Primer formulations

In primer formulations for adhesive bonding of metals, the coupling agents that are most frequently used are those based on epoxy and amine functionalities. Aqueous solutions of aminosilanes have been successfully used for obtaining stable adhesive bonds between epoxy and steel [10] and epoxy and titanium [11,12], while epoxy functional silanes are preferable for applications involving aluminum substrates [13,14], A simple solution of % epoxy functional silane in water is currently used for field repairs of military aircraft [15] where phosphoric acid anodization would be extremely difficult to carry out, and performance is deemed quite acceptable. 

With the exception of coupling agent technology, primers for structural adhesive bonding have received little theoretical treatment in the literature beyond a discussion of mechanisms of corrosion inhibition by primer additives and limited discussion about statistical techniques for primer formulation. Perhaps because of the much more widespread use and greater economic importance of corrosion-protective coatings, the design and function of primers for these systems have... 

Fig. 8 shows a primer formulated with a corrosion-inhibiting pigment such as a chromate. As discussed previously, some permeability to moisture is necessary for these pigments to dissolve and be transported to the interface where passivation of the substrate can occur. Optimum performance is generally found at PVC/CPVC Just below 1 [71]. 

Primer Formulations. Coatings were formulated using standard techniques. Mill bases were prepared by dispersing the oligomer solution with pigments (silica, carbon black, titanium dioxide and barium sulfate in a 1 1 1 10 ratio). The viscosity of the formulation was reduced to spray viscosity by addition of solvent. 

Substrates, Paints and Coatings. Both flash rusting and underfilm darkening studies exployed a white, pH 4.5, primer formulation (see Appendix), designated as Standard, based upon Haloflex 202, a chlorine-containing vinyl acrylic latex. A zinc phosphate free formulation, designated as Non-Standard, of pH6 was prepared by substitution of zinc phosphate for barytes. The comparison paints were a commercial butyl acrylate-methyl methacrylate water borne primer, formulated at pH 9, and a solvent based chlorinated rubber primer. 

Primer Formulation Based on Chlorine Containing Vinyl Acrylic Latex... 

The FPL- or SAA-prepared coupons and panels were Immersed for 30 min In an aqueous (or aqueous/alcohollc) Inhibitor solution at room temperature, followed by rinsing In distilled, deionized water and forced air drying. Coverage levels of phosphonate and silane Inhibitors were determined by XPS from the surface concentration ratios of their characteristic elements, P/Al or Sl/Al, respectively. Selected organosllanes were applied to the metal surface by spraying, after dissolution (0.1 - 0.5%, v/v) In the EPON-Versamld primer formulation. 

Organic primers formulated with corrosion inhibitors are typically applied to pretreated metal surfaces to protect the surfaces prior to adhesive bonding and during environmental exposure. Pike [7-11] found that inorganic primers, such as sec-butyl aluminum alkoxide, improved the durability of aluminum-epoxy bonds when applied to both porous and nonporous aluminum oxide surfaces. It was shown that the effective thickness of the inorganic primer was directly related to the degree of oxide porosity and the depth of the porous oxide layer resulting from the normally used pretreatments for aluminum [10,11]. 

Resins, curing agents, and additives used in primer formulation are much like adhesive or sealant formulations except for the addition of solvents or low-viscosity resins to provide a high degree of flow. 

It is the principal component of -> Chlorate Explosives and is an important component of primer formulations and pyrotechnical compositions, in particular matchheads. 

The three Gulf EMA resins were experimentally evaluated and TD-938 was selected on the basis of film transparency, extrudabll-Ity, and ease of module fabrication by lamination. The TD-938-base resin sells for about 0.60/lb (April 1981). A trial formulation is shown in Table II. Modules have been fabricated with this EMA by the vacuum-bag lamination process, and have successfully passed module engineering qualification tests. Primer formulations for bonding EVA and EMA to glass and polyester film have been developed by Dow Corning and the formulations are given in Table III. 

CUDDIHY ET AL. Polymeric Encapsulation Materials Table III. Primer Formulations... 

Formulations must be adjusted to adhere to various substrates. This requires the addition of suitable plasticizers and adhesion promoters. It is necessary, in some cases, particularly for adhesion to masonry, that primers be used. Primers also are specific to the type of surface and the nature of the formulation. Some primer formulations appear in Table IX. 

Anticorrosive primer formulations are based on epoxy resins that react at ambient temperature with amine adducts, aminoamide resins, or isocyanates (two-pack primers). Zinc or strontium chromates are used as anticorrosive pigments. These electrolytically active pigments prevent dangerous filiform corrosion. Extensive development work is being carried out on chromate-free aircraft primers [11.8], [11.9]. 

Anti-corrosive pigments may be used in etch primer formulations (see above), or as components of the closely related anti-corrosive paints which are based on alkyd resins or other organic binders. Among the compounds used for the latter are [22]... 

For the lower values of PVC studied, the incorporation of conductive reinforcing fibers in increasing levels led to primers with a galvanic activity also increasing (similar amount of white salts than in primers formulated with PVC nearest to CPVC). 

Figure 3 includes values of potential versus immersion time in 0.1 M sodium chloride solution at pH 7.0 and 25 C for primers formulated with 57.5 and 70.0% PVC values and based on 7.5/1.0 nano silica/lithium oxide molar ratio as film-forming material, fine microzinc (D 50/50 4 pm) as pigment inhibiting and graphite as reinforcement fiber in the three levels studied. In addition, this figure displays the corresponding reference primers. 

SEM images of primers formulated with PrjOj in (a) the as-deposited condition and (b) after 500 hours of salt spray exposure primers formulated with Pr O, in (c) the as-deposited condition and... 

Typical metal primer formulations are given below ... 

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