Acrylic Pressure-sensitive Adhesives Research Articles

Free Volume Effect via Various Chemical Structured Monomers on Adhesion Property and Relative Permittivity in Acrylic Pressure Sensitive Adhesives.

Acrylic pressure-sensitive adhesives (PSAs) are used as fixatives between layers of a display. PSAs’ function is an important factor that determines the performance of the display. Of the various display types available, the touch screen panel (TSP) of smart devices is firmly related to the relative permittivity of the elementals. Therefore, adjusting the relative permittivity of the PSA is indispensable for driving the TSP. Accordingly, selected acrylic pre-polymers were polymerized and the pre-polymer was blended and cross-linked with monomers with different chemical structure to adjust the relative permittivity. The monomers were hexametyldisiloxane (HMDS), N-vinylcaprolactam (NVC), tert-butyl acrylate (TBA), and isooctadecyl acrylate (ISTA). The gel fraction and transmittance as a function of the monomers show a similar result to the pure acrylic PSA. However, the gel fraction value decreased to about 90% and the transmittance decreased to about 85%, due to the immiscibility between nonpolar HMDS and acrylic PSA. On the other hand, the adhesion properties were improved when NVC was added because of the polarity of the nitrogen group. In addition, the relative permittivity of the PSA decreased regardless of the monomer chosen. There was, however, a difference in the optimal content of each monomer, and NVC decreased from 4 phr content to about 3.4 in reducing relative permittivity. Through the above results, it was confirmed that NVC having a nitrogen group is most advantageous in lowering adhesion properties and relative permittivity, and necessitates further research based on the findings.

Enhanced Heat Resistance of Acrylic Pressure-Sensitive Adhesive by Incorporating Silicone Blocks Using Silicone-Based Macro-Azo-Initiator

To improve the heat resistance of acrylic-based pressure-sensitive adhesive (PSA), silicone-block-containing acrylic PSAs (SPSAs) were synthesized using a polydimethylsiloxane (PDMS)-based macro-azo-initiator (MAI). To evaluate the heat resistance of the PSA films, the probe tack and 90° peel strength were measured at different temperatures. The acrylic PSA showed that its tack curves changed from balanced debonding at 25 °C to cohesive debonding at 50 °C and exhibited a sharp decrease. However, in the case of SPSA containing 20 wt% MAI (MAI20), the balanced debonding was maintained at 75 °C, and its tack value hardly changed with temperature. As the MAI content increased, the peel strength at 25 °C decreased due to the microphase separation between PDMS- and acryl-blocks in SPSA, but the shear adhesion failure temperature (SAFT) increased almost linearly from 41.3 to 122.8 °C. Unlike stainless steel substrate, SPSA showed improved peel strength on a polypropylene substrate due to its low surface energy caused by PDMS block. Owing to the addition of 20 wt% silicone-urethane dimethacrylate oligomer and 200 mJ/cm2 UV irradiation dose, MAI20 showed significantly increased 90° peel strength at 25 °C (548.3 vs. 322.4 gf/25 mm for pristine MAI20). Its heat resistance under shear stress assessed by shear adhesion failure test (SAFT) exhibited raising in failure temperature to 177.3 °C when compared to non-irradiated sample.

High holding power of acrylic emulsion PSA with sorbitan nonionic surfactants and cross-linker

Since traditional nonyl phenyl type nonionic surfactants have been known as destructive to the ecosystem, sorbitan nonionic surfactants (Tween 20, 40, 60 and 80) were used to make acrylic emulsion type pressure sensitive adhesives (PSA), and the type of effects they have on the adhesive properties were investigated. Also, their adhesive properties were compared with those synthesized using traditional nonyl phenyl nonionic surfactant (NP 40). As a result, PSA made using Tween60 showed higher initial tack and peel strength and a much higher holding power than those properties made using NP 40 at room temperature. PSA made by Tween 60, and cross-linked by DGEBA (Bisphenol A diglycidyl ether) and phenyl aziridine, exhibited over 12 h of holding power at 150 °C, and showed a holding state up to 180 °C during a SAFT test (Shear Adhesion Failure Temperature).

Predictive mechanistic model for single-layered pressure-sensitive adhesive (PSA) joints : Part I: Uniaxial tensile stress-strain response.

