SURFACE MODIFICATIONS

Post 647 -by Gautam Shah

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Natural and Industrially-produced materials require some form of surface modifications or treatments, before being put to functional use, or for readying them for the next process. Surface modification at a basic stage, consist of cleaning and mechanical scrubbing. The surface modifications are for creating use-worthiness by levelling, texturizing, or for application of additional materials for shielding. The surface modification starts with visual observation and touch-feel experience that no foreign materials have remained on the surface, and all loose (removable) materials are removed. These simple processes ensure integrity of the surface.

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The next level of surface modifications are applications like coating, physical-chemical treatments, cladding, mounting, plating, joining, welding, levelling, cleaning, washing, ph balancing, static removal, etc. Surface modifications are intently surface preparation processes and may impart radically different surface qualities such as textures, ionization, etc.

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At another level Surfaces Modifications are not attempted, but such situations are negotiated with technologies. These include defining means to override the hindrances of texture, handling issues, electrical and other properties. These technologies also include forming shields around the users, tools and other equipments rather then over objects. The shields are physical layers and non-physical arrangements like restricting the exposure through time-space management.

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In early ages, the surface modification and applications were an integrated process for exploiting the surface of any object. Primitive arts and crafts had a comprehensive treatment that consisted of 1: Modification of the surface, 2: Application of surface forming materials, and 3: Rendering new textures and tonal variations or shades. At a later stage an additional treatments for protection of the new surface were devised.

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Surface modifications are physical, chemical and mechanical processes.

The Physical processes are mainly used to remove unwanted particles or materials (such as rust, nodules, residual deposits, dust or grease, lubricants, cutting-oils, etc.) adhering to the surface. Rubbing, air-dusting, vacuum cleaning, wiping, water-bathing, etc. remove such adhered materials. The particles have remained on the surface due to the holding by surface texture, bonding or ion attraction, and horizontal storage. Washing with soap or a surface active agent (surfactant) can weaken the ion attraction break the weak molecular bond generate by-products that can be removed easily.

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The Chemical processes include acid-alkali treatments and solvent washing. The processes roughen, etch or smoothen the surface. In many instances the resultant by-product is beneficial or neutral, and so allowed to remain on the surface. In other instances a secondary treatment is required just to remove the by-products of the first treatment. Sometimes Surface preparation agents themselves are the primary surface finishes. Such agents cover the surface area as an intermediary film. Such films help in bonding of the final surface finish. Chemical processes also include burnishing, flame-treatments, surface annealing and hardening, cathodic modification, sputtering and material’s depositions.640px-A_brass_utensil

The Mechanical Processes affect the surface superficially. Cleaning of the surface by removal processes include abrading, grinding, rubbing, blasting, planning, chipping, etc. Other mechanical processes alter the surface with newer textures by engraving, patterning, planning, surface deformation, etc.

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Surface modifications processes have been used for body painting, pottery, home building, agriculture, mural or wall artwork, adornments, jewellery, ornamentation, household utilities, tools, musical instruments, etc. Surface modifications were explored pattern making, texture creation, personalization, cultural expression, totem, abstract or symbolic representation etc.

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Surface levelling is achieved by scrubbing or rubbing off the impurities, removing select protruding sections, or by skinning the entire surface area. In later cases there are chances of removing a seasoned or matured face and exposing a fresh one. Partial scrapping of the surface creates qualitatively unequal zones. This is the reason why over the ages levelling ‘plasters’ have been preferred. The ‘plasters’ can be thin coating, or an application of thicker mass. These were often rendered with patterns and textures or ‘loaded’ with minerals and colourants. Wet surfaces were, either, engraved or embossed with patterns to encourage the penetration of colours, to produce a bas or relief effect, or provide a highlighting boundary to the drawn object. Colours were blown as dry powders or applied as pastes and dabbed (pressed) into the wet plaster.

Gesso, a mixture of plaster of Paris (or gypsum) with size, is the traditional ground. The first layer is of gesso -grosso, a mixture of coarse, un-slaked plaster and size. This provides a rough, absorbent surface for ten or more thin coats of gesso sotile, a smooth mixture of size and fine plaster previously slaked in water to retard drying. This labourious preparation, however, results in an opaque, brilliant white, light-reflecting surface, similar in texture to hard, flat icing sugar.

