 | This article needs additional citations for verification .(February 2010) |
A primer ( /ˈpraɪmər/ ) or undercoat is a preparatory coating put on materials before painting. Priming ensures better adhesion of paint to the surface, increases paint durability, and provides additional protection for the material being painted. [1]
A primer consists of synthetic resin, solvent and additive agent while some primers contain polyethylene (plastic), for better durability. [2]
Primer is a paint product that allows finishing paint to adhere much better than if it were used alone. [3] It is designed to adhere to surfaces and to form a binding layer that is better prepared to receive the paint. Compared to paint, a primer is not intended to be used as the outermost durable finish and can instead be engineered to have improved filling and binding properties with the material underneath. Sometimes this is achieved by chemistry, as in the case of aluminum primer, but more often this is achieved through controlling the primer's physical properties such as its porosity, tackiness, and hygroscopy.
In practice, primer is often used when painting porous materials, including concrete and wood. Using a primer is considered mandatory if the material is not water resistant and will be exposed to the elements. Priming gypsum board (drywall) is also standard practice with new construction because it seals the wall from moisture and can prevent the growth of mold. Primers can also be used on dirty surfaces which cannot be cleaned or before painting light colors over a dark finish.
Some primers can be tinted to match more closely with the color of the finishing paint. If the finishing paint is a deep color, tinting the primer can reduce the number of layers of finishing paint that are necessary for good uniformity across the painted surface. Primers are also used to hide joints and seams to give a finished look.
Other primers require that the topcoat be applied within a certain amount of time after the primer dries to ensure optimal adhesion. This varies from 24 hours to up to two weeks after the primer has dried. Painting after the suggested time-frame may cause performance issues depending on the specific situation. It is common to apply the finishing coat of paint before the primer fully cures in order to improve adhesion between the primer and the topcoat. The level of exposure, such as indoors versus outdoors, may affect how important applying the topcoat within the time-frame will be.
Wood is very porous and will absorb the solvent in paint and cause it to dry more quickly. This is undesirable because most paints undergo chemical reactions during the process of curing (for example, latex- and alkyd-based paints polymerise when curing) which is dependent on the water or solvent evaporating slowly. A layer of primer will prevent the underlying wood from prematurely absorbing the solvents in the finishing paint.
Primer reduces the number of paint coats needed for good coverage and even color.
A thin layer of paint may still be permeable to water. Water can permeate into the wood and cause warping, mildew, or dry rot. Primer improves the waterproofing of the finish. [4] Primers are not used as part of a wood stain treatment because they obscure the wood grain. Primer differs from wood sealers in that sealers typically don't obscure the wood grain completely.
Primers are often comparable in price to finish paints and the price is influenced by the quality of the ingredients. Primers for some specialty applications can be expensive.
Some metals, such as untreated aluminum, require a primer; others may not. A primer designed for metal is still highly recommended if a part is to be exposed to moisture. Once water seeps through to the bare metal, oxidation will begin (plain steel will simply rust). [5] Metal primers might contain additional materials to protect against corrosion, such as sacrificial zinc.
Primers are used on metal hydroxides/oxides to improve the surface condition and to encourage bonding. Without a primer, paint applied to metals are prone to peeling. [6]
Special kinds of primer (rust-converters) can be used to chemically convert rust to the solid metal salts. [7] This process is not recommended for structural steel.
Painting and gluing aluminum are especially important in the aircraft industry, which uses toxic zinc chromate primers and chromating to add the necessary adhesion properties. In addition, primer provides a smooth surface for the paint to adhere to, resulting in a professional-looking finish. [8]
Using a primer on surfaces made of plastic is only necessary when making a drastic change of color (going from dark brown to white, for example) or when a long-lasting coat of paint is desired. This is because most household plastics are not very porous and are not easily damaged by moisture. A primer will reduce the number of layers of paint necessary to completely cover the previous color, and will help the paint make a thorough bond with the surface being painted. Most paints and primers designed for painting plastics are not water based.
