Dr. Christian Schaller*, Dr. Daniel Rogez & Dr. Wolfgang Peter
Ciba Specialty Chemicals, Switzerland
UV as well as the visible fraction of the solar radiation is causing most of the chemical modification and mechanical breakdown of exposed wood. The coating and wood alteration process is the result of photo-oxidation and hydrolysis due to light, heat and humidity (i.e. weathering). Here it is well known that pale wood species tend to coloration and darkening (indoor) followed by graying and finally erosion (outdoor) whereas dark or colored wood species will first lose initial color, i.e. show bleaching and discoloration effects. Unfortunately there is no universal stabilization approach for all wood and coating types, even if wished and loved by the industry. Therefore each wood species and coating type has to be regarded separately for optimal performance. In this paper we want to highlight the latest mechanistic findings and developments in stabilization of different wood species (pale vs colored wood) and various coating systems (clears vs pigmented) and give some theoretical guidelines for efficient light stabilizer use.
Laurence Podgorski1* & Peter Svane2,
2Coating Consultancy, Denmark
This paper presents two different surface cleaning techniques normally applied for other substrates than wood: "hydro-sandblasting" and "micro-sandblasting". In the first method a mixture of water, abrasive particles and air are propelled towards the surface. The second one is similar, but operates without the addition of water. The investigations have shown that these methods both are very efficient to remove old coating material from wood. Scanning Electron Microscopy has revealed that sandblasting particularly affects the structure of the earlywood and leads to cells compression. Electron Diffraction X-ray analysis has shown that some abrasive particles remain in the wood structure. The techniques leave a topography reflecting the variations in wood hardness. Examples of blast cleaned wood samples of various species recoated and then exposed to weathering are presented.
Saila Jamsa* & Pertti Viitaniemi
The moisture performance properties of the structures are very important in planning the service life. Wetting and drying of wood surface cause stresses and deformations in the wood. Resistance to crack formation is one important factor influencing the durability of wood claddings. Deep cracks collect water from rainfall and can develop favourable moisture content for decay fungi. The liquid water absorption studies of Scots pine and Norway spruce sap- and heartwood showed that sapwood of both wood species had higher water absorption than heartwood. Heat treated spruce wood treated to Thermo-S-class had the lowest water absorption. When the wood material is coated with a proper surface treatment system the wood material has no influence on moisture dynamics. Rapid changes in moisture or temperature caused cracking of the wood material. The most sensitive material without coating was pine sapwood and the most durable spruce heartwood. Despite of lower moisture contents and dimensional changes of uncoated heat treated wood the cracking was at the same level as with pine heartwood withhout coating. The cracking of wood was found out to start close to the border of early- and latewood, but typically in the early wood region.
Rosa Perez*, Francisco Juan & Stephan Garcia,
The treatment with chemicals biocides and fungicides, in order to get wood boards with
a good exterior behaviour, against fungus and xylophages, using immersion or
autoclave processes, can
change the superficial characteristics of the wood piece (specially, superficial
absorption and tension), with a high
relationship to the adherence of the varnish applied on it. Any problem related to
this adherence can lead to future damages on the coating film:
- blushing, etc.
Many times this coatings is not needed, but in other cases, depending on the final use of the product and the expected appearance, a coat of varnish has to be applied, in order to fulfill the consumer's requirements. This paper deals with the main changes of the wood superficial characteristics and the behaviour of different kind of varnishes, trying to get the relationship between the superficial modifications and both physical and chemical properties of the liquid varnishes. The film behaviour is analysed by the level of the appearance and physical, chemical and ageing tests. This study is carried out for two kind of exterior treatment, immersion and autoclave.
