Preparation And Application Of Solvent-free Polyurethane Top-coating Resin Used In Synthetic Leather

Polyurethane(PU)synthetic leather is a kind of composite material constituted by PU coating and base fabric,which can be used as a substitute for natural leather.But a large amount of organic solvent is used in the production process of traditional PU synthetic leather,which not only pollutes the environment,but also makes the solvent remain in the finished product.In recent years,the study on solvent-free polyurethane(SFPU)synthetic leather technology gradually becomes the mainstream.Considering the needs of present SFPU synthetic leather technology,SFPU top-coating resin was prepared,which was used to produce synthetic leather.Both the performance and application technology of SFPU top-coating resin were studied.The main research contents and results are as follows:Using liquid diphenylmethane diisocyanate(MDI-50)and modified polyester polyol 2000 as main raw materials,with DH-067 as delayed catalyst,aromatic MDI type SFPU top-coating resin was prepared by one-step process.The effects of R(the molar ratio of NCO/OH in system),hard segment content(HS%),and chain extenders on the properties of SFPU films were investigated.The results showed that when the R value was 1.1,SFPU film achieved the maximum elongation strength as well as the best heat resistance.The soft-segment glass transition temperature(Tg)of SFPU films decreased with the increase of R value from 1.0 to 1.2.When HS% increased from 42% to 51%,the tensile strength of SFPU films increased from 4.3MPa to 39.00 MPa,while the elongation at break of which decreased from 624.76% to 447.46%.When HS%continued to increase,both the tensile strength and the elongation at break decreased.And with the increase of HS%,Tg of SFPU films moved to higher temperature,as well as the heat resistance became better.Furthermore,SFPU films which were prepared by different chain extenders(EG,DG,1.4-BDO,TG)had the tensile strength of 16.9MPa,19.11 MPa,17.2MPa and 13.9MPa,respectively,as well as the elongation at break were 276.64%,455.04%,402.30% and 498.62%,respectively.Using isophorone diisocyanate(IPDI),polytetramethylene glycol(PTMEG),polycaprolactone glycol(PCL)and modified polyurethane polyol 2000 as the main raw materials,with dibutyltin dilaurate(DBTDL)as catalyst,aliphatic IPDI type SFPU top-coating resin was prepared by semi-prepolymer process.The effects of polyols in B compound(compound containing hydroxyl),R value,chain extenders,and HS% on the properties of SFPU films were studied.The results showed that when the relative molecular mass of polyols was 2000,the tensile strength of SFPU film which prepared by PCL was maximum,followed by that of SFPU film prepared by modified polyester polyol,while that of SFPU film prepared by PTMEG was minimum,and the value was 29.5MPa,23.86 MPa and 13.04 MPa,respectively.Furthermore,the hydrolysis resistance of SFPU film prepared by PTMEG was better than that of SFPU film prepared by PCL.Moreover,when the relative molecular mass of polyols increased,the tensile strength of SFPU film prepared by PCL enhanced,while that of SFPU film prepared by PTMEG decreased.What’s more,when R value increased from 1.0to 1.2,the tensile strength of SFPU film increased from 7.25 MPa to 17.11 MPa,while the elongation at break decreased from 459.30% to 408.12%.In addition,with HS% increasing from 40% to 60%,the temperature resistance of SFPU film improved,and the tensile strength increased from 8.71 MPa to 26.20 MPa,while elongation at break decreased from 489.34% to 301.62%.What’s more,the tensile strength of SFPU films prepared by different chain extenders(EG,1.4-BDO,TG)were 19.57 MPa,13.04 MPa and 5.40 MPa,respectively,and the elongation at break were 352.36%,456.32% and 804.86%,respectively.SFPU top-coating resins as film-forming materials were applied in the top-coating production of the superfine fiber synthetic shoe leather base,so that three kinds of SFPU superfine fiber synthetic shoe leathers were prepared,and also the properties and structure was studied.Moreover,the application technology of SFPU top-coating resin was discussed.The results showed IPDI type SFPU superfine fiber synthetic shoe leather,MDI type SFPU superfine fiber synthetic shoe leather with foam coating,and MDI type SFPU superfine fiber synthetic shoe leather without foam coating reached B,C,A grade quality standard of the company,respectively.In addition,the price of raw materials used to prepare the aromatic MDI type SFPU top-coating resin was low,but thistype of resin had poor resistance to yellowing,so it can only be applied to produce dark colored leathers.By contrast,the price of the raw materials used to prepare the aliphatic IPDI type SFPU top-coating resin was higher,and this type of resin showed good yellowing resistance,which can meet the requirements of light colored products.