Probe Tack Test Research Articles

Describing the sticking phenomenon of aminoplastic resins: introduction of a new test method

Changes in formaldehyde emission guidelines led to changes in the resin formulation. These changes include reduced formaldehyde to urea molar ratio which is followed by a change in reactivity of aminoplastic resins. This resulted in an increased occurrence of an undesired type of tack, herein called “sticking”, which causes addition of resinated wood particles onto machine parts in industrial particle board production. Whereas tack measurements for pressure-sensitive adhesives, such as the probe tack test and rolling ball test exist, mature cold tack tests for liquid formaldehyde-based resins are rare. Practical tests such as “finger-dipping” show limitations in terms of reliability and reproducibility. To measure the sticking behaviour, a rheometer test method is enhanced and modified to quantify influencing factors. The test set-up on a Bohlin CVO rheometer consists of a rotating cylinder which runs over a wood surface coated with resin. The established “glue line” dries out and partially cures, while the torque increases up to a maximum point. This change, caused by “sticking”, is accurately measured and recorded. Influences of different surface temperatures can be observed: the higher the temperature, the faster the drying. In addition, resin age significantly contributed to the sticking effect. Although changes in viscosity are only minor, the torque is highly influenced by resin age, both in measuring time and maximum. Besides temperature and resin age, this method might be useful to describe and investigate further factors influencing sticking issues occurring in the board production process, such as humidity, resin composition, material and surface roughness.

Contact time dependence of tack for crosslinked polyacrylic pressure-sensitive adhesives with two different molecular structures

The influence of molecular structure of pressure-sensitive adhesive on the wetting to adherend surface was investigated. For this purpose, crosslinked poly(n-butyl acrylate-acrylic acid) (A) and poly(2-ethylhexyl acrylate-acrylic acid) random copolymer (B) with an acrylic acid content of 5wt% and various crosslinking degrees were used. Tack was measured by a probe tack test with a debonding rate of 10mm/s and various contact times ranging from 3 to 30,000s. The probe was made of stainless steel (SS). The tack increased with contact time and the degree of tack rising was B>A. The tack was A>B below the contact time of about 100s, whereas it was B>A above 100s. The order of molecular mobility was B>A from pulse nuclear magnetic resonance analysis, so the wettability to adherend surface became B>A. This is the reason why tack was B>A above 100s. The interfacial tension at a water/toluene interface was decreased more effectively by A than B. This result indicates that the acrylic acid unit in A forms the interaction with the high energy surface such as SS in short contact time. The 2-ethylhexyl group is bulker than the n-butyl group. The bulky group promotes steric hindrance for the interaction of the acrylic acid unit. This seems to be the reason why tack was A>B below 100s.

Temperature Dependence of Tack for Polyacrylic Block Copolymer/Tackifier Blend

The effect of polymer and tackifier compatibility on tack of pressure-sensitive adhesive (PSA) tape was investigated. Poly(methyl methacrylate)-block-poly(butyl acrylate)-block-poly(methyl methacrylate) triblock copolymer was used as the base polymer and three types of tackifiers, an aliphatic petroleum resin (A), a special rosin ester resin (B), and a rosin phenolic resin (C), were mixed at 10–30 wt.%. Compatibility with the base polymer was greater in the order of C > B > A. Tackifier agglomerates of approximately 10 nm were observed by transmission electron microscopy for the PSA with tackifier C. Similar agglomerates were observed for tackifier B, but the size increased with content. The size for tackifier A was several tens of micrometers. Dynamic mechanical analysis indicated that the glass transition temperature of the poly(butyl acrylate) phase increased upon addition of tackifiers B and C. This trend was more significant for tackifier C. It was not observed for tackifier A. The temperature dependence of tack was measured using a probe tack test. Tack was greater in the order of C = B > A. Tack at higher temperatures was superior for greater tackifier C contents. Tackifier and base polymer compatibility has a strong effect on tack and its temperature dependence.

