Cure of the coating

Adding amines to coating compounds containing other polymers of hydantoin derivatives permits thermal curing of the coating compounds, which are useful as electrical insulators of wires under a broad range of conditions without loss of coating flexibiUty (101). 

Autodeposition is characterized by the growth of the coaling with time of immersion and the ability to withstand water rinsing immediately upon removal from Hie coating bath and before fusion or curing of the coating by heat without loss of coating. 

For the modification of silica with aminosilanes, the liquid phase procedure is usually applied. Only few studies have described the vapour phase APTS modification.6,7 The modification proceeds in three steps, (i) A thermal pretreatment of the silica determines the degree of hydration and hydroxylation of the surface, (ii) In the loading step, the pretreated substrate is stirred with the silane in the appropriate solvent, (iii) Curing of the coating is accomplished in a thermal treatment. On industrial scale ethanol/water is used as a solvent, on lab-scale an organic solvent is used. The reasons for this discrepancy is the increased control on the reaction processes, possible in an organic solvent. This will be clarified by the discussion of the modification mechanism in aqueous solvent and the effect of water in the different modification steps. 

Figure 15 (a) Optical fiber coating run in dual cantilever bending with notched clamp. Total thickness 150 microns. Cure of the coating can be seen between run I and run 2. (b) Peaks due to ionhopping in glass. 

The acetate esters find wide use as active solvents in nitrocellulose, cellulose acetate, acrylic, urethane, and polyester coating formulations. Other solvents used with esters in coatings include glycol ethers, ketones, alcohols, and hydrocarbon diluents. A properly balanced solvent system will control the viscosity, flow, and leveling properties as well as the cure of the coating. Selection of the proper ester solvent for the coating will depend on the relative evaporation rate and solvency characteristics needed for the coating resin. 

Additives may alter certain characteristics of the binder, pigment, or carrier to improve processing and compatibiUty of the raw materials or application and cure of the coating. 

They must not retard oxidative curing of the coating film when... 

The healing agent possesses a low viscosity, which facilitates its flow into the crack plane. The solid-phase catalyst remains reactive during and after curing of the coating, and the catalyst particles quickly dissolve on contact with the monomer in the crack plane and polymerize under ambient conditions, producing a tough cross-linked polymer. 

The level of catalyst used can vary from 0.001% - 0.5% in the case of the metallic salts, calculated as metd on solid resin. The function of the catalyst is to accelerate the cure of the coating by increasing the rate of reaction. This also results in a reduction in pot life and, as a result, a reduction in the working time of the lacquer or paint after mixing. High levels of catalyst can also affect the application characteristics due to the rapid increase in viscosity, although this can be overcome by the use of dual feed application equipment. The metallic salts in general are the more efficient catalyst for use with aliphatic isocyanates. 

The carboxy/epoxy system displays a very fast lacquer type dry but, in comparison to a 2 pack polyurethane, relatively slow through cure. Tertiary amines can be used to enhance the cure of the coating. However, careful selection of the catalyst is critical since some amines can also make the coating water sensitive. There is also the potential to catalyse the system internally by incorporating an amine functional monomer onto the backbone of the acrylic resin by copolymeiisation of amine functional acrylic or vinyl monomers. 

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