Where a paper has more than one author the presenter is indicated by *
Click on a paper's title to go to its session in the Congress Programme
This introductory paper gives a review of the major new technology platforms and performance evaluation protocols under active consideration by the woodcoatings industry.
The latest developments in waterborne technology, renewable raw materials, UV curing and nanotechnology are discussed, together with new initiatives in Life Cycle Analysis and the measurement of service life in terms of outdoor durability.
The paper concludes with suggestions for the direction of future technology developments.
In June 1992, the Rio Conference on Sustainable Development agreed a framework which has significantly impacted the thinking of countries, industries and consumers since that time. Recent raw material shortages suffered by the Coatings Industry have acted as a stern reminder that resources are not infinite and, with the projected expansion of the world population, much has to be done to meet the needs of the present without compromising the ability of future generations to meet their own needs.
The economic, social and environmental pillars of Sustainability, addressed at times as the triple bottom line are now well recognised, and this understanding has spawned some brave commitments and creative initiatives which assist in the drive towards the goal of creating a fully sustainable society.
The Coatings Industry has played its part in this move forward. Retailers, manufacturers, trade federations and NGOs have all contributed to the increasing momentum for change. Indeed, many coatings products including those supplied by the woodcoatings industry can be argued to be part of the solution given the protection that they provide to articles on which they are applied. However, we still have a long way to go to deliver a fully sustainable industry.
Tony Mash will review recent steps taken by the Coatings Industry in its quest to create a fully sustainable industry. Recognising the broad nature of the concept of Sustainability together with the opportunity for different interpretations and priorities around the world, he argues that a global industry approach is required to develop a consistent set of policies world-wide to ensure that our industry’s activities are well coordinated, managed in an efficient manner and communicated effectively to industry stakeholders.
With the multiplication and acceleration of stakeholders’ requests for social and environmental responsibility, decorative paint companies are particularly under the spotlight, having a wide range of markets and customers: DIY consumers following distribution trends, architects looking for green building credits, painters and their end users seeking innovative green products. Moreover decorative paint companies are by essence at the junction of the Chemical and Construction Industries which have their own different drivers for sustainability. Therefore it is vital for the decorative coating industry to have a sustainability roadmap built on a state of the art assessment method. PPG will introduce how it uses Life Cycle Assessment (LCA) for understanding its products footprint and identifying improvements. In order to make LCA results understandable by its customers, PPG developed a dedicated Product Sustainability Scorecard that is linked to LCA. It enables customers to compare products on environmental impact, health and durability aspects and let them select the most sustainable solutions.
There is awareness today that one of the biggest challenges to the world is to further avoid climate change and the fast depletion of raw materials. Life Cycle Assessment (LCA) methodologies are used to understand the impact of the processes and materials we are using. In this paper we compare in more detail the LCA of several solvent borne-, water based- and powder coatings to coat wooden boards (e.g. MDF) for the furniture industry. The study covers the impact of the coating from cradle to the (coaters) gate. The impact of the different paint raw materials, including the resin system, pigment and solvents, the application energy, the paint utilization (overspray), film thickness and waste, has been studied. The highest impact on the footprints is caused by the presence of solvent in the paint and the (in)ability to (re)use the overspray. It has been demonstrated that especially powder coatings have the lowest carbon and eco footprint of a coated MDF panel.
Alkyd based decorative coatings have proven their technical performance for nearly one century, but nowadays they are under threat, because consumers do not accept the use of solvents. In addition the European Directive 2004/42/EC limits emission of VOCs, so paint producers are forced to switch from solvent based alkyds to high solids or to waterborne systems.
Aqueous acrylic binders or hybrid systems may replace solvent borne alkyds. But most of these binders are still suffering from lower gloss level, poor adhesion over aged coatings, blocking tendency and short wet edge. Therefore a broad range of new binders has been developed during the last years in order to overcome those problems. These developments were extensively investigated to prove how innovative water-based acrylic systems may replace solvent based alkyds in decorative wood coatings.
