Synthesis Of High-Temperature Resistant Polyurethane Composites And Its Applications In IMD Ink

Recently, with the increasing requirement of environmental protection, the ink printingindustry has stepped into a new technology transformation stage, traditional printing technologywith low efficiency, high energy consumption and heavy pollution is facing with gradualelimination. Fortunately, the emerging new in-mould decoration (IMD) technology brings goodopportunity and challenge to plastics printing industry, which is high-efficient, relatively low cost,clean and environmentally safe, and has various applications in mobile phone shell, householdappliances, electronic devices, computer parts, appliance panels, automotive parts, etc. And IMDproduct has characteristic of high quality, durability, and variety. However, it is very difficult toformulate suitable IMD ink resins system for their extreme processing conditions, such as high heatresistance of300°C, good flexibility, surface hardness, solvent resistance, and the like. Hitherto, IMDink products are only produced by few companies such as PROELL in Germany, JUJO in Japan, etc.And IMD ink at home is seldomly developed successfully. Therefore, developing IMD ink with goodheat resistance, flexibility, surface hardness and other good performance, has realistic background andgreat research significance.Because polyurethane has good flexibility, impact resistance, processability, quick curing, wechose polyurethane as IMD ink resin in this study. However, the heat resistance and surface hardnessof pure polyurethane is not meeting the requirements of IMD ink resin well. This paper aims to studyand discuss the preparation of polyurethane composite and its application to IMD ink, which shouldhave good heat resistance, hardness, flexibility, adhesion, impact resistance and solvent resistance.Therefore, this paper has carried out the following studies.First of all, novolac epoxy-polyurethane(EPU) was prepared in this paper, it discussed the processcondition for preparing series of hydroxyl terminated bisphenol-A type novolac epoxy resins modifiedby benzoic acid, futher analyzed the influence of the molar ratio of reactants, catalyst content, reactiontemperature, reaction time on its acid value and conversion rate. The structure of reactants andproducts are characterized by FTIR,1H NMR, the results showed that the hydroxyl value of MEPincreased and hydroxyl equivalent reduced with the open loop rate increasing. EPU was obtained bycuring reaction among MEP, isocyanate trimers and phthalic anhydride. Investigated the influence of the different contents of MEP on heat resistance of EPU, the results showed that EPU had betterthermal stability than acrylic based polyurethane (A450/IL1351), the heat resistance of EPU wasimproved with the increasing content of MEP, and studied the influence of MEP on the properties ofcoating, the results showed that hardness, adhesion, water resistance, acid and alkali resistance wereimproved with the increasing content of MEP, however, the film was brittle, its flexibility and impactresistance decreased. Therefore, it is difficult to obtain comprehensive performance of EPU only byintroducing MEP.To improve the flexibility and impact resistance of EPU, introducing a certain amount of acrylicmonomers and reducing the content of EP are to improve it. Epoxy acrylate(EA) was obtained bymodifing EP with acrylic acid, and then phenolic epoxy acrylate copolyme(rEPAc)was prepared fromEA and acrylic monomers by solution polymerization. Novolac epoxy acrylate polyurethane (EPUA)was obtained by curing between EPAc and N3390. The structure of EA and EPAc was characterizedby FTIR and1H NMR, morphology of the fracture surface of EPUA was observed by transmissionelectron microscopy (SEM). The result of TGA demonstrated that heat resistance also increased, whenadding5%,10%,15%of EA, T₅of EPUA increased by5oC,17.4oC,27.4oC compared with pure acrylicbased polyurethane, when the content of EA is above10%, the film was brittle, and the content of MEPis restricted by its flexibility. Therefore, balancing the performance need further studying.Secondly, to further improve the heat resistance and flexibility, adding the nano-SiO₂into EPUA isto improve them. In this study, the SiO₂sol and MPS-SiO₂sol were obtained through the modifiedStober method, using N, N-dimethylformamide (DMF) as cosolvent. To reduce the cost of recyclingthe solvent and improve dispersivity of nano-silica in resin, phenolic epoxy acrylate copolymer(EPAc/SiO₂)were prepared in situ by adding EA and acrylic monomer. Novolac epoxy acrylatepolyurethane/silica(EPUA/SiO₂) was obtained by curing between EPAc/SiO₂and N3390, and theinfluence of reaction condition on particle size was investigated. The structure of MPS-SiO₂wascharacterized by FTIR, TGA and XPS. The result of contact angle showed