Forest Products Laboratory, USA
There is inceasing interest in the use of nanoparticles of iron, titanium, aluminium and zinc oxides in transparent coatings for wood. Such nano-composite coatings have the potential of not only preserving the natural colour of the wood but also of stabilizing the wood surface against the combined degradative effects of sunlight and moisture. The nanoparticles can be added as additives to coating formulations, or can be deposited directly as thin films on substrates. Thin film deposition can be accomplished by plasma enhanced chemical vapour or by sol-gel deposition. This paper describes sol-gel deposition of hybrid inorganic/organic thin films, using a mixture of metal-organic precursors on wood substrates, and their effect on the weathering properties of the wood substrate.
Coating Consultancy, Denmark
The photodegradation of the wood surface under clear or semi-transparent wood coatings is an important cause of premature failure of exterior coated wood products. The complexity of individual factors that influence the photodegradation of wood and exterior wood coatings is typified by the radiation reaching the surface of the samples. The significance of UV radiation wavelengths of 280 to 350 nm is widely reported as the most damaging wavelengths. This paper presents data gathered in defining activation spectra for colour change for four different wood species as part of research to understand the influence of longer wavelengths of incident light. The observed colour changes and the associated chemical changes at the wood surface are discussed. The study indicates that wavelengths of light longer than 350nm cause significant changes and that new generation UVAs designed to filter in this region are an important component of advanced exterior coated wood products.
Martin Arnold1*, Peter Svane2, Laurence Podgorski3, Gerhard Grüll4 & Terry B. Dearling5
1EMPA, Swiss Federal Laboratories for Materials Testing and Research, Switzerland
2Coating Consultancy, Denmark
To establish data on the test precision of the EN 927-3 natural weathering test, five members of CEN/TC139 working group 2 'Coating systems for exterior wood' have started an 'inter-laboratory' study in January 2004. Test procedures are following the latest discussed revisions such as a reduced panel width of 80mm and a more precise definition of the growth ring inclination. The core of the study consists of three consecutive exposure series at five sites with sets of 5x3 replicate panels produced by and exchanged between the five participants. Performance assessments are made after 1 and 2 years of exposure. Based on this round-robin exercise a paragraph on test precision will be proposed for a future revision of EN 927-3. Results after 1 year of exposure will be presented.
Dr Yutaka Kataoka*1, Dr Makoto Kiguchi1, Dr R Sam Williams2 & Dr Philip D. Evans3
1 Forestry and Forest Products Research Institute (FFPRI), Japan
2 Forest Products Laboratory, USA
3 University of British Columbia, Canada
FT-IR microscopy was used to depth profile photodegradation of Japanese cedar earlywood exposed to monochromatic light in the UV and visible ranges (band pass: 20nm). Parallel experiments assessed the transmission of the light through thin sections of Japanese cedar. The depth of photodegradation increased with wavelength up to and including the violet region of the visible spectrum, but decreased in the blue region. In contrast, penetration of light into Japanese cedar was positively correlated with wavelength. We concluded that violet light still has sufficient energy to degrade wood and extends photodegradation into wood beyond the zone affected by UV radiation. Accordingly, surface treatment designed to protect wood used outdoors should protect wood from the effects of violet light.
Dr R. Sam Williams*1, Steve Lacher1, Corey Halpin1 & Christopher C White2
1 Forest Products Laboratory, USA
2 National Institute for Standards and Technology, USA
Ultraviolet radiation, moisture, heat, and cyclic fatigue are some of the stressors that cause materials to degrade outdoors. Considerable research has addressed the effects of ultraviolet radiation and moisture on the rate of this degradation. An often over-looked stressor on materials, during outdoor testing, is the cyclic fatigue. Cyclic fatigue is caused by self-induced dimensional change in the materials itself or by dimensional change of materials in contact with it. For example, changes in the moisture content of wood cause it to shrink and swell, which leads to surface checking; dimensional change of wood may cause paint to crack or sealants to debond. In our research on the service life prediction of sealants, we have developed a computer-controlled cyclic fatigue test apparatus and accessory instrumentation to test materials with cyclic loads and to measure their degradation as they are tested. The changes in modulus, temperature dependence of the modulus, plasticizing effect of water above and below freezing, and evaluation of specimen quality at the beginning of the test were made possible using this equipment.
