- Basic Coating Systems
- Coating Properties
- Additional Considerations
The distinctive colors of copper and copper alloys make them prized for architectural and consumer items and objects of art. Their natural metallic tones range from reddish to silvery and a number of other colors can be obtained by chemical or electrochemical processing. Copper and its alloys are extremely resistant to corrosion, but a superficial discoloring tarnish eventually forms with exposure to the atmosphere or handling. The appearance of these metals can be preserved by applying thin clear protective coatings to their surfaces. These coatings are organic chemicals which harden at room temperature or with baking and are usually applied in a solvent vehicle.
There are hundreds of useful clear coating products on the market, formulated from numerous polymers, solvents, and additives. The user selects from these a coating based upon economics, intended life, desired transparency, and the expected service conditions.
Many coating manufacturers prefer to custom blend coatings and work closely with the user to solve his particular problems. There are also a large number of standard compositions which can be ordered by trade name and which will satisfy many needs.
Because of the wide range of compositions available only general characteristics of the various systems and additives are reviewed here. Test results for representative coating systems are presented to indicate the range and type of properties which may be obtained. But it must be remembered that the effectiveness of a finish also depends on the composition of the underlying metal and on the cleaning and application procedures used when coating.
It is not possible to quantitatively predict from its properties how long or how well a coating will protect the substrate. To answer this question it is necessary to apply the coating to the metal under shop conditions and expose the combination to an environment representative of the intended service.Back to Top
Coatings are available which can protect copper-base metals for many years under ideal conditions. However, handling, humidity, air pollution, sunlight, and abrasion all work to reduce the life of a coating. For example, coating life is usually short in exterior applications in cities with severe air pollution.
In selecting a coating it must be realized that maximizing resistance to one type of service condition may reduce resistance to others. Also, if the life of the article is expected to be longer than any reasonably attainable coating life, a coating that can be stripped off with a solvent must be selected so that the article may be restored when the coating and appearance have degraded to an unacceptable level.
Some examples of coating performance indicate the range of serviceability of organic finishes on copper and its alloys.
An air-drying acrylic lacquer with a tarnish inhibitor ( benzotriazole*) has protected a bronze nameplate outdoors in urban New Jersey for more than five years. The same coating indoors on handrails and other objects subjected to wear failed in less than one year.
A combination of a silicone primer and an acrylic top coat displayed excellent appearance after more than six years of service in interior applications with moderate or no abrasion. The same system darkened significantly in one year of open exterior exposure but indicated good performance for more than three years on sheltered doors of office buildings and churches.
A nitrocellulose lacquer failed in less than one year of open exterior exposure. Urethane lacquers lasted about one year under the same conditions.
Baked alkyd-butyl and butyl coatings looked good after two years of open exterior exposure. Epoxy coatings darkened in four to six months.
Silicone thermoset coatings retain good protective qualities after 62 days at 200 F or 100 hours at 300 F.
Antiqued brass automotive interior trim has been protected with a thermosetting epoxy clear coating.
The copper roof of the Sports Palace in Mexico City is covered with an air drying acrylic lacquer formulated with an inhibitor and organic ultraviolet absorbers.
Bathroom fixtures of brass have been satisfactorily protected for more than five years with a baked epoxy coating.Back to Top
Basic Coating Systems
Nitrocellulose. Nitrocellulose coatings are the least expensive and most common air drying coatings for interior service. They are modified with alkyd or acrylic resins. Nitrocellulose coatings are used in exterior applications; however, they are usually stripped and replaced at intervals of less than one year. They do not have high resistance to chemicals, but they are fast drying and easy to use.
Acrylic. Available in air drying or thermosetting compositions, acrylics are relatively high cost materials. The air drying modifications are popular for exterior applications, while ' the thermosetting types are useful for interior applications requiring high resistance to heat and abrasion. Since the thermosetting coatings are not conveniently stripped, they are unsuitable for major architectural applications.