that the lipophilic ofMPS-SiO₂was improved. The microscopic morphology of nano particle was observed by TEM, theresult showed that unmodified SiO₂is in the form of adhesive agglomerates, however, MPS-SiO₂showed well dispersion in DMF, TEM futher showed that the nanoparticles formed in a core-shellstructure, the thickness of the core was50or100nm and the shell was20-30nm. SEM alsodemestrated that MPS-SiO₂(1wt%-5wt%) showed well dispersion in EPUA/SiO₂and craze density of impact fracture surface increased with the increasing of MPS-SiO₂having a reinforcing andtoughening effect. The result of TGA showed that the heat resistance of EPUA/SiO₂with crosslinkednetwork structure was improved with the increasing content of SiO₂. When adding1%,3%,5%ofMPS-SiO₂, T₅of EPUA/SiO₂increased by3oC,5.7oC,6.9oC, T10of EPUA/SiO₂increased by8.2oC,13.3oC,17oC, T15of EPUA/SiO₂increased by13.2oC,18.3oC,27oC, T₅0of EPUA/SiO₂increased by10.6oC,18.3oC,29.5oC compared with EPUA, and the influence of MPS-SiO₂on the properties ofcoating was studied, the results showed that impact resistance, flexibility, hardness, adhesion, waterresistance, acid and alkali resistance were improved with the increasing content of MPS-SiO₂.Additionally, influence of RMGEO on heat resistance and performance of EPUA/RMGEO wasdiscussed. Firstly GO was synthesized from natural graphite flake according to the Hummers method,and GEO was obtained by ultrasonication treatment. The silanized MGEO was prepared by thechemical coupling reaction between the trialkoxy groups of MPS and the hydroxyl groups on GEO,MGEO was then reduced by NaHSO₃and RMGEO was obtained accordingly, EPAc/RMGEO wasprepared in-situ polymerization adding EA and acrylic monomers, EPUA/RMGEO composites wereobtained by curing reaction between EPAc/RMGEO and N3390. FTIR, XRD, TGA, XPS, SEM andTEM were used to characterize the structures and changes in modified graphene and EPUA/RMGEOcomposites. TGA and XPS showed that the content of oxygen functional groups was about30wt%.The result of XRD showed that the interlayer distance of graphite, GO, GEO, MGEO increasedsuccessively, the interlayer distance was0.3348nm(2θ=26.59°),0.7821nm(2θ=11.30°),0.8210nm(2θ=10.77°)and0.8460nm(2θ=10.44°) respectively. The results of XPS showed that the C/O ratioof GEO, MGEO and RMGEO was1.78,2.59and8.57respectively. As seen from the SEM images,the pristine graphite flakes with flat and layered structures were oriented with their basal planes, andgraphite with a size of4-8μm consisted of millions of graphene sheets stacked together, It was worthto be mentioned that GO showed widespread wrinkled graphene sheets, and suspended overwell-regulated trenches with a size around700nm, In comparison, highly wrinkled GEO displayedtypical buckling-ridged appearance with a size around400nm, MGEO showed more wrinkledappearance with a size around120nm. The results of TEM showed that the average thickness ofstacked graphene layers in GEO and MGEO was9.7nm and6.7nm respectively, which both consistedof below ten graphene sheets stacked together.44.2%partially reduced RMGEO(1wt%,2wt%or3wt%) showed a well dispersion in the EPUA/RMGEO composites, in comparison, the agglomeration phenomenon of graphene sheets was obviously observed in EPUA/RMGEO with completely reducedRMGEO. The result of TGA showed that heat resistance of EPUA/RMGEO with crosslinked networkstructure was improved with the increasing content of RMGEO. Influence of RMGEO on theproperties of coating was studied, the results showed that impact resistance, flexibility, hardness,adhesion, water resistance, acid and alkali resistance were improved with the increasing content ofRMGEO, hardness reached6H, and acid and alkali resistance reached several months.Lastly, choosing EPU, EPUA/SiO₂, and EPUA/RMGEO as main adhesive material, carbon blackor phthalocyanine blue as pigment, ethyl acetate and butanone as solvent and adding wetting anddispersing agent, drying agent, leveling agent, adhesion promoter, defoaming agent, three IMD inkswere formulated with a solid content of25wt%-35wt%. Using the differential scanning calorimetry tostudy the cure kinetics of multi-component polyurethane system, the cure kinetic parameters weredetermined, such as the activation energy, the reaction rate constant, the reaction order, the reactioncuring characteristic temperature, and so on. Finally, the physico-chemical properties of IMD ink weremeasured, the results showed that IMD ink (EPU) could meet the requirements of hardness, adhesion,heat resistance of300oC, water resistance, acid and alkali resistance, but flexibility and impactresistance. IMD ink (EPUA/SiO₂) with the content of3%,5%MPS-SiO₂and IMD ink(EPUA/RMGEO) with the content of2%RMGEO could meet the requirements of hardness,flexibility, adhesion, impact resistance, heat resistance of300oC, water resistance, acid and alkaliresistance.