Anticorrosive paints
Anticorrosive paints are a type of paint used on the surface of objects to protect the inside of objects from corrosion. It is a type of paint that is more commonly used than anticorrosive paints in industrial construction. It is widely used in aviation, ships, chemicals, oil pipelines, steel structures, bridges, oil drilling platforms, and other fields, and is favored by many construction companies.
Types, ingredients and characteristics
• Types
There are many types of anticorrosive paints. According to the ingredients, they can generally be divided into: epoxy anticorrosive paint, polyurethane anticorrosive paint, acrylic anticorrosive paint, inorganic anticorrosive paint;
Perchloroethylene anticorrosive paint, chlorinated rubber anticorrosive paint, high chlorinated polyethylene anticorrosive paint; according to the use, it can be divided into: pipeline anticorrosive paint, ship anticorrosive paint, metal anticorrosive paint, furniture anticorrosive paint, automotive anticorrosive paint, rubber anticorrosive paint; according to the solvent, it can be divided into: water-based anticorrosive paint, oil-based anticorrosive paint;
Anticorrosive paint is a mixture of various hydrated silicate minerals, and the main chemical groups are two oxides, Al2O3 and SiO2. Al2O3 mainly comes from clay minerals, and SiO2 comes from clay minerals as well as micro-quartz. The closer the Al2O3 content and Al2O3/SiO2 ratio are to the theoretical value of kaolinite minerals, the higher the purity of this type of clay.
• Characteristics
It can be used under harsh conditions and has good durability and weather resistance. It can be used for more than 10 or 15 years under harsh conditions such as oceans and underground. Even in acid, alkali, salt, and solvent media, and under certain temperature conditions, it can be used for more than 5 years.
• Composition
The more kaolinite content in the clay, the better its quality. The higher the refractoriness of the clay, the wider the sintering and melting range of the clay. The main impurities in the clay are oxides of alkali metals, alkaline earth metals, iron, titanium, etc., as well as some organic matter. Various oxides act as fluxing agents and reduce the refractoriness of the raw materials. Therefore, the lower the impurity content in the clay, especially the content of Na2O and K2O, the higher its refractoriness. There are many types of clay minerals, but usually only 5 to 6 kinds of minerals are composed, the main mineral is kaolinite. Common impurity minerals include quartz, hydromica, iron-containing minerals, feldspar, rutile, etc. The impurity content and distribution uniformity affect the refractory properties of clay. Anti-corrosion paint will undergo a series of physical and chemical changes during the heating process, such as decomposition, chemical transformation, recrystallization, etc., accompanied by volume shrinkage. These changes have an important impact on the process and properties of clay products. my country's clay raw materials, whether hard clay, soft clay, or semi-soft clay, are mainly kaolinite-type. Therefore, the heating change of clay is the heating change of kaolinite and the physical and chemical reaction between kaolinite and impurity minerals. Hard clay clinker is the main raw material of clay refractory materials, usually obtained by calcining hard clay raw material blocks directly mined in a downdraft kiln, a rotary kiln, or a vertical kiln.
In addition to chemical composition, refractory production requires that clay clinker has high bulk density, low porosity, low water absorption, and is fully sintered. Therefore, calcination temperature and insulation time have a significant impact on the quality of clay clinker. When the calcination temperature is between 1200 and 1250 degrees Celsius, the bulk density and porosity of the clinker are the best. When the temperature is greater than 1350 degrees Celsius, the bulk density decreases and the porosity increases, because at this time, a large amount of cristobalite is generated, the volume expands, and at the same time, the coke layer is developed, causing the clinker block to crack. The main mineral phase of hard clay in anti-corrosion paint is mullite, accounting for 35% to 55%, followed by glass phase and cristobalite.
Varieties: Epoxy series
Epoxy anti-corrosion paint series: Epoxy zinc-rich primer Perchlorethylene anti-corrosion paint Epoxy primer Epoxy coal tar anti-corrosion paint Epoxy micaceous iron intermediate paint
Epoxy paint is usually used as a primer and intermediate paint for anti-corrosion paint.
Epoxy anti-corrosion paint composition: It is composed of epoxy resin, anti-rust pigment, filler as component one, and curing agent as component two.
Epoxy anti-corrosion paint characteristics: Water resistance, acid, and alkali resistance, and good anti-rust performance. Strong adhesion to steel and cement surfaces.
Uses of epoxy anti-corrosion paint: Suitable for pipelines, various steel structures, bridges, oil brick well platforms chemical equipment, etc., for water resistance, oil resistance, and chemical reagent resistance, as a protective primer, and can also be used as a primer for cement substrates or a combination of bottom and surface protection.