Epoxy Coatings. Epoxy coatings have excellent resistance to wear and chemicals. They are relatively expensive and are only available in thermosetting or two part (catalyst activated) compositions with relatively short pot lives. They are good for severe indoor applications, but they degrade rapidly and darken in a few months of exterior service.
Silicone Coatings. Silicones provide the best potential for coatings which must operate at elevated temperatures. Thin films of these high-cost coatings are used and protection by a second coat of a more durable abrasion resistant lacquer may be necessary. Ultraviolet absorbing compounds are added to prevent darkening of the silicone during exterior exposures.
Alkyd Coatings. Slow drying or baking is required when applying the alkyd coatings. Modified with melamine resins, these coatings are low cost and durable enough for exterior applications. Resistance to chemicals is usually good.
Urethane Coatings. Color degradation on exterior exposure has been a problem with urethane coatings. Resistance to chemicals and abrasion are good even for the air drying coatings.
Cellulose Acetate Butyrate. Usually considered for interior applications, cellulose acetate butyrate coatings are air drying and have moderate cost and properties. They have a tendency to darken during exterior applications.
Vinyl. Vinyl coatings require stabilization against ultraviolet degradation. They are usually relatively soft and flexible coatings.
Polyvinyl Fluoride Film ( Tediars). Applied by roll bonding with an adhesive, Tedlar films have been used to protect sheet copper in exterior applications. It has been projected that these clear films can protect a properly prepared substrate for twenty years or more.
Among the common coating additives are the following types:
Ultraviolet Absorbers. Ultraviolet absorbers are organic compounds which are sometimes added to coatings for exterior applications in order to prevent darkening and degradation of the coating. In some cases they may also interact with the substrate and prevent tarnishing.
Leveling Agents. Leveling agents improve the flow properties of coatings and thereby provide better surface appearance. In addition, the likelihood of Dinholing or other defects is reduced.
Chelating Agents. Benzotriazole and other chelating agents interact with copper and its alloys to prevent tarnishing. Chelating agents are preferentially absorbed on the surfaces of the metals and act as an invisible barrier to elements or compounds which might cause corrosion. In this way they protect the metal against oxidants permeating through the coating and continue to protect even after a minor defect has formed in the coating. Chelating agents may be included in the coating formulation or applied as part of a pretreatment procedure.
Antioxidants. Antioxidants reduce the degradation of coatings during long and severe exposure. Examples are hydroquinone, N-propyl gallate, and modified phenol and cresol compounds.Back to Top
No coating can perform to expectations if applied to a poorly prepared surface. The metal surface must be free of contaminants such as dirt, oil, dust, old finishes, and finger prints. Coating should be done with a minimum of delay after cleaning and precautions should be taken to prevent recontamination. Precautions include working in a low dust environment, handling with white gloves, and applying tarnish inhibitors (chelating agents) to the surface.
Ordinary steel wool should not be used in cleaning as the pads may contain chemicals which stain copper metals. Suitable abrasives are silicon carbide (Scotch-brite) pads or wheels, stainless steel pads, and powdered pumice stone. The pumice powder is slurried in a 5% oxalic acid solution and rubbed on with a cloth. All residues must be removed and the surface wiped dry with a clean cloth. Abrasives should not be used on highly polished (mirror) surfaces. When buffing compounds have been used in polishing prior to coating, parts should be degreased or otherwise cleaned to remove any residue.
Degreasing is normally done with solvents such as butyl cellosolve and trichloroethylene. To prevent streaking and staining, it may be necessary to wipe-dry large areas with lint-free wipers. Freshly plated parts must be thoroughly neutralized and rinsed in hot water prior to coating.
The spraying area should be free of dust and dirt and at moderate temperature (between 50 and 900F), at low humidity (certainly less than 80% when organic vehicles are used), and well ventilated.
