Dossiers

Contemporary converting – From an accessory process to a recognized production step

Schobertechnologies offers the RSM IML Digi ­Varicut which combines ­continuous and intermittent processes for die-cutting

What actually is a converter? According to the dictionary, the term can mean transformer, transducer or embellisher. In addition to the printing industry, the term is used in many other areas. In general, every process step in printing is the conversion of original materials and media into a final product. However, let’s explore how this term applies to the label printing industry.

by Herbert Knott

In the past, the term “Finishing” in reel-to-reel label printing used to be associated with the department transforming the continuously printed mother rolls into smaller individual rolls, this usage then became outdated and turned into the “Converting” department.

Contemporary converting

Today, converting means the last processing step of labels prior to sending them to the customer. In times of ever decreasing delivery times, which does not allow reworking, the converting division has to bear even ­greater responsibility for the final product.
However, apart from this transformation of the larger mother rolls into individual ones with a predefined number of printed labels wound on a certain size core the converting departments have for some time been facing extended capacities. In this context, the topic of roll hardness would be a topic on its own. What would be the value of an almost perfect print result, if the reel telescopes and as a result falls to the feet of the customer. Or otherwise, if the layers of the roll stick together when using a smooth flowing adhesive, or if the reel is deformed and shows an inclination of repressing in the direction of the core in relation to the increasing diameter. Therefore, any support to prevent undesired occurrences or the supply of poor quality to the customer is highly appreciated.

Extended capacities
The extended capacities of the converting department mostly refers to control responsibilities but also includes further supplementing and embellishing the process steps. With the exception of a few products, which are finished on the printing press, the quality of the printed web should be inspected. This may be carried out by using a vision system integrated either into the printing press, the finishing unit or both. Applied to the printing press it serves to avoid misprints whereas when mounted on the finishing unit it identifies incorrectly finished labels on the roll.

Which technologies are most suitable for carrying out such functions? With the exception of pharmaceutical products this is a more a philosophical issue, as the control functions are carried out on the basis of various specifications and demands: The detection of missing labels and defects in the printed image like register variations in the print, colour changes, register fluctuations in die-cutting, and matrix residues left on the web are some of the areas covered during the inspection process. On rewinding units, some of these tasks are still carried out “manually” by the operators using optical stroboscope viewing devices. Such devices control the running web with the help of a flash sequence synchronised to the appropriate running speed of the web. This makes the image on the web appear stationary which facilitates web inspection.

However, this process is not enough when it comes to the higher requirements of the branded goods manufacturers in terms of print quality, readability of the EAN code, or even the maintenance of general pharma standards. Customers from this industry want every label to be inspected as well as the whole web. To ensure 100% readability of a pharma code it requires more than just looking at the label but necessitates the integration of a code reading device into the production equipment.

Things become even worse if one has to deal with foreign characters because even if a small stroke is missing or is the wrong length this might completely change the meaning of the character and result in unforeseeable consequences. Such difficult control tasks cannot be reliably carried out without using a sophisticated camera device working with imported reference data for comparison.

Vision control
Electronic proofing compares the original design or the scanned proof print with a random sample or the respective camera image of the production run. Such electronic devices are calibrated in terms of fault tolerances to avoid false alarms. To meet different requirements two different camera systems are available: area cameras and line cameras.
The area camera checks the print result at certain fixed intervals on a predetermined label or a certain area of the printed web. Using a traverse unit a defined print repeat is checked to cover certain areas of the printed web. Missing or faulty single elements are detected, indicated, marked and recorded. The problem with such a process is that they cover only a small area of the entire web. However, if the control is limited to the cut single web, even the use of an area camera may provide 100% control.

With line cameras, a sensor captures only one line. The areal image gets built up via the movement of the web and the repeated capturing of the line. Therefore, such cameras virtually guarantee 100% control of printed webs. As with area cameras, a reference master image is compared with the real online print results. When using line cameras, 100% control is achieved without checking the single webs, even if missing labels are not replaced.
Inline spectral colour measurement: Controls as just described may still be regarded as insufficient by certain customers. Therefore, a new generation of inspection devices offers more opportunities for checking such as the relation of the print and die-cutting register, readability of codes, and completeness and accuracy of the print by using inline spectral colour measurement (e.g. BST Eltromat International). The systems also check the accuracy of the ink reproduction according to the reference master image. To increase the prevention of waste, these control steps should be carried out during the printing ­process.

Booklet labels: The production of booklet labels is often transferred to converting equipment. This means that the difficult manufacturing process of such products with all the complications of feeding the substrate and laminating procedures do not affect the continuous print process. The same applies to the provision of labels with RFID elements.
Inmould labels: The die-cutting of inmould labels definitely belongs to the field of converting, even if it is not a core issue for “ordinary label printers”. For example, the German company Schobertechnologies offers the RSM IML Digi Varicut. According to the manufacturer, this device combines continuous and intermittent processes for die-cutting. This ability is of importance if digitally printed labels in a stacked form must be processed. Moreover, in addition to the stream or stacking delivery, a delivery robot is available which handles both ways at the same time. For sorting out the waste 100% control can also be found at inmould die-cutting stations. The Alhena by Prati is a somewhat more simple variation of the inmould die-cutting station with a stroboscope which can be upgraded with an inkjet inprint unit at the front and/or back side of the web.

