Anti-corrosion coatings knowledge
一 functions
1 shielding effect. Film preventing corrosion medium and material surface contact, partition corrosion battery pathways, increasing the resistance.
2 corrosion inhibition. Some paint, or its and film objects or moisture to the reaction products, metal substrate can act as corrosion inhibition (including passivation).
3 cathodic protection. Paint film electrode potential is lower than substrate metal. In corrosive batteries, it is used as an anode to "sacrifice", thus make the substrate metal (cathode) protected.
二 main influencing factor
1 The influence of coating film components
Anti-corrosion coatings film components in corrosive medium with chemical stability, its standard and film material composition and chemical structure are concerned. Basically is to see it in the dry film conditions, whether is easy to reaction with corrosive medium or decompose into small molecules in medium.
No matter from the electrochemical corrosion or from the pure isolation effect consideration, anti-corrosion coatings shield effect are very important, and paint film called membrane shielding effect depends on the structure of content and coating pinhole porosity
Water, oxygen and ion through the paint film speed is different. The water through speed is faster than ions. Oxygen showing through is more complex, and is related to the temperature. Water and oxygen through the film can form corrosion electricity in the metal surface. Ion through film is less, don't consider them can directly acting on the base metal, but will increase film conductivity.
As membrane molecules of polymer structure has more functional group, film structural stomata is less, and can react each other in film forming process, forming crosslinking density high mesh three-dimensional structure, thereby enhancing the coating anticorrosive performance.
The physical and mechanical properties of the coating great extent affects anti-corrosion coatings anticorrosive effect. They are related to film content molecular weight, chain section, side gene and so on.
2 Pigments, fillers influence
In coatings, shading effect pigments on physical pigment is used to regulate the mechanical properties of the coating or coating liquidity. For anti-corrosion coatings, in addition to the above two kinds of pigment, still has added to prevent corrosion for the purpose of pigment: one kind is to use its chemical properties of metal corrosion inhibition antirust pigments, another is the flake paint, through the physical effects to improve coating shielding effect.
Antirust pigment can divide into alkaline pigment, soluble pigments and metal powder paint three kinds.
（1） Alkaline pigment. Alkaline pigments and oily film react can create metal stearate, such as redlead, Pb2O, cyanogen ammoniation lead, alkali type chromic acid lead, lead calcium and alkali type lead sulfate, etc. After metal stearate contacts with water, the decomposition products can act corrosion inhibition. In addition, when generating metal stearate, paint film improved the environment of shielding effect. Alkaline pigment makes film and metal interface to keep micro alkaline, also play corrosion function.
（2） Soluble pigment. Usually is the chromate salt pigment. After these pigments contact with water, dissolved out chromium acid radical ion, with strong oxidation, can make the metal surface passivation, thus plays corrosion prevention role.
（3） Metal powder paint. Extensive used metal powder pigment is zinc powder. Zinc-rich coating after drying of coating consisting mainly by zinc powder. In zinc powder particles and between substrate and redistillation maintains direct contact between. When the water immersion coating, it has formed by redistillation and steel substrate composed of batteries. Current to flow from zinc iron, thus making the substrate by cathodic protection. In addition, zinc corrosion products accumulate between zinc powder and steel surface, strengthening the coating shielding function.
Flake pigments in coating can shield in water and oxygen and ion corrosive factors, cutting off coatings stoma. Mutual parallel overlapping scales play a labyrinth effect in coating, prolong corrosive medium infiltration way, so as to improve the ability of anti-corrosion coating. The main flake paint has mica powders, aluminum powder, mica iron oxide, glass flake, stainless steel scales, etc.
Besides film content and pigments, anti-corrosion coatings other components, such as fillers, additives, etc must also have better chemical stability
三、 main types
1、 Grease coating
Grease coating is dry oil as the main film content type of paint. Its characteristic is easy to produce, good besmear brushs performance, good wettability, cheap, it is flexible, but film dry slowly, membrane is soft, mechanical performance is poorer, acid-proof alkaline resistance, water resistance and poor organic solvent. Dry oil often matches with antirust pigment composed as corrosion resistant paint, used for not high demand of the atmospheric environment.
2、 Raw lacquer
Raw lacquer is called as country paint, is China's speciality. Raw lacquer is an ivory viscosity fluids from growing on cut out of bark, through cloth to filter and remove impurities. After painting on surfaces, color quickly from the white become red, by red turned to purple, over a long period of time may become hard light black paint film.
Paint phenol is the main component of raw lacquer, content of 30% ~ 70%. Generally speaking, the higher raw lacquer paint phenols content higher quality.
Raw lacquer film adhesion is strong, tough film, good gloss, and its resistance to erosion, water resistance, oil resistance. Faults are toxic, easily make person skin allergy. In addition, it will not endure strong oxidizer, alkali resistance is poor. "There are a lot of modification of raw lacquer coatings, different extent overcomes the shortcomings
3 Resin coating
Phenolic resin coating: basically has alcohol-soluble phenolic resin, phenolic resin, pure phenolic resin, etc. Alcohol-soluble phenolic resin coating corrosion resistant performance is better, but the construction of inconvenience, flexibility, adhesion not too good, applied by certain restrictions. So often need to phenolic resin modified. Such as rosin modified phenolic resin and tung-oil refining, add various pigment, can be obtained by grinding various enamel, the paint film is tough, the price is cheap, widely used in furniture, doors, windows coating. Pure phenolic resin coating strong adhesion, water resistance, corrosion resistance, damp and hot weather resistance.
