Research on the development of high-performance water-based epoxy anti-corrosion primer

Liu Chenglou (Beijing Guotai Ruihua Fine Algae Silicon Special Materials Co., Ltd., Beijing 100083)
Summary: Water-based epoxy resin curing system as a film, aluminum tripolyphosphate, zinc phosphate, zinc phosphate as rust-proof pigment, to the mica,
slip Stone powder
, precipitation of niobium sulfate as a filler, in a variety of functional additives and water distribution, the production of excellent adhesion, corrosion resistance, anti-deformation ability of water-based epoxy anti-corrosion primer, suitable for more difficult to adhere to stainless steel, aluminum alloy and other metal substrates of anti-corrosion protection.
key words: water-based epoxy
coating
; Adhesion; Anti-corrosion; Anti-deformation
: TQ630.7 Document identification code: A Article Number: 1009-1696 (2014) 02-0020-04
0. Introduction
Traditional solvent-based
corrosive coatings
contain more than 50% organic solvents, in the production and construction process, these solvents evaporated into the air, not only waste resources, but also pollute the environment, not only will harm human health, but also the existence of fire hazards. Environmental protection, low pollution coatings are the future direction of development, especially
water-based coatings
, because of its green environmental protection, production and construction convenience, no safety hazards, low cost and other advantages have become a hot research topic. At present, water-based paint in Europe and the United States and other countries in the rail vehicles, automobiles and other industries have been widely used, the general use of water-based paint coating system is: anti-corrosion primer , putty , paint and finish. China's research application in this field is still in its infancy. Because most of the high-speed rail and subway vehicles are made of stainless steel and aluminum alloy sheet, the surface can form an inert, low-surface energy oxide film, the substrate on the anti-corrosion primer adhesion put forward higher requirements, which is also one of the difficulties in the study of water-based anti-corrosion primer.
Anti-corrosion primer as the first layer of the coating system, directly bonded with stainless steel or aluminum substrate, its inter-layer adhesion, anti-corrosion of the coating film, anti-deformation ability has become an important factor affecting the quality of the entire coating system. In this paper, the water-based epoxy resin curing system is selected as a film, with aluminum tripolyphosphate, zinc phosphate and zinc tantalum as anti-rust pigments, with mica, talcum powder, precipitation of sulphate as fillers, in water and a variety of functional additives, made suitable for a variety of metal substrate coating anti-corrosion primer.
1. Experimental part
1.1 raw
water-based epoxy resin and curing agent, domestic; Aluminum tripophosphate, domestic; Zinc phosphate, zinc tantalum, New Bile Pigment International Trade Co., Ltd.; Mica, Luzhou Gree; Talc powder, Liaoning Haicheng; Precipitation of radon sulfate, domestic; Dispersant 5040, Haichuan Chemical; Deblant byK-019, leveling agent BYK-348, substrate wetting agent BYK-346, Byk Chemical, Germany; Silane coupled agent KH-560, Nanjing Dawn; Gas phase SiO2, Ruiyang, Shandong Province; Anti-flash rust agent ZT-709, salt-resistant mist agent ZT-719, Beijing Road Chemical; Glycol butyl ether, Dow Chemical, USA.
1.2 Formula
the basic formula for high-performance water-based epoxy anticorrosive primers is in Table 1.
Table 1 Basic Formula for High-Performance Water-based Epoxy Antiseptic Primer
1.3 Preparation Process
adds water-based epoxy resin to the dispersion tank, and adds dispersants, deionized water, de-ionized water, de-foaming agents, coupled agents, anti-sinking agents,
"Pigment
etc., high-speed dispersion of 30min, and then grinding to a fineness of <35 m of slurry, in the medium and low-speed stirring to add leveling agent, anti-flash rust agent, substrate moisturizer and solvent, stirring evenly after filtration, material.
2. Results and discussion
2.1 Selection of water-based epoxy resin and determination of ratio
This paper selects a water-based epoxy resin with self-emulsification function, the average particle size of emulsion is about 0.3 m. The emulsion particle size is fine, the particle surface area is large, the distribution concentration of the proportionally matched curing agent on the surface of latex particles is low, the curing reaction speed is relatively slow, the curing agent has sufficient time and space to diffuse into the inner latex particles, and the epoxy resin curing reaction, can form an average, solidified complete epidural. In order to make anti-corrosion primer with excellent film-forming and excellent low surface energy substrate adhesion, choose 2 different relative molecular mass of water-based epoxy resin distribution. The water-based epoxy resin (B) with lower relative molecular mass is a self-emulsified water-based emulsion of semi-solid epoxy resin, which has higher hydroxy content and epoxy value, which can enhance the adhesion of the coating film to the substrate. Higher relative molecular quality of water-based epoxy resin (A) is a self-emulsified hydroelectomic emulsion of solid epoxy resin, containing 6% to 9% active thinner, its hydroxyl content is high, epoxy value is low, with excellent film-forming and flexibility.
the effect of the ratio of water-based epoxy resins A and B on the film coating properties of curing materials is seen in Table 2 under the condition that other factors in the basic formula remain unchanged.
