Pressure-sensitive Adhesive Films Research Articles

The use of lignin in emulsion-based pressure-sensitive adhesives

Pressure sensitive adhesive (PSA) films were produced by in situ seeded semi-batch emulsion polymerization of butyl acrylate (BA) and methyl methacrylate (MMA) in the presence of varying amounts of lignin. Two types of Kraft lignin, water-soluble and non-water soluble, were used in this study. Lignin was modified using acrylation (methacryloyl chloride), maleation (maleic anhydride) and acetylation (acetyl bromide and acetic acid) to promote its miscibility with the BA and MMA monomers and encourage its incorporation into the polymer matrix. For the case of the maleated lignin, maximum incorporation of 10 wt% was achieved whereas, for the acrylated lignin case, a maximum of 5 wt% was attained. Lignin was shown to decrease latex viscosity in all cases. At a lignin loading of 1 wt% (relative to the amount of monomer) a tack and shear strength of the PSA films increased significantly while the peel strength remained constant. Thus, maleated lignin was shown to be an effective, renewable modifier for emulsion-based PSA properties.

Shock absorption of semi-interpenetrating network acrylic pressure-sensitive adhesive for mobile display impact resistance

With the development of mobile display shapes from flat to flexible, the conventional glass cover window must be replaced by a film-type window. However, film-type cover windows have low impact resistance owing to their poor shock absorption. Therefore, to realize their application to flexible displays, it is essential to characterize and improve the shock-absorbing characteristics of the display film. In this study, a semi-interpenetrating network (semi-IPN) acrylic pressure-sensitive adhesive (PSA) consisting of a crosslinked network structure with a linear acrylic polymer chain was developed. The influence of the multi-functional monomer content and UV dose on the properties of the semi-IPN PSA was studied. The peel strength of the semi-IPN PSA was higher than 10 N/25 mm, which is generally considered as the PSA standard for mobile displays. With an increase in crosslink density, the storage modulus increased, but the damping factor decreased. To evaluate shock absorption, a falling ball impact tester was used to estimate the shock absorption ratio (ΔF) of the film. The semi-IPN PSA incorporating 30 phr of the multi-functional monomer exhibited higher ΔF (31.2%) than that of a conventional UV-curable PSA film (24.6%). This shows that even with the relatively low damping factor of the semi-IPN PSA, its structure could improve shock absorption. Moreover, we suggested two mechanisms for shock absorption of the semi-IPN PSA, energy dissipation into the PSA layer and extended contact time.

Functionalization of cellulose nanocrystals with γ-MPS and its effect on the adhesive behavior of acrylic pressure sensitive adhesives

In this work, functionalized cellulose nanocrystal (fCNC) was obtained by the grafting of 3-methacryloxypropyltrimethoxysilane coupling agent (γ-MPS) onto CNC. Then acrylic pressure sensitive adhesive (PSA) incorporated with various contents of CNC or fCNC was successfully synthesized by an in-situ emulsion polymerization, and the effects of CNC or fCNC on the sol molecular weight, latex properties, thermal properties, viscoelastic properties, and adhesive performance of the acrylic PSA were investigated. The results illustrated a coinstantaneous improvement of tack, shear strength and peel strength with increasing the loading of both CNC and fCNC. Interestingly, fCNC showed much more improvement than CNC on adhesive performance of acrylic PSA. The fCNC-1/acrylic PSA showed tack of 27#, shear strength of 70 h, and peel strength of 13.4 N/25mm, which were 12.5%, 4%, and 106% higher than those of CNC-1/acrylic PSA and 35%, 100%, and 163% higher than those of neat acrylic PSA, respectively. The superior adhesive performance of the fCNC/acrylic PSA films was supposed to be attributed to better compatibility and dispersion of fCNC in the acrylic copolymer. Thus, this work presents a feasible strategy for utilization of CNC in adhesives and coatings.

Taper Tension Profile in Roll-to-Roll Rewinder: Improving Adhesive Force of Pressure-Sensitive Adhesive Film

The roll-to-roll adhesive film manufacturing process has been widely used in the field of composite film manufacture. Thus far, many research groups have reported on the variation in characteristics of pressure sensitive adhesive film according to application environment characteristics, such as temperature and external forces, failure mechanism, and structures that improve the adhesive force of the film. However, there are few studies that analyze the effects of the manufacturing process conditions on the quality of the adhesive film. In this study, we find that hoop stresses due to winding tension may cause a decrease in the quality of the adhesive layer by generating wear on its surface. Moreover, radial and hoop stresses in the wound film affect the degree of wear. This suggests that the operating conditions of the film manufacturing machine affect the quality of the pressure sensitive adhesive (PSA) film, as do the properties of the film and the environment. To improve the adhesive force of PSA film, we applied two taper tension profiles that determine the distribution of the tension applied to the winding PSA film with respect to the wound ratio, followed by experimental verification of the effects of winding.

