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Coating materials and surface

Since it is the resin in the coating's vehicle that determines its performance properties, coatings can be classified by their resin types. The most widely used resins for manufacturing modern coatings are acrylics, alkyds, epoxies, polyesters, polyurethanes, and vinyls.

Acrylics. Acrylics are noted for color and gloss retention in outdoor exposure. They are formulated as lacquers, enamels, and emulsions. Lacquers and baking enamels are used as automotive and appliance finishes. Both these industries use acrylics as topcoats for multicoat finish systems. Thermosetting acrylics have replaced alkyds in applications requiring greater mar resistance such as appliance finishes. Acrylic lacquers are brittle and therefore have poor impact resistance, but their outstanding weather resistance allowed them to replace nitrocellulose lacquers in automotive finishes for many years. Acrylic and modified acrylic emulsions have been used as architectural coatings and also on industrial products. The chemistry of acrylic-based resins allows them to be used in radiation curing applications alone or as monomeric modifiers for other resins. Acrylic-modified polyurethane coatings have excellent exterior durability.

Alkyds. Alkyd resin-based coatings were introduced in the 1930s as replacements for nitrocellulose lacquers. They offer the advantage of good durability at relatively low cost. These low - to medium-priced coatings are still used for finishing a wide variety of products, either alone or modified with oils or other resins. The degree and type of modification determine their performance properties. They were used extensively by the automotive and appliance industries through the 1960s. Although alkyds are used in outdoor applications, they are not as durable in long-term exposure, and their color and gloss retention is inferior to that of acrylics.

Once the mainstay of organic coatings, alkyds are still used for finishing metal and wood products. Their durability in interior exposures is generally good, but their exterior durability is only fair. Alkyd resins are used in fillers, sealers, and caulks for wood finishing because of their formulating flexibility. Alkyds have also been widely used in architectural and trade sales coatings. Alkyd-modified acrylic latex paints are excellent architectural finishes.

Epoxies. Epoxy resins can be formulated with a wide range of properties. These medium - to high-priced resins are noted for their adhesion, make excellent primers for most coatings over most substrates, and are used widely in the appliance and automotive industries. Their heat resistance permits them to be used for electrical insulation. When epoxy top coats are used outdoors, they tend to chalk and discolor because of inherently poor ultraviolet light resistance. Other resins modified with epoxies are used for outdoor exposure as topcoats, and properties of many other resins can be improved by their addition. Two-component epoxy coatings are used in environments with extreme corrosion and chemical conditions.

Polyesters. Polyesters are used alone or modified with other resins to formulate coatings ranging from clear furniture finishes-replacing lacquers-to industrial finishes-replacing alkyds. These moderately priced finishes permit the same formulating flexibility as alkyds but are tougher and more weather resistant. There are basically two types of polyesters: two-component and single-package. Twocomponent polyesters are cured using peroxides which initiate free-radical polymerization, while single-package polyesters, sometimes called oil-free alkyds, are self-curing, usually at elevated temperatures. It is important to realize that, in both cases, the resin formulator can adjust properties to meet most exposure conditions. Polyesters are also applied as powder coatings.

Two-component polyesters are well known as gel coats for glass-reinforced plastic bathtubs, lavatories, boats, and automobiles

High-quality one-package polyester finishes are used on furniture, appliances, automobiles, magnet wire, and industrial products

Polyurethanes. Polyurethane resin-based coatings are extremely versatile. They are higher in price than alkyds but lower than epoxies. Polyurethane resins are available as oil-modified, moisture-curing, blocked, two-component, and lacquers.

Two-component polyurethanes can be formulated in a wide range of hardnesses. They can be abrasion-resistant, flexible, resilient, tough, chemical-resistant, and weather-resistant. Polyurethanes can be combined with other resins to reinforce or adopt their properties.

Polyurethanes have become very important finishes in the transportation industry, which includes aircraft, automobiles, railroads. ships. Owing to their chemical resistance and ease of decontamination from chemical, biological, and radiological warfare agents, they are widely used for painting military land vehicles, ships, and aircraft.

Polyvinyl chloride. Polyvinyl chloride (PVC) coatings, commonly called vinyls, are noted for their toughness, chemical resistance, and durability. They are available as solutions, dispersions. They are applied as lacquers, plastisols, organisols, and lattices. PVC coating powders have essentially the same properties as liquids.

Vinyls have been used in various applications, including automobile interiors, and office machine exteriors. They are also used as thick-film liquids and as powder coatings for electrical insulation. Owing to their excellent chemical resistance, they are used as tank linings and as rack coatings in electroplating shops. Vinylmodified acrylic latex trade sale paints are used as trim enamels for exterior applications and as semigloss wall enamels for interior applications.

