ECOLOGY and COATINGS

Post 359 – by Gautam Shah 

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Coatings (Paint, Varnish, etc.) consist of organic as well as inorganic substances. Both the categories of materials can be hazardous at several levels such as: production, application, curing or drying, functional use, and disposal level.

Claude Monet Waterloo Bridge London

At production level the handling and use of certain raw materials can be hazardous. Typically handling of extenders and pigments can pose air-bourne particle spread. Some of these silica containing materials are toxic and carcinogenic and not eco-friendly. Resins (amino) with styrene and formaldehyde are carcinogenic. Solvents are known fire prone materials. At application level, the primary hazard occurs, due to high amounts of volatile organic content going into air. Its vapours or odours are noxious, allergic and unpleasant. The odour suppressants added to coatings are not necessarily benign. At application level, old coated surfaces are rubbed or scrapped, the particulate matter of which causes air pollution and the constituents are often unfamiliar.

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Aerosols cause high level of air pollution

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Post application, the wearing surfaces and peel-off cause, dust pollution. Some of the plastic materials continue to deteriorate, evolving pollutants. Coatings used on kitchen shelves, utensils, equipments cause contamination. Accidental high heating and fire scorch a coating. Planned removal of coating by sanding and chemical etchings (paint scrubbers or removers) can also leave unwanted residual products. Disposal of coated items by sawing, forced removal, hammering, chiselling, sanding, scrapping, etc. can desecrate the environment.

PIGMENTSClay colours

Prolonged or high intensity exposure to paint and paint fumes can affect three main organs, lungs, kidney and lever. These manifest as headache, allergies and asthmatic reactions, irritation of skin and eyes, burning in nose, airways, urinary tracts.

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The trend world over is to design entities with their own or integrated surfaces. A variety of metal and polymer surface treatments are available that molecularly change the quality of the surface. Such `surface systems‘, rather than `surface finishes‘ often do not require any application of foreign substances. A variety of single or a combination of treatments like temperature, radiation, sonar, mechanical finishing, stress induction and relief, cathodic protection etc. can eliminate organic coating systems. Such surfaces do not have any applied finishes, but rather have a generated finish.

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There are many inorganic coating systems that are akin to metallizing systems. In such systems the role of medium is to carry and spread the pigment and other substances. On baking or firing the medium is evaporated or burnt off leaving metallic or alloying compounds on the surface. Such substances are generally heat or flame cured to cross links with the substrate material.

Volatile Organic Compounds VOCs

VOCs are volatile solid or liquid organic compounds that evaporate readily due to high vapour pressure (volatility or low boiling point) at ordinary room temperature. VOCs are of many varieties, like natural or man-made materials. Most of the scents or odours have VOC components.

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There are broadly two classes of VOCs, Anthropogenic (caused or produced by humans), are in low concentrations but with cumulative or long-term health effects, and Biogenic (caused through biological processes). VOCs. Anthropogenic, A-VOCs constitute substantial hazards in Urban areas. B-VOCs occur everywhere. Some VOCs are labelled as carcinogenic (cancer causing). Indoor environments may not have very high emissions of VOCs, but the concentrations can reach to be 2 to 5 times (or even more) than in outdoor air. Indoor environments of new buildings generate large amounts of VOC in the immediate time period. VOC concentration in an indoor environment during winter is 3 to 4 times higher than during the summer. High VOC levels in indoor areas are also due to the poor dilution of air resulting from barriers and resulting in air stagnancy.

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VOCs exposure mainly occurs through inhalation and to a smaller extent through skin or touch. Health hazards include, respiratory and allergic effects resulting in burning sensation in eye, nose, throat, nausea, fatigue, dizziness, loss of coordination and damage to the liver, kidney, and central nervous system.Some major sources of man-made VOCs are coatings, especially paints and other coatings (solvents, waterproofing compounds, gums, sealants, paints, thinners, paint removers, cleaning agents, soaps, cosmetics, rubber goods ). Water-based coatings produced from gums, casein, egg-whites etc. and with cementious compounds like lime, gypsum, etc., water emulsified, polymer paints help meet the ecological concerns for VOCs.

