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.     

Modification of Adhesive and Latex Properties for Starch Nanoparticle‐Based Pressure Sensitive Adhesives

Starch nanoparticle (SNP)‐based pressure sensitive adhesives (PSAs) with core‐shell particle morphology (starch nanoparticle core/acrylic polymer shell) are produced via seeded, semi‐batch emulsion polymerization at 15 wt% SNP loading (relative to total polymer weight) and 40 wt% latex solids. Crosslinker and chain transfer agent (CTA) are introduced to the acrylic shell polymer formulation at a range of concentrations according to a 3² factorial design to tailor the latex and adhesive properties of SNP‐based latexes. The crosslinker and CTA show no significant effect on polymerization kinetics, particle size, and viscosity. Latex gel content is predicted using an empirical model, which is a function of crosslinker and CTA concentration. Both the gel content and glass transition temperature strongly affect the adhesive properties (tack, peel strength, and shear strength) of the SNP‐based latex films. 3D response surfaces for the adhesive properties are constructed to facilitate the design of SNP‐based PSAs with desired properties.     

Robust and recoverable dual cross-linking networks in pressure-sensitive adhesives

Pressure-sensitive adhesives (PSAs) demand the ability to simultaneously improve toughness and adhesion. However, these requirements of PSAs have remained a great challenge because robust and recoverable characteristics are usually contradictory properties of PSAs. Dual cross-linking networks developed by incorporating dynamic noncovalent bonds into chemical cross-linking networks have the potential to mitigate these requirements in a wide variety of applications including adhesives, hydrogels, and elastomers. Herein, a facile approach to achieve dual cross-linking networks of acrylic PSAs with excellent mechanical properties and high-adhesive performance that integrate physically cross-linked networks into chemically cross-linked networks is proposed. Diurethane acrylic monomer-pentaerythritol ethoxylate (DAM-PEEL) groups were introduced into the acrylic PSA system through photopolymerization. The PSA/DAM-PEEL dual cross-linking networks led to the development of the chemically cross-linked networks for both PSA and DAM via covalent bonds and the physically cross-linked networks between the amide groups of DAM and the hydroxyl groups of PEEL via hydrogen bonds. Consequently, the PSA/DAM-PEEL dual cross-linking networks were able to simultaneously improve the modulus and stretchability. This design strategy for developing dual cross-linking networks of materials could offer potential applications for various adhesive-related applications.     

Influence of Particle Nucleation in Pressure Sensitive Adhesive Properties: Miniemulsion versus Emulsion Polymerization

Miniemulsion polymerization is a promising approach to produce and tailor pressure sensitive adhesives (PSAs). In this paper, a systematic comparison of the adhesive properties of latexes produced by miniemulsion and conventional emulsion polymerization is presented. Specifically, the influence of the total surfactant concentration, chain transfer agent concentration and chemical composition on the final adhesive properties of the polymer 2-ethyl hexyl acrylate/methyl methacrylate/acrylic acid was discerned using a 2³ factorial design for each polymerization method. In addition to the adhesive properties (i.e., loop tack, peel strength and shear strength), molecular weight distribution, particle size distribution (PSD) and glass transition temperature were analyzed. The results show that under the conditions used in this work, it is possible to produce PSAs using miniemulsion polymerization, a process wherein monomer droplet nucleation is the dominant particle nucleation mechanism. The use of a miniemulsion polymerization process, as opposed to the conventional emulsion technique, produced several differences such as larger particles sizes and narrower molecular weight distributions. Focusing on the PSA films that exhibited adhesive rather than cohesive failure, the PSA films generated via miniemulsion polymerization displayed higher values of loop tack and peel strength compared to those produced via conventional emulsion polymerization. Shear strength results were strongly dependent on the amount of gel content and sol molecular weight for both cases.     