Usually enough coats are applied to achieve a total dry film thickness of 0.5 to 1.5 mils. Greater thicknesses tend to become obvious and the metal takes on a varnished appearance. However, the coating manufacturer may recommend thinner coatings for certain applications.Back to Top
The properties of a number of proprietary commercial coatings are presented in Table 1. Properties of a coating are sometimes dependent on the composition of the substrate (copper, brass, nickel-silver etc.). The properties shown in Table 1 are representative of those found on several different substrates. This compilation illustrates that the differences among coatings of a given organic base can be as great as the differences among the bases. The differences arise because the manufacturers use their own formulations, combinations of polymers, and additives.
The test procedures used to compile the properties in Table 1 were as follows:
Pencil Hardness - Hardness at which transition from scratching of the coating to crumbling of the lead occurs. The scale of hardness from hardest to softest is 7H, 6H, 5H, 4H, 3H, 2H, H, HB, F.
Taber Abrasion Test - A CS 10 Calibrase wheel with a 500 gram load was run on the specimen to failure or to 500 cycles. Results are reported as loss in weight due to abrasion.
Flexibility - Bending was done over a 1/8-in. to 11/2-in. Gardner conical mandrel. Results are reported as no cracking (NC), fine cracking (FC), cracking (C), or severe cracking (SC).
Impact Resistance - A 28 inch-pound impact was performed on a Gardner Impact Tester. Results are reported as no starring (NS), slight starring (SS), starring (S), or extensive starring (ES).
Resistance to Chemicals - Samples were visually examined to detect changes after exposure to solutions for up to 24 hours. Solutions used were 0.5% ammonium sulfide, 1% Tide detergent, and synthetic perspiration.Back to Top
A lustrous metallic surface acts as an excellent back drop to view coating defects and tarnished spots. Therefore, the tolerance for defects is low and clear coatings must have a high degree of effectiveness in order to perform satisfactorily. This is less of a problem on antiqued or colored metals. Of concern on copper alloys is that darkening of the substrate can occur even under a coating that is intact due to interaction of the copper with residual solvents. This is a special problem during outdoor exposures when ultraviolet radiation can stimulate the breakdown of solvents. By proper choice of solvents and additives this problem can be minimized. Ethyl alcohol and isopropyl alcohol cause considerable tarnishing. Benzene, toluene, xylene, butyl acetate, and ethyl acetate are much better.
Discoloration of copper and its alloys also may occur at the curing temperatures normally recommended for thermoset coatings. It is wise to use low curing temperatures and short curing schedules to avoid such in-process discoloration. Catalytic activity by copper sometimes allows lower temperatures or shorter curing schedules to be used.
Short high temperature baking schedules are a requirement for coil coating operations. A considerable amount of research has been carried out in this field and satisfactory coil coating formulations are available. These coatings can be formed after curing and still retain good protective properties. The use of a Tediar film for coil coating is a new innovation. The extremely long life of Tedlar coatings in outdoor applications provides savings in maintenance expenses which may justify the added expense of coating. Tediar coated metal also may be formed.
Adhesion of coatings to copper and its alloys can be a problem. Considerable research is underway in this area also. This work has shown that adhesion of coatings can be improved by the use of primers or conversion coatings. In coil coating operations pretreating solutions may be sprayed on and dried before coating. However, pretreatments have been known to affect the formability of the coating and this must be checked before a pretreatment is adopted. Pretreatment may also be used to provide protection against under-film tarnishing by incorporating inhibitors in the solutions or reoxidizing the surface.
Benzotriazole: An Effective Corrosion Inhibitor for Copper Alloys, Application Data Sheet 108/9, Copper Development Association Inc., New York (1969)
Tediars is a registered trademark of Du Pont Co.
- Barrier coatings. Barrier coatings aim to prohibit water, oxygen and other chemicals from making contact with the substrate. ...
- Inhibitive coatings. ...
- Sacrificial coatings. ...
- Let's talk.
