Thermoplastic Adhesives Research Articles

Adhesive joining technologies activated by electro-magnetic external trims

Joining is a key and fundamental aspect of vehicle design and manufacturing process. The development of efficient, simple, inexpensive and reversible adhesive bonding technologies offers low cost, improved life cycle and recycling solutions for a vehicle. This innovative technology is based on magneto sensitive nanoparticles dispersed into the adhesive. Different typologies of susceptors, embedded in thermoplastic hot-melt adhesives, have been tested to investigate the thermal behavior of these innovative materials when exposed to electromagnetic fields. These innovative technologies are intended to optimize the bonding process offering new opportunities connected with cost reduction, improved resistance to applied loads, easy and rapid dismantling and smart recycling. Experimental procedures to optimize the electromagnetic process have been performed. Results about both shear strength and sliding temperature of the modified adhesives are presented.

Bio‐based adipic acid from renewable oils

AbstractAdipic acid (hexanedioic acid, C6H10O4) is a high‐volume dicarboxylic acid used as a chemical intermediate in the commercial manufacture of nylon 6,6, thermoplastic polyurethane resins, plasticizers, adhesives and synthetic lubricants, with an estimated global market worth approximately $6.3 billion. We report here the development of a robust industrial yeast strain and fermentation process for production of bio‐based adipic acid at high yield and selectivity from any vegetable oil, regardless of its fatty acid composition. Bio‐based adipic acid could alleviate many of the drawbacks associated with adipic acid produced from petrochemical sources and offer a sustainable alternative to benzene price swings as well as a significant reduction in greenhouse gas emissions.

Nano-aluminum oxide as a reinforcing material for thermoplastic adhesives

Nanoparticles of aluminum oxide were used to improve bonding strength of PVA (polyvinyl acetate) in wet conditions and elevated temperatures. Shear strength of wood joints was improved by inclusion of nanoparticles to PVA in all conditions. The improvement on performance of PVA in dry state by adding nanoparticles could be measured in terms of wood failure. In wet conditions and at elevated temperature, nanoparticles significantly increased shear strength of wood joints. Thermal stability of PVA was affected by nanoparticles as well. Nanostructure studies showed that dispersing well nanoparticles in PVA is a crucial step to obtain nanocomposites with superior properties.

Study on the Heat-Press Bonding Optimum Technics of Stitchless Apparel

The heat-press bonding technology of water proof and breathable fabrics with thermoplastic adhesives will play an important role in the processing of stitchless apparels, they will influence not only the stiffness and the processability, but also influence the function and the quality of stitchless apparels. This study will analyze the influence factor about the processability through the test index of the breaking strength. The results showed that pressing time was one of most easily controlled technology in stitchless apparels production.

Addition of precipitated calcium carbonate filler to thermoplastic polyurethane adhesives

Precipitated calcium carbonate filler (PCC) was added to a thermoplastic polyurethane adhesive (TPU). The addition of PCC produced a moderate increase in the rheological and viscoelastic properties of TPU due to the poor dispersion of filler (i.e. found to be clusters) and the weak interactions between the PCC nanoparticles and the polymer chains. The interactions were noticed by ATR-IR spectroscopy by displacement of the bands at 3326, 1729 and 1061 cm −1 to higher wave number of the polyurethane. Furthermore, the first glass transition temperature of the polyurethane was found to decrease by adding PCC filler. The crystallinity of the soft segments in the TPU was decreased by adding PCC because of the disruption of the degree of phase separation in the polymer. The initial adhesive strength in PVC/TPU adhesive/PVC joints increased noticeably by adding PCC filler, the greater the amount of filler in the TPU, the greater the initial adhesive strength found. Finally, the highest final adhesive strength (72 h after joint formation) was obtained in the joint produced with the TPU containing 10 wt% PCC.

ZoneBOND Thin Wafer Support Process for Wafer Bonding Applications

The ZoneBOND process has been developed as an alternative temporary bonding process that bonds at an acceptable temperature (usually less than 200°C), survives through higher-temperature processes, and then debonds at room temperature. The technology utilizes standard silicon or glass carriers and current thermoplastic adhesives developed by Brewer Science, Inc.

