Лако-красочные материалы — производство

Opening remarks Surface pretreatment involves: (a) cleaning (b) removal of weak surface layers (c) re-cleaning. The exact procedures required depend upon the nature of the adherends, and an indication of their inherent suitability for bonding is shown in Table 3.3. (The ranking order might be anticipated from the list of material surface energies collected in […]

Once interfacial contact between the adhesive and adherend has been established under favourable thermodynamic conditions, adhesive curing enables stress to be transmitted. There is some controversy regarding the basic nature of the intrinsic forces then acting across interfaces which prevent them from separating under an applied load. The four main theories of adhesion which have […]

Contact angles between solids and liquids of known surface tension can provide an indirect measurement of solid surface free energy, allowing a comparison between different surfaces. Just as liquids have surface tensions or surface energy, so do solid surfaces by virtue of the fact that they are surfaces. Surface tension of solids goes unnoticed because […]

Clearly the adhesive must wet the adherend, implying the common- sense idea of a thin film of liquid spreading uniformly without breaking into droplets on the surface (Fig. 3.3). The water break — free test is the simplest approach to a qualitative visual assessment; the thermodynamic approach to wetting allows quantitative study. Surface tension is […]

The adhesive has to spread over the adherend surface, penetrating its irregularities, displacing air and any contaminants present. The ideal conditions for this to be realised are that: (1) the surface free energy of the adherend should be higher than that of the liquid adhesive (2) the liquid adhesive should exhibit a zero or near […]

Preliminaries The basic requirements for good adhesion are very simple, viz: (1) intimate contact between adhesive and substrate (2) absence of weak layers or contamination at the interface. When two materials are bonded the resultant composite has several constituents and interfaces, as depicted for example in Fig. 3.2. Being liquid, adhesives flow over and into […]

3.1 Introduction The successful performance of many every-day products, and many common materials and construction techniques, is dependent upon adequate adhesion between two or more constituents. Most engin­eers, however, have only the haziest of ideas about the whole concept of adhesion. For to know ‘how’ to prepare substrate surfaces for bonding does not necessarily require […]

Proper design of bonded joints requires an appreciation of the properties of the different materials to be joined as well as quantitative data on the properties of structural adhesives. In joint design, full account must be taken of the poor resistance of adhesives to peel and to cleavage forces; shear strength itself is unlikely to […]

(3) During cure Rate of strength development. The effect of temperature on curing rate will vary for different adhesives. In general, low temperatures increase the curing period considerably and many epoxy resin formulations stop curing altogether below 5 °С. A rule of thumb often quoted is that the curing period doubles for every 10 °С […]

Viscosity — the shear stress, t, required to displace an element of fluid as shown in Fig. 2.5 is directly proportional to the shear rate D = dvldy where v = velocity. The constant of proportionality is known as the coefficient of viscosity, t|, and fully defines a Newtonian fluid (see Fig. 2.6). However most […]