Other related Blogs

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LIST of BLOGS on COLOURS

COLOURS, COATINGS, PAINTS, PIGMENTS

Post 578 by Gautam Shah

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Colours > Wikipedia image > source Candy by Author terren in Virginia

1 UNDERSTANDING LACQUERS

https://interiordesignassist.wordpress.com/2015/08/16/understanding-lacquers/

2 LACQUERS or NC LACQUERS

https://interiordesignassist.wordpress.com/2014/04/27/lacquers-or-nc-lacquers/

3 SOLVENTS for THINNERS

https://interiordesignassist.wordpress.com/2015/08/09/solvents-for-thinners/

4 WOOD SURFACE FINISHING

https://interiordesignassist.wordpress.com/2015/07/13/wood-surface-finishing/

5 PAINT THINNERS Part 2

https://interiordesignassist.wordpress.com/2015/05/14/paint-thinners-part-2/

6 PAINT THINNERS Part 1

https://interiordesignassist.wordpress.com/2015/05/08/paint-thinners-1/

7 ROSEWOOD

https://interiordesignassist.wordpress.com/2015/03/26/rosewood/

8 INDUSTRIAL PAINT FINISHES

https://interiordesignassist.wordpress.com/2015/03/07/industrial-paint-finishes/

9 APPLICATION of COATINGS

https://interiordesignassist.wordpress.com/2015/01/09/application-of-coatings/

10 COATINGS -Surface finishing technologies

https://interiordesignassist.wordpress.com/2014/11/08/coatings-surface-finishing-technologies/

11 CLEAR COATINGS

https://interiordesignassist.wordpress.com/2014/09/12/clear-coatings/

12 FILM FORMING PROCESS in COATINGS

https://interiordesignassist.wordpress.com/2014/09/03/film-forming-process-in-coatings/

13 WOOD SURFACE PREPARATIONS for CLEAR COATINGS

https://interiordesignassist.wordpress.com/2014/04/28/wood-surface-preparations-for-clear-coatings/

14 SHELLAC COATINGS and FRENCH POLISHES

https://interiordesignassist.wordpress.com/2014/04/26/shellac-coatings-and-french-polishes/

15 VARNISH

https://interiordesignassist.wordpress.com/2014/04/25/varnish/

16 MULTI COATS of PAINT SYSTEMS

http://talking-interior-design.blogspot.in/2014/03/multi-coats-of-paint-systems.html

17 WOOD FINISHES

http://talking-interior-design.blogspot.in/2014/07/wood-finishes.html

18 CLEAR COATINGS

http://talking-interior-design.blogspot.in/2015/03/clear-coatings.html

19 CEMENT SURFACE FINISHES

http://talking-interior-design.blogspot.in/2015/06/cement-surface-finishes.html

Colour Palette

Colour Palette Flickr image by Rocco Lucia

20 CRAFT of WALL PAINTING (Neolithic)

http://talking-interior-design.blogspot.in/2014/02/the-craft-of-wall-painting-neolithic.html

21 CRAFT of WALL PAINTING (Palaeolithic)

http://talking-interior-design.blogspot.in/2014/01/the-craft-of-wall-painting-palaeolithic.html

22 COATINGS

http://talking-interior-design.blogspot.in/2013/09/coatings.html

23 COATINGS Iron age

http://talking-interior-design.blogspot.in/2013/09/coatings-iron-age.html

24 PRIMITIVE COATINGS Surfaces, Materials and Techniques

http://talking-interior-design.blogspot.in/2013/09/primitive-coatings-surfaces-materials.html

25 LIME-WASH

https://interiordesignassist.wordpress.com/2014/06/01/lime-wash/

26 PAINTING WHITE – 1

https://interiordesignassist.wordpress.com/2015/07/27/painting-white-1/

27 PAINTING WHITE – 2

https://interiordesignassist.wordpress.com/2015/07/29/painting-white-2/

28 BLACK Part – 1

https://interiordesignassist.wordpress.com/2015/08/07/black-part-i/

29 COLOURANTS DYES and PIGMENTS

https://interiordesignassist.wordpress.com/2014/07/15/colourants-dyes-and-pigments/

