A Tunable Nanoimprint System to Create New Features

Fabrication of different patterns based on the same nanoimprint mould is very attractive due to the time and cost consumption of fabricating hard mould. This paper demonstrates a tunable photo‐curing nanoimprint system to create new features based on the same polydimethylsiloxane (PDMS) mould and a Ti‐containing resist synthesized by titanium (IV) ethoxide and 2‐(methacryloyloxy)ethyl acetoacetate. The resist exhibits very high oxygen RIE resistance and is able to take the place of traditional polysiloxance based resists to fabricate high‐aspect‐ratio patterns. The resist also has a low shrinkage (about 2.45%) and a high Young’s modulus of 10.85 GPa after photo‐curing. High polarity contrast of PDMS and Ti‐resist makes the release process freely and PDMS mould can be directly used without further anti‐stick treatment. A number of new features are imprinted into Ti‐resist based on the same PDMS mould by controlling the deformation and the stretched PDMS mould can be repeatedly used after relaxation.     

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.     

Cure kinetics of bismaleimides as basis for polyimide-like inks for PolyJet™-3D-printing

Since polyimides are well known for their excellent chemical and thermal stability and outstanding mechanical properties there is increasing interest in developing polyimide-based inks to produce additively manufactured parts with properties superior to those of currently available materials. Usage of bismaleimides (BMI) as precursors allows polyimides to be fabricated via PolyJet™ printing (Stratasys Ltd., Rehovot, Israel). Characterization of the curing kinetics is a central part of process development, as fast curing initiated by UV light is desired. Here, a comprehensive study of thermal and UV curing of BMI oligomers with various molecular weights and chemical structures is presented. Fourier transform infrared spectroscopy serves as a tool for determining the curing degree. Furthermore, an estimation of the activation energy for thermal curing is performed. UV curing of the selected BMIs leads to highly crosslinked, thermoset polymers with excellent chemical resistance and thermal stability which are of great interest for PolyJet™ 3D printing. © 2018 The Authors. Journal of Applied Polymer Science published by Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47244.     

Synthesis of low viscosity,fast UV curing solder resist based on epoxy resin for ink‐jet printing

A novel photosensitive low viscosity epoxy resin was synthesized by polyethylene glycol (PEG)‐modified bisphenol‐A epoxy resin (E51). The resin was modified by ethylene glycol, diethylene glycol, and different molecule weights (200,300,400) PEGs to optimize the minimum viscosity. FTIR was used to determine molecule structure. Cationic photoinitiator (UVI‐6976) mixed with modified resin (10 wt %), was utilized to boost the resin curing under UV light. The curing degree was beyond 90% within 40 s and the whole process was monitored by photo‐DSC. The modified resin diluted with ethylene glycol diglycidyl ether, was screen printed onto polyimide and polyethylene terephthalate substrate, and the properties of solder mask were up to China printed circuit association standard. The solder resist also meet all requirements under ink‐jet printing technology as the viscosity is under 60 mPa·s and the curing duration is <1 min. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Synthesis and ultraviolet‐curing behaviors of vinyl ether functionalized polyurethane oligomers

The vinyl ether functionalized oligomer is one of the most basic components of vinyl ether functionalized materials for cationic UV‐curable coatings. In this study, three types of vinyl ether functionalized polyurethane oligomers (i.e., polyether, polyester, and polydimethylsiloxane) were synthesized with diisocyanate, diol, and hydroxyethyl vinyl ether. These oligomers were characterized by IR, ¹H‐NMR, and ¹³C‐NMR spectroscopy. The effect of the raw material ratio on the oligomer, UV‐curing behaviors, and thermal properties of these oligomers were investigated. The UV‐curing behavior was analyzed by real‐time Fourier transform infrared spectroscopy. The vinyl ether terminated polyester urethane oligomer exhibited better UV curing, with a higher final conversion and maximum UV‐curing rates. In addition, the light intensity was enhanced for oligomers with better UV‐curing properties. Research on these vinyl ether functionalized oligomers is essential to the development and applications of cationic vinyl ethers systems. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40501.     

