At present, water-based wood coatings use relatively few water-based resins, and the quality varies greatly; There are not many types of additives available for painting. Based on the above reasons, there is still a certain gap in the performance of water-based wood coatings compared to solvent based coatings. It is inferior to similar solvent based wood coatings in terms of drying time, hardness, plumpness, water resistance, heat resistance, etc.
Like others, the production and application process of water-based wood paint can cause air pollution and produce bubbles; In addition, some resins undergo chemical reactions during the film-forming process, which can also result in foaming; During the coating process, bubbles in the gaps of the substrate will be displaced. The surface active substances contained in water-based wood paint can promote and stabilize bubbles, including wetting agents, substrate wetting agents, surface smoothing agents, rheological modifiers, and low molecular weight components in the base material. There are always problems in the production, construction, and even drying process of water-based wood coatings during foam suppression and defoaming.
1. The defoaming mechanism of defoamers
It is generally believed that defoaming can be divided into the following four processes: the defoamer adsorbs onto the surface of the foam film; Defoamer penetrates the surface of the foam membrane; Defoamers diffuse on the surface of the foam film and adsorb surfactants; Uneven surface tension of foam film - bubble rupture.
2. Characteristics of defoamers
Defoamers should have the following characteristics: the surface tension of the defoamer should be lower than that of the liquid to be defoamed; The solubility in the defoaming liquid should be minimized as much as possible; Good dispersibility and strong diffusion ability are required; It cannot react with the liquid to be defoamed, and cannot affect the stability of lotion and resin; Good defoaming durability.
A good defoamer should have both anti foaming and anti foaming properties: ① Anti foaming effect: during high-speed dispersion and shearing processes, it can suppress the generation of bubbles, and can aggregate and eliminate small bubbles, thereby increasing the rising speed of bubbles; ② Bubble breaking effect: It can break down the bubbles that have already been generated, usually large bubbles.
A good defoamer should also have long-lasting defoaming ability: after the effective substance of the defoamer reaches the foam film, it adsorbs the surfactant on the foam film, breaks the bubbles, and improves its dispersibility in water, thereby losing its ability to continue defoaming. This is related to the type and amount of surfactant in water-based coatings, and is also the reason why the defoaming ability of the defoamer decreases after long-term storage of water-based coatings.
There are many factors that affect the coating effect of water-based wood paint, some of which are interdependent and mutually restrictive. As long as comprehensive, objective and detailed experiments on water-based additives are carried out and various influencing factors are comprehensively investigated, we can find the most suitable additive for our lotion system. With the increasing development efforts of raw material suppliers such as water-based resins and water-based additives, as well as the maturity of formulation technology and the improvement of construction processes by consumer manufacturers, the performance of water-based wood coatings will further improve, and their application prospects will become increasingly broad.
