Production and application of low VOC epoxy anticorrosive coating

To compound epoxy resin as a film, from the resin selection, curing agent matching, pigment selection, additive application, etc. , to optimize the combination of formulations, in the use of existing process conditions, production equipment, coating equipment, under the premise of the development of high-solid and low-adhesive solvent-based low VOC epoxy antiseptic coating.
key words: low VOC epoxy coatings; anti-corrosion; environmental protection
in the figure classification number: TQ633 document mark code: A article number: 1007-9548 (2014) 11-0021-03
Introduction
in industrial protective coatings, epoxy coatings are mainstream products, mostly solvent-based coatings Volume solidification contains 60%, VOC in 450g/L, where organic solvents evaporated into the air, will cause harm to the health of production and construction personnel, and there is a fire hazard; Therefore, increasingly stringent environmental regulations for the coatings industry is not only a major challenge, but also a great opportunity to achieve technological progress in coatings. However, people often walk into a misunderstanding: a mention of energy conservation and emission reduction, environmental protection green on the link with water-based products, water-based products can completely replace solvent-based products; Today's domestic paint enterprises the biggest pressure and risk may not come from the market, but from environmental protection policy, if strictly in accordance with the standard policy implementation, a large number of small and medium-sized paint enterprises will be difficult to survive, who first grasp the tail of the development trend, who will survive and grow and develop at the time of shuffle.
This paper is based on ordinary solvent-based coatings, compound epoxy resin as a film, from the resin selection, curing agent matching, pigment selection, additive application, to optimize the combination of formulations, in the use of existing process conditions, production equipment, coating equipment, under the premise of the development of high-solid and low-stick solvent-based coatings, adapt to increasingly stringent environmental regulations, reduce organic solvent content Reducing the VOC value of coatings is undoubtedly also an innovation, for saving resources, protecting the environment, and achieving safe production, are of great significance, which is in line with the current heavy anti-corrosion coating energy conservation and emission reduction work theme, but also reflects the domestic coating technology can fully meet the most stringent requirements of the new U.S. Mid-Atlantic Region Act "industrial maintenance coating primers and medium coating VOC content of less than 250g/L" requirements.
1. Production of low VOC epoxy anti-corrosion coatings
1.1 main raw materials and production and testing equipment
raw materials: epoxy resin 1, epoxy resin 2, mica powder, iron oxide red, iron oxide yellow, organic medium yellow, mica iron oxide, zinc phosphate, zinc oxide, talcum powder, quartz powder Sulphate, iron black, titanium white powder, thickener, wetting dispersant, modified polyamide, xylene, butanol, heavy aromatic solvents, silane coupled agents, polyamide resins, ester cyclamide modified polyamide, cashew oil modified phenolic phenolamide curing agents, are commercially available industrial products.
equipment: seasoning kettle, color matching kettle, SFJ dispersion machine, horizontal sander, 101A-1 electric blow air drying box, paint density cup, flow-hanging tester, analytical balance, PosiTest adhesion meter, GPQ12C airless sprayer, precision salt-resistant fog tester, energy dispersion X fluorescence spectrometer, NDJ adhesive spectrometer, impact tester.
1.2 Preparation Method
1.2.1 Iron Red, Engineering Yellow, Grey Zinc Phosphate Epoxy Primer
Iron Red, Engineering Yellow, Grey Zinc Phosphate Epoxy Primer Production Method: 2 ethylene oxides and mixed solvents formulated in the seasoning kettle, silane coupled agents, dispersants, at low speed stirring, According to the pigment density, in accordance with the order of first light and heavy, in order to add a variety of powders, and avoid mixing with other impurities, and finally add thickeners, high-speed dispersion of 20 to 30min, and then filter, into the horizontal sander grinding, dispersion to a fineness of less than 50 m;
the curing agent according to the epoxy value and curing agent lively hydrogen equivalent calculation, according to the packaging ratio, direct filtration, metering, packaging.
1.2.2 epoxy zinc-rich primer
curing agent dosage is calculated according to the packaging ratio, filtration, metering, packaging.
1.2.3 epoxy cloud iron intermediate paintEpoxy cloud iron intermediate paint production methods: in the seasoning kettle to add epoxy resin, mixed organic solvents in low-speed stirring to add silane coupled agents, dispersants, according to the pigment density, in accordance with the order of first light and then heavy, in turn to add a variety of powders, and avoid mixing with other impurities, and finally add tentacles, high-speed dispersion of 30 to 60min, sampling inspection qualified after 120 eye filter measurement packaging.
the solidizer according to the epoxy value and the lively hydrogen equivalent of the curing agent to calculate, according to the packaging ratio, filtration, metering, packaging.
1.3 performance testing
according to the above process formula products, there are current industry standards, according to industry standards for testing, there is no corresponding industry standards, in accordance with the company's enterprise standards for testing.