An overview of this work will be presented and application results will demonstrate whether acrylic emulsions can replace solvent borne alkyds.
Indoor Air Quality is becoming a major topic for the coatings industry. Consequently, the requirements for coatings are getting more demanding.
In Europe the European Commission has adopted the voluntary ECO-label, but next to that initiatives have been taken to go even further and to label paints according to their total emissions of volatile organic compounds (TVOC).
Even though advanced waterborne resin technology has led to a breakthrough in the reduction of the TVOC, they do not necessarily fulfil the strictest requirements.
Chemists at Nuplex Resins have developed a new generation of waterborne binders that enable coating manufacturers to meet the most challenging requirements. Application work with these binders will be presented, including brushable paint formulations for the decorative coatings market.
Micro foam defects in airless or airmix spray coats are not only reason for turbidity in clear coat films but also coating failures with a negative impact on the durability of water-based exterior joinery products.
Formulators approach such problems mainly by playing with the type and amount of defoamers/deairants. But these experiments are empiric, time consuming and not always completely successful. In practice they often end-up with unnecessary high loads of expensive, incompatible defoamers in the formulations, which can cause aside high costs also surface defects (e.g. craters).
The idea of our study was to define in the first step some controlled test parameters (e.g. temperature, humidity, material pressure etc.) to improve the reproducibility and sensitivity of airmix spray experiments of water-based acrylic wood coatings. In a following systematic approach we focused on different formulation parameters to see their influence on the number of air bubbles in spray-applied, acrylic window coating films.
We did find out (and try to explain why) that aside the type of acrylic binder and defoamer/deairant under use indeed other formulation ingredients such as thickeners and coalescents play an important role on the quality of exterior joinery spray coats. By optimization of all parameters also difficult to be defoamed water-based acrylic formulations can be applied at limited or no air inclusions in an airmix spray application process.
Eco-friendly waterborne paints and coatings already gained considerable interest and market shares compared to traditional solvent borne systems driven by stricter legislation as well as the general environmental awareness. A pioneering concept based on metal oxide nanoparticle technology that potentially boosts the performance of waterborne coatings will be introduced. Tailor-made nanoparticles generated by a chemomechanical surface modification process improve the overall coating performance due to direct resin interaction. Performance enhancement of water-based acrylic emulsions formulated as wood stains or sanding sealers and PUD systems also for wood coatings will be presented. In particular the significant enhancement regarding MEK rub stability, drying time, blocking resistance and early sandability will be highlighted. It will be shown by case studies that the additive can lead to a significantly higher productivity if combined with waterborne acrylics due to the earlier peak performance of the coating.
When choosing a suitable preservative for waterborne wood coatings there are various factors to consider – different ingredients, pH value, compatibility, and climate conditions – to name a few. The large number of possible micro-organisms and the enormous diversity of raw materials impose demands that cannot be covered by just one microbial active used at an acceptable dosage. Moreover, environmental acceptability, including the sustainable use of raw materials, is becoming a decisive factor to customers. The synergistic combination of benzisothiazolone (BIT), methylisothiazolinone (MIT) and bis(3-aminopropyl)dodecylamine (BDA) has proved being highly effective by minimizing the level of biocidal actives needed for preservation. With this new sustainable “full-life” protection concept, it is possible to control waterborne contaminations, provide safer manufacturing procedures, to offer an opportunity to eliminate product recalls and downtime issues. Moreover, it allows for sustainable use of raw materials due to low usage concentrations and complies with the standards of various eco-labels.
New developments in acrylic-based waterborne systems have enabled us to obtain performing latices by copolymerization of a hydrophobic monomer, the vinyl ester of neo-decanoic acid with acrylates. These modified acrylic polymers can be designed to reach specific requirements for application such as exterior wood coatings. Wood is a very popular building material that can be affected by climatic conditions. By designing self-crosslinkable polymers, combining the vinyl ester of neo-decanoic acid with acrylates, consisting of a hard core and a soft shell, is possible to obtain binders with an optimal hardness-flexibility balance. Thanks to high hydrophobicity and low surface energy, the hydrophobic vinyl ester enhances the final wood coating ability to repel water and increase the resistance to weathering influence.
