Environmentally friendly photoinitiators

Environmentally friendly photoinitiators

FOCUS air pressures below 1 bar in the feed line and fluidizing pressures above 1 bar must be avoided to improve the transfer efficiency toward the gr...

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FOCUS air pressures below 1 bar in the feed line and fluidizing pressures above 1 bar must be avoided to improve the transfer efficiency toward the grounded substrate. High feeding pressure avoids the packing phenomena of nanoscale TiO2 particles on their way through the ESD system towards the target being coated. The best deposition conditions are: 7 seconds coating time; 70 kV applied voltage, 1.5 bar feeding pressure and 1 bar fluidizing pressure. The different electrical behaviour between the larger particles of the polymeric powders and the nanoscaled TiO2 particles was found to promote a stratification effect with the TiO2 being found towards the outer layers of the polymeric film. In addition, the electrical “wind” primed by the back ionization phenomena inside the deposited but uncured film was found to selectively push the nanoscaled TiO2 particles towards the outer layers of the film, therefore, increasing the stratification effect. Finally, the convection streams in the liquefied film during the curing process causes the nanoscaled TiO2 particles to rise towards the top layer of the film, determining the formation of gradient coatings. Consequently, these gradient coatings are richer in nanoscaled TiO2 particles in the uppermost layers, while they become progressively poorer in nanoscaled TiO2 particles towards the bottom layers of the film. Five significant findings resulted from the analysis of the target locations during ESD: (i) increased ESD distance concurrently results in a decrease of achievable coating thickness because the force of the aerodynamic pulse of the powder delivered by the spray gun is reduced by the time the cloud reaches the target; (ii) the more dense TiO2 particles make deposition conditions still more critical at higher ESD, since gravitational forces have greater effect on particles of higher 4



density causing strong deviation of the linear pattern of powder trajectories, towards the target; (iii) ESD and tilt angles away from the target reduce the achievable coating thickness because there is a smaller area of target exposed to the cloud of charged powder coating delivered by the spray gun; (iv) the presence of the more dense nanoscaled TiO2 particles make the aerodynamic effect on the coating thickness resulting from the lining up of the spray gun with the target surface significantly more critical; (v) the alignment of ESD angle and tilts is of fundamental importance if higher coating thickness is to be achieved, particularly so for the more dense powder formulation used in this study. Finally, the neural network solutions were found to be the best technique for modelling the experimental data as the latter is strongly affected by non-linearity, and consequently not suited to the application of regression models. Article entitled “E/S spray deposition (ESD) of self-organizing TiO2-epoxy powder paints. Experimental Analysis and Numerical Modelling” by M Barletta et al of the University of Rome, Department of Mechanical Engineering, published in Surface and Coatings Technology, 4 Dec 2006, 201 (6), 3212-3228

Environmentally friendly photoinitiators Curing by UV radiation is considered to be one of the most environmentally friendly technologies available for the polymerization of coating films, due to the low level of energy involved in the curing process and the small amount of VOCs released during the process. Though the release of VOCs in the radiation curing process is many times lower than that of conventional curing methods, some concerns have been expressed relating to the release of aldehydic and ketonic compounds generated in the photochemical decomposition of some photoinitiators, in

C OAT I N G S particular of the class of alphahydroxy ketones. It is well known that the beta cleavage process of alkyl-hydroxy-phenones generates two radicals that can further evolve through side reactions in the curing matrix, to benzaldehyde, cyclohexanone, and acetone, where the benzaldehyde is very critical because of its very low volatility threshold that makes it detectable in trace amounts in the air, and it is one of the origins of the unpleasant odour developed in the working place when released from the finished products. This problem has been resolved by Lamberti Chemical Specialities with the development of an alpha hydroxy ketone, which due to its oligomeric structure releases a very low level of VOC ensuring compliance with environmental regulations. The new product, Esacure KIP150 exhibits high reactivity, low yellowing, high scratch resistance and good through curing. In the area of food packaging, a di-functional alpha hydroxy ketone, Esacure ONE has been developed, which shows very low migration and extractability from the cured films. Their success with the alpha hydroxy ketones encouraged Lamberti to develop another difunctional photoinitiator in the ketosulfone compounds The product Esacure 1001 M has very interesting characteristics in pigmented systems and in particular with high pigment loadings of dark colours. It is a fine powder with a melting range of 100-120°C, which is insoluble in water and miscible with most common acrylated monomers. This photoinitiator contains in the same molecule, two different photoinitiating moieties and mainly reacts by a type II mechanism, but also reacts at the same time by beta cleavage. It is shown that the photoinitiator has better reactivity in the presence of hydrogen transfer groups such as amines included as co-initiator, or ethoxylated and propoxylated acrylates. JANUARY 2007

