New corrosion inhibitor for high-performance coatings

In mid-2013, NACE International conducted a study that demonstrated that the total annual cost of corrosion in the United States rose to more than $1 trillion due to the high cost and enormous challenges posed by corrosion. Corrosion is the largest single expense in the U.S. economy, estimated to exceed 6.2 percent of GROSS. Corrosion has brought a very high price tag to the United States, second only to health care
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. A 2001 study funded by the U.S. government estimated the cost of corrosion of military systems and infrastructure alone at about $20 billion a year
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. Most of the losses were due to corrosion of steel used in processing and manufacturing processes such as roads and bridges, pipelines, storage tanks, automobiles, ships, sewer systems, etc. The cost of corrosion is money and life, which can lead to dangerous failures and increase the cost of every application, from utilities to transportation.
the main advantage of providing improved appearance, organic coatings also play a vital role in preventing substrate corrosion. Paint formulators use three basic strategies to protect metal surfaces from corrosion: 1) coatings as barrier technology to prevent oxygen and water from reaching metal surfaces;
barrier coating reduces permeability and prevents oxygen and water from reaching the coating surface. Barrier properties are often achieved by using flaky (mica) additives such as flaky talc, mica and mica iron oxide and flaky metal pigments, such as aluminum pigments.
-rich primer is a good example of providing corrosion protection, or at least some cathode protective coatings. The metal zinc incorporated into the coating film serves as an anode and corrodes first over the iron substrate because zinc has a lower redox potential than iron, providing cathodic protection on the iron surface.
the use of corrosion-resistant pigments is one of the most widely used methods to improve coating corrosion resistance. Anti-corrosion pigments react with the water absorbed by the coating film to release inhibitory ions, which migrate to the metal surface and passivate the metal surface through deposition or adsorption of inorgeous layers on the metal substrate. Metal salts based on zinc, tantalum and lead chromate have long been used to inhibit corrosion, as their cations form insoluble deposits on the metal surface, adding a protective layer to inhibit further corrosion. Because of their toxicity, environmentally safe and non-toxic corrosion-resistant pigments have been developed to replace chromates. These non-toxic pigments are usually metal salts based on phosphates, phosphates, borates, and partial boric acid. Unlike chromates, the pigment function of these anode parts is achieved by limiting the diffusion of oxygen to the metal surface, so the action of the anode passivated metal surface may not be fully effective, resulting in poor corrosion resistance.
regulatory issues will continue to be the driving force for some time to come, particularly corrosion inhibitors. Recent notable developments include the European Union labelling products containing zinc oxide and phosphate as special hazards, and the Occupational Health and Safety Administration (OSHA) reducing the limits allowed for exposure to hexavalent chromium inhibitors.
addition of organic corrosion inhibitors to coatings is another way to improve the corrosion resistance of coatings. These organic corrosion inhibitors are based on a variety of chemical compounds, including amines, aromatics, hemlines, carboxy acid, sulfur and nitrogen-containing hydrometric groups. The effect of these corrosion inhibitors is achieved by passivation of anodes or cathodes on a metal substrate, or by forming a protective layer on a metal surface, which disrupts the flow of corrosive ions on the substrate.
has developed new corrosion inhibitors that give excellent rust resistance in a wide range of water-based and non-water-based high-performance coatings. These new organic corrosion inhibitors can be used as major corrosion inhibitors or in combination with environmentally friendly corrosion-resistant pigments. They are compatible with primers used in a variety of industrial applications and with various resins in coatings (DTM) applied directly to metals. This article describes some of our recent attempts to improve corrosion resistance in a variety of coatings with these new corrosion inhibitors.
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the current dominant trend in the coatings market is not to use primers in high-performance coating systems and to replace them with reinforced finishes in DTM applications. Since primers are not used, this method reduces the total cost by eliminating the costs associated with primer construction. The disadvantage is the reduced corrosion resistance and the adhesion provided by the primer. Adding non-toxic corrosion-resistant pigments to DTM coatings improves the corrosion resistance of coatings, but corrosion resistance is usually not as good as that of primers. The solution to this deficiency is to add an organic corrosion inhibitor to the DTM coating, together with non-toxic corrosion-resistant pigments.
past, organic corrosion inhibitors used in primer systems were based on phosphates, sulfonates, and pyrates. These chemicals work well, but are often found to be defective when used in DTM coatings. Improved corrosion-resistant DTM coatings require stronger organic corrosion inhibitors that work in synergy with non-toxic corrosion-resistant pigments.