2. Construction application
In the actual construction, the viscosity of thick slurry coating in 3000 to 10000mPa.s products, can not add diluent for high-pressure airless spraying. From the test results, it can be seen that the design and production of product performance to meet the standard requirements, heavy metals are not detected, VOC content is less than 250g/L;
3 Results and Discussion
On the basis of using existing production equipment and coating process, in order to obtain high solid score, low VOC, no heavy metal, and performance to meet the performance index of solvent-based coatings, the formulation of the formula must be optimized combination, film, pigment, filler, additive, curing agent screening.
3.1 Epoxy Resin Selection
in the early test process found that: if the full use of relative molecular quality of epoxy resin, some performance indicators can not meet the technical requirements of existing products, and only the relative molecular quality of epoxy resin, VOC content can not meet the design technical indicators. After testing the use of low relative molecular mass and medium relative molecular mass epoxy resin, performance is improved, not only can improve the performance of the product, but also to meet VOC requirements.
3.2 Wetting dispersant use
In order to prevent epoxy primer film adhesion reduction, the formulation is generally not recommended to add dispersants, de-foaming agents and leveling agents; Through the test, the final selection of inoromic pigment fillers have a good wetting effect, but not the substrate adhesion and matching paint between the layers of adhesion has an impact on the anion interface active agent as a dispersant.
3.3 Tactinant Selection
The choice of a good anti-sinking coating system, anti-flow hanging effect on the system viscosity has a small impact on the tentacles, conducive to the production and use of products, to ensure that the final coating products VOC to meet the design requirements. Organic bentonation use is large, thickening effect is good, but when the amount is too much, it will affect the product's media resistance performance, and affect the smooth progress of production; solvent-based tentacles will be brought into the solvent to increase the emission of volatiles, after a variety of tactile agent test screening, the final choice of less dosage, anti-sinking, anti-flow hanging performance, the system viscosity affects small modified polyamide as a tentacle.
3.4 pigment selection
try to choose low oil absorption, relative density, good cover, no heavy metal pigments, reduce solvent consumption, and reduce product density.
3.5 anti-rust pigment selection
choose low oil absorption, relative density, good anti-rust effect, no heavy metal rust pigment.
3.6 filler selection
to meet the VOC as small as possible requirements, according to the VOC content calculation formula:
ρ (VOC) - w×ρs×1000
in: ρ (VOC) - sample VOC content, in g/L;
the mass fraction of volatile content in the w-sample, in units;
ρs-sample density in g/mL;
1000-conversion factor.
Therefore, we should choose fillers with low oil absorption, low relative density, stable chemical properties and no heavy metals to improve the solid content of the product volume, reduce the amount of solvent, and effectively control the product density, and finally select the talcum powder and quartz powder to meet the requirements of all parties as fillers.
3.7 curing agent
In order to meet VOC requirements, curing agents must use low viscosity, high solid content, can be cured at low temperature type epoxy curing agent. Tested on products such as polyamide resin, cashew oil modified phenolamine curing agent, ester cyclamide modified polyamide: polyamide resin itself has a large viscosity, slow drying speed, and low molecular quality epoxy resin does not mix and affect the use; Paint film curing will appear after the problem of change of face, in the situation without requiring color can also use cashew oil modified phenolic amine curing agent, ester cyclamide modified polyamide due to high solid content, low viscosity, drying speed, low temperature curing, unchanged color, is the test process to meet all the conditions of the curing agent, and finally choose ester cyclamide modified polyamide resin as the product curing agent.
3.8 mixed solvent selection and dosing
at present, solvent-based epoxy is mostly xylene and butanol as solvents, but xylene toxicity is relatively large. In order to improve the environmental protection of the product, the use of some heavy aromatic hydrocarbons to replace xylene, can reduce the toxic solvent content of the product, all the use of heavy aromatic hydrocarbons to replace xylene, limited dissolving capacity, affect dryness, with other environmentally friendly solvents to replace xylene is the next goal.
4. Conclusion
solvent-based products VOC control in the 220 to 250g/L range is the limit of existing raw materials and technology, the development of the most stringent U.S. Mid-Atlantic New Act "industrial maintenance coating primers and medium-coated VOC content of less than 250g/L" requirements of products have considerable difficulty, lower VOC content of products difficult to research and development;
solvent-free, solvent-free is still the main direction of the current development of heavy anti-corrosion coatings, hydration products temporarily and even for some time to come may not be able to replace the status of solvent-based products. The products introduced in this paper are the most widely used varieties in the construction machinery and steel structure industry, if the paint coating people take action, strictly in accordance with the policy, standard implementation, the entire industry all use low VOC epoxy anti-corrosion coatings, conservative estimates can reduce hundreds of thousands of t of organic solvent emissions per year, for saving resources, protecting the environment, achieving safe production, improving haze, sustainable development of the industry is of great significance.
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