FOCUS Following the work on free radical type photoinitiators, which is the predominant UV curable technology, Lamberti turned its attention to UV cationic technology. Cationic systems have been developed to minimize film shrinkage and improve adhesion on metal and plastic substrates. These systems are often based on cyclo-aliphatic epoxy resins and polyol or vinyl ethers with the addition of cationic photoinitiators as crosslinking agents. The main reason for the failure of this technology to achieve the success of the free-radical initiated systems was the lack of a suitable range of photoinitiators capable of meeting the demanding requests of the market. The original favoured system based on sulfonium salts, which gave rise to the undesirable odorous diphenyl sulfides or toxic benzene by-products, were eventually replaced by iodonium salt type photoinitiators, but even these products were not entirely satisfactory, and Lamberti instigated different research programmes to develop photoinitiators with the cure characteristics of the sulfonium salts. This work has resulted in the commercialisation of Esacure 1187/1188 with the chemical structure 9-(4-hydroxyethoxyphenyl) thianthrenium hexafluorophosphate, and was selected for its good UV absorption profile, compatibility, and storage stability. A paper presented at the ACT 2006 conference in Warsaw describes the experimentation and results of the evaluation of VOC’s emitted from the new products developed at Lamberti. In all cases the new products were markedly superior to conventional photoinitiators with respect to odours produced during processing and curing. These qualities did not detract from their high reactivity and the performance of cured films. Paper entitled “ Environmentally Friendly Photoinitiators” By R Bottacchiari and M Cattaneo of Lamberti SpA Chemical Specialities, Italy, presented at ACT 2006, held in Warsaw, Poland on 28-30 Nov 2006




INDUSTRY NEWS Rohm and Haas reorganized Rohm and Haas will restructure its business into three principal units, namely, Specialty Materials, Electronic Materials and Performance Materials, effective in the beginning of 2007. The move forms part of the company’s strategy to advance growth and boost profitability. Specialty Materials is the biggest of the three units, with sales of more than €4.5 bn in 2005. The group will combine several distinct operations under three new subunits: Paint & Coatings Materials, Primary Materials, and Packaging and Building Materials, including plastics additives, adhesives and sealants. The Electronic Materials group, comprising the Semiconductor Technologies, Circuit Board Technologies and Packaging & Finishing Technologies units, will retain its current make-up. The group seeks to increase twofold its 2005 sales that exceeded €1 bn by 2010, and make investments in Asia. Various technologies in the healthcare, water treatment and energy areas will be consolidated under the Performance Materials division, which generated sales of roughly €850 M in 2005. Rohm and Haas will operate its Salt and Powder Coatings businesses as independent units. The Salt division had sales of €724 M in 2005, while the Powder Coatings group had sales of €252 M. Speciality Chemicals, Nov 2006, 26 (9), 10

Paints: Kemira consolidates position in Russia Kemira’s paints and coatings subsidiary Tikkurila recently acquired a 70% stake in two Russian companies based in Saint Petersburg: OOO Gamma and OOO Ohtinski Zxavod Proroshkovyh Krasok (OZPK). They will be renamed Gamma

C OAT I N G S Industrial Coatings and Tikkurila Powder Coatings respectively. Gamma is a leading producer of metallic industrial paints and makes annual sales of €8 M. OZPK makes powder paints under the Ohtek brandname and registers annual sales of €3 M. Chimie Pharma Hebdo, 18 Dec 2006, (364), 11 (Website: http://www.france-chimie.com) (in French)

HB Fuller closes sale of powder coatings business HB Fuller Co has completed the sale of its powder coatings business to the Valspar Corporation. The company anticipates the transaction will generate a one-time positive impact to pre-tax income of $64-68 M in 4Q 2006. Press release from: HB Fuller, St Paul, MN, USA. Tel: 651 236 5158. Website: http://www.hbfuller.com (1 Dec 2006)

Nippon Paint adds two China production bases Nippon Paint created two Chinese jvs with Singaporean firm Wuthelam Holdings to establish a wide-ranging and stable powder paint supply network in China. The jvs, Tianjin Nippon Paint Shenglinda and Foshan Nippon Paint Shenglinda, are 60:40 owned by Wuthelam and Nippon Paint. The new companies, which commenced operations in Oct 2006, together with Nippon Paint’s existing bases provide the company with five powder paint manufacturing sites in China. The Chinese powder paint market is expanding at a rate of over 20%/y on the back of growing local demand for home appliances, construction materials and automobiles. Japan Chemical Week, 23 Nov 2006, 47 (2393), 12

BASF expects more than €4 bn/y turnover from product innovations from 2010 onwards German BASF Group expects to generate a turnover of above €4 5