Corona treatment enhances printing on plastic tubes

Tube manufacturing is a huge, yet often overlooked segment of the plastic-packaging and converting industries. Despite the size of the tube business, there are only a small number of highly specialized processors that serve this market. There are an even smaller number of machinery and equipment suppliers that can provide processors with the equipment needed to decorate, fill and seal the tubes prior to shipment to the consumer.

This small fraternity of tubemaking processors and suppliers often needs to work together to improve manufacturing techniques and quality control. This is exactly what happened when one of the largest North American tube packaging/product manufacturers had an application that offered Corotec Corp. (www.corotec.com) and F&L Machinery Design, Inc. (www.fandlmachinery.com) the opportunity to collaborate on the project.

While this feature focuses on tubes, Corotec's corona-treatment system is not limited to plastic tubes. It is used extensively for all types and sizes of plastic containers at speeds up to 600 containers/min.

Corotec Corp. is one of the industry's leading corona-treatment system suppliers. F&L Machinery Design is one of the tube industry's leading offset-printing machinery suppliers. The two companies teamed up to eliminate the existing flame treaters being used on offset-printing machinery in an attempt to reduce rejects, improve product quality and lower production time and costs. The result of their collaboration was a quality enhancement beyond expectations.

To decorate a plastic tube, the tube must first be treated so that the ink will adhere to the tube surface. The industry has traditionally utilized flame treatment to achieve this. "Because flame treaters operate like a gas stove, there is a 'human' factor in adjusting the air-to-gas mixture that controls the heat," says Fred Villaverde, Sr., president of F&L Machinery Design. "From operator to operator, changes can be made that can result in inconsistent product treatment and quality. Additionally, the ink can get tacky and won't adhere to the tube if the flame gets too hot."

Inconsistent flame treatment was the driving force behind the collaboration between Corotec and F&L. Corotec was brought in to work with F&L and the end user to develop a corona-treating solution to the problem. It was determined that by integrating the Corotec Plasma-Jet(R) 3-D corona-treating technology with its specialized cup-and-tube corona-discharge treating system, the tubes could be treated to their full length with superior one-pass coverage, consistency and convenience. Since the Plasma-Jet and the corona-treating system generate very little heat, the tube surface can be treated without distortion, and the viscosity of the ink can remain constant.

"This is a paradigm shift in thinking about offset printing," says Villaverde. "Until now, flame treatment has traditionally been the method of choice over corona treatment. This is because corona treaters utilize an electrical discharge that can arc to the mandrel underneath the tube while it is in the offset printing press, which causes some treatment to occur on the inside of the tube as well as on the outside.

"When both the inside and outside of the tube is treated, the tube ends cannot be sealed," continues Villaverde. "To compensate for this, corona treatment is usually stopped before reaching the edges of the tube. Of course, the problem with this approach is that it would normally mean that printing to the edges would not be possible either, and that's not something our customer could live with."

This challenge was overcome by incorporating the Plasma-Jet into the system along with the traditional corona treatment. The versatile design of the Corotec Plasma-Jet and specialized cup-and-tube corona-treating system enabled F&L to incorporate it right into their equipment, solving the problem of treating and printing right up to the edges of the tube.

Because flame treaters operate like a gas stove, there is a human factor in adjusting the air-to-gas mixture that controls the heat.

Corotec custom designed their Plasma-Jet treating system to accomodate F&L's offset-printing machinery so that the flame treater could be eliminated. This new system provides superior one-pass coverage, consistency and convenience and is capable of handling very high throughput speeds.

"The Plasma-Jet and cup-and-tube corona-treatment units eliminate the distortion, inefficiencies, safety hazards and product damage that often result from flame treaters," says Bruce Stobbe, president of Corotec Corp. "It is now possible to treat to the end of the tube without arcing or treating the inside of the tube, and the heat sealability of the package is no longer a concern. Since the ability to seal the tubes is no longer an issue, there are no limitations on printing."

A quality issue that sometimes arises during the manufacture of tube packaging is the existence of pinholes. They occur prior to the decorating phase of the product development. However, pinholes are typically not discovered until the tubes are filled with the end product, such as lotion or shampoo, and sealed.

The implementation of the Corotec Plasma-Jet corona-treating system eliminated problems with corona between the tube and the mandrel at the edges, and the associated inside treatment. However, arcing does occur when a pinhole in the body of the tube is present and is exposed to the cup-and-tube corona-treating system. "This has turned out to be one of the best features of our equipment; it's the icing on the cake," says Villaverde. "Now, if a pinhole is present, the Corotec cup-and-tube corona treating system will detect it, since the electrical discharge will arc to the mandrel underneath it. The Corotec proprietary fast-fault circuitry will sense the defect, reset the power supply for the next mandrel and signal the PLC that there is a flawed or missing product. Poor-quality parts are rejected before printing, and if a tube is missing, the printer will not print on the mandrel."

Tube-packaged product manufacturers no longer need to wait until the tube is filled in order to discover pinhole leaks. This significantly impacts their bottom line by uncovering a major quality issue much earlier in the manufacturing process and before any product is wasted.

At Corotec, we pride ourselves on being able to custom design and retrofit our equipment to the requirements of virtually any given application.

By eliminating wasted product, cost overruns and delays in shipping, tube-packaged product manufacturers can operate more competitively, while delivering a superior product. "We see this ability to improve product quality to the end user while minimizing product waste to be a major benefit to this market and to our customers," says Stobbe.

Simple and compact, the Corotec Plasma-Jet and specialized cup-and-tube treating systems can be sized and configured to suit virtually any production environment. They are easily matched to the required product throughput, treatment width, product material and configuration. Both the Plasma-Jet power unit and the specialized cup-and-tube corona treating system can be portable or permanently mounted, depending on the application.

"At Corotec, we pride ourselves on being able to custom design and retrofit our equipment to the requirements of virtually any given application. The marriage of our Plasma-Jet and cup-and-tube corona-treating technology with the superior offset printing capabilities of a company like F & L Machine is an example of just how important this capability can be," says Stobbe.

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