Common knowledge of coatings: water -- an important part of Waterborne Coatings

Core tip: over the years, we have been engaged in the research and development and production of waterborne coatings, and we have more and more knowledge of water in coatings There are more and more kinds of waterborne coatings, such as waterborne wood coatings, waterborne metal coatings, waterborne plastic coatings, waterborne automotive coatings, waterborne light curing coatings, and so on In the era of emphasizing low-carbon economy, water-based coating is more significant for reducing carbon emissions and protecting the earth's environment Water is colorless, transparent, tasteless, innocuous and ubiquitous The freezing point of water is 0 Paint agent, top 10 Chinese wall paint brands Recommended introduction: interior wall paint and exterior wall paint can achieve beautiful, clean and pleasant effects, but the effects in different environments are different, so the color of the paint will be different There are ten brands of Chinese paint, ten brands of global paint, ten brands of Chinese wall paint, and ten brands of Chinese paint, Famous trademark of Chinese paint and coating In private rooms, most of us choose according to our own personality, personal hobbies and living habits The younger generation will choose the interior wall paint with rich colors and bright colors, while the older ones will have some working experience Paint Home News: these years has been engaged in the development and production of water-based coatings, coatings in the water also has more and more understanding There are more and more kinds of waterborne coatings, such as waterborne wood coatings, waterborne metal coatings, waterborne plastic coatings, waterborne automotive coatings, waterborne light curing coatings, and so on In the era of emphasizing low-carbon economy, water-based coating is more significant for reducing carbon emissions and protecting the earth's environment Water is colorless, transparent, tasteless, innocuous and ubiquitous The freezing point of water is 0 ℃, the boiling point is 100 ℃, so the water-based coating should be kept above 0 ℃ Water, stable chemical properties, non flammable and non explosive, so water-based coatings are non dangerous goods, production, storage and transportation process are very safe Water is a polar solvent According to the principle of similar phase solubility, the base material and pigments and fillers, as the basic components of coatings, must be emulsified and dispersed in water respectively by means of emulsifier and dispersant Emulsifier is also called surfactant One end of the molecular chain has polarity and the other end is nonpolar The film-forming material, often organic polymer material, is emulsified and exists in the micelle formed by surfactant It is isolated by double electric layer protection or space potential resistance, so it is stable suspended in water The pigments and fillers in the coating are adsorbed on the surface of the pigments and fillers by the dispersant with negative charge, which forms the dispersion size of the pigments and fillers in the water This kind of dispersants can be inorganic salts, such as some metaphosphates In modern coating production, polymer dispersants are often used, such as sodium salt or ammonium salt of polyacrylic acid As the water in the coating industry, not only as a dispersing medium, but also water participates in the production and manufacturing process of waterborne coatings During the production process, it helps to adjust the production process and improve the quality of coatings At the end of production, it is used to clean tools and equipment During the coating construction, water is also used as a diluent This paper focuses on the relationship between water and waterborne coatings 1 Use water reasonably to improve the production process level of water-based coating 1.1 pre dispersion of thickener many thickeners, such as alkali swelling thickener or hydrophobic modified alkali swelling thickener, often need pre dilution to be added to the dispersion tank in the production process Because these thickeners are all acidic, when they are not added to the coating, their molecular chains gather together Once they are added to the coating, they encounter alkaline environment, and the carboxyl groups on the molecular chain repel each other and stretch out On the one hand, they absorb the surrounding water molecules, reduce the free flow of solvent water, on the other hand, because of their large volume, they restrict other coatings With the free movement of the components, the hydrophobic modified thickener can also be adsorbed on the surface of different latex particles, which can restrain each other, so as to achieve the purpose of thickening In the environment with higher pH value, the effect of this kind of thickener is more obvious However, the concentration of the thickener often leads to excessive local thickening, resulting in the greater risk of coating flocculation The solution is to dilute this kind of thickener with water in advance The proportion of thickener and water is generally 1:1 or 1:2 When adding the thickener, drop it slowly and speed up the dispersion, so as to effectively avoid the phenomenon of uneven viscosity and coarsening flocculation 1.2 hydroxyethyl cellulose is generally used in the production of water-based coatings This kind of cellulose is rigid, and many hydrophilic groups are connected on the molecular chain framework In order to play a role in