30 RED Colours of ancient times

https://interiordesignassist.wordpress.com/2015/05/22/red-colours-of-ancient-times/

31 ART COATINGS

https://interiordesignassist.wordpress.com/2015/05/25/art-coatings/

32 PRIMITIVE COATINGS # 1

https://interiordesignassist.wordpress.com/2015/05/03/primitive-coatings-1/

33 NATURAL IRON OXIDE PIGMENTS 4 # SIENNA and UMBER

https://interiordesignassist.wordpress.com/2015/05/01/natural-iron-oxide-pigments-4-sienna-and-umber/

34 NATURAL IRON OXIDE PIGMENTS -3 # Ochers

https://interiordesignassist.wordpress.com/2015/04/28/natural-iron-oxide-pigments-3-ochers/

35 NATURAL IRON OXIDE PIGMENTS – 2 # Red Oxides

https://interiordesignassist.wordpress.com/2015/04/27/natural-iron-oxide-pigments-2-red-oxides/

36 FLOOR PAINTS

https://interiordesignassist.wordpress.com/2015/03/21/floor-paints/

37 ARCHITECTURAL COATINGS -beginnings of OIL PAINTS

https://interiordesignassist.wordpress.com/2015/02/15/architectural-coatings-beginnings-of-oil-paints/

38 SURFACE PREPARATIONS

https://interiordesignassist.wordpress.com/2014/09/26/surface-preparations/

39 WHITE PIGMENTS

https://interiordesignassist.wordpress.com/2014/08/05/white-pigments/

40 CEMENT PAINTS

https://interiordesignassist.wordpress.com/2014/07/09/cement-paints/

 

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Colourful Shoes Morocco Wikipedia image source > http://www.flickr.com/photo/cloudzilla/2718019182/ by cloudzilla

41 OIL BOUND DISTEMPERS -OBD

https://interiordesignassist.wordpress.com/2014/07/03/oil-bound-distempers-obd/

42 CEMENT FINISHES part 2

https://interiordesignassist.wordpress.com/2014/06/27/cement-finishes-part-2/

43 DRY DISTEMPER or CALCIMINE

https://interiordesignassist.wordpress.com/2014/06/03/dry-distemper-or-calcimine/

44 ECOLOGY and COATINGS

https://interiordesignassist.wordpress.com/2015/03/09/ecology-and-coatings/

45 ENCAUSTIC PAINTING

https://interiordesignassist.wordpress.com/2014/06/06/encaustic-painting/

46 COLOURS and BUILDINGS

https://interiordesignassist.wordpress.com/2015/01/20/colours-and-buildings/

47 GLOSS

https://interiordesignassist.wordpress.com/2014/09/20/gloss/

48 COMPOSITION of COATING

https://interiordesignassist.wordpress.com/2014/07/29/composition-of-a-coating-3/

49 COLOURED GLASS

https://interiordesignassist.wordpress.com/2014/08/03/coloured-glass/

50 GRISAILLE -monochrome form of presentation

https://interiordesignassist.wordpress.com/2014/07/28/grisaille-monochrome-form-of-presentation/

51 WATER COLOURS

https://interiordesignassist.wordpress.com/2014/07/10/water-colours/

52 FRESCO PAINTINGS

https://interiordesignassist.wordpress.com/2014/06/24/fresco-paintings/

53 PRIMER COATINGS

https://interiordesignassist.wordpress.com/2015/06/07/primer-coatings/

54 SINGLE or MULTI COAT SYSTEMS

https://interiordesignassist.wordpress.com/2015/05/30/single-or-multi-coat-systems/

55 BRUSHES

https://interiordesignassist.wordpress.com/2015/03/29/brushes/

56 ENAMELS

https://interiordesignassist.wordpress.com/2015/02/18/enamels/

57 TEMPERA

https://interiordesignassist.wordpress.com/2015/01/24/tempera/

58 GP -General purpose paints

https://interiordesignassist.wordpress.com/2014/08/26/gp-general-purpose-paints/

59 COLOURS -Perception and Expression

https://interiordesignassist.wordpress.com/2015/03/07/colours-perception-and-expression/

