Miscibility and shear creep resistance of acrylic pressure-sensitive adhesives: Acrylic copolymer and tackifier resin systems

The miscibility between an acrylic copolymer and a tackifier resin was investigated in terms of phase diagrams, glass transition temperatures (T_g's), and dynamic mechanical properties of blends. Shear creep resistance (holding power, t_b) of the blends was measured as a function of both temperature and stress (σ₀) in order to obtain the master curves. It was found that the shear creep resistance of the pressure-sensitive adhesives (PSAs) was closely related to the miscibility between the components and viscoelastic properties of the blends. The master curve of the miscible blends shifts toward a longer time scale as the amount of tackifier resin in the blend is increased as a result of the modification of the bulk properties, and their behavior greatly depends on the glass transition temperature (T_g) and storage modulus (G′) of the blends. However, the master curve of immiscible blends where two phases exist in the system does not shift greatly toward a longer time scale, because T_g and the storage modulus of the blend do not change greatly. © 1995 John Wiley & Sons, Inc.     

Miscibility and pressure‐sensitive adhesive performances of acrylic copolymer and hydrogenated rosin systems

Relationship between the miscibility of pressure‐sensitive adhesives (PSAs) acrylic copolymer/hydrogenated rosin systems and their performance (180° peel strength, probe tack, and holding power), which was measured over a wide range of time and temperature, were investigated. The miscible range of the blend system tended to become smaller as the molecular weight of the tackifier increased. In the case of miscible blend systems, the viscoelastic properties (such as the storage modulus and the loss modulus) shifted toward higher temperature or toward lower frequency and, at the same time, the pressure‐sensitive adhesive performance shifted toward the lower rate side as the T_g of the blend increased. In the case of acrylic copolymer/hydrogenated rosin acid systems, a somewhat unusual trend was observed in the relationship among the phase diagram, T_g, and the pressure‐sensitive adhesive performance. T_g of the blend was higher than that expected from T_gs of the pure components. This trend can be due to the presence of free carboxyl group in the tackifier resin. However, the phase diagram depended on the molecular weight of the tackifier. The pressure‐sensitive adhesive performance depended on the viscoelastic properties of the bulk phase. A few systems where a single T_g could be measured, despite the fact that two phases were observed microscopically, were found. The curve of the probe tack of this system shifted toward a lower rate side as the T_g increases. However, both the curve of the peel strength and the holding power of such system did not shift along the rate axis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 651–663, 1999     

Phase structure and adhesion properties of acrylic block copolymer/tackifier blends as nanocomposite-like pressure-sensitive adhesives

In a blend of acrylic block copolymer consisting of poly(methyl methacrylate) and poly(n-butyl acrylate) blocks and a special rosin ester resin (RE) tackifier as a model pressure-sensitive adhesive (PSA), RE exists in two states: as nm-sized agglomerated particles (A) and as dissolved molecules (B). The effect of A and B ratio on the PSA properties were investigated using REs with four different weight-average molecular weights (M_ws) in the range from 680 to 1700. The formation of A increased with increasing of M_w because of lowering of miscibility. The glass transition temperature increased with increasing of M_w. The tack at lower temperatures and the fracture energy were improved by B, whereas the tack at higher temperatures was improved by A. A and B enhanced the cohesive strength and the wettability of PSA, respectively. However, the improvement of cohesive strength by the RE with highest M_w was remarkably low. This seems to be caused by the larger size of agglomerated particles. ¹H pulse nuclear magnetic resonance analysis was useful for estimating the degree of A formation. The model PSA investigated in this study was nanocomposite-like.     

Mechanistic studies in tackified acrylic emulsion pressure sensitive adhesives

Twenty‐three wt % aqueous tackifier dispersion based on glycerol ester abietic acid (T_g = 64°C, M_w = 940) was added to emulsion polymer 50/32/15/3 poly(2‐ethyl hexyl acrylate‐co‐vinyl acetate‐co‐dioctyl maleate‐co‐acrylic acid) pressure sensitive adhesive (PSA). From these latices, 25 μm thick films were cast. The films were dried at 25°C for 24 h or at 121°C for 5 min. Dynamic mechanical analysis (DMA) of the films included measuring elastic modulus (G′) and damping factor (tan δ). Under the above drying conditions, the films did not produce significant differences in their DMA and PSA properties as measured by loop tack, peel, and shear holding power. DMA of the tackified acrylic film showed thermodynamic miscibility between the tackifier and polymer regardless of the drying conditions. Microgels formed during emulsion polymerization of the acrylic PSA brought inherent weakness to the tackified film properties. In the neat acrylic PSA film, these discrete networks entangled with the uncrosslinked chains while in the tackified film, these networks could not form entanglements due to the increased molecular weight between entanglements for the uncrosslinked chains. This lack of network entanglements caused shear holding power of the tackified acrylic PSA film to be 4× lower than that of the neat acrylic PSA film. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1965–1976, 2000     

