UV stabilisation of powder clear coats

Powder coatings are gaining importance in exterior applications such as automotive and architectural finishes. The use of additives in powder coating formulations enhance the durability of the coating by reducing the effects of harmful UV light and providing high temperature stability during processing and curing. Customers' increased demands for better retention of aesthetical and mechanical properties has prompted the development of new additives dedicated to powder coatings. This paper presents an overview of the performance of light stabilizers used in powder coatings.     

Free radical photopolymerization initiated by UV and LED: Towards UV stabilized,tack free coatings

UV stabilizers (UV absorbers and Hindered Amine Light Stabilizers‐HALS) are added to UV‐curable formulations to provide long‐term durability. The influence of HALS and the filtering effect of UV absorbers are investigated under UV and LED irradiation by using different photoinitiating systems in free radical photopolymerization. The contribution of irradiation conditions and initiating systems on the filtering effect is discussed by performing Real‐Time Fourier Transform Infrared Spectroscopy (RT‐FTIR) and Confocal Raman Microscopy. Additionally, to get quantitative information about the light absorbed by the photoinitiator, without and with the filtering issue arising from UV stabilizers, series of calculations are carried out by taking into account the amount of light absorbed by the compounds and the intensity of the incident light. Finally, formulations are optimized with respect to surface inhibition to obtain tack free coatings in air atmosphere in the presence of UV stabilizers under visible light. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3597–3607     

Ultraviolet (UV) curing of phosphated polyurethane-acrylic dispersions

Phosphate-containing polyurethane-acrylic dispersions were synthesised for UV curing studies. The effects of light intensity, substrate-dependent temperature increase, soft-segment content and water on conversion were investigated. The effect of the light intensity on conversion was twofold. At first, conversion increased with light intensity. This was attributed to the inability of shrinkage to keep pace with the polymerisation and crosslinking, resulting in the creation of free volume, thereby facilitating reaction and enhanced conversion. At higher intensities, conversion was found to be reversed or, at least, it remained constant, owing to increasing radical-radical termination reactions. Phosphated-polyurethane coatings with high soft-segment content show improved conversion with exposure time. This was found to be related to the chain mobility, caused by the low glass transition temperature of the soft segment. The effect of water on conversion was also twofold. On the one hand, water had a plasticising effect on the UV curing and the polymerisation rate was fast. On the other hand, the gel content was found to be lower when films were cured before the evaporation of water.     

聚合物涂层光稳定化研究进展

用于改造各种材料的表面性质并防止其光老化的聚合物涂层的光稳定化技术近年来已经成为高分子材料科学和光化学领域的又一研究热点。本文以紫外光固化聚合物涂层为重点综述了该研究领域的发展过程、理论研究特点和应用技术的生长点,并对聚合物涂层光稳定化技术的最新进展进行了评述,讨论了聚合物涂层光稳定化技术中新型光固化树脂,多功能单体、光引发剂和光稳定剂（包括紫外吸收剂和受阻胺类稳定剂）的特点及作用机理。     

On-line monitoring of the acrylate conversion in UV photopolymerization by near-infrared reflection spectroscopy

Near-infrared (NIR) reflection spectroscopy was used to determine the conversion in acrylate coatings after UV photopolymerization in order to test it as a method for process control in UV curing. A probe head was developed which is adapted to the specific requirements of UV curing and which is linked to a photodiode array spectrometer by an optical fiber. Reflection spectra from thin acrylate layers which were taken in intervals down to the millisecond range have shown an excellent signal-to noise ratio. Quantitative conversion data show good correlation with results from independent reference methods (FTIR, HPLC). Following thesebasic investigations, it was demonstrated that NIR reflection spectroscopy can be used for on-line monitoring of the acrylate conversion in thin coatings. Some examples of such investigations in pilot scale are presented.     

超支化聚硅氧烷的紫外光固化行为及固化动力学研究

采用等温差示光量热技术(DPC)研究了超支化聚硅氧烷的紫外光固化行为及固化动力学. 探索了引发剂浓度、 光强度、 聚合温度和环境气氛对固化行为的影响规律. 研究结果表明, 增加光引发剂浓度和光强度及提高环境温度均可提高其固化速率和双键最终转化率. 在空气中固化时存在氧阻聚现象, 增大光强度可以显著缩短诱导期. 运用带扩散因子的自催化固化动力学模型研究了其光固化动力学, 计算出特定条件下的光固化动力学参数, 反应总级数约为6—7, 表观活化能为9.95 kJ/mol. 通过超支化聚合物与两种结构类似的低官能度单体光固化行为的对比, 研究了超支化聚合物固化行为与其分子结构的关系, 发现由于超支化大分子的独特结构, 在固化初始阶段便产生凝胶, 因此双键的最终转化率偏低.     