Advanced Package Prototyping Using Nano-Particle Silver Printed Interconnects

To reduce manufacturing cost, lead time, and process complexity, an embedded-active approach that targets rapid prototyping and low-volume production in micro-system packaging is being developed. The approach involves a rapid prototyping of micro-system packaging by a data-driven chip-first packaging process using direct printing of nano-particle metals. In the chip-first process, bare dice are first embedded into a copper or stainless steel carrier substrate, fixed by filling the gap between the chips and the substrate with thermoplastic adhesives, and planarized to a common planar surface. On the coplanar substrate, polyimide film is laminated to form a dielectric layer. Through the dielectric layer to the chip metal pads, micro vias are drilled by laser ablation. The vias are filled with nano-particle silver (NPS). The NPS is deposited by screen printing or aerosol-jet printing and an electrical circuit is formed. This packaging approach is a dry process and it does not require any photo masks for circuit patterning, resulting in reducing packaging turn-around time from months to days. It is also less limited by substrate composition and morphology, eliminates the need for special chip processing such as flip chip solder bumps, and permits using any chip technology and any chip supplier allowing mixed devices. The embedded-active process with NPS avoids the extreme processing conditions required for standard IC fabrication such as wet chemistry processing and vacuum sputtering. The NPS can be sintered at plastic-compatible temperatures as low as 230?C to form material nearly indistinguishable from the bulk metal. The embedded-active packaging shows good reliability performance in terms of thermal shock, which is performed in the range of -40?C and 125?C. These results represent an important step to a system packaging characterized by high-density, low-cost, and data-driven fabrication for rapid package prototyping. This paper presents details of the rapid prototyping process sequence, an initial reliability characterization of the package architecture, and a failure mode analysis of the packages.

ZoneBOND™ Thin Wafer Support Process for Wafer Bonding Applications

Wafer-to-wafer bonding is widely used to support both the production of integrated circuits and MEMS devices. Bonding may be accomplished in a variety of ways including anodic, thermal compression, and adhesive bonding. The bond may be either permanent or temporary. Permanent wafer bonding is used to combine two materials together that remain together for the life of the device, for example, in the production of Si/GaAs wafer heterostructures for integration of an optoelectronic device into silicon integrated circuit technology. Temporary bonding is used to support the device wafer during certain processing steps, and then removed once the device wafer is completed. Currently, there are several temporary bonding processes being developed in industry. The leading technology utilizes some form of polymeric material to temporarily fasten or bond a rigid backing material, usually silicon or glass, to the device wafer for processing. The main issues associated with these techniques are temperature stability of the adhesive, removal from the support wafer, and cleaning the adhesive from the device wafer. The ideal process would require bonding at an acceptable temperature (usually less than 200°C), surviving through higher temperature processes, followed by debonding at lower temperature or even room temperature. In this paper, an alternative solution is reported that utilizes current thermoplastic adhesives and silicon support wafers coupled with a patented technology, developed by Brewer Science, Inc. Support wafers are bonded to device wafers at acceptable temperatures, mechanical integrity is maintained through semiconductor or MEMs processing, and the completely processed device wafer is then safely debonded from the support wafer at room temperature.

Advanced Thin Wafer Support Processes for Temporary Wafer Bonding

The ZoneBOND™ process has been developed to allow temporary wafer bonding at acceptable temperatures (usually less than 200°C), survival through higher-temperature processes, and then demounting at room temperature. The technology utilizes standard silicon or glass carriers and current thermoplastic adhesives developed by Brewer Science, Inc. The separation process consists of three components: removal of the adhesive in the outer zone, lamination of the device side of the pair, and separation of the carrier wafer from the adhesive. Developments of these key areas are the focus of this paper.

Properties of thermoplastic polyurethane adhesives containing nanosilicas with different specific surface area and silanol content