Table 2 Effect of the ratio of water-based epoxy A and B on the performance of curing film
as can be seen in Table 2: With the increase of water-based epoxy resin B, the adhesion of epoxy curing film is enhanced, while flexibility and impact resistance are decreasing. When m(A): m (B) is 3:1, the comprehensive performance of the coating film is the best.
2.2 Selection of water-based epoxy curing agents
The curing film reaction of water-based epoxy coatings is controlled by the diffusion process of the curing agent. The water-like epoxy curing agent selected can be modified polyamine, modified fatty amine, modified lipocamine and aromatic amine water-like emulsion. Among them, the curing application period of the modified polyamine epoxy curing agent water-like emulsion is longer, up to 6h, its curing product performance is similar to that of polyamide curing product, the coating film has excellent adhesion, flexibility and salt spray resistance. Therefore, the study chose modified polyamine water-based emulsion as a curing agent. The experimental results show that in the two-part watery epoxy anti-corrosion primer, when the e9oxy/amine hydrogen equivalent ratio is 1.0, the comprehensive performance of the coating film is better.
2.3 Pigment filler selection
pigment is a secondary film-forming substance
coating
. In water-based anti-corrosion coatings, the contribution of functional pigments to corrosion protection is second only to that of major film-forming substances. In the water-based epoxy anti-corrosion primer, a good covering force, chemical inertness, low oil absorption, good chemical resistance of environmentally friendly active rust-proof pigments should be used; Fillers should be selected with low oil absorption, good chemical stability, strong permeability, neutral and can enhance the physical and mechanical properties of the coating film inert fillers. The water-based epoxy anticorrosive primer selected aluminum tripophosphate, zinc phosphate and zinc tantalum acid as rust-proof pigments; Select mica, talcum powder, precipitation of sulphate as a filler, coating film has excellent rust resistance and salt spray resistance. The amount of pigment added is 2.5%.
Aluminium tripolyphosphate in the coating can be dissopheded out of the tripolyphosphate root ions, which contains 5 lively oxygen bonds can be cross-chelated with metal cations, with a strong ability to capture metal ions, can effectively close metal ions to form inorganic polymer misaligned, passivated metal surface, play a chemical anti-rust effect. Then it slowly decomposes into dense orthophosphate skin film, insulated moisture, oxygen and other contact with the metal surface, play an insulated rust-proof effect, so it has a chemical anti-rust and isolation rust-proof double effect. Zinc phosphate's rust-proofing is similar to chromate's, but its effect is slow, specifically due to the initial corrosion at the damaged coating position and the production of local anodes and cathodes on the steel surface, so that dissolved iron salts and iron salts are hydrolyzed and released. Protons and zinc phosphate act to produce phosphoric acid and zinc ions, Zn2 plus metal surface Fe3 plus to form insoluble insoluble lysate Fe (Zn3(PO4)) precipitation, acting as cathode inhibitors, resulting in cathode protection. Hydrolysed protons can also be combined with hydroxyl and carboxyl in the coating, resulting in a chemical bond between pigment-paint-base-substrates, thereby improving the wet adhesion and impermeability of the coating. Zinc tantalum is an environmentally friendly active rust-proof pigment, and its anti-rust mechanism is: First, the formation of a bond between niobium acid ions and iron ions, playing the role of anode passivation; Second, zinc tantalum hydrolyzed to produce the corresponding roots of niobium acid, the formation of mixed polyic acids, and active rust (FeOOH) to produce hybrid complex, so as to play a stabilizing role in rust.
water-like epoxy anti-corrosion primer, pigment volume concentration (i.e. PVC) has a great impact on the chemical and chemical properties and anti-corrosion properties of the coating film. When PVC is too low, the formation of the coating film pigment particle distribution is sparse, the spacing is large, the coating film materialization performance is poor; When PVC is greater than the critical pigment volume concentration (CPVC), the substation in the coating film is not sufficient to completely immerse and cover all pigment particles, resulting in a large coating pore rate, rough, materialization performance is reduced. The effects of different PVC on the performance of water-like epoxy anticorrosive primers can be found in Table 3.
3 Effect of different PVC on the performance of water-borne epoxy anti-corrosion primer
as can be seen from Table 3: When PVC is low, the salt spray resistance of the coating film is poor; When PVC exceeds 32%, the comprehensive performance of coating film begins to decrease. When the PVC is around 32%, the materialization performance of the coating film is optimal.
2.4 Selection of anti-flash rust agent and its effect
Flash rust is a unique phenomenon of water-based coatings, which is manifested in the surface of the metal coated with water-based coatings, when the coating film is not dry to produce rust spots, reducing the adhesion of the coating film and salt spray resistance. Therefore, anti-flash rust agents must be added to water-based coatings. Although sodium nitrite and sodium benzoate have a better instantaneous anti-flash rust, but because of carcinogenic effect and is not conducive to salt spray resistance and abandoned, this study selected the Beijing-based chemical ZT-709 anti-flash rust agent, it is a can all volatile and can quickly passivate the metal surface of organic matter, not only has instantaneous anti-flash rust effect, but also can greatly improve the coating resistance to salt spray. When its dosing was 0.3% to 0.5%, good results were obtained.
