Advancements in Solventless Technology for Silicone PSAs
The composition of silicone PSAs parallels that of many common organic PSAs. The two main components that dictate the performance of the silicone PSA are a high molecular weight, linear siloxane polymer and a highly condensed, silicate tackifying resin (MQ resin). Figure 1 shows the structure of a typical silicone polymer. Commercially available silicone PSAs use either polydimethylsiloxane (PDMS) or polydimethyldiphenylsiloxane (PDMDPS) polymers that contain silanol functionality at the polymer chain ends.
Comparison of these four adhesives on these figures illustrates an important point. The commercial dimethyl PSA is known in the marketplace to be an all-purpose adhesive, while the commercial diphenyl PSA is reputed to have excellent tack properties for a silicone. When the obsolete solventless was developed, it too had excellent tack and adhesion properties. The focus of making the current prototype was to de-emphasize the need for the best tack and adhesion performance but rather improve the high temperature performance. Although the tack and peel adhesion performance is slightly lower than the commercial diphenyl and that of the obsolete solventless, the performance is well within the acceptable range for a silicone PSA. The biggest step change for the prototype solventless exists in the high temperature area. Figure 7 shows the high temperature shear performance (PSTC-7) for each PSA.