Preparation And Application Of Blocked Aqueous Polyurethane Impregnating Solution For Impregnated Paper

In this study,isophorone diisocyanate was used to prepare a blocked aqueous polyurethane impregnation solution for impregnated paper.This study mainly includes:(1)Blocked isocyanates was prepared by 3,5-Dimethylpyrazole,imidazole,and caprolactam,respectively.Structural characteristics of the blocked products,temperature of deblocking,and deblocking kinetics were studied.(2)Blocked aqueous polyurethane emulsion was prepared by using imidazole as the blocking agent.Influence of prepolymer R value,DMPA content,and neutralization degree on the properties of the emulsion was investigated.(3)Amount of dipped amount and pre-cure degree during the impregnation drying process of the impregnated film paper were investigated by the single factor test method.(4)Effects of heat treatment temperature,time,and pressure during the hot pressing on the physical and chemical properties of the decorative panel was studied by the orthogonal test method.The main conclusions are as fol ows:1.The activation energies,by Kissinger equation,of imidazole,3,5-dimethylpyrazole,and caprolactam were 65.1 kJ/mol,84.3 kJ/mol,and 84.3 kJ/mol,respectibely;by FWO equation,the activation energies of these three blocking agents were 65.8 kJ/mol,75.3 kJ/mol,and 100 kJ/mol,respectively;and the initial deblocking temperatures of them were 139.1 ℃,140.8 ℃,and 153.4℃,respectively.Reaction sequence,n,of the three blocked products is not an integer by the Crane equation,due to the complicate pyrolysis reaction.Imidazole,among the three blocking agents,was selected as the ideal blocking agent in the preparation of the immersion fluid,thanks to its low deblocking temperature,reasonable price,and environmental friendship.2.Imidazole-type water-blocking polyurethane emulsion has a good storage stability at room temperature.The initial deblocking temperature of this blocked system was 140 ℃.A stable homogeneous capped waterborne polyurethane emulsion was prepared with a small particle size and excellent properties,when R,DMPA,and the degree of neutralization of the emulsion were 2.0,6%,and 90%-100%,respectively3.The dipped amount was accelerated by increasing vacuum degree and impregnation time under vacuum pressure.However,the longer vacuum post treatment time has little effect on dipped amount.The pre-cur degree almost unchanged with the vacuum degree from-0.02 to-0.06 MPa.Nevertheless,the pre-cure degree increased with the increase of vacuum,when the vacuum degree was from-0.06 to-0.1 MPa.Under atmospheric pressure,the amount of impregnation increased slightly with prolong time and higher temperature.Increasing drying time and temperature also had a positive effect on the pre-cure degree.Considering the above factors comprehensively,the optimal vacuum degree,impregnation time,drying time,and drying temperature were-0.08 MPa,5 min,45 min,and 90℃,respectively.4.Hot-pressing parameters influenced insignificantly on the surface bonding strength of decorative panels.The study found that the heat treatment temperature has the greatest effect on the surface abrasion resistance,followed by heat treatment time and pressure.Temperature has a notable influence on the surface water vapor resistance.So,considering comprehensively above-mentioned factors,the optimal hot-press should be at 180℃ under 2.5 MPa for 180 s.All the tested properties of decorative panels meeted the national standard requirements:surface adhesive strength of decorative fiberboard,surface abrasion value,and surface water vapor resistance were 1.16 MPa,0.649 mg/r,and 4 degree,respectively.