Two-component Polyurethane Coatings Research Articles

Fully Bio-Based and Solvent-Free Polyester Polyol for Two-Component Polyurethane Coatings

In recent years, many efforts are being devoted to the development of new materials that originate from renewable resources. Polyesters are one of the most important classes of such materials and several bio-based monomers are available for their synthesis. In this work, the development of fully bio-based and solvent-free polyester polyol used for two-component polyurethane coatings on industrial scale is presented. Fossil-based raw materials were substituted with bio-based alternatives that are commercially available on a large scale. Properties of polyols and coatings were determined and measured. Polyols were characterized by the determination of acid number, hydroxyl number, glass transition temperature and refractive index, and measurement of viscosity, color and molecular weight. Coatings were characterized by the determination of mechanical properties, such as hardness, elasticity and impact resistance, and the measurement of optical properties such as gloss, haze, distinctness of image (DOI) and reflected image quality (RIQ) and weathering resistance. Three variations of bio-based polyol were synthesized, then the most suitable version was validated in a clear coat. The results showed that the properties of the bio-based polyol and coating met the requirements and were comparable to the properties of the synthetic counterpart. Results indicate that this newly developed 100% bio-based and solvent-free polyol can be used as a drop-in replacement for synthetic polyol. Furthermore, this work implies that the supply chain is established which allows the green transition in the paint industry.

Hydroxyethylated Coal Extract as Polyols for Two-Component Polyurethane Coatings

Hydroxyethylated Coal Extract as Polyols for Two-Component Polyurethane Coatings

Hygienic assessment of polyurethane coatings in the practice of drinking water supply

Introduction. For many years, two-component polyurethane coatings have been used as suitable systems for the protection and reconstruction of pipes in the practice of domestic drinking water supply. However, polyurethane can be a source of pollutants entering drinking water. Special attention in the hygienic assessment is paid to the main components of plastic, the released solvents and film-forming agents used in the formulation of the material. However, the definition of only priority components (taking into account Uniform sanitary requirements) does not provide complete information about the chemical stability of polymer materials during the hygienic assessment. Materials and methods. Eight different two-component polyurethane coatings of various manufacturers and manufacturers offered for use in drinking water supply are investigated in the work. The evaluation of these samples was carried out taking into account Uniform requirements (2010). Indicators that are not mandatory for the evaluation of polymer materials used in drinking water supply were also investigated. Results. Conducting a hygienic assessment of two-component polyurethane coatings shows fundamentally different chemicals to migrate into the model environment even from materials with the same type of components. When analyzing water extracts, from 9 to 40 organic compounds were identified at different temperatures. Most of them do not have the maximum permissible levels of their content in drinking water and there are no fully conducted toxicological studies of these chemicals to assess their safety for humans. There also were found three samples, from which inorganic components of cadmium and nickel migrated into distilled water above their maximum permissible values. Limitations. This study was conducted on the example of polyurethane coatings, as a particular example of the use of polymer materials in drinking water supply. It is necessary to conduct similar studies on other groups of polymers. Conclusion. At the moment, there are certain contradictions in the methodology and approaches to assessing the migration of chemicals from polymer coatings to drinking water. Therefore, their refinement and standardization is relevant, taking into account the increasing share of the use of polymer materials in human life.

Synthesis and properties of star-shaped polyesters for high-solid-content two-component polyurethane wood coatings

As the laws about emission of volatile organic compounds (VOCs) become more and more stringent, low VOC content coatings, such as high solid polyurethane coating, gradually attract great attention. Herein, a series of star-shaped hydroxyl polyesters (SHPs) were synthesized by methyl hexahydrophthalic anhydride (MHHPA), diisopropanolamine (DIPA), and monoglycidyl ether. The number of their average molecular weights is ranged from 913 to 1390 with 1.55–1.75 of PDI. The viscosities of SHPs are low to 1060 mPa·s. The molecular structures of SHPs were characterized by Fourier transform infrared (FTIR) and 1H nuclear magnetic resonance (1H NMR) spectroscopies. The high-solid two-component polyurethane coatings (2 K-PU) from SHP-3 have a 65% of the solid contents and exhibit 20 mPa·s of the applied viscosity with 310 g/L of VOC contents. Moreover, the polyurethane film displays high coating hardness up to 2H, as well as excellent chemical resistance and good thermal stability.

Effect of polyether/polyester polyol ratio on properties of waterborne two-component polyurethane coatings

In order to obtain waterborne two-component polyurethane (WB 2K-PUR) with good mechanical properties as well as excellent corrosion resistance, a series of hydroxyl-based polyurethane (HO-WPU) were synthesized using isophorone diisocyanate (IPDI), dimethylolpropionic acid (DMPA), and different proportions of polyether polyol (PTMEG) and polyester polyol (P1012) in this paper. Then WB 2K-PUR coatings were prepared with water-dispersible isocyanates (WDPI) as curing agent. The influence of the proportion of polyester polyols and polyether polyols in soft segments on coatings properties was studied. The characteristics of the coatings were analyzed by Fourier transform infrared spectroscopy (ATR-IR), contact angle, differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and atomic force microscopy (AFM). The results showed that the mechanical properties and corrosion resistance of polyester and polyether polyols with appropriate proportion are improved significantly. The mechanism tended to be that with the addition of polyester, more hydrogen bonds were formed between the molecules, which increased the compactness of the coating as a physical crosslinking point. However, the ester groups have a strong affinity to water molecules, so the hydrophilicity of the coating was increased by excessive polyester polyols, and the shielding effect on the corrosion medium was reduced. With the inclusion of 40 % (g/g) P1012 in polyols, the coating has satisfied comprehensive properties.