Modeling the deformation of structures containing pressure-sensitive adhesive (PSA) joints can be a challenging task because of the dependence of the deformation mechanism on a) PSA adhesive properties and b) the bonding substrate's surface properties, such as surface energy and surface roughness. These parameters have significant and unique effects on the mechanical response of the joint. This paper is part of a two-part series, where a mechanism-based predictive modeling approach, supported by empirical observations, is presented for modeling the uniaxial tensile mechanical behavior of single-layered PSA joints based on acrylic PSA materials. This paper (Part I) addresses the stress-strain response, while Part II of this series will address the creep behavior. The underlying model is based on multiple mechanisms: i) cavity nucleation and growth in the bulk adhesive material of the PSA system, as well as at the interfaces between the PSA and the substrate; ii) fibrillation of the cavitated adhesive layer and iii) interfacial slippage between the adhesive and the bonding substrate; iv) PSA delamination from the substrate. This predictive model can be used as a virtual testing tool to generate stress-strain curves for constitutive models of PSA joints under different tensile loading conditions.

Unconventional Passive Enhancement of Transdermal Drug Delivery: toward a Mechanistic Understanding of Penetration Enhancers Releasing from Acrylic Pressure-Sensitive Adhesive of Patches.

Penetration enhancers (PEs) enhancing efficacy depends on two processes: PEs release from patches and action on skin. Compared with their action on skin, PEs release process was poorly understood. Therefore, the purpose of this study was to make a mechanistic understanding of PEs release from acrylic pressure-sensitive adhesive of patches and propose an unconventional enhancement of PEs efficacy. PEs efficacy was evaluated both in drug permeation study and drug pharmacokinetic study. Confocal Raman spectroscopy was employed to observe PEs release behavior by mapping PEs dynamic distribution in skin. The mechanism of PEs release behavior was provided from molecular interaction and rheology using FT-IR, molecular docking, molecular dynamic simulation and rheometer, separately. The release behavior of PEs themselves greatly restricted their efficacy. By using PEG 400, an improvement of oleic acid (OA) release behavior was achieved, and the efficacy of OA was significantly enhanced with enhancing ratio (ER) from 2.69 to 4.10 and AUClast from 1574 ± 87 to 2664 ± 249ng·h/mL, separately. The improvement of OA release behavior was primarily resulted from reduction of the interaction between OA and adhesive, which was caused by other small molecules with a strong ability in forming hydrogen bonds with adhesive. Also, the rigidity of adhesive was a factor in affecting PEs release behavior. An unconventional passive enhancement of transdermal drug delivery was achieved via improving PEs themselves releasing from acrylic pressure-sensitive adhesive. Graphical abstract Influence of PEs release behavior on drug permeation through skin and molecular mechanism.

Change of Characterization and Film Morphology Based on Acrylic Pressure Sensitive Adhesives by Hydrophilic Derivative Ratio.

Hydrophilic acrylic pressure-sensitive adhesives (PSAs) were synthesized by controlling the contents of 2-ethylhexyl acrylate (EHA), isobornyl acrylate (IBOA), and 2-hydroxyethyl acrylate (HEA); especially, the characteristic change of the HEA content was analyzed. Surface contact angle of acrylic PSA film decreased from 77.87° to 70.23° in the case of Acryl-2 to Acryl-8 (below HEA 10 wt %). However, the surface contact angle of Acryl-10 to Acryl-40 (HEA 10 wt % to 40 wt %) increased up to 92.29°, indicating hydrophobicity. All acrylic PSA films showed high adhesive force above 1800 gf/25 mm. According to X-ray diffraction (XRD) measurement, hydrophilic acrylic PSAs exhibited amorphous property and it was confirmed that the morphology of acrylic PSA film was significantly affected by the flexibility of the polymer chain and the strength of hydrogen bonding. The affinity with hydrophilic materials for acrylic PSA films was evaluated by T-type peel test, confirming that the affinity with hydrophilic materials is determined by the hydrophilicity of the acrylic PSA film. The synthesized acrylic PSA film is non-toxic regardless of the hydrophilicity.

Influence of thermal reactive crosslinking agents on the tack, peel adhesion, and shear strength of acrylic pressure-sensitive adhesives

In recent decades, the basic technology of pressure-sensitive adhesive (PSA) acrylics has developed into a sophisticated science. The main properties of acrylic PSAs such as tack, peel adhesion, and shear strength are determined to a large extent by the kind and quantity of crosslinking agents added to the synthesized PSAs. In order to improve their adhesive (tack, peel adhesion) and cohesive (shear strength) properties, a wide range of amino resin thermal crosslinkers are tested. An acrylic PSA based on 2-ethylhexylacrylate, n-butyl acrylate, and acrylic acid was synthesized by performing a radical polymerization in ethyl acetate. After the addition of amino resins to the acrylic PSA and carrying out thermally initiated crosslinking processes to prepare one-sided self-adhesive tapes, their properties were assessed.