Thermoplastic polyurethane (TPU) adhesives containing nanosilicas with different specific surface area and silanol group content were prepared and characterized by FTIR spectroscopy, differential scanning calorimetry (DSC), thermogravimetry (TGA), X-ray diffraction, plate-plate rheology, dynamical–mechanical–thermal analysis (DMTA), transmission electron microscopy (TEM), and strain–stress test. Adhesive strength was obtained from T-peel tests of PVC/polyurethane adhesive joints. Formation of agglomerates of nanosilica particles within the polyurethane matrix were favoured by increasing the silanol content likely due to stronger hydrogen bond interactions between the silanol groups on the nanosilica over those between the polyurethane and the nanosilica. As a consequence, inter-urethane bonds formation rather than ester-urethane bonds were favoured, leaving the soft segment chains more free to interact between them. Thus, addition of nanosilica favoured the phase segregation in the thermoplastic polyurethane. The increase in specific surface area and silanol content in the nanosilica, generally enhanced the degree of phase separation in the polyurethane, being less marked for nanosilicas with more than 200 m 2/g and 0.60 mmol SiOH/g silica. On the other hand, the addition of the nanosilica improved the tensile strength and elongation at break, and the viscoelastic properties of the polyurethane. The immediate adhesive strength of PVC/polyurethane adhesive joints increased in the filled adhesives and it was determined by the rheological properties of the polyurethane–nanosilica mixtures. By increasing the time after joint formation, the crystallization of the polyurethane was produced giving higher adhesive strength and although a cohesive failure in the PVC was always obtained, a slight though progressive increase in joint strength was found with the passage of time with the ordering of the three systems (PU-0.45, PU-0.60 and PU-0.90) remaining unchanged with the PU-0.60 system the stronger and the PU-0.90 system the weaker. This is in agreement with the trends in the viscoelastic and mechanical properties of the filled adhesives.

Addition of nanosilicas with different silanol content to thermoplastic polyurethane adhesives

Three nanosilicas with different silanol contents were prepared by treatment of hydrophilic fumed silica with dimethyldichlorosilane. This treatment reduced the silanol content and produced the particle agglomeration of the nanosilicas. Thermoplastic polyurethane (TPU) adhesives containing nanosilicas were prepared and characterized by FTIR spectroscopy, differential scanning calorimetry (DSC), plate–plate rheology, dynamic mechanical thermal analysis (DMTA), transmission electron microscopy (TEM) and stress–strain testing. Adhesive strength was obtained from T-peel tests of PVC/polyurethane adhesive joints. The addition of hydrophilic nanosilicas favoured the degree of phase separation between the hard (i.e. isocyanate+chain extender) and soft (i.e. polyol) segments in the TPUs; the higher the silanol content on the surface of silica, the higher the degree of phase separation, and the crystallinity of the polyurethane (due to the soft segments) was also increased. Hydrogen bonds between the ester carbonyl groups in the TPU and the silanol groups on the silica surface were created and more favoured by increasing the silanol content. The tensile strength increased and the elongation at break of the polyurethane decreased by increasing the silanol content of the nanosilica. Addition of nanosilica increased the immediate adhesion of the polyurethane adhesives to PVC, irrespective of the silanol content on the nanosilica. The higher the mechanical and the rheological properties of the polyurethanes containing nanosilicas with different silanol content, the higher the final adhesive strength.

Role of Paper Face Stock Properties in Determining Removal Efficiencies of Pressure-Sensitive Adhesive Films from Recycling Operations

Results are presented from a study on the influence of paper face stock properties on the screening removal of two commercial thermoplastic or hot-melt pressure-sensitive adhesives (PSAs). Significantly lower removal efficiencies were found when the adhesives were attached to commercial face stocks as opposed to untreated paper. These differences were only apparent for temperatures within the plateau region of the thermoplastic formulations and were maximized near their shear adhesion failure temperatures (SAFTs). It is proposed that the collapse of PSA films is inhibited by the presence of residual fiber from the laminate face stock, resulting in higher film stress and increased fragmentation. Detachment of the face stock is likely controlled by its strength and adhesion to PSA surfaces during repulping. Removal efficiencies of laminates involving commercial PSAs and fiberizable face stock treated with a poly(amide epichlorohydrin) wet-strength resin were found to correlate with the paper's loss in tensile strength after water saturation (i.e., tensile loss). Removal efficiencies decreased with increasing face stock size (alkenyl ketene dimer) concentration, which should increase PSA−face stock adhesion in aqueous environments. The sigmoidal function previously presented for modeling removal efficiency−temperature data of thermoplastic formulations was found to provide an accurate fit of data for laminates involving various wet-strength and sized face stocks. However, the T50 or inflection points of these curves were shifted to values lower than the SAFTs for the attached PSAs. T50 values were found to be proportional to both face stock tensile loss and surface energy.

