Latent-reactive adhesive films: High-quality bond when the heat is on
Latent-reactive adhesive films that are non-tacky at room temperatures but achieve a tacky state at temperatures in excess of 50° C. They bring clear benefits in applications as varied as decorative films or forgery-proof documents.
Latent-reactive adhesives
Latently reactive adhesive films are composed of a semi-crystalline polyurethane polymer (Dispercoll® U) into which surface-deactivated solid isocyanate particles are integrated. These adhesive films are non-tacky and store well at room temperatures because the polyurethane polymer does not start melting until it is heated to temperatures above 45° C. The molten polymer then flows onto the substrate surface and wets it. After cooling, the polymer crystallizes and soon achieves a high cohesive strength. Unlike purely thermoplastic polyurethane films, latently reactive adhesive films have built-in solid isocyanate particles as crosslinking agents. These particles dissolve in the polymer on melting, react with the OH or NH groups in the polymer chain and convert the low-molecular polymer into high-molecular elastomer. This crosslinking process significantly increases the adhesive bond strength and in particular the heat resistance of the bond.
Properties and advantages of latent-reactive films
Non-tacky to around 45° C.
Glass transition temperature of up to –50° C. ensures polymer does not become brittle, even at low temperatures
Non-sensitive to moisture in the air and stable in storage at up to 35° C.
Crosslinking triggered by melting the polymer; short heat application at relatively low temperatures produces a high-quality bond.
By selecting a suitable Dispercoll® U dispersion the adhesive layer or film can be customized to process and substrate conditions
Greater flexibility in the choice of substrates
Quality of adhesive film controllable at point of bonding
Easier storage
Application process options
This latent-reactive adhesive technology can be applied in two ways:
Positioning the latent reactive film between the two substrates to be bonded
Laminating the latent-reactive adhesive film onto one of the substrates with a roll laminator. This process obviously necessitates a roll laminator. In case of application as an adhesive film on PVC foam film, account must be taken of the limited storage time of around two months
Latent-reactive films are marketed by Epurex GmbH in Bomlitz, Germany, an associated company of Bayer MaterialScience. Epurex GmbH can be contacted here.