The Role of Components in Waterbased Microsphere Acrylic Psa Adhesive Properties

In this paper the batch suspension copolymerization of ethyl acrylate/2 ethyl hexylacrylate (EA/2-EHA) for production of suspension-based microsphere acrylic pressure sensitive adhesives (PSA) is presented. The effects on the adhesion properties of PSA different process (reaction temperature and stirrer speed) as well as chemical parameters (amount of EA, initiator concentration) are discussed. The conversion was monitored in-line using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and the results were compared with the standard gravimetrical method. The glass transition temperatures (T_g) of the PSAs were measured using differential scanning calorimetry (DSC) technique, while molecular weight distribution (MWD) was determined by gel permeation chromatography (GPC). The adhesion properties of PSAs were characterized via the measurements of tack, peel adhesion and peel strength. The results of the experiments have shown that the kinetics of the suspension polymerization for production of PSAs is significantly affected by temperature of polymerization and the initiator concentration, but are shown to be relatively independent of the EA amount and the stirrer speed. The tack, peel and shear strength depend on the mean particle size and particle size (PS) distribution (PSD) and T_g. The mean particle size and PSD depend primarily on the stirrer speed during the PSA synthesis process, while the T_g is most affected by amount of EA used for the synthesis. The results have also shown a rather unexpected relationship between MWD of the PSAs and the applicative properties: tack, peel and shear are seen to be increasing to the decreasing values of weight average MWD, which is the exact opposite of the previously published research. The most likely explanation for this relationship is the formation of a gel during the synthesis of PSA.     

Properties of single-component acrylic pressure-sensitive adhesives synthesized using <Emphasis Type="Italic">tert</Emphasis>-butyl peroxypivalate initiator

In this work, tert-butyl peroxypivalate initiator was newly used in the solution polymerization of acrylic copolymers with 2-ethylhexyl acrylate, butyl acrylate, methyl methacrylate and acrylic acid monomers for application of pressure-sensitive adhesives (PSAs). Its proper dosage was determined to vary from 0.6 to 1.2 wt % when a high monomer conversion (>99%) was ensured. In this amount range, polymer properties and adhesive performance of the PSAs were investigated. The results indicated that with the amount of tert-butyl peroxypivalate increased, the molecular weights of the polymer decreased and the molecular weight distribution became wider. It was also observed that the synthesized PSAs had high interfacial adhesion and low cohesion strength, and thus exhibited cohesive failure during the peel test. So cross-linking agent was employed to improve the shear strength of the PSAs and to eliminate the adhesive residue while at the sacrifice of loop tack and peel strength. As a whole, the optimal performance was obtained by using 1.2 wt % amount of initiator and 0.5 wt % concentration of cross-linker. In this case, the peel and shear strength have achieved the best balance. In addition, for the cross-linked PSA tapes, the peel strength slightly decreased with the dwell time.     

Visible-Light-Curable Solvent-Free Acrylic Pressure-Sensitive Adhesives via Photoredox-Mediated Radical Polymerization

Owing to their excellent properties, such as transparency, resistance to oxidation, and high adhesivity, acrylic pressure-sensitive adhesives (PSAs) are widely used. Recently, solvent-free acrylic PSAs, which are typically prepared via photopolymerization, have attracted increasing attention because of the current strict environmental regulations. UV light is commonly used as an excitation source for photopolymerization, whereas visible light, which is safer for humans, is rarely utilized. In this study, we prepared solvent-free acrylic PSAs via visible light-driven photoredox-mediated radical polymerization. Three α-haloesters were used as additives to overcome critical shortcomings, such as the previously reported low film curing rate and poor transparency observed during additive-free photocatalytic polymerization. The film curing rate was greatly increased in the presence of α-haloesters, which lowered the photocatalyst loadings and, hence, improved the film transparency. These results confirmed that our method could be widely used to prepare general-purpose solvent-free PSAs—in particular, optically clear adhesives for electronics.     

Effects of surface properties of colloidal silica particles on redispersibility and properties of acrylic-based polyurethane/silica composites

Nanosilica particles with different surface properties were designed and prepared using colloidal silica particles and four different qualitative silane coupling agents (SCA), namely methyltriethoxysilane (MTES), octyltriethoxysilane (OTES), vinyltriethoxysilane (VTES) and methacryloxypropyltrimethoxysilane (MATMS), and further applied in acrylic resins and corresponding polyurethane coats by in situ polymerization. It was found that different qualitative SCA molecules had very different impacts on the redispersibility of nanosilica particles, the adsorbed acrylic polyol molecules, the viscosities of acrylic polyol/silica hybrid resins, and the properties of acrylic-based polyurethane/silica composites.     

