How Flexible Foam Is Made
Posted by Nancy Grossbart
When a gas is captured inside another material or resin, you get foam. Because the resin is filled with gas, it makes it expand like a balloon filled with air. This creates many beneficial characteristics such as being lightweight and, sometimes, soft with cushioning capacity. Foams that are made from a plastic resin, start as a solid and then are turned into foam by creating a "gas phase" with a foaming (blowing) agent.
The foaming process begins by creating thousands and thousands of gas bubbles in the melted plastic resin. These thousands of bubbles cause the cubic volume of the base plastic resin to expand as the bubbles increase in size and number. The resulting foam can be open cell foam or closed cell foam.
The next step is for the plastic resin to begin the process of hardening, fixing the shape and size of the bubbles. Foams may be soft and flexible (flexible foam) or hard and rigid, depending on the base resin that is used to make the foam.
When a foam shell wall forms from a rigid material like most metals, plastics, or ceramics, it acts like a tiny ping-pong ball providing lighter weight material. In other words, it has a higher volume-to-weight relationship (lower density) than the same material without a foam shell. This lower density is an important property that plays a key role in many industrial applications such as floatation and insulation, which currently are substantial markets. However, when a shell wall forms from flexible material like rubber or elastomer, it acts like party balloons and provides extra cushioning or softness to the material as well as more volume-to-weight ratio. It can be used in the athletic and furniture industries. Other industries also benefited by the usage of flexible polymeric foams are automotive interiors, seals and gaskets, footwear, medical aid devices and packaging.
You can foam almost anything, if you can find an application that needs it: metal foam, polymeric foam, paper foam, wood foam, and ceramic foam have been developed and used in a variety of products for unique advantages to enrich our lives or to explore the mysterious universe.
In terms of practical perspective, foams can be viewed in three categories; properties, technologies and ingredients.
In general, foam properties can be defined by dimensions, density, softness, cell size, number of cells per cubic volume, shape, and other properties such as surface appearance.
As for technology, it is basically classified as three types of manufacturing: soluble foaming, reactive foaming and melt/solution quenching.
When producing flexible molded foams you will find huge benefits in using some ingredients like polyolefin elastomers (POE). They are known for their flexible characteristics with benefits such as:
- High Durability and Abrasion/Scratch Resistant:
- Chemical Resistance
- High Weathering and UV Stability
Flexible foam can be created in sheet form or by an injection foam molding process. The main difference is that the injection foam molding process produces a "finished part" at the end of the foaming process. The foam molding process that produces a sheet still needs a secondary "fabricating" process to turn it into a usable part.
Learn more about "Understanding Injection Molded Flexible Foam". Download our 8-page white paper.