Acrylic Colours stux

Acrylic art colours Pixabay image by stux

60 EMULSIONS

https://interiordesignassist.wordpress.com/2016/01/30/emulsions/

61 CLEAR versus PIGMENTED COATINGS

https://interiordesignassist.wordpress.com/2015/11/29/clear-versus-pigmented-coatings/

62 SELECTING and APPLYING a COATING

https://interiordesignassist.wordpress.com/2015/11/27/selecting-and-applying-a-coating/

63 COLOUR MODELS (RYB)

https://interiordesignassist.wordpress.com/2015/10/14/colour-models-ryb/

64 BLACK Part – II

https://interiordesignassist.wordpress.com/2015/09/17/black-part-ii/

65 MASONRY PAINT FINISHES

https://interiordesignassist.wordpress.com/2015/11/17/masonry-paint-finishes/

Artists coloursby skeeze

Artists’ colours Pixabay image by skeeze

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EMULSIONS

Post 577 by Gautam Shah

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Egg white, yolk and plant gums have been part of our life since prehistoric times, as thickening and emulsifying agents. Plant gums, like ‘Gum Arabic’ was used as thickening agent (and as a binder) for body paints, pottery colours and as a food emulsifier. Egg yolks and oil do not mix well but slowly whisking it can create a non separating, stable emulsion. This was technique was also used for forming colour pastes for wall paintings. The colours mixed into an emulsion did not drip or run during application. The egg offered substrate binding properties, whereas the oil helped protect the surface.

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Churning cream to make Butter > Wikipedia image by Adam Engelhart from San Fransisco, California, USA 

An emulsion is a mixture of two or more immiscible (that would not normally mix) liquids. It contains very small particles (droplets of microscopic or ultra-microscopic size) of one liquid distributed throughout the other. Chemically, these are colloids with liquids as both phases. In an oil-in-water emulsion, such as butter or margarine, the continuous phase is water and the dispersed phase is oil. Opposite to this, the water-in-oil emulsions, the oil is in continuous phase and water is dispersed into it. Butter and margarine, are examples of water-in-oil emulsions. Mayonnaise is an oil-in-water emulsion, stabilized with lecithin obtained from egg yolk. A mix of oil and water when agitated, forms a temporary emulsion, one where liquids separate immediately. But traditionally emulsifiers like gum Arabic, egg yolk, were used to stop the coalescence of oils droplets.

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Mayonnaise whisking > Wikipedia image >source http://.flickr.com/photos/fotoosvanrobin/3277764542/ author FotoosVanRobin from Netherlands 

Milk is a common example of an oil-in-water emulsion. Cream and Butter are both material combinations with same substances, but in different proportions. A Cream is oil-in-water emulsion whereas a Butter is water-in-oil emulsion. Their tastes and textures are though very different. Emulsion products include mayonnaise, margarine, hollandaise, icing, fillings, chewing gum, confectionery items, face creams, skin lotions, make-up products, hair dressing products, dyes, tanning compounds, medical formulations, lithography inks, oil bound distempers (*OBD), and plastic or latex paints. Emulsions deliver a liquid product dispersed in a carrier liquid to reduce the cost, disperse the applied material and add body to the formulation.

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Shaving Creams consist of an emulsion of oils, soaps, or surfactants and water> Wikipedia image by Coffeeaddict

Emulsions are formed and maintained by single or combination of processes like: Addition of an emulsifier, Mechanical mixing, Thickening agents and Heat energy. Stable emulsions can be undone by nullifying the effect of the emulsifier through chemical agents, freezing or high temperature heating.

Emulsifiers: An emulsifier makes the emulsion stable. Addition of surface-active agents reduces the interfacial tension between the dispersed and the continuous phases.

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Body Creams and Lotions > Wikipedia image by Gryffindor

Mechanical mixing: Vigorous stirring with or without stirrer blades causes the dispersible phase into finer droplets to form suspension in the continuous phase.

