder, centralization of side register mechanism, height of doctor blade position and wiping angle, and wiping pressure, proofing pressure in relation to both cylinder size and substrate type and printing speed. All these settings are initiated on the selection of a job code and push of a button. Proof presses fitted with APS can usually store up to 1,000 sets of cylinder details.

Latest model to be introduced in the JM Heaford range of gravure proof presses is the moving rail ‘Open Fronted’ machine, known as the SC OF.

The open fronted style of machine has proved particularly popular in Asia, says the company, and was originally designed as a moving drum machine with the smaller engraver or converter in mind, who generally processes smaller and lighter hollow cylinders. The low fronted open rail ensures that cylinders can be easily loaded by hand. Elimination of the mechanical hoist means that the loading and unloading is faster and the machine is therefore more productive. Processing times obviously vary by user, but if a conventional machine typically handles six cylinders/hour, the OF design would handle up to 10, claims JM Heaford.

The new SC OF incorporates a larger drum, giving a longer proof length and offers a higher proofing speed.