Resistance of coatings

Other oxazolines synthesized from alkanolamines ate useful as surface-active agents and corrosion inhibitors. Synthetic oxazoline waxes promote lubricity and mat resistance of coatings. 

Amino resins are used by the paper industry in large volume for a variety of apphcations. The resins are divided into two classes according to the mode of appHcation. Resins added to the fiber slurry before the sheet is formed are called wet-end additives and are used to improve wet and dry strength and stiffness. Resins appHed to the surface of formed paper or board, almost invariably together with other additives, are used to improve the water resistance of coatings, the sag resistance in ceiling tiles, and the scuff resistance in cartons and labels. 

TABLE 28-23 Chemical Resistance of Coatings for Immersion Service (Room Temperatures)... 

Impact tests Such tests reveal the resistance of coatings to deformation and destruction by concentrated sudden stresses. They thus throw considerable light on the integrity of the metal-coating bond. Changes in adhesion through chemical reaction at the paint/metal interface will be reflected in the impact-test values. 

D 2247 1987 Practice for testing water resistance of coatings in 100% relative humidity... 

D 2933 1974 (1986) Test method for corrosion resistance of coated steel specimens (cyclic method)... 

Accelerated Corrosion Tests. There are as many as a dozen methods (salt fog, Kesternich, etc.) that are currently being used to investigate corrosion resistance of coating systems and a need to develop a better and more dependable method to predict in-use service. A severe drawback of all these tests is that their results often compare unsatisfactorily with practical experience. One reason for the discrepancies is assumed to be the variability of natural exposure conditions. Accordingly, cyclic testing procedures have been developed with which exposure conditions, especially temperature and humidity. 

Potyrailo RA, Chisholm BJ, Olson DR, Brennan MJ, Molaison CA (2002) Development of combinatorial chemistry methods for coatings high-throughput screening of abrasion resistance of coatings libraries. Anal Chem 74 5105-5111... 

Fig. 12.7. Interaction of mercury vapour with thin gold films coated by self-assembled monolayer of 1-hexadecanethiol (a) comparison of the kinetics of resistive response for bare (open symbols) and coated (filled symbols) gold films on exposure to 10 ng/1 mercury vapour (b) influence of different mercury vapour concentrations on the resistance of coated electrodes (c) kinetics of changes of the resonance frequency of a 1-hexadecanethiol-coated piezo-quartz due to exposure to 8.3 ng/1 of mercury vapour [25].

Oligophenylethoxysiloxanes are used as modifiers for various polymers to improve their weather resistance and other technical characteristics, as well as to increase the heat resistance of coatings. E.g., PES-50 is used to modify polyethers, aciylic and epoxy polymers PES-80 is used to modify alkyd and urea-formaldehyde resins. Besides, PES-80 is used as an additive in paints and enamels (to improve their flow properties, gloss and colour), as well as in concrete mixes (to improve the water resistance and durability of concrete works). 

In this paper the recently developed techniques to characterize the mar resistance of coating systems were presented. The techniques base on methods that create a single scratch onto a surface. Characteristic values like the critical load as a measure for the transition from plastic behaviour to brittle fracture can be determined and used to rank different clearcoat systems and to compare these results with other physical properties. In the field of mar resistance the cross-linking density of the... 

ASTM D1735 Testing the water resistance of coatings using water-fog apparatus (practice). 

With a decrease of the substitution degree of dimethylaminomethyl phenols (DAMPs), the density of the network structure of epoxy resins cured by DAMPs increases. Simultaneous improvement of impact, adhesive and cohesive strength, and chemical resistance of coatings in typical aggressive media takes place (Table 6.1). 

A further complication is that the volume resistivity of coating materials is strongly dependent on their composition and this, in turn, can be greatly affected by contact with different cargoes. Hence, knowledge of this property as a function of contact time with different media is desirable. 

The properties of alkyds have a subsUintial effect on the weather resistance of coatings. Graft-copolymers of castor oil alkyd with methyl and butyl methacrylate substantially reduce the drying rate, improve the weather resistance and mechanical properties of coatings [112]. 

It is necessary to thermally cure the coated plastic in order to achieve full crosslinking of the air dried film. The degree of crosslinking affects not only the abrasion resistance of coating, but also the adhesion and the long term performance under environmental conditions. The temperature and time of cure is also dictated by the thermal stability and properties of the plastic substrate. The following table lists recommended cures for various plastics. 

The electrical resistance of coatings is composed of the active (ohmic) and reactive (polarization) resistances. The latter is a resistance to alternating current through the capacity and inductance of the coating-substrate system. Ohmic resistance makes up an insignificant portion of the total electrical resistance of pol3Tner coatings and characterizes electrolyte diffusion in the... 

Thin films were created after immersion of Mg alloy samples in a specially formulated emulsion of polyacrilic and PPy pol3miers. This resulted in better corrosion resistance of coated Mg foils in neutral aqueous NaCl solutions [23]. 

---