Effects of miscibility on probe tack of natural-rubber-based pressure-sensitive adhesives

Natural rubber (NR) was blended in various ratios with 29 kinds of tackifier resins, which were prepared from rosin, terpenes, and petroleum. Miscibilities of all the blend systems were illustrated as phase diagrams in our previous articles. From these blend systems, we selected 7 systems having typical phase diagrams [completely miscible, completely immiscible, and lower critical solution temperature (LCST) types] and carried out measurements of probe tack. Probe tack values were measured at various rates of separation and temperatures to obtain master curves. In the case of miscible pressure sensitive adhesives (PSAs) at the condition of measurement, the peak position in the master curve of probe tack shifted to the lower velocity (higher temperature) as the tackifier content increased. On the contrary, immiscible PSAs had much smaller probe tack values than miscible ones and did not give manifest shift of peaks. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 771–776, 1998     

Miscibility and tack of blends of poly (vinylpyrrolidone)/acrylic pressure-sensitive adhesive

In this study, miscibility and tack of blends of poly (vinylpyrrolidone) (PVP)/acrylic pressure-sensitive adhesive (PSA) were evaluated. For this purpose, appropriate amounts of PVP (2–30% w/w) were added to an acrylic PSA to obtain visually homogeneous solution. The resulting solution was evenly applied on a polyethylene terephthalate (PET) film with final specific thicknesses of 10, 40, and 70 μm by using a film applicator and miscibility as well as tack values were evaluated. With the addition of 2% (w/w) PVP the tack value decreased and increased in 5% (w/w) PVP and then continuously decreased up to 30%(w/w). It was found that the tack value was related to miscibility as well as to viscosity and the free functional group such as hydroxyl group of the blend. By the morphological analysis performed through scanning electron microscopy (SEM) and also by the study of thermal analysis using the differential scanning calorimetry (DSC) behavior of blends, it was found that the two distinct phases constituted after adding 5% (w/w) of PVP. This resulted in the acrylic PSA forming the continuous phase, and by increasing the concentration of PVP a dispersed phase was developed. The dispersed phase has a higher viscosity than the continuous phase and therefore cannot wet the adherent and hence result in lowering the tack values.     

Miscibility and PSA Performance of Acrylic Copolymer and Tackifier Resin Systems

The influence of miscibility of an acrylic PSA and several tackifier resin systems upon PSA performance was investigated. When the acrylic copolymer and the resins were blended in various proportions, three types of mixing state were found: miscible system, partially miscible system and immiscible system. In the case of miscible systems, PSA performance (tack, peel strength and shear resistance) depended upon the viscoelastic properties of the PSA. In the case of completely immiscible systems, the above PSA performance depended primarily upon the viscoelastic properties of a continuous matrix phase, and the separated resin phase acted as a kind of filler. In the case of partially miscible systems, the PSA performance changed discontinuously at the resin concentration where phase separation occurred. It suggests that the phase structure of a PSA greatly influences the PSA's performance.     

Miscibility and PSA Performance of Acrylic Copolymer and Tackifier Resin Systems

The influence of miscibility of an acrylic PSA and several tackifier resin systems upon PSA performance was investigated. When the acrylic copolymer and the resins were blended in various proportions, three types of mixing state were found: miscible system, partially miscible system and immiscible system. In the case of miscible systems, PSA performance (tack, peel strength and shear resistance) depended upon the viscoelastic properties of the PSA. In the case of completely immiscible systems, the above PSA performance depended primarily upon the viscoelastic properties of a continuous matrix phase, and the separated resin phase acted as a kind of filler. In the case of partially miscible systems, the PSA performance changed discontinuously at the resin concentration where phase separation occurred. It suggests that the phase structure of a PSA greatly influences the PSA's performance.     

