Paint coating: types and methods of application
Coating paint is used today ina lot of different spheres, because it has a lot of advantages. One of the main conditions for ensuring all these advantages is correct use, and that is why it is important to know what kind of coatings are, how to apply them correctly.
What is it?
Paint coating is aa formed film of a paint material applied to a certain surface. It can be formed on various materials. The very chemical process, thanks to which the paint 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 giving any surfaces an attractive appearance, color and texture.
Depending on the performancePaint coating can refer to one of the following types: waterproof, oil-and-oil resistant, weather resistant, heat-resistant, chemical resistant, conservation, electrical insulation, and special purpose. The latter include the following subtypes:
- Anti-fouling coating paint and varnish (GOST R51164-98 and others) is the main material in the ship industry. With the help of it, the risk of fouling of underwater parts of ships, as well as of all kinds of hydraulic structures, by any algae, shells, microorganisms or other substances is excluded.
- Reflective coating paint and varnish (GOST P 41.104-2002 and others). Has the ability to luminescence in the visible spectral region in the presence of exposure to radiation, light.
- Thermal indicator. Allows you to change the brightness or color of the glow when there is a certain temperature.
- Fire-retardant, which prevent the spread of flame or exclude the possibility of exposure to the protected surface of high temperatures.
- Anti-noise. Provide 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 generally accepted to use several types of materials based on:
- thermoplastic film formers;
- thermoset film-forming agents;
- vegetable oils;
- modified oils.
All of the above paint and varnish coatings are now widely used in almost all spheres of the national economy, and have also become widespread in everyday life.
More than 100 million annually are produced worldwidetons of paint and varnish materials, while more than half of all this amount is used in engineering, while a quarter is used in construction and repair.
For the manufacture of paint coatings, whichthen used in finishing, extremely simple manufacturing techniques are used, which basically involve the use of such film-forming agents as aqueous dispersions of polyvinyl acetate, casein, acrylates and other similar components based on liquid glass.
In the majority of cases, suchcoatings are made by applying special materials in several layers, thereby achieving the highest possible safety performance of the protected surface. Basically, their thickness is from 3 to 30 microns, and due to such low indicators, it is quite difficult to determine the thickness of the paint coating in domestic conditions where it is not possible to use special instruments.
To obtain a multilayered protective coating, it is customary to apply several layers of different types of material at the same time, each layer having its own specific function.
Paint testing deviceis used to verify the properties of the lower layer, such as providing primary protection, adhesion to the substrate, slowing of electrochemical corrosion and others.
A coating that has the maximum protective characteristics should include several basic layers:
- phosphate layer;
- from one to three layers of enamel.
In some cases, if the device is to be checkedpaintwork has shown unsatisfactory values, can additionally be applied varnish, with which more effective protective properties are provided, as well as some decorative. When obtaining transparent coatings, varnish is usually applied directly to the surface of products, which requires maximum protection.
The technological process by whichcomplex paint and varnish coatings are obtained, includes several dozens of different operations that relate to surface preparation, application of paintwork, drying and intermediate processing.
The choice of a particular technologicalprocess 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 to which they are applied are taken into account. The quality of the preparation of the surface 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 withusing a manual or mechanized tool, shot blasting or sand blasting, as well as processing using a variety of chemicals, which involves a number of operations:
- Degreasing the surface. For example, this concerns the treatment with specialized aqueous solutions or mixtures containing surfactants and other additives, organic solvents or specialized emulsions, including water and an organic solvent.
- Etching. Complete removal of rust, scales, and other corrosion products from the surface to be protected. In the majority of cases, this procedure is carried out after the paint and varnish coating of the car or other products has been tested.
- Application of conversion layers. It provides for changing the original nature of the surface and is 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 electrochemical method at the anode).
- Formation of metal sublayers. This includes galvanizing and cadmium (mainly using the electrochemical method on the cathode). Surface treatment using chemicals is mainly carried out by dipping or pouring the product with a specialized working solution in fully automated or mechanized conveyor painting. Regardless of what kinds of paint and varnish coatings are used, the use of chemicals allows to achieve a high quality of surface preparation, but at the same time it provides for further washing with water and hot drying of the surface.
How are liquid coatings applied?
After the necessary materials are selected, and also the quality of the paint coating is checked, a method of applying it to the surface is chosen, of which there are several:
- Manual. It is used for painting various large-sized products, as well as for household repairs and removal of all kinds of household defects. In general, it is customary to use natural products of paint and varnish.
- roller. Mechanized application, which involves the use of a roller system. It is used for applying materials to flat products, such as polymer films, sheet and rolled products, cardboard, paper and many others.
- jet. The processed product is carried through a special "curtain" of the appropriate material. With this technology, paint and varnish coating of the machine, various household equipment and a number of other products can be applied, with individual parts being more often used for pouring, while in bulk are processed flat products such as sheet metal, as well as panel furniture elements and others .
Methods of dipping and watering in primaryIn most cases, it is customary to use to apply coating layers to streamlined products having a smooth surface, if you want to paint them in a single color. For the production of paint coatings having a uniform thickness without any build-up or leakage, after painting the product for a certain period of time, it is kept in solvent vapors coming directly from the drying chamber. It is important to correctly determine the thickness of the paintwork.