Danish Technological Institute, Denmark
The Danish Technological Institute is in co-operation with industry partners running a project aiming at predicting the service life of different wood protecting systems. The project focuses on examining the moisture reducing effect of different protecting systems for timber claddings and the ability to maintain the appearance of the surfaces, when the wood is used in service class 3. A façade construction is exposed to weathering at the field test area of the Danish Technological Institute (near Copenhagen). In specific locations of the construction in-situ measurements are measured of the wood moisture by using resistance moisture meters. Once a year the surface is evaluated in relation to appearance, mould growth and degradation. The examination comprises different types of coating treatments (e.g. non-permeable and permeable and solvent and water-based types). In addition, a system based on stabilising oil treatment similar to the Royal process is examined. This paper presents results after three years of exposure. It is intended to extend the testing period for at least 5 years. It is the intention that testing should form the basis of evaluation of the maintenance requirement and the service life of the wood.
Dr Rico Emmler
Institut für Holztechnologie, Germany
In the practical use of flooring surfaces more and more fine scratches are the reason for claims. For some environmentally friendly water based systems also irreversible traces of black rubber shoes cause problems. For a better differentiation of flooring surfaces a multiple scratch test method using a Mini Martindale Tester with Scotch Brite fleeces as scrub material was developed. The results of this method are in good correlation with the results of field tests on parquet surfaces. Current results on different overlay types of laminate floor coverings will be demonstrated. Furthermore another test device for the determination of black shoe mar-resistance using different rubber types decelerated abruptly was developed to differentiate parquet lacquers.
Magdalena Nowaczyk-Organista* & Tomasz Oleszek
Wood Technology Institute, Poland
Changes in colour of natural veneers used in the furniture industry after their exposure to xenon lamp light were compared. Tests were conducted according to a draft of European standard prEN 15187 Furniture – Assessment of the effect of light exposure. Samples were irradiated in the SUNTEST CPS apparatus by Heraeus equipped with a xenon lamp shielded by a quartz filter and window glass. Change in colour expressed as a contrast of a grey scale of standards was assessed by visual (acc. to prEN 15187) and colorimetric (acc. to CIE Lab system) method. Coordinates of veneer colour were measured using ELREPHO 2000 spectrophotometer by Datacolor. It was observed that, depending on a wood species, the agreement between the results of the two methods of lightfastness assessment was different. The greatest conformity was recorded for birch and alder veneers.
Dirk Kruse*1, Sebastian Simon1, Ludmilla Derr1, Anna Gatzke1 & Bjorn Kampmeier2
1 Fraunhofer-Institut für Holzforschung (WKI), Germany
2 Institut fuer Baustoffe, Massivbau und Brandschutz
The use of wood as a structural or cladding material in multi-storey buildings is limited due to its combustibility. Within the last three years two research and development projects were performed to develop high performance fire protection coatings. These coatings can protect wood from ignition over defined periods of time. The formulations were tested under different fire impacts to prove their capability. Furthermore these coatings meet the requirments of decorative coatings relating to their specific functionality. The paper gives an overview of the state of the art of fire protection through coatings and of the performed laboratory work at WKI. It is shown how high performance fire protection coatings could be classified in the future and which are possible applications in the context of legislation.
Ing. Daniela Tesarova, Ph.D
Mendel University of Agriculture and Forestry, Czech Republic
The study investigates the issue of VOC emissions emitted from different wooden products and different types of wooden furniture finishes. The VOC emissions evaporating from bare or finished wooden surfaces were tested in the Equipment for VOC Measuring with a small-space chamber, which device satisfies all conditions mandated in the standard ENV 13 419. The analytical method for qualitative and quantitative assay of the VOC components used was gas chromatography in conjunction with mass spectrometer and Direct Thermal Desorption. The goal of this work was to determine the effects of the finished surface on the amount and chemical composition of VOC released from the finished furniture samples. The lowest VOC emissions from the entire collection of specimens that converged to zero after one-week storage were determined in the sample chipboards with glued veneer coated with UV-curing acrylate lacquers. The UV-curing acrylate film with the so called "prevention effect" demonstrated the possibility of eliminating the emissions from veneered chipboards and MDF.