Other coating resins

In addition to the aforementioned materials, there are a number of other important resins used in formulating coatings. These materials, used alone or as modifiers for other resins, provide coating vehicles with diverse properties.

Aminos. Resins of this type, such as urea formaldehyde and melamine, are used in modifying other resins to increase their durability. Notable among these modified resins are the superalkyds used in automotive and appliance finishes.

Uses. Melamine and urea formaldehyde resins are used as modifiers for alkyds and other resins to increase hardness and accelerate cure.

Cellulosics. Nitrocellulose lacquers are the most important of the cellulosics. They were introduced in the 1920s and used as fast-drying finishes for a number of manufactured products. By modifying nitrocellulose with other resins such as alkyds and ureas, the VOC content can be lowered and performance properties can be increased. Other important cellulosic resins are cellulose acetate butyrate and ethyl cellulose.

Uses. Although no longer used extensively by the automotive industry, nitrocellulose lacquers are still used by the furniture industry because of their fastdrying and hand-rubbing properties. Cellulose acetate butyrate has been used for coating metal in numerous applications.

Chlorinated rubber. Chlorinated rubber coatings are used as swimming pool paints and traffic paints.

Fluorocarbons. These high-priced coatings require high processing temperatures and therefore are limited in their usage. They are noted for their lubricity or nonstick properties due to low coefficients of friction, and also for weatherability.

Fluorocarbons are used as chemical-resistant coatings for processing equipment. They are also used as nonstick coatings for cookware, friction-reducing coatings for tools, and dry lubricated surfaces in many other consumer and industrial products.

Oleoresinous. Oleoresinous coatings, based on drying oils such as soybean and linseed, are slow curing. For many years prior to the introduction of synthetic resins, they were used as the vehicles in most coatings. They still find application alone or as modifiers to other resins.

Phenolics. Introduced in the early 1900s, phenolics were the first commercial synthetic resins. Phenolic resins, used as modifiers, will improve the heat and chemical resistance of other resins. Baked phenolic resin-based coatings are well known for their corrosion, chemical, moisture, and heat resistance.

Phenolic coatings are used on heavy-duty air-handling equipment, chemical equipment, and as insulating varnishes. Phenolic resins are also used as binders for electrical and decorative laminated plastics.

Polyamides. One of the more notable polyamide resins is nylon, which is tough, wear-resistant, and has a relatively low coefficient of friction. It can be applied as a powder coating by fluidized bed, electrostatic spray, or flame spray.

Applied as a powder coating, nylon provides a high degree of toughness and mechanical durability to office furniture.

Polyolefins. These coatings, which can be applied by flame spraying, hot melt, or powder coating methods, have limited usage.

Uses. Polyethylene is used for impregnating or coating packaging materials such as paper and aluminum foil. Certain polyethylene-coated composite packaging materials are virtually moisture-proof. Table 10.19 compares the moisture vapor transmission rates of various coatings and films. Polyethylene powder coatings are used on chemical processing and food-handling equipment.

Polyimides. Polyimide coatings have excellent long-term thermal stability, wear, mar and moisture resistance, as well as electrical properties. They are high in price.

Silicones. Silicone resins are high in price and are used alone or as modifiers to upgrade other resins. They are noted for their high temperature resistance, moisture resistance, and weatherability.

Coating selection is not easy, owing to the formulating versatility of modern coating materials. This versatility also contributes to one of their faults, which is the possible decline in one performance property when another is enhanced. Because of this, the choice of a coating must be based on specific performance properties and not on generalizations.

References

resin acrylic polyester

1. Modern plastics handbook / Modern Plastics, Charles A. Harper (editor in chief). - NY: McGrаw-Hill Prоfessional, 2000. - 1232 p.

2. Resin and plastics // catalog - M: IB «Infoprom», 1991. - 567 p.

3. Egorova E.I., Kopternarmusov V.B. The basic technology of polystyrene plastics - SPb.: KHIMIZDAT, 2005. - 272 p.

1. Харпер Ч.А. Современные пластмассы: справочник - Нью Йорк: McGrawHill Professional, 2000-1232 с.

2. Смолы и пластмассы // каталог - М.: ИБ «Инфопром», 1991. - 567 с.

3. Егорова Е.И., Коптенармусов В.Б. Основы технологии полистирольных пластиков - СПб.: ХИМИЗДАТ, 2005. - 272 с.

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