Preparation and properties of heat and ultraviolet‐induced bonding and debonding epoxy/epoxy acrylate adhesives

Heat and ultraviolet (UV)‐induced bonding and debonding (BDB) adhesives were designed and prepared through blending an epoxy resin, diglycidyl ether of bisphenol A (DGEBA) with an epoxy acrylate resin, bisphenol‐A epoxy acrylate resin (BEA). The variation of the chemical structure of DGEBA and BEA in the sequential heat‐ and UV‐curing processes was characterized by Fourier transform infrared spectroscopy (FTIR). The FTIR results indicate that DGEBA and BEA successfully took part in both the heat‐curing and UV‐curing processes. The effects of the mass ratio of BEA to DGEBA, amount of heat‐curing agent, type of diluents, and UV irradiation time on the BDB properties of BDB adhesive were systematically investigated. The results show that the bonding strength increases with the decrease of the mass ratio of BEA to DGEBA and with the increase of the amount of heat‐curing agent in a certain range. The debonding strength decreases with the increase of the mass ratio of BEA to DGEBA. The mass ratio of BEA to DGEBA was set at 10 to ensure the ratio of the bonding strength to debonding strength greater than 10 times. The debonding strength of BDB adhesives also depends on the UV irradiation time, decreasing with the increase of UV irradiation time in a certain range. Based on the FTIR results and the dependence of the bonding and deboning strengths on the reaction conditions, a possible BDB mechanism of BDB adhesive was proposed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46435.     

UV curable pressure‐sensitive adhesives for fabricating semiconductors. II. The effect of functionality of acrylate monomers on the adhesive properties

In an attempt to control the adhesive properties of acrylic copolymer‐based pressure‐sensitive adhesives, a series of multifunctional acrylate monomers were added and UV cured. The adhesive compound with a difunctional monomer had increased peel strength after UV curing. On the other hand, the compound with a tri‐ or more functional (polyfunctional) monomer had markedly decreased strength after UV curing. Those adhesives containing any polyfunctional monomer also showed much higher storage modulus than an adhesive containing a difunctional monomer. The greater volume contraction of UV‐cured polyfunctional monomer suggested microvoids at the interface between the adhesive layer and the adherent, resulting in poor strength. Estimated values of the peel strength of UV‐cured adhesives according to the theoretical equations proved that the strength is approximately inversely proportional to the elastic moduli. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2889–2895, 2004     

Rheological investigation of cure kinetics and adhesive strength of polyurethane acrylate adhesive

In this work, we used rheological techniques to study both the cure characteristics and the degree of cure of polyurethane acrylate adhesive, a type of reactive adhesive used in hard disk component assembly. These results were then correlated with the tensile shear strengths of adhesives. Here, the cure characteristics of polyurethane adhesive were investigated at isothermal conditions ranging from 25 to 120°C. From the rheological results, the gelation time, the vitrification time, as well as the time required to reach the maximum degree of cure, decreased when increasing the curing temperature. The cure rates of adhesive increased with temperature in three temperature ranges, which were retardation zone, vitrification zone, and reaction‐controlled zone. The cure rates in these zones were controlled by slow diffusion, fast diffusion, and the rate of reaction, respectively. From the temperature sweep of fully‐cured adhesives, we found that the crosslinking level of adhesives increased with curing temperatures at different rates depending on the temperature zones as well. Moreover, the adhesive strength measured by tensile shear test was found to also increase correspondingly with the adhesives' T_g, indicating that the crosslinking level directly affected the adhesive strength. The strong dependence of adhesive strength with crosslinking level indicates that the crosslinking level was essential for high adhesive strength. The correlation of cure characteristics and adhesive strengths at various curing temperatures performed in this study can further provide useful information for planning appropriate curing schemes of polyurethane acrylate adhesives used in electronic and other industries. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of a bioadhesive with poly (vinyl alcohol) crosslinking agent

