External coating applications

Thermoplastic resins, such as vinyl chlorides, vinyl acetates and polyamides are employed, particularly in the water industry, on buried pipes and fittings. To provide both internal and external coating, application may be by one of these principle techniques dipping in a plastisol, fluidised beds or electrostatic spray. 

Isolate the metal from the environment. If environmental alteration is impossible or uneconomical, it may be appropriate to separate the metal from the environment. This is commonly the economically justifiable approach. It generally involves applying an appropriate protective coating to the metal. External coatings must be resistant to cold flow, especially in subterranean applications where the weight of a pipe resting on hard backfill may cause the... 

Colors that have restricted applications (e.g., E 173 may be used for external coating of sugar confectionery and for decoration of cakes and pastries quantum satis)... 

Whereas zinc oxide was originally used as a pigment, its most important modem application is to aid in vulcanizing synthetic and natural rubber. Paint and coating industries use zinc white mainly as an additive to improve anticorrosion properties, mildew resistance, and durability of external coatings. 

Instant foods. Lecithin has been used as a wetting agent and emulsifier in instant foods. Foods including cocoa powder, instant drinks, instant cocoa and flavored coffee, powdered protein drinks, coffee whiteners, instant puddings, cake mixes, and instant toppings are widely employed applications for specific lecithins. The most common method to incorporate lecithin is as an external coating on the powder particles. The particular lecithin to be employed largely depends on the hydrophilicity or lipophilicity of the powder system (7). 

The content of iron is one of important indicators of quality of silica flour for various applications, especially for external coatings. The presence of iron causes formation of rusty streaks which form when the iron oxidizes. The good quality material for these applications should have a Fe203 content below 0.03%. 

There has been a trend in recent years to move towards the electrostatic deposition of paints for exterior automotive applications. Reasons for this include improved paint transfer efficiency. Normally, plastic parts need to be painted with a conductive primer prior to the electrostatic painting of base and clear coats. One of the most recent developments in the area of external automotive applications is that of intrinsically conductive resins for electrostatic painting. Currently there are commercial applications for body panels that utilize PPE/PA that contains carbon black as the conductive component. In the USA, a mirror shell application uses PPE/PA where the conductivity is achieved through the incorporation of graphite nano-tubes. 

FIGURE 8.3 (See color insert.) Corrosion of the external side of the pipe and partial dishondment—due to entrapment of moisture during the coating application. (From A.S. Khanna. Audit report for Gas Authority of India, on the performance evaluation of FEE and 3LPE coatings, March 2000, Delhi, India. With permission.)... 

The external coating provides an additional mechanical strength to the system, since the coating is applied at a thickness of 1.5-2.5 mm depending on pipe diameter and pipe wall thickness. The application process of the coating system is a continuous process. 

Rose, B. R., Simultaneous Internal and External Coating of a First Stage Turbine Bucket with a Chromium Reinforced Aluminide, Eighth National Research Council of Canada Symposium on Industrial Application of Gas Turbines, 1989, Ottawa, Canada, National Research Coxmcil of Canada. 

It should be noted that for internal applications compliance with FDA 175.300 and local regulations are required. This limits the types of materials which can be used for internal coatings. External coatings will only be considered here, because solvent based acrylic resins have little usage in internal lacquers other than PVC organosols. In the following sections, systems based on resins other than acrylics have been included to illustrate the types of formulation acrylic resins have replaced and reasons why, to compare alternative formulations for the same end use and to give an idea of the types of systems acrylic systems may be used in conjunction with. 

The Michael chemistry, although sensitive to acid media, displays exceptional resistance characteristics when fully cured and has been utilised in applications which require extremely high chemictil resistance, such as external coatings for chemictil tankers. 

This is basically an external coating of high-density polyethylene and suitable where the pipe temperature during operation is in the range of -20°C to 55°C. The coating is intended for use in applications where it is not subject to weather or ultraviolet light exposure. 

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