Aluminum primer-adhesive layer

There is an apparent optimum relative humidity level required to achieve good adhesion and durability. Priming the steel adherends at 18% RH caused failure in the wedge samples within the steel (oxide) layer. Adherends primed at 34% RH failed within the alkoxide primer layer, whereas at 51% RH failure occurred primarily within the adhesive layer. This change in locus of failure with humidity was not evident using the wedge crack test when the adherends were primed with aluminum alkoxides. A peel-type test would probably be more sensitive in detecting these shifts in failure mode. 

Decorated aluminum sheets with PVC are used for Shinkansen and limited express cars. Aluminum sheets are joined to the frame using adhesives or screws, and a primer is applied on the surface. Nonrigid PVC sheets having a pressure sensitive adhesive layer are bonded on the surface. 

Adsorbed NTMP exhibits a pH-dependent surface coverage on anodized aluminum, which Includes a region characterized by a multilayer of hydrogen-bonded phosphonate molecules. These thick layers are weak and fall to provide good bond durability in a humid environment. NTMP monolayers are protective against hydration and are compatible with a nitrile-modified epoxy adhesive, but not with an epoxy-polyamide primer topcoat. 

Similarly, Plueddemann has reported [3c] an optimum silane coupling agent layer thickness of 50-200 A for commercial glass fiber treatment for use in composite materials. On the contrary, optimum adhesion of polypropylene to aluminum was obtained with a silane primer layer between 0.5 and 10 pm thick. In... 

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]. 

Chrome complexes have been developed as adhesion promoters by the reaction of chromium chloride with methacrylic acid. The chromium oxide portion of the adhesion promoter reacts with a substrate while the methacrylic portion reacts with a free radical curing outer layer. Chrome-based adhesion promoters are commonly used as a primer for aluminum foil to increase the strength and durability of aluminum/polyethylene interfaces.26... 

A nanofilm of plasma polymer of TMS (typically 50 nm) is applied on an appropriately prepared surface of an aluminum alloy. Then a corrosion-protective primer coating (typically 30 pm) is applied onto the surface of the plasma nanolilm. Adhesion of a multilayer coating system is the prerequisite for success of the SAIE approach. Therefore, adhesion of the first layer of the nanofilm prepared by plasma polymerization is the most crucial factor in this approach because if this layer delaminated from the substrate surface the rest of coatings could not function at all. It should be emphasized, however, that the issue is not the adhesion of a plasma polymer per se, but rather the adhesion that leads to better corrosion protection by the principle of SAIE, which requires the water-insensitive adhesion relevant to the corrosion protection. 

Two different methods, based on flame and laser pretreatments, were investigated. These methods are generally applicable under atmospheric conditions. The first is based on the surface reaction of low-molecular, silane-based precursors which are activated by pyrolysis in a propane gas flame. XPS analysis of the pretreated surface shows a thin silicate layer on the surface which remains active for about 10 days. After a careful parameter optimization, adhesion strength can be greatly improved, especially on steel surfaces. A similar method is commercially available as the Silicoater process. The second method, CLP, is based on a laser pretreatment in combination with a specific primer [4]. With parameters optimized for the specific substrate, adhesion strength can be greatly improved, especially on aluminum surfaces. 

One-Component Polymerization Adhesives. Cyanoacrylate Adhesives. Methyl, ethyl, butyl, and methoxyethyl esters of cyanoacrylic acid are used for cyanoacrylate adhesives [44] soluble polymers and plasticizers are incorporated to regulate viscosity and for elastification. Cyanoacrylate adhesives rapidly polymerize by an ionic reaction mechanism initiated simply by weak bases to form high molecular mass, but largely uncross-linked polymers. In most cases, atmospheric moisture or the film of moisture on the substrate is sufficient to initiate polymerization, because the adhesives are applied in very thin layers. However, this sensitivity to atmospheric moisture means that the adhesives must be stored in tightly sealed form, usually in polyethylene bottles. Cyanoacrylates are used for bonding small items of nearly all substrates. In case of polyethylene or polypropylene special primers are available. Setting is complete with rubbers in seconds, with aluminum in less than one minute. 

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... 

The laminates consist of alternate layers of aluminum (0.2—0.5 mm thick), which has been anodized and then primed with Cytec-Fiberite s BR-127 corrosion-inhibiting primer, bonded together with fiber-rich, epoxy-based adhesive-prepregs (about 0.125 mm thick). The reinforcing fiber is usually unidirectional in nature, although woven fabric is occasionally used. Generally two or three sheets of adhesive separate each sheet of aluminum this can be in the 0° direction or laid up in a cross-plied orientation. 

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