Viscoelastic and adhesion properties of EVA/tackifier/wax ternary blend systems as hot-melt adhesives

Two types of wax were added to a ethylene vinyl acetate (EVA) copolymer/aromatic hydrocarbon resin (tackifier) blend in the molten state and the miscibility, viscoelastic and adhesion properties of ternary blends as hot-melt adhesives (HMAs) were investigated. Miscibility and viscoelastic properties were studied using differential scanning calorimetry (DSC), Brookfield viscometry and dynamic mechanical thermal analysis (DMTA), and their adhesion strength was determined in terms of single lap shear strength. DSC thermograms of both types of waxes showed their melting peaks in a similar region to that of EVA/tackfier blend. It was difficult to evaluate the miscibility of ternary blends using DSC because the melting peaks of the waxes overlapped with those of the EVA/tackifier blend, although the glass transition temperature (T _g) of the ternary blend systems slightly increased with increasing wax concentration. However, their storage modulus (E′) increased slightly and loss tangent (tan δ) showed different peaks when two types of wax were added to the EVA/tackifier blend. Therefore, the miscibility of EVA/tackifier blend altered with addition of waxes. In addition, their melt viscosity decreased with increasing wax concentration. Furthermore, the adhesion strength of the ternary blends decreased with increasing wax concentration, despite the increment of storage modulus. These results suggested that the ternary blends of EVA/tackifier/wax were heterogeneous.     

PSA performances and viscoelastic properties of SIS‐based PSA blends with H‐DCPD tackifiers

Hotmelt pressure sensitive adhesives (PSAs) usually contain styrenic block copolymers like styrene–isoprene–styrene (SIS), SBS, SEBS, tackifier, oil, and additives. These block copolymers individually reveal no tack. Therefore, a tackifier is a low molecular weight material with high glass transition temperature (T_g), and imparts the tacky property to PSA. The SIS block copolymer with different diblocks was blended with hydrogenated dicyclopentadiene (H‐DCPD tackifier), which has three kinds of T_g. PSA performance was evaluated by probe tack, peel strength, and shear adhesion failure temperature. PSA is a viscoelastic material, so that its performance is significantly related to the viscoelastic properties of PSAs. We tested the viscoelastic properties by dynamic mechanical analysis and the thermal properties by differential scanning calorimeter to investigate the relation between viscoelastic properties and PSA performance. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 2839–2846, 2006     

Tack and viscoelastic properties of an acrylic block copolymer/tackifier system

The role of tackifier in a pressure sensitive adhesive tape was investigated. For this purpose, a model pressure sensitive adhesive was prepared using an acrylic block copolymer consisting of poly(methyl methacrylate) and poly(butyl acrylate) as base polymer and a tackifier. The poly(butyl acrylate) oligomer was also used as a diluent to compare the effect on the adhesion properties. Tack was measured using a rolling tack tester in wide temperature and rolling rate ranges, and the master curve was made in accordance with the time–temperature superposition law. The tack increased and the failure mode varied from cohesive failure to interfacial failure with an increase in the rolling rate. The tack was higher in the tackifier added system than in the oligomer added system. From a dynamic mechanical analysis, the modulus at high temperature decreased by the addition of both tackifier and oligomer, however, the glass transition temperature of poly(butyl acrylate) and the modulus at low temperature increased only by the addition of tackifier. The dynamic viscoelastic properties were measured in wide temperature and frequency ranges, and the master curve was also made. The viscoelastic properties varied in the order of viscosity, rubbery and glassy with an increase in the deformation rate. It was clarified that the tack value and the failure mode were strongly dependent upon the viscoelastic properties of adhesive. Both tackifier and oligomer improves the mobility of base polymer, whereas, only tackifier increases the cohesive strength of base polymer.     

Pressure Sensitive Adhesive Properties and Miscibility in Blends of Poly(vinyl ethylene-co-1,4-butadiene) with Hydrogenated Terpene Resin

The pressure sensitive adhesive (PSA) properties of two samples of poly(vinyl ethylene-co-1,4-butadiene) (V-BR) (vinyl content: 47.4 and 60 wt%) blended with hydrogenated terpene resin (CLEARON P125) were measured on blend compositions having CLEARON P125 contents (by weight) of 10%, 30% and 50%. The maximum values of 180° peel adhesion, rolling ball tack and probe tack were observed with a V-BR/CLEARON P125 70/30 blend, whereas the maximum values of holding power were obtained with a 50/50 V-BR/CLEARON P125 blend. In these blends, the miscibility between V-BR and CLEARON P125 was confirmed by means of SEM, DSC and light scattering. The influences of surface tension and dynamic mechanical properties on PSA properties were investigated. The surface tension values were essentially the same in all the V-BR/CLEARON P125 blends. Minimum values of storage modulus G′ and loss modulus G″ at room temperature in V-BR/CLEARON P125 blends were obtained with a 70/30 blend. Thus, it is believed that in V-BR/CLEARON P125 blends, 180° peel adhesion and tack are related to the dynamic mechanical properties.     

