Foaming Agents in High Pressure Molding…

A past student of mine recently posed this question regarding an aspect of injection molding which is not commonly discussed…

I was wondering if you help me locate some references on Processing HDPE and PP with 1% chemical foaming agent? All the information I find focuses on Structural Foam which is a low pressure process. We primarily use high pressure injection molding, using the the chemical foaming agent for weight reduction and cosmetics.
My Response
Since the banning of foaming agents containing CFC’s, the use of chemical blowing agents has obtained an inappropriate stigma in the marketplace. Believe it or not, their use is not as rare as it may seem. Many injection molders will use a small amount of blowing agents to eliminate sinks, lower material costs, and even enlarge the part to help meet dimensional requirements.
In your case, there are many places to find information… when searching online, use terms such as:
or get more specific:
There are also some good articles available online:
Since structural foam molders use the largest volume of additives, much of the literature is focused on their needs… but you will find that many of these resources will also provide great high-pressure molding information… click for an example of this from Bergen.
You may have to register to see some of the materials from the Suppliers, but this is typically free.
Keep in mind, your material providers can be great resources if you ask the correct questions. Some additive providers provide agents specifically formulated for your type of application.
Additional Thoughts
Basically, when you are conducting a high pressure molding process with blowing or foaming agents, you would melt and inject the material in a manner similar to a traditional process, but apply many of the packing and cooling strategies of structural foam. Ultimately, the more blowing agent you add… the more the polymer will behave like a structural foam after it is injected. 

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