Giving preforms a frosted-glass look

Packaging premium liquor in a frosted-glass bottle imparts an upscale, arctic image, as the makers of some brands of vodka have found. But when Bacardi-Martini Canada wanted to give the same look to its Russian Prince premium vodka, it began with injection molded PET preforms, and the effect was far from successful. Bringing the frosty look up to quality standards became a job for preform molder MassiPlast (Mississauga, ON) and colorant supplier Clariant Masterbatches (Easton, MD).

Unlike the U.S., a large percentage of premium spirit products in Canada are packaged in plastic. “This is what our customers prefer,” says David Schroeder, vp of production for Bacardi-Martini Canada. “Unlike the U.S. market, the convenience of plastic outweighs the upscale appeal of glass, but the frosted-glass effect is still important to our marketing efforts.” The brand is currently ranked fourth in Canada with a 10 percent annual growth rate, and the PET containers range in size from 200 ml to l.75l.

Shanta Oudit, operations manager for MassiPlast, explains why the frosted-look preform presents such a molding challenge. “Any translucent or transparent colors not mixed or distributed properly will be barely noticed in the preform. However, these negligible defects are greatly magnified when the preform is blown into a bottle.”

Bacardi had been having problems with swirls and color imperfections in the finished product. Together with Clariant, MassiPlast had to make sure that the colorant was dispersed correctly and the final appearance in the blown bottle consistent. The solution that eliminated the original streaking problem involved adjusting the additive masterbatch package, moving to a micropellet to aid distribution, and setting the processing parameters to ensure consistency of the frosted-glass look.

Based on experience, MassiPlast believed the smaller pellet size would help matters. “It increases the surface area of the colorant that you’re mixing, and makes it melt faster,” Oudit says. “This, in turn, enhances distribution, which also aids in processing and consistency of the color.”

According to Yvon Garneau, sales manager for Clariant-Canada, the frosted-glass additive required some trial-and-error work. “Initially, we tried to match the look of frosted glass using pigments with additives, but the effect wasn’t up to par,” he says. “We do a lot of work in transparent and translucent colors, but this colorant is on the verge of translucent with some opacity.”

After a few iterations, Clariant matched the look using a highly loaded single-pigment concentrate predispersed on a PET carrier. “This type of concentrate can reduce letdown ratios significantly to help processors save money, providing the equipment for dispersing the color is accurate,” says Garneau. “For example, even with the pearl content, letdown ratios for this project are 4 percent.” Pellet sizes can range from 55 mm (micropellet) to 125 mm (for swirl effects). The Bacardi preform uses a standard 80-mm micropellet, and represents the first major commercialization of the frosted-glass effect in North America for Clariant-Canada.

MassiPlast uses Eastman 9921W PET, molding the preforms on a 280-ton MagPlastics injection-compression machine and introducing colorant at the feed throat. The eight-cavity tool required modifications to run the color successfully, and technicians adjusted the processing parameters quite a bit, according to Oudit. While MassiPlast does not wish to publicize the details of these modifications, Oudit explains that they were able to design the preform for subsequent blowmolding because they knew what to expect—the former parent company (MagPlastics, Switzerland) used to manufacture blowmolding machines.

“MassiPlast is now part of Massilly North America, and we are no longer associated with MagPlastics,” she says, “but we still use their preform machines.” The 20,000-sq-ft plant also houses several Husky presses, and employs 25. “We make custom preforms and prototypes for anyone wanting to switch from glass to PET in the liquor and beverage markets, and we serve customers in the cosmetics and bottled water markets as well.” Smaller volume, specialized preforms (from 50,000 to 100,000) are the main focus.