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22ИННОВАЦИОННЫЕ РЕШЕНИЯ
INNOVATIVE SOLUTIONS
The article has entered in publishing office 18.09.09. Ed. reg. No. 604 Статья поступила в редакцию 18.09.09. Ред. рег. № 604
WATERBORNE TECHNOLOGIES FOR POLYURETHANE COATINGS
12 1 E. Avtomonov, V. Ristic , M. Vollmer
'Bayer MaterialScience AG, D-51368 Leverkusen, Germany Fax: +49-2143071173; e-mail: evgueni.avtomonov@bayermaterialscience.com Fax: + +49 2143036498; e-mail: martin.vollmer@bayermaterialscience.com 2A/O Bayer, Bayer MaterialScience, 3-rd Rybinskaya str. 18, build. 2, RUS-107113 Moscow, Russia Fax: +7-4952342056; e-mail: vladmir.ristic.vr@bayer-ag.de
Referred: 28.09.09 Expertise: 03.10.09 Accepted: 08.10.09
Quality, efficiency and environmental protection are the predominant drivers in the coatings market. The demand for green technologies speeds up the shift from solvent-based (solvent-borne) to solvent-free technologies in numerous applications ranging from construction and decorative paints, wood and furniture coatings, metal and plastic coatings to automotive and large vehicle coatings. The aqueous dispersions for coatings (waterborne systems) play the most important role among solvent-free technologies. The current and upcoming VOC legislations of many industrial countries (VOC = volatile organic compounds) are aimed to drastically reduce emitting organic compounds which are harmful to the environment. Not only the statutory limitations but also the self-commitment of many paint manufacturers and users to environmentally friendly technologies facilitate the change from solvent-borne to solvent-free systems. Furthermore, in many market segments as well as in the countries without official regulations green policies appear to exceed by far the legislation requirements in a positive way.
The challenge for the coatings industry and especially for the raw materials suppliers is to translate technical market needs into the "green" chemistry. In particular, the polyurethane chemistry provides an excellent toolbox for the development of aqueous dispersions of binders and polyisocyanates, capable of meeting highest performance requirements in combination with modern and efficient coating processes. Apart from the easier handling the waterborne coatings can even be superior to classical solvent-based systems in certain respects such as e.g. mechanical and chemical resistance or curing time.
Such key words as "Functional Coatings", "Smart Coatings", "Nanotechnology" are often the discussion topic of the experts and it is apparent that waterborne polyurethane systems will play an important role within this context. Functions like "self-healing", "easy-to-clean" or "soft touch" became already famous examples.
Keywords: polyurethane, coatings, aqueous dispersions, waterborne polyurethane, nanotechnology.
ТЕХНОЛОГИИ ПОЛИУРЕТАНОВЫХ ПОКРЫТИЙ НА ВОДНОЙ ОСНОВЕ
Е. Автомонов, В. Ристич, М. Фольмер
Заключение совета рецензентов: 28.09.09 Заключение совета экспертов: 03.10.09 Принято к публикации: 08.10.09
Качество, эффективность и защита окружающей среды являются основными факторами, определяющими рынок покрытий. Спрос на экологически безвредные технологии способствует ускорению перехода от технологий, предусматривающих использование растворителей, к технологиям, не требующим их использования, во многих областях их применения - от покрытий, используемых в строительстве и декоративной отделке, покрытий для дерева и мебели, металлических и полимерных покрытий до покрытий для автомобилей и крупногабаритных транспортных средств. Важнейшую роль среди технологий покрытий без растворителя играют покрытия на основе водных дисперсий (на водной основе). Существующее и развивающееся законодательство в области использования летучих органических соединений (ЛОС) во многих промышленно развитых странах направлено на радикальное снижение их применения как экологически вредных веществ. Переходу от технологий с использованием растворителей к технологиям без растворителей способствуют не только законодательные ограничения, но и курс на применение экологически безвредных технологий, принятый для себя многими изготовителями и потребителями лакокрасочной продукции. Кроме того, во многих сегментах рынка и в странах, где отсутствует официальное регулирование, политика защиты окружающей среды, по-видимому, шагнула далеко вперед по сравнению с законодательными требованиями, что играет положительную роль.
