Rotomolded Antimicrobial Products - Challenges & Opportunities

written by Dr. Burke Nelson, Director, Materials Engineering

What is the manufacturing process for rotomolding?

Rotational Molding (or Rotomolding) is a plastics manufacturing process that has been used for decades to produce large, hollow plastics parts such as tanks and garbage cans. Polymer powder is placed inside a cold mold which is then rotated while heated in an oven. As the mold approaches the melting temperature of the polymer, the material coats the interior walls of the mold to form the part. The mold is removed from the oven and fan cooled to freeze the polymer, then the part is removed. 

Rotomolding has a relatively low initial capital cost compared to injection molding machines, and the molds are less expensive as well. However, the process has long cycle times due to the size of the parts and relatively inefficient convective heating and cooling.

Advances in rotomolding technology have greatly enhanced the complexity of the parts that can be produced. Materials can be layered in a mold to produce multilayer walls, and hollow walls can be filled with insulating or structural foams to produce complex parts like an insulated cooler in a single stage.

Meanwhile, robots can be used to precisely finish molded items for improved quality and repeatability. In addition to inexpensive toys or garbage cans, rotomolding is now used to produce high end products such as advanced coolers or pontoon boats. Both of these items can benefit from the power of antimicrobial technology that inhibits the growth of harmful bacteria, mold, and mildew, especially considering their frequent exposure to moisture.

Rotomolding Antimicrobial Products: Improved Process and Pricing

Using antimicrobial additives in rotomolded parts has been challenging for several reasons. The sheer size and relatively low retail price of rotomolded parts leads to costing issues, while proper incorporation of an antimicrobial can be a challenge in a rotomolding process. Microban® has been working on both issues to allow easy integration of antimicrobials into rotomolded product design.

Microban has developed formulations for rotomolded products that can withstand the heat stresses of rotomolding and lower the cost per treated pound of material. Combined with the advances in rotomolding that allow producers to direct material to certain areas rather than an entire volume, the costs of bringing an antimicrobial benefit to rotomolded parts can be made affordable. 

Rubbermaid coolers are made through rotomolding process with the added benefit of Microban antimicrobial technology that is incorporated during the manufacturing process. It is not surprising that coolers often get put away with a little leftover liquid floating around inside, creating a perfect environment for mold and mildew to grow. Microban has partnered with Rubbermaid to create a customized antimicrobial solution for Rubbermaid coolers that works effectively against a broad spectrum of bacteria, mold, and mildew. This custom solution is easily applied during the rotomolding manufacturing process of the coolers.

The images below show an untreated cooler on the left that has grown mold and has an extremely strong and unpleasant odor. The Microban treated cooler on the right still has the liquid present, but there is no mold, mildew or pungent odors to be seen or smelled.

Microban Antimicrobial Rubbermaid Cooler Antifungal Mold Resistant Case Study 4

Another example of rotomolded antimicrobial products are water storage tanks. The purpose of water storage tanks are often to store water for future use. It is not hard to imagine that microbes can easily grow and multiply on the surface of water tanks, causing product degradation and creating a negative impact on the quality of the water. Microban antimicrobial technology can be built in into plastic water storage tanks at the point of manufacture.

The benefits of Microban antimicrobial protection for water storage tanks include:

  • Effective against harmful bacteria.
  • Resistant to stains & odors. Water tanks will remain fresher for longer.
  • Extended functional lifetime of water tanks.
  • Contain a food-contact approved Microban® technology that will not wash-off, leach out or negatively affect the environment.
  • Contain a technology that has undergone extensive independent laboratory testing and has a long history of safe use.

Microban can also supply antimicrobials as a pellet masterbatch for precompounding operations or as a powder that can be premixed with raw PE powder onsite. Microban is working directly with raw material supplier Rotopolymers to deliver a treated product as cost effectively as possible.

Microban has hundreds of customers with thousands of products on the market today. We are expanding our rotomolding portfolio with the same unsurpassed quality and support with which we have approached all of our endeavors. Contact us today to take advantage of the marketing power and technical know-how of Microban to move your product to the next level.