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Managing the VOCs

  • Avoid use of VOC products.
  • Reduce exposure to VOCs.
  • Increase indoor ventilation while applying such products.
  • Purchase and consume entire mass of VOC products as immediately as possible.
  • Isolate areas of high VOC such as application and storage rooms, if required exploit means of passive micro ventilation.
  • Never mix household care products unless permitted.
  • Some VOCs, such as styrene and limonene, can react with nitrogen oxides or with ozone to produce new oxidation products and secondary aerosols.

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INDUSTRIAL PAINT FINISHES

Post 357 – by Gautam Shah 

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Large number of items and components are available in ready to use state with a suitable finish. These products require no extra treatment or coating, before or after the installation. The industrially finished items are class apart from finishes applied on a site, after assembly or erection.

An industrial plant offers streamline production system, in a batch or a continuous fashion. Industrial plant-based surface finish is a process integrated with production and highly articulated one. It is invariably conducted in a controlled environment and observance.

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Two men on a platform painting Hull of a ship Himalaya >Wikipedia Image by Australian Maritime Museum

Site applied surface finishes, substantially consist of architectural coatings, and are multi surface applications (general purpose or GP systems). Other on site applications, but not forming part of architectural range, include Road marking paints, Marine paints, and re-application systems. On a site coatings are employed in a wide range of weathers and in open environments. Architectural coatings, for ‘drying’, rely mainly on moisture evaporation, induced polymerization, and in few instances on catalyst curing (popularly known as ‘two-pack’) systems. Architectural coatings are applied, chiefly on masonry, and than to lesser extent on wood and metal surfaces.

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Prez Obama and wife help paint Habitat for Humanity site, Washington, Official white house Photo-stream Image by White House (Pete Souza) / Maison Blanche (Pete Souza) 

Industrial finishes are very specific systems, formulated for a particular substrate, object shapes, sizes, pre-treatments, method of application and drying or curing cycles and schedules. As a result, complex surface finish technologies can be used. Industrial finishes offer qualitatively a far superior finish compared to any site-based system.

Dipping treatment for Automotive industrial coating

An industrial coating, forms a very small and often a negligible part of the total cost of the product, its failure in any form destroys the entire value of a product, and manufacturing company’s reputation. Defects of industrial coatings, if any are realized after the product has reached the consumer. Remedial measures are impracticable, and it entails a recall of the product from unknown or far off locations. Industrial coatings must be continuously upgraded. Otherwise, a technologically superior product gets rejected from the market due to its aesthetic and sensorial appeal.

White-goods Consumer appliances

Industrial finishes are generally low in pigments or extenders and high to medium ‘build’. Quality of the finish is largely determined by the type of film forming mediums used. Many industrial finishes are formulated for baking-drying to achieve a hard, stable and durable finish. Amino and epoxy resin coatings dry by catalyst action. In powder coatings thermo-setting materials are heat liquefied to set. Industrial coatings also include air drying, partially air drying & low temp baking, stowing, radiation-curing, solvent-evaporating, oxygen polymerizing (oxidizing) heat polymerizing and catalyst curing, thermo plasticizing carbonating, systems. Industrial products receive pre-treatments to make their surfaces suitable for a single system of coating and through single application. The pre-surface treatment include moisture conditioning, rust inhibiting, galvanic control, texturing and levelling of the surface, etc.

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Wikipedia image > Image by http://flickr.com/photos/mikebabcock/

 

Industrial finishes can be classified as:

  • Traditional systems  

These are based on alkyd resin technology

  • Lacquers

High molecular weight resins, such as vinyls, acrylics, chlorinated rubber, etc. that are dissolved in a solvent and do not undergo any chemical change on drying.

  • Dispersion mediums

  These are dispersions of convertible system.

  • Latex systems

Contain resins dispersed in water or other liquid that do not dissolve them. Resins are invariably high molecular weight polymers.

  • Chemically curable systems

These are made of thermo-setting resins of low molecular weight such as epoxies or urethane, that in the presence of a chemical or catalyst complete the bond formation.

