PAINTS
Paints are made from a vast range of raw materials, however they can be classified according to their function.
Oils, resins, or mixes of the two that form the basis of all paints are referred to as medium, vehicle, or binder. Linseed oil is a type of vegetable oil that is commonly used as a binder. It must be able to transform from a low viscosity liquid to a rigid plastic film while also binding together the fine pigment particles in all circumstances. The pigment can influence the binder’s actual qualities to a great amount. The solid film must have three basic characteristics:
a) It must have the appropriate gloss: All binders are glossy, but there are significant differences.
b) It has to stick to the surface (the surface being painted).
c) It must have the required mechanical properties, which correspond to the qualities of the combined film and substrate, such as bending, scratching, and impact resistance.
Pigments are small, insoluble crystalline particles that give paint its colour. Organic or inorganic substances are both possible. The pigment must be completely below the surface of the cured paint film if it is to be glossy. The quantity of gloss is regulated by the pigment to binder ratio, which is usually quantified in volume. Paints with little pigment have weak binding capacity, while those with a lot of pigment are underbound. Hardness is increased by increasing the pigment quantities, while flexibility is decreased. The quality and quantity of pigment have an impact on other attributes such as corrosion resistance and exterior durability.
Extenders, which have little or no pigmentary value, are employed to increase the paint’s other qualities. They can be used to adjust the amount of gloss, for example. To attain the desired sheen, a semi-gloss paint may require so much pigment that it will not pour and will leave heavy brush traces. The inclusion of a filler, such as china clay, will significantly lower the cost while also improving viscosity and finish. Only enough pigment is required to provide colour and concealment. Depending on the paint, the amount of extender used can be as much as 45 percent. Because the refractive index of the materials used as extenders is so close to that of the original, they have no effect on the colour.
Solvents are volatile liquids that are introduced at the right time to reduce the viscosity of wet paint. They must evaporate quickly when the paint is put to a surface in order for the paint to have a high viscosity and hence be free of runs. The type of solvent used for a given resin system can have an impact on the final product, thus it’s critical to select the right one.
Oil-based paints are given driers to speed up the drying process. Lead, manganese, and cobalt compounds are the most common.
Film Formation:
According to the mechanism by which the hardened film is generated, paints can be separated into two groups. There are two types of paints: non-convertible and convertible.
The drying process for non-convertible systems is totally dependent on solvent evaporation. They have the benefit of being simple to use and drying quickly. They create thin films with weak adhesion and chemical resistance, however. Furthermore, they can be dissolved by the original solvent, which makes recoating difficult unless spraying techniques are used.
Low molecular weight, low viscosity materials are converted to a high molecular weight toughened film in convertible systems. This is a chemical change, not only a physical one, as in non-convertible systems. The hardening procedure is divided into three stages:Solvents dissolve the resin in the uncured state. Before applying any paint, it must be in this stage.Solvents may cause the resin to expand during the part-cured stage.Solvents have no chemical influence on the film at this point.
TYPES OF PAINTS:
Nitrocellulose Lacquers
Nitrocellulose is created when nitric and sulphuric acids react with cellulose in the form of wood pulp. It’s really explosive, therefore dampers have been added. The volatile substance, which will make up 70 to 80 percent of the total, will be made up of seven distinct hydrocarbons. It produces a non-convertible, fast-drying paint that is ideal for applications like automotive spraying.
Lacquers made of vinyl (Non-convertible)
These are made with a vinyl acetate and vinyl chloride copolymer as a binder. A copolymer is a polymer chain made up of two different types of molecules. Vinyl acetate and vinyl chloride are used in this example, as illustrated below. A mixture of methyl ethyl ketone, methyl isobutyl ketone, cyclol-exanon, and toluene in sufficient amounts can be used as the solvent.
Acrylic Lacquers
The polymerization products of methacrylates or alkyl acrylates are thermoplastic acrylic resins. Butyl Acrylate boosts colour retention while lowering hardness.
