Effect of side chain on wettability and adhesion performance of acrylic pressure-sensitive adhesives on thin silicon wafer

Acrylic pressure-sensitive adhesives (PSAs) need to show proper adhesion and improved wettability on the silicon wafer as the wafer becomes thinner. The acrylic copolymers were synthesized by solution radical polymerization of 2-ethylhexyl acrylate, ethyl acrylate, and acrylic acid with AIBN as an initiator. Adhesion performance and wettability of acrylic PSAs were studied depending on the content of lauryl side chains and the degree of crosslinking. The introduction of lauryl side chain was characterized by Fourier transform infrared spectroscopy. The adhesion performance of acrylic PSAs having lauryl side chain was investigated using contact angle, wettability, probe tack, peel strength, and cohesiveness tests. The wettability of acrylic PSAs was improved significantly with increasing the content of lauryl side chain.     

Improvement in wettability of pressure‐sensitive adhesive on silicon wafer using crosslinking agent with siloxane groups

Acrylic copolymers are prepared by radical polymerization of 2‐ethylhexyl acrylate, ethyl acrylate, and acrylic acid followed by crosslinking to manufacture the pressure‐sensitive adhesives (PSAs) for silicon wafer protection. Both higher reliability and wettability are required for the protective acrylic PSAs in the semiconductor processing applications. The siloxane linkages are introduced in the acrylic PSAs via crosslinking with siloxane‐containing crosslinking agent to modify the thermal and wetting properties of PSAs efficiently. The more efficient formation of crosslinked network structure was achieved with higher content of tetra‐functional crosslinking agent, and the surface energy of PSAs decreased significantly with increasing the content of siloxane linkage resulting in the improved areal wetting rate. The thermal stability of PSAs was also improved significantly by incorporation of siloxane linkages. The adhesion properties such as peel strength and probe tack of acrylic PSAs decreased significantly by increasing the content of either crosslinking agent or siloxane linkage. The acrylic PSA with siloxane group showed both satisfactory wetting and clean debonding properties for the optimal protection of thin silicon wafers. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Sustainable isosorbide‐based transparent pressure‐sensitive adhesives for optically clear adhesive and their adhesion performance

A biomass‐based isosorbide acrylate (ISA) was synthesized in a one‐pot reaction at low temperature with a quite slow dropwise technique using a syringe pump. Using the ISA monomer, UV‐cured transparent acrylic pressure‐sensitive adhesives (PSAs) composed of semi‐interpenetrating networks were prepared. The effect of ISA on the adhesion performance of the resulting acrylic PSAs was investigated by changing the ISA content, while fixing the mole ratio between 2‐ethylhexyl acrylate and 2‐hydroxyethyl acrylate in the PSAs. The prepared acrylic PSAs, with ISA content ranging from 3.2 to 14.3 mol%, were evaluated in terms of 180° peel strength, probe tack, static shear testing and optical properties. Increasing the ISA content in the acrylic PSAs improved the adhesion properties, such as 180° peel strength (0.25–0.32 N/25 mm), shear holding power (0.086–0.023 mm) and probe tack (1.21–2.26 N). Dynamic mechanical analysis indicated that ISA is a good candidate monomer, playing the role of adhesion promoter and hard monomer in the acrylic PSAs. © 2017 Society of Chemical Industry     

Optical properties and adhesion performance of acrylic PSAs; influence of functionalized monomer and curing agent

Acrylic pressure–sensitive adhesives (PSAs) were synthesized by solution polymerization using zirconium carboxyethyl acrylate (ZrCEA) with methyl aziridine derivatives (MAZ) as a curing agent. The acrylic PSAs were characterized by Fourier transform-infrared spectroscopy and gel contents. The viscoelastic properties of the acrylic PSAs were determined using an advanced rheometric expansion system. The adhesion performance of the acrylic PSAs was determined by measuring the probe tack, peel strength, shear adhesion failure temperature, and holding power. The optical properties of the acrylic PSAs were evaluated by the transmittance and refractive index. The results show that the adhesion performance and optical properties of the acrylic PSAs are influenced by the ZrCEA and MAZ content.     

Effect of naphthyl curing agent having thermally stable structure on properties of UV-cured pressure sensitive adhesive

Pressure sensitive adhesives (PSAs) with higher thermal stability were synthesized by crosslinking acrylic copolymer with naphthyl curing agent. The acrylic copolymer was synthesized for a base resin of PSAs by solution polymerization of 2-ethylhexyl acrylate, ethyl acrylate, and acrylic acid with N,N′-azobisisobutyronitrile as an initiator. The acrylic copolymer was further modified with glycidyl methacrylate to have the vinyl groups available for UV curing. Thermal stability of acrylic PSAs was improved noticeably with increasing naphthyl curing agent content and UV dose mainly due to the extensive formation of crosslinked structure in the polymer matrix. Although the peel strength decreased with UV curing of acrylic polymer, a proper balance between the thermal stability and the adhesion performance of PSAs was obtained by controlling the UV curing with naphthyl curing agent content and UV dose.     

