July 30, 2015
When it comes to choosing an adhesive material to bond foam blocks for monolithic tools and molds, our General Plastics' sales representatives frequently receive questions from customers concerning which type of adhesive would best fit their polyurethane foam application. Manufacturers offer a wide variety of adhesive options, and choosing the right type can be daunting. There are several important questions to ask to help determine what type of adhesive might best fit your application.
Understanding how your foam will be used is step one. Your specific design and application will drive your particular adhesive need for bonding and sealing. In selecting which adhesive to use, keep in mind the environment the bonded assembly will have to withstand, and make sure your sealant material is compatible with the mold release and surface coating materials you plan to use when completing the tool.
There are several other questions to ask to determine which adhesive will best suit your application. The top five are:
1. What is the service temperature required?
2. How will you secure the blocks while curing?
3. What working time will you need?
4. How large are the surface areas to be bonded?
5. Have you accounted for strength and flexibility and how physical properties relate to the type of adhesive you choose?
Polyurethane, epoxy, and cyanoacrylate adhesives will work for most applications. Polyurethane adhesives are fast curing, chemically reactive formulations that may be one or two part systems. They provide strong resistance to impact and can have exceptional low temperature strength. Epoxy adhesives can be used to join most materials, and consist of an epoxy resin plus a hardener, allowing for great versatility in formulation. Because of this, epoxies are the de facto choice for most boding applications. Cyanoacrylate adhesives cure through reaction with moisture held on the surface to be bonded, and are ideal for small plastic parts and rubber.
Tips for Successful Adhesion
When it comes time for actual adhesion, surfaces to be bonded must be clean, dust-free, and flat. Apply the adhesive to both surfaces so they are completely coated, adding more in the middle, as squeeze-out will occur.
Above all, it is important to understand the properties that you need for your application, and to be sure to follow the manufacturer's safety instructions when using any bonding, filling, or finishing product.
General Plastics' foam adheres to most adhesives, as the nature of our foams lends itself to great bonding. Our high-density LAST-A-FOAM® polyurethane materials are tough, grain-free and non-abrasive. The FR-4500 tooling board in particular is a high-density foam formulation that can be securely bonded with a variety of adhesive systems. General Plastics' knowledgeable customer service team and product experts are ready and available to answer questions you may have to help you attain the best possible results using our products.