The requirements in terms of outdoor durability in the joinery market have increased significantly over the last years. High performance waterborne dispersions have been developed for this purpose. BASF continues to develop products which can meet these stringent performance requirements. The first waterborne UVA / HALS blend using proprietary NEAT technology is Tinuvin® 5333-DW. This new product fulfils these high-end requirements as it is composed of a high performance UV absorber and a non-interacting HALS, making it compatible for all resin types, especially sensitive resins. This novel blend offers a superior photo-permanence and it not only improves the durability of the wood but also the performance of the wood coatings in terms of superior colour and gloss retention. The NEAT technology allows an additional step forward in the reduction of VOCs. The new product is solvent-free and does not require any co-solvent for its addition into the formulation.
Previously, SHR studied minimal and low build paint systems commonly used to give colour to the wood and preserve an even colouration of the wood. Results were presented in the 2010 Woodcoatings Congress. Furthermore, first results of the SHR research project exploring the possibilities of coating wood in a two-step process involving a pre-treatment and finish coat were shown.
The target is to develop a pre-treatment formulation that links the wood substrate to a medium-build finish coat by covalent molecular bonding using hybrid Sol-Gel chemistry; resulting in superior outdoor durability due to increased wet adhesion of the finish coat to the substrate.
This paper presents results after two years of outdoor exposition to the southwest of cladding parts treated with the two-step coating system. A waterborne pre-treatment formulation was prepared showing nearly the same performance in laboratory tests as the original solvent based model formulation. Finally results of FTIR analysis of the wood-treatment interactions will be presented.
Aesthetic ageing of very high gloss finishes, sometimes, has noticeable effects of collapse by end users. The most frequent criticism is that the reflections of the new furniture become “cloudy” in a short time, sometimes less than a year. This rapid ageing is partly related to substrates and partly to coatings. The evolution of wood-based panels, combined with that of finishes and their processes lead to customers no satisfaction. The objective of the study was to assess the risk of collapse of finishes by a combination of short accelerated aging and characterization of appearance change. Two technologies of surface characterisation were used: the DOI (Distinction of Image) to assess the degree of orange peel and the surface topography by an Altimet 500, to characterize the roughness, the shape and especially the ripple. This paper will present and discuss results of experiments. A comparison between combinations, substrates, finishes and processes) will indicate trends for furniture manufacturers.
In the era of increasing individualisation of consumer goods, ink jet printing offers almost boundless possibilities to create decorative surfaces. This paper gives an overview of the opportunities of digital ink jet printing for the production of decorative surfaces on furniture fronts, floorings, wall panels and other products. It shows the advantages and draw-backs of this technique as well as the current technical solutions to obtain high quality images on wooden substrates. Based on own results obtained with an industrial single pass ink jet printer on various substrates, requirements to the properties of substrate surfaces are formulated. Methods of surface characterisation are also presented. In most cases the application of basecoats is necessary. Since the printed images have to be protected from mechanical impact, the interaction of the prints with different coating systems such as UV-curables, water-based coats as well as melamine was also investigated in terms of adhesion strength, mechanical properties and appearance.
UV LED technology has now reached a level of maturity where it is being used commercially as the UV light source of choice in a growing range of commercial applications. Offering significant environmental advantages, much research is now being undertaken to deliver coatings for wood (both clear and pigmented) which will cure using these semi-conductor driven UV light sources. Integration Technology Ltd is part of a Seventh Framework EU Programme (FP7) to develop new formulation components enabling the UV LED curing of wood coatings in air. This paper will outline recent developments in, and the state of the art of UV LED’s; re-visit the environmental and other advantages of this emerging technology; and examine an economic cost model over time as compared with traditional mercury arc UV sources.
