Self-hot-melt joining of polymers to lacquered metal surfaces

Abstract Metal cans represent the dominant form of packaging in the food and beverage markets. Organic coatings i.e., lacquers, are applied to the inside of the cans to prevent undesirable interactions. The most common lacquer is based upon epoxy–phenolic materials. Advances in packaging technology have directed a requirement for the non-adhesive attachment of thermoplastic compounds, lids and fixtures such as gas capsules “Widgets” to the coatings of metal cans. This represents a new challenge and requires adaptation of the joining techniques currently available. This paper examines the joining of thermoplastic materials to epoxy–phenolic-lacquer-coated tin-free steel. A range of thermoplastics was characterised by their mechanical, thermal and surface energetic properties. A particular joining technique was then developed involving the simultaneous heating and pressing of the coated metal against the thermoplastic component. The process parameters of temperature, pressure and time were evaluated in terms of the properties of the bond. The mechanical behaviour of different types of peel joint was investigated, together with the influence of the moisture content of the thermoplastics.