Organic coatings, such as organic polymer coating (OPC) and temporarily protective oil coating (TPOC), are an effective way to prevent metals from corrosion. In general, organic coatings consist of vehicle, pigments and additives such as dryers, hardening agents, stabilising agents, surfactant, dispersion agents, etc.Which coating is best for corrosion resistance? ›
If you need protection against rust, epoxy coatings are highly effective. These coatings are sometimes applied at a 4 to 6 mm thickness. However, sometimes a thicker application of 8 mm may be used in situations where rust is highly likely to occur. Epoxy also has the effect of diminishing chemical erosion.What is anticorrosion coating? ›
Anti-corrosion coatings protect metal components against degradation due to moisture, salt spray, oxidation, or exposure to a variety of environmental or industrial chemicals in a range of industries.Is clearcoat used for corrosion protection? ›
XCP Rust Blocker CLEAR COAT is a powerful corrosion protection spray. It creates a long lasting soft film coating to protect any steel, metal or alloy surface against the effects of rust and corrosion.What are 4 ways to prevent corrosion? ›
- Protective Coating. A fresh coat of paint will enhance the appearance of your metal structure and prevent corrosion. ...
- Metal Plating. Theoretically, plating is almost similar to painting. ...
- Corrosion inhibitors. ...
- Sacrificial coatings. ...
- Environmental Measures. ...
- Modifying the design.
One of the easiest and cheapest ways to prevent corrosion is to use barrier coatings like paint, plastic, or powder. Powders, including epoxy, nylon, and urethane, adhere to the metal surface to create a thin film. Plastic and waxes are often sprayed onto metal surfaces.What are the two methods of prevention of corrosion? ›
- Alloying. It is the method of improving the properties of a metal by mixing the metal with another metal or nonmetal. ...
- Painting. ...
Coatings are specified as organic or inorganic according to the nature of their binder. Organic coatings are those that have an organic binder. Inorganic coatings are those that have an inorganic binder such as a silicate.What are the three types of coating? ›
Coatings are varied, but primarily fall into three categories: Architectural, Industrial, and Special Purpose.
Galvanizing, used as highly effective protection against corrosion, is the most widely used method of metal coating. The process known as “hot dip” galvanizing involves dipping a piece of steel or other ferrous metal into a molten zinc bath, bonding the zinc to the metal.What is the strongest coating for metal? ›
- Epoxy Steel Coatings: Epoxy coatings are one of the most widely used steel coatings in industrial and marine markets. ...
- Polyurethane Steel Coatings: Polyurethane coatings are often used as topcoats over epoxy primers on structural steel. ...
- Zinc Coatings:
Electronic protection shouldn't be necessary and I wouldn't recommend it." Instead of pricey dealer rustproofing gadgets or sprays for new vehicles, spring for mud flaps to protect from damage from rocks and make sure all chips or scratches in the paint are fixed quickly, McDermid says.What is the best way to coat corrosion sensitive metals? ›
One common method is galvanization, in which manufacturers coat the part with a thin layer of zinc. Powder coatings are another effective way to prevent corrosion in metal parts. With proper application, a powder coating can seal the surface of the part away from the environment to guard against corrosion.What is the best rust proof paint for metal? ›
1. Best Rust Resistant Paint for Metal—Rust-Oleum Stops Rust Protective Enamel. When preparing to paint metal, it's important to ensure the surface is protected from rust. That's where Rust-Oleum Stops Rust Protective Enamel can help.How long does clear coat protection last? ›
A clear coat that comes with the car applied by the manufacturer can last up to 15 years if cared for properly. Dirt, grime, snow, mud, leaf stains are the usual suspects that can eat away your car's clear coat. So, in short, the better you care for your car's clear coat, the longer it will last.Is clear paint protection worth it? ›
If you want your car to be perfect with shiny paint, and you want to keep the value as high as possible, the paint protection film is worth it. The paint protection film is practically invisible, has self-healing properties to keep swirls away, and includes a ten-year warranty.Will clear coat stop steel from rusting? ›
Over time, any type of metal is prone to rust or corrosion, it's inevitable. It's very important to protect the surface of your galvanized steel to extend its lifespan. So, how do you achieve this? One simple way is to clear coat the surface.What are the 3 main causes of corrosion? ›
Causes of Corrosion
Metal corrodes when it reacts with another substance such as oxygen, hydrogen, an electrical current or even dirt and bacteria.