Thickening agents: Such agents increase the viscosity of the continuous phase, which prevents the movement and coalescence of dispersed droplets. Nominally emulsions have higher viscosity then their individual ingredients. Most emulsions are shear-thinning fluids where vigorous stirring can reduce the viscosity.

Heat energy: The viscosity and interfacial tension of the dispersing phase is reduced by heating.

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Ancient manner of Butter making in Canada > Wikipedia image

Transparency and Colour of Emulsions: The size of the droplet of the dispersing phase affects the light reflection, changing its transparency and colour. Emulsions are cloudy or milky in appearance when disperse-phase is of finer droplets. If the droplets are very large, then it is closer to simple dispersion or suspension. Emulsion paints are added with thixotropic agents that lower the viscosity on stirring before application, but on storage gain high viscosity to prevent settling of pigments.

Micro-emulsions are thermodynamically stable because the dispersed phase is 0.01–0.2 µm in size. Such emulsions have a characteristic transparency as their droplet size is <25% of the wavelength of visible light. Micro emulsions are stable due to the small size of droplets and high proportion of surfactants in the formulations.

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Screen printing Binders are Acrylic emulsions > Wikipedia image

Polymeric emulsions came into commercial use post 1940s. These are prepared with water as the phase, and stabilized with surfactants (molecules that are hydrophilic (water-loving) in one phase and hydrophobic (water-hating) in the other phase). The polymeric emulsions have very high molecular weight, and so when the water phase evaporates polymers coalesce into a tough film. Plastic or Latex paints as known in USA are plastic paints with polymeric emulsion-based formulations. First acrylic emulsion based ‘binders’ were produced for leather and fabric printing, but soon began to be offered as architectural coatings. Plastic paints were formulated at a time (1940s) when solvent-based paints made with alkyd or linseed oils ruled the markets. Oil paints’ were odorous, toxic, and flammable. Early acrylic paints didn’t bond well to ‘oil painted’ surfaces. Acrylic emulsions offered non yellowing, non cracking, environmentally safe, odourless and non-flammable system.

Plastic Paint

Acrylic Plastic paint application > Flickr image by http://www.charlesandhudson,com

Acrylic emulsion paint formulations are costly to produce in comparison to ‘oil-based’ paints, and other ‘plastic paints’ such as of Vinyl and PVA (polyvinyl acetate) systems. Interior emulsion paints have high vinyl and low acrylic contents. A paint with a high acrylic content will have much better water and stain resistance.

‘Emulsifying effects’ since prehistoric times, have now developed into science of fluid behaviour and mixing. The term emulsion has become synonymous for liquid-mix systems, and is used to designate solutions, suspensions, or gels.

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COATINGS WITH NON POLYMERIC SUBSTANCES

Post 546  by Gautam Shah

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Modern coating technology aims at two distinct targets, improvements in formulations and the technology of application. The formulations have been multipurpose as well as specific. Coating application methods primarily aim at high speed-pressure deposition of maximum proportion of solids, while minimizing the wastage due to over spray, drips etc. and economic use of VOCs (Volatile Organic Compounds). As a result, many combinations of formulation and application have been devised.

Ceramic coating over Metal as cutting edge Wikipedia image by Author SlonikkinolS

Coatings, traditionally were made of natural polymeric materials like starch, shellac, amber, cellulose, and rubbers. Man-made polymers have been known since 1832. Coatings of synthetic polymers provide better adherence and protection. Polymeric substances have been used in paints and other means of covering such as extrusion and dispersion. Such coverings (e.g. Teflon coating, PTFE, PFA) have heavier films than paints. Polymer covering materials replaced tin, chrome and cadmium plating in many instances. Polymer coating materials include alkyds, vinyls, acrylics, epoxies and polyurethane.

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Non-polymeric coatings or coverings are created through following basic routes.

1 Galvanic deposition: A metallic compound migrates from a high potential cathode, to the object, that is an anode. The migration is at molecular level with the formation of an alloy or like substance at the receiving end.

2 Oxidation: An oxygen donor fluid or substance is encouraged or facilitated to migrate and form an oxide coating to protect the substrate.

