Answer: Epoxy adhesives would likely be the best candidates. Both the chromated or anodized surfaces should provide a good bonding surface for these adhesives. The slower-curing varieties might best suit this particular application, as they tend to be somewhat more flexible and impact-resistant than the so-called “5-minute” varieties. These adhesives should also hold up well within the temperature extremes required.

Epoxies themselves may often be hard and brittle, but that is in part dependent upon the curing agent. Hybrid epoxies can offer the flexibility, but we caution against using any nylon epoxy and certain types of elastomeric epoxies because they might absorb water and would not be suitable for exterior applications such as yours. Epoxies are currently successfully used to bond aluminum to aluminum in honeycomb aircraft wings.

-BOB SMITH AND ROGER LOHMAN

Question: I work for a flexible-packaging manufacturing company in South Africa that is interested in finding out about adhesives that are used to laminate two or more layers of different or the same material to each other. We are trying to decrease the amount of curing time that is required to give us the correct bond strength to satisfy our customers’ stringent quality control requirements.

Answer: Flexible lamination is commonly executed via one of four types of technologies: water-based, solvent-based, two-part systems and 100%-solids reactive laminating adhesives. Your particular application will depend upon the precise nature of the substrates you are considering, as well as the coating, drying and laminating equipment you have at your disposal.

Water-based laminating adhesives do require significant oven capacity to remove the water at any reasonable product speeds. Solvent-based adhesives require less oven capacity, but need to be able to deal with the solvents via recovery or incineration. The newer, 100%-solids systems do not require drying ovens, but generally take several days to cure. The two-part systems can be controlled as to how fast the cure will take place and do not require any drying ovens.

-BOB SMITH AND ROGER LOHMAN

Question: I require an adhesive for sticking paper to tins.

Answer: I can only assume you mean applying labels to metal containers. There are a number of adhesives and processes available to accomplish this. Basically, there are two types of labels that are commonly in use. One makes use of a pressure sensitive adhesive that is pre-applied to the label stock (usually in rolls), and the label is then applied to the individual container. The other type of label is typically referred to as a “patch label,” and as the name implies, is supplied pre-cut and stacked. It can be applied either by the pre-application of a pressure sensitive adhesive, or more commonly by using a water-based adhesive to apply the label to the container when required. This latter process usually involves highly automated application equipment and typically is employed for very high-volume applications. For lower-volume applications, the more labor-intensive method of a pre-applied pressure sensitive label is often the most economical approach, despite the significantly higher cost of the label itself.

-BOB SMITH AND ROGER LOHMAN