To tackle items with significant corrosion, submerge your rusty tools or knives in a bowl of white vinegar and let them sit overnight or as long as 24 hours. Once they have had a good soak, remove them from the vinegar and scrub the rust off with steel wool, a scouring pad, or a wire brush.
Quality corrosion protection can extend the lifespan of your equipment by up to 250%. Corrosion protection can reduce the costs of repairs due to corrosive damage.What are the five general steps for complete corrosion treatment? ›
In general, any complete corrosion treatment involves the following: (1) cleaning and stripping of the cor- roded area, (2) removing as much of the corrosion products as practicable, (3) neutralizing any residual materials remaining in pits and crevices, (4) restoring protective surface films, and (5) applying ...What are factors affecting corrosion? ›
- Exposure of the metals to air containing gases like CO2, SO2, SO3 etc.
- Exposure of metals to moisture especially salt water (which increases the rate of corrosion).
- Presence of impurities like salt (eg. ...
- Temperature: An increase in temperature increases corrosion.
Applications Organic finishing, in generic terms, is often defined as the application of an organic film or coating to a surface for the purpose of altering its inherent characteristics. The more widely accepted designation for such coatings is painting.Which type of coating is best? ›
The ceramic coating is very durable and can last 5-7 years depending on the kind of coat applied. Scratch-resistant and helps prevent swirl marks: The hard nature of ceramic coating does a good job of protecting the car's surface against scratches and swirls keeping the surface smooth and shiny.Which chemical is used for coating? ›
Prominent chain-growth polymers in the area of coatings are polyethylene, polystyrene, polymethyl methacrylate, and polyvinyl chloride.What are 3 ways that coating can improve a surface? ›
- Corrosion resistance: ...
- Wear and lubricity: ...
- Extreme Temperatures:
Simply put, paint is for aesthetics and coating is for performance.Can you clearcoat metal? ›
DiamondFinish Clear is a crazy tough Clear Coat that can be applied Direct To Metal or over other coatings. DiamondFinish Clear is a water clear high gloss clear coat that remains permanently flexible and is able to perform in the toughest environments without yellowing, cracking or peeling.Can you clear coat over metal? ›
Over time, any type of metal is prone to rust or corrosion, it's inevitable. It's very important to protect the surface of your galvanized steel to extend its lifespan. So, how do you achieve this? One simple way is to clear coat the surface.
Rust-Oleum 3333 Super Adhesion Primer is ideal for general users looking to paint stainless steel, making a perfect chemical bond without the need for blasting or etching the surface beforehand. It can be recoated with virtually any other Rust-Oleum 2K paint, making it very compatible with a whole range of topcoats.What is the strongest non corrosive metal? ›
Tungsten: The Strongest Metal on Earth
Besides tungsten's superior strength, the metal also has the highest melting point of any unalloyed metal. Because of its strength, tungsten is often used in electrical and military applications.
