| The pressure-sensitive adhesive (PSA) used in POST ITTM products has special microspherical structure and repositionable.There are few reports of industrialization at present, and these peoducts can not meet the requirement of market. A series of acrylic PSA microspheres were prepared by suspension polymerization in this paper. Based on acrylic monomers, an initiator, a polymeric stabilizer, wherein the reaction occurs in water to yield a microsphere adhesive. The copolymer microspheres are having diameters in the range of about 10-100μm. By mixing the cream(the microsphere-rich phase) with certain percentage of the emulsion, thickeners and other additives, then coated it through a 100μm gap mayer bar onto the paper, after drying that have good repositionable PSA. In accordance with the detection of patents, the performance of PSA was similar to products abroad. The specific performance indicators were:average particle size:53μm, tack:6# Ball, peel strength:1.21 N/25mm,100 times paste peel strength:1.16 N/25mm; with 2 kg's pressure during a week it can be easily peeled without injury stripping paper. This adhesive can be used as Post-it self-stick notes or the surface protective film adhesive and even for medical use.The amount of monomer A, the amount of dispersant, oil and water ratio, stirring speed, pH value of aqueous phase were studied in the paper. The results showed that the using of monomer A can significantly reduce the size of microspheres and improve the monodispersity without the complicated process conditions. The appropriate amount was about 3% of the monomer mass. Under laboratory conditions the most appropriate value of this experiment were: the amount of dispersant PVA:less than 1%, oil-water ratio of 1:3, stirring speed: 400-500r/min, pH values of aqueous phase stabilized at 7-8.By the testing of peel strength and repositionability, we have found the influence of microsphere size on adhesive properties. And also derivate the increase of peel strength over time and under pressure of different sizes of microspheres by using the theory of elasticity, which was confirmed by the experimental results.The pilot scale process of two-component polyurethane adhesive for valve bag was also studied in this paper. The factors such as the molecular weight of soft segment, the structure of soft segment, the using of catalyst and tackifiers were disscused. The results showed that the adhesive had the good integration performance including solvent:ethyl acetate, solids content: 15%, viscosity:21s (measured by TU-4 cup viscometer), curing time:24h, peel strength: 32.5N/25mm, destructive experiments:PE film damage, when crystalline PBA2000 and non crystalline polyester polyol were used as main material. The isocyanate index was 0.95-0.98, hard segment content was 12～20% through one-step bulk polymerization. According to the formula and process we have designed a production line which can output 1 thousand tons per year, and have produced the qualified products during pilot scale production, and running smoothly in the automated production line. Our products have excellent performance and lower price and which is gradually into the market to replace the products at home and abroad.Some defects was found in actual production such as slow solvent evaporation and excessive tack because of the high crystalline of PBA. By blending the non-crystalline polyester polyol, we had reduced the crystallinity of adhesive. DSC was used to characterize the crystallinity of the sample and then observed the crystallization conditions by polarizing microscope. The results showed that the addition of 10%-30% ratio of non-crystalline polyester polyol can reduce the drying time from 5-7d to less than 2d, and there was no significant reduction in peel strength.The effect of the catalyst T-12 on curing process was studied. By testing the peel strength of adhesive over time we had found that the T-12 could significantly speed up the curing of two-component polyurethane adhesive, which can shorten the curing time from 2-3d to less than 1d. Structural characteristics of infrared spectra for two-component polyurethane adhesive were analyzed to verify the catalytic effect of T-12 such as the changing of NCO peak.The effect of the tackifier on dry time, curing time, the impact peel strength after curing were also studied in this paper. The most appropriate amount of tackifier was about 5% of glue. The result showed that it can improve the peel strength from 21.3N/25mm to 32.5N/25mm. |
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