UV-LED光固化体系光引发剂的新进展

本文综述了可用于UV-LED光固化体系光引发剂的研究进展，包括传统光引发剂及其衍生物（硫杂蒽酮类、二苯甲酮类和酰基膦氧化物）、新型基团的光引发剂（咔唑基、萘酰亚胺基、吩嗪基、苯丙二茂基、咪唑基和三嗪基）以及高分子光引发剂。传统光引发剂的改性和大分子光引发剂的合成，可以提高引发剂的稳定性。新型光引发剂的吸收波长与UV-LED光固化的发射波长匹配性较好，但该类光引发剂常需要加入助剂。此外，描述了氧阻聚对光固化体系的影响，指出了目前UV-LED光引发剂存在的不足，并展望了其发展应用前景。。     

Colour and gloss properties of pigment‐printed synthetic leather using an ultraviolet‐curable water‐borne polyurethane acrylate binder and two photoinitiators at different ratios

This study reports on the colour and gloss properties of pigment‐printed polyurethane‐based synthetic leather using an ultraviolet (UV)‐curable water‐borne polyurethane acrylate binder and two types of photoinitiators (Omnirad 819 DW and Omnirad 500) at different ratios. The UV curing of printed synthetic leather samples was conducted with gallium and mercury lamps, either singly or in combination, at three different power levels. Chemical changes in the cured films because of the polymerisation of the UV‐curing process were analysed by Fourier Transform‐infrared spectroscopy, which showed that the polymerisation reaction occurred after UV curing in both the clear and in the pigmented films. The Omnirad 500 photoinitiator is more effective in surface curing and the Omnirad 819 DW photoinitiator is more effective in deep curing. The Omnirad 500 photoinitiator caused the gloss values to drop significantly, especially in the formulation including both photoinitiators, Omnirad 819 DW and Omnirad 500, at a 1:2 ratio, respectively. In the formulation including a higher ratio of the Omnirad 819 DW photoinitiator, higher gloss values were obtained compared with the formulation including a higher ratio of the Omnirad 500 photoinitiator. Considering all the results, the highest gloss value of 20.96 was obtained with samples printed with the formulation of the two photoinitiators at an equal ratio (1:1) cured under a gallium/mercury lamp combination at a power level of 90 W/cm. Moreover, the highest K/S value of 10.86 was obtained with samples printed with the formulation of the two photoinitiators at an equal ratio cured under the gallium lamp at 90 W/cm.     

紫外光固化含硫密封剂的制备及性能

以聚硫代醚橡胶为基础胶,利用Thiol-ene点击反应制备了紫外光固化含硫密封剂。考察了光引发剂种类和用量以及烯烃种类、多元硫醇种类等对硫化后密封剂力学性能、热分解温度、玻璃化转变温度的影响。结果表明,相比于光引发剂184,光引发剂1173的固化效果更好,固化后的密封剂热稳定性更佳,且随着光引发剂用量的增加,密封剂的力学性能和热稳定性均下降,光引发剂1173的用量宜为0.03份（质量,下同）。采用三丙二醇二丙烯酸酯（TPGDA）作为固化剂固化的聚硫代醚密封剂力学性能较好,而且随着TPGDA用量的增加,密封剂的力学性能和热稳定性均上升,TPGDA的用量宜为1.00份。多官能度硫醇的加入可提高密封剂的交联度及玻璃化转变温度。     

Effects of the electron‐beam absorption dose on the glass transition,thermal expansion,dynamic mechanical properties,and water uptake of polycardanol containing epoxy groups cured by an electron beam