Synthesis of UV and thermal dual curing oligomer for solder resist ink using ink-jet printing

A novel solder resist ink for inkjet printing containing the ultraviolet (UV) and thermal dual curing oligomer is introduced in this work. Three kinds of acrylic monomers for the synthesis of the oligomer are successful prepared and their structures are determined by Fourier transfer infrared. Both UV curing process and thermostability are monitored under UV differential scanning calorimetry and thermogravimetric analysis. For the photoreaction process, the oligomer using Lauryl methacrylate as the material of copolymerization possesses the highest reactivity and conversion of carbon–carbon double bond. Besides, this kind of oligomer also owns excellent thermostability, just losing 5.9% of its weight at 288 °C. The solder resist inks containing the oligomers and jetting by the inkjet printer are tested with the adhesion, soldering resistance, and other performances, presenting the outstanding heat resistance and wide application prospects. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47428.     

Investigation of cure advancement in dual-cure polyurethane-acrylate coatings over metal substrates

In the present study, a polyurethane acrylate (PUA) system cured via a thermal–UV (dual-cure process) was developed. The system selected for this work was a two-pack polyurethane acrylate with polyester polyol as the main component and urethane monoacrylate (UMA) as hardener. The polyester polyol was synthesized in a way to provide a final film coating containing both a suitable flexibility and high surface hardness. The thermal and photochemical curing behavior of the resin was studied via the chemorheology technique and the real-time FTIR. The Boltzmann sigmoidal model was implemented and well-fitted to the data obtained from the chemorheology measurements. The comparison between two reactive diluents, butanediol diacrylate (BDDA) and trimethylolpropane triacrylate (TMPTA) showed that BDDA reacts faster than TMPTA in the thermal curing condition. Nevertheless, the network buildup is stronger when TMPTA is used. The photopolymerization is also faster for the case of TMPTA. However, its final double bond conversion is restricted to a lower amount due to steric hindrance and higher viscosity of the system.     

Synthesis of UV‐curable hyperbranched polyurethane (meth)acrylate oligomers via thiol‐ene “click” chemistry

First, the second‐generation hyperbranched poly(amine‐ester) (G2‐OH) was successfully prepared by thiol‐ene “click” chemistry. Subsequently, a series of photosensitive hyperbranched oligomers (G2‐ORs) were synthesized by facile modifications of the G2‐OH with acryloyl chloride, methacryloyl chloride, IPDI‐HEA, and IPDI‐HEMA, respectively. The structures of hyperbranched oligomers were characterized by element analysis, FT‐IR, ¹H NMR, GPC and viscosity measurement. It was shown that these synthesized oligomers have narrow molecular weight distribution and low intrinsic viscosity at 30°C. UV–vis spectra results showed that the G2‐ORs had sharp absorption bands at around 202 nm. The results of photosensitivities measurement indicated that the G2‐Macr shows the highest photosensitive than other hyperbranched oligomers in the absence of photoinitiator. In addition, these UV‐cured photosensitive G2‐ORs had good thermal properties. The solubilities of the synthesized hyperbranched oligomers were also examined. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A novel dendritic acrylate oligomer: Synthesis and UV curable properties

An dendritic acrylate oligomer with eight double bonds (DAO) was synthesized by Michael addition reaction of ethylene diamine (EDA) and trimethylolpropane triacrylate (TMPTA) under mild conditions, and was easily separated from the reaction system with methanol. The structure of DAO was characterized by IR, ¹H‐NMR, and elemental analysis. DAO is UV curable oligomer with low viscosity and high curing speed. Its viscosity was 10.85% of that of the linear acrylic oligomers with similar molecule weight (EBECRYL Resin 285). With Darocure 1173 as the photoinitiator, the curing speed of DAO was respectively 7.5 and 10.3 times higher than that of EBECRYL Resin 605 and EBECRYL Resin 285. Furthermore, the effect of the photoinitiator and active diluent on curing speed of DAO UV curing system was studied. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1018–1022, 2004     

紫外光固化涂料—液态光致抗蚀剂

简单介绍了紫外光固化的原理 ,紫外光固化涂料的配方构成、固化设备及原材料的选择 ,并举例描述了液态光致抗蚀剂的组成和特性。     

Fabrication of flexible UV nanoimprint mold with fluorinated polymer-coated PET film

UV curing nanoimprint lithography is one of the most promising techniques for the fabrication of micro- to nano-sized patterns on various substrates with high throughput and a low production cost. The UV nanoimprint process requires a transparent template with micro- to nano-sized surface protrusions, having a low surface energy and good flexibility. Therefore, the development of low-cost, transparent, and flexible templates is essential. In this study, a flexible polyethylene terephthalate (PET) film coated with a fluorinated polymer material was used as an imprinting mold. Micro- and nano-sized surface protrusion patterns were formed on the fluorinated polymer layer by the hot embossing process from a Si master template. Then, the replicated pattern of the fluorinated polymer, coated on the flexible PET film, was used as a template for the UV nanoimprint process without any anti-stiction coating process. In this way, the micro- to nano-sized patterns of the original master Si template were replicated on various substrates, including a flat Si substrate and curved acryl substrate, with high fidelity using UV nanoimprint lithography.     