Перед лакокрасочной промышленностью, а особенно перед поставщиками сырья, стоит непростая задача перевода технических рыночных нужд в русло «зеленой» химии. В частности, химия полиуретанов открывает замечательные возможности для развития технологии получения водных дисперсий связующих и полиизоцианатов, способных обеспечить соответствие самым высоким эксплуатационным требованиям в совокупности с современными и эффективными технологиями нанесения покрытий. В дополнение к простоте использования покрытия на водной основе могут превосходить классические составы на основе растворителя по определенным параметрам, таким как механическая и химическая стойкость или продолжительность отвердевания.
Такие ключевые словосочетания, как «функциональные покрытия», «умные покрытия», «нанотехнологии», часто становятся предметом обсуждений среди специалистов, и очевидно, что полиуретановые составы на водной основе будут играть в этой связи важную роль. Такие возможности, как «самовосстановление», «легкоочищаемость» и «сенсорные свойства», стали уже хорошо известными примерами.
Ключевые слова: полиуретан, покрытия, водные дисперсии, полиуретан на водной основе, нанотехнологии.
International Scientific Journal for Alternative Energy and Ecology № 4 (84) 2010
© Scientific Technical Centre «TATA», 2010
Evgeny Avtomonov Evgeny Avtomonov
Evgeny Avtomonov studied Chemistry at the M.V. Lomonosov Moscow State University (Russia, 1988-1993) and received his PhD in Chemistry from the Philipps-University of Marburg (Germany) in 1996. After post-doctoral research stays in Italy and Germany (University of Venice and Philipps-University of Marburg) he joined A.N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences (INEOS) in 1998 at which he was head of a research group at the Laboratory of Organometallic Compounds. In 1999 he started his industrial career with Bayer AG in Leverkusen (Germany) as head of research laboratory of Bayer's Central Research and Development Department. Then he worked in different leading research & development positions. In 2008 he moved to the Business Unit "Coatings, Adhesives and Specialties" of Bayer MaterialScience AG as the Head of the Segment "Product&Process Development" within the Marketing and Business Development Dispersions.
Vladimir Ristic studied Industrial Engineering and received his B.Sc in mechanical engineering in 1996 at the University of Belgrade (Serbia). He also holds a master's in business administration from the Faculty of Economics, Finance and Administration (FEFA) in Belgrade. After studies he started his industrial career in rubber industry, company FGP Rekord in design equipment bureau and then worked as technical marketing manager in company UTI. He joined Bayer Serbia in 2003 as sales manager and was later responsible for marketing and sales in Southeast Europe. Then he worked at Bayer MaterialScience Germany in Business Unit "Coatings, Adhesives and Specialties" in marketing and sales. Currently, he is the country representative of Business Unit "Coatings, Adhesives and Specialties" in CIS responsible for marketing and sales of products for coatings, adhesives, functional films and carbon nano tubes.
Vladimir Ristic
Martin Vollmer studied Chemistry and received his PhD in chemistry from the University of Stuttgart (Germany) in 1996. After a post-doctoral research at the Scripps Institute in La Jolla (California, U.S.) he started his industrial career with Bayer AG in Leverkusen (Germany) in 1999 as head of research laboratory of Bayer's Central Research and Development Department. Then he worked at Corporate Development and Strategic Planning Department for several years and later he moved to the Business Unit "Coatings, Adhesives and Specialties" and held several leading positions in Research & Development. Until December 2009 he was the Head of Marketing and Business Development Dispersions and was responsible for Research, Development, Application testing and Marketing of aqueous product lines for coatings and adhesives markets.
