Study Of UV Curable Heat Resistant Insulating Coating Base On Epoxy Acrylate Organic-inorganic Composite System

UV curable coating with obvious environment-friendly characteristic such as low VOC (Volatile Organic Compound), energy saving, highly efficient, has been developed rapidly and widely in applications fields since it was discovered. Heat resistant insulating coating is an important functional coating, which plays an important role in industrial production, daily live and many other fields, its main development trend is high efficient, energy saving and environment-friendly. This research put forward the novel idea that the preparation of heat resistant insulating coatings by the UV curable technology, tried to prepare UV curable heat resistant insulating coating base on epoxy acrylate organic-inorganic composite system. During preparation of the coating, the synthesis of the oligomer, UV curing process, various fillers influence on the properties of UV curable coatings and properties of UV curable thermal insulating coatings were studied.The preparation process of the EA (epoxy acrylate) oligomer was studied, the results showed that the reaction temperature was an important factor between epoxy group and acrylic acid esterification. It was analyzed by apparent kinetics that the esterification reaction was the first order reaction when the reaction temperature was80℃～110℃. The reaction rate increased with the increasing amount of N,N-dimethylaniline catalyst. The amount of inhibitor hydroquinone had little effect on reaction rate. Feeding ratio (molar ratio of epoxy to acrylic acid) n(Er):n(AA) had little effect on reaction rate. When acrylic acid was excessive, the viscosity of the synthesis product was lower. The effect of feeding mode on esterification reaction was investigated which little involved in the past. The results showed that the feeding mode had significantly effect on the reaction rate of early esterification reaction, but little effect on the overall reaction time. The feeding mode that the acrylic acid, catalyst and inhibitor are premixed together and then added into epoxy is best feeding mode and it is advantageous to improving the quality of the production. The optimal parameters of EA preparation process was determined by orthogonal experiment:reaction temperature is110℃, the amount of N,N-dimethylaniline is2.0wt%, the amount of hydroquinone is0.2wt%, feeding ratio n(Er):n(AA) is1:1.9. The results of preliminary study on properties of UV curable coating showed that the properties was correlated tightly to the mixture ratio of EA and reactive diluent TPGDA (tripropylene glycol diacrylate), with increasing the content of EA, hardness, corrosion resistance and adhesion on steel substrate of the coatings firstly increased and then decreased.UV curing process of EA/nanoalumina, EA/PI (polyimide) resin powder, EA/mica powder, EA/talc powder and EA/low temperature glass powder composite coatings were studied by IR spectrum and tack free time method. The results showed that the various fillers didn’t change the behavior characteristic of UV curing process. With nanoalumina, PI resin powder, talc powder, low temperature glass powder added to the system, UV curing rate and double bond conversion rate were dropped. Different from other fillers, when the amount of mica powder was2%of total mass of EA and TPGDA, UV curing rate and double bond conversion rate of the system increased slightly, but it was dropped when the amount of mica powder continuously increased. The tack free time of EA/nanoalumina composite coating was shortened with the amount of nanoalumina increased. The tack free time of EA/PI resin powder and EA/low temperature glass powder composite coatings were all prolonged with the amount of fillers increased. The tack free time of EA/mica powder and EA/talc powder composite coatings were firstly shortened and then prolonged with the amount of fillers increased. By mixing photoinitiator BP (benzophenone) and184(1-hydroxycyclohexyl phenyl ketone), photoinitiation efficiency was significantly improved and the tack free time was shortened. UV curing rate and double bond conversion rate of the composite coating were firstly increased and then decreased with the amount of mixing photoinitiator increased. High photoinitiator content was of advantage to curing of the surface layer. By increasing UV radiation intensity, UV curing rate and double bond conversion rate of composite system were significantly increased, the tack free time was shortened at the same time. By using mixed photoinitiator, high UV radiation intensity and appropriately increasing the amount of mixed photoinitiators, it could effectively compensate for the disadvantageous effect caused by fillers.The properties of EA/nanoalumina, EA/PI resin powder, EA/mica powder, EA/talc powder and EA/low temperature glass powder composite coatings were studied. The results showed that appropriate amount of mica powder, talc powder and PI resin powder were all able to improve properties of the coatings, such as enhancing hardness, impact resistance, flexibility, adhesion and corrosion resistance, but excessive fillers caused above-mentioned properties of the coatings to degrade. The appropriate amount of nanoalumina could improve hardness, impact resistance, flexibility and adhesion of the coatings, but it was disadvantageous effect on corrosion resistance of the coatings. Thermal stability of the coatings was all increased by adding nanoalumina, mica powder, talc powder and PI resin powder.The UV curable heat resistant insulating coatings were preparation with EA and TPGDA as organic film-forming materials, low temperature glass powder as high temperature film-forming materials, nanoalumina, mica powder, talc powder and PI resin powder as fillers. The influence of various components on properties of the coatings were investigated. The results showed that the high temperature film-forming properties of PbO-B2O3-ZnO system was better between PbO-B2O3-ZnO and P2O5-B2O3-Al2O3-K2O-Na2O-SiO2system, so properties of the coatings with its as high temperature film-forming materials was better. With the amount of PbO-B2O3-ZnO system low temperature glass powder increased, adhesion, impact resistance, flexibility, corrosion resistance and insulation of the coatings were all increased firstly and then decreased before heat treatment and after heat treatment at300℃and600℃. The optimal adding amount of PbO-B2O3-ZnO system low temperature glass powder was60%-70%of total mass of EA and TPGDA. Talc powder could significantly increase adhesion of the coatings on steel substrate before and after heat treatment, and its optimal adding amount was5%～10%of total mass of EA and TPGDA. Mica powder could significantly increase corrosion resistance and insulation of the coatings before and after heat treatment, and its optimal adding amount was5%～10%of total mass of EA and TPGDA. By adding thermoset heat resistant resin in the coatings is an efficient means to improve the properties of the coatings before "two-step" film-forming. Thermoset PI resin powder could increase various properties of the coatings after heat treatment at300℃, and its optimal adding amount was2%～4%of total mass of EA and TPGDA. A small amount of nanoalumina enables various properties of the coatings were improved before and after heat treatment, and its optimal adding amount was2%～4%of total mass of EA and TPGDA.The UV curable heat resistant insulating coatings with good insulating properties and passable synthetical properties were prepared finally. Before heat treatment, the adhesion of the coatings is up to grade1, impact resistance is not less than31cm, flexibility is not more than6mm, after neutral salt spray (NSS) text for 24h, the ratio of corrosion area is not more than40%, interlamination resistance is basically more than140Ω·cm2/piece; after heat treatment at600℃for1h, its surface smooth, non-cracking, its adhesion is up to grade2, impact resistance is not less than22cm, and flexibility is not more than12mm, after NSS text for24h, the corrosion area ratio is not more than50%, interlamination resistance is more than20Ω·cm/piece. According to the results, the idea that preparation of heat resistant insulating coatings by the UV curable technology is possible.