Adhesion Performance and Microscope Morphology of UV-Curable Semi-interpenetrated Dicing Acrylic PSAs in Si-Wafer Manufacture Process for MCP

UV-curable acrylic pressure-sensitive adhesives (acrylic PSAs) have many applications in industry. As the Si-wafers become thinner, the acrylic PSAs for MCP need to show proper adhesion and leave little residue on the Si-wafer after UV irradiation when released from the dicing tapes. Strong adhesion is required in the dicing process to hold the Si-wafer before UV irradiation. On the other hand, weak adhesion strength is required after UV irradiation to prevent damage to the Si-wafers during the pick-up process. This study employed semi-interpenetrating polymer network-structured dicing of acrylic PSAs in the Si-wafer manufacture process. The binder PSAs contained 2-ethylhexyl acrylate (2-EHA) and acrylic acid (AA). The adhesion performance of the peel strength on a Si-wafer was examined as a function of the UV dose. The results showed that the abovementioned two requirements were achieved using semi-IPN dicing acrylic PSAs using a hexafunctional acrylate monomer and a UV-curing system. FE-SEM and XPS revealed little residue on the wafer after removing the tape. This paper suggests the optimal conditions for the curing agent, the additional hexafunctional monomer, photoinitiator and the coating thickness.     

Synthesis and photopolymerization of acrylic acrylate copolymers

Acrylate‐functionalized copolymers were synthesized by the modification of poly(butyl acrylate‐co‐glycidyl methacrylate) (BA/GMA) and poly(butyl acrylate‐co‐methyl methacrylate‐co‐glycidyl methacrylate). ¹³C‐NMR analyses showed that no glycidyl methacrylate block longer than three monomer units was formed in the BA/GMA copolymer if the glycidyl methacrylate concentration was kept below 20 mol %. We chemically modified the copolymers by reacting the epoxy group with acrylic acid to yield polymers with various glass‐transition temperatures and functionalities. We studied the crosslinking reactions of these copolymers by differential scanning calorimetry to point out the effect of chain functionality on double‐bond reactivity. Films formed from acrylic acrylate copolymer precursors were finally cured under ultraviolet radiation. Network heterogeneities such as pendant chains and highly crosslinked microgel‐like regions greatly influenced the network structure and, therefore, its viscoelastic properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 753–763, 2002     

Eco-friendly UV-curable pressure sensitive adhesives containing acryloyl derivatives of monosaccharides and their adhesive performances

Two different monosaccharide acrylate monomers were designed and synthesized from glucose and galactose, and were then used to prepare transparent acrylic pressure sensitive adhesives (PSAs) comprised of semi-interpenetrated structured polymer networks. The effects of the monosaccharide architecture in the acrylate monomers on the adhesive performance of the acrylic PSAs were investigated. Prepared UV-curable acrylic PSA syrups were characterized and the optical properties of the acrylic PSAs were also examined. All of the acrylic PSAs exhibited high transparency in the visible wavelength region. With increasing monosaccharide acrylate concentration in the acrylic PSAs, adhesive performances such as the peel strength, cohesion strength, and probe tack were increased. However, there was no difference in their adhesive performances regardless of the different chemical structures of monosaccharide acrylate monomers.     

Thermal stability and surface properties of acrylic PSAs modified by hexafluorobutyl acrylate

The article attempted to prepare special acrylic adhesives with preferable adhesion property and better thermal stability by introducing a fluorinated monomer. The FT-IR result showed that fluorinated monomers and acrylic monomers participated in copolymerization successfully. Furthermore, fluorinated groups performed good compatibility with acrylic resins, based on differential scanning calorimetry curve. According to the TG test under different heating rates, the activation energy of PSAs containing different content of fluorinated monomers was calculated to evaluate the effect of hexafluorobutyl acrylate on heat resistance of PSAs. Then, the findings of contact angle test revealed that the fluorinated PSAs also had rather lower surface energy than ordinary PSAs. Finally, the results of peel strength measurements indicated that the fluorinated PSAs demonstrated excellent adhesion property on various materials, especially low surface energy substrates.     

