Primers and Priming

In aerospace applications, once metallic adherends have been pretreated, it can be several weeks before they are bonded. In view of the fact that most of the oxide or fresh metal surfaces are stable for considerably less than 24 h, these surfaces have to be protected during the time that the component is stored prior to bonding. This is invariably achieved by priming the dried adherend immediately after pretreatment such techniques rarely, if ever, apply to fibre-reinforced composite components. 

The perceived drawback with primers, however, is that both the surface protection and, particularly, the corrosion inhibiting systems can be very sensitive to coating thickness. It is possible almost to halve the peel performance of some adhesives when going from primer coating thicknesses in the region of 2-5 xm to thicknesses above 8-10 (xm. 

Currently, the structural adhesive market essentially relies on two classes of primer surface protection primers and corrosion inhibition primers. There is a further class of materials which are said to act as both surface pretreatment agents in their own right as well as surface protection and, it is claimed, bond enhancing 

Beam material Beam thickness Beam areal weight 

These are usually solvent-based systems of low solids content (ca. 10%). Their chemistries should match those of the structural adhesives to be used in the bonding application. To this end, in a commercial range of adhesives, each primer offered is often a simple solution of its equivalent adhesive, where any insoluble fillers, etc., have been removed. 

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Prime Prime with appropriate primer. After the surface has cooled to 90°F (32 C), apply primer and cure with heat lamps. 

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. 

While etch primers, also known as pretreatment primers and wash primers, can be regarded as priming paints which promote their own adhesion by etching the metal surface, they may also be regarded as phosphate/chromate etching treatments which leave an organic residue on the surface to form the basis of the subsequent paint scheme. A detailed account of the etch primers has been given by Coleman . 

A review of the vast amt of work performed in the field of percussion primers reveals what is essentially an empirical approach to the development of both primer designs and priming mixts. It is recognized that a percussion primer must perform two vital functions (1) it must fire , ignite , or otherwise function when provided with the proper mechanical stimulus — a firing pin (with optimum contour to its striking end) and (2) it must perform its other function by which the flame , fire , or output will ignite the proplnt properly so as to provide the projectile with the specified velocity and within... 

For previously painted and fireproofed surfaces, the mastic manufacturer should be consulted to assure compatibility with the existing surface, proposed paint primer, and mastic. New galvanized surfaces should be mechanically abraded to ensure adherence of the prime coating. 

XPS analysis of the debonded specimens showed that the unprimed and primed FPL control and mercaptosilane-treated specimens failed primarily within the oxide, which represented the weakest layer in the system. On the other hand, the NTMP-treated sample debonded between the oxide and the polyamide primer. 

LSt has been used extensively abroad as igniting charge for LA and to some extent in the US as an ingredient of priming compositions (Ref 24, p 7-12). On p 7-18 of Ref 18, it is stated that LSt has been used in electric primers and the following compn is used for that purpose LSt 39.5, Ba nitrate 44.4, Ca silicide 14.1, carbon black 1.0 gum arabic 1.0%... 

Abstract—The structure of films formed by a multicomponent silane primer applied to an aluminum adherend and the interactions of this primer with an amine-cured epoxy adhesive were studied using X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, and attenuated total reflectance infrared spectroscopy. The failure in joints prepared from primed adherends occurred extremely close to the adherend surface in a region that contained much interpenetrated primer and epoxy. IR spectra showed evidence of oxidation in the primer. Fracture occurred in a region of interpenetrated primer and adhesive with higher than normal crosslink density. The primer films have a stratified structure that is retained even after curing of the adhesive. 

These data show that fracture in the primed specimens occurred very close to the oxide surface, leaving a small amount of primer and epoxy on the oxide and a thin, discontinuous film of oxide on the adhesive surface. Significant interdiffusion... 

Integration of sample preparation and analysis [46] is one of the prime objectives of /i-TAS. PCR on a chip is one of the earliest applications of sample preparation. It has been carried out in the sample reservoir of the electrophoretic chip shown in Figure 8.22a. The nucleotides, primers, and other chemicals are added into the sample reservoir, and the entire device is introduced into a conventional PCR thermal cycler. The PCR products from the sample reservoir are then injected into the separation channel and analyzed. A more complex chip with multiple PCR chambers is shown in Figure 8.22 b. 

Preliminary tesfc have shown that the brisance of TNT, initiated by primary mixts alone, was not increased when any of the above booster mixts was placed betw primer and TNT. When Tetryl was used in lieu of TNT, a slight increase in brisance was observed. This increase was, however, of little practical significance, since the above booster charges, being relatively insensitive to initiation, requited abnormally large priming charges Ref J.D.Hopper, PATR 861 (1937)... 

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