Wu Xiaojun, Wang Enqi, Jiang Nan (Zhejiang Yutong New Material Co., Ltd., Wenling, Zhejiang 317511, China)
Abstract : Generally, epoxy coatings cannot satisfy the coating requirements in acute and complex environment, including heavy-duty wearable deck, heavy-duty cargo cabinet and shell plating , etc. In this article, the influence of different process parameter on wearable performance of film is analyzed. The wearable performance of different product is compared. In addition, the environmentalfriendly performance and application properties are discussed. Thus, a novel epoxy anticorrosive coating composition with low VOC, low temperature curing and good wearable performance has been prepared via plenty of experiments, for instance.
The military landing ship carries amphibious armored vehicles and heavy armored equipment, and its deck is subjected to high-intensity crushing; the cargo tanks of large ships are full of cargo, which will inevitably be subject to long-term friction and collision; scientific research vessels are in ice During the voyage, the outer plate parts were constantly hit. Various parts of the ship have suffered unavoidable friction and collision for a long time, which not only affects the life of the ship, but also affects the safety of life and property. The coating of these parts with abrasion-resistant coatings has become the most direct and effective way to reduce material wear. Traditional abrasion-resistant coatings have a good protection effect on the surface of materials with low abrasion resistance and low contact frequency. Parts such as outer plates, wear-resistant decks, especially in the more demanding military ship field, traditional wear-resistant coating products have been unable to meet the requirements of the use environment, and a higher-performance wear-resistant coating is required to meet the requirements.
With the continuous improvement of environmental protection and other requirements, high performance in one aspect is no longer the sole goal of the product, and environmentally friendly coatings are the general trend. At the same time, because the ship runs on rivers, lakes, and lakes, the corrosion environment is very complicated, and the maintenance and repair of the ship is difficult and the cost is very high, which places extremely high requirements on the anticorrosive performance of the product. Due to the limitations of product performance, construction technology, and coating technology, water-based coatings are extremely costly if they are intended to be used in C4 and above environments. In a complex and changing ocean, the anti-corrosion effect of water-based coatings is far from the requirements of the marine environment. The high-solid anti-corrosion coatings developed in this research can achieve the performance of traditional solvent-based products and have low organic volatile content. Is the current mainstream of environmentally friendly anticorrosive coatings. In the field of marine coatings, it is often faced with low-temperature construction, slow film formation rate, severely prolonging the product construction cycle, and the practical difficulties and problems of failing to complete the project as scheduled. Therefore, the development of low-temperature curing products to meet the requirements of low-temperature construction is inevitable Yes.
Aiming at the strict abrasion resistance requirements, the continuous improvement of environmental protection requirements, and the complex and variable construction environment, this study prepared an epoxy anticorrosive coating with low VOC, low temperature curing, and excellent abrasion resistance.
1 Formulation design and analysis
1.1 Selection of resin
Epoxy resin has many characteristics, such as good mechanical wear resistance and outstanding chemical resistance. It can be flexibly used with different curing agents to obtain paint films that meet different performance requirements. It is easy to prepare environmentally friendly high solids. Thick paste coatings, etc., have become the first choice for marine wear-resistant coatings. The phenolic epoxy resin contains more than two epoxy groups in its molecular structure, which has high crosslinking density and good film hardness after curing. However, phenolic resins have a series of shortcomings such as insufficient toughness and low adhesion, which cannot be applied to marine wear-resistant coatings; bisphenol A epoxy resins (such as 601 epoxy resins) with relatively high molecular weight have longer molecular chains and are cured. Low post-crosslinking density makes it impossible to prepare coatings with high abrasion resistance; bisphenol A epoxy resins (such as 128 epoxy resins) with relatively low molecular weight and moderate crosslink density can ensure the product has excellent abrasion resistance It also avoids the lack of toughness of the product, which can not meet the requirements of the marine industry, and the relatively low molecular weight of bisphenol A epoxy resin has a low viscosity, which can be easily used to produce high-solid coatings, which can effectively reduce VOC emissions. , Is the best choice for preparing environmentally friendly marine wear-resistant coatings.