Rosa Perez*, Francisco Blasco & Carlos Soriano
The water from the paint cabinets, in the wood sector, have a lot of problems in order
to be managed due to the high quantity of organic material, needing a previous treatment
before being dropped as waste. Two of the main parameters making this treatment difficut
- a high organic content
- high suspension solids.
The traditional processes to treat this water are based on the use of coagulants and flocculants in order to separate the solids in suspension, followed by an adsorption treatment to eliminate the organic material. Nevertheless, in many cases, after these treatments, the water is not useful enough to be dropped or to be re-used as water for the cabinet. This situation leads to economic losses, because the treatments or other different processes have to be carried out again. This paper shows an approach about the possibilities of the treatments based on advanced oxidation processes, comparing the results obtained from the main mechanisms to produce hydroxyl radicals, more oxidant than the ozone, to the results obtained from traditional treatments. The water analysed is taken from cabinet where the most common kind of paints and varnishes in the wood sector were applied.
Dr Franco Bulian*1, Paolo Ambrosi2, Albert Keiler3, & Hilmar Rauhe4
1 CATAS, Italy
2 Adler, Italy
3 Adler-Werk Lackfabrik, Austria
4 Informium AG, Germany
It is now possible to apply information directly into coatings. Encoded can be information
like manufacturer and product names which can be used for quality-control and
authentication. The presence of specific taggants allows to recognize a coating
material during all its life also years after the application. This circumstance
can be considered of great interest for the coating, joinery and furniture sectors,
in case of possible claims due to in-use faults and for warranty procedures.
The scope of the project presented here can be summarized by three fundamental steps:
- encoding and integration of information into coatings;
- inclusion in different coatings;
- verification of the stability of the markers by proper natural and artificial weathering tests.
Laurence Podgorski*, Véronique Georges & Guillaume Legrand
CTBA, Bordeaux, France
The objective of this project was to study the paintability of wood treated with arsenic-free and chromium-free preservative treatments in comparison with traditional CCA treatment. Four preservative products were selected in accordance with their representativeness of the preservative product market: one CCA reference formulation and three chromium- and arsenic-free formulations. Wettability measurements have shown that the four preservatives treatments lead to very different surface characteristics. Six coatings systems have been applied. Results of artificial weathering test (prEN927-6) and natural weathering test (EN 927-3) are in good agreement: they show that the coating performance is generally better on CCA treated wood certainly due to the chromium influence.
Florian Tscherne*, Gerhard Grüll & Irene Schweiger
Clear coatings on wood in exterior exposure have, compared to brown coloured varnishes, the disadvantage, that even very small cracks and the following discolouration are more severe and the appearance of the coated wood surface is affected in a shorter time. Periodical maintenance can improve the durability of clear coatings during weathering. In an accelerated weathering tester clear coating-systems were exposed to UV-radiation and water-spray. One panel of each system was not maintained, one was maintained every two weeks, one was maintained every four weeks. The effects of the maintenance measures were studied by light-microscopy and SEM (Scanning-Electron-Microscope). With several coating systems significant improvements of durability were observed.
Dr Hrvoje Turkulin
Faculty of Forestry, Zagreb University, Croatia
Several surface treatments for transparent protection of exterior wood have been tested in natural and artificial weathering by measurements of contact angle, liquid water and vapour absorption, colour change and mechanical properties ("thin strip" method). Spruce wood was impregnated wih HALS-containing primer and subsequently treated with UV-modified, nano-scaled hydrophobic emulsion, or by appliction of several transparent coatings. Hydrophobic properties ("pearling effect" and high contact angles) did not correlate well with water absoprtion, and the weathering resistance depended on the amount of UV additives and film thickness. Providing that sufficient depth of primer penetration and resistance to vapour transport are assured, transparent coating systems containing HALS, UV absorber and nano-based water repellent offer very promising enhancement of exterior wood service life.
