Formula evaluation and application of additives for water-based coatings (2)

1. 2 Substrate wetting
1. 2. 1 Substrate wettingis the ability of coatings or inks to spread to the substrate. In order to achieve this, the surface pressure of the liquid must be less than or equal to the surface pressure of the substrate. Silicone surfactants are ideal for this purpose, not only improving the wetting of the substrate, but also promoting flow and leveling properties, eliminating surface defects similar to orange (poor leveling) and shrink holes (locally contaminated). Successful construction of coatings is not possible without ensuring good bonding between coatings and substrates. Wetting is the act of a liquid coating spreading on the surface of a substrate. Considering the interaction between the solid surface and the droplet, whether the droplet can spread to the substrate surface depends on the relative surface energy. When the surface energy of the substrate and the contact angle of the coated paint are lower than the previous coating, a positive spread factor is obtained.surface pressure of a liquid is between 14 mN/m (isoprene) and 73 mN/m (water). Due to the trend towards the development of water-based coatings and low solvent content coatings, problems related to substrate wetting have become more important for coating formulation designers, with surface stresses of some common substances such as Table 1 to 3.
. 1. 2. 2 Improving surface wettingThere are two ways to improve wetting characteristics: (1) by cleaning, de-oiling, surface treatment (corona treatment, acid/alkali washing, etc.) to improve the surface energy of the substrate, and (2) reducing the surface strength of the coating by using special additives. By adding a small amount of substratecan significantly reduce the surface pressure of coatings and inks. This means that some of the substrates previously thought to be water-based paints that are difficult to wet or cannot paint are now easy to solve.. 1. 2. 3 Ingredients of substrate moisturizersLike all surfactants, substrate moisturizers are organic molecules containing hydrophobic and hydrophobic groups. The molecular structure of the additive allows it to produce orientation, which greatly reduces the surface and pressure of the liquid. The nonpolar part of the molecule faces the air, while the polar part remains in the water phase.most of the polar molecules that improve the wetting of the substrate contain ion parts or hydrophobic parts of the polyether chain segment that are usually specially selected carbon-oxygen chain segments. Fluorocarbons or polysilioxane are used in certain situations.. 1. 2. 4 Choice of substrate moisturizereffect of the additive depends on the ability to reduce the surface pressure of the liquid at the lowest dosage. Additives should not cause side effects such as affecting inter-layer adhesion, increasing foaming trends, or reducing water resistance. From a wide range of silicone surfactants, some special molecules called hydrother-modified silicones have been applied and developed. In general, additives are selected because they can meet certain requirements, and the evaluation of additives can be compared based on the amount required to significantly reduce liquid surface stress. Another option is to evaluate the wetting effect on a given substrate. In addition to reducing surface pressure, the best substrate moisturizers must have the following advantages: (1) significantly reduce surface pressure at low additions;. 1. 2. 5 Test method of substrate moisturizerthe efficacy and speed of movement of additives in liquids cannot be inferred directly from the ability to reduce surface stress. The following simple efficacy tests are recommended. Drop 50 mg of liquid containing surfactants on the coated substrate and after a while the droplets will begin to spread. The most effective wetting agent will produce a maximum area of circles, and the test results of several surfactants are shown in Table 4.
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