Styrenic block copolymers (SBCs) are widely used for hot melt pressure sensitive adhesives (HMPSAs). Styrene-Isoprene-Styrene block copolymers (SISs) are preferably used in HMPSA, because of their high aggressive tack, good compatibility with various tackifiers, and good processability. Historically, SIS have been developed with various structures for adjusting PSA performance and its processability. In other applications, SBCs can also be used for elastic films such as diaper films. For elastic films, high modulus and high elasticity are required of SBCs. However these two requirements have a trade-off relationship. We have recently developed newly-designed SIS block copolymers with high modulus and high elasticity to introduce a new design factor. They have a unique morphology (micro segregated structure). Although they are high-styrene content type of SIS (30% or more), the morphology forms a spherical structure by Transmission Electron Microscope (TEM).This means that they are soft polymers with high styrene content. This unique morphology could have various advantages for HMPSA, such as good converting performance and broader temperature performance. It can promote elasticity that shows excellent recovery properties (low tension set). The soft, natural rubber-like film can be accepted in some fields. For the other applications, however, it has some problems because it is too soft. A polymer which shows higher modulus and high elasticity would be required. In order to raise modulus, it is thought that higher styrene content in SIS block copolymers is preferable. SBCs with higher styrene content do show high modulus (SIS-B and SIS-C). On the other hand, they also show higher tension set values. Higher styrene polymers give poorer elasticity and recovery properties. Source:http://www.pstc.org/files/public/TECH33Papers/2010HashimotoSadaharuap.pdf
SIS for Elastic Films Styrenic block copolymers (SBCs) are thermoplastic and elastomeric materials. SBCs are also used in film applications other than PSA applications. The advantages of Styrene-Isoprene-Styrene (SIS) are softness and low gel content. This implies that some excellent elastic films can be produced with SIS by the extrusion process. But SIS has poor durability under sunlight and UV light compared with other SBCs (SEBS, SEPS), which means that SIS is suitable for the films in disposable application fields such as diapers and napkins. A conventional SIS block copolymer which is widely applied to HMPSAs, SIS-A, can provide soft elastic films or sheets by extrusion.