Gerhard Grüll*, Irene Schweiger & Florian Tscherne
Microfoam and air inclusions in coatings on wood are film defects that may occur when coatings are applied by spray technique. Systematic application trials were carried out to study the influence of different parameters during application and drying on the formation of air inclusions in coating systems for joinery. Size and quantity of air bubbles were assessed in the dried coating film by microscopic methods. The results showed major effects of coating formulation, application equipment, distance between spray gun and object as well as climatic conditions during drying. Minor effects were found for different settings of material pressure, material temperature and nozzle dimensions. The results can contribute to improve the quality of coatings on wooden windows to obtain high durability.
Dr Robert A. Monticello
AEGIS Environments, USA
In the world of antimicrobial agents, not all are created equal. For this reason, the application process, performance expectations, and test methods for each antimicrobial agent must also be different. The new and adapted chemistries involved in such applications differ in their ease of use, mode of action, spectrum of activity, and toxicity to humans and the environment. This is true in the established textile market where performance claims for antimicrobial agents can range from simple odor or mold and mildew control to treating with sanitizers and disinfectants to produce hygiene surfaces capable of eliminating infectious microorganisms, both on the textile and for the surfaces they contact. The call for safer, less toxic antimicrobial agents is made in every industry that uses preservatives and protectants as performance enhancers or product stabilizers – the Building/Construction industry is no different.
Traditional antifungal/antialgal agents used in the wood and construction products industry have been eliminated because of their negative environmental and human toxicity legacy. With the loss (voluntary ban) of CCA and the increased awareness of the toxicity profile of other common antifungal/antialgal additives, the wood and composite industry is demanding the availability of new technologies to help combat mold and mildew in and on their products. Test techniques have had to be able to be modified for evaluating new antimicrobial agents.
For biocide product manufacturers, the research and development involved to create new molecules is a relatively simple hurdle compared to regulatory and registration hurdles that must occur on national (US-EPA) and international (EU-BPD) levels. The time and expense involved in creating new antimicrobials almost seals their fate. The use of older, well-tested technologies currently used in other industries provides a new source of registered antimicrobial agents with excellent safety profiles.
This paper presents data on an immobilized antimicrobial agent currently used in the textile industry and the applicability of its use in the building and construction industry, specifically when applied to composite lumber such as OSB and engineered wood/plastic composites such as deckboard or trim materials. In addition, appropriate test methods and their relativity to real-life performance will be presented.
Dr Mari de Meijer
Drywood Coatings, The Netherlands
Providing a moisture barrier is a key function of an exterior wood coating. Waterborne coatings generally show higher moisture permeability, especially shortly after application. The degree of moisture protection if governed by factors on several levels. From a macroscopic level like film thickness, through the meso level of porosity between pigments and binders down the micro level of the binder polymer. This paper will firstly discuss influence of paint formulation variables like binder type, surfactants, coalescing agent and pigmentation on moisture permeability. Secondly influence of application aspects like film thickness and drying conditions will be described. It is shown that the build-up of moisture barrier properties can be considered as a measure of the degree of film formation.
Marie-Lise Roux1*,Thierry Delorme1, Yann Mondain1, Yann Laigle1, Thierry Chave2, &
1CTBA Technical Centre for Wood and Furniture, France
Furniture Industry must find solutions to replace solvent based coatings to meet the VOC European Regulation. Because the majority of companies must reduce their emissions of 50 - 80%, all partners such as raw materials and coatings producers, equipment suppliers and furniture manufacturers, must work together to develop technical and economic solutions. Waterborne coatings are the more studied solution. At present, several technologies are proposed to the companies. A project supported by ADEME, coatings and equipment producers, some furniture manufacturers and UNIFA is now finished. The aim was to give technical and economic information to compare the available products (mono component, bi component, UV cured and dual cured products) and drying processes for furniture. The approach integrated : appearance, performance, criteria of production and energy consumption and some economic data. A first paper was presented in Brussels in March 2006. This paper will present the final results including the feed-backs of visited industrials on the set-up in the plant, the difficulties they encountered and the first approach of the economic balance.