Martin Vollmer
Legislative regulations on VOC and trends to green technologies, Green Policies
In the modern global coatings market the ratio of the solvent-borne systems predominates and accounts for ca. 60% of the total [1]. The need to use organic solvents (or diluents) in solvent-based systems is twofold: on the one hand, it is necessary to dilute the high molecular and, hence, viscous polymer for better handling and applicability, while, on the other hand, the addition of organic solvents helps also to obtain a homogeneous high quality film of the coating material on the substrate at a given application temperature. The coated film is subsequently dried and hardened upon evaporation of the solvent either at ambient or at elevated temperature. The use of high amounts of volatile organic solvents (Volatile Organic Compounds = VOC) negatively affects the occupational hygiene and the environment. A considerable part of environmentally relevant VOC emissions in Western Europe are estimated to stem from the coating applications containing organic solvents. It
is, however, expected that the fraction of solvent-borne coatings will decrease and might drop down to 50% by 2014. Environmentally friendly technologies such as waterborne coatings, radiation curable systems, powder coatings as well as high solids-systems with highly reduced solvent content are on the way up. This development is not driven solely by legislative confinements with respect to VOC emissions but also by increased ecological consciousness of the population as well as self-commitment of many coating manufacturers and end-users to green technologies.
Organic solvent emissions negatively impact the atmospheric ozone equilibrium and affect therefore the climate change in an unfavorable way. Some of organic substances are classified as indirect green-house gases and contribute along with CO2 to the global Earth warming. The so-called Solvent Emission Directive (SED) (1999/13/EC) was adopted by the European Union in 1999 - a law directed towards reduction of solvent emissions stemming from industrial coatings systems. In the time period from 1990 to 2007 the
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solvent emissions should be reduced by 60-70% in order to improve the atmospheric air quality substantially. Clear objectives in terms of maximal emitting solvent amounts per year and market segment were defined for specific coating industry branches and the manufacturers. This led to intensified research and development activities and as a result to the introduction of numerous VOC compliant coating systems to the market, especially in the period 2005-2007.
To provide additional occupational protection of the employees and to further improve the safety at the working place the Deco Paint Directive (2004/42/EC) regarding architectural and painting lacquers has been ratified. Regulation for the use of automotive refinish coatings is a part of this directive. This regulation sets up limits of amounts of organic solvents used in the formulation of the coatings. The first step of this directive sets a VOC-limit of max. 420 g/l and is valid since January 2007. This limitation will further be strengthened to 250 g/l and will become valid in January
2010, while a further reconsideration is planned for
2011. Moreover, in order to provide a better health and hygiene protection the regulations in some countries are even more stringent, especially regarding VOC emissions from indoor applications in the living sector.
The Russian coatings market grew dynamically by averaged 9% per annum during the past decade and summed up to 1.15 Mio. t/a in 2008, including architectural and decorative paints (620 kt, 54%) [2, 3]. The portion of solvent-based coatings is reported to be at 70% of the total amount [2]. Taking into account that the biggest fraction of waterborne coatings and paints of 344 kt came 2008 from architectural and decorative coatings and these 344 kt exactly amount to 30% of the total quantities, the fraction of solvent-based systems for other market segments (i.e. general and industrial coatings, automotive coatings, automotive refinish, other specialties such as wood and furniture coatings etc.) should be at > 99%, i.e. virtually all non-decorative coatings are solvent-based at the present! Though Russian Federation has no specific legal regulations comparable to the VOC-directives of the European Union or other industrial countries, it is clearly pointed out in Russian Ecological Code that any technical progress making ecological and environmental improvements feasible should be supported and implemented [4]. From the prospective of the future development of the Russian coatings market it might be anticipated that the environmentally friendly systems will be paid much more attention.
