Rubber-Based Hot-Melt Pressure-Sensitive Adhesives-2

Mixing equipment for SIS polymers has also been shown in both laboratory and production testing to be limited to lower temperature (< 325°F) and higher shear mixers (dual arm and planetary), as polymer degradation was found using other types of mixers. Indication of formulation problems included viscosity drops of up to 20%, lower shear adhesion failure temperature (SAFT) and noticeable polymer degradation by GPC analysis. The SIBS polymer system has been shown to fare much better, allowing for the use of a wider variety  of process equipment. This has been noted through improved color stability, as well as thermal stability of similarly formulated SIS and SIBS blends.

In practical application, formulations based on SIBS technology do not experience the same type of degradation as seen in SIS, including viscosity decreases or increases in viscosity and gel formation such as with styrene butadiene styrene (SBS) systems in field. These formulations have shown improvements in wet-out of substrates and lower overall energy requirements, as they can be applied at lower temperatures than older, higher viscosity formulas. This, in turn, lowers the maintenance costs on the application equipment and operators can successfully run on a wider variety of application equipment and substrates.

Historically, hot-melt PSAs have also had a difficult time meeting the service range requirements of many tape and label applications. Even with newer radial polymer SIS technologies and or formulations that contain combinations of SIS, SBS, and/or hydrogenated polymers such as SEBS and SIBS, this window of service has only expanded to partially meet the demands of certain industries. On one side, higher heat resistance has been achieved in several different ways as formulators have found newer sources of paraffinic oils and higher softening point tackifying resins, along with polymers previously discussed, which have shown higher shear adhesion failure temperatures (SAFT) but suffer on lower temperature requirements due to a loss of elasticity. Formulations using liquid polymers or tackifying resins and/or high melt index polymers reduce Tg, but lower the heat resistance of the compounded product. It is for this reason that many solvent- and water-based applications still cannot be replaced with hot-melt PSA.

In conclusion, while there are many barriers to entry in the PSA marketplace, rubber-based hot melts show great promise for a wide range of applications in both tape and label segments.