Talking about the technical application of waterborne rust-to-rust coating (2)

1. Resin selection
with rust coating widely used film-forming substances are acetic resin, phenolic resin, epoxy resin, polyurethane resin, acrylic resin and phenyl propylene emulsion. These resins have a poor matching relationship with varnishes and are only suitable for finishes made with ordinary solvents (gasoline, ethanol, etc.). Liquid phenolic resin storage period is generally not more than half a year, the application of more oil-soluble solid pure phenolic resin storage period is not more than half a year, the application of such resins produced primers due to the short storage period will bring inconvenience to production and applicationSuitable for water-based systems commonly used in water-based epoxy resins, acrylic water dispersions and phenylpropyl emulsions.
Epoxy resin as the main component of the preparation of the "wet strip rust coating primer", which can be used with most coatings, can also be used as a separate anti-rust coating, especially can be directly used for high-pressure water rust removal and wet steel plate surface, to solve the high-pressure water surface technology after the application of post-treatment technology problems. However, due to the relatively large molecular mass of epoxy resin, the system viscosity is high, in the construction process needs to be adjusted with toluene and other organic solvents to the suitable construction viscosity to paint;
Synthesized a functional emulsion from butyl acrylates, styrene, acrylic, methyl acrylic and phosphate functional monomers, which can be soaked in 3% salt water for more than 720h.
the rest are natural plant polyphosphate as permeable conversion chelating agent, acrylic latex as a film, potassium iron cyanide as a conversion synergizer and filler preparation of a multi-functional water-based antiseptic coating. And with flax oil, shunbutene adhesive and modified phenolic resin added to the water-based resin as the base material, and rust-proof pigment mixture can also be prepared a new type of water-soluble anti-rust coating.
2. Pigment selection
Rusty steel surface consists of at least 2 layers, the inner layer is relatively dense magnet rust, the outer layer is looser fiber rust, a small amount of crystal needle rust distributed in 2 layers. Rust consists of 2 layers inside and outside, and the outer layer is loose and rusty and the inner layer is firmly rusted.
To the typical pure propylene and phenyl propylene composite emulsion as a membrane substance as an example, it takes aluminum tripolyphosphate, zinc phosphate, zinc oxide, talcum powder, vanadium sulfate and so on for the pigment preparation of the bottom surface of the water-based rust-proof coating. The coating is a rust-proof coating with stable and permeable type as one. It can also be seen that most of the anti-corrosion coatings on the market are to use active pigments or fillers to improve the life of anti-corrosion coatings.
To phosphate as a rust-proof paint filler example:
phosphate as a rust-proof pigment varieties, such as zinc phosphate, iron phosphate, iron phosphate, chromium phosphate, calcium phosphate, palladium phosphate and so on. When zinc phosphate is used, it can form polymeric conjunctiles with metal surfaces and film resins, so it has the best rust resistance. The greatest advantage of the application of zinc phosphate is that the choice of film-forming substances is wide, generally in oil-based, aliclicic resin, nitroculose, epoxy resin and other film-forming substances can be used, in water-based paint and pre-coated primer can also be used. Its biggest drawback is that the volume concentration must be high when used alone, and the effect is not ideal. Generally and four-salt-based zinc yellow, chromate, zinc oxide and other use (its dosing is 20% to 30% of the total pigment amount), rust resistance and anti-foaming properties have been greatly improved, so zinc phosphate-chromate anti-rust primer is generally made of zinc phosphate, tate-based zinc yellow, chromate, talcum powder and alkyd resin paint preparation. It is suitable to use this rustproof primer when it is not suitable to use red Dan anti-rust primer or when the surface treatment is not clean.
trihydrophosphates can destroy the stability of resins due to acidity, water solubility and other reasons. Therefore, the alkaline substance and tripolyphosphate reaction were used to obtain a more suitable pH and solubility. In order to solve this problem, zinc oxide is used as a modified substance, adding more than 15% of tripophosphate can get pH of 6 to 7 pigment products, but the cost and environmental impact restrict its use.
rust-proofing ions of coking phosphate is stronger than that of tripophosphate ions, and is the strongest anti-rust phosphate found to date.
3. The selection of fillers
comparing a variety of pigment systems, including silicate, mica and heavy crystal, it will be found that silicon ash has a very good effect in a wide range of dosing, wherein the surface has been modified by organic groups (silane or titanium) super-fine particle size of silicon ash is particularly effective. Silica ash can not only effectively buffer the acidity of the tripolyphosphate pigment system, but also the needle-like and fibrous particle morphological structure can act as an isolation shield to protect the metal surface from corrosion, while also enhancing the strength of the coating film.
4. The choice of converter
(1) uses phosphoric acid and tingate as rust converters, and the reaction between tinging acid and iron ions produces the iron chelate of tingate. Danning acid-phosphoric acid can penetrate into the rust layer to react to produce danning iron and iron phosphate film, but with the extension of reaction time, the infrared spectrometer shows that the concentration of magnet rust in the inner layer of the rust layer relative to the outer layer fiber rust and needle rust concentration is increasing, indicating that the rust converter did not fully penetrate into the rust layer. Particular attention should be paid to a rust converter based on daninic acid and phosphoric acid, which is low in toxicity and is renewable. The effect of rust converter depends on the type, concentration, concentration of phosphoric acid, corrosion of steel, reaction time of rust and transdulizer, influence of other additives and method of use.
But the existing problems of water-based rust coatings are: most effective rust converters and rust stabilizers such as tyninic acid and phosphate preparation rust conversion agents, aluminum tripophosphate pigments are mostly acidic, it is easy to make the latex system unstable, limiting the development of water-based rust coatings.
rust coating is only suitable for the rust layer thickness of 30 to 40 m of steel surface construction, more than the thickness of rust, surface loose rust should be removed, because these substances are like the surface adhesion of dust, the original and substrate does not have good adhesion, even if painted with rust coating can only convert this part of the rust, and then the paint can not and solid rust layer effect, so it will cause poor adhesion and poor decoration.
water-based rust coating can not be over-diluted, otherwise the coating film is too thin, the coating contains rust converter can not completely convert the rust layer so as not to achieve the desired effect. From the current development trend of technology, this type of coating because it contains acidic substances such as tingate, so its resistance, acid-base performance is not required, and can only do primer to use.
.