Paints
Paints are substances (usually in liquid form) used for creating protective or decorative coatings on the surface of various objects. They consist of a colouring substance (pigment) and a number of additives, such as binders, thinners, dispersing agents, preservatives and many others.
Pigments can be natural or synthetic and they provide the paint with the right colour. The most popular natural pigments are various clays, silicas, calcium carbonate and talcs, whereas synthetics include calcined clays, barium sulphate (so-called blanc fixe), precipitated calcium carbonate or pyrogenic silicas. A special type of pigment are fillers. These are granular solids, designed to increase the volume of paint, strengthen its structure, or reduce the cost of paint production, due to the fact that they are relatively cheap. Examples of widely used paint fillers are diatomaceous earth, talc, lime, barite and clay.
Binders and film-forming substances are ingredients found in all types of paints, varnishes and emulsions. They create a thin film-forming coating on the surface of the painted element and are intended to provide the paint with appropriate properties such as gloss, durability, adhesion, resistance to weather conditions, strength and flexibility. Substances acting as binders in paints can be synthetic or natural resins, such as, polyurethanes, polyesters, vinyl acetate/ethylene (VAE), silanes, epoxy resins or oils,
Thinners are used to dissolve the polymer and reduce the viscosity of the binder. They are characterized by high volatility, resulting in an easy evaporation when drying and do not become part of the paint. Additionaly, they control flow properties and applications while they can also affect the stability of liquid paint. Depending on the diluent, water and oil paints (otherwise known as solvent) are offered the latter usually containing combinations of various organic solvents, such as aromatic compounds (toluene or other xylene derivatives), alcohols or ketones.
Dispersing agents. Modern waterborne paints contain a variety of different components. Therefore, it is particularly important to mix them thoroughly in order to ensure proper consistency and stability of the paint. Dispersing agents are used for this purpose providing in addition to the appropriate performance properties of the paint, the desired colour saturation while ensuring adequate pigmentation.
Μodifying additives are also used in paints to modify their properties of paints changing, among others, their surface tension, improve flow properties and pigment stability, control foaming or prevent freezing. In addition, emulsifiers used in paints and coatings help to create a permanent, uniform emulsion, which directly translates into easier application of paint on any surface.
Depending on their properties and application, paints can be divided in the following general categories:
a) Emulsion paints, also known as dispersion paints, structured in the following sub-categories, depending on the type of adhesive used.
- Acrylic paints with water dispersion of acrylic resin their binder. They are characterized by very good flexibility and adhesion to the substrate. Acrylic paints have a wide range of applications and can be used to cover, for example, wood, concrete, plastics, plasters and many other surfaces. They have high abrasion resistance and allow water vapor, however, the surfaces painted are susceptible to various types of damage,
- Latex paints based on rubber binder. Although usually high priced these paints are extremely resistant to moisture and cleaning, and easily applied. Ceramic paints, containing ceramic particles, consist an example of the most modern latex paints that form a so-called stain resistant coating preventing absorption of dirt and dust in painted surfaces.
- Acrylic-latex paints. They have the characteristics of acrylic paints, i.e. good air permeability and scrub resistance, and flexibility of latex paints,
- Vinyl paints with polyvinyl acetate or polyvinyl chloride as binder. They are used mainly in utility rooms, and their greatest advantage is easy washability. Unfortunately, they also make it difficult for the walls to breathe due to the low vapor permeability.
b) Lime paints with lime putty diluted with water as binder. They are cheap, but not durable. In order to increase the durability, admixtures of other water-borne adhesives (e.g. glue) or the addition of polyvinyl acetate are used. Lime paints are used for painting fresh concrete substrates, lime plasters and walls previously painted with lime paints. Currently, the use of these paints is very rare. This is due to their very low durability, dustiness and tendency to create cracks,
c) Distempers, durable and breathable paints with excellent solubility in water. Plant or animal glues are their binder. Distempers are not very resistant to dirt, they cannot be washed and they absorb moisture from the environment. They are mainly suitable for painting lime and cement-lime plasters. Distempers are practically no longer used because they have been replaced by more modern paints,
d) Silicate paints – their binder is potassium water glass. These paints are durable, non-flammable, resistant to moisture and have high mechanical resistance. They can be applied on brick, concrete and wooden substrates. When drying, they cure under the influence of CO2 contained in the air,
e) Silicone paints based on a silicone resin. They create a durable and weather-resistant coating. Suitable for painting concrete, wooden, brick and plaster substrates. These paints have the ability to self-clean,
f) Epoxy paints. Two-component paints, consisting of an epoxy resin and a hardener. Before applying, both components are mixed together. Epoxy paints show high resistance to mechanical damage and chemicals. They are used, for example, for painting concrete floors. For their production, additives based on phosphate esters from the Roflam series (F5, B7, P) can be used. These products provide high fire resistance to the materials to which they are added. Thanks to that, they can be used in passive fire protection systems, recommended in the protection of steel structural elements against the effects of hydrocarbon and jet fire. They have a wide usage in the petrochemical, energy, oil and gas industries,
g) Chlorinated rubber-based paints in which a binder is obtained by chlorination of the rubber with addition of softening agents. Chlorinated rubber-based paints formed in this way are resistant to water, acids and alkalis, but are very sensitive to all organic solvents (except alcohol). They can be used as protective paints for gates and fences,
h) Vinyl paints resistant to water and various chemical compounds. Polyvinyl chloride is most often used as a binder. Vinyl paints are mainly used as coatings for materials made of galvanized steel, such as gutters and window sills,
i) Polyurethane paints based on polyurethane resins. There are two types of these paints: one and two components. One-component paints are cured under the influence of moisture, while two-component paints require the addition of a hardener. Polyurethane paints create hard and abrasion-resistant coatings. They are used for painting wooden, metal and plastic surfaces. They are characterized by very high toxicity,
j) Structural paints, a special type of paint applied to the surface with a thick layer. After drying it provides a suitable pattern (structure) and therefore used when decorative wall textures are demanded. Structural paints are suitable for covering concrete, wooden, gypsum plasterboards, plasters and many others,
k) Spray and powder paints. Applied to various surfaces using a gun, they are used to obtain special visual effects. Thanks to these types of paints, it is possible to obtain coatings resistant to all kinds of cracks and splinters.