Comparison between thermal crosslinkers based on melamine-formaldehyde and benzoguanamine resin and their influence on main performance of acrylic pressure-sensitive adhesives as tack, peel adhesion, shear strength and pot-life

An acrylic pressure-sensitive adhesive (PSA) was synthesized in ethyl acetate at about 80 °C by the use of 2-ethylhexyl acrylate, ethyl acrylate, methyl acrylate and acrylic acid at presence of thermal radical initiator AIBN. The synthesized acrylic PSA was crosslinked at relatively low temperatures at about 110–125 °C using thermal crosslinkers selected from melamine-formaldehyde resins and benzoguanamine resins. The crosslinking process runs between carboxylic groups of acrylic PSA and reactive groups from investigated amine resins. The choice of suitable thermal reactive crosslinkers has significant and relevant influence at presence of organic acid catalysts on main performance of crosslinked PSA such as tack, peel adhesion and shear strength.

Behavior and Adhesion Performance of Acrylic PSAs using Semi-IPN Structure and UV/UV Stepwise Curing

Pressure-sensitive adhesives (PSAs) and UV-curable acrylic systems are widely utilized. In particular, PSAs have currently attracted significant attention because of their utility and applicability for manufacturing re-useable modules for smart devices. In this study, adhesion properties, UV-curing behavior, viscoelastic properties, and gel fraction were investigated. The UV/UV step curing process was utilized to overcome limitations, such as re-work or gap filling. The difference in physical properties between primary curing and secondary curing was confirmed. In addition, by adjusting the content of the crosslinking agent, the experiment based on controlling the structure of the semi-interpenetrating polymer network was conducted. We determined that physical properties varied with the crosslinking agent content. The degree of crosslinking was high, whereas the crosslinking density was low for 0.1–0.3 phr. However, both the degree of crosslinking and the crosslinking density increased for 0.5–1 phr.

Toward replacement of methyl methacrylate by sustainable bio-based isobornyl methacrylate in latex pressure sensitive adhesive

Sustainable bio-based monomer isobornyl methacrylate (IBOMA) was evaluated as an alternative to traditional petroleum-based methyl methacrylate (MMA) as hard monomer in the application of acrylic latex pressure sensitive adhesive (PSA). The influence of bio-based IBOMA on the viscosity and particle size of the latexes and the gel content, sol molecular weight (Mw, Mn) and adhesive properties (loop tack, peel strength and shear strength) of the PSA copolymers were investigated. In addition, transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), contact angle analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) were used to characterize the structure and properties of latexes and corresponding films. Results were compared with those obtained when using traditional petroleum-based hard monomer MMA. Some interesting phenomena and results were indeed obtained in this work. This article will not only enrich the application of bio-based monomer IBOMA in the field of acrylic emulsion PSA, but also provide sustainable methods for the preparation of high performance acrylic emulsion PSAs (e.g. high water resistance and high cohesion emulsion PSAs).

Conductive acrylic pressure-sensitive adhesives

Conductive acrylic pressure-sensitive adhesives

Grafting of Fatty Acids on Polyvinyl Alcohol: Effects on Surface Energy and Adhesion Strength of Acrylic Pressure Sensitive Adhesives

Chemical grafting with fatty acid chlorides is known to reduce the surface tension of polymer substrates. The aim of this study was to evaluate the effect of different grafting parameters on functional properties such as the surface tension of grafted substrates and adhesion of acrylic pressure sensitive adhesives (PSA) on those substrates in dependence of storage time. There-fore, two substrates, paper and polyethylene terephthalate (PET), were coated with polyvinyl alcohol (PVOH). The PVOH showed similar degrees of hydrolysis but different molecular weights. Fatty acid chlorides (palmitoyl chloride, stearoyl chloride) were grafted on pure PET, pure paper, PVOH coated paper, and PVOH coated PET. On these samples, roughness was measured and peel strength and surface energy were determined over storage time. Peel strength was observed to increase with roughness. The chain length of fatty acid chlorides and storage time did not majorly influence peel strength.