Influence of photoinitiator and curing conditions on polymerization kinetics and gloss of UV-cured coatings

Polymerization kinetics and gloss of different formulations of coatings at different UV curing conditions were studied. The results showed that the photoinitiator type, its concentration, sample coating thickness, as well as the UV light intensity were the most significant factors affecting the polymerization course and the gloss of UV-cured films. The increasing concentration of the photoinitiator and the UV light intensity significantly decreased the gloss of the cured surface. The influence of the sample coating thickness on the kinetics and final gloss was also considerable.     

Accompanying of parameters of color,gloss and hardness on polymeric films coated with pigmented inks cured by different radiation doses of ultraviolet light

In the search for alternatives to traditional paint systems solvent-based, the curing process of polymer coatings by ultraviolet light (UV) has been widely studied and discussed, especially because of their high content of solids and null emission of VOC. In UV-curing technology, organic solvents are replaced by reactive diluents, such as monomers. This paper aims to investigate variations on color, gloss and hardness of print inks cured by different UV radiation doses. The ratio pigment/clear coating was kept constant. The clear coating presented higher average values for König hardness than pigmented ones, indicating that UV-light absorption has been reduced by the presence of pigments. Besides, they have indicated a slight variation in function of cure degree for the studied radiation doses range. The gloss loss related to UV light exposition allows inferring that some degradation occurred at the surface of print ink films.     

Effect of some ultraviolet light absorbers on photo-stabilization of azadirachtin-A

The effect of photo-stabilization of Azadirachtin-A (Aza-A) was examined when exposed to sunlight and ultraviolet light in the presence of four structurally different ultraviolet stabilizers namely 4-aminobenzoic acid, 2,4-dihydroxybenzophenone, 4,4'-dihydroxybenzophenone and phenyl salicylate. The percentages of Aza-A recovered at different time intervals from slides exposed to different light conditions with and without UV stabilizers as well as kinetic studies indicated that the addition of phenyl salicylate in methanolic solution of Aza-A (in 1:1 mole ratio) provides the best photo-stabilization of Aza-A molecule among the four UV stabilizers studied.     

新型紫外线吸收剂1,4-二芳基-1,3-丁二炔类化合物的合成及其性能研究

本文以含有端基炔的芳硫醚为原料，碘苯二乙酯为氧化剂，氯化亚铜为催化剂，室温下反应30 min，合成了1，4-二（2-芳硫基苯基）-1，3-丁二炔化合物。通过¹HNMR、¹³CNMR等对其进行了结构表征，并研究了其光学性质，以及作为紫外线吸收剂在紫外光固化涂料中的应用。结果表明：该类化合物能够有效吸收270~360 nm的紫外光，且光降解程度小，并具有与树脂、单体相容性好、无气味等特点。同时，合成的目标化合物在光固化过程中不参与自由基体系的固化，且增强了涂料及固化涂层的光稳定性，有益于紫外光固化涂料的存储，是一类具有发展前景的紫外光吸收剂。     

聚合物光老化、光稳定机理与光稳定剂(下)

大多数聚合物材料,包括塑料、橡胶、纤维、涂料等,在户外使用时会发生光老化而使使用寿命缩短。为有效防止聚合物材料的光劣化,人们已对聚合物的光老化和光稳定机理进行了广泛的研究并先后研发出了几个类型的光稳定剂。但由于户外应用范围不断扩大和环境不断恶化正使聚合物的光老化变得越来越复杂而光防护难度也日益加大,因此国内外有关聚合物光老化、光稳定机理的研究和光稳定剂的研发一直十分活跃。本文下篇阐述光稳定剂的作用机理并综述光稳定剂的研发进展。     

Polymeric UV-Absorbers of 2-Hydroxybenzophenone Type. I. Polyesters on the Base of 2-Hydroxy-4-(2,3-epoxypropoxy)benzophenone

Some polyester light stabilizers were synthetized by the co-polymerization of an equimolar mixture of 2-hydroxy-4-(2,3-epoxypropoxy)benzophenone with cyclic anhydrides of di-carboxylic acids. This synthesis was carried out in melt by using potassium benzoate or tert-amines as catalysts. The catalytic efficiency of potassium benzoate in heterogeneous phase increases with its surface area. In comparison with potassium benzoate, tert-amines show a higher catalytic effect in homogeneous medium. According to the UV spectra of the products, the 2-hydroxybenzophenone structural units of light stabilizers are not subject to destruction during the polymerization of an equimolar mixture of epoxide with anhydrides. The efficiency of UV stabilization of the stabilizers prepared in polypropylene is comparable with the efficiency of 2-hydroxy-4-n-octyloxybenzophenone with the exception of those samples which contain the structural units of maleinic anhydride and glycidyl-β-naphthyi ether. In contrast to 2-hydroxy-4-n-octyloxybenzophenone, the high molecular weight UV absorbers exhibit a lower extractibility from polypropylene sheets with trichloroethylene.     

