Hot melt adhesives (HMAs) are also termed as hot glues. The hot melt adhesive manufacturers supply HMAs in solid cylindrical sticks that have different diameters. Hot melt adhesives are designed in such a manner that they can be melted only with specially constructed electric hot glue guns. These guns use continuous duty heating elements that melt the plastic glue. Hot melt adhesives can be pushed through the gun manually by the user or through mechanical trigger mechanisms. When the glue gets squeezed out of the hot nozzle of the electric gun, it will be hot enough to blister or burn human skin. It is important that you do not touch it when it is hot and tacky. However, it usually solidifies in a few seconds or within a minute at the most.. You can apply these hot melt adhesives through spraying or dipping processes.
Hot melt adhesives manufacturers have been providing quality glue since its invention in 1894. The adhesive offers several advantages compared to other types of solvent-based adhesives. The curing or drying step is eliminated by the use of HMAs and other volatile organic compounds are also completely eliminated or drastically reduced. These products have long shelf lives and disposal of these adhesives do not need any special precautions. However, hot melt adhesives also have a few disadvantages. They are
? Thermal load of substrate of HMAs
? Limited use in substrates that are insensitive to higher temperatures
? Loss of bond strength of the adhesives at higher temperatures
? Complete melting of HMAs at higher temperatures
Glue
Glue is any adhesive that binds surfaces together when applied to material surfaces. Glue resists separation of the materials joined. Glue and adhesives are interchangeable words. The use of glues offer several advantages compared to other types of binding techniques like welding, screwing, bolting and sewing, etc. The main advantages of glue are
? Ability in binding completely different materials together
? Ability in distributing stress evenly and more efficiently across joints
? Improvement in aesthetic designs
? Higher flexibility in designs
? Cost effectiveness of easily mechanized processes
However, glue or adhesive has certain disadvantages also. They include lower stability at high temperatures, relative weakness when a smaller bonding surface area is used to bond large objects and greater difficultly in separation of objects during testing.
Glues are available naturally and many glue manufacturers produce them synthetically. Humans have been using glues for more than 200,000 years. However, the usage of glue grew rapidly only in the twentieth century after the brisk acceleration in the development of several types of synthetic glues. The innovation in the field of glue continues even now. Marketing research companies forecast an annual turnover of nearly $50 billion in 2019 for the global glue market. It is believed that the significant economic development in the BRIC countries, namely, Brazil, Russia, India and China will enhance the demand for glues strongly in future, bringing in more glue manufacturers into this field.
The various types of glues are drying glues like rubber cement and white glue, pressure sensitive adhesives or PSAs, contact glues like polychloropene or Neoprene and natural rubber and hot glues or thermoplastics that are non-reactive glues. Reactive glues include multi-part glues like polyester resins or polyurethane resins, polyols and acrylic polymers, one-part adhesives, natural glues and synthetic glues. Shelf life of some glues are quite limited and they do not work effectively if the shelf life gets exceeded.
