Building materials - fundamentals of the construction business. Polyester coatings How polymerization works

From the lessons of chemistry, everyone should remember what a polymer is. Even the laziest loser will certainly say what it is. Indeed, polymers are composed of many components and often, thanks to this particular structural feature, they are quality things, whatever it may be.

Today we are talking about polymer roofs. Following the same scheme as in chemistry, let's say for starters that a polymer roof is made of a material that contains many different components. Another thing is what these components are and why they are, in fact, attractive: This is exactly what we have to figure out.

Special polymer coatings are used to give metal roofs decorative properties and additional protection against corrosion. They have been used in the West for over 40 years and are extremely widespread. Steel roofs with a polymer coating have established themselves as a high-quality and durable material.

In general, the process of applying polymer coatings to galvanized steel is very complicated and requires full automation and quality control at every stage of the process chain. steel tape goes through stages pre-treatment, phosphating, priming, and only then a polymer coating is applied. Drying is carried out in a special chamber.

Polymer coated galvanized steel sheet has a multi-layer structure:

• steel sheet;
• zinc layer;
• passivating layer;
• soil layer;
• from the bottom side of the sheet - protective paint;
• with front side- a layer of colored polymer.

Each component of the multilayer structure is carefully selected and performs its function. For the consumer, it is necessary to know that different polymer coatings are characterized by different resistance to ultraviolet radiation (color fastness), temperature (heat resistance), aggressive media, mechanical damage and other factors.

So we have finally come to the most important thing in the study of this issue: we will understand the components of polymer coatings, that is, the polymers themselves.

Acrylic

Acrylic as a polymer coating is nothing more than a paint layer. The catch is that this coating is considered the most unstable, unreliable and fragile. It is very easy to damage it when installing the roof. In general, it fades in the sun (in about 5 years), begins to peel off after 2-3 years due to corrosion. So the acrylic coating loses very quickly and therefore has not been used by Western countries for a long time. construction companies. Only domestic materials with such a coating are found on sale, however, they are recommended to be used only for temporary structures.

Polyester (polyester enamel)

Here is polyester - a more reliable and more serious coating in all respects.

It is one of the most common polymers in the market for polymer coatings for galvanized steel sheet. Polyester is considered a relatively inexpensive material suitable for any climatic zone. It is resistant to mechanical and atmospheric influences (more resistant to mechanical influences polyester with sprinkling quartz sand however, it is significantly more expensive). In addition, when transporting polyester with a sprinkling of quartz sand, a number of problems arise associated with the possibility of damage to the lower layer. metal sheets(quartz sand, like sandpaper, scratches the surfaces of the overlying sheets in contact with it).

Polyester has high color fastness and plasticity. Heat resistance is about +120 0C. Polyester coating can be glossy and matte (modified Teflon).

Using polyester to coat galvanized steel sheet is reasonable and cost effective profitable choice when the building is not in a highly polluted environment environment and the operating load is not too high.

PVF2 (polydifluorionade)

PVF2 is a material composed of 80% polyvinyl fluoride and 20% acrylic. Such a polymer coating is particularly durable - it withstands frost down to -60 0C and does not lose its properties at temperatures up to +120 0C. The most resistant to ultraviolet radiation, practically does not fade, has a beautiful shine. Compared to other coatings, it is the most expensive, highly resistant to aggressive media and mechanical damage. PVF2 has an extremely rich color palette: it exists in both glossy and matte, as well as with a metallic touch in silver or copper tones. To give a metallic sheen, the standard PVF2 finish is completed with a layer of pigmented clear lacquer.

It is most advisable to use PVF2 in aggressive environments, such as the sea coast, industrial building chemical industry etc.

Plastisol (polyvinyl chloride)

Plastisol is a decorative polymer. It consists of polyvinyl chloride and various plasticizers. The thickness of the polymer coating for the roofing steel sheet is 175 or 200 microns. Sheets are also produced with a 2-sided plastisol coating of 100 microns on each side. Such material is used, for example, for the manufacture of pipes and gutters.

Due to its large thickness, the plastisol coating is one of the most resistant to mechanical damage. However, due to its low temperature resistance and low resistance to UV radiation (when heated by direct sunlight above +80 0C, the material ages quickly), it is not recommended to use it in southern regions. Having greater thickness, plastisol has a high corrosion resistance, which creates additional protection in a polluted environment. Its color fastness is significantly lower than polyester (the coating evenly loses color brightness after a few years).

With a thickness of 175 microns, the plastisol coating is produced only smooth. And a stamped pattern can be rolled onto a coating 200 microns thick, an embossed textured surface is given (at the same time, in the places of embossing, the thickness of the coating layer is significantly reduced).