Radiation curable materials – principles and new perspectives

Increasing environmental concerns and the ensuing legislation to cut emissions of volatile organic compounds (VOCs) have been major driving forces behind the development of radiation cured coatings over the past 25 years. Today radiation cured coatings are known for their good overall performance and their excellent resistance against chemical and physical surface damages. Advanced photoinitiator systems allow the light stabilisation of UV‐curable formulations and the outdoor application of the coating. The rapid curing, combined with the possibility of immediate processing of the coated objects opens the way for radiation curing – in 100%‐, water based‐, and dual cure systems as well as for radiation curable powder coatings – for a wide variety of application.     

Photoinitiators for UV and visible curing of coatings: Mechanisms and properties

The radiation curing industry is one of the most rapidly developing fields in the entire coatings industry. The low toxicity, cheapness, speed, control and ease of formulation and operation are some of the main advantages of this growing technology. UV and/or visible light radiation is used to induce photochemical polymerization or crosslinking of a monomer, oligomer or prepolymer formulation containing a certain type of unsaturation, such as an acrylic group, and an appropriate initiator. The latter is used to absorb the light energy and transform it into active species, such as radicals or ions, capable of inducing such reactions. Applications extend to general coatings for paper, board, wood, tapes, compact discs and holograms, inks, photoresists for imaging processes and adhesives for welding and sealing in electronic circuit boards. The photoinitiator is the key to the control of these processes and, in recent years, has seen many new developments. These include the need for water-soluble, co-reactive and polymeric structures with low migration rates, as well as cheaper UV/ visible sensitizers with enhanced speed. New and effective cationic systems are also on the scene and, although expensive, are attracting significant academic and commercial interest.     

Use of chemiluminescence to the study of photostability of automotive coatings

Chemiluminescence (CL) imaging has been used to study the photodegradation of two automotive coatings, a melamine-crosslinked acrylic resin and an acrylic Polyurethane, as a function of artificial weathering time. Characteristics of the CL emission from coatings, the influence of light stabilizers and different types of sample were studied. The results indicate that the method is highly sensitive and can be used to measure photodegradation in unstabilized and stabilized coatings after only 48 h and 100–200 h of exposure, respectively. Measurements can be carried out on free clearcoats or on clearcoats applied on metallic panels. It is also possible to assess the degradation of individual layers in multiple-layer coating systems. Extrapolation to the failure time of coatings by CL is not yet achievable, but results show that the technique is useful for rapidly screening the relative performance of new coating formulations or light stabilizers added to clearcoats.     

A Procedure for Measuring the Viscosity of Formulations Based on Oligourethane Acrylates for UV-Curable Protective Coatings of Fiber Light Guides

A capillary viscometric procedure was developed for measuring the viscosity of formulations based on oligourethane acrylates for UV-curable protective coatings of fiber light guides. The temperature dependences of the viscosities of these formulations were studied. The moduli of elasticity of fibers prepared from these formulations after UV curing were measured. These formulations can be stably applied, using a die, to the surface of fiber light guides in the course of their drawing at a drawing rate of up to 100-120 m min^-1.     

Photopolymerization of maleimide perfluoropolyalkylethers without a photoinitiator

Perfluoropolyalkylethers derived from hexafluoropropylene oxide were functionalized with maleimide groups. Irradiated by UV‐light, the new maleimide macromonomers demonstrated very fast polymerization kinetics with a curing time as fast as 8 s. The effect on photopolymerization of different features such as the molecular weight of the fluorinated chain and the chain length of the hydrogenated spacer were studied, as well as the influence of the type of photoinitiator and the presence of air. Thermal and surface properties of the UV‐cured polymers were examined and were typical to fluoropolymers in view of water–oil repellent coatings. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 699–707     

UV-光固化光纤涂料的研制

本文采用环氧丙烯酸酯与聚氨酯丙烯酸酯共混聚合的方法制备出新型的UV-光固化光纤涂料,其主要性能较好.研究了基体组成、引发剂、稀释剂以及固化工艺对UV-固化光纤涂料的光固化速度的影响.通过实验发现,环氧丙烯酸酯与聚氨酯丙烯酸酯的配比为 4:6～6:4、稀释剂的含量不大于20%时固化速度较快、性能较好,同时固化时灯距与固化膜厚度对固化速度的影响较大.     

INFLUENCE OF WOOD EXTRACTS ON THE UV CURING OF ACRYLATE COATINGS

ABSTRACT

The effect of wood extracts on the kinetics of UV curing of an urethane diacrylate was studied by real-time FTIR spectroscopy. Whereas extracts from rose wood (Dalbergia latifolia) inhibit the reaction, curing is not significantly affected by extracts from teak wood (Tectona grandis). Data of the pendulum hardness of the coatings confirm these results. Moreover, the radical scavenging capacity of the extracts was determined relative to benzoquinone by a radiation-chemical method.     

保形涂料的研究进展

介绍保形涂料的固化机理,比较了各类光固化保形涂料及其修复方法,综述紫外光固化保形涂料的研究进展。