The primary component of the center-seam adhesive used in sanitary napkins is Hot Melt Pressure-Sensitive Adhesive (HMPSA). At its core, this adhesive consists of a polymer-based system. While the specific composition varies depending on the brand and performance requirements, it typically comprises the following categories:
Ethylene-Vinyl Acetate Copolymer (EVA): The most common base material, offering excellent flexibility, thermal stability, and bonding strength, making it suitable for multi-layer lamination.
Styrene-Isoprene-Styrene Block Copolymer (SIS) or Styrene-Butadiene-Styrene (SBS): These provide high initial tack and elasticity, making them ideal for areas requiring flexible bonding.
Tackifying Resins:
Such as rosin resins, petroleum resins, or terpene resins; these are used to enhance the adhesive's bonding strength to materials-such as non-woven fabrics and PE films-thereby ensuring the center seam remains securely bonded.
Plasticizers
Added in small quantities-such as phthalates (within regulatory limits) or eco-friendly alternatives-to adjust the softness and flexibility of the colloid, thereby preventing hardening and cracking.
Antioxidants and Stabilizers
Prevent oxidative degradation of the colloid during high-temperature processing or prolonged storage, thereby enhancing the product's shelf life and operational stability.