The utilization of light emitting diodes (LED) in photopolymerization is a novel and emerging technology. Photocuring of wood coatings with LEDs in air suffers from the detrimental effect of molecular oxygen. Oxygen reacts with a macroradical producing a peroxy radical with low propagating activity. This leads to low double bond conversion, lower rates of polymerization, and poor properties of a cured coating. Traditionally, oxygen inhibition has been mitigated by inerting, physical barriers, high intensity light, high concentration of photoinitiator, and additives. The objective of the current study is to provide an experimental overview of various additives that are already used in industry or published recently in scientific journals (hydrogen donors, singlet oxygen scavengers, CO2-producing compounds, thiolene chemistry, and others). Their performance has been assessed using real-time-FTIR directly coupled with the LED lamps. Bulk cure was monitored by FTIR in transmission mode and the surface cure by ATR-IR.
Industrial wood coating manufacturers are under pressure to provide cost effective products with a low environmental impact. Ultraviolet light emitting diodes (UV LEDs) have emerged as an alternative light source to medium pressure mercury lamps. LEDs are claimed to be 60-80% more energy efficient, provide instant on-off capability and offer numerous environmental benefits. The rate of cure obtained from LED arrays is usually slower than that from mercury lamps systems. An inert atmosphere is generally required to achieve acceptable surface cure when irradiating with UV LED arrays. This paper will address the challenges that arise from UV LED cured coatings whilst attempting to achieve a degree of similar cure to that obtainable with a conventional medium pressure mercury lamp. The work has been undertaken as part of an EU FP7 funded partnership project.
Trends in wood coatings are driven to waterborne systems and to renewable resources. Vegetable oils are well known for wood coatings, e.g. alkyds or polyurethane dispersions. In this context fatty acid methyl ester and derivatives thereof turn out to be an alternative to technical fatty acids and vegetable oils. High contents on hydrophobic oil based monomers improve hydrophobic and oleophobic properties. In this study the synthesis of fatty acid methyl ester derivatives, the preparation of coating resin and the final coating formulation are described. Two types of waterborne coating resins, two-pack system and UV-curing, were applied on beech wood samples to investigate the impact to the resulting coating film properties.
CEN/TC 139/WG2 – Coatings for exterior wood produces standards; mainly descriptions of various test methods. The success of the group and its work is reflected by its
Internal and external factors affect the result; some of those are:
In CEN/TC 139/WG2 we have tried to address these issues by speeding up the production process, and by concentrating on performance test methods instead of prescriptive specifications. The paper gives the state of the art, and highlights some of the challenges of the future work.
During use coated wood surfaces are exposed to various impacts. A suitable resistance of a coating film on wood to impact is of importance to keep the substrate further protected with an intact coating film without cracks or flakes. The simple method described in this paper is being prepared by WG 2 “Coating systems for wood” of CEN/TC 139 "Paints and varnishes". The method provides quick information on whether a coating film on wood is capable to withstand impacts without cracks or not. Results of preliminary research on resistance to impact of coating on a wooden substrate according to this method are presented. It was shown that the method has a great potential to be used either as a means of comparing different coating systems or as a quality control test to ensure that a specified performance level is being achieved or maintained.
Coated panels of pine sapwood with 30 different coating systems were exposed to natural weathering in Vienna (EN 927-3) as well as artificial weathering using fluorescent UV-Lamps and water (EN 927-6). The exposure time until the panels reached a defined limit state, where the coatings required maintenance, was compared between the coating systems and between natural and artificial weathering. In both weathering methods the durability of the coating systems was influenced by film thickness and pigmentation. Three opaque coating systems lasted over 10000 hours in artificial weathering. Comparing natural and artificial weathering by durability of the coating systems (time to limit state) with the present results (after 26 months natural weathering) revealed a relatively good but non-linear correlation. The collected data can be a basis for rough service life estimation of exterior wood coatings based on standardised weathering methods.