In this study, the glass transition, thermal expansion, dynamic mechanical properties, and water‐uptake behaviors of diepoxidized polycardanol (DEPC) cured by electron‐beam radiation in the presence of cationic photoinitiators were investigated. How the type and concentration of cationic photoinitiators and the electron‐beam absorption dose influenced the properties of the cured DEPC was also studied. Two types of cationic photoinitiators, triarylsulfonium hexafluorophosphate (simply referred to as phosphate type or P‐type) and triarylsulfonium hexafluoroantimonate (simply referred to as antimonate type or Sb‐type), were used. Electron‐beam absorption doses of 200, 300, 400, and 600 kGy were applied to the uncured diepoxidized cardanol (DEC) samples, respectively. It was revealed that the Sb‐type photoinitiator was preferable to the electron‐beam curing of DEC; this led to a lower photoinitiator concentration and/or a lower electron‐beam absorption dose compared to that in the phosphate‐type photoinitiator. As a result, the variations in the glass‐transition temperature, coefficient of thermal expansion, storage modulus, and water uptake of the cured DEPC were quite consistent with each other. We found that the optimal conditions for the enhanced properties of DEPC by electron‐beam curing were an Sb‐type photoinitiator at 2 wt % and an electron‐beam absorption dose of 600 kGy. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42570.     

Structural effect of photoinitiators on electro‐optical properties of polymer‐dispersed liquid crystal composite films

Two types of photoinitiators were synthesized: (1) a α,ω‐telechelic oligomeric photoinitiator, by the reaction of poly(propylene glycol) diglycidylether (PPGDGE) and 2‐hydroxy‐2‐methyl‐1‐phenyl‐propan‐1‐one (Darocur 1173), and (2) a polymeric photoinitiator, by copolymerization of a monomer that had a liquid crystalline property, 4‐[ω‐(2‐methylpropenoyloxy)decanoxy]‐4′‐cyanobiphenyl, with a vinyl monomer that had a photosensitive group. For comparison, low‐molecular‐weight (low‐MW) photoinitiator (Darocur 1173) also was used. Attention was directed to the structural effect of the photoinitiators on the electro‐optical properties of polymer‐dispersed liquid crystal (PDLC) film in which the LC phase occupied a major volume (80 wt % of the composite film). For the preparation of PDLC films by the polymerization‐induced phase separation method, the optimum UV‐curing temperature was observed at 50°C, a temperature slightly higher than the cloud temperature (T_cloud) of the low‐MW LC/matrix‐forming material mixture. It was found that the electro‐optical performance of the PDLC cell fabricated with the oligomeric or polymeric photoinitiator was better than that of the PDLC cell made with a low‐MW photoinitiator (Darocur 1173), exhibiting lower driving voltage (V₉₀) and higher contrast ratio under identical formulation conditions. Oligomeric photoinitiators allowed premature phase separation between the LC and matrix phases, resulting in relatively pure LC‐rich phases. For the polymeric photoinitiator, incorporation of mesogenic moieties into the photoinitiator resulted in not only a well‐defined LC/matrix morphology but also in low driving voltage (V₉₀) because of reduced friction at the LC/matrix interfaces. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 162–169, 2006     

常用光引发剂在紫外光固化涂料中的应用研究

针对紫外光固化体系,研究了常用光引发剂在紫外光固化涂料中的应用。讨论了常用光引发剂的用量及其对亮光体系、亚光体系和色漆体系固化性能的影响。得出在紫外光固化涂料中选择引发剂的规律。     

Spatial and temporal evolution of the photoinitiation rate for thick polymer systems illuminated by polychromatic light: selection of efficient photoinitiators for LED or mercury lamps

BACKGROUND: Four common free radical photoinitiators were evaluated for use in thick photopolymerizations illuminated with a medium‐pressure 200 W mercury–xenon arc lamp and a high‐intensity 400 nm light‐emitting diode (LED) lamp. For each photoinitiator/lamp combination, the spatial and temporal evolution of the photoinitiation rate profile was analyzed by solving the set of differential equations that govern the light intensity gradient and initiator concentration gradient for polychromatic illumination. RESULTS: The simulation results revealed that two of the four photoinitiators evaluated were ineffective for photoinitiating thick polymer systems. The photoinitiator bis(2,4,6‐trimethylbenzoyl)‐phenylphosphine oxide, in combination with the 400 nm LED lamp, was shown to be the most efficient photoinitiator/light source combination for photoinitiation of thick systems. CONCLUSION: The results show that some photoinitiators commonly used for photopolymerization of thin coatings are ineffective for curing thick systems. LED light sources provide advantages over traditional mercury lamps, and may have tremendous potential in the effective photoinitiation of thick polymer systems. Copyright © 2008 Society of Chemical Industry     