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Today industrial coatings are also seen in terms of environmental compliance, or the pollution hazard they can cause. The total volatile organic component, VOC. criteria is a factor that defines the worthiness of a coating system.

Water borne coatings: 

These are made from emulsion, water reducible and aqueous colloidal dispersions.

High solid coatings:

High solid coatings are frequently based on conventional polymers but with low molecular weight.

Powder coatings: 

These are based on thermoset and thermoplastic resins with pigments, fillers and additives such as hardeners and flow agents.

Advantages of Industrial coatings: Items which are difficult to coat due to their shape, size or location can be efficiently coated in an industrial set up. Items with sharp corners and edges can be coated evenly. Certain types of pre-treatments, which are not possible on a building site can be carried out at plant level. Materials and methods which are difficult to handle, or are normally hazardous on a site, can be employed at plant level. Industrial application of coating is very efficient and controlled so very thin film thickness can be achieved, and lot of wastage on account of drips and over sprays can be eliminated. Many application techniques, tools, equipment can only be used at plant level set up.

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Industrial Coatings include White goods (consumer products of chiefly white-coloured, but not always; such as refrigerates, washing machines, ovens, gas stoves, geysers, fans, air conditioners); Consumer electronic products such as computer and server cabinets; Industrially produced furniture such as chairs, cabinets, tables, partition systems; Vehicle products such as cycles, scooters, bikes, cars, trucks, buses; Extruded or formed Long products such as steel, aluminium and composite sections, and pipes; Besides these there are several applications where clear (pigment less) or non toxic coatings are used such food containers, toys, etc.

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GP – General Purpose Paints

Post 165  –by Gautam Shah

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In Building Industry many different types of finishes are used for covering non-masonry surfaces such as Ferrous Metals, alloys, aluminium, wood, and wood composites. In many cases the surfaces are composed of many different types of materials, textures and forms. Often the extent of each individual type of surface is so small and its composition so complex that it may not be feasible to attend to different surfaces.

HK_Sai_Ying_Pun_Des_Voeux_Road_West_Dulux_Painting_Material_Shop_3Most paint manufacturers offer a General purpose coating systems (GP) for such situations. The coatings are nominally conceived to be multi layer systems (at least of primer, inner and top-final coat). GP coating systems work for the inner and top coat, however, a primer coat is specific for the surface. It is specifically designed for the substrates such as masonry-cement primer, wood primer, mild-steel or iron primer.

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GP or General Purpose coatings are used for following situations:

On items that are difficult to coat– Such as deep grooves, undersides, inaccessible areas, narrow stripes, engravings, sharp corners and edges, very smooth surfaces, small parts like lattices.

On locations with difficult access– High level ceilings, external sides of windows in multi storey buildings, roof trusses.

In variable atmospheric conditions– Rain and snow storms, very high to very low humidity environments, dust, sun rays, wind, flying insects, very high to very low temperatures.

In single or multi coat systems– Some initial coatings at plant level as specific coating system and rest on the site as GP system.

For specific purpose– As a fresh system (on a virgin surface), as a re-application system (re-coating with a similar but over an aged surface) or as a renovation system (removal of aged coating layer, repairs and coating).

With peripheral hazards– Fire, chemical vapour and odours, colour dropping or running, and over-sprays.

GP enamel Painted Interior of Bang Pa In Chinese style palace

Such site applicable finishes are designed to dry out at normal atmospheric conditions. Most of the GP finishes allow multiple methods of application, and are applicable in widely variable atmospheric conditions.

Brooklyn Bridge painters at work high above New York City

GP = General Purpose Paints, as a term are nominally synonymous with Enamel Paints (Oil resin based), but now the term is also used for ‘Plastic’ emulsion paints (Latex paints in American terminology). Such plastic paints are masonry paints for walls,  roof-tiles, floors and stage-sets. These are often favoured over oil based enamel paints due to non-glossy (matt) finish and faster drying capacity.

