Thin coatings paints

Electrostatic spraying is used in shops to coat conductive objects. It is very useful for odd-shaped objects such as wire fence, cables, and piping. An electrostatic potential of 60,000 volts on the object attracts oppositely-charged paint particles the spray can wrap around and coat the side of the object opposite to the spray gun. This technique produces very uniform finishes and has the least paint loss of the three methods. However, it is slow, requires expensive equipment, produces only thin coats, and is sensitive to wind currents. 

Thin coatings consist of paints and varnishes, which are applied as liquids or powdered resin with a thickness of about 0.5 mm [e.g., epoxy resin (EP) [2]]. Typical thick coatings are bituminous materials [3] and polyolefins [e.g., polyethylene (PE) [4]], thick coating resin combinations [e.g., EP tar and polyurethane (PUR) tar [2]] as well as heat-shrinkable sleeves and tape systems [5]. 

Thin coatings These pigmented materials, commonly known as floor paints, are often based on chlorinated rubber (see Section 12.3.2) or epoxy ester (see Section 12.3.1). They have limited life in heavy traffic but are easy to apply. 

Zinc or aluminum metal spray Sprayed metal coatings are porous and should be sealed after application by applying a sealer coat (i.e. a thin coat such as an etch primer) or a thinned version of the final coating system. Oil-based systems should not be used. Metal spray coatings can have excellent durability without overcoating with paint and, particularly for aggressive conditions it is preferable to leave them with sealer only. 

Extrusion coating is ideal for rods, tube and wire. The article is passed through a paint reservoir and then out via a die, which leaves only the correct thickness of paint in place. There are further techniques suitable for flat articles in sheet or web form. Knife coating is ideal for very thin coats, especially on continuous paper or plastic webs. The knife is either a metal doctor blade or a curtain of high velocity air (an air knife) directed onto the surface and it removes surplus material applied previously. 

Even more widely used are a variety of roller-coating techniques. In forward roller coating a controlled amount of paint is metered onto the surface of a rubber or gelatine roller rotating such that, at its point of contact with the sheet or web, roller and sheet are moving in the same (forward) direction. Even finer control of thin coatings is obtained if the paint is transferred from gravure cells onto the application roller. 

Front-silvered mirrors can be pohshed with optical rouge on a pad of chamois leather over cotton wool. Care is necessary because it is easy to polish completely through the silver. Back-silvered mirrors can be protected by first varnishing the silver and then painting the varnish. Front-silvered mirrors can be protected with a thin coat of lacquer, such as a dilute solution of cellulose nitrate in amyl acetate. The lacquer should not be too thin, or interference colours may be produced. 

In this paper we are concerned with the adhesive systems beneath thick rubber adherends. Unlike the technology for the paint industry, where the science of qualification testing for durable thin coatings has produced paints with 10, possibly 20 years life... 

When the paint is dry, apply a thin coat of varnish to the oil paint. This should be done under a hood with a running exhaust fan. Wear gloves, aprons, and goggles. 

Glaze. A very thin coating of a paint product, usually a semitransparent coating tinted with pigment, applied on a previously painted surface to produce a decorative effect. 

Using a thin artist brush, paint the PZT and the adhesive layer with a thin coat of polyurethane. Spin down at 500 for 5 min in an available spin coater, or in a laboratory centrifuge. 

A problem with the use of thin coatings and paints is the maintenance of the surface coverage. Over a period of time the effectiveness is likely to fall and coating replacement will be necessary. In all but the simplest heat exchangers, this may be difficult and expensive. 

Thin coatings not only are used for mechanical protection and lubrication, but are widely applied to protect against corrosion and chemical reaction [47-49]. The steel body of a car is first covered by a zinc layer, which is further treated in a phosphate bath, to promote the adhesion of the paint. Damaging this sandwich structure, by breaking one of these layers, results in quick corrosion of the car body rust. The improvement in the quality of this protective coating during the last 20 years is shown by the increase of the duration of the corrosion warranty proposed by car manufacturers (from 2 years less than 15 years ago, to 8 years at the present time). 

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