Tubes technology could make its mark—for injection moldersTubes technology could make its mark—for injection molders

Plastic squeeze tubes are a fast-growing segment in consumer, personal care, and industrial packaging. Relatively new technology has given a few injection molders the impetus to try their luck in a market so far dominated by extrusion.

Patented technology from Australian firm Zestron (Mt. Eliza) is helping injection molders get a foot in the market for plastic tubes. A handful of injection molders of packaging, among them Plasticum (Tillburg, the Netherlands) and Yorker Packaging (Greer, SC), a division of Jarden, as well as an unidentified processor in Africa, have licensed Zestron’s patented technology. Jim Smeaton, director of Yorker Packaging, says his firm has been moving rapidly to expand its offerings beyond closures to include other forms of packaging, with acquisition of the tube molding license an integral part of that strategy. He says, “The (injection molded) tubes offer significant cost advantages and their quality and performance is as good, or better, than tubes made from current extrusion technology.”

Zestron was founded in 1989 as a cosmetics and toiletries formulator but the company soon turned to plastics R&D to develop its own formulation suitable for injection molding of tubes. It eventually developed a material that is able to combine both the high melt flow index (MFI) necessary to fill a long, thin mold cavity, as well as the environmental stress crack resistance (ESCR) necessary for molded tubes to withstand stress crack failure once they are filled and sealed. In 2004 Zestron and injection moldmaker Otto Hofstetter AG (Uznach, Switzerland) formed an alliance to develop commercial tooling for Zestron tube production, and one year later Zestron formed an alliance with Waldorf Technik (Engen, Germany), with Waldorf offering inmold labeling systems for Zestron tubes. Stefan Zatti, sales and marketing manager at Hofstetter, says his firm is keeping sales figures for these mold confidential.

Ian Jacobs, managing director at Zestron, in emailed responses to MPW questions, says the Zestron polymer formulations can be classified as elastomeric polyolefins—essentially thermoplastic elastomers (TPEs) but with a much higher MFI. With a license from the firm, a molder receives “the know-how and material sourcing details that [he needs] to produce [his] own blends,” he explains, adding they also have the option to purchase pre-compounded materials from a number of suppliers, among them ExxonMobil.

A higher MFI lets processors mold tubes with high length/thickness ratios without resorting to high injection pressures. This in turn means that tool construction is simpler and less expensive than it would be when processing materials with a lower melt flow index, and also reduces the chances of core shift during injection. The higher MFI also enables lower processing temperatures, and thus lower cycle times. Zestron says its materials’ processing and heat stability window is similar to that of PE and PP. Finally, Zestron claims the cost of its materials is below that of conventional TPEs. Tubes can be molded on standard molding machinery, with no need for special handling, processing equipment, screw designs, drying or venting equipment.

Zestron issues licenses to processors for what it calls ‘coherent trading blocks’; for example, Yorker’s license is for North America, and Plasticum’s is for the European Union. Jacobs says Zestron will limit the number of licenses available in each ‘coherent trading block’ to avoid the commoditization of the technology. The Zestron tubes first received publicity during the Interpack show in Germany in 2005, with both ExxonMobil and Plasticum showcasing the tubes.

Zestron’ patent covers the technology required to test plastics to determine if they have a high MFI with good ESCR, and also the formulation technology necessary to make high MFI polymers with good ESCR suitable for injection molded tubes. However, Jacobs adds, a number of the key patent claims are not polymer-specific, so for all practical purposes the patent covers any polymers/formulations that are used to injection mold tubes longer than 5 cm.

What’s special about molded tubes?

Injection molded tubes offer some options not available with extruded tubes, such as textured and embossed surfaces, inmold labeling, and integral closures (where the closure and tube body are molded in a single shot). The materials used to mold the tubes also allow for hot or warm filling. The closure and the dispensing opening can be freely designed and integrated into the body, thus eliminating the need for a traditional add-on standard closure, and the molded tubes are said to be compatible with existing tube filling/sealing filling lines. And, of course, an extrusion line for tubes is suitable for extrusion of tubes, and nothing more, whereas an injection molder could always remove his tube mold and use his machine for other applications.

According to Plasticum, environmental stress cracking (ESCR), and oxygen and water vapor transmission rates of the molded tubes is similar to that of extruded polyethylene tubes, but at a lower investment compared to extrusion lines for tube processing, as well as using much less floor space. Tubes can be molded with elliptical, square, triangular or other shoulder shapes.

As luck would have it, one of Smeaton’s former colleagues heard about Zestron and couldn’t use its technology at his firm, but called Smeaton, knowing Yorker wanted to expand its packaging portfolio. Smeaton says that Yorker is “in the process of tooling up” for tube molding, with prototype molds already on-hand at the processor and discussions now ongoing with potential customers as well as with Hofstetter.

Smeaton says that, as with many product introductions, there are many questions about the molded tubes from potential customers, especially major brandowners in consumer products and personal care products. As these brand owners are especially interested in some of the “hard-to-do” tasks such as molding of tubes with integrated closures, his firm likely will start with molding of standard tubes for fillers and small-to-medium sized firms.