to solve this problem, a number of new liquid corrosion inhibitors have been developed, which are metal salts based on complex organic acids. These inhibitors provide improved corrosion resistance and wet adhesion when used alone and with non-toxic corrosion-resistant pigments. These products are found to be particularly effective when applied to solvent-based two-part polyurethane systems where acrylic or polyester polyols are cross-linked to adipose isocyanates.
two-component polyurethane DTM coatings
To demonstrate the efficacy of these new corrosion inhibitors, they are used in a variety of DTM coatings and compared to more conventional organic corrosion inhibitors. In the first formulation, a white two-part polyurethane coating was prepared with acrylic polyols and cross-linked with polyols using lipid HDI tripolymers. The ratio of pigments to base materials made by the system is 1:1. The system contains 5% (mass ratio) of radon, zinc, phosphate corrosion-resistant pigments. The coating was modified with a 2% (mass ratio) conventional metal sulfonate corrosion inhibitor and a 2% (mass ratio) new metal compound inhibitor NACORR
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XR-424. Compare two samples with a control plate that contains only anti-corrosion pigments but no organic corrosion inhibitors. Apply to a 1000 Bond plate plate treated with phosphate, prepare a coating with a dry film thickness of 1.5-1.7 mils, then cure at room temperature for 7 days. The plate is then placed in a salt mist tank and exposed for 500 hours in accordance with ASTM test method B117. Immediately after removing the exposed plate from the cabinet, scratch with a metal scraper as described in section 7.2 of ASTM D1654. As can be seen in Figure 1, the new corrosion inhibitors provide better wet adhesion and rust protection than traditional organic inhibitors and controls that use only antiseptic pigments.
In the second formulation, a white two-part polyester polyol formula with more pigments is formulated to make a 1.5:1 pigment-to-base ratio, with a 5% (mass ratio) rust-proof pigment added. In this case, the corrosion-resistant pigment is a calcium silicate type pigment. The formulation was cross-linked with the HDI trimer and modified with a 2% (mass ratio) conventional metal sulfonate corrosion inhibitor and a 2% (mass ratio) new metal complex inhibitor NACORR 1389MS. Compare two samples with a control plate that contains only anti-corrosion pigments but no organic corrosion inhibitors. Apply a coating with a dry film thickness of 1.4-1.6 mils on the Bond plate and cure at room temperature for 7 days. The plate is then placed in a salt mist tank and exposed for 500 hours in accordance with ASTM test method B117. Scratch the exposed plate with a metal scraper. It can also be seen that the use of new corrosion inhibitors can improve corrosion resistance compared to controls using conventional organic inhibitors (Figure 2).
water-based thermosoenstic systems
although these new corrosion inhibitors are developed for DTM coatings that do not use primers, they can also be used in primer systems. A water-based thermo-solid iron-red primer is made by interlinking diluted polyester with hexahydroxy methamphetamine hexaethylene ether. The formula uses iron oxide red as the main anti-rust pigment, and zinc phosphate as the second corrosion-proof pigment, which is 2.5% of the total formulation quality. The pigment-to-base ratio is 1:1. The formula is treated with 2% conventional organic inhibitors and 2% new metal compound inhibitors NACORR XR-419. Compare the two samples again with a control plate that uses only corrosion-resistant pigments. Apply the coating to the 1000 Bond plate to obtain a coating model with a dry film thickness of approximately 1.0-1.2 mils. The model is then cured to 15min in an oven at 150C (300F). Then place the model in a salt mist tank and expose it for 500 hours. Remove the exposed model from it and inspect it. As can be seen in Figure 3, the performance of the new corrosion inhibitors is better than that of the standard inhibitors compared to the control formulation.
conclusion
this new generation of liquid organic corrosion inhibitors can be used to enhance the performance of non-toxic anti-corrosion pigments by applying them directly to metal coatings (DTM). They work in synergy with these pigments to improve corrosion resistance, allowing formulaters to use primers to meet the needs of less demanding metal corrosion-resistant applications.
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References
1 Cost of Corruption Estimates for 2013 by G2MT Labs,
2 Opportunities to Reduces Corruption Costs and Increase Readiness. GAO-03-753: Published: July 7, 2003. Publicly Released: Jul 7, 2003.
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