Dr Roman I. Flyunt*, K. Czihal, F. Bauer, R. Mehnert, M. R. Buchmeiser, H. Bauch, & R. Emmler
Institut für Oberflachenmodifizierung e. V., Germany
Developed at IOM, UV-nanolacquers were used for parquet coating and compared with reference industrial coatings. Abrasion (S-42 and Falling Sand Methods), scratch-(Erichsen Hardness) and mar-resistance (Methods A and B developed at IHD), universal hardness, elasticity and impact resistance tests were applied as major criteria. IOM's nanolacquers with corundum have typically higher abrasion resistance compared to reference materials by a factor of 10-20. IOM's nanocoatings without corundum (applied in one layer, 10 g/m2) revealed the same scratch resistance as existing industrial coatings, but demonstrated enhanced elasticity, impact resistance and universal hardness, and abrasion resistance (about 50 % for each method). Both mar-resistance tests illustrated the advantages of IOM's nanolacquers especially convincingly: IOM coat gets the highest grade, whereas the reference coating is two grades worse.
TRADA Technology Ltd, UK
Initial progress to develop a predictive test procedure for floor lacquers based on nano-indentation response were desribed at the Fourth International Woodcoatings Congress at the Hague. This paper describes subsequent work to further develop, verify and confirm the procedure as a reliable alternative to existing tribological test methods and assesses results returned using the procedure on an extended range of lacquer products against existing field data and in-service experiences. By using the method comparatively the paper describes its potential to aid product selection through a treatment of the data which enables long-term changes in the relative rate of performance between products to be charted.
Akzo Nobel Powder Coatings, France
Powder coatings for MDF is now a well known technology. Many industrial lines are currently
using powder coatings on MDF around the world. Two different technologies can be used:
- Low Bake Powders
- UV curable Powders
Most of the finishes are fine texture, but we are now able to do smooth stain and smooth matt aspect in one coat. MDF is not the only substrate that can be powder coated: plywood and beech wood are the next steps. In order to imitate wood aspect, a new technology is now available: heat transfer of a decor by dyestuffs sublimation on a UV curable powder coatings film. Powder coatings can now answer to most of the market demands in terms of aspects and technical specifications.
N. Lutke Schipholt*, E.P.J. Beckers et al.
SHR Timber Research, The Netherlands
For clear coatings on darker wood species, especially those with a coarse texture, often a "warm" appearance of the coated surface is required. Practice has shown that this, rather subjective, "wet look" effect, also known as "Anfeuerung", can very well be achieved when using most VOC containing coatings. These should be replaced by water based alternatives, which create different and less wet look. Research has been performed to learn more about the mechanism behind and parameters influencing wet look. The effect of both commercially available clear coats and pure binders was evaluated using microscopic and analytical techniques. This information should enable modification of water based coatings and improve their wet look effect.
Paul Swan and Ralf Taube
Eastman Chemical Company, UK
Whilst EU regulations are driving a change in application and coatings technologies, solvent borne systems still predominate, particularly for high quality furniture coatings. The ability of the coatings applicator to combine technologies allow the continued use of 2K acrylic urethane coatings for wooden furniture to achieve desired haptic and technical performance.
A program of work was undertaken by the CTBA (Cenre Technique du Bois et de l'Ameublement) in Paris to determine the effects of Eastman CAB performance additive to a semi-gloss 2K acrylic urethane wood coating system. The work detailed in this paper identified the positive effects of CAB addition in terms of improved hardness development, surface appearance, haptic and ease of application.
