Research and progress on the concept of anti-corrosion of water-based coatings.

Research and progress of the concept of water-based coatings anti-corrosion Zhang Xu1, Zhang Xing 2 (1. Jiabao Chemical Group Co., Ltd., Jiangmen, Guangdong 529305; 2. Dow Chemical Company Microbiological Control Technology Department, Guangzhou 510610) 0 ForewordWater-based coatings are rich in water and various nutrients, providing ideal conditions for microbial growth, so controlling microorganisms in products is one of the essential work. In recent years, due to stricter control of toxic and harmful substances in raw materials, as well as the development trend of environmentally friendly coating products, the use of formaldehyde and its release body preservatives has been severely restricted, and the risk of microbial contamination of water-based coatings has increased. Over the years, the traditional concept of adding preservatives to formulations to solve all antiseptic problems has been challenged, and more and more experience has shown that the concept of preservatives that rely on fungicides in formulations alone is not sufficient to solve real problems. Based on the basic characteristics of microorganisms, this paper analyzes the difficulties of water-based coating anti-corrosion work at this stage, and summarizes the basic principles and concepts of microbial control in the production of a new generation of water-based coatings at home and abroad.. 1 Difficulty with microbial control of water-based coatings 1.1 Microbes everywhere Microbes are the collective name of all tiny organisms, including bacteria, fungi, viruses, and a large group of organisms, including small protons, microalgae, etc. It is small, some visible to the naked eye, covers many species that are beneficial and harmful, and is closely related to human life. It is mainly harmful bacteria that cause the failure of paint corrosion prevention, and the basic characteristics of microorganisms bring many difficulties in coating production.bacteria are widely found in soil, air and water. It is calculated that the total number of bacterial cells in the human body and on the skin is about 10 times the total number of human cells. The raw materials of latex paint include pigments, fillers, slurry, emulsions and resins, thickeners, dispersants, debug agents, leveling agents, film-forming additives, etc., which contain moisture and nutrients and are highly susceptible to bacterial contamination. Table 1 lists the levels of microorganisms detected in common raw materials.. The conditions closely related to microbial survival are water, temperature, acidity and alkalinity, and nutrients. As long as there is water, microorganisms can survive, temperature, acidity, alkaline, nutrients, air, etc. will affect the type and growth of microorganisms. Therefore, in the summer of our country is the most vulnerable to microbial pollution period, need to strengthen the prevention.1.2 detection capability is insufficientrisk of microorganisms cannot be discerned by the naked eye. The size of the bacteria is measured in microns, about 0.5 to 1 m in diameter, invisible to the naked eye. Therefore, whether the coating is contaminated with bacteria can not be distinguished by the naked eye. To identify whether the odorization, color change, decrease of viscosity, pH change and other problems caused by bacterial contamination, it is necessary to test the bacterial content through professional microorganisms to determine.microbial contamination spreads very quickly with microbial reproduction. Bacteria reproduce asexually by two divisions, i.e. a bacterium silkless divides into two subgenerations of bacteria, and the number of reproductions increases exponentially. Each generation takes a short time to reproduce, from a few minutes to a few hours, and most bacteria have multiplyed for generations within 24h. Suppose 20 min reproduces a generation of bacteria, from one bacterium to more than one million bacteria within 7h, see Figure 1. Therefore, microbial contamination is found in any aspect of coating production and will be found in all links within a few days, and must be treated at all levels as soon as possible.. Therefore, not only the need for professional equipment and detection means, but also the need for rapid response and rapid processing methods. At present, water-based coating enterprises generally lack the equipment, personnel and testing methods to detect microbial content, at this stage most enterprises use third-party testing or fungicide suppliers to provide testing services. Depending on the growth characteristics of microorganisms, the shorter the time required for diagnosis and follow-up treatment, the less severe the bacterial contamination and the smaller the amount of contamination, the more damage can be saved.1.3 Control in the process of production, storage and transportation Water-based coatings in the production process, microbial sources everywhere, personnel, environmental air, equipment tools, raw materials, etc. may be the source of pollution, so production, packaging, storage and transportation of all aspects of pollution may occur. As shown in Figure 2, the production of a certain number of microorganisms exists from the beginning of the entry of raw materials, after gradual reproduction and increase, until the number of preservatives added to the sudden decline, so the production process and storage and transportation process on the final arrival of the product when the consumer situation plays an important role. Control the number of microorganisms do not exceed