Synthetic adhesives containing 3,4‐dihydroxy‐L‐phenylalanine and its derivatives have strong adhesion strength and good biocompatibility, which make them prime candidates for adhesives or bioadhesives applications. In this study, a new photocurable poly (vinyl alcohol) (UV‐PVA) derivative was prepared and used as crosslinking agent to further improve adhesion strength of dopamine methacrylamide (DMA) system. The structure of UV‐PVA was confirmed, and the degree of acryloyl group substitution (DS) was easily varied from 10 to 40% by varying the molar ratio of acryloyl chloride to ? OH of PVA. The effects of ultraviolet light intensity, content of DMA and DS values of PVA on the photopolymerization kinetics were studied, and the effects of DS value on the adhesive strength, swelling performance and cell attachment were also investigated. It was found that adhesive containing UV‐PVA with 40% DS value yielded the highest adhesive strength, a relatively low swelling ratio and good biocompatibility. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and characteristics of photoactive‐hydrogenated rosin epoxy methacrylate for pressure sensitive adhesives

Hydrogenated rosin epoxy methacrylate (HREM), based on hydrogenated rosin and glycidyl methacrylate (GMA), was synthesized for use as an advanced tackifier in the UV‐crosslinking pressure sensitive adhesives (PSAs) system. The HREM, as a tackifier, contained UV‐curing sites; thus, allowed photopolymerization to occur by UV irradiation. This UV‐curable tackifier, HREM, can improve the curing rate and adhesion performance of UV‐crosslinking PSAs. The characteristics of HREM were analyzed by GPC and DSC and its synthetic mechanism studied using FTIR and ¹H NMR; the characteristic peaks of hydrogenated rosin and GMA vanished, but new peaks for HREM appeared. The PDI and the T_g by DSC were 1 and ?25.6°C, respectively. The photopolymerization of HREM was studied using photo‐DSC. Heat flow was observed during UV irradiation, and the curing rate and conversion both increased with rising photoinitiator content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Pulsed Laser Activation of Carbene Bioadhesive Boosts Bonding Strength

Light‐activated tissue adhesives are limited to low light doses (50 J) and intensities (<1 W cm^?2) due to photo‐to‐thermal heat generation. Low intensities have the disadvantage of limited penetration depths with retarded crosslinking kinetics, which impairs carbene‐based crosslinking strategies that compete with nitrogen evolution and gas nucleation. These limitations are circumvented by a trade‐off between high‐intensity activation while reducing the exposure surface area. Continuous or pulsed activation by line scanning the carbene precursor adhesive allows curing a higher surface area/volume ratio while preventing localized heat generation. By optimizing irradiation with a pulsed laser scan, the adhesion strength is improved by 17‐fold over ultraviolet A (UVA) light emitting diodes (LEDs) and is on par with bioadhesive gold standard of topical cyanoacrylates. Overall, this improved method of photo‐activation applies to other industrial and clinical photocuring adhesives where limits on UVA dose constrain exposure intensities.     

Adhesive and curing properties of chicken feather/blood-based adhesives for the fabrication of medium-density fiberboards

This study was conducted to investigate the adhesive properties of chicken feather (CF)-based adhesives for wood-based panels. CF was hydrolysed in sodium hydroxide solutions of 5%, 7.5% and 10% (CF-AK). Chicken blood (CB) hydrolysed in sulfuric acid solution of 5% (CB-AC) was used as a hardener. The adhesives were formulated by crosslinking 60% CF-AK, 10% CB-AC and 30% formaldehyde-based crosslinking agents (formalin, melamine-urea-formaldehyde and phenol-formaldehyde prepolymers) on a solid weight basis. The CF-based adhesives were very viscous at room temperature, but the viscosity at 50 °C ranged from 300 to 600 mPa·s resulting in a sprayable adhesive. From the DSC analysis, the use of CF-AK-10% in the CF-based adhesives need longer curing time compared with that of CF-AK-5%. Most mechanical strength properties and dimensional stability of MDF bonded with CF-based adhesives were similar to those of commercial urea-formaldehyde (UF) resin. However, internal bonding strength of most MDF bonded with CF-based adhesives was higher than that with the UF resin. Most adhesive properties of the MDF manufactured with the new CF adhesive met the Korean Standard requirements for interior MDF. These results suggest that CF and/or CB can be used as raw materials for environment-friendly adhesives for producing wood panels.     