In recent years Accoya cladding has increasingly been specified for the purpose of exterior cladding as a direct consequence of its proffered stability credentials. Studies demonstrating a measure of improved coating performance have been carried out on acetylated substrates although no comparable work has been undertaken to demonstrate whether similar improvements in the long-term stability of nail fixings can, likewise, be expected. This trial demonstrates that significant long-term benefits can be achieved when using nail fixings with Accoya in the context of coated exterior cladding despite initial concerns over its greater propensity to exhibit splitting. The trial also confirms that the performance of a translucent stain application over Accoya can be extended well beyond its anticipated lifetime on unmodified softwoods.
This paper compares liquid water absorption of wood surfaces with and without coating, before and after artificial and natural weathering. Samples of spruce, oak and sapelli were exposed to the cycle of EN 927-6, to the cycle of the Garner wheel and to natural weathering. Two opaque coatings (solventborne and waterborne) and two semi-transparent stains (solventborne and waterborne) were applied on these species and exposed to weathering for the same exposure times. Water absorption was assessed according to EN 927-5.
Exposure to weathering led to a significant increase in water absorption of uncoated wood with the biggest increase for oak.
The combination of water absorption measurement and weathering gives more information about long-term performance of coatings than a single measurement of water absorption on fresh and unweathered coated wood. A decrease in water absorption due to weathering was observed for the two pigmented coatings whereas an increase in water absorption was noticed for the two semi-transparent products.
Results showed that low water absorption was not a proof of product quality.
Wood exposed to the outdoor environment is susceptible to weathering due to a series of chemical, biological and physical processes, leading to the degradation of wood back to its elements.
Acetylation of wood is known to improve dimensional stability, resistance to UV degradation and resistance against fungal decay. Due to these improvements, less stress is created due to outdoor exposure in film forming coatings, and thereby maintenance intervals can be reduced and lifetime increased. This paper, which will be split into two parts, gives an overview of the findings of various research activities performed by research institutes and coating manufacturers: and describes the results of the exposure outdoors at Melbourne of uncoated and coated samples of various acetylated wood species (radiata pine, red alder, beech) and reference species such as Western Red Cedar and Ipe. Results obtained from chemical analysis of acetylated lignin will elucidate why acetylation improves resistance towards photochemical and hydrolytic degradation.
Legislation is thoroughly changing the landscape for the wood coatings markets, prompting substitution of old-fashioned solventborne coatings technologies for new waterborne ones.
Driven by innovation, woodcoating producers are putting a higher value on products they produce. In order to do so, they need to be able to deliver real value to their customers. One possibility is coatings that reduce process time and energy consumption, such as ambient waterborne 1K self-cross linking coatings to replace traditional 2K polyurethane topcoats. Even though a most of the requirements can be fulfilled by these waterborne 1K systems, there is still room for improvement of some properties such as chemical resistance. New performance additives have been developed that will allow formulators to address these issues and to significantly improve coating properties.
Natural wood flooring systems for on-site applied parquet coatings is a significant market for suppliers of waterborne coating systems in Europe. Customers in that market value highly the aesthetic and long lasting beauty of wood.
Regulated by the deco paint directive 2004/42/EC on-site applied coatings are mostly water borne and more than 50% of the market is currently using acrylic 1K water-based technology. Despite the wide use very often waterborne coating systems are described as having poor Anfeuerung. The reasons for this often center on the issue of wetting and penetration of the coating into the wood at areas of differing density and porosity. In addition the risk of possible colour change resulting from reaction of the coating with acidic extractable materials present in many wood species provides challenges and room for improvement.
To enhance and maintain the appearance of wood and to preserve the investment for many years to come Eastman is continuously developing ways to improve the coating systems.
Silicone technology has been available to the formulator for wetting, levelling and increased slip performance in wood coatings for some years. Typically problem solvers, performance can vary significantly from one formulation to another, and the technology does not allow the formulator to bring superior properties valued by the end consumer. In this paper we offer the formulator the chance to create a differentiated performance in a number of key properties, including superior wetting on oily woods, high slip and scratch resistance, soft and silky hand feel and high degree of water resistance and beading. Here we compare the performance of silicone based additives with varying architectures and delivery systems and explore how changing the architecture of the silicone brings different properties to the formulator.