The physiochemical, mechanical, and adhesive properties of solvent-cast vitamin E/Soluplus® films

Soluplus® is an amphiphilic graft copolymer used in hot melt extrusion applications and electrospinning. Very little information is available on the use of Soluplus® as a film former and in the development of film-based formulations. The overall aim of this work was to study the mechanical and adhesive properties of Soluplus® films prepared by the solvent casting technique. More specifically, we discovered that vitamin E can serve as a plasticizer for the Soluplus® polymer and to significantly modulate its mechanical and adhesive properties. Vitamin E (0–75% w/w) and Soluplus® were dissolved in ethanol and cast on liners to produce transparent films. Cast films were tested for their physiochemical properties by IR, XRD, and MDSC, and for their adhesive and mechanical properties by texture analysis. Vitamin E was found to be miscible with Soluplus® and to reduce the crystallinity of the films. Vitamin E also decreased the films’ tensile strength and Young’s modulus while significantly increasing their percent elongation. The most notable effect was the observed increase in the adhesiveness (tackiness) and hydrophobicity of the films, which was evidenced by a significant increase in their water contact angle and a decrease in their swelling capacity and disintegration. These observations indicated that vitamin E/Soluplus® blends might be used for the preparation of highly pliable films, especially when made with 30–50% vitamin E, and in the development of a new type of pressure sensitive adhesive films when prepared with ≥65% vitamin E load.

Fabrication of acrylic pressure-sensitive adhesives containing maleimide for heat-resistant adhesive applications

In the area of pressure-sensitive adhesives (PSAs), acrylic PSAs have been successfully applied in many fields, including self-adhesive tapes, sign labels, carrier-free tapes, double-sided tapes and protective films, but applications of heat-resistant acrylic PSAs are relatively rare. In this study, the thermal stability of acrylic polymer containing maleimide (Mal) functional groups has been investigated. The PSAs were synthesized by acrylic monomers and Mal through copolymerization. The influence of Mal on the viscosity, molecular weight (Mw, Mn), glass transition temperature, thermogravimetric analysis and contact angle of acrylic PSAs was also studied. The adhesion performance and thermal stability of acrylic PSAs could be significantly enhanced by increase in Mal content of the synthesized resin. After 3 h of treatment in drying oven at 170 °C, the modified PSAs can be peeled (180°) off from the substrate without residues on substrate surface at room temperature, while the non-modified acrylic PSAs possessed residues after treatment from 110 °C. The maximum 180° peel strength of modified PSA films was 12.7 N/25 mm when the content of Mal was 7.5 wt%.

Origami Microfluidic CD

Employing the centrifugal force for liquid displacement in bioanalytical compact discs (CDs) is becoming more popular for academic and industry applications. Pseudo forces that are controlled by a low-cost spindle motor enables the simultaneous manipulation of several liquids on the microfluidic CD. For this reason, centrifugal microfluidic platforms are considered more robust for extreme point of care (ePOC) applications when compared to stationary microfluidic systems that work with mechanical liquids pumps (e.g., syringe pump). However, the fabrication of microfluidic CDs requires expensive and bulky equipment (e.g., router or laser CNC) that cannot be implemented at ePOC and point of need (PON). To cope with this limitation, we have introduced a rapid microfluidic CD fabrication technique using only a low-cost cutter plotter [1]. The CDs were made through assembly of thin PVC and double-sided pressure sensitive adhesive (PSA) layers that were cut by the plotter machine. However, the technique yet required careful assembly of several disc layers, and the double-sided PSA is an expensive material and not widely available. In this article, we introduce a new origami CD fabrication process using only one type of material, a cutter plotter and a laminating machine. The origami CDs fabrication process prevents the need for PSA film and the tedious/sensitive CD assembly procedure. Therefore, the origami CDs facilitates onsite development of automated diagnosis test at ePOC and PON with minimum and widely available material and equipment. In addition to the origami CD fabrication process, this study includes the characterization of different microchannels made by the cutter plotter blade. Finally, as an application of the CD fabrication technique we developed an origami CD for automated serial dilution that is required for a wide range of bioanalytical applications such as microbial counting and multiplexed assay. [1] M.M. Aeinehvand, P. Magaña, M.S. Aeinehvand, O. Aguilar, M.J. Madou, S.O. Martinez-Chapa, Ultra-rapid and low-cost fabrication of centrifugal microfluidic platforms with active mechanical valves, RSC Adv. 7 (2017) 55400–55407. doi:10.1039/C7RA11532F.

