Hot-Melt Adhesives

Abstract

Hot-melt adhesives facilitate fast production processes because the adhesives set simply by cooling. Formulations contain polymers to provide strength and hot tack (resistance to separation while adhesive is hot), and tackifiers and/or oils to dilute the polymer entanglement network, adjust the glass-transition temperature, lower the viscosity, and improve wet-out (molecular contact of the adhesive with the substrate over the entire bonding area). Some adhesives also contain waxes to speed setting, lower viscosity, and improve heat resistance. Obtaining adequate strength and heat resistance from nonreactive hot melts requires that some component of the hot melt separate out into a dispersed but interconnected hard-phase network upon cooling. The hard phases are commonly either glassy styrene domains (for adhesives based on styrenic block copolymers) or organic crystallites (for adhesives based on waxes, olefinic copolymers, or ethylene copolymers). This article will describe first the material properties relevant to the processing and performance of hot-melt adhesives, then the chemistry and function of the specific raw materials used in hot melts, and will conclude with illustrative application examples and corresponding formulations.

Lignin and lignin derivatives as components in biobased hot melt adhesives

“…HMAs typically consist of a cohesive polymer blended at least with a tackifier (typically resin) and optionally with additional components, such as waxes and diluents (plasticizers) . When applied upon a surface or into an interface, they give rise to a solid structure that is load bearing at temperatures at which the treated surface or interface is being used (also called the operational temperature or service temperature ).…”

“…In HMAs, the most common cohesive polymers are ethylene copolymers, such as ethylene vinyl acetate (EVA), polyolefin, and styrene block polymers . Lactic acid based polymers, starch‐based or cellulose‐based polymers, protein‐based polymers, and biobased polyamides have been studied as biobased alternatives for cohesive polymers .…”

“…Their function is to improve the wetting of the substrate by lowering the viscosity of the base polymer. Tackifiers are usually low‐molecular‐weight, amorphous substances with a glass‐transition temperature ( T g ) above room temperature . Tackifiers should have good interactions between the cohesive polymer and substrate, for example, via hydrogen bonds.…”

“…Tackifiers should have good interactions between the cohesive polymer and substrate, for example, via hydrogen bonds. Finally, waxes are low‐molecular substances that reduce the viscosity . Earlier reports have described HMAs composed of starch‐ or cellulose‐based polymers together with transglycosylated products or hemicellulose derivatives as tackifiers and a plasticizer…”

Preparation of high molecular weight and elastic copolyester by reactive extrusion with diisocyanate compound for laser printing process

“…Hot melt adhesive (HMA) has been used since the 1950s as a solid phase material at room temperature, which can be applied to the surface of a substrate in the molten state without a solvent [1] . Compared to conventional solvent-base adhesives, HMAs exhibit a range of excellent thermal and physical properties [1 -4] .…”