We recommend using ceramic coating due to its longevity. Waxes and sealants need constant application and aren't usually applied often enough to offer constant protection. Ceramic coating lasts a long time and offers the best protection.What is the most waterproof metal? ›
For corrosion resistance, any metal component exposed to seawater should be either brass, bronze, 316 stainless (also known as A4 stainless), titanium, or perhaps aluminum.Should you rust proof your car every year? ›
When Should I Rust Proof My Car? Now that you know why rust occurs and how you stop it, you now can know that you should implement rust proofing in your vehicle once a year. Ideally, it's best to do this at the start of the winter months, so you can safeguard it against the most turbulent time of the year.What are the disadvantages of rust treatment? ›
Traditional chemical rust removal methods can come with a whole host of disadvantages, including serious health and safety risks. Toxic chemicals and fumes present when using acid and alkali removers can be hazardous to health. They can also degrade the building and environment in which they are being used.Do modern cars need rust proofing? ›
The short answer is no. Cars today are manufactured with corrosion protection, which makes this added treatment unnecessary, though it is profitable for car dealerships.Does painting metal prevent corrosion? ›
Paint. Painting is a great, low-cost way to protect against rust. The paint forms a protective barrier between the metal and corrosive elements. Oil-based paints are the best choice if you are trying to prevent water and oxygen from penetrating the metal and causing corrosion.How do you paint metal so it doesn't rust? ›
To properly prepare new metal surfaces, use mineral spirits to remove grease and apply a rust-inhibitive primer before painting. For painted surfaces that are in sound condition, remove dust with a clean, dry cloth, de-gloss the surface with light sanding, and wipe with mineral spirits to ensure good adhesion.Can you paint directly on rusted metal? ›
Simply remove any loose rust with a wire brush or coarse sandpaper and clean the surface with brush cleaner & thinners and allow time to dry. Then apply Hammerite Paint directly onto the rusty metal surface. No primer, no undercoat needed.
An anti corrosion spray can be described as an ultra thin fluid film compound used for spray coating metal to prevent rust. In spray form it can protect for up to a year.What are three 3 ways that steel can be protected from corrosion? ›
Protective coatings, environmental control, and cathodic protection are effective ways of preventing corrosion in metal parts.What are the three 3 primers that can be used to protect metal from corrosion? ›
- Part 1: Zinc-Rich Primer. After surface preparation, the most critical factor in a corrosion protection plan is the primer. ...
- Part 2: Epoxy Intermediate Coat. ...
- Part 3: Aliphatic Polyurethane Topcoat.
One of the easiest and cheapest ways to prevent corrosion is to use barrier coatings like paint, plastic, or powder. Powders, including epoxy, nylon, and urethane, adhere to the metal surface to create a thin film. Plastic and waxes are often sprayed onto metal surfaces.How do you finish steel so it doesn't rust? ›
Galvanize: Galvanizing coats iron or steel in zinc to protect from rust. Zinc corrodes at a much slower rate than iron or steel, so it's highly effective for slowing rust. Blueing: This process creates a layer of magnetite over the metal to prevent rust.What are 4 factors that affect corrosion? ›
Introduction. There are several factors influencing the rate of corrosion including diffusion, temperature, conductivity, type of ions, pH value and electrochemical potential.What are the 2 classifications of corrosion? ›
There are two general classifications of corrosion which cover most of the specific forms. These are: direct chemical attack and electrochemical attack.What's the difference between rust and corrosion? ›
Rust is a type of corrosion. Corrosion is the process by which certain materials, metals and non-metals, deteriorate as a result of oxidation. Rusting is oxidation of iron in the presence of air and moisture. Corrosion can occur on materials such as ceramics or polymers.What is the principle of corrosion? ›
Corrosion can be defined as the deterioration of material by reaction to its environment. Corrosion occurs because of the natural tendency of most metals to return to their natural state; e.g., in the presence of moist air iron will revert to its natural state—iron oxide.What is the best primer to stop rust? ›
Rust-Oleum® Stops Rust® Rusty Metal Primer stops rust and prevents corrosion. Apply to heavily rusted metal (use Rust-Oleum® Stops Rust® Clean Metal Primer on clean or lightly rusted metal). Bonds tightly to rust to form a surface top coats can adhere to.
While a water-based primer is not to be applied on metal surfaces, other primer options such as rust-inhibiting primers, galvanized primers, and iron oxide primers are more suitable options.What is a good rust inhibitor? ›
WD-40 Specialist® Corrosion Inhibitor is an anti-rust spray ideal for preventative maintenance and use in extreme environments such as high humidity. It provides non-drying protection that stays where you spray it.