Application of silicone additives in the coatings industry (2)

2 as a coating desobblicizer silicone additive
as a coating desiccant usually requires a lower surface pressure than the application system, and is incompatible with the application system. Silicone is widely used as a raw material for coating desobbists because of its low polarity structure, which is incompatible with most coating resin systems.
generally, polydimethylsiloxane with a relatively large molecular mass (10,000 to 100,000) can be used as a coating defoulant, which is currently widely used in systems such as heavy antiseptics. In order to improve deblistering efficiency, some white carbon black can also be added as a efficiency group. In addition, due to the high deblistering efficiency of silicones, in very low amount of addition has a very good effect, in order to facilitate the addition, silicone deblisters are usually made into a lower concentration of solution to meet the needs of actual production.
In solvent-based coating system, in order to enhance the foaming capacity of the coating, fluorocarbon modified silicone will be used, by introducing a fluorocarbon chain segment with less compatibility and surface pressure in the main silicone chain, further reduce the compatibility of the coating and the system, greatly improve the defocation effect, usually introduced the longer the fluorocarbon chain, the better the defocage effect, this antifouling agent is usually a high-end variety of silicone defoiling agent.
in water-based coating systems, due to the high polarity of water-based resins, conventional polydimethylsiloxane and system compatible is limited, it is difficult to be used directly as a defoiling agent. Polyethers are often required to modifie polydyrexylsiloxane, especially in high-gloss systems. Generally, the higher the degree of polyether change, the better compatible, but the defoiling effect will also be reduced, generally need to be based on the difficulty of system defocation, choose the appropriate proportion of change, in order to meet the defocation capacity of the conditions, the lower the better.
Aquatic silicone defocusing agent according to its own state, divided into concentrated type and emulsion type 2 categories, concentrated defoulant foam suppression ability is strong, but not easy to disperse, in use need of strong shearing;3 Silicone substrate wetting agent
water-based system because the surface pressure of water is too large, the substrate (especially low surface pressure substrate) is difficult to wet quickly, so in the water-based coating system, the use of substrate moisturizer is particularly important. Silicone substrate wetting agent is widely used in water-based coating systems due to its wide applicability.
(2) is a typical water-based substrate moisturizer structure.from the type (2), it can be seen that the substrate moisturizer is actually a special class of polyether modified silicone oil, its relative molecular mass is usually very small. Because the rapid wetting of the substrate is a dynamic process, and in accordance with the principle of physicochemistry, the principle of the function of the wetting agent is to reduce the surface pressure of the system by rapidly migrating to the surface of the system, so as to achieve the effect of wetting the substrate. According to molecular motion theory, the speed of molecular migration depends to a large extent on the relative molecular mass, the smaller the relative molecular mass, the faster the migration speed. Therefore, polyether-modified silicone oil with relatively small molecular mass is often used as a substrate wetting agent for water-based systems.
Further studies have found that polyether-modified silicone oils used as substrate moisturizers are used in water-based systems, and because of their special structure , the silicone chain segments can be fully stretched, extending a large number of -CH3s outwards, thereby greatly reducing the surface pressure of the system. Usually medium-high relative molecular mass polyether modified silicone oil in the water system can only reduce the surface pressure to 25 to 26 N/m, while the substrate moisturizer of small molecules can usually reduce the surface pressure to 22 N/m below, the lowest can be up to 20 to 21 N/m. Such a low surface pressure, so that added substrate wetting agent of the water-based coating can wet the vast majority of low surface pressure substrate, and even wet Teflon substrate. At the same time, because the substrate moisturizer can reduce the surface strength of the water-based system to a very low degree, so the substrate wetting agent can give the system a good anti-shrink hole performance and spraying when the atomization effect.Because the relative molecular mass of the substrate moisturizer is small, its silicone chain segment is very short, so it is not possible to give the paint film surface a good slip (usually slip from the longer silicone chain segment). When the slip of the paint film is required, the substrate moisturizer is usually used with a silicone leveling agent with high relative molecular mass, which is also the difference between the substrate wetting agent and ordinary silicone leveling agent..