| UV curing is widely used in adhesives, coatings and inks because of high curing speed,high production efficiency, less pollution, energy saving, excellent product performance.UV curing prepolymer with excellent performance and low viscosity is one of the newtrends in the UV curing field. Epoxy acrylate (EA) is the most widely used prepolymer, butwith high viscosity (9.2Pa·s,60℃) and low film flexibity after UV curing. The chemicalmethods to reduce the viscosity of EA and to improve the flexibility of the EA film aftercuring, are often involved in the introduction of soft segments into part of the backbone ofepoxy resin before EA is synthesized. In this work, we are going to introduce flexiblesegments into EA via the less-focused side chains to achieve the same goals. The details ofthe work are as follows:1, Reactive polyurethane modified EAPrepolymers (PUA) with one isocyanate end, and the other double bond ends werefirst synthesized by reacting isophorone diisocyanate, polyethylene glycol (PEG) withdifferent molecular weights and hydroxyethyl methacrylate, then reacted with the hydroxylgroups on the side chains of epoxy acrylate to obtain a series of PUA-modified EAs. Theviscosity, photopolymerization rate, hardness, gloss, abrasion resistance, and chemicalresistance of the modified EAs were compared with those of the raw EA. Thecomprehensive property of the modified EA is the best and very encouraging when themolecular weight of PEG is1000g/mol and the molar ratio of PUA to EA is0.1:1. It has aviscosity of2.2Pa·s (60℃), a75%reduction compared to that of the un-modified EA. Itscuring rate is the same as the raw EA. Its gloss, pensil hardness, and tensile strengthremain unchanged but elongation at break increases from1.8%to5%compared with theraw EA, showing that the flexibility of the cured film of this modified EA increases. Theresistance of its UV-cured film to acid, base and acetone is almost equivalent to those ofthe un-modified EA, but its resistance to ethanol, tetrahydrofuran decrease slightlycompared with EA.Inspired by the above work, a commercial polyoxyethylene allyl ether (F-6) with themolecular weight of1200g/mol was directly selected to react with isophorone diisocyanate, to obtain similarly a prepolymer (PU) with one isocyanate end, the otherdouble bond end. This prepolymer was then reacted with the hydroxyl groups on the sidechains of EA to produce the modified EA. The viscosity, photopolymerization rate of themodified EAs, the hardness, gloss, abrasion resistance, chemical resistance of UV curedfilms of the modified EAs were also investigated. The weight of PU is greater than EAwhen molar ratio of PU/EA is greater than0.4. All things considered, the comprehensiveproperty of the modified EA is better when the molar ratio between PU and EA is0.4:1. Itsviscosity is4Pa·s(60℃), a55%reduction compared to that of the un-modified EA. ItsUV curing rate and pencil hardness remain unchanged, but elongation at break increasedfrom1.8%to9.3%, indicating improved flexibility of the cured film. However, its tensilestrength decreased from16.1MPa to7.6MPa, its gloss decreased from93to84, and itschemical resistance also decreased compared with pure EA.2, Reactive silicon oil modified EASimilarly, a prepolymer with one isocyanate end, and the other double bond ends wassynthesized by reacting isophorone diisocyanate, silicone oil with dual hydroxyl endgroups, hydroxyethyl methacrylate, then reacted with the hydroxyl groups on the sidechains of EA. It was found that the flexibility of the UV cured films of modified EAsincreased. However, its viscosity of the modified EA increases with increasing the siliconeoil content. Besides, its pencil hardness, gloss, tensile strength, brasion resistance, acetoneand base resistance decreased. The acid resistance of the cured film remains unchanged. |
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