3 Melt Deposition: Metal, Ceramic or Polymeric substances in the form of particles, flakes, fine grains or foils are sprayed or fixed to the substrate, and are melted or fluidized with the help of heat (thermic, sonar, radiation, friction), before, during or after the deposition. The fluidized material forms not only a coating but integrates itself into the substrate.

Metalized polymer yarn Wikipedia image by Author rexess

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These techniques of material application are used in commercial processes known as:

  • Electrostatic coating
  • Electrophoretic Coatings
  • Anodization
  • Electrolysis of organic substances
  • Diffusion Coating
  • Electro-deposition
  • Spark hardening
  • Conversion and Conversion – diffusion coating
  • Chemical Vapour Deposition
  • Electro-less and electrolytic metal deposition
  • Welding as surface coating
  • Printing as coating
  • Air and airless spraying
  • Flame spraying
  • Metal sprayed, polymer, impregnated coatings
  • Detonation coating
  • Arc plasma spraying
  • Electric arc spraying
  • Electric harmonic spraying
  • Vacuum metalization of plastics and metals
  • Sputter deposition
  • Ion plating
  • Ion implantation
  • Microwave radiometry coatings

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Electrostatic process based printing-coating Wikipedia image by Author Guruleninn

Air electrostatic processes employ air forces to atomize the liquid material and then charge and deposit these particles using electrostatic forces. Articles to be coated are introduced to a space or chamber which provides negative charged environment. The atomized coating droplet on collision with ionized air picks up the negative charge and as result is attracted to the grounded article (to be coated). In another method the spray gun nozzle has an attachment to charge the coating droplets. In such processes, because of attraction there is no over spray wastage and deposition is very secure. Such processes are readily applicable for coating with suitable electrical properties and for articles that are conductive (metals).

Road Coatings Author English: Cpl. Ryan R. Jackson

For architectural coatings, polymeric formulations rule the scene. As majority of such finishes are based on emulsification with water, requiring negligible-amounts of volatile organic solvents. For wood and metals, modified alkyds that need organic solvents are being replaced with solvent-less formulations like powder-coatings. The products manufacturing at plant level, however are adopting metalizing, surface alloying, ceramic coatings, sputter deposition, Ion plating and Ion implantation sputtering technologies.

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COATINGS as thin Surfacing

COATINGS as thin Surfacing

Post 482  by Gautam Shah

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Coatings are thin surfacing with or without a colourant additive. The colourant if present, may be transparent, translucent or opaque. Coatings consist of many different components, such as a film forming substance, and additives like, colourant, reactive agents, solvents 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. Historically coatings were created as art medium for illustrative and decorative effects. These then began to be used to alter the appearance, improve the tangibility and to provide a protective cover to objects and human body.

Toroid_electronic

Phenolic Varnish coated Copper coil

Coatings are used for 1 changing the quality of the existing surface, and 2 applied as a permanent cover over an object. In the first case the changes are just few molecules deep, like: removal of few molecules of the object or some products from the surface section, rearrangement of the molecules, varied chemical formulation. In second case a composition is applied as a permanent coating, through bonding processes like adhesion, cohesion, chain linking, and material-phase change, intermolecular interactions including van der Waals forces, hydrogen bonds and strong covalent bonds.

Internal coating

Surface Treatments form a very important section of coating technology. Some surface treatments are temporary and are removed once the required action is accomplished, others remain as full or partial deposition. Many surface treatments serve specific purposes such as cleaning, roughening, smoothening, etching, moisture proofing, rust inhibiting, air barriers, static arresters etc. Some others only facilitate the application, setting or drying of the coating.

Anti Glare / Anti reflection coating on Glass

Traditional Coatings are usually liquids of low solids content. These first ‘dried’ by evaporation of substantial content of organic solvents, and later ‘set or hardened through oxidation and long chain formation. This technology began to fad out with use of Plastic or latex paints. These are applied as aqueous dispersions or water-based emulsion of polymers. Now formulations are also solvent less or powder coatings.