• Polyurethane series
Polyurethane anti-corrosion paint composition: It is a two-component self-drying paint, component one is polyester color paste, and component two is a special curing agent.
Polyurethane anti-corrosion paint characteristics: Good anti-corrosion performance. The coating has good adhesion, toughness, wear resistance, elasticity, and acid resistance, alkali resistance, salt resistance, oil resistance, petroleum product resistance, benzene solvent resistance, water resistance, boiling water resistance, seawater resistance, and chemical atmosphere resistance.
Uses of polyurethane anticorrosive paint: Suitable for anticorrosion coating of steel structure facilities, gas pipelines, chemical facilities, oil tanks, bridges, docks, gas tanks, motors, electrical appliances, aluminum alloys, etc.
• Acrylic series
Composition of acrylic anticorrosive paint: Anticorrosive paint is composed of acrylic resin as the main base material, modified resin, pigments, fillers, additives, solvents, etc.
Characteristics of acrylic anticorrosive paint: The paint film has excellent gloss retention, color retention, and weather resistance. It has good physical and mechanical properties. The paint film dries quickly and is easy to apply. It can be applied at temperatures between -20℃ and 50℃.
Uses of acrylic anticorrosive paint: This paint is suitable for anticorrosion protection and decoration of steel structures and concrete.
• Perchloroethylene anticorrosion paint
Composition of perchloroethylene anticorrosion paint: The paint is made by grinding perchloroethylene resin, alkyd resin, toughening agent, and pigment, and then adding mixed solvent to it
Characteristics of perchloroethylene anticorrosion paint: The paint has excellent corrosion resistance, acid and alkali resistance, mildew resistance, and moisture resistance, but poor adhesion, which can be compensated if the matching is good.
Purpose of perchloroethylene anticorrosion paint: It is used on metal and wood surfaces such as various chemical machinery, pipelines, equipment, and buildings to prevent corrosion by acids, alkalis, and other chemicals.
• Chlorinated rubber anticorrosion paint
Composition of chlorinated rubber anticorrosion paint: It is composed of chlorinated rubber, modified resin, pigment, filler, stabilizer, organic solvent, etc.
Characteristics of chlorinated rubber anticorrosion paint: It has good acid and salt corrosion resistance and atmospheric corrosion resistance, and has good physical and mechanical properties.
Purpose of chlorinated rubber anticorrosion paint: It is mainly used for the protective coating of automobile chassis and engineering machinery chassis, or the protective coating of equipment, pipelines, and metal components under mild corrosion.
• Highly chlorinated polyethylene
Highly chlorinated polyethylene anticorrosive paint composition: chlorinated polyethylene resin (HCPE), modified resin, plasticizer, pigment, additive, solvent, etc.
Performance of highly chlorinated polyethylene anticorrosive paint: The paint film is tough, with excellent weather resistance, corrosion resistance, and flame retardancy. It has excellent anti-corrosion properties against the industrial atmosphere, "three wastes" pollution media, and different concentrations of acid, alkali, salt, mineral oil, and other corrosive media (ammonia, chlorine, carbon dioxide)
Use of perchlorinated polyethylene anticorrosive paint: Suitable for anticorrosion projects such as petrochemical, metallurgical mines, construction plants, transportation facilities, ships and bridges, engineering machinery, sewage treatment and other steel structures and concrete facilities, industrial floors.
• Inorganic anticorrosive paint
Inorganic anticorrosive paint ZS is composed of new inorganic polymers and dispersed and activated metal and metal oxide nanomaterials inorganic polymer coatings. It can react quickly with iron atoms on the surface of steel structures to generate dual physical and chemical protection. It is pollution-free to the environment, has a long service life, and its anticorrosion performance reaches the international advanced level. It is a high-tech replacement product that meets environmental protection requirements.
Construction
• Surface pretreatment
If there are impurities, oil, grease, and dirt on the surface, they should be cleaned according to the cleaning method specified in the "Specifications for Steel Surface Pretreatment before Painting" SY/T0407.
The steel surface should be sprayed for rust removal according to the method specified in SY/T0407. When spraying, it should be carried out in the order of top first, then wall, and finally bottom. The rust removal quality should reach the Sa2.5 level specified in the "Rust Level and Rust Removal Level of Steel Surface before Painting" GB/T8923-1998. The anchor pattern depth is selected according to the anti-corrosion level. Ordinary type: about 40μm. Use a 6-8mm nozzle, a compressed air pressure of 0.5-0.6Mpa at the nozzle inlet, a spray angle of 30-75°, an incident distance of 100-200mm, and a sand particle size of 0.8-4 mm. When sandblasting thin steel plates, the sand particle size and air pressure should be appropriately reduced. When the wear of the sandblasting outlet and diameter exceeds 1/2 of the starting inner diameter, the nozzle shall not be used any longer. The surface pretreatment of the accessories should be the same as that of the main parts.