An important point for choosing a primer for plastic is making sure the primer's propellant or solvent will not dissolve or warp the plastic part itself (e.g. most common household spray paint will damage polystyrene foam). For this reason, most manufacturers recommend that both the primer and paint should be tested on a less visible location of the part being painted.
Alternative surface treatments, such as plasma activation, can replace primers in the cases when the latter are used to improve adhesive bonding between the substrate and the paint or the lacquer. Quality of the adhesive bonding, such as varnishing and painting, depends strongly on the ability of the adhesive to efficiently cover (wet) the substrate area. This happens when the surface energy of the substrate is greater than the surface energy of the adhesive. However, high strength adhesives – lacquers and paints – have high surface energy. Thus, their application is problematic for low surface energy materials such as polymers or oxidized metals.
To solve this problem, plasma activation is used as a preparation step before adhesive bonding. It cleans the polymer surface from the organic contaminants, removes a weak boundary layer, strengthens the surface by cross-linking polymer molecules and chemically bonds to the substrate a strong layer with high surface energy and chemical affinity to the adhesive. [9] Moreover, plasma processing can also reduce or remove hard oxides from metal surfaces, enabling painting and gluing of metals such as copper and aluminum. Importantly, plasma activation can be performed at the atmospheric pressure in air with fast processing speeds. It does not use wet chemistry, which positively affects its costs, safety and environmental impact.
Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation.
Acrylic paint is a fast-drying paint made of pigment suspended in acrylic polymer emulsion and plasticizers, silicone oils, defoamers, stabilizers, or metal soaps. Most acrylic paints are water-based, but become water-resistant when dry. Depending on how much the paint is diluted with water, or modified with acrylic gels, mediums, or pastes, the finished acrylic painting can resemble a watercolor, a gouache, or an oil painting, or have its own unique characteristics not attainable with other media and are meant for canvases.
Paint is a liquid pigment that, after applied to a solid material and allowed to dry, adds a film-like layer, in most cases to create an image, known as a painting. Paint can be made in many colors and types. Most paints are either oil-based or water-based, and each has distinct characteristics.
Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.
Metallizing is the general name for the technique of coating metal on the surface of objects. Metallic coatings may be decorative, protective or functional.
Electrophoretic deposition (EPD), is a term for a broad range of industrial processes which includes electrocoating, cathodic electrodeposition, anodic electrodeposition, and electrophoretic coating, or electrophoretic painting. A characteristic feature of this process is that colloidal particles suspended in a liquid medium migrate under the influence of an electric field (electrophoresis) and are deposited onto an electrode. All colloidal particles that can be used to form stable suspensions and that can carry a charge can be used in electrophoretic deposition. This includes materials such as polymers, pigments, dyes, ceramics and metals.
Powder coating is a type of coating that is applied as a free-flowing, dry powder. Unlike conventional liquid paint, which is delivered via an evaporating solvent, powder coating is typically applied electrostatically and then cured under heat or with ultraviolet light. The powder may be a thermoplastic or a thermoset polymer. It is usually used to create a thick, tough finish that is more durable than conventional paint. Powder coating is mainly used for coating of metal objects, particularly those subject to rough use. Advancements in powder coating technology like UV-curable powder coatings allow for other materials such as plastics, composites, carbon fiber, and MDF to be powder coated, as little heat or oven dwell time is required to process them.
Thermal spraying techniques are coating processes in which melted materials are sprayed onto a surface. The "feedstock" is heated by electrical or chemical means.
A release agent is a chemical used to prevent other materials from bonding to surfaces. It can provide a solution in processes involving mold release, die-cast release, plastic release, adhesive release, and tire and web release.
Thermal barrier coatings (TBCs) are advanced materials systems usually applied to metallic surfaces on parts operating at elevated temperatures, such as gas turbine combustors and turbines, and in automotive exhaust heat management. These 100 μm to 2 mm thick coatings of thermally insulating materials serve to insulate components from large and prolonged heat loads and can sustain an appreciable temperature difference between the load-bearing alloys and the coating surface. In doing so, these coatings can allow for higher operating temperatures while limiting the thermal exposure of structural components, extending part life by reducing oxidation and thermal fatigue. In conjunction with active film cooling, TBCs permit working fluid temperatures higher than the melting point of the metal airfoil in some turbine applications. Due to increasing demand for more efficient engines running at higher temperatures with better durability/lifetime and thinner coatings to reduce parasitic mass for rotating/moving components, there is significant motivation to develop new and advanced TBCs. The material requirements of TBCs are similar to those of heat shields, although in the latter application emissivity tends to be of greater importance.