Synthesis and properties of multiarm star hydroxyl-terminated polyesters for two-component polyurethane coatings

A series of multiarm star hydroxyl-terminated polyesters (MHPs) were synthesized through a “one-pot” method with di-trimethylolpropane as the core molecule, 2,2-dimethylolpropionic acid as the AB2-type monomer, e-caprolactone, and monocarboxylic acids as modifiers. The influence of different monocarboxylic acids on the viscosities of polyesters and their 2K-PU films hardness was studied and it was found that MHPs prepared from lauric acid displayed the higher films hardness and lower viscosities. IR spectra of MHPs disclosed the ring-opening reaction between e-caprolactone and hydroxyl groups occurred. 1H NMR spectra demonstrated that the molecular structures of MHPs were irregular due to the multiplicity of reaction processes. The measured number-average molecular weights (M n) of MHPs were around 715–1854 g/mol with the PDI of 1.45–2.05. MHPs exhibited lower viscosities in the range of 3304–9060 mPa s at 100% solid contents and possessed lower intrinsic viscosities compared with linear polymers of similar molecular weight. The cured films of MHPs exhibited excellent impact resistance, adhesion, flexibility, and high hardness and displayed good thermal stability with 5% weight loss at 280°C. The solution viscosities of MHPs were less than 450 mPa s at 80% solid contents, and the VOC contents of 2K-PU coatings obtained from MHPs were low to 300 g/L.

Preparation of Two-Component Polyurethane Coatings from Bleached Liquefied Wood

Liquefied wood-based polyurethane wood coatings of an aesthetically acceptable light colour were prepared and characterised. Liquefied black poplar wood was obtained by solvolysis in a polyethylene glycol/glycerol mixture, and it was bleached with hydrogen peroxide. The bleaching treatment converted liquefied wood from a dark brown to a yellowish product. Polyurethane films were prepared by the curing of liquefied wood with polymeric diphenylmethane diisocyanate or trimethylolpropane toluene diisocyanate prepolymer (TMP/TDI) isocyanate-type hardeners. It was found that the selected properties of the films prepared from the bleached liquefied wood were, in general, equivalent to those prepared from unbleached liquefied wood. The mechanical properties of the films obtained with the TMP/TDI curing agent were acceptable for wood coating applications. The initial poor resistance of the films to water and ethanol was substantially improved by the addition of n-octyltriethoxysilane to the liquefied wood prior to the preparation of the polyurethane coatings; the hardness of the films also increased.

Functionalization of PDMS modified and plasma activated two-component polyurethane coatings by surface attachment of enzymes

This article describes a new strategy for coupling the enzyme horseradish peroxidase to a two-component polyurethane (2C-PUR) coating. A stable polymer conjugate was achieved by combining the enzyme and the 2C-PUR coating which was modified with poly(dimethylsiloxane) (PDMS), located at the surface. An atmospheric pressure plasma jet system was used to convert alkyl groups from the PDMS into polar silanol functionalities. This conversion was proven by X-ray photoelectron spectroscopy and dynamic contact angle measurements. In addition, the stability of the activated 2C-PUR surface containing silanol groups was determined by measuring the contact angle as a function of time. Compared to the non-modified 2C-PUR systems the one with PDMS displayed a higher stability over a time period over 28h. In a silanization process the coating was treated with (3-aminopropyl) trimethoxysilane and the enzyme was subsequently immobilized to the coating via the cross linker glutaraldehyde to receive new biomimetic catalytic/enzymatic functions. The chemical immobilization (chemisorption) of the enzyme to the surface showed statistically significant higher biological activity as compared to references samples without using a cross linker (physisorption). The presented technique offers the opportunity to design new and smart multifunctional surface coatings which employ biomimetic capabilities.

New low-VOC acrylic polyol dispersions for two-component polyurethane coatings

Two-pack water-borne polyurethane coatings are a relatively new technology which promises excellent performance properties combined with a low content of volatile organic compounds (VOCs). In this paper the effects of a polymer structure of acrylic polyol dispersions on film-formation and final coating properties (pot life, hardness, gloss) are investigated. Two kinds of water-borne acrylic polyols have been investigated. Both water-borne polyols show good results in applicability, hardness and chemical stability when elevated temperatures can be used. The polyol based on a single-step synthesis route is superior in pot life, hardness and chemical stability. The low paint VOC of 130g/l indicates that this polyol already fits demands of future VOC regulations.

