Study On The Blocking And Unblocking Of Polyurethane And Its Application In Coated Abrasive Tools

Grinding with coated abrasives as tools is one of the most important machining methods,widely used in precision machining,especially in ultra-precision machining,known as"industrial beautician"reputation.Epoxy resin and phenolic resin are commonly used as binder in coated abrasives.However,because the curing materials of these two resins are brittle,it is necessary to toughen them to meet the requirements of the flexibility of coated abrasives.Polyurethane with hardness,adjustable,stick relay strong,the performance of the characteristics of big range can be used to the toughening modification of epoxy resin and phenolic resin,but due to the higher activities of isocyanate group in polyurethane,storage difficulties,easy water reaction and the reaction rate is fast,toughening epoxy resin with amine curing agent in polyurethane reaction rate too fast,short gel time,limiting its application in the coated with abrasive long-term production of industrialization,at the same time of water-soluble phenolic resin coated with abrasive is commonly used in the water easily isocyanate group in polyurethane reaction,cannot make isocyanate and phenolic hydroxy reaction of phenolic resin,Unable to cross-link toughening effect.In order to solve the above problems,this paper first uses the appropriate blocking agent to block the polyurethane,test the blocking and unblocking conditions,and then uses the blocking type solvent-free polyurethane to modify the epoxy resin,to explore the appropriate blocking rate on its performance,and the application.Water-soluble phenolic resin was toughened by waterborne polyurethane,and its mechanical and thermal properties were studied.The main conclusions are as follows:(1)Blocking agent was verified by FTIR test 3,5-dimethyl pyrazole successfully blocked polyurethane,infrared shows its initial deblocking temperature is 70?,DSC shows that the initial deblocking temperature was 100.7?,quantitative analysis of the degree of unlock shows the heated to 120?for 30 min,BPU offering unlock degree can reach75.71%,indicates that the blocked polyurethane possesses the advantages of low deblocking temperature.The blocked polyurethane has a milk-white appearance and a viscosity of7899MPA.s.It has good storage stability and superior mechanical properties to the unblocked polyurethane.The tensile strength of BPU-cured at 140?for 8h with dimethyl thio-toluene diamine(DMTDA)as curing agent and a blocking rate of 60%is the highest,reaching 34.98MPa.The introduction of blocking agent 3,5-dimethylpyrazole effectively solves the problem of short gel time of polyurethane prepolymers.Controlling the blocking rate can effectively eliminate the effect of blocking agent on the mechanical properties of cured products and eliminate the problem of bubbles in cured products.(2)Toughening modification of epoxy resin with blocked solvent-free polyurethane,FTIR showed BPU offering unlock after to release the isocyanate group,and the epoxy resin and curing agent MOCA crosslinking reaction,generate IPN network,DMA tests show different blocked rate BPU–EP IPN compatibility are better,blocked at a rate of 20%when the theory of crosslinking density maximum(8.88 10^-3 mol/cm³),glass transition temperature(74?),the highest secondary transition temperature minimum,low temperature toughness best,the highest tensile strength and elongation at break,51.72 MPa and 51.27%,respectively,Compared with unblocked PU-EP,the tensile strength and elongation at break are increased by 23.85%and 9.95%,respectively.Blocked rate on the thermal performance is less affected,to take advantage of the blocked polyurethane modified with epoxy resin effectively improve its strength and toughness,and extended the gel time,created a good operating condition for long-term production of industrialization,blocked at a rate of 20%BPU offering-EP as binder,preparation of the hard resin sand belt grinding after 304stainless steel,the surface roughness by 2.033 mu m 0.036 mu m,excellent performance.(3)Toughening modification of water-soluble phenolic resin with blocked water-based polyurethane,FTIR showed that BWPU was successfully synthesized and cross-linked with phenolic hydroxyl groups in PF.The static storage stability of BWPU-PF with different BWPU content>6 months,and the dynamic mechanical stability was normal.DSC showed that the curing temperature range of BWPU-PF should be 116?--192?.When the content of BWPU is 15%,the bending strength,impact strength and hardness are the highest,which are 61.99MPa,6.49k J/m2 and 87HD,respectively,and the heat resistance is slightly lower than that of PF.The reaction between isocyanate group and water in waterborne polyurethane was effectively controlled by using blocking agent,which changed the way of toughening phenolic resin by traditional polyurethane,and the crosslinking reaction between isocyanate group and phenolic resin in waterborne polyurethane effectively improved the toughness of phenolic resin,which could be applied in the field of adhesive.The test results show that the grinding ratio is the highest(34.89)when the adhesive mass ratio is 32.5%.