Study On The Synthesis And Properties Of Solvent-based Acrylic Pressure-sensitive Adhesives Using New Initiators And Monomers

Solvent-based acrylic pressure-sensitive adhesives(PSAs) still play an important role in the market due to the desirable adhesion properties, resistance to water, solvents and ageing performance, and they especially can not be replaced by other ones in high-performance acrylic PSAs. However, seen from the research situation, the PSAs also have such problems as pollution,coating difficultly, low peel strength and use inconveniently. Therefore, in this paper, a series of single-component acrylic PSAs were prepared with the low-toxic ethyl acetate as solvent, AlACA as crosslinker and methanol as stabilizer, and their modification research was also carried out by changing the kind and amount of initiator and monomer, and optimizing the polymerization process. This paper is to provide references for the development of new solvent-based acrylic PSAs.The applied initiators included tert-butyl peroxypivalate(TBPP), tert-amyl peroxypivalate(TAPP) and the frequently-used BPO. The study found that different initiators and amounts have effect on the polymer properties and adhesive performance of PSAs. On the same process condition, the viscosity and molecular weight of PSA polymer were obtained in the order:BPO > TBPP > TAPP; With the increasing initiator amount, the polymer viscosity and molecular weight decreased, and the molecular weight distribution became wider; The initiator TBPP allowed the acrylic PSAs with low molecular weight, wide molecular weight distribution and moderate viscosity, indicating that it can replace the BPO initiator, thus we also applied it to the preparation of single-component crosslinked acrylic PSAs. The result showed that the TBPP amount should be above 0.6 wt% when a high monomer conversion can be ensured, and the adhesive performance also changed with the TBPP amount as well as the crosslinker concentration;As a whole, the optimal performance was obtained by using 1.2 wt% amount of initiator and 0.5wt% concentration of crosslinker.The applied monomers included 1,6-Hexanediol diacrylate(HDDA), tripropylene glycol diacrylate(TPGDA), 4-acryloyl morpholine(ACMO), N,N-dimethylacrylamide(NNDMA) and Isocyanatoethyl methacrylate(IEMA), the structures of which contained different functional groups,respectively, so they had different effects on the performance of PSAs. The study showed that the monomer HDDA, as well used as inner crosslinker to improve the holding power, was much less than the external crosslinker, and when its amount was 0.1 wt%, the 180° peel strength could be up to 25.0 N/25 mm, but the holding power was only 7 h; The amount of TPGDA should be controlled within 0.4 wt%, and its effect on the PSA performance was generally consistent with that of HDDA, but owing to the steric hindrance effect, the addition of TPGDA restrained thecrosslinking of AlACA crosslinker; The use of the monomer ACMO did not influence the crosslinking of PSAs, instead, it improved the adhesive performance, and from the view of performance and cost, w(2-EHA)/ w(ACMO)=38 : 6 was preferred; The monomer NNDMA had the best improvement on the PSA performance, and when choosing w(2-EHA)/ w(NNDMA)=20 : 2 to use,the optimal performance was obtained with the loop tack of 15.6 N/25 mm, the 180° peel strength of 23.4 N/25 mm and the holding power >72 h, as well as good water resistance; However, the addition of the IEMA resulted in the polymer viscosity increasing sharply and the adhesive performance was very poor, so this monomer was not suitable for the preparation of solvent-based acrylic PSAs.In addition, the synthesis technologies were optimized, such as the feeding way, the monomer composition, the amount of functional monomer, the crosslinker and the drying temperature, and their effects on the PSA performance were also discussed. The result showed that the feeding way significantly affected the PSA performance, and it was encouraged for the mixed monomers to feed dropwise in twice, but the dropping proportion before and after also determined the PSA performance; Compared with BA, MEA and PHEA, the THFA provided the PSAs with the best performance; The AA amount should be between 2~3 wt%; The AlACA amount and drying temperature had better be determined according to the actual production requirement.