Influences of debonding rate and temperature on tack properties and peel behavior of polyacrylic block copolymer/tackifier system

The influences of debonding rate and temperature on the peel behavior of polyacrylic block copolymer/tackifier system were investigated. Poly(methyl methacrylate)-block-poly(n-butyl acrylate)-block-poly(methyl methacrylate) triblock copolymer (MAM) with hard block contents of 23 (MAM-23) and 16 wt.% (MAM-16) and a 1/1 blend with a diblock copolymer (MA) consisting of the same components (MAM-23/MA, total hard block content of 15 wt.%) were used as the base polymer. A special rosin ester was used as a tackifier at various contents in the block copolymer/tackifier system. The peeling process at the probe/adhesive interface during probe tack testing was observed using a high-speed microscope at 23 °C with debonding rate of 10 mm/s. Three different peeling mechanisms were observed. Type A, where peeling progressed linearly from the edge to the center of the probe without cavitation (MAM-23). Type B, where peeling progressed linearly from the edge to the center of the probe with cavitation (MAM-16). Type C, where cavitation occurred over the entire adhesive layer, and peeling initiation was delayed (MAM-23/MA). The peel behavior of MAM-23 changed from Type A to Type B with a decrease of the debonding rate (1 mm/s) or increase of the temperature (40 °C). In contrast, there was no change for MAM-16 and MAM-23/MA. Cavity formation in an adhesive layer restrains peeling; therefore, it is desirable for improvement of the adhesion strength. The tack properties increased with the tackifier content, and the formation of cavitation was less than that for the systems without the tackifier.

Modelling the interfacial peeling of pressure-sensitive adhesives

Peel tests were performed using specimens which consisted of a polyester backing membrane supporting an acrylic pressure-sensitive adhesive adhered to a polyethylene substrate. Interfacial separation of the PSA from the polyethylene substrate was observed. Finite element (FE) peeling simulations were conducted which modelled the backing-membrane as an elasto-plastic power-law material, the adhesive as a viscoelastic material and the interfacial properties with a cohesive zone model (CZM). The material properties of the backing membrane and the pressure-sensitive adhesive were measured from tensile and stress relaxation experiments. The cohesive zone parameters were calculated analytically from the peel test data, as well as being measured directly from independent poker-chip probe tack tests. The numerical results from the CZM/FE simulations and the experimental values of the peel forces as a function of the peel angle were found to be in good agreement.

Preparation and adhesion performance of transparent acrylic pressure sensitive adhesives for touch screen panel

Transparent acrylic pressure sensitive adhesives (PSAs) comprised semi-interpenetrated structured polymer networks were prepared with different co-monomer compositions. Emphasis was placed on the effect of functional groups in the co-monomer including morpholine and tetrahydrofurane moieties in the typical acrylic PSA formulation. The synthesized acrylic PSA syrups were characterized and the optical properties of the acrylic PSA film were also examined by ultraviolet–visible spectroscopy, haze meter, and prism coupler. Acrylic PSAs exhibit high transparency in the visible wavelength region. Adhesion performance was measured by the peel strength, cohesion strength, and probe tack tests. With increasing 4-acryloyl morpholine monomer concentration in the acrylic PSAs, the peel strength, cohesion strength, and probe tack increased.

Influence of crosslinking and peeling rate on tack properties of polyacrylic pressure-sensitive adhesives

Tack properties and peeling behavior of crosslinked polyacrylic pressure-sensitive adhesives were investigated. The model adhesive was a crosslinked poly(n-butyl acrylate-acrylic acid) random copolymer with an acrylic acid content of 5 mol% with various crosslinking degrees. Tack was measured using a probe tack test with probe rates of 1 and 10 mm/s and various contact time. The tack increased with contact time. The degree of tack rising with contact time decreased with an increase in crosslinking degree for 10 mm/s, while the tendency was opposite for 1 mm/s. The temperature dependency of tack was measured with a contact time of 30 s. The tack peak shifted to higher temperatures with an increase in crosslinking degree and probe rate. Peeling behavior was observed using high-speed microscopy. The peeling behavior changed from A to C with the decrease of peeling rate and crosslinking degree. A: Cavitation and peeling progressed simultaneously at maximum stress at 10 mm/s independent on the crosslinking degree. B: Cavitation occurred at the edge of the probe at low stress and spread to the center of the probe at maximum stress at 1 mm/s and high crosslinking degree, then peeled out. C: After B, fibrillation occurred at 1 mm/s with low crosslinking degree. The change of peeling behavior was caused by the following: the interfacial adhesion increased, while the cohesive strength decreased as crosslinking degree and probe rate decreased.

