Vistamaxx PBE Improves Impact Strength And Hinge Flexibility Of Food Container Lids

Ningbo Lisi Houseware Co., Ltd. (Lisi), a leading manufacturer of food containers based in Zhejiang Province, China, has turned to Vistamaxx™ propylene-based elastomer (PBE) from ExxonMobil Chemical to improve the impact strength of its food containers made from random copolymer polypropylene (RCP). Vistamaxx PBE also provides better lid hinge flexibility and maintains clarity.

World demand for food containers is forecast to increase 3.8 percent per annum to $115 billion in 2013, according to Freedonia Group: World Food Containers (Industry forecasts for 2013 & 2018). The largest gains are expected in plastic containers with China forecast to account for 25 percent of the growth rate between 2008 and 2013, according to China Food Safety News, No. 2178, 2012. Three key trends are driving food container development: better durability, clarity and food contact safety.

RCP strength an issue
Lisi used RCP to manufacture food containers because it offers good clarity and is odorless. The company discovered, however, that RCP lacked the impact strength, especially at low temperatures, and flexibility required by many of its customers. Also, when RCP is used for the container lid hinge, stress whitening could be an issue.

As the company used the industry standard 0.3-0.6mm thickness for the hinge, it tested strengthening additives to modify the RCP. While impact strength could be increased, clarity could not be maintained and the hinge continued to display stress whitening.

New possibilities with Vistamaxx PBE
Lisi turned to Hersbit Chemical, a distributor of ExxonMobil Chemical’s polymers. Hersbit Chemical recommended using Vistamaxx PBE.  Tests, undertaken by or on behalf of ExxonMobil Chemical, indicated that when RCP is dry blended with 10 percent Vistamaxx 3000 PBE or Vistamaxx 6202 PBE, the impact strength increases within a range from room temperature down to minus 20°C (minus 4°F). The improvement in impact strength is more pronounced at lower temperatures.

The material also becomes more flexible when RCP is dry blended with Vistamaxx™ 3000 propylene-based elastomer (PBE) or Vistamaxx 6202 PBE. Flexibility increases with the dosage of Vistamaxx PBE.

The clarity, light transmittance and haze of the original material are virtually the same when RCP is dry blended with 30 percent Vistamaxx 3000 PBE or Vistamaxx 6202 PBE.

enhanced products
Freezing tests, undertaken by Lisi, indicate that modifying RCP with a small percentage of Vistamaxx PBE improves impact strength of the container lid, even at temperatures between 0°C (32°F) and minus 20°C (minus 4°F).

Meanwhile, Lisi’s cornering fatigue tests show that Vistamaxx PBE delivers improved hinge flexibility which contributes to the durability of the lid.

Of all the additives tested by Lisi, only Vistamaxx PBE increased lid hinge impact strength during the freezing test, maintained clarity and reduced stress whitening.

Easy to use, Vistamaxx PBE can be dry blended with the RCP before injection molding. This is done on existing equipment without additional investment in equipment or technology.

Vistamaxx PBE can also enhance the elasticity of RCP used in the body of the food container. This can improve the seal structure of the container. Because the body is softer, the harder lid can seal without the use of seal rings. This design simplification can result in a 10 percent manufacturing cost reduction.

Vistamaxx PBE is also compliant with many international food contact regulations, such as US FDA, EU and JOSPHA, and is on the Chinese Positive List for resins permitted in food packaging products. This saves time, as no pre-qualification of the material is required and speeds up time to market.

better performance, increased sales
Using Vistamaxx PBE as an RCP modifier has enabled Lisi to offer food container lids with improved durability while remaining transparent. This has increased the company’s competitiveness in the food container industry and, as a result, Lisi’s food containers have enjoyed a significant growth in sales.

“Due to the balance of physical properties delivered by Vistamaxx PBE, the quality and performance of our food container lids have improved significantly. We will use Vistamaxx PBE in other applications,” said Mr. Qinghua Zeng, R&D Manager, Ningbo Lisi Houseware Co., Ltd.