acceptable thresholds to ensure that the product does not erupt microbial contamination, therefore, factory hygiene, packaging, storage and transportation conditions need scientific control. This is also the weak link of most production enterprises at this stage.1.4 Changes in raw materials and regulations In recent years, with the attention of the state and users to environmental protection and safety, China's limit requirements for harmful substances in coatings gradually increased, in the water-based paint national standards and the provisions of the ten ring signs of toxic and harmful substances are strictly restricted. In GB 18582-2008 "Indoor decoration materials in the interior wall paint limit of harmful substances" and GB 24408-2009 "building wall paint in the limit of harmful substances", are volatile organic compounds (VOCs), free formaldehyde and other harmful substances made strict provisions, see Table 2.. In China's "Ten Rings Mark" on water-based coating requirements, formaldehyde limit of 50 x 10
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. These harmful substances themselves also have a certain bactericidal or antibacterial effect, so when the content of such substances decreased, the risk of water-based coatings corrosion prevention also increased.1.5 Potential risk of microbial variationMicrobes have been around the Earth for 3.5 billion to 4 billion years, and scientists now name about 2 million microbe species, accounting for only about 0.5 percent of all microbial species, as well as a large number of non-cultureable microbes (Viable Non-Culturable Microbes, VBNC). For paint manufacturers, when encountering microbial contamination problems, it is difficult to identify microbial strains. Microorganisms taken from the environment are collectively referred to as wild strains, which are different from standard strain manifestations and have different resistance to preservatives.belong to the primary nuclear organism, the cell structure is simple, easy to mutate. Compared to the epidural cells, the primary nucleus does not have a cell membrane-wrapped nucleus, the DNA chain does not spiral and does not form chromosomes, so the genetic material DNA chain in the form of free presence in the cytoste. Bacteria are therefore more susceptible to mutation and have strong environmental adaptability, so the long-term use of the same fungicide in coating products may lead to bacterial resistance problems. Drug-resistant bacteria will gradually lose the effect of the original fungicide until it does not work at all, so the choice of fungicides can not be once and for all.2 The development direction of the microbial control concept of water-based coatings for more thanyears, the addition of preservatives in water-based coating products is the main method of controlling microorganisms, but in reality there is no shortage of use of preservatives will still appear microbial contamination. The antiseptic is a special kind of raw material, its effect is not directly visible, it takes a period of time to see. The environment, process, time, dose and other factors used by the fungicide directly affect its effect, and even after the addition of the storage and placement environment have a great impact on the anti-corrosion effect of the product. Therefore, fungicides can not be used as a common meaning of raw materials, can not be considered to add fungicides to ensure product safety. Production enterprises need to establish the correct concept of microbial control. The concept of microbial control is a scientific system. The concept of controlling microorganisms in water-based coatings includes: factory hygiene control, raw material control, screening of fungicides, control of the effectiveness of fungicides in the coating process, monitoring of drug-resistant bacteria, emergency treatment when pollution is found, and rescue of contaminated products. One of the fungicides refers to a class of additives including disinfectants and preservatives, mold inhibitors, anti-algae agents. After the choice of effective fungicides also need to follow up the use of all aspects, and according to the environment, process changes and make adjustments.2.1 Factory cleaning and disinfectioncleaning and disinfection in factory hygiene are two completely different concepts. Cleaning refers to the removal of residual dirt, skin and other substances on the equipment, while disinfection refers to the killing of residual microorganisms on the equipment. Cleaning with a water cannon alone cannot completely flush out microorganisms, and residual moisture can even lead to a large number of microorganisms breeding at dead ends. For plant equipment and pipes, regular cleaning and disinfection is required.used in cleaning and disinfection in this plant must be different from the preservatives used in the formulation. Commonly used preservatives are slow to work, long time to act, and cleaning and disinfection is a fast treatment, usually less than 24 h processing time, so it is necessary to choose a rapid action of fungicides. In addition, studies have shown that long-term use of the same fungicide for in-tank corrosion and factory disinfection can significantly increase the chances of the emergence of drug-resistant strains. Factory disinfection can be soaked or sprayed with non-oxidizing fungicides, depending on the roughness of the surface, to improve the time of the fungicide contact with the disinfection surface, from 20 min to 24 h.2.2 Pre-treatment of raw materialsthe use of large quantities of raw materials, such as production of