Plastisol-coated steel sheets are an ideal material for the manufacture of seam roofs, since the high plasticity and large thickness of the coating protect the sheets from mechanical stress.

Pural

Pural - relatively new type polymer coating. It has been used relatively recently. It is made on a polyurethane base modified with polyamide. Why is Pural good? It has good chemical resistance, withstands solar radiation, high temperatures and large diurnal temperature fluctuations. Minimum temperature when working with sheets covered with pural, -15 0С, maximum +120 0С. The coating thickness is 50 µm. This coating is suitable for profiled sheets, as it is easy to process, both during profiling and during installation. Its plasticity is guaranteed even at low temperatures. Pural has a silky matt textured surface.

The range of existing industrial polyester coatings is very diverse. Polyester coatings differ in color, application and curing conditions, intended use (primer coating, top coat), purpose.

Epoxy powder paints (polyester coating) are usually applied to the surface by electrostatic spraying. Depending on the operating conditions, 1-2 layers are applied. Epoxy coatings are highly adhesive, mechanical strength and chemical resistance. Operating temperature range from -60 to +120?С. coatings are moisture resistant, resistant to alkalis, aliphatic and aromatic hydrocarbons, lubricating oils, fuels, crude oil. In terms of weather resistance, epoxy coatings are inferior to many other coatings - they quickly lose their gloss and grind. The dielectric properties of the coatings are rather high.

Polyester coatings are distinguished by good atmospheric and light resistance, mechanical and electrical strength, and increased resistance to abrasion. Polyester paints are better than others powder materials applied to electric field, of which coatings of various colors can be obtained. Paints are well applied to the surface by electrostatic spraying, other methods of application are also suitable for them. They have high gloss and satisfactory adhesion to metals.

The alkali resistance of coatings is low. The dielectric performance of polyester coatings is low. Atmospheric testing of coatings was carried out in the conditions of the south, which showed that weather resistance of polyester coatings is superior to all other types of coatings, including polyacrylate and polyurethane.

Epoxy polyester powder paints are attracting a lot of attention due to their relatively low cost and good quality the resulting coatings. Paints are obtained by combining epoxy and polyester oligomer. Paints are applied to the surface by electrostatic spraying. Coatings have a beautiful appearance, good gloss and uniform color, resistant to water, aqueous salt solutions, dilute alkalis and acids.

Table. Chemical resistance of polyesters.

The consumer needs to know that different polymer coatings are characterized by different resistance to UV radiation (color fastness), temperature (heat resistance), aggressive media and mechanical stress, and other factors.

Consider the main types of polymer coatings.

Acrylic

Acrylic polymer roofing is a paint layer that is extremely unstable and can be easily damaged during roof installation. It has heat resistance up to +120°C, but fades in the sun in 5 years, moreover, it has an average resistance to corrosion and begins to peel off after 2-3 years of operation. Layer thickness 25 µm. The minimum processing temperature is -10°C. It is recommended to use only for temporary structures.

Polyester (polyester enamel)

Thickness roofing is 25-30 microns, and therefore the resistance to mechanical stress is not high. Polyester coated with quartz sand is more resistant to mechanical stress, but it is much more expensive. In addition, during its transportation, a number of problems arise associated with the possibility of damage to the lower layer of metal sheets.
Polyester has high color fastness and plasticity. Heat resistance is about +120°C. Polyester coating can be glossy and matte (modified Teflon). It is suitable for buildings with a low operational load.

Plastisol (polyvinyl chloride)

The polymer plastisol coating due to its large thickness (175-200 microns) is one of the most resistant to mechanical damage. However, due to its low temperature resistance and low resistance to UV radiation (when heated by direct sunlight above + 80 ° C, the material ages quickly) is not recommended for use in southern regions.
Having a large thickness, plastisol has a high corrosion resistance, which creates additional protection in a polluted environment. Ideal material for the manufacture of seam roofs. Its color fastness is significantly lower than polyester (the coating evenly loses color brightness after a few years).

Pural

This is a new type of roof covering based on polyurethane modified with polyamide. The material has good chemical resistance, withstands solar radiation, high temperatures and large daily temperature fluctuations. The minimum temperature when working with sheets coated with Pural is 15°C, the maximum is +120°C. The coating thickness is 50 µm. It is easy to process both during profiling and during installation. Has a silky matte finish.

PVF2 (polydifluorionate)

PVF2 is 80% polyvinyl fluoride, 20% acrylic. The coating is durable, withstands frost down to -60°C and does not lose its properties at a temperature of +120°C. The most resistant to UV radiation, practically does not fade. Has a rich color palette, can be glossy or matte surface, with a touch of metallic. Compared to others, the coating is the most expensive, highly resistant to aggressive media and mechanical damage.
It is most expedient to use on sea coasts, chemical industry buildings, etc.