电润湿纳米压印光刻胶的制备及其特性研究

实现对微纳米模板的充分填充是传统纳米压印胶的一个重要难题.本文设计和制备了一种类离子液体的丙烯酸酯化合物I-M-PET3A.以N,N-二甲基乙醇胺为助引发剂,二苯甲酮为光敏剂,丙烯酸羟丙酯为活性稀释剂与I-M-PET3A共混制备的纳米压印胶具有相对小的粘度（530mpa·s）和好的导电性能（33.98μs/cm）,从而表现出良好的电润湿特性.在200V,10Hz方波交流电额外施加的电毛细驱动下,复配的压印胶大约10s即可充分填充30μm×120μm的微槽.经光固化和脱模后能保持完美的微纳米图案.该纳米压印胶同时具有光固化和电润湿特性,为高性能纳米压印胶的开发提供了新思路.     

Synthesis,characterization, and UV curing kinetics of hyperbranched polycarbosilane

Hyperbranched polycarbosilane with allyl end groups was synthesized via hydrosilylation of methyldiallyldilane, and characterized by Fourier transform infrared spectroscopy, ¹H, ¹³C, ²⁹Si nuclear magnetic resonance, and size exclusion chromatography/multiangle laser light scattering. The degree of branching and average number of branches of the resulted polymer determined by ²⁹Si NMR spectroscopy is 0.58 and 0.42, and the exponent α in Mark–Houwink equation is 0.33 based on the relationship between viscosity and molecular weight. UV curing behaviors of the hyperbranched polycarbosilane were investigated using differential scanning photocalorimeter, and the effects of diluent's concentration, light intensity, reaction atmosphere, and temperature on the curing behaviors and kinetics were studied in detail. It was found that curing reaction can be accomplished rapidly under UV irradiation within 40 s both in air and in nitrogen atmosphere if acrylic reactive diluent was employed. The result suggests that it is an effective way to increase the curing reactivity by incorporating acrylic reactive diluents with high UV sensitivity into the polycarbosilane system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

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。     

Photo- and thermoinitiated curing of epoxy resins by sulfonium salts

A number of benzylthiolanium salts have been synthesized, analysed and evaluated by differential scanning calorimetry and viscosity measurements with respect to their potential use as thermal curing agents for epoxy resins. Over a wide range of Hammett constants a correlation exists between initial reactivity, shelf life and the electronic substituent effects of the benzyl group. A combination with arylsulfonium salts leads in singular cases to dual cure systems with attractive properties of thermal and UV induced curing. The sensitization of benzylthiolanium salts also leads to dual cure systems. This opens up new possibilities for UV curable epoxy resins in electronic applications requiring additional curing in shaded areas.     

Rheology and curing characteristics of dual-curable automotive clearcoats using thermal radical initiator derived from O-imino-isourea and photo-initiator

The curing characteristics of clearcoats, including a thermal curing initiator (TRI) newly designed from O-imino-isourea and photo-initiator (PI), were investigated by means of different mono-curing and dual-curing pathways. The competitive relationship between TRI and PI on the curing pattern, reacting with acrylate double bonds in a clearcoat was elucidated by altering the UV and thermal sequence in the dual-curing process, through various experimental methods. From the rheological properties of clearcoats along the curing time, two dual-curing methods showed the different evolution of curing patterns. In the UV–thermal dual-curing case, the initial infusion of UV light promoted free radical polymerization during the subsequent thermal curing by generating considerable free radicals, and exhibiting a higher growth rate of elastic modulus during the curing in comparison with the thermal–UV dual-curing case. However, the final modulus value in the thermal–UV dual-curing case was higher due to the suppression of thermal curing by the steric hindrance in the UV–thermal dual-curing. The level of crosslinked networks in clearcoats via different curing steps can be explicitly figured out from the double bond conversion from FT-IR, curing pattern from rigid-body pendulum test, and scratch properties from nano-scratch test.     