waterborne coatings, cellulose must be well dispersed Due to the large molecular weight, it is difficult to dissolve well directly in the production process It can not play a thickening role in the coating, and the formation of small particles affects the fineness of the coating The solution is to make the pre dispersion slurry of cellulose, first add the cellulose into the high-speed mixing water, then add some organic amines to adjust the pH value, under the alkaline condition, the cellulose can be better dissolved, generally the concentration of the cellulose slurry is about 2%, this process can also be directly completed in the dispersion tank before the coating grinding stage The same method is also applicable to the pre dispersion of extinction powder The difference is that the cellulose slurry needs to be added with organic amine to help dissolve, while the extinction slurry needs to be added with a small amount of dispersant to help the dispersion in water 1.3 the pre dilution film forming assistant of film forming assistant is the necessary component of most waterborne coatings It can help the water-based coating to reduce the minimum film-forming temperature and form a film with better performance According to the molecular weight and polarity, the drying speed and the film forming effect of the film forming assistant are different In water-based coatings, film-forming AIDS exist in the interior of latex particles and the interface between latex particles and water according to the strength of nonpolarity The solvents completely dissolved in water can only be solvents rather than film-forming AIDS, such as alcohol and glycol The film-forming auxiliaries commonly used in waterborne coatings include dodecanol ester (alcohol ester 12), dipropylene glycol butyl ether, etc For those solvents with large molecular weight and strong nonpolarity, such as alcohol ester 12, it is recommended to use water in the proportion of 1:1 or 1:2 to pre dilute and then add them in the process of coating mixing Alcohol ester 12 is insoluble in water, and the purpose of stirring is to form a small oil droplet dispersion If the alcohol ester 12 is added directly without dilution, a large amount of film forming aids can be incorporated into the latex particles locally, which may lead to rapid expansion of the volume and break through the protection of the double layer of the emulsifier, resulting in the demulsification of the gel For non-polar film-forming AIDS, water pre dilution can be avoided 1.4 the Prediluted waterborne coatings of preservatives are usually anionic protective systems, that is, the hydrophilic end of emulsifier is negatively charged The preservative used in this kind of waterborne coating is usually isothiazolinone preservative In addition, there are copper ions in the preservative, so this kind of preservative tends to be transparent blue-green Because the copper ion is divalent cation, if the local concentration is too high, it is easy to break the emulsion protected by anion Sodium nitrite anti flash rust agent used in water-based metal antirust coating is usually prepared into 15% solution with water, which is added slowly in the process of coating mixing to avoid demulsification In coating construction, water is often added to adjust the construction viscosity If there are more calcium and magnesium particles in the water, that is to say, the hardness of the water is higher, adding to the coating will easily lead to the demulsification of the coating The author once encountered such an event that the sales of engineering interior wall coatings of a well-known coating enterprise were very good in Shanghai, but after they were sold to Sichuan, local customers found that every barrel of water added to the coating would flocculate and agglomerate, because the underground water was mostly used in Sichuan, the water quality was relatively hard, which damaged the anionic double electric layer protection of latex particles, resulting in the demulsification of the coating We can't change the consumer's usage habits, and require them to use deionized water to dilute the coating Only the enterprise can increase the calcium ion stability of the coating by changing the formula, such as adding certain emulsifier to enhance the stability of latex particles Therefore, it is necessary to pre dilute the components with cations with water According to the above requirements, in the coating production process, many places need water to adjust the process In addition, some raw barrels have residual materials, especially some high viscosity emulsions, which need to be washed with water and then added into the cylinder The total water of the formula can be calculated first, and the weight of the meter can be weighed separately If there is water added through the prefabricated slurry, this part of the water will be deducted In the actual production, do not add all the water at one time, but combine the process requirements, step-by-step pre dilution and pre mixing, to ensure that the paint components are fully and evenly distributed and mixed, and it is better to add or reduce a certain amount of water to meet the requirements of the factory viscosity For the same formula, adding the same amount of components, the viscosity may not be the same Finally, water is needed to adjust Home of coatings is specialized in coatings, diatom mud, paint coating, coating technology, fire retardant coating news and coating, diatom mud, 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