Textiles can be combined with a varied selection of materials together. Special reinforcing fibres or hot melt that is applied as a coating to prevent fraying. The advantage over stitching can be to lower costs, full surface bonding, offer bonding between dissimilar substrates, lamination with foils and paper. With hot melt adhesives and coatings new improved products can be made. Hot melt adhesives are ofte used in the textile industry because of their ease of use and ability to meet unique industry needs and new developments.
What is a hot melt?
Hot melts are in basic thermoplastics, sold in a solid form, melted in specialized hot dispensing equipment such as Nordson or Robatech and applied hot to one of the glued surfaces. Normally the second surface is applied rapidly after application of the hotmelt, and a short compression time of less than a second is often sufficiënt to handle the product further in the process. Hot melts are known for its high initial tack (green strength) typically allowing quick processing in automated production areas. When cooled, hot melt adhesives are most comparable with a thermoplastic resin.
Open and set times
Hot melt formulations can be adjusted to accommodate specific assembly methods. Especially the open time and setting time are important parameters. Traditional thermoplastic hot melts do not cure. Thermoplastic hot melt adhesives are mostly based on EVA (ethyl vinyl acetate) or PO (Polyolefin). These hot melts can be formulated with a variety of properties using additional waxes, resins, anti oxidants, fire retardants, adhesion improveres and many other chemical or plastic additives. Hot melts are generally flexible, and depending on the formulation offer some resistance to water and chemicals,
Reactive hot melt adhesives
Most hot melts are known as thermoplastic EVA or PO, these are nonreactive. Non-reactive HMAs do not cure and only get in a solid state after cooling. Reactive hot melts, mostly Polyurethane based, will becom solid quickly through cooling and in addition a chemical curing process starts to form crosslinked bonds. Reactive Polyurethane hot melt adhesives are most used because it increases adhesion, resistance to chemicals and offer a more structural bond.
Hot melt adhesives keep developing
Hot melt formulations still develop rapidly, some may think there’s no future for ethyl vinyl acetate (EVA) based hot melts because there can be associated with low-strength and low resistance to water and chemicals. But new formulations can provide an improved strong and resilient bond. Even traditonal EVA hot melt adhesives are still widely used, for example in footwear applications, providing low-cost and flexibility. In the textile industry reactive polyurethane hot melts are implemented more often as this is a relatively new technique. PUR hot melt adhesives enable applications that has to withstand harsher life cycles. Hot melt PUR can also be used in breathable textiles. It is often used in protective clothing for emergency workers and harsh environments. For waterproof textiles and flame-retardant applications hot melt pur can offer unique solutions.