Plasticization and antiplasticization of an acrylic pressure sensitive adhesive by ibuprofen and their effect on the adhesion properties

In transdermal patches, an unpredictable alteration of the mechanical behavior of the pressure sensitive adhesive (PSA) can occur if a drug is added. In the present study, the suitability of Dynamic Mechanical Analysis (DMA)/Dynamic Mechanical Thermal Analysis (DMTA) as methodologies to detect the change in adhesion properties caused by the addition of an API was examined. With DMA/DMTA, time- and temperature-dependent viscoelastic properties were determined. Tack and shear adhesion of blends of the acrylic adhesive DuroTak® 87-4287 and ibuprofen at increasing concentrations were investigated. Interestingly, the probe tack test showed highest values at 1% ibuprofen concentration in the PSA and decreasing values with increasing ibuprofen concentrations. The shear adhesion of the PSA was decreased at all investigated ibuprofen concentrations. With DMA/DMTA, it could be demonstrated that antiplasticization and plasticization are responsible for the change in tack. The main reason for the decrease in shear adhesion is a shift of the Tg to lower temperatures, while antiplasticization only has a marginal effect. The term “antiplasticizing space” was introduced because antiplasticization depends on time, temperature, stress, strain, and API concentration. In general, this antiplasticizing space can have an impact on processing, stability, and in vivo behavior of API/polymer blends in drug formulations.

Tailoring the adhesion properties of polyacrylamide-based hydrogels. Application for skin contact

In the present study, we investigated the adhesive performances of polyacrylamide-based hydrogels intended to be used as dermatological patches. Accordingly, we have prepared conventional copolymer poly(acrylamide-co-hydroxyethyl methacrylate) hydrogels and nanocomposite copolymer poly(acrylamide-co-hydroxyethyl methacrylate) hydrogels filled with poly(butyl acrylate) nanoparticles. We evaluated their adhesive properties when they were applied to different substrates (equivalent human skin, stainless steel) using a probe tack test. The adhesion energy was found to be related to the chemical composition and the rheological properties of the hydrogels which were also measured.

Effect of side chain on wettability and adhesion performance of acrylic pressure-sensitive adhesives on thin silicon wafer

Acrylic pressure-sensitive adhesives (PSAs) need to show proper adhesion and improved wettability on the silicon wafer as the wafer becomes thinner. The acrylic copolymers were synthesized by solution radical polymerization of 2-ethylhexyl acrylate, ethyl acrylate, and acrylic acid with AIBN as an initiator. Adhesion performance and wettability of acrylic PSAs were studied depending on the content of lauryl side chains and the degree of crosslinking. The introduction of lauryl side chain was characterized by Fourier transform infrared spectroscopy. The adhesion performance of acrylic PSAs having lauryl side chain was investigated using contact angle, wettability, probe tack, peel strength, and cohesiveness tests. The wettability of acrylic PSAs was improved significantly with increasing the content of lauryl side chain.

Large-Area Patterning of the Tackiness of a Nanocomposite Adhesive by Sintering of Nanoparticles under IR Radiation

We present a simple technique to switch off the tack adhesion in selected areas of a colloidal nanocomposite adhesive. It is made from a blend of soft colloidal polymer particles and hard copolymer nanoparticles. In regions that are exposed to IR radiation, the nanoparticles sinter together to form a percolating skeleton, which hardens and stiffens the adhesive. The tack adhesion is lost locally. Masks can be made from silicone-coated disks, such as coins. Under the masks, adhesive island regions are defined with the surrounding regions being a nontacky coating. When optimizing the nanocomposite's adhesive properties, the addition of the hard nanoparticles raises the elastic modulus of the adhesive significantly, but adhesion is not lost because the yield point remains relatively low. During probe-tack testing, the soft polymer phases yield and enable fibrillation. After heating under IR radiation, the storage modulus increases by a factor of 5, and the yield point increases nearly by a factor of 6, such that yielding and fibrillation do not occur in the probe-tack testing. Hence, the adhesion is lost. Loading and unloading experiments indicate that a rigid skeleton is created when the nanoparticles sinter together, and it fractures under moderate strains. This patterning method is relatively simple and fast to execute. It is widely applicable to other blends of thermoplastic hard nanoparticles and larger soft particles.