Synthesis of poly(isobutyl acrylate/n‐butyl acrylate/methyl methacrylate)/CNC nanocomposites for adhesive applications via in situ semi‐batch emulsion polymerization

Pressure sensitive adhesive (PSA) films were prepared from in situ semi‐batch emulsion polymerizations using isobutyl acrylate, n‐butyl acrylate, and methyl methacrylate in the presence of cellulose nanocrystals (CNCs). The CNCs at loadings of up to 1 wt% with respect to monomer resulted in significant and simultaneous improvement in tack, peel strength and shear strength for the PSA films. While most latex properties were unchanged, the CNCs also led to increased latex viscosity. A range of compositions were used to test the limits of the application. Microscopy was used to demonstrate that the CNCs were dispersed throughout the latex but outside of the polymer particles. Comparison to latex/CNC blends showed that the in situ technique provided higher shear strength PSA films. POLYM. COMPOS., 40:1365–1377, 2019. © 2018 Society of Plastics Engineers

Pressure sensitive adhesive property modification using cellulose nanocrystals

The impact of cellulose nanocrystals (CNCs) as a property modifier for pressure sensitive adhesives (PSAs) was investigated. Stable CNC/poly(n-butyl acrylate-co-methyl methacrylate) latex nanocomposites with different CNC loadings ranging from 0.25 to 1wt% (based on monomer weight) were synthesized by both an in situ seeded semi-batch polymerization and a blending technique. The PSA films obtained from both techniques demonstrated a concurrent enhancement of shear strength, tack, and peel strength with increasing CNC content. However, the performance enhancement for the PSAs prepared via the in situ technique was substantially greater: increases of up to 3.8x for tack, 6x for peel strength and 20x for shear strength for the in situ technique compared to increases of up to 2.4x for tack, 1.5x for peel strength and 6.4x for shear strength for the blending technique. The difference in mechanical performance of the CNC/PSA films synthesized via the in situ technique vs. blending was a result of better interaction of CNCs with the polymer matrix during both latex synthesis and film formation.

Construction and adhesion performance of biomass tetrahydro-geraniol-based sustainable/transparent pressure sensitive adhesives

Abstract Using the tetrahydro-geraniol acrylate (TGA) synthesized from biomass tetrahydro-geraniol, UV-cured transparent acrylic pressure sensitive adhesives (PSAs) composed of semi-interpenetrating networks were successfully fabricated. The utility for optically clear adhesive on adhesion performances according to various concentrations of TGA in the acrylic PSAs were investigated. After characterizing the photo-polymerized PSA syrups, the optical properties for the acrylic PSA films were examined using UV–vis spectroscopy, a color-difference meter, and a haze meter. The acrylic PSAs exhibited high transparency and stable weather-ability under reliability testing (85/85 test). With increasing TGA concentration in the acrylic PSAs, adhesion properties such as the 180° peel strength, shear holding power, and probe tack had decreased.

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 (Mc) and sol molecular weight (Mw, Mn) 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.

Factors Affecting Gloss and Color of Decorative Pressure Sensitive Adhesive Films During Thermomechanical Deformation

Decorative polymer films are finding applications in processes that require forming at elevated temperatures and significant strain. In order to satisfy their function in these applications, the appearance of these films must remain unaltered or at least any changes must be predictable. This paper examines four different high gloss decorative films comprised of different materials in the layers of their construction. The films were uniaxially stretched up to failure (which was up to 75% strain) at isothermal conditions of 25, 40, or 75°C and then examined. Gloss (at 20°) was the most strongly altered parameter concerning the appearance of the films after thermomechanical deformation while color intensity was relatively unaffected. The change in gloss was higher for the two amorphous films compared to the two that exhibited crystallinity. The films were analyzed for their surface roughness using a white light interferometer, for their crystallinity by X‐ray diffraction and for their morphology by atomic force microscopy (AFM). Surface roughness increased with crystallinity for the two films that exhibited crystals but overall showed no correlation to the gloss measurements. Only evidence of altered domain morphology in the films as determined by AFM appeared to correlate with the changes in gloss reported. POLYM. ENG. SCI., 56:1357–1365, 2016. © 2016 Society of Plastics Engineers

Comparison of Surfactant Distributions in Pressure-Sensitive Adhesive Films Dried from Dispersion under Lab-Scale and Industrial Drying Conditions.