A new development in UV matting technology provides the ability to replace silica matting agents and/or standard micronized matting waxes in UV coating systems. Efficient matting is possible regardless of film thickness with negligible impact to the final system rheology. The technology offers broader formulation latitude when compared to standard matting agents as well as excellent soft touch feel. The ability to supply it in liquid form aids to significantly reduce production time and eliminates dispersion related issues that occur with powdered matting agents such as agglomerated particles, post wetting effects and other issues.
Various aspects that are of importance to the formulator of matted UV coatings have been investigated:
This unique approach adds a new and effective way of matting UV coatings that is unprecedented.
Polyurethanes have been used for many years to produce high performance materials such as solvent-borne coatings. However, though possible to formulate water-borne polyurethane systems, the widely used adipate polyester backbones often cause problems, such as reduction in storage stability and hydrolytic resistance. Additionally the slow water evaporation of polyurethane dispersions is seen as a drawback in certain applications. Croda has countered these deficits through its range of hydrolytically stable polyester polyols using biobased technology. The reduced number of ester bonds and the hydrophobic environment make these polyols practically immune for water, while keeping the resistance against UV characteristic for polyesters. Their hydrophobic nature enables fast removal of water out of the system, shortening processing times dramatically. Striving to maximize the amount of biobased content in the products in combination with ultimate performance, Croda is now able to bring a 100% biobased polyester polyol on the market, increasing the percentage of renewable carbon in PUD's significantly to well over 60%.
Legislations and recommendations regarding emissions and labeling have strongly influenced coatings market and new developments. Waterborne systems are being established as an alternative to traditional systems in the market, having 2K waterborne systems clearly demonstrated that the high level of the traditional solventborne standards is nowadays achievable. Bayer MaterialScience has developed a new OH functional self-crosslinking acrylic dispersion that allows both the formulation of 1K as well as 2K systems, offering to the formulator maximal flexibility. The self-crosslinking mechanism present in its structure provides enough resistance to the polymer to be able to reach an acceptable level of performance in 1K formulation. Besides the 1K application, the addition of polyisocyanate can upgrade the level profile of the coating to a higher performance, resulting in a product with a well-balanced profile between application flexibility and coating's properties.
Wood has the potential for being a competitive and sustainable material. However, for outdoor use it is necessary to enhance its performance and long term durability. Inorganic nanoparticles can be used as UV-absorbers to help protect wood from outdoor weathering. To achieve this, a latex could be physically mixed with a nanoparticle dispersion to give a UV-absorbing clear coating. However, if it were possible to immobilize the nanoparticles inside the polymer particles, not only would the clear coat formulation process be simplified, but also the risk of nanoparticle aggregation during film formation would be eliminated.
In this work we report on the synthesis of new hybrid latexes, describing the kinetics and microstructure (sol molecular weight distribution and gel contents) of the polymerizations, as well as application properties of these latexes as binders of clear coatings.
A number of clear coating formulations containing newly developed ceria and zinc oxide nanoparticles for improved UV protection have been produced within the EU FP7 funded project WoodLife - Extended service-life and improved properties of wood products through the use of functional nanoparticles in clear coating and adhesive systems. UV-visible spectroscopy measurements on nanoparticle dilutions and clear coatings containing nanoparticles indicate potential performances. An outdoor exposure test according to EN 927-3 was started in September 2011 simultaneously in Sweden and United Kingdom. Artificial ageing in QUV and ATLAS Weatherometer (WoM) is being performed at present. Comparisons on the performance of different types of nanoparticles as well as between inorganic and organic UV absorbers will be presented.
WoodLife is an on-going project under the EU Seventh Framework Programme which aims to develop a novel water-based clear coating system with functional nanoparticles. By the addition of nanoparticles, the coating can potentially improve the service-life of exterior wood products. The environmental performance was studied using life cycle assessment (LCA) and ecotoxicological testing of the nanoparticles in order to guide the development of the coating system. The LCA shows that a wooden window frame with the new coating has the potential to be environmentally superior to plastic and aluminium window frames. However, it was found that the LCA result in part depends on parameters (disposal practices, recycling rates, etc.) which are highly uncertain for a product that is to function in a future, rather unknown society. The ecotoxicological testing indicates low toxicity of the nanoparticles but more research is needed and suitable testing methods are warranted.
