Corrosion inhibiting primer

Non-corrosion-inhibiting primers Corrosion-inhibiting primers Inorganic barrier primers Rubber to metal primers... 

Corrosion-inhibiting primers based on this technology have been in continuous service since they were first utilized with nitrile epoxies in the late 1960s. These inhibitors function by passivating the aluminum. In this process, water permeating the adhesive bondline carries a certain amount of inhibitor to the oxide surface. 

Effect of corrosion inhibiting primer on strength retention after exposure to salt spray [29]... 

The need to identify replacements for chromate-based technologies has also resulted in the development of alternatives to resin-based corrosion-inhibiting primers. These are primarily inorganic barrier coating techniques, such as sol-gel processes, which may or may not include corrosion inhibitors. These are discussed in a later section. 

The vinyl copolymers can be used most efficiently in special applications such as hospital and dental equipment where durability is more important than initial cost. For laboratory equipment, epoxy resins may be preferred because the vinyls are sensitive to some solvents. The vinyl coating systems consisting of corrosion-inhibiting primer and chemical-resistant finish coats are used on new equipment for chemical plants. The metal conditioner based on zinc chromate and polyvinylbutyral are widely used over sandblasted steel as a use for vinyl systems on both industrial and marine equipment. 

The presence of NTMP resulted in a four-fold increase in bond durability of adherends etched in FPL over that of untreated adherends. Durability can also be improved by the incorporation in a primer of a corrosion-inhibitor such as strontium chromate. Corrosion inhibiting primers are generally used with bonded components in U.S. Air Force aircraft (24). 

After Pre-treatment of metals prior to bonding, it may be several weeks before the adhesive is applied. Most pre-treated surfaces are stable for considerably less than 24 h, so protection by priming is needed. However, the effectiveness of primers, particularly of the corrosion inhibiting primers, can be very sensitive to coating thickness a change in thickness from 2-5 ftm to above 8-10 p.m can halve the peel performance of some adhesives. 

Three classes of primer are in current use surface protection primers , corrosion inhibition primers and organosilanes, (which are claimed both to protect the surface and enhance the adhesion). By far, the greatest numbers of commercial products fall into the second class. 

More complex bis-silanes are being considered as replacements for conventional metal pre-treatment and for chromate in corrosion-inhibiting primers, van Ooij advocates the use of both mono- and di-amino based bis-silanes (see Silanes as metal pre-treatments) ... 

Thus, bonds made with 6061-T6 alloy will normally last about four times longer than those prepared with the less corrosion-resistant 2024-T3 alloy, when exposed to a marine environment. Similarly, after three weeks exposure to 5% salt spray at 95°F, joints prepared with 2026-T4 alloy had failed, those prepared with 6151-T4 alloy had weakened considerably, but had not fallen apart, and those prepared with X5085-H-111 alloy had retained about 30% of their initial strength. The effects described are for bonds formed with only minimal preparation of the adherend surface, under which conditions bondline corrosion becomes the dominant factor in determining durability. The same trends may not be apparent when anodized surfaces, or corrosion-inhibiting primers, are used. Also the same order of relative durabilities may not apply to noncorrosive exposure conditions. For example, long-term tropical exposure indicates that more durable bonds are formed with 2024-T3 clad alloy than with 6061-T6 alloy. ... 

With the increased usage of 120°C cured, rubber modified epoxy structural adhesives for aluminum airframes, certain service problems have been observed which have been attributed to environmental factors. The problems associated with the combined effects of sustained load, elevated temperature and high humidity upon the aluminum substrate, corrosion inhibiting primers, and the structural epoxy adhesive matrix are discussed. A particular type adhesive matrix, based on acrylonitrile/butadiene rubber modified bisphenol type epoxy systems is discussed in detail, and important advances in the preparation of more moisture resistant aluminum (oxide) surfaces are reviewed. 

It is important to recognize that these corrosion inhibiting primers are fixed at the interface by the curing reaction, and that the primer forms a discrete layer which is the adhesive bond of fundamental importance for interface protection, and indeed for environmental resistance, since interfacial failure is the primary failure mode in the 120 C curing systems in question. Due to the balance of properties required of this primer, e.g., the spreading, wetting function, the protective function, subsequent bondability, durability under load, and fundamental environmental protection for the aluminum bonding surface, there are many limitations on the resin... 

A corrosion inhibiting primer of maximum protection against moisture should be employed. 

Many of the primers developed during the past 20 years contain corrosion inhibitors. These primers have a second function to further improve hydrolytic stability at the adhesive to metal interface and prevent corrosion during exposure to salt spray. Table 1 shows the difference in strength retention of 2024-T3 alclad aluminum lap shear coupons exposed to salt spray. Both sets of coupons were bonded with a 250°F cure elastomer modified epoxy adhesive. One set of coupons was primed with BR 123 primer (a non-corrosion inhibiting primer) while the other set was primed with... 

BR 127 corrosion inhibiting primer. Both primers are manufactured by the American Cy-anamid Company. 

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