Film-forming latex dispersions are an important class of material systems for a variety of applications, for example, pressure-sensitive adhesives, which are used for the manufacturing of adhesive tapes and labels. The mechanisms occurring during drying have been under intense investigations in a number of literature works. Of special interest is the distribution of surfactants during the film formation. However, most of the studies are performed at experimental conditions very different from those usually encountered in industrial processes. This leaves the impact of the drying conditions and the resulting influence on the film properties unclear. In this work, two different 2-ethylhexyl-acrylate (EHA)-based adhesives with varying characteristics regarding glass transition temperature, surfactants, and particle size distribution were investigated on two different substrates. The drying conditions, defined by film temperature and mass transfer in the gas phase, were varied to emulate typical conditions encountered in the laboratory and industrial processes. Extreme conditions equivalent to air temperatures up to 250 °C in a belt dryer and drying rates of 12 g/(m(2)·s) were realized. The surfactant distributions were measured by means of 3D confocal Raman spectroscopy in the dry film. The surfactant distributions were found to differ significantly with drying conditions at moderate film temperatures. At elevated film temperatures the surfactant distributions are independent of the investigated gas side transport coefficients: the heat and mass transfer coefficient. Coating on substrates with significantly different surface energies has a large impact on surfactant concentration gradients, as the equilibrium between surface and bulk concentration changes. Dispersions with higher colloidal stability showed more homogeneous lateral surfactant distributions. These results indicate that the choice of the drying conditions, colloidal stability, and substrates is crucial to control the surfactant distribution. Results obtained under lab-scale drying conditions cannot be transferred directly to the industrial application. The results were similar for both tested adhesive material systems, despite their different properties. This indicates that other properties, such as the particle size distribution and glass transition temperature, have surprisingly little effect on the development of the surfactant distribution.

Unique adhesive properties of pressure sensitive adhesives from plant oils

We report novel insights into the adhesive performance of bio-based pressure sensitive adhesives (PSAs). Three different homopolymers based on renewable fatty acid methyl esters were characterized in terms of their mechanical and adhesive properties. The polymers display the typical dependence of adhesive properties on molecular weight and degree of crosslinking, as quantified by shear modulus, tack and peel measurements. The absolute values of characteristic adhesion parameters are in the range of commercially available petrochemical PSAs. Curing of applied PSA films at elevated temperature results in a pronounced maximum in tack and peel strength at a critical curing time, which corresponds to a change from cohesive to adhesive failure. Thus, demand-oriented tailoring of adhesive properties can be achieved via an appropriate choice of curing time. Moreover, these bio-based adhesives offer improved adhesion on hydrophobic substrates and high water-resistance without any whitening, thus rendering them an attractive alternative to conventional petroleum-based products. These peculiar features are attributed to the high hydrophobicity of the used monomers.

Preparation and adhesion performance of transparent acrylic pressure sensitive adhesives: effects of substituent structure of acrylate monomer

Three different acrylate monomers containing a cyclohexyl moiety were designed and synthesized to prepare transparent acrylic pressure sensitive adhesives (PSAs) comprised of semi-interpenetrated structured polymer networks. The effects of substituent structure in the acrylate monomer on the adhesion performance of the acrylic PSA were investigated. The prepared UV-curable acrylic PSA syrups were characterized and the optical properties of their acrylic PSA film were also examined. The acrylic PSAs exhibited high transparency in the visible wavelength region. Adhesion performance was evaluated using the peel strength, cohesion strength, and probe tack tests. The adhesion properties of the acrylic PSAs depended on the substituent structure in the acrylate monomer.

Characterization of an acrylic polymer under hygrothermal aging as an optically clear adhesive for touch screen panels

Optically clear adhesives (OCAs) are key components of touch screen panels (TSPs). It is important that OCAs do not affect the transparent electrodes in TSPs because OCAs are contacted to the transparent electrodes. Therefore, N-vinyl caprolactam (NVC) was incorporated in the composition of an acrylic pressure sensitive adhesive (PSA) with excluding an acidic component to maintain the cohesion for OCA preparation. With increasing amounts of NVC, the tack and peel strength of UV-cured PSA increased, but high amounts of NVC led to decreased peel strength. The UV-cured PSA films were placed in a high temperature and humidity chamber for 8 weeks to investigate the durability and corrosion property under hygrothermal conditions. In this study, the corrosion test method using copper foil was suggested as a simple and economical method and was used to evaluate the effect of NVC on the corrosion property of PSA. This method helped identify suitable OCAs that do not have corrosive property. PSA films containing more than 20wt% of NVC promoted the corrosion of copper foil under hygrothermal aging conditions. The caprolactam ring was opened by moisture, and the PSA structure morphed into a polar structure during the aging process. This change caused a glass transition shift, an increase in the storage modulus at the rubbery plateau, and an increase in peel strength. The surface free energy of the PSA films also increased due to the increase in the polar property. However, high amounts of NVC caused a decrease in the peel strength after 8 weeks of aging because of increased molecular interactions.

