Difference between revisions of "Coating"

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! '''Disadvantages'''
 
! '''Disadvantages'''
 
|-
 
|-
| Acrylic
+
| [[Acrylic resin|Acrylic]]
 
| Premixed solutions of acrylic  polymer bits dispersed in water; cures by drying, multiple options for clear  or colored coatings.
 
| Premixed solutions of acrylic  polymer bits dispersed in water; cures by drying, multiple options for clear  or colored coatings.
 
| May emit acetic acid vapors  (allow 4 weeks cure); cleans with soap and water while wet
 
| May emit acetic acid vapors  (allow 4 weeks cure); cleans with soap and water while wet
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| Surface must be well-prepared  for optimal adhesion
 
| Surface must be well-prepared  for optimal adhesion
 
|-
 
|-
| Alkyd
+
| [[Alkyd resin|Alkyd]]
 
| Oil-modified polyester that  cures through oxidation
 
| Oil-modified polyester that  cures through oxidation
 
| May release peroxides and  carboxylic acids; cleans with solvent based products
 
| May release peroxides and  carboxylic acids; cleans with solvent based products
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| Cannot be used directly on a  substrate; provides little protection from tensile or compressive stress
 
| Cannot be used directly on a  substrate; provides little protection from tensile or compressive stress
 
|-
 
|-
| Epoxy
+
| [[Epoxy]]
 
| Two component solution (epoxy  resin and hardener) carefully mixed prior to used; water-based options  available
 
| Two component solution (epoxy  resin and hardener) carefully mixed prior to used; water-based options  available
 
| Careful mixing and curing  required
 
| Careful mixing and curing  required
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| Surface must be well-prepared to  ensure adhesion
 
| Surface must be well-prepared to  ensure adhesion
 
|-
 
|-
| Polyester
+
| [[Polyester resin|Polyester]]
 
| Synthetic resin that hardens  with a catalyst
 
| Synthetic resin that hardens  with a catalyst
 
|  
 
|  
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| Application requires precise  control over temperature and humidity to fully cure.
 
| Application requires precise  control over temperature and humidity to fully cure.
 
|-
 
|-
| Polyurethane  (aliphatic)
+
| [[Polyurethane |Polyurethane]]   (aliphatic)
 
| Pre-mixed solution of a polyol  with an isocyanate; cures with moisture in air; water-based options available
 
| Pre-mixed solution of a polyol  with an isocyanate; cures with moisture in air; water-based options available
 
| Must be cured completely at  optimal conditions of moisture and temperature; isocyanate is a carcinogen
 
| Must be cured completely at  optimal conditions of moisture and temperature; isocyanate is a carcinogen
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| Requires spray booths and ovens,  difficult to achieve thin coatings
 
| Requires spray booths and ovens,  difficult to achieve thin coatings
 
|-
 
|-
| Silicone
+
| [[Silicone resin|Silicone]]
| Oligosiloxanes dispersed in  water that dry into a flexible siliocne resin
+
| Oligosiloxanes dispersed in  water that dry into a flexible silicone resin
 
| Spray, dip or paint; clean with  soap and water; does not need primer; non toxic
 
| Spray, dip or paint; clean with  soap and water; does not need primer; non toxic
 
| Heat and moisture resistant,  good adhesion, highly flexible, may be used on multiple surfaces even fabric  and concrete
 
| Heat and moisture resistant,  good adhesion, highly flexible, may be used on multiple surfaces even fabric  and concrete

Revision as of 13:10, 13 October 2024

Coated wood soldier
MFA# 55.801

Description

A thin layer deposited or applied on the surface of an object (substrate). The primary purpose of applying a coating is to improve an objects critical properties and to create a protective barrier against deterioration of the surface. Secondary purposes may be aesthetic. Coatings may be applied as liquids, gases or solids e.g. powder coatings.

Examples of the types of materials are used for coatings include:

Often coatings are used to achieve multiple goals. For example, coatings can be formulated to:

  • Seal a surface, form a barrier, change color, produce or minimize texture, maintain surface appearance, be anti-corrosive, be anti-reflective, decrease friction, increase wearability, minimize light transmission, provide adhesion, prevent adhesion (non-stick), provide flame resistance, and to provide identification.

A major consideration for most coating processes is to control coating thickness and adhesion. Methods of achieving this range from a simple brush to expensive precision machinery.

