Tuesday, September 3, 2013

COATINGS

INTRODUCTION :COATINGS:

Coatings are thin surfacings. A coating is mainly created through a change in the physical state of a material (change of phase). At application-stage a coating material is in various state or phases such as liquid, solid or vapour, or a combination thereof like: suspension, solution, dispersion, emulsion, thermoplastic compound, thixotropic compound, etc. Coatings, however, once applied ultimately settle down to a heavier phase, usually (but not necessarily) a solid phase.

At an application stage a lower phase helps in many ways:

1.     Easy, uniform and thin level of application.
2.    Better dispersion of costly or rare constituents.
3.     Easy and thorough mixing of constituents such as film forming materials and other additives.
4.     Less energy is required for application.
5.     A controlled rate of deposition through phase conversion.

Coatings are generally capable of forming a film on the relevant surface. However to form a film through coating, the surface may require some modification or treatment. Surface treatments form a very important section of coating technology. Surface treatments are specific for the surface to be coated, and include processes like: cleaning, roughening, smoothening, etching, and also moisture proofing, rust inhibiting, barriers, static arresters, etc. Other surface treatments are designed to facilitate the application or deposition of the surface forming component and its setting or drying.

Coating as a surface finish system has certain advantages. Such as:
  • Coated surfaces can be very extensive because there are no joints (except at junctions where an adjacent coating application is delayed, such as a dried out portion and a fresh coat touch each other or overlap).
  • Coatings are thin surfacing and being malleable and allow post-forming operations (such as bending, shaping etc. of coated metal sheets).
  • Coatings by themselves are a surface finish (unlike an adhered surface finish involving the adhesive and the surface component) so allow creation of thinnest possible applied surface over an object.
  • Coatings allow creation of a multi layered system, where each layer has a distinctive quality.

Coatings are not considered adhered-finishes, because the coating film is formed and bonded through a lower to higher phase conversion process.

Coatings are deposited on objects by many different techniques and in variety of conditions. Common coatings are applied at normal environmental conditions. However, high end coatings require conditions that are usually unavailable at construction sites, such as exact environment and controlled application, drying and handling techniques.

Coating is a thin Surface Finishing Technique. A coating with or without a colourant and other additives is nominally first transformed into a liquid phase (solution, suspension, emulsion, etc.), applied over a surface by using many diverse processes, and then allowed to ‘dry’ out or ‘cured’ to convert into stable or solid state.

Coatings are applied to entities to alter the feel, appearance and other sensorial qualities. Coatings also provide insulation, conductive properties and protection. Coatings have been used for expression that is for art, illustration and decorative effects.

Primarily a  coating consists of a material that is in a liquid state or is convertible into a liquid phase. At least at the application stage most of the coatings are liquid, or brought to a molecularly very active stage of a colloidal system, such as gel, suspension, emulsion, foam, solution, etc. However, complex coatings may be formulated of materials in various colloidal states and possibly these materials are changeable into phases other than liquid.

Generally a coating consists of many different components, such as a film forming substance, colourant, reactive agents, solvents, and additives, etc. In a very complex coating composition such clear-cut distinctions are not apparent, because film forming substances and additives serve purposes beyond their nominal roles.



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