Even further from the norm for a “normal” label printer inmould die-cutting devices like the one provided by Berhalter might be used, which pushes the labels from the clocked web into a punch stamping device and stacks them at the same time. The tool costs for such a device are very high and therefore it is most suited for long prints runs with no changes to the image.

Do not neglect die-cutting
Converting equipment is often provided with magnetic cylinders for using flexible dies. However, in spite of digital workflows and short print runs, laser die-cutting systems are still hard to find. Significant reasons for this include anti­cipated bottlenecks in speed (one converting unit for several printing presses), the additional environmental regulations for exhaust air, and also the fact that some substrates are harder to cut than others. This will only change in favour of laser die-cutting, if such devices offer significantly higher running speed than are available today.

Magnetic cylinders and flexible dies offer cost effective solutions particularly when only one size of cylinders and intermittent web guiding are used. Some converting equipment like the AB Graphics’ Digicon 300 offers automatic mounting and demounting of flexible dies which are very useful tools for reducing job change-over times.

Also equipment running with changing magnetic cylinders are provided with fast change systems for the cutting tools, which also results in significant reduction of make-ready times. The cutting of the basic mother roll into individual rolls is the final task of some converting equipment. This is done with the use of razor blades, crush knives, or disk knives. Devices which can be preset while the previous job is still running are often used. However, the most comfortable solutions use a job controlled mode and adjust the knives automatically at their respective position. If sheets have to be produced, some of these systems also offer cross cutting.

Converting systems tomorrow
The increasing use of digital print engines for label printing, means that converting is evolving into new areas. Because of physical restrictions, digital print engines, no matter if toner-based or inkjet, cannot compete with the running speed of conventional processes like flexo, offset or letterpress. For companies with several digital presses it appears to be economically acceptable, to establish a separate converting system for two or three such presses. Hence, many, but not all digital presses are provided with a die-cutting station or even a laser die-cutting station.

Within the area of high-quality labels there is a need to meet customer requirements for embellishment. Certain manufacturers of digital print engines now offer cold foil embossing like the French company MGI. Whatever progress might be made, the place for high-quality foil embossing might still be carried out on the converting device. There seems to be little economic reason to provide each digital print engine with all the converting tools – which is the same with conventional presses. The unfulfilled requirements of print shops using digital engines are strongly pushing the manufacturers of converting equipment. This has resulted in integrated units for lamination, hot foil embossing, gravure printing units for primer coating, flexo units for spot coatings or even full-cover coating of protective or special varnish and even screen printing units.

Corona pre-treatment is just as natural as web cleaning. Web guiding with systems for web tension and web-edge control as well as the accurate positioning of the units for printing and die-cutting through servo drives are crucial elements for the subsequent processing of printed webs.
For example, the FE 52 colour line sensor provided by Erhardt+Leimer offers the opportunity to guide the web by using arbitrary elements of the printed image without the need for using the web edge as a reference. The colour line sensor is based on a colour matrix chip. The integrated lighting system ensures the lines or colour contrasts are reliably scanned, even if the surface is very reflective reflecting. Thanks to the new evaluation technology and the learning process not only the conventional lines or contrasts are reliably detected but also combinations of lines and contrasts. Especially with multiple identical lines the criterion entered is reliably detected which avoids unintentional switching to a neighbouring line.

Individualisation, which in this context means offering each customer a personal approach to the respective product, seems to be an impossible task. On the other hand, this is what the market increasingly demands in the struggle to win the customers interest and to affect the respective purchasing decision. By using inkjet inprint units this demand can be satisfied in the same way as the demand for the inprint of batch numbers.
“In general, automation and job change optimisation are gaining increased importance for the technology behind the printing presses”, explains Thorsten Saathoff, managing director for Nilpeter Minden and also responsible for the distribution of Prati products in Germany. “A practical example for this is the fully automatic knife exchange process and also the intuitive machine operating concepts.” In addition, customer are increasingly demanding packaging stand-alone solutions for printing and finishing integrated into a common workflow.

Worldwide access of the control results via the internet and cloud solutions and the alignment with results from other continents are among the challenges which print shops will have to deal with in the future when working for international customers. Stage-of-the-art converting equipment is already remote controlled with all adjustment parameters derived from the data base or via printed job codes. Plug and play – this basic idea of our fast-moving times relates also to the instant application of all control devices. Whoever offers training sessions for operators to ensure the safe handling of such devices has an obvious communications problem – however useful a well-trained operator might be.

Conclusion
The converting department has long since developed from an accessory process to a recognized production step. In addition, with the increasing importance of digital printing it will gain even more significance in the field of label production. Therefore, it deserves the appropriate attention concerning automation, efficiency and human resources. In any case, the market offers a broad portfolio of options ranging from the most simple roll slitter to the almost fully automated high-tech embellishing equipment.

Angela

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