Adhesive primer

The scale of the microscopic surface roughness is important to assure good mechanical interlocking and good durability. Although all roughness serves to increase the effective surface area of the adherend and therefore to increase the number of primary and secondary bonds with the adhesive/primer, surfaces with features on the order of tens of nanometers exhibit superior performance to those with features on the order of microns [9,14], Several factors contribute to this difference in performance. The larger-scale features are fewer in number... 

After drying, the anodized parts are primed with the adhesive primer. Time between anodize and priming is limited to prevent contamination of the active oxide layer. The primer is air-dried for a time to allow the solvents to evaporate and then baked at elevated temperature to cure. Many adhesive primers have very tight thickness requirements, for instance 0.00015" to 0.001", and require skilled spray operators to apply. A primer layer that is too thick can result in low peel strength while a layer that is too thin might not be continuous and could result in insufficient wetting of the surface by the adhesive during cure. 

Application of adhesive primer presents another challenge. Most adhesive primers require a high-temperature cure, which presents the potential for damaging existing bondlines. Infrared curing can be used to reduce the likelihood of problems. 

P.V.D.F. Polyvinylidene fluoride (p.v.d.f. or p.v.f.2) dispersions are applied by the coil-coating process. They are blends of p.v.d.f. resin and acrylic. The combination produces a system which has excellent weather-ability and which can be bonded via an adhesive primer to a galvanised steel or aluminium substrate. 

After metal pretreatment it is essential that a suitably formulated adhesive primer is used, because p.v.c. does not itself adhere to metals. 

Materials. The adhesives and primers used in this study were model and commercial materials that were cured according to conditions appropriate for the specific adhesive chemistry. Adhesives A and B were conventional epoxy/Versamid and epoxy/dlcyandiamlde adhesives, respectively. Adhesives C and D were commercial urethane and epoxy/polyamlde adhesives, respectively. Adhesive E was a conventional two-part epoxy/amldoamlne adhesive. Adhesive F was a vinyl plastlsol adhesive. The adhesive primers used in this study were a urethane crosslinked epoxy electrocoat primer and spray primers based on tall oil modified epoxy ester, and polyesterpolyol/isocyan-ate chemistry. Dicyandlamlde was obtained from Aldrich Chemical Company. Epon 828 was obtained from Shell Chemical Company. 

The Effect of Adhesive Primers. In practice, adhesive bonds involving metal adherends often use primers as pretreatments of the metal surface prior to bonding. Table IV shows the durability of composite-metal bonds prepared with adhesive C over a series of primers (of varying corrosion resistance) in 240 hour salt spray test. The results indicate that the performance of bonds is directly related to the corrosion resistance of the primer used to prepare the adherend surface. In general, the adhesion of the primer to the steel adherend, rather than the adhesive chemistry. 

GEV EMICODE (2001) Labelling Scheme for Flooring Installation Products including flooring adhesives, primers and levelling compounds http //www.emicode.com/ gev-uk/gev.htm... 

Primers usually require solvent evaporation and several curing steps before the adhesive or sealant can be applied. Adhesive primers are usually not fully cured during their initial application. They are dried at room temperature, and some are forced-air dried for 30 to 60 min at 65°C. This provides a dry, nontacky surface that can be protected from contamination and physical damage by good housekeeping practices until the substrate is ready to be bonded with an adhesive. Full primer cure is generally achieved during the cure of the adhesive. 

The application of corrosion-resistant primers has become standard practice for the structural bonding of aluminum in the automotive and aerospace industries. The adhesive-primer combinations are chosen to provide both maximum durability in severe environments and higher initial joint strength. Improved service life is typically achieved by establishing strong and moisture-resistant interfacial bonds and protecting the substrates surface region from hydration and corrosion. 

Representative data are shown in Fig. 10.5 for aluminum joints bonded with an epoxy film adhesive and a standard chromate-containing primer. Up until recently, standard corrosion-resistant primers contained high levels of solvent, contributing to high levels of volatile organic compounds (VOCs) and chromium compounds, which are considered to be carcinogens. As a result, development programs have been conducted on waterborne adhesive primers that contain low VOC levels and little or no chrome. Data are presented on several of these primers in Tables 10.8 and 10.9. 

TABLE 10.9 Tensile Lap Shear Strengths Using Environmentally Acceptable Adhesive Primers for 121 °C Curing Adhesives33... 

E 866 Specification for Corrosion Inhibiting Adhesive Primer for Aluminum Alloys to be Adhesively Bonded in Honeycomb Shelter Panels... 

Polyvinyl butyral etch primer 10 13 5 min 1 h Adhesion primer for ferrous and nonferrous metals... 

Poly(carbodiimides) are sometimes used as adhesive primers. Film forming carbodiimide homo- or copolymers have been used in microencapsulation techniques for pressure sensitive copy paper. Oligomeric acylureas are obtained from polyunsaturated carboxylic acids and carbodiimides as monomers for coatings. ... 

While this book was in its final preparation stage, two additional types of adhered sheet linings for chemical exposures have come to our attention. One is a sheet with, as the exposed face, a Tedlar(sf film adhered to a layer of rubber-asphalt blend. The sheet is applied with rollers to a substrate surface that has been coated with an adhesive primer. Sheet edges are butted with an adhesive lap strip of Tedlar applied over the joint to protect it. This is a proprietary product presently available from only one source, which will supply particulars of the application procedure and chemical resistance tables upon request. 

Diaziridine systems are used in adhesive primer composition for plastic films <86JAP6i23354i>, as... 

Y. Tsuo, K. Yoshida, and M. Atsuta. Effects of alumina-blasting and adhesive primers on bonding between resin luting agent and zirconia ceramics. Dent. Mater J. 2006 25 669-74 (2006). 

Binder Application method Preheating and stoving temperature [3.48], °C Adhesive primer required [3.48], [3.49] Weight loss during stoving, wt% Other properties... 

Formation of durable chemical bonds is an obvious means to stabilize the interface and has been demonstrated for phenolic/alumina joints [25] and for silane coupling agents [26,27]. However, for most structural joints using epoxy adhesives and metallic adherends, moisture-resistant chemical bonds are not formed and mechanical interlocking on a microscopic scale is needed between the adhesive/primer and adherend for good durability. In these cases, even if moisture disrupts interfacial chemical bonds, a crack cannot follow the convoluted interface between the polymer and oxide and the joint remains intact unless this interface or the polymer itself is destroyed. 

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