The UV-curable powder coatings allow the finishing of temperature-sensitive substrates such as wood, MDF (medium-density fibreboard), plastics and paper. The binder system is mostly comprised of unsaturated polyester, a vinyl ether and acrylic polyurethane. The curing mechanism consists of free radical polymerisation of the double bonds.
Cross-linking hydroxy-functional stars and copolymer precursors with a triisocyanate and associated structural changes were studied theoretically and experimentally. The model of network formation was based on the statistical generation of structures from units which were in different reaction states. The differences in gel point conversion and cross-link density were interpreted in terms of precursor functionality and functionality distribution, and differences in the reactivity of functional groups. Hydroxy-functional copolymer systems containing precursors of the same number-average functionality gel at lower conversions than stars which are monodispersed mainly due to functionality distribution. The structure of copolymers characteristic of several internal cross-links contributes more to the concentration of elastically-active network chains than stars with a single cross-link. Cyclization accompanies intermolecular cross-linking; its intensity is higher for copolymer systems compared with stars.
A review on the transformation of triplet oxygen to singlet oxygen via sensitising agents commonly found in fatty oils is presented. The Wigner spin conservation rule restricts the direct reaction of triplet oxygen with organic molecules possessing singlet multiplicities. Sensitisers present in fatty oils are energetically and mechanistically capable of changing oxygen from its triplet state to its singlet state. Lowering the oxygen multiplicity overcomes the spin restriction, thus allowing for the oxidative curing of fatty acids commonly used in alkyd resins.
The fundamentals of pigment solubility and migration phenomena are described. A technique was developed to evaluate the solubility of Cl Pigment Blue 15:4 and Cl Pigment Red 122 in model compounds that were designed to represent the major phases of a Xenoy® blend. Diphenyl carbonate was used to represent the polycarbonate. Propyl benzoate was used to represent poly(butylene terephthalate). The pigments were observed to exhibit solubility in the model compounds. This could have relevance to the use of these pigments in plastics formulations that are based on bis-phenol A polycarbonate (PC) and poly(butylene terephthalate) (PBT).
Monoglycerides (MGs) of four oils (castor, linseed, soybean and sesame) were prepared. They were reacted with a trimer in definite proportions to prepare polyurethane (PU) coatings. These coatings were applied in the form of thin films on tin plates and analysed for various coating properties such as gloss, scratch resistance, flexibility properties and physicochemical tests. A highly cross-linked product was obtained due to the higher functionality associated with MGs compared with their molecular weight. The trimer also imparted cross-linking due to its trifunctionality, and a hard yet flexible, tough, glossy polyurethane coating was obtained.
The scratch and mar resistance of UV-cured acrylic clear coats was evaluated by means of the Taber scratch and Scotch-Brite tests. The influence of the chemical structure of the acrylate oligomer, of the photoinitiator and of the UV dose on the scratch resistance of various UV-cured coatings was evaluated quantitatively. No direct correlation could be found between the scratch resistance and the hardness of the UV-cured polymer. The scratch resistance was evaluated through measurements of the ductile/brittle transition and was significantly enhanced by the addition of a siloxane slip agent and of acrylated silica nanoparticles. A self-healing process of ductile scratches was shown to occur in most of these coatings upon storage at ambient temperatures or upon moderate heating.
Fears have been expressed about the difficulty of deinking waste paper generated by the Indigo printing process. In this study, high-intensity ultrasound has been used to remove ink from Indigo digitally printed papers and break the ink particles down to sizes which are compatible with the flotation process used in deinking plants. The influences of temperature and power density have been studied and both found to have a significant effect on the resultant ink particle-size distributions. Almost 100% ink detachment has been achieved using a combination of ultrasound and aqueous washing. The conclusion is that detachment and particle-size reduction using ultrasound and aqueous washing suggests that Indigo digitally printed papers may not be so difficult to deink and recycle as originally thought.
Cycloaliphatic epoxide-functionalised polydimethylsiloxanes were coated onto a gel-coated fibreglass substrate and cured using two different light sources: UV light and visible light. Curing was accomplished through the use of an acid-generating photoinitiator, and a photosensitiser was used to shift the initiating wavelength into the visible region. The release potential, mechanical properties, surface tension, and contact angle of the cross-linked polymer were measured. The contact angle and surface tension of the UV-cured coatings were found to be 103° ± 0.05 and 10.93 ± 0.05mJ/m2, respectively. The contact angle and surface tension of the visible light-cured coatings were 102° and 11.42 ± 0.05mJ/m2, respectively. Pull-off adhesion tests revealed that a consistent 0.2MPa of normal force was required to remove the mould from both the UV- and visible light-cured coatings even after 30 releases. Both methods of cure offered the same release properties, but the visible light sample required a much longer cure time.
Steady-state moisture diffusion through wood/aluminium windows was simulated by using computer software utilising the finite-element-method. The water-vapour permeability of the coating was varied on different model-windows. The results showed that wood coatings can help to reduce the differences in equilibrium wood moisture between the exterior and interior sides of the wooden profiles when interior humidity stress occurs. Coatings with low permeability can promote the accumulation of moisture on the exterior side. The same, or even a better quality of protection against interior humidity stress, as with high-built coatings, can be obtained by medium-built coatings with higher permeability. An optimal moisture balance in the wooden profiles was achieved by using a low permeable coating on the interior side and a more permeable coating on the exterior side.
