InFORMED containers

Once the domain of simply-conceived, short-run products, the market for rigid thermoformed packaging is now being driven by many of the technical and production features common to injection molding. Volumes for a given package are higher, frequently in the millions, and designs are increasingly complex. The similarities with injection molding, however, end there.

“Injection molding margins are generally measured in pennies, but packaging margins are measured in tenths of pennies,” says Chris Singleton, director of sales at Ontario Tool and Die, a manufacturer of tooling for plastic thermoforming and other processes.

Singleton reports that the company’s thermoforming customers are asking for faster turnarounds on tooling orders. He says the average delivery time on an order for a complete tool (mounted molds and dies) has dropped to four to five weeks, from six or more weeks only a few years ago, and anticipates requests for even shorter delivery times in the near future.

In effect, today’s packaging thermoformers often need to operate with the speed and efficiency of high-volume blow molding or film houses; as well as have the design expertise and full-service capabilities of a custom injection molder. Success in this market depends on a thorough understanding of the customer’s needs and the role tooling, materials and machinery can play in meeting them.

NEW APPLICATIONS PUSHING THE FLOOR, TOOLING

Universal Plastics specializes in medium- to thin-gauge thermoformed packaging for the medical, food, safety and consumer markets. The Chicopee, MA-based company has eight vacuum, cut-sheet molding machines supplied by AAA Plastics Processing Equipment Co., as well as one fully-automated blister thermoforming machine from Sencorp.

The company has recently received an order for 1.6 million clear PVC votive candle display cartons from Yankee Candle, according to vice-president Michael Peters. The holders, which roughly resemble an egg carton, are produced on the blister thermoforming machine in a two-cavity mold at a rate of 15 cycles a minute. The operation consumes one 350 lb. roll of PVC approximately every two hours. The cartons are molded with a living hinge and lid specified to have a snap fit. The requirement, which demands trial and error tooling adjustments, usually means holding a much tighter tolerance than the +/- 0.030 in. typical for a given clamshell dimension. Each holder contains 18 individual cavities for holding candles. Nominal wall thickness of the item is 0.010 in.

“This was a challenge to design, because the lid has to close tight, but be easy to open,” says Peters. He reports that molded parts are die-cut with heated steel-rule dies, which produces the carton’s smooth, clean edges, as required by the customer.

Peters says Universal has seen a growth in demand for industrial in-plant safety packaging, such as holders, cases for accessories and other items. The company is molding a safety eyewash holder, that holds one or two bottles, in two different sizes, a 14 in. x 14 in. holder, and a 20 in. x 20 in. holder, for a total of four different parts. The holders, which are designed to be attached to a wall, are molded from green, high-impact polystyrene with a nominal wall thickness of 0.025 in.

Singleton says there is a growing trend to incorporate more complex shapes and cuts into rigid consumer and retail packaging. For example, a flashlight package may have an area cut out so that a customer can touch the elastomer or rubber grip. Such designs usually require matched metal tooling for an in-line cutting process or a secondary operation.

Ontario Die is one of the largest manufacturers of forged steel dies in North America. In plastics molding, forged dies are primarily used to make packaging such as cake trays and clamshells from clear PS or PET, run on roll-fed vacuum thermoforming machines. Singleton says the heat-treated edge of a forged die is ideal for cutting PET and other tough materials. Forged dies are an ideal replacement for steel rule dies on high volume applications.

“Typically, with a steel rule die, you have to re-rule after every run,” notes Singleton. “A forged die is more accurate and can be resharpened, which makes it more cost-effective in the long run.”

MATERIALS MAKE THE PACKAGE

“The highest growth for rigid packaging in North America is in case-ready packaging for fresh meat and deli items,” says Jeffery Best, business market manager for Eastman Chemical Company. For 2001-2002, this market is estimated to be in the vicinity of 12 billion trays, up from approximately 10 billion trays in 1999-2000. Best says the growth is being driven by increasingly sophisticated grocery retailers who are more aware of how packaging can increase store efficiency and sales.

Buying meat in case-ready packaging relieves the retailer from the burden of packaging meat at the store. It can also improve meat-case management and display aesthetics. As the meat remains in the package longer, packaging for case-ready meat requires enhanced oxygen barrier properties. VersaTray plastic trays made from Eastman’s crystalline PET have better oxygen barrier resistance in comparison to the traditional expanded polystyrene (EPS) tray used for meat packaging. Eastman has also found that VersaTray plastic has equivalent or better oxygen barrier properties compared to EPS or PP trays with a barrier film. VersaTray packages also provide consumers with the additional convenience of serving as a dual ovenable cooking dish, in which the meat or food can be heated or cooked without removing, says Best.

VersaTray PET packages can withstand temperatures ranging from -40 F to 400 F. These properties, along with consumer preference for more convenience, are allowing PET to challenge polystyrene and polypropylene as the material of choice for meat and deli packaging used in groceries, delis and take-out restaurants, according to Best. Dierbergs Markets, a grocery chain based in St. Louis, MO, increased its sales 35 percent over the same period last year by selling meal-sized portions of pasta and other foods in the containers.

Bruce Ligo, NOVA Chemicals marketing manager, food packaging, reports continued high growth for oriented polystyrene (OPS) used to make deli clamshells, cake trays and other packages. Ligo says that while it is difficult to put an accurate figure on the growth, nonetheless, “when I go into a restaurant or grocery store I see a lot of food going out in clear OPS containers.”

Ligo says package designers and processors continue to prefer OPS because it is easy and fast to process, which makes it more cost effective than PET. OPS also makes a well-functioning hinge on clamshells and trays. Ligo reports that Nova has launched an R&D effort to improve the temperature performance capabilities of OPS, an initiative that would appear to be aimed at the case-ready meat and deli portion of the market.

Best says that for case-ready food and many other applications, material performance is more important than a resin price.

“Once performance is addressed, from a business standpoint there are really two big issues for packaging producers. One is price volatility of resin and the ability to pass along cost. The other is environmental and the ability to recycle the package. PET is the most recycled plastic on a worldwide basis.”