VOC regulations in Western Europe cannot be considered any longer as the sole driver for green technologies. The trend is rather to provide market with green technologies and to contribute to a sustainable development. Bayer MaterialScience is a part of the Bayer Holding - a company which has long been committed to the sustainable development - and has set up clear targets for environmental protection and sustainable development within the framework of the "Bayer Climate Program" started in 2007. Substantial
investments into production capacities along with research and development of water based coatings and adhesives are a part of this program. Apart from the further development of the product portfolio the process and technology improvement play a more and more important role to guarantee the high quality standards of the products and production processes.
Chemistry & Technology of aqueous dispersions
The Business Unit "Coatings, Adhesives and Specialties" (CAS) of Bayer MaterialScience AG unequivocally focuses on green and, therefore, ecologically friendly technologies. „WATER IS GREEN" is the motto with which the modern, in particular waterborne raw materials for coatings (dispersions) stand in the focus.
The range of aqueous dispersions of Bayer MaterialScience can be subdivided into three segments: two-component water-based coatings (1), one-component water-based coatings for low temperature drying (2) and one-component stoving systems (3). Bayer MaterialScience is the leading provider of raw materials in the field of two-component polyurethane aqueous coatings, having a very rich product portfolio for polyol-dispersions and polyisocyanates, whereas the product line Bayhydrol® plays the central role for all three segments mentioned above. Polyurethane, polyacrylate, polyester dispersions as well as hybrid systems based on polyurethane-polyacrylate or polyester-polyacrylate belong to this important brand. Each of the segments has its particular characteristics and offers tailored solutions for various customer needs and application fields.
The principle of two-component polyurethane systems is based on the common polyaddition reaction between a polyol and polyisocyante as discovered by O. Bayer in 1937 at Bayer [5, 6]. A clean polyurethane C film formation from a polyol A and polyisocyanate B takes place only in the absence of water, for water also reacts with the isocyanate group upon formation of carbamoic acid intermediate which subsequently decarboxylates, forming CO2 and an amine. While CO2 is released from the reaction (uncontrolled and extended evolution of CO2 may lead to undesired incorporation of gas bulbs into the film), the amine group formed in this reaction further reacts with another isocyanate group to make a urea linkage (Fig. 1).
«HO-Rj -OH + «OCN-R2-NCO->
A B
-> HO-(Rj-O-C(=O)-NH-R2-NH-C(=O)-O-RJ)w-OH
C
RNCO H 2° >[RNHCO2H] -c°2 >
-C°2 > RNH2 rnco > RNHC(=O)NHR
Fig. 1. Principal and side reactions proceeding during formation of polyurethanes
16 International Scientific Journal for Alternative Energy and Ecology № 4 (84) 2010
© Scientific Technical Centre «TATA», 2010
The preparation of a two-component solvent-based coating system turns out to be quite simple, unless the solvent chosen for the system does not react with isocyanate itself. The preparation of an aqueous two-component polyurethane coating, however, requires know-how since it includes water as continuous phase and the system must remain stable for a time sufficient for an industrial application. The challenge is, hence, to transfer solvent-borne polyurethane chemistry into waterborne poylurethane chemistry and to handle reactive polyisocyanates in water. 20 years ago, Bayer scientists observed that polyisocyanates can be dispersed in water and that the polyisocyanate droplets form a polyurea surface layer which protects them from further hydrolysis. The next step was to develop aqueous polyol
dispersions as reaction partners and the concept for two-component waterborne polyurethane coatings was born [7]. Waterborne two-component coatings require tailored polyol binder dispersions in which hydroxy functional polymers (e.g. polyacrylate or polyurethane polyols) are present in very dispersed form, preferably at nanometer scale, with particles typically ranging from 50 to 200 nm in diameter. The nanometer-sized polyacrylates or polyurethane-polyol dispersions are then combined with tailored polyisocyanate crosslinkers which are specifically designed for waterborne applications. In principle, both hydrophobic (preferably low viscous) and hydrophilic polyisocyanate curing agents (hardeners) can be used to formulate waterborne two-component polyurethane coatings (Fig. 2, 3) [8].
