| Digital inkjet printing technology has many characteristics, such as high image precision, realistic colors, simple operation and low cost. It developed rapidly driven by information industry in recent years. The demand of backing adhesives and ink absorbency layer for carrier is increased with vigorous development of digital inkjet printing industry. Polyacrylates have been widely used for adhesive layer and ink absorbency layer in application of digital inkjet printing, due to their advantages of good optical clarity, chemical resistance and weatherability. The common methods for synthesizing polyacrylates are emulsion polymerization and solution polymerization in industrial production. Solution polymerization is unsatisfied for environmental safety, since organic solution is used for dispersion medium. Water-based polymerization processes are preferred because of the growing consciousness of safty and environmental protection, and the strict regulations regarding the removal of volatile organic compounds(VOCs). Emulsion polymerization is a perfect candidate for preparing the polymers due to the emphasis on environmental-friendly. But some problems are still exsiting. For backing adhesives, repeated adhesive ability was not good enough, in addition, left residue on the adherend, and low properties when adhesion to special surfaces. When they were used for ink absorbency layer, their resistance was not good enough, and it was not suitable for eco-solvent ink. Hence, different types of traditional adhesive layer and ink absorbency might bring inconvenience in production, use and storage. According to the above discussions, it is necessary to design and synthesize novel polyacrylate emulsion with high stabilities and performance suitable for digital inkjet printing.Polyacrylate emulsion with average particle size of 4 nm was obtained in the presence of emulsifier N4SES-AQ of 1 mass%, which caused smaller dosage of free emulsifier in the system, and decreased the distribution of emulsifier at the adhesion interface after film formed. Meanwhile, the peel strength increased, since the small particle size increased the contact areas between the adhesive layer and the surface of adherend. Hence, the trial production experiment of 5 t was performed. The overall properties of the final product with the tack of 13 #, the 180° peel strength of 525.6 N/m, and the shear strength o f 22.3 h were better than representative emulsion backing adhesives, which were suitable to permenant pressure sensitive for digital inkjet printing.Removable properites of backing adhesives are needed in some situations of digital inkjet printing, so that the adhesives can be peeled off adherend easily with no residue. To improve the adhesion properties and removability, polyacrylate emulsion was synthesized in the presence of reactive emulsifier SR-10 instead of low-weight molecular emulsifier. The application range of temperature became wider, since SR-10 improved the freeze-thaw stability. Hence, the good removable adhesion properties with high shear holding power were obtained, since no traditional emulsifier with low-weight molecular was used, which results in the defects of problems with its migration to interface between the adhesive layer and adherend. The peel strength of the product still kept more than 50% of the initial property after repeatedly bonding and peeling for 1000 times. On this basis, IBOMA was introduced to increase the binding strength between adhesive layer and PP carrier. The peel strength of adhesives coated on un-treated PP could reach 99.4% of that of corona PP.In order to improve the shear strength, a novel porous material for digital inkjet printing has been successfully prepared by a simple and cost-effective method using polyacrylate emulsion. The optimal amount of foam stabilizer of ammonium stearate was 5 mass% for the preparation of the porous material, which formed a large amount of well-distributed pores. This porous material could bond to various kinds of surface, especially smooth surfaces like glass, due to the bonding between functional groups of the adhesive and the adherend, as well as the effect from removing air of pores. Hence, the shear strength was as high as 0.70 MPa. And its 180° peel strength was satisfied for removable material. In this study, besides removable adhesion properties, the porous material also had ink absorbency. The tack was less than 3 #, which was suitable for digital inkjet printing. The low tack was caused by the formation of porous structure, since it increased the roughness. The image is gorgeous with no halo ink phenomenon, due to the good absorbency to eco-solvent ink. And the material had resistance to various kinds of chemical mediators after printed. All these properties fulfilled the requirements of ink absorbance layer. In addition, the printed material could also be attached to various adherends. Thus, the unity of adhesives layer and absorbance layer has been realized. The results of adhesion properties, ink absorbency and t rial production experiment show that the porous material can satisfied for practical applications of digital inkjet printing. |
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