After the blasting treatment, the surface should be blown clean with dry, clean, oil-free compressed air.
After blasting and rust removal, the defects exposed on the steel surface and welds must be treated.
Safety measures: Keep ventilation to keep the solvent gas concentration below the dangerous concentration. The blasting workers wear protective clothing and masks. The blasting pipe should be cleaned immediately after it touches the nose.
• Paint Preparation
If the anti-corrosion paint is a two-component paint, the two components can be mixed and prepared before application. Before preparation, confirm whether the A and B components are matched, whether they are consistent with the required application model, and whether they are invalid.
Before preparation, the A and B components must be stirred until there is no sediment at the bottom and they are evenly distributed up and down.
Prepare a small amount of uniform A and B components according to the proportion required by the instructions for trial coating, and use a special diluent to adjust the viscosity to achieve the best coating process conditions to ensure the thickness and quality of the single film.
Calculate the amount of A and B components according to the coating area and the thickness of the single coating film, and control the amount of ingredients to be used up within 6 hours to prevent excessive dosage, excessive coating, and excessive maturation and thickening of the coating, which will affect the quality of the coating film.
The amount of special paint diluent should be controlled not to exceed 15% (spraying) or 8% (brushing) of the total weight. Add it to component A according to the calculated proportion and stir evenly, then add component B and stir for 10-15 minutes to mature components A and B, and finally let it stand for 15-20 minutes to eliminate the air bubbles introduced by stirring. The length of stirring and standing time depends on the amount of ingredients.
The mixed paint can be sprayed after filtering with a 100-mesh filter. If the paint overreacts and thickens during the spraying process, stop spraying immediately. If the paint has been scrapped, it should be re-mixed. The overreaction time of the coating is related to the ambient temperature. When the temperature is high, the time is short and the material should be less. On the contrary, when the temperature is low, the time is long and the amount of material should be appropriately increased.
• Coating process
During the specific construction, the coating process regulations and measures to ensure the quality of the anti-corrosion layer should be formulated according to the structure of the anti-corrosion items.
The environmental conditions during coating should meet the requirements of the instructions. The outdoor construction of the anti-corrosion layer should be stopped in case of rain, snow, fog, wind sand, and other climatic conditions. When the construction environment temperature is lower than -5℃ or higher than 40℃, or the relative humidity is higher than 80%, it is not suitable for construction. The uncured anti-corrosion layer should be protected from rain.
If rust occurs during the interval between the qualified surface pretreatment and the application of the first primer, the rusted part should be re-prepared before coating. Large containers that cannot be sandblasted within one day, should be sealed to prevent convection with the external gas and prolong the rusting time.
Chlorosulfonated polyethylene anticorrosive paint can be applied by airless spraying, air spraying, brushing, or rolling. It should be applied from top to bottom. The coating should be uniform and no omissions should be allowed. The coating method to be used should be determined according to the anticorrosive construction plan.
The coating operation should comply with the following regulations:
A. When using the brushing method, apply uniform force and brush in the same direction to avoid surface fuzzing.
B. When spraying, the movement speed of the spray gun should be uniform, and the nozzle should be kept perpendicular to the sprayed surface.
C. When using the rolling method, the roller should be dipped evenly and not too much. The force should be uniform and not too large when rolling, and the speed should be kept uniform; the roller should roll in the same direction, and the direction of each pass can be different. Edges, corners, accessories, and other parts that cannot be coated by the roller should be repainted with a brush tool.
Welds, corners, and uneven surfaces should be dipped in more paint or the number of coatings should be increased.
The interval between each coat of paint should not exceed 24 hours, and the next coat of paint should be applied after the previous coat of paint has dried. If the previous coat of paint has been cured, it should be roughened before applying the next coat of paint. After the last coat of topcoat is applied, it should be cured for more than 7 days at room temperature 25°C before it can be put into use. If the curing temperature is lower than 10°C, it should be cured for more than 10 days before it can be put into use.
During the construction process, the wet film thickness of the coating should be measured at different parts, and the viscosity of the coating and the coating process parameters should be adjusted in time to ensure that the final thickness of the anti-corrosion layer meets the design requirements.
Precautions
Before the anti-corrosion paint is applied, two points must be noted: one is the danger to human health; the other is the danger of explosion. It is important to understand the safety regulations of the product before the paint is applied. For example, in Jinnuoxin acrylic engineering primer and Jinnuoxin acrylic engineering topcoat, although there is only one-word difference and the functions are similar, but attention should be paid to the proportion and use. Once an accident occurs, it will endanger human health.