Skinned Sponge Rubbers

Often we have materials that we deal with on a daily basis that come with a surface finish. The materials that we most often encounter with notable surface finishes are sponges. These sponge materials typically come with a “skin” on both sides. The difference between the skin and polymer is typically immediately evident, from the sharp contrast between the rippling feeling of the individual cells against your hand, and the smooth or scaled surface of the sponge. Some of the polymer sponges we convert that may have skins include:

• Viton® Sponge
• Silicone Sponge*
• Neoprene® Sponge
• Nitrile Sponge

The skin can provide a number of things, but typically the skins provide a greater degree of protection against encroachment such as unwanted intrusion of medias such as water. A solid rubber skin may be required for a greater degree of protection against abrasion. Some of the sponges listed above have a closed cell configuration, so even if a medium were to get past the initial surface, the integrity would be somewhat maintained. As discussed previously, this is a result of the ‘closed’ cells keeping the intruding media away. However, open cell sponges may entail something drastically different in this regard. A puncture to the skinned finish would prove detrimental to the integrity of the material on that respective side, as a result of the cells being open. When die-cutting & waterjet cutting parts, it is inevitable that one side of the sponge will be exposed. As ASTM D1056 notes: an open-celled material typically has a greater necessity for a solid rubber finish, while sometimes a skinned finish is not required for a closed-cell material. One of the most amazing things about a skin finish on a material is that it tells you how it was manufactured. Materials that are cut out of buns do not have the smooth skin or fabric finish.

Typically the skins of sponges come in two formats:

• Smooth Skinned, as in Viton® Sponge
• Fabric Finish, as in Silicone Sponge

Another element that the fabric finish or smooth skin surface provides is an excellent contact surface for pressure-sensitive adhesives. If the PSA were to be adhered to the top of the cells it may prove difficult to gain a decent bond. The more surface area the PSA has to adhere to, typically the better the bond. With a smooth surface, the PSA has an opportunity to adhere consistently. For more information on sponge materials, or you have an application that you believe could utilize a sponge material, please contact sales@nedc.com.

*The silicone sponge fabric finished skin typically available with the material originates from the manufacturing process, either from the mould or a conveyor belt.