1 Preface
Water-based paints have many advantages such as no solvent poisoning, no fire hazard and no atmospheric pollution. With the growing awareness of environmental protection, more and more attention is being paid to the development of water-based paints. In recent years, China has achieved certain results in this area. However, most of them are architectural coatings, and most of them are made of acrylic and vinyl resin. In this paper, a new emulsification process was used to produce a waterborne epoxy ester anti-corrosion coating. With the help of flash corrosion inhibitors and active pigments, the problem of flash corrosion has been solved. The performance of the formulated waterborne epoxy ester anti-corrosion coating reached the technical index of solvent-based epoxy cool anti-corrosion coating. At present, no research in this area has been reported in China.
2 Experimental part
2.1 Apparatus and raw materials
2.1 .1 Apparatus
Electric stirrer, three-neck flask, spherical condenser, vacuum pump, colloid mill, conical mill.
2 .1.2 Raw materials
Epoxy resin . Industrial: Linoleic acid . Industrial products; dehydrated ricinoleic acid, industrial products; xylene, industrial products; catalysts; emulsifiers; protective gum; deionised water; drying agents; iron oxide red, industrial products; red china clay, industrial products; active pigments; resting pigments; flash corrosion inhibitors; dispersion aids. Home-made.
2.2 Principle
Epoxy resin and dry oil fatty acid esterification reaction in the presence of catalyst to produce polymer epoxy ester resin viscous liquid. It is then diluted and emulsified. The solvent is removed by vacuum, and then it is emulsified in a colloid mill, after which color fillers and various additives are added and ground and dispersed to obtain a waterborne epoxy ester anti-corrosion coating with room temperature curing.
2.3 Synthesis process
Add linoleic acid and dehydrated ricinoleic acid, epoxy resin and reflux xylene into a three-necked bottle. Seal the bottle, pass nitrogen gas, heat up the temperature, add catalyst at 120℃. Stirring is started. When reflux occurs, stop passing nitrogen. Slowly increase the temperature. Hold the esterification at 200-210°C. After about 2h, start to take samples to measure the viscosity and acid value, and stop the reaction when the viscosity reaches 3s (Grignard tube) and the acid value is 8-18, then cool down and dilute, that is, the epoxy ester resin liquid.
2.4 Preparation of emulsion
Add the emulsifier, protective adhesive and epoxy ester resin into a three-necked bottle. After 30 min, start to evacuate and desolventize. The solvent is removed, the drying agent is added and the emulsion is re-emulsified in the colloid mill to produce the epoxy ester emulsion.
2.5 Formulation of the paint
Mix iron red, other pigments and various additives, add water. Grind twice on a conical mill to produce a colour paste. Mix the colour paste and the epoxy ester emulsion evenly to obtain the coating product.
2.6 Coating performance
The performance of water-based epoxy cool anti-corrosion coating is shown in Table 1,
3 Results and discussion
3.1 Factors affecting the performance of the emulsion
3.1.1 Epoxy resin
The epoxy resin with larger molecular weight is chosen, and its esterification has good chemical resistance. However, if the molecular weight is too large, there will be more base hydroxyl in the resin. When heating esterification, the viscosity rises fast, the operation is difficult to control, emulsification is difficult and the emulsion is unstable. It is better to use E20 or E12 epoxy resin.
3.1.2 Fatty acid
Choose dry oil fatty acid, so that the resin contains enough fatty acid double bonds to facilitate oxidation polymerization and drying. The performance of the epoxy ester is closely related to the amount of fatty acid. When the amount of fatty acid increases, the brushability and leveling improves, but the viscosity, hardness and solvent resistance decreases. The drying properties of waterborne epoxy esters with medium oil content are better.
3.1.3 Acid value
The higher the acid value, the easier the water emulsification. However, the chemical resistance of the resin is poor; the acid value is too low. Emulsification is difficult and the prepared emulsion is not stable. The acid value should be controlled at 8-18.
3.1.4 Emulsification process
For the pre-emulsification of epoxy esters, we use four methods: (1) solvent-free resin emulsification; (2) emulsification after dilution with hydrophilic solvents; (3) emulsification after dilution with hydrophobic solvents; (4) emulsification after solvent dilution and then deemulsification. Experiments show that the fourth method is good. The dilution of the epoxy ester wilting degree is reduced, in the role of emulsifier, easy to form a uniform emulsion. The resulting coating film performance is good, the storage stability of the emulsion in more than a year. The first method is difficult to emulsify, probably because the viscosity of the epoxy ester generated by the reaction is very high, and it is very difficult to make it into an emulsion by the emulsifier and stirring alone. The second and third methods are difficult because the solvent remains in the emulsion after emulsification. Easy delamination. The storage stability of the resin is poor.
3.2 Flash corrosion problem
A prominent problem with water-based coatings applied to steel substrates is flash corrosion. Flash corrosion occurs after construction, the coating film is not dry before the presentation of about 1mm diameter dotted rust spots, this phenomenon is particularly easy to occur in the sandblasted substrate. To solve this problem. In this experiment, flash corrosion inhibitors and active pigments are used in conjunction. Commonly used flash corrosion inhibitors are ammonium chromate, sodium carbonate, sodium molybdate, sodium nitrite, tert-butylamine, N. N a dimethylethanolamine, alkyl miva and ammonium octanoate. Active pigments include zinc phosphate, zinc borate, organically modified zinc phosphate, modified zinc borate, zinc chromate and lead silichromate. In this experiment, the weight ratio of flash corrosion inhibitor to active pigment is 0.25:1.
4 Conclusion
(1) The prepared single can of room temperature curing waterborne epoxy ester anti-corrosion coating is comparable to solvent-based epoxy ester anti-corrosion coating in all properties.
(2) The storage stability and flash corrosion problems of the waterborne epoxy ester anti-corrosion coating were solved.
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