A new test method for weatherability prediction using a remote plasma reactor has been studied. The degradation mechanism was studied, focusing on the fact that the exposure to radicals strongly influences the durability of coatings. As a means of radical irradiation on the coatings, a plasma-generating machine was used. More specifically, the weatherability of enamel-type coatings, surface changes (3D-SEM observations), as well as changes in colour and gloss, were studied using a down-flow-type machine (remote plasma reactor). The polarity index was also defined.
The digital imaging revolution continues apace, affecting the whole spectrum of the photographic industry. In many part of the world digital cameras now outsell conventional film cameras, and many of the disadvantages associated with digital image capture in the very recent past1.2 have been nulified.
Modified alkyd resins were produced by alcoholysis of soya bean oil with pentaerythritol followed by esterification with pentaerythritol and phthalic anhydride. Various catalysts with different contents, including LiOH, butyl tin oxide and dibutyl tin chloride, were used for alcoholysis and/or esterification reactions. The effect of the catalyst on the reduction of the process time of alkyds, and their physicochemical and film properties, were investigated and evaluated. The catalytic system LiOH 0.07% - dibutyl tin chloride 0.2% proved to be the best catalyst system followed by LiOH 0.07%. The coating film characteristics of two paints, formulated with selected alkyds, were measured and compared.
Spiro-orthosilicates, prepared from tetraethyl orthosilicate and a diol (2-butyl-2-ethyl-1,3-propanediol or 2-ethyl-1,3-hexanediol), are used as latent reactive diluents in two-pack polyurethane coatings. A fast curing and long pot life have been achieved because of the latency in the can. Spiroorthosilicates hydrolyse with moisture into a diol and a polysiloxane. Kinetic data on hydrolysis and curing are given. The formation of polysiloxane has been characterised by solid-state29Si NMR. The film properties obtained are excellent. The spiro-orthosilicates-based films are tested as clear coats for car refinishes. In particular, a very good car wash resistance has been obtained, which is combined with other properties, also at a good, competitive level.
This review summarises the developments in adhesion, VOC emissions, coatings, transparent conductive coatings, hybrid organic-inorganic coatings, UV curing, biocidal coatings, paints, weathering, wood coatings, surface treatment of concrete, metal corrosion, pigments, film formation, printing, modelling fluid flow in printing, dot gain and inkjet printing reported inSurface Coatings International Part B: Coatings Transactions,88, 2005.
In this work a new optical technology, ASII, is presented, for the study of film formation from all kinds of dispersed systems, such as latexes, emulsions or solvent-borne suspensions. Various film-forming products have been investigated, including water-borne coatings, on various types of substrates. A wide range of information can be extracted such as objective drying times (dust-free, dry-hard times, etc) or mechanism taking place, thereby offering new possibilities to analyse film formation from complex colloidal systems.
A method of treating timber before applying a coating has been developed and tested. An organofunctional silane coupling compound was found that was capable of reacting and forming bonds with both wood and a range of coatings. Wet and dry adhesion strength between a range of coatings and wood has been determined by the direct pull-off test under a variety of test conditions. The data presented show how the bridging of the interface between wood and coating can, with some coatings, improve not only the initial bond strength but also provide significantly higher wet adhesion strength and long-term bond durability.
Plates of stainless steel were coated with a thin film of seven different types of oxidative drying oils in order to follow the development charge in mass and volume during 42 days of curing. The plates were weighed in air and in water, and the volumes determined by applying Archimedes' principle. All of the oils gained considerably in mass, with a maximum of 12% within seven days. The volume, however, decreased with large individual differences from one oil to another. A cold-pressed raw linseed oil decreased in volume by almost 15% whereas the volume of an alkali-refined linseed oil only decreased by a few percent. It is well known that linseed oil-based coatings are prone to crocodiling ( surface crack formation); it is suggested that the severity of this phenomenon may be related to the volumetric reduction of the binder during curing. The described method is suggested as a simple means of screening linseed oil binders for formulation and development purposes.
Summaries Polymers, and even more so polymer blends, are selected for their particular properties and processing characteristics. It is often necessary to include additives in the polymer formulations, either to facilitate processing, or to extend the life of the polymeric product that is created. Colourants are additives that are principally used for aesthetic purposes. However, the addition of a colourant to a thermoplastic system can lead to unexpected and sometimes detrimental changes in the material properties of that system. In this review, the general characteristics of polymer blends and the processes involved in manufacturing them are discussed. Additives that may be included in the formulation and the interactions that can arise among the blend components are also described. The relevance of these components and processes are then discussed in regard to blends of polycarbonate and poly(butylene-terephthalate).
Imparting oil and water repellency on surfaces is easily achieved with the use of fluoroalkyl-modified silanes. Whilst perfluoroalkyl-modified silanes exhibit high static and advancing water and oil contact angles, their low receding contact angles mean that water and oil will not readily slide over treated surfaces. However, modified perfluoropolyether (PFPE) silanes, whilst exhibiting high static and advancing water and oil contact angles, also exhibit high receding contact angles, resulting in surfaces where the sliding contact angle is very low. The influence of structure modification of the silane and the perfluoropolyether component are examined along with the organic linking group. Their impact on performance using both the dip coating method and the chemical vapour adsorption method is discussed.