New Developments in the Area of Solvent-Borne Acrylic Pressure-Sensitive Adhesives

Since their introduction half a century ago, acrylic pressure-sensitive adhesives have been successfully applied in many fields. In the last fifty years or so, acrylic pressure-sensitive adhesives (PSAs) have made tremendous strides from what was virtually a black art to what is now a sophisticated science. So much so that larger manufacturers of pressure-sensitive adhesives and even their polymer suppliers now use very expensive equipment to study pressure-sensitive adhesive behavior. The three properties which are useful in characterizing the nature of pressure-sensitive adhesives are tack, peel (adhesion) and shear (cohesion). The first measures the adhesive's ability to adhere quickly, the second its ability to resist removal by peeling, and the third its ability to hold in position when shear forces are exerted. The performances of pressure-sensitive adhesives, such as tack, peel and shear, based on polyacrylates synthesized through co-polymerization of acrylate monomers and formulated in organic solvents mixtures are, to a large degree, determined by the molecular weight of acrylic copolymer, polymerization method and especially by the type and quantity of the crosslinking agent added to the PSA. Newly developed solvent-borne PSAs are used in protective foils, removable and repositionable self-adhesive products, water-soluble PSAs and water-dispersible self-adhesive products, photoreactive UV-crosslinkable self-adhesive tapes, and dual-crosslinkable PSAs for self-adhesive tapes with post-crosslinking potential characterized by enhanced cohesion at higher temperatures. The mentioned water-soluble PSAs, water-dispersible self-adhesive products and photoreactive UV-crosslinkable self-adhesives are synthesized in organic solvents as solvent-borne acrylic PSAs.     

Fabrication of optically clear acrylic pressure–sensitive adhesive by photo-polymerization: UV-curing behavior,adhesion performance,and optical properties

Acrylic pressure–sensitive adhesives (PSAs) with 2-phenoxy ethyl acrylate (PEA) were polymerized using UV-curing technology. This study examined the effects of PEA content and UV dose. The photo-polymerization behavior of the pre-polymer was examined by viscosity measurements, real-time Fourier transform infrared spectroscopy, and photo-differential scanning calorimetry. The curing behaviors of the acrylic PSAs were investigated by shrinkage test, a modular advanced rheometer system, and gel content. differential scanning calorimetry and Advanced Rheometric Expansion System were used to characterize the acrylic PSAs. Adhesion performances were measured by probe tack, peel strength, and shear adhesion failure temperature. The optical properties of acrylic PSAs were examined by UV–visible spectroscopy and prism coupler. The PEA content had a larger effect on improving the optical properties, than did the UV dose. The transmittances of the acrylic PSAs with <75% PEA were >95%. The refractive indices of the acrylic PSAs increased with increasing PEA content, due to its high refractive index, >1.5, which affected the overall refractive indices, particularly in the visible region.     

2-Ethylhexyl acrylate/4-acryloyloxy benzophenone copolymers as UV-crosslinkable pressure-sensitive adhesives

Summary It has been previously shown that copolymer of 2-ethylhexyl acrylate with an 4-acryloyloxy benzophenone can be used as PSA. This paper presents synthesis and application of solvent-based polymer system for the preparation of acrylic pressure-sensitive adhesives (PSA). 2-Ethylhexyl acrylate benzophenone copolymers, having molecular mass in the range of 120 000 to 380 000 Dalton were prepared by free-radical solution polymerization. These copolymers were tacky but possessed insufficient cohesive strength after UV-crosslinking to be useful as PSAs. These copolymers resulted in materials having a balance of cohesive and adhesive characteristics required of a good PSA. Some of the parameters affecting the pressure-sensitive adhesive properties of the copolymer are: amount of the 4-acryloyloxy, molecular mass of the polymeric components, UV-reactivity and such properties like tack, peel adhesion and cohesion.     

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.     

Resultant synergism in the shear resistance of acrylic pressure‐sensitive adhesives prepared by emulsion polymerization of n‐butyl acrylate/2‐ethyl hexyl acrylate/acrylic acid

Acrylic emulsion pressure‐sensitive adhesives (PSAs) were synthesized by the copolymerization of n‐butyl acrylate with various levels of 2‐ethyl hexyl acrylate (2EHA) and a small constant amount of acrylic acid. The effect of varying the n‐butyl acrylate/2EHA monomer composition on the kinetic behavior of the polymerization and the characteristics of the copolymers prepared in a batch process were investigated. The results showed that increasing the amount of 2EHA in the monomer caused the polymerization rate and the glass‐transition temperature of the acrylic copolymers to decrease. Increasing the amount of 2EHA caused the gel content of the copolymers to decrease, reaching a minimum at 50 wt %; thereafter, the gel content increased at higher 2EHA levels. For the acrylic emulsion, the peel‐fracture energy of the PSAs decreased as the amount of 2EHA in the monomer was increased up to 50 wt %. At higher 2EHA levels, the peel‐fracture energy was relatively constant. Interestingly, a synergistic effect of increased shear resistance at 25 wt % 2EHA was observed without a significant trade‐off in terms of the peel and tack properties. This behavior was attributed to a good interconnection between the microgels and the free polymer chains inside the contacting particles in the adhesive film. Cooperation between various levels of 2EHA in the copolymer structure simultaneously changed the crosslink molecular weight (M_c) of the microgels and the entanglement molecular weight (M_e) of the free chains in the adhesive network morphology. The adhesive performance of the PSAs was found to be correlated with their M_c/M_e values as the 2EHA proportion was varied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Polyacrylate-N-vinyl lactam polymer or copolymer blends as pressure-sensitive adhesives

