What is the role of "water" as an important part of water-based coatings?

Water is colorless, transparent, tasteless, non-toxic and harmless, and everywhere. The freezing point of water is 0 degrees C and the boiling point is 100 degrees C, so water-based coatings are required to be kept above 0 degrees C. Water, chemical properties are stable, non-combustible, so water-based coatings are non-hazardous, production, storage and transport processes are

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water is a polar solvent, according to the principle of similar phase solubility, as the basic ingredients of the coating base and pigment must be emulsified and dispersed in the water with the help of emulsifying agents and dispersants respectively. Emulsifying agent is also known as surfactant, one end of the molecular chain with polarity, the other end is non-polar, film-forming substances, often organic polymer material is emulsified, present in the surfactant formation of the glue beam, through double-layer protection or space resistance way isolated from each other, and thus stable suspension in the water.
paint fillers in coatings are absorbed on the surface of the pigment by a dispersant with a negative charge, forming a pigment dispersing slurry in the form of water. Such dispersants can be inormeric salts, such as certain partial phosphates, modern coating production often use polymer dispersants, such as polyacrylic sodium salts or ammonium salts.
has become the new favorite of the furniture industry, and water is closely related. Its biggest feature is to replace the organic solvent in oily paint with water as a dispersion medium, compared with oily paint, do not use organic solvents, no benzene, toluene, xylene, formaldehyde and other harmful substances, non-toxic non-irritating odor, save resources and more environmentally friendly.
water used in water-based coatings is not a tap water in the general sense. Instead, deionized water is obtained after special treatment. The basic requirement of deionized water is clean and free of mechanical impurities. Calcium and magnesium plasma contained in ordinary water can affect the stability of the lacquer and slot paint (especially the deposition of swimwear) in electrophoresis paint. Ordinary water also contains bacterial microorganisms, but also affect the quality of paint product stability. However, deionized water due to the need for professional equipment operation, so will produce more production costs. But on the whole, deionized water is still much cheaper than organic solvents.
coatings are made up of resins, pigments, fillers, additives and solvents. The type of resin determines the type of coating. Different kinds of coatings, their film-forming process varies greatly. In order to have a principled understanding of the performance, characteristics and construction application of water-based coatings, we must first fully understand its film-forming system.
water-based single, two-component coating film-forming different
water-based coatings are mainly composed of water-based resins, pigments, additives, water, its film-forming process and solvent-based coatings have a completely different structure, and relatively complex, mainly because of the water-based coatings in the special structure of water-based resin and the presence of moisture.
when the water-based single-part coating is applied to the surface of the furniture, the moisture begins to evaporate. With the decrease of moisture, the arrangement of discrete latex particles becomes more closely by evacuation, and deformation is squeezed under capillary pressure and surface tension, and latex particles merge with each other, diffuse and eventually become filmed.
Water-based two-part coatings in the film-forming process also have polycyanate and water reaction, polyol and polycyanate particle coagulation, polyol and polycyanate reaction, etc. , these will affect the entire drying process of two-group water-based coatings.
Moisture volatilization is key, but not the only factor
the evaporation of moisture, such as whether the water is volatile in order, whether it is completely volatile, has a very important impact on the film quality of water-based coatings. Water-based coating film can not be a single consideration of the paint itself, but should be combined with furniture substrate type, coating method, coating equipment, drying mode and other factors to consider, so that the performance of water-based paint to the best, in order to make excellent surface coating effect.
the film-forming process of water-based wood coatings is more complex than solvent-based coatings, affecting film-forming factors more, water is more easily absorbed by wood than solvents; It can be said that the most uncertain factors and the most difficult process to control is the drying process!
this can be seen, "water" is simply the life gate of water-based paint, can be said to be also "water", defeat is also "water".
As water in the coating industry, not only as a dispersion medium, but also water is involved in the production and manufacturing process of water-based coatings, the production process to help adjust the production process, improve the quality of coatings, the end of production used to clean tools and equipment, paint construction water as a thinner. Reasonable water use, improve the level of water-based paint production technology.
pre-dispersion of thickeners
many thickeners, such as alkali-soluble thickeners or hydrophobic modified alkali-soluble thickeners, often require pre-dilution to be added to the dispersion tank during the production process. Since these thickeners are acidic, when they are not added to the coating, their molecular chains are reunited, once added to the coating, encountered alkaline environment, the molecular chain of the base groups of nircotine mutually exclusive, stretched, on the one hand, adsorption of the surrounding water Molecules, reduce the free flow of solvent water, on the other hand, due to their large size, restricting the free movement of other coating parts, hydrophobic modified thickeners can also be adsorbed to different latex particle surface, holding each other, so as to achieve the purpose of thickening.
in environments with higher pH, the more obvious the effect of such thickeners, but concentrated additions often lead to excessive local thickening, resulting in a greater risk of coating flocculation. The solution is to pre-dilute the water of this thickener, thickener and water ratio is generally 1:1 or 1:2, when adding slow drip, while accelerating the dispersion speed, so as to effectively avoid the phenomenon of unearability of viscosity, flocculation back rough.
