The Preparation Of Flame Retardant Polyurethane Prepolymer And Its Application In Pressure Sensitive Adhesive

Polyurethane(PU)is multifunctional block copolymer containing repeating carbamate(-NHCOO-)groups in the molecular chain.PU has good impact resistance,chemical resistance and low temperature resistance,excellent flexibility and viscoelasticity.Therefore,it is widely used in light industry,electronics,textile,automobile,national defense and other fields.Polyurethane pressure-sensitive adhesive(PU-PSA)with different viscoelasticity could be prepared by selecting different polymerization methods and adjusting formula design of PU.At present,PU-PSA had become one of the fastest growing adhesives.However,PU is easy to burn,which limits its application in some special fields(such as aviation and electrical equipment,etc.),so the requirements for PU-PSA are put forward.The purpose of this project is to prepare PU-PSA with flame retardancy.In this paper,PU-PSA was prepared by changing the molecular weight,type and ratio of mo-nomer.Then,Ammonium polyphosphate(APP)and Aluminum hydroxide(ATH)were used as additive flame retardants,10-(2,5-dihydroxyphenyl)-10-H-9-oxo-10-phosphenanthrene-10-oxide(DOPO-HQ),N,N-bis(hydroxyethyl)aminomethylene phosphate diethyl ester(FRC-6)and(6-oxo-6H-dibenzo[c,e][1,2]oxphosphine-6-yl)hydroxymethylthiophene(DOPO-SF)were used as reactive flame retardant to modify PU,and the flame retardant PU-PSA was prepared.The flame retardant and adhesion properties of PU-PSA were characterized by FTIR,TG,oxygen index test,vertical combustion,cone,180° peeling and inclined ball rolling method.The results were as follows:(1)Using PPG3000 and TDI as raw materials,PU prepolymer was prepared at n(-NCO):n(-OH)=2.5(R=2.5).When the crosslinking agent was trimethylolpropane(TMP)and the curing agent(amino resin)was 10wt%,the rapid surface drying of PU-PSA prepared by PU prepolymer could be realized.When Tackifier(terpene resin,TR)was 40 wt% and Plasticizer(epoxy soybean oil,ESO)was 5w t%,PU-PSA had good adhesive property,and the peel strength could reach 8.60±0.2 N/25 mm.(2)The additive flame retardant PU-PSA was prepared with APP and ATH,the limiting oxygen index(LOI)value of PU/15 wt%APP/5 wt%ATH was 30.5%,reached UL 94 V-0rating.Compared with pure PU,the peak heat release rate(PHRR),total heat release(THR)and average mass lost rate(av-EHC)were 43.1%,21.0% and 29.4% respectively.However,the initial viscosity and peel strength of PSA decreased with the increase of the content of flame retardant;The reactive flame retardant PU-PSA was prepared by DOPO-HQ,FRC-6and DOPO-SF.The LOI values of PU/50 mol%DOPO-HQ,PU/50 mol%FRC-6 and PU/20wt%DOPO-SF could reach 30.7%,29.3% and 25.0%,and the vertical combustion could reach UL 94 V-1 rating.The peel strength of PU/50 mol%DOPO-HQ and PU/50 mol%FRC-6 was3.88 N/25 mm and 3.42 N/25 mm,and the initial viscosity was also good.(3)In order to further improve the flame retardancy of reactive flame retardant PSA,the composite PSA was prepared by PU/50 mol%DOPO-HQ and PU/50 mol%FRC-6 with 5 wt%and 10 wt% additive flame retardants(the mass ratio of APP to ATH is 3:1).When the flame retardant was 10 wt%,the composite PSA passed UL 94 V-0 rating,and the LOI value was greater than 33.The peel strength of commercial PSA products was 0.10?4.15 N/25 mm,reactive flame retardant PU-PSA and composite PU-PSA prepared by the author in this paper could meet the peel strength of different commercial PSA products and realized the application.