Improvement of adhesion and electrical properties of reworkable thermoplastic conductive adhesives

The adhesion and electrical properties of a PAE-2-based isotropically conductive adhesive (ICA) material were investigated. PAE-2 (thermoplastic polymer)-based ICAs, as well as a commercial epoxy-based ICA, showed dramatic reduction in adhesion to a NiAu surface after the 85°C/85% RH aging test, while the adhesion to a SnPb surface did not change much. To improve the adhesion strength of PAE-2 to a Ni:Au surface after the humidity aging test, coupling agents and epoxy blends were used. The formulation with a higher amount of epoxy showed a higher adhesion strength. The combined use of epoxy blending and coupling agents was effective in increasing the adhesion strength of PAE-2 before aging and also in maintaining adhesion at a 50% level after humidity aging. However, its adhesion strength to NiAu was reduced to less than 50% after 85°C/85% RH aging. PAE-2-based ICAs showed excellent reworkability.

Novel reagents for heat-activated polymer crosslinking

The present invention is directed to nitrile-oxide precursor compounds, and their preparation and use as an irreversible cross-linking agent in polymers having appropriate functionality, i.e., alkenes, alkynes nitriles, and isocyanates. The present invention is also directed to the use of nitrile oxide compound in filled or unfilled applications such as pressure sensitive adhesives, reactive hot melts, polyurethane dispersions, thermosetting adhesives, thermoplastic adhesives or coatings.

Thermoplastic film adhesives based on phenol-functional acrylic copolymers: synthesis, mechanical and adhesion properties

Acrylic polymers possessing varying proportions of pendant phenol groups were synthesized by the free radical copolymerization of N-(4-hydroxyphenyl) maleimide (HPM) with butyl acrylate (BuA) and acrylonitrile (AN) and characterized. These thermoplastics form excellent films and their mechanical and adhesion properties were evaluated as a function of the phenol content. Enhancing the HPM content increased both the tensile strength and the modulus but decreased the elongation. A nominal increase in the phenol content was found to be conducive for improving the adhesion properties of the films. At higher concentrations, the adhesion properties showed a decreasing trend due to the embrittlement caused by the rigid maleimide groups. The adhesion property at 50°C increased linearly with the HPM content due to an increased T g, whereas a reverse trend was observed for the adhesion property measured at-196°C, due to the dominance of the embrittlement effect. The reduced flow characteristics of the high HPM-loaded systems led to a diminished honeycomb flat-wise tensile strength. Enhancing the HPM concentration in the chain promoted the adhesion properties for the vulcanization bonding of nitrile rubber to aluminium. Addition of silica filler marginally improved the lap shear strength (LSS) for the metal-metal system, but was detrimental for rubber-metal bonding; a reverse trend was observed for the carbon-filled system. The diminished performance for metal-metal bonding by carbon could be attributed to the weakening of the interphase, whereas the enhanced rubber-metal bonding could be due to possible reinforcement of the rubber phase by carbon. The fillers generally improved the high temperature adhesion. However, they impaired the flow properties of the resin and, thereby, adversely affected the flat-wise tensile strength in both cases.

Reliability evaluation of adhesive bonded SMT components in industrial applications

This paper compares the efficiency of two thermosetting and one thermoplastic conductive adhesives for surface mount technology (SMT) assemblies. Their reliability is evaluated during accelerated life tests through electrical and mechanical measurements. Contact metallizations are taken into account. Finite element simulations confirm the experimental results, and a parametric study permits us to define some choice criteria for the physical properties of adhesives.

Synthesis and characterization of new thermoplastic polyurethane adhesives containing rosin resin as an internal tackifier

Three thermoplastic polyurethane elastomers (TPUs) were prepared using the prepolymer method. MDI (diphenylmethane-4,4′-diisocyanate) and the polyadipate of 1,4-butanediol (Mw = 2400) were reacted to produce a prepolymer containing unreacted isocyanate groups; chain extenders were different mixtures of 1,4-butanediol and a rosin resin (0-50%). The specific feature of this procedure was the introduction of a rosin resin as an internal tackifier to provide higher immediate adhesion to the TPUs. The new TPUs were characterized using gel permeation chromatography, wideangle X-ray diffraction, differential scanning calorimetry, stress-controlled rheology, and stress-strain measurements. The TPUs were used as raw materials to prepare solvent-based polyurethane adhesives, the adhesion properties of which were obtained from T-peel tests on PVC/polyurethane adhesive/PVC and leather/polyurethane adhesive/PVC joints. The addition of rosin resin as an internal tackifier contributed to the production of two types of hard segments, which affected the properties of the TPUs. Therefore, rosin resin as an internal tackifier produced an increase in the average molecular weight, an increase in the viscosity, and improved the rheological properties. The glass transtition temperature decreased if the TPUs contained rosin resin, due to a greater degree of incompatibility between the hard and soft segments. Consequently, slower kinetics of crystallization was obtained in the TPUs containing rosin resin. Depending on the amount of rosin resin in the TPU, different structures and properties were obtained. On the other hand, the immediate T-peel strength in all joints was improved if the TPU contained rosin resin.