阳离子光引发剂研究进展

阳离子型光引发剂是一类新型的紫外光固化材料的引发剂。本文介绍了阳离子光引发剂的主要种类及各自的特点 ,讨论了其光引发机理 ,并简述了阳离子光引发剂的的发展概况和主要用途。     

Photocrosslinkable modified vegetable oil based resin for wood surface coating application

An acrylated epoxidized linseed oil (AELO) was synthesized from epoxidized linseed oil through ring opening of the oxirane group using acrylic acid as ring opening agent. The occurrence of the acrylate group and the ring opening of oxirane group was monitored using FT-IR spectroscopy. The AELO was mixed with three different photoinitiators at two different concentrations. Wood surfaces were coated with the mixtures, subsequently cured under UV light and the resulting surface properties of the coated samples gloss, scratch resistance, solvent resistance, and coating adhesion were characterized. The efficiency of the photoinitiators and the influence of their concentration on the rate and the extent of the curing were studied by curing the AELO mixtures under a monochromatic wavelength of 365 nm and measuring absorption spectra during the cure by real time FT-IR spectroscopy. The decrease of absorption in the measured spectra at 1406 cm⁻¹ was used to calculate the conversion of acrylic double bonds with increasing time of UV light exposure to obtain information on the cure kinetics for each photoinitiator and concentration.     

用FTIR跟踪监测环氧丙烯酸酯胶粘剂光固化过程的研究

用FTIR跟踪监测环氧丙烯酸酯胶粘剂光固化过程并研究了光引发剂体系中辐射时间与双键转化率的关系。研究结果显示,合理配合使用不同特征吸收波长的光引发剂,能有效利用紫外光源,提高固化速度。夺氢型光引发剂的引发活性低于断裂型光引发剂,断裂型光引发剂中α-羟基酮衍生物(1173)比α-胺基酮衍生物(907)和酰基膦氧化物(TPO)引发效率低。在α-羟基酮衍生物中185的引发活性又远远高于1173与184。复合型光引发体系和光引发剂与助引发剂联用的引发效率明显高于单一引发剂体系。     

UV curing of aqueous polyurethane acrylate dispersions. A comparative study by real-time FTIR spectroscopy and pilot scale curing

Real-time FTIR spectroscopy was used to study the chemical and physical factors, e.g., photoinitiator and temperature, affecting the UV curing of dried films from aqueous polyurethane acrylate dispersions. Poor conversion of the acrylate double bonds (67%) observed at room temperature can be overcome by irradiation at elevated temperatures. At 353 K almost complete conversion is observed, even with reduced photoinitiator content. Single or multiple UV-light flash experiments were performed to simulate technical parameters, e.g., cure speed and number of required UV lamps, with the help of RTIR spectroscopy. The results obtained were confirmed by pilot-scale UV curing experiments: one or, at most, two UV lamps of high intensity are sufficient for the curing process with respect to the double-bond conversion. The coatings based on the polyurethane acrylate dispersion show low sensitivity towards oxygen from air. Moreover, in comparison to UV curing under inert nitrogen atmosphere, a small “positive” effect on the conversion in the presence of air has been observed, which might be due to the contribution of peroxyl radicals or their decomposition products to curing. Permoserstra?e 15, D-04318 Leipzig, Germany.     

