To achieve and maintain desired production output and quality, flexographic label printers must manage all aspects of the printing operation in close unison. If only one area backs up, the entire operation is jeopardized.

The removal of trim and matrix waste, if not managed properly, can create just such a back-up. This paper discusses the current method of removing this waste and addresses the industry trends driving the choice of pneumatic type waste removal. It also will delve into a description of how these systems work and the determining factors to consider in specifying them.

Industry Trends

Production Speed and Efficiency
As with all aspects of the business, increased competition, narrower profit margins and greater end-use demands are compelling flexographic label printers to be ever alert to ways to fine-tune their operations to achieve and sustain maximum speed and efficiency in their equipment. Anathema to good business practices is equipment downtime because it is money not earned. If personnel are "on the clock" and the bank is holding paper on your presses, money not earned represents lost profits and lost business opportunities.

Though it is often overlooked, the efficient and easy removal of trim and matrix waste is a critical part of sustaining maximum productivity in the printing operation. The conventional method of rewinding trim and matrix waste has become an impediment to efficient operation. To minimize waste and, thereby, maximize profits, label printers are decreasing the trim width and the amount of matrix. This makes it more difficult to rewind waste because it is more susceptible to breakage causing interruption of the printing operation. Similarly, the substrate gauge is decreasing to breakage, again interrupting operation.

Non-stop operation is critical to cover the cost of the printing equipment and recoup a respectable profit. Line interruption represents an impediment to that goal. In addition to trim and matrix breakage, the operation is stopped when the rewound waste has to be removed. These are more than minor annoyances when you consider that many printers now employ butt splicing on the unwind and rewind to attain continuous operation. In fact, they run counter to this trend.

Product Quality
Because waste rewinds compel machine operators to monitor waste removal in addition to monitoring the money-making aspect of their job, label printing, print quality is vulnerable.

You cannot ensure total quality management if an operator spends anything less than all his or her time monitoring the proper application of inks and coatings on substrate. If that operator has to make sure the trim rewind is running properly, that the matrix has not broken, that the spool is not overfilling, then he or she is not devoting his or her full attention to the most important aspect of his or her job. In the end, product quality is vulnerable and, by extension, so is your business relationship with your customers.

Safety Concerns
Similarly, if the operator is not devoting full attention to the printing operation, but is also monitoring waste rewind, the waste rewind becomes a further distraction that can negatively impact on his or her safety. Safety experts insist - quite correctly - that machine operator safety is decreased in direct relation to the number and diversity of tasks he or she must manage. Why add a non-productive task that can only add to his or her risk?

Waste Recycling
To recycle waste, as many jurisdictions now dictate, it has to be segregated properly. Wound waste presents problems here, too, by adding paperboard rewind cores to the mix.

Pneumatic Waste Removal

There are basically two types of pneumatic waste removal that address all of these potential impediments to productivity, profitability, safety and recyclability: centralized waste removal systems and venturi waste removal systems. Each has its appropriate applications.

Regardless of the specific application, by ridding the individual printing operation of the burden of managing waste rewind, the accompanying threats to productivity, product quality, worker safety and recyclability are eliminated.

Centralized Waste Removal

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The core of the centralized waste removal system is a material handling fan. A typical layout of such a system is illustrated in Figure 1. Waste is drawn by vacuum from each press to a centralized handling area. A chopper before the fan is necessary to ensure that the chopped pieces of waste can pass through the fan blades and into the waste collection bin. A centralized waste removal system is the most energy and labor efficient means of waste removal and is appropriate where all presses are handling the same type of substrate. Collection for recycling of the waste then becomes a simple matter.

On the downside, these systems tend to be very noisy because of the combination of chopper and material handling fan. Also, they limit the plant to a single type of substrate if recycling is an imperative.

Venturi Waste Removal Systems

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Because of their modular design, the venturi type systems enable waste removal appropriate to the type of material being handled. They operate on the simple Venturi effect whereby motive air is introduced into the removal tube and directed toward the collection end, drawing a suction on the other end and pulling trim and matrix waste along with it (Figure 2). In most applications, venturi systems are installed on per machine. This allows for separate waste removal and more quiet operation.

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Two different configurations show in Figures 3 and 4, accommodate either matrix or trim waste, respectively. A chopper can be added at the discharge end to allow for a smaller waste collection area, or to discharge a long distance.

Adhesive-backed matrix can be removed without sticking, either through injection of oil directly into the venturi or with a PTFE (Teflon) lining in the tubes.

Complete systems can be designed to accommodate several machines by combining both types of pneumatic systems, if desired. Individual venturi waste removal systems at each press can be tied together in the manner of the centralized system with a single chopper. To manage different substrates simultaneously, collection bins can be separated according to substrate.

Proper Specification of Pneumatic Waste Removal Systems

When considering a pneumatic waste removal system, several factors come into play in deciding what type and size of system is required for a particular application. These include the following:

Type of Machine
The type and size of printing press on which the pneumatic waste removal system is to be mounted is important to know because it can give several clues as to how the system will have to be mounted, the kind of mounting brackets required, and the type of pick-up nozzles needed.

Materials Considerations
Substrate is another important consideration because different substrates vary in thickness and stiffness and therefore respond differently to the vacuum effect of the pneumatic removal system. For instance, a nonwoven material exhibits relative flimsiness compared to the stiffer quality of most papers. Additionally, there is normally a direct relationship between a material's thickness and its stiffness. The stiffness of the substrate has a direct impact on the ease with which it passes through the pneumatic waste removal system. The system has to be specified and designed to accommodate the full range of stiffness the user expects to handle.

A stiffer material will mean that the system has to be as close to "straight line" in layout as possible. If flimsier material is the rule, more bends and curves can be built into the removal ductwork to accommodate limitations of the room in which it is to be installed. Similarly, the width of the waste to be removed, whether it is matrix or trim, impacts on the size and drawing capacity of the removal system to be specified.

System Distance
The total conveying distance helps determine the blower size appropriate to the particular application. If also will help specify the right size venturi for maximum airflow.

Operating Speed
The maximum operating speed of the machine on which the removal system is to be mounted will also determine the appropriate removal system. Typically, venturi waste systems are sized so the air speed is about double, in feet per minute, that of the maximum speed of the press.

Continuous or Pieced Trim
Whether waste is continuous or in pieces is another consideration. Continuous trim is relatively easy to pick up because, in effect, it pulls itself along. On the other hand, trim in pieces requires a different configuration and a stronger draw to overcome the gravity that would otherwise pull the individual pieces down.

PS Adhesives
The presence of pressure-sensitive adhesives, as previously discussed, requires one or two added design features. Either the ductwork has to be coated with PTFE (Teflon) or an oil injection system has to be built into the venturi.

Conclusion

As the flexographic printing industry continues to move forward with technological advances in the productive end of the business, some of the ancillary areas that indirectly support that productivity cannot be neglected. Waste removal is one of those critical areas.

Fortunately, technological advances have favorably impacted waste removal, too. The wise manager will not overlook these considerations as he or she strives for greater production efficiencies and speed, always with an eye toward profitability.