Soft foam in Injection molding.

Hello,

Foams can be produced in this way by using a physical blowing agent such as expancel

Expancel is composed of hollow microcellular spheres containing a low melting point liquid. When heat is applied to the compound containing the spheres the shells soften and the liquid expands, causing controlled, homogenous foaming of the compound. A shut off nozzle is required on the injection moulding machine to prevent pre-expansion in the barrel. With this technique very low densities can be achieved, but with higher loadings of Expancel the compound can become stiffer/harder due to the hardness of the shells. This is a very reliable and controllable method of foaming, but you have to be careful not to produce too much shear otherwise the spheres can be broken. Additionally, a low melt strength material is preferable since this will encourage better expansion of the spheres.

Alternatively there is the mucell process

This involves injecting super-critical fluids into the melt which expand once the pressure is released, within the tool. This method requires machine modifications and a license from trexel, and I don`t believe it is easy to get good results with TPE's.

Chemical blowing agents such as azodicarbonamides could be used, but I don`t think these would be very easy to control in an injection moulding process. These are well established for extrusion processes, though.

Hope this has been some help.

Regards,