Photopolymerization synthesis of poly(N-isopropylacrylamide) hydrogels

Poly(N-isopropylacrylamide) (NIPAAm) gels were formed by photopolymerization of NIPAAm in the absence of a crosslinker using a water solvent at 25°C. Factors affecting formation were the wavelength region of irradiated light, the type of photoinitiators, and the concentrations of the photoinitiator and monomer. A high-pressure mercury lamp (400 W) was used as a light source. An NIPAAm concentration of 10 wt % and irradiation time of 15 h was used for the photopolymerization. The gel (68% yield) was formed when the quartz glass system was used, but no gelation was observed for the Pyrex glass system that transmits light with π > 290 nm. The gel (100% yield) was easily formed, even in the latter system, when 30 mmol/L of hydrogen peroxide and potassium persulfate were used as the photoinitiator. Water soluble photoinitiators such as ferric chloride and sodium anthraquinone-2,7-disulfonate were not effective for the gel formation. Yield of the gel increased with increasing the potassium persulfate concentration (1–30 mmol/L), but it decreased when a high concentration of hydrogen peroxide (60 mmol/L) was used. The gel yield increased with the NIPAAm concentration (5–20 wt %). The degree of swelling of the resultant poly(NIPAAm) gels, which was measured by immersing the gels in water at various temperatures (0–50°C) for 24 h, steeply decreased at about 30°C with increasing temperature, exhibiting a temperature-responsive character. The gels swelled and shrank in water below and above the temperature, respectively. The extent of the character depended on the concentrations of hydrogen peroxide and monomer. The formation mechanism of the gel in the photopolymerization of NIPAAm using hydrogen peroxide photoinitiator was discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1313–1318, 1997     

On the structure/properties relationships in photoinitiators of polymerization

The choice of photoinitiators is partly governed by the requirement of a high curing speed. Many reactive monomers and efficient photoinitiators have been synthesized and are commercially available. However, improved photoinitiator systems, exhibiting increasingly faster curing speeds and/or increased photosensitivity, are increasingly required. The intrinsic reactivity in the exicited states determines te interest of a given photoinitiator with reference to its efficiency. However, other factors e.g. high molecular absorption coefficients and a broad spectral absorption range, synergistic effects, yellowing, extractability, and th effect on the long-term stability, must be considered as important. An attractive field of research and development is found in the role played by decisive parameters affecting the reactivity of a given structure, such as chemical substitution in well-chosen positions, the character of water solubility, acid release ability, and copolymerization potential. Laser spectroscopy proved a most convenient tool for the real time investigation of the excited state dynamics and the processes involved.     

Ultraviolet‐curable epoxidized sunflower oil/organoclay nanocomposite coatings

Hybrid nanocomposite coating films, prepared by the incorporation of epoxidized sunflower oil into organoclay, can be cured by ultraviolet radiation with either cationic or hybrid initiation. The organoclay used in this study was prepared by a cationic exchange process in which sodium ions were replaced by alkyl ammonium ions. The effects of types of photoinitiators on energy consumption in the curing process were studied. Formulations with a hybrid photoinitiator required less energy in the curing process than those with a cationic photoinitiator. Moreover, the physical properties of dried films were examined as a function of the organoclay incorporation, and it was found that the hardness of the films increased as the amount of organoclay in the formulation increased. The X‐ray diffraction patterns of an ultraviolet‐curable organoclay‐incorporated film showed an exfoliated structure of the organoclay in the ultraviolet‐curable coating film. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Electron beam curing of polymer composites

Electron‐beam (E‐Beam) curing of an epoxy polymer matrix and its composite (reinforced with IM7 Carbon fibers) was studied using a cationic photoinitiator. Photoinitiator concentration, dose, and process temperature were varied to understand their influence on E‐beam curing. Optimal photoinitiator concentration was found to be 5 phr. The curing was due to a primary α reaction with a strong dependence on dose, and a secondary β reaction with a weak dependence on dose and a strong dependence on initiator concentration. The extent of cure increased rapidly with dose until 100 kGy and it approached a plateau value beyond 100 kGy. This plateau value corresponded to incomplete curing by 27% for resin and 22% for composite at a process‐temperature of 22°C. The causes for incomplete curing appear to be the secondary β reaction and diffusional limitation. Increase in process temperature resulted in higher extent of cure at a dose level. The material used in this study was also found to be thermally curable and the reaction onset temperature (measured in a DSC ramp experiment) reduced from about 150°C at 0 kGy to about 50°C at 30 kGy. This indicates that simultaneous thermal curing during E‐beam curing of resin and composite is possible. After thermal post‐curing, the T_g of the E‐beam cured resin increased from 130°C at 200 kGy to a value greater than 370°C and the modulus decreased by 10%. The service temperature and the modulus of the 100% thermally cured resin and the thermally post‐cured (after E‐Beam irradiation) resin were comparable.     