Epoxy resin coating: good epoxy coating adhesion, to metal, concrete, wood, glass, etc. have excellent adhesion, alkali, oil and water resistance, electrical insulating performance is excellent. But anti-aging is poor. Epoxy anti-corrosion coatings, usually by epoxy resin and curing agent two components. Curing agent nature also affects film performance.
Common curing agent are: fat amine and their modified content, characteristic is temperature curing, unmodified fat amine bigger toxicity, aromatic amine and their modified content, the characteristic is response is slow, often have to be heat cure, toxicity, weaker, polyamide resin, the characteristic is weathering resistance is good, lower toxicity, good flexibility, corrosion resistance is a bit poor, phenolic resin, urea-formaldehyde resin and other synthetic resin.
These resins and epoxy resin use high-temperature baking paint membrane, film has outstanding corrosion resistance and good mechanical properties and adornment performance.
Epoxy resin coating is using epoxy resin as film that one kind of one-component coating system. Epoxy resin vinegar by epoxy resin and vegetable oil fatty acids compound. This epoxy coating has low cost, poor alkaline resistance, compared with general epoxy coating. Commonly used for various metal primer and chemical plant outdoor equipment anti-corrosion paint.
Ceramic coating: America's ICT - FREECOM company invented C - K54 ceramic - epoxy coating has already been countries extensively. It is by more than 90% of the ceramic powder and different types of epoxy resin and auxiliary agent formed. With good wear resistance, corrosion resistance, high temperature resistance, impact resistance and high insulation. It can be coated on carbon steel, stainless steel, aluminum, copper, composites, concrete, plastic and glass fiber surface.
Ceramic coating continuous working temperature can reach 149 ℃, the short time (within 15min) working temperature can reach 371℃. Temperature curing, also can heat cure. It has been applied in oil drilling and refining, sea naval ships and platform, transportation tank, electrical equipment, aviation spacecraft, sewage treatment equipment, chemical pump and valve manufacturing.
Ethylene resin coating: ethylene resin anti-corrosion coatings mainly refers to vinyl chloride, vinyl acetate, ethylene, propylene etc monomer made resin film content coatings. One of the high-ch coating has been large produced and applied.
High-ch coating can form the density film, chemical corrosion-resistant performance is good, but to light and heat stability is poor, long-term use unfavorable exceeds 60 ℃, poorer metal adhesion. The coating material source is rich, atmospheric corrosion in preventing chemical has used in large amounts.
Furan resin coating: furan resin coating resistant to all kinds of oxidizing inorganic acid, electrolyte solution, all kinds of organic solvent, alkali resistance, but also very outstanding antioxidant bad.
Furan resin series anti-corrosion coatings include furfuryl alcohol resin coating, furfural formaldehyde resin coating and modified acetone furan resin coating etc.
4、 Pu coatings
Used for anti-corrosion coatings polyurethane resin often contain two components: Dudley cyanate vinegar base NCO and hydroxyl. When using mixed reaction will two-component curing generating poly carbamate vinegar (pu).
5、 Rubber kind coating
Rubber class anti-corrosion coatings after chemical processing or mechanical processing of natural rubber or synthetic rubber for film components, plus the solvent, packing, pigment, catalyst processed.
Chlorinated rubber paint. This coating has good water resistance, salt and fog resistance, with certain salt and acid or alkali corrosion resistance, below 50 ℃ can resistant 10% HCl, H2S04, HN03, different concentrations of NaOH and wet Cl2. But not resistant solvent, ageing resistance and heat resistance is poor. This coating is widely used in ship, harbor, chemical and so on.
Neoprene coating, chlorinated neoprene coating is the 1980s developed new coating, with acid, alkali, salt, anti-humidity, water resistant, resist atmosphere and water permeability, etc. Compared with chlorosulfonated polyethylene coating, chlorinated neoprene paint construction simpler, cut corners of surface treatment, low request, the effect is good, especially facilitate old equipment maintenance. This coating ozone-resisting and chemicals, alkaline outstanding, good oil resistant and heat-resistant, can be made strip coating. Defect is poor storage
stability. Coating color is easily changed, not easily made white or light color paint.
Chlorosulfonated polyethylene rubber paint. Our country in the 1970s, it has begun to use, already in synthetic ammonia, urea, phosphate, pesticide, dye and other production equipment in use. Its main characteristic is antioxidant, resistance to mould, water resistant, atmospheric and ozone resistance, weather resistant and ageing resistance, anti-ionizing radiation, stable color, good flexibility, good membrane entirety and strong binding force, using temperature range - 50 ~ 120 ℃, resistant to acid, alkali, salt and other chemicals, low viscosity, quick dry, can low temperature construction, besmear brushs process is simple. It is made by polyvinyl resin and chlorine and sulfur dioxide (or chlorosulfonic) reaction.
6 asphalt paint
Asphalt is one of the important anti-corrosion coatings. Especially asphalt as the best, asphalt coating price is low.
7 Heavy anti-corrosion coatings
Heavy anti-corrosion coatings is relative commonly concerned as anti-corrosion coatings. It means in harsh conditions, anti-corrosion effect is many times higher than general corrosive coating. Its characteristic is resistant to strong corrosive medium performance and durability is excellent, service life reaches several years. It is mainly used for Marine structures and chemical equipment, tanks and pipeline etc.
