Crosslinking Control In Easily Peelable Waterborne Acrylic Pressure Sensitive Adhesive Articles Prepared By Transfer Coating Method

Waterborne acrylic pressure-sensitive adhesives(PSA)prepared by transfer coating method have great prospects in the fields of labels,protective films and outdoor posters.When PSA article is peeled off from surface of the adherend,the key to leave no adhesive residue on the surface of adherend is to select suitable crosslinking system.In this way,the adhesive force between the supporting substrate and the adhesive layer is higher than the peeling strength.The crosslinking speed of crosslinking systems which are commonly used in waterborne acrylic PSAs is too fast,resulting in high degree of cross-linking of adhesive.The effective adhesive area is reduced due to the decrease of the wetting ability of the adhesive layer.And the adhesive force between the adhesive substrate and the adhesive layer is lower than the peeling strength.Therefore,adhesive residue will remain on the surface of the adherend.In order to solve the problem mentioned above,crosslinking system with slower crosslinking speed or another crosslinking system with thermally reversible hydrogen bonds were introduced into waterborne acrylate PSA to control the cross-linking degree and crosslinking speed.And easily peelable waterborne acrylic PSAs with "high tack,low peeling strength" were successfully prepared.The main studies were as follows:1.The optimum preparation conditions were obtained by investigating effects of species of monomers and emulsifiers,dosage of initiator and the polymerization temperature on the properties of acrylic emulsions and PSAs.Emulsion of PSAs with high tack and low 180° peeling strength were prepared by using n-butyl acrylate(BA)and 2-ethylhexyl acrylate(2-EHA)as main monomers,C0436 and A501 as emulsifier,ammonium persulfate as the initiator.2.Waterborne acrylic PSA which is suitable for transfer coating method was successfully prepared by introducing "(N-butoxymethyl)acrylamide/acrylic acid" crosslinking system with slow cross-linking speed into the basic acrylic emulsion system.The effects of dosage of monomer and crosslinker,the species and dosage of molecular weight modifier on the properties of emulsions and PSAs were investigated.The emulsion with 99.03%conversion,0.02%flocculation,556mPa.s viscosity and PSA of which tack was 14#ball,the holding force exceeds 48h,the peeling strength was as low as 2.78N/25mm were prepared when dosage of AA and NBMA was 3.0 wt%and 1.5 wt%,dosage of chain transfer agent ME was 700 ppm or dosage of t-DM was 500 ppm,and dosages of BA and 2-EHA were 35.5wt%and 60wt%.This PSA meets the requirements of easily peelable waterborne acrylic PSA.PSA meets the requirements of easily peelable waterborne acrylic PSA.3.Waterborne acrylic PSA which is suitable for transfer coating method was successfully prepared by introducing thermoreversible hydrogen bond into the basic acrylic PSA through polymerizing 2-methyl-N-[2-(2-oxo-1-imidazolidinyl)ethyl]-2-propenamide(MAEEU).Through variable temperature FTIR and DSC testing,it was proved that hydrogen bonds can be formed at room temperature and the hydrogen bond disappears at high temperature in acrylic PSA with MAEEU.The effect of dosage of monomer,crosslinker,and molecular weight modifier on the properties of emulsions and PSAs were investigated.The emulsion with 98.67%monomer conversion,0.11%flocculation percentage,635mPa.s viscosity and PSA of which tack was 15#ball,the holding force exceeds 48h,the peeling force was 3.11N/25mm was prepared when dosage of MAEEU,AA,ME,BA and 2-EHA were 5.0 wt%,1.5 wt%,500 ppm,48.5wt%and 45wt%.This PSA also meets the requirements of easily peelable waterborne acrylic PSA.