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     

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.     

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.     

Viscoelastic and adhesive properties of single‐component thermo‐resistant acrylic pressure sensitive adhesives

Poly(butyl acrylate‐vinyl acetate‐acrylic acid) based acrylic pressure sensitive adhesives (PSAs) were synthesized by solution polymerization for the fabrication of high performance pressure sensitive adhesive tapes. The synthesized PSAs have high shear strength and can be peeled off substrate without residues on the substrate at temperature up to 150°C. The PSAs synthesized in the present work are single‐component crosslinked and they can be used directly once synthesized, which is convenient for real applications compared to commercial multi‐component adhesives. The results demonstrated that the viscosity of the PSAs remained stable during prolonged storage. The effects of the preparation conditions such as initiator concentration, cross‐linker amount, organosiloxane monomer amount and tackifier resin on the polymer properties, such as glass transition temperature (T_g), molecular weight (M_w), surface energy and shear modulus, were studied, and the dependence of the adhesive properties on the polymer properties were also investigated. Crosslinking reactions showed a great improvement in the shear strength at high temperature. The addition of tackifier resin made peel strength increase compared to original PSAs because of the improvement of the adhesion strength. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40086.     

Rheology,composition, and peel-mechanism of block copolymer–tackifier-based pressure sensitive adhesives

Three samples of styrene–isoprene–styrene (S–I–S) block copolymers were chosen; copolymer A had 25% styrene, and copolymers B and C had 14% styrene. Copolymers A and B contained 20% diblock polymer and copolymer C contained 40% diblock polymer. All copolymers were mixed with a terpene type tackifier to make 56% and 48% weight tackifier concentration. These represent our model samples of pressure sensitive adhesives. The determination of tack, room-temperature peel-strength, and failure temperature under static shear were performed. The above results have been interpreted with the basic rheological data. The dynamic viscoelastic measurements and tensile stress–strain measurements were used. The effects of tackifier on the rubbery plateau moduli were treated with the Guth–Gold-type equation. The implications of the deviation from the equation are discussed in terms of the connectivity between polystyrene domains and the stability of the hard domains affected by inclusion of rubber segments.     

Acrylic pressure‐sensitive adhesives with nanodiamonds and acid–base dependence of the pressure‐sensitive adhesive properties

A high performance and functional properties in pressure‐sensitive adhesives (PSAs) are attractive in fundamental and industrial fields. To control the performance of PSAs, nanofillers have been loaded into them. In this study, we focused on composites of acrylic PSAs and nanodiamonds (NDs). The loaded NDs reinforced the mechanical properties and increased the performance of the PSAs. NDs in a PSA formed a network structure. In this study, we revealed that the acidic–basic state was a key factor in the control of the dispersion of the NDs. When a PSA emulsions and ND aqueous dispersion was mixed under basic conditions, the composites demonstrated higher PSA properties (tack, holding, and peeling strength). We investigated the effect of the ND loading on the PSA properties from the viewpoints of the nanostructure and acid–base interactions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46349.     

Shear creep resistance of styrene–isoprene–styrene (SIS)‐based hot‐melt pressure‐sensitive adhesives

The effects of the properties of substrates and tackifier on the shear creep of SIS‐based HMPSAs were investigated. The holding power (t_b) and shear adhesion failure temperature (SAFT) were measured. The relationship between the complex viscosity and the holding power was examined. The holding power and SAFT values of the triblock SIS blends were higher than those of the diblock‐containing SIS blends, perhaps because blends using triblock SIS have higher crossover temperature and complex viscosity than those using diblock‐containing SIS. Higher levels of aromatic resin‐modified aliphatic tackifier and rosin ester were found to decrease the holding power of the HMPSAs. This maybe due to the fact that rosin ester and aromatic‐modified aliphatic resin are compatible with both the ends and midblocks of SIS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 825–831, 2006     

Rheological and adhesion properties of acrylic pressure‐sensitive adhesives

Different pressure‐sensitive adhesives (PSAs) based on acrylic monomers were synthesized under different reaction conditions. The synthesized PSAs have good adhesive properties and without leaving any residue can be easily peeled off from the surface of a substrate. The relationship between PSAs rheological behavior and its adhesion properties (e.g., peel, tack, and shear resistance) has been studied at constant adhesive thickness. The samples were examined for their surface energy and viscoelastic characteristics. It was observed that increase in reaction temperature and reaction time results in decreased storage modulus due to lowered molecular weight, which finally leads to lower elasticity of the PSA. While the storage (G′) and loss (G″) modulus of samples increase with increased initiator concentration, the elasticity of PSA is increased as well. High G″ at high frequency (100 Hz) represents high peel strength because of higher dissipation of viscoelastic energy during debonding. The tack values increase by lowering storage modulus at 1 Hz due to higher M_e. Shear values are increased by higher storage modulus at low frequency (0.1 Hz) due to hydrogen bonding of the different components. Some parallel investigations on the surface energy of the samples showed that they have different properties because of the nature of different monomeric units with their corresponding orientations. Our results reveal that the peel strength is not affected by surface energy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Melt versus solvent coating: Structure and properties of block–copolymer‐based pressure‐sensitive adhesives