-made slurry
for water-based coatings is generally hydroxyethyl cellulose, which is rigid and connects many hydro-hydro-based groups on the molecular chain skeleton. For cellulose to function in water-based coatings, it must first be well dispersed. Because the molecular weight is relatively large, directly in the production process is often difficult to dissolve well, in the coating can not play a thickening role, but also formed small particles affecting the fineness of the coating.
The solution is to make cellulose pre-dispersed slurry, first add cellulose to the high-speed stirring water, and then add some organic amines to regulate pH, in alkaline conditions, cellulose can be better dissolved, the concentration of cellulose slurry is generally about 2%, this process can also be done directly in the dispersion tank before the coating grinding phase. The same method is also applicable to pre-dispersion of light powder, the difference is that cellulose slurry needs to be added organic amines to help dissolve, while the light slurry is added by adding a small amount of dispersant to help disperse in water.
dilution of film-forming additives
film-forming additives are the ingredients that most water-based coatings must add. It can help water-based coatings reduce the minimum film-forming temperature and form better-performing coatings. Film-forming additives vary in drying speed and film-forming effect according to the size of the molecular weight and the strength of molecular polarity.
In water-based coatings, film-forming additives are present in the interior of latex particles and in the interface between latex particles and water, and are completely dissolved in water solvents, only solvents rather than film-forming additives, such as alcohol and glycol. Membrane additives commonly used in water-based coatings include diosterol esters (alcohol esters 12), dipropanol butyl ether and so on. For those solvents with large molecular weight and strong non-polarity, such as alcohol esters12, it is recommended to use water according to 1:1, or 1:2 ratio of pre-diluted in the process of coating stirring.
12 insoluble in water, stirring is intended to form a short-lived small oil droplet dispersion. If alcohol esters 12 are not diluted, directly added, local latex particles into the internal integration of a large number of film-forming additives and may lead to a rapid expansion of volume, breaking through the emulsizer double layer protection, and ultimately lead to gel milk break. For non-polar membrane additives, it is necessary not to pre-dilute with water.
dilution of antiseptics
water-based coatings are often anion protection systems, i.e. emulsifying agent hydro-water ends are negatively charged. The preservatives used in this water-based coating are often isoprain preservatives, in addition to copper ions in preservatives, so these preservatives are often transparent blue-green. Since copper ions are two-priced cations, if the local concentration is too high, it is easy to make anion-protected latex break milk. Water-based metal rust-proof coatings used in sodium nitrite anti-flash rust agent is often configured with water into 15% solution, in the process of mixing the paint slowly added, so as not to cause milk breakage.
in the paint construction, often add water to adjust the construction viscosity. If the water contains more calcium and magnesium particles, that is, the hardness of the water is generally said to be higher, added to the coating, easy to lead to the coating of broken milk. The author has encountered such an event, a well-known paint enterprise's engineering interior wall paint sales in Shanghai area is very good, but after sales to Sichuan, local customers with water to add paint found that every bucket will flocculate blocks, because Sichuan area more groundwater, water quality is hard, destroyed latex particles anion double layer protection, resulting in paint broken milk.
We can not change the consumer's usage habits, require them to use deionized water dilution paint, only the enterprise itself by changing the formula to increase the stability of calcium ions paint, such as adding a certain amount of emulsifying agent to enhance the stability of latex particles. Therefore, for the addition of parts with cations, it is important to pre-dilute with water. In accordance with the above requirements, in the production of coatings, a number of places need to use water to adjust the process.
other raw materials have residual raw materials, especially some high viscosity emulsions, need to be flushed with water the barrel wall and added to the cylinder. The total water used in the formula can be calculated first, weighed separately, and this part of the water can be deducted if it is added through prefabribrilated slurry. In the actual production, do not add all the water at once, but combined with process requirements, step-by-step pre-dilution, pre-mixing, to ensure that the coating parts fully evenly dispersed mixing, it is best to add or reduce a certain amount of water to achieve factory viscosity requirements. The same formula, adding the same number of ingredients, results in a viscosity that may not be the same and needs to be adjusted with water.
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