Substrate is a term used in materials science and engineering to describe the base material on which processing is conducted. Surfaces have different uses, including producing new film or layers of material and being a base to which another substance is bonded.
Automotive paint is paint used on automobiles for both protective and decorative purposes. Water-based acrylic polyurethane enamel paint is currently the most widely used paint for reasons including reducing paint's environmental impact.
Adhesive bonding describes a wafer bonding technique with applying an intermediate layer to connect substrates of different types of materials. Those connections produced can be soluble or insoluble. The commercially available adhesive can be organic or inorganic and is deposited on one or both substrate surfaces. Adhesives, especially the well-established SU-8, and benzocyclobutene (BCB), are specialized for MEMS or electronic component production.
According to EN 13523-0, a prepainted metal is a ‘metal on which a coating material has been applied by coil coating’. When applied onto the metallic substrate, the coating material forms a film possessing protective, decorative and/or other specific properties.
Osmotic blistering is a chemical phenomenon where two substances attempt to reach equilibrium through a semi-permeable membrane.
Pressure-sensitive tape or pressure-sensitive adhesive tape is an adhesive tape that will stick with application of pressure, without the need for a solvent or heat for activation. It is known also in various countries as self-stick tape, sticky tape, or just adhesive tape and tape, as well as genericized trademarks, such as Sellotape, Durex (tape), Scotch tape, etc.
The conservation and restoration of outdoor artworks is the activity dedicated to the preservation and protection of artworks that are exhibited or permanently installed outside. These works may be made of wood, stone, ceramic material, plastic, bronze, copper, or any other number of materials and may or may not be painted. When applied to cultural heritage this activity is generally undertaken by a conservator-restorer.
The chemistry of pressure-sensitive adhesives describes the chemical science associated with pressure-sensitive adhesives (PSA). PSA tapes and labels have become an important part of everyday life. These rely on adhesive material affixed to a backing such as paper or plastic film.
Titanium adhesive bonding is an engineering process used in the aerospace industry, medical-device manufacture and elsewhere. Titanium alloy is often used in medical and military applications because of its strength, weight, and corrosion resistance characteristics. In implantable medical devices, titanium is used because of its biocompatibility and its passive, stable oxide layer. Also, titanium allergies are rare and in those cases mitigations like Parylene coating are used. In the aerospace industry titanium is often bonded to save cost, touch times, and the need for mechanical fasteners. In the past, Russian submarines' hulls were completely made of titanium because the non-magnetic nature of the material went undetected by the defense technology at that time. Bonding adhesive to titanium requires preparing the surface beforehand, and there is not a single solution for all applications. For example, etchant and chemical methods are not biocompatible and cannot be employed when the device will come into contact with blood and tissue. Mechanical surface roughness techniques like sanding and laser roughening may make the surface brittle and create micro-hardness regions that would not be suitable for cyclic loading found in military applications. Air oxidation at high temperatures will produce a crystalline oxide layer at a lower investment cost, but the increased temperatures can deform precision parts. The type of adhesive, thermosetting or thermoplastic, and curing methods are also factors in titanium bonding because of the adhesive's interaction with the treated oxide layer. Surface treatments can also be combined. For example, a grit blast process can be followed by a chemical etch and a primer application.
Adhesive bonding is a joining technique used in the manufacture and repair of a wide range of products. Along with welding and soldering, adhesive bonding is one of the basic joining processes. In this technique, components are bonded together using adhesives. The broad range of types of adhesives available allows numerous materials to be bonded together in products as diverse as vehicles, mobile phones, personal care products, buildings, computers and medical devices.
| Authority control databases: National |
|---|
