Curing of composite components by ultraviolet radiation: A review

Curing of polymer matrices by ultraviolet (UV) irradiation can be applied to a variety of processes in the production of composite components, as long as the component can be directly irradiated. Wet lay‐up techniques, vacuum infusion type processes with UV‐transparent membranes, filament winding, and prepreg processes have been adapted to UV curing. Unlike in thermal curing, the curing time is in the order of magnitude of minutes rather than hours, which means a significant reduction in cycle time. The radiation can be generated by a variety of sources suitable for various specific applications and different curing strategies. The most frequently used radiation sources are mercury arc lamps. Because of the absorption of radiation passing through matter, the thickness of laminates for efficient application of UV curing is limited. The curing mechanism is either radical polymerization for acrylate‐based resins or cationic polymerization for epoxies and vinyl ethers. The properties of the UV‐cured polymer matrix are determined by the cross‐linking density. This depends on the type and concentration of the photoinitiator and of the (optional) diluents, the intensity and the duration of the irradiation, and the temperature at which the curing process takes place. POLYM. COMPOS., 27:119–128, 2006. © 2006 Society of Plastics Engineers.     

Rheological study of the curing kinetics of epoxy–phenol novolac resin

The curing reaction of an epoxy–phenolic resin under different conditions was monitored using rheological measurements. The evolution of viscoelastic properties, such as storage modulus, G′, and loss modulus, G″, was recorded. Several experiments were performed to confidently compare the rheological data obtained under varied curing conditions of temperature, catalyst concentration, and reactive ratios. The values of G′ measured at the end of the reactions (at maximum conversion) were independent of the frequency and temperature of the tests in the range of high temperatures investigated. The overall curing process was described by a second‐order phenomenological rheokinetic equation based on the model of Kamal. The effects of the epoxy‐to‐phenolic ratio as well as the curing temperature and the catalyst concentration were also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4430–4439, 2006     

Preliminary study on the utilization of lignin as filler in ultra‐violet (UV) curable system

In this study, Alcell lignin was used as filler in aliphatic urethane acrylate ultra violet (UV) curable resin system. The coating system was UV cured in the presence of free radical photoinitiator and cationic photoinitiator. The results showed that those with free radical photoinitiator produced coating film with higher degree of curing than those with cationic photoinitiator. The result of iodine number determination also showed that the unsaturated groups present in the UV curable system had reduced. This indicated that radical polymerization had taken place in the curing process of UV curable resin incorporated with lignin. In addition, the lignin content did not influence the curing process of the coating film. As for the coating film, it showed that the mechanical properties of the film were significantly influenced by the lignin content. This phenomenon was contributed by inherent stiffness of the lignin. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

The Effect of Radiation Dosages and UV/EB Radiation on the Properties of Nanocomposite Coatings

The aim of this study was to compare the effects of ultraviolet (UV) and electron beam (EB) radiation on the properties of cured nanocomposite coatings. Surface hardness increased with increasing radiation dosages (number of passes) for all samples. This was due to the increase in crosslinking with increasing radiation dosages. Pendulum hardness, gel content, and thumb twist results were analyzed to choose the appropriate curing dosage for both curing techniques. The selected dosages were then used to cure coatings for scratch and abrasion resistance tests. It was found that the UV curing produced coatings with better abrasion resistance, whereas EB curing was more suitable for producing scratch-resistant coatings.     

UV固化不饱和聚酯树脂在涂料中的应用研究

以不饱和聚酯为光敏预聚物,加入光引发剂制得天然大理石表面紫外光固涂层(流水线作业)。研究了光引发剂用量对涂层性能的影响,并将UV固化与化学固化浇注体的力学性能和耐热性进行了对比。结果表明,紫外光固化不饱和聚酯树脂涂层的固化效果,硬度和亮度都达到化学固化的效果,且生产效率大大提高。     

Dual-curing behavior and scratch characteristics of hydroxyl functionalized urethane methacrylate oligomer for automotive clearcoats

UV–thermal dual-curable, hydroxyl- and methacrylate-functionalized urethane oligomers with different contents of unsaturated double bonds and hydroxyl groups have been synthesized and incorporated into automotive clearcoats to investigate their curing and scratch behaviors. Dynamic mechanical analyses (DMA) and FT-IR analyses were performed to observe the variation of the crosslinking networks that resulted from the chemical reactions by UV and thermal dual-curing operations with varying curing conditions, such as UV dose, thermal curing time, thermal curing temperature, and curing sequence. The scratch behaviors of dual-cured automotive clearcoats were analyzed via nano-scratch tests, accompanied with scratch images simultaneously visualized using scanning electron microscopy (SEM). The mechanical and chemical properties, such as impact resistance, pencil hardness, acid-etch resistance, and stone-chip resistance, of dual-curable clearcoats were also compared with those of UV mono-cure and 1 K thermal-cure clearcoats. The results clearly showed that the dual-curing process induced a considerably higher degree of crosslinking for the cured clearcoats prepared from the dual-curable oligomers, melamine crosslinkers, and photoinitiators. Their mechanical properties including scratch resistance were also noticeably improved via the UV–thermal curing sequence, which led to an increased conversion rate of double bonds compared with clearcoats produced using the thermal–UV curing sequence. The best conditions for high crosslinking density as well as high hardness and modulus were 2400 mJ/cm² at 150 °C for 10 min in the UV–thermal curing process. This result was corroborated from the reaction kinetics and surface images of the scratched clearcoats captured by SEM.     

