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.     

Novel pyridinium derivatives as very efficient photoinitiators for UV-activated synthesis of acrylic pressure-sensitive adhesives

During the development of synthesis of acrylic pressure-sensitive adhesives, newly synthesized pyridinium derivatives were used by the UV-initiated polymerization quarantines of new polymer design for the synthesized self-adhesive acrylics with excellent performance, for which tack, peel adhesion, shear strength and shrinkage were measured. For example, the best tack and peel adhesion performances were achieved after 30 and 60 s UV radiation for 3.0 wt% pyridinium photoinitiator PPP, after 60 and 90 s UV exposure for 4.0 wt% pyridinium photoinitiator HPP and after 90 s UV-crosslinking in the case of 5.0 wt% pyridinium photoinitiator OPP. An increase of novel pyridinium photoinitiators concentration causes in an increase of the monomers conversion. For high photoinitiator content, characterized for each investigated photoinitiator, ranging from about 3.0 (PPP) to 5.0 wt% (OPP), the degree of monomer conversion reaches a maximum value of about 99.6 wt%.Preliminary results are reported illustrating the effectiveness of the acrylic PSA development.     

Pressure-Sensitive Adhesives Based on Nanostructured Latex Particles

Conceivably, when a polymer with two opposite properties is required, two different monomers may chemically be combined by a simple copolymerization reaction. One of the commonest techniques is to synthesize copolymers by an emulsion polymerization. The homogeneous particles obtained by this method simply show a balance between the individual properties of the homopolymers. In contrast, two-stage emulsion polymerization affords simultaneously an improvement of both opposing properties (synergy). In order to study the influence of particle structure on adhesion properties, a series of nanostructured particles based on a copolymer of vinyl acetate and butylacrylate P(VA-co-BuA) and polybutylacrylate (PBuA) were synthesized by semicontinuous emulsion polymerization. The particle size and P(VA-co-BuA)/P(BuA) ratio were varied. The obtained dispersions were characterized by quasi-elastic light scattering. The adhesion properties (tack, peel, and shear strength) of the particles were evaluated according to industrial methods. It was found that improved values of peel and tack were obtained when a P(VA-co-BuA) rigid core was enveloped with a thin shell made of PBuA. A strong influence of the particle size and PBuA content on the adhesion properties was detected. The best performance was found at large particle sizes and thick shells.     

Effect of the rheological properties of industrial hot-melt and pressure-sensitive adhesives on the peel behavior

Three factors govern the adhesion properties of hot-melt and pressure-sensitive adhesives: (1) thermodynamic interfacial properties (Dupré adhesion energy); (2) interfacial losses due to specific interactions; and (3) viscoelastic losses in the bulk related to the rheological properties of the adhesive. In the present paper, we focus on the main factor in the adhesion properties, which is the viscoelastic factor. We extend in this paper the results obtained on a series of model adhesives to the case of industrial formulations: one SIS triblock copolymer-based PSA formulation and one EVA copolymer-based hot-melt formulation. After studying the rheological properties of these adhesives over a wide frequency range using time-temperature equivalence, we present data obtained on peel tests at various temperatures. As with model adhesives, the peel rate-temperature equivalence leads to the same shift factors as rheology. The experiments demonstrate that there is a one-to-one relationship between the cohesive fracture domain and the terminal region of relaxation exhibited in rheological testing. The first interfacial fracture mode is related to the rubbery plateau, and the brittle interfacial fracture mode observed at high peel rates to the glassy behavior exhibited at very high frequencies in rheological measurements.     

The effect of particle size and composition on the performance of styrene/butyl acrylate miniemulsion-based PSAs

Styrene/butyl acrylate batch miniemulsion copolymerizations were performed in a 1.2 L stainless steel reactor. Conversions were monitored off-line using gravimetry and in-line using ATR-FTIR spectroscopy. The final latexes were coated on a polyethylene terephthalate carrier and dried at room temperature for 2 days. Their performance as pressure-sensitive adhesives (PSAs) was evaluated by measuring their tackiness, peel strength and shear strength. By using a constrained mixture design, the influence of particle size and copolymer composition was investigated. Particle size was found to be the most influential factor for both tack and peel strength models. Tack showed a concave upward trend whereas peel strength decreased with increasing particle size. Shear strength decreased with increasing particle size but was also significantly influenced by copolymer composition. The final forms of the models allowed 3D response surfaces to be built and an optimal adhesive performance region (highest combined tack, peel strength and shear strength) was located near the smallest particle diameter investigated with the highest styrene composition. The positive effect of smaller particles on every adhesive property relates to the tighter packing provided by smaller particles during the drying process, thus increasing the area of contact between the adhesive and the substrate.     

