Paint - Definition

Paint is a liquid, liquifiable, or mastic composition which after application to a substrate in a thin layer is converted to an opaque solid film.

Paint is used to protect, decorate (such as adding color), or add functionality to an object or surface by covering it with a pigmented coating. An example of protection is to retard corrosion of metal. An example of decoration is to add festive trim to a room interior. An example of added functionality is to modify light reflection or heat radiation of a surface.

As a verb, painting is the application of paint. Someone who paints artistically is usually called a painter or artist, while someone who paints commercially is often referred to as a painter and decorator, or house painter.

Paint can be applied to almost any kind of object. It is used, among many other uses, in the production of art, in industrial coating, as a driving aid (road surface marking), or as a barrier to prevent corrosion or water damage. Paint is a semifinished product, as the final product is the painted article itself.

Paint can also be mixed with glaze to create various textures and patterns. This process is referred to as faux finish and is quite popular with discerning homeowners, architects and interior designers.
Contents

Components
* 1 Pigment
* 2 Binder
* 3 Vehicle, or solvent
* 4 Additives
* 5 Misc
* 6 Art
* 7 Application
* 8 Product variants
* 9 History
* 10 See also
* 11 External links


Components

There are three primary components to a paint:

* Pigments

* Binder, also known as non-volatile vehicle or resin

* Vehicle, also known as volatile vehicle, also called solvent

Pigment

Main article: Pigment

Pigments impart such qualities as color and opacity (sometimes inappropriately called 'hiding'), and influence properties such as gloss, film flow, and protective abilities. Pigment can generally be categorized into two main types: Prime, or hiding, pigments, and Inert, or extender, pigments.

The main modern white hiding pigment is Titanium dioxide. Zinc oxide is a weaker white pigment with some important usages. Color hiding pigments fall also into two main categories, those being Inorganic, mostly duller earth tone colors, and Organic, generally brighter but more expensive colors.

Inert pigments break down into natural or synthetic types. Natural pigments include various clays, calcium carbonate, mica, silicas, and talcs. Synthetics would include calcined clays, blanc fix, precipitated calcium carbonate, and synthetic silicas.

Hiding pigments, in making paint opaque, also protect the substrate from the harmful effects of ultraviolet light.

Some pigments are toxic, such as the lead pigments that are used in lead paint. Paint manufacturers began replacing white lead pigments with the less toxic substitute, which can even be used to color food, titanium white (titanium dioxide), even before lead was functionally banned in paint for residential use in 1978 by the U.S. Consumer Product Safety Commission.

Titanium dioxide was first used in paints in the 19th century. The titanium dioxide used in most paints today is often coated with silicon or aluminum oxides for various reasons such as better exterior durability, or better hiding performance (opacity) via better efficiency promoted by more optimal spacing within the paint film. Opacity is also improved by optimal sizing of the titanium dioxide particles.

Binder

The binder, or resin, is the actual film forming component of paint. It imparts adhesion, binds the pigments together, and strongly influences such properties as gloss potential, exterior durability, flexibility, and toughness.

Binders include synthetic or natural resins such as acrylics, polyurethanes, polyesters, melamine resins, epoxy, or oils.

Binders can be categorized according to drying, or curing, mechanism. The four most common are simple solvent evaporation, oxidative crosslinking, catalyzed polymerization, and coalescence.

Note that drying and curing are two different processes. Drying generally refers to evaporation of vehicle, whereas curing refers to polymerization of the binder. Depending on chemistry and composition, any particular paint may undergo either, or both processes. Thus, there are paints that dry only, those that dry then cure, and those that do not depend on drying for curing.

Paints that dry by simple solvent evaporation contain a solid binder dissolved in a solvent; this forms a solid film when the solvent evaporates, and the film can re-dissolve in the solvent again. Classic nitrocellulose lacquers fall into this category, as do non-grain raising stains composed of dyes dissolved in solvent.