In the last decades the production of window frames has evolved towards the production of fully factory processed window joinery including the application of coatings. Collaborative research in Belgium has initiated a methodology for assessing these coatings taking into account the specific quality parameters used by the window manufacturers. Although this concept can easily be aligned with EN 927 standard test procedures, the experience gained allows some recommendations to be made which could lead to improved or extended assessment of the coating performance. Besides substrate impact parameters related to moisture dynamics should also be taken into account. A flow chart of sample preparation and extraction for assessment of performance based testing using service life principles is proposed as an option to work towards CE related activities for exterior wood coatings.
The aim of the present study was to find and develop a sensor for dosage of natural and artificial weathering using a material of known and controlled decomposition. For this purpose, a signal coloured and weathering resistant poly(methyl methacrylate) substrate was coated with several photolabile topcoats. With proceeding time of weathering, the topcoat should be photo degraded and subsequently washed off from the substrate, finally uncovering the signal orange coloured substrate. For photolabile top coats, alkyd resin, various poly(alkyl acrylates), poly(ethenol) and copolymers of poly(vinyl acetate) were used as binders. Photo oxidation of the topcoats was accelerated using photoactive TiO2 (anatase modification) and a Fe2+ redox catalyst. Best results were obtained with a copolymer of poly(vinyl acetate) as binder in combination with Fe2+ as redox catalyst. First calibration trials showed an approximately linear reduction of the dry film thickness during weathering and the possibility to control durability by dry film thickness, Fe2+ concentration and additional pigments. One application of this sensor for wood coatings is to indicate the need of maintenance.
Extending the service life of wooden window joinery requires regular maintenance and/or renovation of the coating. Failure due to water penetration/infiltration and leading to structural weaknesses like flaking and/or blistering mainly close to corner joints obviously induces the need for a total renovation of a wood coating system. However when no striking failure can be observed and only degradation through erosion and/or cracking is apparent, it can be difficult to determine a point in time where a maintenance application is still possible or when a more drastic renovation is preferred. The paper presented here is an attempt to define the critical limit state of maintenance and renovation for wooden window joinery coatings based on the erosion phenomena studied in natural weathering as well as artificial ageing trials of over 50 wood coating systems. To allow focussing on merely the performance of a wood coating system itself, tropical hardwood species were used avoiding as such the impact of biological degradation coming from the substrate. The definition of critical limit state will allow developing a protocol for preventive maintenance through regular inspection and hence working towards a longer overall service life of window joinery.
Gloss reduction in liquid paints is commonly achieved using particulate silica matting agents, which induce surface micro-roughness in the coating film. Surface roughness development is usually regarded as depending primarily on coating layer shrinkage during film formation.
However, the trend to VOC compliant technology has resulted in coatings of increasing solids contents, characterized by minimal film shrinkage during drying. A mechanism is now proposed, suggesting that surface roughness can be generated whether or not shrinkage takes place. This is related to elastic forces developing during film formation and to unstable flow behaviour of the resulting liquid.
The present article reviews the various mechanisms to explain how a matt coating is formed from an initially level and glossy liquid film. The article then considers the performance of recent matting agent developments and shows how the newer products are universally applicable in VOC compliant coatings as well as in traditional coatings.
The challenge of surface coating industry on one hand is to provide coatings with environmental compliancy and sustainable design. On the other, is to be able to exhibit high coating performances. In this paper we describe the design of achieving thixotropy in waterborne paint system, while providing excellent wet and dry paint properties. Paper will address the salient design factors including synthetic and colloidal features on an emulsion polymerized acrylic polymer leading to step change in rheological and dry coating properties. Comparison will also be made to solventborne and existing waterborne thixotropic paints. Properties such as gel strength and recovery for the wet system and enhanced chemical and mechanical properties for the coating will be illustrated.