Comparison between microwave and thermal curing of glass fiber–epoxy composites: Effect of microwave‐heating cycle on mechanical properties

The objective of this study was to compare the mechanical properties between epoxy composites cured by thermal heating and microwave heating. Epoxy‐anhydride resins reinforced with glass fiber were cured in a domestic microwave oven and in a thermal oven. Hardening agents included methyl tetrahydrophthalic anhydride and methyl hexahydrophthalic anhydride. Microwave curing was carried out at various conditions, including 1‐, 2‐, and 3‐step heating cycle, whereby each cycle employed different power level and time. Mechanical properties were tested according to ASTM standards. It is found that the microwave‐cured composites produced mechanical properties as good as the thermally cured composites. The 2‐ and 3‐step heating cycle used in the microwave curing process produced better mechanical properties higher than those obtained from the microwaved 1‐step and thermally curing process. This is attributed to the slow increase in temperature during the beginning of the microwave curing process whereby the very low power level was applied in the first cycle of the multistep heating process. This affected the slower rate of viscosity increment, resulting in better wettability of the glass fiber with enhanced interfacial adhesion between the fibers and the resins. The viscosity of resins affected the homogeneity of the crosslinked structure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1059–1070, 2006     

中国光固化材料生产与市场近况

光固化是一种先进的表面加工技术,其配方产品（如涂料、油墨和胶黏剂）在高强度紫外光或电子束作用下发生固化反应。目前这一光固化工艺已在工业部门的很多领域得到广泛应用。光固化配方产品主要是由低聚物、反应性稀释剂和光引发剂等原材料组成。自2005年以来,我国几乎所有的光固化材料（除光引发剂以外）都在持续增长,即使在2008年国际金融危机期间受到的冲击也不大。2010年的行业数据表明,我国光固化材料市场依然充满生机,不过高端应用的光固化材料仍然需要进口。     

Effects of compaction and UV exposure on performance of acrylate/glass‐fiber composites cured layer by layer

With an aim to reducing manufacturing costs, in general and specifically to provide a solution to the thick laminate curing depth issue for composite materials, UV curing technology was combined with a fiber placement process to fabricate acrylate/glass‐fiber composites. A novel layer‐by‐layer UV in situ curing method was employed in this article and interlaminar shear strength (ILSS) tests and SEM were used to evaluate the effect of processing parameters, including compaction force and UV exposure dose, on ILSS. The SEM images from short‐beam strength test samples and the results of ILSS showed that the fibers' distribution was uniform in the cured matrix resin resulting from the compaction forces and that beneficially influenced the ILSS of the composite greatly. However, the matrix resin produced large shrinkage stresses when it reached a high degree of conversion (DC) in one‐step, which resulted in poor interlaminar adhesion. In addition, the fast curing speed of UV on the composite resulted in poor wetting between fiber and resin, and accordingly resulted in lower ILSS. To overcome these problems and obtain high ILSS value composites, an optimized compaction force and UV exposure dose were determined experimentally. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

UV固化粉末涂料组成与性能的研究

采用功率热补偿型扫描量热仪和INSTRON32 11毛细管流变仪测定了UV固化粉末涂料用主体树脂的玻璃化温度 (Tg)和流变性能 ,研究了该涂料中不同光引发剂体系对涂料光固化性能和涂膜物理性能的影响 ,及添加不同纳米材料对涂料涂膜物理性能的影响。     

Properties of Biobased Epoxy Resins from Epoxidized Soybean Oil (ESBO) Cured with Maleic Anhydride (MA)

Epoxidized soybean oil (ESBO), obtained from a renewable resource was used in the production of thermoset resins. Samples of the ESBO were initially treated with maleic anhydride, equal mixture of catalyst (1,3-butanediol anhydrous and benzyldimethylamine) and the mixture was cured for 5?h at different temperatures. After the curing process, the ratio between the ESBO and the anhydride (ratio EEW:AEW) was evaluated in terms of the different mechanical properties produced using flexural, Shore D hardness and Charpy impact tests. The sample with the best mechanical properties was that with an EEW:AEW ratio of 1:1.0 which leads to best balanced behavior and this could be representative for the maximum crosslinking degree. Also, thermal characteristics were evaluated during the crosslinking process using differential scanning calorimetry, In addition, other thermal characteristics of the cured materials were obtained by determining the heat deflection temperature and the Vicat softening temperature. The coefficient of thermal expansion was determined using thermo-mechanical analysis. In accordance with the mechanical behavior, the best thermal properties were obtained for samples with an EEW:AEW ratio of 1:1.0. As a result of this work, a biologically based epoxy resin with good mechanical properties and flexibility was obtained.     