water, lotions, powders, etc., regularly test the microbial content. If higher microbial content is found, pre-treatment can be carried out with fungicides. The fungicides selected for pre-treatment of raw materials need to have rapidly degrading properties and need to be considered and reduced by preservatives in formulations to ensure that they do not affect subsequent production and that products are safe.2.3 The most common in-tank preservative in the existing main preservatives water-based coatings industry is Kathon( Cassum), a registered trademark of an efficient industrial fungicide developed by Dow Chemical Microbiological Control Technologies (formerly Roman haas) in the 1960s. Its active ingredients are methyl chlorocethione (CMIT) and methyl isoproteosterone (MIT), and extensive use has proven its highly effective broad-spectrum corrosion resistance. In addition, phenylamphetamine (BIT) class due to its excellent long-lasting, temperature and alkaline resistance, is widely used. Bronopol is also being used by a growing number of manufacturers due to its excellent performance with caron-resistant microorganisms. A variety of active ingredients compound fungicides, can be combined with the advantages of a variety of active ingredients, and even have synergies, play a better anti-corrosion effect.effects of water-based paint escapes on human health have been paid more attention to, and raw materials with low toxicity, safety and natural biodegradability are more in line with the toxicity and human health requirements of water-based coatings. EU BPR, EPA, FDA have specific provisions and restrictions for fungicides. In this trend, the fungicide dosage form from the previous solvent-based, to zero VOC water-based formulation development. Developing the active ingredients of new fungicides is more difficult, not only requires higher sterilization effect, but also requires more stringent toxicology environmental data. In the past 10 years, only Taoshi microbial control technology has released a new fungicide active ingredient MBIT (methylbenzene isoprene). MBIT's outstanding performance on drug-resistant wild bacteria opens up a new way to solve the problem of resistance to existing fungicides.2.4 Preservative screening methodThe difficulty in selecting preservatives lies in the difference between practical application and experimental testing, and preservatives that perform well in antiseptic tests sometimes do not play their proper antiseptic role in actual production. Due to the mutant nature of microorganisms, wild strains produced in actual factories are different from standard strains used in laboratories for testing, and wild strains tend to exhibit greater resistance, resulting in a very high risk in actual production using preservatives tested using standard strains. Therefore, in the test of preservative screening, the actual pollution time and intensity of production can be simulated by using wild strains from factories preserved in advance, which can better reflect the real effect of preservatives. Foreign studies have long shown that adding wild strains for preservative screening testing is a more effective method, but also more international use of the method. At present, anti-corrosion testing in the domestic market is still dominated by standard strains, only a few companies have wild species preservation technology, collecting wild strains of enterprises upstream and downstream of the coating industry to establish wild strains, to provide simulation plant production of anti-corrosion challenge testing.2.5 The correct use of fungicidespreservatives added use process also has a lot to pay attention to, the use of methods directly affect the preservatives on the product's anti-corrosion effect. According to the factory process of each production enterprise is different, but the general principle is as follows: (1) try to add in the later stages of the process, avoid the influence of other raw materials;(2) try to add after the pH is stable, especially avoid direct contact with the liant, amine substances;(3) avoid strong redox agent;(4) avoid adding at high temperatures.the equipment, processes, raw materials and technical requirements of the products used in each plant, the way preservatives are added also needs to be determined in accordance with the actual situation. The low amount of preservative additives and the active chemical properties are sensitive to many factors in production, so it is necessary for the factory to have a certain amount of experience in the use of specific preservatives in order to ensure safe use. Although the microbial control of water-based coating products uses microbial fungicides in small doses, but the quality assurance of water-based coatings plays an extremely important role, so the correct control methods and concepts are of great significance. In recent years, more and more water-based coating enterprises began to establish microbial detection capabilities, to quickly judge and solve microbial problems have a good help, but also reflects the importance of enterprises to such problems. China's industrial microbial control industry started late, so far there are no specific regulations and institutions specifically for the use and monitoring of fungicides, so the concept of microbial control is far behind the European Union, the United States and other regions. By China's water-based paint manufacturers, low degree of automation and other factors, this field to achieve international standards still have a long way to go.
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