NCO
OCN'
o. / Vn
N H \ H
(CHANCO
oYnYo
-.Nv____
OCN(CH2)/ Y (CHANCO
O
NCO
HDI biuret, "Desmodur N 100"
O
A
OCN-(CH2)6—N N—(CH2)6-NCO
Y
O
HDI trimer, "Desmodur N 3300"
(C^H^NCO
OCN(CMH18^^ Y (C10H18)NCO
O
HDI dimer, Desmodur N 3400 Isophorone diisocyanate trimer, "Desmodur Z 4470" Fig. 2. Examples of aliphatic polyisocyanates for aqueous two-component polyurethane coating systems O
OCN(CH2)64 £
N N'
o^IAO
(CH2)6NCO
Nonionic modified aliphatic polyisocyanate, e.g. Bayhydur 3100
O
OCN(CH2)64 Я
N ..
N "O (CHANCO
г
-SO,
NHR,
Ionic modified aliphatic polyisocyanate, e.g. Bayhydur XP 2655
Fig. 3. Examples of hydrophilic aliphatic polyisocyanates for aqueous two-component polyurethane coating systems
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mixing \
w*.
h
y«*
polyisocyanate
.fcL
nano-sized polyol dispersion
film formation
application
TAf&tfiW&ftg
homogeneously dried film
Fig. 4. Illustration of the formulation and application process of waterborne two-component polyurethane coating system (easy-dispersion: hydrophilic polyisocyanates - high homogeneity and high gloss film appearance; less easy-dispersion: non-modified polyisocyanates - lower homogeneity or stronger requirements to the mixing equipment and system stability)
The former can be co-dispersed with the nano-sized polyol dispersions by applying high shear forces; the dispersion degree of the isocyanate component may range from hundreds of nanometers to many micrometers. The dispersion process usually requires addition of organic solvents for the ease of dispersion. On the contrary, the hydrophilic polyisocyanates are easy to disperse into the aqueous phase due to their hydrophilicity. They are used preferably without any additional organic solvent and are ideal for applications in which no or only simple mixing equipment is available. High-gloss coating films with good properties can be easily achieved in this manner (Fig. 4).
On the other hand, the hydrophobic polyisocyanates can be used for applications in which the films must meet high requirements with respect to weather stability and resistance to moisture and chemicals. Particularly well-suited for such applications are low-viscous aliphatic polyisocyanate crosslinkers which can be dispersed by using the right mixing equipment.
The hydrophilic polyisocyanates contain surface-active, hydrophilic groups which are preferably chemically linked to the isocyanate molecule as shown in Fig. 3. There are a number of possibilities in selecting the base isocyanate as well as the nature of the hydrophilic modifier when designing a hydrophilized polyisocyanate. Aminosulfonate modified polyisocyanates represent the latest generation of hydrophilic polyisocyanate crosslinkers. They are suitable for applications with further improved drying as well as hardness and chemical resistance of the coating films.
Apart from the polyisocyanate crosslinker, the polyol dispersion (e.g. hydroxy-functionalized polyacrylate or polyurethane) has a significant influence on the property level of the coating film. The polyol dispersions are perfect emulsifiers for polyisocyanate crosslinkers: they facilitate the dispersion of the polyisocyanates into the aqueous phase and stabilize them in small droplets minimizing the reaction of isocyanate groups with water. On the other hand, the acrylic backbone, incorporated into a polyurethane network, provides excellent chemical resistance of the coating films. The hydrogen-bonding within the polyurethane matrix can be considered as non-covalent network and these bonds can release under
strain. This unique property of polyurethane based systems accounts for the "self-healing" mechanism.
