Sabel Plastechs Inc. doesn’t flinch at challenging development projects that stretch the limits of blow molding. Two years ago, the Ohio-based R&D consulting firm produced one of the largest stretch-blow molded PET parts from a 1-lb preform. Now, the company, headed by Plastics Hall of Fame inductee Sam Belcher, has developed one of the world’s smallest injection-blow molded PET containers.
The over-the-counter, single-dose vial is slated for U.S. commercialization in the first half of 2008. It has a 6-mm neck diameter and weighs just 1.3 g. Belcher shared many of the details exclusively with Plastics Technology. He conceded the difficulty in signing up technology partners for this project: “Most of them just thought it couldn’t be done.”
Tiny core rods
The primary challenge was construction of tiny core rods that would maintain concentricity within less than 0.002 in. Broadway Companies built the 0.211-in.-diam. rods, which have a slick diamond/PTFE coating that facilitates release from the parison.
After several product design iterations, moldmaker Abramo Div. of Big 3 Precision developed a patented pillow-like vial design that worked well for squeezing and dispensing the product. The 0.022-in.-thick bottles are molded of PET from DAK Americas. The monolayer construction provides sufficient oxygen barrier for the unit-dose vial, which holds 30 cc.
Belcher declined to disclose the maker of the all-electric injection-blow machine that was used in the development project. That multi-cavity machine has a special air-filtration system to allow clean-room use. Other special features include a 30-in. trigger bar, nickel-coated platens, and water manifolds for each platen.
The challenge of making such a small part also required some enhancements for shot-size control, Belcher notes. With a cycle time of 10 to 12 sec, Belcher expects up to 40 million clear or colored vials to be produced each year.
The snap-on cap, injection molded of LDPE, was also a challenge due to its size. The 0.1-g cap is unique because of a hollow stem extending from the cap at a 45º angle. The 1-in.-long stem has a 0.025 opening at the end that is ultrasonically sealed shut. The user twists off the end of the stem to dispense the product. The complete package is in final field testing.