Лако-красочные материалы — производство

Acrylic adhesives cure by addition polymerization reactions. These chain reactions are initiated by the formation of free radicals that result in the adhesive curing by way of a very rapid polymer chain growth. This cure chemistry is significantly more rapid than a typical cure curve (i. e., condensation type) found in epoxy and urethane adhesives. A comparison of the cure profile of condensation (epoxy and urethane) versus addition

(acrylic) polymerization is shown in Fig. 1. The free radical reaction or addition polymer­ization used in acrylic adhesives offers the user certain advantages over other types of adhesives, again, namely epoxies and urethanes.

As can be seen from the cure curve only little polymerization is noticeable in the early stage of the reaction after the adhesive is mixed. This allows the user to position and re-position parts for longer periods of time after the adhesive is mixed. The time to re­position parts is relatively longer for acrylics when considered as a percentage of the overall cure time than is typically possible with other types of adhesives. This can be a significant advantage for some manufacturing methods.

Once cure is initiated with acrylics, it tends to proceed at an increasingly accelerated pace until full cure is reached. This rapid achievement of final properties is in contrast to urethanes and epoxies which tend to more gradually build properties to full cure. The rapid setting (cure) feature of acrylics allows the user to more clearly determine when parts are securely bonded (i. e. the adhesive is fully cured) and finished goods are suitable for shipment. The fact that this rapid setting is possible at room temperature is also a unique feature of acrylic adhesives.

Due to the availability of a large number of formulating tools and choice of poly­merization initiators, it has also been possible for formulators to develop systems that have a whole spectrum of cure rates. This allows manufacturing and design engineers to custom-fit specifically designed adhesives to a variety of different production schedules.