Paint coating is used today in many different areas, because it has a lot of advantages. One of the main conditions for ensuring all these advantages is the correct use, and that is why it is important to know what such coatings are, how to apply them correctly.
What is this?
Paint coating is a formed film of a paint and varnish substance applied to a certain surface. It can form on various materials. The chemical process itself, due to which the paintwork coating is formed, includes, first of all, drying, and then the final hardening of the applied material.
The main function of such coatings is to provide effective protection against any damage, as well as to give any surface an attractive appearance, color and texture.
Depending on the operational properties, the paintwork coating can be one of the following types: waterproof, oil and petrol resistant, weatherproof, heat-resistant, chemical-resistant, conservation, electrical insulating, and also for special purposes. The latter include the following subtypes:
- Anti-fouling paintwork (GOST R 51164-98 and others) is the main material in the ship industry. With it, the risk of fouling of the underwater parts of ships, as well as all kinds of hydraulic structures with any algae, shells, microorganisms or other substances is eliminated.
- Reflective paint coating (GOST P 41.104-2002 and others). Has the ability to luminescence in the visible zone of the spectrum when exposed to irradiation, light.
- Thermoindicator. Allows you to change the brightness or color of the glow at a certain temperature.
- Flame retardant, which prevent the spread of flame or exclude the possibility of exposure to high temperatures on the protected surface.
- Anti-noise. Provides protection against the penetration of sound waves through the surface.
Depending on the appearance, the paintwork can belong to one of seven classes, each of which has a unique composition, as well as the chemical nature of the film former.
It is common to use several types of materials based on:
- thermoplastic film formers;
- thermoset film formers;
- vegetable oils;
- modified oils.
All of the above paint and varnish coatings today are quite widely used in almost all areas of the national economy, and are also widespread in everyday life.
Worldwide, more than 100 million tons of paints and varnishes are produced annually, with more than half of this amount used in engineering, while a quarter is used in construction and repair.
For the manufacture of paint coatings, which are then used in decoration, extremely simple production technologies are used, which mainly involve the use of such film formers as aqueous dispersions of polyvinyl acetate, casein, acrylates and other similar components based on liquid glass.
In the vast majority of cases, such coatings are made by applying special materials in several layers, thereby achieving the highest possible safety of the protected surface. Basically, their thickness is from 3 to 30 microns, while due to such low rates it is quite difficult to determine the thickness of the paintwork in domestic conditions, where it is not possible to use special devices.
To obtain a multi-layer protective coating, it is customary to apply several layers of material of various types at once, with each layer having its own specific function.
The paint tester is used to verify the properties of the underlying layer, such as providing primary protection, adhesion to the substrate, retardation of electrochemical corrosion, and others.
The cover thatcharacterized by maximum protective characteristics, should include several basic layers:
- phosphate layer;
- one to three layers of enamel.
In some cases, if the paintwork tester showed unsatisfactory values, additional varnish can be applied, which provides more effective protective properties, as well as some decorative effect. When obtaining transparent coatings, it is customary to apply varnish directly to the surface of products that require maximum protection.
The technological process by which complex paint and varnish coatings are obtained includes several dozens of different operations that relate to surface preparation, application of paintwork material, drying and intermediate processing.
The choice of a specific technological process directly depends on the type of materials used, as well as the operating conditions of the surface itself. In addition, the shape and dimensions of the object on which they are applied are taken into account. The quality of surface preparation before painting, as well as the correct choice of which paintwork to use, significantly determines the adhesive strength of the material, as well as its durability.
Surface preparation includes cleaning with hand or power tools, shot blasting orsandblasting, as well as processing using various chemicals, which involves a number of operations:
- Degreasing the surface. For example, this applies to processing with specialized aqueous solutions or mixtures that include surfactants and other additives, organic solvents or specialized emulsions that include water and an organic solvent.
- Etching. Complete removal of rust, scale, and other corrosion products from the protected surface. In the vast majority of cases, this procedure is carried out after the paintwork of the car or other products has been checked.
- Application of conversion layers. It provides for a change in the original nature of the surface and is quite often used when it is necessary to create complex paint coatings with a long service life. In particular, this includes phosphating and oxidation (in most cases by the electrochemical method at the anode).
- Formation of metal sublayers. This includes galvanizing and cadmium plating (mainly using the electrochemical method on the cathode). Surface treatment using chemicals is mainly carried out by dipping or dousing the product with a specialized working solution in a fully automated or mechanized conveyor painting. Regardless of what types of paint and varnish coatings are used, the use of chemicals allows you to achieve high qualitysurface preparation, but includes further washing with water and hot drying of the surface.
How are liquid coatings applied?
After the necessary materials are selected, and the quality of the paintwork is checked, the method of applying it to the surface is selected, of which there are several:
- Manual. It is used for painting various large-sized products, as well as for household repairs and the elimination of all kinds of household defects. It is generally accepted to use air-drying paint products.
- roller. Mechanized application, which involves the use of a roller system. It is used for applying materials to flat products, such as polymer films, sheets and rolls, cardboard, paper and many others.
- jet. The workpiece is passed through a special "veil" of the appropriate material. With the help of this technology, a paint and varnish coating of a machine, various household equipment and a number of other products can be applied, while pouring is more often used for individual parts, while flat products, such as sheet metal, as well as panel elements of furniture and others, are processed in bulk..
The dipping and pouring methods are generally used to apply layers of paint to streamlined products that have a smooth surface if you want to paint them in one color. For gettingpaint and varnish coatings having a uniform thickness without any sagging or smudges, after painting the product, they are kept for a certain time in solvent vapors coming directly from the drying chamber. Here it is important to correctly determine the thickness of the paintwork.