2.5 The role of salt-resistant aerosols
poor salt spray resistance of water-based antiseptic coating film is its Achilles heel, general water-resistant anti-corrosion coating salt spray resistance in 240 to 300h, if you want to make salt-resistant anti-corrosion coatings more than 500h, in addition to the selection of good performance resins and pigments, appropriate PVC, suitable functional additives, should also add salt spray. The salt-resistant spray ZT-719 selected in this study is a mixture made from a variety of nano-powders using nanotechnology, which can cross-link with the polymer in the coating filming process, making the coating film dense and improving salt spray resistance. Also because the salt-resistant spray contains a large number of insulating silicones, the coating film can prevent chlorine ions from passing through, thereby improving salt-resistant fog resistance. The effect of the dosage of the salt-resistant mist ZT-719 on coating performance is seen in Table 4.
Table 4 Effect of salt-resistant spray on coating performance
As can be seen from Table 4: With the increase of ZT-719 dosage, the adhesion, water resistance and salt-resistant fog resistance of the coating film are correspondingly improved, and when the dosage exceeds 3%, the coating performance shows a downward trend, which may be directly related to the uneven dispersion of nanomaterials due to the amount of dosage and particle reunification. Considering the cost-effective problem, the amount of salt-resistant mist is suitable at 2.5%.
2.6 adhesion promoter selection
adhesion promoter achieves the purpose of increasing adhesion by increasing one or more forces between the coating film and the substrate. Silane coupled agents have two different reaction groups: pro-inorganic and pro-organic. The pro-inorgeline group reacts with the chemical group on the surface of the inorgetable body to form a strong chemical bonding; The pro-organic group reacts with the organic molecule to form a physical entanglement, which enables the organic and inorganic material interface to achieve chemical bonding and enhances the adhesion of the coating film to the substrate. In addition, the silane coupling agent can also be inorent pigment particles in the coating and epoxy resin through chemical bonds or hydrogen bonds close bonding, improve the denseness of the coating film, thereby preventing the migration of corrosion factors, enhance the adhesion of the coating film and corrosion resistance. In this study, the silane coupled agent KH-560 was selected as an adhesion promoter, and its dosage was 0.3% to 0.5%.
2.7 Choice of other additives
dispersant selection 5040, it is a kind of sodium polycarbonate, in the coating system, by adsorption on the surface of the pigment particles to produce charge refractive force and spatial resistance, the pigment dispersed into fine particles, to prevent flocculation precipitation, so that the coating in a stable state.
-selected defoulant BYK-019 is a polyether-modified polymethylsilane, in the water-based coating system has an efficient foam suppression, defouling effect, can effectively prevent the film from producing pinholes, fisheyes and other surface defects. Anti-sinking agent selected gas phase silica, in the water-based epoxy anti-corrosion primer to add 0.3% gas phase SiO2, can make the coating produce tentacles, to achieve the purpose of anti-sinking, anti-flow hanging. At the same time, nanoscale SiO2 fine particles can be dispersed and filled between thicker pigment particles to form a dense coating film, which is conducive to enhancing the salt spray resistance of the coating film.
selected substrate wetting agent BYK-346 is a polyether modified polymethylsiloxane solution, not only can reduce the surface pressure of water, but also wetting the substrate is good, at the same time can not bubble, unstable bubble, do not affect re-painting, its dosage of 0.2% to 0.5% is appropriate.
, the leveling agent BYK-348 and the solvent ethylene glycol butyl ether were also selected.
2.8 Performance index of water-based epoxy anti-corrosion primer
the performance test of the prepared water-based epoxy anti-corrosion primer was carried out, the results are seen in Table 5.
5 Water-based epoxy anti-corrosion primer performance indicators
as can be seen from Table 5: Water-based epoxy anti-corrosion primer performance indicators fully meet the standard requirements of solvent-based epoxy anti-corrosion coatings.
3. Conclusion
developed high-performance water-based epoxy anti-corrosion primer, with water-based epoxy resin and water-based epoxy curing agent supporting system for film-forming substances, according to the epoxy/ amine hydrogen material equivalent ratio of 1.0 paint; With aluminum tripolyphosphate, zinc phosphate and zinc phosphate as environmentally friendly rust-proof pigments, pVC was determined to be 32% with mica, talcum powder and precipitated sulphate as fillers. Under the reasonable combination of anti-flash rust agent, salt-resistant mist agent, adhesion promoter and other additives, the performance index of solvent-based epoxy antiseptic coatings meets the performance requirements, and VOC (volatile organic compounds) emissions are greatly reduced.
anti-corrosion primer can be used on most metal surfaces, including low-surface energy stainless steel, aluminum substrate corrosion protection.
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