紫外光固化松香基聚酯丙烯酸酯的合成研究

通过两步法合成了涂料用紫外光固化(UV)松香基聚酯丙烯酸酯(APAPEA)预聚物。对产物结构进行了红外表征,并采用DSC分析研究了其光固化行为。考察了酸醇物质的量比、合成工艺、反应温度及催化剂用量对APAPEA收率的影响。结果表明,适宜的合成条件为:醇酸物质的量比1.1∶1,慢速升温,反应温度120℃,催化剂用量0.8%~1.2%。合成的APAPEA涂膜固化速度67 s,硬度3H,柔韧性2 mm,附着力1级,耐冲击性50 cm,较市售聚酯丙烯酸酯(PEA400)固化速度快,涂膜硬度高,柔韧性及附着力相当,可作为UV固化涂料用低聚物。     

两种典型环氧树脂基覆铜板加工工艺的对比研究

采用差示扫描量热仪和旋转流变仪对比研究了双氰胺(DICY)/环氧树脂和酚醛树脂(PN)/环氧树脂两种典型的环氧树脂基覆铜板用环氧树脂体系的固化行为和流变特性,求出了固化动力学参数,同时考察了填料对PN/环氧树脂固化体系流变特性的影响,优化了层压工艺参数.     

Adhesion of UV-Cured Laminates of Poly(ethylene-2,6-naphthalate) (PEN) and Poly(ethylene terephthalate) (PET) films

This paper describes the properties of an ultraviolet (UV) curable laminating adhesive system that can be used with PEN, PET and UV-stabilized PET films. The adhesive system that contains (2,4,6-trimethylbenzoyl) diphenylphosphine oxide (TPO) as photoinitiator was optimally cured with a V-bulb fitted ultraviolet irradiator. The laminated structures built with this adhesive system and PEN, PET and UV-stabilized PET films showed a large manufacturing operating window, both in terms of adhesive layer thickness, initial peel strengths above 1500 N/m, V- and D-bulb UV sources and curing speeds from 5– 10 m/min. The 600-h dry heat aging tests indicated that the UV-stabilized PET films underwent less than approximately 1% decrease in light transmission and less than a 1% gain in color. The UV-stabilized PET film and its laminate showed particularly strong retention of optical properties under damp aging and QUV weathering, compared to PEN and non-UV-stabilized PET films. Finally, the peel strengths of the laminates were retained to greater than 1300 N/m for laminate structures of 50 μm film thickness, whereas structures made from thicker films retained approx. 40–60% (700–1100 N/m) of their initial peel strength.     

Allyl ether‐modified unsaturated polyesters for UV/air dual‐curable coatings. I: Synthesis and characterization of the oligomers and their cured films

Allyl ether (AE)‐modified unsaturated polyester oligomers were synthesized from polyethylene glycol (PEG), maleic anhydride (MAH), and trimethylolpropane mono allyl ether (TMPAE), and characterized by Fourier transform infrared (FTIR) spectra. The UV/air dual‐curable coatings were prepared from the oligomers using vinyl ether (VE) as a reactive diluent. FTIR spectra showed that C?C bonds in the coating composition had polymerized partially after cured by UV or air. The investigation of rheological behavior of the dual curable composition suggested that all the systems belonged to pseudoplastic fluid, and the increasing allyloxy content in oligomer resulted in a higher viscosity. Differential scanning calorimetry (DSC) analysis showed that the increasing TMPAE‐PEG molar ratio resulted in lower T_g, and all samples had the same glass transition temperature irrespective of the type of curing. The results of TGA for cured films indicated that UV‐cured film had better thermal stability than the air‐cured one. The air‐cured film showed superior pencil hardness, impact strength, and flexibility to the UV‐cured counterpart. However, the air‐cured film had poor adhesion and electric resistance properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2765–2770, 2004     

Process cure monitoring of unsaturated polyester resins,vinyl ester resins,and gel coats by Raman spectroscopy

