| Solvent based two-component polyurethane coating(2k-PU)has excellent physical and mechanical properties,chemical resistance and construction convenience,and its development trend is high solid content coatings.The present hydroxyl resin with high solid content 2k-PU has some disadvantages including high viscosity,high content of volatile organic compounds(VOC)and strong odor of residual organic solvents in dry coating,which is difficult to meet the needs of consumers.In view of this,two kinds of high solid and low odor hydroxyl resins,namely high transparent hydroxyl polyurethane(HPU)and high solid alkyd resin(HAR),were developed in this project,2k-PU wood coatings with high solid content and low odor were prepared by the combination of HPU and HAR.The main contents are as follows:(1)Aiming at the problems of strong polarity,poor solubility and poor compatibility with curing agent of hydroxyl polyurethane resin,high transparent hydroxyl polyurethane was prepared by the reaction of polyol and polyisocyanate,and then was modified by star hydroxyl polyester EPE and polyaldehyde resin.The effect of hydroxyl structure of polyol on resin appearance and film performance was explored.It was found that the more regular the structure of diol,the stronger the polarity of resin,the worse the solubility,the more opaque the appearance of resin and film.Using irregular polyols such as 1,3-DBO,BEPD,TMP and polyether N303,and to introduce EPE resin can increase the disorder of HPU resin structure,improve the solubility of resin and compatibility with curing agent,reduce the viscosity of resin,improve the transparency and hardness of film,and improve the taste effect of film;The effect of OH:NCO on the properties of resin and film was studied,and found that with the increase of OH content,the viscosity of resin gradually increased,the polarity of resin increased,the pot life of coating decreased,the hardness of film increased first and then decreased.When OH:NCO=2.6(molar ratio),the comprehensive performance of the film was good and the effect of pure taste was also good.The structure of the resin was characterized by NMR,the number average molecular weight of the resin was 2246-2565 with 3.12-4.21 of the PDI index tested by GPC,and the thermal stability of the film was characterized by TGA.(2)In order to solve the problems of alkyd resin with heavy oil smell and poor odourless effect of coating,vegetable oil fatty acid was used to prepare hydroxyl alkyd resin with high solid content.The effects of formulation parameters on coating performance and odourless effect were studied.It was found that mechanical properties,chemical resistance and odourless effect of coating film were better when soybean oleic acid was used to replace vegetable oil with 40% oil content.The influence of the molar ratio of pentaerythritol and glycol on the alkyd resin was explored,and found the K value decreases with increasing of the content of pentaerythritol,when the molar ratio of pentaerythritol and butylene glycol is 1.6:1,the comprehensive performance of the film is good;adding 3-4% KR-120 polyaldehyde resin,the odourless effect index of the film is 9.1 points(full score 10 points).The structure of the resin was characterized by FTIR.The molecular weight of the resin was 2564-4528 with 10.25-12.56 of the PDI index tested by GPC.TGA analysis showed that the film had good thermal stability.(3)Self-made resin HPU-6: HAR-8=4:6(mass ratio)was used as hydroxyl resin,G21:MDI-50=7:3(mass ratio)as curing agent,NCO/OH=1.05:1(molar ratio),0.2 ? 0.3% leveling agent,0.3 ? 0.5% defoamer,the viscosity of 2k-PU paint is low to 15 s tested with Yantian cup at 25?,with 70% of the solid content,and 285 g/L of the VOC contents,in line with the requirements of national environmental protection regulations of less than 420 g / L,the film has excellent chemical resistance and good thermal stability,the odourless effect index of the film is 9.2 points(full score of 10 parts),to meet customer requirements. |
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