A challenge may arise from the fact that waterborne coatings are behind solvent-borne systems in many cases regarding curing speed and thus productivity. To overcome this drawback novel waterborne dispersions for accelerated drying and curing have been developed which beat their solvent-borne counterparts without sacrificing properties, e.g. in terms of scratch and water resistance as well as gloss. The key to success lies in this case in a novel, patented technology by means of which the polyisocyanate-polyol reaction is activated internally: the crosslinking reaction proceeds significantly faster with no meaningful change in viscosity or pot life. This internal activation mechanism is an advantage, for example, to floor coverings that should cure as quickly as possible at room temperature. The undesired shortening of the pot life of two-component polyurethane systems prohibits the use of conventional catalysts. Internal activation raises the reactivity of light-stable, waterborne, two-component polyurethane systems to the level of waterborne, two-component epoxy systems. Correspondingly, internally activated formulations cure completely in less than 20 minutes at approximately 60° C. To achieve the same level of hardness, a standard waterborne coating system would require an entire additional day at room temperature; a solvent-borne, high-solids coating may take even longer. Possible applications for this new concept include site-applied, industrial, but also fast running roll-to-roll applications.
Special classes of polyol dispersions offered by Bayer Material Science for waterborne two-component polyurethane coatings are secondary polyacrylic dispersions (Bayhydrol® A) which help to achieve film properties beyond the classical solvent-borne analogues such as faster drying speed and chemical resistance. To obtain optimal results, these secondary polyacrylates are best combined with special hydrophilic polyisocyanates of the Bayhydur® product line and/or with asymmetric low viscous hydrophobic polyisocyanates from the Desmodur® portfolio [9, 10]. Current research and development efforts are focused on low emission (ideally emission-free) dispersions to afford better
International Scientific Journal for Alternative Energy and Ecology № 4 (84) 2010
© Scientific Technical Centre «TATA», 2010
occupational safety level and working hygiene and to provide the end-user with maximal possible degree of freedom for coating formulations. The spectrum of the offered products spans to system solutions, i.e. offering tailored polyols and polyisocyanates for general and industrial coatings, coatings for large vehicles and agricultural equipment, wood and furniture coatings, floor coatings as well as automotive interior coatings, especially those having "soft touch" effect. The application areas for waterborne two-component polyurethanes are currently being expanded to automotive refinish systems and metal anti-corrosion protection. Further promising applications are coating systems for textiles, leather and paper.
The segment of waterborne one-component polyurethane coatings comprises a broad choice of modern, solvent-free polyurethane dispersions. While the polyurethane formation from two-component polyurethane systems takes place in situ during the application, non-crosslinked polyurethane polymer for one-component system is formed in a melt or in a solution of an organic solvent and is either directly equipped with hydrophilic polar groups which make the polymer dispersible in water or is treated with an external emulsifier to produce the final polyurethane dispersion. Ionic, both cationic and anionic, as well as non-ionic groups can be introduced into the polyurethane polymer chain (or be added as external emulsifier) to render the polyurethane water-dispersible (Fig. 5) [11].
HO-R1-OH + OCN-R2-NCO + HO-R3(-CO2H)-OH
optionally solvent
OCN-R2-NHC(=O)O-R1-OC(=O)NH-R2-NHC(=O)O-R3(-CO2H)-OC(=O)NH-R2-NCO
neutralization with e.g. NR3
OCN-R2-NHC(=O)O-R1-OC(=O)NH-R2-NHC(=O)O-R3(-CO2NHR3)-OC(=O)NH-R2-NCO
water dispersion
chain extension with e.g. H2N-R4-NH2
-NHC(=O)NH-R2-NHC(=O)O-RrOC(=O)NH-R2-NHC(=O)O-R3(-CO2NHR3)-OC(=O)NH-R2-NHC(=O)NH-R4-
final polyurethane dispersion
Fig. 5. Example of the synthesis of a polyurethane dispersion by means of the melt process upon incorporation
of an internal anionic hydrophilizing agent
H2O
n
Those, who develop such products, have access to a very rich pool of building blocks such as polyester-, polycarbonate- or polyoxyalkylene diols which may be combined with each other but also with different diisocyanates to give tailored polyurethane dispersions.
