Guangzhou Longkai Chemical Co., Ltd.
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Development of Water-borne Anticorrosive Coatings and Prevention of Common Defects
Author:LongKom  Time:2018-4-2

The research and development of waterborne anticorrosive coatings began in the 1980s. Because of the well-known reasons, waterborne anticorrosive coatings are in a state of slow development, small amount of application and ordinary performance. They have been staggering for 30 years.

Over the past few years, the relevant state departments have issued a series of documents restricting the use of solvent-based coatings in some areas and projects, imposing consumption tax on VOC over-standard coatings, promulgating standards for water-borne acrylic acid, water-borne polyurethane, water-borne epoxy, water-borne alkyd resin coatings, water-borne inorganic phosphate solvent-resistant anticorrosive coatings, and the limits of harmful substances of the above-mentioned coatings, and environmental standards. Zhi products include the technical requirements of waterborne coatings, etc. In this way, waterborne paint research and development units have a direction, so that some paint enterprises see business opportunities, so that waterborne paint research and development technicians have a basis. Since this year, more and more resins, pigments and auxiliaries have been used for water-borne paints. Many solvent-based coatings enterprises have been busy with the upsurge of "oil-to-water" and some coatings enterprises are increasingly favoring water-borne paints. Since then, China's water-based industrial paint has entered a new period of development.

1 Common Defects of Water-borne Anticorrosive Coatings

The advantages and disadvantages of a newly prepared and packaged paint are not clear. Only when the cans and barrels are opened can the appearance and stability of the paint be seen. At this time, the defects include floating water, caking, surface bubbles, deterioration and mildew. In addition, the effect can only be seen after painting construction. At this time, the defects include coating hanging, poor covering force, shrinkage of film surface, pinholes, uneven surface, lack of fullness and gloss of external paint, etc. After a period of time, if the paint or coating quality is not good, there will be cracking, peeling, foaming, rusting and other defects. Waterborne paint may have more defects than solvent-based paint due to its inherent weaknesses.

2. Reasons for Common Defects of Water-borne Antiseptics
1) or too many hydrophilic substances in the paint, water is easy to infiltrate, produce air pressure, top the paint film. If there are more bubbles, the whole coating will lose its adhesion.
2) Film bubble: The main reasons are: inappropriate selection and collocation of defoamers; the defoamers are not dispersed uniformly in beating and varnishing stages; the paint viscosity is too low in roll coating and the spray gun is not adjusted to the best level in spraying. 
3) coating shrinkage: the main reasons are: the components in the coating system have not been stirred evenly, and the material with high surface tension, such as emulsion, has poor flowability, defoamer, film-forming agent and so on. Many shrinkage holes, rust prone primer, poor appearance of topcoat.
4) Hardness problem: The main reasons are related to Tg and addition of the base material, oil absorption and addition of the powder, and environmental conditions during film formation, namely temperature and humidity. If the film is too hard, the flexibility, flexibility and impact resistance will not pass through. If the film is too soft, the effect of water permeation plasticizing and corrosion retention will be obvious.
5) the poor water resistance (salt): the main reasons are: the film forming property of the base material, the poor water and white property, the coarse solid particles, the insufficient base material, and the fact that the Antirust Emulsion does not rust; because the surface tension of the coating is greater than the surface tension of the substrate, the adhesion between the primer and the substrate is poor, and the fatal defects such as frothing, shrinkage holes and pinholes are also found. Some coatings contain the above defects and are less water resistant and resistant. Saltwater and even salt spray resistance are remarkable.

6) Appearance defect of paint film: As far as the external paint is concerned, the main reasons are: uneven paint film, less fullness, because the surface tension of the paint is large, the internal flow is not spread, the film surface leveling is poor; glossiness is not high, the visual effect is poor, which is related to the higher base or Pvc, the quality of the base and pigment, and the levelness of the bottom layer.

Prevention and treatment of common defects of waterborne anticorrosive coatings

According to the experience of R&D practice, we have taken the following measures to prevent and solve these defects:

Prevention from the source of formulation is to try to reduce the surface tension of coatings. The main difference between waterborne coatings and solvent-based coatings is the use of different dispersing and diluting media, which results in different surface tensions of the two coatings. Water-borne coatings have more problems than solvent-based coatings. Therefore, water-borne anticorrosive paints, whether high-grade or low-grade, should reduce the surface tension of coatings and improve the adhesion of coatings in the first place. This requires the choice of the right additives: first, the use of a small amount of high-performance base material wetting agent; second, the addition of water-based coatings with adhesion promoters. Silane coupling agents have strong fluidity and can migrate freely to the organic / inorganic interface. Therefore, emulsion is the rationale for adding silane attachment, and the most effective adhesive on the surface of iron and steel is two oxygen functional silane, which is more expensive.

Titanate coupling agent has the function of wetting the base material and assisting defoaming and leveling. Thirdly, using high efficiency and low surface tension leveling agent can not only enlarge the spreading surface of primer on the base material and increase its adhesion point, but also benefit the flow leveling of the coating surface and reduce the appearance of filling. Fourthly, adding a certain amount of alcohol and ether combined solvents with different volatilization rates. On the one hand, it can help the base material to form film better, on the other hand, it can also reduce the surface tension of coatings, but the relationship between dosage and drying and construction should be taken into account. The primary and secondary positioning of these additives, synergistic effect, coating surface tension will be reduced, adhesion will be improved.

The measures mentioned above have been taken reasonably. The defects of self-drying primer or baking varnish, such as peeling, foaming and insensitivity, surface irregularity, non-smoothness and non-fullness, and the short service life of the paint layer are the following.