Peel resistance characterization of localized polymer film bonding via thin film adhesive thermally activated by scanned CO 2 laser Colin Dowding a,n , Robert Dowding b , Jonathan Griffiths a , Jonathan Lawrence a a Laser and Photonics Engineering Group, School of Engineering, University of Lincoln, Brayford Pool, Lincoln, Lincolnshire LN6 7TS, UK b Department of Mechanical Engineering, The University of Sheffield, Sheffield S1 3JD, UK article info Article history: Received 21 August 2012 Received in revised form 1 November 2012 Accepted 6 November 2012 Available online 7 December 2012 Keywords: Polymer Laser Peel–seal abstract Thermal laser polymer bonding is a non-contact process for the joining of polymer laminates using thermally activated adhesives. Conventional, contact based bonding techniques suffer from mechanical wear, geometric inflexibility and poor energy efficiency. The application of lasers offers the potential for highly localized delivery of energy and increased process flexibility whilst achieving controlled and repeatable bonding of polymer laminates in a contact free process. Unlike previously reported techniques, here it is reported that laser based non-contact bonding is both viable and highly desirable due to the increased levels of control it affords the user. In this work, laser polymer bonding of 75 mm thick linear low density polyethylene (LLDPE) film backed with a thermally activated adhesive to a 640 mm thick polypropylene (PP) substrate was conducted using continuous wave 10.6 mm laser radiation and scanning galvanometric optics. The effect of laser power and scanning traverse speed on the peel resistance properties of the bonded polymer laminates is presented, with a threshold specific energy density for successful adhesive activation determined. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction Localized bonding between polymers has found widespread application in various industrial processes, from primary manu- facture to packaging and logistics [1]. In 2005, packaging applica- tions worldwide totaled approximately £420b, a figure that was following an upward trend; this is likely to have increased due to the commercial drive toward ever greater convenience [2]. A good seal is critical to the preservation of packaged food; hence, much research has been conducted on the conditions needed to create various types of seal [1]. Conventional thermal bonding of polymers, such as that currently used for packaging in the food industry, requires a film coated with a thermally activated polymer adhesive to be held in contact with the substrate during adhesion, as shown schemati- cally in Fig. 1. This currently requires a mechanical contact process involving a large, permanently heated steel element (machined to suit specific geometry) which is pressed onto the film to heat, provide contact with the bulk substrate and also trim the film. If the element is heated to above the threshold bonding temperature (approximately 410 K) bond strengths in the region of 0.5 N/mm can be achieved [3]. However, this technique suffers from limited speed, geometric inflexibility, great energy con- sumption [4], lengthy service downtime [5] and poor thermal efficiency due to its reliance upon thermal conduction and diffusion [6]. The literature concerning contact based methods states that three parameters must be satisfied for a successful polymer bond using a thin adhesive film: contact between material layers, thermal dwell time and application of heat [7]. Element tempera- ture has been found to effect bond strength [8]. Depending upon the heat transfer qualities of the adhesive, dwell time (the contact duration of the heating element and the film) must be sufficient to supply a thermal load that activates the adhesive [7]. It has been shown that variation of contact pressure acting orthogonal to the bonding plane has little effect on bond strength [7]. Since contact pressure is not of any consequence (once contact is ensured), the use of a non-contact adhesive activation method is viable. Laser heat sealing is a non-contact process for the thermal bonding of polymers through application of continuous wave infrared radiation, without the need for permanent dies or tools [9]. Through accurate control of process parameters, loca- lized thermal build up at the interface between polymer layers, as required for thermal bonding, can be achieved. Current contact based systems use 3 kW to seal at a rate of 22 pots per minute [10], thus, requiring a minimum energy require- ment of 8.2 kJ per pot. Application of concentrated thermal Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/optlastec Optics & Laser Technology 0030-3992/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.optlastec.2012.11.009 n Corresponding author. Tel.: þ44 1522 837914. E-mail address: cdowding@lincoln.ac.uk (C. Dowding). Optics & Laser Technology 48 (2013) 358–365