Keep It Clean

Clean, clean, clean! It is one of the keys to successful package printing. The substrate must be substantially free of contaminants to stand any chance of providing consistent high-quality printing.

Various systems are used to help keep printing surfaces clean, including static control systems and web cleaning systems. Although George Zuments, president of Web Systems, Inc., points out that static control and web cleaning are separate systems, they typically work in conjunction with each other.

Static control systems are used to enhance the cleaning process by reducing or eliminating static levels. Static poses two problems relative to web cleaning. First, static can attract contamination to the surface of the substrate and secondly, it can make the contamination more difficult to remove because the static attraction between the particles and the substrate can be very high, says Zuments.

Web-cleaning systems physically remove contaminants from the surface of the substrate. These systems can be categorized in two broad classifications—contact and non-contact. Within these categories are a variety of different type cleaners. Zuments lists several: air knives; fixed brushes, with or without vacuum; rotating brushes; semi-contact rotating buffs; vacuum only; ultrasonic and vacuum; pressure and vacuum; and “tacky” rolls.

Each of these different cleaning systems has its own advantages and disadvantages and can be a good selection for a particular application. The key is defining what the application needs and then researching potential solutions using readily available supplier expertise to narrow the options.

Considerations for selection

“It is most important to match both the static control and web-cleaning technology to the specific range of products being manufactured,” emphasizes Mark Gibis, vice president of sales for Doyle Systems. “One technology will not solve all the problems if multiple substrates are involved in the process. Consider working with manufacturers that will consult with you and can provide many choices in technology that will best match your needs. If the manufacturer you consult with is reputable, it will steer you toward the technology that best meets your needs, even if it does not offer that technology.”

For both web cleaning and static control, there are a number of factors to be considered. Some of these include line speed, physical restrictions, material, humidity, temperature, and customer requirements, notes Jim Patterson, president, Static Clean International. He also points out other important considerations. “Not all applications require the most sophisticated systems with all of the bells and whistles,” he says. “A common-sense approach is to have a knowledgeable applications engineer visit the facility to evaluate the best solution to solve any problems or to determine if a problem exists and more to the point, even if it is a static-related problem at all.”

According to Matt Fyffe, general manager for Meech Static Eliminators, “Static control is more of an art than a ‘cookie-cutter’ solution. One particular product will work for one application, but not necessarily another. It is very important to consult with a static control specialist whenever possible.”

He also notes that it is not necessarily important to remove the static charge everywhere on a production line. “It is best to just focus on the area where static electricity is causing you the most problems,” he says. “By focusing only on the problem areas, we can effectively solve the problem with as minimum a cost to the customer as possible.”

Terrance Clark, sales manager for TAKK Industries, agrees with this assessment. “One of the top considerations to determine is the key location(s) to implement your static elimination equipment to achieve the desired results.” And again, he mentions a recurring theme, this should be done “in consultation with an experienced static control applications engineer.”

The location on the process line where static control needs to occur can dictate the range requirements for the static bars. And the range requirement plays a big part in the type of static system that needs to be employed.

Within a 6˝ range, Fyffe says that most of the high-intensity AC ionizing bars can easily neutralize the static charges. At ranges greater than 6˝, more specialized equipment is needed. “Pulsed DC (PDC) technology is ideal for longer ranges,” he says. “For PDC ionizers to work effectively at these greater ranges, they will often need to be ‘tuned in’ by adjusting the ion output to neutralize the charge on the web. This can be done either manually with the use of a handheld static meter, or automatic “feedback” systems can be used that will measure the residual charge on the web and feed this information back to the PDC controller, which will then automatically adjust the ion output accordingly.”

Clark reports that TAKK’s IonStorm XR2 Ionizer has been designed to optimize its static elimination performance to match specific needs of the application. “For the majority of processes, standard performance settings deliver highly effective results,” he says. “However, the ability to optimize the system adds an extra level of static elimination performance and effectiveness for the most challenging static problems and high-speed processes.”

For web-cleaning systems, part of the challenge is knowing what levels of contamination removal are needed. For pre-coating, Zuments recommends removal of particles greater than five microns for films and 40 microns for paper labels. In printing applications, he says flexible packaging should be at levels greater than 25 microns and paper labels at 40 microns. He emphasizes two key points: these targets are simply guides and not the “final word” and also that “no cleaning system can remove 100 percent of all particles of all sizes.”

Ron Sweet, manager of operations and sales for Polymag Tek, says that non-contact cleaners are traditionally vacuum-type systems. These cleaners need to overcome limitations due to both static effects and a boundary layer of air that can form and travel along with the moving substrate. “These two conditions can trap particles of contamination and not allow them to be removed without direct contact,” he says.

According to Sweet, contact cleaning systems typically can include rotating brushes used in conjunction with a vacuum system and contact cleaning rolls (CCRs). The rotating brushes loosen the surface contamination for vacuum removal. One of the risks with this type of cleaner is the potential to scratch the surface of the substrate.

A CCR system relies on a polymer-covered idler roll running in contact with the customers’ substrates, says Sweet. “This system has proven to be the most effective way to remove contamination, if used properly.”

With CCRs, Patterson cautions that operators need to inspect the adhesive layer on the contact roll several times during every shift “and more frequently if excessive slitter dust is present on the adhesive roll. Peeling away the dirty layer to expose a new layer of the tacky adhesive is what is required in most contact cleaning systems,” he says.

Sweet reports that Polymag Tek has developed a CCR system that requires no operator attention for three to five days. With this nip-style cleaner, two CCRs are used together, with one cleaning the substrate while the other is being water-washed by a robotic device.

Good housekeeping

To keep the substrate clean, the equipment that cleans it must be kept clean. There it is again—clean, clean, clean.

“All electrical ionizers will attract dirt and dust to their ionizing points,” notes Greg Gumkowski, director of sales and marketing for NRD LLC. “If not cleaned on a periodic basis, this will cause the ionizer to operate inefficiently, drawing more power and reducing its effectiveness.”

Jay Perry, marketing manager for SIMCO Industrial Static Control, expands on this point and offers some practical advice. “Maintenance of the ionizer involves keeping the emitter points clean (free of debris) and dry. The points can be cleaned using compressed air or a soft brush. As odd as it may sound, a pencil eraser can also be used because the abrasive texture of the rubber aids in maintaining the sharpness of the point, which helps the efficiency of ionizer.”

“High voltage on a sharp emitter in proximity to ground is the basis for creating ions, and keeping both the emitter and the ground free of slitter dust, oil, and other contaminants found in the printing process is important,” adds Patterson.

Surface contamination should not be a problem in a well-run printing operation. The equipment to address this problem is readily available from a number of suppliers. The key is to use their expertise to ensure that the right process is implemented, and then perform proper maintenance and housekeeping to keep it running at effective performance levels. pP

Do you need to upgrade?

• Are you still receiving complaints from your customers relating to defects such as hickeys, voids, color variations, etc.?

• Is your press uptime well under 90+ percent?

• Are your operators running the press well below machine operating speeds to try to print defect free?

• Are you spending any time with your substrate suppliers trying to get them to accept the return of materials that are too dusty?

• Have your operators quit using the static elimination/web cleaning system on the press because it does not work or requires too much maintenance?

• Do you find your operators are constantly trying to augment the cleaning device with other simple approaches and technologies to try to reach a higher cleaning performance?

Answering yes to any of these questions suggests that you need to find a better performing system and the existing system is costing your operation money.

Mark Gibis, VP of sales, Doyle Systems