Despite the widespread use of polyesters in the production of paints and varnishes, the development of polyester powder paints was significantly delayed due to the lack of industrial production of solid polyesters. They appeared only in the mid-60s and in 1975 they accounted for about 15-20% of the production of thermoset powder paints in world production.

Polyester powder paints are usually divided into several groups. First of all, these are widely used triglycidyl isocyanurate (TGIC) cured polyesters. For many years, developments have been carried out to improve only such PCs, despite the increased toxicity as volatile substances, released during curing, and the coatings themselves, compared with the epoxies and epoxy-polyesters described above.

However, in recent years, due to the special attention to the environment and the safety of the materials used, polyester powder paints have been developed and began to be produced, which have all the advantages of the former with reduced toxicity. Coatings based on them are allowed to come into contact with food products, can be used for coloring children's toys and furniture; when cured, no particularly harmful substances are released. At the same time, the cost of PC and, accordingly, the cost of painting a unit area increases slightly.

Polyester coatings are distinguished primarily by weather resistance, mechanical strength and increased abrasion resistance. In terms of weather resistance, these coatings are not inferior to any other powder material. The dielectric properties are close to those of epoxy coatings. However, the alkali resistance of polyester coatings is low.

Typically, coatings with a thickness of 60-120 microns are used. They have high gloss and good adhesion to metals, including light alloys.

Polyester topcoats with high weather resistance and high gloss are used in multi-layer technology (eg wheel rims) to finish the product.

Purpose of polyester coatings: aluminum shaped profiles, architectural and building structures, wheel disks and machine parts, agricultural equipment, garden tools, etc.

POLYESTER POWDER PAINTS

Polyester PCs also include the so-called “polyurethanes”, which are cured with blocked isocyanate and differ in a number of features.

The main disadvantage of the first polyurethanes was the problem of volatile compounds released during the curing of the coating, and as a rule, leading to a defect in the coating (formation of craters), and with a large layer thickness, to porosity. The maximum limit of the coating thickness was 100 µm. Despite this, users of polyurethanes were attracted by the exceptional hardness, chemical resistance, gloss and surface texture of these coatings. The developments of recent years on the creation of new isocyanates made it possible not only to solve this problem, but to achieve that modern polyurethanes are comparable in weather resistance to polyesters containing TGIC.

Polyurethane coatings are characterized by stable gloss, water and weather resistance, resistance to liquid fuels, mineral oils, solvents.

They are used to protect products subjected to friction, abrasive wear, some types of chemical equipment and containers for storing liquid and gaseous chemical substances. Also suitable as a primer when applying other powder paints (epoxy, polyacrylate, etc.).

The technology for obtaining coatings based on powder paints is largely the same as the technology for obtaining coatings from conventional liquid coatings. The difference lies in the absence in the composition of PC of a liquid phase under normal conditions, which must be removed or turned into a solid, and, of course, by the physical state of the paint itself: a solid body in the form of a finely divided powder, which requires temporary transfer to a liquid in order to form a coating film on the surface of the product to be painted. condition.

In accordance with this, in the technological chain of coating processes, the liquid removal process is excluded when the mandatory heat treatment stage is included at a temperature above the melting point of the PC material, and the PC deposition equipment is adapted to work with powder. The processes of surface preparation before application remain almost unchanged. Thus, the technological chain of painting a product with powder paint consists of the following stages and processes:

Surface preparation: degreasing, removal of contaminants and oxides, if necessary and possible - transformation (conversion) of the surface to increase adhesion and protection against corrosion (phosphating, chromating).

Layer application powder paint on the painted surface.

Coating film formation: reflow, curing, cooling.

The polymer coating is unique opportunity protect metal surfaces. This is the most efficient and modern way fight against corrosion, which sooner or later still appears on metal products.

What is the point?

To improve the performance properties of the metal, polymers are used that can react in certain conditions. Such coatings are dry compositions based on a fine dispersion powder, to which hardeners, fillers and pigments are additionally added. The polymer coating was chosen to enhance the metal not by chance: metals conduct electricity As a result, the charge is transferred to the product, as a result of which it is formed It attracts powder particles, holding them on the surface of the workpiece. Feature of a polymeric covering - in high degree resistance to any kind of impact. In addition, it is aesthetic.

How does polymerization work?

