Requirements for good adhesive

An apparently universal truth is that intimate contact between adhesive and adherend is a necessary (but not sufficient) requirement for good adhesion. 

Low surface tension causes excellent wetting of substrate which is required for good adhesion of the coating to the surface. Good adhesion promotes good corrosion resistance, impact resistance, and chip resistance. 

The basic requirements for good adhesion are very simple, viz ... 

In the quest for the ideal adhesive system to suit an application needs, it is essential to understand the effect of the silicone properties on the mechanisms of Silicone adhesion. The primary requirement for good adhesion is the creation of an intimate interface through Wetting and spreading of the silicone onto the substrate. The low surface tension and viscosity range of silicones satisfy this necessary condition. Therefore, the mechanical mechanism of adhesion is operative and plays a key role in adhesion of silicones to many different substrates such as leather, textile fabrics, porous metals like anodized aluminium, porous plastic and composite materials, and specialty papers like glassine, super calendered kraft and clay-coated papers. 

Besides water vapor and gas diffusion, other requirements for good edge sealants are water resistance, uv resistance, heat/cold resistance (—40 to 80°C), adhesion to glass and metal, and good characteristics for appHcation. Polysulfide sealants have maintained an exceUent record in use since the 1950s. Development of new polysulfides and sealant formulations continues in order to meet market needs of the 1990s. 

Two general varieties of aromatic nylons are often employed. A less stiff variety is employed when some flexibility is important, whereas a stiffer variety is used for applications where greater strength is required. While good adhesion with the resin is often desired, poor adhesion is sometimes an advantage such as in the construction of body armor where delamination is a useful mode for absorbing an impact. 

The above results are certainly unexpected in light of an earlier report on adhesion of polyimide films [47]. Here it was shown that adhesion between two polyimide films could only be achieved when polyimide chains from the one surface extended approximately 300 A into the other surface. Because of the extended nature of the polyimide chains the potential for significant entanglements near the respective interfaces is low, thus requiring much deeper penetration by the PI to provide the necessary frictional forces for good adhesion. In the... 

The formation of the interfacial layer is very strongly influenced by the coating process. In general, for good adhesion between film and substrate, an energy input is necessary to produce the required activation energies to allow important physical and chemical processes to occur. 

It is most important to develop good working practices for adhesive bonding applications so that physical contact with these substances is avoided as far as possible. A clean working environment and careful, methodical workmanship that are required for successful adhesive bonding go a long way towards meeting this objective. 

Taking poly(methyl methacrylate) as an example. Me = 10,013 g/mol (Table 10.2), Me should be equal or greater than 10,013 g/mol. Experiments by Zosel and Ley (27) on cross-linked latex films show that values of Me > Me are required for good mechanical properties, the oversimplified model above providing the minimum net size. Aspects of adhesion are discussed further in Section 12.8. 

The main application of poly(vinyl butyral) is as interlayers in safety glass laminates. In this application, a pure (colourless, light-stable) product with high hydroxy content (for good adhesion) is required. Such material is preferably prepared from poly(vinyl alcohol) rather than directly from poly(vinyl acetate). In a typical process, completely hydrolyzed poly(vinyl alcohol) is suspended in ethanol and then butyraldehyde and a small quantity of sulphuric acid (catalyst) are added. The mixture is heated at 80°C for 6 hours. Water is then added to the product with rapid agitation and the poly(vinyl butyral) is precipitated as granules, which are washed with alkali and dried. 

Saret 633 clearly increases adhesion to synthetic fibres like Nylon and polyesters. Thus, with Saret 633, it may not be necessary to RFL treat fibres and fabric for good adhesion. This could simplify applications where rubber reinforcement is required. 

In 1966, Dahlquist(i7) defined the requirement for a good pressure-sensitive adhesive as an adhesive with one-second shear creep compliance greater than J(t) = 1 x 10cm /dyn (Figure 17). Recently, we characterized the viscoelastic properties of many conmiercial tapes and label adhesives and found that the glass transition temperature and modulus (G ) at the application temperature are the most important requirements for good performances (Figures 18, 43, and 52). The requirements for tape and label adhesives are somewhat different for... 

So far we have discussed the dynamic mechanical properties of elastomers and tackifying resins separately. We have also examined the dynamic mechanical properties of the commercial tape and label adhesives and defined their requirements for good pressure-sensitive adhesives. We will explain how to obtain PSA with the specific requirements in T, G (co), and G"(w) values from the nontacky elastomer and glassy tackifying resin. First, the simple two-component formulations will be examined for various elastomeric systems. 

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