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    Home > Coatings News > Paints and Coatings Market > Preparation of low-surface treatment low VOC universal epoxy primers

    Preparation of low-surface treatment low VOC universal epoxy primers

    • Last Update: 2020-12-28
    • Source: Internet
    • Author: User
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    Sheng Yu, Zhu Xiaoying
    (Jiangsu Lanling Chemical Group Co., Ltd., Changzhou, Jiangsu 213119)
    Abstract: Introduced a new general-purpose epoxy primer preparation method, and the film, curing agent, liquid phenolic resin, rust-proof pigment and other raw materials are discussed. The results show that the product has the characteristics of low VOC, all-weather construction, low surface treatment, fast drying, re-painting and coating and curing at -10 to 40 degrees C. Suitable for steel structures such as ships, machinery, bridges, etc. for primer and intermediate coating.
    key words: universal primer; Epoxy resin; Low surface treatment; Low VOC; Versatile;
    anti-corrosion coatings
    in the figure classification number: TQ630 document identification number: A article number: 1006-2556 (2012) 09-0054-04
    0.0. Foreword
    Today's anti-corrosion
    coatings
    has become the main force of China's paint industry, my defense corrosion coatings in particular, anti-corrosion coatings widely used. Its main applications include emerging marine engineering, modern transportation, energy industry, large industrial enterprises and municipal facilities. The requirements of these applications for corrosion-resistant coatings are very demanding, and their foundation is particularly important to achieve good corrosion protection and protection results. In order for corrosion-resistant coatings to play a full role, the primer and middle layer selected are particularly important. Existing universal anti-rust primer can not meet the low surface treatment, even with light rust conditions in spring, summer, autumn and winter all-weather construction, as well as low VOC and can be re-coated without losing its corrosion resistance, such as the comprehensive requirements, people hope that at low temperatures, especially below 0 degrees C construction curing and in the summer high temperature to maintain a suitable period of use for the benefit of the operation, and in the absence of surface treatment conditions and reduce labor intensity under the conditions of coating operations. At the same time can reduce environmental pollution, and can be in a coating interval of up to half a year can still be repainted, but also with various types of paint matching primers appear. The versatility of this primer can not only be applied to the surface of steel structures such as ships, machinery and bridges, but also to the surfaces of non-metallic structures such as concrete, which can play an effective anti-corrosion protection effect.
    In this paper, bisphenol A-type low-molecular epoxy resin is used as the main
    film-forming substance
    , modified with liquid phenolic resin, adding active rust-proof pigments, fillers (including functional fillers), adhesion promoters, despoticants, fluidizers and so on. Using cashew phenol modified phenolic amine as a curing agent, add a few solvents, equipped with a general purpose primer to meet the above comprehensive requirements. The following is called a universal multi-purpose primer.
    1 test part
    1.1 test equipment
    pull-out adhesion tester (F108-2A), elcometer, United Kingdom; The rest of the equipment is routine.
    1.2 Universal epoxy primer reference formula (see Table 1)
    table 1 General epoxy primer reference formula
    1.3 General epoxy primer preparation
    first add E44 epoxy resin, liquid petroleum resin and xylene, butanol solvent for full mixing, and then add zinc phosphate, calcium phosphate, composite iron titanium powder,
    filite powder
    and anti-foam powder For high-speed dispersion, and then add iron oxide red,
    mica powder
    again high-speed dispersion, and then sanding to a fineness of less than 60 m, slowly add organic
    benzyme soil
    SD-2, and then high-speed dispersion, and then with xylene and butanol mixed solvent adjusted to the viscosity of 800 to 1500mPa.s, filtration, packaging for the beetle.
    the JT-6015A cashew phenol modified phenol amine curing agent and xylene and butanol were stirred and filtered, and the acetylene was divided.
    the ratio of A to B is (4 to 5): 1 (quality ratio).
    before use, the A and B parts in accordance with the above ratio of mixing, full stirring, static 15 to 25min can be used, can be used brush, spray method for construction, 25 degrees C when the applicable period of 6h.