1.2 Selection of curing agent
Marine coatings have imposed strict requirements on the abrasion resistance of products. Fatty amine curing agents are a type with two or more amino groups in the molecule and a hydrocarbon chain as the main chain. The compound, the paint film is dense, high in hardness and not too brittle, and is an indispensable component for preparing abrasion-resistant coatings for ships. Diethylaminopropylamine has low viscosity (DEAPA), which is easy to prepare high-solids coating products, and has excellent adhesion properties, and it is easy to prepare high wear-resistant coatings.
The corrosion environment facing marine coatings is complex, and the requirements for product corrosion resistance are extremely high. With the continuous requirements of PSPC and other requirements, it is even more necessary for us to consider the product’s resistance to salt spray and cathodic peeling when developing marine coatings. With other properties, it is difficult for a single fatty amine curing agent to meet complex corrosive environments. In addition, at low temperatures, the fatty amine curing agent has incomplete curing, the cured product is soft, and the strength is low, which is not conducive to the performance of the product.
In this study, by using a reasonable mix and match of different curing agents, not only the characteristics of high crosslinking density of fatty amine curing agents are retained, but also the product has excellent anticorrosive properties, and at the same time, low temperature construction can be achieved. The curing agents used in marine anticorrosive coatings are mainly polyamide curing agents and cashew nut modified amides.
Polyamide curing agent makes epoxy paint film both flexible and impact resistant. Due to its outstanding cost performance, it still has a large application in epoxy coatings. G640 polyamide curing agent has low viscosity, excellent corrosion resistance, and is easy to prepare high solids coatings. Cashew nut modified amide is an improved variety of phenalkamine, which is an organic combination of phenalkamine and polyamide. It not only retains the rapid curing and excellent water resistance of phenalkamines, but also has the advantages of polyamide flexibility. NX-2015 in phenol-modified amine epoxy curing agent has good low-temperature curability and excellent corrosion resistance, and is suitable for application in marine coatings.
In this study, the drying performance was compared at different temperatures (+20 ℃, -5 ℃). The results are shown in Tables 1 and 2.
Note: BKⅢ refers to the actual drying time, that is, the BK drying time recorder is used to test the actual drying time of the paint on the painted glass with some trailing needle bars. It can be seen from Tables 1 and 2 that under 20 ℃, the drying performance of different curing agents is not much different, and at -5 ℃, products with cashew nut modified curing agent have outstanding drying performance. After 24 hours, the fatty amine curing agent products have not dried the paint film, and the paint film is still sticky. This is mainly because the cashew nut oil prepared with the cashew nut modified curing agent has phenolic hydroxyl groups. The cross-linking reaction between the base and the amine played a good catalytic role, and the paint film dried quickly. This study conducted cathodic peeling experiments on products using different curing agents, as shown in Table 3.
The test results show that when the peeling radius of the cashew nut modified amide curing agent is within 2 mm, the cathodic peel resistance is significantly better than that of polyamide products. Even if the cashew nut modified amide curing agent is mixed with fatty amine, the product is resistant to cathodic peeling. Still performing well. The reason for this is mainly due to the high reactivity of cashew oil modified amide and the increase in the cross-linking density of the paint film, which increases the glass transition temperature (Tg) of the paint film and ensures that the attachment point does not change after water absorption. Due to the loosening of the coating, it is still fixed at the original attachment point; in addition, its molecular structure has a long fatty chain with excellent hydrophobicity and a benzene ring structure that is resistant to chemical corrosion, so that the coating’s resistance to cathodic peeling is obtained Greatly improved. At the same time, the cashew nut modified amide has a long-chain polyamide portion. The long-chain can also balance the internal stress of the paint film after curing, reducing the risk of the paint film falling off the substrate due to the internal stress, thereby increasing the resistance of the paint film to the cathode. Peeling ability.