Crosslinkable propyleneimine pressure‐sensitive adhesive acrylates and their pot life

In this article a new generation of crosslinkers based on multifunctional propyleneimine derivatives involving crosslinking reactions of acrylic pressure‐sensitive adhesives (PSAs) were investigated. Their tack, peel adhesion, and shear strength after crosslinking, as well as their viscosity and pot life were also measured. Crosslinking of PSAs is an established technology used in many industrial manufacturing processes. Their novel applications and technical specifications stimulate continuous research and development into new crosslinkers with very interesting characteristics. Copyright © 2004 John Wiley & Sons, Ltd.     

Waterborne polyurethane-acrylic hybrid nanoparticles by miniemulsion polymerization: applications in pressure-sensitive adhesives

Waterborne polyurethane-acrylic hybrid nanoparticles for application as pressure-sensitive adhesives (PSAs) were prepared by one-step miniemulsion polymerization. The addition of polyurethane to a standard waterborne acrylic formulation results in a large increase in the cohesive strength and hence a much higher shear holding time (greater than seven weeks at room temperature), which is a very desirable characteristic for PSAs. However, with the increase in cohesion, there is a decrease in the relative viscous component, and hence there is a decrease in the tack energy. The presence of a small concentration of methyl methacrylate (MMA) in the acrylic copolymer led to phase separation within the particles and created a hemispherical morphology. The tack energy was particularly low in the hybrid containing MMA because of the effects of lower energy dissipation and greater cross-linking. These results highlight the great sensitivity of the viscoelastic and adhesive properties to the details of the polymer network architecture and hence to the precise composition and synthesis conditions.     

Effect of the structure of latex particles on adhesion. Part I: Synthesis and characterization of structured latex particles of acrylic copolymers and their peel adhesion behavior

This is a series of articles that deals with fundamental aspects of the effects of the structure of latex particles of acrylic copolymers on their adhesion behavior. Specifically, relationship or analogy between rheological properties and adhesion performance of the acrylic copolymers was demonstrated. The first part of this series concerns the synthesis and characterization of latex particles with desired structures and compositions, and the experimental results of peel adhesion. The second part develops an analogy between the peel adhesion performance of the adhesives and rheological properties of the corresponding copolymers. The third part addresses the generalities and particularities of three major tests for adhesion: peeling, blistering, and spontaneous peeling. Three types of structured latex particles were synthesized by three different emulsion polymerization processes: the first type had a uniform composition over the entire particles with a glass transition temperature (T_g) varying between ?40°C and 0°C, depending upon the compositions of monomers involved in the copolymer; the second type was of core-shell structure. As for the third type, the composition of monomers varied gradually across the particle radii. The glass transition behavior and the dynamic mechanical properties in the solid state of the copolymers confirmed the structures of the corresponding latex particles. On the other hand, the peel adhesion performance of the films of these latex particles varied with the dynamic mechanical properties of the corresponding copolymers. This implies that a correlation could be found between the structure of the latex particles, dynamic mechanical properties in the solid state of the corresponding copolymers, and the peel adhesion performance of the adhesive films. ©1995 John Wiley & Sons, Inc.     

Influence of Block Copolymer on Formation and Acid Resistant Properties of Hybrid CaCO_3 Particles

Block copolymer polystyrene-b-poly(acrylic acid)(PS-b-PAA) was used as structural template for the synthesis of CaCO3 microparticles. Through this procedure, acid resistant hybrid CaCO3 micro-spheres were obtained. Acid resistant properties of this type of hybrid CaCO3 were studied. Size mea-surement shows that the acid resistant properties of the hybrid particles are different in different solutions, such as HCI, EDTA, and H2SO4 solutions.     