Pressure‐sensitive adhesives (PSAs) composed of a styrene–isoprene–styrene triblock copolymer and a midblock‐associating resin were prepared via solvent and hot‐melt coating. The formulations and thermal histories up to the point of coating were identical, yet significant differences in the properties were observed as a function of the coating method. The solvent‐coated PSA showed superior shear holding power, and the hot‐melt‐coated PSA performed better in tack and peel tests. Two factors resulting from the processing conditions were responsible for these property differences. The quick cooling process occurring after hot‐melt coating led to a poorly defined microstructure and, therefore, less physical crosslinking. Rheological data for melt‐pressed and solvent‐cast PSA films confirmed these microstructural differences. The increased solubility of the tackifier in the solvent additionally created a composition gradient in the solvent coating. Annealing improved the long‐range order of both hot‐melt and solvent coatings, producing a body‐centered cubic microstructure identified by small‐angle X‐ray scattering. This microstructure improved the shear strength of both types of adhesive coatings, whereas the peel and tack properties of the solvent coatings remained inferior to those of the hot‐melt coatings because of differences in the surface compositions. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3355–3367, 2002     

Surface Property and Compatibility of Poly(styrene-isoprene-styrene) Triblock Copolymer/Tackifier Blend System

The frictional forces between pressure sensitive adhesives (PSAs) and a probe tip were measured with a scanning probe microscopy (SPM). A peak appeared in the scanning rate-frictional force curve shifted to a lower scanning rate with decreasing temperature. In the case of the miscible system of isoprene matrix of SIS base polymer, the tendency of a peak to shift to a lower scanning rate was observed with increasing tackifier content; however, in the case of the immiscible system of styrene domain of SIS base polymer, no remarkable shift was observed. The frictional force is influenced by viscoelastic properties of the PSA which systematically changed with miscibility.

In this study, it is aimed to clarify the correlation between the observation of phase structure and the behavior of surface rheology by using two kinds of tackifiers that have different miscibility with the polyisoprene phase or the polystyrene phase of SIS triblock copolymer.     

Synthesis and characteristics of photoactive‐hydrogenated rosin epoxy methacrylate for pressure sensitive adhesives

Hydrogenated rosin epoxy methacrylate (HREM), based on hydrogenated rosin and glycidyl methacrylate (GMA), was synthesized for use as an advanced tackifier in the UV‐crosslinking pressure sensitive adhesives (PSAs) system. The HREM, as a tackifier, contained UV‐curing sites; thus, allowed photopolymerization to occur by UV irradiation. This UV‐curable tackifier, HREM, can improve the curing rate and adhesion performance of UV‐crosslinking PSAs. The characteristics of HREM were analyzed by GPC and DSC and its synthetic mechanism studied using FTIR and ¹H NMR; the characteristic peaks of hydrogenated rosin and GMA vanished, but new peaks for HREM appeared. The PDI and the T_g by DSC were 1 and ?25.6°C, respectively. The photopolymerization of HREM was studied using photo‐DSC. Heat flow was observed during UV irradiation, and the curing rate and conversion both increased with rising photoinitiator content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Adhesion performance of UV-cured semi-IPN structure acrylic pressure sensitive adhesives

UV-curable solvent-free pressure sensitive adhesives (PSAs) are gaining importance in the area of adhesives because of increasing environmental concerns and the goal to reduce volatile organic compounds (VOCs) in work areas and consumption places. These PSAs have advantages such as low emission of VOCs, a solvent-free process, a fast producton rate at ambient temperature and only a modest requirement for operating space. In this study, UV-curable PSAs were investigated by measuring their adhesion performance in terms of probe tack, peel strength, shear adhesion failure temperature (SAFT) and holding power. PSAs were synthesized from 2-ethylhexyl acrylate (2-EHA), acrylic acid (AA) and vinyl acetate (VAc), using variations in AA concentration to control the glass transition temperature (T _g) of the prepared PSAs. In addition, two types of trifunctional monomers, trimethylolpropane triacrylate (TMPTA) and trimethylolpropane ethoxylated (6) triacrylate (TMPEOTA), which have different chain lengths, were used to form semi-interpenetrating polymer network (semi-IPN) structures after UV exposure. With increasing AA concentration in the PSAs, both the T _g and viscosity increased. Also, probe tack and SAFT increased, but peel strength decreased. After UV irradiation, probe tack decreased, and SAFT and peel strength increased as AA concentration increased in the PSAs. In most cases, cohesive failure changed to interfacial failure after UV exposure. Also, TMPTA increased the cohesion of PSAs; however, TMPEOTA affected the mobility of PSAs due to the different chain lengths of the two types of trifunctional monomer in a different way. The increase of TMPEOTA content diminished the cohesion of PSAs. Consequently, the adhesion performance of the PSAs was closely related to the T _g of the PSAs, and the two types of trifunctional monomer showed different adhesion performances.     