The advantage of polyurethane dispersions is that they already contain polyurethane polymer of high molecular weight and can be applied as one-component system. Prospective application areas of one-component polyurethane dispersions are metal, wood and plastic coatings. Emulsion polymerized (primary) polyacrylate dispersions have also high potential in these segments. Several novel acrylic dispersions were developed at
Bayer MaterialScience and broadly introduced to the customers at the European Coatings Show 2009 in Nuremberg, Germany. The novel product line Bayhydrol® AH (A = acrylate and H = high molecular weight) offers possibilities for cost effective coating formulations for quite a number of applications at reasonable level of performance and rounds up the product line for waterborne one-component coatings [9, 10]. Interesting possibilities are opened up when hybrid systems of one-component polyurethane and acrylic systems are considered, being preferably designed in such a way to combine the most advantageous properties of each class of compounds.
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A special class of aqueous one-component polyurethane coatings is represented by one-component stoving systems. The hydroxy-functional polyurethane, polyacrylate and/or polyester dispersions can be reacted not only with melamine resins but also increasingly with blocked polyisocyanates from the product line Bayhydur® BL. The working principle of the blocked isocyanates consists in that fact that the isocyanate groups are first reacted with a Zerewitinoff-type nucleophile which can be split off at elevated temperatures liberating the free isocyanate groups. Typical blocking agents are e.g. e-caprolactam, bulky dialkylamines, butanone oxime, 3,5-dimethylpyrazole, malonic acid esters etc.. There is a possibility to combine hydroxy-groups and blocked isocyanate groups in one and the same polyurethane dispersion to afford self-crosslinkable one-component waterborne stoving systems - such materials are offered by Bayer MaterialScience under the trade name Bayhytherm® [9]. Original automotive manufacturers, e.g. at the step of primer surfacer coatings, have already established this technology. Shortly, applications of waterborne one-component stoving systems were started for classical industrial coating applications. Right in this application field, there is a high potential for innovations.
Interesting coatings properties and functions
Regarding the chemical, technical and optical performance waterborne coatings show no gaps anymore compared to solvent-based systems and find applications in more and more areas. There is a growing interest in and tendency to functional coatings which make highest demands on the raw materials for coating applications. The most prominent examples are "easy-to-clean", "soft-touch" ("soft-feel") or "self-healing" effects. The fast developing discipline of nano-technology offers opportunities for further improvements and creation of new property profiles. Along with the requirements to the quality of the products the system efficiency is one of the key success factors which are sought for - the radiation curable water-borne systems of the product line Bayhydrol® UV matches the requirements with respect to both quality and efficiency.
Over the last 15 years waterborne "soft-touch" coatings based on two-component polyurethane systems have become state of the art in particular in automotive interior surfaces. The desired effect is achieved through the use of special raw materials of high flexibility. The first generation of waterborne soft-touch coatings was lacking some key performance properties. The most recent product generation based on new design principles further extends the versatile possibilities of the toolbox of waterborne two-component soft-feel coatings systems. They are hydrolytically stable and show high elasticity. Resulting formulations show significantly lowered VOC emission and improved resistance against thermal yellowing. Another breakthrough is the improved chemical resistance and in particular suntan lotion resistance without negatively affecting the haptics.
The systems developed for "easy-to-clean" applications are another example of interesting coating functions which are based on a special hydroxy-functional acrylate dispersion developed for two-component waterborne coatings that are resistant to graffiti and are perfectly suited for the high-end coating of industrial goods, trains, commercial vehicles and even aircraft thanks to their extraordinary chemical resistance. Furthermore, the coatings formulated with the new waterborne binder are extremely resistant to weathering and are very scratch-resistant. This system even outperforms solvent-borne reference coatings in some tests, for example, marker pen stains can be removed easier and completely from panels coated with clearcoats than from the surfaces coated with established solventborne products. The high chemical resistance results in an "easy-to-clean" effect. The substrates are resistant even against "aggressive" liquids ranging from coffee and wine to brake fluid stains and can be easily cleaned.
