Hot Melt Adhesives (HMAs) have revolutionized the footwear industry, enabling the creation of innovative shoe designs. These adhesives, including types like SBC, EVA, APO-based HMAs, Polyesters, Polyamides, and PUR, are crucial for bonding specific shoe components.
The history of shoe manufacturing is intertwined with technological advancements. Since the 1800s, shoe lasting machines have streamlined the process of shaping the upper part of a shoe over a last. A significant breakthrough came with Jan Matzeliger’s invention of the automatic shoe lasting machine, which significantly increased production efficiency. In the mid-1990s, HMAs were widely adopted in the sports footwear industry. These adhesives are applied in three primary stages of the shoemaking process: parts preparation, upper stitching, and upper-sole assembly. During the lasting process, HMAs replace traditional nails to secure the upper in its desired shape. Modern lasting machines, designed for specific areas like the toe, side, or heel, require HMAs that set quickly and can withstand high temperatures.
Two primary types of HMAs dominate the lasting process: Polyester and Polyamide. Polyester HMAs, characterized by their stiffness and rapid setting time, are well-suited for toe and heel lasting where flexibility is less critical. They offer high tensile strength and perform well at elevated temperatures. Polyamide HMAs, on the other hand, are flexible and ideal for side and seat lasting, as well as mounting shanks and heels. They exhibit excellent bonding properties, especially with materials like thick leather and PVC. However some polyamides, like nylon 66, can exhibit brittleness at low temperatures. This is due to a phenomenon called the glass transition temperature (Tg), where the polymer transitions from a flexible state to a rigid, brittle state. The specific behavior depends on various factors, including the type of polyamide, its molecular structure, and any additives or modifications.
The future of HMA in shoe manufacturing is marked by a strong emphasis on sustainability and innovation. The industry is actively exploring biodegradable and compostable HMA options to minimize environmental impact. Incorporating recycled materials into HMA formulations reduces waste and conserves resources. Additionally, reducing volatile organic compounds (VOCs) in HMA formulations improves air quality within manufacturing facilities and mitigates harmful emissions.