Dipping into the bath
Traditional paintwork is bestIt is retained on 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 thermo-deposition. In accordance with the sign of the charge of the surface of the product to be treated, the catho- and anophoretic electrodeposition is different.
When cathode technology is used,such coatings that have a sufficiently high corrosion resistance, while the use of the technology of electrodeposition itself allows to achieve effective protection against corrosion of the edges and sharp parts of the product, as well as internal cavities and welds. The only unpleasant feature of this technology is that only one layer of material is applied in this case, since the first layer, which is a dielectric, will interfere with the electrodeposition of the subsequent layer. Also worth noting is the fact that this method can be combined with the preliminary application of a special porous precipitate formed from a suspension of the film former.
During chemo-precipitation, dispersionpaint and varnish material, which includes all kinds of oxidants. During 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 the use of thermal precipitation, the precipitateis created on a heated surface, and in this situation a special additive is introduced into the water-dispersion paint material, losing its solubility in the case of heating.
This technology is also divided into three main types:
- Pneumatic. It provides for the use of automatic or manual pistol-shaped sprayers with paint and varnish materials at a temperature of 20-85aboutC, which are fed under high pressure. The application of this method is distinguished by a sufficiently high productivity, and also allows to achieve a good quality of paint coatings, regardless of the shape of the surfaces.
- Hydraulic. It is carried out under pressure, which is created by a specialized pump.
- Aerosol. Cans filled with propellant and paint and varnish materials are used. According to GOST paint coating of cars can be applied using this method, but in addition it is actively used for painting furniture and many other products.
A rather important shortcoming,practically all existing methods of spraying, is the presence of quite a significant loss of material, since the aerosol is carried away by ventilation, settles on the walls of the chamber and in the used hydrofilters. It is worth noting that losses due to pneumatic spraying can reach 40%, which is a rather significant indicator.
In order to somehow reduce such losses, it is customaryUse the spraying technology in a special high-voltage electric field. Particles of the material, as a result of corona discharge or contact charging, receive a charge, after which they settle on the painted product, which in this case serves as an electrode of the opposite sign. With this method, in the majority of cases, it is customary to apply various multilayer paint coatings to metals and simple surfaces, among which, in particular, wood or plastic with a conductive coating can be isolated.
How are powder materials applied?
In total, three main methods are used for the application of paint coatings in the form of a powder:
- fluidized bed application.
The predominant majority of application technologiesLMC is used in the process of painting products directly on the flow conveyor lines, so that at elevated temperatures, stable coatings are formed, characterized by sufficiently high consumer and technical properties.
Also gradient paintworkare obtained by means of a single application of materials, which include mixtures of powders, dispersions or solutions of film formers that are not thermodynamically compatible. The latter can separate themselves during the evaporation of a common solvent, or when the film-formers are heated above the flow temperatures.
Due to the selective wetting of the substrate, onefilm-forming agent provides enrichment of surface layers of paint coatings, while the second, in turn, enriches the lower ones. Thus, the structure of the multilayer coating is created.
It should be noted that the technology in thisthe sphere is constantly improving and improving, while the old methods are forgotten. In particular, today paint and varnish coating (system 55) in accordance with GOST 6572-82 is no longer used for processing engines, tractors and self-propelled chassis, although earlier its use was very common.
Drying of applied coatings is carried out at a temperature of 15 to 25aboutC, when it comes to cold or natural technology, and can also be carried out at elevated temperatures using "furnace" methods.
Natural applies when usedpaint and varnish materials based on thermoplastic fast drying film-forming agents and those that have unsaturated bonds in molecules using moisture or oxygen as hardeners, such as polyurethanes and alkyd resins. It is also worth noting that quite often natural drying occurs when using two-pack materials, in which the hardener is applied before application.
Drying of materials in industry is often carried out at a temperature of 80 to 160aboutC, while powder and some special materials can be dried at a temperature of up to 320aboutFROM. Due to the creation of such conditions, accelerated volatilization of the solvent is provided, as well as thermosetting of various reactive film-forming agents, for example melamine-alkyd, alkyd, and also phenol-formaldehyde resins.
The most popular technologies for thermal curing of coatings are the following:
- Convective. The product is heated with circulating hot air.
- Thermoradiation. As a source of heating, infrared radiation is used.
- Inductive. For drying, the product is placed in an alternating electromagnetic field.
To obtain paintwork based on unsaturated oligomers, it is also customary to use curing technology under the influence of ultraviolet radiation or accelerated electrons.
During the drying process, manychemical and physical processes, which ultimately lead to the creation of highly protected paint and varnish coatings. In particular, this includes the removal of water and organic solvent, wetting of the substrate, as well as polycondensation or polymerization, when it comes to reactive film-forming agents with the formation of networked polymers.
Creating coatings from powder materialsincludes mandatory melting of various particles of the film former, as well as the adhesion of the formed droplets and their wetting of the substrate. It is also worth noting that in some situations it is customary to use thermal curing.
Intermediate processing provides:
- Grinding with the help of abrasive skins of the lower layers of the paint to remove any foreign inclusions, as well as to give opacity and improve adhesion between several layers.
- Polishing of the top layer usingspecialized pastes, so that the paint and varnish have a mirror shine. As an example, we can cite technological color schemes used in the processing of car bodywork and include degreasing, phosphating, cooling, drying, priming and curing the surface, followed by applying sealing, noise-insulating and inhibiting 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 by the structure of the coating itself.