Coated Lidding Speeds Processes, Cuts Costs
A number of new coatings are helping medical device packagers save time and money.
by Daphne Allen, Editor
It is no secret that packaging engineers are being encouraged to save money wherever they can. Many have been able to economize by downgauging their materials or switching to flexible packaging, which typically costs less than rigid packaging. But for those engineers who are charged with the task of packaging a heavy or delicate device like a pacemaker, making the change to a pouch or form-fill-seal package simply won't do.
There are other ways to reduce costs, fortunately. When a device requires the support of a rigid tray, a packaging engineer can save money on the lid. A number of new coatings for die-cut lids, the standard for topping off rigid trays, are helping medical device packagers save time and money by speeding up sterilization and sealing. Coating is also improving the peelability of paper, making this cost-effective material more suitable for medical lidding.
One significant way to lower costs is to shorten sterilization time. Ethylene oxide (EtO) sterilization can be a time-consuming process, mostly because engineers need to give the EtO gas ample time to penetrate and exit the porous element of the package. This aeration process can take as long as seven days. Lidding suppliers, however, are trying to shorten the cycle by offering highly porous materials that allow the gas to enter and exit faster than standard materials do.
The most widely used lidding stock in the United States, DuPont Tyvek, is porous by nature, but it must be coated with a heat-seal adhesive in order for it to seal to tray materials like PETG and polypropylene. The coating doesn't turn Tyvek into a nonporous material; instead, it leaves openings over some of its pores.
The coating process varies from supplier to supplier. According to Robert Hagood, marketing specialist for DuPont Tyvek, the most common method of coating Tyvek is by aqueous dispersion, which involves mixing adhesive particles into a water solution. The Tyvek is then coated with the formulation using an air knife, gravure roll, or screen. As the coating dries, gaps are formed between the adhesive particles, creating a porous coating on the surface of the lidding material.
To offer a more-porous lid, some suppliers have devised coating formulations that block fewer pores. For instance, Tolas Health Care Packaging (Feasterville, PA), unveiled its new TPT-021C coating for Tyvek in January at the Medical Design & Manufacturing (MD&M) West 99 Conference and Exposition in Anaheim, CA. The water-based coating is comparable in cost to conventional coatings and has a Gurley reading of 50–75 seconds, compared to 100–150 seconds for the company's previous coating for Tyvek. Uncoated Tyvek has a reading of 22 seconds, says Hagood.
Other suppliers are offering similar coatings for Tyvek. About two years ago Perfecseal (Philadelphia) introduced SBP2000, and, also at MD&M West 99, Rexam (Mundelein, IL) unveiled Integra Peel PTH045. These companies maintain that the coatings enable engineers to achieve faster EtO aeration cycles.
High porosity is only one way to decrease sterilization cycle time. "These days, medical device manufacturers are using more-rigorous sterilization cycles—higher humidity, higher vacuum—to get the sterilant in and out of the package faster," says John Merritt, Rexam's business director for coated products. The new adhesive coatings not only feature higher porosity, they are also formulated to resist the higher humidity and higher vacuum of these cycles.
The performance of the more-extreme adhesive is extremely important, explains Perfecseal's Tom Jeziorski, converting business unit leader. "Vacuum, pressure, and humidity all stress the seals of a tray-and-lid combination. The adhesive can start to release from the tray." He says that engineers can spot this particular defect—creeping—by looking for a half-moon shape in the seal area that works its way out from the inside of the package. According to Perfecseal, Rexam, and Tolas, the new-generation coatings resist such sterilizer creep.
Oliver Products Co.'s (Grand Rapids, MI) unique dot-coating process also helps engineers reduce EtO cycle times. According to the firm, it is the only one to coat Tyvek 1073B using a hot-melt gravure process called Dotcoat. The 10MP coating is a 100% solid hot-melt wax formulation that is unaffected by moisture or sterilizer creep.
The improved coatings also allow medical device packagers to hasten package sealing, which increases production speed and reduces costs. These coatings can accommodate a variety of temperatures, dwell times, and pressures during sealing. Carl Marotta, president of Tolas, explains that its TPT-021C coating has a wider sealing window than previous coatings. "The medical packaging industry uses a wide variety of heat sealers—shuttle sealers, in-line bar sealers, and rotary sealers. The industry needed a material that could perform consistently under such varying conditions," Marotta says.
Oliver Products Co.'s 10MP coating for Tyvek 1073B, which has been available for 10 years, also helps speed sealing. "Our adhesives seal at lower temperatures with lower pressure and less dwell time than comparable materials," says John Green, director of Oliver's medical marketing unit. "That means greater production output with less wear and tear on equipment."
Speeding up sterilization and package sealing can help companies get their products to market faster, maybe even before the competition does. And, according to some suppliers, the coatings could help save money in other ways.
Coated-paper lidding can be a cost-effective alternative to Tyvek, but, because it contains fibers that can become airborne when pulled away from a tray, paper has been unsuitable for medical environments like surgery. However, Rollprint Packaging Products (Addison, IL) is currently developing a new coating for paper that will help it compete with the fiber-free peel of Tyvek. "The coating has been designed to provide a cohesive split when the paper is peeled from the tray or film versus more-conventional coatings that pull out or release totally from the paper," explains Craig Livingston, Rollprint's vice president. "It takes the fiber-tearing problems out of paper lidding." Livingston expects the new paper lidding to be available in April.
Oliver's Green says that packaging engineers can also save money by choosing its dot-coated or zone-coated lidding made of Tyvek. "It is more economical because less adhesive is used during the coating," he explains.
If a company needs multiple-layer coatings, Livingston says it is more costeffective if the converter applies the coatings in a single pass. Rollprint, for instance, recently used its eight-station gravure coating system to apply multiple coatings to a lid meant for steam sterilization. The firm applied several coatings to Tyvek so that the adhesive would split apart and leave an even transfer pattern both on the Tyvek and on the tray.
CAN COATINGS BE ELIMINATED?
Engineers can reduce costs in a number of ways, but eliminating the coating on die-cut lids used with rigid trays isn't one of them.
"Rather than trying to eliminate coatings to minimize costs, engineers should reconsider their choice of packaging style," says Michael Scholla, business manager for DuPont Tyvek. "You can reduce costs by reevaluating the total packaging system, not just lidding material," he explains. If a product really doesn't need the strength of a tray-and-lid combination, consider a flexible package. When considering a flexible package, there is a new product available to meet quality, performance, and cost requirements. "Tyvek 2FS, introduced at MD&M West 99, was specifically designed for form-fill-seal applications," says Scholla. "This lower basis weight product, which features excellent printability, exceptional machinability, and suitability for both coated and uncoated systems, is a better alternative to paper for less-demanding applications."
While the pressure to reduce costs is strong, the packaging materials must still be appropriate for the task. The newest coatings promise to speed sterilization and production times—but are they right for your application? Experts recommend that engineers consider elements such as device type, sealing method, and packaging style when they evaluate lidding.
Both Oliver and Perfecseal report that demand for their more-porous lid stock keeps increasing. Interested engineers who want to cut costs would do well to review their packaging systems and processes to see whether they stand to benefit from faster sterilization and sealing cycles. If so, it's important to evaluate how the alternative package will be required to perform throughout its entire life cycle.