  • Application processes include: draping, brushing, rolling, dipping, spraying, baking, shrink-wrapping, vapor deposition, electroplating, anodizing, printing and laminating.
Common coatings Process Application Advantages Disadvantages
Acrylic Premixed solutions of acrylic polymer bits dispersed in water; cures by drying, multiple options for clear or colored coatings. May emit acetic acid vapors (allow 4 weeks cure); cleans with soap and water while wet Cost effective, dry quickly easy to use, resists weathering and fading, environmentally friendly Surface must be well-prepared for optimal adhesion
Alkyd Oil-modified polyester that cures through oxidation May release peroxides and carboxylic acids; cleans with solvent based products Glossy finish, robust; resistant to weathering and wear; glossy finish Slow drying, strong odor during application
Ceramic coating Resin made of silica and titanium dioxide applied using a spray gun, chemically bonds to paint below Primarily used as a high gloss top coat for autos Improves durability and wear resistance; has low surface tension; Cannot be used directly on a substrate; provides little protection from tensile or compressive stress
Epoxy Two component solution (epoxy resin and hardener) carefully mixed prior to used; water-based options available Careful mixing and curing required Excellent for metal surfaces, high moisture resistance; resistant to corrosion and damage Surface must be well-prepared; coatings are sensitive to UV light and temperature; low flexibility
Polyaspartic Polyurea coatings formed by reaction with polyisocyanates and aspartic esters Buildings, bridges, automobiles Cures rapidly; highly durable, resistant to weathering and wear; maintains high gloss, does not yellow Surface must be well-prepared to ensure adhesion
Polyester Synthetic resin that hardens with a catalyst Strong, durable surface; withstands abrasion, weathering and wear; flexibility minimizes cracking Application requires precise control over temperature and humidity to fully cure.
Polyurethane (aliphatic) Pre-mixed solution of a polyol with an isocyanate; cures with moisture in air; water-based options available Must be cured completely at optimal conditions of moisture and temperature; isocyanate is a carcinogen Often used as a top coat, highly durable, resistant to wear and weather; excellent gloss and color retention; low VOC formulations available
Powder Coating An electrostatic process to adhere powder-based substance onto a charged metal surface followed by heat curing. Metals, household applieances, automobile parts Coatings are durable with many color options; no solvents are used thus no VOCs emissions; typically used on metals Requires spray booths and ovens, difficult to achieve thin coatings
Silicone Oligosiloxanes dispersed in water that dry into a flexible silicone resin Spray, dip or paint; clean with soap and water; does not need primer; non toxic Heat and moisture resistant, good adhesion, highly flexible, may be used on multiple surfaces even fabric and concrete Requires up to 48 hours to fully cure; heat and UV light can speed curing
Polysiloxane Option that combines silicone and polyurethane properties, without using isocyanates Applied directly to primed steel or previously painted substrates by brush, roller or spray; low VOCs Durable, glossy finish; highly resistant to UV, weather, and chemicals; retains color and gloss Surface must be well-prepared to ensure adhesion; low flexibility

Synonyms and Related Terms

coat; surface coat; Anstrich (Deut.); enduit (Fr.); revêtement (Fr.); recubrimiento (Esp.); rivestimento (It.); revestimento (Port.)

Collection Risks

(from Tetreault 2017) "Coatings formed by oxidative polymerization, such as oil-based paints, oil-based urethanes, alkyds, melamine and epoxy esters (one-component or one-part systems), should be avoided in museums because they release acids and peroxides that can harm objects, especially papers, metal objects (lead, copper and their alloys) and black and white photographs. Fortunately, with new volatile organic compound (VOC) regulations in Canada and the United States, these coatings are becoming less and less available. The coatings that are generally acceptable in archival and museum contexts are acrylic or acrylic-urethane emulsion paints (latex) and, for special applications, two-part epoxy and two-part urethane paints."

Resources and Citations

  • Jean Tétreault, Products Used in Preventive Conservation CCI, December 2017. Link
  • Corrosionpedia: Coatinghttps://chansmachining.com/types-of-industrial-coating/ Accessed October 2024
  • Wikipedia: Coating Accessed Oct 2024
  • Chans Machining: Industrial coatings Accessed October 2024
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • ASTM, "Standard Terminology Relating to Paint, Varnish, Lacquer and Related Products", Annual Book of ASTM Standards, Section 6, Paints, Related Coatings and Aromatics, ASTM, D16, 7-Jan, Jul-96
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • Art and Architecture Thesaurus Online, http://www.getty.edu/research/tools/vocabulary/aat/, J. Paul Getty Trust, Los Angeles, 2000

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