Study On Preparation And Performance Of Two-Component Solvent-Free Laminating Adhesives

As a medium for flexible packaging composite materials, the characteristics of thelaminating adhesives have an important impact on the quality of flexible packaging compositeproducts.Currently, the function requirements on composite flexible packaging materials arebecoming more diverse, and with its increasingly stringent requirements on quality andhygiene, the environmental and quality standards for the adhesive of the industry areimproving. However, the solvent-based adhesives are still the leading products of thecomposite adhesive areas, with the inevitable presence of VOCs emissions. In addition, rawmaterials used in the domestic polyurethane are aromatic isocyanate and aromatic polyester orpolyether polyols, which could produce potentially carcinogenic aromatic amines due to itshydrolysis. These issues have aroused people’s attention, laminating adhesives therefore haveundergone several replacements. And now, the most popular kind of adhesive is thesolvent-free two-component polyurethane, which has a high bond strength, hardnessadjustable, storage stability and with no VOCs emissions. So to prepare the adhesives withhigh performance, environment-friendly and matching with the composite materials, is thekey point.This paper focused on main performance parameters of the solvent-free two-componentpolyurethane adhesive, i.e. its viscosity, T-style peel strength and damp heat resistance. Thestructure of synthesized products was analyzed by IR spectrum. The NCO content ofpolyurethane prepolymers and the hydroxyl value of alcoholysis products were tested bychemical titration. The thermal performance was analyzed through DSC and TG. In addition,the hardness, water absorption and T-style peel strength of adhesives were also determined.Based on this above, the appropriate technological parameters, raw materials andformulations were obtained through analysis and compare.Based on the experimental study, the two-component solvent-free polyurethane adhesivewith low viscosity, short curing cycle and good damp-heat resistance had prepared. Firstly, thepolyurethane prepolymer terminated with isocyanates (i.e.Component A) was synthesizedwith polyester/polyether polyols and IPDI, with castor oil, PBA and PPG as its hydroxypolyol raw materials. Wherein, the Isocyanate Index R was3. The addition of PPG400reduced the viscosity of component A and improved water resistance and T-style peel strengthof the adhesive with a proportion of15to35%. The addition of castor oil in component Areduced the viscosity compared to PBA, while increased the viscosity compared to PPG, sothe optimum content of castor oil would be50%to70%. Secondly, the addition of the silane coupling agent KH550or its transesterification products significantly improved the T-stylepeel strength and the damp-heat resistance of the adhesive. However, the catalyst added to theB component improved the cure speed at the cost of the adhesive’s T-style peel strength.Finally, the castor oil was alcoholysisd with glycerol using the ratio of1:2at180°C for2hours. Then the alcoholysis products in component B improved the curing speed of theadhesive and the curing time was shortened from36to18hours, and improved the bondstrength of the adhesive.