Paints that cure by oxidative crosslinking are generally single package coatings that when applied, the exposure to oxygen in the air starts a process that crosslinks and polymerizes the binder component. Classic alkyd enamels would fall into this category.


Paints that cure by catalyzed polymerization are generally two package coatings that polymerize by way of a chemical reaction initiated by mixing resin and hardener, and which cure by forming a hard plastic structure. Depending on composition they may need to dry first, by evaporation of solvent. Classic two package epoxies or polyurethanes would fall into this category.

Latex paints cure by a process called coalescence where first the water, and then the trace, or coalescing, solvent, evaporate and draw together and soften the latex binder particles together and fuse them together into irreversibly bound networked structures, so that the paint will not redissolve in the solvent/water that originally carried it.

Recent environmental requirements restrict the use of Volatile Organic Compounds (VOCs), and alternative means of curing have been developed, particularly for industrial purposes. In UV curing paints, the solvent is evaporated first, and hardening is then initiated by ultraviolet light.

Vehicle, or solvent

The main purpose of the vehicle is to adjust the viscosity of the paint. It is volatile and does not become part of the paint film. It can also control flow and application properties. Its main function is as the carrier for the non volatile components.

Water is the main vehicle for water based paints.

Solvent based, sometimes called oil based, paints can have various combinations of solvents as the vehicle, including aliphatics, aromatics, alcohols, and ketones. These include organic solvents such as petroleum distillate, alcohols, ketones, esters, glycol ethers, and the like. Sometimes volatile low-molecular weight synthetic resins also serve as diluents.

Additives

Besides the three main categories of ingredients, paint can have a wide variety of miscellaneous additives, usually added in very small amounts. Some examples include additives to improve wet edge, improve pigment stability, impart antifreeze properties, control foaming, control skinning, etc. Other additives might be thickeners, coalescent solvents, or biocides to fight bacterial growth.

Misc

Fillers serve to thicken the film, support its structure and simply increase the volume of the paint. Not all paints include fillers. Pigments that also function as fillers are called simply "pigments"; "fillers" are generally color-neutral and opaque. It is necessary to adjust the resulting off-white color with pigments to give the desired color. Common fillers are cheap and inert, such as talc, lime, baryte, clay, etc. Depending on the paint, most of the paint film may consist of pigment/filler and binder, the rest being other additives.

Besides pigments and dyes, other types of additives include catalysts, thickeners, stabilizers, emulsifiers, texturizers, adhesion promoters, flatteners (de-glossing agents), and the like.

After application, the paint solidifies and becomes tack-free. Depending on the type of binder, this hardening may be a result of curing (polymerization), evaporation, or even phase change brought about by cooling. In oil-based paint, curing takes the form of oxidation, for example oxidation of linseed oil to form linoxin to create a varnish. Other common cured films are prepared from crosslinkers, such as polyurethane or melamine resins, reacted with acrylic polyester or polyurethane resins, often in the presence of a catalyst which serves to make the curing reaction proceed more quickly or under milder conditions. These cured-film paints can be either solvent-borne or waterborne.

Latex paint is a water-based dispersion of sub-micron polymer particles. The term "latex" in the context of paint simply means an aqueous dispersion; latex rubber (the sap of the rubber tree that has historically been called latex) is not an ingredient. These dispersions are prepared by emulsion polymerization. When the water evaporates, the polymer particles coalesce to form a solid film. The polymer itself resists water (and typically some other solvents). Residual surfactants in the paint as well as hydrolytic effects with some polymers cause the paint to remain susceptible to softening and, over time, degradation by water.

Still other films are formed by cooling of the binder. For example, encaustic or wax paints are liquid when warm, and harden upon cooling.