Rubber that has been chlorinated (Non-convertible)
Rubber is treated with chlorine to produce a creamy white powder that can be used as a binder. As with the previous three, the solvents are appropriate hydrocarbons. This sort of paint’s main benefit is its chemical resistance, which comes at the cost of appearance.
Paints that are bound in oil (Convertible)
Until the turn of the century, almost all paints were made from lead dispersed in linseed oil. In reality, all natural oils, both animal and vegetable, belong to the glycerol tri-series.
Fatty acids have a molecular chain of eighteen carbon atoms or more.
Evaporation of the volatile solvent is followed by polymerization of the fatty acid and molecules with the addition of oxygen in the hardening process. The resulting polymer is distinct from the original oil and is not soluble in the solvent, ensuring that subsequent coatings are applied without difficulty. The thickness of the coat that can be applied is limited by the thinner’s evaporation. They require a lengthy drying period.
Alkyd Resins are a type of alkyd resin (convertible)
They are based on linseed oil again, but contain a polymeric ester formed by the reaction of glycerol with phthalic anhydride. They require a quicker drying time. There are three primary types that are used:
Long oil alkyds containing more than 60% oilAlkyds with less than 40% oil content (short-oil alkyds)The nitrocellulose resins require a non-drying variety. The thixotropic alkyds are made from the same raw materials as the thixotropic alkyds, but with the addition of minor amounts of polyamide resin.
Two Can Paint
There are numerous varieties that include a base and a hardener. The key benefit is that some of them do not require a solvent, which theoretically eliminates the thickness limitation. There are two major obstacles to overcome. The first stems from the fact that once the base and hardener are mixed, the reaction begins, and the paint becomes ineffective if it is not applied within 30 minutes of the start of gelation. The second occurs when a second coat is applied before the first has completed the hardening process entirely. Damage will be done to earlier coats if later coats are applied too quickly.
Lacquer
It’s a natural or synthetic resin solution in a volatile solvent. It’s made by dissolving nitro cellulose or shellac resin and film-forming nitro cellulose or shellac in a solvent. Nitrocellulose is made by reacting cellulose from wood or cotton fibre with a mixture of sulphuric and nitric acid.In a mixture of ketone alcohol hydrocarbon and the plasticizer, the solvent is utilised. The solvent dissipates quickly.
Fire Proof Paints:
Solution that is resistant to fire Fire is slowed by a covering of sodium tungstate and asbestos paints. As a result, either of these solutions can be used to coat timber work to make it fire resistant.
Cellulose Paints:
Chemically processed natural cellulose is transformed to nitrate, acetate, or methyl of ethyl cellulose. The cellulose derivative produced is dissolved in either petroleum or coaltar hydrocarbon. Plasticiser is a low-volatility organic ingredient that is added to cellulose paints to improve adhesion, toughness, smoothness, and elasticity. This paint is easier to wash and clean than typical oil paints since it has more hardness, flexibility, and smoothness, and it can endure temperature fluctuations and hot water better.
It generates a more glossy and long-lasting ornamental finish than metallic oxide-based oil paints. It is more expensive than oil paints. Spray paint, often known as duce, is a sort of paint that comes in a variety of colours. These are the paints that are used to paint autos.
Aluminium paints:
It’s made out of aluminium powder that’s been suspended in varnish. It has a high covering power and provides excellent corrosion protection for iron and steel against seawater and acid gases. It is heat resistant. It is resistant to oxidation and fading. It can be seen in the dark. It’s a cost-effective way to paint electric and telegraph poles, hot water lines, naval piers, and oil storage tanks, among other things.
Zinc Paint
It is currently widely used for white paints both indoors and outdoors, particularly on metallic surfaces. Zinc oxide has a high weathering resistance. Luminous and fluorescent paints made from zinc sulphate are used to illuminate maps and aviation equipment at night. Luminous paint is another name for the paint.
Vanish
Varnish is a resin solution in oil, turpentine, or alcohol. It dries to a firm, transparent, and glossy resin coating over the varnished surface following application.
Varnish is applied to painted surfaces to enhance their brilliance and preserve them from the elements, as well as to untreated hardwood surfaces to highlight the aesthetic aspect of the wood grains.