Design and evaluation of adhesive type transdermal patches of carvedilol

The transdermal adhesive patches of carvedilol were designed using pressure sensitive acrylic adhesives such as DUROTAK® 87-235A, DUROTAK® 87-8301 and DUROTAK® 87-4287. The patches were evaluated for physicochemical characterization, in-vitro drug permeation across dialysis membrane and ex-vivo drug permeation through the pork ear skin using diffusion cell, stability studies and skin irritability study. The Scanning Electron Microscopy (SEM) of patches does not show any evidence of recrystallization indicating the presence of drug in the molecular form in the adhesive matrix. The physicochemical properties of patches were found to be in acceptable limit. Among the three acrylic adhesives used, DUROTAK® 87-4287 exhibited maximum flux (8.47 ± 0.18 μg/cm2.hr). To enhance the drug permeation, peppermint oil was used as penetration enhancers (2%) in the patches. Out of those, formulation A6 exhibited a flux of 10.04 ± 0.83 μg/cm2.hr revealing that formulation A6 was the optimized formulation. The patches of A6 formulation showed excellent in-vitro-ex-vivo correlationship. The stability study was carried out using optimized fresh (A6) formulation for 3 months old patches stored at room (25 ± 2 °C/60 ± 5%RH) and at accelerated condition (40 ± 2 °C/75 ± 5%RH). The investigation reveals that the adhesive type patches of carvedilol were stable and devoid of skin irritation and hypersensitive response. Therefore, may serve as a potential drug delivery system for carvedilol.

Preparation of environmentally friendly acrylic pressure-sensitive adhesives by bulk photopolymerization and their performance

Polyacrylic pressure-sensitive adhesives (PSAs) based on butyl acrylate (BA), 2-hydroxyethyl acrylate (HEA), and acrylic acid (AA) were prepared by a bulk polymerization process triggered by a radical photoinitiator under UV irradiation and UV-crosslinking. 1,6-Hexanediol diacrylate (HDDA) with difunctional groups was introduced into the PSAs to modify semi-interpenetrating network structures. The effect of HDDA content on the pressure-sensitive performance was comprehensively tested. The viscosity of the prepolymer was measured by a rotational viscometer. Prepolymers obtained by a photoinduced process and UV crosslinking process were confirmed via Fourier transform infrared spectroscopy (FTIR). All double bonds participated in the copolymerization without any remaining monomers, which reflected the concept of green environmental protection. Gel content in the crosslinked portion was examined by Soxhlet extraction, whilst the soluble molecular weight of PSAs was characterized by gel permeation chromatography (GPC). The viscoelastic properties of polymer films were determined by dynamic mechanical analysis (DMA). The Tg value and storage modulus (G′) of the PSAs were enhanced with the addition of HDDA. Moreover, three fundamental adhesive properties, i.e. loop tack force, peel force and shear strength of PSAs, were measured. The results showed that UV crosslinking technology achieved a good balance of the three forces with excellent pressure-sensitive properties.

Biosourced terpenoids for the development of sustainable acrylic pressure-sensitive adhesivesviaemulsion polymerisation

Terpenoid-based (meth)acrylates are introduced in waterborne acrylic pressure-sensitive adhesivesviaemulsion polymerization. These materials showed good tack, peel strength and shear resistance properties, comparable to a petroleum-based benchmark.

Synthesis of solvent-free acrylic pressure-sensitive adhesivesviavisible-light-driven photocatalytic radical polymerization without additives

Solvent-free acrylic pressure-sensitive adhesives were preparedviavisible-light driven photocatalytic free radical polymerization. Combined experiments and quantum calculations divulged the origin of the enhanced rate of polymerisation in the presence ofN-vinyl monomers.

Adhesion Performance and Recovery of Acrylic PSA with Acrylic Elastomer (AE) Blends via Thermal Crosslinking for Application in Flexible Displays.

