Preparation Of Water-based Strippable Coatings

Strippable coatings are widely used in devices and instruments surface protection owingto their advantages like simple preparation process, good protective performance, convenientpost-processing,etc. Water-based strippable coatings meet the demand of consumers forenvironment protection because such coatings avoid using volatile organic compound.Therefore, researches on water-based strippable coatings are significant both for technologicaland social development. It is one of the most popular areas which attract much attention inrecent years.The formulation and preparation process of water-base strippable were studied in thisthesis. The most suitable kind of film-forming material, filler, and additives as well as theiramount in coating were decided according to their effects on properties of water-basedcoating and film. Besides, the best preparation process and the final coating formulation weredecided. Finally, water-based strippable coating was applied to equipment for surfaceprotection, and the effects of various factors on coating stability, film tensile strength,elongation at break,180°peel strength, corrosion resistance, water permeability and UVresistance were studied.Polyurethane emulsion A was outstanding compared with other emulsions on film tensilestrength, elongation at break and strippable property. Besides, film of this emulsion hasexcellent property in acid, alkaline and water resistance. Therefore, this emulsion was suitableto be the film-forming material of the water-based strippable coating. Modified silica sol wasadded to polyurethane emulsion to prepare organic/inorganic composite emulsion. Themodification process was as follow: using5%(mass proportion of SiO2) KH-560to modifyalkaline silica sol with1:1(mass ratio to SiO2) alcohol as a cosolvent. Time for modificationwas8h. When the amount of modified silica sol in composite emulsion was10%, good filmtensile performance, corrosion resistance and strippable performance were achieved thoughthe adhesion of film to substrate was slightly increased. Tests on the effects of different fillersto film properties showed that mica was outstanding in enhancing film tensile performance, corrosion resistance and UV resistance, and in reducing film moisture transmittance comparedwith wollastonite and calcium carbonate because of its special crystal structure. When amountof mica in coating was5%~10%, the performance of film was excellent.Types and amount of additives in coating were decided according to their effects oncoating and film performance. The formulation of water-based strippable coating was asfollows: polyurethane emulsion55%~65%, modified silica sol6%~7%, mica5%~10%,wetting agent0.2%, dispersant2%~4%(of filler content), thickener0.8%~0.9%, defoamingagent0.2%~0.3%, water-based stripping agent1%~2%, flatting agent0.4%~0.6%, waterappropriate. For preparation of the water-based strippable coating, dispersing some additivesin water at low agitation speed, then adding mica to form mica dispersion at high speed,further mixing the mica dispersion and the above composite emulsion at medium speed, thewater-based strippable coating may be finally prepared by adding the rest of additives at lowspeed.