Art

Main article: Painting

Since the time of the Renaissance, siccative (drying) oil paints, primarily linseed oil, have been the most commonly used kind of paints in fine art applications; oil paint is still common today. However, in the 20th century, water-based paints, including watercolors and acrylic paints, became very popular with the development of acrylic and other latex paints. Milk paints (also called casein), where the medium is derived from the natural emulsion that is milk, were popular in the 19th century and are still available today. Egg tempera (where the medium is an emulsion of egg yolk mixed with oil) is still in use as well, as are encaustic wax-based paints. Gouache is a variety of watercolor paint which was also used in the Middle Ages and Renaissance for manuscript illumination. The pigment was often made from ground semiprecious stones such as lapis lazuli and the binder made from either gum arabic or egg white. Gouache is commercially available today.

Poster paint has been used primarily in the creation of student works, or by children.

[edit] Application

Paint can be applied as a solid, a gaseous suspension (aerosol) or a liquid. Techniques vary depending on the practical or artistic results desired.

As a solid (usually used in industrial and automotive applications), the paint is applied as a very fine powder, then baked at high temperature. This melts the powder and causes it to adhere (stick) to the surface. The reasons for doing this involve the chemistries of the paint, the surface itself, and perhaps even the chemistry of the substrate (the overall object being painted). This is commonly referred to as "powder coating" an object.

As a gas or as a gaseous suspension, the paint is suspended in solid or liquid form in a gas that is sprayed on an object. The paint sticks to the object. This is commonly referred to as "spray painting" an object. The reasons for doing this include:

* The application mechanism is air and thus no solid object ever touches the object being painted;
* The distribution of the paint is very uniform so there are no sharp lines
* It is possible to deliver very small amounts of paint or to paint very slowly;
* A chemical (typically a solvent) can be sprayed along with the paint to dissolve together both the delivered paint and the chemicals on the surface of the object being painted;
* Some chemical reactions in paint involve the orientation of the paint molecules.

In the liquid application, paint can be applied by direct application using brushes, paint rollers, blades, other instruments, or body parts. Examples of body parts include fingerpainting, where the paint is applied by hand, whole-body painting (popular in the 1960s avant-garde movement), and cave painting, in which a pigment (usually finely-ground charcoal) is held in the mouth and spat at a wall (Note: some paints are toxic and might cause death or permanent injury).

Rollers generally have a handle that allows for different lengths of poles which can be attached to allow for painting at different heights. Generally, roller application takes two coats for even color. A roller with a thicker nap is used to apply paint on uneven surfaces. Edges are often finished with an angled brush.

After liquid paint is applied, there is an interval during which it can be blended with additional painted regions (at the "wet edge") called "open time." The open time of an oil or alkyd-based emulsion paint can be extended by adding white spirit, similar glycols such as Dowanol™ (propylene glycol ether) or commercial open time prolongers. This can also facilitate the mixing of different wet paint layers for aesthetic effect. Latex and acrylic emulsions require the use of drying retardants suitable for water-based coatings.

Paint may also be applied by flipping the paint, dripping, or by dipping an object in paint.

Interior/exterior house paint tends to separate when stored, the heavier components settling to the bottom. It should be mixed before use, with a flat wooden stick or a paint mixing accessory; pouring it back and forth between two containers is also an effective manual mixing method. Paint stores have machines for mixing the paint by shaking it vigorously in the can for a few minutes.

Water-based paints tend to be the safest, and easiest to clean up after using -- the brushes and rollers can be cleaned with soap and water.

It is difficult to reseal the paint container and store the paint well for a long period of time. Store upside down, for a good seal, in a cool dry place. Protect from freezing.

Proper disposal of paint is a challenge. Avoid acquiring excess paint. Look for suitable recycled paint before buying more. Try to find recycled uses for your left over paint. Paints of similar chemistry can be mixed to make a larger amount of a uniform color. Old paint may be usable for a primer coat or an intermediate coat.

If you must dispose of paint, small quantities of water based paint can be carefully dried by leaving the lid off until it solidifies, and then disposing with normal trash. But oil based paint should be treated as hazardous waste, and disposed of according to local regulations.