Preparation and characterization of UV/thermal dual-curable polyurethane acrylate adhesive for inertial confinement fusion experiment

A new type of polyurethane acrylate (APUE) oligomer, which contains both acrylic and epoxy group in its molecular structure, was synthesized. UV/thermal dual-curable adhesives were prepared using various contents of APUE oligomers, reactive diluent, photoinitiators and thermal-curing agent. The curing behaviors of the dual-curable adhesives were investigated using photo-DSC, on-line FT-IR spectroscopy, the determination of gel fraction and dynamic mechanical thermal analysis (DMTA). The reaction rate and extent of UV curing were studied and found to be strongly dependent on the concentration of C=C bonds in the APUE oligomers. The gel fraction was also evaluated as a function of C=C bond concentration, demonstrating that gel fraction increased with increasing C=C bond contents in the APUE oligomers. Moreover, when the dual-curable adhesive was thermally-cured, the gel fraction was largely improved, due to the thermal-curing agent initiating the unreacted epoxy groups to allow the formation of further crosslinking. The adhesion strength at −196 °C increased with increasing C=C bond content. The latent thermal-curing agent contributed to the enhancement of the adhesion strength.     

Synthesis and UV-curing behaviors of novel rapid UV-curable polyorganosilazanes

A novel ultraviolet-curable polyorganosilazane ceramic precursor was synthesized via ammonolysis from modified chorosilane, which had been synthesized by alcoholysis of trichloro(methyl)silane and 2-hydroxyethyl acrylate. The polyorganosilazane was well characterized by using Fourier transformed infrared spectroscopy (FTIR), ¹H nuclear magnetic resonance (¹H NMR), and multi-angle laser light scattering (LLS). Its UV curing behaviors investigated via FTIR and differential scanning calorimeter (DSC) clearly indicated that this polyorganosilazane precursor could be cured rapidly at either air atmosphere or nitrogen atmosphere. The curing reactions take place rapidly within about 15 and 40 s at nitrogen and air atmosphere under UV irradiation, respectively. After exposed under UV light for 40 s at air atmosphere, the conversion percentage of the unsaturated bond of the cured polyorganosilazane sample is near to 90%. The results suggest that incorporating acrylic pendant groups with high UV sensitivity into polyorganosilazane molecular structure is an effective way to increase its curing speed.     

Rheological studies of ultraviolet curing with an oscillating plate rheometer

The dynamic viscoelastic behavior during UV curing was studied for thin liquid films of epoxy acrylate prepolymer by the use of an oscillating plate rheometer. The dynamic viscosity rapidly increases after a certain period of irradiation, so that the UV curing process has the minimum exposure energy required to start polymerization. The minimum exposure energy markedly increases with increasing sample thickness; this results from the inconsistency of degree of curing in the direction perpendicular to the shearing surface. Since free radicals which initiate polymerization are formed by photochemical decomposition of initiator, the ability to cure a film depends on the light intensity at a given depth of the film. the attenuation of light in the film is primarily responsible for this inconsistency. When UV light is applied through a UV filter, the curing behavior is analyzed by a single exponential decay of light with depth because the curing is induced by absorption of a monochromatic light of 365 nm. On the other hand, when UV light from a UV lamp whose output spectrum is a continuum is directly applied, the curing behavior is explained by a combination of energy absorption at different wavelengths. In both cases, the theoretical curves of dynamic viscosity predicted in relation to spectral sensitivity show a good agreement with the experimental results.     

Synthesis and cationic photopolymerization of fluorine‐containing vinyl ether monomers for the hydrophobic films

Fluorine‐containing vinyl ether monomer is a combination of UV‐curing technology and low surface energy materials. In this article, a type of fluorine‐containing vinyl ether monomer was synthesized by the reaction of fluorinated alcohols, hexafluorobenzene, 2‐vinyloxy ethanol, and sodium hydride. These monomers exhibit low viscosity and good fluidity. The effect of the fluorine content of the monomers on their UV‐curing behavior was monitored by photo‐differential scanning calorimetry. The photo‐polymerization process was efficient because the double‐bond conversed sufficiently (>85%) and the curing rate was fast (<20 s). In addition, the surface energy of homopolymer and copolymer films was researched. The surface free energy was very low and could even reach 0.92 mJ m^?2. The low surface energy was due to high fluorine content and the diffusion of uncured monomers, which was on the basis of X‐ray photoelectron spectroscopy data and observed conversions. The structure of homopolymers and copolymers was one of the most important influences on the surface free energy and the thermal properties. The copolymers exhibited better thermal stability than the homopolymers. All of these results demonstrated that these monomers are suitable for a wide range of practical applications such as UV coatings, UV inks, and photoresists. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41019.