Adhesive bond strength requirements

Such adhesives are required to remain stable at elevated temperatures over periods of several hours (during normal daily operation of production equipment) and formulations that decompose under such conditions or in which pronounced changes of viscosity occur are not suitable. In order to achieve the bond strength required the adhesive must wet properly the substrates as soon as it is applied—so the temperature of the substrates can be important (if too cold they may absorb heat, cause cooling of the adhesive prematurely—before the surfaces are wetted—and impede bonding). 

Films. Both structural and nonstructural adhesives are commonly available in film form. Adhesives applied in the form of dry films offer a clean, hazard-free operation with minimum waste and excellent control of film thickness. However, the method is generally limited to parts with flat surfaces or simple curves. Optimum bond strength requires curing under heat and pressure, which may involve considerable equipment and floor space, particularly for large parts. Film material cost is high in comparison to liquids, but waste or material loss is the lowest of any application method. 

High cohesion and adhesion bond strength to corroded metals, high water resistance, low levels of interior stress, and glue line resistance to vibration stresses are basic requirements for polymer composites utilized for these operations. To achieve these goals, a polymer mixture featuring interpenetrating polymer networks has been used. The... 

Most structural film adhesives require a primer. Adhesive primers are usually spray-applied by air or airless spray systems. Roller or brush apphca-tion is sometimes used in small areas, or where spray equipment is not available. The primer coat must be air-dried and sometimes over-baked to remove solvents. The thickness of the prime coat will usually affect the adhesive bond strength and must be controlled and verified. This is usually accomplished by periodically certifying the primer applicator, and by monitoring primer thickness after drying. ... 

The carboxylic polyacrylates are effective as laminating adhesives for both flexible and rigid surfaces. The particular carboxylic acrylate used for a given laminating application is determined by the characteristics of the surfaces to be adhered, whether adhesive or cohesive bond failure is desired, the bond strength required of the adhesive, and many other factors. These may include stiffness, friability, extensibility, clarity, cold flow, moisture resistance, solvent or chemical resistance, heat and light insensitivity, radiation resistance, compatibility with resins and other polymeric materials or pigments, and vulcanizability. The carboxylic polyacrylates may be varied to meet the adhesive requirements of a specific application by ... 

All the other test requirements deal with the performance and reliability of the adhesive joint, starting with the cure schedule that very often conditions the quality of the attachment. The bond strength requirements have been established to ensure that the assembly can be subjected to the subsequent manufacturing steps... 

The objective of any surface treatment method is to enhance the adhesive bond strength and durability when it is exposed to environmental factors of service. There are, however, other considerations for the formation of an adequate adhesive bond. The basic requirements for a good adhesive bond are the following ... 

Theoretically, these intermolecular interactions could provide adhesion energy in the order of mJ/m. This should be sufficient to provide adhesion between the adhesive and the substrate. However, the energy of adhesion required in many applications is in the order of kJ/m. Therefore, the intermolecular forces across the interface are not enough to sustain a high stress under severe environmental conditions. It is generally accepted that chemisorption plays a significant role and thus, physisorption and chemisorption mechanisms of adhesion both account for bond strength. 

As with PSA, the phenolics are added primarily for increased cohesive strength and temperature resistance ([216], pp. 284-306). More phenolic is used in adhesives with higher strength requirements, e.g. for metal-metal bonding. Resins based on /j-/-butyl phenolics are most commonly selected ([216], pp. 284-306). They are usually present in the adhesive at 35-50 parts per 100 rubber (phr), with typical optima at 40-45 phr ([216], pp. 284-306). Significant deviation from this optimum may have drastic effects. 

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