The curing process of unsaturated polyester resins, vinyl ester resins, and gel coats was studied by using a process Raman spectrometer, equipped with a remote fiber‐optic probe. The resins were cured and Raman spectra were recorded during the curing reaction. The spectral changes were identified and, from the intensities, the cure process could be monitored. Gel times given by the resin suppliers correlated well with the Raman results. It could also be seen that the curing process continues for a long time, up to several weeks. Postcuring will finally complete the curing process. White and lightly colored gel coats could easily be monitored by Raman spectroscopy, but fluorescent problems were encountered with heavily colored pigments. The curing of laminates containing 50–70 wt % glass fiber mat could also be followed by Raman spectroscopy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1285–1292, 2004     

Alternative to latent catalysts for curing UF resins used in the production of low formaldehyde emission wood-based panels

This paper studies alternative catalysts to ammonium sulfate for curing urea-formaldehyde (UF) resins. When using a latent catalyst like ammonium sulfate, hexamine is formed as by-product of curing reaction. It is believed that hexamine hydrolysis may contribute to formaldehyde release during the life-time of wood-based panels produced with UF resins. Orthophosphoric acid, on the other hand, catalyzes resin cure without by-product formation and was compared to ammonium sulfate. The pot-life of adhesives with both catalysts was evaluated at 40 °C with a Brookfield rheometer. Mechanical resistance tests performed with ABES (Automated Bonding Evaluation System) showed that orthophosphoric acid effectively catalyzes UF resin cure. Particleboards were produced using both catalysts and the most important properties evaluated, according to European Standards: formaldehyde content, internal bond, moisture content, thickness swelling and density. Particleboards cured with orthophosphoric acid and stored under forceful conditions of humidity and temperature presented similar internal bond and lower formaldehyde content than those produced with ammonium sulfate.     

Dual crosslinking of carboxylated nitrile butadiene rubber latex employing the thiol‐ene photoreaction

At present, the most common used crosslinking process for carboxylated nitrile butadiene rubber (XNBR) latex is an accelerated sulfur curing system with zinc oxide. To avoid allergenic reactions related to residual accelerator levels in dipped XNBR latex articles such as medical gloves, a dual curing process has been developed combining thermal and photochemical crosslinking reactions. The two‐step procedure involves the formation of covalent and ionic bonds to ensure good mechanical properties of the final products. The photochemical thiol‐ene reaction is used to generate covalent crosslinks between the remaining C?C double bonds of the butadiene units whereas the carboxylic moieties are conventionally cured with divalent metal oxides (ZnO) under elevated temperature (formation of ionic crosslinks). The photochemical curing step is carried out both in the latex phase using a falling film photoreactor (prevulcanization) as well as in the solid phase by UV irradiation of dried XNBR films (postvulcanization). The mechanical properties and crosslink densities of the cured XNBR films are determined and the influence of selected curing parameters is assessed. The results give evidence that a combined approach of thermal prevulcanization and photochemical postvulcanization makes the production of latex articles (e.g., gloves) with tailored properties and good skin compatibility feasible. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

含苯并恶嗪及联苯结构双邻苯二甲腈共聚树脂

将联苯结构的双邻苯二甲腈树脂(4,4'-二-3,4-二腈基苯氧基联苯,简称BPH)熔融后与含有苯并恶嗪单元的双邻苯二甲腈树脂(简称BZ-BPH)共混。通过示差扫描量热法(DSC)、流变测试研究了共混树脂的固化工艺性能,通过热重分析(TGA)研究了共混树脂固化物的耐热性能。此外采用SEM观察了浇注样的断面结构。结果表明,通过调节BZ-BPH的加入量可实现对固化工艺的调控。经过240℃/4 h+280℃/4 h+320℃/4 h+375℃/6 h的固化,产物在空气和氮气下5%热失重温度均高于500℃(高于BPH固化物)。BZ-BPH与BPH之间共聚形成了均相的交联网络。     

Comparison of the curing kinetics of the RTM6 epoxy resin system using differential scanning calorimetry and a microwave‐heated calorimeter

The cure of a commercial epoxy resin system, RTM6, was investigated using a conventional differential scanning calorimeter and a microwave‐heated calorimeter. Two curing methods, dynamic and isothermal, were carried out and the degree of cure and the reaction rates were compared. Several kinetics models ranging from a simple nth order model to more complicated models comprising nth order and autocatalytic kinetics models were used to describe the curing processes. The results showed that the resin cured isothermally showed similar cure times and final degree of cure using both conventional and microwave heating methods, suggesting similar curing mechanisms using both heating methods. The dynamic curing data were, however, different using two heating methods, possibly suggesting different curing mechanisms. Near‐infrared spectroscopy showed that in the dynamic curing of RTM6 using microwave heating, the epoxy‐amine reaction proceeded more rapidly than did the epoxy‐hydroxyl reaction. This was not the case during conventional curing of this resin. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3658–3668, 2006