Effect of a Gradient in Viscoelastic Properties on the Debonding Mechanisms of Soft Adhesives

The effect of a composition gradient along the thickness in soft adhesive films was investigated. The adhesion properties of bilayer films made from acrylic solutions, one layer being more cohesive and the other more dissipative, were studied by performing probe tack experiments. To understand the mechanisms that determine the bulk and the interfacial contributions to the debonding, tests on different surfaces were carried out. The results show that the presence of a composition gradient can enhance the adhesive properties, particularly on a low-energy surface such as polyethylene. On steel, the presence of the thin layer of a more elastic adhesive in contact with the adherent can influence significantly the debonding mechanism, transforming the fracture from cohesive to adhesive.     

Effect of Blend Ratio and Testing Rate on the Adhesion Properties of Epoxidized Natural Rubber (ENR 25)/Styrene–Butadiene Rubber (SBR) Blend Adhesive

The effect of rubber blend ratio and testing rate on the adhesion properties of epoxidized natural rubber (ENR 25)/styrene–butadiene rubber (SBR) blend adhesive were studied using 40 parts per hundred parts of rubber (phr) of coumarone-indene resin as the tackifying resin. Toluene and poly(ethylene terephthalate) (PET) film were used as the solvent and substrate, respectively. A SHEEN hand coater was used to coat the adhesive on the PET substrate at 30, 60, 90, and 120 µm coating thickness. Viscosity was determined by a Brookfield viscometer whereas loop tack, peel strength, and shear strength were measured by a Llyod Adhesion Tester at various testing rates from 10 to 60 cm/min. Results show that viscosity increases gradually with % ENR 25. However, loop tack, peel strength, and shear strength of adhesives indicate a maximum value at 40% ENR 25, after which the adhesion properties decreases with further increase in % ENR 25. This observation is attributed to the varying degree of wettability which culminates at an optimum value of 40% ENR 25 blend ratio. In all cases, the adhesion properties increase with increasing coating thickness and rate of testing.     

Novel versatile pressure-sensitive adhesives for polarizing film of TFT-LCDs: Viscoelastic characteristics and light leakage performance

One of the main problems in thin film transistor liquid crystal displays (TFT-LCD) is a phenomenon called “light leakage”, seriously affecting black–white contrast and color brightness. It occurs due to a thermal shrinkage of the polarizing film in TFT-LCDs, caused by a heat from the backlight unit. A pressure-sensitive adhesive (PSA) used for assembling of the polarizing film to the TFT-LCD panel can relieve the stress and minimize the light leakage. PSAs are designed specifically for a certain size LCDs, and cannot be used for another size LCD because of poorer light leakage. Obviously, there is a certain necessity to develop a universal PSA applicable simultaneously for LCDs with different sizes, such as mobile phones, digital cameras, navigation systems, computer monitors, HDTVs, etc.In this paper, we introduced N-vinyl pyrrolidone as a comonomer to a conventional copolymer of butyl acrylate, acrylic acid, and 2-hydroxy ethyl methacrylate. It resulted in a higher elasticity modulus and a higher shrinkage resistance of the PSA. A significant reduction of the light leakage to some extend was observed at increase of the hardener content for 2.5 and 7 in samples. However, it was accompanied by deterioration of the peel strength below spec requirements. Lowering molecular weight of the polymers from 626,000 to 205,000 Da resulted in excellent light leakage of both small and large specimens. Dynamic mechanical analysis confirmed that zero light leakage was achieved through a synergy of two mechanisms: high modulus, i.e. resistance to thermo-induced shrinkage, and high stress relaxation of lower molecular weight polymers. The results of this work are perspective for creation of a universal PSA for polarizing film in TFT-LCDs of different sizes.     