Acrylic pressure-sensitive adhesive (PSA) is used to fix each layer of a flexible display. Acrylic PSA needs to satisfy specific elongation and recovery requirements so that reliability of the flexible display can be achieved. For this reason, we aimed to design an acrylic PSA/acrylic elastomer (AE) blend and to study how some viscoelastic and adhesion properties are influenced by the AE content into the mixed, blended system. Samples were characterized by UV–Vis spectrophotometry for transmittance, texture analysis for adhesion performances, and dynamic mechanical analysis (DMA) for recovery and viscoelasticity. When acrylic PSA/AE was simply blended, the adhesion performance changed due to the influence of the long molecular chains of AE. Based on this result, the AE content was fixed at 10 wt %, and acrylic PSA prepolymer was crosslinked at different concentrations of crosslinking agent. Peel strength and probe tack decreased as the concentration of crosslinking agent increased, as reported in previous studies. On the other hand, as the content of the crosslinking agent increased, recovery characteristics were improved. Additionally, as the content of the crosslinking agent increased, the storage modulus also increased, although the glass-transition temperature was not affected. According to these findings, we successfully proved the possibility of using AE to adjust adhesion performance and recovery of acrylic PSA for designing flexible displays.

Contact-induced molecular rearrangement of acrylic acid-incorporated pressure sensitive adhesives

Although recent literatures have pointed out that viscoelastic dissipation is the main mechanism affecting the adhesion of pressure sensitive adhesives (PSAs), the controversial issue found previously has spurred us to be interested in the contribution of surface chemistry and physics. Herein, it was found that changes in the surface energy of PSAs caused a significant increase in the adhesion energy via rearrangement of the polymer chains, inducing reorientation of the polar group toward the metallic adherend. The adhesion energy increased with increasing contact time on the adherend, where the adhesion performance of acrylic acid-incorporated PSA increased by more than 300% after 24 h contact with stainless steel. The surface energy of the adhesives were calculated as a function of contact time via contact angle measurements and using the Fowkes theory in order to substantiate the changes in the surface properties influencing the adhesion. The surface chemistry of the PSAs was analyzed by Fourier-transform infrared analysis and time-of-flight secondary ion mass spectrometry, which suggest that the enhanced adhesion of acrylic acid-incorporated PSA is due to the contact time-dependent mechanism, in which induces the polymer chains rearranged and polar groups exposed at the interface.

Preparation of acrylic pressure-sensitive adhesives by UV/UV step curing as a way of lifting the limitations of conventional dual curing techniques

Pressure-sensitive adhesives (PSAs) and UV-curable acrylic systems are widely utilized in different industries, with particular attention currently directed at their use in the production of re-useable modules for smart devices. Herein, we developed a two-step UV/UV curing technique to overcome the limitations of dual curing methods conventionally used for PSA preparation and characterized the thus obtained acrylic adhesives by a range of techniques to determine the uncured marginal portion of the pre-polymer, viscoelastic properties, and adhesive properties (peel and tack). Insufficient primary curing resulted in marked physical property deterioration, while the expression of secondary curing was weak when excessive irradiation energy was supplied. Thus, it was concluded that the physical properties of acrylic PSAs could be controlled by adjustment of primary curing energy.

Enhanced Adhesion and Cohesion of Bioinspired Dry/Wet Pressure-Sensitive Adhesives.

The byssus-mediated adhesion of marine mussels is a widely mimicked system for robust adhesion in both dry and wet conditions. Mussel holdfasts are fabricated from proteins that contain a significant amount of the unique catecholic amino acid dihydroxyphenylalanine, which plays a key role in enhancing interfacial adhesion to organic and inorganic marine surfaces and contributes to cohesive strength of the holdfast. In this work, pressure-sensitive adhesives (PSAs) were synthesized by copolymerization of dopamine methacrylamide (DMA) with common PSA monomers, butyl acrylate and acrylic acid, with careful attention paid to the effects of catechol on adhesive and cohesive properties. A combination of microscopic and macroscopic adhesion assays was used to study the effect of catechol on adhesion performance of acrylic PSAs. Addition of only 5% DMA to a conventional PSA copolymer containing butyl acrylate and acrylic acid resulted in 6-fold and 2.5-fold increases in work required to separate the PSA from silica and polystyrene, respectively, and a large increase in 180° peel adhesion against stainless steel after 24 h storage in both ambient and underwater conditions. Moreover, the holding power of the catechol PSAs on both steel and high-density polyethylene under shear load continuously increased as a function of catechol concentration, up to a maximum of 10% DMA. We also observed stark increases in shear and peel adhesion for the catecholic adhesives over PSAs with noncatecholic aromatic motifs, further underlining the benefits of catechols in PSAs. Overall, catechol PSAs perform extremely well on polar and metallic surfaces. The advantage of incorporating catechols in PSA formulations, however, is less straightforward for peel adhesion in nonpolar, organic substrates and tackiness of the PSAs.