Typically, acrylate pressure-sensitive adhesives can control their adhesion by adjusting the type and amount of monomers. However, to expand their application performance, such as increasing the surface wettability of the adhesive and enhancing the adhesion to low surface energy substrates, it is necessary to add tackifying resins to the base resin to improve the interfacial bonding between the adhesive and the adherend.
Due to the strong polarity of acrylic copolymers, they have poor compatibility with most tackifying resins. Therefore, studying the compatibility between tackifying resins and base resins is crucial. With the addition of tackifying resins, the pressure-sensitive adhesive will reach a maximum adhesion value. However, if the amount of tackifying resin is further increased, the adhesion will drop sharply. In fact, once the amount of tackifying resin exceeds the critical concentration, phase separation occurs, damaging the structure of the pressure-sensitive adhesive. Thus, poor compatibility of the resins can negatively impact the performance of the adhesive.
Examining compatibility through Tg, if the blend is a homogeneous system, it will exhibit a single Tg; otherwise, it will show their individual Tg values. For instance, in the case of pressure-sensitive adhesives blended with styrene resin, the system is fully compatible when the styrene content is below 30%, but incompatible above 30%. For terpene resin-based pressure-sensitive adhesives, the system is miscible at 50% resin content, but two Tg points appear at 70% concentration.
Therefore, selecting tackifying resins compatible with the base resin and controlling the amount of tackifying resin added are key factors in enhancing the aforementioned adhesion.
