Natural rubber is a polyisoprene produced by Hevea trees that consists of approximately 99% cis-1,4 repeating units. Natural rubber latex (NRL) has been used in cold-seal adhesive formulations for over 100 years. The term “cold seal” describes an adhesive that bonds to itself under pressure at ambient temperature without adhering to other materials. Cold-seal adhesives (CSAs) are ideal for bonding heat-sensitive substrates, such as plastic film, since no heat is required for bond activation. They are also capable of bonding many additional substrates, including film, foam, paper, foil and linerboard.
CSAs made with NRL are commonly used in the manufacture of medical devices and food packaging products due to NRL’s excellent flexibility, high initial tack, and good tack retention properties. However, NRL has several notable disadvantages that are causing manufacturers to look at NRL-free formulations.