Effects of polyaniline chain structures on proton conduction in a PEM host matrix

This study examined the effects of the conjugated chain structure of polyaniline (PAn) on proton transport in a proton exchange membrane (PEM) containing a small amount of PAn colloidal particles. The PEM host matrix consisted of a hydrophobic three-component polymer blend (TCPB) of poly(4-vinylphenol-co-methylmethacrylate) P(4-VP-MMA), poly(butyl methacrylate) (PBMA), and Paraloid^® B-82 acrylic copolymer resins; in which a hydrophilic network of 2-acrylamido-2-methyl propanesulfonic acid (AMPS), 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol)dimethylacrylate (PEGDMA) was formed upon embedded polymerization. Colloidal PAn particles were added to the PEM matrix during the embedded polymerization of PEM. Two types of PAn colloidal particles with different chain structures and morphologies were synthesized by inverse miniemulsion polymerization and interfacial polymerization. The PAn(1) particles from inverse miniemulsion polymerization were bar-shaped, contained a higher fraction of quinoid diimine units than the scaffold-like PAn(2) particles from interfacial polymerization, and displayed a strong promotional effect on proton conduction. The oxidation state of the PAn particles was also varied by post-synthesis treatments to evaluate the effect of oxidation state on proton conduction. It was found that a mixed oxidation state such as the emeraldine form of PAn had the best enhancement effect. The PAn loading optimal for proton conductivity enhancement of the composite PEM was determined to be about 2 wt% of PAn(1).     

交联剂对无皂P(MMA-EA-MAA)种子聚合乳胶粒成孔的影响

采用完全无皂种子乳液聚合技术合成了粒径窄分布的P(MMA-EA-MAA)乳胶粒,通过对上述胶乳进行碱处理,制备出了具有空腔结构和多孔结构的聚合物乳胶粒,研究了交联剂的种类和用量对聚合过程、胶粒特性及胶粒结构形态的影响.结果表明,体系中加入交联剂后,单体转化率都有不同程度的提高;随交联剂用量的增加,乳胶粒粒径略有减小,交联剂用量较高时,乳胶粒粒径分布加宽;二乙烯基苯(DVB)的交联效率稍高于双甲基丙烯酸乙二醇酯(EGDMA);不加入交联剂及EGDMA用量低于0.5%时,处理后乳胶粒呈空腔结构,加入DVB及EGDMA用量高于1.0%时,处理后乳胶粒呈多孔结构,并且乳胶粒体积增量随交联剂用量的增加而减小.     

Investigation of the peel test for measuring self-cleanable characteristic of fluorine-modified coatings

The self-cleanable ability of coatings is important to prevent or remove polluting fingerprints, dust, water and oils for a number of applications. Fluorocarbon polymers have been used to provide self-cleanable ability due to their low surface energy. The efficiency of fluorine-modified coatings has been evaluated by measuring surface free energy using a contact angle measurement. However, this method is not sufficient to define the polluting-preventive ability or removability of fluorine-modified coatings due to the amount of fluorine content.A peel test can be used to determine the self-cleanable characteristics of fluorine-modified coatings by evaluating adhesion between the coating surface and pressure sensitive adhesives (PSAs). In addition, adhesion can be used to predict the amount of polluting-preventive ability or removability of coatings by comparing the peel strength of commercial PSAs. We designed fluorine-modified acrylic resins with different fluorine contents for a new testing method. Comparing the contact angle measurement with the peel test results, the peel test for the self-cleanable characteristic of coatings was more suitable than the contact angle measurement to predict the polluting-preventive ability and removability of coatings.     

Rheology of acrylic latices as a function of carboxyl neutralization

Latexes based on acrylic acid, acrylamide, ethyl methacrylate, and ethyl acrylate were synthesized via emulsion polymerization with different monomer compositions. The resultant latices were thickened with different molar ratios of NaOH to acrylic acid and were analyzed in terms of acid-basis titrimetry, turbidimetry, rheology, and tensiometry. Titrimetry, turbidimetry and rheometry were used to analyze factors such as carboxyl group availability and particle solubilization, tensiometry monitoring the influence of carboxyl neutralization on polymer-surfactant interactions. For the acrylic acid content used in this work (20 wt%), the results indicated that as carboxyl groups distribution became more homogeneous, the process of latex thickening became more effective.     