Recent developments in aqueous two-component polyurethane (2K-PUR) coatings

In the field of environmentally friendly coatings waterborne two-component polyurethane systems represent a new technology, combining the good film properties of solventborne two-component polyurethane coatings with the low VOC values of waterborne technology. Recently, waterborne two-component polyurethane coatings have matured to the point that they offer realistic alternatives to the corresponding solventborne systems in various application fields. For industrial finishing and automotive refinish we are introducing rapid drying coatings exhibiting well-balanced range of properties at low VOC level. We developed high-performance OEM-clearcoats which combine good chemical resistance with excellent mar resistance. Waterborne soft-feel lacquers are already well established in the market. Development of a new generation of water dispersible polyisocyanates as well as improvements in application technology have contributed substantially to this. Additionally, progress in understanding the fundamental principles of aqueous two-component-PUR systems like side reactions during pot life and film formation or the cause of blistering supported our developments. We expect that waterborne two-component polyurethane coatings will gain a significant share of the market where high-performance coatings are demanded.

Surfactant-free emulsions for waterborne, two-component polyurethane coatings

Catalytic chain transfer polymerisation based on cobalt II or III chelates is a free radical technique which allows the synthesis of functional oligomers with a terminal α-substituted acrylate group. This paper will review the applications of such oligomers in the design of low molecular weight, graft and block copolymer emulsions and dispersions for waterborne, two-component polyurethane paints. Such emulsions and dispersions have a composition and molecular weight control and offer unique properties when compared with binders prepared via conventional techniques.

Application of graft copolymers using macromonomer method to two-component polyurethane coatings

Graft copolymers as acrylic polyols in two-component polyurethane coatings were prepared by the free-radical copolymerization of methyl methacrylate, n-butyl methacrylate, n-butyl acrylate, acrylic acid, 2-hydroxyethyl methacrylate and poly(methyl methacrylate)-macromonomers. The poly(methyl methacrylate) macromonomer was prepared by the polymerization of methyl methacrylate in the presence of thiopropionic acid as a transfer agent followed by the reaction with glycidyl methacrylate. These polymers, whose numbers of poly(methyl methacrylate) macromonomer branches and the molecular weights of the poly(methyl methacrylate) macromonomer branches were controlled, offer an advantage over conventional resins with respect to the application/appearance of coatings as well as the final film properties. Some of these advantages were higher solids and a better control of the coating rheology, an increase in the cross-linking reactivity of the polyols with polyisocyanate and improvement in film toughness. The change in the morphological structure of the films under tensile stress was of particular interest.

Zur Synthese aliphatischer Polyisocyanate - Lackpolyisocyanate mit Biuret-, Isocyanurat- oder Uretdionstruktur

The Synthesis of Aliphatic Polyisocyanates Containing Biuret, Isocyanurate or Uretdione Backbones for Use in Coatings Two-component polyurethane coatings („2K-PUR”︁) are made from polyols and polyisocyanates. Polyisocyanates based on aliphatic diisocyanates with low monomer content are employed for light stable coatings. An overview of the patent literature regarding the synthesis of such aliphatic polyisocyanates will be given. Methods of preparing biuret polyisocyanates, the formation of isocyanurate polyisocyanates by catalysed cyclotrimerisation, as well as cyclodimerisation which leads to the formation of uretdione polyisocyanates will be discussed. These different types of polyisocyanates are to gain increasing economic importance in the area of high quality automobile and heavy duty industrial coatings as well as construction protection and maintenance.

Polyurethanes for “Two-dimensional” applications

The unsurpassed versatility of polyurethanes is remarkably evident in the areas of two-dimensional applications. Polyurethanes are tailor-made for the wide range of rigid surface coatings, eg; for metal, concrete and wood; for flexible surface coatings; for textile substrates and leather; and for a wide variety of adhesives. Polyurethanes give unexcelled performance in almost all of these applications. In many cases this superiority is achieved by the fact that polyurethanes are generally reactive processing polymers which can be intrinsically cross-linked to the optimal degree. This key fact can be accounted for by the versatility of the NCO group, an “energy package” of unique quality. Two-component polyurethane coatings based on aliphatic polyisocyanates have experienced significant breakthroughs in automotive applications and for powder coatings. A prime target of coating textiles with polyurethanes is the achievement of the quality of natural leather. A highly water vapor permeable, but water repellent textile coating has recently become possible using a direct coating process. The application of a microporous polyurethane film on split leather by a reaction process leads to prime quality leather for shoe uppers. For many years, elastomeric polyurethanes have been the top-ranking adhesives for highly plasticized PVC articles. More recently, polyurethanes have been introduced into the market as structural adhesives, especially for the bonding of automotive body parts. A new principle of heterogeneous cross-linking of polyurethanes which has potential for one-package structural adhesives is presented. Aqueous polyurethane can also be tailor-made for the whole range of two-dimensional applications. They complement the high solids and the powder polyurethane coatings, as well as the solvent-free polyurethane adhesives in the fulfillment of ecological and industrial hygiene requirements.