Adhesion properties of polyurethane pressure-sensitive adhesive

In this study, the adhesion properties of polyurethane (PUR) pressure-sensitive adhesive (PSA) were investigated. The PUR-PSA was prepared by the cross-linking reaction of a urethane polymer consisting of toluene-2,4-diisocyanate and poly(propylene glycol) components using polyisocyanate as a cross-linking agent. The peel strength increased with the cross-linking agent content and exhibited cohesive failure until the maximum value, after which it decreased with interfacial failure. The PUR-PSA exhibited frequency dependence of the storage modulus obtained from dynamic viscoelastic measurements, but did not show dependence of the tack on the rolling rate measured using a rolling cylinder tack test under the experimental conditions used, which is quite different from the acrylic block copolymer/tackifier system. The PUR-PSA showed strong contact time dependence of tack measured by a probe tack test. The tendency was significantly larger than for the acrylic block copolymer/tackifier system. Therefore, the storage modulus increased, whereas the interfacial adhesion seems to be decreased with increase in the rolling rate for this PUR-PSA system. It was estimated that the influence of rolling rate on the interfacial adhesion and the storage modulus was offset, and, as a result, the rolling cylinder tack did not exhibit rate dependency.

Crack propagation at the interface between soft adhesives and model surfaces studied with a sticky wedge test

The motion of the triple line during the debonding of a soft viscoelastic adhesive from a rigid polymer surface has been investigated quantitatively. In order to make the debonding geometry simpler than the probe tack test, a new technique, called the sticky wedge test, has been developed where the probe is constituted by a horizontal cylinder instead of a flat punch. The crack propagates in the elongated contact area between the cylinder and the flat surface, thereby, allowing us to measure optically in situ the crack-tip velocity and the receding contact angle of the debonding adhesive. Two model pressure sensitive adhesives (PSA) based on poly(n-butyl acrylate-co-acrylic acid) with different molecular weights and branching levels and four polymer substrates (rubbery or glassy at room temperature) were used. Due to the soft and incompressible nature of the adhesive, the strain energy release rate for this test geometry has been estimated by the equations for the pure shear test geometry. The results show three main new insights: first, despite significant approximations, this novel approach holds promise to characterize more quantitatively the interfacial crack propagation between soft viscoelastic solids and hard surfaces and the relationship between the applied energy release rate and the crack-tip velocity v has been reliably established for eight combinations of the model viscoelastic adhesives and surfaces. Second, at equivalent values of the thermodynamic work of adhesion, the adhesion energy of both the adhesives against the rubbery surface was much lower than that against the glassy polymers. Third, surprisingly, the measured receding contact angle of debonding was close to 90° for all adhesive/surface combinations used.

OS1703 粘着剤のはく離変形挙動の観察によるタック強度評価

A tack is important physical property for pressure-sensitive adhesive that shows instantaneous adhesiveness. Recently, thinner adhesive has been developed and often applied in industry while the occurrence and the mechanism of the tack have not been clarified yet. It is known that as adhesive is thinner than 5μm, the tack becomes much weaker. To improve and develop the thin but strong adhesive it is necessary to observe the peeling phenomena of the adhesive. In this study, the aim is to investigate the effect of the adhesive's thickness on peeling behaviors and tack strengths with probe tack tests. We confirmed that as adhesive is thicker, peel force becomes larger but the rate of increase of peel force becomes lower and the amount of adhesive deformation becomes larger. We observed the displacement of fine particles mixed in adhesive. As result, as the particles reaches deeply from the surface of the adhesive to its inside, the displacement of the particles becomes smaller and the movement of the particles isn't seen at 25 μm from the surface.

Tack energy and switchable adhesion of liquid crystal elastomers

The mechanical properties of liquid crystal elastomers (LCEs) make them suitable candidates for pressure-sensitive adhesives (PSAs). Using the nematic dumbbell constitutive model, and the block model of PSAs, we study their tack energy and the debonding process as could be measured experimentally in the probe-tack test. To investigate their performance as switchable PSAs we compare the tack energy for the director aligned parallel, and perpendicular to the substrate normal, and for the isotropic state. We find that the tack energy is larger in the parallel alignment than the isotropic case by over a factor of two. The tack energy for the perpendicular alignment can be 50% less than the isotropic case. We propose a mechanism for reversibly switchable adhesion based on the reversibility of the isotropic to nematic transition. Finally we consider the influence of several material parameters that could be used to tune the stress-strain response.

