THE INTERACTIONS OF PRESSURE SENSITIVE ADHESIVE WITH PAPER SURFACES

Abstract

<p>The interactions of pressure sensitive adhesive (PSA) with paper surfaces were investigated by using peel adhesion testing as a probe. The objectives of this work were to reveal the fracture mechanism of paper/adhesive laminates and establish the links between paper properties and the performance of PSA tapes. Particular attention was given to analyzing paper/adhesive peel curves. It was found that the peak peel force (i.e. the maximum force in a peel curve) was more effective for analyzing peelings from paper than the conventionally used steady-stateforce. Based on this, we developed a new peel data analysis method by which the overall peel behavior of a paper/adhesive combination is conveniently summarized by plotting the log peak peel force as a function of the log peel rate. This approach yielded a generalized peel curve consisting of a rate-dependent interfacial domain and a rate independent failure domain. The force generated at the paper surface in peeling was analyzed; it was found to be proportional to the overall peel force. By varying peel rates, the two types of forces were shown to have a linear relationship for the two tape types and two paper types investigated. This result justifies the use of the easily measured peel force as an estimate of the real force at the interface. Rapid peelings induce paper delamination in which paper is separated into two layers. Microscopic analysis revealed that there are three sub-processes: 1) initially, the top layer of fibers, beneath the peel front, is lifted; but, 2) it must be fractured in order for the fiber layer to be peeled from the paper sheet; and, 3) in the steady-state delamination region, the top layer of paper fibers are peeled from the paper. Processes 1 and 2 only occur initially, whereas delamination (process 3) occurs continuously during peeling. The initiation of paper delamination from the surface was found to require more than double the steady delamination force because of the need to fracture the top fiber layer (process 2). For the first time, links between paper properties and the performance of PSA have been identified by the use of advanced statistical analysis and the newly developed approach for analyzing paper/adhesive peel curves. The paper properties influencing peel force in the interfacial failure domain are, primarily, the paper surface chemistry characterized by oxygen/carbon ratio (determined by X-ray photoelectron scanning analysis) and, secondarily, the surface roughness. The governing paper property in the paper failure domain is the paper internal (Scott) bond strength. The log-log slope in the interfacial failure domain is independent of paper properties, and it is found to be governed by adhesive rheology. Finally, the fundamental research was extended to solve a practical problem. We developed a new peel-based test for paper surface strength, in which the force required to initiate paper delamination when peeling a strip of adhesive tape is proposed as a measure of paper surface strength. This method makes it possible to compare surface strength with other strength properties of paper. Further, this surface strength was found to be independent of peel rate and strongly correlated to the IGT strength (an industrial measUre of paper surface strength).</p>