Micro Surfacing Road Paver

At application-stage the film-forming mediums are in various phases such as liquid, solid or vapour, or a combination thereof like, suspensions, solutions, dispersions, emulsions, thermoplastic compounds, thixotropic compounds, etc., but coatings once applied ultimately settle to a heavier phase, usually (but not necessarily) a solid phase.

Roof underside fireproof coating

At an application stage a lower phase helps in many ways. Mainly due to liquid state there is uniform and thin level of application. Liquid state of the material permits better dispersion of costly or rare constituents. During application the integrity (thorough dispersion of constituents) can be maintained. Energy required for application of coating is very small. Liquid coatings can be formulated for varied but controlled deposition and rate of phase conversion, to match the substrate and environmental conditions.

Glazed Bakery products

Coatings form a continuous film and so do not have joints, except at junctions where coating application is delayed (a dried out portion and a fresh coat touch each other or overlap). Coatings are thin surfacing so the coated entity remains malleable, and allow the post-forming operations (e.g. coated metal sheets). A coating film has a thickness ranging from 0.0005 to 0.5 mm (0.00002 to 0.02 inch). Coatings are deposited on the entity by many different techniques such as daubing, brushing, spraying, screen printing, roller coating, and dipping.

Wood Deck staining – Coating

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PRIMER COATINGS

Post 442 -by Gautam Shah

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Primer coat is the first surface build up on any substrate. It is designed to receive one or several more coats, immediately or some times later. A primer-coat is a surface preparation layer. It covers the surface irregularities like, chemical reactivity, and physical variations -colour, texture, porosity. A primer coat also offers a next application worthy surface.

Eiffel Tower Painting.jpg

A primer coat serves two distinct purposes: 1 It touches the substrate, often of many different types, and so must adhere to it, well, 2 It receives the next coat so functionally must be compatible with it. A primer coat helps in levelling the surface, and must have ‘body’ to fill up the pores, micro crevices, etc. Primer coat is sand papered for levelling, and to roughen up for application of second coat. Its some superfluous part gets rubbed and removed.

Primer coat is nominally applied on ‘virgin’ or an uncoated surface, and sometimes on very old coated surface. In the later case, the primer coat is slightly coloured white, off-white or some colour closer, but lighter then the final intended colour. When an old coat colour is to be ‘masked’ completely, primer coats or undercoats are coloured by a ‘masking colour’, such as Green by darker Red or Red by Blue. It is desirable to have primer of a slightly different and lighter colour shade than the subsequent coat, to differentiate a freshly coated surface and uncoated surface.

Primer failure

Primer coat is a technical coat, so its colour is not very important. The Primer-colours that we see are mainly due to the filler or body-pigments, called extenders. These are chosen for their protective effects and other technical qualities. Primer coats protect the virgin surface, and so are applied soon after the primary manufacturing is over, such as on pipes, sections, sheets, castings, etc. Good primer must remain adhered to the surface, even after other top coats are removed accidentally, or for renovation.

Brocha

Clear Sealer Coats: These are priming coats for application of clear coats, mainly wood surfaces. A sealer coat, like a primer prepares the fresh surface (of wood) for subsequent application. Sealer coat must be to be low viscosity, but high solid content material. Nitro cellulose clear has been found to be the most versatile sealer material. Other materials include variety modified pine Rosins. Clear sealer coats are often not categorized as priming coat, where the first application is a coat of ‘extender’ such as china clay, barytes or Calcium carbonate mixed with oxide colour. Such a coat covers, the irregularities of colour and grain patterns, fill up pores and micro crevices on wood surfaces. After sand papering-level rubbing it may be coated with a sealer coat. Sealer coats are preceded by staining compounds or coats, to add a translucent tinge on the surface.

white undercoat

A primer or sealer coat is the first coating applied to the objects’ surface, so it is required to:

● Regulate moisture movement in case of wood or masonry surfaces and provide corrosion resistance on metals

● Regulate the PH value and galvanic activity of the surface.

● Seal the surface so that oils, waxes, gases, vapours, salts and other reactive exudations from the object mass do not leach out in adverse conditions

● Fill up micro pores and crevices to level out the surface

● Provide temporary protection to the substrate from actions like abrasion, oxidation, sparking, ignition, insects attack.