Dipping in the bath
Traditional paintwork is best adhered to the surface after the product is removed from the bath after wetting. If we consider water-borne materials, then it is customary to use dipping with chemo-, electro- and thermal deposition. In accordance with the sign of the surface charge of the product that is being processed, catho- and anophoretic electrodeposition are distinguished.
When using the cathode technology, coatings are obtained that have a sufficiently high corrosion resistance, while the use of the electrodeposition technology itself makes it possible to achieve effective protection against corrosion of the edges and sharp nodes of the product, as well as internal cavities and welds. The only unpleasant feature of this technology is that in this case only one layer of material is applied, since the first layer, which is a dielectric, will prevent subsequent electrodeposition. It is also worth noting the fact that this method can be combined with the preliminary application of a special porous precipitate formed from a film former suspension.
When chemoprecipitation, a dispersion paint and varnish material is used, which includes various oxidizing agents. ATin the process of their interaction with a metal substrate, a sufficiently high concentration of special polyvalent ions is formed on it, which ensures coagulation of the near-surface layers of the material used.
In the case of thermal deposition, a deposit is created on a heated surface, and in this situation, a specialized additive is introduced into the water-dispersion paintwork material, which loses solubility when heated.
This technology is also divided into three main varieties:
- Pneumatic. Provides for the use of automatic or manual pistol-shaped spray guns with paints and varnishes at a temperature of 20-85 оС, which are supplied under high pressure. The use of this method is characterized by a fairly high productivity, and also allows you to achieve good quality paint coatings, regardless of the shape of the surfaces.
- Hydraulic. It is carried out under pressure, which is created by a specialized pump.
- Aerosol. Spray cans filled with propellant and paints are used. According to GOST, the paintwork of passenger cars can also be applied using this method, and in addition, it is actively used when painting furniture and a number of other products.
A rather important drawback, which distinguishes almost all existing spraying methods, is the presence of quite significant material losses, since the aerosol is carried awayventilation, settles on the walls of the chamber and in the used hydrofilters. At the same time, it should be noted that losses during air atomization can reach 40%, which is a fairly significant indicator.
To somehow reduce such losses, it is customary to use sputtering technology in a special high-voltage electric field. As a result of a corona discharge or contact charging, the particles of the material receive a charge, after which they settle on the product being painted, which in this case serves as an electrode of the opposite sign. Using this method, in most cases it is customary to apply various multi-layer paint coatings on metals and simple surfaces, among which, in particular, wood or plastic with a conductive coating can be distinguished.
How are powder materials applied?
In total, there are three main methods by which powder coatings are applied:
- fluidized bed application.
The predominant majority of coating technologies are usually used in the process of painting products directly on production conveyor lines, due to which stable coatings are formed at elevated temperatures, which are distinguished by sufficiently high consumer and technical properties.
Also, gradient coatings are obtained by a single application of materials that include mixtures of powders, dispersions or solutions of film formers, notcharacterized by thermodynamic compatibility. The latter can separate on their own during the evaporation of a common solvent or when the film formers are heated above the pour point.
Due to selective wetting of the substrate, one film former enriches the surface layers of paint and varnish coatings, while the second, in turn, enriches the lower ones. Thus, a multilayer coating structure is created.
It is worth noting that technologies in this area are constantly being improved and improved, while old methods are forgotten. In particular, today paint and varnish coating (system 55) according to GOST 6572-82 is no longer used for processing engines, tractors and self-propelled chassis, although earlier its use was very common.
Drying of the applied coatings is carried out at a temperature of 15 to 25 оС, when it comes to cold or natural technology, and can also be carried out at elevated temperatures using "furnace" methods.
Natural is used when using paints based on thermoplastic fast-drying film formers and those that have unsaturated bonds in the molecules using moisture or oxygen as curing agents, such as polyurethanes and alkyd resins. It is also worth noting that quite often natural drying occurs in the case of using two-pack materials in which the use of a hardenercarried out before application.
Drying of materials in industry is often carried out at temperatures from 80 to 160 оС, while powder and some special materials can be dried at temperatures up to 320 oS. By creating such conditions, accelerated volatilization of the solvent is ensured, and various reactive film formers, for example, melamine-alkyd, alkyd, and phenol-formaldehyde resins, are thermally cured.
The most popular heat curing coating technologies are as follows:
- Convective. The product is heated by circulating hot air.
- Thermoradiation. Infrared radiation is used as a heating source.
- Inductive. For drying, the product is placed in an alternating electromagnetic field.
To obtain unsaturated oligomer-based coatings, it is also customary to use the technology of curing under the influence of ultraviolet radiation or accelerated electrons.
During the drying process, many chemical and physical processes take place, which ultimately lead to the creation of highly protected paint coatings. In particular, this includes removal of water and organic solvent, wetting of the substrate, as well as polycondensation or polymerization, in the case of reactive film formers with the formation of cross-linked polymers.
Creating powder coatings includesobligatory melting of various particles of the film-forming agent, as well as adhesion of the formed droplets and wetting of the substrate by them. It is also worth noting that in some situations it is customary to use a heat cure.
Intermediate processing involves:
- Sanding with abrasive skins of the lower layers of paint and varnish to remove any foreign inclusions, as well as to give a dull finish and improve adhesion between several layers.
- Polishing the top coat with specialized pastes to give the paintwork a mirror finish. As an example, we can cite the technological schemes of painting used in the treatment of car bodies and including degreasing, phosphating, cooling, drying, priming and curing the surface, followed by the application of sealing, soundproofing and inhibitory compounds, as well as a number of other procedures.
The properties of the applied coatings are determined by the composition of the materials used, as well as the structure of the coating itself.