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OIL BOUND DISTEMPERS -OBD

 

Post by – Gautam Shah

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Oil bound distemper is one of the most common and oldest oil and water dispersion coating system for masonry surfaces. These emulsion-distempers, are better then Calcimine. This is now outdated technology in many parts of the world. Such  paint, however, are produced and used in many developing countries of the world. It is rather easy to procure the raw materials and produce it with very little use of power, tools or equipments. It is comparatively an eco-friendly system, as it has very small amounts toxic materials or petroleum solvents.

The Oil Bound Distempers are made by emulsifying Bodied drying oils or their alkyds with water in the presence of casein, glue dextrine (which also provide the film).

Traditionally distemper or glue based interior paints were made with either animal hide glue or rabbit skin glue. Glue is heated and mixed with a paste of slaked (water soaked) whiting or calcium carbonate and pigment paste. Glue-based distempers were preferred as its pH was compatible with alkaline masonry and plaster surfaces. Oil paints were difficult and costly to produce, and peeled of from the alkaline surfaces. Distemper are water based systems and so dry out very fast, so preferred for not only interior surfaces but wood, paper and canvas  surfaces in art works. These are used for restoration of architectural heritage of 19th C later periods.

Distemper on palm leaf Buddhist art 12th C

Water is mixed with casein, glue or dextrine and an alkali, such as lime or soap, is combined with the oil component such as the Bodied drying oils or their alkyds. The mixture is heavily agitated and emulsion is formed. Stabilizers (to preserve the state of suspension) and antibacterial agents are then incorporated for prolonged storage life.

The film is first formed due to evaporation of water, The Glue component, on removal of water provides the binding. The oil component then forms a latticed (porous) film on the top part of the surface. Oil oxidation of the oils may take more then 24 hours. The hardened film becomes moderately wipe-able or the commercial signature ‘washable distemper’ (compared with the Calcimine) .

After two or three coats over a period of 5/10 years, repainting becomes difficult. Fresh coat of OBD over old OBD softens it to some extent, and causes it to swell. The strength of coating is less than that of oil paint. During drying, the OBD film shrinks substantially and exerts a considerable pull over the underlying film.

Raphael The Miraculous Draught of Fishes 1515

Distempers are essentially masonry coatings so contain substantial amounts of, extenders as bodying agent. Extenders are low refractivity white mineral powders like Calcium Carbonate, Barytes, talc, etc. Extenders also reduce the need for White pigments (high refractivity powders) such Zinc Oxide, Titanium Dioxide. etc.

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Oil Bound Distempers do not have rich hue colours. Majority of commercial shades are of pastel variety(white added tones). Due to a low amount of Oil or related constituents in the emulsion the finish is low gloss or dull (low sheen or matt).

Oil bound-distempers or OBD, are sold in viscous paste form, reducible with plain water or special thinning liquids, to brush-able viscosity. Proprietary thinning compounds are very light <oil in water> emulsions, often with additives such as silicone oil, stabilizers, plasticizer, and antibacterial agents and occasionally organic solvents.

MiG-3 aircraft in winter Washed out distemper as a camouflage World_War II

Water-based latex paints

Oil bound distempers are difficult for re-coating purposes. Their water resistance is also not very good. So some time in 1950-1960s a range of Vinyl-based emulsion polymers began to replace the caseins and natural gums -the most moisture susceptible components. Later even the oils were eliminated. Resultant new product was known as the water-based latex paint. Latex is a term more used in USA, where all plastic emulsion products were also known as Latex systems. In most other countries Plastic emulsion paint is popular term.

Dieric Bouts The Entombment Artron

Vinyl-based emulsion coating systems had good binding and slightly better water resistance, but their UV (solar light) resistance was poor. It made the film tacky -attracted moisture (on the breakdown of polymer chain). The product soon saw a replacement with Acrylic Polymer-based emulsions. Both the products were marketed as Latex or Plastic Distempers, fully washable distempers or synthetic distempers.

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Water bound systems are favoured by films, drama and TV scenographers for set making and and scenery backdrops, for three reasons, Fast drying quality, matt (non reflective) surface and high level of opacity (presence of whiting offers better hiding power).

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