Miscibility and Probe Tack of Acrylic Pressure Sensitive Adhesives—Acrylic Copolymer/Tackifier Resin Systems

Miscibility between acrylic copolymers and tackifier resins are investigated in terms of phase diagrams, and the probe tack of the blends are measured as a function of both temperature and rate of separation in order to obtain the master curves. It is found that the probe tack of the pressure sensitive adhesives are closely related to the miscibility between the components. The master curves of the miscible blends shift along the X(rate)-axis according to the change of T_g of the bulk materials with a gradual variation of the peak heights. However, those of the immiscible blends will not shift along the X(rate)-axis, but the magnitude will decrease with increase of a dispersed phase.     

Fundamental Understanding in Rolling Ball Tack of Tackified Block Copolymer Adhesives

In the pressure sensitive adhesive (PSA) industry, rolling ball tack is a very common tack test, which is simple, inexpensive and easy to operate. This work attempts to search for key parameter(s), which will affect the rolling ball tack of a PSA based on a blend of styrene-isoprene-styrene triblock copolymer(SIS) and hydrocarbon tackifier(s). We want to better understand whether this particular PSA performance is controlled by the surface or bulk properties of the adhesive.

Firstly, to test the contribution from the surface properties, we employ a model system of SIS/aliphatic tackifier in 1/1 wt. ratio as the control. Part of the tackifier in this PSA is then replaced by various amounts of low molecular weight diluents with different surface tensions. The idea is to vary the surface properties of the PSA because these low surface tension and low molecular weight diluents tend to migrate to the PSA surface. It is observed that the incorporation of a lower surface tension and a lower molecular weight diluent in the PSA tends to produce a larger increase in rolling ball tack compared with the unmodified PSA. On the other hand, the incorporation of a higher surface tension and a more compatible diluent tends to produce a larger increase in loop, peel and quick stick. Each diluent lowers the shear adhesion failure temperature (SAFT) of the diluent-modified PSA. These observations are explained in terms of tackifier molecular weight, and surface tension and compatibility of the various components (polyisoprene, tackifier, diluent and oil) in the adhesive formulation.

Secondly, to test the contribution from the bulk properties, we derive an equation for rolling ball tack in terms of the bulk viscoelastic behavior of the block copolymer PSA. However, experimental values of rolling ball tack do not follow this equation. Also, with increasing tackifier concentration in SIS, rolling ball tack has very different behavior compared with loop, peel, quick stick and probe tack. The latter set of performance criteria is known to be related to PSA bulk viscoelastic behavior. Therefore, these suggest that rolling ball tack is related more to the surface properties than to the bulk properties of the adhesive based on these results and those of the diluent-modified PSA systems.     

Study on modified phenolic resin. III. Modification with p-hydroxyphenylmaleimide/acrylic ester copolymer

The improvement of toughness and heat resistance of phenolic resin was examined by blend of novolac and copolymers prepared from p-hydroxyphenylmaleimide (HPMI) and acrylic ester. Copolymers of HPMI and acrylic esters, such as methyl acrylate, ethylacrylate, n-butylacrylate, or 2-ethylhexyl acrylate, were synthesized. Average molecular weights, glass transition temperatures (T_g) and thermal decomposition temperatures were measured. The miscibility of the copolymers with novolac was evaluated. It was found that these copolymers had higher average molecular weight and higher thermal decomposition temperature than those of novolac; they also had good miscibility with novolac. Molding compounds were prepared by hot roll-kneading of mixtures, which involved novolac, the copolymer, hexamethylenetetramine (hexamine), and glass fiber. Test pieces of the modified phenolic resins were prepared by transfer molding from the molding compounds. It was found that phenolic resin, modified with HPMI/ethylacrylate copolymer or HPMI/n-butylacrylate copolymer, which consisted of numerous units of acrylic ester, showed both good toughness and good heat resistance.     