Structure, composition, and adhesion properties of thermoplastic polyurethane adhesives

The composition and hard segment content of 13 commercial thermoplastic polyurethane elastomers (TPUs) were obtained using 1H-nuclear magnetic resonance (1H-NMR). The properties of the TPUs were studied using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), dynamic mechanical thermal analysis (DMTA), and contact angle measurements. Solventbased adhesives were prepared by dissolving the TPUs in 2-butanone. Films of the TPUs were obtained by solvent evaporation, and their properties were studied. Adhesion properties were determined from T-peel tests on solvent-wiped poly(vinyl chloride) (PVC)/polyurethane adhesive joints. The influence of the segmented structure on the properties of the TPUs was assessed. The increase in the hard segment content in TPUs favoured the incompatibility (i.e. reduced phase separation) between hard and soft domains. TPUs with a high hard segment content had a low crystallinity, a low wettability, and a high joint strength. The storage and loss moduli obtained using DMTA decreased as the hard segment content in the TPUs increased. Furthermore, the TPUs prepared using ε-polycaprolactone as the macroglycol had a slower crystallization rate than those prepared using the polyadipate of 1,4-butanediol or the polyadipate of 1,6-hexanediol. The increase in the length of the hydrocarbon chain of the macroglycol improved both the rheological and the thermal properties of the TPUs. Finally, TPUs prepared using MDI as the isocyanate showed a higher crystallinity and a higher degree of crosslinking than those prepared using TDI.

Pros and cons of thermoplastic and thermoset polymer adhesives in microelectronic assembly applications

Reviews the traditional use of thermoset (epoxy) adhesives for various bonding applications and highlights some limitations in today’s microelectronics arena. In particular, concerns for thermal and stress management associated with large area silicon bonded to a wide variety of substrate materials has led to an increasing interest in thermoplastic adhesive technology. Thermoplastics are not always the best solution for every application. This paper sets out to address the “pros and cons” of each polymer technology for different microelectronic applications taking into account some of the key physical properties such as Tg, TCE and modulus. In addition, practical issues such as handling, storage and processing are considered in detail.

Fracture behavior of centrifugally cast multilayer alumina/alumina composites

Increased fracture toughness in brittle materials can be achieved by incorporating weak (porous) interfaces (1,2). These improvements have been attributed to energy absorption through crack deflection and frictional bridging along the weaker interfaces (1). While improved fracture properties are attractive for thermal and structure ceramic components, difficulties in producing a specific degree of interfacial porosity for a wide range of ceramics have limited application of this approach. Studies investigating the influence of weak interlayers in brittle composites (1–10) have examined systems ranging from tape cast multilayered composites of alternating fully dense and porous interlayers (7) to brittle plates bonded with weaker thermoplastic adhesives (8–9). During flexural loading, cracks typically deflect along the weaker interfaces, giving rise to a step-wise drop in the loaddisplacement behavior rather than a catastrophic failure typical of non-deflecting brittle materials. Residual stress distributions within layered ceramic composites can also produce similar fracture behavior, where alternating layers of tensile and compressive stress states due to thermal expansion mismatch can promote crack bifurcation (10). Advances in centrifugal consolidation of colloidal suspensions (11–14) have made the technique an attractive alternative for producing layered composites. Tailored microstructures can be achieved by incorporating suspensions that are either flocculated (11) to inhibit particle segregation or dispersed (12–14) to allow segregation due to differences in particle size and density. This paper summarizes the initial results on the fracture behavior of alumina and alumina/agglomerated alumina multilayered composites produced by centrifugal consolidation.