The mixture of fatty amine curing agent and cashew oil modified amide is used to ensure that the product has a high crosslink density and excellent anticorrosive performance. At the same time, the product can be applied at low temperature. Easy to prepare high performance marine abrasion resistant coatings.
1.3 Selection of toughening resin
Due to the strict requirements on abrasion resistance in marine abrasion-resistant coatings, the product must have a very high cross-linking density, which will lead to general flexibility of the product. Toughening resin was used in this study to increase its toughness and improve the application effect of the product. At present, the toughening resin with obvious toughening effect and high cost performance on the market mainly includes hydrocarbon petroleum resin, nonylphenol, cardanol active epoxy resin. Toughening agent.
Nonylphenol is widely used as an accelerator, toughener and diluent in epoxy system formulations. But nonylphenol is harmful to the human body and has been banned in EU countries.
Hydrocarbon petroleum resin is a phenol-modified petroleum resin, which has good miscibility with epoxy resin. Mixing hydrocarbon petroleum resin in epoxy resin can improve the toughness of the coating film and play a plasticizing effect. Low viscosity, single function cardanol active epoxy toughener, combined with long hydrophobic fat side chain characteristics of cardanol, gives the product lower viscosity and good water resistance, toughness and thermal shock resistance.
In this study, Cardolite’s NC513 cardanol active epoxy toughener and hydrocarbon petroleum resin were selected for a series of comparisons. The experimental results show that the addition of NC513 not only increases toughness, but also has excellent wear resistance. As NC513 participates in the curing reaction, it has almost no effect on the cross-linking density, and while toughening, it has no effect on the wear resistance of the product; and the hydrocarbon resin is a physical blending method with the system, which weakens the cross-linking of the product Density, thus weakening the abrasion resistance of the product.
of fillers As wear-resistant fillers, they usually have high strength, high hardness and wear resistance. This research uses alumina (Al2O3) as the main filler. Alumina is a high hardness compound with a Mohs hardness of 9 and a melting point of 2 054 ℃ and a boiling point of 2 980 ℃. It is insoluble in acids and alkalis, resistant to corrosion, and insulated. Good performance and chemical resistance. The fillers of traditional epoxy wear-resistant coatings are talc powder (Mohs hardness 1), feldspar powder (Mohs hardness 6.5), and quartz powder (Mohs hardness 7), which can not meet the requirements of high hardness. The selection of high hardness fillers brings good mechanical properties to the paint film, and the oil absorption value of alumina is not high, which is
the best choice for preparing marine wear-resistant coatings .
2 Test section
2.1 Test raw materials
128 epoxy resin, NC513 epoxy reactive diluent, epoxy curing agent NX-2015, fatty amine curing agent DEPAA, accelerator, auxiliary agent, solvent, pigment and filler.
2.2 Formulation and technology
According to the formula in Table 5, the component A is weighed first to disperse the resin, additives, pigments, fillers, and solvents at high speed for 15 minutes, and the fineness is 60 μm. Add other raw materials, and then adjust the viscosity, sagging and other indicators.
Add the corresponding curing agent according to Table 6
2.3 Test results and analysis
According to the corresponding design of this coating, after testing, the coating has excellent wear resistance and impact resistance; after the cathode peel test, the peel radius is 1.8 mm, and there is no rust and no Foaming, excellent corrosion resistance. In addition, its VOC can be as low as 250 g / L, which complies with domestic and foreign laws and regulations, and has outstanding energy saving and environmental protection benefits. The product has excellent wear resistance and corrosion resistance, see Table 7.
This research product uses an epoxy resin with an appropriate molecular weight in the formulation. In the selection of the curing agent, an organic combination of aliphatic and cashew oil modified amides was used. It was further supplemented with high hardness and wear-resistant fillers. Effectively improved the physical and mechanical properties of the product. The three components are complementary and used after mixing to prepare an epoxy anticorrosive coating with low VOC, low temperature curing, and excellent abrasion resistance.