It has been previously shown that blends of a homopolymer or a copolymer of an N-vinyl lactam with an acrylate or a related copolymer containing a small proportion of acidic groups exhibit macroscale compatibility and a phase separated microstructure. This paper presents an application of this two-phase polymer system for the preparation of melt processable acrylic pressure-sensitive adhesives (PSA). 2-Ethylhexyl acrylate-acrylic acid copolymers, having molecular weights in the range of 50 000 to 115 000 were prepared by free-radical solution polymerization. These copolymers were tacky but possessed insufficient cohesive strength at ambient temperatures to be useful as PSAs. Blending such acrylate copolymers, having some acidic functionality, with minor proportions of a glassy homopolymer or a copolymer of an N-vinyl lactam resulted in materials having a balance of cohesive and adhesive characteristics required of a good PSA. Due to low molecular weights of the components of the polymer blend acrylic PSAs, they are amenable to hot melt processing. Some of the parameters affecting the pressure-sensitive adhesive properties of the polymer blend are: (a) fraction of the glassy polymer in the blend, (b) molecular weights of the polymeric components, (c) acidic functionality of the low molecular weight acrylate copolymer, and (d) N-vinyl lactam functionality of the glassy polymer.     

Molecular parameters and their relation to the adhesive performance of acrylic pressure‐sensitive adhesives

Model acrylic pressure‐sensitive adhesives (PSAs) based on poly(2‐ethyl‐hexyl acrylate‐stat‐acrylic acid) and poly(n‐butyl acrylate‐stat‐acrylic acid) at 97.5/2.5 wt % were synthesized using semicontinuous emulsion and solution polymerizations. Microgels formed in the lattices retained their discrete network morphology in the film. In contrast, acrylic solution was essentially gel free and crosslinking in the film was provided by the reaction of acrylic acid and post added Al Acetyl Acetonate after solvent evaporation, which led to continuous network morphology. The difference in film network morphology caused significantly lower shear holding power for the film from emulsion PSA compared with that of solvent‐borne film. Unlike shear holding power, loop tack and peel of acrylic PSAs were mainly controlled by the same sol/gel molecular parameters, regardless of emulsion or solution PSAs. The important molecular parameters are sol‐to‐gel ratio, entanglement molecular weight, weight average molecular weight, and to a lesser extent, glass transition temperature. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 2230–2244, 2001     

Optical properties and adhesion performance of optically clear acrylic pressure sensitive adhesives using chelate metal acetylacetonate

Optically clear acrylic pressure-sensitive adhesives (PSAs) with different co-monomers were synthesized. This study employed metal chelate aluminum acetylacetonate and zirconium acetylacetonate as curing agents. The optical properties of the acrylic PSAs were examined by UV–visible spectroscopy and a prism coupler. In addition, the adhesion performance was obtained by assessing the peel strength, the tack, and the shear adhesion failure temperature. The decrease in the adhesion performance may be related to a higher crosslinking density, which also resulted in a higher gel content.     

Crosslinking of pressure sensitive adhesive based on water‐borne acrylate

This publication shows how the kind of crosslinking agents and their contents influence important properties of acrylic based pressure‐sensitive adhesive (PSA) dispersions such as tack, adhesion and cohesion. Synthesized PSAs based on acrylic polymers, containing 2‐ethylhexyl acrylate, butyl acrylate, vinyl acetate, styrene and acrylic acid are used in the preparation of self‐adhesive dispersions used as coating of polyethylene foams and poly(vinyl chloride) and polyester foils. © 2003 Society of Chemical Industry     

Adhesion Performance and Thermal Stability of Fluorinated PSAs as a Crosslinking System

The use of pressure sensitive adhesives (PSAs) is becoming increasingly popular in many industrial fields. In the automobile industry the main reasons for using PSAs are that they reduce the overall weight of the vehicles and because they are easy to use. However, in the case of acrylic PSAs, the non-crosslinked linear chains results in low thermal stability. In this study, a fluorinated acrylic pressure sensitive adhesive was synthesized under UV irradiation and crosslinking was applied to the linear chain of acrylic PSAs to improve the thermal stability. The adhesion performance was evaluated by analyzing the peel strength, probe tack and shear adhesion failure temperature (SAFT) as a function of the type of crosslinking system. In particular, the peel strength and probe tack were measured at 25, 50 and 80°C. The viscoelastic properties, which were measured using an advanced rheometric expansion system (ARES), revealed a proper balance between the thermal stability and adhesion performance.     

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.