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A great variety of primers are available in the market, but of following basic THREE categories:

Wood primers generally function as sealers, so have a high pigment + extender ratio. Wood sealers for clear coats are colourless coatings that help in sealing the grain. Commercial wood primers for pigmented paints are white or pinkish in colour due to the presence of white pigments and extenders, compared to metal primers (red-oxide) which, are dark coloured.

Wood Primer

Metal primers have rust inhibitive pigments or extenders like red lead, zinc oxide, zinc chromate, red oxide, calcium boro-silicate, barium metaborate, zinc molybdate, chromium fluoride, basic lead silico chromate, zinc ferrite, calcium ferrite. Under water (submerged) metal structures are coated with zinc rich primers based on epoxy, polyurethane systems or chlorinated rubber paints are used.

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Primer on Metal surface

Masonry primers are applied to alkaline surfaces, so are designed as non acidic mediums. Often such surfaces have high degree of loose particles, so Masonry primers have high proportion of binding materials. Commercially these types of primers are known as cement primers, and are available as water or oil-based formulations. Water-based formulations are mainly used on virgin masonry surfaces.

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SINGLE or MULTI-COAT SYSTEMS

Post 437 – by Gautam Shah 

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Coatings are applied as Single or Multi coat systems. The choice depends on several factors, such as:

  • Economics
  • Opportunity offered by technology
  • Emergency or routine application
  • Site accessibility in terms of location, weather, and tools available
  • First or virgin application or a re-coating job
  • Thickness of film required

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One-coat system has inherent efficiency, as it requires lesser amounts of material, solvents, curing energy, and takes less time for application. However, in one-coat systems, the coating is required to provide adhesion with the substrate, necessary film build or thickness, and also fully cover up the surface. Single coat systems have to be fail-proof, as there are no remedial opportunities. Performances of single-coat system, depends very closely on the type of (readily available) substrate. If the substrates are large then one has to select different coating system for different substrates or go for ‘All purpose system’.

Ship re painting involves huge effort of surface cleaning before multi-coat application

Multi-coat systems consist of two, three or more layers of applications, such as, Priming-coat (filler or sealing coats), Undercoat (sub coat or intermediate coats) and Finish-coat (top coat or surface coat) These multiple layers are designed to perform specific functions and also take care of any shortcomings of the preceding coats. In multi-coat systems, different coats can be applied at different times and locations, as required. Primer-coat can be a factory application, Intermediate-coat could be part of the installation procedure, while, the Final coat could be applied with other finish systems, just prior to usage. Multi-coat systems have an advantage over many high-build or one coat systems, in that the final coat can be of the same type for different substrates or undercoats. In multi-coat systems, the sub layers could be of economic materials, as it is the final layer that is exposed to the atmosphere, and provides the tangible surface finish.

Rubbing - Sand Papering the primer

Single coat systems are applied to save time and cost of application. Very large walls, giant structures (Eiffel tower, pylons, or Bridges), Road side barricades, Road marking signs, Ships, Marine structures, are some of the entities that must be re-coated in one effort. These are re-application systems, so the substrates have some form of existing coating. The condition could be, severely weathered surface, fatigued or peeled original coating, presence of salts and other reaction products, deposits of dust, grime, etc. Some of these extraneous or by-product matters cannot be removed easily or completely from where they exist (height, nooks, corners, etc.). Such structures are exposed to vagaries of weather, such as very high or low surface temperature, condensation, rains, humidity, high winds and environmental pollution. Where the technology of stripping of aged coatings is available, it may not work for such an extensive surface, including undersides.

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Multi-coat systems are as varied as their modes of applications are. Multi-coat systems have a prime or primer coat, followed by one or more finishing coats. Multi-coat systems need an interim ‘rest’ or through drying period, before next coat can be applied. Finishing coats are often designed as ‘removable or stripping system’ by mechanical grinding or chemical scrubbing, or both. Primer coats are specifically designed for the surface to be applied, such as wood, metal or masonry. Multi-coat systems are applied by exclusively by brushing, roller, spraying, dipping, or in combinations of it. With brush application final coating is by vertical strokes.

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