Polypropylene modifier helps park toy garage under Christmas trees

The Pack Away Garage packs a lot of fun into a small package—witness its top-selling status for toymaker Halsall Toys Europe. It crammed in so many fun features, though, that initial designs failed to pass a key drop test, threatening to keep the toy off store shelves in advance of the holiday selling season.

Injection molded from 10 different tools by Ever Force Toys & Electronics Ltd. (Dongguan, China), the Pack Away Garage is a three-level structure that includes a helipad, gas station, car wash, ramps, and a car lift between levels, as well as diecast cars. Molded from an impact copolymer polypropylene (PP), the entire toy, which folds up into a compact tire-shaped carrying case, weighs 6.94 lb (3.15 kg) and measures 16.5 by 14.8 by 7.52 inches (41.91 by 37.59 by 19.10 cm).

Ever Force eventually turned to resin distributor Kin Sang Chemical Ltd. (Shenzhen, China) and polymer manufacturer ExxonMobil Chemical (Houston, TX) to solve its drop-test dilemma, preferring to avoid any costly and time-consuming tool changes, if possible.

Drop tested, 
ASTM approved
Under the test in question, ASTM F963, the folded case was dropped five times from six different directions at a height of 36 inches (91.44 cm), with the impact copolymer PP failing on the surface of the tire case and in the internal support ribs. Jonathan Stoneley, Halsall’s buying controller, feared the holiday retail window might be closing, given that the lead time from design to launch of a new toy is typically six to eight months, and the clock was ticking. “It was critical that the toy would be ready for commercial launch in the early second half of the year, during the run up to Christmas,” Stoneley said.

As Ever Force weighed its options to fix the toy, it began with the assumption that it could adjust the production process; assess the material being used; and, lastly, modify the molds. Gloria Leung, Ever Force executive and operations officer, called mold changes “a last resort” due to cost and the fact that it would push back the commercial launch date. “We had to find an innovative solution that
would be successful within the other two options,” Leung says.

Elastomer enables 
passing part
After adjustments to the production process failed to help the toy garage pass the drop test, Kin Sang Chemical and ExxonMobil Chemical proposed altering the formula of the impact copolymer by adding ExxonMobil Chemical’s Vistamaxx propylene-based elastomer. Vistamaxx can affect flexibility within a part, increasing impact strength down to -4°F (-20°C) while improving adhesion. In particular, dry blending 10%-30% of Vistamaxx into PP at the molding machine had improved impact strength in past cases without mold modification or an increase in part thickness.

For three weeks, Ever Force tested different concentrations of Vistamaxx propylene-based elastomer within the impact copolymer before settling on a 15% Vistamaxx loading, with which it comfortably passed the drop test. The original 100% impact copolymer part could only pass the drop test from a height of 20 inches, far less than the 36 inches required.

Perhaps most importantly from a cost perspective, the addition of Vistamaxx allowed the part to pass muster without any costly or time-consuming tool modifications. Stonely estimated that any changes to the mold would have pushed back commercialization by at least four months. “This innovative solution meant we did not miss the peak sales period leading up to Christmas,” Stonely says.
Launched in the summer of 2009, the Pack Away Garage sold 80,000 units in Europe during the run up to Christmas that year, making it Halsall’s third-best seller. In 2010, Halsall expects the garage to become its best seller, estimating that sales will reach 120,000 units in Europe and Australia. Going forward, Ever Force notes that it now considers Vistamaxx an important compound modifier to be used in future projects, with two more toys having already been initiated this year. —Tony Deligio