* http://muextension.missouri.edu/xplor/wasteman/wm6001.htm "Safe Use, Storage and Disposal of Paint"
* http://www.epa.state.oh.us/pic/facts/hhwpaint.html "Storage and Disposal of Paint Facts"

Product variants

* Primer 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.
* Varnish and shellac provide a protective coating without changing the color. They are paints without pigment.
* Wood stain is a type of paint that is very "thin," that is, low in viscosity, and formulated so that the pigment penetrates the surface rather than remaining in a film on top of the surface. Stain is predominantly pigment or dye and solvent with little binder, designed primarily to add color without providing a surface coating.
* Lacquer is usually a fast-drying solvent-based paint or varnish that produces an especially hard, durable finish.
* An enamel paint is a paint that dries to an especially hard, usually glossy, finish. Enamel can be made by adding varnish to oil-based paint.
* A Glaze is an additive used with paint to slow drying time and increase translucency, as in Faux Painting and Art Painting.
* A Roof coating is a fluid applied membrane which has elastic properties that allows it to stretch and return to their original shape without damage. It provides UV protection to polyurethane foam and is widely used as part of a roof restoration system.
* Fingerpaint
* Inks are similar to paints, except they are typically made using dyes exclusively (no pigments), and are designed so as not to leave a thick film of binder.
* Titanium dioxide is extensively used for both house paint and artist's paint, because it is permanent and has good covering power. Titanium oxide pigment accounts for the largest use of the element. Titanium paint is an excellent reflector of infrared, and is extensively used in solar observatories where heat causes poor seeing conditions.
* Anti-Graffiti paints are used to defeat the marking of surfaces by graffiti artists. There are two categories, sacrificial and non-bonding. Sacrificial coatings are clear coatings that allow the removal of graffiti, usually by pressure washing the surface with high-pressure water, removing the graffiti, and the coating (hence, sacrificed.) They must be re-applied afterward for continued protection. This is most commonly used on natural-looking masonry surfaces, such as statuary and marble walls, and on rougher surfaces that are difficult to clean. Non-bonding coatings are clear, high-performance coatings, usually catalyzed polyurethanes, that allow the graffiti very little to bond to. After the graffiti is discovered, it can be removed with the use of a solvent wash, without damaging the underlying substrate or protective coating. These work best when used on smoother surfaces, and especially over other painted surfaces, including murals.
* Anti-climb paint is a non-drying paint that appears normal while still being extremely slippery. It is usually used on drainpipes and ledges to deter burglars and vandals from climbing them, and is found in many public places. When a person attempts to climb objects coated with the paint, it rubs off onto the climber, as well as making it hard for them to climb.
* No-VOC paints, which are solvent-free paints that do not contain volatile organic compounds, have been available since the late 1980s. Low VOC paints, which typically contain anywhere between 0.3%-5.0% VOCs as coalescent, or coalescing solvent have been available since the 1960s

History

Cave paintings drawn with red and yellow ochre, hematite, manganese oxide and charcoal may have been made by early homo sapiens as long as 40.000 years ago.

Ancient painted walls, to be seen at Dendera, Egypt, although exposed for many ages to the open air, still possess a perfect brilliancy of color, as vivid as when painted, perhaps 2000 years ago. The Egyptians mixed their colors with some gummy substance, and applied them detached from each other without any blending or mixture. They appeared to have used six colors: white, black, blue, red, yellow, and green. They first covered the field entirely with white, upon which they traced the design in black, leaving out the lights of the ground color. They used minium for red, and generally of a dark tinge.

Pliny mentions some painted ceilings in his day in the town of Ardea, which had been executed at a date prior to the foundation of Rome. He expresses great surprise and admiration at their freshness, after the lapse of so many centuries.

Paint was made with the yolk of eggs and therefore, the substance would harden and stick onto the surface applied.