Ludger Overhageboeck1*, Stefan Friebel2 & Peter Goletz1
2WKI Fraunhofer, Germany
A very recent research topic is the development of transparent UV-coatings for exterior wood applicatons. After more than five years of development, the final results of a governmental funded research project conducted by Fraunhofer WKI and Remmers Baustofftechnik GmbH will be presented. The aim of this project was the development of a transparent UV-curing wood coating with a maintenance interval of 8 years and longer. Physical data such as polymer decay during weathering, the conflict of sufficient UV-protection and UV-curing and the solution therefore as well as the polymer basis will be discussed. Additionally to the artificial and outdoor weathering testing results, the first practical experiences of this new product generation is shown.
Barbora Vymetalikova & Dr E.J. Yaacoub
Fraunhofer-Institut für Holzforschung (WKI), Germany
Novel aqueous polymer dispersions based on renewable resources were synthesized via free-radical emulsion polymerization Monosaccharide and fatty alcohol based acrylates gave latexes with interesting properties compared to the petochemical and commercially available latexes. These organic nanoparticles are applied as binders for wood coatings and water-based adhesives. Starting from D-glucose radical polymerizable sugar methacrylate was synthesized. Fatty alcohol based acrylates, such as amyl acrylate and lauryl acrylate commercially available were copolymerized with the sugar methacrylate. These monomers are hydrophobic so that suitable for the conventional and miniemulsion radical polymerization of the type "oil in Water". In addition renewable surfactants based on fatty alcohols, such as sodium lauryl sulfate and fatty alcohol ether sulfates such as Disponil series from Cognis are also applied in the formulations.
Dr Thomas Easton* & Stuart Poultney
Dow Corning Ltd, UK
The use of silicone resins as the primary binders in wood coatings has met with limited success since most commercial silicone resins require relatively high curing temperatures. This is frustrating since the well-established features of silicone coatings, particularly their durability, could offer excellent protection to wooden surfaces. Another limiting factor is that most commercial silicone resins are supplied as solutions in aromatic solvents.
In this paper we will describe aromatic-free silicone resins which cure at ambient temperature to give hard glossy coatings. They are tack-free within thirty minutes. Multiple layers can be built up since the recoatability of these coatings is excellent. Formulation guidelines will be given that provide optimised combinations of cure time, hardness development and chemical resistance.
Dr Michel Tielemans* & Jean-Pierre Bleus
Cytec Surface Specialties, Belgium
The chemical structure of radiation curable polyurethane dispersions (called UV-PUD) is screened towards new coatings with improved outdoor resistance. The polymer modifications involve the diisocyanate and several telechelic diols including polyester, polyether, polyacrylate, polybutadiene, polycarbonate and polysiloxane. The formulation of the aqueous dispersions and their spray application on wood are described in detail. The test method for artificial weathering uses repeated cycles of temperature & relative humidity under ultraviolet light exposure (Atlas Weather-O-Meter). The coatings are and on a neutral substrate. The best performance is obtained with a particular polycarbonate-based variant. In that case, it is possible to significantly increase the longevity of the coated wood in our test conditions, while offering a high level of mechanical and chemical resistance.
Felix Baah* & Lendert Berkhout
Johnson Polymer BV, The Netherlands
Certain wood species such as Merbau, Western Red Cedar, Mahogany, Pine (knots) and the like are prone to extractive bleeding. In contact with conventional water based coatings, the water soluble extractives migrate to the coatings surface, staining and discolouring it upon drying. As a result, the coatings lose their decorative value. The water soluble extractives are effectively blocked by solvent based coatings; however, environmental legislation is the main driver to convert to water based systems.
There are two objectives for the studies. Firstly to develop a reliable and reproducible test method for evaluating tannin bleeding. Secondly to develop a polymer that can be used to produce a primer that will prevent discoloration due to water soluble wood extractives. In addition to its excellent wet adhesion, the new polymer is tailored to create a good barrier to water soluble extractives.