The powder coating shop consists of several sections:

• Product preparation area: in order for the polymer coating to be applied correctly and evenly, the metal product is first thoroughly cleaned of dust, rust, and dirt. It is advisable to use efficient and phosphating. An obligatory stage is the degreasing of the metal surface.
• Spray chambers: the spray booth is directly thermal, it is able to heat up to a temperature of 200 degrees and warms up evenly. The powder begins to melt, due to which an even and smooth coating is formed over the entire surface of the metal, and its pores are also filled.
• The polymerization of the product is carried out in the cooling chamber: here the temperature gradually drops, and polymer film becomes harder. After 24 hours, the polymer coating is ready for use.

Coloring technology: what is the point

Application powder coating is carried out in several stages. At the first, surfaces are processed. It is very important that metal products are thoroughly cleaned of dirt, oxides, and degreasing the surface will contribute to improved adhesion. After preparation, the masking stage is performed, that is, those elements are hidden metal product on which the powder composition should not fall.

The parts to be processed are hung on the transport system, then sent to the painting booth. After spraying, a powder layer is formed on the metal. At the polymerization stage, a coating is formed, which is a melting of the paint layer.

What are the features?

Polymer-coated metal is durable and increased strength. This is explained by the fact that a sealed monolithic film is formed that completely covers the surface of the product and firmly adheres to it. Thanks to the polymer coating, the metal has:

• high adhesion to the surface;
• high strength and wear resistance;
• long service life while maintaining the original properties;
• rich colors;
• fast production cycle.

Polymer is performed on the basis various materials and coloring powders. The choice of a particular substance depends on the purpose for which the coating is applied, how important decorative properties.

Polyester

For the polymer coating of metal, polyester is most often used. This is inexpensive material, possessing high level flexibility, formability, besides, it can be used in any climatic conditions. Polyester-based polymer coated sheet is UV resistant and corrosion resistant. The material forms a high-quality and durable film on the surface, due to which, under any conditions of transportation, steel sheets are delivered intact.

Matte polyester is also widely used: the coating has a very small thickness, and the surface of the metal is matte. Peculiarity this material- in high color fastness, good resistance to corrosion and mechanical stress.

Plastisol

Another popular polymer coating for metal is plastisol. As part of this decorative material- polyvinyl chloride, plasticizers; externally, it attracts attention with an embossed surface. Exactly this expensive coverage, and at the same time the most resistant to mechanical damage due to the large thickness of the coating. On the other hand, the material does not have high temperature resistance, and therefore, under the influence sun rays at high temperature coating will deteriorate. Due thick plastisol corrosion resistance is high.

Pural-based polymer-coated steel is popular, which has a silky-matte structural surface. Resistance to temperature extremes and exposure to chemicals makes this composition popular for metal processing.

Characteristics of color coated steel

Features of materials with a polymer coating - in strength, formability, high corrosion resistance. After processing, the steel acquires a beautiful appearance, which can be given any colors and shades. Rolled products are made in accordance with GOST, the polymer coating is of high quality. Painted rolled products can have a one- or two-layer coating, options are possible when the substance is applied on one or both sides. Thanks to the polymer coating, improved operational properties become:

• polymer-coated metal can be processed into finished products;
• the coating is distributed evenly over the surface, therefore the degree of protection is uniform;
• the absence of pores is a guarantee good level protective properties;
• steel has good adhesion;
• metal can retain protective and decorative properties for more than 10 years.

From an economic point of view, with a polymer coating is more profitable: firstly, it contributes to high productivity and quality, as the cost of coating is reduced. Secondly, the buyer does not need to invest in additional processing steel to protect its surface. Note that the anti-corrosion properties of galvanized steel, which is treated with a polymer coating, depends on the thickness of the layer. To increase the service life of steel products, they are additionally coated with two layers of polymer, which makes metal protection even higher.

Coating features

A polymer coating is a film that has a whole range of unique performance characteristics. Pre-painted rolled products are based on several types of polymers. Any material processed on the basis of this method - steel sheet or mesh with a polymer coating - is characterized by impact resistance, corrosion resistance and high adhesion. It is also important that powder coating allows you to make the surface of the metal any in terms of color, including artificially aged, for example, antique style.

Today, such a method of painting rolled steel as Coil Coating is popular. The essence of the method is that the coating is applied to automated line, that is, sheets of rolled products are processed on the line, after which they are coated with roller machines. This technology has become widespread due to the fact that there is no loss of materials, and the line itself is more productive, and therefore profitable.

As with any other finishing work, you first need to prepare the surface, after which it is painted. This technology allows for quality processing steel, aluminum and tinplate. Thus, a polymer coating is an opportunity to improve the performance properties of a metal, increase its protective properties and ensure longevity.