    1.4 Performance Test Results for Universal Epoxy Primers (Tables 2 to Tables 5)
    Performance Test Results for Table 2 General Epoxy Primers
    Table 3 Performance Test Results for General Epoxy Primers
    Table 4 Universal Epoxy Performance Test Results of Primer
    Table 5 Performance Test Results of Universal Epoxy Primer
    Results and Discussion
    2.1 Choice of Filmed Substances
    The protagonist of many film-forming substances used in corrosion-resistant coatings is epoxy resin. At present, the common use of BPA epoxy resin, its structure contains high polarity, not easy to hydrolysate the fat family hydroxyl and ether bonds, the substrate has excellent adhesion, resulting in a coating with excellent corrosion resistance.
    In BPA epoxy resins, several types of epoxy resins are compared, of which E-51, E-44 is viscous at room temperature, other types of epoxy resins are basically solid, but E-51 meets the conditions for the preparation of high solid coatings, because its molecular chain has less hydroxyl content, so the lack of catalytic action and reduce its reaction activity. Comprehensive comparison, the selection of E44 epoxy resin, its less volatile, epoxy value is also higher, so that cross-link density is also higher, so that the coating made of high density.
    2.2 Curing agent selection
    Curing agent with unsaturated double-bonded C-15 straight chain instead of phenol cashew phenol modified phenolic aldehyde, because compared with adipose polyamide, the latter even in 5 At 3d time and epoxy resin curing only 40%, and cashew phenol modified phenolic aldehyde even in -5 to 10 degrees C can be completely cured with epoxy resin, which has characteristics of non-polyamide energy ratio. This curing agent contains benzene ring, with bisphenol A epoxy resin has better compatibility, thereby reducing the viscosity of the coating, and has a good permeability, so it can be coated on rusty surface; The hydroxyl can increase the polarity of the curing agent, the wetting and adhesion of the substrate can be enhanced, so it can be used for low surface treatment level steel surface, and the cured coating surface is smooth and smooth; The polyurethane introduced by reaction and the adjacent weak acidic phenol hydroxyl are the catalysts of epoxy resin curing reaction, which can be cured quickly at low temperature. Its unsaturated double-bonded C-15 straight chain provides the system with internal toughness and good water resistance, and has the initial spatial resistance effect on the curing reaction of the system, so that the system with high solid content has a good application period at the same time, so the test uses JT-6015A epoxy curing agent with the above characteristics.
    2.3 Liquid phenolic resin selection
    liquid phenolic resin viscosity is very low, so it can play the role of ordinary solvents, epoxy resin into a low viscosity solution, so can reduce the use of organic solvents for the benefit of construction, and it can be with low relative molecular weight epoxy compounds in the curing process, become part of the coating, In this way can also improve the toughness of the coating film, and can meet the requirements of environmental protection, so that the voC of the coating is reduced to as low as possible, the resin contains hydroxyl and phenol hydroxyl (1% to 2%), has a better wetting, so it can moisten and penetrate into the rust, it is also a kind of osmosis rust inhibitor, for which the resin was selected.
    2.4 active rust-proof pigment selection
    In this experiment, three active rust-proof pigments were selected: zinc tantalum, calcium phosphate and composite iron-titanium powder.
    zinc phosphate and zinc phosphate are pollution-free rust-proof pigments, the role of zinc phosphate has long been known; And zinc tantalum anti-rust effect is two: First, the acid ions or phosphate ions and iron ions form a binding, play a similar to zinc chromium yellow anode passivation effect; Second, the hydrolytic acid hydrolysate produces the corresponding niobium acid root, forming a hybrid polyic acid. The hybrid acid can form a hybrid compound with the active rust (FeOOH), which can stabilize the rust.
