The water-based (VOC & HAPs) free coating can be prepared from liquid aliphatic epoxy and narrow polymerized capropone polyols and can be applied with conventional equipment and has the potential to replace powder coatings.What are the points of attention in the preparation of waterborne aliphatic epoxy liquid coatings?Chinese epoxy resin industry association expert made special introduction a few days ago.
The basic equipment investment necessary for a new powder coating line can be avoided by using traditional liquid coating spraying equipment. These coatings can be modified by diluting them with water or by thickening water-based coatings with cellulose thickeners.With the conventional diglycidyl ether of bisphenol A (bpa) resin, alicyclic epoxy has the following several aspects: the difference between A as the main chain aliphatic, reaction with acid rapidly, but with amine/amides epoxy curing agents commonly used basically don’t react, do not contain chlorine, viscosity of 350 centipoise and diglycidyl ether of bisphenol A (bpa) resin as 11000 centipoise, at the same time it also has excellent weather resistance.The application of low viscosity aliphatic epoxy in cationic UV coatings has been significantly increased. There have been many reports on the preparation and properties of this kind of 100% solid coatings without “VA”, but there are few detailed literatures on its application in thermal curing coatings.In principle, cationic UV coating formula technical know-how can also be used for thermal curing system, but the two also have different such as UV coating is generally not spraying construction, thus the construction viscosity is higher than spraying thermal curing coating, in baking type cationic coating water can be used as VOC diluent.
Cepolactone polyols have been used as effective diluents for solvent-based coatings and can accelerate the curing of cationic UV coatings. The hydroxyl groups of these polyols in cationic UV coatings can not only accelerate the curing, but also lead to a certain curing sensitivity to humidity.In the heat curing coating because of the low humidity in the oven, humidity does not inhibit curing.The presence of polyols increases the tolerance of water, so that water can be used as a VOC-free thinner in paint formulations composed of aliphatic epoxies and polyols, which are actually high solid organic coatings diluted with water.Water dilution has two advantages: low viscosity in the absence of VOC, and the use of common and well-known water-based paint measures to prevent hanging and rheological control.Since each component in the formula is only partially miscible with water, the amount of water that can be absorbed is limited. Care should be taken to avoid adding too much water to cause phase separation.
Cellulosic thickeners are effective in water-based coatings, but it is not clear whether they are effective in 100% solid, water-diluted aliphatic epoxy coatings.Early work showed that water-diluted 100% solid epoxides were thixotropic when measured with a Brookfield viscometer.The investigation of various thickeners shows that cellulose thickeners have the best comprehensive properties.When heated to 40 ~ 60℃, the best appearance of the film can be obtained by applying the spray gun. The low construction temperature makes the cured film produce more orange peel.China epoxy resin industry association experts said that the main advantage of powder coating is coated with high efficiency, high efficiency is mainly through the recovery of powder to achieve, to powder coating equivalent to this kind of liquid coating need some way to recover fly paint.Since the paint formulation described here contains no organic solvents for much easier recovery, the water lost in the recovery process can be easily adjusted by measuring the electrical conductivity when necessary, saving energy by requiring lower baking temperatures compared to the relatively higher baking temperatures required for powder coatings.Another option being evaluated is to spray anhydrous epoxies, polyols, and pigments with the “Unicarb” method, which is more efficient than powder coating. If no VOC free coating is required, simply add solvents to the formula.
About the formula note, China epoxy resin industry association experts said, for cationic curing because the alkali will stop curing, so all additives and rheological control agents must not contain alkaline, alkaline pigments and amines treated pigments will inhibit curing.Alkalescent if damine pigments will also inhibit cationic curing, alkaline pigments and additives in cationic curing coatings can not be used, curing depends on the catalyst FC-520 in a small amount of amine sealant volatilization, if the film is too thick or the oven is not ventilated, the amine can not be completely removed from the film and inhibit curing.Viscosity increased with the increase of polyols branched degree increase: dibasic alcohol than three or four yuan income lower viscosity of paint, alcohol and glycol share the need to increase the amount of epoxy value (R) can be obtained by hard coating, high dosage of epoxy corrosion can be improved, the increase of catalyst dosage can accelerate the curing speed but also can reduce the corrosion, the molar ratio of epoxy and hydroxyl R has significant influence on the curing speed.
Anyhow, alicyclic epoxy with caprolactone polyols are low viscosity and even no VOC coating, the coating can be diluted with water to spray viscosity, cellulose thickener can give water dilute of 100% solid epoxy and polyols coating to effectively prevent sagging, system of curing speed is decided by the following variables: the molar ratio of epoxy and hydroxyl, multivariate alcohol and epoxy functionality, the dosage of the catalyst and the curing temperature, the formula can be easily used in the preparation of paint, because this kind of coating for cationic curing basic paint and substrate can inhibit curing.
Post time: Apr-06-2021