UV固化无溶剂型丙烯酸酯压敏胶的合成与性能表征

以丙烯酸异辛酯(2-EHA)、丙烯酸丁酯(BA)、甲基丙烯酸甲酯(MMA)和四氢化糠基丙烯酸酯(THFA)为主要单体,以丙烯酸(AA)和N,N-二甲基丙烯酰胺(DMAA)为功能性单体,以4-丙烯酰氧基二苯甲酮(ABP)为光引发剂,以十二烷基硫醇(NDM)为链转移剂,通过本体聚合法制备了UV固化无溶剂型丙烯酸酯压敏胶(PSA)。分别探讨了两种功能单体AA和DMAA用量,光引发剂ABP和链转移剂NDM用量对PSA性能的影响。结果表明,当DMAA和AA用量分别为单体总质量的10%和2%时,PSA的120℃熔融黏度适中且粘接性能较优;光引发剂ABP用于PSA体系,且用量为单体总质量的0.2%时,光固化效果最佳;当NDM用量为单体总质量的1.5%时,PSA综合性能最佳。     

聚氨酯-聚丙烯酸酯互穿聚合物网络压敏胶及其耐热性研究

为了提高丙烯酸酯压敏胶的耐热性能,本文采用聚氨酯/聚丙烯酸酯(PU/PAA)互穿聚合物网络(IPN)技术对丙烯酸酯压敏胶进行改性,研制出一种软化点达到125℃左右的耐热压敏胶。分析讨论了不同制备工艺因素对该压敏胶性能的影响,并对其耐热性机理进行了探讨。     

Effect of Testing Rate on Adhesion Properties of Benzoyl-Peroxide-Cured ENR 25/NBR Blend Adhesive Using Gum Rosin and Coumarone-Indene Resin as Tackifiers

Dependence of adhesion properties of benzoyl-peroxide-cured epoxidized natural rubber (ENR 25)/acrylonitrile-butadiene rubber (NBR) blend adhesive on testing rate was systematically studied. Coumarone-indene resin and gum rosin were used as tackifiers. Toluene was used as solvent throughout the study. The SHEEN hand coater was used to coat the adhesive on polyethylene terephthalate at 30 and 120 µm coating thickness. The adhesion properties were measured by a Lloyd adhesion tester operating at different rates of testing. Results showed that the loop tack, peel strength, and shear strength increased with increasing testing rate, an observation that was attributed to the viscoelastic nature of adhesive. In all cases, the adhesion properties of the adhesives also increased with increasing coating thickness.     

聚氨酯-聚丙烯酸酯互穿聚合物网络压敏胶及其耐热性研究

为了提高丙烯酸酯压敏胶的耐热性能,本文采用聚氨酯/聚丙烯酸酯(PU/PAA)互穿聚合物网络(IPN)技术对丙烯酸酯压敏胶进行改性,研制出一种软化点达到125℃左右的耐热压敏胶。分析讨论了不同制备工艺因素对该压敏胶性能的影响,并对其耐热性机理进行了探讨。     

Power feed synthesis of pressure-sensitive latex adhesives

Latex particles with the same core composition of poly(MMA-co-ALMA) and different shell compositions of poly(BA-co-AA) were prepared by semibatch emulsion polymerization using ‘power feed’ monomer and chain transfer agent addition methods in the shell layers. The seed stage involved formation of seed particles of 111 nm in diameter with a batch process. After that, two growth stages formed the final particle diameter, d_z = 300 nm measured by dynamic light scattering. The gel content and the molecular parameters of the polymer were determined. The adhesive properties including loop tack, peel force and shear resistance were measured according to the FINAT test methods No. 9, 1 and 8. An evaluation was also made for the relationship between pressure-sensitive properties and molecular parameters. Introducing power feed to semibatch emulsion polymerization had no significant effect on the latex preparations and could improve the final conversion and the colloidal stability. The observed particles were grown without significant secondary nucleation. The power feed methods had no effect on the glass transfer temperature (T_g) of the shell layer also. Emulsion polymerization conducted by positive power feed resulted in the formation of longer primary polymer chains at the beginning than that conducted by negative power feed and standard uniform feed, which caused a very high gel fraction. As pressure-sensitive adhesives prepared by using the positive power feed had the highest gel content and strongest core–shell interaction, they exhibited the highest shear resistance, but the lowest tack and peel force.