Temperature dependence of tack and pulse NMR analysis of polystyrene block copolymer/tackifier system

The influence of tackifier structure on the temperature dependence of tack for a polystyrene block copolymer/tackifier system was investigated. A blend of polystyrene-block-polyisoprene-block- polystyrene triblock and polystyrene-block-polyisoprene diblock copolymers was used as the base polymer. Four different tackifiers were used: special rosin ester resin (RE), rosin phenolic resin (RP), hydrogenated cyclo-aliphatic resin (HC), and aliphatic petroleum resin (C5). Tack at 20?°C increased with the tackifier content for both RE and HC tackifier systems. Tack is affected by two factors: the work of adhesion at the adherend interface and the viscoelastic properties of the adhesive. The good balance of these two factors brought high tack. The adhesive with 10 wt.% tackifier exhibited the highest tack at 20?°C, whereas those with 30 and 50 wt.% tackifier were lower than those systems with 10 wt.% of the RP or C5 tackifiers. The adhesive with overly high hardness lowered the work of adhesion and the tack was not improved with more than 30 wt.%. A compatibility test in toluene solution and in solid state showed that tackifier RE has good compatibility with both polyisoprene and polystyrene, whereas tackifier RP has lower compatibility. Tackifiers HC and C5 had good compatibility with polyisoprene, but poor compatibility with polystyrene, and that of C5 was poorer. Pulse nuclear magnetic resonance (NMR) analyses indicated that tackifiers RE and HC effectively restrict the molecular mobility of polyisoprene phase.     

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

The 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     

Rheological analysis of the adhesion surface with a scanning probe microscope (SPM)

The frictional forces between pressure sensitive adhesives (PSAs), including rosin tackifier resin, and a probe tip were measured with scanning probe microscopy (SPM). A peak that appeared in the scanning rate-frictional force curve shifted to a lower scanning rate with decrease in temperature. The frictional force reflects rheological behavior of the PSA. In the case of the miscible system, the tendency of a peak to shift to a lower scanning rate was observed with increase in tackifier content; however, in the case of the immiscible system, no remarkable shift was observed. The frictional force is influenced by viscoelastic properties of the PSA, which systematically changed with miscibility. The high-scanning rate resulted in the interfacial failure on the surface, while the low-scanning rate resulted in the cohesion failure.     

Effect of trifunctional cross-linker triallyl isocyanurate (TAIC) on the surface morphology and viscoelasticity of the acrylic emulsion pressure-sensitive adhesives

Acrylic pressure sensitive adhesive (PSA) latexes were synthesized via a starved monomer-seeded semi-continuous emulsion polymerization process with butyl acrylate (BA), methyl methacrylate, acrylic acid (AA), 2-hydroxyethyl acrylate and trifunctional cross-linker, triallyl isocyanurate (TAIC). Influences of TAIC on the resultant latex and PSA properties were comprehensively investigated. The results indicated that latex particle size was independent of the amount of TAIC in the pre-emulsion feed, while the viscosity of the latex increased remarkably with TAIC content increased. Thermal gravimetric analysis result showed that the thermal stability of the polymers was improved significantly with the addition of TAIC. Besides, with the increase in TAIC content, gel content of the polymer increased significantly, while molecular weight between cross link points (M_c) and sol molecular weight (M_w, M_n) of the polymer decreased remarkably. Moreover, for the cross-linked adhesive film, the shear strength was improved greatly while at the sacrifice of loop tack and peel strength, when compared with the uncrosslinked counterparts. Finally, dynamic mechanical analysis and atomic force microscopy were also used to evaluate the viscoelastic properties and surface morphology of the acrylic emulsion PSA film, respectively.     

The effects of substrate surface properties on tack performance of acrylic Pressure-Sensitive Adhesives (PSAs)

The effects of substrate surface free energy (SFE) and substrate roughness on tack performance of adhesive tapes containing synthesized model acrylic pressure-sensitive adhesive (PSA) have been investigated. In order to study the influence of substrate SFE on tack the adherents with the same surface roughness (expressed by selected amplitude parameters) were used: PTFE, PP, PE, ABS, PC, PMMA, stainless steel and glass. The relationship between substrate roughness and tack was investigated using two polypropylene plates (PP and PP_rough) characterized as having the same wettability (SFE). For tack determination the most common method in the PSA tapes industry was employed (loop tack test). The conducted experiments showed that substrate SFE is a crucial factor governing tack properties of acrylic PSAs. In general, a larger difference between the SFE values of the substrate and adhesive were correlated with greater tack values. The dependence of tack and SFE was significantly influenced by crosslinking degree and layer coat weight of model acrylic PSA. The experiments carried out in the second part of the study revealed that the adhesive׳s viscoelastic properties control the tack properties on rough substrates, however, the final tack performance was found to be strongly affected by the level of substrate roughness and PSA thickness.