Liquid adhesives waterborne systems

Single-component epoxy adhesive formulations are the largest type of epoxy adhesives sold, with about 55 percent of the consumption, while two-component formulations account for another 44 percent of the volume. Radiation cure formulations represent the remainder of the market. Epoxy adhesives can also take many forms including solids, solvent-free liquids, solvent-borne systems, and waterborne systems. 

Formulation details are then presented in Chapters 11 through 14 for the various possible forms of epoxy adhesive systems room temperature and elevated-temperature curing liquids, pastes, and solids. The more or less unconventional forms of epoxy adhesives are also identified and discussed, since these are now achieving prominence in industry. These include uv and electron beam radiation curable, waterborne systems, and epoxy adhesives capable of curing via the indirect application of heat or energy. 

In this paper/ we shall describe the development of adhesives during the last several years and the trends for further advances. In general/ traditionally used / solvent-borne systems (4) will be gradually replaced by waterborne systems/ hot-meltS/ nonvolatile solid (or liquid) systems/ two-part adhesiveS/ radiation-curable adhesiveS/ and powder and reactive liquid systems (Table 1). 

Reactive liquid adhesives can consist of waterborne emulsion- or solvent-based adhesives. These are adhesive systems similar to those described above but here a cross-linking agent is added to the formulation. They most notably are acrylics and PUs where a cross-linking agent is added to the adhesive immediately before application to provide improved heat and chemical resistance. 

Some adhesives solidify simply by the evaporation of a carrier liquid (water or solvent). Others harden as a result of going from a molten liquid to a cooled solid. Still others solidify by means of a chemical reaction. Some adhesive systems may require several mechanisms to harden. For example, thermosetting waterborne adhesives require the water carrier to first evaporate and then chemical cross-linking occurs before a final bond is achieved. 

Designed for epoxy resin systems, Anquamine 401 and Ancamide 2424 (by Air Products) are a modified aliphatic curing agent at 70% solids in water for waterborne two-component epoxy coatings and a modified polyamide curing agent for liquid epoxy resins in two-component structural adhesives. 

Synthetic, petroleum-based adhesive products that are supposed to be green are based on either solventless liquid, waterborne, or 100% solid adhesive systems. The study adds that over the last few years, green adhesives have experienced a positive growth rate at the expense of solvent-based adhesive systems. 

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