Solvent‐free radiation‐curable polyacrylate pressure‐sensitive adhesive systems

This article shows radiation‐curable solvent‐free pressure‐sensitive adhesive polyacrylates, their synthesis, chemical modifications, important properties and use after crosslinking with UV‐lamps and UV‐lasers for the production of self‐adhesives tapes. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 182–191, 2003     

Long‐term development of thermophysical and mechanical properties of cold‐curing structural adhesives due to post‐curing

The long‐term changes in the thermophysical and mechanical properties of a cold‐curing structural epoxy adhesive were investigated by accelerating the curing reaction by post‐curing at elevated temperatures. Experimental data concerning the glass transition temperature for periods of up to 7 years and tensile strength and stiffness measurements could be extrapolated for a period of up to 17 years. An existing model for the long‐term development of concrete properties was modified for the prediction of the long‐term mechanical properties of adhesives. The applicability of the acceleration procedure and the new model was confirmed by several verification procedures. Structural adhesives exhibit significant increases in glass transition temperature, strength and stiffness over the long term provided that joints are adequately sealed and protected from humidity and UV radiation. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

UV/heat dual‐curable adhesive tapes for fabricating stacked packages of semiconductors

To facilitate the fabrication of a reliable stacked package for a semiconductor, UV/heat dual curing of adhesives was investigated. The formulated adhesives contained acrylic monomer and epoxy resins. First, UV curing was conducted on the acrylic monomer, followed by heat curing. It was found that UV‐curable acrylic monomers affected the adhesive's properties, e.g., adhesion, water absorption, and viscoelasticity. As the acrylic monomer, neopentylglycol diacrylate (NPGDA), trimethylolpropane triacrylate (TMPTA), dipentaerythritol hexaacrylate (DPHA), and tricyclodecanedimethanol acrylate (TCDDA) were used to investigate the effect of functional group numbers and structure. As a result, an acrylic monomer that has two functional groups with a rigid moiety (TCDDA) showed acceptable properties as adhesives for the fabrication, and thus a UV/heat‐curing adhesive has been successfully developed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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.     

Polymeric reaction of polymer-monomer system irradiated by low energy electron beam. III. Adhesive property of pressure sensitive adhesive

Application of low-energy electron beam to nonsolvent-type pressure-sensitive adhesive is investigated. Adhesive properties such as peel strength, dead load strength, and ball tack were closely related to the reaction behavior (gel fraction and graft efficiency) of the acrylate polymer-monomer system. The reaction behavior is eluciadated by combining the measurements of gel fraction, infrared spectrum of gel, and molecular weight distribution detected by gel permeation chromatogrophy. It was found that the adhesive property of electro beamcured adhesives depends on the molecular weight of added polymer, monomer concentration, and irradiation dose. Graft polymerization and moderate crosslinking by electron beam irradiation especially contribute to superior high adhesive properties.     

Preparation of nanosilica reinforced waterborne silylated polyether adhesive with high shear strength

Waterborne adhesives are extremely environment‐friendly but unfortunately deficient in mechanical properties. In this article, nanosilica, stemming from tetraethyl orthosilicate (TEOS), silica sol, and/or fumed silica powder, was employed to reinforce the waterborne silylated polyether adhesives. Effects of TEOS content, silica sol content, and the type and content of fumed silica on the shear strength of the adhesive were investigated using a scanning electronic microscope and an electronic instron tester and the strengthening mechanisms of different silica source were discussed. All the shear strengths of silylated polyether adhesives first increased and then decreased as TEOS content, silica sol content or fumed silica content increased. Colloidal silica particles was less efficient than fumed silica particles for reinforcing the polyether adhesive but can increase the shear strength of hydrophobic fumed silica embedded adhesive. Comparing the adhesives with the hydrophilic fumed silica (HS‐5) or the extremely hydrophobic fumed silica (TS‐720), the adhesive with moderate hydrophobic fumed silica (TS‐610) had the highest shear strength. The maximal shear strength of 2.5 MPa was achieved when TEOS, silica sol, and fumed silica were combined. It seemed that TEOS, silica sol, and fumed silica played crosslinking (with polyether chain), dispersing (for fumed silica), and reinforcing roles on waterborne adhesive, respectively. This reinforcing mechanism opened a new way to fabricate waterborne adhesives (or coatings) with high performances. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Ultraviolet/heat dual‐curable film adhesives with pendant‐acryloyl‐functional‐group‐modified epoxy resin

