Primer Layer

Fig. 5. (a) Schematic of the Philips 2P Process for video disk repHcation (79) (b) configuration of a double-sided LaserVision disk where the hole at the center is not shown. S represents the transparent substrate A, the primer layer L, lacquer with picture and sound information in the form of pits M,... 

To be effective, there must be a certain minimum concentration of inhibitor at the interface to be protected. Therefore, there must be sufficient inhibitor in the primer, and these inhibitors need to be soluble enough in water to enable transport of inhibitor to the oxide surface as water permeates the adhesive joint. However, too high of a solubility will rapidly deplete the primer layer of inhibitor resulting in a loss of protection. One of the fortuitous properties of zinc and strontium chromates is the limited solubility of these compounds in water (about 1.2 g/1 at 15°C [33]). 

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. 

Conjugated polymers such as polylliiophcnc are used as a primer layer lor the galvanic deposi-lion of copper in consumer clcclronics in lliis ease lire long lerm slabiliiy of lire conjugaicd polymer is no issue. 

Generally, the preparation of washcoated structured catalysts is governed by several parameters, such as the nature and particle size of the precursor powder, loading of powder, nature and concentration of dispersants, temperature of the slurry, use of binders in the slurry and deposition of a primer layer on the monolith. 

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... 

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. 

Primers are applied quickly after surface preparation and result in a dry or slightly tacky film. It is generally recommended that they have a dried coating thickness range of tenths of a mil to approximately 2 mils. It is necessary to control the primer thickness, since if the primer layer becomes too thick, its bulk properties may predominate, and the primer could become the weakest part of the joint. 

Using the aluminum sheet substrate as the cathode of a direct current (DQ glow discharge, cathodic plasma polymerization is carried out. Dealing with metal surfaces, cathodic plasma polymerization is the most practical means to provide the best corrosion protection (see Chapter 13). A primer is applied on the surface of the plasma polymer. The thickness of the plasma polymer is roughly 50 nm on average and that of the primer layer is about 30,000 nm (30 pm). Primers used included E-coat (electrolytic deposition of paint) and spray primers, but no top coat was applied in the study of corrosion protection. 

The hardcoat is a silicone-silica composite prepared by hydrolysis of alkoxysilanes in the presence of water and colloidal silica, and can contain an alkoxysilylated UV absorber for protection of the polycarbonate. Adhesion of the topcoat to polycarbonate is provided by a primer, which is a solution of acrylic polymer. The primer is coated on polycarbonate and air dried to a 0.5 pm thick film. The topcoat is applied over the primer layer and air dried before curing at 130 °C for at least 30 min. 

It is expedient to form single-layer inhibited coatings in a fluidized bed consisting of a homogeneous mixture of the polymer and inhibitor (Fig. 3.23a). The double-layer coatings with inhibited primer layer are commonly formed in a separated layer whose scheme is presented in Fig. 3.23b. A heated article is first dipped in the upper layer enriched with the inhibitor and then into the lower layer with content dominating by the polymer binder. 

Photomechanical Responses of Azobenzene-Containing Materials. Ji et al. (2004) reported that a self-assembled monolayer (SAM) of azobenzene molecules on a silicon microcantilever created a photon-driven switch. Commercial silicon microcantilevers were electron-beam coated on one side with 3nm of primer layer (chromium), followed by 20 nm of gold. An azobenzene derivative with a decanthiol substituent on one ring was used to functionalize the gold surface. The thiol (-SH) end attached to the gold surface and the other azobenzene end disposed outward. 

Self-etching primers are blends that can both etch and prime the surface in one step. They contain at least one acidic monomer, in order to allow them to undertake the etching process. They also eliminate the need to rinse away the solubilized products to the etching step. Instead, these substances become incorporated into the primer layer. This has the advantage of reducing the technique sensitivity associated with the process of bonding [4]. However, there is some evidence that the resulting adhesive bonds are weaker than those with substances that do not incorporate any mineral components of the smear layer [24]. 

In essence, only 1% of OM in the paint, which has to form a 20 (jim primer layer containing a nanosized complex OM particle network, provides a drastic change in the metal surface behavior it stops corroding. This can be measured, for example, by scanning the voltage potential and by impedance spectroscopy [76]. Here, the nanostructures cause the following macroscopic consequences ... 

Real joints do not of course consist of simple, separate, elastic materials with a clear mathematical geometry. Metal adherend surfaces are micro-rough, possessing oxide layers, while concrete surfaces are macro-rough comprising aggregates and cement paste, and both surfaces readily adsorb air-bome contamination. The thickness and modulus of primer layers, if employed, is often unknown, and the thickness and properties of the adhesive layer are difficult to regulate and to determine. 

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