Production and Application of Low VOC Epoxy Anticorrosive Coating

China Paint Online News Information
Wu Yuanguang (Fujian Baihua Chemical Co., Ltd., Fujian Liancheng 366211)
Abstract: Composite epoxy resin as a film, from the resin selection, curing agent matching, pigment selection, additive application, etc., to optimize the formulation combination, 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 low-voC anti-oxycodyclic 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
0. Introduction
in industrial protective coatings, epoxy coatings are mainstream products, mostly solvents Type paint, volume solid containing 60%, VOC in 450 g/L, where the organic solvent volatile 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, formula optimization combination, 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 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 250 g/L" requirements.
1. Production of low VOC epoxy antiseptic 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, tulphate, iron black, titanium white powder, thickener, wetting dispersant, modified polyamide, xylene, butanol, heavy aromatic solvents, silane coupled agent, polyamide resin, ester ring amine modified polyamide, cashew oil modified phenol aldehyde curing agent, are commercially available industrial products.
equipment: seasoning kettle, color matching kettle, SFJ dispersion machine, horizontal sander, 101A-1 electric blow drying box, paint density cup, flow-hanging tester, analytical balance, PosiTest adhesion analyzer, GPQ12C airless sprayer, precision salt-resistant spray tester, energy dispersion X fluorescence spectrometer, NDJ adhesive spectrometer, impact tester.
1.2 preparation method
1.2.1 iron red, engineering yellow, gray zinc phosphate epoxy primer
iron red, engineering yellow, gray zinc phosphate epoxy primer formula see Table 1.
Iron red, engineering yellow, gray zinc phosphate epoxy primer production method: in the seasoning kettle to add the formula amount of 2 kinds of epoxy resin and mixed solvents, in low-speed stirring to add silane coupled agents, dispersants, according to the pigment density, in order of first light and then 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 grinder 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 zinc-rich primer
the formula for a zinc-rich primer is below Table 2.
curing agent is calculated according to the packaging ratio, filtration, metering, packaging.
1.2.3 epoxy cloud iron intermediate paint
the formula of epoxy cloud iron intermediate paint can be found in Table 3.
Epoxy cloud iron intermediate paint production method: in the seasoning kettle to add epoxy resin, mixed organic solvent in low-speed stirring to add silane coupled agent, dispersant, 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 60 min, sampling inspection qualified after 120 filter metering packaging.
is calculated according to the aerobic value and the active hydrogen equivalent of the curing agent, 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.
zinc-rich primer in accordance with HG/T 3668-2009, the results are found in Table 4.
iron red, engineering yellow, gray zinc phosphate epoxy primer in accordance with the enterprise standard Q/FJBH 016-2011 testing, the results can be seen in Table 5.
iron intermediate paint in accordance with HG/T 4340-2012 testing, the results can be seen in Table 6.
2 construction application
In the actual construction, the viscosity of thick slurry coating in 3,000 to 10,000mPa.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 250 g/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, additives, curing agent screening.
3.1 Epoxy Resin Selection
in the previous 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 to improve the performance of products, but also to meet VOC requirements.
3.2 Wetting the use of dispersants
In order to prevent the film adhesion of epoxy primers from decreasing, the addition of dispersants, desolation agents and leveling agents is generally not recommended in the formulation, and due to the high volume solid content of pigments in the product formulation, in order to reduce the VOC content, conducive to production operations, help the seasoning and grinding process to reduce solvent use, it is necessary to add moisturizing dispersants. Through the test, the final selection of inorder pigment has a good wetting effect, but not the substrate adhesion and matching paint between the layers of adhesion impact of the anion interface active agent as a dispersant.
3.3 The choice of tentacles
the choice of coating system has a good anti-sinking, 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 bentonous soil 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 tactile agent 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-sink, anti-flow hanging performance, the system viscosity affects small modified polyamide as a tentacle.
3.4 Pigment Selection
Try to choose pigments with low oil absorption, low relative density, good cover and no heavy metals, reducing solvent usage and product density.
3.5 anti-rust pigment selection
choose a low oil absorption, relative density, good anti-rust effect, no heavy metal anti-rust pigment.
3.6 Filler selection
to meet the VOC as small as possible requirements, according to the VOC content calculation formula:
ρ (VOC) s w×ρs×1 000
type: ρ (VOC) - sample VOC content, in g/L;
the mass fraction of the volatile content in the w-sample, in
ρs-sample density, in g/mL, and
1 000-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 Agents
To meet VOC requirements, curing agents must use low viscosity, high solid content, and epoxy curing agents that can be cured at low temperatures. 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 Choice and dosing of mixed solvents
At present, solvent-based epoxy is mostly xylene and butanol as solvents, but xylene is relatively toxic. 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 aromatics to replace xylene, limited dissolving capacity, affecting dryness, with other environmentally friendly solvents to replace xylene is the next goal.
4. Conclusion
Solvent-based product VOC control in the 220 to 250 g/L range is the limit of existing raw materials and technology, the development of the most stringent new U.S. Mid-Atlantic Law "industrial maintenance coating primers and medium-coated VOC content of less than 250 g/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, standards, 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.