Reactive hot-melt adhesive

Reactive hot-melt adhesives Adhesives setting both by cooling of the melt and also by an ensuing chemical reaction. 

Polyurethane pressure-sensitive adhesives began appearing in the early 1970s [15]. By 1978 advanced two-component automotive structural adhesives (Goodyear) were commercially available. Waterborne polyurethane adhesives received additional attention during this period [16]. In 1984, Bostik developed reactive hot-melt adhesives [17]. Polyurethane adhesives are sold into an ever-widening array of markets and products, where they are known for their excellent adhesion, flexibility, low-temperature... 

CAPA Thermoplastic is a family of linear PCL-based polymers (MW 10,000-80,000 D). It is mainly used as reactive hot-melt adhesives, orthopaedic splints, fabric... 

The porous coat system (Nordson) allows the application of discrete, random, and open patterns of hot-melt adhesive to substrates such as films, papers, fabrics, and nonwovens. With the control coat system, hot melt adhesives are applied continuously or intermittently by air-controlled nozzles without contact to the substrate. This technique is used as well for reactive hot-melt adhesives such as moisture-curing polyurethane hot-melt adhesives. 

Polyurethane reactive hot melt adhesives (PURhma) consist of an isocyanate-terminated polyurethane or high molecular weight hydroxyl-terminated polyurethane which is solid at ambient temperature, but which melts at low temperature. They bond through the physical process of rapid solidification from the melt as well as through chemical reaction with ambient moisture. As a result of... 

This chapter attempts to classify the different adhesives based on a few key points concerning storage. Based on storage criterion, adhesives can be classified into four main groups solvent-based, water-based, hot-melt, and reactive adhesives. These groups mainly differ in their shelf lives and potential hazards. Nonetheless, within such classifications, overlaps are possible. For instance, there are reactive hot-melt adhesives and reactive solvent-based adhesives. 

OC-Methylstyrene. This compound is not a styrenic monomer in the strict sense. The methyl substitution on the side chain, rather than the aromatic ring, moderates its reactivity in polymerization. It is used as a specialty monomer in ABS resins, coatings, polyester resins, and hot-melt adhesives. As a copolymer in ABS and polystyrene, it increases the heat-distortion resistance of the product. In coatings and resins, it moderates reaction rates and improves clarity. Physical properties of a-methylstyrene [98-83-9] are shown in Table 12. 

The vast majority of reactive hot melts are moisture-curing urethane adhesives. Radiation (UV/EB) curable adhesives have been explored in the laboratory since the mid-1970s, but are only recently beginning to gain significant market penetration, particularly for PSA applications. The formulation and properties of these two classes of adhesives are discussed below. 

Pot life is several hours versus several days for conventional non-reactive hot melts. A good reactive urethane is one which exhibits a viscosity rise of less than 10%/h. The slow increase in viscosity with urethane adhesives is due to chain extension via the slow reaction of the active hydrogen of the urethane groups with... 

While the chemistry of radiation curable hot melt adhesives is the same as that used in liquid (syrup) adhesives and coatings discussed elsewhere in this volume, there is a fundamental difference between the objectives of reaction in the two types of systems. Syrups consist largely or entirely of reactive monomeric and/or oligomeric materials. Radiation is used to initiate the polymerization of virtually the entire mass. In contrast, hot melts generally contain polymers initially, and these polymers are capable of reaction via radiation to produce chain extension and... 

As mentioned at the outset, hot melt adhesive s primary advantage is process speed. Fleat resistance and substrate penetration are typically inferior to liquid adhesives (neat reactive systems, solvent, or water-based). Current research and development is therefore focused on maximizing the process advantages of hot melts and minimizing their performance deficiencies. Optimizing hot melt... 

One-component reactive adhesives have to be distinguished from the physically setting adhesives described in Chapter 5, which generally occur only in the form of one component, namely, the already finished polymer, for example, in the case of hot-melt adhesives, dispersion adhesives and solvent-based adhesives. They are called one-component adhesives. 

Reactive Polyurethane Hot-Melt Adhesives (Solvent-Free)... 

Adhesives with short cure time or setting speed (cyanoacrylate, reactive adhesives with short pot lives, hot-melt adhesives) are only suitable to a limited extent for more extensive bonded joints (dm2/m2), since the application time may exceed the cure time. The bondable surface depends on the... 

Fire protection In contrast to solvent-free reactive or hot-melt adhesives, the processing of solvent-containing adhesives requires expensive measures for fire and explosion protection as well as for the disposal of the solvents. 

A unified science of adhesion is still being developed. Adhesion can result from mechanical bonding between the adhesive and adherend and/or primary and/or secondary chemical forces. Contributions through chemical forces are often more important and illustrate why nonpolar polymeric materials such as polyethylene are difficult to bond, although polycyanoacrylates are excellent adhesives. Numerous types of adhesives are available such as solvent-based, latex, pressure-sensitive, reactive, and hot-melt adhesives. 

Polyurethane reactive hot melts are 100% solid, hot-melt thermoplastic prepolymers that moisture cure slowly after application. Conventional hot melts are known for their quick setting, excellent green strength, ease of application, and low toxicity. Their primary limitation is low heat resistance (at elevated temperatures, the adhesive will soften and flow) and poor adhesion to some substrates, due to insufficient wetting. The use of a polyurethane prepolymer with low levels of free isocyanates as a hot melt offers distinct... 

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