THE QUALITY ASSESSMENT OF BOOKBINDING STRENGTH FOR POLYVINYL ACETATE ADHESIVE (PVAc) AND NANO-MODIFIED PVAc ADHESIVES

One of the most common and cost-effective book binding method is adhesive binding method suitable for medium volume books (50-250 pages). Depending on run volume and printing technology, different adhesive binding techniques can be used. In this research, for short run book production, doublefan binding was used, because it can achieve up to 20% higher binding strength compared to perfect binding technique. In addition, for adhesive binding book production, polyvinyl acetate dispersions (PVAc), hot-melts (HM) and polyurethane adhesives (PUR) can be used. Today, water-based PVAc adhesives are more environmentally acceptable and numerous studies dealing with modification of PVAc adhesives have been carried out, in order to achieve the comparable or higher quality of adhesive joints for selected application. The aim of this research is to improve the binding performance of PVAc adhesive by adding 1% of nanoparticles, specifically hydrophobic fumed silica (SiO2) or hydrophilic fumed titanium dioxide (TiO2) powder. ISO specifies a test method (ISO 19594) for the quality assessment of adhesive binding by pulling out a single sheet from a book block, page-pull test. Pulled sheets have to be evaluated visually and in a consistent manner, since during the procedure the sheet can be pulled out completely without significant damage, raptured roughly parallel to the binding edge, raptured not parallel to the binding edge or show significant adhesive penetration. In this research, the binding strength of 8 specimens, at 4 different test positions (10%, 25%, 50% and 90% of the total number of pages), for 5 different groups of book blocks and 3 different types of PVAc adhesive (neat PVAc, PVAc + 1% SiO2, PVAc + 1% TiO2) was evaluated. All the measurements were performed under the same conditions (volume, trimmed size, binding technique and conditions, drying and pressing time). For the evaluation of quality assessment of bookbinding strength, different paper types were used for each group -woodfree uncoated, woodfree coated, containing woodbulky, woodfree office and office paper containing recycled fibres. According to ISO 19594 standard, quality levels for the binding strength of adhesive bound products are not enough. It is also necessary to calculate the coefficient of variation in order to evaluate the consistency of binding quality. According to obtained results, visual evaluation of test sheets and book blocks opening behaviour, the best quality was achieved for book blocks with PVAc + 1% SiO2 adhesive. Compared to a neat PVAc, the binding strength for all groups of book blocks was 10 -26% higher while coefficient of variation was 43 -71% lower. Results for PVAc + 1% TiO2 adhesive did not show any significant improvement or deterioration of the binding strength while coefficient of variation was notably lower, 4% -58%, compared to neat PVAc.