Cut growth properties of styrene–butadiene copolymers

The cut growth properties of styrene–butadiene block and random copolymers are considered in terms of the tearing energy theory. It is found that the value of T₀ (the minimum value of tearing energy below which no cut growth takes place in the absence of chemical effects) is far higher for a styrene–butadiene resin copolymer system with a high amount of bound styrene resin than for a conventionally vulcanized SBR elastomer. Similarly, it is shown that the value of T₀ for a butadiene–styrene block copolymer (thermoplastic rubber) is considerably reduced when the material is crosslinked. It is proposed that the value of T₀ is influenced by the hystersial properties of the rubber.     

Microhardness of styrene/butadiene block copolymer systems: Influence of molecular architecture

The influence of molecular architecture on the mechanical properties of styrene/butadiene block copolymers was investigated by means of the microhardness technique. It was found that the microhardness of the styrene/butadiene block copolymers is dictated by the nature of microphase separated morphology. In contrast to polymer blends and random copolymers, in which the microhardness generally follows the additivity rule, the behavior of the investigated block copolymers was found to significantly deviate depending on their molecular architecture. The glass‐transition temperature of the polystyrene phase (T_g‐PS), which practically remained constant and that of the polybutadiene phase (T_g‐PB), which varied with the change in the block copolymer architecture, apparently do not influence the microhardness values of the block copolymers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1670–1677, 2003     

Influence of addition of styrene–ethylene/butylene–styrene copolymer on rheological,mechanical, and tribological properties of polyamide nanocomposites

To develop new tribomaterials for mechanical sliding parts, investigations were carried out on the influence of adding styrene–ethylene/butylene–styrene block copolymer (SEBS) on the rheological, mechanical, and tribological properties of polyamide 6 (PA6) nanocomposite, which is a commercial product of layered silicate (clay) filled polyamide 6 (PA6/Clay). Two kinds of block copolymers, unmodified SEBS (SEBS) and maleic anhydride‐grafted SEBS (SEBS‐g‐MA), were added with PA6/Clay nanocomposite. Dynamic viscoelastic properties in the molten state of these nanocomposites and their tensile, impact, and tribological properties of these nanocomposites were evaluated. Dynamic viscoelastic properties were found to increase with the addition of SEBS and were influenced, in particular, by block copolymers containing SEBS‐g‐MA. Influence of the addition of SEBS on mechanical properties of these systems differed for each mechanical property. Although tensile properties decreased with SEBS, Izod impact properties were improved with the addition of SEBS‐g‐MA. Tribological properties were improved with the addition of block copolymer, and the influence of the amount of addition was higher than the type of block copolymer used. These results indicate that new tribomaterials developed have sufficient balance amongst moldability, mechanical, and tribological properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Composition and Performance of Styrene-Isoprene-Styrene (SIS) and Styrene-Butadiene-Styrene (SBS) Hot Melt Pressure Sensitive Adhesives

Styrenic block copolymers are widely used in HMPSA formulations, with tackifier resins and oil plasticizer. Although most commercial formulations are based on SIS, mixtures of SIS and SBS are also used to reduce cost. However, the use of SBS is restricted because it generally leads to decrease in tack. In this work, pure SIS and SBS and a SIS/SBS mixture were used in formulations with aliphatic, aromatic, aliphatic hydrogenated, and aliphatic-aromatic copolymer resins, at three different oil contents, according to a 3^3–1 factorial design. Interaction effects among the components were evaluated, showing a strong dependence of the HMPSA final properties on the combination of resin/rubber used. It was found that a blend of aliphatic and aromatic resins is the best tackifier for SIS, while for SBS the best choice is an aromatic-aliphatic copolymer. These results were explained in terms of specific compatibility, which was correlated to the polarizability of the material.     

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 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 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.     

Synthesis and properties of ethylene‐substituted styrene copolymers

The copolymerization of ethylene and substituted styrenes [RSt's; p‐methylstyrene (MSt), p‐tert‐butylstyrene (BSt), 2‐vinylnaphthalene (VN), and p‐(tert‐butyldimethylsilyloxy)styrene (BMSiOSt)] were investigated with dimethylsilylene(tetramethylcyclopentadienyl)(N‐tert‐butyl)titanium dichloride to yield the corresponding ethylene–RSt copolymers. The substituent on the styrene (St) monomers did not affect the monomer reactivity ratio. The effect of the substituent structure of RSt on the thermal and mechanical properties was studied with differential scanning calorimetry, dynamic mechanical thermal spectroscopy, and elongation testing. The glass‐transition temperature (T_g) of the copolymers increased with increasing RSt content, and the order of T_g was as follows: BSt > VN > MSt = St. A copolymer with p‐hydroxystyrene (HOSt) was successively synthesized by means of deprotection of the copolymer with BMSiOSt. The copolymer showed a much higher T_g than the other copolymers because of the hydrogen connection of its OH groups. The mechanical properties of the copolymer in the glass state, at a lower temperature than T_g, were almost independent of the nature of the RSt. The substituent of the St monomers affected the pattern of the stress–strain curve in the elongation testing in the amorphous state. An improvement in the shape memory effect was observed in poly(ethylene‐co‐BSt). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008