Photoreactive UV-crosslinkable acrylic pressure-sensitive adhesives containing type-II photoinitiators

UV-crosslinking is an established technology used in many industrial manufacturing processes. New applications and technical specifications of UV technologies stimulate the continuous development of photoinitiators that can efficiently meet specific requirements. A typical class of radical-reactive type-II photoinitiators has been used for the UV-initiated crosslinking of acrylic pressure-sensitive adhesives (PSAs).The activity of type-II photoinitiators such as: benzophenone derivatives, thioxanthone derivative, antraquinone derivative and fluorenone (without tertiary amine as a co-initiator) in the photoreactive UV-crosslinkable acrylic pressure-sensitive adhesives was described. The effect of the type-II photoinitiators on the acrylic PSA properties (tack, peel, and shear strength) was summarized.     

Design and Preparation of Highly Filled Water‐Borne Polymer–Gibbsite Nanocomposites

Highly filled, high solids content, water‐borne polymer–Gibbsite nanocomposites are prepared with Gibbsite contents as high as 35 wt%. The polymer–Gibbsite nanocomposites are synthesised via conventional starved feed emulsion polymerization using negatively charged butyl acrylate‐co‐acrylic acid oligomers, which functioned as electrosteric stabilizers for the initial platelets and the subsequently formed latex particles. A simple mathematical model describing the amount of cooligomer required for the colloidal stability of the initial Gibbsite platelets and the subsequently formed particles was derived. This model was used to determine the reaction conditions required for obtaining colloidally stable nanocomposites with a targeted filler content. Cryogenic transmission electron microscopy characterization of the resulting nanocomposites with filler contents up to 20 wt% revealed fully encapsulated Gibbsite platelets and a mixed morphology of “muffin‐like” and encapsulated particles was obtained at higher filler contents.     

Synthesis, characterization, and thermal properties of diacrylic/divinylbenzene copolymers

In this article, synthesis, characterization, and thermal properties of diacrylic/divinylbenzene copolymers based on the new aromatic tetrafunctional acrylate monomers are presented. The new monomers were generated by treatment of epoxides derived from various aromatic diols: naphthalene-2,3-diol (NAF), biphenyl-4,4′-diol (BIF), bis(4-hydroxyphenyl)methanone (BEP) or 4,4′-thiodiphenol (BES), and epichlorohydrin with acrylic acid. The addition reaction was carried out by a ratio of 0.5 mol of suitable epoxy derivative and 1 mol of acrylic acid in the presence of 0.7 wt% of triethylbenzylammonia chloride (TEBAC) as a catalyst and 0.045 wt% of hydroquinone as a polymerization inhibitor. The chemical structure of the prepared acrylate monomers was confirmed by ¹³C NMR and GC MS spectra. The emulsion–suspension polymerization of acrylate monomers with divinylbenzene (DVB) in the presence of pore-forming diluents (toluene + decan-1-ol) allowed obtaining microspheres containing pendant functional groups (hydroxyl groups). This process was carried out at constant mol ratio of acrylate monomers: DVB (1:1), and constant volume ratio of pore-forming diluents to monomers (1:1). The different concentrations of toluene in the mixture with decan-1-ol were used for qualifying the effect of the diluents on the microsphere characteristics. The influence of synthesis’s parameters on the properties of copolymer beads, e.g., pore size and surface area by BET method, the surface texture by AFM, swelling behavior in polar and non-polar solvents as well as thermal stability by differential scanning calorimetry (DSC), and thermogravimetric analysis (TG) was studied and discussed.     

Pressure and concentration profiles in filter cake consisting of core/shell latex particle

Poly(styrene-co-acrylic acid) latex particles with different acrylic acid contents have been synthesized and used for filtration studies. Effective pressure and dry matter concentrations were measured at different positions in the filter cakes during the filtration processes, and dry matter concentration was not found to change significantly with effective pressure. Nevertheless, the local dry matter concentration did increase with time for latex particles containing 1 and 3%, w/w acrylic acid, which indicate that filter cake comprising latex particles with a high acrylic acid content will creep during the filtration stage. The filter cakes were examined using stepped-pressure filtration experiments as well, and an almost instantaneous deformation of the filter cake was observed after the pressure step. Furthermore, a minor deformation was observed over the following 2 h for latex particles both containing and not containing acrylic acid. This is thought to be due to the rearrangement of particles in the filter cake.