Preparation and adhesion performance of transparent acrylic pressure-sensitive adhesives containing menthyl acrylate

Using the synthesized menthyl acrylate derived from the menthol as biomass, transparent acrylic pressure-sensitive adhesives (PSAs) composed of semi-interpenetrated structured polymer networks were prepared successfully. The effect of menthyl acrylate concentration in the PSAs was investigated on adhesion performances of the acrylic PSAs. The prepared syrups for acrylic PSAs were characterized and the optical properties for their acrylic PSA films were also examined by UV–Vis spectroscopy, haze meter and prism coupler. The acrylic PSAs exhibited high transparency in the visible wavelength region regardless of reliability test (85/85 test). With increasing menthyl acrylate concentration in the acrylic PSAs, adhesion performances such as the peel strength, cohesion strength, and probe tack were increased.

Effect of propyleneimine external cross-linker on the properties of acrylate latex pressure sensitive adhesives

Acrylate pressure sensitive adhesive (PSA) latexes were synthesized via a starved monomer seeded semi-batch emulsion polymerization process with butyl acrylate (BA), methyl methacrylate (MMA), acrylic acid (AA) and 2-hydroxyethyl acrylate (HEA). These PSA polymers were then cross-linked with trifunctional propyleneimine external cross-linker (SAC-100) to study the cross-linking reaction between carboxylic group of the polymer chain and cross-linking agent. It was found that cross-linking provided a significant influence on the film formation process based on the result of SEM analysis. In addition, with the increase of SAC-100 content, the gel content of the polymer increased significantly, while molecular weight between cross-link points (Mc) and the sol molecular weight (Mw, Mn) of the polymer decreased remarkably. The TGA result showed that the addition of the external cross-linker can enhance the thermal stability of the latex film. 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 uncross-linked counterparts. Besides, dynamic mechanical analysis (DMA) was also used to evaluate the viscoelastic properties of the acrylate emulsion PSA film.

Ultraclean patterned transfer of single-layer graphene by recyclable pressure sensitive adhesive films.

We report an ultraclean, cost-effective, and easily scalable method of transferring and patterning large-area graphene using pressure sensitive adhesive films (PSAFs) at room temperature. This simple transfer is enabled by the difference in wettability and adhesion energy of graphene with respect to PSAF and a target substrate. The PSAF-transferred graphene is found to be free from residues and shows excellent charge carrier mobility as high as ∼17,700 cm(2)/V·s with less doping compared to the graphene transferred by thermal release tape (TRT) or poly(methyl methacrylate) (PMMA) as well as good uniformity over large areas. In addition, the sheet resistance of graphene transferred by recycled PSAF does not change considerably up to 4 times, which would be advantageous for more cost-effective and environmentally friendly production of large-area graphene films for practical applications.

Mechanical properties of a waterborne pressure-sensitive adhesive with a percolating poly(acrylic acid)-based diblock copolymer network: Effect of pH

Copolymerizing an acrylic acid comonomer is often beneficial for the adhesive properties of waterborne pressure-sensitive adhesives (PSAs). Here, we demonstrate a new strategy in which poly(acrylic acid) (PAA) is distributed as a percolating network within a PSA film formed from a polymer colloid. A diblock copolymer composed of PAA and poly(n-butyl acrylate) (PBA) blocks was synthesized using reversible addition–fragmentation chain transfer (RAFT) polymerization and adsorbed onto soft acrylic latex particles prior to their film formation. The thin adsorbed shells on the particles create a percolating network that raises the elastic modulus, creep resistance and tensile strength of the final film. When the film formation occurs at pH 10, ionomeric crosslinking occurs, and high tack adhesion is obtained in combination with high creep resistance. The results show that the addition of an amphiphilic PAA-b-PBA diblock copolymer (2.0wt.%) to a soft latex provides a simple yet effective means of adjusting the mechanical and adhesive properties of the resulting composite film.