To facilitate the fabrication of a reliable semiconductor package, the UV/heat dual curing of film adhesives was investigated. The curing system of the epoxy resin affected the film adhesive properties. As the UV/heat dual‐curable epoxy resin, a modified o‐cresol novolak epoxy resin, in which half of the glycidyl groups were substituted by acryloyl groups (OCN‐AE), was applied to the film adhesive. The formulated film adhesive contained acrylic copolymer, OCN‐AE, phenolic aralkyl resin as a heat‐curing agent of the glycidyl groups, and 1‐hydroxycyclohexyl phenyl ketone as a photoinitiator of the acryloyl groups. The formulated reference film adhesive contained unmodified o‐cresol novolak epoxy resin (OCN‐E) in place of OCN‐AE. Formulated film adhesives containing a mixture of OCN‐E and o‐cresol novolak epoxy acrylate were also used as references. The morphology and the film adhesive properties were investigated. In these investigations, the film adhesive of OCN‐AE showed better adhesive properties, lower modulus, and a better stress‐relaxation ability than the referenced adhesives. As a result, a reliable film adhesive for semiconductor packages was successfully developed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Electron beam curing of aliphatic unsaturated polyesters. I. Mechanistic study on converting to pressure‐sensitive adhesives

Aliphatic unsaturated polyesters (UPEs) mixed with N, N‐diethylaminoethyl methacrylate (DEAEMA) were convertible by electron beam irradiation to soft solids of high peeling strength. Double bond conversions, gel contents, molecular weight distributions, and crosslinking densities of the irradiated mixtures were studied in comparison with those of UPE–vinyl acetate mixtures, which gave very low peel strength on irradiation. The latter system started gel formation even at earlier stages of irradiation and had higher cross‐linking densities as a result of copolymerization between polyester and monomer double bonds. In contrast, the UPE–DEAEMA system exhibited slow gel formation with predominant conversion of monomer double bonds, indicating formation of graft copolymers. This system also had lower crosslinking densities than the other system. Therefore, it was concluded that the pressure‐sensitive adhesive nature of the electron‐beam‐cured UPE–DEAEMA mixtures could be attributed to the formation of flexible graft polymers entangled in a loosely crosslinked network. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1854–1857, 2003     

UV-initiated crosslinking of photoreactive acrylic pressure-sensitive adhesives using excimer-laser

UV-initiated crosslinking technology is well established in the market and allows the production of a wide range of ultraviolet (UV)-crosslinkable pressure-sensitive adhesives (PSA) with interesting features. The balance between such properties as adhesive and cohesive strengths within the crosslinked self-adhesive coatings is critical for their performance. The UV crosslinking of acrylic PSA, especially for following properties: tack, peel adhesion, and shear strength of self-adhesive polymer layers, has been investigated using UV excimer-laser and UV lamp as UV sources. It was observed that after UV crosslinking of acrylic PSA using excimer-laser in comparison with typical UV lamp, high-quality PSA products with excellent properties, such as tack, peel adhesion, shear strength, and shrinkage were received.     

Influence of selected photoinitiators on important properties of photoreactive acrylic pressure‐sensitive adhesives

Photoreactive solvent‐borne pressure‐sensitive adhesives are not commercially available in the market. The reason for it is that the UV‐initiated crosslinking has sense only in the case of solvent‐free self‐adhesive systems. Investigations conducted in Institute of Chemical Organic Technology have shown that the photoreactive solvent‐borne acrylic PSA are conventional crosslinked solvent‐borne acrylic PSA used as crosslinking agents typical metal chelates as titanium acetylacetonate (TiACA), aluminum acetylacetonate (AlACA) or thermal reactive crosslinker melamine‐formaldehyde resin Cymel 303 clear considered. The main purpose of the investigation was to study the influence of diverse photoinitiators on main properties, such as shrinkage, tack, peel adhesion, and shear strength of solvent‐based acrylic pressure‐sensitive adhesives. The interesting alternative to conventional photoinitiators is unsaturated photoinitiators described in this article. Following unsaturated photoinitiators were used: 4‐acryloyloxy benzophenone, 4‐acryloyloxyethoxy benzophenone, and 4‐acryloyloxybutoxy benzophenone. The influence of the crosslinking agents or crosslinking methods was determined in relation to the reaction time and to the concentration versus adhesion properties. The increase of photoinitiator concentration causes in the decrease of the shrinkage. Increasing the UV dose during the crosslinking of acrylic PSA film leads clearly to better shrinkage resistance. The best results of the lowest shrinkage value of 0.35% were given by using 4‐acryloyloxy benzophenone. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Formulation of a novel soybean protein‐based wood adhesive with desired water resistance and technological applicability

