2021-09-26
Hot melt adhesives are gaining in popularity due primarily to their lower processing costs and regulatory requirements. They also provide the fastest method of bonding, and hot melt equipment occupies a much smaller factor footprint than other methods of bonding. However, they must be carefully chosen. For good durability, their softening and melting point must be well above their service temperature. As with other adhesives, there are many different types of hot melt base polymers and hot melt formulations available, each with advantages and disadvantages.
In addition, there are many forms of hot melt adhesives (pellets, blocks, ropes, sticks) and application patterns (dots, spiral spray, random spray, continuous lines, etc.). The form of the adhesive is important. For example, hot melt films are ideal for lamination of wide webs and discontinuous coating is preferred for applications requiring soft hand. The form of the hot melt adhesive is also an important cost consideration. Hot melt adhesive powders are available in most chemical types and in varying particle size ranges. There are a number of processes by which hot melt adhesive powders can be applied. A common method in the textile industry is the paste dot process.
Chemical types of hot melt adhesive include polyolefins, polyamide, polyester, and polyurethane. These are described in Table. Their serviceability must be balanced with ease of application. There are copolymer variants of each type, allowing a wide range of application and performance properties. Although nonreactive hot melt adhesives have been available for many decades and are widely used in many applications, they have certain performance limitations, such as poor heat resistance, water or solvent permeation, and creep. These limitations generally prevent their use in many critical or structural bonding applications.
Properties of hot melt textile adhesives：
Adhesive | Special characteristics | Usual adherends | Price range |
Low density polyethylene (LDPE) | Low cost, inert | Used for fusible interlinings, automotive carpets | Low |
High density polyethylene (HDPE) | Low cost, inert, higher temperature resistance than LDPE | Used in carpets and for fusible interlining, shirt collars and cuffs | Low |
Ethylene vinyl acetate (EVA) | Good tack and adhesion, relatively low cost | Used in footwear and to bond leather and paper, good flexibility | Low |
Polyamide and copolymers | Wide range of properties and melting points, better heat resistance than polyethylene and EVA but more expensive, some reactive types available | Used in garments and applications where solvent resistance is required (e.g., dry cleaning) | Medium tohigh |
Polyester and copolymers | Wide range of properties, temperature resistance, good durability, high cost, some reactive types available | Automotive interior trim, specialty applications where heat and chemical resistance is important | High |
Polyurethane | Good adhesion to many substrates, good durability, good flexibility and toughness, expensive, reactive types are available | Used in automotive interior trim, laminates for protective clothing, shoe manufacture, reactive hot melt polyurethane used in structural applications | High |
Hot melt adhesives are used for bonding fusible interlinings, in seam and hem sealing, fabric lamination, and a variety of other textile applications. The melting point of hot melt adhesives must be above the minimum temperature that the application will see in service. This could provide a problem in that many textile substrates are heat sensitive, and conventional hot melt adhesives must be applied at high temperatures. To avoid this problem, formulators have developed hot melts with lower application temperature, sometimes known as ‘warm melts’. The most popular adhesive in this category is polyurethane thermoplastic and reactive polyurethane adhesives described below.