    Calcium phosphate rust-proof performance is comparable to red Dan, better than zinc chromium yellow, trigeminal dihydrohydroelate, zinc phosphate anti-rust pigment, it can react with iron to produce iron phosphate, in the metal surface to form a passivation film, to prevent metal corrosion, the formation of passivation film on the steel surface blocked many small holes, reducing the permeability of the coating film, so that passivation greatly enhances the anti-corrosion effect.
    composite iron titanium powder is an environmentally friendly anti-rust pigment developed in recent years. By selecting iron oxide as the carrier, the nano-powder material is evenly attached to the carrier powder to form a composite iron titanium powder. There are many anti-corrosion factors: First, the phosphate ions in the carrier react with the iron molecules on the steel surface to produce iron chromium phosphate, which is firmly attached to the steel surface, thus protecting the steel parts; Second, iron titanium powder has affinity and strong adhesion to steel, can be directly oxidized into a passivation film on the surface of steel, to prevent electrochemical corrosion; Third, nano-powder material to a large extent changed the overall structure of the coating film, and the amount is not large, so that the coating film flat, dense and no pinholes and pores, effectively blocking the erosion of the steel surface, such as H2O, Cl-, and O2, so the anti-corrosion coating prepared with composite iron titanium powder has a strong anti-rust effect.
    2.5 general anti-rust pigment selection
    in this test, the choice of iron oxide red and mica powder as the general rust-proof pigment. Iron oxide red heat resistance is high, has good weather resistance, the effect on light, water and atmosphere is very stable, and can strongly absorb ultraviolet rays, so that iron oxide red protected objects from UV damage, used in anti-corrosion coating is based on its film dense, the covered items have a physical shielding effect, at the same time it has rust resistance to the substrate, corrosion-resistant gas, alkali resistance, coloring force, strong cover, low price.
    Mica powder belongs to mica-type minerals, is a subseed of potassium silicate aluminum compound, white cloud mother, its crystal structure is a fine flaky structure, high diameter thickness ratio, has a certain elasticity and mechanical strength, heat resistance in 550 to 600 degrees C It has better chemical stability and acid-alkaline resistance, has a better shielding effect on ultraviolet rays, and it is arranged in parallel with flaky orientation in the coating film, and its aspect ratio is quite high, so it is easy to form a denser protective layer, so that the coating film strength, impermeability, elasticity have been improved.
    2.6 additive selection
    2.6.1 adhesion promoter selection
    coating and substrate bonding good or bad, directly affect the anti-corrosion properties of the coating, in order to further improve the adhesion strength of the coating, we added a moderate amount of silane coupled agent, this additive Not only can improve the pigment, filler particles and epoxy resin bonding capacity, but also with the film-forming material particles between the formation of chemical bonds or hydrogen bonds, thereby preventing the migration of corrosion factors, so that the coating and substrate adhesion greatly enhanced, improve the corrosion resistance of the coating, based on this, the choice of KH-560.
    2.6.2 Other additives
    because the formula contains a higher density of iron titanium powder, it is necessary to use a sunsum inhibitor in this formulation. The use of highly dispersed organic bento-earth SD-2, the effect is very good. Because the primer solid content is high for anti-coating foaming, in order to help prevent corrosion, so the use of BYK066N as a deboist, the effect is obvious.
    3. Conclusion
    using E44 epoxy resin and JT-6015A cashew phenol modified phenolic amine curing agent, supplemented by the selected liquid phenolic resin, active rust-proof pigments and adhesion promoters and other additives, can be made into a universal multi-functional epoxy primer.
    This universal multi-functional epoxy primer, according to test tests show that it belongs to the low VOC type, can be matched with all kinds of paint, low temperature curing, low surface treatment requirements for substrates, rust coating, re-painting, so its application range is widespread, can be used as primer and intermediate paint on steel surfaces such as ships, machinery, bridges, etc., with broad potential application prospects.
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