Varnishes
Varnishes are finishes which contain a solid binder dissolved in a solvent and they are dried out as a result of its evaporation.They also have the ability to quickly cure in a very wide temperature range and can create transparent or pigmented coatings, where the main raw material is a hard and linear polymer. The nature and properties of varnishes are strongly dependent on the type of their structure but can be generally divided into two groups: solvent-based and water-based.
Solvent-based varnishes form very hard coatings that show high resistance to mechanical damage. By creating a homogeneous structure, they also prevent the penetration of moisture. The most important component of this type of varnish is the solvent, which is usually characterized by an unpleasant and intense smell. Solvent-based varnishes can be divided into a number of subgroups:
a) Solvent-based polyurethane varnishes. One- and two-component varnishes considered among the best varnishes available on the market. One-component polyurethane varnishes use the moisture contained in the air to harden. In contrast, the characteristic feature of varnishes based on two components are two stages of drying. During the first stage, the solvent evaporates, then the chemical drying takes place and the varnish is hardened. The advantages of polyurethane varnishes are their resistance to moisture, as well as high flexibility. Their main drawback is their usual high toxicity. They can be used to achieve a wide range of finishes, from satin to gloss. Polyurethane varnishes, due to their abrasion resistance, are mainly used for varnishing floors in rooms with high intensity of movement, such as halls and lounges,
b) Nitrocellulose lacquers with nitrocellulose resin as the main raw material for their production.The nitrocellulose varnishes also contain a number of other substances, such as polyester and alkyd resins, which improve their hardness and gloss. Plastifying additives are also used, most often phthalates, which increase resistance to light and temperature. Nitrocellulose varnishes are used as materials for painting furniture and various wooden elements. They are also used as a base layer for polyurethane varnishes,
c) Oil-resin varnishes produced from drying oils, natural or synthetic resins, thinners and usually a large number of additives modifying their appearance or properties. These varnishes are characterized by high resistance to atmospheric factors, in particular to UV radiation. However, they show poor hardness and abrasion resistance. They can be used for painting all wooden surfaces, from panelling to windows and doors. They can also be used as floor coatings in rooms with low traffic,
d) Spirit varnishes, produced from solutions of natural or synthetic resins dissolved in ethyl alcohol, with their key advantage their very short drying time (usually does not exceed 60 minutes). Unfortunately, they are not resistant to all impacts and atmospheric conditions. Spirit varnishes can be used to paint toys and various wooden elements in interiors.
In the case of water-based varnishes, the main diluent is water. The methyl ester is responsible for their flexibility and surfactants are substances that reduce their surface tension. Water-borne varnishes can be divided into three groups based on the type of adhesive used:
a) Acrylic varnishes, substances commonly used in woodworks creating transparent coatings, without changing the colour of the wood. They are characterized by low abrasiveness and mechanical resistance and their biggest advantage is low toxicity. They are mainly used for painting wooden household products and painting floors in places with low traffic,
b) Water-based polyurethane varnishes featuring a very high resistance to abrasion and mechanical damage. In addition, they are insensitive to moisture and temperature changes. Like polyurethane solvent-based varnishes, they are divided into one- and two-component varnishes. Due to the creation of very durable coatings, they are often used on floors,
c) Polyurethane-acrylic varnishes with their properties depending on the proportion of both components. Varnishes containing more polyurethane in composition are characterized by higher hardness. Polyurethane-acrylic varnishes exist in one or two-component form. They can also contain a number of hardeners that improve their mechanical strength and abrasion resistance but they also increase their toxicity.