Blowmolding: Processor’s development raises the bar for heat-set bottles

Developments in blowmolded bottles for heat-set bottles have been a hot sector of late. Processor Liquid Container (West Chicago, IL) has weighed in with what it calls its ThermaSet line. Improved clarity and less shrinkage are two of the benefits promised.

The line of stock and custom jars, available with wide mouths or standard openings, is said by the processor to be the first to offer sustained hot-fill performance at 205°F (96°C), so that the bottles can see use for filling of viscous food items (apple and pasta sauces, jams and jellies, and tomato-based products) which tend to fill at higher temperatures. Hot filling generally is done at temperatures of 90-95°C for 15-30 seconds. If more time is needed, PET tends to soften, creating problems for fillers. Liquid Container says its ThermaSet bottles handle the heat for longer, easing package fillers’ concerns.

The proprietary process developed by Liquid Container increases PET’s glass transition point, which is about 70°C (exact Tg is affected by a material’s molecular weight, thermal history, and more). The end result is sustained thermal stability at 205ºF and shrinkage of less than 1%, claims the processor. Typical PET container shrinkage following the thermal cycle is between 1.5-4%. Shrinkage can cause seals to break and thus lead to spoilage of products or reduction of a product’s shelf life. It also impacts labeling of packages.

According to Mark Schneider, senior director of the processor’s PET technology group, the company’s development is process-based and not material-specific. In answer to questions from MPW, he wrote, “We use standard bottle-grade PET resins, which can be obtained from all of the major PET suppliers. There are no resin additives or enhancers used in our process to increase thermal performance characteristics. Our proprietary process, which changes the thermal characteristics PET, involves all aspects of molding the finished article. This involves, but is not exclusive to, molding the preform, preform design, reheating, conditioning and stretch blowing.”
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The benefits continue: “Depending on container design, we are experiencing between 8-19% improvement in oxygen barrier performance,” added Schneider. He credits this improvement to an improved crystalline structure of the material being processed through the company’s proprietary process. “Since we do not add any material additives in the bottle-grade resins that we use, the material is much clearer than current market containers,” he says.

The patent-pending structural design of the packages includes a base designed to absorb pressure and vacuum, and thus minimize distortion during cooling. The bottles now are offered in five different stock designs: 18-, 24-, 32-oz round, and 45- and 48-oz “grip” jars.  —Matt Defosse