Cyclic Olefin Copolymer/Photoinitiator Proton Exchange Membranes for Direct Methanol Fuel Cells

This article investigates cyclic polyolefin copolymer/photoinitiator blend membranes that contain 10, 30, and 50 PHR (parts per hundred resins) cationic photoinitiator (PI) used in direct methanol fuel cells. We analyze the morphology, electrical, methanol barrier, mechanical and thermal properties of COC/PI-blend membranes. The results show that superacid photoinitiators can enhance the conductivity and methanol barrier of COC. However, the mechanical properties decrease with the amount of photoinitiator. COC/PI blend membranes have heat stability below 200°C. They can meet the direct methanol fuel cells operating temperatures.     

The preparation and physical properties of UP/montmorillonite nanocomposite by UV radiation curing

This article describes the preparation and properties of unsaturated polyester (UP)/montmorillonite (MMT) nanocomposite by UV radiation. Benzildimethylketal and 1‐hydroxy cyclohexyl phenyl ketone (HCPK) as a photoinitiator in UP were photolyzed under nitrogen condition. Analysis of X‐ray diffraction patterns of the composites shows that the interlayer spacing of MMT is substantially increased. The type and amount of photoinitiator affects the level of improvement in mechanical properties, and our results suggest that HCPK is a more efficient photoinitiator of UP curing reaction. The interaction between photoinitiators and MMT should be considered to acquire the reinforcement effect of the dispersed MMT nanolayers. The properties of nanocomposite are dependent upon the amount of MMT. The effect of MMT concentration on thermal and dielectric properties is also investigated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3609–3615, 2006     

Solid state NMR investigation of cationic polymerized epoxy resins

Cationic UV-polymerized resins, based on cycloaliphatic epoxides with aryl sulfonium salts as photoinitiators and polypropylene glycols of variable length as flexibilizers, have been investigated with respect to the network-forming reactions and the morphology of the resulting polymers. The combination of UV-curing and thermal postcure makes the chemical process complex and dependent on many variables, such as photoinitiator, exposure time, reaction temperature, and polyol components. Structure and curing of the epoxide were investigated by ¹³C CPMAS NMR. Morphology and domain sizes were studied by spin diffusion experiments using the novel “dipolar filter” technique for selective magnetization of mobile components.     

Photopolymerization kinetics of bis-aromatic based urethane acrylate macromonomers in the presence of reactive diluent

The present work deals with the photopolymerization of bis-aromatic based urethane acrylate macromonomers in the presence of excess end capping agent as reactive diluent and estimation of their kinetic parameters. Formulations were made by independently homogenizing the macromonomers with photoinitiators of three different classes. Three different compositions of photoinitiators were used to study the effect of concentration of photoinitiator on cure kinetics. These compositions obtained were tested for photo curing performance using photo DSC under polychromatic radiation. The heat flows against time were recorded for all formulations under isothermal condition and the rates of polymerization, peak maximum times as well as the percentage conversions were estimated. It was observed that due to a longer timescale for reaction diffusion, formulations with macromonomer containing propoxylated backbone showed higher conversions than the corresponding ethoxylated analogue. The photopolymerization and kinetic estimations of the formulations including evaluation of kinetic model are discussed.     

A simple Raman technique to measure the degree of cure in UV curable coatings

The curing behavior of four UV curable clearcoats was examined using spectra from a confocal Raman microscope. The disappearance of the C=C line near 1636 cm⁻¹ provides the signature for the curing of the samples, but quantification of the degree of cure by standard peak-fitting and baseline subtraction methods does not work well because of sample fluorescence, baseline shifts and overlapping peaks. A smoothed second-derivative processing approach overcomes all of these difficulties and provides a simple, fast and objective quantification procedure. Steep cure gradients through the thickness of the clearcoat, due to screening of the bottom of the clearcoat by both the UVA and photoinitiator, were observed. Cure gradients at the top of the clearcoat due to oxygen inhibition were also observed. The most complete cure throughout the film thickness was obtained with a mixture of standard and red-shifted photoinitiators.