Conclusion
Waterborne polyurethane coating technology has proven to improve quality, efficiency and environmental aspects and represents a promising alternative to high performance solvent-borne systems, mostly due to the development of novel low viscosity hydrophobic polyisocyanates as well as special hydrophilic polyisocyanates in combination with new tailor-made acrylic and polyurethane based polyol dispersions for two-component waterborne coatings.
The target No. 1 is the reduction of the VOC content of coatings formulations based on co-solvent free dispersions. Thus, the slogan for the current developments and for the foreseeable future will be "From low to zero VOC".
Bayer MaterialScience as a global player offers a broad product spectrum for prospective, ecologically compliant technologies and focuses in the innovation pipeline and key developments on waterborne technology. Bayer MaterialScience will remain the trendsetter for green technologies as the awareness of environmental protection. Improvement of the occupation hygiene and safety as well as for sustainable development will gain more and more importance worldwide.
The potential of waterborne polyurethane coatings has not yet been fully tapped. There is unlimited room for innovation. Development partnerships between raw materials suppliers, formulators, end users and academia will meet the challenge.
References
1. Except for decorative paints for architectural applications.// Source: Bayer MaterialScience 2008.
2. Kudinova I.N., Barabanova O.P. Rossijskij rynok lakokrasochnoj produktsii k nachalu 2009 goda // Lakokrasochnaya Promyshlennost'. 2009. No. 8. P. 8-11.
International Scientific Journal for Alternative Energy and Ecology № 4 (84) 2010
© Scientific Technical Centre «TATA», 2010
3. Abramov V.N. Rossijskij rynok lakokrasochnykh materialov: novye realii // Lakokrasochnaya Promysh-lennost'. 2009. No. 4. P. 8-10.
4. Russian Federation. Federal Law about industrial waste and residuals from the production processes. Accepted by Russian Parliament on May, 22nd, 1998. Ratified by the Council of Federation on June, 10th, 1998, Chapter 1, Article 3.
5. Deutsches Reichspatent DRP 728981. Verfahren zur Herstellung von Polyurethanen bzw. Polyharnstoffen. // Bayer O., Siefken W., Rinke H., Orthner L., Schild H. 1937. IG Farben.
6. Bayer O. The diisocyanate polyaddition process (polyurethanes). Description of a new principle for building up high-molecular compounds (1937-1945) // Angew. Chem. 1947. Vol. 59. P. 257-272.
7. European Patent EP 358879B1. Coating masses, process for their preparation and the use of selected two-component polyurethane systems as binding agents in this kind of coating masses. // Kubitza W., Gruber H., Probst J. 1988. Bayer AG.
8. Meier-Westhues U., Editor. Polyurethanes. Coatings, Adhesives and Sealants. Hannover: Vinzenz Network, 2007. Engl. Ed. P. 32-34 and 43-45;
Meier-Westhues U., Editor. Poliuretany. Pokrytiya, klei i germetiki. Moscow: Paint Media, 2009. Russian Ed., P. 33-36 and 45-48.
9. Internet-address: http://www.bayercoatings.de/ BMS/DB-RSC/BMS_RSC_CAS.nsf/id/EN_Portal.
10. Bayer MaterialScience AG. Novye produkty serii Bayhydrol® dlya lakokrasochnoj promyshlennosti // Lakokrasochnaya Promyshlennost'. 2009. No. 7. P. 23-26.
11. Meier-Westhues U., Editor. Polyurethanes. Coatings, Adhesives and Sealants. Hannover: Vinzenz Network, 2007. Engl. Ed. P. 52-55 and the references cited therein;
Meier-Westhues U., Editor. Poliuretany. Pokrytiya, klei i germetiki. Moscow: Paint Media, 2009. Russian Ed. P. 56-61 and the references cited therein.
Международный научный журнал «Альтернативная энергетика и экология» № 4 (84) 2010 © Научно-технический центр «TATA», 2010
