Physically setting adhesives

The chances of adhesive technology could be exploited more fully if advances to counter these risk factors could be made. The reactive and physically setting adhesives will be used mainly in the field of construction, with natural adhesives used more often in the areas of consumer goods, foodstuffs, and packaging. Water-based adhesives will continue to replace solvent-based products, a process supported in particular by the food processing and packaging industries. 

Chemically curing Physically setting Adhesives with special setting characteristics... 

A typical characteristic of physically setting adhesives is the evaporation of solvents or heatup to a molten state. Application is then in liquid form (solvent adhesives, contact adhesives, dispersion adhesives, hotmelt adhesives) or from the solid phase (adhesive films, laminate adhesives). In all of these types there is a liquid state during processing from which emissions are always a possibility due to the volatility of the basic polymer or other adhesive components. 

Adhesives Curing without Chemical Reaction (Physically Setting Adhesives)... 

Thus, adhesives are products that - according to their chemical composition and the given physical state - are applied to the adherends where they develop an adhesive layer either by chemical reaction or by physical setting. 

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. 

In their processible mixture, these one-component products, also belonging to physically setting adhesives, consist of two components PVC (polyvinyl chloride-) particles and plasticizers (Section 9.2.9). The solid PVC particles are disperged in the high-viscosity plasticizer. The adhesive layer formation occurs by heating (120-180 °C), when the thermoplastic PVC swells and is thus able to absorb the plasticizer (no chemical reaction ). This process is called a sol-gel process. The formerly two-phase system (sol) is turned into a single-phase system (gel) by the inclusion of the plasticizer. 

The development of the adhesive layer follows the principle of physical setting (Section 2.2.2) on simultaneous evaporation or absorption of the water by the (porous) adherends. 

The information is limited to the most important materials, metals, plastics, (thermoplastics, thermoset materials, foams), ceramics, glass and their possible combinations. For papers, cardboards, wood, rubber polymers, usually physically setting systems (solvent-based, dispersion, hot-melt adhesives) are utilized. In these cases, the adhesive selection with regard to the manufacturing conditions and demands is of less problematic nature. 

Adhesive films Consisting of two-component reactive adhesives applied to a nonadhesive substrate for transport and storage purposes that is removed prior to processing. Curing occurs via chemical reaction under application of heat and pressure. Adhesive films are also commercially available as physically setting films, see heat-sealing adhesive. 

Hot-melt Adhesive applied as melt at elevated temperature, physically setting when cooled, see hot-melt adhesive. 

Physically setting adhesives Adhesives already existing in the form of polymers transferred into a liquid form by solvents or water, respectively, by melting, forming an adhesive layer after evaporation or cooling (e.g., solvent-based, dispersion and hot-melt adhesives). 

While alkyl cyanoacrylate-based adhesives are used globally in a large variety of domestic and commercial settings, their physical and toxicological properties must be considered. Alkyl cyanoacrylate polymerization is a very exothermic reaction, so care must be taken to prevent the contamination of large quantities with any materials, which might initiate a very rapid, runaway reaction. Also, alkyl cyanoacrylate monomers and the polymers which they form, will burn, and users should avoid their use near sparks or open flames. 

PVAc is another important type of adhesive, especially in furniture manufacturing and for carpentry. They form the bond line in a physical process by losing their water content to the two wooden adherends. PVAc adhesives are ready to use, have short setting time and give flexible and invisible joints. They are easy to clean and show long storage life. Limitations are their thermoplasticity and the creep behavior. 

The number of basic polymeric resin chemistries available for use as adhesives is large and each has their own set of application and performance properties. The ability to further modify these with other chemical or physical additives means that adhesives can be tailored for particular application or performance requirements quite readily. 

A set of physical characteristics for the product under consideration is presented in Table 7. SLC1015 s adhesion result is presented by Figure 7. 

---