Owing to the evaporation, toxicity and environmental of evaporating components, the solvent-free polymerization has been widely used in the PSA industry. Ultra-violet(UV) curing technique is one of the most popular of the new cure system, which has many advantages such as fast and solvent-free process, highly efficient and cost effective.
The key point of this study is preparation of solvent-free acrylic PSA by UV radiation. Effect of amount of photoinitiator on the adhesion properties and the correlation between the chemical structure of photoinitiator and the adhesion properties of acrylic PSA was investigated. 2-ethylhexyl acrylate(2-EHA) and acrylic acid(AA) were used for main-monomer and co-monomer, respectively. Benzyldimethyl ketal(BDK, Irgacure® 651), Methyl- benzoylformate(MBF, Darocur® MBF), 1-Hydroxy-cyclohexyl-phenyl-ketone (HCPK, Irgacure® 184), 2-Hydroxy-2-methy-1-phenyl-propane-1-one (HMPP, Darocur® 1173) and Bis(2,4,6-trimethyl benzoyl)-phenyl phosphine oxide (BAPO, Irgacure® 819) were used for our studies.
Adhesion properties were monitored by tack and peel strength of PSA using a prove tack tester and a universal testing machine after the UV polymerization, respectively.
BDK(Irgacure® 651) gives the best adhesion properties of all the photo- initiators in our studies, which may be attributed to its strong absorption far and near 350nm wavelength and good solubility in monomer mixture. Acrylic copolymer with α-hydroxy alkyl phenones derivative, HCPK(Irgacure® 184) and HMPP(Darocur® 1173) having a weak absorption at long wavelength, exhibits poor adhesion properties. These may be also due to the intra-molecular hydrogen bond between α-hydroxy-substituent and carbonyl group, which gives a negative effect on polymerization. It is observed that BAPO(Irgacure® 819) exhibits cohesive failure with high loading, which may due to low solubility in monomer mixture though its high absorptivity at long wavelength region. It can be thought that this poor adhesion properties may be attributed to the migration of insoluble photoinitiators.