Influence of diblock addition on tack in a polyacrylic triblock copolymer/tackifier system measured using a probe tack test

AbstractThe influence of diblock copolymer addition on the tack properties of a polyacrylic triblock copolymer/tackifier system was investigated. For this purpose, poly(methyl methacrylate)‐block‐poly(n‐butyl acrylate)‐block‐poly(methyl methacrylate) triblock copolymer (MAM) and a 1/1 blend with a diblock copolymer consisting of the same components (MA) were used as base polymers, and a tackifier was added in amounts ranging from 10 to 30 wt %. The temperature dependence of tack was measured by a probe tack test. The tack of MAM/MA at room temperature was significantly higher than that of MAM, and the improvement of MAM/MA upon the addition of the tackifier was higher than that of MAM. The peeling process at the probe/adhesive interface during the probe tack test was observed using a high‐speed microscope. It was found that for MAM/MA, cavitation was caused in the entire adhesive layer, and peeling initiation was delayed by the absorption of strain energy due to deformation of the adhesive layer. In contrast, for MAM, peeling progressed linearly from the edge to the center of the probe. The greater flexibility of the soft block chain in the diblock copolymer resulted in improved interfacial adhesion. 1H pulse nuclear magnetic resonance analysis showed that the addition of the tackifier improved the cohesive strength of the adhesive. Adhesion strength is affected by two factors: the development of interfacial adhesion and cohesive strength. In the MAM/MA/tackifier system, the presence of MA and the tackifier improved the interfacial adhesion and cohesive strength, respectively. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Variational scheme towards an optimal lifting drive in fluid adhesion

One way of determining the adhesive strength of liquids is provided by a probe-tack test, which measures the force or energy required to pull apart two parallel flat plates separated by a thin fluid film. The vast majority of the existing theoretical and experimental works in fluid adhesion use very viscous fluids, and consider a linear drive L(t)∼Vt with constant lifting plate velocity V. This implies a given energy cost and large lifting force magnitude. One challenging question in this field pertains to what would be the optimal time-dependent drive Lopt(t) for which the adhesion energy would be minimized. We use a variational scheme to systematically search for such Lopt(t). By employing an optimal lifting drive, in addition to saving energy, we verify a significant decrease in the adhesion force peak. The effectiveness of the proposed lifting procedure is checked for both Newtonian and power-law fluids.

Structure and Macroscopic Tackiness of Ultrathin Pressure Sensitive Adhesive Films

Ultrathin layers of the statistical copolymer P(nBA-stat-MA) with a majority of n-butyl acrylate (nBA) and a minority of methyl acrylate (MA) are characterized with respect to the film morphology and the mechanical response in a probe tack test. The probed copolymer can be regarded as a model system of a pressure sensitive adhesive (PSA). The films are prepared by spin-coating which enables an easy thickness control via the polymer concentration of the solution. The film thickness is determined with x-ray reflectivity (XRR) and white light interferometry (WLI). Grazing incidence small angle x-ray scattering (GISAXS) provides detailed and statistically significant information about the film morphology. Two types of lateral structures are identified and no strong correlation of these structures with the PSA film thickness is observed. In contrast, prominent parameters of the probe tack test, such as the stress maximum and the tack energy, exhibit an exponential dependence on the film thickness.

Optical properties and UV-curing behaviors of optically clear semi-interpenetrated structured acrylic pressure sensitive adhesives

Acrylic pressure-sensitive adhesives (PSAs) with different side-chain lengths in the co-monomer were synthesized. This study employed semi-interpenetrated structured polymer networks using UV-curing with a hexafunctional monomer, dipentaerythritol hexacrylate (DPHA). The optical properties of the acrylic PSAs were examined by UV-visible spectroscopy and a prism coupler. ARES was used to characterize the viscoelastic properties of the acrylic PSAs. Adhesion performance was conducted by the peel strength and probe tack tests. Also UV-curing behavior of the acrylic PSAs was investigated by FTIR.

Effect of fluid inertia on probe-tack adhesion

One way of determining the adhesive strength of liquids is provided by a probe-tack test, which involves measuring the force required to pull apart two parallel flat plates separated by a thin fluid film. The large majority of existing theoretical and experimental work on probe-tack adhesion use very viscous fluids and considers relatively low lifting plate velocities, so that effects due to fluid inertia can be neglected. However, the employment of low-viscosity fluids and the increase in operating speeds of modern lifting apparatus can modify this scenario. By dealing with a proper gap averaging of the Navier-Stokes equation, we obtain a modified Darcy-law-like description of the problem and derive an adhesion force which incorporates the effects of fluid inertia, fluid viscosity (for Newtonian and power law fluids), and the contribution of the compliance and inertia of the probe-tack apparatus. Our results indicate that fluid inertia may have a significant influence on the adhesion force profiles, inducing a considerable increase in the force peaks and producing oscillations in the force-displacement curves as the plate-plate separation is increased. The combined role of inertial and non-Newtonian fluid behaviors on the adhesion force response is also investigated.