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.
Posted by Nancy Grossbart
When my company (MDI Products) first began to work with product designers who wanted to create a foam product and had lots of plastic molding experience, it was very difficult to get them to "think differently" about how to design a product that took advantage of our
injection molded foam process. There are only some things about both processes that are similar. Both plasticize raw materials in a hot barrel. Both inject in the materials into a closed mold. Pretty much the similarity stops there.
Understanding the fundamentals is key to designing a great part. To really comprehend what is happening, you need to first know that injection molded foam is actually a foam manufacturing process which manufactures foam in the shape of your part.
The next area to understand that, unlike the single mold plastic process, the machines used in the injection molded foam process are multi-station presses, which utilize multi-molds.
Again, unlike plastic injection, the mold cavities are designed smaller than the final part size. The parts expand rather than shrink. The amount of expansion is dependant on the material softness you require.
The material remains in the heated mold during the cross-linking or cooking process. The cooking time is dependent on the thickness of the part. The mold opens very quickly when the cooking is complete. The part expands and explosively self ejects from the mold cavity. The part is removed from the mold station and set to cool.
Learn more about self-ejection, draft, corners, edges, and undercuts later.
Posted by Nancy Grossbart
Polyolefin foam is a great material for kid's products. It works well in lots of applications from padding for sporting goods to sandals (Crocs) and now, products for kids.
To begin with, it's closed-cell. That means it's waterproof and won't absorb bodily fluids. It also means it resists mold and mildew because the bacteria has no place to reside.
It's so light that it floats and can be used for bath or pool toys and has no adverse chemicals so when kids put the toy in their mouths, there is no need to worry.
Polyolefin foam has a high tear and tensile strength so it can't easily rip and won't crack or peel. This means it will not only last a long time but, when kids put it in their mouths, it will pass the bite test.
The chemistry of polyolefin foam makes it resistant to most chemicals. This allows you to clean and disinfect it with any household cleaner keeping it safe from any surface bacteria.
Parts can be also designed with lots of features and benefits including molded-in logos and graphics. And can be made in extremely bright, attractive to kids, colors.
If you're wondering if it will pass the new CPSIA standards, it will!
MDI Products' offering of formulas known as PolyCellTM are phthalate free, PVC free, AZO dye free, with insignificant metal content. In addition to all the other reasons why it is great for kid's products, you can also be confident of its safety.
I'd love to get your feedback on what other specifications might be important for kid's products.
Download 8-page white paper on
"Understanding Flexible Foam".