1 Introduction 1 2 3 4 .5 Adhesive perfect-bound product is Paperback, a general binding technique which uses hot-melt adhesive in book binding. Application of the hot-melt adhesive includes book-block spine preparation. Furthermore, adhesive binding quality control includes critical factors, such as paper surface properties and paper grain direction [ ]. The adhesive bond strength mainly depends on paper surface properties. Paperback handling is the second most critical quality factor after binding process. The Flat-back binding method includes assembling loose leaves together at binding edge to create a text block [ ]. Furthermore, the text block spine is filled with thick layered film of rigid adhesive. The loose leaves are locked in the fixed text block spine without radius. Therefore the Paperback openability is reduced. Paperback handling describes book block quality of adhesive joint strength. Adhesion of the adhesive to adherends and cohesion of adhesive film are main contributors to the loose leaf adhesive joint strength [ ]. On the other hand, short times of thermoplastic adhesive setting induce adhesive rigid film on the top of the text block spine. The adhesive rigid characteristics mainly influence the loose leaf adhesive joint strength changes after Paperback opening [ ]. These changes are mostly different given the loose leaf position in text block. In the past, several studies analyzing Paperback adhesive binding strength on different high paper grades were conducted. Leekley et al [ ] studied the relationship between paper properties and Paperback adhesive binding behavior. The study was concerned with determining the critical paper surface tension and importance of its 43 S. Pasanec Preprotić et al. ISSN 1330-3651 UDC/UDK 686.1.03:676.017.42 RESEARCH ON ADHESIVE JOINT STRENGTH DEPENDENCY ON LOOSE LEAF POSITION IN A TEXT BLOCK Suzana Pasanec Preprotić, Darko Babić, Amra Tuzović This paper deals with the binding ability of commercial high grade paper used in a perfect binding process. The adhesive binding strength changes happen as a consequence of adhesive rigid characteristics. Paperback bond strength evaluation is performed by pull-test measurement and visual assessment. Paperback contains a number of the loose leaves' binding edges that are bonded into assembly. The bonded assembly is discussed in terms of adhesion between hot-melt adhesive and paper (substrate). Adhesion strength within the inter phase includes the terms of adhesive joint strength. The research shows that a loose leaf position in a text block has a strong influence on adhesive joint strength changes, although other independent variables (paper and adhesive properties, binding process) have significant impact on the paperback mechanical durability. For this reason measurements of paper properties were included. The adhesive joint strength analysis results were obtained by the statistical regression method. The main goal of the paper is to determine the adhesive joint strenght dependency on a loose leaf position in the text block. Keywords: adhesive joint strength, loose leaf binding edge, mechanical interlocking adhesion Original scientific paper Ovaj rad bavi problematikom uvezivanja papira, prilikom korištenja "perfect binding" tehnike sobnom povezivanju raspravlja kroz termin djelovanja sile adhezije i podloge. oj površini izravno odnosi na u m metodom. Glavna svrha rada je odrediti položaju lista papira u knjižnom bloku. uvezivanja. Promjena čvrstoće uvezivanja pojavljuje kao posljedica karakteristične krutosti ljepila. Procjena čvrstoće spoja provedena mjerenjem sile kidanja pojedinačnog lista papira i vizualnom vrednovanjem. Određeni broj pojedinačnih listova papira su međusobno povezani preko linije veza u meko uvezanu lijepljenu knjigu. O njihovom među zmeđu taljivog ljepila i papira kao Jakost djelovanja sile adhezije na graničn čvrstoć slijepljenog spoja. Istraživanja potvrđuju kako položaj pojedinačnog lista papira u knjižnom bloku ima snažan utjecaj na promjenu rezultata čvrstoće slijepljenog spoja, iako ostale nezavisne varijable (svojstava papira i ljepila, proces uvezivanja) imaju značajan utjecaj na mehaničku izdržljivost meko uvezane lijepljene knjige. Stoga su obuhvaćeni rezultati mjerenja svojstava papira. Rezultati analize čvrstoće slijepljenog spoja izvedeni statističkom regresijsko ovisnost čvrstoće slijepljenog spoja o pojedinačnog se se se se je su Klju ne rije i: č č č ć č č č vrsto a slijepljenog spoja, linija veza pojedina nog lista papira, mehanizam lijepljenja mehani kim zaklju avanjem Izvorni znanstveni članak Istraživanje ovisnosti čvrstoće slijepljenog spoja o položaju pojedinačnog lista papira u knjižnom bloku Istraživanje ovisnosti čvrstoće slijepljenog spoja o položaju pojedinačnog lista papira u knjižnom bloku Tehni ki vjesnik č 19, 1(2012) 43-49 , properties for the Paperback adhesive binding strength. Gastel [ ] studied loose leaf adhesion joint strength in adhesive binding. He established that loose leaf binding edge characteristics are the most important criterion of Paperback adhesive binding strength. Korhonen [ ] studied all factors affecting the Paperback adhesive binding strength. She established process variables of perfect binding techniques due to Paperback volume binding edges roughness characteristics influence on Paperback mechanical durability. Paperback adhesive binding strength is defined as the force necessary to pull apart the substrates that are bonded together. Adhesion refers to the interaction of the adhesive (hot-melt) and substrate (paper) surface. Mechanical strength is dependent upon chemical bonds in adhesive, substrate and adhesive-substrate interface. Adhesive strength is measurement of failure; the process determines where the localized stress exceeds the bond strength under specific test conditions. The bond strength includes two factors: stress concentration and weakness in surface layers. One concept is the idea of the bonded assembly being a series of links representing each phase with the failure occurring in the weakest link [ ]. Generally the adhesive bond is stronger than the substrate so that the failure mechanism is one of substrate fracture mostly on loose leaf binding edge. Also surface preparation provides the adhesive and substrate interaction. Furthermore, material science (surface chemistry and morphology) has a strong influence on the interaction. The paper surface preparation involves mechanical treatment which contributes to adhesive wetting. Furthermore the adhesive's rheological property contributes to adhesive strength. Adhesive solidification describes adhesive film 6 7 8