A novel soybean protein‐based wood adhesive with good bond strength, excellent water resistance, and the desired technological applicability was formulated by combining thermal alkali degradation, thermal acid treatment, and crosslinking. The characterization results indicated that thermal alkali degradation could effectively improve the technological applicability, thermal acid treatment could positively improve the water resistance, and appropriate crosslinking modification could significantly enhance the bond strength and water resistance of the soybean protein adhesive. The crosslinker species, crosslinker level, and ratio of thermal alkali‐degraded soybean protein (DSP) to thermal acid‐treated soybean protein (TSP) had important effects on the primary properties of the soybean protein adhesives. The modified polyamide aqueous solution was the most preferable crosslinker because of its low viscosity, good crosslinking efficiency, and excellent miscibility with soybean protein solution. The optimal soybean protein adhesive that was formulated from 20 wt % modified polyamide as the crosslinker and a DSP/TSP ratio of 1:3 had a solid content of more than 35 wt %, suitable viscosity (～2180 mPa s), a long work life (>16 h), good dry bond strength (2.94 MPa), and 28 h of boiling–dry–boiling cycled wet strength (1.29 MPa) that met the required values for structural use according to JIS K6806‐2003 commercial standards. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43586.     

UV crosslinkable microsphere pressure sensitive adhesives—influence on adhesive properties

In the following study, a synthesis and characterization of UV crosslinkable acrylic pressure sensitive adhesives are presented. Different amounts of unsaturated photoinitiator 4-acryloyloxy benzophenone (4-ABF) were added in t-butyl acrylate/2-ethylhexyl acrylate monomer mixture and then polymerized using a suspension polymerization technique. The adhesive suspension was coated on a pilot coating machine, dried by application of IR and subsequently crosslinked under UV light. The copolymerized 4-ABF photoinitiator will produce reactive radicals upon absorption of UV light, which are capable of initiating a rapid chain reaction with neighboring C-H positions of polymer side chains, what leads to formation of crosslinked polymer structures. UV crosslinking process was monitored by ATR-FTIR spectroscopic technique. Adhesion properties of the synthesized materials were determined using standard measurements of tack, peel and shear strength. Results have shown that all adhesive properties are strongly influenced by the degree of crosslinking of the microspheres, which increased with higher amounts of added 4-ABF photoinitiator. All the three measured adhesive properties showed a substantial decrease even at small amounts of added 4-ABF. The decrease in adhesion may be correlated with higher crosslinking density, what also resulted in higher gel phase amounts. Determination of glass transition temperature showed minor difference between adhesive coatings.     

Effects of typical soybean meal type on the properties of soybean-based adhesive

In order to effectively apply soybean meal for the preparation of water-resistant soybean-based adhesives for plywood, the effects of three typical soybean meal products, namely, low-temperature soybean meal (LM), high-temperature soybean meal (HM), and physical soybean meal (PM), on the properties of soybean-based adhesive were investigated. The results indicated that the number of reactive groups in the three soybean meals followed the order LM > HM > PM, which in turn led to various crosslinking densities when these soybean meals were crosslinked by epichlorohydrin-modified polyamide (EMPA) during the curing process. The LM soybean adhesive had 6.6% higher soaking bond strength and 16.5% higher boiling-dry-boiling bond strength than the HM soybean adhesive, and 19% higher soaking bond strength and 33% higher boiling-dry-boiling bond strength than the PM soybean adhesive, respectively. These three soybean meals could be used to prepare soybean adhesives for interior-use plywood because all plywood panels bonded with their adhesives passed a water-soaking test at 63 °C for 3 h, but only the LM soybean adhesive achieved the desired water resistance for floor-base plywood. Among the three evaluated soybean meals, LM was the most promising raw material for the preparation of soybean-based adhesive because of a greater number of reactive groups, higher crosslinking density, and superior bond strength. Plywood panel bonded with HM soybean adhesive had a water resistance lower than, but very close to, the standard required value (>0.8 MPa) for floor-base plywood.